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.     

Preparation of electrospun heterostructured hollow SnO<Subscript>2</Subscript>/CuO nanofibers and their enhanced visible light photocatalytic performance

Heterostructured SnO₂/CuO nanofibers with a hollow morphology were successfully fabricated by a one-step electrospinning method. The electrospun nanofibers were transformed into hollow nanostructures in the presence of camphene after a calcination process, and the obtained samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflection spectroscopy (DRS), photoluminescence spectra (PL), and photodegradation measurements. The scanning electron microscopy (SEM) images displayed a rough and hollow structure for the obtained nanofibers. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) identified the molecular composition and chemical interactions of the nanofibers. Photoluminescent (PL) measurements indicated that a recombination of the photoinduced electrons and holes was further inhibited due to the hollow nanostructure. Furthermore, the photodegradation of methylene blue suggested that the heterostructured SnO₂/CuO hollow nanofibers possessed higher charge separation and photodegradation abilities than those of the other samples under visible light irradiation. This work can be potentially applied to the fabrication of other inorganic oxide photocatalysts with enhanced photodegradation activity in the field of environmental remediation.     

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.     

Synthesis,Characterization and Photocatalytic Activity of Mg‐Impregnated ZnO–SnO2 Coupled Nanoparticles

ZnO–SnO₂ nanoparticles were prepared by coprecipitation method; then Mg, with different molar ratios and calcination temperatures, was loaded on the coupled nanoparticles by impregnation method. The synthesized nanoparticles were characterized by X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X‐ray spectroscopy (EDX), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), and Brunauer–Emmett–Teller (BET) techniques. Based on XRD results, the ZnO–SnO₂ and Mg/ZnO–SnO₂ nanoparticles were made of ZnO and SnO₂ nanocrystallites. According to DRS spectra, the band gap energy value of 3.13 and 3.18 eV were obtained for ZnO–SnO₂ and Mg/ZnO–SnO₂ nanoparticles, respectively. BET analysis revealed a Type III isotherm with a microporous structure and surface area of 32.051 and 49.065 m² g^?1 for ZnO–SnO₂ and Mg/ZnO–SnO₂, respectively. Also, the spherical shape of nanocrystallites was deduced from TEM and FESEM images. The photocatalytic performance of pure ZnO–SnO₂ and Mg/ZnO–SnO₂ was analyzed in the photocatalytic removal of methyl orange (MO). The results indicated that Mg/ZnO–SnO₂ exhibited superior photocatalytic activity to bare ZnO–SnO₂ photocatalyst due to high surface area, increased MO adsorption and larger band gap energy. Maximum photocatalytic activity of Mg/ZnO–SnO₂ nanoparticles was obtained with 0.8 mol% Mg and calcination temperature of 350°C.     

Tuning physical surface properties of tin dioxide nanopowders using zinc oxide as template

With a view to energetic and (opto)electronic applications, tin (IV) oxide (SnO₂) nanoparticles have been successfully prepared at the nanoscale by a templating approach based on the use of zinc (II) oxide (ZnO) as template. The procedure consisted in preparing a mixture of tin precursor and template, subsequently calcined at 650 °C under air to lead to the formation of a SnO₂/ZnO composite material. Finally, the material was washed with an alkali solution to remove the template. The template/tin precursor mass ratio was varied in order to tailor the tin (IV) oxide material, especially with a view to main particle size. The resulting SnO₂ nanomaterials were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, nitrogen adsorption and electron microscopy. The tin (IV) oxide nanomaterial exhibited enhanced textural and physical surface properties (particle size, surface area, pore size) correlated to an increasing template/tin precursor mass ratio. For instance, from optimized experimental conditions, the specific surface area and pore volume were heightened twofold, reaching values of 49 m²/g and 0.32 cm³/g, respectively.     

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.     

Enhanced photocatalytic activities of ZnO thin films: a comparative study of hybrid semiconductor nanomaterials

Nanostructure single ZnO, SnO₂, In₂O₃ and composite ZnO/SnO₂, ZnO/In₂O₃ and ZnO/SnO₂/In₂O₃ films were prepared using sol?Cgel method. The obtained composite films were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV?CVis spectroscopy. The photocatalytic activities of composite films were investigated using phenol (P), 2,4-dichlorophenol (2,4-DCP), 4-chlorophenol (4-CP) and 4-aminophenol (4-AP) as a model organic compounds under UV light irradiation. Hybrid semiconductor thin films showed a higher photocatalytic activity than single component ZnO, SnO₂ and In₂O₃ films. The substituted phenols degrade faster than phenol. The ease of degradation of phenols is different for each catalyst and the order of catalytic efficiency is also different for each phenol. The use of multiple components offered a higher control of their properties by varying the composition of the materials and related parameters such as morphology and interface. It was also found that the photocatalytic degradation of phenolic compounds on the composite films and single films followed pseudo-first order kinetics.     

