Home A facile method to synthesize nZVI-doped polypyrrole-based carbon nanotube for Ag(i) removal
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A facile method to synthesize nZVI-doped polypyrrole-based carbon nanotube for Ag(i) removal

  • Wen-Juan Zhang EMAIL logo , Ye-Zhi Ding , Ya-Xian Wang , You-Liang Wang EMAIL logo , Yu-Long Fei and Meng-Yu Ran
Published/Copyright: October 25, 2023
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Nanotechnology Reviews
From the journal Nanotechnology Reviews Volume 12 Issue 1

Abstract

The pollution of silver ion (Ag(i)) has become a serious environmental threat and hazard to ecosystem and human health. Thus, the nanoscale zero valent iron (nZVI)-doped polypyrrole-based carbon nanotube (nZVI/CNT) composites were synthesized by a facile method to remove Ag(i) from wastewater due to the toxicity and scarcity nature of Ag(i). In this process, Fe3+ initiated the self-assembly of polypyrrole tubes in the presence of methyl orange, while it also served as an iron source generated nZVI/CNTs by carbothermal reduction method. The nZVI/CNT composites exhibited a homogeneous tubular structure, and the nZVI formed were uniformly dispersed in the nZVI/CNT composites. The nZVI/CNT composites were used as an adsorbent for the removal of Ag(i) and showed a higher adsorption capacity compared to nZVI and CNTs, with a maximum adsorption capacity of 522.41 mg g−1. Ag(i) was adsorbed on nZVI/CNT composites by ion exchange and chelation, where Ag(i) was reduced to non-toxic Ag due to the redox reaction among pyrrolic-N, nZVI, and Ag(i). The adsorption process of Ag(i) on nZVI/CNT composites was dominated by monolayer adsorption. According to our results, nZVI/CNT composites can be used as economical treatment for wastewater containing Ag(i).

Keywords: nZVI; CNTs; Ag(i); adsorption; polypyrrole

1 Introduction

As one of the valuable metals, silver shows extensive applications in the fields of catalysis, electronics, photography, and antibiotics because of its brilliant photosensitivity, electrical and thermal conductivity, ductility, and antimicrobial properties [1]. The extensive use of silver has led to an increase in its release into the environment, particularly in water sources. Silver ions (Ag(i)) are second only to mercury among metal ions in terms of toxicity to aquatic organisms and cause serious pollution to the environment [2]. Through the food chain, Ag(i) can tend to bioaccumulate in the human body, causing several health problems [3] for humans. On the other hand, silver is a scarce and non-renewable resource [4]. Therefore, the removal and recovery of silver from water is essential from an economic and environmental protection point of view.

In recent decades, many approaches have been employed to reduce/remove Ag(i) from aqueous environment, including ion exchange, chemical precipitation, membrane filtration, adsorption method, etc. [5,6]. In these approaches, adsorption method has attracted great attention due to its simple operating procedures, low cost, and friendly environment [7].

Nanoscale zero valent iron (nZVI) particles are ideal candidates to remove toxic Ag(i). Despite micron- and millimeter-sized ZVIs have been proven very useful for removing contaminants [8], the smaller size of nZVI has gained more attention because it shows higher reaction rates and better removal rate of heavy metal ions [9]. nZVI has been shown to enjoy considerably effective abilities in the treatment of Ag(i) because of its high specific surface area and noteworthy characteristics for the reduction of contaminants. Despite the efficacy of ZVI as adsorption materials for the removal of Ag(i), nZVI particles are more susceptible to such problems as aggregation [10], passivation [11], poor transportability [12], and instability [13]. To overcome these problems, various methods have been reported to obtain more stable and efficient nZVI, such as employing a cheap short-abundant surfactant [14], immobilization of nZVI onto support materials [15], and impregnation of a second non-toxic inert metal (which can enhance the production of free radicals) [16]. However, these techniques may additionally inhibit the response of nZVI with pollutants or entrust nZVI with undesirable properties for environmental remediation. For instance, the inhibitory of surfactants are probably connected with blockage of reactive sites, scavenging of reactive free radicals, reduction in diffusion channels, partitioning of contaminants to the surfactants, and inhibition of electron transfer from the nZVI core to contaminants [17]. The usage of bimetallic particles might result in faster corrosion, which brings about shorter lifetime, and might introduce extra environmental concerns associated with the second metal [18]. nZVI is immobilized in some porous materials such as silica [19], resin [20], activated carbon [21], and biochar [22] which can provide sufficient loading sites for the stable dispersion of nZVI, and prevent it from oxidizing and agglomerating [14].

Carbon nanotubes (CNTs) have a lot of oxygen-containing functional groups like carboxyl and hydroxyl groups, and have gotten increasing attention in the fields of wastewater treatment because of their unusual hollow tube structure and exceptional physicochemical qualities [23]. Many studies have been widely reported on nZVI/CNTs due to excellent magnetic properties, high adsorption capacities, and large specific surface areas. It was reported that Xu et al. [24] synthesized nZVI-multiwalled carbon nanotube (MWCNT) nanocomposites by depositing nZVI particles onto MWCNTs via in situ reduction of ferrous sulfate, then they used the nanocomposites to remove Cr(vi) from wastewater. It was shown that nZVI-MWCNT nanocomposites were about 36% more efficient in the removal of Cr(vi) than bare nZVI or nZVI-activated carbon composites, which indicated that nZVI/CNT could significantly improve the reduction of Cr(vi) to Cr(iii).

Other researchers have prepared nZVI/CNTs using comparable methods, and the CNTs played the role of substrate in composites, then nZVI was immobilized on CNTs by NaBH4 reduction method. The composites were employed as nano-adsorbents for the removal of hexavalent, Se, Co [25], Pb [26], Te [27], etc. The composites exhibited the highest affinity for metal ions and were effective in removing heavy metal ions from aqueous solution. As a result, introducing CNTs into the nZVI system can not only solve the agglomeration of nZVI but also combine the superior reduction ability of nZVI with the high adsorption capacity of CNTs [25].

However, the full-scale application of CNT-supported nZVI in water treatment generally requires overcoming some technical difficulties, such as the low adsorption capacity for heavy metal ions, tedious synthesis processes, and lack of adsorption mechanism of nZVI in composites. Hence, it is vital to exploit accessible technologies to make nZVI/CNT composites with outstanding adsorption property. The introduction of nitrogen-containing functional groups is an effective way. Nitrogen-containing functional groups can effectively bind heavy metal ions, which were conducive to improving the adsorption capacity of CNTs. Polypyrrole (PPy), a conducting polymer containing pyrrolic-N and imino group [28,29], was a good precursor to prepare nZVI/CNTs. And most of the processes for preparing nZVI/CNT composites were time consuming and expensive. Thus, the development of accessible technology to create magnetic CNT composites with good hydrophilicity and high adsorption capacity was still a significant challenge.

