Photocatalytic activities of multilayered ZnO-based thin films prepared by sol–gel route: effect of SnO2 heterojunction layer

In present study, ZnO/SnO₂/ZnO/SnO₂/ZnO multi–layer, ZnO/SnO₂/ZnO triple layer and ZnO single layer films have been deposited on glass substrate by sol–gel dip–coating technique. The structural and optical properties of thin films have been investigated by X-ray diffractometer, UV–visible, photoluminescence spectroscopies and scanning electron microscopy. The structural analysis reveals structural inhomogeneities and different crystallite growth processes as function of number of deposited layers. A comparison between photocatalytic activity of zinc oxide samples toward photodegradation of phenol, 4-aminophenol and 4-nitrophenol has been performed under UV light irradiation. Experiments were conducted to study the effects of operational parameters on the degradation rate. Pseudo-first-order photodegradation kinetics was observed on all films and the reaction constants were determined. The results showed that the photocatalytic activity of ZnO multi–layer film was superior to that of the ZnO single- and triple-layer films. Differences in film efficiencies can be attributed to differences in crystallinity, surface morphology, defect concentration of oxygen vacancy and to presence of SnO₂ sublayer that may act as trap for electrons generated in the ZnO layer thus preventing electron–hole recombination. The results reveal that SnO₂ hetrojunction layers improve crystalline quality, optical and photocatalytic properties of ZnO multilayered films.     

In2O3敏化ZnO纳米棒阵列的性能及其光电催化活性

以掺氟SnO₂ (FTO)导电玻璃为基底, 采用水热法制备了ZnO纳米棒阵列. 通过In(NO₃)₃水溶液水洗的方法, 合成了In₂O₃敏化ZnO纳米棒阵列光催化剂. 采用场发射扫描电子显微镜(FESEM), X射线能谱(EDX), X射线衍射(XRD)及紫外-可见漫反射光谱(UV-Vis DRS)对样品的形貌、结构、组成、晶相等进行一系列的表征. 以罗丹明B (RhB)为目标降解物, 探究了In₂O₃敏化ZnO 纳米棒阵列光电催化活性. 采用场诱导表面光伏技术(FISPV)研究了不同含量的In₂O₃敏化ZnO纳米棒阵列在光照射下的光生电荷行为. 结合电化学工作站检测不同样品的光电流, 随着In₂O₃敏化量的改变, 光电流和开路电压也随之改变. 并探讨了In₂O₃敏化ZnO纳米棒阵列光生电荷行为与光电催化活性之间的关系. 结果表明, 适量In₂O₃敏化的ZnO光催化剂在可见光下2 h内对罗丹明B的降解效率达到95%, 是单纯ZnO纳米棒阵列的2.4倍.     

In2O3/ZnO heterostructured nanotubes: electrospinning fabrication,characterization, and highly enhanced photocatalytic properties

In₂O₃/ZnO heterostructured nanotubes with cubic In₂O₃ and hexagonal ZnO were successfully synthesized via the combination of electrospinning and calcination process. The as-prepared materials are investigated by using thermogravimetric and differential scanning calorimetry, fourier transform infrared spectroscope, X-ray diffraction, scanning electron microscope and high-resolution transmission electron microscope techniques. The formation mechanism of In₂O₃/ZnO heterostructured nanotubes based on the kinetics of phase separation which results from the decomposition of polyvinyl pyrrolidone during the calcination process is also discussed in detail. The photocatalytic degradation tests reveal that In₂O₃/ZnO heterostructured nanotubes exhibit the highly improved photocatalytic properties compared with the single-component ZnO and In₂O₃ materials.     

Sensors based on SnO<Subscript>2</Subscript> + In<Subscript>2</Subscript>O<Subscript>3</Subscript> composite films for detecting CO in air

The sensor properties of nanostructured films of SnO₂, In₂O₃, and their combinations for detecting CO in air in the temperature range of 330–520°C were investigated. It was found that SnO₂ films show the least sensitivity to CO. Sensitivity grows as the concentration of In₂O₃ in SnO₂ increases, and it reaches its maximum value in pure In₂O₃. At the same time, the maximum of sensitivity to CO in air shifts towards low temperatures. Sensor response time was found to be about 1 s for the studied SnO₂ and In₂O₃ films, and about 0.5 s for the composite film. The mechanism of sensor sensitivity for the studied metal oxide films in detecting CO in air is discussed.     