Size-controlled synthesis of SnO2 nanoparticles using reverse microemulsion method

Tin oxide nanoparticles were prepared using an ionic surfactant (sodium dodecyl sulfate) and tin (IV) chloride as an inorganic precursor via the reverse microemulsion method. The size of the nanoparticles is controlled by variation of water-to-surfactant ratio. Eliminating of surfactant in prepared nanoparticles was confirmed by the infrared spectroscopy after sequential calcinations. Transmission electron microscopy, surface area, pore volume, average pore diameter, pore size distribution and X-ray diffraction results were used for evaluation of size distribution, shape and structure of prepared SnO₂ nanoparticles. Transmission electron micrographs confirmed that the obtained materials are spherical nanoparticles. The X-ray diffraction results show the crystalline phases of all samples are SnO₂ with tetragonal structured crystal. In addition, the X-ray diffraction and transmission electron microscopy data showed that the size of SnO₂ nanoparticles decreased with decreasing the water-to-surfactant ratio.     

NiO@ZnO heterostructured nanotubes: coelectrospinning fabrication, characterization, and highly enhanced gas sensing properties

Novel NiO@ZnO heterostructured nanotubes (NTs) were fabricated by the coelectrospinning method, consisting of external hexagonal ZnO shell and internal cubic NiO NTs. They are carefully investigated by scanning electron microscopy, transmission electron microscopy, scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy mapping, X-ray diffraction, and X-ray photoelectron spectroscopy techniques. A reasonable formation mechanism of the hierarchical NiO@ZnO NTs is proposed, which is discussed from the view of degradation temperature of different polymers and the amount of inorganic salts. They were then explored for fabrication of H(2)S gas sensors. The gas sensing test reveals that compared with the pure ZnO, NiO, and the ZnO-NiO mixed gas sensors, hierarchical gas sensor exhibits highly improved sensing performances to dilute hydrogen sulfide (H(2)S) gas. The response of the optimum NiO@ZnO NTs sensor to 50 ppm H(2)S increases as high as 2.7-23.7 times compared to the other sensors, whereas the response and recovery times also become shorter considerably. These enhanced gas sensing properties are closely related to the change of nanostructure and activity of ZnO and NiO nanocrystals as well as combination of homo- and heterointerfaces in the optimum gas sensor, which are confirmed by a series of well-designed experiments.     

微波诱导燃烧法合成类花状ZnO纳米材料及其晶体结构、荧光性质研究

以硝酸锌[Zn(NO3)2.6H2O]和尿素[CO(NH2)2]作前驱体,通过微波诱导燃烧技术可控合成具有不同形貌的ZnO纳米晶体,并用热重分析和差热分析进行了研究。对各种生长条件:微波功率,辐射时间和尿素/Zn2+物质的量的比对ZnO纳米晶体形貌的影响作了分析。结果表明:尿素/Zn2+物质的量的比对ZnO纳米材料的形貌具有显著影响。X衍射图表明合成的ZnO纳米结构呈六角形。傅里叶变换红外光谱图中400~500 cm-1处明显的峰为Zn-O的振动峰。ZnO纳米结构的发光光谱在366 nm的带边发射,因缺陷又由许多可见光发射峰组成。用扫描电子显微镜、透射电子显微镜、选区电子衍射研究了花状ZnO纳米结构的增长机理。本方法仅需几分钟就获得的了ZnO纳米结构。     

Synthesis,characterizations, and electrochemical studies of ZnO/reduced graphene oxide nanohybrids for supercapacitor application

Herein the present article reports the fabrication of ZnO/reduced graphene oxide (ZnG) nanohybrid following a reduction-based process using a non-hazardous material, i.e., ascorbic acid. The morphology, structure, and bonding in the nanohybrid were analyzed using different techniques. Atomic force microscopy and scanning electron microscopy images show spherical particles of ZnO distributed over reduced graphene oxide (rGO). The X-ray diffraction analysis gives calculated values of crystallite size for ZnO as 15.62 nm. The successful incorporation of ZnO nanoparticles into rGO was confirmed using energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses. The electrochemical studies were performed using an electrolyte (0.5 M H₂SO₄). The calculated value of specific capacitance for the nanohybrid was 345 Fg^-1, which was found to be almost double as compared to that of rGO, which is having a value of only 190.5 Fg^-1 at the same scan rate. The nanohybrid also showed excellent capacitance retention after 1,000 cycles.     

