Cu NPs@covalent organic framework: An efficient photocatalyst for light-assisted selective formylation of phenol derivatives utilizing carbon dioxide

Our study presents a novel synthetic approach for the visible-light-assisted photocatalytic production of 2-hydroxybenzaldehyde from phenol via CO₂ reduction, using copper nanoparticles (Cu NPs)-incorporated two-dimensional covalent organic framework (TR-PDA COF) photocatalyst. The Cu@TR-PDA catalyst exhibited a low band gap energy (2.14 eV), enabling efficient visible light absorption and photocatalytic activity. Under optimized conditions, this catalyst achieved 87 % conversion of phenol to 2-hydroxybenzaldehyde under 20 W white LED light. The reaction was light-dependent and required a base. Mechanistic studies revealed that formaldehyde (HCHO), generated from CO₂ photoreduction, served as a key intermediate, which reacted with phenol to form the desired product. Furthermore, the Cu@TR-PDA catalyst demonstrated excellent reusability over six cycles, and showed minimal metal leaching, confirming its heterogeneous nature. This work offers a promising strategy for the sustainable conversion of CO₂ into valuable chemicals using a metal-based photocatalyst under visible light.