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Revisiting hydrotalcite synthesis: Efficient combined mechanochemical/coprecipitation synthesis to design advanced tunable basic catalysts

  • Eliana Nope , Ángel G. Sathicq , José J. Martínez , Zeid A. ALOthman , Gustavo P. Romanelli , Elena Montejano Nares , Francisco Ivars-Barceló , Juan Rubio Zuazo , Rafael Luque EMAIL logo and Alina M. Balu EMAIL logo
Published/Copyright: July 1, 2024
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Nanotechnology Reviews
From the journal Nanotechnology Reviews Volume 13 Issue 1

Abstract

Hydrotalcite materials (HTs) were synthesized by a facile and swift combined mechanochemistry/coprecipitation approach, and their catalytic activity was evaluated and compared with conventionally synthesized hydrotalcites (co-precipitation method) in the Knoevenagel condensation between furfural and ethyl cyanoacetate/malononitrile. Characterization and catalytic activity results clearly demonstrate that the proposed combined mechanochemical/coprecipitation approach provides an improvement in crystallinity, morphology, tunable basicity, and textural properties (higher surface area and enhanced surface properties) as compared to HTs obtained via conventional coprecipitation methods. In addition, mechanochemically synthesized HTs largely improve catalytic activities, including conversion and product selectivity to Knoevenagel condensation products under solventless conditions, short reaction times, or reaction at room temperature as compared to conventional counterparts (e.g., 30–40 vs > 99% product yields).

1 Introduction

Layered double hydroxides (LDH), known as hydrotalcite (HT), are basic materials with a layered structure, which present divalent and trivalent cations and belong to the family of anionic clays. Generally, the structure of these materials is described starting from Mg(OH)2 layers with a brucite-type structure, where Mg2+ cation coordinates six times with hydroxyl groups, forming octahedrons that share their edges with neighboring atoms, creating two-dimensional sheets. These sheets are stacked on top of the other, forming layered networks held together by hydrogen bonds. The substitution of a fraction of the divalent cations in the brucite layer by trivalent cations generates a layer with a positive charge, which is compensated by anions in the interlamellar space, where crystallization water is also found [1,2]. The wide spectrum of divalent and trivalent cations, as well as interlamellar anions, have allowed the design of a wide variety of hydrotalcite with specific properties for various catalytic processes, becoming increasingly important in chemical synthesis [3].

HTs can be synthesized using various methodologies, such as hydrothermal treatment, coprecipitation, and sol–gel method, among others, with coprecipitation being the most widely utilized method in the literature. However, this methodology requires prolonged synthesis times (4 or more days), which makes the process highly time and energy-consuming [4,5]. Several investigations have focused on finding viable routes that allow a reduction in synthesis times for the preparation of these materials, with mechanochemistry proven to be a promising green alternative for such syntheses due to its versatility and simplicity [6,7].

Chitrakar et al. [8] described a solvent-free procedure for the synthesis of Zn Al-LDH, first grinding and then autoclaving the solid precursors at 150°C for 24 h. Tongamp et al. synthesized meixnerite, a type of layered hydroxide, grinding anhydrous magnesium and aluminum hydroxides in a planetary ball mill for 1 h and later for 2 h in the presence of water [9]; this was milled again with a certain amount of magnesium nitrate in the second stage for another 2 h [10]. Salmones et al. used the grinding process for 44 h on hydrotalcites synthesized by the coprecipitation method [11]. Mg-Al-LDHs were synthesized by manual grinding for 1 h in the absence of water; however, the results showed low crystallinity, so they were peptized to improve their properties [12]. CaAl-layered double hydroxide was obtained from two grinding stages: the first consisting of dry grinding of the precursors for 1 h, followed by the addition of water and grinding for 2 h [13]. Li-Al-OH LDH was synthesized by combining the grinding process and hydrothermal treatment. For this, the aluminum precursor Al(OH)3 was first ground for 1 h, followed by the addition of the LiOH·H2O precursor and ground for an additional 1 h; finally, it was subjected to hydrothermal treatment at 80°C for 1 h [14]. Madhusha et al. synthesized ascorbic acid intercalated layered double hydroxides (AA-LDHs) by milling NaOH pellets with magnesium and aluminum nitrates (the molar ratio of Mg and Al was 2:1) using manual milling for 1 h. The resulting solid was washed with distilled water and dried, mixed with ascorbic acid and NaOH, and manually milled for 1.5 h [15]. For the synthesis of Cu–Al layered double hydroxide and a methyl orange (MO)-intercalated one (MO-LDH), copper and aluminum precursors were ground for 2 h and then stirred in water or methyl orange solution for 4 h [16]. Chlorine-intercalated Mg–Al layered double hydroxides (Mg–Al–Cl–LDH) were synthesized using a one-step mechanochemistry method with high purity after 5 h of milling. Fahami et al. studied different grinding times and found that 1 h of grinding is not enough to form the hydrotalcite-type structure and that grinding times longer than 5 h significantly affect the structure of these materials [17]. In another investigation, these authors compared the hydrothermal method with the mechanochemical method for hydrotalcite synthesis and found that the characteristic layered structure for these materials can be simple and swiftly obtained using a ball mill as compared to that synthesized by the hydrothermal method. However, better crystallization was still achieved using the hydrothermal method [18].

Recently, Mg2Al-CO3 LDHs were synthesized by grinding a mixture of magnesium and aluminum hydroxide in a planetary ball milling for 5 h. Water was added to the resulting solid and was stirred for 30 h at 95°C [19]. Although these processes present a reduction in the synthesis time compared to the conventional coprecipitation method, all require high-energy consumption and yield materials with low crystallinity, according to literature reports.

This work presents a new methodology that combines the mechanochemical process (using a ball mill) with coprecipitation for the synthesis of advanced hydrotalcite systems, significantly shortening the synthesis time, improving crystallinity, and with the possibility of controlling basicity, all remarkably beneficial to enhance their catalytic activity. HTs were synthesized using different grinding times (10, 30, and 60 min), and their catalytic activity was tested in the Knoevenagel condensation reaction under solvent-free conditions with respect to conventionally synthesized HTs, offering significantly improved tunability and catalytic activity.

2 Experimental

2.1 Synthesis of hydrotalcites using the coprecipitation method

Layered double hydroxides with the general formula M2+ 1−x M3+ x (OH)2CO3·nH2O were synthesized using the coprecipitation method detailed in our previous work [20]. A M2+/M3+ ratio of 3 with x = 0.25 was employed. Initially, 2.56 g of Mg(NO3)2·6H2O and 1.35 g of Al(NO3)3·9H2O were dissolved in 10 mL of distilled water in a 250 mL flask, and the solution was stirred for 20 min. Then, 2.91 g of urea was added to the solution, followed by continuous stirring for 12 h at 60°C. Subsequently, the temperature was increased to 100°C, and stirred for an additional 24 h. Finally, a 2 M alkaline solution containing NaOH and Na2CO3 was gradually added until the pH reached 10. The resulting mixture was allowed to age for 24 h at 140°C. The white precipitate obtained was filtered, washed with distilled water, and dried overnight at 80°C. The resulting solid is denoted as HT-C.

The molar ratio [urea]/[NO3] greater than 1 leads to the formation of NH3 and CO2, as the pH during the hydrolysis process remains close to 9 (HTs were synthesized at a molar ratio [urea]/[NO3] = 3). Therefore, the carbonate provided by the decomposition of urea serves as the compensating anion in the HT phase, which follows the following reaction mechanism [21,22]:

NH 2 – CO – NH 2 + 3 H 2 O → NH 4 + + CO 3 2 −

( NH 4 ) 2 CO 3 → 2 NH 3 ↑ + CO 2 ↑ + H 2 O

NH 3 + H 2 O ↔ NH 4 OH ↔ NH 4 + + OH −

CO 2 + H 2 O ↔ H 2 CO 3 ↔ H + + HCO 3 − ↔ 2 H + + CO 3 2 −

OH − + ( 1 − x ) Mg 2 + + x Al 3 + + ( x / 2 ) CO 3 2 − + y H 2 O → [ Mg ( 1 − x ) Al x ( OH ) 2 ] ( CO 3 ) x / 2 ⋅ y H 2 O

18 OH − + 6 Mg 2 + + 2 Al 3 + + 9 CO ( NH 2 ) 2 + 12 H 2 O → Mg 6 Al 2 ( OH ) 16 CO 3 ⋅ 4 H 2 O + 18 NH 3 + 8 CO 2

A 2M alkaline solution with a molar ratio of 1:1 (NaOH and Na2CO3) was prepared by dissolving NaOH in distilled water. Then, Na2CO3 and distilled water were slowly added until the desired final volume was reached (creating an entirely alkaline solution). The mixture was then continuously stirred until a translucent solution was obtained.

2.2 Synthesis of hydrotalcites by the combined mechanochemistry/coprecipitation method

Layered double hydroxides with the general formula M2+ 1−x M3+ x (OH)2CO3·nH2O were synthesized using a combination of mechanochemistry and the coprecipitation method. The mechanochemical step was conducted in a planetary ball mill (PM 100 from Retsch, 50 mL stainless steel vessel, and stainless steel 18 balls of 10 mm diameter). The synthesis was carried out using a M2+/M3+ ratio = 3 and consisted of two stages. Initially, the precursor salts of divalent and trivalent cations were mixed with urea, employing the same amounts described above for the coprecipitation method, but this time utilizing a mechanochemical method, i.e., ball milling at 300 rpm for 5 min. Subsequently, the resulting mixture was dissolved in distilled water (50 mL), and the pH was adjusted to 10 by slowly adding a 2 M alkaline solution of NaOH and Na2CO3. The solid obtained by coprecipitation was returned to the grinding process for 5 min at 300 rpm (second stage). Finally, the resulting solid was washed several times with distilled water and dried at 80°C for 12 h (Scheme 1). This process was also conducted using different syntheses times, aiming to complete 30 and 60 min of the milling process. In this regard, the first stage comprised mixing the precursor salts with an M2+/M3+ ratio of 3 and urea, followed by grinding (15 and 30 min). Once the pH reached 10, adjusted with a 2 M alkaline solution of NaOH and Na2CO3, the solid obtained by coprecipitation was returned to the grinding process for 15 and 30 min, respectively. The resulting solids are henceforth denoted as MHT10, MHT30, and MHT60.