Influence of crystal size on the electron–phonon coupling in ZnO nanocrystals investigated by Raman spectroscopy

We have synthesized ZnO nanocrystals of different sizes (25–41 nm) using the sol–gel method and characterized them using different techniques such as: transmission electron microscopy (TEM) and X-ray diffraction (XRD). Raman spectra of different sizes of ZnO nanocrystals were recorded at two excitation wavelengths, 514 and 647 nm, in the spectral range 300–1200 cm⁻¹. The vibrational modes were assigned on the basis of group theory analysis. The influence of mean crystallite size on the strength of the electron–phonon coupling is experimentally estimated by the variation of relative intensities of second order Raman band and the first order Raman band for ZnO nanocrystals of different sizes. We found that the intensity ratio of the 2E₂ and 1E₂ Raman bands decreases almost linearly for both excitation wavelengths with decreasing crystallite size, which reveals that the Fröhlich interaction plays a dominant role in the electron–phonon coupling of the ZnO nanocrystals.     

Tin oxide nanoparticles (NP-SnO2): preparation, characterization and their catalytic application in the Knoevenagel condensation

Tin oxide (SnO₂) nanoparticles were synthesized by modified thermal decomposition process. Taguchi analysis was used and three important synthetic factors, molar concentration ratio of [NaNO₃]/[SnCl₄], temperature and time of calcinations, which affect the size of SnO₂ particles, were studied. The optimal conditions were determined using Taguchi robust design method and nano-sized SnO₂ particles (~2 nm) were obtained. Nanoparticles were characterized by X-ray diffraction, transmission electron microscopy and UV–visible spectroscopy techniques. The results show that tin oxide nanoparticles could be one of the most active and reusable catalysts in the Knoevenagel condensation. Different active methylene group compounds and diverse range of aldehydes were chosen to react in the presence of tin oxide nanoparticles at ambient temperature at solvent-free condition (SFC) with excellent isolated yields.     

Influence of Size and Shape on the Photocatalytic Properties of SnO2 Nanocrystals

Tuning the functional properties of nanocrystals is an important issue in nanoscience. Here, we are able to tune the photocatalytic properties of SnO₂ nanocrystals by controlling their size and shape. A structural analysis was carried out by using X‐ray diffraction (XRD)/Rietveld and transmission electron microscopy (TEM). The results reveal that the number of oxygen‐related defects varies upon changing the size and shape of the nanocrystals, which eventually influences their photocatalytic properties. Time‐resolved spectroscopic studies of the carrier relaxation dynamics of the SnO₂ nanocrystals further confirm that the electron–hole recombination process is controlled by oxygen/defect states, which can be tuned by changing the shape and size of the materials. The degradation of dyes (90 %) in the presence of SnO₂ nanoparticles under UV light is comparable to that (88 %) in the presence of standard TiO₂ Degussa P‐25 (P25) powders. The photocatalytic activity of the nanoparticles is significantly higher than those of nanorods and nanospheres because the effective charge separation in the SnO₂ nanoparticles is controlled by defect states leading to enhanced photocatalytic properties. The size‐ and shape‐dependent photocatalytic properties of SnO₂ nanocrystals make these materials interesting candidates for photocatalytic applications.     

Hierarchical SnO2 with double carbon coating composites as anode materials for lithium ion batteries

Hierarchical SnO₂ with double carbon coating (polypyrrole-derived carbon and reduced graphene oxide in order) composites have been successfully synthesized as anode materials for lithium ion batteries. The composites were characterized and examined by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, cyclic voltammetry, and galvanostatic discharge/charge tests. Such a novel nanostructure can not only provide a high conductivity but also prevent aggregation of SnO₂ nanoparticles, leading to the improvement of the cycling performance. Comparing with pure hierarchical SnO₂ and polypyrrole-derived carbon-coated hierarchical SnO₂, hierarchical SnO₂ with double carbon coating composite exhibits higher lithium storage capacities and better cycling performance, 554.8 mAh g^?1 after 50 cycles at a current density of 250 mA g^?1. In addition, the rate performance of hierarchical SnO₂ with double carbon coating composite is also very well. For all the improved performances, this double carbon coating architecture may provide some references for other electrode materials of lithium ion batteries.     

Highly Sensitive Electrochemiluminescent Insecticide Sensor Based on ZnO Nanocrystals Anchored Nickel Foam for Determination of Imidacloprid in Real Samples

In this work, a novel electrochemiluminescent (ECL) pesticide sensor based on zinc oxide nanocrystals decorated nickel foam is proposed for determination of imidacloprid for the first time. The silica film was used as a morphology‐controlling factor for modification of the electrode with zinc oxide nanocrystals. Zinc oxide was selected as luminescent material due to its cheapness, non‐toxicity, high thermal stability and excellent luminescence properties which truly adhered on the surface of nickel foam. The K₂S₂O₈ was used as strong co‐reactant for this purpose. The silica template plays an important role in controlling the size of ZnO nanocrystals. The Physical morphology of the ZnO/Ni‐foam electrode was performed by electrochemical impedance spectroscopy, Brunauer‐Emmett‐Teller (BET), X‐Ray diffraction analysis, field emission scanning electron microscopy, and energy‐dispersive X‐ray analysis. The ultra‐sensitive electrochemiluminescence method was successfully used for ultra‐trace determination of imidacloprid. The linear dynamic range and low detection limit were obtained 3×10^?14 ?8×10^?8 M and 4.4×10^?15 M, respectively. Also, the relative standard deviation for 15 repetitive optical signals was calculated 1.09 %.The present ECL sensor exhibited superior performance toward the accurate determination of imidacloprid with good reproducibility and stability.     

