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.     

Determination of phenol in the presence of its principal degradation products in water during a TiO2-photocatalytic degradation process by three-dimensional excitation-emission matrix fluorescence and parallel factor analysis

This paper describes a simple and rapid way of monitoring a photocatalytic degradation of phenol in aqueous suspensions of TiO₂. A three-way analytical methodology based on fluorescence excitation-emission matrix (EEM) and parallel factor analysis (PARAFAC) was developed to resolve the species present in the reaction mixture and quantify the concentration of phenol and its principal degradation products throughout the degradation. Parameters such as core consistency, fit% and correlation coefficients between recovered and pure spectra were used to determine the appropriate number of factors for the PARAFAC model. The accuracy of the model was evaluated by the root mean square error of prediction (RMSEP). Using a four-factors PARAFAC model, phenol, hydroquinone, resorcinol and catechol, were satisfactorily determined. The proposed method is an interesting alternative to the traditional techniques normally used for monitoring degradation reactions.     

煅烧温度对花朵状钨酸铋光催化活性的影响

钨酸铋在水相体系中能光催化降解有机污染物,而对于钨酸铋光催化活性影响因素的研究非常少.本文研究了煅烧温度对花朵状钨酸铋光催化活性的影响.以钨酸钠和硝酸铋为原料,在160°C下水热反应20 h,合成催化剂,并经不同温度煅烧3 h.用X射线衍射(XRD)、拉曼(Raman)光谱、紫外-可见漫反射吸收光谱(UVVis DRS)和荧光(PL)光谱表征样品.结果表明,这些样品具有十分相似的相组成和电子结构.然而,对于水中苯酚的降解,钨酸铋的光催化活性显示出了很大的差异.钨酸铋的光催化活性随着煅烧温度的升高,先上升后下降,最优煅烧温度为350°C,并且不受样品比表面积大小的影响.这些样品的活性差异主要归结于钨酸铋的结晶度、吸光性和表面缺陷对其光生载流子分离效率的综合影响.     

Kinetic studies of direct blue photodegradation over flower-like TiO<Subscript>2</Subscript>

The kinetics of photocatalytic oxidation reaction for direct blue solution was studied by using flower-like TiO₂ under the irradiation of ultraviolet (UV) light. A series of possible affecting factors were studied, including pH value, the additive amount of light catalyst, H₂O₂ and with or without Ag modification. The kinetics of photocatalytic degradation under UV was found following a pseudo-second-order reaction kinetic model with high regression coefficients (R ²). It has been demonstrated that the initial concentration and its related factors have influenced the photocatalytic degradation efficiency and corresponding kinetic parameters. Also, the kinetic parameter k is increasing with the degradation efficiency.     

Enhanced photocatalytic activity and stability of AgBr/BiOBr/graphene heterojunction for phenol degradation under visible light

In this work, we have reported synthesis of AgBr/BiOBr photocatalyst supported on graphene (Gr) using facile precipitation method. AgBr/BiOBr/Gr was characterized using various spectral techniques like FESEM, TEM, XRD, FTIR, XPS, Raman and PL analyses. AgBr/BiOBr/Gr had improved visible light absorption. PL studies indicated the reduction in recombination of photogenerated electron hole pair of AGBr/BiOBr/Gr. AFM analysis confirmed the thickness of AGBr/BiOBr/Gr was less than 8.0 nm. The higher dispersibility of photocatalyst was ascertained by Tyndall effect. AgBr/BiOBr/Gr photocatalyst was effectively used for the photodegradation of phenol from simulated water. The phenol degradation process was remarkably influenced by adsorption process. The concurrent adsorption and photocatalytic was effective for degradation of phenol. The phenol was completely mineralized into CO₂ and H₂O in 6 h. The degradation process followed pseudo first order kinetics. The results confirmed that integration of AgBr/BiOBr with graphene caused an increase in photocatalytic activity due to reduced recombination of photogenerated electron hole pair and electron sink behavior of graphene for photogenerated electrons of BiOBr. AgBr/BiOBr/Gr photocatalyst displayed significant stability and recyclability for ten catalytic cycles.     

