Review of recent nano TiO2 film coating methods, assessment techniques, and key problems for scaleup
-
Jiaxin Liu
,
Junfeng Dai
,
Lei Gan
Abstract
The growing demand for green and sustainable development positions TiO2 film coatings at the forefront of novel technologies. Applications of TiO2-based materials in photocatalytic, optic, energy, electronic, aerospace, automotive, decorative, and other fields have accelerated on a large scale. Various coating processes are widely used in order to prepare nano TiO2 filmcoated supports for different purposes. Each technique offers numerous advantages, such as the potential to be produced in large quantities and surface areas, acceptable adherence and reactivity of the resulting product, cost-effectiveness, simplicity, etc. This work provides a comprehensive overview of the most recent as well as commonly applied wet and dry TiO2 deposition methods in terms of principals, advantages, applications, coating assessment techniques, required equipment, and key technical problems for mass production and commercialization such as coating durability, fouling, cost-effectiveness, environmental impacts, etc. This information provides a basis to better understand the new and conventional coating processes and the relative contribution rate of the influencing factors that are necessary to control the physicochemical properties of resulting coated substances for the applications aimed.
Graphical abstract
1 Introduction
Nanomaterials exhibit enhanced characteristics due to their high surface area-to-volume ratio and quantum effects. Generally, when materials are produced at the nano scale, the following happens at the surface: (a) A higher percentage of their atoms are exposed on the surface compared to those atoms inside the bulk material, (b) A higher surface energy (particles free energy) will be available due to bigger surface area, and (c) hence, these will enhance the reaction rates of the chemical components [1]. Moreover, what possibly can occur at the volume are: (a) A shorter wavelength which causes high frequency and energy, consequently, (b) atoms blue shift will take place in terms of their optical spectra absorption, (c) change in magnetic properties since materials in nanoscale can have minor scale than their magnetic domain (for ferromagnetic such as iron, cobalt, etc. [2], and (d) for the free electrons scheme, energy spacing raises averagely, followed by a reduction in the atom’s quantity, which improves the catalytic characteristics of nanomaterials [1].
Therefore, the preparation of nanoparticles (NPs) has been among the hot-spot research areas owing to their novel properties, and investigation in this line of research is currently ongoing [3]. Nanomaterials have a wide range of applications, such as in medical science, electronic devices, industrial and agricultural sectors, and so on. Among which, applying advanced oxidation processes (AOPs) via nanomaterials (especially semiconductors) for environmental remediations has drawn much attention from the research works. Nano TiO2 photocatalysis, as one of the most promising AOPs, uses UV energy (photoinduced processes) to enhance the pollutant degradation efficiency of water purification systems [1]. Studies on the photocatalysis ability of TiO2 and its different applications have been ongoing over the past four decades, from hydrogen generation as fuel in 1972 by Fujishima for the first time [4], until recently, which has been studied for disinfection of SARS virus and COVID-19 during the pandemic [5]. Applications of nano TiO2 in the removal of water and air pollution [6,7,8,9,10,11] have been exemplified elsewhere.
Titanium (Ti), with the atomic number of 23 is the nineth most abundant material (and seventh metal) on earth. It is available in nature as its oxidized form (TiO2). Yearly around four million tons of TiO2 are being produced as white pigment to be utilized in different industries. Its three known phases (or polymorphs) include anatase, brookite, and rutile which the latest is also the most stable phase. In their most thermodynamically stable forms, brookite occurs from 11 to 35 nm in size, while below this range of size would be anatase, and above this range is rutile. Figure 1 shows the titanium dioxide crystal structures in its three various forms, schematically [12].
TiO2 crystal structures in its three various forms: (a) rutile, (b) brookite, and (c) anatase.
For water treatment purposes, although nano TiO2 has been extensively used as suspension form (in slurry-type reactors) with outstanding efficiency; however, it will need post-separation and secondary treatment, which is a costly process. Different attempts have been made for the easy removal of suspended form catalysts such as magnetic nano-structured photocatalyst [13] since TiO2 is paramagnetic (unlike magnetic materials such as iron, nickel, cobalt, and steel). This technique is similar to polymer coating magnetic NPs, which are being used in medical science [14,15]. Immobilization of nano TiO2 for photocatalytic contamination removal or self-cleaning applications [16] on various kinds of support such as zeolite [17], cement [6,8], bricks [12,18], silicalite-1 [19], borosilicate glass spheres [7], sintered glass [20], low iron float glass [21], glass wafers [22], ceramics [23,24], polypropylene nano composites [23,25,26], polymers [27,28,29], rubber [30,31], aluminum [32], etc., can prevent such post separation requirements. In this way although the efficiency will decrease to half or lower [33] compared to suspended form, secondary treatment would not be needed.
The selection of the immobilization method and its success rate greatly depends on the type of substrate and the final product application. Besides, other parameters such as cost-effectiveness, scaleup feasibility, simplicity, technology, and required equipment can play important roles. Considering these criteria, a wide range of substrates are examined as support to be coated via different immobilization methods. In fact, an ideal support media for an efficient coating and performance must provide a good affinity and adhesion via high surface energy [34], durability, recyclability, thermal stability, and resistance to high temperature (for annealing and calcination purpose) [33]. It also must be transparent to ultraviolet (for efficient photocatalytic activity) while UV resistance, with largescale applicability, compatibility with the method used, resistant to degradation via TiO2 oxidation ability, and able to offer sufficient surface area for the NPs and contaminants contact maximization, beside a base for well adherence and crack free layers of coatings [7,29].
Generally, the immobilization can take place in three ways including cementing, thermal bounding (hot press such as for polymeric supports [35,36]), or film coating [8,25,37]. Compared with coating and cementing techniques, in thermal bounding methods (such as melt mixing via screw extruder [38], solution mixing [26,39], and in situ polymerization [40] less dissolution, erosion, and leaching of semiconductor will happen; however, other problems such as degradation of the substrate via embedded semiconductors might arise [33]. As for the cementing, besides the abovementioned problems, UV transparency, durability, and available surface area to volume can avoid largescale applicability of such methods. Film-coating however seems to be a more promising technique when it comes to water quality enhancement reactors.
Taking into consideration the variety of supports applied as substrates for different purposes, various nano TiO2 coating methods are studied and developed. To achieve the right functionality and efficiency would require explicit materials and methods selection, tailored to specific protocols. Especially, the morphology and properties of the final NP coated product is inseparable from the coating method used. Hence, the key in preparing the most desirable coating lies in method selection. From practical point of view, the choice of coating method would be challenging in the absence of a comprehensive reference to compare different methods. Nevertheless, a relatively lesser number of research works have focused on the TiO2 coating methods and mechanisms in detail. This review aims to introduce and compare different film-coating methods applied to fix TiO2 NPs on a wide range of supports. Moreover, it illustrates their advantages and disadvantages, key problems, and assessment methods, technically. Using 214 references, this work adds value to the body of science in this field via offering helpful guidelines about the coating process and methods, that can be a practical source for scholars to provide the TiO2 materials they aim for, with a desired coating technique.
2 Film-coating in brief
Nanomaterial film coating refers to the application of a thin film coating made of nanomaterials onto a surface (support). In other words, it is the immobilization of NPs as a thin layer on a surface to change, control, or enhance the physiochemical properties of the support or just for the purpose of the film application. The deposition of thin films on supports can be done through different methods to fix NPs onto the surface of materials at a thickness of 0.1–1,000 nm [41]. Nanomaterial film coatings have applications in various industries, such as electronics, environment, photocatalysis, aerospace, automotive, healthcare, energy, etc. They are employed to enhance the performance, durability, and functionality of surfaces, leading to improved product quality and enhanced capabilities based on the requirements. But if the application of the film itself is the main target, then the support will just provide a surface for the immobilization of the NPs. Nanomaterials used in film coating offer several advantages such as:
2.1 Enhanced functionality
Nanomaterials can provide improved functionality to the coated surface. For instance, they can enhance the surface’s mechanical, electrical, thermal, or optical properties, depending on the specific characteristics of the nanomaterial used [42,43].
2.2 Barrier properties
Nanofilm coatings can create an exceptional barrier against moisture, gases, or other environmental factors by preventing the permeation of substances, thereby protecting the underlying surface [44,45,46].
2.3 Self-cleaning and antimicrobial properties
Certain nanomaterials such as TiO2 possess self-cleaning properties, preventing the accumulation of dirt, dust, or other contaminants on the coated surface [47]. Additionally, they exhibit antimicrobial properties, inhibiting the growth of bacteria or other microorganisms on the surface.
2.4 Controlled release
Nanofilm coatings can be engineered to enable the controlled release of substances such as in agents or drug carriers where the coating can release substances at a controlled and sustained rate [48,49,50].
Based on the purpose of coating, the method can be selected depending on multiple criteria such as the available technology, cost, size, application, etc. In a more general perspective, there is a great deal of research on thin film preparation for a wide range of NPs via different techniques, depending on the coating purpose, the kind of nanomaterial used, the applied support surface, the required properties, and the available technology. These methods and materials can be such as vacuum evaporation technique used for vanadium pentoxide (V2O5) coating on glass substrate for film structural characteristics analysis [51], high target utilization sputtering, which is a plasma assisted method used to coat indium tin oxide (ITO) on glass and polyimide for solar cells with high transparency to visible light [52], plasma assisted molecular beam epitaxy (MBE) for ZnO film coating on sapphire substrate [53], chemical bath deposition, which is a wet method to grow ZnO film on glass substrates for gas sensors [54], electrolytic deposition of cerium oxide on stainless steel for corrosion avoidance [55], cadmium oxide thin film fabricated via Langmuir–Blodgett technique [56], liquid–liquid interfacial methods used to produce thin films of gold and other metals [57], liquid-phase deposition of TiO2 NPs applied on steel in flow boiling equipment for a better heat transfer [58], and matrix assisted pals laser evaporation which is a laser deposition based method used for TiO2 coating on gas sensors [59]. Also, some advanced techniques described in the literature are pulsed laser deposition (PLD), radio frequency (RF) magnetron sputtering, reactive ion beam assisted deposition, vacuum arc deposition [29], and much more. However, here in this review, we will only focus on the most frequently applied methods of TiO2 film coating for different applications.
3 TiO2 film-coating categories and methods
TiO2 film coatings can be achieved through various techniques to ensure the uniform deposition of nanomaterials onto the surface, resulting in a thin layer with desirable properties and advantages. The coating on the support surface for TiO2 (just to differentiate from the coatings on NPs), can be categorized into two main groups including dry particle coating [60] and wet chemical synthesis [19] with various methods within these two categories. Dry methods are such as physical vapor deposition (PVD), atmospheric plasma [34], chemical vapor deposition (CVD) [61], atomic layer deposition (ALD), photo-assisted deposition (PAD) [62], fluidized bed deposition, and MBE method, while wet methods are such as sol–gel [63], incipient wetness impregnation (IWI) method [19], and electrophoretic deposition (EPD). Another categorization method broadly divides the coating methods into physical, chemical, and sol–gel methods. Here the ten most frequently used techniques for TiO2 coating are briefly explained and exemplified.
3.1 Dry TiO2 coating methods
In this category, dry TiO2 particles are vaporized, electrocuted, or sprayed to be deposited on the surface and no solution-based reactions are involved. Below are the top seven methods with several techniques within each, to coat titanium NPs dryly, on different support surfaces.
3.1.1 PVD
This method is a thin film deposition technique through the physical transfer of material atoms from a solid or liquid source to a substrate, without any chemical reactions involved [64,65]. As a vacuum-based method, PVD generally involves either one of the two primary processes: evaporation or sputtering. In evaporation, the material to be deposited (in this case, TiO2) is heated to a high temperature, causing it to vaporize and then condense. In sputtering, energetic ions (such as Argon) as plasma are used for bombarding the titanium source to dislodge and eject Ti atoms from the target material surface [66,67]. The schematic diagram of this method is shown in Figure 2. PVD is carried out in a vacuum environment to eliminate interference from air molecules and reduce contamination. This is crucial for the control and quality of the thin film being deposited. The vaporized or sputtered material is then directed toward a substrate, where it condenses in the presence of oxygen or other oxidizing agents such as ozone, and forms a thin film.
Schematic illustration of the PVD process.
Five different PVD techniques include thermal evaporation, electron beam evaporation, magnetron sputtering, laser ablation (PLD), and ion beam sputtering. In PLD, a laser is applied to ablate the Ti target, vaporizing it which later reacts with O2 to form TiO2 on the support surface, applied for dense and nanostructured film deposition [68,69,70,71,72]. Each method has its advantages and is chosen based on the specific requirements of the application. PVD is widely used in industries such as semiconductor devices, electronics and protective coatings, optics and antireflection, aerospace, and automotive for purposes like decorative coatings, and hard coatings. It is a versatile process that allows for the deposition of a wide range of materials onto diverse substrates, including flat surfaces (for evaporation) or complex geometrics (for sputtering). Although high cost, oxygen control, and slow deposition rate are reported to be the disadvantages [73,74,75], PVD is favored for its ability to produce thin films with excellent adhesion, uniformity, durability, and control over thickness. Coating properties such as its thickness can be controlled by deposition rate/time adjustment, substrate temperature control, oxygen pressure, and the amount of power supplied to the sputtering target or source of evaporation.
3.1.2 Plasma coating methods
Plasma is a highly ionized (using strong voltage) gas (normally air, argon, or oxygen), which contains free ions and electrons [76]. Plasma coating applies a plasma jet under the atmospheric pressure to deposit nano TiO2 film on the support surface. The plasma is usually produced via an atmospheric pressure plasma jet or a dielectric barrier discharge. For TiO2 coating via this method, after the Ti-based precursor vaporization, it will be injected into the plasma. Finally, the high energy of the plasma gas causes the precursor breakdown, resulting in Ti particle’s oxidization, followed by TiO2 film deposition on the support surface. The schematic diagram of the method is shown in Figure 3. Atmospheric plasma treatment prior to the coating procedure can enhance the NPs decoration on the substrate surface and increase the final product durability [77]. This technique is helpful for coating on supports with low surface tension such as polymers; however, the increased surface tension and plasma-assisted hydrophilic features can greatly reduce during the time [29]. Different techniques are practiced within the plasma coating method such as plasma spray coating and RF plasma coating.
The working principal schematics of plasma spray coating method.
In the plasma spray coating method, a high-temperature plasma arc melts the TiO2 powder injected into it. The melted nano TiO2 particles will be driven by the plasma arc (sprayed) toward the support surface, where it condenses quickly to form a robust film [78,79]. This kind of coating is more suitable for wear resistance, corrosion protection, thermal stability, and barrier applications. The high deposition rate in this method produces high adhesion strength and hardness of the coated film. RF plasma coating method applies RF power to produce the required plasma field which causes precursor (mixed with oxygen) to be activated and react with oxygen to form and deposit thin and uniform TiO2 film [80]. By regulating factors such as plasma power, precursor injection rate, support temperature, and the type of gas applied, the coating features can be adjusted. This method is known as a low-temperature method which offers thin and uniform coating, even on complex geometries, that makes it appropriate for thermo-sensitive supports; however, it is relatively complex, costly, and might require high maintenance. This technique is widely used in photocatalysis, antimicrobial surfaces, anti-corrosion, and optical coatings, or wherever precise control over thickness and uniformity is vital.
3.1.3 CVD methods
In the CVD method, a precursor gas containing Ti (such as TiCl₄, Ti(OiPr)₄) chemically reacts on the substrate surface in a heated vacuum chamber (from 200 to 700°C) to deposit (condenses) a thin film in the vapor phase. The process is illustrated graphically in Figure 4. Besides the thermal CVD, which uses the precursor in the presence of an oxygen source (such as O2, or H2O vapor) as a reactant to form the film, other six CVD techniques within this method are as follows.
Schematic diagram of TiO2 thin film preparation by CVD technology.
Atmospheric pressure CVD (APCVD), in which the process is carried out at the atmospheric pressure, is a simple and cost-effective method while it might have limitations in terms of coating quality or uniformity. This technique is more applicable for industrial use or coating of large surfaces [47]. Low-pressure CVD (LPCVD), which can be performed under a reduced pressure, enhances the coating uniformity and quality. This method is more suitable for high-performance applications such as the manufacturing of semiconductors, coating for optical purposes, as well as for advanced photocatalysis applications [81,82]. Metal organic CVD (MOCVD) method as another type uses a metal-organic precursor (such as Ti(OiPr)₄) to form the film. This process has the advantage of having a precise control over the film deposition rates as well as its composition. The main applications of this method are for high-quality films or nanostructured coating [83].
Hybrid physical CVD (HPCVD) is another technique which combines and leverages principles of both PVD and CVD methods. In the PVD part of it, titanium is sputtered or vaporized from a solid Ti metal or its alloy and directed toward the support surface, where it can condense and deposit a thin film. At the same time (the CVD part), oxygen gas will be injected inside the deposition chamber. This causes the reactions between the O2 and Ti atoms to form high-quality TiO2 film in situ, on the support surface. This hybrid and low-temperature method offers precise control over the component ratio, morphology, thickness, and other properties of the film as compared to both PVD and CVD. The method is known as complex, slow, and costly, which makes it not suitable for large-scale applications, unless economically justified [35,36].
