A novel hybrid nanoadsorbent for effective Hg²⁺ adsorption based on zeolitic imidazolate framework (ZIF-90) assembled onto poly acrylic acid capped Fe₃O₄ nanoparticles and cysteine

This research reports a new mercury adsorbent in which Fe₃O₄ as a core was embedded into the shell of ZIF-90 in a one-pot synthesis and the subsequent post synthesis modification (PSM) of its surface with cysteine covalently, via a Schiff's base reaction. Poly acrylic acid (PAA) was capped on the surface of nanoparticles to prevent agglomeration of the nanoparticles. In addition, −COOH groups of PAA coordinated with Zn²⁺ of ZIF-90 and this provided the platform for ZIF-90 to grow on the nanoparticles forming the core-shell structure. Based on the strong interactions between the thiol groups on the adsorbent and mercury ions as elucidated by the XPS analysis, the as-synthesized adsorbent showed selectivity for Hg²⁺. The sorbent exhibited high adsorption capacity of 900 mg g⁻¹ towards Hg²⁺ as calculated at pH 4 and the adsorption kinetics followed pseudo-second-order kinetics model better. The Hg²⁺ loaded adsorbent was easily regenerated and it maintained about 70 % efficiency after the third use. Low-cost, readily available and green materials, facile preparation, efficient removal and the breakthrough in three times recyclability give the novel ZIF-90 based hybrid nanoadsorbent wide prospects in the field of environmental remediation as a good adsorbent for Hg²⁺ removal in wastewater.