N-doped ZnO-MoS2 binary heterojunctions: the dual role of 2D MoS2 in the enhancement of photostability and photocatalytic activity under visible light irradiation for tetracycline degradation

In this work, we report the fabrication of binary semiconductor heterojunctions comprising N-doped ZnO nanorods loaded with two-dimensional MoS2 nanoflowers in varying amounts, using a facile hydrothermal synthesis method. These semiconductor heterojunctions have been demonstrated to be highly efficient photocatalysts with enhanced performance under visible light irradiation for the degradation of a pharmaceutical pollutant, tetracycline. The superior photocatalytic activity of the heterojunctions can be attributed to the synergistic effect of N-doping of ZnO and loading of MoS2 leading to higher absorption of visible light, efficient separation of photogenerated charge carriers and rapid charge transfer to reaction sites, as per the conduction band potentials of both N-doped ZnO and MoS2. In addition, the two-dimensional nanoflower morphology of MoS2 provides more reaction sites for the adsorption of pollutants, due to its large surface area. Furthermore, the transfer of holes from the valence band of N-doped ZnO to the valence band of MoS2 prevents the photocorrosion of N-doped ZnO resulting in enhanced photostability of the catalyst during the reaction.