Porous Fiber Membrane Research Articles

Rough and porous silica-modified fiber membranes decorated with oleic acid for ultra-high flux and pH-responsive oil/water separation

The design of fiber membranes with both ultra-high flux and pH-responsive oil/water separation is challenging but of great significance to environmental protection and human health. In this work, the pH-responsive fiber membranes were prepared by immersing the silica-modified polyacrylonitrile fiber substrates into oleic acid solution. The obtained membranes exhibited highly rough surface structures (Ra = 14.26 µm), large pore sizes (5.35 µm), high porosities (86.04%), and pH-responsive functional groups, respectively. The pH-responsive fiber membranes also had superhydrophobic surfaces and excellent selective separation for oil/water mixtures, for example, a trichloromethane permeation flux of 87,829 L m-2h-1 for immiscible oil/water separation, and a water permeation flux of 69,802 L m-2h-1 after turning the pH of water from 7 to 13. The above data were much higher than those of stimulus-responsive fiber membranes used for oil/water separation. In addition, the pH-responsive fiber membranes were also used for separating water-in-oil emulsions and oil-in-water emulsions, and achieved the highest separation flux of 15,120 L m-2h-1. This work provides a simple strategy for the preparation of a stimulus responsiveness and high-performance material that can be used in the direction of treating practical oily wastewater.

Coordination-based synthesis of Fe single-atom anchored nitrogen-doped carbon nanofibrous membrane for CO2 electroreduction with nearly 100% CO selectivity

Carbon-based materials with single-atom (SA) transition metals coordinated with nitrogen (M-Nx) have attracted extensive attention due to their superior electrochemical CO2 reduction reaction (CO2RR) performance. However, the uncontrolled recombination of metal atoms during the typical high-temperature synthesis process in M-Nx causes deterioration of CO2RR activity. Herein, by using electrospinning, we propose a novel strategy for constructing a highly active and selective SA Fe-modified N-doped porous carbon fiber membrane catalyst (Fe-N-CF). This carbon membrane has an interconnected three-dimensional structure and a hierarchical porous structure, which can not only confine Fe to be single atom as active centers, but also provide a diffusion channel for CO2 molecules. Relying on its special structure and stable mechanical properties, Fe-N-CF is directly used for CO2RR, which presents an excellent selectivity (CO Faradaic efficiency of 97%) and stability. DFT calculations reveals that the synthesized Fe-N4-C can significantly reduce the energy barrier for intermediate COOH* formation and CO desorption. This work highlights the specific advantages of using electrospinning method to prepare the optimal SA catalysts.

KH550‐SiO2/polyimide insulating paper preparation and characterisation

AbstractOil‐paper insulation material is an essential component for oil‐filled transformers, and polyimide (PI) insulation paper is a novel material in the field of electricity. The improvement of insulation class for insulation paper has gained significant attention in recent years. In this study, SiO2 nanoparticles were modified with a silane coupling agent (KH550), and the KH550‐SiO2 was added to the fibre membrane through in situ polymerisation. The chemical composition and microcosmic characteristics of the PI porous fibre membrane were characterised using FT‐IR and SEM FT‐IR and SEM. Consequently, the dielectric constant of the composite paper was reduced to 2.3 upon adding 3 wt% of KH550‐SiO2, and the dielectric strength reached its maximum value of 85 kV/mm. The results demonstrate that the insulation performance of the KH550‐SiO2/PI composite was significantly improved due to the incorporation of nano‐SiO2. This establishes an efficient approach for achieving excellent electrical and thermal properties in practical applications using the KH550‐SiO2/PI fibre membrane.

