Microenvironments Enabled by Covalent Organic Framework Linkages for Modulating Active Metal Species in Photocatalytic CO2 Reduction

Covalent organic frameworks (COFs) are promising platforms for understanding photocatalytic CO2 reduction processes owing to their predesignable structures and tailor-made functions. Herein, a nickel-modified COF composed of N-acylhydrazone-linked electron-donor and electron-acceptor dyads (H-COF-Ni) is reported. H-COF-Ni generates 5694 mu mol g(-1) of CO with 96% selectivity over H-2 evolution in 2 h under visible light irradiation, which greatly outperforms that of typical imine-linked counterpart. Experimental and theoretical results have demonstrated that metal active sites in host frameworks are deprived by 2,2 '-bipyridine additive to form new catalytic active species, the separation and transfer process of the photogenerated charge carriers are not main reason for their activity difference. The linkage-dependent activation of CO2 molecules on Ni centers is responsible for high photocatalytic efficiency. This study provides new protocols to improve CO2 photoreduction performance through the modification of linkage microenvironments.