Synthesis of novel silver chromate incorporated copper-metal-organic framework composites with exceptionally high photocatalytic activity and stability

Metal–organic frameworks are potential materials for the development of high performance catalysts. However, photocatalytic use of MOFs for water treatment has remained, by and large, unexplored. Therefore, in this study a novel Ag₂CrO₄–HKUST-1 photocatalyst was synthesized by a solvothermal route followed by chemical precipitation method. The as synthesized pure and composite photocatalysts were characterized by XRD, FTIR, SEM, TEM, N₂-adsorption–desorption isotherms, UV–vis DRS, and Photoluminescence techniques. The Ag₂CrO₄/HKUST-1 composites were implied for photocatalytic degradation of two azo dyes, Congo Red (CR) and Ponceau BS (PBS) under Uv–vis light irradiation. The Ag₂CrO₄–HKUST-1 composites not only showed superior photocatalytic ability for CR and PBS degradation but also exhibited good catalyst stability. The photocatalytic performance of Ag₂CrO₄/HKUST-1 samples with different Ag: Cu molar ratio was investigated to find the optimum Ag₂CrO₄ content in the Ag₂CrO₄/HKUST-1 composite. The mechanism for the photocatalytic degradation of CR and PBS over Ag₂CrO₄/HKUST-1 composites was studied in detail by introducing different scavengers of active species involved in the Photocatalytic oxidation process. It was proposed that Ag₂CrO₄/HKUST-1 transforms into Ag₂CrO₄/Ag/HKUST-1 in the early stages of photocatalytic reaction due to the reduction of Ag₂CrO₄ by photogenerated electrons. The formation of ‘Ag’ nanoparticles on the surface of composite catalyst enhances the photocatalytic degradation of dyes significantly because these ‘Ag’ nanoparticles act as electron traps and promote interfacial charge transfer through the internal charge transmission via Z-scheme pathway. Moreover, Ag₂CrO₄–HKUST-1 composites did not show any significant loss of activity for CR and PBS degradation during three recycle experiments indicating their high stability.