Photocatalytic degradation of azo dyes catalyzed by Ag doped TiO2 photocatalyst

In this paper, photocatalytic degradation of commercial textile azo dyes catalyzed by titanium dioxide and modified titanium dioxide with Ag metal (1% w/w) in aqueous solution under irradiation with a 400 W high-pressure mercury lamp is reported. The effect of various parameters such as irradiation time of UV light, amount of photocatalyst, flow rate of oxygen, pH and temperature for the Ag-TiO₂ photocatalyst were investigated. Kinetic investigations of photodegradation indicated that reactions obey improved Langmuir-Hinshelwood model and pseudo-first-order law. The rate constant studies of photocatalytic degradation reactions for Ag-TiO₂ and TiO₂ photocatalysts indicated that in all cases the rate constant of the reaction for Ag-TiO₂ was higher than that of TiO₂.     

Photocatalytic degradation of hexachlorocyclohexane (HCH) by TiO2-pillared fluorine mica

A significant effect of clay host was observed on the photocatalytic activity of TiO2; TiO2-pillared fluorine mica exhibited two orders of magnitude higher activity than TiO2 and TiO2-pillared montmorillonite for the photocatalytic degradation of gamma-HCH.     

Photocatalytic degradation of deltamethrin by using Cu/TiO2/bentonite composite

In the present work, titanium dioxide nanoparticles and Cu/TiO₂/bentonite composites were prepared by using thermal decomposition and reduction method. The samples were characterized by FTIR, XRD, TGA and SEM. The photocatalytic properties of the prepared composites were studied for the degradation of deltamethrin. Several factors on degradation process were investigated such as total time of light irradiation, pH of the solution and concentration of catalyst to optimize the reaction conditions. It was observed that the prepared metal doped composite possesses high efficiency for the degradation of the insecticide. The degradation process follows first order kinetics. Antibacterial activity of the synthesized composites was also studied and the result shows that obtained composites possess good antibacterial activity.     

Photocatalytic degradation of phenolic syntan using TiO2 impregnated activated carbon

Investigations were carried out to study the photocatalytic degradation of phenolic syntan (PS), a widely used environmentally polluting chemical in the leather tanning industry. Photocatalytic inactive commercial TiO(2) was used as the precursor for the preparation of TiO(2) impregnated activated carbon (Ti-AC) photocatalyst. Experiments were conducted by varying the concentrations of PS solution (50-1000 mg/l), pH (2.5-10) and time intervals to optimize the working parameters. A 254 nm UV light was used throughout the study. The effect of PS degradation using Ti-AC was also compared with direct UV photolysis. The Ti-AC was characterized using X-ray Diffraction (XRD), Diffuse Reflectance Spectroscopy (DRS), Scanning Electron Microscopy (SEM) and energy dispersive X-ray analysis (EDX) to determine the structural, optical, surface morphology and elemental analysis respectively. X-ray studies revealed the formation of catalytically active anatase phase in Ti-AC. Photodegradation of PS was examined by chemical oxygen demand (COD) method. PS degradation occurred at both the extreme end of acidic and alkaline pH conditions. However, the percentage degradation was comparatively higher at pH 2.5. The photodegradation followed pseudo first order kinetics. UV-Visible studies substantiated the occurrence of bathochromic and hyperchromic effects as a result of ring opening in the PS molecule.     

Photocatalytic degradation of methylene blue by a combination of TiO2 and activated carbon fibers

Photocatalytic degradation of methylene blue (MB) in aqueous solution was investigated using TiO2 immobilized on activated carbon fibers (ACFs). The TiO2 and ACF combination (TiO2/ACF) was prepared by using epoxy as the precursor of the link between TiO2 and ACFs, followed by calcination at 460 degrees C in a N2 atmosphere. The TiO2/ACF composite prepared was easier to handle than the original TiO2 powder in suspension. More significantly, the TiO2/ACF composite can be used repeatedly without a decline in photodegradation ability. After six cycles, the amount of MB removal for the TiO2/ACF composite was still slightly higher than that for fresh P25 TiO2 in suspension. Through measurement of chemical oxygen demand in the solution and the concentration of ammonium generated during degradation of MB, it was confirmed that MB molecules are mineralized instead of adsorbed by ACFs.     

