Electronic-Level Insight into the Adsorption and Surface Diffusion Kinetics of a Simplified Glyphosate Model on a
Leslie L Alfonso T1,2, Jimena A Olmos-Asar1, Marcelo M Mariscal1,2
1Instituto de Investigaciones en Fisicoquímica de Córdoba (INFIQC-CONICET), X5000HUA Córdoba, Argentina.
Langmuir : the ACS Journal of Surfaces and Colloids
|July 31, 2023
Summary
This study models glyphosate's environmental mobility using methylphosphonic acid (MPA) adsorption on goethite (GOT). MPA strongly bonds to goethite, diffusing significantly slower than water, impacting pesticide fate in soils.
Area of Science:
- Environmental Chemistry
- Surface Science
- Computational Mineralogy
Background:
- Diffusive processes in minerals are key to understanding environmental anion mobility.
- Glyphosate, a widely used pesticide, poses environmental concerns due to its mobility.
- Goethite (GOT) is a prevalent Fe(III) mineral in soils and sediments, influencing contaminant fate.
Purpose of the Study:
- To investigate the adsorption and surface diffusion of methylphosphonic acid (MPA), a glyphosate model, on the goethite (010) surface.
- To elucidate the chemical interactions and proton transfer mechanisms at the goethite-water interface.
- To quantify the diffusion rates and estimate the environmental persistence of MPA on goethite.
Main Methods:
- Density Functional Theory (DFT) with Hubbard correction (DFT + U) was employed for calculations.
- Simulations focused on the (010) plane of goethite and its interface with water.
- Activation energy barriers were computed to determine diffusion half-lives.
Main Results:
- MPA exhibits strong adsorption to the goethite surface with significant covalent character.
- A double proton transfer mechanism (MPA to GOT and GOT to GOT) was observed.
- MPA diffusion on the goethite surface is approximately 3000 times slower than water diffusion.
Conclusions:
- MPA's strong adsorption and slow diffusion on goethite suggest limited mobility in soil environments.
- The findings provide insights into the environmental fate and transport of glyphosate-based pesticides.
- Computational modeling offers a powerful approach to study mineral-contaminant interactions.
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