Direct double Z-scheme O-g-C3N4/Zn2SnO4N/ZnO ternary heterojunction photocatalyst with enhanced visible photocatalytic activity

For the heterostructure-based photocatalytic system, the most critical hindrance is to simultaneously achieve high photoelectric conversion efficiency and strong redox ability of photoinduced e(-)-h(+) pairs. Herein, a direct double Z-scheme O-g-C3N4/Zn2SnO4N/ZnO ternary heterojunction was designed according to the band bending theory, which was prepared via a simple UV light irradiation method. The transformation from II-I-type to Z-Z-type heterostructure was attributed to the construction of dual build-in electric fields due to the interface charge transfer caused by the different work functions and the formation of the new bonds at the interface, which had been demonstrated by charge difference density. The prepared g-C3N4/Zn2SnO4N/ZnO composite exhibited enhanced photocatalytic performance for the photo-degradation of organic dyes and NO removal compared with the O-g-C3N4/Zn2SnO4N/ZnO. The improved photocatalytic activity was ascribed to the synergistic effects of double Z-scheme heterojunction, build-in electric fields and impurity levels, resulting in the wide light response range, rapid interfacial transfer, prolonged lifetime and strong redox ability of the photoinduced charge carriers. This work provided a new idea to design and synthesize the photocatalysts with high visible light activity and understand the enhanced photocatalytic mechanism.