Organic-inorganic artificial ion channel polyvinylidene fluoride membranes for controllable selectivity transport of alkali metal cations

In this article, organic–inorganic hybrid materials with different functional groups were used to form organic–inorganic hybrid dense membranes for selective separation of mono/divalent ions by blending these materials and polyvinylidene fluoride (PVDF) in dimethylacetamide with HCl as the catalyst. The membranes prepared by 3-(ureido benzene) propyltriethoxysilane (H1), 3-(ureido-4-methoxyphenyl) propyltriethoxysilane (H2), 3-(ureido-3-chloro-4-methoxyphenyl) propyltriethoxysilane (H3), 3-(ureidoindazolyl) propyltrieth-oxysilane (H4), or 3-(ureidopentanol) propyltriethoxysilane (H5) were labeled as HM1–HM5, respectively. The transport properties of different chlorides were tested. The effects of different anions on sodium cation transport were also tested. The results showed that HM1–HM4 could transport monovalent Li⁺, Na⁺, and K⁺ except Ca²⁺ and Mg²⁺, and the permeability of Li⁺, Na⁺, and K⁺ through the hybrid membranes followed the order of P_Na+ > P_K+ > P_Li+. Moreover, membranes with different H2 content were also prepared due to HM2 having the best ion transport performance. The ion transport performance increased accordingly with the mass ratio of H2 to PVDF, and the permeability of Na⁺ was twice that of Li⁺ and K⁺ when the mass ratio was 15/10. Under this condition, it was also proved that NH₄⁺ could not transport through the hybrid membrane with various selectivity for different anions as Cl⁻> NO₃⁻ > HCO₃⁻ > SO₄²⁻.