High-flux thin film composite membranes for nanofiltration mediated by a rapid co-deposition of polydopamine/piperazine

A novel thin film composite (TFC) membrane was rationally originated using an interfacial polymerization (IP) process mediated by a rapid Cu2+/H2O2-induced co-deposition of PDA and piperazine (PIP). The co-deposition strategy distinctly shortens modification times while also promoting the high, stable loading of aqueous monomers through covalent bonding with PDA, thus being beneficial for subsequent crosslinking with trimesoyl chloride (TMC). The controlled diffusion of aqueous monomers during the IP process enabled the formation of a thin, smooth, and hydrophilic polyamide (PA) film at the top of a polyacrylonitrile (PAN) membrane substrate. ATR-FTIR, XPS, SEM, AFM, and water contact angle analyses confirmed the presence of the selective PA layer. Zeta potential measurements also revealed a negatively charged surface, which resulted in a salt retention order of NaCl < MgCl2 < MgSO4 < Na2SO4. The roles of the co-deposition time and the PIP/dopamine ratio in the membrane morphology and separation properties were systematically studied to explore the optimal functionalization parameters. A high-performance TFC membrane (TFC2.0_5) was achieved after identifying optimal conditions as 2/1 mass ratio for PIP/dopamine, 5 min co-deposition, 0.1% w/v TMC, and 30 s IP reaction. In addition to achieving high water permeability (14.5 LMH bar(-1)), this membrane also attained high mono/bivalent salt selectivity (NaCl/Na2SO4, 24.1) and long-term stability in treating saline solutions. This simple, and cost-effective strategy provides an improved guideline in designing high-performance TFC membranes with vast potential in water treatment.