Decomposition and mineralization of glyphosate herbicide in water by radical and non-radical pathways through peroxymonosulfate activation using Co3O4/g-C3N4: a comprehensive study

Abstract

In this study, Co₃O₄ nanoparticles were deposited on g-C₃N₄ nanoplates to produce a Co₃O₄/g-C₃N₄ composite with high activity for peroxymonosulfate (PMS) activation. The materials were characterized by SEM, BET, FTIR, XRD, Raman, TGA, and EDX to explore their properties. In herbicide removal tests, the Co₃O₄/g-C₃N₄ ratio of 9 : 1 gave the strongest PMS activation effectiveness. Glyphosate (Gly) was decomposed rapidly in the first 30 s of reaction with a decomposition efficiency of 87.18% and a mineralization efficiency of 73% under optimum conditions (e.g., 50 mg L⁻¹ catalyst, 200 mg L⁻¹ PMS, 50 mg L⁻¹ Gly, pH 11, and temperature of 25 °C). The Gly decomposition rate by the Co₃O₄/g-C₃N₄(10%)/PMS system was 3, 1.6, and 1.45 times higher than those of g-C₃N₄/PMS, Co₃O₄/PMS, and ZIF-67/g-C₃N₄/PMS systems, respectively. The effects of catalyst dosage, PMS content, oxidants, initial glyphosate concentration, and the existence of anions on glyphosate decomposition were also investigated. The presence of g-C₃N₄ not only enhances the glyphosate decomposition but also reduces the dissolution of Co in water by around 3.2 times as compared to pure Co₃O₄. In the presence of anions, the Gly decomposition decreased in the order SO₄²⁻ < NO₃⁻ < Cl⁻ < HCO₃⁻. The radical scavenging test showed that ¹O₂ and O₂˙⁻ are the key reactive oxygen species, and the glyphosate decomposition mechanism was proposed for Co₃O₄/g-C₃N₄via heterogeneous catalytic activation of PMS. The mass spectrometry results indicate that the decomposition pathway of glyphosate occurs by cleaving the C–N bond and forming major intermediates such as methyl phosphonic acid, glycine, and inorganic ions (e.g., phosphate, nitrate, and ammonium). In durability tests, the glyphosate treatment efficiency decreased by only around 11% after five consecutive test cycles, implying its great potential application for the treatment of hazardous pollutants in wastewater.