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Article

Structural Engineering of Photocatalytic ZnO-SnO2-Fe2O3 Composites

by
Larissa L. Khomutinnikova
1,
Sergey K. Evstropiev
1,2,*,
Dmitry P. Danilovich
2,
Igor K. Meshkovskii
1 and
Dmitry V. Bulyga
1,*
1
Technical Physics Department, ITMO University, Saint-Petersburg 197101, Russia
2
Department of Chemistry of Compounds and Materials, Saint-Petersburg State Technological Institute, Technical University, Saint-Petersburg 190013, Russia
*
Authors to whom correspondence should be addressed.
J. Compos. Sci. 2022, 6(11), 331; https://doi.org/10.3390/jcs6110331
Submission received: 27 September 2022 / Revised: 7 October 2022 / Accepted: 1 November 2022 / Published: 3 November 2022
(This article belongs to the Section Nanocomposites)
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Abstract

:
The ZnO-SnO2-Fe2O3 composites containing flower-like particles were prepared by the non-isothermal polymer-salt method. Thermochemical processes proceeding during composites synthesis was studied by DTA/TG method. The structure and morphology of obtained composites were studied by the SEM and XRD analysis. Prepared composites containing small amounts of SnO2 and Fe2O3 demonstrate the high adsorption and photodecomposition of the organic dye Rhodamine 6G in its solutions. Obtained materials show the ability of the photogeneration of the chemically active singlet oxygen under the visible irradiation. The synergistic effect of the flower structure and Fe2O3 doping can significantly improve the photocatalytic and adsorption activities.

1. Introduction

The research and development of new effective photocatalytic materials are the subject of numerous and intensive studies being carried out all over the world. It is known that materials based on zinc oxide are one of the most efficient photocatalysts [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19].
The structural engineering is the effective way to the fabrication of different materials with high photocatalytic properties [1,2,3,16,20,21,22,23,24]. This approach includes different aspects of the materials structure optimization: the preparation of nanomaterials with the high specific surface area and special shapes of nanoparticles (nanorods [25,26], nanowires [5,15,27], “flowers” [14,28,29,30,31], etc.); the control of structural defects [1,5,24,32,33,34]; the application of porous matrixes [23,28,35,36]; materials doping [2,7,8,9,26,28,37,38] and others.
It is well-known that photocatalytic and bactericidal properties of ZnO-based materials can be enhanced by the small addition of some modifying components (Mn [2], Sn [11], Ag [28], Co [37], Al [39]). This addition can decrease the size of ZnO crystals and increase their specific surface area [11,37,39,40], prevent the recombination of photogenerated electron-hole pairs [7,9,10,11,12], widening the spectral diapason of the radiation effectively exciting the photocatalysts [2,7,28,37].
The morphology engineering promotes the significant improvement of photocatalytic properties of ZnO-based materials [2,3,17]. High photocatalytic properties were demonstrated by materials having high specific surface areas and consisting of ZnO particles having specific shapes of wires [5,15], rods [18,34], flowers [25,28,31], cones [4], sheets [10,29], porous nanospheres [23], etc.
The method used for the fabrication of ZnO-based materials affect strongly their morphology and photocatalytic characteristics [30,40]. Different liquid-phase methods are widely used for their synthesis: hydrothermal method [5,6,25,28,41], electrodeposition [6], sol-gel [30,40], precipitation [2,30,42], polymer-salt method [11,13,40,43], microwave synthesis [3].
1-D nanostructures (nanowires; nanorods), which are known to have a high surface-to-volume ratio, with a high surface defect density, are very efficient photocatalysts [5,15,27]. Synthesis of these structures often proceeds through the heterogeneous crystallization of ZnO on preliminary prepared seeds [5,6,44]. So, photocatalytic ZnO nanowires were grown by hydrothermal [5,6,41] and electrodeposition [6] methods on the substrates preliminarily covered by ZnO nanoparticles. In [34], ZnO nano-/micro-rods were synthesized by the hydrothermal route with the presence of polyvinylpyrrolidone (PVP).
The hydrothermal method was applied also for the fabrication of flower-like ZnO structures using as surfactants cetyl-trimethyl-ammonium bromide [25] and sodium dodecel sulfate [29]. In [28,30], flower-like ZnO structures were synthesized by the hydrothermal method without any surfactants. Sol-gel-based hydrothermal method was used in [16] for the synthesis of 3D flower-like ZnO microstructures composed of nanosheets for photocatalytic applications. Flower-like composite ZnO/Au and ZnO/Ag structures were prepared by the liquid deposition method in [45]. The liquid-phase synthesis and applications of 3D ZnO hierarchical nanostructures were described in detail in [46].
The formation of ZnO wires, rods, and flower-like structures having high photocatalytic properties often proceeds through the heterogeneous crystallization of zinc oxide [30,45]. Different preliminary formed nanoparticles (such as modifying additions (Au or Ag nanoparticles [45]), so as firstly formed ZnO nanoparticles [47]) can play the role of seeds for the main part of ZnO crystallization.
Polymer-salt method based on the application of composite solutions containing metals salts and organic polymer is used for the preparation of nanopowders as transparent coatings having high photocatalytic properties [11,13,40,43]. Composite solutions are subjected to drying and the following thermal treatment for the full decomposition of organics and metals salts and the formation of metal oxides nanoparticles.
This method was successfully applied for the fabrication of multicomponent photocatalytic materials [40] and semiconductor heterostructures [11,13]. Different metals salts can decompose at various temperatures during non-isothermal thermal treatment. In this case, the heterogeneous crystallization can proceed and form particles of the one metal oxide that can play the role of seeds for the crystallization of other part of the material. It was found [48] that kinetics features of the thermal precursor decomposition and oxidation can determine the morphology of the obtained oxide nanostructure.
In this work we synthesized ZnO-SnO2-Fe2O3 composites by the non-isothermal polymer-salt method and studied their structure, morphology, and different properties.

