Core-shell composite via MOF-on-MOF strategy: Boosting CO2 photoreduction and Cr(VI) detoxification through interfacial function

Excessive carbon dioxide (CO 2 ) emissions and heavy metal pollution caused by industrial development and fossil fuel consumption have become two critical challenges urgently requiring environmental governance. A core-shell ZIF-67/ZIF-8 composite was rationally designed via a MOF-on-MOF method. This composite exhibits bifunctional capabilities for photocatalytic CO 2 reduction and Cr(VI) sequestration. The results demonstrate that the composite efficiently converts CO 2 into carbon monoxide (CO) under light irradiation. Its yield reached as high as 1260.53 μmol·g −1 ·h −1 , which is respectively 1.71 times and 30.75 times higher than that of the original ZIF-67 and ZIF-8. Concurrently, the composite exhibited a remarkable Cr(VI) adsorption capacity of 37.24 mg·g −1 . The effects of solution pH, adsorbent dosage, coexisting ions and temperature on Cr(VI) adsorption were systematically investigated through batch experiments, complemented by kinetic and thermodynamic analyses. The adsorption process follows a heterogeneous chemisorption mechanism involving electrostatic attraction, Co 2+ coordination and interfacial reduction. The material displayed remarkable reusability and cycling stability, maintaining relatively stable performance with only a slight decline over ten consecutive cycles, retaining 81% of its initial CO production yield and 92% of its initial Cr(VI) adsorption capacity. Overall, the as-fabricated ZIF-67/ZIF-8 composite offers a feasible approach for the integrated control of atmospheric CO 2 and aqueous heavy-metal pollution.