Flash dual-engineering of surface carboxyl defects and single Cu atoms of g-C3N4 via unique CO2 plasma immersion approach for boosted photocatalytic activity

Single transition metal atom embedding and functional group defect engineering is commonly utilized to optimize the electronic band structure of g-C3N4. However, most dual modification method suffers from the destruction of structure and active sites. Herein, single atom Cu and carboxyl group dual-endowed g-C3N4 nanosheets with a tunable bandgap were prepared by employing a facile CO2 plasma method. Experiments and density functional theory calculation show that the dual modification leads to a decreased bandgap and reconstructed local charge distribution to promote the separation of photogenerated charge carriers. As a result, the optimal Cu–CN–CO2-6min perform well in photo-Fenton degradation of dye and photocatalytic generation of H2. The synergy mechanism can be ascribed to the local imbalance electronic environment, in which single-atom Cu sites serve as H2 evolution center, and the carboxyl defect sites provide separate derivative site for various free radicals. The unique CO2 plasma method developed here can be completed in minutes with merits of environmental-friendless and waste-free, thus provides a promising route not only for the precise complex multiple modification of photocatalysts, but also for the sustainable industrial use of carbon dioxide.