Recyclable Fe3O4/ZnO/PPy composite photocatalyst: Fabrication and photocatalytic activity

In this work, a magnetically separable polypyrrole (PPy) modified Fe₃O₄/ZnO composite photo-catalyst was synthesized and its photocatalytic activity was tested. The as-prepared Fe₃O₄/ZnO/PPy nanocomposite was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra. Furthermore, three different photocatalysts including the Fe₃O₄/ZnO/PPy composite were tested using methyl orange (MO) degradation reaction under UV light irradiation. The relative results demonstrated that the Fe₃O₄/ZnO/PPy composite has the highest photochemical activity after 4 h photocatalytic experiment. It can be easily separated using an external magnetic field. This kind of composite photocatalysts with easiness of separation can have potential applications in the treatment of water contaminated by organic pollutants.     

Conductivity of SnO<Subscript>2</Subscript>-In<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocrystalline composite films

The conductivity of films consisting of a mixture of SnO₂ and In₂O₃ nanocrystals at 200–500°C was studied. Based on the experimental data, it was assumed that in films containing less than 20 wt % In₂O₃, the current flows along SnO₂ nanocrystals. A model of conductivity in these films is presented; it includes an electron transfer from In₂O₃ to SnO₂, which forms positively charged In₂O₃ nanocrystals that contact the negatively charged SnO₂ nanocrystals. In the presence of In₂O₃ nanocrystals, the activation energy of the electron transfer between SnO₂ nanocrystals decreased substantially because of a decrease in the barrier of electron transfer between SnO₂ crystals under the action of the negative charge. As a result, a percolation cluster of charged SnO₂ crystals formed. At high contents of In₂O₃ (over 20 wt %), the conductivity increased dramatically. The curve of the temperature dependence of conductivity changed because of the appearance of a percolation cluster of In₂O₃ nanocrystals, in which the current passed. The conductivity of a mixed film of this kind differed from that of the nanocrystalline film of pure In₂O₃.     

SnO2/TiO2纳米管复合光催化剂的性能及失活再生

基于微波水热法和微乳液法合成SnO₂/TiO₂纳米管复合光催化剂. 通过X射线衍射（XRD）、配有能量色散X射线光谱仪（EDX）的透射电镜（TEM）和电化学手段对光催化剂进行表征. 以甲苯为模型污染物,考察光催化剂在紫外光（UV）和真空远紫外光（VUV）下的性能及失活再生. 结果表明,SnO₂/TiO₂纳米管复合光催化剂形成三元异质结（锐钛矿相TiO₂（A-TiO₂）/金红石相TiO₂（R-TiO₂）、A-TiO₂/SnO₂和R-TiO₂/SnO₂异质结）,促使光生电子-空穴对的有效分离,提高光催化活性. SnO₂/TiO₂表现出最佳的光催化性能,UV和VUV条件下的甲苯降解率均达100%,CO₂生成速率（k₂）均为P25的3倍左右. 但由于UV光照矿化能力不足,中间产物易在催化剂表面累积. 随着UV光照时间的增加,SnO₂/TiO₂逐渐失活,20 h 后k₂由138.5 mg·m^-3·h^-1下降到76.1 mg·m^-3·h^-1. 利用VUV再生失活的SnO₂/TiO₂,过程中产生的·OH、O₂^-·、O（¹D）、O（³P）、O₃等活性物质可氧化吸附于催化剂活性位的难降解中间产物,使催化剂得以再生,12 h后k₂恢复到143.6 mg·m^-3·h^-1. UV和VUV的协同效应使UV降解耦合VUV再生成为一种可持续的光催化降解污染物模式.     

