Search

Polytetrafluoroethylene (PTFE) is an attractive membrane material due to its superior chemical resistance, thermal stability and strong hydrophobicity. However, PTFE hollow fiber membranes are challenging to produce by conventional technique due to the high solvent resistance and high melt viscosity of PTFE. In this study, novel PTFE hollow fiber membranes composed of pure PTFE nanofibers were firstly fabricated via a scalable and environment-friendly method based on emulsion electrospinning with a non-rotating collector and followed by a high-temperature sintering process. The effects of PTFE/PEO mass ratio and sintering temperature on the morphologies and properties of the resulting membranes were investigated. The prepared PTFE hollow fiber membrane shows the excellent characteristics combining the advantages of both electrospun nanofibers membrane and hollow fiber membrane, such as high porosity (more than 82%), self-supporting and superhydrophobicity. The membrane sintered at 380 °C present the highest mechanical strength, which shows the tensile strength, Young's modulus, strain at break of 30.5 Mpa, 53 Mpa, and 315%, respectively. The permeate flux of the prepared PTFE hollow fiber membrane is about 4.6–8.8 times as that of the commercial PTFE hollow fiber membranes, as well as is approximately 3.2–11.6 times higher than the date of the reported PTFE hollow fiber membranes. Additionally, the prepared membrane shows high and stable flux in long-term and rising salinity experiments, indicating it is very promising for membrane distillation (MD) application and even for the treatment of hyper-saline wastewater. Image 1 • Novel hollow fiber membranes composed of pure PTFE nanofibers. • Scalable and environment-friendly method was proposed. • Membranes are high porous, self-supporting and superhydrophobic. • 3.2–11.6 times higher than the flux of reported PTFE hollow fiber membranes. • Stable and high flux in treatment of hyper-saline wastewater. [ABSTRACT FROM AUTHOR]

Highlights • Welding electrospun hollow fiber membrane is firstly applied in ammonia removal. • The effect of membrane thickness on selectivity was intensively investigated. • Self-made membrane with high flux and selectivity favors ammonia recovery. • Self-made membrane demonstrates its potential in membrane absorption application. Abstract Excessive ammonia nitrogen in wastewater seriously endangers ecological environment, so high-flux and selectivity membrane is urgently needed for ammonia removal using membrane absorption (MA). In this paper, a high-performance electrospun hollow fiber membrane was fabricated and solvent vapor welding treatment was adopted to enhance mechanical strength. The post-treatment membrane showed 103.8% higher in the Young's modulus than the pristine membrane. High mechanical strength, porosity and hydrophobicity of the membrane make it superior in mass transfer and selectivity. The effects of membrane thickness, pH and temperature of feed solution on experimental overall mass transfer coefficient (K OE) and selectivity coefficient (S NH3/H2O (g)) were intensively investigated to examine the membrane performance in MA application. The results show K OE is 1.35 * 10−5 m s−1 and S NH3/H2O (g) is 7.58 when pH is 11, which are higher than that of commercial membrane. Moreover, the selectivity can be improved greatly from 6.91 to 9.74 by increasing the thickness of the hollow fiber membrane from 55 ± 5 μm to 115 ± 5 μm. The welded electrospun hollow fiber membrane demonstrates great potential for ammonia removal in MA application. [ABSTRACT FROM AUTHOR]

A novel omniphobic nanofiber membrane for membrane distillation (MD) was successfully fabricated by one-step electrospinning of PVDF-HFP and fluorinated-decyl polyhedraloligomeric silsesquioxane (F-POSS) colloidal suspension solution. The fabricated F-POSS/PVDF-HFP membrane possessed uniform fiber structures and had extreme high F-POSS concentration on the surface. This F-POSS based membrane exhibited excellent omniphobicity, as indicated by its wetting resistance to different low surface tension liquids, including ethanol with a contact angle of 128.2°. Membrane distillation (MD) experiments showed that the water flux and water quality were stably maintained in highly saline feed solutions containing low surface tension substances, which successfully demonstrated its potential application for desalination of challenging industrial wastewater. [ABSTRACT FROM AUTHOR]

Novel nanofibers-covered hollow fiber membrane (N-HFM), combining the advantages of both electrospun nanofibers film and hollow fiber membrane was fabricated via electrospinning with non-rotational collectors. The key parameters of electrospinning including positive voltage, negative voltage, polymer concentration and working distance were optimized to examine their effects on the morphology and structure of N-HFM. Meanwhile, a solvent vapor welding post-treatment was firstly applied to enhance the mechanical strength of hollow fiber membranes. The welding can improve the mechanical property and water repellency as well as maintain the high porosity, by fusing the nanofibers just at junctions. After a 40 min welding, the Young's modulus, strain at break and tensile strength of the welded N-HFM increased by 117%, 79% and 90% respectively, compared to the pristine N-HFM. Furthermore, the welded N-HFM was able to present a high flux of 13.2 L m −2 h −1 and a stable salt rejection of over 99.9% during the 5 h of direct contact membrane distillation (DCMD) test, suggesting the competency of the welded N-HFM for MD applications. [ABSTRACT FROM AUTHOR]

