Photoelectrical And Photocatalytic Properties Of TiO₂, ZnO And Their Composites

Environment problem is becoming more and more severe with the rapid developmentof economy. Metal oxides such as TiO₂and ZnO have been widely applied to destroy awide variety of pollutants due to their specific advantages. However, it is difficult todevelop high-performance photocatalysts efficiently. In this paper, TiO₂, ZnO and theircomposites were used to investigate the relationship between composition, microstructureand photoelectrical properties as well as photocatalytic properties.The photoelectrical responses of TiO₂/ZnO composites were measured. The carriertransport mechanism was discussed by analyzing the photoelectrical responses, whichcould offer the information about processes of photocatalysis. Based on the amplitude ofthe photoelectrical response and the decay, the composition with the best photoelectricalproperty was found, which was TiO₂: ZnO=1:9. It might be with a high catalytic activity.Then, TiO₂, ZnO and TiO₂: ZnO=1:9were sintered at different temperatures, whichwere applied to change their microstructures. The photocatalytic properties were tested bydecomposing100ppm formaldehyde （HCHO） gas. The results showed that with thesintering temperature increasing, the photocatalytic property became worse due tovariations of the particle sizes, phase composition and oxygen vacancy, etc. The highestcatalytic activity was appeared in TiO₂sintered at500°C, whose rate constant was4.3×10-2min-1. In addition, the photocatalytic property might have no direct relation withthe photoelectrical property in the dry air.Finally, the photoelectrical properties of TiO₂, ZnO and TiO₂: ZnO=1:9sintered atdifferent temperatures were measured in both dry air and50ppm formaldehyde gas. Theamplitudes of the photoelectrical responses were enhanced with the introduction offormaldehyde gas. The ratio of the amplitudes of the photoelectrical responses informaldehyde and air （Imax-F/Imax-A） was obtained for each sample. There had a directrelation between the ratio and the photocatalytic property. The better the photocatalyticproperty was, the larger the ratio was. The ratio of TiO₂sintered at500°C was as high as335, which was much larger than the other samples. According to the results above, the relationship between photoelectrical andphotocatalytic properties was obtained. Because the measurement of photoelectricalresponse was much easier, the discovery of high-performance photocatalysts would bemuch more efficient.