Tailoring Alkyl Side Chains of Benzotriazole‒Based Covalent Organic Frameworks for Enhancement of Photocatalytic CO2 Reduction

Various molecular design strategies of covalent organic frameworks (COFs) are employed to enable highly efficient and selective photocatalytic reduction of CO₂ for carbon neutralization and the production of value‒added chemical products. Instead of frequently‒studied variation in main frameworks of COFs, side‒chain engineering is adopted in this study to tailor their photocatalytic CO₂ reduction performance. Alkyl side chains with different lengths are attached to benzo[d][1,2,3]triazole‒based β‒ketoenamine COFs. It is found that alkyl side chains can alter the properties of the as‒synthesized COFs, including interlayer stacking, crystallinity, specific surface area, light harvesting and charge transfer behavior. After loading Co²⁺, COFs featuring a moderate ethyl side chain length exhibit superior photocatalytic performance compared to those with shorter methyl or longer butyl side chains. The CO production rate of 21.74 mmol g⁻¹ h⁻¹ and apparent quantum yield of 13.3% rank at the top among COFs-based photocatalytic systems. This study may not only help to get in‒depth understanding of photocatalytic mechanism of COFs, but also offer an alternative approach for achieving efficient and selective photocatalytic CO₂ reduction.