Photocatalytic degradation of methyl orange on arrayed porous iron-doped anatase TiO2

Arrayed porous iron-doped TiO₂ was prepared by sol–gel with polystyrene spheres as template and used as photocatalyst for the degradation of methyl orange. The structure and performances of the prepared photocatalyst were characterized with X-ray diffractometer, inductively coupled plasma-atomic emission spectrometer, scanning electron microscope, UV-visible spectrometer, and methyl orange degradation tests. It is found that the iron dopant does not change the crystal phase of TiO₂ but affects its lattice constant, optical absorption, electronic conductivity, charge-transfer resistance, and activity toward the degradation of methyl orange. The sample doped with 0.01 wt.% Fe (based on Ti) and with smaller pore size exhibits the better photocatalytic activity. The degradation rate of methyl orange on the sample with a pore size of 190 nm is 2.3 times that on the undoped sample with the same pore size.     

Photocatalytic degradation of triazine dyes over N-doped TiO2 in solar radiation

Photocatalytic degradation of the reactive triazine dyes Reactive Yellow 84 (RY 84), Reactive Red 120 (RR 120), and Reactive Blue 160 (RB 160) on anatase phase N-doped TiO₂ in the presence of natural sunlight has been carried out in this work. The effect of experimental parameters like initial pH and concentration of dye solution and dosage of the catalyst on photocatalytic degradation have also been investigated. Adsorption of dyes on N-doped TiO₂ was studied prior to photocatalytic studies. The studies show that the adsorption of dyes on N-doped TiO₂ was high at pH 3 and follows the Langmuir adsorption isotherm. The Langmuir monolayer adsorption capacity of dyes on N-doped TiO₂ was 39.5, 86.0, and 96.3 mg g^?1 for RY 84, RR 120, and RB 160, respectively. The photocatalytic degradation of the dyes follows pseudo first-order kinetics and the rate constant values are higher for N-doped TiO₂ when compared with that of undoped TiO₂. Moreover, the degradation of RY 84 on N-doped TiO₂ in sunlight was faster than the commercial Aeroxide^® P25. However, the P25 has shown higher photocatalytic activity for the other two dyes, RR 120 and RB 160. The COD of 50 mg l^?1 Reactive Yellow-84, RR 120 and RB 160 was reduced by 65.1, 73.1, and 69.6 %, respectively, upon irradiation of sunlight for 3 h in the presence of N-doped TiO₂. The photocatalyst shows low activity for the degradation of RY 84 dye, when its concentration was above 50 mg l^?1, due to the strong absorption of photons in the wavelength range 200–400 nm by the dye solution. LC–MS analysis shows the presence of some triazine compounds and formimidamide derivatives in the dye solutions after 3 h solar light irradiation in the presence of N-doped TiO₂.     

Photocatalytic degradation of aniline at the interface of TiO2 suspensions containing carbonate ions

The degradation of aniline has been investigated using aqueous TiO2 suspensions containing carbonate ions as photocatalyst. The addition of carbonate to Degussa P-25 increased the number of active adsorption sites at its surface. For the TiO2 suspensions containing carbonate ions the intensity of adsorption of aniline increased to 6.9 x 10(2) from 5.5 x 10(2) mol(-1) dm(3) in case of bare TiO2 suspensions. This in turn results in the increased interfacial interaction of the photogenerated charge carriers with the adsorbed aniline and thus enhancing the rate of its photodecomposition to 6.5 x 10(-6) mol dm(-3) s(-1) compared to 2.7 x 10(-6) mol dm(-3) s(-1) in the absence of Na(2)CO(3). The maximum efficiency of this photocatalyst has been obtained upon addition of 0.11 mol dm(-3) of Na(2)CO(3) at pH 10.8. The photocatalytic action is understood by the simultaneous interaction of intermediates, *OH and CO*-(3), and their reactivity with aniline. Azobenzene, p-benzoquinone, nitrobenzene, and NH(3) have been identified as the major products of the photooxidation of aniline. Both the reactant and products have been followed kinetically. The photodegradation follows Langmuir-Hinshelwood Model. The mechanism of the occurring reactions has been analyzed and discussed. In the presence of Na(2)CO(3), 3 x 10(-3) mol dm(-3) of aniline could be photodegraded completely in about 6 h while all organic intermediates decomposed completely within about 10 h.     