Mechanism of the conductivity and sensor response of nanostructured In2O3+ZnO films

The conductivity and sensor properties of mixed nanostructured In₂O₃+ZnO metal oxide systems with different component ratios are investigated. It is found that maximum sensor sensitivity in detecting hydrogen and CO in composite films containing 15 and 80 wt % In₂O₃ considerably exceeds the sensitivity of individual oxides. A mechanism of the sensor action, which is largely determined by the dependency of the paths of conductivity in a composite metal-oxide film on its composition, is proposed. It is established that the main factors determining the conductivity and sensor sensitivity of In₂O₃ + ZnO composite are modifications in the electron structure of crystals (mainly by In₂O₃) during the formation of composites, electron transfer from In₂O₃ to ZnO, and the catalytic activity of ZnO. It is shown in particular that ZnO effectively catalyzes the reaction of hydrogen dissociation and, in contact with In₂O₃, favors the chemical sensibilization of the sensor response of such mixed metal oxide systems in detecting H₂ and CO.     

Semiconductor‐photocatalyzed degradation of carboxylic acids: Enhancement by particulate semiconductor mixture

Degradation of oxalic acid on particulate TiO₂, ZnO, CuO, Bi₂O₃, In₂O₃, and Nb₂O₅ under UV‐A light exhibits first‐order kinetics, and the degradation rates increase linearly with the photon flux. All the oxides show sustainable photocatalytic activity, and the photonic efficiencies of degradation of oxalate are very much lower than those of the acid. The ease of degradation of carboxylic acids is the following: formic > oxalic > acetic > citric. Intimate mixtures of two different particulate semiconductors kept under suspension and at continuous motion exhibit higher photocatalytic activity, revealing interparticle charge transfer. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 716–726, 2009     

Preparation of novel visible-light-driven In<Subscript>2</Subscript>O<Subscript>3</Subscript>–CaIn<Subscript>2</Subscript>O<Subscript>4</Subscript> composite photocatalyst by sol–gel method

Novel visible-light-activated In₂O₃–CaIn₂O₄ photocatalysts were developed in this paper through a sol–gel method. The photocatalytic activities of In₂O₃–CaIn₂O₄ composite photocatalysts were investigated based on the decomposition of methyl orange under visible light irradiation (λ > 400 nm). The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrum (EDS), X-ray photoelectron spectroscopy (XPS) and UV–vis diffused reflectance spectroscopy (DRS). The results revealed that the In₂O₃–CaIn₂O₄ composite samples with different In₂O₃ and CaIn₂O₄ content can be obtained by controlling the synthesis temperature, and the composite photocatalysts extended the light absorption spectrum toward the visible region. The photocatalytic tests indicated that the composite samples demonstrated high visible-light activity for decomposition of methyl orange. The significant enhancement in the In₂O₃–CaIn₂O₄ photo-activity under visible light irradiation can be ascribed to the efficient separation of photo-generated carriers in the In₂O₃ and CaIn₂O₄ coupling semiconductors.     

Photocatalytic decomposition of dyes using ZnO doped SnO2 nanoparticles prepared by solvothermal method

ZnO doped SnO₂ has been successfully synthesized by the solvothermal method using methanol as organic solvent. The effect of ZnO/SnO₂ molar ratios on the crystal structure, microstructure, optical and photocatalytic properties has been investigated. The synthesized samples are characterized by X-ray diffraction, transmission electron microscopy, N₂ physical adsorption, FT-IR spectroscopy and UV–Vis spectroscopy. XRD results revealed that all diffraction peaks positions agree well with the reflection of a tetragonal rutile structure of SnO₂ phase without extra peaks at 0.1ZnO:0.9SnO₂ and 0.2ZnO:0.8SnO₂ molar ratios. However, the secondary phase of ZnO at 0.3ZnO:0.7SnO₂ molar ratio was investigated. TEM images revealed that the shape of SnO₂ particles was spherical and the particle sizes of SnO₂ and 0.3ZnO:0.7SnO₂ molar ratio were 6.2 and 16.4 nm, respectively. The newly prepared samples have been tested by the determination of photocatalytic degradation of methylene blue (MB). The results indicated that Zn²⁺ doping at 0.3ZnO:0.7 SnO₂ molar ratio showed the highest photocatalytic activity for the MB photodegradation. The heightened photocatalytic activity of ZnO/SnO₂ could be ascribed to the enhanced charge separation derived from the coupling of ZnO with SnO₂ due to the potential energy differences between SnO₂ and ZnO. The recycling tests demonstrated that 0.3ZnO:0.7 SnO₂ photocatalysts were quite stable during that liquid–solid heterogeneous photocatalysis since no decrease in activity in the first four cycles was observed.     

