(539a) An Emerging Adsorptive Membrane Platform for Effective Separation of Transition Metal Ions from Water Environment

This study aims at the design and fabrication of an emerging adsorptive membrane platform for metal ion capture. Specifically, the membrane composes of a selective layer built from stacks of zinc imidazole salicylaldoxime (ZIOS) crystalline nanosheets on a polyvinylidene fluoride (PVDF) supporting layer pretreated with polydopamine and polyethyleneimine. The dimensional and morphological textures of ZIOS layers were tuned by varying the concentrations of poly(vinyl alcohol) (PVA, Mw = 146,000-186,000 g/mol) in the reaction media. Additionally, textural properties (e.g., morphology, crystal size, particle orientation, and uniformity) and the adhesion of the ZIOS selective layer to the PVDF-PDA-PEI supporting substrate were controlled by tuning the synthetic conditions. Our results show that these ZIOS/PVDF-PDA-PEI membranes feature distinct ion transport and adsorption efficiency, which are critical for selective metal ion removal and/or capture. The Cu²⁺/Ni²⁺ separating factor was calculated to be 136.8 at pH 2.5 after 30 minutes. Furthermore, we observed that the metal ion behaviors of ZIOS at different pH values follows different uptake mechanism. We use in-situ Raman spectroscopy to help elucidate the underlying mechanisms governing the preferential metal ion uptake by the adsorptive membranes, of which the ZIOS layer functions as a selective layer in capturing transition metal cations. Coupled with DFT calculations, results from this study synergistically provide insight into mechanistic understanding of metal ion removal/capture behaviors of an emerging membrane platform based on ZIOS, a crystalline adsorbent system that we designed specifically for copper/nickel removal.