Insight on graphitic carbon nitride prepared by LiCl molten salts for photocatalytic H2O2 evolution: Crucial role of bulk N-defects

Molten salt method was effective to improve the photocatalytic performance of graphitic carbon nitride (CN). Nevertheless, various complex reactions took place in flux, leading to the complicated CN molecular structure. Therefore, besides high photoactivity, it was necessary to illustrate the structure-function relationship. Herein, CN nanosheets (CN-S) were prepared. After post-treated by LiCl molten salts, the photocatalytic H 2 O 2 rate over as-obtained CN-S-LiCl- x was dramatically increased from 22.3 to 81.4 mM·g −1 ·h −1 , much higher than the sample post-treated by NaCl and KCl molten salts. Compared to the initial CN-S, the -C N groups, bulk N-defects and surface N-defects were controllably introduced in CN-S-LiCl- x. These critical structural factors on photocatalytic H 2 O 2 performance were quantitatively studied, and the bulk N-defects displayed the correlation of linear relationship as high as 0.945. Electrochemical tests and DFT calculation indicated bulk N-defects were served as the main O 2 adsorption sites with adsorption energy of −4.33 eV, which not only accelerated surface reaction, but also extended light harvest and improved separation efficiency of photoinduced charge carriers. In photocatalytic H 2 O 2 mechanism study, one-step two-electron reduction and two-step single-electron reduction performed simultaneously, while the latter was primary. Our work has conducted a detailed analysis on the relationship between various structural factors and H 2 O 2 yield, and identified the key role of bulk N-defects. This provides new ideas to investigate photocatalytic H 2 O 2 evolution mechanism and design efficient CN-based photocatalysts.