Rapid conversion of hydrophobic polytetrafluoroethylene (PTFE) hollow fiber membranes to superhydrophilic ones by surface polydopamine coating accelerated by sodium periodate (NaIO4) and crosslinked with polyethyleneimine

Superhydrophilic PTFE hollow fiber membranes were achieved through a rapid PDA/PEI coating under oxidation of NaIO 4. • PDA/PEI-coated membranes showed pure water flux of 3665 L/m 2 ·h, 277 L/m 2 ·h for saturated brine with turbidity removals ≥ 99%. • NaIO 4 expedited PDA coating, whereas PEI was responsible either for accelerated PDA coating or improved hydrophilicity. PTFE is an excellent membrane material for water treatment because of its outstanding chemical resistance and thermal stability. However, its inherent surface hydrophobicity restricts its use in water treatment. Recently, bio-inspired polydopamine (PDA) has been used to surface hydrophilization of PTFE membranes. Nonetheless, a single PDA surface coating on PTFE membranes offers only limited improvements in hydrophilicity and requires a lengthy reaction time. In this study, we present a rapid PDA surface coating process for PTFE hollow fiber membranes that leverages the stronger oxidizing power of sodium periodate (NaIO 4 ) and the crosslinking capabilities of polyethyleneimine (PEI) to accelerate PDA polymerization and improve hydrophilicity. Characterization results, in terms of membrane morphology, surface composition, wettability, and water permeation/filtration tests, collectively show that the inclusion of NaIO 4 and PEI during PDA coating accelerates the co-deposition of PDA/PEI on PTFE membrane surfaces and produces membranes with superhydrophilicity: a 3-hour PDA/PEI coating on hydrophobic PTFE membranes results in water contact angles near 0° and water fluxes up to 3665 L/m 2 ·h with pure water feed and 277 L/m 2 ·h with saturated salt brine feed under 0.1 MPa applied presure, while achieving over 99% of turbidity removal rate. Comparing membranes coated with PDA alone to those coated with PDA and NaIO 4 highlights the roles of each additive: NaIO 4 enhances dopamine polymerization rate, while PEI accelerates PDA coating through cross-linking and contributes to superhydrophilicity via its -NH groups. The PDA/PEI-coated membranes also maintain stable water permeability after cycles of drying and exposure to acidic, alkaline, and oxidative environments. This work provides insights into PDA/PEI coating processes on PTFE membranes and supports future development of hydrophilic PTFE membranes for practical water treatment. Download: Download high-res image (103KB) Download: Download full-size image