Visible-light responsive TiO₂ for the complete photocatalytic decomposition of volatile organic compounds (VOCs) and its efficient acceleration by thermal energy

Titanium dioxide (TiO2 ) semiconductors are known to exhibit photocatalysis by bandgap excitation upon UVlight (hv > 3.2 eV) irradiation. TiO2 has been extensively investigated in the challenge to address the urgent need for environmental remediation such as the degradation of volatile organic compounds (VOCs). In this study, it was striking that the TiO2 exhibited effective reactivity for the complete degradation of various VOCs such as benzene, toluene and m-xylene (BTX) into CO(2 )under visible-light irradiation (2.3 eV < hv). This is because the adsorption of various VOCs on TiO2 results in the formation of an interfacial surface complex (ISC) that provides weak light absorption in the visible light region. In particular, the correlation between the apparent quantum yields in the photocatalytic decomposition of toluene and the light absorption wavelengths of the ISC was clearly demonstrated. By density functional theory (DFT) simulations, the mechanism for origin of the visible-light responsive TiO2 was clarified. Furthermore, thermal effects on the visible-light responsive TiO2 photocatalysis were investigated. It was found that the combination of visible light-energy and its excess thermal energy significantly enhanced activity for the degradation of toluene.