Role of Surface/Interfacial Cu²⁺ Sites in the Photocatalytic Activity of Coupled CuO−TiO₂ Nanocomposites

Abstract

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 TiO2. 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.

On the Origin of Enhanced Photocatalytic Activity of Copper-Modified Titania in the Oxidative Reaction Systems

“…The ambiguity over the positions of the conduction and valence bands in CuO (and Cu2O) results in different explanations for the mechanistic aspects of heterojunction systems. For example, Li et al prepared CuO/TiO2 (rutile) nanocomposites by impregnation and subsequent calcination in air [86]. They tested photocatalytic properties of this material using methylene blue as a model compound under UV/vis irradiation.…”

“…Li et al concluded that efficient electron transfer from the CB of TiO 2 to CuO led to the absence of Ti 3+ (trapped electrons) in CuO-TiO 2 at high CuO loadings. They formulated a hypothesis that the form of CuO (clusters or nanocrystallites) had a significant influence on the type of charge transfer kinetics between TiO 2 and CuO [86].…”

Understanding the Reaction Mechanism of Photocatalytic Reduction of CO2 with H2O on TiO2-Based Photocatalysts: A Review

“…4(c) The addition of too high a concentration of CuO x beyond the optimum value would lead to decreased photocatalytic efficiency. It is possibly because of (1) the shading effect of CuO x that reduces the light absorption of TiO 2 and (2) CuO x acting as charge recombination centers at high concentrations (Li et al, 2008a;Irie et al, 2009).…”

Structural and optical properties of Ag-doped copper oxide thin films on polyethylene napthalate substrate prepared by low temperature microwave annealing

“…Transition metal oxides have gained considerable interest recently due to their potential application in solar cells, 1 displays, 2 sensors, 3 and supercapacitors. 4 Among them, copper oxides are nontoxic and the abundant availability of copper makes these oxides a cheap material available for many applications.…”