A new method for fabrication of thin film nanofibrous composite (TFNC) ultrafiltration (UF) membrane consisting of an ultrathin poly(acrylonitrile-co-acrylic acid) (PAN-AA) barrier layer based on a polyacrylonitrile (PAN) nanofibrous support layer was proposed in this study. First, a thin PAN-AA nanofibrous layer was electrospun and deposited on a thicker PAN nanofibrous substrate. Then, the as-prepared PAN-AA nanofibers were swollen in the alkaline buffer solution and merged imperceptibly as an integrated nonporous hydrogel layer on the PAN substrate. The PAN-AA hydrogel layer was cross-linked with different bivalent metal cations (Ca2+, Mg2+) to form an ultrathin barrier layer, of which the thickness and porosity were optimized by controlling the depositing time of PAN-AA nanofibers and pH value of buffer solution. Proteins with different molecular weights were used to evaluate the ultrafiltration performance of the resultant composite membranes. Due to its hydrophilic and negative charged barrier layer, the PAN-AA-Mg and PAN-AA-Ca TFNC UF composite membranes exhibited excellent permeate flux (221.2 and 219.2 L/m2 h) and rejection efficiency (97.8% and 95.6%) for bovine serum albumin (BSA) aqueous solution (1 g/L) at 0.3 MPa. The PAN-AA TFNC UF membranes could be used to retain solutes, of which the radius was larger than 4.6 nm.

•Novel two-tier thin-film nanofibrous composite membrane was used for hemodialysis.•The optimized PVA/PAN membrane exhibited high permeability and great selectivity.•The two-tier structure resulted in more efficient middle-molecule removal.•The hydrophilic surface of the PVA/PAN membrane reduced protein absorption.•The membrane showed excellent overall mechanical properties and hemocompatibility.Membrane structure design is critical for the development of high-performance hemodialysis membranes. Here, a thin-film nanofibrous composite (TFNC) membrane, consisting of a two-tier composite structure, i.e., an ultrathin hydrophilic separation layer of chemically cross-linked polyvinyl alcohol (PVA), and an electrospun polyacrylonitrile (PAN) nanofibrous supporting layer, was demonstrated as the hemodialysis membrane for the first time. The optimized PVA/PAN TFNC membrane exhibited high permeability (~ 290.5 L/m2h at 0.1 MPa) and excellent selectivity which should be attributed to its unique structure with ultrathin separation layer and highly porous supporting layer. In addition, the TFNC membrane also possessed excellent overall mechanical properties, good hydrophilicity and comparable hemocompatibility properties (protein adsorption, platelet adhesion, complement activation, hemolysis ratio). The hemodialysis simulation experiments on optimized TFNC membrane showed that 82.6% of urea and 45.8% of lysozyme were cleaned and 98.8% of bovine serum albumin (BSA) was retained. The TFNC membranes exhibited excellent hemodialysis performances, especially for the middle-molecule uremic toxin removal, which was more efficient than conventional hemodialysis membranes reported so far, suggesting PVA/PAN TFNC membranes as promising alternatives for hemodialysis applications.

Here, a novel thin-film nanofibrous composite (TFNC) membrane consisting of an electrospun polyacrylonitrile (PAN) nanofibrous substrate and a robust graphene oxide barrier layer was developed through a facile vacuum filtration method for pervaporation desalination application. The exfoliated hydrophilic graphene oxide (GO) nanosheets were sturdily integrated together onto the PAN nanofibrous support with the aid of a flexible connector poly(vinylalcohol) (PVA) and a crosslinking agent glutaraldehyde (GA) via vacuum filtration. The hydrophilic PVA chains acting as the spacing bridges ensured that the stacked GO nanosheets were interlinked successfully with sufficient bonding by GA to provide adequate stability in a water environment. Benefiting from the superiority of an ultra-thin hydrophilic peculiar GO skin layer and a fully interconnected porous nanofibrous substrate, the resultant optimized robust GO/PAN TFNC membranes displayed an excellent permeate flux of 69.1 L m−2 h−1 and a stable high rejection (99.9%) over a testing period of 24 h from aqueous salt solution with NaCl concentrations of 35 g L−1 at 70 °C. This separation performance was superior to those of homogeneous membranes and composite membranes used in pervaporation desalination reported so far, indicating that this work may facilitate the development of pervaporation in practical desalination application.

