Truxenone-based donor–acceptor covalent organic frameworks incorporated with metal sites for enhanced photocatalytic CO2 reduction

Abstract

Photocatalytic reduction of carbon dioxide (CO₂) into valuable chemicals offers a potential strategy to alleviate environmental pollution and has attracted great attention. Covalent organic frameworks (COFs) are known as a novel class of promising materials to boost CO₂ reduction, although it is still an enormous challenge. Incorporating metal sites into COFs serves as a strategic design for product selectivity regulation as it increases the number of active sites. Herein, the electron donor–acceptor (D–A)-structured truxenone (TRO)-based COFs with biphenyl (BPD-COF) and bipyridine (BPY-COF) units were constructed through a simple Schiff-base reaction, which offered a coordination environment for the metal ions and facilitated the adsorption and activation of CO₂ molecules. The photocatalytic CO production rate for the optimal sample of BPY-COF–Co was up to 870 μmol g⁻¹ in 3 h, and the selectivity under visible light was 100%, which was over 9-fold higher than that of pristine BPY-COF. Experimental and theoretical results revealed that the synergistic effect of the D–A structure and metal active sites facilitated the charge transfer and separation abilities to enhance the photocatalytic CO₂ reduction. This study offers molecular-level perspectives into a mechanistic understanding in enhancing the photocatalytic CO₂ reduction reaction (CO₂RR).