A single-atom COF/CdS S-scheme photocatalyst for COF thickness-dependent CO2 photoreduction
Photocatalytic CO2 reduction is an attractive route to address sustainable energy crises and environmental issues, yet its efficiency is limited by poor charge separation, narrow light absorption, sluggish kinetics, and low CO2 adsorption/activation. Here, a series of Co SA-TT-COF/CdS S-scheme heterojunction photocatalysts were synthesized by integrating Co single atoms (Co SA) decorated covalent organic frameworks (COFs) with CdS nanotubes via in situ condensation and post-modification. The TT-COF layer thickness on CdS was regulated to optimize active site density and accessibility. The optimal Co SA-TT-COF/15 wt% CdS heterojunction, with a TT-COF thickness of 50.5 nm, achieved a CO production rate of 14157 μmol g−1 h−1 and a selectivity of 90.9%, among the best COF-based photocatalysts reported. Theoretical calculations, experiments, and femtosecond transient absorption spectroscopy revealed that the S-scheme heterojunction enhances the built-in electric field, optimizes energy levels, narrows bandgaps, extends light harvesting, improves charge separation and transfer kinetics, and lowers energy barriers for CO2 adsorption/activation, directly contributing to superior performance.