Highly-efficient photocatalytic removal of methyl orange on CuO hierarchical hollow microspheres modified by ultrathin and porous g-C3N4 nanosheets.

Photocatalytic degradation technology is taken as an efficient strategy to alleviate organic dye pollution in wastewater. In order to achieve high catalytic activities, morphology regulation and structure design are crucial for photocatalytic system. In this work, the hierarchical CuO hollow microspheres self-assembled by nanowires (CuO HMS) were successfully synthesized by solvothermal process. Graphitic carbon nitride (g-C3N4) nanosheets (CNN) with ultrathin and porous feature were anchored on the spherical shell of CuO HMS to manufacture the CuO/g-C3N4 p-n heterojunction via one-step calcination. The unique CuO/g-C3N4 composite possesses the nanowire self-assembled hollow hierarchical microstructures, as well as the self-doped CuO by the C and/or N atoms, which conduces to increasing specific surface area, narrowing band gap, improving visible-light-harvesting capacity, promoting the segregation of photo-induced electron-hole pairs, and accelerating carrier movement. Therefore, CuO/g-C3N4 shows outstanding photocatalytic properties of methyl orange (MO) degradation, compared with CuO HMS and CNN. Especially, the CuO/g-C3N4 composite with 10 wt% CuO HMS (CC-3) achieves almost complete decomposition of MO, and its apparent rate constant (kapp) is superior to that of CuO HMS (19.1 times) and CNN (22.5 times). Compared with the similar materials such as CuO/BiVO4, CuO/TiO2 and CuO/ZnO p-n heterojunctions, the resulting CuO/g-C3N4 composite demonstrates the satisfactory photocatalytic performance. The close cooperation of unique hollow hierarchical morphology, C and/or N self-doping, and p-n heterojunction is proposed to account for the extraordinary photocatalytic MO decomposition. This work proposes a feasible and effective paradigm for the construction of CuO/g-C3N4 composite, which demonstrates excellent photocatalytic performance for pollutant removal in wastewater by establishing hollow structure, non-metallic self-doping and p-n junction.