Efficient removal of a glyphosate-based herbicide from water using ZnO nanoparticles (ZnO-NPs)

Though there may not be consensus regarding the toxicity of glyphosate, given the strong interest in its removal from water sources nanotechnology was used in this work to that end. Nanoparticles of zinc oxide (ZnO-NPs) were synthesized in a controlled manner by chemical route. The ZnO powders were then characterized by infrared and UV-Vis absorption spectroscopies, X-ray diffraction and scanning electron microscopy. To evaluate the capacity for removal, aqueous solutions of the Monsanto herbicide Roundup 747 SG containing 679 g/kg of glyphosate were adjusted to obtain glyphosate-ZnO-NP suspensions of 250 ppm-250 ppm, 700 ppm-700 ppm, 1000 ppm-1000 ppm, 1000 ppm-250 ppm and 1000 ppm-700 ppm and these were used to carry out the tests. The % Removal curves obtained indicate that the ZnO-NPs removed between similar to 70% and 90% of the herbicide in the system. While the UV-Vis absorption spectra showed small displacements of the absorption maximum and the appearance of other small bands, indicating herbicide degradation, adsorption proved to be the most important removal mechanism. The kinetics of the process was suitably described by a pseudo second order equation, although it is not possible to rule out, for some glyphosate-ZnO-NP concentration ratios, the importance of intraparticle diffusion. These results indicate that the synthesized ZnO nanoparticles were efficient in the removal of glyphosate in aqueous solutions at the laboratory level.