Effective Interfacing of Surface Homojunctions on Chemically Identical g‐C3N4 for Efficient Visible‐Light Photocatalysis without Sacrificial Agents

Abstract Developing efficient homojunctions on g‐C3N4 promises metal‐free photocatalysis to realize truly sustainable artificial photosynthesis. However, current designs are limited by hindered charge separation due to inevitable grain boundaries and random formation of ineffective homojunctions embedded within the photocatalyst. Here, efficient photocatalysis is driven by introducing effective surface homojunctions on chemically and structurally identical g‐C3N4 through leveraging its size‐dependent electronic properties. Using a top‐down approach, the surface layer of bulk g‐C3N4 is partially exfoliated to create sheet‐like g‐C3N4 nanostructures on the bulk material. This hierarchical design establishes a subtle band energy offset between the macroscopic and nanoscopic g‐C3N4, generating homojunctions while maintaining the chemical and structural integrities of the original g‐C3N4. The optimized g‐C3N4 homojunction demonstrates superior photocatalytic degradation of antibiotic pollutants at >96% efficiency in 2 h, even in different real water samples. It achieves reaction kinetics (≈0.041 min−1) up to fourfold better than standalone materials and their physical mixture. Mechanistic studies highlight the importance of the unique design in boosting photocatalysis by effectively promoting interfacial photocarrier manipulation and utilization directly at the point‐of‐catalysis, without needing co‐catalysts or sacrificial agents. This work presents enormous opportunities for developing advanced and green photocatalytic platforms for sustainable light‐driven environmental, energy, and chemical applications.