Plasma enhanced CVD (PECVD) or plasma assisted CVD (PACVD), on the other hand, as a low-temperature method, is applicable for thermal sensitive supports, which cannot withstand high temperatures [84]. The technique uses plasma (ionized argon gas) to enhance the chemical reactions (precursor breakdown) that produce the film. The vaporized precursor is ionized in the plasma field and forms TiO2 film after reacting with oxygen. It can lower the reaction temperature while raising the deposition rates. It is mostly applied in the production of electronics, solar cells, photocatalysis, coatings for optical purposes, or wherever a coating at low temperature is required. If this process is carried out under low-pressure plasma conditions, the method is called low-pressure PECVD as a kind of PECVD. Laser chemical vapor deposition (LCVD) is a process that combines CVD principles with the laser ablation method [85,86]. It uses laser to break down the Ti precursor exposed to oxygen in order to directly deposit titanium dioxide on the support surface. This technique can be applied where small areas with precise coatings are required.
Although CVDs are known as low-temperature methods for precise control of film thickness, high purity, excellent adhesion, uniformity, scalability, and versatility, in general, they are costly with high technologies required, complexity, and can introduce toxicity [33].
3.1.4 ALD method
This technique allows for precise and controlled growth of thin films at the atomic level [87]. Although the method works based on the CVD principles, the key characteristic of ALD is its ability to deposit materials in a self-limiting chemical reaction [88], one atomic layer at a time, that is, in each deposition cycle, a pair of precursors react with the substrate in a sequential manner alternatively. This self-limiting behavior ensures that only one layer of material is deposited per cycle which typically is about 0.1–0.3 nm of TiO2 film. After each precursor is introduced (Ti-containing precursor and then water vapor or O2), the reaction byproducts (such as HCl) and excess precursor are purged from the reaction chamber to ensure that only the desired reaction products remain on the substrate surface. By repeating the deposition cycles (sequential exposure of the support to Ti precursor and O2), precise control can be achieved at the atomic level. This technique generally operates in low to moderate temperature ranging from 100 to 300°C, which makes it more suitable for thermal-sensitive supports. The specific steps are shown in Figure 5.
Schematic illustration of ALD cycle.
Although ALD is known as slower process [88] (comparatively, as the final coating characteristics is time-sensitive to the steps of each cycle), which requires costly equipment (for maintaining precise control over temperature, pressure, chemicals flow rate, as well as purging cycles), with finite ultrathin coating thickness (suitable for small scale coating), it is extensively used in semiconductor manufacturing, photovoltaics, dielectrics, super-capacitors, batteries (to enhance their charge storage, lifetime, and stability), micro-electro-mechanical systems, surface protection (as corrosion/water-resistant coating), and other fields wherever accurate control over pure, thin, and uniform film properties is crucial, especially for complex surfaces such as three dimensional or porous supports.
3.1.5 Flame spray pyrolysis method (FSP)
For this technique (as a rapid thermal decomposition method), Ti precursor (as aerosol or vapor) will be introduced into a high-temperature flame (normally made by a fuel such as hydrogen) to form TiO2 and deposited onto a support surface [89,90]. The schematic diagram of the method is shown in Figure 6. This technique is applicable for large-scale coatings with high deposition rates, to produce thin and uniform films [89,91,92]. Factors such as the flame temperature, concentration of the precursor, and the distance between the flame and the support surface can regulate the final product properties. Some advantages of films produced via the FSP method can be such as high purity, nanostructure control, scalability, and versatility [92].
Graphical diagram of the preparation of TiO2 films by FSP method.
3.1.6 MBE method
MBE is a vacuum-based deposition method which is carried out through elemental Ti evaporation in the presence of O2 gas. Two beams of Ti and O2 are heated in different effusion cells and pointed to the support surface (normally kept at a certain temperature), where they interact and condense to form a crystalline nano TiO2 layer [53]. This process can provide a precise control to enable an epitaxial growth of the film, by which it grows in conjunction with the crystal structure of the support surface. The process is illustrated graphically in Figure 7. The technique is known for its capability to form a well-defined smooth film at the atomic level, with high purity, and tuned stoichiometry (Ti to O2 ratio). The coatings via MBE can be tailored for special applications such as sensors, electronic/optoelectronic products, or advanced research projects where crystalline quality is crucial. Besides high cost, and complexity, another disadvantage of this method can be, support type limitation since temperature control of the support is necessary, and the material properties of the support can impact the final product quality.
Schematic diagram of TiO2 thin film preparation by MBE method.
3.1.7 Fluidized bed deposition method
TiO2 NPs are fluidized in a bed in this method and then coated on the support surface. The technique is applicable for coating powders or irregular shape supports [93,94,95]. The principle of this method is to have a bed (container) of suspended particles as powder which can behave like liquid using an upward flow of gas (air flow through a perforated plate) for fluidization from the bottom. The targeted support will be immersed into the fluidized bed, where the suspended NPs can be collided and deposited on it. If the support is heated, or any binder or adhesive is applied, the particles will better adhere to the surface. In this dry method, the coating thickness is controlled via deposition time and support movement within the fluidized bed, to build a uniform coating [93]. Further heat treatment (of around 500°C) will result in an improved bonding strength, crystallinity, phase transformation, and can remove any residual moisture or organic matter. Simplicity, cost-effectiveness, applicability for complex geometrics, and thicker coating with acceptable adhesion (especially if the support is preheated or if any binder is applied) are features of fluidized bed coating. This technique is suitable for large-scale and industrial applications such as in corrosion-resistant coatings. Particle agglomeration possibility is reported if the NPs are not well-dispersed in the fluidized bed [96].
3.2 Wet chemical TiO2 coating methods
In wet chemical synthesis methods normally, reactions are involved within chemical solutions and therefore, are also known as chemical solution deposition methods. The technique/s can be carried out via applying a Ti precursor solution onto a heated support for the deposition of TiO2 film [97,98,99]. Although the techniques are generally simple and low in cost, they might result in less precise film fabrication, comparatively [100,101]. The three most frequently applied wet coating methods with their sub-categories are explained and illustrated as follows.
3.2.1 Sol–gel coating methods
Among the well-known wet chemical methods for large-scale film coating are the sol–gel-based methods [34]. Prior to the coating, a liquid precursor is transformed into the sol (solution containing the NPs) or the gel (the denser phase of the sol whose formulation methods are explained elsewhere, stoichiometrically [102]) will be provided. Then, a thin layer of the gel would cover the support surface through methods such as dip coating [32,103], spin coating [104,105,106,107,108,109,110], spray coating [34,111], or Dr. blade [11], which are separately explained below. Most of these coating methods are followed by a hydrothermal treatment step (annealing) at high temperatures (around 550°C and above in muffle) to crystallize the coated NPs to the desired crystal type and remove the intermediates. Multiple cycles of coating and annealing can be performed to maximize the Brunauer–Emmett–teller (BET) surface area, anatase crystal rates, and adhesion. This mechanism is graphically presented in Figure 8. Some literature reported an enhanced coating features if UV light exposure is applied prior to the hydrothermal step as PAD [62] method.
Sol to gel and to film conversion steps: air drying, oven and muffle, multiple annealing, gel to xerogel, and then dens film.
3.2.1.1 Dip coating
Gently immersing the support into the gel, holding it deep into the gel for a certain period of time (around a minute), and lifting it out at a low speed are the principles of the dip coating method, as the process is illustrated graphically in Figure 9a. It has been reported that dip coating is preferred over spin coating due to higher adherence and efficiency [81,82], although is challenging for large samples [34]. When using dip coater equipment, parameters such as immersion speed, pulling speed, gel viscosity, and support type can greatly impact the coating thickness and homogeneousness [112,113]. In some cases, due to the shape or the size of the support, such as crushed glass pieces [63], adding the gel into a container containing the support and draining it after, could be applied. If multiple layers of coating are required, then repetitive cycles can form a layer-by-layer film on the surface (an optimum of 5–6 layers of TiO2 coating on glass support was recommended by Gong et al. [9]). A less viscous gel in multiple rounds of coating will result in a more uniform and crack-free film with less agglomerations [102,114].
Different sol–gel coating methods: (a) Spin film coating method, (b) dip coating method steps for film deposition, (c) spray film coating method, and (d) Dr. Blade film coating method steps.
3.2.1.2 Spin coating
For the spin coating method, after the substrate is thoroughly washed and dried, it will be fixed on the spinner, and then an adequate amount of TiO2 gel would be placed (or dropped) on top of the support surface (at the center) before being rotated (spun) horizontally at certain rpm (rapidly) and time (800 rpm for 25 s was reported by Wang et al. [32]). This will disperse a thin uniform layer of the coating solution due to centrifugal force [81], the specific steps are shown in the Figure 9b. The spin coating generally includes two rounds of rotation at the wet and drying phase (at 200–2,500 rpm), each followed by a holding period of 10–20 s [27]. The higher rotation speed (3,000–5,000 rpm) will result in a thinner layer, especially since a considerable amount of the sol will be thrown away from the support surface during the spinning step [115,116,117], although other parameters such as the viscosity of the sol are also important in controlling the thickness [118].
3.2.1.3 Spray coating
The spray coating usually is carried out using a fine nozzle sprayer at a certain discharge rate, pressure, and distance. In this method, a precursor solution containing TiO2 NPs is sprayed onto a heated substrate. The solvent evaporates, leaving behind a deposited TiO2 film. The process is illustrated graphically in Figure 9c. To avoid nozzle blockage, a very thin gel (or sol) with low viscosity must be used to coat every corner of the surface with the desired thickness. This method is more suitable for non-flat samples [34].
3.2.1.4 Dr Blade
Dr blade or tape casting method is a technique in which the moving substrate can have a controlled thickness of the coated material (started from around 20 micron thickness of the slurry [119]) since the blade meters the gel to produce a uniform thickness on the moving substrate. The detailed steps of this method are shown in Figure 9d. This method can be applied to coat large surfaces [11].
3.2.2 IWI method
This method takes place via impregnation of a porous support using liquid Ti precursor but to use just enough of it so that the support pores are filled (or wet), but not the surface. Knowing the pore volume in this method is critical for deciding the amount of the precursor solution required. For impregnation, the support is immersed into the precursor, or the precursor is added dropwise in an orderly manner. The amount of precursor is accurately measured to make sure that it just fills the support pores, without any extra precursor being left on the support surface [120,121]. This will also minimize the precursor waste. After drying the substrate in oven, it will further go through the calcination process (of about 500°C) for TiO 2 crystallization and phase transformation. Porous supports with high surface area will have a controlled film thickness through this technique and are applicable in various fields such as water/air purification, contamination removal, surface modification, and self-cleaning.
3.2.3 EPD method
EPD is a coating technique which employes an electric field to charge TiO2 particles (as suspended), and drive toward a conductive substrate (electrode). This migration of charged particles leads to the deposition of a uniform and thin film coating [122]. For this method, after preparing the sol (TiO2 suspension as electrolyte solution) the particles are positively/negatively charged through pH modification or via using stabilizers, which causes them to migrate when an electric field is available. In this process, two electrodes (negative and positive) are required in the sol for the migration of charged particles. The support (submerged in TiO2 sol) will be used as cathode (negative), and another counter-electrode (a plate made of stainless steel or platinum) will serve as the anode (positive). After anodization, a direct current (DC) electric field is applied in the sol, driving the charged NPs toward the support surface [123,124]. Applying the right charge type (−/+) is necessary to ensure the correct direction of particles migrating toward the substrate. The schematic diagram of this method is shown in Figure 10. The TiO2 particle accumulation rate depends on multiple parameters such as the DC current voltage and its duration, the concentration of NPs in the sol, and the distance between the two electrodes [125]. After deposition, the coated support is dried followed by annealing process at a high temperature (around 500°C) for crystallization.
Diagram of EPD apparatus.
Besides simplicity, the method offers a cost-effective, dense, durable, and uniform coating, with an even distribution of NPs that is applicable to coat on supports with complex geometries. However, the applied substrate in this method must be conductive (like metal) for the migration of charged NPs, otherwise, it might require pretreatment steps. Also, to maintain TiO2 particle suspension stability is critical in this technique, to ensure the coating quality [126]. The usual applications of nano TiO2 coating via other methods (such as optical, environmental remediation, energy saving, protective layers, etc.) are also available via this technique.
3.3 Summary of TiO2 Coating Methods
See Table 1.
Summary of the TiO2 coating methods with their sub-methods, advantages, disadvantages, and applications, comparatively
| Method | Description | Applications and advantages |
|---|---|---|
| PVD (PLD, electron beam and thermal evaporation, magnetron and ion beam sputtering) | Evaporation or sputtering of atoms, and condensation on substrate in vacuum environment | Wide range of application: optical, wear resistant layers, photocatalysis; thin film and good adhesion, slow and high cost |
| Plasma coating (plasma spray, RF plasma coating) | Vaporized Ti is injected into highly ionized gas, which oxidizes the particles and drive toward support, for supports with low surface tension | Antimicrobial, optic, anticorrosion, thermo-sensitive supports, barrier, made at low temperature, costly, controlled thickness, high adhesion |
| CVD (thermal CVD, MOCVD, HPCVD, LCVD APCVD, LPCVD, PECVD | Gaseous Ti precursor reacts on substrate in heated vacuum to deposit vaporized thin film | For electronics, and precise control applications, thin film, high purity, excellent adhesion, low temperature, costly. |
| ALD | Self-limiting chemical reaction, one atomic layer at a time based on CVD principles | Low temperature, thin film, slow, costly, precise control industries, semiconductors |
| FSP | Uses fuel for high-temperature flame decomposing vaporized precursor into film | High deposition rates, high temperature, thin film, scalable |
| MBE | Vacuum-based, elemental Ti evaporates in presence of O2 beam, pointed to the support to interact | Smooth ultra-thin film, high temperature, sensors, electronic/optoelectronic products |
| Fluidized bed deposition | Suspended particles using an upward gas flow fluidized to coat the support | Thick coating, for large scale, corrosion resistance |
| Sol–gel (dip, spin, spray, and Dr. blade coating) | Liquid precursor is transformed to sol and then gel, followed by thermal treatment for crystallization | Low cost, simple, thick coating, for photocatalysis, self-cleaning |
| IWI | Impregnation of a porous support via enough liquid Ti precursor so just pores are filled, but not the surface | High temperature, low cost, self-cleaning, water/air purification, surface modification |
| EPD | migration of charged particles via pH modification, and drive toward conductive substrate in electric field | Low cost, high temperature, simple, dense film, wide range of application |
4 Coating characteristics assessment
Once the coating is done, a set of tests is required to examine the coating morphology, obtained NP type and size, roughness and cracks of the film, surface area, adherence, defects, etc., which are important as influencing factors on the mechanical and chemical desired properties of the coating, based on the targeted application. The commonly used testing equipment and techniques are as follows.
4.1 X-ray diffraction (XRD)
XRD is a powerful and widely applied non-destructive method for structure characterization [127], phase composition identification, and crystallinity level (in terms of size, structure, and orientation) of coatings with highly accurate and reliable results. These are necessary parameters for analysis and coating assessment which influence the properties of the final product during the film fabrication, for the targeted application. For this test, an X-ray tube produces X-ray beams and illuminates them at the coating surface (sample). Due to the interaction of X-ray beams with the material crystal lattice, the beams will diffract in certain directions according to the atomic planes (or lattice planes) space of the crystal structure. This will cause the diffracted X-ray beams to form a pattern which can be distinguished by a detector. Through analyzing the diffraction pattern features (such as peaks, intensity, and angles) the arrangement of atoms in the crystal can be identified [128,129,130]. The frequently used term of 2θ in this test is referring to the angle between the incident and diffracted X-ray beams, as a comparison basis to classify the diffraction pattern intensity. Moreover, the internationally approved diffraction features information (such as ICCD) provides standard databases of distinct XRD patterns for comparison and phase identification of the coated material [131] (such as the relative amounts of anatase or rutile phases in case of TiO2).
The average crystal size can be identified via the Scherrer equation (equation (1)) from the broadening of the diffraction peaks. Based on equation (1)
where
Normally, the larger peak width shows a smaller crystal size. The coated TiO2 level of crystallinity can be extracted from the diffraction peaks sharpness as well as intensity. The sharper and the more well-defined peaks, show the more well-crystallized films, while the more broad peaks indicate less crystallized films [133]. XRD can also be used to identify any lattice strain in the crystal. This phenomenon is referred to the deformation of the crystal structure, caused by stress or any defect, that is assessed from diffraction peaks broadening. Besides, the diffraction peaks relative intensity can be used for orientation and crystallographic plane analysis [134]. Some peak standards of XRD patterns, corresponding to anatase and rutile TiO2, can be mentioned as: 25.3°, 38°, 48°, 55°, and 62.5° corresponding to 101, 004, 200, 105, and 204 crystal planes of anatase, respectively, and 27.4°, 36.1°, 41.2°, 54.3°, and 56.7° corresponding to the 110, 101, 111, 211, and 220 crystal planes of rutile, orderly, all at 2θ values.
The known limitation of the XRD test for film coating assessments is resolution imperfection when the film thickness is low (generally lower than 100 nm) because the primary analysis goal of this method is the bulk crystal structure but not the films. This might cause a weak diffraction signal which leads to difficulties in TiO2 phase identification, roughness, and amorphous surface layers unless the thicker film is being analyzed.
