Suppressing toxic intermediates during photocatalytic degradation of glyphosate by controlling adsorption modes

The increasing presence of glyphosate has raised concerns about its potential impact on the environment and human health. The oxidative degradation of glyphosate during biotic and abiotic pathways usually leads to the formation of the toxic and persistent intermediates aminomethylphosphonic acid (AMPA). In this work, we report that the formation of AMPA during the photocatalytic degradation of glyphosate can be determined by its adsorption modes on the photocatalyst. The maximum accumulation of AMPA reached 31% on TiO2 photocatalyst. However, the formation of AMPA was markedly suppressed in the presence of F– ions, while the production of inorganic species such as PO43– and NO3– was largely enhanced. In situ attenuated total reflectance Fourier transforms infrared (ATR-FTIR) spectroscopy revealed that the glyphosate was adsorbed on surface of TiO2 by its phosphate and carboxylate groups, while the adsorption site was changed to its amine group in the presence of F– ions. Such a change in the adsorption mode of glyphosate would facilitate the C–N bonds cleavage in glyphosate molecules, and inhibit the formation of AMPA, which makes the degradation of glyphosate go along a less toxic degradation pathway. The present study reveals a new relationship between the degradation pathway and the adsorption mode of glyphosate, which may also be helpful in other systems of abiotic degradation of glyphosate.