Interaction of ZIF-8 with Cu2+ in water solutions for remediation applications

Water pollution is a global environmental problem and now more topical than ever. Among several pollutants, heavy metals are of particular interest due to their toxicity and high bioaccumulation capacity. Metal-organic frameworks (MOFs) are exceptional adsorbents for capturing metal ions in water. Between them, ZIF-8 has high sequestration capacity of copper ions in water, but the capture mechanism remains unclear. The scope of this work is to investigate the interaction of ZIF-8 with copper ions in aqueous solution at pH=7, discriminating between effects due to water, copper and those resulting from their concomitant presence. Several samples were prepared dispersing a certain amount of ZIF-8 in an aqueous Cu2+ solution at a fixed concentration in the range between 0-300 mg/L. X-ray diffraction, Raman Spectroscopy, gas porosimetry, Thermogravimetry, X-ray photoelectron spectroscopy (XPS) and Electron Paramagnetic Resonance (EPR) were used to evaluate the structural features of the ZIF-8 before and after Cu2+ capture. Our results indicates that ZIF-8 is capable to capture high amounts of Cu2+, but in aqueous solution it undergoes a dissolution and reorganization process that affect its applications in simply powder form.