Preparation of superhydrophilic polyimide fibrous membranes by electrostatic spinning fabrication for the efficient separation of oil-in-water emulsions

Membrane separation is considered an effective technology for treating oily wastewater. Hydrophilic, underwater oleophobic water removal membranes prepared by electrostatic spinning have received significant attention due to their excellent antifouling properties, small pore blockage, and high permeation flux. Herein, a simple and effective method was proposed for fabricating fabrics with superhydrophilic and submerged superoleophobic properties. First, the materials were co-blended with sodium dodecyl benzene sulfonate by electrostatic spinning, and then the porous fiber membrane was obtained by a step-up temperature for thermal imidization. The obtained membranes showed superhydrophilic and underwater oleophobic properties and could separate oil–water emulsions with or without surfactant stabilization while also exhibiting certain retention of methylene blue dye. The separation efficiency was driven by gravity alone, and the oil–water separation efficiency was always above 98.5% for 10 separation cycles, with a separation flux of up to 700 L·m−2·h−1. The modified membranes were tested and evaluated for various oil–water emulsions, and the separation efficiency was found to be consistently above 98.5%. In addition, the membranes showed satisfactory mechanical strength, high-temperature resistance, and excellent contamination resistance, suggesting that these membranes could serve as promising candidates for the treatment of industrial oil-in-water emulsions.

Controlled preparation of polyimide/polysulfone amide (PI/PSA) porous micro-nano fiber membranes by microemulsion electrospinning for excellent thermal insulation

In order to obtain fiber membrane materials with excellent thermal insulation properties, we successfully prepared lightweight PI/PSA porous micro-nano fiber membranes by microemulsion electrospinning technology combined with calcination in this work. The morphology, tensile strength and thermal insulation properties of the fiber membranes were fully characterized. The PI/PSA micro-nano fiber membranes prepared at the PI concentration of 17 wt%, the dispersed phase/continuous phase mass ratio of 1/10, the PI/PSA mass ratio of 7/3, and the voltage of 16 kV exhibited the best morphology and the most uniform fiber diameter. Besides, the PI/PSA porous micro-nano fiber membrane obtained after calcination had excellent tensile properties (breaking stress: 10.54 ± 1.96 MPa) and thermal insulation performance (thermal conductivity: 44.7 mW·m−1·K−1). The thermal imaging and thermocouple results showed that the thermal insulation performance of PI/PSA porous micro-nano fiber membrane was superior to that of PI/PSA membrane, and the thermal insulation properties became more excellent as the number of membrane layers increased. The PI/PSA porous micro-nano fiber membrane with low thermal conductivity acquired in this work is expected to broaden the application of protective clothing.

Preparation of Copper Ion Adsorbed Modified Montmorillonite/Cellulose Acetate Porous Composite Fiber Membrane by Centrifugal Spinning.

The natural adsorption material montmorillonite (MMT) was selected, and cellulose acetate (CA) was used as the loading substrate to design and prepare a kind of green and environment-friendly recyclable porous composite fiber membrane with good heavy metal ion adsorption performance. Acetic acid modified montmorillonite (HCl-MMT), sodium dodecyl sulfonate modified montmorillonite (SDS-MMT), and chitosan modified montmorillonite (CTS-MMT) were prepared by inorganic modification and organic modification, and the porous MMT/CA composite fiber membrane was constructed by centrifugal spinning equipment. The morphological and structural changes of MMT before and after modification and their effects on porous composite fiber membranes were investigated. The morphology, structure, and adsorption properties of the composite fibers were characterized by scanning electron microscopy (SEM) and atomic absorption spectrometry (ASS). The experimental results showed that the maximum adsorption capacity of Cu2+ on the prepared 5 wt% CTS-MMT composite fiber membrane was 60.272 mg/g after 10 h static adsorption. The adsorption of Cu2+ by a porous composite fiber membrane conforms to the quasi-second-order kinetic model and Langmuir isothermal adsorption model. The main factor of the Cu2+ adsorption rate is chemical adsorption, and the adsorption mechanism is mainly monolayer adsorption.

