Correlation between the H2 response and its oxidation over TiO2 and N doped TiO2 under UV irradiation induced by Fermi level

In the previous work, we have ever found that the photocatalytic oxidation of a reactant gas over TiO2 would be somewhat dependent on the electron transfer behavior between the adsorbed gas and TiO2 under UV irradiation. To further confirm the viewpoint, in this work, a TiO2 (in-situ) sample was prepared by an in-situ method, and was tested its gas-sensing performance to 1-12 and its photocatalytic performance of oxidizing H-2 as compared to a TiO2 (commercial) sample. It was found that TiO2 (in-situ) would increase the conductivity with the introduction of H-2 under UV irradiation, but TiO2 (commercial) would decrease the conductivity in the same case. Based on the surface structural and electrochemical characteristics of samples, it was proposed that the existence of surface defects over TiO2 (in-situ) would decrease the Fermi level (Es), resulting in the electron transfer from the adsorbed H-2 to TiO2, while the adsorbed H-2 accepted electrons from TiO2 (commercial) due to its higher Es. Moreover, the adsorbed H-2 on TiO2 (in-situ) could be oxidized under UV irradiation but that on TiO2 (commercial) could be hardly. This indicated that the photocatalytic oxidation of H-2 over TiO2 would be dependent on the electron transfer direction between the adsorbed H-2 and TiO2, i.e., the electron-donated H-2 could be oxidized, while the electron-accepted H-2 could be not. This above effect induced by the surface defects could be further demonstrated by a N-doped TiO2 (N-TiO2) sample. This N-TiO2 owned a lower EF than TiO2 (in-situ) due to the introduction of a more impurity defects, resulting in a more electron transfer from the adsorbed H-2 to NTiO2 and then the oxidation of more H-2. This study also indicated that the adjustment of BF could improve the photocatalytic activity of oxidizing H-2 by changing the adsorbed behavior of H-2 over TiO2, which may be applicable for investigating other reactants' oxidation behaviors over other semiconductor photocatalysts.