Synthesis of Ce-doped GN/ZnO architectures with enhanced photocatalytic activity

The novel flower-like GN/ZnO architectures composed of curved cone are synthesized with hydrothermal method at 120?°C for 4?h. The GN/ZnO composite was doped with GN during preparation, the photocatalytic activity of GN/ZnO was evaluated by photodegradation of Rhodamine B (RhB) under simulated visible light. The results showed that the photocatalytic activity of α-CNTs/SnO₂ for degradation of RhB was up to 90% within 50?min, which was much higher than that of pure compound. It was significantly found that the introduction of GN, which may suppressed the recombination of photogenerated electron-hole pairs on the interface of SnO₂, leading to enhanced photocatalytic activity.     

Effect of solution concentration on surface morphology and photocatalytic activity of ZnO thin films synthesized by hydrothermal methods

ZnO thin films were synthesized via hydrothermal method on silicon substrate at various solution concentrations. The thin films were characterized by X-ray diffraction, field-emission scanning electron microscope and UV–Vis spectrophotometer. The results show that the thin films are polycrystalline with wurtzite hexagonal structure. The T _c values of (101) surface of the thin film increase from 0.929 to 1.840 at first, and then decrease to 0.779 with increasing solution concentration. The preferential orientation along the (101) crystal surface can be controlled by changing the solution concentration. Solution concentration has a significant effect on surface morphology of the thin films. The optical band gap of the thin films decreases, when the solution concentration of zinc nitrate hexahydrate increases from 0.01 to 0.06 mol/L and then increases when the solution concentration of zinc nitrate hexahydrate further increases to 0.08 mol/L. Photocatalytic activity of the thin films on degradation of methyl orange under UV light irradiation was studied in detail. The ZnO thin film with many cracks prepared from 0.01 mol/L shows the higher photocatalytic activity but the tower-like ZnO thin film prepared from 0.08 mol/L reveals the lower photocatalytic activity. Therefore, the photocatalytic activity of the thin films are mainly relate to surface morphology and crystallographic orientation.     

The effect of sputtering gas pressure on structure and photocatalytic properties of nanostructured titanium oxide self-cleaning thin film

Titanium oxide thin films were deposited by DC reactive magnetron sputtering on ZnO (80 nm thickness)/soda-lime glass and SiO₂ substrates at different gas pressures. The post annealing on the deposited films was performed at 400 °C in air atmosphere. The results of X-ray diffraction (XRD) showed that the films had anatase phase after annealing at 400 °C. The structure and morphology of deposited layers were evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface grain size and roughness of TiO₂ thin films after annealing were around 10-15 nm and 2-8 nm, respectively. The optical transmittance of the films was measured using ultraviolet-visible light (UV-vis) spectrophotometer and photocatalytic activities of the samples were evaluated by the degradation of Methylene Blue (MB) dye. Using ZnO thin film as buffer layer, the photocatalytic properties of TiO₂ films were improved.     

多晶纳米ZnO薄膜的溶胶-凝胶法制备及光催化性能研究

在石英玻璃衬底上用溶胶-凝胶法制备了纳米级的多晶ZnO薄膜,通过XRD、AFM和UV-Vis吸收光谱对薄膜进行了表征;以苯酚作为被降解的物质,研究了退火温度、降解温度、苯酚溶液的初始浓度和空气流量对ZnO薄膜光催化降解苯酚性能的影响,以及其光催化活性的失活与恢复.实验结果证明,溶胶-凝胶法制备的纳米级ZnO薄膜光催化效果显著,并且可以再生.     

Fabrication and photocatalytic property of ZnO nanorod arrays on Cu2O thin film

ZnO nanorod arrays were fabricated on Cu₂O thin film by a simple low-temperature liquid-phase-deposition method. The samples were characterized by X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FESEM). The UV-Vis spectroscopy showed that the obtained sample was able to absorb a large part of visible light (up to 650 nm). Their photocatalytic activities were investigated by degradation of dye methylene blue (MB) under UV-Vis and visible light irradiation. It was found that the photocatalytic activity of the ZnO/Cu₂O NRs was higher than the ZnO/ZnO NRs under UV-Vis light. In a word, Cu₂O played an important role in enhancing the photocatalytic activity of the ZnO/Cu₂O NRs.     