Photocatalytic Degradation of Glyphosate in Water by N‐Doped SnO2/TiO2 Thin‐Film‐Coated Glass Fibers

Photocatalytic degradation of glyphosate contaminated in water was investigated. The N‐doped SnO₂/TiO₂ films were prepared via sol–gel method, and coated on glass fibers by dipping method. The effects of nitrogen doping on coating morphology, physical properties and glyphosate degradation rates were experimentally determined. Main variable was the concentration of nitrogen doping in range 0–40 mol%. Nitrogen doping results in shifting the absorption wavelengths and narrowing the band gap energy those lead to enhancement of photocatalytic performance. The near optimal 20N/SnO₂/TiO₂ composite thin film exhibited about two‐ and four‐folds of glyphosate degradation rates compared to the undoped SnO₂/TiO₂ and TiO₂ films when photocatalytic treatment were performed under UV and solar irradiations, respectively, due to its narrowest band gap energy (optical absorption wavelength shifting to visible light region) and smallest crystallite size influenced by N‐doping.     

Efficient Decomposition of Organic Pollutants Over In2O3/TiO2 Nanocomposite Photocatalyst Under Visible Light Irradiation

The heterojunction structures of In₂O₃/TiO₂, exhibiting visible light photocatalytic efficiency, has been synthesized by utilizing maleic acid as an organic linker to combine In₂O₃ and Degussa P25 (TiO₂) nanoparticles. The prepared nanocomposite has been characterized by FESEM, TEM, XRD and UV?CVisible reflectance spectra. The photocatalytic efficiency of the composite photocatalyst has been investigated based on the decomposition of 2-propanol (IP) in gas phase and 1,4-dichlorobenzene (DCB) in aqueous phase under visible light (??????420?nm) irradiation. The results reveal that the In₂O₃/TiO₂ composite photocatalyst with 7?wt% In₂O₃ demonstrated 6.3 times of efficiency in evolving CO₂ from gaseous IP and 8.7 times of efficiency in removing aqueous DCB in compare with Degussa P25. In this In₂O₃/TiO₂ composite system, TiO₂ seems to be the principal photocatalyst whereas the function of In₂O₃ is to sensitize TiO₂ by absorbing visible light (??????420?nm). The extraordinary high photocatalytic efficiency of this composite In₂O₃/TiO₂ under visible light has been explained on the basis of relative energy band positions of the component semiconductors.     

Photoluminescence and photocatalytic properties of Er<Superscript>3+</Superscript>-doped In<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films prepared by sol–gel: application to Rhodamine B degradation under solar light

The effect of Er³⁺ doping (1%) on the structural, optical and photocatalytic properties of In₂O₃ thin films deposited on quartz substrates by spin coating was investigated. The In₂O₃:1% Er³⁺ films, annealed in the temperature range 800–1000 °C, were characterized by X-ray diffraction, scanning electron microscopy (SEM), atomic force microscopy, UV–Vis spectroscopy, ellipsometry and photoluminescence (PL). The films are polycrystalline with a cubic structure and the lattice parameter increases with the incorporation of Er³⁺ owing to its larger radius. The SEM images of the film show a granular morphology with large grains (~ 200 nm). The doped In₂O₃ film exhibits less transparency than In₂O₃ in the UV–visible region with band gaps of 3.42 and 3.60 eV, respectively. PL shows strong lines at 548 and 567 nm, assigned to Er³⁺ under direct excitation at 532 nm. The energy diagram of the junction In₂O₃:1% Er³⁺/Na₂SO₄ (0.1 M) solution plotted from physical and photoelectrochemical characterizations shows the feasibility of the films for Rhodamine B (RhB) degradation under solar light. The conduction band at 2.22 V deriving from the In³⁺:5s orbital is suitably positioned with respect to the O₂/O ₂ ^· level (~ 1.40 V_SCE), leading to oxidation of 32% of 10 ppm RhB within 40 min of solar irradiation.     

