Polysulfone substrates modified with polyethylene glycol-grafted graphene oxide nanosheets for enhanced forward osmosis performance

Tuning the physico-chemical properties and morphology of the substrate layer is of great importance for designing thin film composite membranes (TFC) with high performance in the forward osmosis (FO) process. Here, polyethylene glycol grafted graphene oxide (PEG-g-GO) nanosheets were added to the casting solution of a porous polysulfone (PSf) substrate, and the characteristics of the resulting substrate prepared by the non-solvent-induced phase separation (NIPS) process were investigated. Compared to the pristine PSf substrate, the PEG-g- GO loaded substrate showed higher surface hydrophilicity, more porous and highly connected finger-like structure and thinner dense skin layer. Due to these differences, the selective polyamide layer interfacially polymerized atop the modified substrate was thinner and smoother compared to that polymerized atop the pristine substrate. The FO performance tests conducted on the prepared TFC membranes showed that the water flux increased, while the specific selectivity (as the reverse salt flux, J_S, to water flux, J_W, ratio) and structural parameter (S) decreased when the modified substrate was used for TFC fabrication. Furthermore, the molecular weight (Mw) of PEG grafted onto GO affected the properties of the substrate and thus the performance of the final FO-TFC. PEG with the highest Mw investigated (6000 g/mol) resulted in a 40 % and 23 % reduction in the parameter S and J_S/J_W, respectively, compared to TFC with the bare substrate. These improvements were greater than those obtained using PEG with lower Mw, 1500 and 600 g/mol, respectively.