One-step co-sintering of hierarchical mullite whisker/fiber membranes with gradient pore structures for effective filtration of dust-laden gas

Porous ceramic fiber membranes with high gas permeance have shown great potential for the treatment of dust-laden gas. However, a major challenge is posed by the micro or nano-sized solid particles which can easily block the pore channels of the fiber membranes due to the larger surface pore size. Therefore, in this work, a novel method was proposed for the in-situ growth of mullite whiskers around the surface of the mullite fibers. This method aimed to decorate the pore channels of the fiber membranes by using a layer-by-layer construction strategy. For this purpose, a dry-pressing technique was employed to prepare a “green” mullite fiber support. It was followed by the preparation of another “green” fiber layer with the addition of catalysts on this support. After the co-sintering process, hierarchical mullite whiskers with gradient pore structures were produced. The in-situ growth of mullite whiskers around the fibers decorated the pore structure. As a result, it helped in effectively capturing the solid particles in the dust-laden gas. Additionally, the co-sintering process significantly reduced the sintering consumption and fabrication period. Moreover, a detailed investigation was carried out on the construction parameters including the sintering system atmospheres, Si–Al sol addition content, AlF3 concentration, mechanism of whisker growth and stability. The findings showed that hierarchical mullite whisker/fiber membranes obtained from the proposed method had a mean pore size of 2.7 μm and gas permeance of ∼106 m3 m−2 h−1·kPa−1. The Darcy's permeability coefficient of the membranes was also higher than the membranes prepared from existing methods. Moreover, the optimized membrane showed 99.9% rejection of the solid particles in the dust-laden gas, including micron-size (2.5 μm) and nano-size (300 nm) solid particles. This work provides a novel method for the fabrication of hierarchical mullite whiskers with gradient pore structures having the capability to filter industrial dust-laden gas.

GAS ELECTRIC VALVE DESIGN

In this era of globalization, science and technology has developed rapidly, especially in the industrial world. As for science and technology that is beneficial to industry, namely for components of the production process, one of which is Valve control. This technology is used to modify the fluid flow or pressure rate in a process system by using power for its operation. The application of this control valve is used to control a pressure rate or quantity, such as the amount of oxygen gas content (O₂) and carbon dioxide (CO₂) in fruit and vegetable plants. In the research that has been carried out on the carbon dioxide (CO₂) process using a porous fiber membrane contactor, the gas model is absorbed in a pure state at cold room temperature. In this study, it is still an obstacle when applied in the field because there are many factors that have not been taken into account, so in an effort to control the wasted gas, an electric gas valve control system device is needed which is designed to determine the value of wasted gas. This system is designed with valve components, servo motors, solenoid valves, Arduino uno, and relays, where all these components are built and programmed with Arduino uno microcontroller. The results of the test are carried out to determine the level of accuracy of each input to the control valve and to determine the value of the gas wasted at the degree of opening of the valve. The test results on the ten forms of angular movement are when the valve works and opens at a movement angle of 0° to the movement, the valve opens at 0%. When the valve works and opens at an angle of movement of 10° to rotation, the valve opens by 11.1%, and when the valve works and opens at an angle of movement of 20° to 80° to the movement, the valve opens by 22.2% to by 88.8%, then when the valve works and opens at an angle of movement of 90° to the movement, the valve opens by 100% or fully opens. The benefits of this research in the performance process of production technology in industry are to meet consumer demand by producing safe, minimally processed, additive-free, and stable quality food.

Preparation and performance for CO2 adsorption of large‐scale microporous fiber membrane based on electrostatic spinning technology

AbstractAlthough nano‐porous materials are widely used, they are still difficult to prepare in large size and expand flexibly. In this work, a new method for the synthesis of porous materials is proposed. First, the block polymers were prepared by atom transfer radical polymerization. Through electrostatic spinning, the fiber films were fabricated, then the fibers were modified by surface post‐treatment and related Friedel–Crafts alkylation reaction. The pore and CO2 adsorption properties of the porous fiber films are characterized by nitrogen adsorption–desorption isotherm. In order to improve the pore properties and CO2 adsorption properties of thin films, the additives and pretreatment process are optimized. The maximum specific surface area of the porous fiber membrane is determined to be 640 m2/g, and the CO2 adsorption capacity is high up to 36.3 wt.% (8.68 mmol/g). Moreover, the porous fiber membrane derived from this strategy is superior in the aspects of large size, convenient adjustment and simple processing, which makes up for the drawbacks of traditional porous materials. The fiber membrane obtained by this strategy has high productivity, and the fiber membrane is easy to be postprocessed, which can be integrated into functional devices, and is widely used.

