Construction of triazine/heptazine carbon nitride homojunction for photocatalytic reduction of high-concentration 4-nitrophenol

Homogeneous carbon nitride (C₃N₄) photocatalysts with their suitable electronic structure, environmental benignity, and outstanding chemical stability properties have been exhibiting excellent performances in various fields. However, their mechanism is still relatively unclear, and there is limited research on treating high-concentration water pollutants. This work presents a crystallized carbon nitride homojunction (HCN) catalyst originating from triazine-based C₃N₄ (TCN) and bulk phenazine-based C₃N₄ (BCN) via one-step calcination. As a result, the optimized HCN first demonstrates significantly enhanced photocatalytic reduction efficiency (≈1.44 min⁻¹) towards 150 mg/L high-concentration 4-nitrophenol (4-NP) under visible light irradiation, up to two-fold better than BCN. The concentration and pH were meticulously adjusted, accompanied by a thorough exploringly the underlying mechanisms. Subsequently, comprehensive verification was conducted to confirm the existence of a type-II homojunction and the establishment of an interfacial electric field (IEF) in HCN, which serve as potent facilitators for the separation and migration of photo-excited carriers. This novel study provides a comprehensive understanding of homojunction catalyst design and advances the development of efficient metal-free photocatalysts for degrading high-concentration pollutants.