Graphene oxides as support for the synthesis of nickel sulfide–indium oxide nanocomposites for photocatalytic,antibacterial and antioxidant performances

NiS (nickel sulfide)–In₂O₃ (indium oxide) nanostructures and NiS–In₂O₃ decorated on graphene oxide (GO) were demonstrated by ultrasonic/hydrothermal method. The structural study demonstrates the preparation of bixbyite and hexagonal phase of In₂O₃ and NiS for all of the synthesized catalysts. The band gap of the synthesized catalyst was determined to be in the range of 2.30–3.00 eV. A morphological evaluation by field emission scanning electron microscopy of NiS–In₂O₃ decorated on graphene oxide shows support for the NiS–In₂O₃ on the graphene oxide layer. Different test parameters were performed to study the phase and morphology. The particle sizes of the In₂O₃, NiS–In₂O₃ and NiS–In₂O₃/GO nanocomposites were 56.0, 62.0 and 66.0 nm, respectively. The photocatalytic performance of NiS–In₂O₃/GO nanocomposites was examined for the degradation of methylene blue dye under a UV lamp. The prepared sample shows 98.25% photocatalytic degradation within 40 min and at pH 9. With the presence the NiS and GO, the photo-degradation capacities of In₂O₃ and NiS–In₂O₃ are improved owing to the low band gap being calculated in UV–vis DRS analysis. The high ratio of NiS causes the highest photocatalytic properties of NiS–In₂O₃ nanocomposites owing to the enhancement of charge separation efficiency and generation of hydroxyl radicals. This study presents a facile and low-cost method to prepare highly active NiS–In₂O₃/GO nanocomposites. The antibacterial data indicate the significant properties of NiS–In₂O₃/GO nanocomposites for this study.     

The sensor properties of SnO<Subscript>2</Subscript> · In<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposite oxides in the detection of hydrogen in air

The sensor properties of In₂O₃ · SnO₂ polycrystalline films having different compositions were studied in the detection of 2% hydrogen in air over the temperature range 330–530°C. Films containing 19% In₂O₃ were most sensitive to hydrogen. The temperature dependence of the sensitivity of sensors passed a maximum, the position of which depended on the composition of the film. The temperature at which sensor sensitivity was maximum decreased as the content of indium oxide increased. This temperature was 485°C for the SnO₂ film and 425°C for the In₂O₃ film. The response and relaxation times of sensors also decreased as the amount of In₂O₃ in the composite metal oxide film increased. Possible mechanisms of the sensor sensitivity of the films are discussed.     

Fe2O3/ZnO/ZnFe2O4 composites for the efficient photocatalytic degradation of organic dyes under visible light

In this study, novel ternary Fe₂O₃/ZnO/ZnFe₂O₄ (ZFO) composites were successfully prepared through a simple hydrothermal reaction with subsequent thermal treatment. The as-prepared products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) analysis, Barrett-Joyner-Halenda (BJH) measurement, and UV–vis diffuse reflectance spectroscopy (UV–vis DRS). The photocatalytic degradation of rhodamine B (Rh B) under visible light irradiation indicated that the ZFO composites calcined at 500 °C has the best photocatalytic activity (the photocatalytic degradation efficiency can reach up to 95.7% within 60 min) and can maintain a stable photocatalytic degradation efficiency for at least three cycles. In addition, the photocatalytic activity of ZFO composites toward dye decomposition follows the order cationic Rh B > anionic methyl orange. Finally, using different scavengers, superoxide and hydroxyl radicals were identified as the primary active species during the degradation reaction of Rh B.     