•Superhydrophobic PSU-PDMS ENMS are prepared for desalination by DCMD.•The PDMS concentration dictates the surface morphology and hydrophobicity.•ENMs are prepared using a cold-press post-treatment step under different pressures.•The applied pressure strongly affects the morphological characteristics of the ENMs.•PSU-PDMS ENM is promising in MD desalination for their high quality produced water.Superhydrophobic electrospun nanofibrous membranes (ENMs) with a fully interconnected porous web structure and high void volume fraction have been proposed for membrane distillation (MD). This study describes a novel and facile design strategy for the fabrication of superhydrophobic and self-cleaning polysulfone-polydimethylsiloxane (PSU-PDMS) ENMs for direct contact membrane distillation (DCMD) via electrospinning PSU nanofibers followed by PDMS coating and cold-press post-treatment. A comprehensive investigation of the effects of PDMS concentration and cold-press post-treatment pressure on the membrane surface morphology, wettability, membrane characteristics and DCMD performance was carried out. The best ENM in this study, PSU-PDM-1-4, prepared with 1 g PDMS in 40 mL hexane and 4 MPa applied cold-press post-treatment pressure, exhibited a competitive permeate flux of about 21.5 kg/m2h and a stable low permeate concentration with an electrical conductivity of 4.224 – 4.523 µS/cm when using 30 g/L NaCl aqueous solution as feed and a temperature difference of 50 °C over a DCMD period of 12 h without detecting inter-fiber space wetting. The proposed PSU-PDMS ENM type of membrane is promising in MD desalination.Download high-res image (198KB)Download full-size image

A novel kind of thin-film nanofibrous composite (TFNC) nanofiltration membrane consisting of a polypiperazine amide (PPA) barrier layer, an ultrathin electrospun poly(acrylonitrile-co-acrylic acid) (PAN–AA) transitional mid-layer and an electrospun polyacrylonitrile (PAN) nanofibrous supporting layer, was successfully fabricated by interfacial polymerization with piperazine (PIP) and trimesoyl chloride (TMC) onto the PAN–AA/PAN double-layer substrate. The PAN–AA nanofibrous mid-layer played two important roles between the PPA barrier layer and the PAN nanofibrous supporting layer. It could be swollen in the alkaline aqueous monomer (PIP) solution to form an intermediate hydrogel film, which acted as the transitional mid-layer to cover the majority of the large surface pores of the electrospun PAN nanofibrous substrate. On the other hand, the hydrophilic PAN–AA hydrogel film could capture and reserve abundant PIP monomer to facilitate interfacial polymerization with TMC to form an endurable ultrathin PPA barrier layer, resulting in an integrated composite membrane confirmed by the mechanical properties. The resultant TFNC membranes demonstrated a high rejection rate (98.2%) and high permeate flux (64.4 L m−2 h−1) for MgSO4 aqueous solution (2.0 g L−1), and also exhibited excellent structural stability due to the strong interactions between the barrier layer and the nanofibrous support that were enhanced by the transitional PAN–AA mid-layer.

Combined with the features of electrospun nanofibers and the nature of hydrogel, a novel choreographed poly(acrylic acid)–silica hydrogel nanofibers (PAA-S HNFs) scaffold with excellent rare earth elements (REEs) recovery performance was fabricated by a facile route consisting of colloid-electrospinning of PAA/SiO2 precursor solution, moderate thermal cross-linking of PAA-S nanofiber matrix, and full swelling in water. The resultant PAA-S HNFs with a loose and spongy porous network structure exhibited a remarkable adsorption capacity of lanthanide ions (Ln3+) triggered by the penetration of Ln3+ from the nanofiber surface to interior through the abundant water channels, which took full advantage of the internal adsorption sites of nanofibers. The effects of initial solution pH, concentration, and contact time on adsorption of Ln3+ have been investigated comprehensively. The maximum equilibrium adsorption capacities for La3+, Eu3+, and Tb3+ were 232.6, 268.8, and 250.0 mg/g, respectively, at pH 6, and the adsorption data were well-fitted to the Langmuir isotherm and pseudo-second-order models. The resultant PAA-S HNFs scaffolds could be regenerated successfully. Furthermore, the proposed adsorption mechanism of Ln3+ on PAA-S HNFs scaffolds was the formation of bidentate carboxylates between carboxyl groups and Ln3+ confirmed by FT-IR and XPS analysis. The well-designed PAA-S HNFs scaffold can be used as a promising alternative for effective REEs recovery. Moreover, benefiting from the unique features of Ln3+, the Ln-PAA-S HNFs simultaneously exhibited versatile advantages including good photoluminescent performance, tunable emission color, and excellent flexibility and processability, which also hold great potential for applications in luminescent patterning, underwater fluorescent devices, sensors, and biomaterials, among others.Keywords: adsorption; colloid-electrospinning; hydrogel nanofibers; lanthanide ions; photoluminescent

