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 investi-gated to reveal that the PSf-b-PEG membrane exhibited intertwined and fused nanofibrous structure with rela-tively 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.