Computational Investigation on the Adsorption and Photodegradation of Glyphosate in its zwitterionic form on a Rutile (110) Titanium Dioxide Surface

In times of steadily increasing demand for food due to the continuous growth of the world population, herbicides like glyphosate are heavily used to ensure the supply of crops all around the world [C. Benbrook, Environ. Sci. Eur. 28, 2016, 3.]. Therefore, the leaching of these chemicals into ground and surface waters has become an increasingly troubling issue since several ways of exposure to humans are possible [Singh et al. Environ. Chem. Lett. 18, 2020, 663.].

The investigation of possibilities for adsorption and degradation of pollutants like glyphosate can be approached from a computational point of view to provide insight while being less expensive than experimental studies. Earlier studies using DFT and higher-level wave function methods have proven to give valuable results and show the ability of TiO2 to fixate and degrade the glyphosate dianion [L. Gerhards, PhD thesis, Carl-von-Ossietzky-Universität Oldenburg, 2021; Balzaretti et al. ChemRxiv, 2021, DOI 10.26434/chemrxiv.14465436.v1].

In this work the adsorption, photoexcitation and degradation of zwitterionic glyphosate on a rutile (110) surface is considered and different adsorption geometries and degradation pathways are evaluated using DFT methods. Additionally, the effect of an acidic environment on the surface and the adsorption is investigated. The calculations have shown that the adsorbed zwitterion is hardly affected by electronic excitation of the system, furthermore several degradation pathways have been evaluated, showing that the zwitterion tends to behave and degrade differently from the dianion on the surface, being in agreement with experimental data [Muneer et al. Int. J. Photoenergy, 2008, 2008, 1.].