We investigated the effect of carbon nanotubes (CNTs) location on the property and performance of prepared membranes. Four different types of membranes were prepared, including (1) thin film composite (TFC, polyamide active layer on polysulfone substrate), (2) nanocomposite-supported thin film composite (nTFC, polyamide active layer on CNT-embedded polysulfone substrate), (3) thin film nanocomposite (TFN, CNT-incorporated polyamide active layer on polysulfone substrate), and (4) nanocomposite-supported thin film nanocomposite (nTFN, CNT-incorporated polyamide active layer on CNT-embedded polysulfone substrate). The water permeability followed the sequence of nTFN > TFN > nTFC > TFC. However, the rejection and salt permeability exhibited the opposite trend. The incompatibility between CNTs and polymers provided nanocorridors, through which both water and solutes could pass. The nTFN membrane exhibited the highest porosity and lowest structural parameter. Moreover, the nTFN membrane possessed the best antifouling capacity by preventing foulants to attach to the surface and clog the substrate pores. This work offered some systematic knowledge to design novel membranes with improved performance for desalination and water purification applications.Keywords: Antifouling; CNTs; Forward osmosis; Nanocomposite membrane; Nanofiltration

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 for the 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 cm2. With deionized water and 2 mol L−1 MgCl2 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 by a constant reverse salt flux of 3.1 gMH, due to more AqpZ being embedded in the mixed bilayer. From the nanofiltration (NF) test, the water permeability (A) could reach 6.31 LMH per bar with a relatively low solute permeability (B) of 1.7 LMH for the AqpZ-DOPE/DOTAP SLB membrane. When rinsed with a 0.24 mmol L−1 TritonX-100 (TX-100) surfactant solution, water flux and reverse salt flux of the biomimetic membrane with covalent bonds only slightly increased, whereas the membrane without covalent bonds showed a significant increase in both water flux and reverse salt flux after TX-100 treatment. This paper presented an effective method for the preparation of biomimetic FO membranes with good separation performance as well as excellent stability and durability.

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.

•The effects of CNT diameter and concentration on MMMs performances were investigated.•MMMs showed a 660% higher flux than PES membranes and a Na2SO4 rejection of 87.2%.•The mechanisms of CNT diameter and concentration were attempted to be explained.Polyethersulfone/carbon nanotubes (PES/CNTs) based mixed matrix membranes (MMMs) were prepared by phase inversion method for nanofiltration (NF) application. Carboxylated CNTs with different diameter and concentration were incorporated into the polymer matrix to enhance the performances of the NF membranes. The prepared PES/CNTs membranes were characterized and evaluated in terms of membranes morphology, structure, surface properties, and separation performances. Two types of CNTs with different diameters (20 and 40 nm, marked as CNT1 and CNT2, respectively) were chosen to investigate the effect of CNT diameter on membrane performances. The effect of CNT concentrations (from 0.01 to 1 wt%) was also tested by introduction of CNT2 in the MMMs. As a result, the MMMs embedded with CNT1 achieved better NF performances. When CNT2 concentration reaches 0.1 wt%, the PES/CNT2 membranes obtained the highest water flux (38.91 L/m2 h) and Na2SO4 rejection (87.25%) at 4 bar. The solute rejection was in a sequence of R(Na2SO4) > R(MgSO4) > R(NaCl).

•Double-skinned FO membrane was prepared by interfacial polymerization of dopamine/CNTs with TMC on PSf.•Double-skinned membranes exhibited excellent water flux without sacrificing solute rejection.•The TFN0.05 membrane demonstrated remarkable antifouling capacity because of CNT addition.Novel carbon nanotubes (CNTs) incorporated double-skinned thin film nanocomposite (TFN) membranes were fabricated by interfacial polymerization of polydopamine/CNTs and trimesoylchloride (TMC) on polysulfone (PSf) substrate. As controls, thin film composite (TFC) membrane without CNTs and FO membranes with single-skinned structures (top-skinned or bottom-skinned) was also fabricated. The prepared membranes were characterized and evaluated in terms of membrane morphology, structure, surface property, separation performance and antifouling capacity. The effect of membrane orientation, composition and concentration of draw solutions on FO performance was studied as well. It was found that CNTs had significant influence on the properties and the performances of the synthesized FO membranes. The double-skinned membranes owned excellent solute rejection without sacrificing water flux. By incorporation of CNTs, TFN membranes exhibited higher FO water flux than TFC membranes. The double-skinned TFN0.05 membrane, the optimal FO membrane, showed a 54% enhancement in water flux than double-skinned TFC membrane at TOP-FS orientation by using MgCl2 as draw solution and DI water as feed solution. Moreover, the double-skinned TFN0.05 membrane demonstrated remarkable antifouling capacity because of the prominent foulant resistance induced by CNT addition. This work paved a new way to fabricate high performance FO membrane by the utilization of double-skinned structure and incorporation of CNTs.Download full-size image

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 for the 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 cm2. With deionized water and 2 mol L−1 MgCl2 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 by a constant reverse salt flux of 3.1 gMH, due to more AqpZ being embedded in the mixed bilayer. From the nanofiltration (NF) test, the water permeability (A) could reach 6.31 LMH per bar with a relatively low solute permeability (B) of 1.7 LMH for the AqpZ-DOPE/DOTAP SLB membrane. When rinsed with a 0.24 mmol L−1 TritonX-100 (TX-100) surfactant solution, water flux and reverse salt flux of the biomimetic membrane with covalent bonds only slightly increased, whereas the membrane without covalent bonds showed a significant increase in both water flux and reverse salt flux after TX-100 treatment. This paper presented an effective method for the preparation of biomimetic FO membranes with good separation performance as well as excellent stability and durability.

Graphene-based nanomaterials have opened a new era in the fabrication of novel membranes with outstanding performance. In this study, we propose a new method of fabricating a graphene oxide quantum dot (GOQD)-incorporated thin-film nanocomposite (TFN) membrane for reverse osmosis (RO) applications. Inspired by free-standing graphene membranes prepared by vacuum filtration, an aqueous suspension of GOQD/m-phenylenediamine (MPD) was first filtered onto a polysulfone (PSf) substrate to obtain a cushion layer. A GOQD-incorporated polyamide (PA) selective layer was then constructed by interfacial polymerization between MPD and trimesoyl chloride (TMC). This method can easily be scaled up owing to its simple preparation procedures. The newly developed TFN membrane exhibited stable high performance with a flux of 37.5 L m−2 h−1 and a NaCl rejection of 98.8% at 16 bar. Remarkably, this represents a 51.8% increase in permeate flux relative to a GOQD-free TFC membrane without compromising the solute rejection. In addition, the GOQD-incorporated TFN membrane displayed long-term durability over 120 h of RO testing. More importantly, the introduction of GOQD into the TFN membrane resulted in improved antifouling and chlorine resistance properties, which are greatly desired in the membrane desalination and water reclamation processes.