Study On Preparation Of UV-induced One-dimensional TiO₂ Photocatalysts And Photocatalytic Degradation Of Toluene

Photocatalytic reaction has advantages of mild reactive conditions, no secondary pollutants, etc.Photocatalytic technology has broad application prospects in environmental purification, especially in the removal of gas phase pollutants. TiO2 is one of the most promising photocatalytic materials due to its excellent photocatalytic performance, stable chemical property and low cost. However, there are still challenges for inhibiting the recombination of photo-induced hole-electron pairs and improving the coating methods. This paper focuses on improving the synthesis methods of high activity TiO2 photocatalysts, such as one-dimensional TiO2 and mesoporous TiO2 with high surface area. Novel modification process for the parapration of noble metal deposited TiO2 and in-situ metal doped TiO2 are also discussed.The reaction kinetics of one typical TiO2 photocatalyst is studied, using continuous toluene flow as target pollutants.The study provides theoretical supports for the preparation of high performance UV-induced TiO2Firstly,TiO2 nanotube arrays are prepared by anodization method in ethylene glycol electrolyte with titanium foils as starting material.The effects of anodic voltage and time on the TiO2 nanotube arrays'morphology and photocatalytic activity are studied. Furthermore, immobilized composite TiO2 nanostructure of nanowires covered nanotubes are synthesized by adjusting the concentration of H2O and HF.The higher activity of this novel catalyst for photocatalytic removal of gaseous toluene is also demonstrated. The reproducible simple synthesis route for efficient immobilized photocatalysts shows great application potential in air purification.Secondly, TiO2 nanobubes are synthesized by hydrothermal treating of industrial titanium powder in alkali solution. Then, the TiO2 nanobubes are further modified by Ag, Pt and Pd deposition, which is carried out by a simple dip-coating process. The diameter and length of the Ag-TNTs are about 20 nm and 100 nm, respectively. The porous structure of Ag-TNTs is characterized to be hierarchical micro-meso porous structure. The optimum photocatalytic activities of the samples are 2.2 and 2.1 times that of P25 for Ag-TNTs and Pt-TNTs, respectively. To simplify the preparation and modification process of UV-induced TiO2 a simple one-step hydrothermal method is developed to synthesize In-situ metal doped TiO2 nanotubes.The influences of doping metal type and doping ratio on the photocatalytic activity are studied. The as prepared photocatalysts are tested by the photodegradation of gas phase toluene. It is found that the apparent reaction rates are 1.2 and 1.5 times that of P25,respectively.To avoid the high temperature and pressure in the hydrothermal route, a mild template-free sonochemical method is developed to synthesize mesoporous TiO2 nanorods using industrial bulk Ti powder. The sonochemical synthesis process was carried out under normal atmospheric pressure and relative low temperature. The as prepared TiO2 nanorods contain numerous irregular olive-like nanorods aggregates. The photocatalytic degradation of gas phase toluene shows that the activity of the sample is 2.8 times that of P25.Compared with normal hydrothermal technique, this novel sonochemical method is simple and low cost. A mechanism of Oxidation-Shaking off-Rolling up-Shrinkage (OSRS) is proposed to explain the crystal growth.Finally, the reaction kinetics of photocatalytic degradation of gas phase toluene is studied in a homemade continuous flow reactor. The sample made by sonochemical oxidation method is chosed as typical photocatalyst. Carefully considering the influnce of humidity and oxygen concentration, a kinetics model with multifactors is built and solved by amending the L-H model.