Electrospun superhydrophobic organic/inorganic composite nanofibrous membranes exhibiting excellent direct contact membrane distillation (DCMD) performance were fabricated by a facile route combining the hydrophobization of silica nanoparticles (SiO2 NPs) and colloid electrospinning of the hydrophobic silica/poly(vinylidene fluoride) (PVDF) matrix. Benefiting from the utilization of SiO2 NPs with three different particle sizes, the electrospun nanofibrous membranes (ENMs) were endowed with three different delicate nanofiber morphologies and fiber diameter distribution, high porosity, and superhydrophobic property, which resulted in excellent waterproofing and breathability. Significantly, structural attributes analyses have indicated the major contributing role of fiber diameter distribution on determining the augment of permeate vapor flux through regulating mean flow pore size (MFP). Meanwhile, the extremely high liquid entry pressure of water (LEPw, 2.40 ± 0.10 bar), robust nanofiber morphology of PVDF immobilized SiO2 NPs, remarkable mechanical properties, thermal stability, and corrosion resistance endowed the as-prepared membranes with prominent desalination capability and stability for long-term MD process. The resultant choreographed PVDF/silica ENMs with optimized MFP presented an outstanding permeate vapor flux of 41.1 kg/(m2·h) and stable low permeate conductivity (∼2.45 μs/cm) (3.5 wt % NaCl salt feed; ΔT = 40 °C) over a DCMD test period of 24 h without membrane pores wetting detected. This result was better than those of typical commercial PVDF membranes and PVDF and modified PVDF ENMs reported so far, suggesting them as promising alternatives for MD applications.Keywords: colloid electrospinning; membrane distillation; nanofibrous membrane; silica nanoparticles; superhydrophobicity

In this study, micro-nano structured p-sulfonatocalix[8]arene (calix8) complex membranes prepared by electrostatic adsorbing anionic calix8 onto the cationic nanofibrous mats with micro-nano structure were utilized as an affinity membrane for the selective adsorption of lanthanum(III) ions, where the cationic nanofibrous mats were fabricated by wet-electrospinning technique from polyacrylonitrile (PAN) solution with the aid of pore-forming agent poly(vinyl pyrrolidone) (PVP) and followed by the amination with diethylene triamine (DETA). The as-prepared nanofibrous calix8 complex membranes were subject to selective adsorption of La(III) ions in aqueous solution and showed very high adsorption capacity and selectivity for La3+ from other metal ions such as Fe3+, Al3+, Cu2+, Ca2+, Mg2+ and K+. The resultant membranes adsorbed with La(III) ions could be desorbed and regenerated successfully without significantly affecting their adsorption capacity. The adsorption data at equilibrium were well fitted to Langmuir isotherm equation with a maximum adsorption capacity of 155.1 mg g−1 for La(III) ions. Furthermore, the possible adsorption mechanism of La(III) ions onto the calix8 membrane was discussed based on the FTIR and XPS data. This study demonstrated a facile route for highly efficient and selective separation of lanthanide ions from aqueous solutions.