4.2 Scanning electron microscopy (SEM)
SEM is an important method applied for morphological and structural characterization such as surface morphology, delamination, grain structure, thickness, integrity, and uniformity of films. The method offers high-resolution images of the surface as well as the cross-sectional structure of the film, providing valuable information about the coating. The principles of SEM work are based on scanning an illuminated beam of electrons with high energy at the substrate surface. Reflection of different signals emitted from the surface after the electron beam strikes are then detected by various detectors, and employed to form high-resolution images [135,136]. These reflected signals might be including secondary electrons (used for surface morphology analysis such as roughness, porosity, and distribution of particles) or backscattered electrons employed in composition and structure assessment [137]. SEM can also be coupled with energy dispersive X-ray spectroscopy or characteristic X-ray applied for elemental composition identification, and impurity assessment [138].
As a non-destructive method, SEM provides quick and efficient high-resolution images for TiO2 coating examination to assess both surface and cross-section properties of films, which is vital to the analysis of coating characteristics. However, it also has its drawbacks and sensitivities such as thin film features detection limitations, conductivity requirement for imaging, which needs coating surface modification with conductive materials, and limited areas imaging, which may not represent the entire film surface.
4.3 BET
BET measurement is a commonly used method to test the specific surface area and pore structure of materials or coatings. This technique applies N2 gas as adsorbate to determine how much of it is adsorbed on the surface of the object at certain temperature that is the liquid nitrogen temperature. For this examination, the film is exposed to N2 gas stream at −196°C, and the amount of gas adsorbed is tested at different relative pressures. Then, based on adsorption isotherm, the BET formula (equation (2)) is used to compute the specific surface area in m2/g [139].
where
Combined with other methods such as Barrett-Joyner-Halenda (BJH) the BET test can be applied to calculate the pore size range, distribution, as well as total pore volume (void space) of the film coatings [140]. This non-destructive method provides accurate and reliable measurement for the coating’s specific surface area; however, it might not be suitable for heterogeneous coatings or very thin films with thicknesses of less than a few nm, due to limitations in N2 gas absorption.
4.4 Fourier transform infrared spectroscopy (FTIR)
FTIR is applied for composition verification, phase recognition, and to identify the presence of different chemicals in the coatings. This will enable to detect contaminants or any functional groups (such as when using surfactants, doping, hydrophobicity assessment, etc.) involved on the deposition surface, for coating quality assessment. This spectrophotometry method uses the infrared light spectrum to analyze the vibration peaks (of Ti–O, O–H, etc.) as well as other films’ characteristics [141,142].
4.5 Durability
Durability test for coatings is necessary to know their life cycle and possible treatment/recoating requirements [143]. This result will ensure that the film maintains its performance during the desired lifetime under targeted environmental conditions. It shows the film’s ability to tolerate criteria including abrasion, corrosion, weathering, UV, and chemical exposure while keeping its physical and/or chemical properties [144,145]. Different examinations have been applied to assess the coating’s durability, taking into consideration the targeted application. Here the eight most frequently practiced durability testing techniques for TiO2 coating are introduced with the details explained in Appendix A including the Abrasion resistance test: such as Taber Abraser, and scratch test; Weathering and UV exposure test: such as accelerated weathering, and outdoor exposure; Corrosion resistance test: such as salt spray test, and electrochemical impedance spectroscopy (EIS); Chemical resistance test: such as immersion, and surface interaction assessments; Photocatalytic stability test: such as degradation efficiency, reusability, and temperature cycling tests; Adhesion test: such as cross-hatch adhesion, and pull-off adhesion tests; Mechanical durability test: such as impact resistance assessment; and finally, Hydrophobicity test such as contact angle measurement.
4.6 Transparency
Since opacity can cause reduction in the transmission of light, transparency test for TiO2 coating takes place where optical properties and clarity is a necessary criterion for the coating application. These applications can be self-cleaning windows, solar panels, optical coatings, and transparent conductive layers where transparency can impact the applicability of the final product. The seven common transparency test techniques for TiO2 film coating are including: First, the UV-vis Spectrophotometry that is a test of transmittance and absorption of the light spectrum in which high transmittance (400–700 nm) shows a good transparency while UV blockage can be observed when high absorptions occur in the range of 100–400 nm [146,147]; second method is optical coherence tomography (OCT) imaging which measures the thickness as well as uniformity of the coating [148,149,150]; Refractive index measurement (RIM) uses a refractometer or ellipsometer, which quantifies how much of the light transmitted or refracts through the film (for TiO2 this index is 2.5–2.9) is the third method [151]; fourth is the film thickness test through optical profilometry or contact profilometry which measures the coating thickness as it impacts transparency [152]; fifth is the visual coating inspection, which offers a quick evaluation of its optical clarity and cloudiness; sixth is the coatings’ color assessment method that applies the CIE Lab system to check the color changes or coatings’ tints via colorimeter which quantifies the L, a, and b values as the film lightness and chromatic components [153]; and finally seventh is the light scattering test via dynamic light scattering (DLS) or light scattering goniometers which evaluates scatterings’ angle to check the potential opacity [154,155,156].
4.7 Summary of TiO2 coating characteristics evaluation methods
See Table 2.
Summary of coating assessment methods, equipment, and application areas
| Method | Applications | |
|---|---|---|
| XRD | Crystal structure, phase composition, lattice parameters, and stress state. Disadvantage: Has resolution limitation when the film thickness is low | |
| SEM | Surface morphology (roughness, porosity, and distribution of particles), delamination, grain structure, thickness, integrity, and uniformity of films. Disadvantage: Thin film features detection limitations, conductivity requirement for imaging which needs coating surface modification with conductive materials, and limited areas imaging | |
| BET | Specific surface area and pore structure, calculate pore size range, distribution, as well as total pore volume (Combined with other methods such as BJH). Disadvantage: Not suitable for heterogeneous coatings or very thin films with thickness of less than few nm due to limitations in N2 gas absorption | |
| FTIR | Composition verification, phase recognition, to identify the presence of chemicals in the coatings | |
| Durability test | Abrasion | Quantifies the film ability to tolerate mechanical wearing or friction using abrasion or scratch tests |
| Weathering/UV | Evaluate the ability of film to withstand harsh weather conditions & sunlight exposure in real scenarios | |
| Corrosion | Assess their resistance abilities to the environments including salt or humidity | |
| Chemical | It shows the ability of film to resist degradation in environment exposed to chemicals | |
| Photocatalytic | It evaluates the photocatalytic stability of the coating, including degradation efficiency and reusability | |
| Adhesion | It tests the possibility of coating damage, i.e., peeling, cracking, and delamination under stress | |
| Mechanical | It tests the resistance of the film to impact/deformation when coating is subjected to mechanical stress | |
| Hydrophobicity | It tests the ability of films to repel water droplets when applied for self-cleaning | |
| Transparency | UV-vis | A test of transmittance and absorption of the light via spectrophotometer |
| OCT | To measure the thickness as well as uniformity of the coating | |
| RIM | Uses refractometer to test the amount of light transmitted/refracted through the film | |
| Thickness | It measures the coating thickness by optical or contact profile method | |
| Visual coating | It offers a quick evaluation of its optical clarity and cloudiness | |
| Coating color | It applies the CIE Lab system to check the color changes or coatings’ tints | |
| DLS | It evaluates scatterings angle to check potential opacity | |
5 Key problems of coating
Considering the type of application expected for TiO2 coating, the possible challenges which the coating might face may come from a variety of reasons before, during, and after the coating, as listed below. These can range from the choice of applied materials such as support type or chemicals used (before coating) to the selected coating methods (during coating), and even during the practical application (after coating), which can lower the final product/system efficiency.
5.1 Durability
TiO2 film coatings, normally, must withstand different conditions, such as harsh environmental exposure (to UV, humidity, temperature, and flow rate), and chemical/electrical interactions. During time, these conditions will decrease the effectiveness and structural integrity of the film. Therefore, improving the chemical and mechanical strength of the film is vital. This will necessitate to develop a more stable coating through different techniques such as applying hybrid coatings with improved properties, such as to combine titanium dioxide with other materials including silica, carbon, etc. Some coating methods might require surface modification to enhance the affinity of the film with the support surface, which is called functionalization [27]. These techniques are post modification, applying surfactants, or pre-treatment (for instance surface etching for efficient adherence via H2SO4 or SO3) [157] which act like anchor points to better decorate the NPs in a matrix or skeleton, on the targeted surface [27]. Besides the choice of deposition methods, material selection (like precursors and substrates) is also vital. Employing the wrong substrates can impact the photocatalytic activity, and may cause effectiveness reduction due to residues by the synthesis of photocatalyst, and the film contamination by intermediates produced through different reactions [157]. For example, organic polymers are transparent, light, flexible, cheap, environmentally resistant, and available; however, due to their low surface free energy and thermodynamic characteristics, only low temperatures (up to 170°C [9]) coating methods could be applied on them; while nano TiO2 crystallization requires temperature of around 500–550°C for anatase phase transformation and acceptable adherence [7,9,23]. Besides, most polymers are highly degradable under UV light radiation [29], due to a process called photo-aging which causes the loss of structural integrity through a decreased molecular weight induced by UV [158]. Moreover, the weak van der Wall force between the NPs and the polymers along with hydrophobic nature and low wettability [27,159] of the surface, ease the coating detachment [160].
5.2 Low efficiency
Film coating’s efficiency might be limited by parameters including surface area, NP size, TiO2 phase and crystallinity level, coating thickness, and the presence of pollutants [70,161,162]. To achieve a coating with the most desired properties through selecting the best match method and chemical compounds is the first step to minimize future efficiency issues. Developing a self-cleaning TiO2 coating, which is capable of resisting the formation of biofilms over the application time, is a necessary action to maintain high efficiency. Moreover, nano TiO2 doping via employing other elements (such as nitrogen, sulphur, and carbon) can enhance its efficiency under the visible light spectrum, which will improve its performance under natural daylight [163,164,165]. For other applications such as optical, protective barrier, etc., where certain properties such as transparency or thickness are the priority, control over the fabrication process would be the key to enhance the coating efficiency and minimize maintenance or recoating requirements. Coating heterogenicity or weak adhesion will lead to delamination and localized degradation, which will reduce the coating efficiency and life cycle of the film. Applying more advanced methods such as EPD or plasma spraying which ensures uniform deposition, strong adhesion, and longevity is recommended, if the cost-effectiveness allows.
5.3 Scale up and commercialization
The scale-up of nano TiO2 film production for practical, outdoor, and industrial applications is a well-known challenge compared to lab-scale production [166]. Here the production cost-effectiveness, reproducibility, and scalability are to be taken into consideration. This will be difficult when the film coating goes through precise processes such as coating uniformity or curing, which requires full control over the ambient condition. For this purpose, cost-effective coating methods (such as sol–gel or spray pyrolysis) or materials (supports or hybrid compounds) are preferred, while these solutions might also need to be optimized for commercially viable large-scale production [167]. Moreover, standardization and automation of processes can cause cost reduction and/or coatings properties enhancement. This will help to unlock the full potential of TiO2 film coatings in diverse applications.
5.4 Fouling and biofilm formation
When it is exposed to the outdoor environment, TiO2 film coatings can face the problem of fouling, which is the accumulation of biofilms or byproducts remaining from oxidation/reduction processes on the coating surface. The unwanted settled and accumulated byproducts or “foulants” are inorganic ions and compounds, microorganisms, carbonaceous species, colloids, metals, and solutes on the surface or within the substrate structure caused by interactions between contaminants and support [6,168]. This is more common in aquatic or wastewater environments of bioreactors, which reduces the efficiency. This phenomenon can decrease the catalyst’s active surface area, interrupt the photocatalytic activities, and lead to shorter intervals of maintenance requirements.
Developing coatings with antibiofouling ability, through surface modification or self-cleaning properties (such as hydrophobic coatings, doping via silver or other materials, etc.), can help to minimize this problem. Some scholars reported that a dynamic cleaning systems such as a periodic UV exposure, can help to better manage the expected photocatalytic activities [169,170]. It was suggested that occasionally applying pure water instead of contaminated samples in the reactor for photocatalysis can completely remove the degradable intermediates and foulants from the coated film [7].
5.5 Photocatalytic activation and UV light limitations
Technically, TiO2 particles on the film require UV light for activation. However, for industrial and/or outdoor applications, there may not always be enough natural UV available. Besides, an evenly illuminated light might not irradiate at the coating surface, which impacts its overall effectiveness. Doping TiO2 with other materials such as N2 or C can, to some extent, improve its expected efficiency. Using solar panels to convert a bigger portion of the light spectrum to UV is another option. In terms of transparency, some support such as polymers (due to degradation over time or due to additives which are used as UV stabilizers to reduce the photooxidative process [171]) or glass (owing to iron compounds [172]) are opaque to ultraviolet radiation [29]. In polymers, this opacity will increase since C–C and C–H bonds can be broken down to lower molecular weight compounds by the photon’s energy from the UV light [173]. Using supports such as low iron glass [174] can increase the UV penetration for enhanced TiO2 activation.
5.6 Environmental impacts and toxicity
While titanium dioxide itself is considered as a non-toxic element, when it comes to nano-scale, it can pose human health risk or environmental risks, if not properly handled during production or application [175]. This is a concern for commercialization and scale-up production of TiO2-coated materials. Following safety protocols and standards for handling and disposal of TiO2 needs to be taken seriously into consideration, to ensure its eco-friendliness and minimized risks.
5.7 Impact of support type
Nanomaterial film coating is the immobilization of NPs as a thin layer on a surface to change, control, or enhance the physiochemical properties of the support surface or just for the purpose of the film application. However, the substrate will also have an effect on the TiO2 thin film in turn. Although there are various types of substrates, the selection of support type is based on the application, requirements, and method used for preparing TiO2 films. Nanostructured TiO2 films could be grown on different types of substrates such as glasses (quartz glass, sodium-lime glass, borosilicate glass), metal plates (such as stainless steel and aluminum), as well as ceramic tiles, rubber sheets, and even some substrates with poor thermal stability like polymers [176,177,178,179,180]. Surface tension, thermal stability, scalability, availability, transparency and transmittance, cost-effectiveness, UV resistance ability, porosity, durability, coating method, chemical stability, and available technology are of important parameters to consider when selecting the support type [181,182,183,184,185].
In fact, the substrate not only affects the formation of crystal phase of TiO2 films but also the microstructure, and surface morphology of the films, greatly, which all will have impact on the performance of the final product (such as photocatalytic [186,187]). For instance, the roughness of the substrate is of great significance when preparing TiO2 thin films. Substrate roughness promotes the retention of TiO2 colloid. The rougher the substrate, the more TiO2 can be carried on the prepared film, and the thicker it will be [188]. This also indirectly affects the photocatalytic performance of the TiO2 film.
Krýsa et al. found that after preparing titanium dioxide films using three different types of glass with different Na contents as substrates, the higher the Na+ content in the glass, the worse the photocatalytic activity of the titanium dioxide photocatalyst. This is because sodium ions in the glass used as the substrate diffuse onto the titanium dioxide film during calcination, and sodium ions prevent the formation of the photoactive anatase phase, thereby affecting the photocatalytic activity of the titanium dioxide film [189,190].
Qiu et al. prepared TiO2 films on glass, ITO glass, and P-type single crystal silicon. They observed the surface morphology of the titanium dioxide films through atomic force microscopy. It was found that nearly circular particles of about 80 nm were uniformly arranged on the glass surface. For P-type monocrystalline silicon, they observed perfect round particles within the range of 50–150 nm, and the surface roughness is larger than the other ones. They found slender particles closely packed on ITO, with a grain size of approximately 20 nm and a relatively small surface roughness. It can be seen from this that the surface topography, including the shape and arrangement of particles, also largely depends on the substrate [186].
Harizanova et al. prepared TiO2 films on silicon wafers, ordinary glass, and ITO glass using the sol–gel method. They found that the optical behavior of the TiO2 films obtained on ITO substrates was significantly different. The coatings reveal very high transparency in the visible spectral range up to 85%, despite the increase in the number of layers and the heat treatment, reaching the transparency of bare ITO substrate. However, as the number of layers and annealing temperature increase, the transparency of TiO2 films on ordinary glass decreases. This indicates that the optical properties of titanium dioxide films obtained from different substrates are also different [191].
Daoud et al. found in their research that the thermal stress caused by the difference in the coefficient of thermal expansion between the substrate and the film would lead to the formation and propagation of microcracks along the grain boundaries after crystallization. In their research, they used glass ceramics and aluminum as substrates to prepare titanium dioxide films and reached the above conclusion by comparing the thermal expansion coefficients of the three materials and titanium dioxide (anatase phase) [188]. Overall, the importance of the support type must be taken into account for any coating considering its application as well as all the abovementioned parameters as an influencing factor.
6 Concluding remarks and future perspectives
Development of TiO2 coating methods will continue to be among the hot topics, taking into consideration its versatile and exceptional photocatalytic, antibacterial, UV protection, and optical properties which will unlock new applications. As research works will continue, TiO2 coating methods are expected to have more broad applications in a variety of fields, from environmental to energy, electronics, and health in order to enhance the quality of life. Some of the future key drivers in advancements of film coating technologies for its widespread adoption of coatings might be as follows.
Development of low-cost coating technologies: novel techniques for applying TiO2 coating uniformly onto large surface areas will enhance its scalability and decrease the process costs, making the TiO2 film coating technologies more viable, commercially.
