Fabricating novel high-performance thin-film composite forward osmosis membrane with designed sulfonated covalent organic frameworks as interlayer

Herein, a novel highly selective thin-film composite (TFC) forward osmosis (FO) membrane with high water flux (Jw) and low reverse salt flux (Js) was fabricated with a rationally designed sulfonated covalent organic frameworks (COFs) as an interlayer. This membrane was designed to be negatively charged, hydrophilic and has the synergistic effect of the selective rejection ability of the COFs. The sulfonation of the COFs enhanced its hydrophilicity, offered negative charges and narrowed its pore size, benefiting the salt rejection. Hydrolyzed nylon membrane support with freed surface amino groups was firstly reacted with trimesoyl chloride (TMC) to become hydrophilic and negatively charged. The sulfonated COFs was then firmly mounted on the modified support via H-bonding. A PA layer was finally formed on the support via interfacial polymerization. The prepared TFC-FO membrane overcame the trade-off between Jw and Js with an enhanced FO permeation and superior selectivity (Jw/Js = 24.7 L/g) in FO mode. Both the sulfonated COF interlayer and TMC modification of nylon support were tested to be crucial to the high performance. The new strategy reported here paves a way for taking the advantages of COFs for preparing high-performance FO membranes.