PVDF-CaAlg nanofiltration membranes with dual thin-film-composite (TFC) structure and high permeation flux for dye removal

Novel polyvinylidene fluoride-calcium alginate (PVDF-CaAlg) nanofiltration (NF) membranes were prepared by impregnating electrospun PVDF substrates with sodium alginate solution and crosslinking with CaCl2 solution. The NF membranes were characterized via field emission scanning electron microscopy (FESEM) equipped with an energy-dispersive spectrometry (EDS), attenuated total reflectance Fourier transform infrared spectra (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS). The results show that the prepared PVDF-CaAlg NF membranes exhibit dual thin-film-composite (TFC) structure and superior surface hydrophilicity. The highest pure water flux can achieve 63.8 L·m−2·h−1·bar−1 accompanied with a 98.5% rejection rate for methyl blue (MB), which is superior to many polymeric NF membranes. The prepared PVDF-CaAlg NF membranes exhibit much higher rejections for seven typical dyes, and the rejection slightly rises with the increase of impregnating time. In the long-term filtration process, the permeation flux for dye solution remains stable. PVDF-CaAlg NF membranes show good anti-fouling performance to BSA protein and lactobacillus.