g-C3N4-based homojunction induced by Ag and P selective doping for improved photocatalytic H2 evolution coupled with tetracycline degradation: Type-II versus S-scheme mechanism

The reasonable design of g-C3N4(CN)-based homojunctions is a promising method to improve the photocatalytic performance. Controlling the interfacial charge-transport process is challenging. Herein, Ag and P-doped CN (ACN and PCN) were selectively synthesized. The band edges of CN move downward continuously with increasing Ag or P doping concentration. CN/4ACN (type-II), CN/8PCN (S-scheme) and 4ACN/8PCN (S-scheme) were formed by suitable energy level matching, and their charge transfer mechanisms were confirmed via VBXPS, UPS and ESR analysis. In the presence of the hole sacrificant triethanolamine (TEOA), both CN/4ACN and 4ACN/8PCN exhibited better H2 evolution reaction (HER) rate than CN/8PCN due to the improvement in conductivity caused by Ag doping. However, only CN/8PCN and 4ACN/8PCN exhibited HER coupled with tetracycline (TC) degradation performance owing to the high redox potential of the S-scheme. Benefiting from a good carrier transport property and high redox potential, 4ACN/8PCN exhibited the best HER rate (2305.6 mu mol center dot g- 1 center dot h-1) with TEOA as the hole sacrificant, which was 11.7 times than that of pure CN, respectively, and achieved a high HER rate (117.8 mu mol center dot g- 1 center dot h-1) coupled with simultaneous TC degradation. This study provides a basic understanding of CN homojunctions, which shows potential for expanded applications in photocatalytic H2 evolution and pollutant degradation.