A novel nanofibers-covered hollow fiber membrane (N-HFM) with high porosity (83.5%) was prepared via employing electrospinning to deposit nanofibers onto a porous supporting tube. Electrospun nanofibers covered on a porous supporting tube serve as the outer layer of the N-HFM. The supporting tube fixed on the soft electrode serves as the collector as well as the inner layer of the N-HFM. When the feeding rate was 1 ml L −1 , it was possible to continuously fabricate N-HFM with a non-rotational collector. The prepared N-HFM was used for desalination by direct contact membrane distillation (DCMD), and a high distillate flux of 17 kg m −2 h −1 was obtained while the feed and permeate temperatures were fixed at 333 K and 293 K, respectively. It is expected that the novel hollow fiber membranes with high porosity fabricated by this continuous electrospinning technique may be attractive in various separation and purification processes. [ABSTRACT FROM AUTHOR]

In this study, the effects of titanium oxycompound templates on carbon nanofibers electrodes for supercapacitors application were investigated. Meanwhile, hybrid titanium that contains organic and inorganic titanium templates acted as another modification method. The organic and inorganic titanium oxycompounds referred to titanium (IV) oxy-acetylacetonate and titanium dioxide nanopowder, respectively. The morphology structure, and electrochemical properties of the three composite electrodes (TiO 2 @CNFs, OCTi@CNFs, HybTi@CNFs) were studied. Hierarchical pore structure with specific surface area of 697 m 2 g −1 was achieved in HybTi@CNFs, in which TiO 2 revealed amorphous, tetragonal rutile and anatase structure. The electron charge transfer resistance and specific capacitance of HybTi@CNFs were calculated to be 0.34 Ω and 280.3 F g −1 (at current density of 1 A g −1 ), respectively. After 4000 cycles with galvanostatic charge/discharge, HybTi@CNFs can maintain 97.5% of its initial capacitance under 8 A g −1 in a symmetric two-electrode system (6 M KOH). These results indicate that OCTi@CNFs is superior to TiO 2 @CNFs, and HybTi@CNFs has combined the advantages of OCTi@CNFs and TiO 2 @CNFs, suggesting HybTi@CNFs is an excellent electrode material for supercapacitors. [ABSTRACT FROM AUTHOR]

The practical applications of membrane distillation (MD) are hindered by the absence of effective membranes with high porosity, sufficient strength, and durable wetting repellency for long term operation. In this study, we developed a facile method to construct composite membranes with high MD performance via one-step electrospinning of PVDF solutions blended with hydrophobic silica nanoparticles (NPs). The characterizations reveal that the incorporation of silica NPs have altered the membrane surface morphology and endowed the composite membrane with hierarchical structure on both surface and bulk layers (three-dimensional (3D) superhydrophobic membrane). The hydrophobicity of the membranes can be easily tailored by the dosage of silica NPs, and the water contact angle (WCA) of the membranes can be optimized to be 157 ± 1°, which was close to that of the lotus leaf (160°). Furthermore, the incorporation of silica NPs have promoted the mechanical strength, salt rejection, and water permeation flux of the membranes. The composite membrane containing 7.47 wt% silica NPs (designated as SIL40) can achieve a high MD performance with a water flux of 25.73 kg m −2 h −1 and a permeate conductivity below 5.0 μS cm −1 during a 100 h test-period. The SIL40 also shows a tensile strength and a Young’s modulus of 3.18 and 12.8 MPa, respectively; the values surpassed those of the pristine PVDF membrane (1.5 and 5.4 MPa, respectively). In addition, the MD test indicates that the 3D superhydrophobic membrane exhibits a more durable wetting resistance and a more stable MD performance than the surface-modified superhydrophobic membranes. [ABSTRACT FROM AUTHOR]

Highly porous membranes with superhydrophobic structures throughout their depth were successfully fabricated via simultaneous electrospraying of silica/DMAc colloids and electrospinning of PVDF/DMAc solutions. The morphology of the membranes could be tuned by adjusting the time of ultrasonication to disperse the silica/DMAc colloids. The newly developed membrane with hierarchical nanoparticle-microbead-fiber structures exhibited a high water contact angle of 163° and an extraordinary low sliding angle of 3°; it also showed superior performance in both membrane distillation and oil-water separation. This facile method presents great potentials for scalable fabrication of porous materials with stable superhydrophobicity. [ABSTRACT FROM AUTHOR]