Surface-state-induced upward band bending in P doped g-C3N4 for the formation of an isotype heterojunction between bulk g-C3N4 and P doped g-C3N4: photocatalytic hydrogen production

The staggered type heterojunction with g-C3N4 based nanomaterials has received much attention owing to its change in chemical potential between two semiconductors. As a result, the migration of charge carriers occurs via the interface electric field when the semiconductor band bends upward or downward. Herein, we made an isotype heterojunction between bulk g-C3N4 and bulk P-g-C3N4 by forming a surface P-C bond between them. The maximum hydrogen production of 1.6 mmol h(-1) g(-1) is obtained for the optimized heterojunction catalysts, which is 5.3 and 2.6 times higher than those of bulk g-C3N4 (0.30 mmol h(-1) g(-1)) and bulk P-g-C3N4 (0.60 mmol h(-1) g(-1)). Thus, the formation of surface P-C bonds hinders the charge carrier recombination on various parts of the heterojunction via enhancing the spatial charge separation and prolonged carrier lifetime. Besides, the altered electronic structure, interaction between g-C3N4 and P-g-C3N4, relocated work functions of P-g-C3N4 and distinct band edge positions were formed, which are responsible for the improved photocatalytic activity. Furthermore, the upward band bending of P-g-C3N4 and its higher delocalization ability led to higher conductivity and largely prevented electron-hole pair recombination.