Halogen Doped TiO₂ For Photoelectrocatalysis And The Study Of Its Degradation Mechanism

With the development of society and the acceleration of industrialization,water pollution caused by huge amounts of organic contaminants is becoming more and more serious.Dyes,chemicals and pharmaceuticals are the main common recalcitrant organic pollutants in the polluted water.The photoelectrocatalytic?PEC?is a new type of advanced oxidation technology,which can degrade most kinds of refractory organic contaminants.The PEC technology has attracted increasing attention in environmental area,due to its advantages of simple equipment,mild operation conditions and no secondary pollution.Among the numerous catalysts,TiO₂ is considered to be the most promising catalyst to fabricate the photoanode for its advantages of low cost,low toxicity and high chemical stability.However,some issues still exist in the PEC technology,such as low visible utilization efficiency,high preparation cost and poor stability of TiO₂ film photoelectrode,which restrict its industrial application in the wastewater treatment.In addition,recent studies on PEC degradation of organic contaminants mainly focus on the characterization and catalytic performance of the catalyst,but the degradation mechanism has not been adequately studied.Therefore,it is significant to develop a simple preparation method of TiO₂ film photoelectrode with low cost and high visible PEC performance,as well as to investagtae the PEC degradation mechanism of organic contaminants.Halogen?F and I?doped TiO₂ is the optimal catalyst to fabricate the photoelectrode due to its simple preparation method and excellent visible photocatalytic activity.In this thesis,in order to solve the problems above,the halogen doped TiO₂ catalysts were synthesized via simple methods?sol-gel and hydrolysis methods?,exhibiting an excellent visible light catalytic activity.The halogen doped TiO₂ film photoelectrodes which were prepared by the screen printing method showed high PEC degradation efficiency of organic contaminants under visible light irradiation.In addition,the photoelectrodes also exhibited excellent stability.Meanwhile,the PEC degradation mechanisms of organic contaminants were also investigated.The details of this thesis are as follows:1.The halogen doped TiO₂ catalysts were successfully synthesized by the simple sel-gel and hydrolysis methods,and they were characterized by the physical and chemical analyses.The results indicated that the visible absorption ability and photogenerated charges separation rate of TiO₂ were significantly enhanced by halogen?F and I?doping and multielement?F-Sn and I-P?co-doping.Then,an FTO glass was chosen as the conductive substrate of catalysts and the halogen doped TiO₂ film photoelectrodes were prepared by a simple screen-printing method.In order to inhibit the detachment of catalysts from the FTO substrate,low melting-point glass powders were added during the photoelectrode preparation process to enhance the attachment between the catalysts and FTO substrate.2.The common organic contaminants?methylene blue,phenol,diclofenac and tetracycline?and wastewater?landfill leachate and pharmaceutical wastewater?were chosen to evaluate the PEC performance of the halogen doped TiO₂ film photoelectrodes.The results suggested that the photoelectrodes exhibited an excellent PEC performance in the degradation of organic contaminants and wastewater under visible light irradiation.And the PEC performance was affected by the element doping content,applied bias,pH of solution,concentration of H₂O₂ and type of electrolytes.In addition,among the halogen doped film photoelectrodes,the I,P co-doped film photoelectrodes showed the highest PEC performance.3.The PEC degradation mechanisms of organic contaminants were investigated by the first-order kinetic model,Langmuir-Hinshelwood kinetic model and active species trapping experiments.The results implied that the PEC degradation of organic contaminants mainly occurred on the surface of halogen doped photoelectrodes,and the surface adsorption was the controlling factor in the organic contaminants degradation process.In the PEC process,holes?h⁺?and hydroxyl radicals?.OH?were the major active species contributing to the decomposition of organic contaminants,and the dominant roles of h⁺and.OH were not significantly affected by the element doping content and initial concentration of organic contaminants.The degradation rate of organic contaminants could be significantly enhanced under the condition of high Cl^-concentration,which was caused by the participation of chloride radicals?Cl.,created by h⁺and.OH?in the PEC process.Under this condition,the organic contaminants were mainly degraded by the Cl..In addition,the dominant roles of h⁺and.OH in the PEC process were further demonstrated by the investigation of PEC degradation pathways of organic contaminants.