In this study, CNT composites doped with nZVI were synthesized by in situ carbon thermal reduction method. First, the polymerization of pyrrole (Py) monomer into PPy nanotubes was initiated by Fe3+ in the presence of methyl orange (MO). Second, Py was pyrolyzed to CNTs and provided a matrix with a large specific surface area and abundant active sites, which benefits the uptake and enrichment of Ag(i). Meanwhile, Fe3+ was used as an iron source to synthesize nZVI/CNT composites by a one-step carbothermal reductive method. The morphologies and properties of nZVI/CNT composites were characterized and analyzed by Transmission Electron Microscope (TEM), Diffraction of X-Ray (XRD), Fourier Transform Infrared Spectrometer (FT-IR), and Thermal Gravimetric Analyzer (TGA). The adsorption capacity of nZVI/CNT composites for Ag(i) in aqueous solution was investigated, and the impact of various adsorption conditions (contact time and initial concentration of Ag(i)) on adsorption capacity was analyzed. Moreover, kinetic models and isothermal models of Ag(i) onto nZVI/CNT composites were studied.

2 Materials and methods

2.1 Materials

Py (AR, Aladdin Chemistry Co. Ltd) was distilled under reduced pressure, and MO was provided by Tianjin Tianxin Fine Chemical Co. Ltd, FeCl3·6H2O and AgNO3 were purchased from Sinopharm Group Chemical Reagent Co., Ltd. All trials were conducted with deionized water.

2.2 Synthesis of nZVI/CNT composites

We developed a novel method to synthesize nZVI/CNT composites through a one-pot route (Figure 1). In a typical synthesis process, 0.98 g MO and certain amount of FeCl3·6H2O were dissolved in 480 mL of deionized water, and the mixture was stirred slowly for 30 min at room temperature until completely dissolved. Then, after adding 0.7 mL of Py to the above mixture, the new mixture was allowed to react for 24 h at room temperature with continuous slow stirring. Finally, the collected product was dried at 120°C for 8 h. The product was carbonized for 5 h at 850°C with a heating rate of 3 °C/min in a tubular furnace under nitrogen atmosphere. In order to understand how FeCl3·6H2O affects the morphologies and properties of nZVI/CNT composites, we set the molar ratios of Py to Fe3+ at 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6, corresponding to the masses of FeCl3·6H2O as from 27.00, 13.50, 9.00, 6.75, 5.40, and 4.50 g. Therefore, the resulting composites were named as S6, S5, S4, S3, S2, and S1, respectively.

Figure 1 Schematic representation of synthesis procedure of nZVI/CNT composites.
Figure 1

Schematic representation of synthesis procedure of nZVI/CNT composites.

For comparison purposes, PPy-based CNTs were prepared by mixing MO and FeCl3·6H2O. Then, Py was progressively added to the mixture and it was slowly stirred for 24 h at room temperature. The obtained PPy nanotubes were washed thoroughly with deionized water and anhydrous ethanol to remove the excess Fe3+. Finally, PPy nanotubes were carbonized in a tubular furnace under nitrogen atmosphere, and the obtained product was named CNTs.

2.3 Characterization of nZVI/CNTs composites

The morphology of nZVI/CNT composites were examined using TEM, scanning electron microscope (SEM) image with energy dispersive spectroscope (EDS) spectra, and selected area electron diffraction (SAED). The crystalline structures of nZVI/CNT composites were determined by XRD. The surface functional groups of the nZVI/CNT composites were analyzed using FT-IR. The magnetic properties of nZVI/CNT composites were confirmed with vibrating sample magnetometer. The thermostability of the nZVI/CNT composites were evaluated by TGA.

2.4 Adsorption experiments

The stock solutions of Ag(i) (1,000 mg L−1) were prepared by dissolving an appropriate amount of AgNO3 in 1,000 mL of deionized water. Various concentrations of Ag(i) were freshly prepared by diluting the stock solution with ultrapure water. The standard calibration curve of Ag(i) was generated at 365 nm by measuring absorbance of different concentrations of Ag(i) standard solution with UV-Visible spectrophotometers.

A batch approach was carried out for the adsorption experiments. nZVI/CNT composites (10 mg) were added to 50 mL of Ag(i) solution and ultrasonicated for 30 min to obtain a dispersion. Then, the dispersion was agitated at 120 rpm, 25°C for 24 h using a constant-temperature oscillator. Effects of the initial concentration of Ag(i) and contact time on adsorption capacity were explored. The initial concentration of Ag(i) solution was varied from 20 to 200 mg L−1, and the reaction time was fixed from 0 to 24 h. The removal rate of Ag(i) (adsorption efficiency) and equilibrium adsorption capacity were determined using equations (1) and (2) as follows:

(1) R = ( C 0 − C e ) C 0 × 100 % ,

(2) Q e = ( C 0 − C e ) V m ,

where R is the removal rate of Ag(i) (mg g−1), Q e is the equilibrium adsorption capacity of Ag(i) (mg g−1), C e and C o are the equilibrium and initial concentrations (mg L−1) of Ag(i), respectively, V is the experimental solution volume (L), and m is the adsorbent mass (g).

The effect of reaction time on the adsorption capacity of Ag(i) with nZVI/CNT composites was investigated by adjusting the reaction time from 0 to 24 h while the initial concentration of Ag(i) was 180 mg L−1. The adsorption capacity was determined using equation (3) as follows:

(3) Q t = ( C 0 − C t ) V m ,

where Q t was the adsorption capacity (mg L−1) of Ag(i) at t and C t was the concentration (mg L−1) of Ag(i) at t.

3 Results and discussion

3.1 Morphology and structure of nZVI/CNT composites

The crystalline structure of the adsorbent was characterized by XRD as shown in Figure 2. A broad peak appeared in the range of 15–25° was shown in CNTs (Figure 2(a)) and various nZVI/CNT composites (Figure 2(b)–(g)), this peak was mainly for amorphous carbon due to carbonization of PPy [30,31]. However, a decrease in peak intensity was observed in various nZVI/CNT composites, which was mainly due to the formation of nZVI by carbothermal reduction. After loading nZVI, various nZVI/CNT composites (Figure 2(b)–(g)) show diffraction peaks at 44.8°, 65.02°, and 82.45°, indexed as (110), (200), and (211) reflections of nZVI, respectively (Figure 2(h)), and these peaks are consistent with standard profile JCPDS (No. 06-0696) and also reveal that the core of the nanocomposites is nZVI.

Figure 2 XRD pattern of CNTs (a), S1 (b), S2 (c), S3 (d), S4 (e), S5 (f), S6 (g), and nZVI (h).
Figure 2

XRD pattern of CNTs (a), S1 (b), S2 (c), S3 (d), S4 (e), S5 (f), S6 (g), and nZVI (h).