2. Materials and Methods

The polymer-salt method previously described in [11,13,40] was used for the composite synthesis. Aqueous solutions of Zn(NO3)2, SnCl2, and FeCl3 in pre-determined volumes were mixed with the solution of high-molecular polyvinylpyrrolidone (PVP, Mw = 1,300,000; Sigma Aldrich, St. Louis, MO, USA) in ethanol. Prepared mixed solutions were dried in air atmosphere at 70 °C, and then the obtained organic-salt composites were calcined at 550 °C in the electric laboratory furnace. Chemical compositions of prepared solutions are given in Table 1.
The thermal evolution of dried PVP-salts composites was studied by DTA-TG method using a STA 449F1 Jupiter (Nietzsche) device. SEM analysis using the instrument TESCAN MIRA3 was applied to study the morphology of the obtained composites.
It is known [49] that chemically active singlet oxygen demonstrates characteristic photoluminescence in NIR spectral range (λmax. = 1270 nm) under the external irradiation. In this work we study the photogeneration of singlet oxygen by preparing composites under the visible irradiation using the experimental setup described in detail in [50]. The luminescence excitation was carried out using LED (HPR40E set) (λmax = 405 nm; power density 0.90 W/cm2).
To study the adsorption and photocatalytic properties of composites, we used organic dye Rhodamine 6G, whose properties are well studied [51]. The solutions of this dye in ethanol (C = 10−5 M; volume 5 mL) and powders samples (0.1 g) were used in photocatalytic experiments. Dye solutions containing powder composite additions were subjected to the radiation of HPR40E (λex. = 370 nm). Dye concentrations in solutions were obtained by the measurements of their adsorption spectra using Perkin-Elmer Lambda 650 dual-beam UV-visible spectrophotometer.