Scheme 1 Synthesis of hydrotalcites by the combined mechanochemistry/coprecipitation method.
Scheme 1

Synthesis of hydrotalcites by the combined mechanochemistry/coprecipitation method.

2.3 Characterization of the hydrotalcite materials

Conventional X-ray diffraction (XRD) analysis of powder samples was performed using a Bruker D8 Discover diffractometer (Bruker, German) operated at a voltage of 40 kV and a current of 40 mA, with Cu kα (k = 1.54056 Å) radiation in the 2ϴ range of 5°–80°, a count time of 1 s, and a step size of 0.05° s−1. Further crystallography analyses were carried out using high-resolution X-ray diffraction (HR-XDR) with synchrotron light source radiation. These experiments were performed in the BM25-SpLine beamline at the European Synchrotron Radiation Facility (ESRF) in Grenoble (France) [23]. HR-XRD diffractograms were collected employing a step size of 0.02° s−1 with an incident wavelength of 0.8 Å and an excitation energy of 15.5 keV.

Textural properties were measured by N2 isotherms at 77 K using a Micromeritics ASAP 2000 porosimeter. The samples were previously degassed at 100°C for 12 h. The surface area was calculated using a Brunauer–Emmett–Teller (BET) multipoint model. Infrared spectra (IR) were obtained with a Nicolet iS50 spectrometer by the ATR method, using sample dilution in KBr at a concentration of approximately 10%. SEM-FEI Quanta200 scanning electron microscope (SEM) was used to observe the surface structure of the samples and the shape of particles. IR spectra were obtained at a resolution of 4 cm−1 in the middle IR (4,000–400 cm‒1). CO2 adsorption was measured using a Thermo Scientific model Nicolet iS50 FT-IR spectrometer, and infrared spectra were collected by the DRIFTS method. The materials were cleaned with a He flow of 30 mL/min at 100°C for 30 min. After the He flow, the adsorption of CO2 was carried out at room temperature. In addition, volumetric titration with benzoic acid was carried out to measure the proportion of basic sites. In this method, 0.025 g of catalyst, a 0.01 M benzoic acid solution, and 1 mL of phenolphthalein (strong basic sites indicator) and bromothymol blue (weak basic sites indicator) were used.

2.4 Catalytic studies

The Knoevenagel condensation reaction between furfural and ethyl cyanoacetate was selected as a model reaction to evaluate the activity of the synthesized materials under solvent-free conditions (Scheme 2). Furfural (1 mmol), ethyl cyanoacetate or malononitrile (1 mmol), and 80 mg of catalyst were mixed in a reaction vessel and heated at 25, 40, and 80°C, respectively, for 10 or 30 min under magnetic stirring. After the reaction, acetone was added as an extraction solvent. Finally, the catalyst was separated and washed with acetone (3 × 2 mL), and dried at 80°C to evaluate its reusability. Quantitative analysis was conducted by gas chromatography using a series II Agilent 5890 GC, equipped with a Supelco Equitytm-1 (60 m × 0.25 mm × 0.25 µm) column and an FID detector (Supelco Analytical, Bellefonte, PA, USA). The temperature in the injector was 280°C. The oven temperature program used was as follows: initial temperature of 70°C for 1 min, ramped up to 190°C at a heating rate of 3°C/min, and remained constant at that temperature for 6 min. The products were identified using GC-MS.

Scheme 2 Knoevenagel condensation of furfural with ethyl cyanoacetate/malononitrile.
Scheme 2

Knoevenagel condensation of furfural with ethyl cyanoacetate/malononitrile.

3 Results and discussion

The crystalline properties of the synthesized materials were studied using powder X-ray diffraction. Generally, the coprecipitation method leads to the formation of a layered structure with high crystallinity; however, after long synthesis times (ca. 48 h). In this work, the synthesis of hydrotalcites was carried out by combining mechanochemistry using ball milling followed by the coprecipitation method in short synthesis times (typically 10 min).

X-ray diffraction patterns for these materials (10-, 30- or 60-min milling) are shown in Figure 1. In all cases, the strongest diffraction appears at 2ϴ 11.3°, followed by that at 22.8° and three weaker lines at ca. 34.3°, 60.1°, and 61.6°, as well as two characteristic broad bands with the maximum centered at 38.4° and 45.5°. These line maxima and their relative intensities match those from JCPDS ref 22-0700, being fully consistent with those reported for carbonate-intercalated Mg–Al layered double hydroxide with Mg:Al ratio of 3 [24], which is also in good agreement with the nominal Mg:Al ratio employed in the syntheses. This phase was described as a disordered structure containing a random sequence of rhombohedral and hexagonal stacking layers or 3R1 and 2H1 polytypes [24].

Figure 1 XRD patterns of HTs synthesized by the conventional coprecipitation method (HT-C sample) vs the novel combined mechanochemistry/coprecipitation strategy (MHT10, MHT30, and MHT60 samples).
Figure 1

XRD patterns of HTs synthesized by the conventional coprecipitation method (HT-C sample) vs the novel combined mechanochemistry/coprecipitation strategy (MHT10, MHT30, and MHT60 samples).

The formation of layered structures is confirmed by the presence of diffractions at 11.3°, 22.8°, and 34.3°, which correspond to the (003), (006), and (009) planes, respectively, and indicate multilayer stacking [25]. From the maximum of the reflection associated with the (003) plane, the interplanar distance or basal spacing d of the HT structure can be calculated (e.g., 7.78 Å for MHT10). The spacing d between consecutive layers corresponds to the c parameter of the unit cell, i.e., 23.35 Å for MHT10 [26]. The reflection related to the (110) plane is not dependent on the layer stacking arrangement [24], which is used to calculate the parameter a (equal to parameter b) as twice d (110), i.e., 3.08 Å for MHT10.

Most importantly, powder XRD patterns of the solid obtained using the conventional coprecipitation method (employing ca. 48 h of synthesis) exhibit a higher number of narrow diffractions, with the absence of the broad bands displayed for HTs obtained by the combined mechanochemical/coprecipitation approach. In general, the pattern shows a significantly more complex X-ray diffractogram with a larger number of overlapped lines, which point to a mixture of phases.

Aiming to identify different crystalline phases, high-resolution X-ray diffraction (HR-GIXRD) experiments using synchrotron light source radiation were subsequently performed for both conventionally synthesized (HT-C) vs combined mechanochemical/coprecipitation method (MHT10), as depicted in Figure 2. The high-resolution diffractogram confirmed the complete absence of impurities in MHT10 prepared by the novel combined method as compared to several mixed phases clearly observed for HT-C, even after 48 h coprecipitation synthesis. The 2ϴ maximum positions and relative intensities, characteristic of a hydrotalcite with rhombohedral R3m structure and chemical formula Mg6Al2(CO3)(OH)16·4H2O, reported as JCPDS ref. 00-041-1428 [27], was found in the HR-XRD pattern of HT-C. The reflections of this hydrotalcite phase are displayed together with those characteristic of a mixed carbonate phase, denoted as Eitelite (JCPDS ref. 00-025-0847), described as a rhombohedral R3 structure with chemical formula Na2Mg(CO3)2 [28]. Additionally, MgO (JCPDS ref. 00-043-1022) and Na2O (JCPDS ref. 00-003-1074) appeared as minor crystalline phases.

Figure 2 High-resolution powder XRD patterns of the solid prepared by the conventional co-precipitation method (HT-C), and the most representative solid obtained by combining the mechanochemistry method and coprecipitation using 10 min of synthesis time (MHT10). Symbols: Mg6Al2(CO3)(OH)16·4H2O phase with JCPDS ref. 22-0700 (numbers above the dotted lines), Mg6Al2(CO3)(OH)16·4H2O phase with JCPDS ref. 00-041-1428 (•), Na2Mg(CO3)2 Eitelite phase with JCPDS ref. 00-025-0847 (◊), MgO phase with JCPDS ref. 00-043-1022 (*), and Na2O phase with JCPDS ref. 00-003-1074 (!).
Figure 2

High-resolution powder XRD patterns of the solid prepared by the conventional co-precipitation method (HT-C), and the most representative solid obtained by combining the mechanochemistry method and coprecipitation using 10 min of synthesis time (MHT10). Symbols: Mg6Al2(CO3)(OH)16·4H2O phase with JCPDS ref. 22-0700 (numbers above the dotted lines), Mg6Al2(CO3)(OH)16·4H2O phase with JCPDS ref. 00-041-1428 (•), Na2Mg(CO3)2 Eitelite phase with JCPDS ref. 00-025-0847 (◊), MgO phase with JCPDS ref. 00-043-1022 (*), and Na2O phase with JCPDS ref. 00-003-1074 (!).

The formation of the observed phases in HT-C obtained by the coprecipitation method may arise from several mechanisms, including partial hydroxylation occurring during the initial synthesis stage, where MgO transforms to Mg(OH)2, or the formation of highly stable intermediates, such as MgCO3 and Al(OH)3, which potentially engage in reactions with the alkaline solution composed of NaOH and Na₂CO₃ [29,30]. While the hydrolysis of urea generates carbonate ions ( CO 3 2 − ) , the combined approach of coprecipitation and urea hydrolysis may serve to finely modulate the nucleation and crystallization processes, thereby fostering the development of hydrotalcite structures characterized by their fine and homogeneous morphology [22,31]. Nevertheless, the emergence of alternative phases via the coprecipitation method could also be contingent upon factors such as the concentration of metal precursors, the quantity of urea utilized, the alkaline solution concentrations, temperature, the pH value needed for the precipitation, and aging time [30,32]. Consequently, the synergistic employment of mechanochemical and coprecipitation methodologies represents a compelling strategy for achieving hydrotalcites with high purity in a short time.

