Study on Glyphosate Adsorption onto ZIF-8 Modified with Fe3O4 Nanoparticles

Abstract

Glyphosate (GLYPi) is an organophosphorus herbicide that behaves as an anionic substance in the aqueous phase. Even though it is stated as safe and non-toxic, the widespread use of GLYPi has raised environmental issues that need attention. This work used the positively charged metal-organic framework (MOF) of ZIF-8 to remove GLYPi via adsorption. Fe₃O₄ particles were hybridized with ZIF-8 to obtain Fe₃O₄@ZIF-8 via an in-situ deposition strategy to enhance the adsorption capacity toward GLYPi. The composite material (Fe₃O₄@ZIF-8) was characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction, revealing rhombic dodecahedron-shaped particles and oxygen-rich functional groups. The adsorption results show that there is a synergistic effect of adding Fe₃O₄ to ZIF-8 in increasing the rate and capacity of adsorption on GLYPi, that is 0.0012 g/mg·min (Pseudo-second-order) and 73.57 mg/g (Langmuir), respectively, on pH 7 and 50 °C. GLYPi adsorption by Fe₃O₄@ZIF-8 was not influenced by coexisting anions (e.g., Cl^-, NO₃^-, SO₄^2-, and HCO₃^-). The reusability study showed that the adsorption efficiency of GLYPi by Fe₃O₄@ZIF-8 decreased significantly after the first cycle, which should be considered a future challenge for further studies. The adsorption mechanisms of GLYPi by Fe₃O₄@ZIF-8 involve electrostatic interaction and pore-filling. The results indicate that Fe₃O₄@ZIF-8 is a promising candidate for removing organophosphate compounds, which could be an excellent strategy for environmental protection.