A new type of dual-biomimetic hierarchically rough polystyrene (PS) superhydrophobic micro/nano-fibrous membrane was fabricated via a one-step electrospinning technique at various polymer concentrations from 15 to 30 wt %. The obtained micro/nano-fibers exhibited a nanopapillose, nanoporous, and microgrooved surface morphology that originated from mimicking the micro/nanoscale hierarchical structures of lotus leaf and silver ragwort leaf, respectively. Superhydrophobicity and high porosity of such resultant electrospun nanofibrous membranes make them attractive candidates for membrane distillation (MD) application with low energy water recovery. In this study, two kinds of optimized PS nanofibrous membranes with different thicknesses were applied for desalination via direct contact MD. The membranes maintained a high and stable permeate water vapor flux (104.8 ± 4.9 kg/m2·h, 20 g/L NaCl salt feed for a thinner PS nanofibrous membrane with thickness of 60 μm; 51 ± 4.5 kg/m2·h, 35 g/L NaCl salt feed for the thicker sample with thickness of 120 μm; ΔT = 50 °C) for a test period of 10 h without remarkable membrane pores wetting detected. These results were better than those of typical commercial polyvinylidene fluoride (PVDF) MD membranes or related PVDF nanofibrous membranes reported in literature, suggesting excellent competency of PS nanofibrous membranes for MD applications.Keywords: membrane distillation; nanofibrous membrane; polystyrene; superhydrophobic;

Superhydrophobic and superoleophilic electrospun nanofibrous membranes exhibiting excellent oil/water separation performance were green fabricated by a facile route combining the amination of electrospun polyacrylonitrile (APAN) nanofibers and immobilization of a Ag nanocluster with an electroless plating technique, followed by n-hexadecyl mercaptan (RSH) surface modification. By introducing the hierarchically rough structures and low surface energy, the pristine superhydrophilic APAN nanofibrous membranes could be endowed with a superhydrophobicity with water contact angle of 171.1 ± 2.3°, a superoleophilicity with oil contact angle of 0° and a self-cleaning surface arising from the extremely low water contact angle hysteresis (3.0 ± 0.6°) and a low water-adhesion property. Surface morphology studies have indicated that the selective wettability of the resultant membranes could be manipulated by tuning the electroless plating time as well as the hierarchical structures. More importantly, the extremely high liquid entry pressure of water (LEPw, 175 ± 3 kPa) and the robust fiber morphology of the APAN immobilized Ag nanocluster endowed the as-prepared membranes with excellent separation capability and stability for oil/water separation by a solely gravity-driven process. The resultant membranes exhibited remarkable separation efficiency in both hyper-saline environment and broad pH range conditions, as well as excellent recyclability, which would make them a promising candidate for industrial oil-contaminated water treatments and marine spilt oil cleanup, and provided a new prospect to achieve functional nanofibrous membranes for oil/water separation.Keywords: electrospinning; immobilization; nanocluster; oil/water separation; superhydrophobicity

In this study, a new class of high performance thin film nanocomposite (TFNC) ultrafiltration membrane based on a polyacrylonitrile (PAN) nanofibrous substrate coupled with a thin hydrophilic nanocomposite barrier layer was fabricated by electrospinning technique combined with solution treatment method, and was used as an ultrafiltration media to separate an oil/water emulsion. The hydrophilic nanocomposite barrier layer was composed of crosslinked poly(vinyl alcohol) (PVA) thin layer incorporating surface oxidized multi-walled carbon nanotubes (MWNTs), and was prepared by immersing electrospun PVA–MWNT/PAN nanofibrous double-layer mats into optimized water/acetone solution and then chemically crosslinked by glutaraldehyde in water/acetone solution. The electrospun PVA–MWNT nanofiber top layer would be swollen to merge imperceptibly into an integrated barrier film on the supporting PAN layer. The variation of the free volume of PVA barrier layer with different MWNTs contents was investigated by positron annihilation lifetime spectroscopy (PALS). The PALS results proved that the free volume of PVA–MWNT/PAN TFNC membranes increased markedly with the increase of MWNTs concentration in the PVA layer, and the filtration evaluation also confirmed that the incorporation of MWNTs into PVA barrier layer could improve the water flux significantly, which indicated that more effective water channels were generated in the nanocomposite barrier layer by the incorporation of MWNTs into PVA barrier layer. The PVA–MWNT/PAN TFNC (10 wt.% MWNT) membrane showed very high water flux (270.1 l/m2 h) with high rejection rate (99.5%) even at very low feeding pressure (0.1 MPa). In addition, the PVA–MWNT/PAN composite membranes showed very good overall mechanical properties.Highlights► High flux low pressure thin film nanocomposite filtration membranes were prepared. ► PVA–MWNT/PAN nanofibrous double layer mats were prepared by electrospinning. ► Electrospun PVA–MWNT top layer was solution treated to an integrated barrier film. ► The free volume characteristics of the PVA–MWNT barrier layers were studied. ► Filtration performances of the PVA–MWNT/PAN nanocomposite membranes were evaluated.