Nanostructured and 3D coating: Advancements in nanotechnology can lead to the formation of nano TiO2 coated supports having complex geometries and 3D nanostructured with improved surface area which causes enhanced efficiency. These new coatings can offer new opportunities in fields such as textile, building, and electronic materials.
Automation and optimization: Automation in processes (from production to application) and optimization of deposition methods, chemicals used, and support types can cause cost/time savings with more efficient methods for mass production and scaleup. TiO2 coatings can be integrated with an automated surface cleaning system, which their functionality can be optimized if applying AI to respond to the changes in the environment intelligently.
Sustainability and green engineering: As the world moves toward sustainable development, TiO2 film coating can have a leading role in decreasing environmental contaminants of industrial activities such as through low-carbon manufacturing. Advancements in low-energy processes in TiO2 film coating production, such as low-temperature methods, can help in carbon reduction associated with such processes. TiO2-based coatings can be applied in green roofs or carbon capturing technologies, which can help CO2 conversion into useful materials.
Longevity and recyclability: Material modifications will be a hot spot research area for scalable TiO2 coatings production, and integration with emerging technologies, cost-effectively. This can lead to produce durable coatings which can last longer under harsh environments for outdoor/practical uses. Efforts need to be made toward production of TiO2 coatings with simple recyclability and/or re-manufacturability, so that at the end of the coatings’ lifecycle, they can be reused as more economic products.
New fields and applications: The wide range of TiO2 coatings applications will bring this technology into new industries. Advancement of coating features for its different usage can bring it to the key areas where TiO2 film deposition is likely to evolve and bring substantial impacts in the future. These might further expand the TiO2 film coating scopes in a variety of industries as below.
6.1 Photocatalytic applications
The ability of nano titanium dioxide to decompose different chemical compounds and biological contaminants as a catalyst when it is activated by UV offers a vast potential for its diverse applications. Marketable building materials including photocatalytic concrete for the reduction of air pollution, tiles with self-cleaning ability, or smart windows with enhanced optical properties and self-cleaning abilities are already in use, as the fields where TiO2 applications can be expanded in. The future of TiO2 coatings can be scaled up for air/water treatment in industrial purification systems. Products such as anti-fog, self-healing, and self-cleaning windows for vehicles or aircraft might be future active areas of research via such coatings.
6.2 Enhanced bandgap energy under visible light
The photocatalytic activities of nano TiO2 are dependent on the UV light intensity, that is just a small portion of the sunlight and consequently, is limited in practical large-scale use. Research works will most likely concentrate on enhancing its photocatalytic efficiency using natural visible light, improving its reactivity for various fields. This might be possible through doping with other elements to enhance its bandgap energy and develop its light absorption range to visible light as a broader spectrum. Such hybrid combination of semiconductors can have an improved activity, with higher charge separation ability, for an efficient catalyst under natural daylight.
6.3 Energy harvesting fields
TiO2’s capability in generating electricity from sunlight through photocatalytic and photovoltaic effects has caused such coatings to be explored for application in solar panels. It has already been employed in dye-sensitized solar cells as the photoanode material. The concentration of the research work is to improve TiO2-based solar cells in terms of their efficiency, stability, and cost-effectiveness. Advancements may bring more economically affordable solar energy with higher efficiency to the end-users. This might also play a great role in supercapacitors, batteries, or energy storage devices in general, with enhanced charge storage and cycling stability.
6.4 Healthcare and biocompatibility
As biocompatible materials, TiO2 coatings exhibited antimicrobial and pathogen removal properties. Their application in the medical field can develop considerably. Such coating and material can be employed to heal wounds, antivirals, implant devices, use in antibacterial or self-sterilizing surfaces, or even to integrate with bandages, prosthetics, biosensors, and food processing plants. It has been studied to be applied in photodynamic therapy for cancer treatment, in which through the generation of reactive oxygen species it can eliminate the cancer cells. Moreover, TiO2 might emerge for drug delivery or imaging agents to enhance public health.
6.5 Smart coatings and sensors
TiO2 coatings can also play an active role in the smart materials market. This could include devices like sensors which are able to respond to environmental stimuli such as for detecting gases or pollutants. Another innovative coating can be self-healing TiO2 that will be able to repair itself after mechanical damage or wear, for long-term applications. Moreover, TiO2 is being further researched for applications in transparent and conductive coatings for touchscreens, displays, and smart windows.
-
Funding information: This work was mainly supported by the National Natural Science Foundation of China (No. 52150410408); the Science and Technology Planning Project of Guangxi, China (No. AB 23026045 and AA20161001); and the Science and Technology Plan Project of Guilin (No. 20230102-2).
-
Author contributions: In this review, Jiaxin Liu was responsible for methodology and visualization. Saeed Rad was responsible for project management, conception, and writing the first draft. Junfeng Dai assisted in supervising, reviewing and editing. Lei Gan was responsible for formal analysis and data curation. Cheng Chang provided resources and assisted in reviewing. All authors have accepted responsibility for the entire content of this manuscript and approved its submission.
-
Conflict of interest: The authors state no conflict of interest.
-
Data availability statement: Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.
TiO2 coating durability can be tested through different methods. Below are the eight common techniques, in brief, used for this purpose.
A1 Abrasion resistance test
This method quantifies the film’s ability to tolerate mechanical wearing or friction using abrasion or scratch tests, that is important for coatings that are subjected to friction.
A1.1 Taber Abraser test
The test is carried out via applying an abrasive wheel which rotates to wear the film and then quantifies the amount of change or loss in the coating’s surface. The weight difference or deformation after certain rotation rounds will be measured to calculate the abrasion resistance of the film [192,193].
A1.2 Scratch test
Using a sharp object (such as a needle), a line is drowned across the film surface in a controlled load manner to measure the film’s scratch resistance and solidity. This can indicate that how difficult or easy the surface might be damaged when a mechanical force applied to simulate the real environment situations [194,195,196].
A2 Weathering and UV exposure test
Harsh weather conditions and UV or sunlight illumination can damage films during time [197]. Exposing TiO2 films to such an environment is a test to assess their ability to withstand real scenarios.
A2.1 Accelerated UV exposure
Films will be exposed to UV light via xenon arc weathering hollow or fluorescent UV lamp which in fact simulates the long-term exposure of the film outdoor [198]. After a certain period of illumination time (<1,000 h), the changes in the film’s physical appearance such as color, cracks, or its photocatalytic ability can be evaluated.
A2.2 Outdoor exposure
Also, films can be examined in real environmental conditions for certain periods (up to a few years based on feasibilities). Afterward, criteria such as changes in color, cracks appearance, functionality effectiveness, and degradation level can be assessed.
A3 Corrosion resistance test
Films applied as anticorrosion should be examined to assess their resistance abilities to the environmental criteria including salt or humidity.
A3.1 Salt spray test
Exposing the TiO2 film to salt mist for a certain time (<1,000 h) in a chamber is called salt spray test in which the film’s physical appearance can be monitored for corrosion marks, delamination, or coating degradation after the exposure. This method is normally used for metal coatings assessment [199,200].
A3.2 EIS
It evaluates the electrical impedance of TiO2 film exposed to various electrochemical environments, such as saline or acidic solutions. The value of impedance indicates the protective ability of the film, including corrosion resistance or being a protective barrier [201,202,203].
A4 Chemical resistance test
TiO2 films might be applied in different environments and hence exposed to various chemicals. This test shows how good the film can resist degradation in such environments.
A4.1 Immersion tests
Immersing TiO2 film in a variety of chemicals (solutions with different acidities, oils, solvents, etc.) during certain times (1–3 days) can be performed in this method to evaluate the coating for degradation marks such as swelling, change in color, delamination [204].
A4.2 Surface interaction test
TiO2 film can be exposed to smaller amounts of chemical compounds under a more controlled condition (such as spraying or wiping) to examine their effect on the film properties.
A5 Photocatalytic stability test
For photocatalytic applications of TiO2 film, it is necessary to evaluate how stable is the coating functionality during time. For this purpose, there are three methods to employ.
A5.1 Degradation efficiency
It is the exposure of TiO2 film-coated support to UV light while it is in use for contamination removal and evaluate the degradation rates during time to monitor if any changes in terms of degradation efficiency will happen [63].
A5.2 Reusability test
This test is in fact the films’ photocatalytic effectiveness stability measurement after certain cycles of use [63].
A5.3 Temperature cycling test
If the TiO2 film is supposed to be applied in a high-temperature environment, monitoring its characteristics after certain cycles of heating and cooling is a measure of its thermostability [205].
A6 Adhesion test
A firm adhesion of the film onto the support surface is a measure of durability [206,207]. The possibility of damages to the coating such as peeling, cracking, and delaminating when it is stressed is called the adhesion test [208]. There are two methods to measure these parameters as follows.
A6.1 Cross-hatch adhesion test
This technique is carried out based on the ability of a tape to remove the TiO2 film when it is sticked on the support and pulled off from its surface. For this test initially, network shape cuts are made on the film’s surface and then the tape is applied. The amount of film that remains on the support or the tape surface can be a measure to determine the coatings’ adhesion strength [209].
A6.2 Pull-off adhesion test
In this method, the amount of force required to remove the film from the support surface is used as the direct measure of the adhesion strength. This test uses a special device which is attached to the coating surface and then pulled [210].
A7 Mechanical durability test
When the coatings are mechanically stressed, different properties of the film such as impact resistance or deformation tolerance would play important roles in the overall durability and functionality of the coating. The below test can measure the resistance ability of the film when it is under physical stress.
A7.1 Impact resistance test
This method calculates the resistance ability of the coating against being cracked or detached when an external force is applied. For this test, normally a swinging weight is released to apply a controlled force of a falling object on the coating. Then, the damage resulted from this force will be assessed to measure the resistance ability of the coating [204,211].
A8 Hydrophobicity testing
When TiO2 film is being applied for self-cleaning purposes, its hydrophobic properties in repelling water droplets will be a critical element for its functionality. The hydrophobicity of TiO2 coating can be reduced during time, due to wearing or exposure to the pollutant.
A8.1 Contact angle test
This technique is a measurement of water droplet contact angle when it is dropped on the film surface before and after being exposed to ultraviolet, abrasion, or weathering. The higher the contact angle of the droplet, the better the hydrophobicity of the film [212,213,214].
References
[1] Macwan DP, Dave PN, Chaturvedi S. A review on nano-TiO2 sol–gel type syntheses and its applications. J Mater Sci. 2011;46(11):3669–86.10.1007/s10853-011-5378-ySuche in Google Scholar
[2] Smit M, Lutz M. Polymer-coated magnetic nanoparticles for the efficient capture of Mycobacterium tuberculosis (Mtb). SN Appl Sci. 2020;2(10):1658.10.1007/s42452-020-03403-9Suche in Google Scholar
[3] Nakata K, Fujishima A. TiO2 photocatalysis: Design and applications. J Photochem Photobiol C: Photochem Rev. 2012;13(3):169–89.10.1016/j.jphotochemrev.2012.06.001Suche in Google Scholar
[4] Fujishima A. Photocatalitic and self clinging functions of TiO2 coatings. In Third Asia-Pacific Conference on Sustainable Energy and Environmental Technologies, Hong Kong. 2000.Suche in Google Scholar
[5] De Pasquale I, Porto CL, Dell’Edera M, Curri ML, Comparelli R. TiO2-based nanomaterials assisted photocatalytic treatment for virus inactivation: perspectives and applications. Curr Opin Chem Eng. 2021;34:100716.10.1016/j.coche.2021.100716Suche in Google Scholar PubMed PubMed Central
[6] Suárez S, Hernández-Alonso MD, Martínez C, Sanchez B. Evaluation of the photocatalytic performance of construction materials for urban air depollution. Euro-Mediterr J Environ Integr. 2020;5(2):25.10.1007/s41207-020-00162-2Suche in Google Scholar
[7] Miranda-García N, Suárez S, Sánchez B, Coronado JM, Malato S, Maldonado MI. Photocatalytic degradation of emerging contaminants in municipal wastewater treatment plant effluents using immobilized TiO2 in a solar pilot plant. Appl Catal B: Environ. 2011;103(3–4):294–301.10.1016/j.apcatb.2011.01.030Suche in Google Scholar
[8] Rad S, Shamsudin S, Taha MR, Shahid S. Tropical stormwater nutrient degradation using nano-TiO2 in photocatalytic reactor detention pond. Water Sci Technol. 2016;73(2):405–13.10.2166/wst.2015.465Suche in Google Scholar PubMed
[9] Gong X, Wang H, Yang C, Li Q, Chen X, Hu J. Photocatalytic degradation of high ammonia concentration wastewater by TiO2. Future Cities Environ. 2015;1(1):12.10.1186/s40984-015-0012-9Suche in Google Scholar
[10] Gopinath KP, Madhav NV, Krishnan A, Malolan R, Rangarajan G. Present applications of titanium dioxide for the photocatalytic removal of pollutants from water: A review. J Environ Manag. 2020;270:110906.10.1016/j.jenvman.2020.110906Suche in Google Scholar PubMed
[11] Sirirerkratana K, Kemacheevakul P, Chuangchote S. Color removal from wastewater by photocatalytic process using titanium dioxide-coated glass, ceramic tile, and stainless steel sheets. J Clean Prod. 2019;215:123–30.10.1016/j.jclepro.2019.01.037Suche in Google Scholar