Figure 3 shows the TEM and the SAED images of CNTs and various nZVI/CNT composites. The TEM images (Figure 3(a)) of CNTs show uniform tubular structures with an average diameter of about 130 nm. In Figure 3(b)–(f), the diameters of various nZVI/CNT composites decrease with the increase in the concentration of Fe3+, because the increasing concentration of Fe3+ will partially solubilize the MO–FeCl3 micelle template resulting in the formation of CNTs having smaller diameters [32]. As shown in (Figure 3(b)–(f)), with the increase in the concentration of Fe3+, S1, S2, and S3 composites (Figure 3(b)–(d)) still keep intact the tube structures, but the tube structures of S4 and S5 were broken. The breaking of tube is caused by excessive Fe3+ content. The formation process of PPy nanotubes is a coating growth process, and the Fe3+ content directly affects the integrity and diameter of PPy nanotubes. The increase in Fe3+ content is conducive to the polymerization of pyrrole monomer and improves the structural integrity of the tube. However, Fe3+ content makes pyrrole monomer polymerize too fast when the molar ratios of Py to Fe3+ is lower than 0.4, which leads to smaller diameter of PPy nanotubes and even broken tube structure. And mass nanoparticles were dispersed homogeneously on CNTs, and the SAED pattern of S3 (Figure 3(g)) revealed diffraction rings of nZVI, which was consistent with the XRD pattern (Figure 2).

Figure 3 TEM images of CNTs (a), S1 (b), S2 (c), S3 (d), S4 (e), S5 (f), SAED and SEM images (g), distribution of S3 Fe (h), and distribution of S3 N (i).
Figure 3

TEM images of CNTs (a), S1 (b), S2 (c), S3 (d), S4 (e), S5 (f), SAED and SEM images (g), distribution of S3 Fe (h), and distribution of S3 N (i).

On the other hand, elemental mapping has been carried out to verify the doping of N and Fe in the CNT. The nitrogen content was about 3.9%, which was slightly higher than the other nitrogen-doped materials reported in the literature [33]. Furthermore, the mapping images (Figure 3(h)–(i)) showed that the nitrogen, and iron atoms are overlapped, confirming the uniform distribution of N and Fe in the S3 composite.

The FT-IR spectra of Fe (a), CNTs (b), and S3 (c) composites are shown in Figure 4. In the nZVI spectrum (Figure 4(a)), the weak absorption peak at 521 cm−1 corresponds to the stretching vibration of Fe–O [33]. In CNTs spectrum (b), 3,420 cm−1 arises from the stretching vibration of N–H. The peak of 1,584, 1,390 cm−1 correspond to the C═C symmetric stretching vibrations and C–N stretching vibration of the pyrrole ring. In-plane and out-of-plane C–H, as well as N–H bending vibrations generate the wide peaks at 1,240 and 1,170 cm−1. Compared with these peaks in CNTs, the Fe–O bond at 532 cm−1 was observed for S3 composites. It is worthy to note that the peak corresponds to Fe–O stretching vibration blue-shifts to high frequency, indicating that the magnetic and nonmagnetic components are strongly combined rather than blended.

Figure 4 FT-IR spectra of nZVI (a), CNTs (b), and S3 (c).
Figure 4

FT-IR spectra of nZVI (a), CNTs (b), and S3 (c).

To test the thermal properties of CNTs, S3 composites, and nZVI, TGA-DSC was carried out at a heating rate of 10°C/min from 50 to 80°C in an air atmosphere (Figure 5). The TGA curves of the CNTs show a two-step weight loss during the heating processes, and the first step between 50 and 250°C was mainly due to the desorption of CO2, the loss of bound water, and residual moisture. In the temperature range of 350–600°C, CNTs exhibited a sharp weight loss corresponding to the exothermic process, which was attributed to the continuous decomposition of the residue carbon–nitrogen complex. The S3 composites showed a similar trend to that of CNTs, but in the temperature range of 300–800°C, the weight loss of the S3 composites was 23.68%, which was lower than that of the CNTs (87.91%). For nZVI, the weight loss of 7.23% between 50 and 250°C was primarily due to the loss of adsorption water and bound water. Whereas, in the temperature ranges of 450–800°C, the weight of nZVI gradually increased and the weight gain was about 6.2%. The DSC curves of the nZVI exhibited a clear exothermic peak at 548.3°C, which was mainly due to the oxidation of nZVI into FeO and Fe2O3. Only 34.7% of weight loss was observed for S3 composites and it had a weak exothermic peak at around 500°C in DSC, which was due to the loading of nZVI on S3 composites. nZVI content in S3 composites was about 66.2%, indicating the high nZVI content in S3 composites.

Figure 5 TGA (a) and DSC (b) curves of CNTs, S3 composites, and nZVI in air.
Figure 5

TGA (a) and DSC (b) curves of CNTs, S3 composites, and nZVI in air.

3.2 Magnetic behavior of nZVI/CNT composites

The magnetic hysteresis loops of the nZVI (a) and S3 (b) composites are shown in Figure 6, and the magnetic parameters of the nZVI and S3 composites are listed in Table 1. In Figure 6, the S3 composites exhibited a saturation magnetization of 64.85 emu g−1, which indicates that S3 composites have excellent magnetic properties. S3 composites with high saturation magnetization quickly responded to the external magnetic fields, which will provide an easy and efficient avenue for separating nZVI and S3 composites from solution, which is easily recycled and avoids secondary pollution.

Figure 6 Hysteresis loops of nZVI (a), S3 (b), and local magnification of S3 (c).
Figure 6

Hysteresis loops of nZVI (a), S3 (b), and local magnification of S3 (c).

Table 1

Magnetic properties of nZVI (a) and S3 (b)

Sample M s (emu g−1) M r (emu g−1) M r/M s H c/O e
nZVI 142.31 10.51 0.073 61.74
S3 64.85 1.45 0.022 11.52

3.3 Removal effect of Ag(i)

The ratio of Py to iron affects the morphology of nZVI/CNTs, thereby affecting the adsorption of Ag(i). Therefore, we investigated the adsorption capacity and removal rate of Ag(i) for CNTs and various nZVI/CNTs (Figure 7).

Figure 7 Adsorption capacity of CNTs (S0) and various nZVI/CNTs for Ag(i).
Figure 7

Adsorption capacity of CNTs (S0) and various nZVI/CNTs for Ag(i).

The adsorption capacity of nZVI/CNTs increased with the decrease in the molar ratio of Py to Fe3+. The increase in adsorption capacity gradually slows down when the molar ratio of Py to Fe3+ is lower than 0.4:1(S3) as shown in Figure 7. At the same time, S3 has complete tubular morphology. Based on the above considerations, S3 is specifically chosen to treat wastewater containing Ag(i).

