The separation and purification of chemical molecules from organic media under harsh chemical environments are of vital importance in the fields of water treatment, biomedical engineering, and organic recycling. Herein, we report the preparation of a flexible SiO2/SnO2 nanofibrous membrane (SiO2/SnO2 NFM) with high surface area and hierarchical porous structure by selecting poly(vinyl butyral) as pore-forming agent and embedding crystalline phase into amorphous matrix without using surfactant as sacrificial template. Benefiting from the uniform micropore size on the fibers and negatively charged properties, the membranes exhibit a precise selectivity toward molecules based on electrostatic interaction and size exclusion, which could separate organic molecule mixtures with the same electrostatic charges and different molecular sizes with a high efficiency of more than 97%. Furthermore, the highly tortuous open-porous structures and high porosity give rise to a high permeate flux of 288 000 L m–2 h–1. In addition, the membrane also displays excellent stability and can be reused for ten consecutive filtration–regeneration cycles. The integration of high filtration efficiency, large permeate flux, good reutilization, and easy to industrialization provides the SiO2/SnO2 NFM for potential applications in practical molecular purification and separation science.Keywords: electrospinning; flexible; high permeate flux; molecular filtration; porous SiO2/SnO2 nanofibrous membrane;

In this study, for the first time, we fabricated flexible, high-heat-resistant, and amphiphobic mats by (fluoroalkyl)silane (FAS) modification of electrospun pure silica nanofibrous mats. The inorganic silica nanofibrous mats were obtained via electrospinning the blend solutions of poly(vinyl alcohol) (PVA) and silica gel, followed by calcination to remove the organic component. The PVA/silica and silica fibers were found to be randomly oriented as nonwoven mats with fiber diameters in the range of 150−500 nm. After the FAS modification, the surface wettability of the silica mats was converted from amphiphilic to amphiphobic. The fluorinated mat with the bead-on-string structure showed the highest water contact angle (WCA) of 154° and oil contact angle (OCA) of 144°. Additionally, the fluorinated inorganic fibrous mats exhibited a high heat resistance; they kept their hydrophobicity (WCA of 138°) and oleophobicity (OCA of 132°) even after the annealing treatment at 450 °C for 30 min. Potential applications of the fluorinated fibrous mats include high-temperature filtration, selective filtration, and self-cleaning coatings.

Functional nanoparticles modified silica nanofibrous materials with good flexibility, a hierarchical mesoporous structure, and excellent durability would have broad applications in efficient removal of contaminants, yet have proven to be enormously challenging to construct. Herein, we reported a strategy for rational design and fabricating flexible, hierarchical mesoporous, and robust ZrO2 nanoparticle-embedded silica nanofibrous membranes (ZrO2/SiO2 NM) for phosphate removal by combining the chitosan dip-coating method with the electrospinning technique. Our approach allows ZrO2 nanoparticles to be in situ firmly and uniformly anchored onto SiO2 nanofibers to drastically enlarge the specific surface area and porosity of membranes. Therefore, the resultant ZrO2/SiO2 NM exhibited a prominent removal efficiency of 85% and excellent adsorption amount of 43.8 mg P g–1 membranes in 30 min toward phosphates. Furthermore, the removal performance toward different types of phosphates revealed that the resultant membranes also could be used to remove phosphates in detergent and fertilizer water samples. More importantly, the membranes with good flexibility could directly be taken out from solution after use without any post-treatment. Such a simple and intriguing approach for fabricating nanofibrous membranes may provide a new platform for constructing membranes with superb phosphate removal performance.Keywords: electrospinning; flexible; nanofibrous membranes; phosphates removal; ZrO2 nanoparticle-embedded SiO2 nanofibers;

