We fabricated a biomimetic nanofiltration (NF) membrane by immobilizing an Aquaporin Z (AqpZ)-incorporated supported lipid bilayer (SLB) on a layer-by-layer (LbL) complex polyelectrolyte membrane to achieve excellent permeability and salt rejection with a high stability. The polyelectrolyte membranes were prepared by LbL assembly of poly(ethylenimine) (PEI) with positive charges and poly(sodium 4-styrenesulfonate) (PSS) with negative charges alternately on a porous hydrolyzed polyacrylonitrile (H-PAN) substrate. AqpZ-incorporated 1,2-dioleloyl-sn-glycero-3-phosphocholine (DOPC)/1,2-dioleoyl-3-trimethylammo-nium-propane (chloride salt) (DOTAP) vesicles with positive charges were deposited on the H-PAN/PEI/PSS polyelectrolytes membrane surface. The resulting biomimetic membrane exhibited a high flux of 22 L·m(-2)·h(-1) (LMH), excellent MgCl2 rejection of ∼97% and NaCl rejection of ∼75% under an operation pressure of 0.4 MPa. Due to the attractive electrostatic interaction between SLB and the polyelectrolyte membrane, the biomimetic membrane showed satisfactory stability and durability as well as stable NF flux and rejection for at least 36 h. In addition, the AqpZ-containing biomimetic membrane was immersed in a 0.24 mM (critical micellar concentration, CMC) Triton X-100 solution for 5 min. The flux and rejection were slightly influenced by the Triton X-100 treatment. The current investigation demonstrated that the AqpZ-incorporated biomimetic membranes fabricated by the LbL method led to excellent separation performances and robust structures that withstand a high operation pressure for a relatively long time.

AquaporinZ (AqpZ)-containing, planar, biomimetic membranes hold great application potential in water purification and seawater desalination, due to the excellent permeability and selectivity of AqpZ. However, there remain many challenges to production of robust and defect-free supported lipid bilayer (SLB) biomimetic membranes. By forming amide bonds between the lipid bilayer and microporous substrate, we fabricated an AqpZ-incorporated SLB forward osmosis (FO) membrane, with a large area of 36 cm 2 . With deionized water and 2 mol/L MgCl 2 draw solution, the AqpZ-incorporated biomimetic membrane exhibited a water flux of ~19.2 L·m −2 ·h −1 (LMH) and a reverse solute flux of ~3.2 g·m −2 ·h −1 (gMH). When positively charged phospholipid 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) was blended in the 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) bilayer, a higher flux (~23.1 LMH) could be reached accompanied with a constant reverse salt flux of 3.1 gMH, due to more AqpZ being embedded in the mixed bilayer. From nanofiltration (NF) test, the water permeability (A) could reach 6.31 LMH/bar with a relative low solute permeability (B) of 1.7 LMH for AqpZ-DOPE/DOTAP SLB membrane. When rinsed by a 0.24 mmol/L TritonX-100 (TX-100) surfactant solution, water flux and reverse salt flux of the biomimetic membrane with covalent bond only slightly increased, whereas the membrane without covalent bonds showed significant increase in both water flux and reverse salt flux after TX-100 treatment.This paper presented an effective method for preparation of biomimetic FO membrane with good separation performance as well as excellent stability and durability. Graphical Abstract IntroductionIn recent decades, forward osmosis (FO) has gradually emerged as one of the most promising water purification and desalination technologies in water supply, energy generation, and food processing. 1-4 Unlike pressure-driven membrane processes, like reverse osmosis (RO) and nanofiltration (NF), FO is a naturallyoccurring osmosis-driven membrane process that takes advantage of the osmotic pressure gradient to impel water across a semipermeable membrane, from the feed solution side with high chemical potential,

In the present study, hydrophilic Al 2 O 3 nanoparticles were used as additives in both substrate and polyamide active (PA) layer to improve forward osmosis (FO) membrane properties. Via incorporation of 0.5 wt% Al 2 O 3 into the substrate and 0.05 wt% Al 2 O 3 into the PA layer (PS 0.5 -TFN 0.05 membrane), the water flux reached 27.6 L m À2 h À1 with a relatively low solute reverse flux of 7.1 g m À2 h À1 using DI water as a feed solution and 1 M NaCl as a draw solution. Simultaneously, we found that the incorporation of Al 2 O 3 nanoparticles into both the substrate and PA layer resulted in a better enhancement of FO performance and a higher increase in water flux than the simple incorporation of nanoparticles in substrate. Moreover, the PS 0.5 -TFN 0.05 membrane remained stable during long-term FO tests and under serious water environment. To the best of our knowledge, this is the first study to report the effect of Al 2 O 3 nanoparticles on FO performance, and the results verify the potential use of these nanoparticles in the fabrication of highly permeable FO membranes.

We demonstrated a novel AquaporinZ (AqpZ)-incorporated double-skinned forward osmosis (FO) membrane by layer-by-layer (LbL) assembly strategy. Positively charged poly(ethyleneimine) (PEI) and negatively charged poly(sodium 4-styrenesulfonate) (PSS) were alternately deposited on both the top and bottom surfaces of a hydrolyzed polyacrylonitrile (H-PAN) substrate. Subsequently, an AqpZ-embedded 1,2-dioleloyl-sn-glycero-3-phosphocholine (DOPC)/1,2-dioleoyl-3-trimethylammonium- propane (chloride salt) (DOTAP) supported lipid bilayer (SLB) was formed on PSS-terminated (T-PSS) membrane via vesicle rupture method. The morphology and structure of the biomimetic membranes were characterized by in situ atomic force microscopy (AFM), scanning electron microscope (SEM), Fourier transform infrared spectrometer using the attenuated total reflection technique (ATR-FTIR), and contact angle. Moreover, the FO performance of the resultant membrane was measured by using 2 M MgCl2 solution as draw solution and deionized (DI) water as feed solution, respectively. The membrane with a protein-to-lipid weight ratio (P/L) of 1/50 exhibits 13.2 L/m2h water flux and 3.2 g/m2h reversed flux by using FO mode, as well as 15.6 L/m2h water flux and 3.4 L/m2h reversed flux for PRO mode (the draw solution is placed against the active layer). It was also shown that the SLB layer of the double-skinned FO membrane can increase the surface hydrophilicity and reduce the surface roughness, which leads to an improved anti-fouling performance against humic acid foulant. The current work introduced a new method of fabricating high performance biomimetic FO membrane by combining AqpZ and a double-skinned structure based on LbL assembly.