The effect of different initial concentrations of Ag(i) on the adsorption capacity of CNTs, nZVI, and S3 for Ag(i) is depicted in Figure 8. As can be noticed that the adsorption capacity of the adsorbents increased with the increase in the initial concentration and then tended to a dynamic equilibrium. The maximum adsorption capacities of the CNTs, nZVI, and S3 for Ag(i) were 238.49, 401.49, 522.41 mg g−1. The adsorption capacity of S3 composites for Ag(i) was higher than that of CNTs and nZVI, because nZVI-doped CNTs can improve the agglomeration and oxidation of nZVI, and CNTs have pyrrole-N and imino functional groups, which can react with Ag(i). Therefore, the S3 composites showed good adsorption capacity for Ag(i).

Figure 8 Effects of different initial concentrations on adsorption capacity of CNTs (a), nZVI (b), and S3 (c) for Ag(i).
Figure 8

Effects of different initial concentrations on adsorption capacity of CNTs (a), nZVI (b), and S3 (c) for Ag(i).

The effect of varying contact time of Ag(i) on the adsorption capacity of CNTs, nZVI, and S3 for Ag(i) is depicted in Figure 9. The adsorption capacities had a sharp increase in the first 30 min, and then adsorption capacities increase slowly until an adsorption equilibrium was reached at about 4 h. This rapid adsorption of Ag(i) process could be explained by the large number of active sites on the nZVI/CNTs during the initial stage. However, in the second stage, when the remaining active sites on the free surface sites were not facilely occupied, the adsorption process slowed down and the adsorption rates were limited by increasing the repulsive force between the solute ions in the adsorbent and those in the liquid phase [34].

Figure 9 Effects of different adsorption times on adsorption capacity of CNTs (a), nZVI (b), and S3 (c) for Ag(i).
Figure 9

Effects of different adsorption times on adsorption capacity of CNTs (a), nZVI (b), and S3 (c) for Ag(i).

In order to understand the porosity of nZVI/CNT microsphere, N2 adsorption–desorption isotherms were performed. As Figure 10 shown, the specific surface area of the nZVI/CNT composite was 712.56 m² g−1, nZVI/CNT had type IV adsorption isotherm defined by the International Union of Pure Chemistry and Applications, and an H4 type hysteresis loop appeared between the relative pressure P/P 0 = 0.4–1.0, and the pore size distribution showed that the pore size of nZVI/CNT composite was mainly mesopores and microporous.

Figure 10 N2 adsorption and desorption curves of nZVI/CNT, with the pore size distribution curve as inset.
Figure 10

N2 adsorption and desorption curves of nZVI/CNT, with the pore size distribution curve as inset.

3.4 Adsorption kinetics

In order to explore the adsorption process and mechanism of Ag(i) on the nZVI/CNT composites, the pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetic models were employed to fit the experimental data under different adsorption times to explore the adsorption kinetics. The pseudo-first-order, pseudo-second-order, and intraparticle diffusion rate equations were expressed as follows [35,36,37]:

(4) Pseudo - first - order model ln ( Q e 1 − Q t ) = ln Q e 1 − k 1 t ,

(5) Pseudo - second - order model t Q t = 1 k 2 Q e 2 2 + t Q e 2 ,

(6) Intraparticle diffusion model Q t = k i t 1 / 2 + C ,

where Q e1 and Q e2 (mg g−1) are the adsorption capacities of Ag(i) at equilibrium on the nZVI/CNTs composites, k 1 is the equilibrium rate constant (min−1) of Pseudo-first-order, k 2 is the equilibrium rate constant (min−1) of the pseudo-second-order model, k i is the intraparticle diffusion rate constant (mg g−1 min−0.5), and C is the intercept in intraparticle diffusion.

The kinetic curves were obtained by further fitting the experimental data to pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetic models (Figure 11). The corresponding adsorption kinetic model linear correlation coefficients (R 2) and rate constants are listed in Table 2. The correlation coefficients of the pseudo-second-order equation (R 2 = 0.9999) were obviously larger than those of the pseudo-first-order equation (R 2 = 0.9456), and the Q e calculated by the pseudo-second-order equation was quite near to the experimental value. Therefore, the adsorption process of Ag(i) on CNTs, nZVI, and S3 composites was well described by the pseudo-second-order kinetic model, which revealed that the adsorption process was controlled by a chemisorption mechanism involving electron transfer or electron transfer between the adsorbent and Ag(i).

Figure 11 Experimental data fitted using pseudo-first-order (a), pseudo-second-order (b), and intraparticle diffusion (c) models for Ag(i) adsorption on S3.
Figure 11

Experimental data fitted using pseudo-first-order (a), pseudo-second-order (b), and intraparticle diffusion (c) models for Ag(i) adsorption on S3.

Table 2

Parameters of adsorption kinetics model for adsorption of Ag(i) by S3 (C 0 = 180 mg L−1, T = 298 K)

Pseudo-first-order
R 1 2 K 1 (min−1) Q t (mg g−1) Q e (mg g−1) Equation
0.9456 0.0021 525.47 552.11 log(Q e−Q t) = 1.4652−0.0021t
Pseudo-second-order
R 2 2 K 2 (min−1) Q t (mg g−1) Q e (mg g−1) Equation
0.9999 0.0008 525.47 526.31 t/Q t = 0.0019t + 0.0044
Intraparticle diffusion
Rate constant value R² Equation
k i1 (mg g−1 min−0.5) 119.2749 1 Q t = 119.2749t 1/2 + 4.0194 × 10−14
k i2 (mg g−1 min−0.5) 1.8965 0.8257 Q t = 1.8965t 1/2 + 477.6804

With the intraparticle diffusion model, the adsorption process was investigated to confirm the primarily rate-controlling phase. From Figure 11(c), we can see that the Ag(i) was adsorbed on the adsorbent in two steps as follows: a rapid step and a subsequent slow step. In the first rapid step, Ag(i) moved to the surface of the adsorbent by surface or film diffusion. In this stage, the rate of adsorption was proportional to the number of active sites present on the surface of the adsorbent, which indicated physical adsorption. In the other stage, because a large amount of adsorbed Ag(i) on the adsorbent needs to be further diffused into the adsorbent, Ag(i) was combined with the adsorption active sites of the inner surface, and gradually be absorbed by inner surface of adsorbent [38], which involves both physical and chemical adsorption. The results indicate that the adsorption rate may be mainly controlled by the intraparticle diffusion step in the integrated adsorption process of Ag(i).

3.5 Adsorption isotherms

Adsorption isotherm experiments were conducted to study the adsorption behavior of Ag(i) on the adsorbent at equilibrium, and the adsorption data are presented in Figure 11. The Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherms adsorption models given in equations (7)–(16) were used to describe the experiment results [39,40].

