Role of surface/interfacial Cu²⁺ sites in the photocatalytic activity of coupled CuO-TiO₂ nanocomposites

Coupled CuO-TiO₂ nanocomposite photocatalysts were prepared by a deposition precipitation method and were characterized with a variety of techniques. Electron paramagnetic resonance (EPR) spectroscopy was employed to study the local structures of surface/interfacial Cu²⁺ sites using Cu²⁺ as a sensitive paramagnetic probe. The addition of bulk CuO to TiO₂ led to decreased photocatalytic efficiency in the degradation of methylene blue. However, doping with a very small amount of CuO (0.1 wt % copper loading) significantly enhanced the photocatalytic activity of TiO ₂. EPR study of the TiO₂ surface revealed the presence of both highly dispersed CuO clusters and substitutional Cu²⁺ sites (Ti-O-Cu linkages) at 0.1 wt % copper loading. The data suggest that the Ti-O-Cu linkages contributed to the improved photooxidative activity of the 0.1% CuO-TiO₂ nanocomposite. In contrast, at higher loadings the bulk form of CuO created charge recombination centers lowering the photoactivity of the composites.