The unit cell parameters calculated for the hydrotalcite phase contained in HT-C were a = 3.05 Å and c = 22.84 Å. These parameters are significantly lower than those found for MHT10 (a = 3.08 Å and c = 23.35 Å). Remarkably, MHT10 exhibits a more expanded structure than HT-C, either within layers or between them. Considering that parameter a corresponds to the closest average cation–cation distance within a layer [33,34], and a higher a indicates an increase in Mg content with respect to Al, as the ionic radius of Mg2+ (0.065 nm) is comparatively larger than that of Al3+ (0.050 nm) [35,36]. These facts are in good agreement with the accompanying increase obtained in the interlayer distance, related to the observed increase in parameter c. The enhancement of interlayer distance is generally related to the lower number of carbonate anions, which are partially substituted with bicarbonates ( HCO 3 − ) due to a decrease in the cationic charge from the brucite layer to be compensated [37,38]. In essence, these results clearly pointed out that the proposed combined mechanochemical/coprecipitation approach offers access to highly pure and crystalline LDHs in short times (10 min), with no significant differences observed among powder XRD patterns for MHT materials regardless of the synthesis time (10–60 min milling).

The average crystallite size values, determined by the Scherrer equation, are listed in Table 1. It is evident that the milling time influences the crystallite size, with longer milling times (1 h) resulting in larger crystallite sizes, while shorter times result in smaller sizes. In the case of HT-C, a larger crystallite size is obtained compared to the rest of the synthesized materials. These outcomes can be linked to the nucleation and crystallization processes occurring during the synthesis. Nucleation initiates upon adding an alkaline solution at constant pH to a solution containing precursor metal salts of M2+ and M3+ cations, and simultaneously, crystal growth begins with the addition. Several authors have reported that these processes affect crystallinity and crystallite size, being highly influenced by temperature and time in the synthesis. Coral et al. studied different microwave irradiation times in the synthesis of HT and observed that with 300 min of irradiation at 110°C, crystalline properties significantly improved compared to 10 min of microwave irradiation at the same temperature [39]. In treatments involving hydrothermal conditions at increasing temperatures and longer aging times, crystallinity and crystallite size tend to increase [40,41].

Table 1

Textural properties of hydrotalcites synthesized and crystallite sizes

Catalyst S BET (m2 g−1) Pore volume (cm3 g−1) Pore size (nm) Crystallite size* (nm)
HT-C 17 0.11 8 4.1
MHT10 88 0.29 13 2.7
MHT30 78 0.39 20 2.7
MHT60 63 0.31 18 3.5

*D (003) was calculated using the Scherrer equation.

The results obtained from the combination of mechanochemistry/coprecipitation suggest that the change in the crystallite size depends on the second milling stage after coprecipitation, where nucleation and crystal growth processes occur simultaneously and are influenced by milling time; longer milling time in this stage generates larger crystallite sizes. In the first stage, milling of the metal precursors with urea allows them to be reduced to an amorphous phase, creating active sites for water molecules and compensation anions to be incorporated into the structure [10]. However, for HT-C, these processes occur during coprecipitation and aging, which require more synthesis time, resulting in a larger crystallite size.

The slight change in the crystallite size (approximately 1.5 nm) in the synthesis methods for HTC and MHT suggests that these results could primarily be related to the presence of urea, which finely modulates nucleation and crystallization processes, as described above. The small crystallite sizes observed for MHT materials may indicate high particle agglomeration. Since the crystallite size in D 003 is related to the stacking distance of layers like brucite [42], it is plausible that the structure widens due to the agglomeration of extremely small particles, as evidenced by the “c” parameter value for MHT10. The presence of small crystallites suggests a higher amount of grain boundaries and surface defects, which could increase the surface reactivity of the materials as well as lead to a greater number of pores or the formation of small pores.

Textural properties of the synthesized HTs are summarized in Table 1. All pure solids (carbonate-intercalated Mg–Al layers double hydroxide) synthesized by the novel combined mechanochemical method also exhibited remarkably improved surface areas (ca. 70–80 m2 g−1) compared to conventionally synthesized HTs, which are typically poorly porous-defined (usually <20 m2 g−1). Volume and, importantly, pore size (potentially relevant for catalysis and adsorption applications) also significantly improved for materials synthesized via the combined mechanochemically/coprecipitated method, likely due to the alteration in microscopic morphology related to the presence of different cations within the layered structure (isomorphic substitution of divalent cations [43]), which are highly favored under mechanochemical conditions. The intimate mixing (and enhanced interaction) between the precursor salts of the divalent and trivalent cations during ball milling leads to the formation of bicarbonate species, significantly enhancing the textural properties of the combined mechanochemical/coprecipitation materials, as described in the XRD analysis. Therefore, this synthesis method enables achieving results comparable to those obtained with hydrotalcites synthesized by other methods [44,45,46,47]; however, this work highlights short synthesis times.

The grinding time significantly influences the textural properties of the materials, as observed in the comparison in Table 1, where the surface area decreases with grinding time, indicating that a grinding time of 10 min could represent an optimal time. However, the volume and pore size values do not follow this trend. The change in the textural properties of MHT is linked to particle growth. Previous research, such as that by Benito et al., explored the synthesis of hydrotalcites using different microwave irradiation times and found that an increase in irradiation time leads to a decrease in surface area, associating these results with hydrotalcite particle growth [48]. In our synthesis process, changes in textural properties could also be attributed to particle agglomeration and modification over the grinding time. This suggests that, despite presenting similar surface areas, pore size and distribution vary within these materials, as described later. This phenomenon arises because the porosity of layered double hydroxides emerges due to the imperfect fitting of particles in a hexagonal sheet form, which can result in slit-shaped pore formation [49].

Adsorption–desorption isotherms of the synthesized materials are shown in Figure 3, with all solids exhibiting type IV isotherms, characteristic of mesoporous materials with hysteresis loop H3 [50]. This type of loop indicates the formation of materials in the form of plates, where particle pores have slit shapes, characteristic of hydrotalcite-type materials [51]. Although the shape of the isotherms is the same in all cases, the adsorption capacity (approximately taken from the amount of nitrogen adsorbed at a relative pressure of 0.95) in HT-C is very low (almost non-porous) with respect to MHT materials. These results could be related to the aging time (24 h) required in HT-C synthesis, during complete dissolution and reprecipitation of small particles probably take place, contributing mostly to the specific surface area and leading to the formation of larger crystals potentially blocking the pores, significantly influencing the textural properties of these materials [3,52]. The proposed combined mechanochemical/coprecipitation approach avoids the aging step, notably enhancing HT textural properties.

Figure 3 N2 adsorption–desorption isotherms of hydrotalcites synthesized by the combined mechanochemical/coprecipitation method (MHT10, MHT30, MHT60) as compared to conventional coprecipitation method (HT-C, shown in the inset due to the difference in adsorbed volumes).
Figure 3

N2 adsorption–desorption isotherms of hydrotalcites synthesized by the combined mechanochemical/coprecipitation method (MHT10, MHT30, MHT60) as compared to conventional coprecipitation method (HT-C, shown in the inset due to the difference in adsorbed volumes).

Pore size distribution for these materials, calculated according to the Barrett, Joyner, and Halenda (BJH) method (Figure 4), reveals significative modifications in the pore diameter values between HT synthesized by the conventional method and the hydrotalcites obtained by the combination of mechanochemistry/coprecipitation. The HT-C material presents a pore diameter range between 8 and 10 nm, indicating the presence of mesopores with a uniform structure. The materials synthesized by mechanochemistry/coprecipitation present pore size enlargement with a range of 5–45 nm for MHT-30 and MTH-60 materials and 3–40 nm for MHT-10, suggesting the presence of mesopores in the structure of these materials [53,54]. However, for the synthesized materials with longer grinding times (30 and 60 min), non-uniform mesopores are present due to the contribution of pores in the range between 1.5 and 4 nm, which can be attributed to mesopores with a very small structure (smaller mesopores and some micropores), possibly related to crystallite size [55]. In general, these results indicate that the combination of the mechanochemical/coprecipitation process promotes an increase in pore density due to the aggregation of the laminar-shaped layers with slit-shaped pores characteristic of hydrotalcites.

Figure 4 Pore size distribution of the hydrotalcites synthesized by the combined mechanochemical/coprecipitation method (MHT10, MHT30, MHT60) as compared to the conventional coprecipitation method HT-C.
Figure 4

Pore size distribution of the hydrotalcites synthesized by the combined mechanochemical/coprecipitation method (MHT10, MHT30, MHT60) as compared to the conventional coprecipitation method HT-C.

The SEM micrographs of the synthesized materials are shown in Figure 5. The materials prepared by the mechanochemical/coprecipitation combination method exhibit a notable propensity for agglomeration, displaying a spongy structure attributable to the overlapping of the typical sheets found in these materials. This agglomeration arises from a high surface/volume ratio, where the agglomerates are composed of numerous round particles possessing a very fine laminar structure characteristic of hydrotalcite materials [18]. In the mechanochemical process, when two adjacent particles collide, they share a common crystallographic orientation, leading to the amalgamation of two particles into a secondary one, thus promoting the spread of agglomeration and the formation of diminutive sheets [17]. In contrast, materials synthesized via the coprecipitation method (HT-C) show well-defined sheets with a larger laminar morphology. These results suggest that the combination of the coprecipitation/mechanochemistry method enhances the formation of smaller overlapping sheets, thereby generating compact agglomerates, corroborating the crystallite size and textural properties results. The morphology achieved by this method closely resembles that reported by other researchers utilizing coprecipitation, hydrothermal, and mechanochemical methods that necessitate extended synthesis durations (>5 h) [56,57,58].

Figure 5 SEM images of hydrotalcites synthesized by the combined mechanochemical/coprecipitation method (MHT10, MHT30, MHT60) and the conventional coprecipitation method (HT-C).
Figure 5

SEM images of hydrotalcites synthesized by the combined mechanochemical/coprecipitation method (MHT10, MHT30, MHT60) and the conventional coprecipitation method (HT-C).

