Enhanced Generation and Effective Utilization of Cr(V) for Simultaneous Removal of Coexisting Pollutants via MOF@COF Photocatalysts

Simultaneous removal of coexisting aqueous pollutants is urgently needed in the face of higher demands for wastewater purification. Using pollutant intermediates with strong oxidizing ability to degrade other coexisting pollutants is a novel, energy-saving, and environmentally friendly way. Increased generation and effective utilization of these intermediates are vital to boost the decontamination performance. Here, we fabricated a core–shell MOF@COF (MIL-125@PC–COF) heterojunction photocatalyst for the synergistic removal of Cr(VI) and the coexisting organic pollutant tetracycline (TC). The removal efficiency of TC and Cr(VI) in the coexistence system was increased by 2.1- and 1.1-fold compared to that in single-pollutant system, respectively. The unique heterojunction structure in the composite photocatalysts can hinder the recombination of photogenerated electrons and holes, thus promoting the production of Cr(V) from Cr(VI) reduction. Quenching tests, in situ variable-temperature electron paramagnetic resonance (EPR) analysis, and UV–vis absorbance verified the effective utilization of Cr(V) and its positive contribution to TC degradation. The mechanism of Cr(V) generation and utilization and its key role in dual-pollutant removal were clarified.