Fabrication of Z-scheme VO-Bi2WO6/g-C3N4 heterojunction composite with visible-light-driven photocatalytic performance for elemental mercury removal

Photocatalytic Hg0 oxidation under visible light radiation is an economic and feasible approach to deal with energy and pollution problems. In this paper, the photocatalytic oxidation capability of gaseous elemental mercury by Bi2WO6 under visible light radiation was further improved by introducing oxygen vacancies and forming the Z-scheme heterojunction with g-C3N4. Firstly, the experimental results demonstrate that oxygen vacancies were beneficial to reduce the band gap, with nearly trebling increase in mercury removal efficiency than that before modification (6.5%) under visible light. Secondly, the Vo-Bi2WO6/g-C3N4 composite with 10 wt% g-C3N4 content exhibited an optimal Hg0 removal efficiency of 87.2% compared with Vo-Bi2WO6 (17.8%) and pure g-C3N4 (12.4%) under the N2 + 4%O2 atmosphere. The improved photocatalytic efficiency could be primarily due to the formation of a built-in electric field between g-C3N4 and Vo-Bi2WO6 through the carrier transmission mechanism of Z-scheme heterojunction, enhancing the light absorption intensity in the visible range, facilitating the movement and separation of photoinduced carriers as well as improving the interfacial charge-transfer efficiency. Finally, DFT calculations provides a theoretical basis for the role of oxygen vacancies and the internal electric field generated between two interfaces.