The infrared spectrum for the synthesized materials shows characteristic bands typical of HT-type materials (Figure S1). Signals between 2,700 and 3,700 cm−1 correspond to stretching vibrations of the hydrogen bond in −OH groups and water molecules within the interlamellar region [36] (e.g., band at 1,647 cm−1 is associated with deformation vibrations of water molecules present between layers) [26,59]. Interestingly, these bands display slight variations in the mechanochemical/coprecipitation materials, indicating a higher abundance of hydroxyl groups between the layers [60]. The band at 1,368 cm−1 is attributed to the antisymmetric stretching mode of the carbonate anion of the interlayer, while those at 667 and 871 cm−1 are related to vibrational modes of CO 3 2 − species [61,62]. These bands suggest that carbonate ions are present as free anions, compensating for the positive charge of the laminar layers [63]. Notably, vibrational modes of the bicarbonate species are observed and designated to the region between 428 and 760 cm−1, with small shoulders at 555 and 863 cm−1 [60]. The band around 452 cm−1 is attributed to the O–M bonds (M = metal) of the brucite layer, associated with the vibrational modes δHO-M-OH and δO-MO [64]. The characteristic signals of the vibrational modes of carbonate anions considerably decrease in mechanochemical/coprecipitated materials due to the observed increase in the parameter c in these materials, linked to the formation of bicarbonate species in the interlaminar space, as described in XRD analysis.

To determine basic properties of the materials, CO2 adsorption was conducted and analyzed using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). CO2 adsorption occurs by the formation of bidentate, monodentate, and bridged species arising from different types of basic surface sites [65]. Specifically, CO2 adsorption on oxygen ions with the lowest coordination number leads to strong basic sites (monodentate species), whereas adsorption of bidentate carbonate species, bridged carbonates, and bicarbonate species leads to moderate and weak basic sites [23]. The signals at 1,680, 1,666, 1,640, 1,600, and 1,350 cm−1 correspond to v 3 vibrational modes of the bidentate species, bridged carbonates, or bicarbonates (weak basic species), while signals between 1,308 and 1,248 cm−1 correspond to v 3 vibrational modes of the monodentate species, associated to strong basic sites [65,66]. MHT materials exhibited a higher prevalence of basic sites (both strong and weak) compared to HT-C (Figure 6). Surprisingly, strong basic sites were observed to increase with longer grinding times, while weak basic sites decreased. This increase in strong and weak basic species in materials synthesized via the mechanochemical/coprecipitation approach could be attributed to the partial substitution of carbonate anions with the bicarbonate species due to a lower cationic charge in the layered structure, which is compensated for these species (consistent with the XDR results). Importantly, the proposed mechanochemical/coprecipitation approach allows for fine-tuning of the basic properties in HTs based on the milling time, which is critical for designing advanced catalytic (basic) materials in chemical reactions.

Figure 6 DRIFT-CO2 analysis of hydrotalcites synthesized by combined mechanochemical and coprecipitation methods (MHT10, MHT30, and MHT60) or conventional coprecipitation method (HT-C). Monodentate species (blue) and bidentate species or bicarbonate (red).
Figure 6

DRIFT-CO2 analysis of hydrotalcites synthesized by combined mechanochemical and coprecipitation methods (MHT10, MHT30, and MHT60) or conventional coprecipitation method (HT-C). Monodentate species (blue) and bidentate species or bicarbonate (red).

The synthesized materials underwent testing in the Knoevenagel condensation reaction between furfural and ethyl cyanoacetate/malononitrile under solvent-free conditions. Initially, the reaction was conducted at 80°C for 30 min, with the results from Table S1 indicating high yields of the condensation product and high catalytic activity for all materials (>95% yields). Blank runs yielded low conversion (<10%) in the systems, confirming the necessity of a catalyst for the reaction. No significant differences were observed between HT-C and MHT materials under these preliminary investigated reaction conditions.

Subsequently, the reaction temperature was lowered to 40°C and room temperature (RT), revealing notable differences in terms of catalytic activity between HT-C and MHT materials (Figure 7). Compared to quantitative product yields (for ethyl cyanoacetate and malononitrile) obtained for MHT materials, HT-C exhibited a lower product yield of 35–50% under otherwise identical reaction conditions. These results clearly illustrate the observed enhancements in textural, morphological, and surface properties, as well as tunable basicity, exerting a critical influence on the catalytic activity of HT materials.

Figure 7 Knoevenagel condensation with hydrotalcites synthesized by mechanochemistry and the hydrotalcite synthesized by conventional coprecipitation. Reaction conditions: furfural (1 mmol), ethyl cyanoacetate/malononitrile (1 mmol), 80 mg catalyst, 10 min, and solvent-free.
Figure 7

Knoevenagel condensation with hydrotalcites synthesized by mechanochemistry and the hydrotalcite synthesized by conventional coprecipitation. Reaction conditions: furfural (1 mmol), ethyl cyanoacetate/malononitrile (1 mmol), 80 mg catalyst, 10 min, and solvent-free.

To gain a deeper understanding of the behavior of these materials, the reaction was studied using smaller amounts of the catalyst (Figure 8). As expected, a reduction in catalyst mass resulted in lower yields of the desired product. However, no significant differences were observed between the materials when the catalyst mass was decreased, maintaining an almost constant trend in yields toward the desired product. For instance, yields close to 30% were obtained with 10 mg of catalyst, while yields between 30 and 35% were achieved with 40 mg.

Figure 8 Mass of the catalyst in the Knoevenagel condensation. Reaction conditions: furfural (1 mmol), ethyl cyanoacetate (1 mmol), 10 min, solvent-free, and room temperature.
Figure 8

Mass of the catalyst in the Knoevenagel condensation. Reaction conditions: furfural (1 mmol), ethyl cyanoacetate (1 mmol), 10 min, solvent-free, and room temperature.

These findings suggest that the catalytic activity in the Knoevenagel condensation of furfural with ethyl cyanoacetate is not determined by the proportion of basic sites in the materials but rather by their basic character. CO2-DRIFT analysis revealed the presence of both strong and weak basic species in all materials, with different proportions. For example, in the case of HT-C, weak basic sites (1.3 mmol/g titration with benzoic acid/bromothymol blue) predominated over strong basic sites (0.4 mmol/g titration with phenolphthalein). This suggests that the high presence of weak basic species in HT-C leads to lower yields, as Knoevenagel condensations are favored by strong basic sites. It is well known that extracting a proton from a methylene compound with a high pK a value necessitates the presence of a catalyst with strong basic properties. Therefore, malononitrile and ethyl cyanoacetate, with pK a values of 11.4 and 9, respectively, require strong basic sites for their deprotonation and the formation of the corresponding carbanion [67]. The grinding process facilitates the generation of strong basic sites, which exhibit an escalating trend with extended grinding time (MHT10 = 0.723, MHT30 = 0.781, and MHT60 = 0.985 mmol/g), while concurrently reducing the presence of weak basic sites (MHT10 = 0.345, MHT30 = 0.140, and MHT60 = 0.187 mmol/g). However, there were variations in the abundance of strong basic sites between the different modified hydrotalcite (MHT), catalytic activity was affected by this parameter.

This behavior may be attributed to the crystallite size (2.7–3.5 nm), as no significant difference is observed among them. Moreover, the presence of small crystallites could promote higher surface activity in these materials due to increased pore density. However, a yield close to 45% is achieved for HT-C, which also has a small crystallite size (4.1 nm) under mild reaction conditions (room temperature and 10 min of reaction). These results indicate that the catalytic activity of these materials is not only influenced by their basic properties and crystallite size but may also be related to their morphological properties. It is noteworthy that HT-C exhibits a plate-like morphology, while MHT displays a granular morphology. This morphological variation significantly impacts the textural properties of the materials, as evidenced by an increase in the surface area for MHT. This increase facilitates greater availability of basic sites on the surface, thereby promoting the Knoevenagel condensation between furfural and malononitrile under mild reaction conditions. Consequently, the induced change in the morphology of these materials by the combination of mechanochemical/coprecipitation processes leads to a significant improvement in the catalytic activity of hydrotalcites in the Knoevenagel condensation reaction, in good agreement with previous investigations [68,69].

The presence of strong basic sites in modified hydrotalcite materials (MHT) and granular morphology provides a highly promising approach to obtaining high-value-added chemicals through the Knoevenagel condensation reaction of furfural. Various investigations have explored different reaction conditions, such as the use of solvents, acidic or basic materials as catalysts, and different reaction times and temperatures. In this context, catalysts such as Darco (commercial carbonaceous materials) for 6 h [70], sulfated polyborate for 60 min at 70°C in water: ethanol (1:1) [71], ZrPO4 for 8 h at 100°C [72], BCN (dicyanamide/boric acid) for 15 min in methylbenzene at 80°C [73], and recently organocatalysts in ethanol for 30 min at room temperature [67], have been evaluated, showing promising results but with considerable reaction times and energy consumption.

Table 2 shows the results of solvent-free reaction conditions for the Knoevenagel condensation of furfural with malononitrile, a significant reduction in reaction times with high yields towards the Knoevenagel product. These results underscore the versatility of the Knoevenagel condensation reaction mediated by acidic or basic sites, wherein the presence of strong basic species in MHT materials facilitates obtaining high yields of the condensation product in reduced reaction times at room temperature.

Table 2

Conditions and yield in the Knoevenagel condensation between furfural and malononitrile using other catalysts

Entry Catalyst Temperature (°C) Time (min) Yield (%) Ref
1 SO 4 2 − /ZrO2 Heated reflux 30 87 [74]
2 Co-MOF 40°C 30 100 [75]
60°C 20 100
3 Prol-MSN (mesoporous silica nanoparticles) RT 30 76 [67]
4 SBA-15-Alanine 150°C 15 91 [76]
5 16Alanine-MCM-41 100°C 30 88 [77]
6 ILS ionic (liquid-functionalized SBA-15) 120°C 3 95 [78]
Microwave
7 HT commercial/dimethylformamide 100°C 15 99 [79]
8 Calcined hydrotalcite/dimethylformamide RT 30 98 [80]
9 MHT RT 10 99 This work

RT: room temperature.

