From precious metal recovery to value-added MOF synthesis: Stable ZIF-8-hydrogel beads for sustainable multistage pollutant treatment

Abstract

Traditional copper-containing wastewater management has raised attention of remediation and recovery of precious metal, while the removal of emerging organic pollutants has become one of the more challenging issues in water treatment. Hence, ZIF-8 doped Sodium alginate (SA) is used to prepare ZIF-8@SA gel beads for Cu²⁺ recovering, and 2-methylimidazole is introduced into ZIF-8@SA coordinating with the recovered Cu²⁺ to prepare an adsorbent (named ZIF-8@SA@Cu-MOF) for the efficient removal of tetracycline hydrochloride (TC) in this study. The excellent adsorption performance of ZIF-8@SA is significantly optimized due to the electrostatic attraction, complexation reaction, coordination reaction, and ion exchange. The adsorption capacity for Cu²⁺ reaches 182.61 mg/g, indicating a substantial presence of Cu²⁺ in the material that offers ample synthesis sites for the in-situ formation of Cu-MOF. The maximum adsorption capacity of prepared ZIF-8@SA@Cu-MOF for TC reached 152.2 mg/g, attributed to the stability of material and strong interaction with TC molecules. Safety evaluation experiments show that the maximum leaching concentration (1.57 mg/L) of Cu²⁺ from ZIF-8@SA@Cu-MOF is below the regulatory limit of 2 mg/L, confirming its safe application. This study addresses the gap in heavy metal recovery and organic pollutant treatment, with significant implications for industrial wastewater management and contaminant remediation.