Efficiency of various semiconductor catalysts for photodegradation of Safranin-T

Semiconductor photocatalysis often leads to partial or complete mineralization of organic pollutants. In this study, photocatalytic degradation of Safranin-T, a hazardous textile dye, has been investigated using various semiconductors such as titanium dioxide (TiO₂), zinc oxide (ZnO), bismuth oxide (Bi₂O₃), cerium oxide (CeO₂), yttrium oxide (Y₂O₃), and zirconium oxide (ZrO₂). The experiments were carried out by irradiating the aqueous solution of Safranin-T containing photocatalysts with UV and air. Maximum decolorization of Safranin-T occurred with TiO₂ (99.8%), followed by ZnO (80.3%), Bi₂O₃ (57.1%), CeO₂ (13.1%), Y₂O₃ (12.2%), and ZrO₂ (10.2%). The rate of photocatalytic degradation varied with increasing concentration of Safranin-T. The equilibrium degradation data of Safranin-T by TiO₂ and ZnO were fitted to the Langmuir and Freundlich isotherm models. The Freundlich and Langmuir model showed satisfactory fit to the equilibrium degradation data for TiO₂ and ZnO, respectively. Photocatalytic degradation of Safranin-T followed pseudo second-order kinetics.     

Morphology‐controlled Fabrication of SnO2/ZnO Nanocomposites with Enhanced Photocatalytic Performance

In this work, a series of novel SnO₂/ZnO nanocomposites with different morphologies were fabricated via a facile hydrothermal technique followed by calcination in air. The morphological, structural and photocatalytic properties of the SnO₂/ZnO nanocomposites were studied using different methods. The results showed that the synthesized nanocomposites possessed crystal phases of wurtzite hexagonal phase ZnO and tetragonal rutile phase SnO₂. In addition, the morphologies of SnO₂/ZnO nanocomposites strongly depended on the molar ratios of Sn and Zn. Compared with ZnO and SnO₂, the SnO₂/ZnO nanocomposites exhibited considerably higher degradation efficiency for the photodegradation of methylene blue and quinolone antibiotics under mercury lamp irradiation. The SZ‐2 nanospheres exhibited the highest degradation efficiency of 95.81%, which was about 2.63 times higher than that of ZnO nanoparticles. Moreover, the trapping experiments confirmed that ˙OH played the dominant role in MB degradation. Finally, the charge carriers potential transfer pathway and photocatalytic degradation mechanism were put forward. This study provides an economical way to prepare hybrid nanocomposites with controlled morphology for practical applications in the photocatalytic degradation of organic dyes and residual antibiotics.     

ZnO/In2O3复合空心球的制备及其光电催化葡萄糖降解性能

通过葡萄糖协助的水热以及随后的退火处理两步法成功制备了系列ZnO/In₂O₃复合空心球. X射线衍射谱(XRD)表明, 经500 ℃退火制得的ZnO/In₂O₃复合空心球中ZnO以非晶态存在, 但是随着退火温度的提高, 其逐渐转变为纤锌矿结构. 场发射扫描电子显微镜(FE-SEM)和透射显微镜(TEM)结果表明, ZnO/In₂O₃复合材料具有空心球结构, 复合纳米颗粒之间结合紧密. 将ZnO/In₂O₃复合空心球组装成薄膜光电极, 研究了其光电催化降解葡萄糖的性能. 结果表明, 700 ℃退火处理的ZnO/In₂O₃复合空心球薄膜电极可产生最高的光致电流密度. 通过光致发光光谱(PL)发现, 与ZnO或In₂O₃空心球相比, ZnO/In₂O₃复合空心球的发光强度猝灭效果明显. 这是由于复合材料中晶界处产生的p-n结电场, 降低了光生电子-空穴对的复合几率, 从而使更多的光生电子可迁移到电极表面.