Characterization of Titanium Dioxide Doped with Nitrogen and Sulfur and its Photocatalytic Appraisal for Degradation of Phenol and Methylene Blue

The degradation of organic dyes in the presence of modified TiO₂ is still under intensive investigation. We report here an evaluation of the photocatalytic activity of nitrogen‐ (N‐) and sulfur‐ (S‐) doped TiO₂ for the degradation of phenol and methylene blue (MB). N‐doped TiO₂ (N–TiO₂), S‐doped TiO₂ (S–TiO₂), and N–S‐doped TiO₂ (N–S–TiO₂) were prepared using the sol–gel method. The photocatalytic activity was evaluated in a batch reactor using phenol and MB as models of pollutants. In addition, this investigation was performed using a household lamp as the visible light source. Properties of the synthesized materials in terms of Brunauer–Emmett–Teller (BET) surface analysis, field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and photocatalytic ability were examined. Our study shows that N–S–TiO₂ exhibits better photocatalytic degradation ability for all the considered dyes compared to the other doped TiO₂ materials. In conclusion, we have successfully prepared and evaluated the photocatalytic activity of N‐ and S‐doped TiO₂ for the degradation of phenol and MB using an ordinary household lamp.     

Physical properties of nano-titania hollow fibers and their photocatalytic activity in the decomposition of phenol

A series of nano-titania (TiO₂) photocatalytic materials with a hollow fiber structure were successfully prepared using tetra-n-butyl titanate (Ti(OC₄H₉)₄) as precursor and cotton fiber as the template. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and N₂ adsorption-desorption measurements were employed to characterize the morphology, crystal structure, and surface structure of the samples. The photocatalytic activities of the samples were studied by phenol photodegradation in water under UV irradiation. The effect of calcination temperature, photocatalyst dosage, initial concentration of phenol and irradiation time on the photodegradation of phenol was studied. Results showed that the TiO₂ fiber materials have hollow structures, indicating that these materials had a large specific surface area. The fiber structure material showed better photocatalytic properties for the degradation of phenol than pure TiO₂ under UV light, and the sample calcined at 500°C exhibited the highest phenol photodegradation efficiency. In addition, the possibility of cyclic usage of the photocatalyst was also confirmed, the photocatalytic activity of TiO₂ fiber remained ca. 90% of photocatalytic activity of the fresh sample after being used four times. Moreover, TiO₂ fiber was easily recovered by centrifugal separation from water.     

Porous F-doped BiVO4: Synthesis and enhanced photocatalytic performance for the degradation of phenol under visible-light illumination

Fluoride-doped BiVO₄ with the F/Bi molar ratios of 0, 0.09, 0.13, and 0.29 (denoted as BiVO₄–F0, BiVO₄–F0.09, BiVO₄–F0.13, and BiVO₄–F0.29, respectively) were synthesized using the hydrothermal strategy with the hydrothermally derived BiVO₄ as the precursor and NH₄F as the fluoride source. Physicochemical properties of the materials were characterized by means of a number of analytical techniques. Photocatalytic activities of the fluoride-doped BiVO₄ samples were evaluated for the degradation of phenol under visible-light irradiation. It is shown that compared to the undoped BiVO₄–F0 sample, the fluoride-doped BiVO₄ samples retained the monoclinic structure, but possessed higher surface areas and oxygen adspecies concentration, better light-absorbing performance, and lower bandgap energies. Among the four samples, the porous spherical BiVO₄–F0.29 sample exhibited the best photocatalytic activity for the degradation of phenol in the presence of a small amount of H₂O₂ under visible-light illumination. It is concluded that the higher surface area and oxygen adspecies concentration, stronger optical absorbance performance, and lower bandgap energy were responsible for the excellent photocatalytic performance of BiVO₄–F0.29 for the photocatalytic degradation of phenol.     

