Fine pore tailoring of PSf-b-PEG membrane in sub-5 nm via phase-inversion

It is highly important but challenging to fabricate polymeric separation membranes with pore size in sub-5 nm via the non-solvent induced phase separation (NIPS) process. Herein, we reported a simple but effective method to precisely tailor the pore size of polysulfone-block-polyethylene glycol (PSf-b-PEG) membrane in sub-5 nm via NIPS. Selective solvents of tetramethylene sulfone (Ts) and tetrahydrofuran (THF) towards the corresponding PEG block and PSf block in PSf-b-PEG were mixed at various ratios to tailor the casting solution properties and to finely tailor the pore size of the PSf-b-PEG membranes. The membrane formation mechanism was also investigated to reveal that the PSf-b-PEG membrane exhibited intertwined and fused nanofibrous structure with relatively high porosity and extremely strong mechanical strength. As the content of evaporative THF in the casting solution increased from 42.5 wt% to 85.0 wt%, the MWCO of the PSf-b-PEG membranes decreased from 127 kDa to 6.6 kDa, and the mean effective pore size of the membranes shrank from 15 nm to 2 nm, greatly exceeding the tailorable range and the minimum threshold of the pore size of PSf and PES membranes. Impressively, even if the pore size of the membrane was 2 nm, the pure water permeance of the membrane was still as high as 7 L m−2 h−1 bar−1, indicating the great potential of the PSf-b-PEG membranes for practical applications.