Comparing the abiotic removal of glyphosate by β-MnO 2 and δ-MnO 2 colloids: Insights into kinetics and mechanisms

• Published in: Environmental pollution (1987) 2024-06, p.124432
• Main Authors: Xiong, Ruihan, Zhang, Caixiang, Xiong, Hanxiang, Huang, Shuxin, Li, Jiasen
• Format: Article
• Language: English
• ISSN: 1873-6424
• DOI: 10.1016/j.envpol.2024.124432

Glyphosate as an effective broad-spectrum herbicide is frequently detected in various water and soil resources. Given the ubiquity of β-MnO and δ-MnO colloids in groundwater and soil, the abiotic removal of glyphosate by MnO colloids was investigated. β-MnO colloids exhibited superior glyphosate removal efficiency, up to 37%, compared to 21% for δ-MnO colloids at a pH of 4.0. Glyphosate removal involved simultaneous adsorption and oxidation process, identified by HRTEM, NH -TPD, XPS, LC-MS, FTIR analyses and the occurrence of aminomethylphosphonic acid (AMPA) and Mn . Moreover, adsorption dominated the removal of glyphosate by two MnO colloids. The solution pH had a substantial effect on glyphosate removal. Co-existing ions in the solution, such as carbonate (CO ), phosphate (Na HPO , NaH PO ) and humic acid (HA), were also found to impede glyphosate removal. Phosphate, in particular, exhibited a strong competitive effect for adsorption sites on both MnO colloids. Of them, the removal of glyphosate by β-MnO colloids was more prone to occur due to its higher specific surface area, abundant oxygen vacancies, and moderate acid sites. However, δ-MnO colloids presented a stronger oxidation capacity than that of β-MnO colloids due to the quicker generation rate of Mn . Finally, AMPA was the same products by two MnO colloids in the oxidation process, revealing the degradation pathway based on the cleavage of C-N bond. Therefore, by comparing kinetics and mechanisms of glyphosate removal by β- and δ-MnO colloids, this study improves us better understanding for the behavior of glyphosate in the environment.