Role of oxygen-containing groups on MWCNTs in enhanced separation and permeability performance for PVDF hybrid ultrafiltration membranes

•PVDF ultrafiltration membranes were prepared with pristine and oxidized MWCNTs.•Contact angle of membranes decreased from 75.8° to 54.7° (1 wt.% oxidized MWCNTs).•The water flux of membrane increased 11 times by adding 1 wt.% oxidized MWCNTs.•Oxidized MWCNTs outperformed remarkably pristine MWCNTs in membrane performance.

To investigate the effect of the oxygen-containing groups of inorganic modifiers on polyvinylidene fluoride (PVDF) membrane performance, the PVDF/multi-walled carbon nanotube (MWCNT) hybrid ultrafiltration membranes were prepared via phase inversion by dispersing pristine and different dosage oxidized MWCNTs ranging from 0.2 wt.% to 2 wt.% in PVDF casting solutions. An increment in the porosity, pore size and surface roughness of the membranes was observed by the addition of pristine and oxidized MWCNTs. The rejection increased 22.2% in the content of 0.5 wt.% oxidized MWCNTs. The contact angle of membranes decreased from 75.8° (pure PVDF) to 54.7° (PVDF/1 wt.% oxidized MWCNTs), and 11 times increase in water flux was also indicated with the incorporation of 1 wt.% oxidized MWCNTs, which was considered as the optimum dosage. More importantly, the architecture and performance of PVDF/oxidized MWCNTs hybrid membranes outperformed PVDF/pristine MWCNTs hybrid membranes remarkably in the same content (1 wt.%), which can be ascribed to the presence of hydrophilic oxygen-containing groups. This work demonstrated that the oxygen-containing groups of inorganic fillers played a critical role in determining the structures, morphologies and performances of ultrafiltration membranes.