Photocatalytic treatment under visible light applied to aqueous glyphosate solution

Numerous chemical residues produced by industries and agricultural activities harm the environment. Pesticides and herbicides pollute soil and water and have toxic effects on living beings. Glyphosate – N-(phosphonomethyl)glycine – is an herbicide extensively used for the non-selective control of weeds. This systemic and post-emergent organophosphorus compound accounts for 60% of the world market of non-selective herbicides. Photocatalysis is one of the safest and least expensive methods for removing pesticides from wastewater. Evidence in the literature shows that photocatalysis has the potential for the removal of herbicides from surface waters and soil. The present study aimed to investigate the photocatalytic degradation and reduction of phytotoxicity of glyphosate in the presence of cerium dioxide (CeO2), titanium dioxide (TiO2) and zinc oxide (ZnO) as catalysts (2 g L-1) under a visible radiation source. Among the catalysts, CeO2 had the best efficiency, achieving 17% degradation, followed by ZnO (6.8%) and TiO2 (6.4%). The concentration of CeO2 was diminished to 1 g L-1 to assess its influence, leading to a reduction in degradation from 17% to 15%. Phytotoxicity of the product of the reactions was also evaluated and revealed a nonphytotoxic compound was formed in the photocatalytic reaction solution using CeO2 as the catalyst.