The results obtained in this work indicate a significant reduction in reaction times and high yields of the Knoevenagel product when utilizing MHT materials as catalysts in the absence of solvent within 10 min of reaction, representing a substantial improvement in terms of efficiency and energy consumption. Previous studies have demonstrated the efficiency of hydrotalcite-type materials (Table 2, entries 7 and 8). However, this work highlights the advantages of using hydrotalcite synthesized by a combination of mechanochemical process and coprecipitation method. This innovative approach opens new possibilities for designing more efficient and sustainable processes (less energy and time-consuming, solventless protocols) in the synthesis of materials and fine chemicals, thereby contributing to a more sustainable (nano)materials design.

In addition to the superior catalytic activities registered for MHT materials, reusability studies also confirmed the high stability and relevant unchanged activities preserved after 4 reaction cycles (Figure 9, Table S2) for all MHT materials.

Figure 9 Reusability studies of MHT materials in four reaction cycles. Reaction conditions: furfural (1 mmol), ethyl cyanoacetate (1 mmol), 80 mg catalyst, 10 min, solvent-free (Reaction = starting reaction).
Figure 9

Reusability studies of MHT materials in four reaction cycles. Reaction conditions: furfural (1 mmol), ethyl cyanoacetate (1 mmol), 80 mg catalyst, 10 min, solvent-free (Reaction = starting reaction).

4 Conclusions

The synthesis of hydrotalcite-type materials was revisited using a simple and efficient combined mechanochemical/coprecipitation approach that allowed the preparation of better crystalline, porous, and basicity-tuned HTs in short synthesis times (typically 10–30 min), avoiding aging steps and long synthesis times (ca. 48 h, conventional coprecipitation synthesis) that were proved to lead to the formation of impurities. Textural, morphology, crystalline, and basic properties could be remarkably improved by the partial replacement of carbonate anions with bicarbonate species in the mechanochemical step. Importantly, layered structure formation was not influenced by the grinding time, with 10 min being sufficient to obtain well-defined and highly active HT materials. Importantly, basic properties (and species) in the layered structure could also be fine-tuned and controlled on the basis of grinding time in the mechanochemical step, developing weak and strong basic species at short milling times and strong basic sites at longer grinding times. The catalytic activity is highly influenced by the change in the morphology of the hydrotalcites, and novel MHT materials provided quantitative yields to Knoevenagel products under solventless conditions at room temperature (10 min reaction), without any loss of catalytic activity after four reaction cycles, as compared to moderate to low product yields (35–50%) obtained for HT-C counterparts. The proposed innovative combined approach has the potential to pave the way to the design of advanced LDH-related materials in large quantities (typically over 10 g material per batch, highly reproducible) for additional catalytic/adsorption-related applications that will be reported in due course.

Acknowledgments

MCIN and CSIC are acknowledged for providing synchrotron radiation facilities. This research has been supported by the Researcher Supporting Project Number (RSP2024R1), King Saud University, Riyadh, Saudi Arabia.

  1. Funding information: The Spanish beamline (BM25, SpLine) in the ESRF (Grenoble, France) through the proposal ref. 25-02-1011. F. Ivars-Barcelo gratefully acknowledges MCIN for the “Ramón y Cajal” fund with ref. RYC2020-029470-I. This publication was supported by the RUDN University Strategic Academic Leadership Program (R. Luque).

  2. Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission.

  3. Conflict of interest: The authors state no conflict of interest.

  4. Data availability statement: The datasets generated and/or analysed during the current study are available from the corresponding author on reasonable request.

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Received: 2023-12-11
Revised: 2024-04-10
Accepted: 2024-05-17
Published Online: 2024-07-01

© 2024 the author(s), published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

