Effect of substrate morphology on characteristics of layer-by-layer self-assembly nanofiltration membrane for micropollutants removal

Layer-by-layer (LBL) hollow fiber nanofiltration (NF) membranes have emerged as a promising technology for the removal of micropollutants (MPs). Previous research has been largely focused on polyelectrolyte pairs and coating parameters. This paper studied the substrate morphology, a critical factor often being overlooked. Poly (allylamine hydrochloride) /poly (styrene sulfonic acid) sodium salt (PAH/PSS) coating was utilized to evaluate the impact of the substrate morphology. Two polyethersulfone substrates were selected: Substrate 1# with dense skins at both lumen/shell and Substrate 2# with skin at the lumen and an open shell surface. All LBL NF membranes showed molecular weight cut-off ranging from 180 to 223 Da and MgCl 2 rejection around 94 %. For LBL membrane 1#, with coatings on both shell/lumen sides, the outer coating was defective due to scratches. For LBL membrane 2# with a coating at the lumen, significant PAH overcompensation was observed, because of the open inner and outer surfaces comparing to LBL membrane 1#. Higher rejection to positively charged MPs was resulted from Donnan effect , outperforming steric exclusion. The backwash stability of both membranes was excellent and independent of the substrate structure. This work provides a basis for substrate selection for fabricating LBL NF membranes.