3. Results

3.1. DTA/TG

Figure 1 shows the data of DTA/TG analysis of dried PVP/salts composites. During the thermal treatment all samples are decomposed with significant weight losses and exothermic effects. Weight changes in the observed samples at relatively low temperatures (T < 200 °C) are determined by removing water. The heating of PVP-salts composites to higher temperatures leads to their structural transformations which are completed at 550 °C with oxide formation.
The intensive exothermal peak and corresponding weight losses are observed at ~500 °C in DTA/TG plot of PVP/Zn(NO3)2 composite. This phenomenon is related to the nitrate anions and PVP decomposition and ZnO particles formation. Similar results of DTA/TG analysis of PVP/Zn(NO3)2 and PVP/Zn(NO3)2/SnCl2 composites were reported earlier in [13]. Comparing the experimental data given in [13] with the results shown in Figure 1d, we can conclude that the addition of small amounts of FeCl3 has no significant influence on the behavior of the thermal evolution of PVP/Zn(NO3)2/SnCl2 composites.
Thermal evolution of tin (II) oxyhydroxide Sn6O4(OH)4 and the subsequent oxidation to tin (IV) oxide SnO2 during thermal treatment in the air atmosphere was studied in [48]. The oxidation of SnO and the formation of SnO2 particles, according to chemical reaction is [52]:
SnO   ( s )   +   1 2   O 2   ( g )   →   SnO 2   ( s ) ,
proceeding in the temperature diapason 300 ÷ 350 °C [48]. It is worth to notice that obtained DTA/TG data (Figure 1b) agree with the behavior of the thermal evolution of tin oxide materials described in [48].
Obtained DTA/TG curves suggest the stepped behavior of the thermal evolution of PVP/FeCl3 composite (Figure 1c). The process of thermal decomposition of FeCl3 and synthesis of Fe2O3 crystals proceeds through the formation of numerous intermediate compounds (Fe(OH)2Cl; FeOCl; β-FeOOH) [53].
The presence of PVP in the PVP/salts composites determines additional weight losses and exothermic effects due to the polymer oxidation and decomposition at the diapason 200 ÷ 500 °C [43,54,55]. The heating of composites simultaneously containing metal nitrates and PVP leads to the exothermic oxidation–reduction reaction accompanying the formation of gaseous products [25,34]. This phenomena inputs some increase in observed exothermic effects in DTA curves (Figure 1a,d).
Thus, DTA/TG data show that the heating of PVP-salts composites is accompanied by significant weight losses and exothermal effects that are related to the material structural transformation. The thermal treatment of these composites to 550 °C leads to the full decomposition of salts and PVP. Obtained data fully agree to previously reported results [13,43,48,52,53,54,55] and indicate that the small addition of Sn and Fe compounds have no remarkable influence on the thermal evolution of PVP-Zn(NO3)2 composite.
Thus, the experimental data of DTA/TG analysis indicate that structural transformations (salts and PVP decomposition; different oxide crystals formation) proceed at different temperatures in the wide temperature diapason (300 ÷ 550 °C) during the non-isothermal precursors heating.

3.2. XRD Analysis

As shown in Figure 2, the crystal structures of formed composites were investigated by XRD. The most intensive peaks in all diffraction patterns correspond to the hexagonal wurtzite ZnO phase (PDF#36-1451) that is related to chemical compositions of prepared samples. The ratios between the measured relative intensities of diffraction peaks of ZnO crystals are close to the standard data (PDF#36-1451) for all samples that indicate the absence of texture in their structures.
Regarding samples 2–4, after annealing at 550 °C in air, the measurements showed diffraction peaks at 26.6°, 33.9°, and 38.3°, which correspond to the (110), (101), and (111) planes of cassiterite structure of SnO2 (PDF#41-1445), respectively. Beside tetragonal cassiterite crystals, the addition of tin compound led to the formation of zinc stannate (Zn2SnO4) crystals which have high photocatalytic and bactericidal properties [56,57] and are more stable against acidic dyes than ZnO [58].
The peaks of ZnFe2O4 crystals (JCPDS card 79-1150) are observed in XRD pattern of the sample 4 containing 10.0 mol.% Fe2O3. It is worth to notice that these crystals demonstrate photocatalytic properties also [59].
Thus, XRD data indicate the formation of many different photoactive crystals in obtained ZnO-SnO2-Fe2O3 composites. The main crystal phase of all composites is hexagonal ZnO crystals that corresponds to the chemical composition of prepared materials (Table 1).

3.3. SEM Analysis

Figure 3 demonstrates SEM photo of samples 1, 3, and 4 calcined at 550 °C. The structure of samples 3 and 4 contains flower-like aggregates, consisting of hexagonal ZnO rods (Figure 3d) growth from the one seed (Figure 3b,d). Similar morphology was observed earlier in [45] in ZnO/Ag and ZnO/Au composite materials. In these materials the heterogeneous crystallization of ZnO crystals occurred on preliminary formed metallic (Ag, Au) nanoparticles. In pure ZnO coatings prepared by the polymer-salt method in [60], the formation of flower-like aggregates was not observed and materials consisted of small uniform spherical ZnO nanoparticles. Figure 3a shows that flower-like aggregates are also absent in the structure of the prepared powder ZnO-SnO2 (sample 1).
Besides these flower-like aggregates, numerous sub-micron particles are present in the composite structures. SEM photo shows that composites have disperse structures that can provide high photocatalytic activity of these materials.

