Surface modification of micro-sized CuO by in situ-growing heterojunctions CuO/Cu2O and CuO/Cu2O/Cu: effect on surface charges and photogenerated carrier lifetime

In photocatalyst design, the rapid recombination of photo-generated electron-hole pairs in the bulk or on the surface of semiconductors is a major limiting factor in achieving high photocatalytic efficiency, which is a key scientific issue. Surface modification is used to change the surface properties of photocatalyst related to dark adsorption and photocatalytic efficiency. In this work, micro-sized CuO powder was surface modified by in situ-growing heterojunctions CuO/Cu2O and CuO/Cu2O/Cu when simply calcinating a mixture of CuO and urea, in which urea acted as a reducing agent. The phases, microstructure, composition, photogenerated carrier lifetime, dark adsorption rate, photodegradation rate, and surface charges of the as-modified powder were investigated. The surface modification was found to change the negative surface charge of micro-sized CuO to a positive one, resulting in enhanced dark adsorption (nearly twice that of pristine CuO). Furthermore, the surface modification prolonged the photogenerated carrier lifetime, which in turn enhanced the photocatalytic efficiency. Overall, this work implies that the electric properties of surface charges and carrier lifetime can be altered by constructing an appropriate heterojunction on the surface of the photocatalyst.