Enhanced visible photocatalytic oxidation of NO by repeated calcination of g-C3N4

Abstract Much attention has been paid to g-C 3 N 4 (gCN), a visible-light-responsive metal-free polymeric photocatalyst. However, bulk gCN suffers from the small BET surface area and quick recombination of carriers. The photocatalytic activity of bulk gCN still needs to be improved. Herein, we systematically studied the effect of post calcination times (PCT) on the visible photoreactivity of bulk gCN towards NO oxidation and hydrogen production. It was found that aggregated gCN nanosheets (gCN-NSs) were formed after repeated calcination of bulk gCN. The BET surface areas of gCN-NSs increased 6.6 times (from 9.1 to 60.5 m 2  g −1 ) after repeated calcination of bulk gCN for 7 times. The exfoliation of bulk gCN by post calcination results in a reduced PL intensity, increased photocurrent, diminished arc radius of EIS Nynquist plot. DFT calculation confirms the enlarged bandgap of gCN after post calcination. After repeated calcination for 7 times, the visible photoreactivity of gCN-NSs towards NO oxidation increased from 20.6% to 35.8% in a continuous reactor, and the hydrogen production rate improved from 31.3 to 764.8 umol g −1  h −1 in a batch reactor, enhanced by a factor of 24.4. The post calcination induced enhancement on the visible photocatalytic activity of gCN-NSs can be attributed to the combined effects of (1) enlarged BET surface area, (2) improved crystallinity, (3) negatively shifted CB position, and (4) exposure of (0 0 2) and (1 0 0) facets for g-CN-NSs which retarded the recombination of electron and hole pairs.