In this work, poly(l-lactic acid) (PLLA) ultrafine fibers with different morphology and structure were fabricated by a novel linear-jet electrospinning method which relies on a conventional electrospinning set-up with continuous rotating drum. To control the morphology and structure of PLLA electrospun fibers, different solution systems and electrospinning conditions were investigated. Two PLLA solution systems (PLLA/DMF/CH2Cl2 and PLLA/CH2Cl2) with different concentration and conductivity were used for the electrospinning and their influences on the formation of the linear electrospinning jet were discussed. Two types of collecting patterns with aligned buckling and linear structure were achieved under the linear electrospinning jet. Highly aligned PLLA electrospun fibers with porous surface could be formed by using the highly volatile solvent CH2Cl2. Here, it should be emphasized that the diameter and surface porosity of such highly aligned PLLA electrospun fibers can be fine tuned by varying the winding velocity. The results of SEM images and polarized FTIR investigations verified that the as-spun PLLA porous surface fibers were highly aligned and molecularly oriented, leading to the enhanced mechanical performance as compared to the non-woven PLLA electrospun fibers.

A novel strategy for building a Cu2+ sensor based on electrospun rhodamine dye doped poly(ether sulfones) (PES) nanofibers was reported. The rhodamine dye containing the spirolactam moiety acting as an electron acceptor and salicylaldehyde acting as an electron donor was doped into PES solution, and the mixture was electrospun to obtain a nanofibrous sensor usable in aqueous media for Cu2+. Morphology of the nanofibrous sensor was characterized by SEM, which showed that the nanofibers with a diameter of 250–600 nm formed a non-woven mat. The resultant nanofibrous sensor showed very good sensitivity toward Cu2+ detection, and the limit of quantification (LOQ) was 1.1 × 10−9 M. Furthermore, other metal ions showed almost no interference. The proposed sensing mechanism has been ascribed to the stabilization of the rhodamine dye after complexation with Cu2+ and a 1:1 stoichiometry has been deduced. This reusable nanofibrous sensor can be utilized conveniently to achieve practical sensing in aqueous medium just like using a test paper. For this approach, the fluorescent probe can be replaced by other one, making this approach a widely applicable strategy for metal ion sensing.

In this study, high flux thin film nanofibrous composite (TFNC) membrane consisting of a nonwoven nanofibrous supporting layer and a thin hydrophilic barrier layer was developed and used as an ultrafiltration media to separate an oil/water emulsion at low feeding pressure. Firstly, the hydrophilic barrier layer was fabricated by electrospraying polyvinyl alcohol (PVA) on nanofibrous polyacrylonitrile (PAN) substrate. Secondly, the deposited PVA top layer was swollen to merge imperceptibly into an integrated barrier film on the supporting layer by immersing PVA/PAN double-layer membranes into suitable solvent water and nonsolvent acetone mixture, and then chemically crosslinked by glutaraldehyde in water/acetone solution. The water content of water/acetone solution and the immersion time were optimized to achieve the integrated and nonporous PVA barrier layer. Filtration performance of the resulting PVA/PAN TFNC membranes was evaluated by the oil/water emulsions separation system. Results showed that the optimized TFNC membrane possessed high flux (347.8 l/m2 h) with high rejection rate (99.6%) at very low feeding pressure (0.2 MPa). It is believed that the strategy for fabricating TFNC membranes described here can be extended easily to fabricate TFNC membranes from many other polymeric membrane materials simply by choosing the suitable solution system for post-treatment.Highlights► Beaded PVA layer was fabricated via electrospraying on nanofibrous PAN substrate. ► The solution treatment bath was composed of water and acetone. ► Electrosprayed PVA top layer was swollen to an integrated barrier film. ► Ultrafiltration performances of the PVA/PAN composite membranes were evaluated.

