Dual-layered nanocomposite membrane incorporating graphene oxide and halloysite nanotube for high osmotic power density and fouling resistance

This study introduces a thin-film composite (TFC) membrane with a dual-layered nanocomposite substrate synthesized using a dual-blade casting approach for application in osmotic power generation by the pressure-retarded osmosis (PRO) process. The approach incorporates halloysite nanotubes (HNTs) into the bottom polymer substrate layer and graphene oxide (GO) on the top layer substrate, on which a thin polyamide active layer is formed. The fabricated membrane substrate showed highly desirable membrane substrate properties such as a high porosity, opened-bottom surface, suitable top-skin surface morphology for subsequent active layer formation and high mechanical strength, which are essential for high-performance PRO processes. At a GO loading of 0.25 wt% and HNT loading of 4 wt%, the power density (PD) of the nanocomposite membrane was 16.7 W/m(2) and the specific reverse solute flux (SRSF) was 2.4 g/L operated at 21 bar applied pressure using 1 M NaCl as draw solution and deionized water as feed, which is significantly higher than the those for a single-layered or commercial PRO membrane. This membrane performance was observed to be stable in the pressure cycle test and under long-term operation. The membrane substrate with HNTs incorporated exhibited high fouling resistance to sodium alginate and colloidal silica foulants, with the PD decreasing by 17% after 3 h of operation, compared to a membrane substrate without HNTs and commercial PRO membranes, which decreased by 26% and 57%, respectively. A fluorescence microscope study of the membranes subjected to feed water containing Escherichia coli confirmed the good antibacterial properties of the dual-layered TFC membrane. The study provides an attractive alternative approach for developing PRO membranes with high PD and fouling resistance.