The Studies Of Photocatalytic Degradation Of Heptene/Sulfur Dioxide On TiO₂/SiO₂ Compound Semiconductor Photocatalyst

In 1972, Fujishima and Honda discovered the photocatalyticsplitting of water on TiO₂ electrodes. This event marked thebeginning of a new era in heterogeneous photocatalysis. Since then,research efforts in understanding the fundamental processes and inenhancing the photocatalytic efficiency of TiO₂ have come fromextensive research performed by chemists and physicists. Studiesinvolving gas-solid heterogeneous photocatalysis are relatively few innumber compared with the substantial literature on photocatalyticwater treatment, but are now of growing interest because of thepotential application to contaminant control in contained airatmospheres as found in aircraft and spacecraft, office buildings andfactories. Photocatalysis is rapidly developing in recent years, and ithas been a promising process for remediation environmental airpollution by volatile organic compounds. At moderate conditions(room temperature, one atmosphere pressure and with molecularoxygen as the only oxidant), the above mentioned semiconductorshave proved to be effective photocatalysts for the dynamicallyfavored transformations of many organic compounds to CO₂ andH₂O.In this paper, firstly we prepare the supported catalyst by using asol-gel method. TBOT and TEOS as crude materials proceedhydrolytic decomposition and condensation polymerization in theorganic mediator (ammonia liquor), after sol-gel and drying processthe particle is calcined at 600℃. Composited TiO2/SiO2 catalysthave lots of merits of photoresponse red shift, delayed recombination,high-catalysis activity, large specific surface area, greatly adsorptedorganic matter than TiO2.Heptene is one of the most important vaporous organiccontaminants, while sulfur dioxide is one of the most importantinorganic contaminants. Heptene and sulfur dioxide not only do harmto environment as the primary products,but also can form secondaryproducts under the influence of the sun. The photochemical reactionbetween heptene and sulfur dioxide plays an important role in theformation of acid rain, aerosol, and photochemical smog.In the chapter two of this paper, we used nano-TiO2/SiO2 ascatalyst to investigate the influence of different calcined temperatureson the photocatalytic activity of the catalyst for the photocatalyticdegradation of heptene. The photocatalytic activity of the catalyst isthe highest when the calcination temperature is 600°C. In the reactionprocess of SO2-C7H14-O2-TiO2/SiO2, the structure of SO42-/TiO2-SiO2formed on the surface of TiO2-SiO2 enhanced the rate ofphotocatalytic oxidation of heptene and it wad studied using IR.Meanwhile the studies involved the effects of initial concentration ofreactant, oxygen content, water vapor content and light intensity onthe photocatalytic reaction. The photocatalytic degradation rate ofheptene increased with increasing the initial concentration of sulfurdioxide, but maintained almost a constant beyond a certainconcentration. When the concentration of sulfur dioxide was fixed,the reaction rate increased separately with increasing oxygen contentand water vapor content, when oxygen content was 20%, the reactionrate was the highest , while water vapor content was 444μmol/L,there was an optimum value for the photocatalytic degradation rate ofheptene. The degradation rate of heptene increased with lightintensity but the rate approached to level off when the lightintensity rose to 8.32mW/cm2. The reaction products were identifiedby FT-IR and GC-MS.In the chapter three of this paper, we mainly researched thedeactivation and regeneration of nano-TiO2/SiO2. Two differentsystems, C7H14-O2-TiO2/SiO2 and SO2-O2-TiO2/SiO2 were studiedrespectively, and gived the exhaustive explanation. The regenerationmethod of the TiO2/SiO2 catalyst was investigated at the same time.