(7) Langmuir : C e Q e = 1 K L Q m + C e Q m ,

(8) R L = 1 1 + K L C 0 ,

(9) Freundlich : ln Q e = ln K F + 1 n ln C e ,

(10) Temkin : Q e = RT b ln ( K T C e ) ,

(11) Q e = A + B ln C e ,

(12) A = RT b ln K T ,

(13) B = RT b ,

(14) Dubinin − Radushkevich : ln Q e = ln Q m − β ε 2 ,

(15) ε = RT ln 1 + 1 C e ,

(16) E = 1 2 β ,

where C e is the equilibrium concentration (mg L−1), Q m is the equilibrium adsorption capacity (mg L−1), K L is the equilibrium constant (mg L−1) of Langmuir, K F is the equilibrium constant (mg L−1) of Freundlich, K T is the equilibrium binding constant (L g−1), T is the reaction temperature (K), and the value of R is 8.314.

In addition, the kinetic curve was obtained by fitting the isothermal adsorption model of Langmuir, Freundlich, Temkin and Dubinin Radushkevich to experimental data (Figure 12) [39,40,41], the constants and value parameters calculated from the above models are listed in Table 3. From the R 2 value (0.9957, 0.9915, 0.9895, and 0.9047), we could see that the Langmuir isotherm adsorption model was significantly higher than the other three models in the concentration range studied. These findings revealed that the adsorption isotherms of Ag(i) onto adsorbents was more compatible with the Langmuir isotherm adsorption model, revealing that the adsorption process was single layer adsorption on a homogeneous surface, and the adsorption sites provided by adsorbents had the same adsorption energies. Moreover, the values of R L determined for all considered initial concentrations of Ag(i) (20–200 mg L−1) were also in the range of 0–1, implying the favorable adsorption of Ag(i).

Figure 12 Ag(i) adsorption on samples described by: Langmuir (a), Freundlich (b), Temkin (c), and Dubinin-Radushkevich (d) isotherm adsorption models.
Figure 12

Ag(i) adsorption on samples described by: Langmuir (a), Freundlich (b), Temkin (c), and Dubinin-Radushkevich (d) isotherm adsorption models.

Table 3

Adsorption isotherm model parameters for adsorption of Ag(i) on S3 (t = 24 h, T = 298 K)

Models Constants Value R 2 Equation
Langmuir Q max (mg g−1) 555.56 0.9957 C e/Q e = 0.1728 + 0.0018C e
K L (L mg−1) 0.0104
Freundlich K F (mg g−1) 12.1813 0.9915 ln Q e = 2.4999 + 0.7353ln C e
n (mg L−1) 1.3599
Temkin K T (L g−1) 0.0689 0.9895 Q e = 203.5599ln C e − 544.5347
b (J mol−1) 12.1712
Dubinin−Radushkevich Q max (mg  g−1) 430.69 0.9047 ln Q e = 6.0654 − 110.1037 ε 2
β (mol2 kJ−2) 110.103
E (kJ mol−1) 0.06739

3.6 Adsorption mechanisms

XPS was employed to study the element states to further understand the adsorption mechanism of Ag(i) on the surface of nZVI/CNTs composites. As depicted in Figure 13(a), the XPS survey indicates that C, O, N, and Fe are the main elements in the nZVI/CNT composites before adsorption, and Ag3d peak was detected after adsorption, which shows that the nZVI/CNT composites successfully adsorbed Ag. Ag0 (3d5/2) and Ag0 (3d3/2) signals appear at 368.28 and 374.43 eV in the spectrum of Ag3d (Figure 13(b)), respectively. The 3d doublet split at 6.0 eV shows that the deposited Ag on the adsorbent surface was mainly in the Ag0 state [37]. At the same time, the binding energies of 367.13 eV (3d5/2) and 373.17 eV (3d3/2) correspond to Ag(i), implying that the Ag(i) in solution was chelated with the nZVI/CNT composites. Those results suggested that the adsorption process involves chemical adsorption, which is consistent with the kinetic results. Figure 13(c) and (d) reveals three major energy peaks of the O1s atom located at 530.13, 531.74, and 533.52 eV, corresponding to the oxygen of oxide (O2−), −C−O, and O−C═O, respectively. The oxide (O2−) group at 529.88 eV corresponds to the Fe–O group in the oxidized Fe3O4 crystal structure of nZVI/CNTs composites [42], which is consistent with the XRD characterization results [43]. The Fe2p peaks observed before and after adsorption are shown in Figure 13(e and f), there are two energy bands before adsorption at 708.11 eV (2p3/2) and 720.61 eV (2p1/2), which corresponds to the Fe0(15.89%). The binding energies of 710.2 eV (2p3/2) and 723.02 eV (2p1/2) correspond to Fe(ii) (26.94%), 711.98 eV (2p3/2) and 725.23 eV (2p1/2) correspond to Fe(iii) (57.17%). The peaks corresponding to Fe0 after adsorption were visibly different. Due to the high reactivity of nZVI, when the adsorbent is present in a solution containing Ag(i), a considerable number of electrons can be released to reduce Ag(i) to Ag0, and the resulting Ag0 will adhere to the surface of nZVI. The layer of Ag0 with a few nanometers thick will have a certain shielding effect on X-rays, which caused the peak intensity of Fe0 to be greatly lowered. On the other hand, Fe(ii) (32.17%), Fe(iii) (67.83%), and the O2− groups in O1s showed an obvious increase in area, which was caused by partial Fe0 being oxidized to Fe3O4 during reduction. The deconvolution of N1s spectrum before adsorption produced three peaks at 398.65, 401.11, and 402.89 eV, ascribed to the quinoid imine (═N−), amino group (−NH−), and positively charged nitrogen (−NH+), respectively, as shown in Figure 13(g). The area of the peak had decreased to 399.64 and 402.88 eV after adsorption (Figure 13(h)). The chelation might occur between Ag(i) and the amino group (−NH−) and amino group (−NH2), and redox adsorption could occur between Ag(i) and nitrogen with free −NH2, resulting in partially reducing Ag(i) to Ag0 [41].

Figure 13 XPS spectra (a) of nZVI/CNT composites before and after adsorption of Ag(i), high-resolution spectra of Ag3d (b) after adsorption of Ag(i). XPS spectra of O1s (c) and (d), Fe2p (e) and (f), and N1s (g) and (h) for nZVI/CNT composites before and after adsorption of Ag(i).
Figure 13

XPS spectra (a) of nZVI/CNT composites before and after adsorption of Ag(i), high-resolution spectra of Ag3d (b) after adsorption of Ag(i). XPS spectra of O1s (c) and (d), Fe2p (e) and (f), and N1s (g) and (h) for nZVI/CNT composites before and after adsorption of Ag(i).

