Ion-Selective Membranes for Critical Materials Seperation

This study aims at the design and fabrication of an emerging adsorptive membrane platform for transition 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 capture. The Cu2+/Ni2+ separating factor was calculated to be 193. We use in-situ Raman spectroscopy to 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 discriminating the guest metal cations. Coupled with first-principles calculations, results from this study synergistically provide insight into mechanistic understanding of metal ion separating behaviors of an emerging membrane platform based on ZIOS, a crystalline adsorbent system that we designed specifically for copper/nickel separation.<br/><br/>Keywords: supramolecules; nanosheet; organic-inorganic membrane; metal ion separation; insitu crystal growth; interfacial growth, in-situ Rama