3.4. Photoluminescence Properties and Singlet Oxygen Photogeneration

Luminescence properties of ZnO-based materials in the visible spectral range are often related to intrinsic defects of ZnO crystals (oxygen vacancies, Zn interstitials, and others) [61,62,63]. These defects can play an important role in photocatalytic processes [64,65] and their formation in crystal structures of photocatalysts is the subject of many studies [61,62,63,64,65,66].
Figure 4a shows photoluminescence spectra of powder sample 3 in the visible diapason. Numerous luminescence peaks are observed in these spectra. Intensive peaks observed in the blue part of luminescence spectra (λmax = 420, 440 and 455 nm) can be assigned to structural defects of ZnO (Zn interstitials [62,66]) and SnO2 crystals [67,68]). The luminescence of ZnO-SnO2 nanocomposites was observed in the blue spectral region in [13]. The luminescence bands in the green-yellow spectral range (525 ÷ 575 nm) correspond to oxygen vacancies in ZnO [63] or SnO2 [69] crystals. Obtained results suggest that prepared composites contain different structural defects modifying the electronic structure of materials and determining their luminescent properties in the visible spectral range.
Reactive oxygen species (ROS) play an important role in photocatalytic processes [13,24,49,70,71,72,73]. Figure 4 shows the photoluminescence spectrum of powder sample 3 in NIR spectral range. The luminescent band (λmax = 1270 nm) which is characteristic of the 1Δg-3Σg electronic transition of singlet oxygen [49] is observed in this spectrum.

3.5. Photocatalytic Properties

Orange-colored solutions of Rhodamine 6G become colorless under the action of UV radiation, and the addition of synthesized powders to them significantly accelerates this process. Figure 5a illustrates changes in absorption spectra of a dye solution containing powder sample 2 under UV irradiation.
The kinetic equation of pseudo-first order which is often used in the photocatalysis in integral form can be written as [13,74,75,76]:
C C 0 = e − k t
where C0 and C—initial and current dye concentrations; (mM), t—duration of UV irradiation (min) and k—reaction rate constant (min−1).
Figure 5b demonstrates kinetic dependencies of the dye photodecomposition in the solutions containing addition of different prepared composites. It can be seen that experimental dates are sufficiently (R2 > 0.9) described by exponential dependencies only for samples 1 and 4, which demonstrate the relatively low effectiveness of dye photodecomposition (curves 1 and 4, Figure 5b). Experimental results of the dye photodecomposition in solutions containing samples 2 and 3 are poorly (R2 < 0.9) described by exponential dependences.
In [77], the kinetic model of the pseudo-second order of the photocatalysis reaction rate was used. The kinetic equation in this model describes the linear dependence 1/C = f(t) [77]:
1 C = 1 C 0 + k 2 × t ,
where k2—constant of the photochemical reaction rate of pseudo-second order. Figure 5c present plots 1/C = f (t) drawn for the dye photodecomposition in solutions containing powder samples. Pseudo-second order kinetics model somewhat better than pseudo-first order model corresponds to experimental data.

3.6. Adsorption Kinetics

It is known that the pollution adsorption plays an important role in a photocatalytic process [30]. Figure 6a demonstrates the kinetic dependencies of the dye adsorption from solutions on surfaces of powder samples.
The adsorption kinetics on the surface of solid materials often described using the Lagergren’s model [78] and the corresponding equation which can be written in the integral form as:
ln ( q e − q t ) = ln   q e − k f t ,
where qt (mmol/g)—the current amount of dye adsorbed by 1 g of adsorbent up to time t; qe—equilibrium adsorption capacity of the adsorbent; kf (min−1)—adsorption rate constant; t—adsorption duration (min). According to (4), the adsorption rate decreases as the adsorbent surface is filled with dye molecules.
Figure 6b demonstrates dependencies ln(qe − qt) = f(t) calculated based on experimental data. The experimental data are close to linear dependencies and are described sufficiently (R2 > 0.96) by the Equation (4).
The adsorption proceeds faster on the surface of samples 2 and 3 comparing with the adsorption on the sample 4. The comparison of Figure 5b and Figure 6a shows the similarity of the influence of Fe2O3 additions on kinetic dependencies of the dye adsorption and its photodecomposition. Similar phenomenon was observed earlier for kinetics of the different dyes adsorption and photodecomposition by Cr-doped ZnO nanorods [79].

