(Europe Section Heinz Gerischer Award Address) TiO2-Based Visible Light Photocatalysts Based on Interfacial Charge Transfer Process

Abstract

TiO2 is known as an efficient photocatalyst and is well studied aiming for environmental and energy application. However, TiO2 absorbs only UV light and thus its application had been limited. We recently demonstrated that the surface modification of TiO2 with Cu(II) or Fe(III) nanoclusters produced a new optical absorption in the visible light region. We also found that those surface modified TiO2s show an efficient visible-light-sensitivity in photocatalysis under ambient conditions. Its reaction mechanism can be explained as follows. In the case of Cu(II) nanocluster-grafted TiO2 (Cu(II)-TiO2) for example, electrons in the valence band (VB) of TiO2 are excited to the Cu(II) nanoclusters under visible-light irradiation through an interfacial charge transfer (IFCT) process. The introduction of excited electrons into the Cu(II) nanoclusters leads to the formation of Cu(I) species, which efficiently reduce oxygen molecule through two-electron process. In other words, Cu(II) nanocluster serves as a multi-electron catalyst for molecular oxygen reduction reaction. In addition, during the IFCT process, holes are generated in the deep VB of TiO2 and are used for the decomposition of organic compounds. Thus, these nanocluster-modified TiO2s show very strong oxidation power even under visible light excitation and are promising materials for visible-light-sensitive photocatalytic applications under ambient conditions. In this lecture, I will review our studies on these IFCT-based TiO2 visible light sensitive photocatalysts, and also show the results of their demonstration tests obtained in some public spaces such as airports and hospitals towards anti-bacterial and anti-virus building material application..