The development of antifouling ion exchange membranes (IEMs) is of great significance to the application of electrodialysis (ED). Membrane fouling is a ticklish question affecting the membrane performance, which results in an increase in energy consumption in ED and unnecessary economic loss. In this work, we report poly(vinyl alcohol) (PVA) as an IEM substrate; a large number of hydroxyl groups on the aliphatic chain react with a small rigid molecule of 4-(bromomethyl)benzaldehyde (QBMB) prepared by us and then adjust the time of quaternization by trimethylamine to design a series of antifouling anion exchange membranes (AEMs) named PVA-QBMB-X (X = 2, 4, 6, and 12). The as-prepared AEMs with a cross-linking structure within the matrix exhibit low surface area resistance and reduced swelling ratios of <16.2%. The optimized PVA-QBMB-12 AEM shows better antifouling performance in terms of a much longer transition time (1150 min) than commercial membrane AEM-Type-II (620 min) by possessing excellent hydrophilicity and superior ED performance compared with the commercial membrane. The optimized AEM shows a superior NaCl removal rate of 99.80 ± 1.5%, a current efficiency of 82.64 ± 0.8%, and an energy consumption of 2.98 ± 0.3 kWh kg–1 NaCl, which are better than those of AEM-Type-II (97.51 ± 1.5, 76.26 ± 0.7%, and 4.54 ± 0.6 kWh kg–1 NaCl, respectively). Thus, the investigation demonstrates the potential application of the as-prepared AEMs for ED in organic pollutant systems.
Muhammad Irfan,Liang Ge,Yaoming Wang,Zhengjin Yang,Tongwen Xu
Developing anion exchange membranes that have high anion selectivity and can avoid membrane swelling is a critical, but challenging, target for electrodialysis, which has witnessed great success in a wide range of applications including saline wastewater treatment and resource recovery. We found in this work that by tuning the hydrophobicity of alkyl spacers which connect the positively charged ammonium groups and polymeric backbones of the anion exchange membrane, high anion selectivity, and low membrane swelling of anion exchange membrane can be achieved. The membranes developed here are capable of discriminating monovalent and divalent anions, with a selectivity for Cl–/SO42– reaching up to 13.07, and our results suggest the chain length of the spacers determines the anion selectivity of membrane. We attribute such phenomenon to the change in side chain hydrophobicity. This is a particularly interesting finding that could facilitate the development of advanced anion exchange membranes for electrodialysis.
Mesoporous silica submicrospheres with –NH 2 groups or –PO 3 H 2 groups on the outer surface, and –PO 3 H 2 groups on the inner pore walls are prepared and designated as N–P–SiO 2 and P–P–SiO 2 , respectively. Both kinds of silica submicrospheres are introduced into Nafion membrane matrix to fabricate hybrid membranes . The water uptake, membrane swelling properties, and proton conductivities at different temperatures and different relative humidities of the hybrid membranes are characterized. Proton conducting performances of the hybrid membranes are all enhanced compared to that of the pristine Nafion membrane, and the highest proton conductivity is 0.339 S cm −1 (115 °C, 100% RH). At 100% RH, Nafion/N–P–SiO 2 membranes exhibit higher proton conductivities than the Nafion/P–P–SiO 2 counterparts; while at low humidities, the proton conductivities of the Nafion/P–P–SiO 2 membranes are enhanced more pronouncedly than those of the Nafion/N–P–SiO 2 counterparts. The different increasing tendencies of the proton conducting performance could be attributed to the varied synergistic effects between the proton conducting groups introduced by the mesoporous silica and the groups anchored on the membrane matrix.
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