Clay interaction on MOF for 2,4-D removal: effect on adsorptivity, reusability, phytotoxicity and interference from co-existing ions

A MOF-Clay composite (ZM-1) was fabricated via a green method from thermally activated montmorillonite (AMT) and ZIF-8 with the intent of bringing about enhanced binding efficiency, absorptivity and reusability for the removal of pesticides and pharmaceuticals from wastewater. BET, XRD and FTIR analysis revealed a change from microporous ZIF-8 having a pore diameter of 23.4Ǻ, surface area of 871 m²/g, to a mesoporous ZM-1 with a pore diameter of 202.7Ǻ and surface area of 24.8 m²/g. ZM-1 achieved removal efficiencies of 94.5 % for 2,4-D, 90 % for TTC and 80.8 % for CIP removals from a single system, but comparatively lower removals of 2,4-D in the presence of TTC (83.4 %) and CIP (81.6 %) reflect the adsorptive potential of ZM-1. Regeneration studies reflect 6 % lower 2,4-D removals after five cycles in ZM-1 as compared to 20 % lower removals in ZIF-8. Another observation was the reduced phytotoxicity of ZM-1 towards the germination of mung seeds in comparison to that of ZIF-8. ZM-1-treated 2,4-D water showed reduced phytotoxicity. The binding interactions were physical, with electrostatic forces contributing to the highest removal at pH 5.9. The study has advanced knowledge of the positive aspects of clay immobilisation on the porosity, adsorptivity, stability, reuse, and phytotoxicity of the MOF-based composite for the bio-compatible removal of emergent pollutants from water.