A Multiscale Modeling Approach to Understand the Degradation of Glyphosate under Dark and Light Conditions

Glyphosate is an organophosphate herbicide that has been used for decades in agriculture. Its potential to cause carcinogenic effects and many other neurological diseases in humans has been well reported. Due to its significant environmental impact, considerable attention has been given to the removal of glyphosate from soil. A promising route is the degradation of glyphosate induced by titanium dioxide surfaces. Even though a number of experimental and theoretical studies have already addressed this topic, the exact mechanistic pathways of the degradation process, depending on the environmental conditions, are still unknown. In this work we use a multiscale approach based on classical and ab initio molecular dynamics combined with ground-state and excited-state electronic-structure simulations to unravel the degradation pathways under dark and light conditions. A detailed chemical bond analysis of the most predominant adsorption configuration of glyphosate on TiO₂ is used to discuss the molecular degradation in terms of molecular strain, charge transfer, and occupation of antibonding orbitals upon adsorption. Transition-state analyses of competitive degradation pathways suggest that aminomethylphosphonic acid and sarcosine are the main initial degradation products under dark and light conditions, respectively.