Articles in the same Issue

  1. Research Articles
  2. Tension buckling and postbuckling of nanocomposite laminated plates with in-plane negative Poisson’s ratio
  3. Polyvinylpyrrolidone-stabilised gold nanoparticle coatings inhibit blood protein adsorption
  4. Energy and mass transmission through hybrid nanofluid flow passing over a spinning sphere with magnetic effect and heat source/sink
  5. Surface treatment with nano-silica and magnesium potassium phosphate cement co-action for enhancing recycled aggregate concrete
  6. Numerical investigation of thermal radiation with entropy generation effects in hybrid nanofluid flow over a shrinking/stretching sheet
  7. Enhancing the performance of thermal energy storage by adding nano-particles with paraffin phase change materials
  8. Using nano-CaCO3 and ceramic tile waste to design low-carbon ultra high performance concrete
  9. Numerical analysis of thermophoretic particle deposition in a magneto-Marangoni convective dusty tangent hyperbolic nanofluid flow – Thermal and magnetic features
  10. Dual numerical solutions of Casson SA–hybrid nanofluid toward a stagnation point flow over stretching/shrinking cylinder
  11. Single flake homo p–n diode of MoTe2 enabled by oxygen plasma doping
  12. Electrostatic self-assembly effect of Fe3O4 nanoparticles on performance of carbon nanotubes in cement-based materials
  13. Multi-scale alignment to buried atom-scale devices using Kelvin probe force microscopy
  14. Antibacterial, mechanical, and dielectric properties of hydroxyapatite cordierite/zirconia porous nanocomposites for use in bone tissue engineering applications
  15. Time-dependent Darcy–Forchheimer flow of Casson hybrid nanofluid comprising the CNTs through a Riga plate with nonlinear thermal radiation and viscous dissipation
  16. Durability prediction of geopolymer mortar reinforced with nanoparticles and PVA fiber using particle swarm optimized BP neural network
  17. Utilization of zein nano-based system for promoting antibiofilm and anti-virulence activities of curcumin against Pseudomonas aeruginosa
  18. Antibacterial effect of novel dental resin composites containing rod-like zinc oxide
  19. An extended model to assess Jeffery–Hamel blood flow through arteries with iron-oxide (Fe2O3) nanoparticles and melting effects: Entropy optimization analysis
  20. Comparative study of copper nanoparticles over radially stretching sheet with water and silicone oil
  21. Cementitious composites modified by nanocarbon fillers with cooperation effect possessing excellent self-sensing properties
  22. Confinement size effect on dielectric properties, antimicrobial activity, and recycling of TiO2 quantum dots via photodegradation processes of Congo red dye and real industrial textile wastewater
  23. Biogenic silver nanoparticles of Moringa oleifera leaf extract: Characterization and photocatalytic application
  24. Novel integrated structure and function of Mg–Gd neutron shielding materials
  25. Impact of multiple slips on thermally radiative peristaltic transport of Sisko nanofluid with double diffusion convection, viscous dissipation, and induced magnetic field
  26. Magnetized water-based hybrid nanofluid flow over an exponentially stretching sheet with thermal convective and mass flux conditions: HAM solution
  27. A numerical investigation of the two-dimensional magnetohydrodynamic water-based hybrid nanofluid flow composed of Fe3O4 and Au nanoparticles over a heated surface
  28. Development and modeling of an ultra-robust TPU-MWCNT foam with high flexibility and compressibility
  29. Effects of nanofillers on the physical, mechanical, and tribological behavior of carbon/kenaf fiber–reinforced phenolic composites
  30. Polymer nanocomposite for protecting photovoltaic cells from solar ultraviolet in space
  31. Study on the mechanical properties and microstructure of recycled concrete reinforced with basalt fibers and nano-silica in early low-temperature environments
  32. Synergistic effect of carbon nanotubes and polyvinyl alcohol on the mechanical performance and microstructure of cement mortar
  33. CFD analysis of paraffin-based hybrid (Co–Au) and trihybrid (Co–Au–ZrO2) nanofluid flow through a porous medium
  34. Forced convective tangent hyperbolic nanofluid flow subject to heat source/sink and Lorentz force over a permeable wedge: Numerical exploration
  35. Physiochemical and electrical activities of nano copper oxides synthesised via hydrothermal method utilising natural reduction agents for solar cell application
  36. A homotopic analysis of the blood-based bioconvection Carreau–Yasuda hybrid nanofluid flow over a stretching sheet with convective conditions
  37. In situ synthesis of reduced graphene oxide/SnIn4S8 nanocomposites with enhanced photocatalytic performance for pollutant degradation
  38. A coarse-grained Poisson–Nernst–Planck model for polyelectrolyte-modified nanofluidic diodes
  39. A numerical investigation of the magnetized water-based hybrid nanofluid flow over an extending sheet with a convective condition: Active and passive controls of nanoparticles
  40. The LyP-1 cyclic peptide modified mesoporous polydopamine nanospheres for targeted delivery of triptolide regulate the macrophage repolarization in atherosclerosis
  41. Synergistic effect of hydroxyapatite-magnetite nanocomposites in magnetic hyperthermia for bone cancer treatment
  42. The significance of quadratic thermal radiative scrutinization of a nanofluid flow across a microchannel with thermophoretic particle deposition effects
  43. Ferromagnetic effect on Casson nanofluid flow and transport phenomena across a bi-directional Riga sensor device: Darcy–Forchheimer model
  44. Performance of carbon nanomaterials incorporated with concrete exposed to high temperature
  45. Multicriteria-based optimization of roller compacted concrete pavement containing crumb rubber and nano-silica
  46. Revisiting hydrotalcite synthesis: Efficient combined mechanochemical/coprecipitation synthesis to design advanced tunable basic catalysts
  47. Exploration of irreversibility process and thermal energy of a tetra hybrid radiative binary nanofluid focusing on solar implementations
  48. Effect of graphene oxide on the properties of ternary limestone clay cement paste
  49. Improved mechanical properties of graphene-modified basalt fibre–epoxy composites
  50. Sodium titanate nanostructured modified by green synthesis of iron oxide for highly efficient photodegradation of dye contaminants
  51. Green synthesis of Vitis vinifera extract-appended magnesium oxide NPs for biomedical applications
  52. Differential study on the thermal–physical properties of metal and its oxide nanoparticle-formed nanofluids: Molecular dynamics simulation investigation of argon-based nanofluids
  53. Heat convection and irreversibility of magneto-micropolar hybrid nanofluids within a porous hexagonal-shaped enclosure having heated obstacle
  54. Numerical simulation and optimization of biological nanocomposite system for enhanced oil recovery
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  66. Significance of nanoparticle aggregation for thermal transport over magnetized sensor surface
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  68. Effect of annealing time on bending performance and microstructure of C19400 alloy strip
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  70. Electrospinning of MNZ/PLGA/SF nanofibers for periodontitis
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  74. One-pot fabrication of open-spherical shapes based on the decoration of copper sulfide/poly-O-amino benzenethiol on copper oxide as a promising photocathode for hydrogen generation from the natural source of Red Sea water
  75. A penta-hybrid approach for modeling the nanofluid flow in a spatially dependent magnetic field
  76. Advancing sustainable agriculture: Metal-doped urea–hydroxyapatite hybrid nanofertilizer for agro-industry
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  78. Plant-mediated synthesis, characterization, and evaluation of a copper oxide/silicon dioxide nanocomposite by an antimicrobial study
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  80. Investigating silver and alumina nanoparticles’ impact on fluid behavior over porous stretching surface
  81. Potential pharmaceutical applications and molecular docking study for green fabricated ZnO nanoparticles mediated Raphanus sativus: In vitro and in vivo study
  82. Effect of temperature and nanoparticle size on the interfacial layer thickness of TiO2–water nanofluids using molecular dynamics
  83. Characteristics of induced magnetic field on the time-dependent MHD nanofluid flow through parallel plates
  84. Flexural and vibration behaviours of novel covered CFRP composite joints with an MWCNT-modified adhesive
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  86. Analysis of variable fluid properties for three-dimensional flow of ternary hybrid nanofluid on a stretching sheet with MHD effects
  87. Biodegradability of corn starch films containing nanocellulose fiber and thymol
  88. Toxicity assessment of copper oxide nanoparticles: In vivo study
  89. Some measures to enhance the energy output performances of triboelectric nanogenerators
  90. Reinforcement of graphene nanoplatelets on water uptake and thermomechanical behaviour of epoxy adhesive subjected to water ageing conditions
  91. Optimization of preparation parameters and testing verification of carbon nanotube suspensions used in concrete
  92. Max-phase Ti3SiC2 and diverse nanoparticle reinforcements for enhancement of the mechanical, dynamic, and microstructural properties of AA5083 aluminum alloy via FSP
  93. Advancing drug delivery: Neural network perspectives on nanoparticle-mediated treatments for cancerous tissues
  94. PEG-PLGA core–shell nanoparticles for the controlled delivery of picoplatin–hydroxypropyl β-cyclodextrin inclusion complex in triple-negative breast cancer: In vitro and in vivo study
  95. Conduction transportation from graphene to an insulative polymer medium: A novel approach for the conductivity of nanocomposites
  96. Review Articles
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  98. Overview of amorphous carbon memristor device, modeling, and applications for neuromorphic computing
  99. Advances in the synthesis of gold nanoclusters (AuNCs) of proteins extracted from nature
  100. A review of ternary polymer nanocomposites containing clay and calcium carbonate and their biomedical applications
  101. Recent advancements in polyoxometalate-functionalized fiber materials: A review
  102. Special contribution of atomic force microscopy in cell death research
  103. A comprehensive review of oral chitosan drug delivery systems: Applications for oral insulin delivery
  104. Cellular senescence and nanoparticle-based therapies: Current developments and perspectives
  105. Cyclodextrins-block copolymer drug delivery systems: From design and development to preclinical studies
  106. Micelle-based nanoparticles with stimuli-responsive properties for drug delivery
  107. Critical assessment of the thermal stability and degradation of chemically functionalized nanocellulose-based polymer nanocomposites
  108. Research progress in preparation technology of micro and nano titanium alloy powder
  109. Nanoformulations for lysozyme-based additives in animal feed: An alternative to fight antibiotic resistance spread
  110. Incorporation of organic photochromic molecules in mesoporous silica materials: Synthesis and applications
  111. A review on modeling of graphene and associated nanostructures reinforced concrete
  112. A review on strengthening mechanisms of carbon quantum dots-reinforced Cu-matrix nanocomposites
  113. Review on nanocellulose composites and CNFs assembled microfiber toward automotive applications
  114. Nanomaterial coating for layered lithium rich transition metal oxide cathode for lithium-ion battery
  115. Application of AgNPs in biomedicine: An overview and current trends
  116. Nanobiotechnology and microbial influence on cold adaptation in plants
  117. Hepatotoxicity of nanomaterials: From mechanism to therapeutic strategy
  118. Applications of micro-nanobubble and its influence on concrete properties: An in-depth review
  119. A comprehensive systematic literature review of ML in nanotechnology for sustainable development
  120. Exploiting the nanotechnological approaches for traditional Chinese medicine in childhood rhinitis: A review of future perspectives
  121. Twisto-photonics in two-dimensional materials: A comprehensive review
  122. Current advances of anticancer drugs based on solubilization technology
  123. Recent process of using nanoparticles in the T cell-based immunometabolic therapy
  124. Future prospects of gold nanoclusters in hydrogen storage systems and sustainable environmental treatment applications
  125. Preparation, types, and applications of one- and two-dimensional nanochannels and their transport properties for water and ions
  126. Microstructural, mechanical, and corrosion characteristics of Mg–Gd–x systems: A review of recent advancements
  127. Functionalized nanostructures and targeted delivery systems with a focus on plant-derived natural agents for COVID-19 therapy: A review and outlook
  128. Mapping evolution and trends of cell membrane-coated nanoparticles: A bibliometric analysis and scoping review
  129. Nanoparticles and their application in the diagnosis of hepatocellular carcinoma
  130. In situ growth of carbon nanotubes on fly ash substrates
  131. Structural performance of boards through nanoparticle reinforcement: An advance review
  132. Reinforcing mechanisms review of the graphene oxide on cement composites
  133. Seed regeneration aided by nanomaterials in a climate change scenario: A comprehensive review
  134. Surface-engineered quantum dot nanocomposites for neurodegenerative disorder remediation and avenue for neuroimaging
  135. Graphitic carbon nitride hybrid thin films for energy conversion: A mini-review on defect activation with different materials
  136. Nanoparticles and the treatment of hepatocellular carcinoma
  137. Special Issue on Advanced Nanomaterials and Composites for Energy Conversion and Storage - Part II
  138. Highly safe lithium vanadium oxide anode for fast-charging dendrite-free lithium-ion batteries
  139. Recent progress in nanomaterials of battery energy storage: A patent landscape analysis, technology updates, and future prospects
  140. Special Issue on Advanced Nanomaterials for Carbon Capture, Environment and Utilization for Energy Sustainability - Part II
  141. Calcium-, magnesium-, and yttrium-doped lithium nickel phosphate nanomaterials as high-performance catalysts for electrochemical water oxidation reaction
  142. Low alkaline vegetation concrete with silica fume and nano-fly ash composites to improve the planting properties and soil ecology
  143. Mesoporous silica-grafted deep eutectic solvent-based mixed matrix membranes for wastewater treatment: Synthesis and emerging pollutant removal performance
  144. Electrochemically prepared ultrathin two-dimensional graphitic nanosheets as cathodes for advanced Zn-based energy storage devices
  145. Enhanced catalytic degradation of amoxicillin by phyto-mediated synthesised ZnO NPs and ZnO-rGO hybrid nanocomposite: Assessment of antioxidant activity, adsorption, and thermodynamic analysis
  146. Incorporating GO in PI matrix to advance nanocomposite coating: An enhancing strategy to prevent corrosion
  147. Synthesis, characterization, thermal stability, and application of microporous hyper cross-linked polyphosphazenes with naphthylamine group for CO2 uptake
  148. Engineering in ceramic albite morphology by the addition of additives: Carbon nanotubes and graphene oxide for energy applications
  149. Nanoscale synergy: Optimizing energy storage with SnO2 quantum dots on ZnO hexagonal prisms for advanced supercapacitors
  150. Aging assessment of silicone rubber materials under corona discharge accompanied by humidity and UV radiation
  151. Tuning structural and electrical properties of Co-precipitated and Cu-incorporated nickel ferrite for energy applications
  152. Sodium alginate-supported AgSr nanoparticles for catalytic degradation of malachite green and methyl orange in aqueous medium
  153. An environmentally greener and reusability approach for bioenergy production using Mallotus philippensis (Kamala) seed oil feedstock via phytonanotechnology
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  155. Mechanism exploration of ion-implanted epoxy on surface trap distribution: An approach to augment the vacuum flashover voltages
  156. Nanoscale engineering of semiconductor photocatalysts boosting charge separation for solar-driven H2 production: Recent advances and future perspective
  157. Excellent catalytic performance over reduced graphene-boosted novel nanoparticles for oxidative desulfurization of fuel oil
  158. Special Issue on Advances in Nanotechnology for Agriculture
  159. Deciphering the synergistic potential of mycogenic zinc oxide nanoparticles and bio-slurry formulation on phenology and physiology of Vigna radiata
  160. Nanomaterials: Cross-disciplinary applications in ornamental plants
  161. Special Issue on Catechol Based Nano and Microstructures
  162. Polydopamine films: Versatile but interface-dependent coatings
  163. In vitro anticancer activity of melanin-like nanoparticles for multimodal therapy of glioblastoma
  164. Poly-3,4-dihydroxybenzylidenhydrazine, a different analogue of polydopamine
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  166. Advancing resource sustainability with green photothermal materials: Insights from organic waste-derived and bioderived sources
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  169. Intelligent explainable optical sensing on Internet of nanorobots for disease detection
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  171. Tracking success of interaction of green-synthesized Carbopol nanoemulgel (neomycin-decorated Ag/ZnO nanocomposite) with wound-based MDR bacteria
  172. Green synthesis of copper oxide nanoparticles using genus Inula and evaluation of biological therapeutics and environmental applications
  173. Biogenic fabrication and multifunctional therapeutic applications of silver nanoparticles synthesized from rose petal extract
  174. Metal oxides on the frontlines: Antimicrobial activity in plant-derived biometallic nanoparticles
  175. Controlling pore size during the synthesis of hydroxyapatite nanoparticles using CTAB by the sol–gel hydrothermal method and their biological activities
  176. Special Issue on State-of-Art Advanced Nanotechnology for Healthcare
  177. Applications of nanomedicine-integrated phototherapeutic agents in cancer theranostics: A comprehensive review of the current state of research
  178. Smart bionanomaterials for treatment and diagnosis of inflammatory bowel disease
  179. Beyond conventional therapy: Synthesis of multifunctional nanoparticles for rheumatoid arthritis therapy
https://doi.org/10.1515/ntrev-2024-0042
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Articles in the same Issue

