Performance enhancement of TFC FO membranes with polyethyleneimine modification and post-treatment

• SIP modification of TFC membranes by PEI with various molecular weights.
• Post-treatment of PEI-modified membranes in basic or acidic solution is conducted.
• Modified membranes exhibit higher hydrophilicity and fractional free volume.
• Modified membranes possess better separation performance and antifouling property.

In this work, simple and effective second interfacial polymerization (SIP) of thin-film composite (TFC) membranes is performed with polyethyleneimine (PEI) of various molecular weights, in order to improve the separation performance for forward osmosis (FO) applications. Various characterization techniques are employed to examine the modification mechanism. Compared to the control TFC membrane, PEI-modified membranes exhibit higher water permeabilities, acceptable salt rejection and lower fouling propensity. The effects of PEI molecular weight on the membrane morphology and separation performance are investigated systematically with various characterizations. Post-treatment of PEI-modified membranes in alkaline and acidic aqueous solutions is further investigated, and its effects on the FO performance, intrinsic separation properties and antifouling properties of these post-treated membranes are studied. In comparison with pristine PEI-modified TFC membranes, the post-treated TFC membranes show further enhanced water flux and improved anti-fouling properties.

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