4. Discussion

Non-isothermal polymer-salt method was successfully applied to the synthesis of photoactive ZnO-SnO2-Fe2O3 composites consisting of different oxide crystals. The data of SEM analysis show the presence of flower-like aggregates composed of hexagonal ZnO crystals in the structure of ZnO-SnO2-Fe2O3 composites. Based on the results of DTA/TG analysis, we can suggest that the formation of the observed “flowers” can be related to the heterogeneous ZnO crystallization on oxide nanoparticles which could form faster than other during the non-isothermal thermal treatment.
The study has showed that obtained oxide composites demonstrate the ability of the chemically active singlet oxygen photogeneration. It is worth to notice that the photogeneration of singlet oxygen is observed under visible irradiation. This fact indicates the possibility of composites application to the air and water cleaning using the visible irradiation.
Obtained experimental results showed (Figure 5a, curves 2 and 3) that small Fe2O3 additions into ZnO-SnO2 composites provide significant acceleration of the dye decomposition. This phenomenon could have been attributed to some changes of the electronic structures and optical properties of these composites. The band gap value Eg of Fe2O3 is 2.0 ÷ 2.1 eV [80,81] that is remarkably less than Eg of ZnO or SnO2 (~3.4 eV [40,42,82] and 3.6 eV [82], correspondingly). The addition of Fe2O3 can decrease the band gap value of composites [83] and increases the visible light absorption of composites [8]. High photocatalytic properties of SnO2/α-Fe2O3 and ZnO/α-Fe2O3 heterostructures were described earlier in [8,26].
Changes in the electronic structure of ZnO-SnO2 materials at the addition of Fe compounds play an important role in the observed high photocatalytic activity of ZnO-SnO2-Fe2O3 composites prepared in this work. However, Figure 5b shows that composite 4 containing 10 mol. % of Fe2O3 demonstrate lower photocatalytic properties than composites 2 and 3 with lower content of Fe2O3. This phenomenon could be related to the difference of the materials structure and morphology so as to some features of the interactions between Rhodamine 6G molecules and the surface of prepared composites. In particular, the features of the interaction of dyes molecules with the surface of the photocatalytic material determine the significant differences of the photodecomposition and adsorption kinetics observed for different dyes [79]. Moreover, it was found [84] that the molecular structure of dyes and their interaction with the surface of photocatalytic material played a key role in visible-light photodegradation reactions on F-TiO2 particles.
Moreover, according to XRD data (Figure 2), obtained composites also contain, besides ZnO, SnO2, and Fe2O3, the crystals ZnFe2O4 and ZnSnO3. The band gap of ZnFe2O4 crystals is ~1.9 eV [85] and this material demonstrates high photocatalytic properties. Therefore, the correct analysis of the influence of Fe compounds on the electronic structure of the prepared composites requires additional study in future.
The study of adsorption activity of the prepared composites suggests that observed high photocatalytic properties of ZnO-SnO2-Fe2O3 composites with small (0.5 and 2.0 mol.%) content of Fe2O3 are significantly related to the features of their morphologies providing fast adsorption of dye molecules from the solutions.

