Mechanism of glyphosate removal by biochar supported nano-zero-valent iron in aqueous solutions

The widespread use of glyphosate and the resulting environmental residues pose a serious threat to both crops and human health. The aim of this study was to investigate the adsorption process and removal mechanism of glyphosate by modified biochar (BC). Nano-zero-valent iron (NZVI) was loaded on the palm BC through liquid-phase chemical reduction. The composite material ((BC-NZVI)) was characterized using scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy, revealing that it had a high specific surface area, rich oxygen-containing functional groups and complex ligands. Adsorption experiments were conducted with modified BC to study the effects of contact time (0-3750 min), initial concentration (5-40 mg/L), pH (2.00-7.00) and coexisting pollutants (0-20 mg/L). The adsorption data could be fitted well with the pseudo second-order kinetic model and Langmuir isotherm, indicating that the adsorption of glyphosate on the BC supported NZVI was a chemical and surface process. The maximum adsorption capacity was 80 mg/g at pH= 4, twice that of the original BC. At low concentrations, there was no influence on the adsorption of coexisting pollutants, sulfamethazine, cadmium ions, or phosphate; however, it had antagonistic effect (Rq < 1) when the initial concentration of H2PO4+ was higher than 10 mg/L. The adsorption mechanisms involved porefilling, hydrogen-bond, electrostatic interactions and complexation. Such strong absorbability, along with being easy to obtain and inexpensive, makes (BC-NZVI) potentially suitable for the treatment of agricultural wastewater and acidic farmland soils contaminated with organic pollutants.