Photocatalytic ozonation and Fenton-like properties of in-situ-grown zinc peroxide on g-C₃N₄: Unlocking multimodal reactivity under ambient and visible light

ZnO₂ is an efficient catalyst for generating H₂O₂ under ambient conditions, surpassing ZnO in Fenton-like and catalytic ozonation processes. However, its wide band gap of 3.7 eV restricts its activity under visible light. This study investigates ZnO₂/g-C₃N₄ composites, hypothesizing that their heterojunction enables catalysts to produce reactive oxygen species (ROS) under visible light. The composites were synthesized and characterized using XRD, HRTEM, UV-DRS, and XPS, confirming the successful integration of ZnO₂ into the g-C₃N₄ matrix. The catalytic performance of ZnO₂/g-C₃N₄ was evaluated through multiple pathways, including Fenton-like, catalytic, and photocatalytic ozonation, for ROS generation and degradation of persistent organic pollutants under ambient and visible light. OH[rad] production by the composite after 60 min was measured as follows: Fenton-like (1.2 × 10⁻¹⁰ M), photocatalysis (3.2 × 10⁻¹⁰ M), ozonation (6.5 × 10⁻¹⁰ M), and photocatalytic ozonation (22 × 10⁻¹⁰ M), indicating the superior efficiency of the photocatalytic ozonation process. The composite's pollutant degradation efficiency was tested using cyclophosphamide and iohexol as model micropollutants. ZnO₂/g-C₃N₄ significantly degraded and mineralized both compounds, even in tertiary wastewater effluents, highlighting its practical applicability. Moreover, the composite demonstrated excellent stability, retaining over 95 % of its catalytic activity after five consecutive treatment cycles.