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Composite forward osmosis hollow fiber membranes: Integration of RO- and NF-like selective layers for enhanced organic fouling resistance
- Fang, Wangxi, Liu, Chang, Shi, Lei, Wang, Rong
- Journal of membrane science 2015 v.492 pp. 147-155
- artificial membranes, dextran, electrolytes, fouling, humic acids, hydrophilicity, lysozyme, models, osmosis, pH, permeability, polyamides, polymerization, sodium chloride
- Novel composite forward osmosis (FO) hollow fiber membranes with two selective skin layers were developed in the present work. The polyethersulfone (PES) hollow fiber substrate was firstly fabricated by a phase inversion method. The RO-like polyamide skin layer was then prepared on the inner surface of the hollow fiber substrate via interfacial polymerization (IP), while the NF-like outer skin layer was prepared via polyelectrolyte layer-by-layer (LBL) assembly. Three double-skinned membranes with negative (DS#1.5), positive (DS#2.0) and minimal (DS#2.5) outer surface charges under neutral pH environment were evaluated for their capabilities against organic fouling in the FO process.The newly developed double-skinned membranes possess water permeability greater than 2l/m²hbar and NaCl rejection higher than 95% under 2bar pressure, and have superior water flux and less salt leakage than the commercial HTI FO membranes as well as all the reported double-skinned FO membranes with RO-like selective layers. Most importantly, the double-skinned DS#2.5 hollow fiber membrane exhibits exciting organic fouling resistance because of its highly hydrophilic NF-like secondary layer with minimal surface charge and tightened surface structure to mitigate possible substrate pore clogging and fouling layer formation. A stable water flux of around 25l/m²h was attained for DS#2.5 membrane using <0.5M NaCl as the draw solution and a water containing 200ppm dextran (DEX) or Aldrich humic acid (AHA), or lysozyme (LYS) and 10mM NaCl as the model feed in the active layer against the draw solution (AL-DS) configuration, suggesting its great potential for practical FO applications.