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 μmol 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.