  1. Research Articles
  2. Tension buckling and postbuckling of nanocomposite laminated plates with in-plane negative Poisson’s ratio
  3. Polyvinylpyrrolidone-stabilised gold nanoparticle coatings inhibit blood protein adsorption
  4. Energy and mass transmission through hybrid nanofluid flow passing over a spinning sphere with magnetic effect and heat source/sink
  5. Surface treatment with nano-silica and magnesium potassium phosphate cement co-action for enhancing recycled aggregate concrete
  6. Numerical investigation of thermal radiation with entropy generation effects in hybrid nanofluid flow over a shrinking/stretching sheet
  7. Enhancing the performance of thermal energy storage by adding nano-particles with paraffin phase change materials
  8. Using nano-CaCO3 and ceramic tile waste to design low-carbon ultra high performance concrete
  9. Numerical analysis of thermophoretic particle deposition in a magneto-Marangoni convective dusty tangent hyperbolic nanofluid flow – Thermal and magnetic features
  10. Dual numerical solutions of Casson SA–hybrid nanofluid toward a stagnation point flow over stretching/shrinking cylinder
  11. Single flake homo p–n diode of MoTe2 enabled by oxygen plasma doping
  12. Electrostatic self-assembly effect of Fe3O4 nanoparticles on performance of carbon nanotubes in cement-based materials
  13. Multi-scale alignment to buried atom-scale devices using Kelvin probe force microscopy
  14. Antibacterial, mechanical, and dielectric properties of hydroxyapatite cordierite/zirconia porous nanocomposites for use in bone tissue engineering applications
  15. Time-dependent Darcy–Forchheimer flow of Casson hybrid nanofluid comprising the CNTs through a Riga plate with nonlinear thermal radiation and viscous dissipation
  16. Durability prediction of geopolymer mortar reinforced with nanoparticles and PVA fiber using particle swarm optimized BP neural network
  17. Utilization of zein nano-based system for promoting antibiofilm and anti-virulence activities of curcumin against Pseudomonas aeruginosa
  18. Antibacterial effect of novel dental resin composites containing rod-like zinc oxide
  19. An extended model to assess Jeffery–Hamel blood flow through arteries with iron-oxide (Fe2O3) nanoparticles and melting effects: Entropy optimization analysis
  20. Comparative study of copper nanoparticles over radially stretching sheet with water and silicone oil
  21. Cementitious composites modified by nanocarbon fillers with cooperation effect possessing excellent self-sensing properties
  22. Confinement size effect on dielectric properties, antimicrobial activity, and recycling of TiO2 quantum dots via photodegradation processes of Congo red dye and real industrial textile wastewater
  23. Biogenic silver nanoparticles of Moringa oleifera leaf extract: Characterization and photocatalytic application
  24. Novel integrated structure and function of Mg–Gd neutron shielding materials
  25. Impact of multiple slips on thermally radiative peristaltic transport of Sisko nanofluid with double diffusion convection, viscous dissipation, and induced magnetic field
  26. Magnetized water-based hybrid nanofluid flow over an exponentially stretching sheet with thermal convective and mass flux conditions: HAM solution
  27. A numerical investigation of the two-dimensional magnetohydrodynamic water-based hybrid nanofluid flow composed of Fe3O4 and Au nanoparticles over a heated surface
  28. Development and modeling of an ultra-robust TPU-MWCNT foam with high flexibility and compressibility
  29. Effects of nanofillers on the physical, mechanical, and tribological behavior of carbon/kenaf fiber–reinforced phenolic composites
  30. Polymer nanocomposite for protecting photovoltaic cells from solar ultraviolet in space
  31. Study on the mechanical properties and microstructure of recycled concrete reinforced with basalt fibers and nano-silica in early low-temperature environments
  32. Synergistic effect of carbon nanotubes and polyvinyl alcohol on the mechanical performance and microstructure of cement mortar
  33. CFD analysis of paraffin-based hybrid (Co–Au) and trihybrid (Co–Au–ZrO2) nanofluid flow through a porous medium
  34. Forced convective tangent hyperbolic nanofluid flow subject to heat source/sink and Lorentz force over a permeable wedge: Numerical exploration
  35. Physiochemical and electrical activities of nano copper oxides synthesised via hydrothermal method utilising natural reduction agents for solar cell application
  36. A homotopic analysis of the blood-based bioconvection Carreau–Yasuda hybrid nanofluid flow over a stretching sheet with convective conditions
  37. In situ synthesis of reduced graphene oxide/SnIn4S8 nanocomposites with enhanced photocatalytic performance for pollutant degradation
  38. A coarse-grained Poisson–Nernst–Planck model for polyelectrolyte-modified nanofluidic diodes
  39. A numerical investigation of the magnetized water-based hybrid nanofluid flow over an extending sheet with a convective condition: Active and passive controls of nanoparticles
  40. The LyP-1 cyclic peptide modified mesoporous polydopamine nanospheres for targeted delivery of triptolide regulate the macrophage repolarization in atherosclerosis
  41. Synergistic effect of hydroxyapatite-magnetite nanocomposites in magnetic hyperthermia for bone cancer treatment
  42. The significance of quadratic thermal radiative scrutinization of a nanofluid flow across a microchannel with thermophoretic particle deposition effects
  43. Ferromagnetic effect on Casson nanofluid flow and transport phenomena across a bi-directional Riga sensor device: Darcy–Forchheimer model
  44. Performance of carbon nanomaterials incorporated with concrete exposed to high temperature
  45. Multicriteria-based optimization of roller compacted concrete pavement containing crumb rubber and nano-silica
  46. Revisiting hydrotalcite synthesis: Efficient combined mechanochemical/coprecipitation synthesis to design advanced tunable basic catalysts
  47. Exploration of irreversibility process and thermal energy of a tetra hybrid radiative binary nanofluid focusing on solar implementations
  48. Effect of graphene oxide on the properties of ternary limestone clay cement paste
  49. Improved mechanical properties of graphene-modified basalt fibre–epoxy composites
  50. Sodium titanate nanostructured modified by green synthesis of iron oxide for highly efficient photodegradation of dye contaminants
  51. Green synthesis of Vitis vinifera extract-appended magnesium oxide NPs for biomedical applications
  52. Differential study on the thermal–physical properties of metal and its oxide nanoparticle-formed nanofluids: Molecular dynamics simulation investigation of argon-based nanofluids
  53. Heat convection and irreversibility of magneto-micropolar hybrid nanofluids within a porous hexagonal-shaped enclosure having heated obstacle
  54. Numerical simulation and optimization of biological nanocomposite system for enhanced oil recovery
  55. Laser ablation and chemical vapor deposition to prepare a nanostructured PPy layer on the Ti surface
  56. Cilostazol niosomes-loaded transdermal gels: An in vitro and in vivo anti-aggregant and skin permeation activity investigations towards preparing an efficient nanoscale formulation
  57. Linear and nonlinear optical studies on successfully mixed vanadium oxide and zinc oxide nanoparticles synthesized by sol–gel technique
  58. Analytical investigation of convective phenomena with nonlinearity characteristics in nanostratified liquid film above an inclined extended sheet
  59. Optimization method for low-velocity impact identification in nanocomposite using genetic algorithm
  60. Analyzing the 3D-MHD flow of a sodium alginate-based nanofluid flow containing alumina nanoparticles over a bi-directional extending sheet using variable porous medium and slip conditions
  61. A comprehensive study of laser irradiated hydrothermally synthesized 2D layered heterostructure V2O5(1−x)MoS2(x) (X = 1–5%) nanocomposites for photocatalytic application
  62. Computational analysis of water-based silver, copper, and alumina hybrid nanoparticles over a stretchable sheet embedded in a porous medium with thermophoretic particle deposition effects
  63. A deep dive into AI integration and advanced nanobiosensor technologies for enhanced bacterial infection monitoring
  64. Effects of normal strain on pyramidal I and II 〈c + a〉 screw dislocation mobility and structure in single-crystal magnesium
  65. Computational study of cross-flow in entropy-optimized nanofluids
  66. Significance of nanoparticle aggregation for thermal transport over magnetized sensor surface
  67. A green and facile synthesis route of nanosize cupric oxide at room temperature
  68. Effect of annealing time on bending performance and microstructure of C19400 alloy strip
  69. Chitosan-based Mupirocin and Alkanna tinctoria extract nanoparticles for the management of burn wound: In vitro and in vivo characterization
  70. Electrospinning of MNZ/PLGA/SF nanofibers for periodontitis
  71. Photocatalytic degradation of methylene blue by Nd-doped titanium dioxide thin films
  72. Shell-core-structured electrospinning film with sequential anti-inflammatory and pro-neurogenic effects for peripheral nerve repairment
  73. Flow and heat transfer insights into a chemically reactive micropolar Williamson ternary hybrid nanofluid with cross-diffusion theory
  74. One-pot fabrication of open-spherical shapes based on the decoration of copper sulfide/poly-O-amino benzenethiol on copper oxide as a promising photocathode for hydrogen generation from the natural source of Red Sea water
  75. A penta-hybrid approach for modeling the nanofluid flow in a spatially dependent magnetic field
  76. Advancing sustainable agriculture: Metal-doped urea–hydroxyapatite hybrid nanofertilizer for agro-industry
  77. Utilizing Ziziphus spina-christi for eco-friendly synthesis of silver nanoparticles: Antimicrobial activity and promising application in wound healing
  78. Plant-mediated synthesis, characterization, and evaluation of a copper oxide/silicon dioxide nanocomposite by an antimicrobial study
  79. Effects of PVA fibers and nano-SiO2 on rheological properties of geopolymer mortar
  80. Investigating silver and alumina nanoparticles’ impact on fluid behavior over porous stretching surface
  81. Potential pharmaceutical applications and molecular docking study for green fabricated ZnO nanoparticles mediated Raphanus sativus: In vitro and in vivo study
  82. Effect of temperature and nanoparticle size on the interfacial layer thickness of TiO2–water nanofluids using molecular dynamics
  83. Characteristics of induced magnetic field on the time-dependent MHD nanofluid flow through parallel plates
  84. Flexural and vibration behaviours of novel covered CFRP composite joints with an MWCNT-modified adhesive
