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

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 degrees 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 O-1(2) and O-2(-) are the key reactive oxygen species, and the glyphosate decomposition mechanism was proposed for Co3O4/g-C(3)N(4)via 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.