Xuefen Wang

Facile immobilization of ag nanocluster on nanofibrous membrane for oil/water separation.

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.

Dual-biomimetic superhydrophobic electrospun polystyrene nanofibrous membranes for membrane distillation.

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/m(2)·h, 20 g/L NaCl salt feed for a thinner PS nanofibrous membrane with thickness of 60 μm; 51 ± 4.5 kg/m(2)·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.

Electrospun Superhydrophobic Organic/Inorganic Composite Nanofibrous Membranes for Membrane Distillation

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/(m(2)·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.

High recovery of lead ions from aminated polyacrylonitrile nanofibrous affinity membranes with micro/nano structure.

In this paper, highly porous polyacrylonitrile (PAN) nanofibrous membranes were successfully fabricated by wet-electrospinning technique from PAN and poly(vinyl pyrrolidone) (PVP) blended solution using hot water bath as extractor, and then aminated with diethylene triamine (DETA). The obtained aminated PAN (APAN) nanofibrous mats showed unique micro/nano structures and possessed extra high extraction capability for the removal of lead ions (Pb(2+)) from aqueous solution (maximum uptake capacity of Pb(2+) was up to 1520.0mg/g), and could maintain over 90% of its extraction capacity at the sixth cycle of extraction-dissociation. Interestingly, the hexagonal crystals of basic lead(II) carbonate (Pb3(CO3)2(OH)2) grown on micro/nano structured APAN nanofibers were observed when APAN membrane was immersed in Pb(II) ions aqueous solution. The results provided new insights for the removal of metal ions by metal crystal growth from wastewater with high recovery.

Electrospun Poly(acrylic acid)/Silica Hydrogel Nanofibers Scaffold for Highly Efficient Adsorption of Lanthanide Ions and Its Photoluminescence Performance

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 (Ln(3+)) triggered by the penetration of Ln(3+) 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 Ln(3+) have been investigated comprehensively. The maximum equilibrium adsorption capacities for La(3+), Eu(3+), and Tb(3+) 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 Ln(3+) on PAA-S HNFs scaffolds was the formation of bidentate carboxylates between carboxyl groups and Ln(3+) 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 Ln(3+), 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.

Low pressure UV-cured CS–PEO–PTEGDMA/PAN thin film nanofibrous composite nanofiltration membranes for anionic dye separation

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.

Micro-nano structure nanofibrous p-sulfonatocalix[8]arene complex membranes for highly efficient and selective adsorption of lanthanum(III) ions in aqueous solution

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.

Robust construction of a graphene oxide barrier layer on a nanofibrous substrate assisted by the flexible poly(vinylalcohol) for efficient pervaporation desalination

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.

A novel profiled core–shell nanofibrous membrane for wastewater treatment by direct contact membrane distillation

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.

A durable thin-film nanofibrous composite nanofiltration membrane prepared by interfacial polymerization on a double-layer nanofibrous scaffold

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.