Immobilizing Isatin-Schiff Base Complexes in NH2-UiO-66 for Highly Photocatalytic CO2 Reduction

Reducing carbon dioxide (CO2) via photocatalysis to carbon-based materials is a challenging process due to the complexity of the process and the production of several byproducts. Therefore, it is crucial to develop photocatalysts with high yield and selectivity for CO2 reduction. Herein, we present a strategy for creating high-performance catalysts by immobilizing Ni, Co, and Cu ions in NH2-UiO-66 by covalently linking the isatin-Schiff base metal complexes (IS) to the micropores. The as-synthesized NH2-UiO-66/IS-complex (66-IS -M, M = Ni, Co, Cu) photocatalysts exhibit special photocatalytic activity for the reduction of CO2 because of the immobilized metal ions serving as active sites during the reaction. Among them, 66-IS-Ni has a maximum CO generation rate of 1350 smol g-1 h-1 and a CO selectivity of 87%, both of which are significantly higher than those of previously reported metal-organic framework (MOF)-based photocatalysts. Experimental characterizations and density functional theory (DFT) calculations reveal that the effective charge separation and lowered free energy of CO2 reduction on 66-IS-Ni promote CO2 conversion. This study presents a universal strategy for the uniform dispersion of molecular catalysts in amino-functionalized MOF for efficient photocatalytic applications.