Electrocatalytic oxidation of formaldehyde using electrospinning porous zein-based polyimide fibers

In this work, electrode coated with electrospinning porous polyimide fibers were prepared. The fiber is made by electrospinning zein from corn by-products and polyacrylic acid (PAA). The prepared porous fiber film was loaded with copper and prepared as working electrode material.The specific surface area of the porous fiber membrane is 304.6313 m2/g. The Polyimide (PI)-Cu nanoparticle electrochemical sensor was prepared by supporting non-noble metal Cu on the porous polyimide for the oxidation of formaldehyde. The prepared electrode can be used to catalyze the oxidation of formaldehyde, and the oxidation peak potential is around −0.41 V. Catalytic oxidation for 300 s at the oxidation peak potential can consume formaldehyde 0.758 × 10−6g, and the coulombic efficiency reaches 74.96%. Electrodes made of cheap metals can quickly remove formaldehyde in solution through electrochemical catalytic oxidation.

Cobalt embedded in porous carbon fiber membranes for high-performance lithium-sulfur batteries

Lithium-sulfur (Li–S) batteries have received quite significant attention rooted from its ultra-high energy density. Nevertheless, the shuttle effect of dissoluble sulfurous intermediates is the primary obstacle which hinders their practical application. Herein, a porous carbon fiber membrane embedded with cobalt nanoparticles (Co–PCNF) was prepared by electrostatic spinning, then the active material was firmly fixed between the two layers of Co–PCNF to form a unique sandwich structure. With this strategy, an aluminum foil current collector can be replaced by the Co–PCNF sandwich structure, which is helpful to improve the energy density of Li–S battery as well as coordinate the volume change of sulfur in the process of charge and discharge, what's more, the shuttle effect is significantly inhibited. Results show that the as-assembled battery delivers an initial discharge specific capacities of 1013.3 mAh g−1 and 933.4 mAh g−1 at 0.5C and 1C, together with the decay rate of only 0.04% and 0.08% per cycle over 500 cycles, respectively. Moreover, the larger sulfur load (2.2 mg cm−2) still has the discharge specific capacity of 1009.8 mAh g−1 after 150 cycles at 0.2C. This Co–PCNF sandwich electrode may provide a new idea for the structural design for Li–S batteries.

Excellent electrical performance and thermal properties insulation paper based on polyimide porous fiber membrane modified by nano-SiO2

Excellent electrical performance and thermal properties insulation paper based on polyimide porous fiber membrane modified by nano-SiO2

Flexible, Mechanically Stable, Porous Self‐Standing Microfiber Network Membranes of Covalent Organic Frameworks: Preparation Method and Characterization

AbstractCovalent organic frameworks (COFs) show advantageous characteristics, such as an ordered pore structure and a large surface area for gas storage and separation, energy storage, catalysis, and molecular separation. However, COFs usually exist as difficult‐to‐process powders, and preparing continuous, robust, flexible, foldable, and rollable COF membranes is still a challenge. Herein, such COF membranes with fiber morphology for the first time prepared via a newly introduced template‐assisted framework process are reported. This method uses electrospun porous polymer membranes as a sacrificial large dimension template for making self‐standing COF membranes. The porous COF fiber membranes, besides having high crystallinity, also show a large surface area (1153 m2 g−1), good mechanical stability, excellent thermal stability, and flexibility. This study opens up the possibility of preparation of large dimension COF membranes and their derivatives in a simple way and hence shows promise in technical applications in separation, catalysis, and energy in the future.

Simulation of coupled transient heat and water vapor transfer in porous fiber membrane with different fiber orientations and porosity

