Electronic-Level Insight into the Adsorption and Surface Diffusion Kinetics of a Simplified Glyphosate Model on a Goethite Surface

The diffusive processes that occur in minerals involvechemicaland physical surface phenomena of great interest that allow for understandingthe mobility of different anions of environmental importance. Oneof them is glyphosate, which is widely used as a pesticide. In thiswork, we performed Hubbard-corrected density functional theory (DFT+ U) calculations to study the adsorption and surfacediffusion of methylphosphonic acid (MPA), as a model of glyphosate,on the (010) plane of goethite (GOT), one of the most important Fe(III)minerals in soils and sediments. In particular, the MPA adsorptionwas studied at the GOT-water interface, finding a strong covalentcharacter in the bond. We also corroborated the occurrence of doubleproton transfer (MPA to GOT and GOT to GOT). Finally, activation energybarriers were calculated to estimate the half-lives for moleculardiffusion, showing that MPA moves almost 3000 times slower than waterat the GOT surface.