[12] Janczarek M, Klapiszewski Ł, Jędrzejczak P, Klapiszewska I, Ślosarczyk A, Jesionowski T. Progress of functionalized TiO2-based nanomaterials in the construction industry: A comprehensive review. Chem Eng J. 2022;430:132062.10.1016/j.cej.2021.132062Suche in Google Scholar
[13] Ambigadevi J, Kumar PS, Vo DV, Haran SH, Raghavan TS. Recent developments in photocatalytic remediation of textile effluent using semiconductor based nanostructured catalyst: A review. J Environ Chem Eng. 2021;9(1):104881.10.1016/j.jece.2020.104881Suche in Google Scholar
[14] Yao H, Fan M, Wang Y, Luo G, Fei W. Magnetic titanium dioxide based nanomaterials: synthesis, characteristics, and photocatalytic application in pollutant degradation. J Mater Chem A. 2015;3(34):17511–24.10.1039/C5TA03215FSuche in Google Scholar
[15] Mylkie K, Nowak P, Rybczynski P, Ziegler-Borowska M. Polymer-coated magnetite nanoparticles for protein immobilization. Materials. 2021;14(2):248.10.3390/ma14020248Suche in Google Scholar PubMed PubMed Central
[16] Roslizar A, Dottermusch S, Vüllers F, Kavalenka MN, Guttmann M, Schneider M, et al. Self-cleaning performance of superhydrophobic hot-embossed fluoropolymer films for photovoltaic modules. Sol Energy Mater Sol Cell. 2019;189:188–96.10.1016/j.solmat.2018.09.017Suche in Google Scholar
[17] Suárez S, Jansson I, Ohtani B, Sánchez B. From titania nanoparticles to decahedral anatase particles: Photocatalytic activity of TiO2/zeolite hybrids for VOCs oxidation. Catal Today. 2019;326:2–7.10.1016/j.cattod.2018.09.004Suche in Google Scholar
[18] Chen XF, Kou SC, Poon CS. Rheological behaviour, mechanical performance, and NOx removal of photocatalytic mortar with combined clay brick sands-based and recycled glass-based nano-TiO2 composite photocatalysts. Constr Build Mater. 2020;240:117698.10.1016/j.conbuildmat.2019.117698Suche in Google Scholar
[19] Suárez S, Postolache R, García-García FJ, Sánchez B, Rothon R, Doyle AM, et al. Silicalite-1 synthesized with geothermal and Ludox colloidal silica and corresponding TiO2/silicalite-1 hybrid photocatalysts for VOC oxidation. Microporous Mesoporous Mater. 2020;302:110202.10.1016/j.micromeso.2020.110202Suche in Google Scholar
[20] Mansilla HD, Mora A, Pincheira C, Mondaca MA, Marcato PD, Durán N, et al. New photocatalytic reactor with TiO2 coating on sintered glass cylinders. Appl Catal B: Environ. 2007;76(1–2):57–63.10.1016/j.apcatb.2007.04.025Suche in Google Scholar
[21] Jesus MA, Neto JT, Timò G, Paiva PR, Dantas MS, Ferreira AD. Superhydrophilic self-cleaning surfaces based on TiO2 and TiO2/SiO2 composite films for photovoltaic module cover glass. Appl Adhes Sci. 2015;3(1):5.10.1186/s40563-015-0034-4Suche in Google Scholar
[22] Noman MT, Ashraf MA, Ali A. Synthesis and applications of nano-TiO2: a review. Environ Sci Pollut Res. 2019;26(4):3262–91.10.1007/s11356-018-3884-zSuche in Google Scholar PubMed
[23] Cámara RM, Portela R, Gutiérrez-Martín F, Sánchez B. Photocatalytic activity of TiO2 films prepared by surfactant-mediated sol–gel methods over commercial polymer substrates. Chem Eng J. 2016;283:535–43.10.1016/j.cej.2015.07.080Suche in Google Scholar
[24] Xu Q, Anderson MA. Sol–gel route to synthesis of microporous ceramic membranes: preparation and characterization of microporous TiO2 and ZrO2 xerogels. J Am Ceram Soc. 1994;77(7):1939–45.10.1111/j.1151-2916.1994.tb07074.xSuche in Google Scholar
[25] Curcio MS, Canela MC, Waldman WR. Selective surface modification of TiO2-coated polypropylene by photodegradation. Eur Polym J. 2018;101:177–82.10.1016/j.eurpolymj.2018.01.036Suche in Google Scholar
[26] Sievers NV, Pollo LD, Corção G, Cardozo NS. In situ synthesis of nanosized TiO2 in polypropylene solution for the production of films with antibacterial activity. Mater Chem Phys. 2020;246:122824.10.1016/j.matchemphys.2020.122824Suche in Google Scholar
[27] Vázquez-Velázquez AR, Velasco-Soto MA, Pérez-García SA, Licea-Jiménez L. Functionalization effect on polymer nanocomposite coatings based on TiO2–SiO2 nanoparticles with superhydrophilic properties. Nanomaterials. 2018;8(6):369.10.3390/nano8060369Suche in Google Scholar PubMed PubMed Central
[28] Camara RM, Portela R, Gutiérrez-Martín F, Sánchez B. Evaluation of several commercial polymers as support for TiO2 in photo-catalytic applications. Global NEST J. 2014;16(6):525–35.10.30955/gnj.001446Suche in Google Scholar
[29] Cámara RM, Crespo E, Portela R, Suárez S, Bautista L, Gutiérrez-Martín F, et al. Enhanced photocatalytic activity of TiO2 thin films on plasma-pretreated organic polymers. Catal Today. 2014;230:145–51.10.1016/j.cattod.2013.10.049Suche in Google Scholar
[30] Sriwong C, Wongnawa S, Patarapaiboolchai O. Photocatalytic activity of rubber sheet impregnated with TiO2 particles and its recyclability. Catal Commun. 2008;9(2):213–8.10.1016/j.catcom.2007.05.037Suche in Google Scholar
[31] Sriwong C, Wongnawa S, Patarapaiboolchai O. Rubber sheet strewn with TiO2 particles: photocatalytic activity and recyclability. J Environ Sci. 2012;24(3):464–72.10.1016/S1001-0742(11)60794-8Suche in Google Scholar
[32] Wang X, Shi F, Gao X, Fan C, Huang W, Feng X. A sol–gel dip/spin coating method to prepare titanium oxide films. Thin Solid Films. 2013;548:34–9.10.1016/j.tsf.2013.08.056Suche in Google Scholar
[33] Singh S, Mahalingam H, Singh PK. Polymer-supported titanium dioxide photocatalysts for environmental remediation: A review. Appl Catal A: Gen. 2013;462:178–95.10.1016/j.apcata.2013.04.039Suche in Google Scholar
[34] Jacobs M, De Vos Y, Middelkoop V. Thickness controlled SiO2/TiO2 sol-gel coating by spraying. Open Ceram. 2021;6:100121.10.1016/j.oceram.2021.100121Suche in Google Scholar
[35] Fabiyi ME, Skelton RL. Photocatalytic mineralisation of methylene blue using buoyant TiO2-coated polystyrene beads. J Photochem Photobiol A: Chem. 2000;132(1–2):121–8.10.1016/S1010-6030(99)00250-6Suche in Google Scholar
[36] Tennakone K, Tilakaratne CT, Kottegoda IR. Photocatalytic degradation of organic contaminants in water with TiO2 supported on polythene films. J Photochem Photobiol A: Chem. 1995;87(2):177–9.10.1016/1010-6030(94)03980-9Suche in Google Scholar
[37] Han H, Bai R. Highly effective buoyant photocatalyst prepared with a novel layered-TiO2 configuration on polypropylene fabric and the degradation performance for methyl orange dye under UV–Vis and Vis lights. Sep Purif Technol. 2010;73(2):142–50.10.1016/j.seppur.2010.03.017Suche in Google Scholar
[38] Bahloul W, Mélis F, Bounor-Legaré V, Cassagnau P. Structural characterisation and antibacterial activity of PP/TiO2 nanocomposites prepared by an in situ sol–gel method. Mater Chem Phys. 2012;134(1):399–406.10.1016/j.matchemphys.2012.03.008Suche in Google Scholar
[39] Li S, Chen G, Qiang S, Yin Z, Zhang Z, Chen Y. Synthesis and evaluation of highly dispersible and efficient photocatalytic TiO2/poly lactic acid nanocomposite films via sol-gel and casting processes. Int J Food Microbiol. 2020;331:108763.10.1016/j.ijfoodmicro.2020.108763Suche in Google Scholar PubMed
[40] Zhuang W, Liu J, Zhang JH, Hu BX, Shen J. Preparation, characterization, and properties of TiO2/PLA nanocomposites by in situ polymerization. Polym Compos. 2009;30(8):1074–80.10.1002/pc.20658Suche in Google Scholar
[41] Pasini SM, Valério A, Yin G, Wang J, de Souza SM, Hotza D, et al. An overview on nanostructured TiO2-containing fibers for photocatalytic degradation of organic pollutants in wastewater treatment. J Water Process Eng. 2021;40:101827.10.1016/j.jwpe.2020.101827Suche in Google Scholar
[42] Baer DR, Burrows PE, El-Azab AA. Enhancing coating functionality using nanoscience and nanotechnology. Prog Org Coat. 2003;47(3–4):342–56.10.1016/S0300-9440(03)00127-9Suche in Google Scholar
[43] Lines MG. Nanomaterials for practical functional uses. J Alloy Compd. 2008;449(1–2):242–5.10.1016/j.jallcom.2006.02.082Suche in Google Scholar
[44] Nguyen-Tri P, Nguyen TA, Carriere P, Ngo Xuan C. Nanocomposite coatings: preparation, characterization, properties, and applications. Int J Corros. 2018;2018(1):4749501.10.1155/2018/4749501Suche in Google Scholar
[45] Duncan TV. Applications of nanotechnology in food packaging and food safety: barrier materials, antimicrobials and sensors. J Colloid Interface Sci. 2011;363(1):1–24.10.1016/j.jcis.2011.07.017Suche in Google Scholar PubMed PubMed Central
[46] Rovera C, Ghaani M, Farris S. Nano-inspired oxygen barrier coatings for food packaging applications: An overview. Trends Food Sci Technol. 2020;97:210–20.10.1016/j.tifs.2020.01.024Suche in Google Scholar
[47] Dunnill CW, Aiken ZA, Pratten J, Wilson M, Morgan DJ, Parkin IP. Enhanced photocatalytic activity under visible light in N-doped TiO2 thin films produced by APCVD preparations using t-butylamine as a nitrogen source and their potential for antibacterial films. J Photochem Photobiol A: Chem. 2009;207(2–3):244–53.10.1016/j.jphotochem.2009.07.024Suche in Google Scholar
[48] Gao P, Nie X, Zou M, Shi Y, Cheng G. Recent advances in materials for extended-release antibiotic delivery system. J Antibiotics. 2011;64(9):625–34.10.1038/ja.2011.58Suche in Google Scholar PubMed
[49] Mattos BD, Tardy BL, Magalhaes WL, Rojas OJ. Controlled release for crop and wood protection: Recent progress toward sustainable and safe nanostructured biocidal systems. J Control Release. 2017;262:139–50.10.1016/j.jconrel.2017.07.025Suche in Google Scholar PubMed
[50] Singh AP, Biswas A, Shukla A, Maiti P. Targeted therapy in chronic diseases using nanomaterial-based drug delivery vehicles. Signal Transduct Target Ther. 2019;4(1):33.10.1038/s41392-019-0068-3Suche in Google Scholar PubMed PubMed Central
[51] Kumar RR, Karunagaran B, Kumar VS, Jeyachandran YL, Mangalaraj D, Narayandass SK. Structural properties of V2O5 thin films prepared by vacuum evaporation. Mater Sci Semicond Process. 2003;6(5–6):543–6.10.1016/j.mssp.2003.08.017Suche in Google Scholar
[52] Calnan S, Upadhyaya HM, Dann SE, Thwaites MJ, Tiwari AN. Effects of target bias voltage on indium tin oxide films deposited by high target utilisation sputtering. Thin Solid Films. 2007;515(24):8500–4.10.1016/j.tsf.2007.03.124Suche in Google Scholar
[53] Ding P, Pan XH, Huang JY, He HP, Lu B, Zhang HH, et al. p-type non-polar m-plane ZnO films grown by plasma-assisted molecular beam epitaxy. J Cryst Growth. 2011;331(1):15–7.10.1016/j.jcrysgro.2011.07.004Suche in Google Scholar
[54] Gurav KV, Patil UM, Shin SW, Pawar SM, Kim JH, Lokhande CD. Morphology evolution of ZnO thin films from aqueous solutions and their application to liquefied petroleum gas (LPG) sensor. J Alloy Compd. 2012;525:1–7.10.1016/j.jallcom.2012.01.082Suche in Google Scholar
[55] Yang L, Pang X, Fox-Rabinovich G, Veldhuis S, Zhitomirsky I. Electrodeposition of cerium oxide films and composites. Surf Coat Technol. 2011;206(1):1–7.10.1016/j.surfcoat.2011.06.029Suche in Google Scholar
[56] Matsuura N, Johnson DJ, Amm DT. Fabrication of cadmium oxide thin films using the Langmuir-Blodgett deposition technique. Thin Solid Films. 1997;295(1–2):260–5.10.1016/S0040-6090(96)09283-8Suche in Google Scholar
[57] Rao CN, Kulkarni GU, Agrawal VV, Gautam UK, Ghosh M, Tumkurkar U. Use of the liquid–liquid interface for generating ultrathin nanocrystalline films of metals, chalcogenides, and oxides. J Colloid Interface Sci. 2005;289(2):305–18.10.1016/j.jcis.2005.04.005Suche in Google Scholar PubMed
[58] Liu MY, Wang H, Wang Y. Enhancing flow boiling and antifouling with nanometer titanium dioxide coating surfaces. AIChE J. 2007;53(5):1075–85.10.1002/aic.11150Suche in Google Scholar
[59] Rella R, Spadavecchia J, Manera MG, Capone S, Taurino A, Martino M, et al. Acetone and ethanol solid-state gas sensors based on TiO2 nanoparticles thin film deposited by matrix assisted pulsed laser evaporation. Sens Actuators B: Chem. 2007;127(2):426–31.10.1016/j.snb.2007.04.048Suche in Google Scholar
[60] Kim DJ, Pham HC, Park DW, Kim KS. Preparation of TiO2 thin films on polypropylene beads by a rotating PCVD process and its application to organic pollutant removal. Chem Eng J. 2011;167(1):308–13.10.1016/j.cej.2010.12.069Suche in Google Scholar
[61] Kuo CS, Tseng YH, Huang CH, Li YY. Carbon-containing nano-titania prepared by chemical vapor deposition and its visible-light-responsive photocatalytic activity. J Mol Catal A: Chem. 2007;270(1–2):93–100.10.1016/j.molcata.2007.01.031Suche in Google Scholar
[62] Shironita S, Mori K, Shimizu T, Ohmichi T, Mimura N, Yamashita H. Preparation of nano-sized platinum metal catalyst using photo-assisted deposition method on mesoporous silica including single-site photocatalyst. Appl Surf Sci. 2008;254(23):7604–7.10.1016/j.apsusc.2008.01.120Suche in Google Scholar
[63] Chang C, Li Z, Rad S, Gan L, Dai J, Shahab A. Preparation and application of nano TiO2 filmcoated recycled low-iron crushed glass in a novel packed-bed photocatalytic reactor for efficient removal of biodegradable contaminants. Environ Technol Innov. 2024;33:103541.10.1016/j.eti.2024.103541Suche in Google Scholar
[64] Rossnagel SM. Thin film deposition with physical vapor deposition and related technologies. J Vac Sci Technol A: Vac Surf Films. 2003;21(5):S74–87.10.1116/1.1600450Suche in Google Scholar
[65] Rockett A. Physical vapor deposition. In: The materials science of semiconductors. Boston: Springer US; 2008. p. 505–72.10.1007/978-0-387-68650-9_11Suche in Google Scholar
[66] Mattox DM. Physical vapor deposition (PVD) processes. Met Finish. 2002;100:394–408.10.1016/S0026-0576(02)82043-8Suche in Google Scholar
[67] Shahidi S, Moazzenchi B, Ghoranneviss M. A review-application of physical vapor deposition (PVD) and related methods in the textile industry. Eur Phys J Appl Phys. 2015;71(3):31302.10.1051/epjap/2015140439Suche in Google Scholar
[68] Wu JM, Shih HC, Wu WT. Formation and photoluminescence of single-crystalline rutile TiO2 nanowires synthesized by thermal evaporation. Nanotechnology. 2005;17(1):105.10.1088/0957-4484/17/1/017Suche in Google Scholar
[69] Mangrola MH, Joshi VG. Synthesis, characterization and study of influence of pure TiO2 nanoparticles thin film developed by e-beam evaporation. Mater Today: Proc. 2017;4(2):3832–41.10.1016/j.matpr.2017.02.281Suche in Google Scholar
[70] Wang YH, Rahman KH, Wu CC, Chen KC. A review on the pathways of the improved structural characteristics and photocatalytic performance of titanium dioxide (TiO2) thin films fabricated by the magnetron-sputtering technique. Catalysts. 2020;10(6):598.10.3390/catal10060598Suche in Google Scholar
[71] Nechache R, Nicklaus M, Diffalah N, Ruediger A, Rosei F. Pulsed laser deposition growth of rutile TiO2 nanowires on Silicon substrates. Appl Surf Sci. 2014;313:48–52.10.1016/j.apsusc.2014.05.123Suche in Google Scholar
[72] Bundesmann C, Lautenschläger T, Spemann D, Finzel A, Thelander E, Mensing M, et al. Systematic investigation of the properties of TiO2 films grown by reactive ion beam sputter deposition. Appl Surf Sci. 2017;421:331–40.10.1016/j.apsusc.2016.08.056Suche in Google Scholar
[73] Matthews A, Leyland A. Widening the market for advanced PVD coatings. J Mater Process Technol. 1996;56(1–4):757–64.10.1016/0924-0136(95)01889-1Suche in Google Scholar
[74] Medvids A, Varnagiris S, Letko E, Milcius D, Grase L, Gaidukovs S, et al. Phase transformation from rutile to anatase with oxygen ion dose in the TiO2 layer formed on a Ti substrate. Mater Sci Semicond Process. 2020;106:104776.10.1016/j.mssp.2019.104776Suche in Google Scholar
[75] Vahl A, Veziroglu S, Henkel B, Strunskus T, Polonskyi O, Aktas OC, et al. Pathways to tailor photocatalytic performance of TiO2 thin films deposited by reactive magnetron sputtering. Materials. 2019;12(17):2840.10.3390/ma12172840Suche in Google Scholar PubMed PubMed Central
[76] Banerjee S, Adhikari E, Sapkota P, Sebastian A, Ptasinska S. Atmospheric pressure plasma deposition of TiO2: a review. Materials. 2020;13(13):2931.10.3390/ma13132931Suche in Google Scholar PubMed PubMed Central