The comparison of this work and similar works reported (the Q m, initial concentration of Ag(i) and separation methods of different sorbents) in literature is depicted in Table 4 [41,44–49]. These results indicated that nZVI/CNT composites prepared in this study could be a promising adsorbent for the selective adsorption of Ag(i). The adsorption of Ag(i) on nZVI/CNT composites has various mechanisms including ion exchange and chelation. Among them, Ag(i) was partially reduced to Ag because of the existence of nZVI and –NH– in the nZVI/CNT composites. Compared to other adsorbents, the nZVI/CNT composites exhibited much higher adsorption efficiency on Ag(i) due to the large specific surface areas and more active adsorption sites in CNTs preventing the agglomeration of the nZVI (Figure 14). In addition, the nZVI/CNT composites can be easily separated from the wastewater and quickly recovered by applying an external magnetic field to achieve its reuse. The excellent properties of nZVI/CNT composites provide a good prospect for cost-effective application with the adsorption of Ag(i) in wastewater treatment.

Table 4

Comparison of Q max of different sorbents for Ag(i)

Adsorbents Q max (mg g−1) Initial concentration of Ag(i) (mg L−1) Separation Ref.
nZVI/HPAC 350 200 Magnetic [40]
Biochar-supported ZVI 600 1,000 Magnetic [37]
nZVI/BBH 534.5 300 Magnetic [41]
PPy/Fe3O4 nanocomposite 169.41 180 Magnetic [42]
PPy/Fe3O4 nanocomposite 230.17 180 Magnetic [43]
PPy/γ-Fe2O3 209 180 Magnetic [44]
nZVI/CNTs 522.41 180 Magnetic (Our work)
Figure 14 The process of adsorption for Ag(i) by nZVI/CNT composites.
Figure 14

The process of adsorption for Ag(i) by nZVI/CNT composites.

3.7 Adsorption reusability

The reusability of adsorbent is very important factors in industrial application of wastewater treatment. The reusability ability of nZVI/CNT composite was investigated by consecutive sorption–desorption cycles for five times as shown as in Figure 15. After 5 cycles, the adsorption capacity of the composite to Ag(i) can reach 60% of the initial property, indicating that the nZVI/CNT composite has good reusability.

Figure 15 Adsorption capacity on Ag(i) for five consecutive adsorption–desorption cycles.
Figure 15

Adsorption capacity on Ag(i) for five consecutive adsorption–desorption cycles.

4 Conclusion

nZVI-doped nZVI/CNT composites were synthesized by in situ carbothermic reduction method in one-pot using nitrogen-rich PPy as a precursor, FeCl3·6H2O as an initiator, and MO as a template. The diameter of nZVI/CNTs composites decreased with the increase in the concentration of Fe3+, and the nZVI/CNT composites formed a uniform tubular structure when n(Py:Fe3+) was 0.4, and the nZVI formed by in situ carbothermal reduction were dispersed in the composites. The saturation magnetization of the composites was 64.85 emu/g when n(Py:Fe3+) was 0.4 and showed excellent magnetic property. Furthermore, when the initial concentration of Ag(i) was 180 mg L−1, the maximum adsorption capacities of nZVI/CNT composites for Ag(i) was up to 522.41 mg g−1. The adsorption process of Ag(i) on nZVI/CNT composites can be well described by the pseudo-second-order kinetic model and the Langmuir isotherm model, which revealed that the adsorption process was controlled by a monolayer chemical adsorption and a favorable process. And intraparticle diffusion was the main rate-controlling step during the adsorption process of Ag(i).

  1. Funding information: The authors kindly thank the National Natural Science Foundation of China (52262013, 51703088); Key laboratory of polymer materials opening fund project in 2018 (KF-18-03); Hongliu Youth Fund of Lanzhou University of Technology (061805); the Natural Science Foundation of Gansu Province (21JR7RA259); Gansu Province for young doctor (2021QB-048).

  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.

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Received: 2023-05-03
Revised: 2023-06-27
Accepted: 2023-08-04
Published Online: 2023-10-25

