Zwitterionic functionalized layered double hydroxides nanosheets for a novel charged mosaic membrane with high salt permeability
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© 2016 Elsevier B.V.. Charged mosaic membranes containing equivalent cationic and anionic exchange capacities are capable of decreasing the Donnan effect and thus accelerating salts permeation, while maintaining a high rejection of low molecular weight organics. In this study, charged nanosheets zwitterion-hydrotalcite (ZHT) was synthesized by grafting sulfobetaine methacrylate (SBMA) on the surface of positively charged Mg/Al hydrotalcite via surface initiated reverse atom transfer radical polymerization (RATRP). Subsequently, charged mosaic membranes were prepared by embedding different amounts of zwitterion-hydrotalcite into polyethersulfone (PES) casting solution via non-solvent induced phase separation (NIPS). Fourier transforms infrared spectra (FT-IR) and transmission electron microscopy (TEM) indicates that the zwitterion-hydrotalcite was successfully synthesized and well exfoliated. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), ionic exchange capacity (IEC), surface zeta potential measurement and water contact angle were employed to investigate the effect of ZHT content on overall performance of prepared membranes. It was found that charged mosaic membranes manifested an enhanced ionic exchange capacity, surface hydrophilicity and hydraulic permeability compared to original membrane. Importantly, the charged mosaic membranes presented excellent dyes retention (86.7% for Reactive Red 49), superior salt permeation, and high water flux (80.2 L m-2h-1) under 0.4 MPa. Furthermore, the retention of MgCl2, Na2SO4and NaCl was as low as 9.3%, 7.6% and 0.53%, respectively. It is worth noting that ultra-high salt permeation as a bright spot of charged mosaic membranes could be achieved, which was ascribed to the introduction of zwitterion-hydrotalcite. A mechanism of salt transport through charged mosaic membranes is proposed in this study. Overall, these promising results demonstrate the potential of charged mosaic membranes and suggest their comfortable use in dyes separation.
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