[77] Cruz NK, Semblante GU, Senoro DB, You SJ, Lu SC. Dye degradation and antifouling properties of polyvinylidene fluoride/titanium oxide membrane prepared by sol–gel method. J Taiwan Inst Chem Eng. 2014;45(1):192–201.10.1016/j.jtice.2013.04.011Suche in Google Scholar
[78] Gill BJ, Tucker RC. Plasma spray coating processes. Mater Sci Technol. 1986;2(3):207–13.10.1179/026708386790123396Suche in Google Scholar
[79] Fauchais P, Vardelle M, Vardelle A, Bianchi L. Plasma spray: study of the coating generation. Ceram Int. 1996;22(4):295–303.10.1016/0272-8842(95)00106-9Suche in Google Scholar
[80] Heimann RB. Plasma-spray coating: principles and applications. Hoboken, New Jersey: John Wiley & Sons; 2008.Suche in Google Scholar
[81] Kern W, Schnable GL. Low-pressure chemical vapor deposition for very large-scale integration processing – a review. IEEE Trans Electr Devices. 2005;26(4):647–57.10.1109/T-ED.1979.19473Suche in Google Scholar
[82] Martinu L, Poitras D. Plasma deposition of optical films and coatings: A review. J Vac Sci Technol A: Vac Surf Films. 2000;18(6):2619–45.10.1116/1.1314395Suche in Google Scholar
[83] Sun L, Yuan G, Gao L, Yang J, Chhowalla M, Gharahcheshmeh MH, et al. Chemical vapour deposition. Nat Rev Methods Primers. 2021;1(1):5.10.1038/s43586-020-00005-ySuche in Google Scholar
[84] Nizard H, Kosinova ML, Fainer NI, Rumyantsev YM, Ayupov BM, Shubin YV. Deposition of titanium dioxide from TTIP by plasma enhanced and remote plasma enhanced chemical vapor deposition. Surf Coat Technol. 2008;202(17):4076–85.10.1016/j.surfcoat.2008.02.023Suche in Google Scholar
[85] Allen SD. Laser chemical vapor deposition: A technique for selective area deposition. J Appl Phys. 1981;52(11):6501–5.10.1063/1.328600Suche in Google Scholar
[86] Mazumder J, Kar A. Theory and application of laser chemical vapor deposition. New York: Springer Science & Business Media; 2013.Suche in Google Scholar
[87] Leskelä M, Ritala M. Atomic layer deposition (ALD): from precursors to thin film structures. Thin Solid films. 2002;409(1):138–46.10.1016/S0040-6090(02)00117-7Suche in Google Scholar
[88] Johnson RW, Hultqvist A, Bent SF. A brief review of atomic layer deposition: from fundamentals to applications. Mater Today. 2014;17(5):236–46.10.1016/j.mattod.2014.04.026Suche in Google Scholar
[89] Teoh WY, Amal R, Mädler L. Flame spray pyrolysis: An enabling technology for nanoparticles design and fabrication. Nanoscale. 2010;2(8):1324–47.10.1039/c0nr00017eSuche in Google Scholar PubMed
[90] Bettini LG, Dozzi MV, Della Foglia F, Chiarello GL, Selli E, Lenardi C, et al. Mixed-phase nanocrystalline TiO2 photocatalysts produced by flame spray pyrolysis. Appl Catal B: Environ. 2015;178:226–32.10.1016/j.apcatb.2014.09.013Suche in Google Scholar
[91] Dimitriou C, Psathas P, Solakidou M, Deligiannakis Y. Advanced flame spray pyrolysis (FSP) technologies for engineering multifunctional nanostructures and nanodevices. Nanomaterials. 2023;13(23):3006.10.3390/nano13233006Suche in Google Scholar PubMed PubMed Central
[92] Ismael M, Sharma A, Kumar N. An extensive catalytic potential of sustainable TiO2-based materials fabricated via flame spray pyrolysis: A comprehensive review. Sustain Mater Technol. 2024;40:e00826.10.1016/j.susmat.2024.e00826Suche in Google Scholar
[93] Foroughi-Dahr M, Mostoufi N, Sotudeh-Gharebagh R, Chaouki J. Particle coating in fluidized beds. Reference module in chemistry, molecular sciences and chemical engineering. Oxford: Elsevier; 2017. p. 1–89.10.1016/B978-0-12-409547-2.12206-1Suche in Google Scholar
[94] King DM, Liang X, Zhou Y, Carney CS, Hakim LF, Li P, Weimer AW. Atomic layer deposition of TiO2 films on particles in a fluidized bed reactor. Powder Technol. 2008;183(3):356–63.10.1016/j.powtec.2008.01.025Suche in Google Scholar
[95] Martín V, Romero-Díez R, Rodríguez-Rojo S, Cocero MJ. Titanium dioxide nanoparticle coating in fluidized bed via supercritical anti-solvent process (SAS). Chem Eng J. 2015;279:425–32.10.1016/j.cej.2015.05.014Suche in Google Scholar
[96] Van Ommen JR, Valverde JM, Pfeffer R. Fluidization of nanopowders: a review. J Nanopart Res. 2012;14(3):737.10.1007/s11051-012-0737-4Suche in Google Scholar PubMed PubMed Central
[97] Wang CM, Lin SY, Chen YC. Electrochromic properties of TiO2 thin films prepared by chemical solution deposition method. J Phys Chem Solids. 2008;69(2–3):451–5.10.1016/j.jpcs.2007.07.113Suche in Google Scholar
[98] Schwartz RW, Schneller T, Waser R. Chemical solution deposition of electronic oxide films. C R Chim. 2004;7(5):433–61.10.1016/j.crci.2004.01.007Suche in Google Scholar
[99] Schneller T, Waser R, Kosec M, Payne D, editors. Chemical solution deposition of functional oxide thin films. Vienna: Springer Vienna; 2013.10.1007/978-3-211-99311-8Suche in Google Scholar
[100] Obradors X, Puig T, Pomar A, Sandiumenge F, Pinol S, Mestres N, et al. Chemical solution deposition: a path towards low cost coated conductors. Supercond Sci Technol. 2004;17(8):1055.10.1088/0953-2048/17/8/020Suche in Google Scholar
[101] Xin Z, Lei M, Jian-gang W, Hui-min Z. Investigation on ultrathin titanium oxide films synthesized by surface sol–gel method. Optik. 2016;127(5):2780–3.10.1016/j.ijleo.2015.11.183Suche in Google Scholar
[102] Chang C, Rad S, Gan L, Li Z, Dai J, Shahab A. Review of the sol–gel method in preparing nano TiO2 for advanced oxidation process. Nanotechnol Rev. 2023;12(1):20230150.10.1515/ntrev-2023-0150Suche in Google Scholar
[103] Balasubramanian G, Dionysiou DD, Suidan MT, Baudin I, Laıné JM. Evaluating the activities of immobilized TiO2 powder films for the photocatalytic degradation of organic contaminants in water. Appl Catal B: Environ. 2004;47(2):73–84.10.1016/j.apcatb.2003.04.002Suche in Google Scholar
[104] Elfanaoui A, Elhamri E, Boulkaddat L, Ihlal A, Bouabid K, Laanab L, et al. Optical and structural properties of TiO2 thin films prepared by sol–gel spin coating. Int J Hydrogen Energy. 2011;36(6):4130–3.10.1016/j.ijhydene.2010.07.057Suche in Google Scholar
[105] Khan MI, Bhatti KA, Qindeel R, Althobaiti HS, Alonizan N. Structural, electrical and optical properties of multilayer TiO2 thin films deposited by sol–gel spin coating. Results Phys. 2017;7:1437–9.10.1016/j.rinp.2017.03.023Suche in Google Scholar
[106] Johari ND, Rosli ZM, Juoi JM, Yazid SA. Comparison on the TiO2 crystalline phases deposited via dip and spin coating using green sol–gel route. J Mater Res Technol. 2019;8(2):2350–8.10.1016/j.jmrt.2019.04.018Suche in Google Scholar
[107] Kment Š, Gregora I, Kmentová H, Novotná P, Hubička Z, Krýsa J, et al. Raman spectroscopy of dip-coated and spin-coated sol–gel TiO2 thin films on different types of glass substrate. J Sol-Gel Sci Technol. 2012;63(3):294–306.10.1007/s10971-012-2787-6Suche in Google Scholar
[108] Malliga P, Pandiarajan J, Prithivikumaran N, Neyvasagam K. Influence of film thickness on structural and optical properties of sol–gel spin coated TiO2 thin film. IOSR. J Appl Phys. 2014;6(1):22.10.9790/4861-06112228Suche in Google Scholar
[109] Hosseini A, Içli KÇ, Özenbaş M, Ercelebi C. Fabrication and characterization of spin-coated TiO2 films. Energy Procedia. 2014;60:191–8.10.1016/j.egypro.2014.12.332Suche in Google Scholar
[110] Wu CY, Lee YL, Lo YS, Lin CJ, Wu CH. Thickness-dependent photocatalytic performance of nanocrystalline TiO2 thin films prepared by sol–gel spin coating. Appl Surf Sci. 2013;280:737–44.10.1016/j.apsusc.2013.05.053Suche in Google Scholar
[111] Shan AY, Ghazi TI, Rashid SA. Immobilisation of titanium dioxide onto supporting materials in heterogeneous photocatalysis: A review. Appl Catal A: Gen. 2010;389(1–2):1–8.10.1016/j.apcata.2010.08.053Suche in Google Scholar
[112] Butt MA. Thin-film coating methods: a successful marriage of high-quality and cost-effectiveness – a brief exploration. Coatings. 2022;12(8):1115.10.3390/coatings12081115Suche in Google Scholar
[113] Brinker CJ. Dip coating. In Chemical solution deposition of functional oxide thin films. Vienna: Springer Vienna; 2013. p. 233–61.10.1007/978-3-211-99311-8_10Suche in Google Scholar
[114] Sarah MS, Hasmi BA, Shariffudin SS, Hashim H, Herman SH. Crack-free TiO2 thin film via sol-gel dip coating method: investigation on molarity effect. In IOP Conference Series: Materials Science and Engineering. Vol. 340, No. 1, IOP Publishing. 2018. p. 012009.10.1088/1757-899X/340/1/012009Suche in Google Scholar
[115] Tsay CY, Fan KS, Wang YW, Chang CJ, Tseng YK, Lin CK. Transparent semiconductor zinc oxide thin films deposited on glass substrates by sol–gel process. Ceram Int. 2010;36(6):1791–5.10.1016/j.ceramint.2010.03.005Suche in Google Scholar
[116] Sukanek PC. Dependence of film thickness on speed in spin coating. J Electrochem Soc. 1991;138(6):1712.10.1149/1.2085860Suche in Google Scholar
[117] Rehg TJ, Higgins G. Spin coating of colloidal suspensions. AIChE J. 1992;38(4):489–501.10.1002/aic.690380403Suche in Google Scholar
[118] Tyona MD. A theoritical study on spin coating technique. Adv Mater Res. 2013;2(4):195.10.12989/amr.2013.2.4.195Suche in Google Scholar
[119] Aegerter MA, Mennig M, editors. Sol-gel technologies for glass producers and users. New York: Springer Science & Business Media; 2013.Suche in Google Scholar
[120] Mehrabadi BA, Eskandari S, Khan U, White RD, Regalbuto JR. A review of preparation methods for supported metal catalysts. Adv Catal. 2017;61:1–35.10.1016/bs.acat.2017.10.001Suche in Google Scholar
[121] Munnik P, De Jongh PE, De Jong KP. Recent developments in the synthesis of supported catalysts. Chem Rev. 2015;115(14):6687–718.10.1021/cr500486uSuche in Google Scholar PubMed
[122] Djošić MS, Mišković-Stanković VB, Janaćković DT, Kačarević-Popović ZM, Petrović RD. Electrophoretic deposition and characterization of boehmite coatings on titanium substrate. Colloids Surf A: Physicochem Eng Asp. 2006;274(1–3):185–91.10.1016/j.colsurfa.2005.08.048Suche in Google Scholar
[123] Besra L, Liu M. A review on fundamentals and applications of electrophoretic deposition (EPD). Prog Mater Sci. 2007;52(1):1–61.10.1016/j.pmatsci.2006.07.001Suche in Google Scholar
[124] Cabanas-Polo S, Boccaccini AR. Electrophoretic deposition of nanoscale TiO2: technology and applications. J Eur Ceram Soc. 2016;36(2):265–83.10.1016/j.jeurceramsoc.2015.05.030Suche in Google Scholar
[125] Mohammadi MM, Vossoughi M, Feilizadeh M, Rashtchian D, Moradi S, Alemzadeh I. Effects of electrophoretic deposition parameters on the photocatalytic activity of TiO2 films: optimization by response surface methodology. Colloids Surf A: Physicochem Eng Asp. 2014;452:1–8.10.1016/j.colsurfa.2014.03.048Suche in Google Scholar
[126] Dor S, Rühle S, Ofir A, Adler M, Grinis L, Zaban A. The influence of suspension composition and deposition mode on the electrophoretic deposition of TiO2 nanoparticle agglomerates. Colloids Surf A: Physicochem Eng Asp. 2009;342(1–3):70–5.10.1016/j.colsurfa.2009.04.009Suche in Google Scholar
[127] Pandey A, Dalal S, Dutta S, Dixit A. Structural characterization of polycrystalline thin films by X-ray diffraction techniques. J Mater Sci: Mater Electron. 2021;32(2):1341–68.10.1007/s10854-020-04998-wSuche in Google Scholar
[128] Giannini C, Ladisa M, Altamura D, Siliqi D, Sibillano T, De Caro L. X-ray diffraction: a powerful technique for the multiple-length-scale structural analysis of nanomaterials. Crystals. 2016;6(8):87.10.3390/cryst6080087Suche in Google Scholar
[129] Ali A, Chiang YW, Santos RM. X-ray diffraction techniques for mineral characterization: A review for engineers of the fundamentals, applications, and research directions. Minerals. 2022;12(2):205.10.3390/min12020205Suche in Google Scholar
[130] Harris KD, Tremayne M. Crystal structure determination from powder diffraction data. Chem Mater. 1996;8(11):2554–70.10.1021/cm960218dSuche in Google Scholar
[131] Epp J. X-ray diffraction (XRD) techniques for materials characterization. In Materials characterization using nondestructive evaluation (NDE) methods. Cambridge: Woodhead Publishing; 2016. p. 81–124.10.1016/B978-0-08-100040-3.00004-3Suche in Google Scholar
[132] Aydoghmish SM, Hassanzadeh-Tabrizi SA, Saffar-Teluri A. Facile synthesis and investigation of NiO–ZnO–Ag nanocomposites as efficient photocatalysts for degradation of methylene blue dye. Ceram Int. 2019;45(12):14934–42.10.1016/j.ceramint.2019.04.229Suche in Google Scholar
[133] Hassanzadeh-Tabrizi SA. Precise calculation of crystallite size of nanomaterials: A review. J Alloy Compd. 2023;968:171914.10.1016/j.jallcom.2023.171914Suche in Google Scholar
[134] Ameh ES. A review of basic crystallography and x-ray diffraction applications. Int J Adv Manuf Technol. 2019;105(7):3289–302.10.1007/s00170-019-04508-1Suche in Google Scholar
[135] Titus D, Samuel EJ, Roopan SM. Nanoparticle characterization techniques. In Green synthesis, characterization and applications of nanoparticles. New York: Elsevier; 2019. p. 303–19.10.1016/B978-0-08-102579-6.00012-5Suche in Google Scholar
[136] Ebnesajjad S. Surface and material characterization techniques. In Handbook of adhesives and surface preparation. Norwich, NY: William Andrew Publishing; 2011. p. 31–48.10.1016/B978-1-4377-4461-3.10004-5Suche in Google Scholar
[137] Brabazon D, Raffer A. Advanced characterization techniques for nanostructures. In Emerging nanotechnologies for manufacturing. Norwich, NY: William Andrew Publishing; 2015. p. 53–85.10.1016/B978-0-323-28990-0.00003-8Suche in Google Scholar
[138] Mishra RK, Zachariah AK, Thomas S. Energy-dispersive X-ray spectroscopy techniques for nanomaterial. In Microscopy methods in nanomaterials characterization. Amsterdam, Netherlands: Elsevier; 2017. p. 383–405.10.1016/B978-0-323-46141-2.00012-2Suche in Google Scholar
[139] Hwang N, Barron AR. BET surface area analysis of nanoparticles. Houston, TX, USA: Rice University; 2011. p. 1.Suche in Google Scholar
[140] Hayati‐Ashtiani M. Characterization of nano‐porous bentonite (montmorillonite) particles using FTIR and BET‐BJH analyses. Part Part Syst Charact. 2011;28(3–4):71–6.10.1002/ppsc.201100030Suche in Google Scholar
[141] Kumar PM, Badrinarayanan S, Sastry M. Nanocrystalline TiO2 studied by optical, FTIR and X-ray photoelectron spectroscopy: correlation to presence of surface states. Thin Solid Films. 2000;358(1–2):122–30.10.1016/S0040-6090(99)00722-1Suche in Google Scholar
[142] Zhang JY, Boyd IW, O’sullivan BJ, Hurley PK, Kelly PV, Senateur JP. Nanocrystalline TiO2 films studied by optical, XRD and FTIR spectroscopy. J Non-Cryst Solids. 2002;303(1):134–8.10.1016/S0022-3093(02)00973-0Suche in Google Scholar
[143] Gemici Z, Shimomura H, Cohen RE, Rubner MF. Hydrothermal treatment of nanoparticle thin films for enhanced mechanical durability. Langmuir. 2008;24(5):2168–77.10.1021/la703074rSuche in Google Scholar PubMed
[144] Calia A, Lettieri M, Masieri M. Durability assessment of nanostructured TiO2 coatings applied on limestones to enhance building surface with self-cleaning ability. Build Environ. 2016;110:1.10.1016/j.buildenv.2016.09.030Suche in Google Scholar
[145] Graziani L, Quagliarini E, Bondioli F, D’Orazio M. Durability of self-cleaning TiO2 coatings on fired clay brick façades: Effects of UV exposure and wet & dry cycles. Build Environ. 2014;71:193–203.10.1016/j.buildenv.2013.10.005Suche in Google Scholar
[146] Khalid K, Ishak R, Chowdhury ZZ. UV–Vis spectroscopy in non-destructive testing. In Non-destructive material characterization methods. Amsterdam, Netherlands: Elsevier; 2024. p. 391–416.10.1016/B978-0-323-91150-4.00021-5Suche in Google Scholar
[147] Miyazaki H, Teranishi Y, Ota T. Fabrication of UV-opaque and visible-transparent composite film. Sol Energy Mater Sol Cell. 2006;90(16):2640–6.10.1016/j.solmat.2006.02.030Suche in Google Scholar
[148] Markl D, Hannesschläger G, Sacher S, Leitner M, Khinast JG. Optical coherence tomography as a novel tool for in-line monitoring of a pharmaceutical film-coating process. Eur J Pharm Sci. 2014;55:58–67.10.1016/j.ejps.2014.01.011Suche in Google Scholar PubMed
