Enhancing visible light absorption for efficient CO₂ reduction with black carbon nitride hollow microspheres

Pristine carbon nitride (PCN) suffers from poor absorption of light above 460 nm and rapid recombination of photo-induced charge carriers. We report a unique type of black carbon nitride hollow microspheres (3D-BCN) with nitrogen defects, which have larger specific surface area (106.3 m(2) g(-1)vs. 6.5 m(2) g(-1)) and stronger solar absorption (200-1000 nm), narrower bandgap (1.63 eV), slower recombination of excitons, higher photo-generated current (1063 nA vs. 218 nA) and more efficient CO2 reduction to CO (6.8 times as compared to PCN).