Hydrolytically stable nanosheets of Cu-imidazolate MOF for selective trapping and simultaneous removal of multiple heavy metal ions

The global water security crisis necessitates the pursuit of cost-effective and sustainable water purification solutions that can be deployed at large scales. The current class of adsorbents are predominantly tailored towards highly specific unary metal ion systems, largely constraining their applicability to realistic scenarios. Thus, to create effective decontamination processes, it is essential to understand the adsorbent's potential in multicomponent systems. Here, hydrolytically stable copper-imidazolate (Cu-Im) metal-organic framework (MOF) nanosheets are presented as molecular sieves for trapping multiple heavy metal contaminants. These nanosheets are synthesized rapidly (within 30 minutes), at ambient temperature and atmospheric pressure, obviating the necessity for post-modification or functionalization. Adsorption experiments targeting four heavy metal ions revealed remarkable adsorption capacities: 492 mg g⁻¹ for Pb(ii), 327 mg g⁻¹ for Cd(ii), 233.1 mg g⁻¹ for Mn(ii) and 72.6 mg g⁻¹ for Ni(ii). Notably, in multi-component and industrial effluent settings, Cu-Im exhibited superior removal efficiency compared to other non-functionalised MOFs and classes of porous materials such as zeolites. Furthermore, Cu-Im demonstrated robust recyclability, maintaining removal efficiencies of 99% for Pb(ii), 90% for Mn(ii), 60% for Cd(ii) and 70% for Ni(ii) over three adsorption cycles. Compatibility assessments using a model aquatic organism cell model, the zebrafish ZF4 cell line, revealed no significant reduction in cell viability up to 48 hours. Cu-Im's stability is benchmarked against a global spectrum of 125 MOFs using machine learning algorithms. Moreover, Cu-Im complies with seven of the twelve principles of ‘Green Chemistry’, establishing itself as a sustainable, scalable, stable and reusable solution to a pressing global challenge.