Fabrication of a Z-scheme Zn₃V₂O₈/g-C₃N₄ nano-heterojunction with high interfacial charge transfer for superior photocatalytic removal of diazinon pesticide under visible light

In this work, we report fabrication of a new Zn₃V₂O₈/g-C₃N₄ Z-scheme nano-heterojunction for superior photodegradation of organo-phosphorous pesticide diazinon under visible light irradiation. The crystal structure, morphology, elemental composition, photo-electrochemical response and band structure of nano-photo-catalysts were investigated using various analytical techniques. The as-synthesized photocatalyst with best optimized ratio Zn₃V₂O₈/40 wt% g-C₃N₄ (ZC-40) composites led to 95.2% diazinon (DZN) degradation in 60 min exposure and maintaining high structural stability after multiple reuse cycles (10 mg L⁻¹ initial DZN concentration, pH = 6, catalyst dosage 0.35 g L⁻¹ and visible light intensity 180 mW cm⁻²). Moreover, the experiments were performed under various reaction conditions as pH conditions, co-existing electrolytes, humic acid, tap water, river water and natural solar light. The improved photocatalytic activity of the heterojunction was ascribed to the synergistic effect of Z-scheme mechanism, high visible light absorption, oxygen vacancies, charge separation and metallic redox mediator. The reduced recombination and high charge transfer capacity was confirmed by electrochemical impedance spectroscopy and photoluminescence. The Z-scheme transfer between Zn₃V₂O₈ and g-C₃N₄ boosted by V⁵⁺/V³⁺ metallic redox mediator retains the strong redox capacity, and diminishes the recombination. LC–MS results confirm the degradation intermediates and a detailed degradation mechanism were also predicted. Superoxide radicals (^●O₂^–) and hydroxyl radicals (HO^●) were found as major oxidative species involved in the photocatalytic degradation. The ZC-40 photocatalyst exhibited high degradation of other pesticides as malathion (90.1%), glyphosate (85.4%) and chlorpyrifos (97.4%) in water system under visible light. This work provides new approaches in designing new photocatalytic heterojunctions with high efficiency and structural robustness for utilizing visible light and efficient water treatment based on advanced oxidation technology.