Visible Light-Sensitive Cu(II)-Grafted TiO2 Photocatalysts: Activities and X-ray Absorption Fine Structure Analyses

We investigated the role of Cu(II) ions and their associated structural features, such as chemical state and environment, in the Cu(II)-grafted TiO2 photocatalyst by means of 2-propanol oxidative decomposition under visible light and X-ray absorption fine structure (XAFS) measurements. The 2-propanol decomposition activity under visible light (1 mW cm−2, 450−580 nm) was highly reproducible (three repetitions). The XAFS results indicated that the Cu(II) is incorporated in a distorted amorphous CuO-like structure, having a five-coordinated square pyramidal form. The distorted CuO formed clusters and attached to the TiO2 surface. The chemical state and environment of the Cu(II) ions were not changed, even after the photocatalytic oxidative reaction. Thus, Cu(II)-grafted TiO2 can be regarded as a stable photocatalyst. In addition, in situ XAFS measurements were performed under visible light in the presence of 2-propanol and absence of oxygen. Under these conditions, Cu(I) was generated. However, the latter converted back to Cu(II) when it was exposed to oxygen, indicating the oxygen reduction activity of Cu(I).