A novel cobalt-anchored covalent organic framework for photocatalytic conversion of CO2 into widely adjustable syngas

The photocatalytic conversion of CO2 into widely adjustable syngas (CO/H-2 mixture) has been considered as an extraordinarily promising but challenging strategy to realize high value-added utilization of CO2 to alleviate worldwide environmental problems and energy crisis. To achieve this goal, we report a newly designed crystalline covalent organic framework (COF-TVBT-Bpy) that embedded a series of metal active sites to efficiently convert CO2 and H2O into syngas under visible-light illumination. COF-TVBT-Bpy not only provides a coordination environment for the metal center, but also enhances electron delocalization by the extended conjugated moiety, thus facilitating electron transfer. The optimized Co@COF-TVBT-Bpy achieves the highest photocatalytic CO2-to-syngas conversion efficiency in pure CO2 (up to 2291.1 mu mol g(-1) h(-1), CO/H-2 approximate to 1 : 1). The intrinsic reason for a CO/H-2 ratio of 1 : 1, electron transfer pathway, and syngas generation mechanism over Co@COF-TVBT-Bpy are explored by the combination of in situ measurements and theoretical calculations. The experimental results confirm that the ratio of CO/H-2 can be widely modulated by adjusting the metal active sites and photoreaction conditions. This work proves the immense potential of utilizing COFs as platforms to anchor metal active sites for syngas formation and provides a facile method to regulate the ratio of syngas in a wide range.