Fabrication and characterization of carbon nanotubes-based porous composite forward osmosis membrane: flux performance, separation mechanism, and potential application

Abstract In this study, novel porous composite forward osmosis (FO) membranes were prepared via coating polydopamine modified multiwalled carbon nanotubes (PDA-modified MWCNTs) onto the polyethersulfone (PES) microfiltration (MF) membrane. The separation performances of these MWCNTs coated PES membranes (PES-MWCNTs) were evaluated in the FO process for oil-water separation. Results show that the structure and properties (i.e., pore size, surface roughness, zeta potential, pure water flux and solute rejection) of the PES-MWCNTs membrane could be tailored easily by adjusting the loadings of PDA-modified MWCNTs. The optimized PES-MWCNTs membrane exhibited an excellent rejection of about 91% towards the polyelectrolyte draw solute of poly(sodium 4-styrene-sulfonate) (PSS) and a superior perm-selectivity. The optimized membrane flux was 31.20 LMH and its reverse salt flux was 0.14 mmolMH when tested in the FO process with the membrane orientation of the MWCNTs layer facing to feed solution and 0.50 wt.% PSS used as a draw solution. Importantly, oil-water emulsion separation experiments demonstrate that the optimized PES-MWCNTs membrane showed a negligible membrane fouling behavior with only ∼ 3% of water flux decline during 2 h of the cross-flow test when operated in the FO process as a comparison with that operated in the UF process (∼25% of water flux decline). Our work provides some insights on the design of the high-performance UF-like FO membranes for oil-water separation.