Photodegradation pathway of rhodamine B with novel Au nanorods @ ZnO microspheres driven by visible light irradiation

A series of Au–ZnO photocatalysts were successfully synthesized from ZnO microspheres impregnated with Au nanorods by the seed-mediated method, and their photocatalytic activity of degradation of rhodamine B (RhB) was investigated. The nanocomposite catalyst exhibited high photocatalytic activity and degraded 92% of RhB solution under visible light irradiation in 330 min. The enhancement of photocatalytic effects was mainly ascribed to the surface plasmon resonance effect of Au nanorods; therefore, Au–ZnO spheres can absorb resonant photons and transfer the electron to the conduction band (CB) of ZnO leading to the separation of electrons and holes under visible light. Meanwhile, the photocatalytic performance was beneficial from the flower-like porous structure of ZnO, which enhances adsorption of the dye molecules and dissolved oxygen on the catalyst surface and facilitates the electron/hole transfer. Furthermore, the degradation pathway was proposed on the basis of the intermediates during the photodegradation process using liquid chromatography analysis coupled with mass spectroscopy (LC–MS). The degradation mechanism of pollutant is ascribed to the superoxide radicals (^·O^2?), which is the main oxidative species for the N-deethylated degradation of RhB. Moreover, the Au–ZnO photocatalysts demonstrated excellent photostability after five cycles. This work provides a facile and effective approach for removal of organic dyes under visible light and thus can be potentially used in the environmental purification.     

Porous photocatalytically active ZnO films obtained from ethylcellulose modified solutions by spray pyrolysis

Nanocrystalline porous ZnO films are deposited onto alumina foil substrates by polymer-modified spray pyrolysis of zinc nitrate and zinc acetate solutions. The dependence of the concentration of added ethylcellulose and the type of zinc precursor on both the photocatalytic properties and films morphologies is investigated. It is established that the addition of ethylcellulose as a modifier in the spray solution leads to the formation of a porous structure with crystallites sizes about 15 nm, when zinc acetate is used as precursor. These films show better photocatalytic activity for degradation of Malachite Green (MG) dye than the films obtained from zinc nitrate modified solution. The zinc nitrate films exhibit weaker activity for degradation of MG regardless of their smaller crystallite size (8–12 nm). This can be explained with their lower porosity than that of polymer-modified zinc acetate films. It is established that 450 °C is the limit temperature of treatment for the preparation of ZnO films with good photocatalytic activities. This photocatalytic activity in films shows a drop in the comparison to the films treated at lower temperature, due to decreasing of the pore number and deterioration of the surface morphology.     

Study of Nd-doping effect and mechanical cracking on photoreactivity of TiO2 thin films

Pure and Nd-doped TiO₂ thin films were fabricated by reactive d.c. magnetron sputtering at low-temperature from a pure Ti target. The structure of films was analyzed by X-ray diffraction (XRD). In order to study the Nd-doping effect on TiO₂ photocatalytic activity, some films were deposited on microscope glass substrates under a constant total sputtering pressure and using different Nd-doping concentrations. The effect of different Nd-dopant concentrations and its influence on the photocatalytic efficiency has been explored by measuring the photodegradation of rhodamine-B (RhB) aqueous solution under radiation of UV light. It is principally that for comparison between heat treatment and doping process on TiO₂ photocatalytic efficiency (important under the point of view of energy costs related with industrial sputtering techniques), crystalline TiO₂ films were also produced by thermal annealing. It was found that comparing with annealed pure TiO₂ films, Nd-doping do not improve the photocatalytic activity. At the same time, it was observed that there seems to exist a dopant concentration band for optimal photoreactivity. In order to study the effect of the film mechanical strength on photocatalytic activity, fragmentation tensile tests were also done on TiO₂/PET (polyethylene terephthalate) substrates at increasing applied strains. It was found that increasing the magnitude of the applied tensile strain, pure TiO₂ becomes more photocatalytic efficient.     