[149] Lin H, Dong Y, Markl D, Zhang Z, Shen Y, Zeitler JA. Pharmaceutical film coating catalog for spectral domain optical coherence tomography. J Pharm Sci. 2017;106(10):3171–6.10.1016/j.xphs.2017.05.032Suche in Google Scholar PubMed
[150] Koller DM, Hannesschläger G, Leitner M, Khinast JG. Non-destructive analysis of tablet coatings with optical coherence tomography. Eur J Pharm Sci. 2011;44(1–2):142–8.10.1016/j.ejps.2011.06.017Suche in Google Scholar PubMed
[151] Mohan S, Kato E, Drennen III JK, Anderson CA. Refractive index measurement of pharmaceutical solids: a review of measurement methods and pharmaceutical applications. J Pharm Sci. 2019;108(11):3478–95.10.1016/j.xphs.2019.06.029Suche in Google Scholar PubMed
[152] Giurlani W, Berretti E, Innocenti M, Lavacchi A. Measuring the thickness of metal coatings: A review of the methods. Coatings. 2020;10(12):1211.10.3390/coatings10121211Suche in Google Scholar
[153] Soares L, Alves A. Analysis of colorimetry using the CIE-L* a* b* system and the photocatalytic activity of photochromic films. Mater Res Bull. 2018;105:318–21.10.1016/j.materresbull.2018.05.012Suche in Google Scholar
[154] Ramos AP. Dynamic light scattering applied to nanoparticle characterization. In Nanocharacterization techniques. Norwich, NY: William Andrew Publishing; 2017. p. 99–110.10.1016/B978-0-323-49778-7.00004-7Suche in Google Scholar
[155] Murdock RC, Braydich-Stolle L, Schrand AM, Schlager JJ, Hussain SM. Characterization of nanomaterial dispersion in solution prior to in vitro exposure using dynamic light scattering technique. Toxicol Sci. 2008;101(2):239–53.10.1093/toxsci/kfm240Suche in Google Scholar PubMed
[156] Lim J, Yeap SP, Che HX, Low SC. Characterization of magnetic nanoparticle by dynamic light scattering. Nanoscale Res Lett. 2013;8(1):381.10.1186/1556-276X-8-381Suche in Google Scholar PubMed PubMed Central
[157] Cedillo-González EI, Riccò R, Montorsi M, Montorsi M, Falcaro P, Siligardi C. Self-cleaning glass prepared from a commercial TiO2 nano-dispersion and its photocatalytic performance under common anthropogenic and atmospheric factors. Build Environ. 2014;71:7–14.10.1016/j.buildenv.2013.09.007Suche in Google Scholar
[158] Luo H, Xiang Y, Li Y, Zhao Y, Pan X. Photocatalytic aging process of Nano-TiO2 coated polypropylene microplastics: combining atomic force microscopy and infrared spectroscopy (AFM-IR) for nanoscale chemical characterization. J Hazard Mater. 2021;404:124159.10.1016/j.jhazmat.2020.124159Suche in Google Scholar PubMed
[159] Gomes J, Maniezo B, Alves P, Ferreira P, Martins RC. Immobilization of TiO2 onto a polymeric support for photocatalytic oxidation of a paraben’s mixture. J Water Process Eng. 2022;46:102458.10.1016/j.jwpe.2021.102458Suche in Google Scholar
[160] Hou J, Dong G, Ye Y, Chen V. Enzymatic degradation of bisphenol-A with immobilized laccase on TiO2 sol–gel coated PVDF membrane. J Membr Sci. 2014;469:19–30.10.1016/j.memsci.2014.06.027Suche in Google Scholar
[161] Pant B, Park M, Park SJ. Recent advances in TiO2 films prepared by sol-gel methods for photocatalytic degradation of organic pollutants and antibacterial activities. Coatings. 2019;9(10):613.10.3390/coatings9100613Suche in Google Scholar
[162] Varshney G, Kanel SR, Kempisty DM, Varshney V, Agrawal A, Sahle-Demessie E, et al. Nanoscale TiO2 films and their application in remediation of organic pollutants. Coord Chem Rev. 2016;306:43–64.10.1016/j.ccr.2015.06.011Suche in Google Scholar
[163] Won Y, Schwartzenberg K, Gray KA. TiO2-based transparent coatings create self-cleaning surfaces. Chemosphere. 2018;208:899–906.10.1016/j.chemosphere.2018.06.014Suche in Google Scholar PubMed
[164] Piątkowska A, Janus M, Szymański K, Mozia S. C-, N-and S-doped TiO2 photocatalysts: a review. Catalysts. 2021;11(1):144.10.3390/catal11010144Suche in Google Scholar
[165] Asahi R, Morikawa T, Irie H, Ohwaki T. Nitrogen-doped titanium dioxide as visible-light-sensitive photocatalyst: designs, developments, and prospects. Chem Rev. 2014;114(19):9824–52.10.1021/cr5000738Suche in Google Scholar PubMed
[166] Muscetta M, Ganguly P, Clarizia L. Solar-powered photocatalysis in water purification: applications and commercialization challenges. J Environ Chem Eng. 2024;12(3):113073.10.1016/j.jece.2024.113073Suche in Google Scholar
[167] Butt MA, Tyszkiewicz C, Karasiński P, Zięba M, Kaźmierczak A, Zdończyk M, et al. Optical thin films fabrication techniques – Towards a low-cost solution for the integrated photonic platform: A review of the current status. Materials. 2022;15(13):4591.10.3390/ma15134591Suche in Google Scholar PubMed PubMed Central
[168] Zhang H, Wang F, Guo Z. The antifouling mechanism and application of bio-inspired superwetting surfaces with effective antifouling performance. Adv Colloid Interface Sci. 2024;325:103097.10.1016/j.cis.2024.103097Suche in Google Scholar PubMed
[169] Al-Mamun MR, Kader S, Islam MS, Khan MZ. Photocatalytic activity improvement and application of UV-TiO2 photocatalysis in textile wastewater treatment: A review. J Environ Chem Eng. 2019;7(5):103248.10.1016/j.jece.2019.103248Suche in Google Scholar
[170] Fattahi A, Arlos MJ, Bragg LM, Liang R, Zhou N, Servos MR. Degradation of natural organic matter using Ag-P25 photocatalyst under continuous and periodic irradiation of 405 and 365 nm UV-LEDs. J Environ Chem Eng. 2021;9(1):104844.10.1016/j.jece.2020.104844Suche in Google Scholar
[171] Gugumus F. Current trends in mode of action of hindered amine light stabilizers. Polym Degrad Stab. 1993;40(2):167–215.10.1016/0141-3910(93)90208-ZSuche in Google Scholar
[172] Guo MZ, Li JS, Poon CS. Improved photocatalytic nitrogen oxides removal using recycled glass-nano-TiO2 composites with NaOH pre-treatment. J Clean Prod. 2019;209:1095–104.10.1016/j.jclepro.2018.10.303Suche in Google Scholar
[173] García-Montelongo XL, Martínez-De La Cruz A, Vázquez-Rodríguez S, Torres-Martínez LM. Photo-oxidative degradation of TiO2/polypropylene films. Mater Res Bull. 2014;51:56–62.10.1016/j.materresbull.2013.11.040Suche in Google Scholar
[174] Weng KW, Huang YP. Preparation of TiO2 thin films on glass surfaces with self-cleaning characteristics for solar concentrators. Surf Coat Technol. 2013;231:201–4.10.1016/j.surfcoat.2012.06.058Suche in Google Scholar
[175] Wright JS. Colloidal characterisations for environmental exposure assessment in support of the risk assessment of nano-biomaterials for biomedical applications. 2020. p. 79. https://hdl.handle.net/20.500.14247/6638.Suche in Google Scholar
[176] Yang JH, Han YS, Choy JH. TiO2 thin-films on polymer substrates and their photocatalytic activity. Thin Solid Films. 2006;495(1–2):266–71.10.1016/j.tsf.2005.08.195Suche in Google Scholar
[177] Singh P, Kumar A, Kaur D. Substrate effect on texture properties of nanocrystalline TiO2 thin films. Phys B: Condens Matter. 2008;403(19–20):3769–73.10.1016/j.physb.2008.07.021Suche in Google Scholar
[178] Zhang L, Zhu Y, He Y, Li W, Sun H. Preparation and performances of mesoporous TiO2 film photocatalyst supported on stainless steel. Appl Catal B: Environ. 2003;40(4):287–92.10.1016/S0926-3373(02)00154-6Suche in Google Scholar
[179] Sezgin A, Čtvrtlík R, Václavek L, Tomáštík J, Nožka L, Menşur E, et al. Optical, structural and mechanical properties of TiO2 and TiO2-ZrO2 thin films deposited on glass using magnetron sputtering. Mater Today Commun. 2023;35:106334.10.1016/j.mtcomm.2023.106334Suche in Google Scholar
[180] Levchuk I, Guillard C, Dappozze F, Parola S, Leonard D, Sillanpää M. Photocatalytic activity of TiO2 films immobilized on aluminum foam by atomic layer deposition technique. J Photochem Photobiol A: Chem. 2016;328:16–23.10.1016/j.jphotochem.2016.03.034Suche in Google Scholar
[181] Balzano V, Cavaliere E, Fanetti M, Gardonio S, Gavioli L. The role of substrate on thermal evolution of Ag/TiO2 nanogranular thin films. Nanomaterials. 2021;11(9):2253.10.3390/nano11092253Suche in Google Scholar PubMed PubMed Central
[182] Labuto G, Sanches S, Crespo JG, Pereira VJ, Huertas RM. Stability of polymeric membranes to UV exposure before and after coating with TiO2 nanoparticles. Polymers. 2021;14(1):124.10.3390/polym14010124Suche in Google Scholar PubMed PubMed Central
[183] Chen L, Zheng K, Liu Y. Geopolymer-supported photocatalytic TiO2 film: Preparation and characterization. Constr Build Mater. 2017;151:63–70.10.1016/j.conbuildmat.2017.06.097Suche in Google Scholar
[184] Danfá S, Oliveira C, Santos R, Martins RC, Quina MM, Gomes J. Development of TiO2-based photocatalyst supported on ceramic materials for oxidation of organic pollutants in liquid phase. Appl Sci. 2022;12(15):7941.10.3390/app12157941Suche in Google Scholar
[185] Kayani ZN, Saleem M, Riaz S, Naseem S, Saleemi F. Structure and optical properties of TiO2 thin films prepared by a sol-gel processing. Z Naturforsch A. 2019;74(7):635–42.10.1515/zna-2019-0011Suche in Google Scholar
[186] Ma Y, Qiu JB, Cao YA, Guan ZS, Yao JN. Photocatalytic activity of TiO2 films grown on different substrates. Chemosphere. 2001;44(5):1087–92.10.1016/S0045-6535(00)00360-XSuche in Google Scholar PubMed
[187] Leprince-Wang Y, Yu-Zhang K, Van VN, Souche D, Rivory J. Correlation between microstructure and the optical properties of TiO2 thin films prepared on different substrates. Thin Solid Films. 1997;307(1–2):38–42.10.1016/S0040-6090(97)00293-9Suche in Google Scholar
[188] Lopez L, Daoud WA, Dutta D, Panther BC, Turney TW. Effect of substrate on surface morphology and photocatalysis of large-scale TiO2 films. Appl Surf Sci. 2013;265:162–8.10.1016/j.apsusc.2012.10.156Suche in Google Scholar
[189] Yu J, Zhao X. Effect of substrates on the photocatalytic activity of nanometer TiO2 thin films. Mater Res Bull. 2000;35(8):1293–301.10.1016/S0025-5408(00)00327-5Suche in Google Scholar
[190] Krýsa J, Novotná P, Kment Š, Mills A. Effect of glass substrate and deposition technique on the properties of sol–gel TiO2 thin films. J Photochem Photobiol A: Chem. 2011;222(1):81–6.10.1016/j.jphotochem.2011.05.005Suche in Google Scholar
[191] Ivanova T, Harizanova A, Petkov N, Dulev V, Benkovski A, Ganchev M. Titanium dioxide thin films prepared on different substrates by sol–gel process: Optical and morphological properties. In Journal of Physics: Conference Series. Vol. 2952, No. 1, IOP Publishing. 2025. p. 012002.10.1088/1742-6596/2952/1/012002Suche in Google Scholar
[192] Suzuki S, Ando E. Abrasion of thin films deposited onto glass by the Taber test. Thin Solid Films. 1999;340(1–2):194–200.10.1016/S0040-6090(98)01360-1Suche in Google Scholar
[193] Rutherford KL, Hutchings IM. A micro-abrasive wear test, with particular application to coated systems. Surf Coat Technol. 1996;79(1–3):231–9.10.1016/0257-8972(95)02461-1Suche in Google Scholar
[194] Bull SJ, Berasetegui EG. An overview of the potential of quantitative coating adhesion measurement by scratch testing. Tribol Int. 2006;39(2):99–114.10.1016/j.triboint.2005.04.013Suche in Google Scholar
[195] Valli J, Mäkelä U. Applications of the scratch test method for coating adhesion assessment. Wear. 1987;115(1–2):215–21.10.1016/0043-1648(87)90211-0Suche in Google Scholar
[196] Jaworski R, Pawlowski L, Roudet F, Kozerski S, Petit F. Characterization of mechanical properties of suspension plasma sprayed TiO2 coatings using scratch test. Surf Coat Technol. 2008;202(12):2644–53.10.1016/j.surfcoat.2007.09.044Suche in Google Scholar
[197] Jacques LF. Accelerated and outdoor/natural exposure testing of coatings. Prog Polym Sci. 2000;25(9):1337–62.10.1016/S0079-6700(00)00030-7Suche in Google Scholar
[198] Lim RX, Khor MS, Cheong KY. Adhesion of electron-beam evaporated SiO2/TiO2 anti-reflective coating on ion-treated polycarbonate substrate under xenon arc accelerated weathering test. Mater Chem Phys. 2024;315:128960.10.1016/j.matchemphys.2024.128960Suche in Google Scholar
[199] Buchheit RG, Cunningham M, Jensen H, Kendig MW, Martinez MA. A correlation between salt spray and electrochemical impedance spectroscopy test results for conversion-coated aluminum alloys. Corrosion. 1998;54(1):61–72.10.5006/1.3284829Suche in Google Scholar
[200] Wan C, Zhang L, Liu X. Corrosion assessment of Sn–Ni alloy coatings using neutral salt spray tests and electrochemical methods. Int J Electrochem Sci. 2020;15(1):26–38.10.20964/2020.01.20Suche in Google Scholar
[201] Rammelt U, Reinhard G. Application of electrochemical impedance spectroscopy (EIS) for characterizing the corrosion-protective performance of organic coatings on metals. Prog Org Coat. 1992;21(2–3):205–26.10.1016/0033-0655(92)87005-USuche in Google Scholar
[202] McIntyre JM, Pham HQ. Electrochemical impedance spectroscopy; a tool for organic coatings optimizations. Prog Org Coat. 1996;27(1–4):201–7.10.1016/0300-9440(95)00532-3Suche in Google Scholar
[203] Ângelo J, Magalhães P, Andrade L, Mendes A. Characterization of TiO2-based semiconductors for photocatalysis by electrochemical impedance spectroscopy. Appl Surf Sci. 2016;387:183–9.10.1016/j.apsusc.2016.06.101Suche in Google Scholar
[204] Fadl AM, Abdou MI, Al-Elaa SA, Hamza MA, Sadeek SA. Evaluation the anti-corrosion behavior, impact resistance, acids and alkali immovability of nonylphenol ethoxylate/TiO2 hybrid epoxy nanocomposite coating applied on the carbon steel surface. Prog Org Coat. 2019;136:105263.10.1016/j.porgcoat.2019.105263Suche in Google Scholar
[205] Bierwagen GP, He L, Li J, Ellingson L, Tallman DE. Studies of a new accelerated evaluation method for coating corrosion resistance – thermal cycling testing. Prog Org Coat. 2000;39(1):67–78.10.1016/S0300-9440(00)00106-5Suche in Google Scholar
[206] Mittal KL. Adhesion measurement of thin films. Active Passive Electron Compon. 1976;3(1):21–42.10.1155/APEC.3.21Suche in Google Scholar
[207] Valli J. A review of adhesion test methods for thin hard coatings. J Vac Sci Technol A: Vac Surf Films. 1986;4(6):3007–14.10.1116/1.573616Suche in Google Scholar
[208] Chen Z, Zhou K, Lu X, Lam YC. A review on the mechanical methods for evaluating coating adhesion. Acta Mech. 2014;225(2):431–52.10.1007/s00707-013-0979-ySuche in Google Scholar
[209] Chen Y, Dionysiou DD. Effect of calcination temperature on the photocatalytic activity and adhesion of TiO2 films prepared by the P-25 powder-modified sol–gel method. J Mol Catal A: Chem. 2006;244(1–2):73–82.10.1016/j.molcata.2005.08.056Suche in Google Scholar
[210] Mirabedini SM, Mohseni M, PazokiFard S, Esfandeh M. Effect of TiO2 on the mechanical and adhesion properties of RTV silicone elastomer coatings. Colloids Surf A: Physicochem Eng Asp. 2008;317(1–3):80–6.10.1016/j.colsurfa.2007.09.044Suche in Google Scholar
[211] Liu G, Xia H, Niu Y, Zhao X, Zhang G, Song L, et al. Photocatalytic performance of doped TiO2/AC coating and its UV stability research. Prog Org Coat. 2020;148:105882.10.1016/j.porgcoat.2020.105882Suche in Google Scholar
[212] Sharma HK, Singh BP, Sharma SK. CNT-TiO2 nanocomposite thin films enhanced photocatalytic degradation of methylene blue. Hybrid Adv. 2024;5:100152.10.1016/j.hybadv.2024.100152Suche in Google Scholar
[213] Kapridaki C, Maravelaki-Kalaitzaki P. TiO2–SiO2–PDMS nano-composite hydrophobic coating with self-cleaning properties for marble protection. Prog Org Coat. 2013;76(2–3):400–10.10.1016/j.porgcoat.2012.10.006Suche in Google Scholar
[214] Nomeir B, Lakhouil S, Boukheir S, Ait Ali M, Naamane S. Recent progress on transparent and self-cleaning surfaces by superhydrophobic coatings deposition to optimize the cleaning process of solar panels. Sol Energy Mater Sol Cell. 2023;257:112347.10.1016/j.solmat.2023.112347Suche in Google Scholar
© 2025 the author(s), published by De Gruyter
This work is licensed under the Creative Commons Attribution 4.0 International License.