© 2023 the author(s), published by De Gruyter

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

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  70. Comparative investigations of Ag/H2O nanofluid and Ag-CuO/H2O hybrid nanofluid with Darcy-Forchheimer flow over a curved surface
  71. Study on deformation characteristics of multi-pass continuous drawing of micro copper wire based on crystal plasticity finite element method
  72. Properties of ultra-high-performance self-compacting fiber-reinforced concrete modified with nanomaterials
  73. Prediction of lap shear strength of GNP and TiO2/epoxy nanocomposite adhesives
  74. A novel exploration of how localized magnetic field affects vortex generation of trihybrid nanofluids
  75. Fabrication and physicochemical characterization of copper oxide–pyrrhotite nanocomposites for the cytotoxic effects on HepG2 cells and the mechanism
  76. Thermal radiative flow of cross nanofluid due to a stretched cylinder containing microorganisms
  77. In vitro study of the biphasic calcium phosphate/chitosan hybrid biomaterial scaffold fabricated via solvent casting and evaporation technique for bone regeneration
  78. Insights into the thermal characteristics and dynamics of stagnant blood conveying titanium oxide, alumina, and silver nanoparticles subject to Lorentz force and internal heating over a curved surface
  79. Effects of nano-SiO2 additives on carbon fiber-reinforced fly ash–slag geopolymer composites performance: Workability, mechanical properties, and microstructure
  80. Energy bandgap and thermal characteristics of non-Darcian MHD rotating hybridity nanofluid thin film flow: Nanotechnology application
  81. Green synthesis and characterization of ginger-extract-based oxali-palladium nanoparticles for colorectal cancer: Downregulation of REG4 and apoptosis induction
  82. Abnormal evolution of resistivity and microstructure of annealed Ag nanoparticles/Ag–Mo films
  83. Preparation of water-based dextran-coated Fe3O4 magnetic fluid for magnetic hyperthermia
  84. Statistical investigations and morphological aspects of cross-rheological material suspended in transportation of alumina, silica, titanium, and ethylene glycol via the Galerkin algorithm
  85. Effect of CNT film interleaves on the flexural properties and strength after impact of CFRP composites
  86. Self-assembled nanoscale entities: Preparative process optimization, payload release, and enhanced bioavailability of thymoquinone natural product
  87. Structure–mechanical property relationships of 3D-printed porous polydimethylsiloxane films
  88. Nonlinear thermal radiation and the slip effect on a 3D bioconvection flow of the Casson nanofluid in a rotating frame via a homotopy analysis mechanism
  89. Residual mechanical properties of concrete incorporated with nano supplementary cementitious materials exposed to elevated temperature
  90. Time-independent three-dimensional flow of a water-based hybrid nanofluid past a Riga plate with slips and convective conditions: A homotopic solution
  91. Lightweight and high-strength polyarylene ether nitrile-based composites for efficient electromagnetic interference shielding
  92. Review Articles
  93. Recycling waste sources into nanocomposites of graphene materials: Overview from an energy-focused perspective
  94. Hybrid nanofiller reinforcement in thermoset and biothermoset applications: A review
  95. Current state-of-the-art review of nanotechnology-based therapeutics for viral pandemics: Special attention to COVID-19
  96. Solid lipid nanoparticles for targeted natural and synthetic drugs delivery in high-incidence cancers, and other diseases: Roles of preparation methods, lipid composition, transitional stability, and release profiles in nanocarriers’ development
  97. Critical review on experimental and theoretical studies of elastic properties of wurtzite-structured ZnO nanowires
  98. Polyurea micro-/nano-capsule applications in construction industry: A review
  99. A comprehensive review and clinical guide to molecular and serological diagnostic tests and future development: In vitro diagnostic testing for COVID-19
  100. Recent advances in electrocatalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid: Mechanism, catalyst, coupling system
  101. Research progress and prospect of silica-based polymer nanofluids in enhanced oil recovery
  102. Review of the pharmacokinetics of nanodrugs
  103. Engineered nanoflowers, nanotrees, nanostars, nanodendrites, and nanoleaves for biomedical applications
  104. Research progress of biopolymers combined with stem cells in the repair of intrauterine adhesions
  105. Progress in FEM modeling on mechanical and electromechanical properties of carbon nanotube cement-based composites
  106. Antifouling induced by surface wettability of poly(dimethyl siloxane) and its nanocomposites
  107. TiO2 aerogel composite high-efficiency photocatalysts for environmental treatment and hydrogen energy production
  108. Structural properties of alumina surfaces and their roles in the synthesis of environmentally persistent free radicals (EPFRs)
  109. Nanoparticles for the potential treatment of Alzheimer’s disease: A physiopathological approach
  110. Current status of synthesis and consolidation strategies for thermo-resistant nanoalloys and their general applications
  111. Recent research progress on the stimuli-responsive smart membrane: A review
  112. Dispersion of carbon nanotubes in aqueous cementitious materials: A review
  113. Applications of DNA tetrahedron nanostructure in cancer diagnosis and anticancer drugs delivery
  114. Magnetic nanoparticles in 3D-printed scaffolds for biomedical applications
  115. An overview of the synthesis of silicon carbide–boron carbide composite powders
  116. Organolead halide perovskites: Synthetic routes, structural features, and their potential in the development of photovoltaic
  117. Recent advancements in nanotechnology application on wood and bamboo materials: A review
  118. Application of aptamer-functionalized nanomaterials in molecular imaging of tumors
  119. Recent progress on corrosion mechanisms of graphene-reinforced metal matrix composites
  120. Research progress on preparation, modification, and application of phenolic aerogel
  121. Application of nanomaterials in early diagnosis of cancer
  122. Plant mediated-green synthesis of zinc oxide nanoparticles: An insight into biomedical applications
  123. Recent developments in terahertz quantum cascade lasers for practical applications
  124. Recent progress in dielectric/metal/dielectric electrodes for foldable light-emitting devices
  125. Nanocoatings for ballistic applications: A review
  126. A mini-review on MoS2 membrane for water desalination: Recent development and challenges
  127. Recent updates in nanotechnological advances for wound healing: A narrative review
  128. Recent advances in DNA nanomaterials for cancer diagnosis and treatment
  129. Electrochemical micro- and nanobiosensors for in vivo reactive oxygen/nitrogen species measurement in the brain
  130. Advances in organic–inorganic nanocomposites for cancer imaging and therapy
  131. Advancements in aluminum matrix composites reinforced with carbides and graphene: A comprehensive review
  132. Modification effects of nanosilica on asphalt binders: A review
  133. Decellularized extracellular matrix as a promising biomaterial for musculoskeletal tissue regeneration
  134. Review of the sol–gel method in preparing nano TiO2 for advanced oxidation process
  135. Micro/nano manufacturing aircraft surface with anti-icing and deicing performances: An overview
  136. Cell type-targeting nanoparticles in treating central nervous system diseases: Challenges and hopes
  137. An overview of hydrogen production from Al-based materials
  138. A review of application, modification, and prospect of melamine foam
  139. A review of the performance of fibre-reinforced composite laminates with carbon nanotubes
  140. Research on AFM tip-related nanofabrication of two-dimensional materials
  141. Advances in phase change building materials: An overview
  142. Development of graphene and graphene quantum dots toward biomedical engineering applications: A review
  143. Nanoremediation approaches for the mitigation of heavy metal contamination in vegetables: An overview
  144. Photodynamic therapy empowered by nanotechnology for oral and dental science: Progress and perspectives
  145. Biosynthesis of metal nanoparticles: Bioreduction and biomineralization
  146. Current diagnostic and therapeutic approaches for severe acute respiratory syndrome coronavirus-2 (SARS-COV-2) and the role of nanomaterial-based theragnosis in combating the pandemic
  147. Application of two-dimensional black phosphorus material in wound healing
  148. Special Issue on Advanced Nanomaterials and Composites for Energy Conversion and Storage - Part I
  149. Helical fluorinated carbon nanotubes/iron(iii) fluoride hybrid with multilevel transportation channels and rich active sites for lithium/fluorinated carbon primary battery
  150. The progress of cathode materials in aqueous zinc-ion batteries
  151. Special Issue on Advanced Nanomaterials for Carbon Capture, Environment and Utilization for Energy Sustainability - Part I
  152. Effect of polypropylene fiber and nano-silica on the compressive strength and frost resistance of recycled brick aggregate concrete
  153. Mechanochemical design of nanomaterials for catalytic applications with a benign-by-design focus
https://doi.org/10.1515/ntrev-2023-0114
Keywords for this article
nZVI; CNTs; Ag(i); adsorption; polypyrrole
Creative Commons
BY 4.0