Fabrication and characterization of nano TiO2 thin films at low temperature

Anatase TiO₂ thin films were successfully prepared on glass slide substrates via a sol–gel method from refluxed sol (RS) containing anatase TiO₂ crystals at low temperature of 100 °C. The influences of various refluxing time on crystallinity, morphology and size of the RS sol and dried TiO₂ films particles were discussed. These samples were characterized by infrared absorption spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission-scanning electron microscopy (FE-SEM) and UV–vis absorption spectroscopy (UV–vis). The photocatalytic activities of the TiO₂ thin films were assessed by the degradation of methyl orange in aqueous solution. The results indicated that titania films thus obtained were transparent and their maximal light transmittance exceeded 80% under visible light region. The TiO₂ thin films prepared from RS-6 sol showed the highest photocatalytic activity, when the calcination temperature is higher than 300 °C. The degradation of methyl orange of RS-6 thin films reached 99% after irradiated for 120 min, the results suggested that the TiO₂ thin films prepared from RS sol exhibited high photoactivities.     

热处理对Ag-ZnO异质结构光催化性能的影响

用溶胶-凝胶法制备纯ZnO和Ag修饰ZnO复合光催化剂,并分别对其进行了400℃、450℃、500℃保温2 h的热处理。使用XRD、SEM、TEM、XPS、PL、BET等手段对其进行了表征。结果表明,纯ZnO和Ag修饰ZnO均为六方纤锌矿晶型,Ag颗粒沉积在ZnO表面形成了Ag-ZnO异质结构。以罗丹明B为目标污染物研究了样品的光催化活性。结果表明,热处理温度对纯ZnO的光催化性能的影响较大,在450℃热处理后光催化效果最佳;热处理温度对Ag修饰ZnO的光催化性能没有显著的影响;Ag修饰ZnO比纯ZnO的光催化活性均有所提高,因为Ag修饰提高了ZnO表面羟基的含量并抑制了光生电子与空穴的复合。在500℃热处理后Ag修饰ZnO对罗丹明B的60 min降解率达到98%,其反应速率常数为0.063 min^-1。     

Photocatalytic activity studies of TiO2 thin films prepared by r.f. magnetron reactive sputtering

A series of transparent titanium dioxide thin films have been obtained on microscope glass slides by means of r.f. magnetron reactive sputtering using Ar and O₂ mixed gases. The photocatalytic activity of the TiO₂ thin films was evaluated by the degradation of rhodamine B dye wastewater. The influences of substrate temperatures and total sputtering pressures on the photocatalytic activity of the TiO₂ films were investigated. It was observed that substrate temperature had little influences on the photocatalytic activity, but the photocatalytic activity of the TiO₂ thin films was improved by decreasing the total sputtering pressure.     

Visible light photocatalytic degradation of paraoxon and parathion pesticides on carbon-doped TiO<Subscript>2</Subscript> nanorod thin films

In the present work the nanostructured carbon-doped TiO₂ thin films with nanorod morphology were deposited on glass substrate by a combination of ultrasonic and chemical vapor deposition methods, and for the first time were applied for the photocatalytic degradation of paraoxon and parathion organophosphorus pesticides under visible light irradiation. X-ray Diffraction, X-ray photoelectron spectroscopy, diffuse reflectance spectroscopy, and scanning electron microscopy techniques were used for characterization of the prepared thin films. Obtained results show that presence of carbon element and also special nanorod morphology of the thin films remarkably improve the optical properties of TiO₂ in visible light region and results in the good visible light photocatalytic activity of the thin films for degradation of the pesticides. The photonic efficiencies of the prepared thin films were also examined based on the international ISO-10678:2010 standard protocol for photocatalytic degradation of methylene blue under UV light irradiation. The results show a maximum photonic efficiency of 0.0312% for the carbon-doped TiO₂ thin film with 570 nm thickness, which compared to a reference standard TiO₂ films indicates a 30% improvement in photonic efficiency.     