Enhanced photocatalytic performance of magnetite/TS-1 thin film for phenol degradation

Photocatalytic degradation method is an emerging technique for complete removal of pollutants. Several semiconductor photocatalysts are reported as photocatalysts for industrial wastewater treatment in environmental applications. In this study Magnetite/TS-1 composite materials was used for photocatalytic degradation of phenol. Magnetite nanoparticles (MNP) (10 wt%) were dispersed with nanocrystalline Titanium Silicate-1 zeolite (TS-1). The Magnetite/TS-1 composite materials were characterized with various techniques. The structural analysis reveals the presence of MNP and zeolite-MFI phases in Magnetite/TS-1 composite materials. The average particles size of the magnetite nanoparticles is less than 5 nm and that of the composite nanoparticles are in the range of about 90 nm with micropore volume 0.110 cm³/g and the external surface area 120 m²/g. The photocatalytic experiments were carried out in a thin film flow photoreactor under UV radiation. The results showed that Magnetite/TS-1 composite materials exhibited improved activity for the degradation of phenol compared to TS-1. Preliminary studies proves that aeration is necessary for the photocatalytic reaction. The reaction parameters such as flow rate, pH and phenol concentration are optimized as 8 ml/min, pH 7.0 and 75 mg/L respectively. To understand the active species involved in the degradation of phenol radical scavengers such as NaI, benzoquinone and isopropyl alcohol are used to trap hole (h⁺), superoxide anion radical and hydroxyl radical (OH), respectively. From the obtained results it is envisaged that hydroxyl radicals are predominantly involved in complete oxidation of phenol. The extent of degradation of phenol was determined by measuring the amount of CO₂ formed in the reaction. The results confirms that 99.6 % carbon in phenol is converted to CO₂.     

钛基TiO2纳米管阵列电极的光电催化性能

应用电化学阳极氧化法在纯Ti基底上制备高度有序的TiO2纳米管阵列,考察了Ti/TiO2光阳极的光电化学响应.以苯酚溶液为目标污染物,研究Ti/TiO2电极的光电催化性能,并与光催化性能进行比较.结果表明,该电极光电催化性能优于光催化性能.施加0.6 V电压时,光电催化性能最好.电化学阻抗谱分析显示,光电催化和光催化降解过程的速控步骤均为表面反应步骤,外加偏压减小了界面电荷转移阻抗,提高了光生载流子的分离效率.     

Degradation of the herbicide isoproturon by a photocatalytic process

In this study, the adsorption and photocatalytic degradation of isoproturon (one of the most widely used herbicides in agriculture) was investigated in an annular photoreactor packed with a TiO₂ photocatalyst. The results highlighted that the monolayer Langmuir adsorption isotherm model was well obeyed. The isoproturon adsorption equilibrium constant was determined experimentally. The codegradation of isoproturon and of other copollutants such as salicylic acid and phenol occurred, demonstrating that within the catalyst, the same type of sites can be involved in the adsorption of the two pollutants. The heat of adsorption fell in the range of 20 to 50 °C and was found to be ∼43 kJ/mol. As expected, the adsorption constant K_a decreased with increasing the fluid flow due to the temperature rise. The kinetics of the photocatalytic degradation of isoproturon revealed a first-order reaction for initial concentrations between 3 and 43 ppm. In our experimental conditions, no by-products were detected and total disappearance of isoproturon was observed.     

浅池型TiO2/ACF光催化降解水中苯酚的研究

为了提高光催化过程的降解速率，本文以涂覆法制得的二氧化钛/活性炭纤维（TiO2/ACF）为光催化剂，300 W(365 nm)高压汞灯为光源，研究了浅池型反应器中苯酚在TiO2/ACF上的光催化降解动力学；探讨了光强度、高压汞灯滤光以及光源种类对降解反应的影响，并对光氧化，光催化和吸附过程进行了比较。结果表明：光氧化对苯酚的降解无效果，光催化降解速率常数与吸附速率常数之比为3.35/1；光强越大，光催化降解速率越快；高压汞灯不滤光时光催化降解速率明显加快，但光催化反应仍遵循准一级反应动力学方程；波长为254 nm紫外杀菌灯的降解效果高于波长为365 nm高压汞灯滤光后的降解效果。     

