Solid-state in situ synthesis of g-C3N4/ZnO nanocomposites for photocatalytic water cleaning

We present a scalable, solvent-free two-step route to g-C₃N₄/ZnO heterostructured nanocomposites for solar-driven wastewater remediation. g-C₃N₄ is first obtained by conventional thermal polymerization of melamine; in the second step, ZnO is introduced mechanochemically, yielding intimate g-C₃N₄/ZnO interfacial contact and robust heterojunctions. Composites with 2–20 wt% g-C₃N₄ were synthesized and comprehensively characterized. The optimized ZOCN10 (10 wt% of g-C₃N₄) exhibits rate constant k = 0.0389 min⁻¹ and achieves ∼95% methylene blue removal within 90 min under simulated solar irradiation, outperforming both pristine ZnO and g-C₃N₄ 4.6 and 5.5 times, respectively and clearly surpassing a physical mixture. Reactive-species trapping indicates h⁺ and O₂⁻ as the dominant actors in the degradation pathway. The catalyst remains reusable across multiple cycles, retaining a substantial portion of its activity and thereby supporting practical deployment scenarios in water treatment. By eliminating organic solvents while enabling scalable processing and efficient solar-light operation, this mechanochemically assisted approach provides a green and cost-effective path to high-performance photocatalysts for wastewater purification.