The Studies Of Gas-solid Phase Photocatalytic Degradation Of Pollutants On TiO₂/SiO₂ Compound Semiconductor Photocatalyst

In 1972, Fujishima discovered the photocatalytic splitting of water on TiO₂ electrodes. Since then, research efforts in understanding the fundamental processes and in enhancing the photocatalytic efficiency of TiO₂ have come from extensive research performed by chemists and physicists. Photocatalysis is rapidly developing in recent years, and it has been a promising process for remediation environmental air pollution by volatile organic compounds. At moderate conditions (room temperature, one atmosphere pressure and with molecular oxygen as the only oxidant), the above mentioned semiconductors have proved to be effective photocatalysts for the dynamically favored transformations of many organic compounds to CO₂ and H₂O. In this paper, firstly we prepare the supported catalyst by using a sol-gel method. TBOT and TEOS as crude materials proceed hydrolytic decomposition and condensation polymerization in the organic mediator (ammonia liquor), after sol-gel and drying process the particle is calcined at 600℃. Composited TiO₂/SiO₂ catalyst have lots of merits of photoresponse red shift, delayed recombination, high-catalysis activity, large specific surface area, greatly adsorpted organic matter than TiO₂. Secondly, This investigation concerned the photocatalytic oxidation of toluene over TiO₂/SiO₂ in the gas-phase. The feasibility studies involved the effects of initial concentration of reactant, oxygen content, water vapor content and light intensity on the photocatalytic reaction. The photocatalytic degradation rate increased with increasing the initial concentration of toluene, but maintained almost constant beyond a certain concentration. It matched well with the Langmuir-Hinshelwood kinetic model. The reaction rate increased with increasing oxygen content, but for higher than 18%(v/v), the reaction rate reversed. For the influence of water vapor in the gas-phase photocatalytic degradation rate of toluene, there was an optimum concentration of water vapor (0.2%(v/v)). The photocatalytic degradation rate increased with light intensity but the rate approached to level off when the light intensity rose to 3mW/cm2. The photocatalytic degradation rate constant and the adsorption constant of toluene were obtained using the Langmuir-Hinshelwood model, and the reaction products (CO2, benzoic acid, phenyl--aldehyde, benzyl alcohol, micro-content benzene) were also identified by FI-RT and GC-MS. Thirdly, we study different system about heptane and SO2,heptane and NOx (NO2,NO) over TiO2-SiO2 catalyst. In the photocatalytic reaction process of C7H16-O2-TiO2/SiO2 and SO2-O2-TiO2/SiO2, degradation of SO2 is faster than heptane and its agree first-order reaction. In the reaction process of SO2-C7H16-O2-TiO2/SiO2, the structure of SO42-/TiO2-SiO2 formed on the surface of TiO2-SiO2 enhanced the rate of photocatalytic oxidation of hepane and it wad studied using IR. In SO2-C7H16-O2-TiO2/SiO2 system, returns on investment of heptane is the best when oxygen...