Engineering redox metal covalent organic frameworks for efficient chromium(VI) photoreduction

Developing efficient and sustainable photocatalysts for reducing toxic chromium (VI) is paramount in environmental remediation. The atomic-level integration of redox-active copper clusters into crystalline covalent organic frameworks (COFs) presents a transformative approach for designing high-performance environmental photocatalysts. In this work, we demonstrate the successful construction of copper(I) cluster-incorporated MCOFs as high-performance redox-active photocatalysts for the solar-driven reduction of chromium(VI) contaminants. This innovative design synergistically combines the photoredox capabilities of Cu(I) clusters with the structural advantages of MCOFs, thereby achieving exceptional photocatalytic efficiency in chromium(VI) detoxification. The prepared Cu(I) cluster-based MCOFs possess high crystallinity, permanent porosity, outstanding stability, and promising photoredox properties. Under visible light irradiation, the Cu(I) cluster-based MCOFs exhibit exceptional photocatalytic activity with fast rate and efficient removal, after 1 hour of visible light irradiation, all Cu(I) cluster-based MCOFs show significant photocatalytic activity for the reduction of Cr(VI) to Cr(III) with the conversion rate exceeding 99 %. After five recycling, no significant decline in the photocatalytic efficiency was observed. Detailed spectroscopic and electrochemical studies elucidated that Cu(I) clusters play a crucial role in the photocatalytic process. This work provides valuable insights into the design and development of novel metal covalent organic frameworks for environmental remediation applications. The structure-activity relationships revealed herein (e.g., conduction band modulation through ligand electronic effects) offer rational design principles applicable to broader environmental and energy applications.