Implementation of layer-by-layer assembly to ameliorate dopamine-incorporated PAN nanofiltration membrane: application toward forward osmosis process

In the present study, poly acrylonitrile (PAN) nanofiltration membrane has been tailored for applying in forward osmosis (FO) process via the combination of two modification approaches including blending and layer-by-layer (LBL)-surface modification techniques. Firstly, dopamine was embedded in PAN nanofiltration membrane to improve its hydrophilicity and antifouling features so that at the optimal loading rate (0.1 wt%) water contact angle (WCA) of the bare membrane declined from 62.7 degrees to 54.5 degrees, its pure water flux augmented from 3.59 to 7.2 kg/m2 h, and its flux recovery ratio (FRR) increased from 70.6 to 92.3%. Secondly, LBL technique has been performed on the optimal MM membrane's surface (with 0.1 wt%) by using poly diallyl dimethyl ammonium and poly(4-styrenesulfonic acid-co-maleic acid) sodium salt as poly cation and poly anion, respectively. From the obtained results, the insertion of 5 bilayers on the optimally dopamine-incorporated membrane's surface showed an outperformance compared to the others with FRR and WCA of 99.2% and 34.5 degrees, respectively. Finally, the performances of the synthesized membranes were evaluated in a FO setup containing NaCl (1M) as a draw solution and deionized water as a feed solution. Pursuant to the obtained results, the optimally tailored membrane by using both the modification methods revealed the lowest reverse solute flux (3.9 g/m2 h) and a moderate pure water flux (3 l/m2 h), corroborating its potential to be used in an effectual FO process.