In this work, a new strategy for fabrication of high flux thin film nanofibrous composite (TFNC) ultrafiltration membrane containing a hydrophilic barrier layer and a nanofibrous substrate was developed. Firstly, the double-layer nanofibrous mat containing very thin hydrophilic nanofiber top layer and nanofibrous supporting layer was manufactured via electrospinning technique. Then the hydrophilic nanofibrous top layer was remelted by suitable solvent vapor exposure and chemical crosslink in the crosslinking bath to form a barrier film on the supporting layer. Here, poly(vinyl alcohol) (PVA)/polyacrylonitrile (PAN) nanofibrous composite membranes were prepared by electrospinning of a very thin PVA nanofibrous layer with thickness of several micrometers on the electrospun PAN nanofibrous substrate, followed by remelting PVA nanofibrous layer to form a barrier PVA film by water vapor treatment and chemical crosslinking in glutaraldehyde water/acetone solution. The depositing time during PVA electrospinning and the water content of the crosslinking solution were utilized to control the thickness and the swelling degree of the PVA barrier layer. In this method, the shortcoming of easy penetration of the coating solution into the porous substrate in typical fabrication of surface coated anti-fouling composite membranes can be overcome, and the thickness of the barrier layer can be easily controlled by the depositing time of the PVA electrospinning. Filtration performances of the PVA/PAN composite membranes were evaluated by the oil/water emulsions separation system. The highest permeate flux of 210 l/m2h was achieved with the rejection of 99.5% for the composite membrane under the operating pressure of 0.3 MPa. It is believed that the strategy for fabricating TFNC membranes described here can be extended easily to fabricate nanofibrous composite membranes from many other polymeric materials simply by choosing the suitable solvent vapor treatment.

⿢Overview of the fabrication and applications of electrospun nanofiber membranes.⿢Recent advances in nanofiber-based membranes for water filtration.⿢Recent development of nanofibrous affinity membranes for adsorption.The development of nanofiber technology offers viable means to produce nanofibrous articles, useful for many health, energy and environmental applications. In specific, polymeric nanofibers fabricated by electrospinning can be used as effective membrane materials for environmental remediation due to the light weight, high surface area, and interconnected porous structure. In this paper, we review some recent advances in electrospinning for mass production of nanofiber membranes, especially suitable for water purification. These electrospun nanofibers not only can form highly porous membranes with controlled pore size, but also can be functionalized to enhance the separation performance. Various composite membrane formats containing different arrangements of nanofibers have been demonstrated for many sorts of water applications, including microfiltration, ultrafiltration, nanofiltration, reverse osmosis, membrane distillation, and adsorption.Download high-res image (309KB)Download full-size image

In this study, a new class of high performance thin film nanocomposite (TFNC) ultrafiltration membrane based on a polyacrylonitrile (PAN) nanofibrous substrate coupled with a thin hydrophilic nanocomposite barrier layer was fabricated by electrospinning technique combined with solution treatment method, and was used as an ultrafiltration media to separate an oil/water emulsion. The hydrophilic nanocomposite barrier layer was composed of crosslinked poly(vinyl alcohol) (PVA) thin layer incorporating surface oxidized multi-walled carbon nanotubes (MWNTs), and was prepared by immersing electrospun PVA–MWNT/PAN nanofibrous double-layer mats into optimized water/acetone solution and then chemically crosslinked by glutaraldehyde in water/acetone solution. The electrospun PVA–MWNT nanofiber top layer would be swollen to merge imperceptibly into an integrated barrier film on the supporting PAN layer. The variation of the free volume of PVA barrier layer with different MWNTs contents was investigated by positron annihilation lifetime spectroscopy (PALS). The PALS results proved that the free volume of PVA–MWNT/PAN TFNC membranes increased markedly with the increase of MWNTs concentration in the PVA layer, and the filtration evaluation also confirmed that the incorporation of MWNTs into PVA barrier layer could improve the water flux significantly, which indicated that more effective water channels were generated in the nanocomposite barrier layer by the incorporation of MWNTs into PVA barrier layer. The PVA–MWNT/PAN TFNC (10 wt.% MWNT) membrane showed very high water flux (270.1 l/m2 h) with high rejection rate (99.5%) even at very low feeding pressure (0.1 MPa). In addition, the PVA–MWNT/PAN composite membranes showed very good overall mechanical properties.Highlights► High flux low pressure thin film nanocomposite filtration membranes were prepared. ► PVA–MWNT/PAN nanofibrous double layer mats were prepared by electrospinning. ► Electrospun PVA–MWNT top layer was solution treated to an integrated barrier film. ► The free volume characteristics of the PVA–MWNT barrier layers were studied. ► Filtration performances of the PVA–MWNT/PAN nanocomposite membranes were evaluated.