Artikel in diesem Heft
- Research Articles
- MHD radiative mixed convective flow of a sodium alginate-based hybrid nanofluid over a convectively heated extending sheet with Joule heating
- Experimental study of mortar incorporating nano-magnetite on engineering performance and radiation shielding
- Multicriteria-based optimization and multi-variable non-linear regression analysis of concrete containing blends of nano date palm ash and eggshell powder as cementitious materials
- A promising Ag2S/poly-2-amino-1-mercaptobenzene open-top spherical core–shell nanocomposite for optoelectronic devices: A one-pot technique
- Biogenic synthesized selenium nanoparticles combined chitosan nanoparticles controlled lung cancer growth via ROS generation and mitochondrial damage pathway
- Fabrication of PDMS nano-mold by deposition casting method
- Stimulus-responsive gradient hydrogel micro-actuators fabricated by two-photon polymerization-based 4D printing
- Physical aspects of radiative Carreau nanofluid flow with motile microorganisms movement under yield stress via oblique penetrable wedge
- Effect of polar functional groups on the hydrophobicity of carbon nanotubes-bacterial cellulose nanocomposite
- Review in green synthesis mechanisms, application, and future prospects for Garcinia mangostana L. (mangosteen)-derived nanoparticles
- Entropy generation and heat transfer in nonlinear Buoyancy–driven Darcy–Forchheimer hybrid nanofluids with activation energy
- Green synthesis of silver nanoparticles using Ginkgo biloba seed extract: Evaluation of antioxidant, anticancer, antifungal, and antibacterial activities
- A numerical analysis of heat and mass transfer in water-based hybrid nanofluid flow containing copper and alumina nanoparticles over an extending sheet
- Investigating the behaviour of electro-magneto-hydrodynamic Carreau nanofluid flow with slip effects over a stretching cylinder
- Electrospun thermoplastic polyurethane/nano-Ag-coated clear aligners for the inhibition of Streptococcus mutans and oral biofilm
- Investigation of the optoelectronic properties of a novel polypyrrole-multi-well carbon nanotubes/titanium oxide/aluminum oxide/p-silicon heterojunction
- Novel photothermal magnetic Janus membranes suitable for solar water desalination
- Green synthesis of silver nanoparticles using Ageratum conyzoides for activated carbon compositing to prepare antimicrobial cotton fabric
- Activation energy and Coriolis force impact on three-dimensional dusty nanofluid flow containing gyrotactic microorganisms: Machine learning and numerical approach
- Machine learning analysis of thermo-bioconvection in a micropolar hybrid nanofluid-filled square cavity with oxytactic microorganisms
- Research and improvement of mechanical properties of cement nanocomposites for well cementing
- Thermal and stability analysis of silver–water nanofluid flow over unsteady stretching sheet under the influence of heat generation/absorption at the boundary
- Cobalt iron oxide-infused silicone nanocomposites: Magnetoactive materials for remote actuation and sensing
- Magnesium-reinforced PMMA composite scaffolds: Synthesis, characterization, and 3D printing via stereolithography
- Bayesian inference-based physics-informed neural network for performance study of hybrid nanofluids
- Numerical simulation of non-Newtonian hybrid nanofluid flow subject to a heterogeneous/homogeneous chemical reaction over a Riga surface
- Enhancing the superhydrophobicity, UV-resistance, and antifungal properties of natural wood surfaces via in situ formation of ZnO, TiO2, and SiO2 particles
- Synthesis and electrochemical characterization of iron oxide/poly(2-methylaniline) nanohybrids for supercapacitor application
- Impacts of double stratification on thermally radiative third-grade nanofluid flow on elongating cylinder with homogeneous/heterogeneous reactions by implementing machine learning approach
- Synthesis of Cu4O3 nanoparticles using pumpkin seed extract: Optimization, antimicrobial, and cytotoxicity studies
- Cationic charge influence on the magnetic response of the Fe3O4–[Me2+ 1−y Me3+ y (OH2)] y+(Co3 2−) y/2·mH2O hydrotalcite system
- Pressure sensing intelligent martial arts short soldier combat protection system based on conjugated polymer nanocomposite materials
- Magnetohydrodynamics heat transfer rate under inclined buoyancy force for nano and dusty fluids: Response surface optimization for the thermal transport
- Fly ash and nano-graphene enhanced stabilization of engine oil-contaminated soils
- Enhancing natural fiber-reinforced biopolymer composites with graphene nanoplatelets: Mechanical, morphological, and thermal properties
- Performance evaluation of dual-scale strengthened co-bonded single-lap joints using carbon nanotubes and Z-pins with ANN
- Computational works of blood flow with dust particles and partially ionized containing tiny particles on a moving wedge: Applications of nanotechnology
- Hybridization of biocomposites with oil palm cellulose nanofibrils/graphene nanoplatelets reinforcement in green epoxy: A study of physical, thermal, mechanical, and morphological properties
- Design and preparation of micro-nano dual-scale particle-reinforced Cu–Al–V alloy: Research on the aluminothermic reduction process
- Spectral quasi-linearization and response optimization on magnetohydrodynamic flow via stenosed artery with hybrid and ternary solid nanoparticles: Support vector machine learning
- Review Articles
- A comprehensive review on hybrid plasmonic waveguides: Structures, applications, challenges, and future perspectives
- Nanoparticles in low-temperature preservation of biological systems of animal origin
- Fluorescent sulfur quantum dots for environmental monitoring
- Nanoscience systematic review methodology standardization
- Nanotechnology revolutionizing osteosarcoma treatment: Advances in targeted kinase inhibitors
- AFM: An important enabling technology for 2D materials and devices
- Carbon and 2D nanomaterial smart hydrogels for therapeutic applications
- Principles, applications and future prospects in photodegradation systems
- Do gold nanoparticles consistently benefit crop plants under both non-stressed and abiotic stress conditions?
- An updated overview of nanoparticle-induced cardiovascular toxicity
- Arginine as a promising amino acid for functionalized nanosystems: Innovations, challenges, and future directions
- Advancements in the use of cancer nanovaccines: Comprehensive insights with focus on lung and colon cancer
- Membrane-based biomimetic delivery systems for glioblastoma multiforme therapy
- The drug delivery systems based on nanoparticles for spinal cord injury repair
- Green synthesis, biomedical effects, and future trends of Ag/ZnO bimetallic nanoparticles: An update
- Application of magnesium and its compounds in biomaterials for nerve injury repair
- Micro/nanomotors in biomedicine: Construction and applications
- Hydrothermal synthesis of biomass-derived CQDs: Advances and applications
- Research progress in 3D bioprinting of skin: Challenges and opportunities
- Review on bio-selenium nanoparticles: Synthesis, protocols, and applications in biomedical processes
- Gold nanocrystals and nanorods functionalized with protein and polymeric ligands for environmental, energy storage, and diagnostic applications: A review
- An in-depth analysis of rotational and non-rotational piezoelectric energy harvesting beams: A comprehensive review
- Advancements in perovskite/CIGS tandem solar cells: Material synergies, device configurations, and economic viability for sustainable energy
- Deep learning in-depth analysis of crystal graph convolutional neural networks: A new era in materials discovery and its applications
- Review of recent nano TiO2 film coating methods, assessment techniques, and key problems for scaleup
- Antioxidant quantum dots for spinal cord injuries: A review on advancing neuroprotection and regeneration in neurological disorders
- Special Issue on Advanced Nanomaterials for Carbon Capture, Environment and Utilization for Energy Sustainability - Part III
- Efficiency optimization of quantum dot photovoltaic cell by solar thermophotovoltaic system
- Exploring the diverse nanomaterials employed in dental prosthesis and implant techniques: An overview
- Electrochemical investigation of bismuth-doped anode materials for low‑temperature solid oxide fuel cells with boosted voltage using a DC-DC voltage converter
- Synthesis of HfSe2 and CuHfSe2 crystalline materials using the chemical vapor transport method and their applications in supercapacitor energy storage devices
- Special Issue on Green Nanotechnology and Nano-materials for Environment Sustainability
- Influence of nano-silica and nano-ferrite particles on mechanical and durability of sustainable concrete: A review
- Surfaces and interfaces analysis on different carboxymethylation reaction time of anionic cellulose nanoparticles derived from oil palm biomass
- Processing and effective utilization of lignocellulosic biomass: Nanocellulose, nanolignin, and nanoxylan for wastewater treatment
- Retraction
- Retraction of “Aging assessment of silicone rubber materials under corona discharge accompanied by humidity and UV radiation”
Artikel in diesem Heft
- Research Articles
- MHD radiative mixed convective flow of a sodium alginate-based hybrid nanofluid over a convectively heated extending sheet with Joule heating
- Experimental study of mortar incorporating nano-magnetite on engineering performance and radiation shielding
- Multicriteria-based optimization and multi-variable non-linear regression analysis of concrete containing blends of nano date palm ash and eggshell powder as cementitious materials
- A promising Ag2S/poly-2-amino-1-mercaptobenzene open-top spherical core–shell nanocomposite for optoelectronic devices: A one-pot technique
- Biogenic synthesized selenium nanoparticles combined chitosan nanoparticles controlled lung cancer growth via ROS generation and mitochondrial damage pathway
- Fabrication of PDMS nano-mold by deposition casting method
- Stimulus-responsive gradient hydrogel micro-actuators fabricated by two-photon polymerization-based 4D printing
- Physical aspects of radiative Carreau nanofluid flow with motile microorganisms movement under yield stress via oblique penetrable wedge
- Effect of polar functional groups on the hydrophobicity of carbon nanotubes-bacterial cellulose nanocomposite
- Review in green synthesis mechanisms, application, and future prospects for Garcinia mangostana L. (mangosteen)-derived nanoparticles
- Entropy generation and heat transfer in nonlinear Buoyancy–driven Darcy–Forchheimer hybrid nanofluids with activation energy
- Green synthesis of silver nanoparticles using Ginkgo biloba seed extract: Evaluation of antioxidant, anticancer, antifungal, and antibacterial activities
- A numerical analysis of heat and mass transfer in water-based hybrid nanofluid flow containing copper and alumina nanoparticles over an extending sheet
- Investigating the behaviour of electro-magneto-hydrodynamic Carreau nanofluid flow with slip effects over a stretching cylinder
- Electrospun thermoplastic polyurethane/nano-Ag-coated clear aligners for the inhibition of Streptococcus mutans and oral biofilm
- Investigation of the optoelectronic properties of a novel polypyrrole-multi-well carbon nanotubes/titanium oxide/aluminum oxide/p-silicon heterojunction
- Novel photothermal magnetic Janus membranes suitable for solar water desalination
- Green synthesis of silver nanoparticles using Ageratum conyzoides for activated carbon compositing to prepare antimicrobial cotton fabric
- Activation energy and Coriolis force impact on three-dimensional dusty nanofluid flow containing gyrotactic microorganisms: Machine learning and numerical approach
- Machine learning analysis of thermo-bioconvection in a micropolar hybrid nanofluid-filled square cavity with oxytactic microorganisms
- Research and improvement of mechanical properties of cement nanocomposites for well cementing
- Thermal and stability analysis of silver–water nanofluid flow over unsteady stretching sheet under the influence of heat generation/absorption at the boundary
- Cobalt iron oxide-infused silicone nanocomposites: Magnetoactive materials for remote actuation and sensing
- Magnesium-reinforced PMMA composite scaffolds: Synthesis, characterization, and 3D printing via stereolithography
- Bayesian inference-based physics-informed neural network for performance study of hybrid nanofluids
- Numerical simulation of non-Newtonian hybrid nanofluid flow subject to a heterogeneous/homogeneous chemical reaction over a Riga surface
- Enhancing the superhydrophobicity, UV-resistance, and antifungal properties of natural wood surfaces via in situ formation of ZnO, TiO2, and SiO2 particles
- Synthesis and electrochemical characterization of iron oxide/poly(2-methylaniline) nanohybrids for supercapacitor application
- Impacts of double stratification on thermally radiative third-grade nanofluid flow on elongating cylinder with homogeneous/heterogeneous reactions by implementing machine learning approach
- Synthesis of Cu4O3 nanoparticles using pumpkin seed extract: Optimization, antimicrobial, and cytotoxicity studies
- Cationic charge influence on the magnetic response of the Fe3O4–[Me2+ 1−y Me3+ y (OH2)] y+(Co3 2−) y/2·mH2O hydrotalcite system
- Pressure sensing intelligent martial arts short soldier combat protection system based on conjugated polymer nanocomposite materials
- Magnetohydrodynamics heat transfer rate under inclined buoyancy force for nano and dusty fluids: Response surface optimization for the thermal transport
- Fly ash and nano-graphene enhanced stabilization of engine oil-contaminated soils
- Enhancing natural fiber-reinforced biopolymer composites with graphene nanoplatelets: Mechanical, morphological, and thermal properties
- Performance evaluation of dual-scale strengthened co-bonded single-lap joints using carbon nanotubes and Z-pins with ANN
- Computational works of blood flow with dust particles and partially ionized containing tiny particles on a moving wedge: Applications of nanotechnology
- Hybridization of biocomposites with oil palm cellulose nanofibrils/graphene nanoplatelets reinforcement in green epoxy: A study of physical, thermal, mechanical, and morphological properties
- Design and preparation of micro-nano dual-scale particle-reinforced Cu–Al–V alloy: Research on the aluminothermic reduction process
- Spectral quasi-linearization and response optimization on magnetohydrodynamic flow via stenosed artery with hybrid and ternary solid nanoparticles: Support vector machine learning
- Review Articles
- A comprehensive review on hybrid plasmonic waveguides: Structures, applications, challenges, and future perspectives
- Nanoparticles in low-temperature preservation of biological systems of animal origin
- Fluorescent sulfur quantum dots for environmental monitoring
- Nanoscience systematic review methodology standardization
- Nanotechnology revolutionizing osteosarcoma treatment: Advances in targeted kinase inhibitors
- AFM: An important enabling technology for 2D materials and devices
- Carbon and 2D nanomaterial smart hydrogels for therapeutic applications
- Principles, applications and future prospects in photodegradation systems
- Do gold nanoparticles consistently benefit crop plants under both non-stressed and abiotic stress conditions?
- An updated overview of nanoparticle-induced cardiovascular toxicity
- Arginine as a promising amino acid for functionalized nanosystems: Innovations, challenges, and future directions
- Advancements in the use of cancer nanovaccines: Comprehensive insights with focus on lung and colon cancer
- Membrane-based biomimetic delivery systems for glioblastoma multiforme therapy
- The drug delivery systems based on nanoparticles for spinal cord injury repair
- Green synthesis, biomedical effects, and future trends of Ag/ZnO bimetallic nanoparticles: An update
- Application of magnesium and its compounds in biomaterials for nerve injury repair
- Micro/nanomotors in biomedicine: Construction and applications
- Hydrothermal synthesis of biomass-derived CQDs: Advances and applications
- Research progress in 3D bioprinting of skin: Challenges and opportunities
- Review on bio-selenium nanoparticles: Synthesis, protocols, and applications in biomedical processes
- Gold nanocrystals and nanorods functionalized with protein and polymeric ligands for environmental, energy storage, and diagnostic applications: A review
- An in-depth analysis of rotational and non-rotational piezoelectric energy harvesting beams: A comprehensive review
- Advancements in perovskite/CIGS tandem solar cells: Material synergies, device configurations, and economic viability for sustainable energy
- Deep learning in-depth analysis of crystal graph convolutional neural networks: A new era in materials discovery and its applications
- Review of recent nano TiO2 film coating methods, assessment techniques, and key problems for scaleup
- Antioxidant quantum dots for spinal cord injuries: A review on advancing neuroprotection and regeneration in neurological disorders
- Special Issue on Advanced Nanomaterials for Carbon Capture, Environment and Utilization for Energy Sustainability - Part III
- Efficiency optimization of quantum dot photovoltaic cell by solar thermophotovoltaic system
- Exploring the diverse nanomaterials employed in dental prosthesis and implant techniques: An overview
- Electrochemical investigation of bismuth-doped anode materials for low‑temperature solid oxide fuel cells with boosted voltage using a DC-DC voltage converter
- Synthesis of HfSe2 and CuHfSe2 crystalline materials using the chemical vapor transport method and their applications in supercapacitor energy storage devices
- Special Issue on Green Nanotechnology and Nano-materials for Environment Sustainability
- Influence of nano-silica and nano-ferrite particles on mechanical and durability of sustainable concrete: A review
- Surfaces and interfaces analysis on different carboxymethylation reaction time of anionic cellulose nanoparticles derived from oil palm biomass
- Processing and effective utilization of lignocellulosic biomass: Nanocellulose, nanolignin, and nanoxylan for wastewater treatment
- Retraction
- Retraction of “Aging assessment of silicone rubber materials under corona discharge accompanied by humidity and UV radiation”
