Effects of a dual nanofiller, nano-TiO2 and MWCNT, for polysulfone-based nanocomposite membranes for water purification

•Two mixed nanoparticles (TiO2 and MWCNT) were studied in polysulfone membranes.•Filler content was kept at 1% (w/w) and ratio of nanoparticles varied.•One TiO2/MWCNT ratio gave optimal enhancement in permeability and TOC rejection.•Mixed nanofillers gave flexible response at two different fouling conditions.

Polysulfone/nano-TiO2/multiwalled carbon nanotube (MWCNT) ultrafiltration membranes with variable nanoparticle (NP) ratios (total filler content at 1%(w/w)) were fabricated by the phase inversion method. Effects of the ratio of TiO2/MWCNT nanoparticles on membrane pore size and morphology, permeation, fouling and rejection of humic acid (HA) were examined. In terms of membrane characterization, scanning electron microscopy images showed that addition of TiO2 (approximately 21 nm) or MWCNTs resulted in finger-like interconnected pores and increased numbers of pores in the surface layer of the membrane. Membranes with a greater amount of MWCNTs also had an increased pore size, and therefore greater pure water flux. Membranes with greater TiO2 composition showed lower flux declines in the presence of HA. The membranes in which the NPs were combined (e.g., 0.5% TiO2 and 0.5% MWCNT (w/w)) exhibited an optimal balance of performance and synergism in terms of increased flux combined with increased total organic carbon rejection at 2 ppm HA. Additionally, the mechanisms for membrane fouling at 2 ppm HA and 700 ppm HA were different. The presence of an equivalent mixture of both NPs (e.g., the 0.5%/0.5% mixture) provided the flexibility to improve properties of a single membrane under both types of fouling conditions.

Graphical abstractTotal organic carbon rejection at TMP = 0.16 MPa and 0.16 m·s− 1 cross flow filtration velocity for 2 ppm and 700 ppm humic solution. The ratio of 0.5/0.5 (wt. %) of TiO2 and MWCT showed a synergistic effect on membrane performance: optimized TOC rejection.Figure optionsDownload full-size imageDownload as PowerPoint slide