不同载体对负载型氧化钨催化剂在己二酸合成反应中的结构及性能影响

以SBA-15、六角介孔二氧化硅（HMS）和SnO₂为载体,通过浸渍法合成了含钨负载型催化剂,并考察了三种催化剂在环氧环己烷选择氧化制备己二酸反应中的催化性能. 通过X射线衍射（XRD）,透射电镜/场发射透射电镜（TEM/FETEM）,紫外-可见漫反射光谱（UV-Vis DRS）,拉曼（Raman）光谱,X射线光电子能谱（XPS）以及傅里叶变换红外（FTIR）光谱等手段对各种催化剂的结构进行表征. 结果表明,载体与催化剂的性能有密切的关系. 以SnO₂为载体的WO₃/SnO₂催化剂活性最高,其次是WO₃/HMS催化剂,WO₃/SBA-15 催化剂的活性最差.XRD 分析显示WO₃/SnO₂催化剂中氧化钨物种的晶化程度最低,TEM 和XPS 结果表明氧化钨物种在WO₃/SnO₂催化剂表面高度分散并且粒径尺寸很小（约2 nm）,UV-Vis DRS结果表明在WO₃/SnO₂催化剂中存在孤立[WO₄]四面体和低聚态的钨物种,这些物种的存在可能是WO₃/SnO₂催化剂具有高活性的主要原因. 此外,WO₃/SnO₂催化剂可以重复使用多次,6 次反应后己二酸（AA）得率仍然保持在80%以上,说明氧化钨物种与SnO₂载体间存在强烈的相互作用,从而提高了催化剂的稳定性.     

Synthesis of tin oxide nanoparticles by sol–gel process: effect of solvents on the optical properties

Tin oxide (SnO₂) nanoparticles were synthesized by the reaction of SnCl₄·5H₂O in methanol, ethanol and water via sol–gel method. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared, Scanning electron microscopy and Transmission electron microscopy. The optical properties of the as-prepared samples were investigated. The XRD analysis showed well crystallized tetragonal SnO₂ can be obtained and the crystal sizes were 3.9, 4.5 and 5 nm for the sample calcined at 400 °C for 2 h. It was found that solvents played important roles in the particle size effect of nanocrystalline SnO₂.     

Hierarchically Structure SnO2/ZnO Nanocomposites: Preparation,Growth Mechanism and Gas Sensing Property

SnO₂/ZnO nanocomposite was synthesized from mixed ethanol and water systems and the ethanol-sensing properties of sensors based on SnO₂/ZnO were investigated. The structure and morphology of the products was characterized by x-ray diffraction (XRD) and a field emission scanning electron microscope (FE-SEM). The results showed that the diameter of the liked pine needle SnO₂ was about 40 nm with a length about 300 nm, which are uniformly dispersed on the surface of the ZnO nanosheets. The growth process of the SnO₂/ZnO nanocomposite was discussed. The results of gas sensing properties of SnO₂/ZnO nanocomposite sensor showed high and quick response to ethanol vapor at 5.0 v. This sensor showed the advantages of high selectivity, strong stability, and prompt response/recovery characteristics in detecting ethanol vapor at 5.0 v.     

Gas‐Sensing Properties of Needle‐Shaped Ni‐Doped SnO2 Nanocrystals Prepared by a Simple Sol–Gel Chemical Precipitation Method

The preparation of needle‐shaped SnO₂ nanocrystals doped with different concentration of nickel by a simple sol–gel chemical precipitation method is demonstrated. By varying the Ni‐dopant concentration from 0 to 5 wt %, the phase purity and morphology of the SnO₂ nanocrystals are significantly changed. Powder XRD results reveal that the SnO₂ doped with a nickel concentration of up to 1 wt % shows a single crystalline tetragonal rutile phase, whereas a slight change in the crystallite structure is observed for samples with nickel above 1 wt %. High resolution scanning electron microscopy (HRSEM) results reveal the change in morphology of the materials from spherical, for SnO₂, to very fine needle‐like nanocrystals, for Ni‐doped SnO₂, annealed at different temperatures. The gas sensing properties of the SnO₂ nanocrystals are significantly enhanced after the nickel doping.