Oxidant-assisted solar photocatalytic degradation of glyphosate using ZnO and ZnFe₂O₄ in compound parabolic collector reactors

Glyphosate is among the most extensively used herbicides worldwide and is frequently detected in surface water, groundwater, and drinking water sources because of its high persistence and resistance to conventional treatment processes. Advanced oxidation processes driven by solar energy offer a sustainable alternative for the degradation of such recalcitrant contaminants. In this study, the solar-driven photocatalytic degradation of glyphosate was evaluated using ZnO and ZnFe₂O₄ photocatalysts in outdoor compound parabolic collector reactors operated under natural sunlight. The influence of key operational parameters, including the photocatalyst loading, solution pH, solar start time, oxidant type, and oxidant concentration, was systematically investigated. ZnFe₂O₄ consistently exhibited higher degradation efficiency than ZnO under identical conditions, reflecting its enhanced visible light absorption and more effective utilization of solar photons. The addition of oxidants significantly improved the degradation efficiency, with potassium peroxymonosulfate outperforming hydrogen peroxide because of the generation of highly reactive sulfate radicals. Experiments conducted in tap water, groundwater, and surface water revealed a progressive decrease in degradation efficiency with increasing matrix complexity, primarily because of photon attenuation and radical scavenging by dissolved constituents. Nevertheless, the ZnFe₂O₄-based system retained substantial activity across all the water matrices. Reusability tests demonstrated that ZnFe₂O₄ maintained stable photocatalytic performance over multiple cycles, with performance losses attributed mainly to surface fouling rather than structural degradation. These results demonstrate the potential of visible light-active photocatalysts combined with solar-oriented reactor design for the sustainable treatment of glyphosate-contaminated water under realistic environmental conditions.