Photocatalytic degradation of actual textile industrial wastewater in aqueous suspensions of polycrystalline TiO2

Heterogeneous photocatalytic oxidation of contaminants present in wastewater produced by a textile industry was carried out. The samples were withdrawn from the plant before and after a traditional biological treatment. The effluents were named A and A' (before the biological treatment), B and B' (after the biological treatment). Polycrystalline TiO2 (Degussa P25) was used as the catalyst in a batch photoreactor with immersed lamp. An almost complete decolorization was observed after about 0.5 divided by 1 hours for both kinds of effluents, but the decrease of the total organic carbon (TOC) concentration occurred more slowly. The influence of some chemical oxidants, i.e. ozone, hydrogen peroxide and peroxydisulfate on the photo-oxidation rate was also investigated. After addition of H2O2 or S2O8(2-) TOC decreased more quickly only for B and B'. The runs performed by using O3 as bubbling gas showed a mineralization rate higher than that observed in the presence of O2.     

Photocatalytic degradation of methyl orange over metalloporphyrins supported on TiO2 Degussa P25

The photocatalytic activity of meso-tetraphenylporphyrins with different metal centers (Fe, Co, Mn and Cu) adsorbed on TiO(2) (Degussa P25) surface has been investigated by carrying out the photodegradation of methyl orange (MO) under visible and ultraviolet light irradiation. The photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance UV (DRS-UV-vis) and infrared spectra. Copper porphyrin-sensitized TiO(2) photocatalyst (CuP-TiO(2)) showed excellent activity for the photodegradation of MO whether under visible or ultraviolet light irradiation. Natural Bond Orbital (NBO) charges analysis showed that methyl orange ion is adsorbed easier by CuP-TiO(2) catalyst due to the increase of induced interactions.     

Photocatalytic degradation of dimethyl phthalate ester using novel hydrophobic TiO2 pillared montmorillonite photocatalyst

TiO₂ pillared montmorillonites were prepared by introducing Ti⁴⁺ into a layer of montmorillonite modified with or without cetyltrimethylammonium bromide. The components and texture of the prepared composites were characterized by thermogravimetric analysis, X-ray powder diffraction and scanning electron misroscopy. The adsorption and photocatalytic degradation performance of a model environmental endocrine disruptor, dimethyl phthalate ester, were investigated using this newly prepared hydrophobic TiO₂ pillared montmorillonite photocatalyst. The adsorption of dimethyl phthalate ester from water varied from 9% to 28% on the prepared hydrophobic photocatalyst. Although the experimental results showed that the photocatalytic activity of the hydrophobic photocatalyst was slightly lower than that of hydrophilic one, electron spin resonance verified that hydroxyl radicals were also generated in hydrophobic TiO₂ pillared montmorillonite photocatalyst under UV irradiation. To elucidate the decomposition mechanism of dimethyl phthalate ester, 12 main photocatalytic intermediates were identified during the photocatalytic degradation process, and a plausible degradation mechanism was also proposed.     

Photocatalytic degradation of pathogenic bacteria with AgI/TiO2 under visible light irradiation

The photocatalytic disinfection of pathogenic bacteria in water was investigated systematically with AgI/TiO2 under visible light (lambda > 420 nm) irradiation. The catalyst was found to be highly effective in killing Escherichia coli and Staphylococcus aureus. The adsorbed *OH and hVB+ on the surface of the catalyst were proposed to be the main active oxygen species by study of electron spin resonance and the effect of radical scavengers. The process of destruction of the cell wall and the cell membrane was verified by TEM, potassium ion leakage, lipid peroxidation, and FT-IR measurements. Some products from photocatalytic degradation of bacteria such as aldehydes, ketones, and carboxylic acids were identified by FT-IR spectroscopy. These results suggested that the photocatalytic degradation of the cell structure caused the cell death. The electrostatic force interaction of the bacteria-catalyst significantly affected the efficiency of disinfection on the basis of the E. coli inactivation under different conditions.     

