Abstract
The traditional ion-exchange membranes face the trade-off effect between the ion flux and perm-selectivity, which limits their application for selective ion separation. Herein, we amalgamated various amounts of the ZSM-5 with the polyvinyl alcohol as ions transport pathways to improve the permeability of monovalent cations and exclusively reject the divalent cations. The highest contents of ZSM-5 in the mixed matrix membranes (MMMs) can be extended up to 60 wt% while the MMMs with optimized content (50 wt%) achieved high perm-selectivity of 34.4 and 3.7 for H+/Zn2+ and Li+/Mg2+ systems, respectively. The obtained results are high in comparison with the commercial CSO membrane. The presence of cationic exchange sites in the ZSM-5 initiated the fast transport of proton, while the microporous crystalline morphology restricted the active transport of larger hydrated cations from the solutions. Moreover, the participating sites and porosity of ZSM-5 granted continuous channels for ions electromigration in order to give high limiting current density to the MMMs. The SEM analysis further exhibited that using ZSM-5 as conventional fillers, gave a uniform and homogenous formation to the membranes. However, the optimized amount of fillers and the assortment of a proper dispersion phase are two critical aspects and must be considered to avoid defects and agglomeration of these enhancers during the formation of membranes.
Highlights
Electrodialysis (ED) based on ion-exchange membranes (IEMs) is an important separation technology, which has been widely used for seawater/brackish water desalination, wastewater treatment, acid-base recovery, selective ion separation due to the low energy consumption, no phase transition, and high productivity [1,2,3,4,5,6,7]
The permselectivity of the traditional IEMs could be improved in multiple approaches: (i) crosslinking to get high density of the membranes’ structure, [24] (ii) membranes surface coating with a positively charged layer to facilitate the exclusion of multivalent cations via electrostatic repulsion [23,25], and (iii) blending of polymers with either other polymers or microporous crystalline materials such as zeolites to systematize the permselectivity of mixed matrix membranes (MMMs) [26,27]
Theresearch, high fluxthe of monovalent cations canzeolite-based be characterized by ion size and
Summary
Electrodialysis (ED) based on ion-exchange membranes (IEMs) is an important separation technology, which has been widely used for seawater/brackish water desalination, wastewater treatment, acid-base recovery, selective ion separation due to the low energy consumption, no phase transition, and high productivity [1,2,3,4,5,6,7]. The commercial monovalent ion selective membranes are expensive and show low permselectivity. We focused on developing a facile way to prepare selective membranes for monovalent/divalent cations separation. (i) crosslinking to get high density of the membranes’ structure, [24] (ii) membranes surface coating with a positively charged layer to facilitate the exclusion of multivalent cations via electrostatic repulsion [23,25], and (iii) blending of polymers with either other polymers or microporous crystalline materials such as zeolites to systematize the permselectivity of mixed matrix membranes (MMMs) [26,27]. Due to the sieving effect and cationic exchange sites of the ZSM-5 zeolite, we developed low-cost MMMs with various contents of zeolite in the PVA backbone for selective separation of monovalent cations via the ED process. The prepared MMMs were investigated for the H+ /Zn2+ and Li+ /Mg2+ systems, respectively
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