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  70. Comparative investigations of Ag/H2O nanofluid and Ag-CuO/H2O hybrid nanofluid with Darcy-Forchheimer flow over a curved surface
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  74. A novel exploration of how localized magnetic field affects vortex generation of trihybrid nanofluids
  75. Fabrication and physicochemical characterization of copper oxide–pyrrhotite nanocomposites for the cytotoxic effects on HepG2 cells and the mechanism
  76. Thermal radiative flow of cross nanofluid due to a stretched cylinder containing microorganisms
  77. In vitro study of the biphasic calcium phosphate/chitosan hybrid biomaterial scaffold fabricated via solvent casting and evaporation technique for bone regeneration
  78. Insights into the thermal characteristics and dynamics of stagnant blood conveying titanium oxide, alumina, and silver nanoparticles subject to Lorentz force and internal heating over a curved surface
  79. Effects of nano-SiO2 additives on carbon fiber-reinforced fly ash–slag geopolymer composites performance: Workability, mechanical properties, and microstructure
  80. Energy bandgap and thermal characteristics of non-Darcian MHD rotating hybridity nanofluid thin film flow: Nanotechnology application
  81. Green synthesis and characterization of ginger-extract-based oxali-palladium nanoparticles for colorectal cancer: Downregulation of REG4 and apoptosis induction
  82. Abnormal evolution of resistivity and microstructure of annealed Ag nanoparticles/Ag–Mo films
  83. Preparation of water-based dextran-coated Fe3O4 magnetic fluid for magnetic hyperthermia
  84. Statistical investigations and morphological aspects of cross-rheological material suspended in transportation of alumina, silica, titanium, and ethylene glycol via the Galerkin algorithm
  85. Effect of CNT film interleaves on the flexural properties and strength after impact of CFRP composites
  86. Self-assembled nanoscale entities: Preparative process optimization, payload release, and enhanced bioavailability of thymoquinone natural product
  87. Structure–mechanical property relationships of 3D-printed porous polydimethylsiloxane films
  88. Nonlinear thermal radiation and the slip effect on a 3D bioconvection flow of the Casson nanofluid in a rotating frame via a homotopy analysis mechanism
  89. Residual mechanical properties of concrete incorporated with nano supplementary cementitious materials exposed to elevated temperature
  90. Time-independent three-dimensional flow of a water-based hybrid nanofluid past a Riga plate with slips and convective conditions: A homotopic solution
  91. Lightweight and high-strength polyarylene ether nitrile-based composites for efficient electromagnetic interference shielding
  92. Review Articles
  93. Recycling waste sources into nanocomposites of graphene materials: Overview from an energy-focused perspective
  94. Hybrid nanofiller reinforcement in thermoset and biothermoset applications: A review
  95. Current state-of-the-art review of nanotechnology-based therapeutics for viral pandemics: Special attention to COVID-19
  96. Solid lipid nanoparticles for targeted natural and synthetic drugs delivery in high-incidence cancers, and other diseases: Roles of preparation methods, lipid composition, transitional stability, and release profiles in nanocarriers’ development
  97. Critical review on experimental and theoretical studies of elastic properties of wurtzite-structured ZnO nanowires
  98. Polyurea micro-/nano-capsule applications in construction industry: A review
  99. A comprehensive review and clinical guide to molecular and serological diagnostic tests and future development: In vitro diagnostic testing for COVID-19
  100. Recent advances in electrocatalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid: Mechanism, catalyst, coupling system
  101. Research progress and prospect of silica-based polymer nanofluids in enhanced oil recovery
  102. Review of the pharmacokinetics of nanodrugs
  103. Engineered nanoflowers, nanotrees, nanostars, nanodendrites, and nanoleaves for biomedical applications
  104. Research progress of biopolymers combined with stem cells in the repair of intrauterine adhesions
  105. Progress in FEM modeling on mechanical and electromechanical properties of carbon nanotube cement-based composites
  106. Antifouling induced by surface wettability of poly(dimethyl siloxane) and its nanocomposites
  107. TiO2 aerogel composite high-efficiency photocatalysts for environmental treatment and hydrogen energy production
  108. Structural properties of alumina surfaces and their roles in the synthesis of environmentally persistent free radicals (EPFRs)
  109. Nanoparticles for the potential treatment of Alzheimer’s disease: A physiopathological approach
  110. Current status of synthesis and consolidation strategies for thermo-resistant nanoalloys and their general applications
  111. Recent research progress on the stimuli-responsive smart membrane: A review
  112. Dispersion of carbon nanotubes in aqueous cementitious materials: A review
  113. Applications of DNA tetrahedron nanostructure in cancer diagnosis and anticancer drugs delivery
  114. Magnetic nanoparticles in 3D-printed scaffolds for biomedical applications
  115. An overview of the synthesis of silicon carbide–boron carbide composite powders
  116. Organolead halide perovskites: Synthetic routes, structural features, and their potential in the development of photovoltaic
  117. Recent advancements in nanotechnology application on wood and bamboo materials: A review
  118. Application of aptamer-functionalized nanomaterials in molecular imaging of tumors
  119. Recent progress on corrosion mechanisms of graphene-reinforced metal matrix composites
  120. Research progress on preparation, modification, and application of phenolic aerogel
  121. Application of nanomaterials in early diagnosis of cancer
  122. Plant mediated-green synthesis of zinc oxide nanoparticles: An insight into biomedical applications
  123. Recent developments in terahertz quantum cascade lasers for practical applications
  124. Recent progress in dielectric/metal/dielectric electrodes for foldable light-emitting devices
  125. Nanocoatings for ballistic applications: A review
  126. A mini-review on MoS2 membrane for water desalination: Recent development and challenges
  127. Recent updates in nanotechnological advances for wound healing: A narrative review
  128. Recent advances in DNA nanomaterials for cancer diagnosis and treatment
  129. Electrochemical micro- and nanobiosensors for in vivo reactive oxygen/nitrogen species measurement in the brain
  130. Advances in organic–inorganic nanocomposites for cancer imaging and therapy
  131. Advancements in aluminum matrix composites reinforced with carbides and graphene: A comprehensive review
  132. Modification effects of nanosilica on asphalt binders: A review
  133. Decellularized extracellular matrix as a promising biomaterial for musculoskeletal tissue regeneration
  134. Review of the sol–gel method in preparing nano TiO2 for advanced oxidation process
  135. Micro/nano manufacturing aircraft surface with anti-icing and deicing performances: An overview
  136. Cell type-targeting nanoparticles in treating central nervous system diseases: Challenges and hopes
  137. An overview of hydrogen production from Al-based materials
  138. A review of application, modification, and prospect of melamine foam
  139. A review of the performance of fibre-reinforced composite laminates with carbon nanotubes
  140. Research on AFM tip-related nanofabrication of two-dimensional materials
  141. Advances in phase change building materials: An overview
  142. Development of graphene and graphene quantum dots toward biomedical engineering applications: A review
  143. Nanoremediation approaches for the mitigation of heavy metal contamination in vegetables: An overview
  144. Photodynamic therapy empowered by nanotechnology for oral and dental science: Progress and perspectives
  145. Biosynthesis of metal nanoparticles: Bioreduction and biomineralization
  146. Current diagnostic and therapeutic approaches for severe acute respiratory syndrome coronavirus-2 (SARS-COV-2) and the role of nanomaterial-based theragnosis in combating the pandemic
  147. Application of two-dimensional black phosphorus material in wound healing
  148. Special Issue on Advanced Nanomaterials and Composites for Energy Conversion and Storage - Part I
  149. Helical fluorinated carbon nanotubes/iron(iii) fluoride hybrid with multilevel transportation channels and rich active sites for lithium/fluorinated carbon primary battery
  150. The progress of cathode materials in aqueous zinc-ion batteries
  151. Special Issue on Advanced Nanomaterials for Carbon Capture, Environment and Utilization for Energy Sustainability - Part I
  152. Effect of polypropylene fiber and nano-silica on the compressive strength and frost resistance of recycled brick aggregate concrete
  153. Mechanochemical design of nanomaterials for catalytic applications with a benign-by-design focus
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