Author Contributions

Conceptualization, S.K.E.; methodology, I.K.M.; validation, L.L.K.; formal analysis, D.V.B.; investigation, D.P.D.; data curation, D.P.D.; writing—original draft preparation, S.K.E. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Informed Consent Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Thermal evolution of PVP-salts composite materials. (a) PVP-Zn(NO3)2; (b) PVP-SnCl2; (c) PVP-FeCl3; (d) PVP-Zn(NO3)2-SnCl2-FeCl3. 1—DTA curves; 2—TG curves.
Figure 1. Thermal evolution of PVP-salts composite materials. (a) PVP-Zn(NO3)2; (b) PVP-SnCl2; (c) PVP-FeCl3; (d) PVP-Zn(NO3)2-SnCl2-FeCl3. 1—DTA curves; 2—TG curves.
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Figure 2. XRD patterns of samples 1 (a), 2 (b), 3 (c), 4 (d).
Figure 2. XRD patterns of samples 1 (a), 2 (b), 3 (c), 4 (d).
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Figure 3. SEM photo of samples 1 (a), 2 (b) 3 (c,e) and 4 (d).
Figure 3. SEM photo of samples 1 (a), 2 (b) 3 (c,e) and 4 (d).
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Figure 4. (a) Photoluminescence spectra of powder sample 3 in the visible diapason. Excitation wavelengths, nm: 300 (curve 1); 350 (curve 2); 400 (curve 3). (b) Photoluminescence spectra of powder sample 3 in NIR spectral range. Excitation wavelength 405 nm.
Figure 4. (a) Photoluminescence spectra of powder sample 3 in the visible diapason. Excitation wavelengths, nm: 300 (curve 1); 350 (curve 2); 400 (curve 3). (b) Photoluminescence spectra of powder sample 3 in NIR spectral range. Excitation wavelength 405 nm.
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Figure 5. (a) Changes in absorption spectra of Rhodamine 6G solution containing powder sample 2 under UV irradiation. Irradiation duration, min.: 0 (curve 1); 5 (curve 2); 10 (curve 3); 15 (curve 4); 20 (curve 5); 25 (curve 6); 30 (curve 7); (b) kinetics of dye photodecomposition under UV radiation in solutions containing powder samples 1 (curve 1); 2 (curve 2); 3 (curve 3); 4 (curve 4); (c) dependencies 1/C = f(t) drawn for the dye photodecomposition in solutions containing powder samples.
Figure 5. (a) Changes in absorption spectra of Rhodamine 6G solution containing powder sample 2 under UV irradiation. Irradiation duration, min.: 0 (curve 1); 5 (curve 2); 10 (curve 3); 15 (curve 4); 20 (curve 5); 25 (curve 6); 30 (curve 7); (b) kinetics of dye photodecomposition under UV radiation in solutions containing powder samples 1 (curve 1); 2 (curve 2); 3 (curve 3); 4 (curve 4); (c) dependencies 1/C = f(t) drawn for the dye photodecomposition in solutions containing powder samples.
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Figure 6. (a) Kinetic dependencies of the dye adsorption from solutions on surfaces of powder samples 2 (curve 1), 3 (curve 2), 4 (curve 3). (b) Dependencies ln(qe − qt) = f(t) which were obtained from experimental data for the dye adsorption on the surfaces of powder samples 2 (curve 1), 3 (curve 2), 4 (curve 3).
Figure 6. (a) Kinetic dependencies of the dye adsorption from solutions on surfaces of powder samples 2 (curve 1), 3 (curve 2), 4 (curve 3). (b) Dependencies ln(qe − qt) = f(t) which were obtained from experimental data for the dye adsorption on the surfaces of powder samples 2 (curve 1), 3 (curve 2), 4 (curve 3).
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Table
Table 1. Chemical compositions of prepared solutions and oxide composites.
Table 1. Chemical compositions of prepared solutions and oxide composites.
SampleChemical Compositions, mol. %
SolutionsComposites
H2OEthanolZn(NO3)2SnCl2FeCl3PVPZnOSnO2Fe2O3
147.6247.622.260.12-2.3895.05.0-
247.6247.622.300.070.012.3896.53.00.5
347.6247.622.260.070.052.3895.03.02.0
447.6247.622.070.070.242.3887.03.010.0
Nominal chemical compositions.
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Khomutinnikova, L.L.; Evstropiev, S.K.; Danilovich, D.P.; Meshkovskii, I.K.; Bulyga, D.V. Structural Engineering of Photocatalytic ZnO-SnO2-Fe2O3 Composites. J. Compos. Sci. 2022, 6, 331. https://doi.org/10.3390/jcs6110331

AMA Style

Khomutinnikova LL, Evstropiev SK, Danilovich DP, Meshkovskii IK, Bulyga DV. Structural Engineering of Photocatalytic ZnO-SnO2-Fe2O3 Composites. Journal of Composites Science. 2022; 6(11):331. https://doi.org/10.3390/jcs6110331

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Khomutinnikova, Larissa L., Sergey K. Evstropiev, Dmitry P. Danilovich, Igor K. Meshkovskii, and Dmitry V. Bulyga. 2022. "Structural Engineering of Photocatalytic ZnO-SnO2-Fe2O3 Composites" Journal of Composites Science 6, no. 11: 331. https://doi.org/10.3390/jcs6110331

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