Construction of CoTiO3/BiOI p-n heterojunction with nanosheets-on microrods structure for enhanced photocatalytic degradation of organic pollutions

Herein, a novel CoTiO₃/BiOI (CTOB) p-n heterojunction with nanosheets-on microrods structure were prepared via a simple coprecipitation method for the first time. The catalysts were carefully characterized by various instruments. The CTOB heterostructures display improved photocatalytic performance towards RhB degradation. Among CTOB composites, CTOB-15 exhibits the optimal photocatalytic performance. Moreover, CTOB-15 also shows enhanced photocatalytic activity for MO and TC degradation compared to bare catalysts. The degradation rate constants for RhB and MO by CTOB-15 heterostructure are ca 1.6 and 1.4-fold higher than bare BiOI. The improved photocatalytic performance could be on account of the efficient separation of photoinduced carriers as well as enhanced light absorbance. Trapping experiments indicates that holes (h⁺) and superoxide anion radical (O₂^–) play a significant role in the removal of RhB by CTOB composites. The excellent photocatalytic activity and stability make it a promising photocatalyst in environmental remediation.     

Growth and characterization of flower-like Ag/ZnO heterostructure composites with enhanced photocatalytic performance

Flower-like Ag/ZnO heterostructure composites were prepared through a solvothermal method without surfactants or templates. The products were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and photoluminescence (PL) spectroscopy. Results demonstrate that flower-like Ag/ZnO heterostructure composites were composed of wurtzite ZnO flowers coated by face-center-cubic Ag nanoparticles. The growth process of flower-like ZnO crystals was investigated, and a possible growth mechanism was proposed. The photocatalytic activity of the as-prepared flower-like Ag/ZnO samples, pure ZnO samples, and commercial TiO₂ (Degussa, P-25) was tested with the photocatalytic degradation of methylene blue. Results show that the Ag/ZnO heterostructures were superior in photocatalytic activity to the pure ZnO samples and the commercial TiO₂ (Degussa, P-25), but the mixture of Ag (0.1 wt%) particles and ZnO flowers did not, which implies that the heterostructure promoted the separation of photogenerated electron–hole pairs, enhancing the photocatalytic activity. That was primarily verified by the PL results.     

Comparative study of the structural, optical and photocatalytic properties of semiconductor metal oxides toward degradation of methylene blue

Indium oxide (In₂O₃), zinc oxide (ZnO), stannic oxide (SnO₂), and titanium dioxide (TiO₂) thin films were prepared on glass substrates using electron beam evaporation. The samples characterized by UV-vis spectroscopy, diffraction ray-X and scanning electron microscopy techniques. The photocatalytic degradation of methylene blue in an aqueous solution, as a model compound, was investigated using different metal oxides in an attempt to compare the decomposition reaction rate. The progress of degradation was monitored using UV-vis spectrophotometry. The effects of various experimental parameters such as initial concentration of methylene blue (5-10 mg/l), pH of the solution (2-8), annealing temperature (250-550 °C), and catalyst nature and its microstructure were systematically studied in order to achieve maximum degradation efficiency. The results obtained were fitted with the Langmuir-Hinshelwood model to study the degradation kinetics and discussed in detail. Nearly complete degradation was obtained at optimal operational parameters including the higher annealing temperature of thin film and the increase in MB solution pH. The degradation with In₂O₃ was more efficient than with SnO₂, ZnO and TiO₂ films.     

Fabrication of novel ZnO/MnWO4 nanocomposites with p-n heterojunction: Visible-light-induced photocatalysts with substantially improved activity and durability

We report, for the first time, binary ZnO/MnWO₄ nanocomposites with p-n heterojunction fabricated by a simple ultrasonic-calcination route. The phase structure, morphology, and optical along with textural properties were comprehensively characterized. The photocatalytic performance was studied via degradations of rhodamine B, methyl blue and methyl orange (RhB, MB, MO), and fuchsine pollutants under visible-light illumination. The ZnO/MnWO₄ nanocomposites exhibited better photocatalytic performance than their single components and the nanocomposite with 30?wt% MnWO₄ showed the highest activity. Photocatalytic performance of this nanocomposite is 22.5, 17.7, 26.8, and 23.9 times higher than that of the ZnO sample in degradations of RhB, MB, MO, and fuchsine dyes, respectively. The improved photocatalytic performance was ascribed to the formation of p-n heterojunction between ZnO and MnWO₄ with high charge separation efficiency as well as strong visible-light absorption ability. The possible mechanism for the improved photocatalytic performance was proposed. This study revealed that the novel ZnO/MnWO₄p-n heterojunction can act as a promising visible-light-active photocatalyst for environmental applications.     