Waterproof and breathable membranes that provide a high level of protection and comfort are promising core materials for meeting the pressing demand for future upscale protective clothing. However, creating such materials that exhibit environmental protection, high performance, and ease of fabrication has proven to be a great challenge. Herein, we report a novel strategy for synthesizing fluorinated polyurethane (C6FPU) containing short perfluorohexyl (-C6F13) chains and introduced it as hydrophobic agent into a polyurethane (PU) solution for one-step electrospinning. A plausible mechanism about the dynamic behavior of fluorinated chains with an increasing C6FPU concentration was proposed. Benefiting from the utilization of magnesium chloride (MgCl2), the fibrous membranes had dramatically decreased maximum pore sizes. Consequently, the prepared PU/C6FPU/MgCl2 fibrous membranes exhibited an excellent hydrostatic pressure of 104 kPa, a modest water vapor transmission rate of 11.5 kg m–2 d–1, and a desirable tensile strength of 12.4 MPa. The facile fabrication of PU/C6FPU/MgCl2 waterproof and breathable membranes not only matches well with the tendency to be environmentally protective but also fully meets the requirements for high performance in extremely harsh environments.Keywords: electrospinning; environmentally friendly; magnesium chloride; short perfluorohexyl chains; waterproof and breathable;

AbstractHigh performance lightweight and flexible supercapacitors with superior electrochemical performance are in extremely high demand for wearable electronic device applications. Herein, a novel synthesis process is reported for developing highly flexible supercapacitor electrodes from carbon black doped carbon nanofiber/polyaniline core–shell nanofibers via electrospinning followed by carbonization and electrospray techniques. Resultant supercapacitor electrodes offer exceptional specific capacitance (SC) of 501.6 F g−1 at 0.5 A g−1, excellent capacitance retention of 91% even after 5000 cycles, demonstrating a long and stable life of the fabricated device. Moreover, solid state supercapacitor shows no obvious change in SC when subjected to various bending angles up to 180°. This simple three step (i.e., electrospinning, carbonization, and electrospray) fabrication technique paves new insights into the development of lightweight flexible supercapacitors.

Liquid moisture (sweat) transport properties of textile materials play critical role in maintaining the comfort of body which are mainly controlled by surface chemistry, structure, and morphology of substrate. Herein, a dual layer surface treated nonwoven (NW)/electrospun nanofiber membrane with excellent differential liquid moisture transport characteristics is reported. NW is used as inner layer for its high moisture releasing and low moisture absorbing features, and polyacrylonitrile (PAN) as outer layer because of its decent hydrophilic nature. Wettability of NW is tailored by surface treatment with polydopamine, and the wicking characteristics of PAN nanofibers are enhanced by inducing hydrophilic SiO2 nanoparticles (PAN-SiO2). Performance of resultant surface treated NW (TNW)/PAN-SiO2 nanofiber composite membranes is thoroughly characterized by moisture management tester (MMT). Subsequent composite membranes offer high wettability gradient which leads to their marvelous MMT performance with an outstanding one-way transport capacity of 1413%, excellent overall moisture management capacity of 0.99, and a decent water vapor transfer rate of 12.73 kg m−2 d−1, indicating a potential candidate for faster sweat release applications.

High-water-content hydrogels that are both mechanically robust and conductive could have wide applications in fields ranging from bioengineering and electronic devices to medicine; however, creating such materials has proven to be extremely challenging. This study presents a scalable methodology to prepare superelastic, cellular-structured nanofibrous hydrogels (NFHs) by combining alginate and flexible SiO2 nanofibers. This approach causes naturally abundant and sustainable alginate to assemble into 3D elastic bulk NFHs with tunable water content and desirable shapes on a large scale. The resultant NFHs exhibit the integrated properties of ultrahigh water content (99.8 wt%), complete recovery from 80% strain, zero Poisson's ratio, shape-memory behavior, injectability, and elastic-responsive conductivity, which can detect dynamic pressure in a wide range (>50 Pa) with robust sensitivity (0.24 kPa−1) and durability (100 cycles). The fabrication of such fascinating materials may provide new insights into the design and development of multifunctional hydrogels for various applications.