The transfer process of heat and water vapor in a porous fiber membrane was investigated through the simulation of a 3D model for optimizing the configuration design. 3D models with different fiber orientations and porosity were constructed by the parameter input method, and the accuracy of the model was validated by the coefficient of determination (R2) between the apparent velocity of the model and the air permeability of the membrane. The permeability of 3D model was used to reflect the discrepancy in fiber orientation of the model. The influences of fiber orientation and porosity on heat and water vapor transfer were surveyed by the coupled physics of heat transfer and dilute substance transfer. Since there was no temperature difference in the entire domain, heat conduction (10−9 W/m2) and moisture convection (10−14 mol·m−2·s−1) were faint in the model. With the diffusion of water vapor in the moisture, the heat convection flux and water vapor diffusion flux gradually decreased and reached equilibrium. When the permeability was increased by adjusting the fiber orientation (from 1.002 to 1.200 m2), the heat convection flux and water vapor diffusion flux followed a similar growth pattern due to the coupling effect of heat transfer and water vapor transfer. The R2 for the heat convection flux and water vapor transmission rate of the simulations and experiments with different porosity (44.87, 47.64 and 50.15%) were 0.999 and 0.923, respectively, which demonstrated the validation of the simulation in heat and water vapor transfer.

Comparative analysis of sound and thermal insulation properties of porous and non-porous polystyrene submicron fiber membranes

Interior and surface porous materials have widespread use in a wide variety of applications, especially for thermal and sound insulation due to their porous structure. Both sound and thermal insulation have great importance in a wide range of technical textile application areas including clothing and transportation such as train, car, aerospace and so on. In this study, for the first time, porous and non-porous polystyrene submicron fibers membranes have been compared for both sound absorption insulation and thermal insulation properties at the same time. Porous polystyrene electrospun fibers were produced at two different ratios of DMF:THF (4:1 and 7:3 ratio of DMF:THF) under conrolled humidity environment (60% RH). The results show that higher sound absorption insulation (SAC values) were obtained for non-porous fiber membrane (PS-ref) produced under ambient condition (30% RH) than porous fiber membrane (PS/7:3/RH and PS/4:1/RH) produced under controlled humidity condition (60% RH) by use of DMF:THF in 7:3 ratio and 4:1 ratio. Similar tendency was observed for thermal conductivity coefficient. Thus, all these results show that thinner fiber leading higher surface area has more dominant effect on both thermal insulation and sound absorption insulation than the formation of porous structures on the surface or internal structure of the fiber.

Free-Standing N-Doped Porous Carbon Fiber Membrane Derived From Zn-MOF-74: Synthesis and Application as Anode for Sodium-Ion Battery With an Excellent Performance.

It is important to develop new energy storage and conversion technology to mitigate the energy crisis for the sustainable development of human society. In this study, free-standing porous nitrogen-doped carbon fiber (PN-CF) membranes were obtained from the pyrolysis of Zn–MOF-74/polyacrylonitrile (PAN) composite fibers, which were fabricated in situ by an electrospinning technology. The resulting free-standing fibers can be cut into membrane disks and directly used as an anode electrode without the addition of any binder or additive. The PN-CFs showed great reversible capacities of 210 mAh g−1 at a current density of 0.05 A g−1 and excellent cyclic stability of 170.5 mAh g−1 at a current density of 0.2 A g−1 after 600 cycles in sodium ion batteries (SIBs). The improved electrochemical performance of PN-CFs can be attributed to the rich porous structure derived by the incorporation of Zn–MOF-74 and nitrogen doping to promote sodium ion transportation.

Laser irradiation method to prepare polyethylene porous fiber membrane with ultrahigh xylene gas filtration capacity

In recent years, volatile organic compound (VOC) gases have caused potential harm to people's health. This study reveals the preparation of polyethylene porous fiber membrane with excellent low-concentration VOCs filtration performance via laser irradiation technology. A neodymium-doped yttrium aluminum garnet (Nd:YAG) pulsed laser beam was used to scan the laser-sensitive low-density polyethylene/carbon black (LDPE/CB) fibers prepared by nanolayer coextrusion in the air. The controllable thermal energy generated by laser irradiation makes the surface of the fiber membrane to produce a porous carbon layer in situ. Laser power and scanning speed are important parameters for controlling laser-induced carbonization. The results indicate that the rich "fluffy" carbon structures on the surface of the porous fiber membrane can efficiently adsorb xylene gas. This study can provide a positive reference for the large-scale preparation of polyolefin porous fiber membrane with VOCs filtration by simple and efficient laser irradiation method.

