Polyvinylidene fluoride-based ultrafiltration composite membranes via in-situ biomineralization

This paper develops a polyvinylidene fluoride (PVDF) / polyacrylic acid (PAA)/calcium carbonate (CaCO3) composite membrane using the in-situ mineralization method. PAA is used as polyanionic macromolecule to induce the generation of CaCO3 particles. The mineralization condition was optimized based on CaCl2 content in the selection process of the casting solution and carbonate source. The structures and surface hydrophilicity were characterized by field emission scanning electron microscope (FESEM), Fourier transform infrared/attenuated total reflection (FT-IR/ATR) spectrometer, energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and water contact angle for the prepared composite membranes. The results demonstrate that CaCO3 particles consisting of calcite and vaterite disperse uniformly on the membrane surface and in the membrane cross-section; the membrane hydrophilicity increases with the increase of CaCl2 content in the casting solution. The improved hydrophilicity is resultant of the membrane structure in the in-situ mineralization process and the collapse of PAA chains in the membrane pores, facilitating the tenfold improvement of the membrane's pure water fluxes. Due to the electrostatic repulsion between the positively charges lysozyme and CaCO3 particles, the mineralized membranes possess a high rejection (85.13%) and flux recovery ratio (77.21%). Therefore, in-situ mineralization is a convenient and effective method to prepare hydrophilic composite PVDF membranes.