Metallic functionalization of magnetic nanoparticles enhances the selective removal of glyphosate, AMPA, and glufosinate from surface water

Abstract

Glyphosate (GLY) is the most used herbicide worldwide, raising concerns due to its toxicity and mobility in water. The concurrent spread of similar herbicides, i.e., glufosinate (GLUF) and aminomethylphosphonic acid (AMPA, a metabolite of GLY), also causes a serious concern to the environment. The application of magnetic nanoparticles (MNPs) gained wide attention as a promising approach for the environmental remediation of GLY. However, the fast agglomeration, low removal efficiency, and saturation of MNPs by non-target chemicals remain a challenge. Herein, we used polydopamine as a coating agent followed by functionalization with different metal ions, i.e. Ti(IV), Zr(IV), and Cu(II), for selective removal of GLY, AMPA, and GLUF from deionised water in laboratory trials. Finally, we tested the performance of MNPs in surface waters contaminated with GLY at 0.17 ± 0.02 μg L⁻¹. The GLY removal efficiency (RE, %) of MNPs was optimized by using different GLY to MNP ratios and incubation times, in the presence of GLY-analogues and competitive species, i.e., phosphates. The results indicate that all metallic functionalized MNPs are more stable toward aggregation and effective in removing GLY than bare MNPs, up to 150 μg L⁻¹. The optimal ratio was 500 μg_GLY g_MNPs⁻¹ (50 μg GLY to 100 mg MNP), with RE > 80%. MNPs functionalized with Ti(IV) and Zr(IV) performed more efficiently than MNPs functionalized with Cu(II), reaching an RE of 99.9% after a incubation time of 15 min. The presence of Ti(IV) and Zr(IV) in the MNPs increased the selectivity of the particles toward GLY and GLY analogues that can be removed with similar efficiency, and prevented competition with phosphates at much higher concentrations (1000 μg L⁻¹). Finally, GLY analogues can be easily re-eluted with ammonia, and the functionalized MNPs can be efficiently re-used up to four cycles. The use of metal-functionalized MNPs is a promising approach for the removal of target pollutants from contaminated water.