Boosting photocatalytic CO₂ reduction through self-nitrogen-functionalization on bifunctional porous carbon...

It is rather important to develop a photocatalyst with high sunlight response, efficient CO₂ adsorption and reduction performance for solar-driven CO₂ reduction. Herein, self-nitrogen-functionalized porous carbon macro-spheres by using melamine as both carbon source and nitrogen source were successfully prepared via suspension polymerization and carbonization strategy, and the effects of different monomer ratios and carbonization temperatures on the photocatalytic reduction of CO₂ were investigated. Our experimental and characterization results demonstrated that N-CS-2 exhibited excellent CO₂ adsorption performance (1.76 mmol g^-1) and photocatalytic reduction activity (122.49 μmol g^-1) while the molar percentage of melamine and formaldehyde was 2%, and the CO₂ reduction performance can still remain around 97.6% after ten cycle tests under the same conditions. Furthermore, the photocatalytic performance decreased with the increase of carbonization temperature, and the sample N-CS-600 °C obtained by carbonizing at 600 °C under the optimal amount of melamine showed the highest photocatalytic CO₂ reduction performance, and the pyridine-N and pyrrole-N in the structure of carbon spheres were the main active species and reaction sites for photocatalytic reduction reaction, while the graphite-N acted as an electron transfer channel for reducing the recombination of electron and hole pairs. In addition, the change of carbonization temperature showed little effect on the specific surface area and pore volume of the samples according to the analysis of pore structure, and the pyridine-N and pyrrole-N played an important role in improving the photocatalytic performance under the circumstances. Finally, our results will provide a feasible strategy to synthesize bifunctional metal-free photocatalysts for high-efficiency CO₂ adsorption and photoreduction.