  85. Experimental research on mechanically and thermally activation of nano-kaolin to improve the properties of ultra-high-performance fiber-reinforced concrete
  86. Analysis of variable fluid properties for three-dimensional flow of ternary hybrid nanofluid on a stretching sheet with MHD effects
  87. Biodegradability of corn starch films containing nanocellulose fiber and thymol
  88. Toxicity assessment of copper oxide nanoparticles: In vivo study
  89. Some measures to enhance the energy output performances of triboelectric nanogenerators
  90. Reinforcement of graphene nanoplatelets on water uptake and thermomechanical behaviour of epoxy adhesive subjected to water ageing conditions
  91. Optimization of preparation parameters and testing verification of carbon nanotube suspensions used in concrete
  92. Max-phase Ti3SiC2 and diverse nanoparticle reinforcements for enhancement of the mechanical, dynamic, and microstructural properties of AA5083 aluminum alloy via FSP
  93. Advancing drug delivery: Neural network perspectives on nanoparticle-mediated treatments for cancerous tissues
  94. PEG-PLGA core–shell nanoparticles for the controlled delivery of picoplatin–hydroxypropyl β-cyclodextrin inclusion complex in triple-negative breast cancer: In vitro and in vivo study
  95. Conduction transportation from graphene to an insulative polymer medium: A novel approach for the conductivity of nanocomposites
  96. Review Articles
  97. Developments of terahertz metasurface biosensors: A literature review
  98. Overview of amorphous carbon memristor device, modeling, and applications for neuromorphic computing
  99. Advances in the synthesis of gold nanoclusters (AuNCs) of proteins extracted from nature
  100. A review of ternary polymer nanocomposites containing clay and calcium carbonate and their biomedical applications
  101. Recent advancements in polyoxometalate-functionalized fiber materials: A review
  102. Special contribution of atomic force microscopy in cell death research
  103. A comprehensive review of oral chitosan drug delivery systems: Applications for oral insulin delivery
  104. Cellular senescence and nanoparticle-based therapies: Current developments and perspectives
  105. Cyclodextrins-block copolymer drug delivery systems: From design and development to preclinical studies
  106. Micelle-based nanoparticles with stimuli-responsive properties for drug delivery
  107. Critical assessment of the thermal stability and degradation of chemically functionalized nanocellulose-based polymer nanocomposites
  108. Research progress in preparation technology of micro and nano titanium alloy powder
  109. Nanoformulations for lysozyme-based additives in animal feed: An alternative to fight antibiotic resistance spread
  110. Incorporation of organic photochromic molecules in mesoporous silica materials: Synthesis and applications
  111. A review on modeling of graphene and associated nanostructures reinforced concrete
  112. A review on strengthening mechanisms of carbon quantum dots-reinforced Cu-matrix nanocomposites
  113. Review on nanocellulose composites and CNFs assembled microfiber toward automotive applications
  114. Nanomaterial coating for layered lithium rich transition metal oxide cathode for lithium-ion battery
  115. Application of AgNPs in biomedicine: An overview and current trends
  116. Nanobiotechnology and microbial influence on cold adaptation in plants
  117. Hepatotoxicity of nanomaterials: From mechanism to therapeutic strategy
  118. Applications of micro-nanobubble and its influence on concrete properties: An in-depth review
  119. A comprehensive systematic literature review of ML in nanotechnology for sustainable development
  120. Exploiting the nanotechnological approaches for traditional Chinese medicine in childhood rhinitis: A review of future perspectives
  121. Twisto-photonics in two-dimensional materials: A comprehensive review
  122. Current advances of anticancer drugs based on solubilization technology
  123. Recent process of using nanoparticles in the T cell-based immunometabolic therapy
  124. Future prospects of gold nanoclusters in hydrogen storage systems and sustainable environmental treatment applications
  125. Preparation, types, and applications of one- and two-dimensional nanochannels and their transport properties for water and ions
  126. Microstructural, mechanical, and corrosion characteristics of Mg–Gd–x systems: A review of recent advancements
  127. Functionalized nanostructures and targeted delivery systems with a focus on plant-derived natural agents for COVID-19 therapy: A review and outlook
  128. Mapping evolution and trends of cell membrane-coated nanoparticles: A bibliometric analysis and scoping review
  129. Nanoparticles and their application in the diagnosis of hepatocellular carcinoma
  130. In situ growth of carbon nanotubes on fly ash substrates
  131. Structural performance of boards through nanoparticle reinforcement: An advance review
  132. Reinforcing mechanisms review of the graphene oxide on cement composites
  133. Seed regeneration aided by nanomaterials in a climate change scenario: A comprehensive review
  134. Surface-engineered quantum dot nanocomposites for neurodegenerative disorder remediation and avenue for neuroimaging
  135. Graphitic carbon nitride hybrid thin films for energy conversion: A mini-review on defect activation with different materials
  136. Nanoparticles and the treatment of hepatocellular carcinoma
  137. Special Issue on Advanced Nanomaterials and Composites for Energy Conversion and Storage - Part II
  138. Highly safe lithium vanadium oxide anode for fast-charging dendrite-free lithium-ion batteries
  139. Recent progress in nanomaterials of battery energy storage: A patent landscape analysis, technology updates, and future prospects
  140. Special Issue on Advanced Nanomaterials for Carbon Capture, Environment and Utilization for Energy Sustainability - Part II
  141. Calcium-, magnesium-, and yttrium-doped lithium nickel phosphate nanomaterials as high-performance catalysts for electrochemical water oxidation reaction
  142. Low alkaline vegetation concrete with silica fume and nano-fly ash composites to improve the planting properties and soil ecology
  143. Mesoporous silica-grafted deep eutectic solvent-based mixed matrix membranes for wastewater treatment: Synthesis and emerging pollutant removal performance
  144. Electrochemically prepared ultrathin two-dimensional graphitic nanosheets as cathodes for advanced Zn-based energy storage devices
  145. Enhanced catalytic degradation of amoxicillin by phyto-mediated synthesised ZnO NPs and ZnO-rGO hybrid nanocomposite: Assessment of antioxidant activity, adsorption, and thermodynamic analysis
  146. Incorporating GO in PI matrix to advance nanocomposite coating: An enhancing strategy to prevent corrosion
  147. Synthesis, characterization, thermal stability, and application of microporous hyper cross-linked polyphosphazenes with naphthylamine group for CO2 uptake
  148. Engineering in ceramic albite morphology by the addition of additives: Carbon nanotubes and graphene oxide for energy applications
  149. Nanoscale synergy: Optimizing energy storage with SnO2 quantum dots on ZnO hexagonal prisms for advanced supercapacitors
  150. Aging assessment of silicone rubber materials under corona discharge accompanied by humidity and UV radiation
  151. Tuning structural and electrical properties of Co-precipitated and Cu-incorporated nickel ferrite for energy applications
  152. Sodium alginate-supported AgSr nanoparticles for catalytic degradation of malachite green and methyl orange in aqueous medium
  153. An environmentally greener and reusability approach for bioenergy production using Mallotus philippensis (Kamala) seed oil feedstock via phytonanotechnology
  154. Micro-/nano-alumina trihydrate and -magnesium hydroxide fillers in RTV-SR composites under electrical and environmental stresses
  155. Mechanism exploration of ion-implanted epoxy on surface trap distribution: An approach to augment the vacuum flashover voltages
  156. Nanoscale engineering of semiconductor photocatalysts boosting charge separation for solar-driven H2 production: Recent advances and future perspective
  157. Excellent catalytic performance over reduced graphene-boosted novel nanoparticles for oxidative desulfurization of fuel oil
  158. Special Issue on Advances in Nanotechnology for Agriculture
  159. Deciphering the synergistic potential of mycogenic zinc oxide nanoparticles and bio-slurry formulation on phenology and physiology of Vigna radiata
  160. Nanomaterials: Cross-disciplinary applications in ornamental plants
  161. Special Issue on Catechol Based Nano and Microstructures
  162. Polydopamine films: Versatile but interface-dependent coatings
  163. In vitro anticancer activity of melanin-like nanoparticles for multimodal therapy of glioblastoma
  164. Poly-3,4-dihydroxybenzylidenhydrazine, a different analogue of polydopamine
  165. Chirality and self-assembly of structures derived from optically active 1,2-diaminocyclohexane and catecholamines
  166. Advancing resource sustainability with green photothermal materials: Insights from organic waste-derived and bioderived sources
  167. Bioinspired neuromelanin-like Pt(iv) polymeric nanoparticles for cancer treatment
  168. Special Issue on Implementing Nanotechnology for Smart Healthcare System
  169. Intelligent explainable optical sensing on Internet of nanorobots for disease detection
  170. Special Issue on Green Mono, Bi and Tri Metallic Nanoparticles for Biological and Environmental Applications
  171. Tracking success of interaction of green-synthesized Carbopol nanoemulgel (neomycin-decorated Ag/ZnO nanocomposite) with wound-based MDR bacteria
  172. Green synthesis of copper oxide nanoparticles using genus Inula and evaluation of biological therapeutics and environmental applications
  173. Biogenic fabrication and multifunctional therapeutic applications of silver nanoparticles synthesized from rose petal extract
  174. Metal oxides on the frontlines: Antimicrobial activity in plant-derived biometallic nanoparticles
  175. Controlling pore size during the synthesis of hydroxyapatite nanoparticles using CTAB by the sol–gel hydrothermal method and their biological activities
  176. Special Issue on State-of-Art Advanced Nanotechnology for Healthcare
  177. Applications of nanomedicine-integrated phototherapeutic agents in cancer theranostics: A comprehensive review of the current state of research
  178. Smart bionanomaterials for treatment and diagnosis of inflammatory bowel disease
  179. Beyond conventional therapy: Synthesis of multifunctional nanoparticles for rheumatoid arthritis therapy
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