•We present a solution to power the wearable electronics by fabricating a NM-TENG, using economically viable materials and scalable fabrication technologies.•Electrospinng method was rationally introduced to prepare the triboelectric layers of NM-TENG, since it is a versatile approach to make micro/nanofibers with advantageous features for surface triboelectrification.•The electric output can reach as high as 110 µA and 540 V, which was capable of sustainably powering a commercial thermal meter, electronic watch, and lighting up about 560 LEDs.With a rapid expansion in the field of wearable electronics, powering them entirely by batteries has become more and more unpractical and unfavorable. Here, we developed a lightweight, flexible and sustainable power source by fabricating a nanofibrous membrane constructed wearable triboelectric nanogenerator (NM-TENG), which is capable of converting human biomechanical energy into electricity for next-generation wearables. With an effective device area of 16 cm2 under gentle hand tapping, it can deliver a current and voltage output respectively up to 110 µA and 540 V. And the electrospun nanofibrous membranes were tailored to enhance the triboelectric polarity, mechanical strength as well as surface hydrophobicity, which will eventually improve the device output performance, robustness and capability of operation even with high environmental humidity. Via harvesting the biomechanical energy from body motion, the wearable NM-TENG was demonstrated to sustainably power a commercial thermal meter, electronic watch, and light up about 560 LEDs. Given a collection of compelling features of being flexible, breathable, environmentally friendly and cost-effective, the NM-TENG can be extensively applied not only to self-powered wearable electronics but also possibly to power generation at a large scale.Download high-res image (207KB)Download full-size image

Exploiting high-added-value textiles equipped with multiple functionalities like ultraviolet (UV) resistance, waterproofness, and thermal-moisture comfort is facing tremendous demand by a more discerning consumer market. However, the major challenge is to realize the equilibrium among the multifunction. Herein, a new attempt of fabricating superhydrophobic electrospun polyacrylonitrile (PAN)/polyurethane (PU)/titanium dioxide (TiO2) nanofibrous membranes has been tried, and the membranes exhibited multifunction of UV resistance, waterproofness and breathability by coating modification with 2-hydroxy-4-n-octoxybenzophenone (UV531) and fluorinated acrylic copolymer (FAC). TiO2 NPs as inorganic blocker and UV531 as organic absorber were utilized to impart the excellent double UV resistant function for the modified nanofibrous membranes. The hydrophobic coating with FAC endowed the pristine membranes with enhanced superhydrophobic wettability and the advancing contact angle was 152.1°. Regulating the addition amount of TiO2 NPs, the UV531 and FAC concentration, the multiple functionalities of the modified PAN/PU/TiO2 were systemically optimized: robust tensile strength (14.6 MPa), good ultraviolet protection factor of 1485, modest waterproofness (62 kPa), and moisture breathability (12.9 kg m−2 d−1). The equilibrium among the multifunction of the as-prepared membranes indicated their diverse possibilities can be used in various applications, including high-altitude garments, protective clothing, covering materials, self-cleaning materials, and other medical products.Superhydrophobic PAN/PU/TiO2 multiple functional membranes are imparted with UV resistance, water repellency and moisture breathability through electrospinning and doctor-blading coating modification. The modified membranes exhibit double UV resistant function with both reflection and absorption.Download high-res image (203KB)Download full-size image

Construction ion-exchange membranes with superb biomolecules adsorption and purification performance plays a greatly important role in the fields of biotechnological and biopharmaceutical industry, yet still remains an extremely challenging. Herein, we in situ synthesized the cis-butenedioic anhydride grafted poly(vinyl alcohol) hydrogel nanofibrous membranes (CBA-g-PVA HNFM) by combining electrospinning technique with the grafting-copolymerization crosslinking. Taking advantages of the large specific surface area which could provide numerous sites available for functional groups and biomolecules binding, highly tortuous and interconnected porous channel for biomolecules transfer, and enhanced mechanical strength, the resultant CBA-g-PVA HNFM exhibited relatively high binding amount of 170 mg g−1, rapid equilibrium time of 8 h towards the biomolecule template of lysozyme, and the performance could be tailored by regulating the buffer properties and protein concentrations. Additionally, the resultant functional HNFM also possessed superior acid resistance property, excellent reversibility and regeneration performance. More importantly, the obtained CBA-g-PVA HNFM could directly extract lysozyme from fresh chicken eggs with capacity of 125 mg g−1, exhibiting excellent practical application properties. The fabrication of proposed CBA-g-PVA HNFM offers a feasible alternative for construction of ion-exchange chromatograph column for bio-separation and purification engineering.Negatively charged ion-exchange hydrogel nanofibrous membranes that can adsorb positively charged biomolecules with high selectivity and large capacity.Download high-res image (98KB)Download full-size image

