Preparation of bifunctional PVDF ultrafiltration membranes modified with co-blending of chitin nanowhiskers and hydroxyapatite for biomolecule and surface water filtration

The antifouling and antimicrobial properties of polyvinylidene difluoride (PVDF) ultrafiltration membranes were improved by adding hydroxyapatite (HA) and chitin nanowhiskers (CN), alone and in combination, to the casting solutions. The particle sizes were determined using a laser particle analyzer. The morphology, crystallinity, surface chemistry, and hydrophilicity of each membrane were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses, Fourier transform infrared (FTIR) spectroscopy, and contact angle (CA) measurements. The addition of HA and CN led to an increase in water flux, with the highest value determined to be 89.5 Lm⁻²h⁻¹ (at 3 bar pressure). At the same time, the molecular weight cut-off decreased by modification; the lowest value was 68 kg/mol for a membrane containing HA and CN. Addition of PEG as a pore-198.6 forming agent increased pure water flux significantly to Lm⁻²h⁻¹. Furthermore, the addition of CN and HA lowered the membrane CA from 88° to 57°. Separation performance was examined using crossflow filtration experiments, which showed that modification increased both flux and bovine serum albumin rejection. In addition, the modified membranes demonstrated both higher reversible fouling and irreversible fouling resistances. Further, the modified membranes containing both HA and CN showed promising performance for the filtration of bacterial and humic acid solution as well as for lake water treatment. While some leaching of additive over time was observed for all modified membranes, the membranes containing both CN and HA were generally more stable.