Study On The Relationship Between The Photocatalytic Activity Of TiO₂ And Its Gas Sensing Property Enhanced By Ultraviolet Light

TiO2 semiconductor materials have been paied wide attention and researched.in the field of gas sensor and photocatalysis. In the photocatalytic process, the adsorption of reaction gas at semiconductor surface may change semiconductor conductivity, thus affecting its photocatalytic performance. Also, photocatalytic reaction will occur during the process of gas sensitive tests under ultraviolet light, and the change of surface species and electron transfer in the reaction can also exert an effect on the performance of gas sensor. Therefore, it is great significance to explore on the relationship between the photocatalytic activity and gas sensing property for deep understanding the mechanism of photocatalytic and gas sensitive.In this paper, the relationship between photocatalytic activity and gas sensing property was studied and investigated. The following experiments had been carried out in details:On the one hand, the performances of anatase and rutile TiO2 for photocatalytic oxidation of CO and H2 were studied, respectively; the gas sensitive performance of sensors made by anatase and rutile TiO2 on CO, H2 and O2 gas in high purity nitrogen under ultraviolet light were compared. Based on the infrared spectra of two kinds of TiO2 adsorbing reaction gases, the electron transfer behaviors during the process of two crystal type TiO2 adsorbing gases were explored. On the other hand, TiO2 with a high percentage of exposed{001} were synthesized, its photocatalytic activity and gas sensing property to ethylene and acetone were tested, and the influence of the photocatalytic performance on the gas sensing property over TiO2 was discussed.The main results and conclusions are presented as follows:(1) CO can be photocatalytic oxidized by both anatase and rutile TiO2, and the CO adsorption can cause the increase in surface conductivity of both two TiO2 under UV irradiation. Anatase exhibits a higher activity of photocatalytic oxidation of CO than rutile, and also presents a higher photo-induced sensitive response to CO than rutile. (2) H2 cannot be oxidized over both anatase and rutile under UV irradiation, and the surface resistance of both two crystal types of TiO2 are increased by the H2 adsorption under UV irradiation. (3) Adding H2 into CO/O2 reactants can suppress the photocatalytic oxidation of CO over anatase, but promote that over rutile. This result may be somewhat concerned with the different processes of H2 response on anatase and rutile sensor under UV irradiation. For anatase sensor, adsorbing H2 will first cause the decrease and then the increase in the surface resistance of sensor. For rutile sensor, adsorbing H2 will cause the continuous increase in the surface resistance of sensor. Based on the further analysis, the results can be attributed to the adsorption behavior of H2 at the lattice oxygen of anatase. (4) The as-prepared TiO2 with a high percentage of exposed{001} exhibits a good gas sensing response to ethylene or acetone under UV irradiation in both high purity nitrogen atmosphere and air atmosphere. This result shows the gas sensing properties of TiO2 are not only related to the photocatalytic activity, but also to the material properties.Based on the above results and analysis, it can be further inferred as follows:(1) Reductive reaction gas can be photocatalyticly oxidized by TiO2 provided that the gas can offer electrons to TiO2; (2) The differences in photocatalytic oxidation performance between anatase and rutile may be somewhat related to the role of surface lattice oxygen in photocatalytic reaction.The innovations of this study can be concluded as follows:Based on the theory of the adsorption of the semiconductor, the gas-sensing properties of semiconductor is successfully investigated the adsorption behaviors and then the electron transfer of semiconductor adsorbing reactant gases. This work maybe provides a new approach to study the photocatalytic process of semiconductor.