Rapid and sequential removal of polyphenols and heavy metals from water by zeolitic imidazolate framework-67 (ZIF-67)

Over the past decade, metal-organic frameworks (MOFs) have garnered significant scientific attention owing to their exceptional physicochemical properties and versatility across a wide range of applications. In this work, a circular economy strategy is adopted to address critical challenges associated with excessive waste generation, resource limitations, and economic sustainability. Specifically, the performance of the zeolitic imidazolate framework ZIF-67 was evaluated for the sequential removal of organic and inorganic contaminants from water. Pristine ZIF-67 was first employed for the adsorption of polyphenols, using gallic acid as a model compound, after which the spent material (ZIF@GA) was reutilised for the removal of heavy metal ions, including cadmium, lead, and chromium. ZIF-67 exhibited a maximum adsorption capacity of 171 mg/g for gallic acid, while ZIF@GA demonstrated an exceptionally high adsorption capacity of 1020 mg/g for Pb(II) ions, along with removal efficiencies of 58% and 45% for Cd(II) and Cr(VI), respectively under batch conditions. Rapid and quantitative adsorption of gallic acid was maintained even under complex water matrices. To overcome the practical limitations associated with dispersed MOF powders, a simple and rapid method was developed to fix ZIF-67 nanostructures directly onto conventional laboratory-grade filter sheets. Overall, these findings highlight the strong potential of ZIF-67 as a sustainable, efficient, and scalable material for advanced water remediation applications.