Constructing a dual-layer PTFE nanofiltration membrane for enhanced salt solution permeability

Abstract

Polytetrafluoroethylene (PTFE) nanofiltration (NF) membrane has gained increasing attention due to its comprehensive outstanding performance. However, the inherent low surface energy of PTFE makes it difficult to construct a functional NF layer on its surface. In this study, we have presented a novel three-layer of PTFE composite NF membrane with the electrospun PTFE nanofiber membrane as the substrate. During which, the cross-linked polyvinyl alcohol (PVA) was utilized to ensure the high adhesion strength between the polyamide (PA) selective layer and the substrate of PTFE nanofiber membrane. Furthermore, we have further optimized the physical and chemical structure of the composite NF membrane by adjusting the structure and thickness of the PA selective layer and the PVA-GA (glutaraldehyde) layer. When the TMC (1,3,5-benzenetricarbonyl trichloride) and PIP (piperazine) concentration were 2 % and 6 %, the PVA concentration was 2 %, the obtained composite membrane achieved a high multivalent salts rejection rate (99.2 % for Na₂SO₄) and permeation flux (14.41 L∙m⁻²∙h⁻¹∙bar⁻¹). Additionally, the obtained PTFE composite NF membranes demonstrated durability against solvents and long-term reliability after ultrasonic treatment, acid/alkali treatment, sustained operation for 48 h, and cyclic experiments. These findings offer a practical method for the industry's utilization of PTFE NF substrates in the separation of salt solutions.