Three-Dimensional Porous Alginate Fiber Membrane Reinforced PEO-Based Solid Polymer Electrolyte for Safe and High-Performance Lithium Ion Batteries

The rational design and optimization of solid polymer electrolytes (SPEs) are critical for the application of safety and high efficiency lithium ion batteries (LIBs). Herein, we synthesized a novel poly(ethylene oxide) (PEO)-based SPE (PEO@AF SPE) with a cross-linking network by the introduction of alginate fiber (AF) membranes. Depending on the high-strength supporting AF skeleton and the cross-linking network formed by hydrogen bonds between the PEO matrix and AF skeleton, the obtained PEO@AF SPE exhibits an excellent tensile strength of 3.71 MPa, favorable heat resistance (close to 120 °C), and wide electrochemical stability window (5.2 V vs Li/Li+). Meanwhile, the abundant oxygen-containing groups in alginate macromolecular and the three-dimensional (3D) porous structure of the AF membrane can greatly increase Li+ anchor points and provide more Li+ migration pathways, leading to the enhancement of Li+ conduction and interfacial stability between the SPE and Li anode. Furthermore, the assembled LiFePO4/PEO@AF SPE/Li cells also exhibit satisfactory electrochemical performance. These results reveal that PEO incorporating with AFs can boost the mechanical strength, thermostability, and electrochemical properties of the SPE simultaneously. Furthermore, one will expect that the newly designed PEO@AF SPE with cross-linked networks thus provides the possibility for future applications of safety and high-performance LIBs.

Preparation of PI porous fiber membrane for recovering oil-paper insulation structure

PI fiber insulation paper has excellent insulation and heat resistance, which can replace traditional insulation paper to provide a new high-performance material. In this paper, we adopt a two-step method to synthesize PI, that is, firstly synthesize polyamic acid, and then perform electrospinning and thermal imidization to prepare PI porous fiber membrane. The test results show that the breakdown field strength of the PI porous film is 50 kV/mm. Further research shows that the insulation structure has the characteristics of continuous multiple breakdown. When the fiber film is repeatedly broken down to 25 times at the same point, the field strength of each breakdown of the fiber film changes between 40 and 55 kV/mm, and the average breakdown field strength is 53 kV/mm. Nano-Al2O3 was introduced into the fiber membrane by in situ polymerization. The breakdown field strength of the composite fiber film can reach 74.89 kV/mm after doping 2 wt% nano-Al2O3, which is higher than that of the pure film. At the same time, this kind of fiber paper also has repeatable breakdown characteristics, and the breakdown voltage distribution width of multiple breakdown is reduced. This characteristic provides the maintenance free characteristic of DC over-voltage for the insulation structure composed of this fiber paper, and can improve the service life of transformer under DC over-voltage such as lightning stroke.

Fabrication of zeolite NaX-doped electrospun porous fiber membrane for simultaneous ammonium recovery and organic carbon enrichment

To achieve ammonium recovery and organic matter enrichment simultaneously, a novel zeolite NaX-doped electrospun porous fiber membrane (Z-EPFM) was fabricated by using the electrospinning technique with the addition of polyvinylidene fluoride (PVDF), zeolite NaX and polyvinylpyrrolidone (PVP) as porogen. The strategy of using PVP as a pore-forming agent to obtain porous Z-EPMFs is more efficient to achieve ammonium adsorption than improving the hydrophilicity of the zeolite NaX-doped electrospun fiber membrane (Z-EFM) by simply adding PVP. As the molecular weight and content of PVP increase, the ammonium adsorption efficiency, hydrophilicity and membrane pore size of Z-EPFMs increase, while their mechanical strength decreases, which is due to the formation of pore structures. The most efficient Z-EPFM (zeolite NaX load density of 0.78 mg/cm2) achieved 96.91% ± 0.50% ammonium adsorption efficiency and 95.48% ± 4.52% organic carbon enrichment efficiency, which were maintained steadily over five regeneration cycles. Therefore, the Z-EPFM offered a novel approach for simultaneous ammonium recovery and organic matter enrichment, which could be proposed as an efficient method to regulate energy flow and control nitrogen nutrient in municipal wastewater.