Synergistic surface modulation of Ag/ZnO@ZIF-8 hybrid microspheres for enhanced photocatalytic degradation efficiency of rhodamine B

Abstract

Semiconducting ZnO has shown great potential as a photocatalyst for wastewater treatment owing to its advantages such as bandgap, high efficiency, and low cost. Unfortunately, photocatalytic activity of ZnO is limited as it aggregates in solution due to its small specific surface area, reducing the number of reaction sites and causing weak solar light absorption and rapid charge recombination. Therefore, we developed a novel Ag/ZnO@ZIF-8 hybrid microsphere photocatalyst with a transparent conductive adsorption layer. The poor capacity of surface ZIF-8 layer to conduct electrons was overcome by the large uniform distribution of Ag nanoparticles over the ZnO microspheres and small amount at the interface of the ZIF-8 overlay. The uniform thickness of the ZIF-8 shell increased the specific surface area of Ag/ZnO@ZIF-8. This reduces the aggregation in solution, thus creating more chemically active sites and charge carriers for photoexcitation and allowing vector transfer of excited electrons and charge separation. In addition, the significant red shift and narrowing in the bandgap of Ag/ZnO@ZIF-8 contributes toward its improved photocatalytic performance. Therefore, compared to pure ZnO microspheres, the Ag/ZnO@ZIF-8 hybrid microspheres showed exceptional performance in the degradation of rhodamine B (RhB) with a significant increase in dye degradation efficiency from 49.7% to 99.8% within 100 min. Compared to ZnO (25.2%), Ag/ZnO@ZIF-8 exhibited a degradation efficiency after three cycles of 81.5%. Meanwhile, the mineralisation rate of Ag/ZnO@ZIF-8 also reached 0.675. The hybridisation of ZnO with Ag nanoparticles and a ZIF-8 layer offers innovative approaches for creating highly effective photocatalysts.