Insights into glyphosate adsorption on Lewis acidic zeolites from theoretical modelling

Abstract

The removal of glyphosate via the adsorption process is one of the essential routes for decreasing its harmful impact. Here, we investigate the glyphosate adsorption on the Lewis acidic zeolites through density functional theory (DFT) calculations. We found that Hf-BEA provides the highest adsorption energy (−44.1 kcal/mol) as compared to ones of other zeolites. This result corresponds to its highest ordered Lewis acidity calculated by ammonia adsorption. There is a strong correlation between glyphosate and ammonia adsorption energies, as shown in a linear scaling relationship. This result implies the significant role of the Lewis acidity strength of zeolite in glyphosate adsorption process. The adsorption activity which related to zeolite pore structures (BEA, FAU, ZSM-5 and MOR) are found in the order of Hf-BEA > Hf-ZSM-5 ∼ Hf-MOR > Hf-FAU. The effect of water on the glyphosate adsorption is also investigated. Water is adsorbed on Sn-BEA zeolite much weaker than glyphosate and thus the active site of zeolite cannot be blocked by it. The trend of adsorption energies remains the same as in vacuum. Finally, the hydrolysis of metal-substituted active sites to form open sites strengthens the adsorption of glyphosate.