Inspired by the profiled structure of polar bear hair that possesses excellent thermal insulation properties, a novel profiled polyacrylonitrile-polystyrene (PAN-PS) core–shell nanofibrous membrane with peculiar groove structures and excellent direct contact membrane distillation (DCMD) performance was designed and manufactured by using an eccentric-axial electrospinning technique. Fiber surface morphology analyses indicated the major contributing role of applied voltage and the shell feeding rate in determining the stability of the electrospinning fluid jet, groove length and width, and membrane structural characteristics. The superhydrophobic properties resulting from the surface hierarchical roughness, prominent void volume fraction, fabulous gas permeability, appropriate mean flow pore (MFP) size and relatively considerable liquid entry pressure of water (LEPw) of the free-standing electrospun nanofibrous membranes (ENMs) could completely satisfy the requirements of the MD process. The resultant choreographed PAN-PS core–shell ENMs with a delicate groove morphology presented an outstanding permeate flux of 60.1 kg m−2 h−1 and high quality water permeate (20 g L−1 NaCl and 1000 ppm Sunset Yellow FCF aqueous solution as feed, ΔT = 40 °C) over a DCMD test period of 36 h without detection of membrane pore wetting. This result was better than those of typical commercial PVDF membranes and exhibited considerable competitiveness as compared with the well-designed ENMs reported so far, suggesting the grooved PAN-PS core–shell ENMs as promising alternatives for MD applications.

Here, a novel thin-film nanofibrous composite (TFNC) membrane consisting of an electrospun polyacrylonitrile (PAN) nanofibrous substrate and a robust graphene oxide barrier layer was developed through a facile vacuum filtration method for pervaporation desalination application. The exfoliated hydrophilic graphene oxide (GO) nanosheets were sturdily integrated together onto the PAN nanofibrous support with the aid of a flexible connector poly(vinylalcohol) (PVA) and a crosslinking agent glutaraldehyde (GA) via vacuum filtration. The hydrophilic PVA chains acting as the spacing bridges ensured that the stacked GO nanosheets were interlinked successfully with sufficient bonding by GA to provide adequate stability in a water environment. Benefiting from the superiority of an ultra-thin hydrophilic peculiar GO skin layer and a fully interconnected porous nanofibrous substrate, the resultant optimized robust GO/PAN TFNC membranes displayed an excellent permeate flux of 69.1 L m−2 h−1 and a stable high rejection (99.9%) over a testing period of 24 h from aqueous salt solution with NaCl concentrations of 35 g L−1 at 70 °C. This separation performance was superior to those of homogeneous membranes and composite membranes used in pervaporation desalination reported so far, indicating that this work may facilitate the development of pervaporation in practical desalination application.

Novel low pressure UV-cured chitosan–polyethylene oxide–polytriethylene glycol dimethacrylate/polyacrylonitrile (CS–PEO–PTEGDMA/PAN) thin film nanofibrous composite nanofiltration membranes for anionic dye separation are demonstrated. Firstly, a double-layer mat containing an ultrathin electrosprayed CS–PEO–triethylene glycol dimethacrylate (TEGDMA) hydrophilic nanobeaded top layer and an electrospun PAN nanofibrous substrate layer was manufactured. Then the hydrophilic top layer was acidic moist-cured followed by hot pressing to form an integrated barrier film on the supporting layer. Here, acidic moisture was utilized to soften the nanobeads and facilitate the CS melting process. Finally, the top layer was UV-cured to form CS–PEO–PTEGDMA semi-interpenetrating polymer networks to physically crosslink CS. Different conditions were selected to achieve an optimized integrated barrier layer on PAN nanofibrous substrate. The optimized membrane possessed high nanofiltration performance for anionic dye separation with superior permeate flux (∼117.5 L m−2 h−1) and high rejection (∼99.9%) to Direct Red 80 solutions under low applied pressure of 0.2 MPa for energy saving purposes. An adsorption-assisted nanofiltration process was proposed for the CS–PEO–PTEGDMA membranes to separate anionic dyes. Moreover, the resultant CS–PEO–PTEGDMA nanofiltration membranes exhibited excellent antifouling properties (the flux recovery ratio reached 96.0% after 3 runs for 18 h), and they also possessed good reusability over repeated operations with a simple regeneration process. This work may pave the way for other intriguing polymer materials and provide a practical feasibility for water purification.