Direct Surface Modification of Graphitic C₃N₄ with Porous Organic Polymer and Silver Nanoparticles for Promoting CO₂ Conversion

The development of novel heterogeneous catalysts for converting CO₂ into fine chemicals under mild conditions is extremely attractive but challenging. In this study, graphitic carbon nitride modified by porous organic polymer (POP) and highly dispersed Ag nanoparticles (Ag/POP@g-C₃N₄) was prepared as a highly efficient heterogeneous catalyst for CO₂ conversion for the first time. The POP modifying g-C₃N₄ remarkably increases specific surface area and nitrogen species (NH and CN); as a result, the abundant porous structures together with anchoring sites allow tight immobilization and homogeneous dispersion of Ag nanoparticles. Benefiting from the effective incorporation, Ag/POP@g-C₃N₄ exhibited superior catalytic performance for the carboxylative cyclization of propargyl alcohols with CO₂ under mild conditions. From the perspective of CO₂ adsorption and controlled ¹H NMR analyses, a plausible synergistic catalytic mechanism was proposed for the adsorption and activation of CO₂ in combination with Ag/POP@g-C₃N₄ and 1,8-diazabicyclo­[5.4.0]­undec-7-ene (DBU).