Continuous-Flow Photocatalytic Degradation of Glyphosate and Aminomethylphosphonic Acid Under Simulated Sunlight with TiO2-Coated Poly(vinylidene fluoride) Membrane

Abstract

Degradation of glyphosate (GLY) and its primary metabolite, aminomethylphosphonic acid (AMPA) is investigated at environmentally relevant concentrations using a poly(vinylidene fluoride) membrane with immobilized titanium dioxide (PVDF-TiO2) in a continuous flow-through operation. The photocatalytic degradation under the solar spectrum (AM1.5 g 350–1150 nm) is comparable with that under UV Light (365 nm) at equivalent absorbed irradiance with 63–65% GLY and 21–25% AMPA removal. Hence, non-UV wavelengths do not contribute to degradation. The limiting factors affecting degradation (irradiance, flux, initial concentration, and pH) are investigated. The scavenger study indicated •O2− as the primary contributor to GLY/AMPA degradation, while (Formula presented.) played a significant role as well. One of the most possible degradation pathways for GLY and AMPA in the photocatalytic membrane reactor is elucidated using the G3MP2B3 composite method via bond dissociation enthalpy (BDE) values. GLY degradation to AMPA and oxalic acid is identified as the preferred pathway due to the weak C─N bond. Under optimized conditions (highest irradiance of 98 mW cm−2, and lowest flux of 60 L m−2 h−1), 95% GLY and 80% AMPA are removed by the PVDF-TiO2 membrane. The potential of photocatalytic membranes for the degradation of low molecular-weight, charged micropollutants in continuous operations is highlighted.