Removal of Glyphosate from Water by Adsorption Using the Zeolitic Imidazolate Framework ZIF-8: Characterization of Equilibrium Isotherms and Adsorption Kinetics

Abstract

Glyphosate, an anionic organophosphorus herbicide, is frequently detected in surface waters alongside other emerging contaminants (ECs). Effective removal strategies are essential to reduce their environmental impact. This study synthesized a metal organic framework (MOF) called Zeolitic Imidazolate Framework-8 (ZIF-8), a material recently recognized for its exceptional versatility, and employed it for the removal of glyphosate from aqueous systems via adsorption. ZIF-8 particles were synthesized using zinc nitrate hexahydrate as the metal source, 2-methylimidazole as the ligand, and methanol as the solvent. ZIF-8 was characterized by XRD, BET, zeta potential, and FTIR. Adsorption data were well described by both Langmuir and Freundlich models (R2 = 0.99), indicating contributions from monolayer and multilayer adsorption mechanisms. The maximum adsorption capacity was 67.67 mg/g at 308 K according to the Langmuir model. The adsorption mechanism involved a combination of physisorption and chemisorption and was influenced by coexisting chloride anions. Thermodynamic analysis indicated that glyphosate adsorption is endothermic and involves chemical interactions between glyphosate and ZIF-8. FTIR spectra showed new bands corresponding to the phosphoryl group after adsorption, confirming glyphosate binding. Overall, this study demonstrates that ZIF-8 is a promising adsorbent for the removal of ECs, offering an effective strategy for environmental protection.