Spatial Confinement of Pd Nanoclusters in Pyrene-Based Covalent Organic Frameworks for Boosting Photocatalytic CO2 Reduction.

Photocatalytic CO2 reduction offers a promising strategy to mitigate the greenhouse effect, yet it remains a challenging process due to the high energy barrier associated with the high stability of CO2. In this study, we synthesized Py-bTDC, a pyrene-based covalent organic framework (COF) enriched with nitrogen and sulfur atoms, and anchored palladium nanoclusters (Pd NCs) onto its structure to enhance CO2 reduction efficiency. The confined Pd NCs amplify the built-in electric field (IEF), enabling efficient photogenerated carrier migration and suppressing electron-hole recombination. Simultaneously, Pd NCs serve as catalytic active sites, optimizing CO2 adsorption and activation. Density functional theory (DFT) calculations reveal that Pd reduces the energy barrier for forming the critical intermediate (*COOH), thereby accelerating CO production. Under visible-light irradiation in a gas-solid system using water as a proton donor, the Pd3/Py-bTDC composite achieved a CO evolution rate of 17.75 μmol·h-1·g-1 with 86.0% selectivity. This study advances the design of COF-based photocatalysts by synergistically modulating IEF and the engineering active sites for efficient CO2 reduction.