High-flux anti-fouling nanofibrous composite ultrafiltration membranes containing negatively charged water channels

Abstract

High-flux nanofibrous composite ultrafiltration (UF) membranes consist of nanocellulose integrated polyacrylonitrile (PAN) as the barrier layer and electrospun PAN nanofibers deposited on a polyethylene terephthalate (PET) non-woven mat as the supporting layer were fabricated by solution coating approach. The chemical composition of nanofibrous composite membranes was investigated with ATR-FTIR, TGA, and EDX measurements, while the top and cross-sectional morphology of the membranes were observed via SEM and AFM scans. An interpenetrating nanofiber-polymer network was created in the barrier layer which drastically enhanced the mechanical strength of the composite membrane. The hydrophilicity of the nanofibrous composite membranes increased with nanocellulose component evidenced by water contact angle measurements, which could enhance the anti-fouling properties of the membranes. The as-prepared membranes were investigated for protein separation and wastewater treatment. The ultrafiltration performance of nanofibrous composite membranes with different composition ratios of nanocellulose to PAN was demonstrated using a cross-flow filtration system, the highest pure water permeability of 1508 L/(m2h·MPa) was achieved with a coating solution of 0.10 wt% of nanocellulose and 0.05 wt% of PAN where it created optimized water channels in the barrier layer of the composite membranes. The molecular weight cut-off (MWCO) of these membranes was determined with dextran as a marker, where the maximum pore size of the membranes varied in the range of 20.8–46.0 nm. Moreover, proteins and polypeptides with different molecular weights were employed to challenge the nanofiber composite membrane performance. High permeation flux of 147.1 L/m2h and high rejection ratio of 98.4% were accomplished; meanwhile, the high selectivity against protein and polypeptides was attained, indicating the membrane's applicability for the selective separation. The anti-fouling properties of the nanofibrous composite membranes were also intensely investigated and the filtration efficiency, in terms of permeation flux and rejection ratio, was evaluated and compared with that of commercially available UF membranes (UN100, US050, and UE050) that possess similar membrane pore size. The permeation flux of the nanofibrous composite membrane was 2–3 times higher than that of commercial membranes, due to the formation of water channels in the barrier layer, while the rejection ratio remained the same as 99.6%, indicating that the nanofibrous composite membrane could be a good candidate for wastewater treatment, in addition to the highly selective separation of proteins.