The effect of dosage on the photocatalytic degradation of organic pollutants

Heterogeneous photocatalytic degradation of many organic pollutants, such as phenol and phenol derivatives, may be optimised if the catalyst surface saturation and the appearance and accumulation of non-photocatalytically degradable intermediates is avoided. It has been shown that under certain concentration threshold the highest degradation efficiencies are achieved. Over these concentrations, degradation rates become constant owing to the limited catalyst surface. By the dosage of the contaminant, currently in an aqueous solution, the process may be optimised, thus avoiding the formation of inert intermediates which may be more toxic than the parental compound. The effect of dosage on the photocatalytic degradation of phenol and phenol derivatives, such as salicylic acid and 4-aminophenol has been studied. Comparatively notably higher efficiencies have been obtained compared to those of the high initial single dose experiments (non-dosage), for which high initial concentrations of the organics resulted in the catalysts poisoning. Degussa P-25 and its combination with 13% (w/w) activated carbon, namely AC?TiO₂, have been used as catalysts. Almost complete degradations are achieved at low dosage rates (1–2 pmm/min). At higher dosage rates, different processes such as catalyst poisoning predominate, resulting in lower degradation efficiencies.     

Photocatalytic membrane processes,and respective modelling,for removal of pharmaceutical residues in wastewaters. A case study with 2-[2,6-(dichlorophenyl)amino]phenyl acetic acid as model molecule

Non linear modelling of data in photomineralization kinetics of organic micropollutants, by photocatalytic membranes immobilizing semiconductors (TiO₂ particularly) has been previously applied to methane, phenol and to 2,4-dichlorophenol as model molecules, by using a four parameters kinetic modelling based on substrate disappearance and total organic carbon (TOC) in laboratory scale experiments, as a function of initial concentration of substrate and of irradiance.In the present paper, the photocatalytic degradation of diclofenac as model molecule was investigated in a pilot plant module, fitted with 2–3 concentric membranes. Maximum allowable quantum efficiencies corresponded to equal distances between 3 membranes immobilizing photocatalyst. This arrangement fully behaves as if a photocatalyst nanopowder would be homogeneously suspended in the reactor, but obviating all drawbacks of a nanopowder suspension.     

Fe2BiTaO7纳米催化剂的组织结构及光催化性能

用固相反应合成法合成了光催化剂Fe2BiTaO7,通过XRD、SEM、TEM、紫外-可见漫反射等表征方法对其组织结构及光催化性能进行了研究。结果表明Fe2BiTaO7为立方晶系烧绿石结构,空间群为Fd3m,禁带宽度为1.72 e V。通过比较Fe2BiTaO7、P25TiO2、掺氮Ti O2和Bi2In Ta O7的可见光光催化降解罗丹明B,发现Fe2BiTaO7降解效果及催化活性均高于其它催化剂,并且Fe2BiTaO7降解罗丹明B效率是掺氮二氧化钛的1.5倍。Fe2BiTaO7降解罗丹明B的曲线符合一级动力学,一级动力学常数为0.022 93 min-1。研究了罗丹明B可能的降解路径和Fe2BiTaO7在可见光下降解苯酚的效果。Fe2BiTaO7(可见光)光催化剂系统适用于纺织工业废水处理。     

Modification of the Optical and Electronic Properties of TiO<Subscript>2</Subscript> By N Anion-Doping for Augmentation of the Visible Light Assisted Photocatalytic Performance

In this work, a nitrogen-doped anatase TiO₂ nanocrystal is prepared by a modified sol-gel preparation method using the nonionic surfactant (polyoxyethylene sorbitan monooleate) as a structural controller and a soft template. The as-prepared samples are characterized by X-ray diffraction, Raman spectroscopy, UVVis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy techniques. Then the photocatalytic activity of these samples is assessed by the photocatalytic oxidation of phenol under visible light irradiation. The phenol concentration is measured using a UV-Vis spectrometer. Experimental results show that N-doping leads to an excellent visible light photocatalytic activity of the TiO₂ nanocatalyst. Furthermore, the formation energy and electronic structure of pure and N-doped anatase TiO₂ are described by density functional theory (DFT) calculations. It is found that N-doping narrowed the band gap of bare TiO₂, which leads to an excellent visible light photocatalytic activity of N–TiO₂ nanocatalysts. Therefore, the prepared N–TiO₂ photocatalyst is expected to find the use in organic pollutant degradation under solar light illumination.     