TiO2 thin films for dyes photodegradation

The aim of the present study is to investigate the influence of the TiO₂ specific surface (powder, film) on the photocatalytic degradation of methyl orange. Porous TiO₂ films were deposited on transparent conducting oxide substrates by spray pyrolysis deposition. The films were characterized by X-ray diffraction (XRD), Scanning Electronic Microscopy, and the UV-Vis spectroscopy. The XRD spectra of nanoporous TiO₂ films revealed an anatase, crystalline structure that is known as the most suitable structure in photocatalysis. The average thickness of the films was 260 nm and the measured band gap is 3.44 eV. The influence of the operational parameters (dye concentration, contact time) on the degradation rate of the dye on TiO₂ was examined. There were calculated the kinetic parameters and the process efficiency. Using thin films of TiO₂ is technologically recommended but raises problems due to lowering the amount of catalyst available for the dye degradation.     

Room temperature magneto-optics of nanostructured ZnO:Mn thin film grown by spray pyrolysis

Undoped ZnO and ZnO:Mn thin films with different amounts of Mn concentration (5, 10 and 15 mol%) were grown on glass substrates by spray pyrolysis technique. X-ray diffraction patterns showed that the undoped ZnO thin film exhibited wurtzite structure preferably oriented in c-axis direction and the doped samples were polycrystalline. The surface morphology and topography of the films were investigated by SEM and STM micrographs. Magneto-optical characterizations of the samples were carried out by using Kerr and Faraday effects spectroscopy. Kerr effect studies showed that all Mn doped thin films exhibited the room temperature ferromagnetism. The magnetic ordering observed in the film with 5 mol% Mn concentration was stronger comparing to the other doped samples. The carrier densities of the samples were calculated by using a method based on the Faraday rotation. A clear relation between sp-d coupling and strength of magnetic ordering with carrier density was observed.     

溶胶-凝胶法制备ZnO薄膜及其光催化性能

用溶胶-凝胶法在普通玻璃表面制备了薄膜型ZnO光催化剂,通过XRD、Ab2d、UV-VIS等测试技术对ZnO薄膜进行了表征;以偶氮胭脂红为降解物,考察了薄膜退火温度、镀膜层数、溶液初始质量浓度和反应体系初始pH值对ZnO薄膜光催化性能的影响,并进行了相关机理的探讨．研究表明：溶胶-凝胶法制备的ZnO薄膜呈透明状,薄膜表面均匀分布着球形ZnO晶粒;随着退火温度的升高,ZnO晶粒在17～30mm范围内逐渐增大．光催化实验中ZnO薄膜光催化降解偶氮胭脂红的最佳工艺条件是：退火温度为300℃,镀膜层数为5层,溶液初始pH值为8～9．     

Comparison of zinc oxide nanoparticles and its nano-crystalline particles on the photocatalytic degradation of methylene blue

Comparison of ZnO nanoparticles and its nano-crystalline particles on the photocatalytic degradation of methylene blue was investigated. ZnO nanoparticles and its nano-crystalline particles were synthesized from sprayed droplets of an aqueous zinc nitrate solution by flame spray pyrolysis and spray pyrolysis assisted with an electrical furnace, respectively. ZnO nanoparticles of 20 nm in average diameter and ZnO nano-crystalline particles of 20 nm in the grain size were prepared to compare the photocatalytic activity. The photocatalytic activity of those ZnO particles was evaluated by measuring the degradation of methylene blue in water under the illumination of ultraviolet rays. Effect of the particle morphology, initial concentration of methylene blue, and photocatalyst loading on the degradation of the methylene blue was investigated under the illumination of ultraviolet rays. The photocatalytic degradation capacity of the ZnO nanoparticles was higher than that of the ZnO nano-crystalline particles. The efficiency of photocatalytic degradation of methylene blue increased with increase in photocatalyst loading and decrease in initial concentration regardless of particle morphology.