Calcium alginate and barium alginate hydrogel filtration membrane coated on fibers for molecule/ion separation

Calcium alginate (CaAlg) hydrogel has good anti-pollution performance. However, the self-supporting CaAlg hydrogel filtration membrane is difficult to be batch prepared due to its poor mechanical properties. In this paper, polyester (PET) non-woven fabric, polypropylene (PP) non-woven fabric and polyhydroxybutyrate (PHB) nanofibers were used as support layer to prepare CaAlg composite membranes. A series of studies proved that CaAlg-PET membrane showed higher stability and flux, which revealed that PET non-woven fabric was the best carrier among the three fiber carriers to enhance the various properties of hydrogel. Methyl blue (MB) and sodium chloride (NaCl) were used as the representatives of molecules and ions, respectively. The effects of concentration, operating pressure and temperature on the separation performance of MB/NaCl by CaAlg-PET membrane were investigated. The flux of CaAlg-PET membrane was 19.3 L·m−2·h−1·bar−1, and the membrane showed a high selectivity of 183.4 to MB/NaCl mixture (99.5% rejection of MB and 8.3% rejection of NaCl). Moreover, Barium ion was used to cross-link sodium alginate to prepare barium alginate (BaAlg) hydrogel coated composite membrane (BaAlg-PET) using PET fiber as the carrier. The BaAlg-PET membrane exhibited higher strength, stability, flux and better separation performance than CaAlg-PET membrane. BaAlg-PET membrane exhibited a high flux of above 35.5 L·m−2·h−1·bar−1, and the molecular ion selectivity was 306.3 (99.7% rejection of MB and 8.1% rejection of NaCl). Membrane pore structure and pore size distribution of BaAlg hydrogel membrane were generated by molecular dynamic (MD) simulations. In sum, this work provided a green, economical and expandable new idea and membrane material for the separation of molecules and ions.