Impact of pore-forming agents on the performance and structure of TFC polyamide NF membrane

Thin-film composite (TFC) polyamide (PA) nanofiltration (NF) membranes are essential for separating ions and small molecules in the industries, including water treatment, chemical processing, energy production, and pharmaceuticals. These membranes are typically fabricated via interfacial polymerization (IP) on polysulfone (PSf) or polyethersulfone (PES) ultrafiltration (UF) supports. Apparently, optimizing the physicochemical properties of the UF support is very important for achieving TFC-PA NF membranes with superior separation performance. This study systematically investigated the influence of common pore-forming agents used in UF membrane fabrication, specifically polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and lithium chloride (LiCl), on the desalination performance of resulting TFC-PA NF membranes. We characterized the zeta potential, pore structure, and surface wettability of PSf UF membranes prepared with each pore agent. These characteristics were then correlated with the adsorption and desorption behavior of piperazine (PIP) monomers during the IP process. Our findings indicate that employing PVP as a pore-forming agent not only enhanced PIP adsorption within the UF support but also facilitated its rapid release during the IP reaction. This dual effect resulted in a PA selective layer with reduced thickness and smaller pore size. Consequently, the TFC-PA NF membrane fabricated on the PVP-modified UF support exhibited both higher water permeance and improved salt rejection. This research highlights the significant role of the pore-forming agent in determining the performance of TFC-PA NF membranes. The results suggest that UF supports prepared using PVP as a pore agent may be optimal for creating NF membranes with enhanced overall performance.