The Studies Of Photocatalytic Degradation Of Pollutants In Gas Phase On TiO₂-SnO₂ Compound Semiconductor Catalyst

In this paper, we chose TiO2 and SnO2 as the representative semiconductor oxides to study the photocatalytic reactions in the atmosphere. TiO2－SnO2 compound semiconductor was prepared by co-precipitation method and Sol-Gel method. We investigated the photocatalytic activities of samples prepared by different methods and different conditions and different predecessors in the system of C7H16 (0.1%)-O2(20%)-N2-TiO2 by the photocatalytic degradation of heptane. From the repeated experiments, we concluded that activities of samples prepared by Sol-Gel method are better than those of co-precipitation method and the optimal conditions to prepare TiO2-SnO2 compound semiconductor by Sol-Gel method:Use SnCl2·2H2O as the predecessor of Sn; The level of HCl is 5.28mL; n(Sn):n(Ti)=0.06; The aging stage of sol is 132h; Calcinate the dry gel powders at 300℃ for 2h directly.According to the conditions of above and the actual concentration range of Sn and Ti element in the atmosphere, compound semiconductor samples of different Sn/Ti specific values were prepared and they were characterized by XRD ,TG-DTA,UV-vis spectrum,XPS and IR spectrum. Experiment results indicate that when the value of n(Sn)/n(Ti) is higher than 0.53, the best calcination temperature of samples should be 400℃ . This is because excessive SnO2 in the samples can inhibit the transition of TiO2 from undefined structure to anatase phase. In the system of C7H16(0.1%)-O2(20%)-N2- TiO2-SnO2 , the same sample was used for many times and we found the photocatalytic activity of the sample has no change.We studied the photocatalytic degradation of heptane and methylbenzene and SO2 separately, checked the reaction rates; Use the increased concentration of CO2 as the index to assessment the nineralization of heptane and methylbenzene. We also studied the kinetic indexes of those reactions preliminarily. All the degradation reactions of the three pollutants showed that the photocatalytic activities of different samples vary within a large range, the sample of n(Sn):n(Ti)=0.06 has the highest photocatalytic activity and the more SnO2 in compound semiconductor, the lower photocatalytic activity it would be. One reason is the catalyst use level was fixed to 0.1g, so the value of TiO2 will be decreased as the value of SnO2 increased; the other is as SnO2 increased in sample the negative effect for photocatalytic activity increased correspondingly. The results of kinetic analyses showed that most of the reactions match the first-order reaction and the value of the apparent rate constant increased as the photocatalytic activity got higher, a few reactions of samples with low activities match the zero order reaction.