Modified polyvinylidene fluoride membranes for effective removal of iron ions (Fe2+) from water

Paper introduces an efficient technique for removing excess Fe(II) ions from water using modified polyvinylidene fluoride membranes. Capability for Fe(II) removal was investigated for three types of PVDF membranes (pristine PVDF, PVDF/Fe3O4 blend, and PVDF/Fe3O4 blend membrane with additional immobilization of Fe3O4 nanoparticles using polymer spacer. Structures and morphologies of membranes were analyzed through various techniques (IR, SEM, AFM, water contact angle, zeta potential), revealing that Fe3O4 nanoparticles were successfully incorporated into the membrane matrix and/or the membrane surface. The surface modification resulted in increased hydrophilicity of the membrane surface, as indicated by a decrease of WCA from 106.1°±3° to 74.8°±2°. The isoelectric point changed from 3.5 ± 0.2 to 7.9 ± 0.2 after the attachment of polyethyleneimine (PEI) owing to the cationic nature of the polymer linker. Membranes were tested in an ultrafiltration process using polyacrylic acid (PAA) as an agent for the binding of Fe(II) into the coordination complex. The modified membranes demonstrated a hydrodynamic permeability coefficient of 17.1 LMH·bar-1, which is approximately 2.5 times higher than the pristine PVDF membrane. The surface-modified PVDF membranes maintained a high rejection of Fe(II)-PAA coordination complex (97.1 and 99.4 %, respectively) at a pH of 8, leading to the decrease of concentration of Fe(II) in permeate from 20 ppm to 0.08 ppm and 0.11 ppm, meeting the standards set by the World Health Organization (0.3 ppm) and European Union Regulation (0.2 ppm). Modified PVDF/Fe3O4 membranes show potential applications in water purification from heavy metals owing to many advantages, including higher flux rates and rejection ability.