Fe2BiTaO7纳米催化剂的组织结构及光催化性能

用固相反应合成法合成了光催化剂Fe₂BiTaO₇,通过XRD、SEM、TEM、紫外-可见漫反射等表征方法对其组织结构及光催化性能进行了研究.结果表明Fe₂BiTaO₇为立方晶系烧绿石结构,空间群为Fd₃m,禁带宽度为1.72eV.通过比较Fe₂BiTaO₇、P₂₅TiO₂、掺氮TiO₂和Bi₂InTaO₇的可见光光催化降解罗丹明B,发现Fe₂BiTaO₇降解效果及催化活性均高于其它催化剂,并且Fe₂BiTaO₇降解罗丹明B效率是掺氮二氧化钛的1.5倍.Fe₂BiTaO₇降解罗丹明B的曲线符合一级动力学,一级动力学常数为0.02293 min^-1.研究了罗丹明B可能的降解路径和Fe₂BiTaO₇在可见光下降解苯酚的效果.Fe₂BiTaO₇(可见光)光催化剂系统适用于纺织工业废水处理.     

A novel route for waste water treatment: Photocatalytic degradation of rhodamine B

The direct photocatalytic degradation of rhodamine B (RB) has been reported by thiocyanate complex of iron and hydrogen peroxide. The rate determining parameters like, pH of the medium, concentration of the complex and dye, amount of H₂O₂, and light intensity on the degradation process were studied in detail. The rate of photocatalytic degradation of the dye was observed spectrophotometrically and it follows pseudo-first-order kinetics.     

Fabrication of electrospun polyethersulfone/titanium dioxide (PES/TiO2) composite nanofibers membrane and its application for photocatalytic degradation of phenol in aqueous solution

The main objective of this research is to use the photocatalytic properties of PES/TiO₂ nanofibers membranes to remove the phenol as a toxic pollutant in various effluents. The uniform fibers in terms of minimum bead formation and fibers diameter were fabricated. Therefore, more TiO₂ catalysts are on the surface of the fibers which increase the active surface area of nanoparticles and consequently improve the phenol degradation efficiency. The effects of TiO₂ concentration on hydrophilicity, mechanical properties, porosity, mean pore size, and water flux of membranes were studied. The PES/TiO₂ nanofibers were evaluated for phenol degradation under UVA irradiation through a transparent membrane module. The amount of removable phenol was analyzed with high‐performance liquid chromatography. Central composite design was used as a statistical experimental design. Finally, the effect of TiO₂ content in nanofibers and initial phenol concentrations were investigated as well as pH values in synthetic wastewater, on phenol degradation. The results from analysis of variance (ANOVA) analysis indicated that TiO₂ content in nanofibers was the most important and effective parameter on phenol degradation. It was also presented that there is no significant interaction between parameters so that the effect of each parameter was investigated separately. Maximum phenol degradation was 43.0 ± 0.3% and found under conditions of TiO₂ content, initial phenol concentration, and pH value of 8%, 120 ppm, and 7, respectively.     

MoS_2负载量对MoS_2/TiO_2光催化降解苯酚效率的影响及其作用机理研究

通过水解法制备TiO_2纳米颗粒,与经过超声处理后的MoS_2片层纳米材料复合制备MoS_2/TiO_2纳米催化剂,考察不同MoS_2负载量对其光催化降解苯酚效率及路径的影响。XRD、SEM、EDS、FT-IR和UV-vis DRS等表征结果表明,复合催化剂主要由锐钛矿型TiO_2和MoS_2组成;剥离后的MoS_2呈现薄片层状结构,均匀地分散在TiO_2纳米颗粒当中。光催化降解苯酚性能测试结果显示,对于MoS_2/TiO_2催化剂,MoS_2负载量的提高有利于光催化降解苯酚效率的提高;当MoS_2负载量为27%时,复合M o S2/TiO_2纳米颗粒的光催化性能最佳,反应80 min后可将苯酚完全降解。通过对苯酚降解过程中生成中间产物跟踪发现,MoS_2负载量的提高有利于促进中间产物苯醌、对苯二酚以及邻苯二酚的生成,进而提升了MoS_2/TiO_2复合材料的光催化性能。