Photocatalytic degradation and adsorption of 2-naphthol on suspended TiO2 surface in a dynamic reactor

The photocatalytic oxidation of 2-naphthol has been investigated at room temperature in a dynamic photoreactor with system UV/O2 (air) and aqueous suspension of titanium dioxide TiO2 irradiated under a variety of conditions. The kinetics of disappearance of pollutant were affected by several operating parameters such as TiO2 mass, concentration of the substrate and reaction pH. The experiments were measured by high performance liquid chromatography. A Langmuir-Hinshelwood model was found to be accurate for photocatalytic degradation and indicates that adsorption of the solute on the surface of semiconductor particles plays a role in photocatalytic reaction.     

TiO2/SiO2气凝胶对吡啶的光催化降解

TiO2/SiO2气凝胶对吡啶的光催化降解;吡啶     

负载型TiO2／玻璃弹簧的光催化杀菌作用

 研究了自主开发的负载型TiO2／玻璃弹簧光催化剂对大肠杆菌的光催化杀菌作用．结果表明，光催化杀菌效果明显好于单独紫外光的杀菌效果．光催化杀菌过程存在一个诱导期．用扫描电镜和透射电镜观察经不同时间杀菌处理的菌液，结果显示光催化作用于细菌的细胞壁和细胞膜，使其破裂并导致细胞死亡．探讨了光催化剂的制备条件（如浸涂浆料浓度、浸涂次数、热处理条件等）对光催化杀菌效率的影响．     

BiVO4光催化去除废水中的四环素和环丙沙星

利用微波水热法制备单斜白钨矿型BiVO4为光催化剂,探讨其对抗生素类污染物的去除效果.同时利用X射线衍射(XRD)、傅里叶红外(FT-IR)和场发射扫描电镜(FE-SEM)等测试手段对样品结构和性能进行了表征.以四环素(TC)和环丙沙星(CIP)为目标污染物,研究光照时间、pH及Cu(Ⅱ)共存对BiVO4光催化降解抗生素性能的影响.结果表明:BiVO4对TC和CIP的光催化具有较为宽泛的pH适用范围,其中TC在pH为5~12之间具有良好的效果,pH=8时,降解效率达到74%;CIP在pH为4~9之间适用范围最好,降解率由26%升高到37%.此外,对TC和CIP光催化降解机理和可能的降解途径进行探讨,光催化降解主要机理是有效光生电子-空穴与OH-和O2结合,将TC和CIP分解为中间产物CO2和H2O.总之,单斜白钨矿型BiVO4用于模拟抗生素废水的研究,取得一定效果,可为实际抗生素废水的处理提供参考.     

Photocatalytic reduction of nitrate over TiO2 and Ag-modified TiO2

This research work presents the efficiency of the TiO₂ and Ag–TiO₂ thin films prepared by the sol–gel method and coated onto the surface of 304 stainless steel sheets used in the photocatalytic nitrate reduction processes. The Ag–TiO₂ thin films had the weight by weight (w/w) ratio of Ag⁺/TiO₂ of 0.1% as Ag atom. The XRD results showed that the crystalline phase structure of TiO₂ on the Ag–TiO₂ thin films was anatase. The optical band gaps of the TiO₂ and 0.1% Ag–TiO₂ thin films were respectively 3.27 and 2.70 eV, while the surface of the prepared catalysts was hydrophobic with the respective average water contact angles of 94.8° and 118.5° for the TiO₂ and 0.1% Ag–TiO₂ thin films. The net efficiencies of photocatalytic nitrate reduction of TiO₂ and 0.1% Ag–TiO₂ were 41.4% and 70.0%, respectively. The loading of Ag only influenced the nitrate removal efficiency without affecting the stoichiometric ratio of formate to nitrate. The net stoichiometric ratio of formate to nitrate of all experiments was 2.8:1.0, which is close to the stoichiometric ratio of 2.5:1.0 of the nitrate reduction to nitrite and then to nitrogen gas.