ZnO-CuxO heterostructure photocatalyst for efficient dye degradation

A simple aqueous solution process was used for the synthesis of Cu-loaded ZnO nanorod structures in which highly crystalline and hexagonal wurtzite ZnO, cubic CuO and Cu2O phases coexist. Absorption/emission characteristics identify band gap narrowing, which facilitates visible light absorption, as a consequence of hybridization of O 2p bands with Cu(3)d bands of the ZnO-CuxO heterostructure system. With use of the specific band energy position of the individual components (i.e., ZnO, Cu2O, and CuO), photogenerated electrons and holes could be made to migrate separately and thereby the carrier recombination could be delayed, making them amply available for photocatalytic reactions. The available electrons plausibly produce superoxide radical anion (O-2(center dot-)), while holes generate hydroxyl radicals (center dot OH), which are reactive agents for dye degradation. Furthermore, the formation of a depletion region via Cu-induced charge separation within the ZnO-CuxO heterostructure and thermal-energy-mediated abstraction of the electric field barriers and subsequent migration of the positively charged defects from the subsurface region toward the interface lead to efficient photocatalytic performance.