A novel superhydrophilic and underwater superoleophobic nanofibrous membrane with a hierarchical structured skin for the separation of oil-in-water emulsions was prepared via electrospinning and electrospraying methods, and was found to exhibit excellent separation efficiency, robust antifouling properties, and extremely high flux solely driven by gravity.

•Poly(vinyl alcohol) (PVA) nano-fiber/net (NFN) membranes were prepared.•The electro-spinning/netting (ESN) technique was studied to make PVA NFN membranes.•Dual effects of formic acid as solvent and crosslinking agent were investigated.•PVA NFN membranes could be used as innovative filtration/separation materials/media.A technique of electro-spinning/netting (ESN) has been investigated to prepare poly(vinyl alcohol) (PVA) nanofibrous membrane with unique morphological structure of nano-fiber/net (NFN). The prepared NFN membrane consists of both common electrospun nanofibers (with diameters in hundreds of nanometers) and two-dimensional nano-nets (with nanofibril diameters smaller than 50 nm). It is revealed that formic acid has dual effects (i.e., as solvent and crosslinking agent) on solution properties and membrane morphological structures, and systematic analyses on rheological properties of three different 10 wt% PVA solutions with solvents being water, formic acid, and their 1/1 (wt./wt.) mixture have been conducted. Results indicate that the molecular interactions (particularly hydrogen bonding) among water, formic acid, and PVA macromolecular chains, as well as the acetal formation (i.e., chemical crosslinking), have significant influences on macromolecular conformation, solution rheological properties, and morphological structure of membranes. The acetal formation, which leads to improved tensile strength of PVA NFN membrane, has been verified by FT-IR and DSC. Additionally, the PVA NFN membrane has been assembled into a gravity-driven filtration device; and the membrane exhibits high rejection ratio (> 99%) for polystyrene microspheres (with diameters of ~ 0.2 μm) and high water flux (3773 L/m2 ∙ h) under the pressure of 40 kPa.Download high-res image (134KB)Download full-size image

•The hydrophobic surface was constructed using environmental friendly raw materials rather than conventional fluorinated polyurethane with notorious long fluorocarbon chain.•The multilevel porous structure was designed by taking advantage of differentiated pore size and porosity of PVDF and PU/FPU membranes.•The resultant composite PVDF/PU membrane presented ultrahigh hydrostatic pressure (140 kPa) and water vapor transmission rate (11.3 kg m-2 d-1), which was unreachable for the existing materials.Porous membranes that can resist water droplet and transmit water vapor simultaneously have aroused wide attention due to their promising application in individual protection. However, the fabrication of such materials remains a challenge. Here we fabricated electrospun fibrous membranes exhibiting ultrahigh waterproofness and excellent breathable performance simultaneously by constructing a multilevel porous structure. The careful control over the concentration of polyvinylidene fluoride (PVDF) generated improved hydrostatic pressure and water vapor transmitting rate (WVTR). More importantly, by coupling polyurethane/fluorinated (PU/FPU) membrane with PVDF membrane layer by layer, the resultant composite PVDF/PU membrane presented ultrahigh hydrostatic pressure (140 kPa) and WVTR (11.3 kg m-2 d-1). We unveiled that this excellent waterproof/breathable performance was achieved benefitting from the differentiated pore size and porosity of the two membranes. The creation of such an encouraging membrane could establish a new optimization methodology for waterproof/breathable membranes.Download high-res image (371KB)Download full-size image

•PA/CNT membranes shows spider-web-like fibrous structure via electrospinning/netting and subsequent impregnation approach.•Pure PA/CNT membranes offered 3D fibrous structure having an average fiber diameter of 153 nm.•The PA/CNT-75-PEI has the highest adsorption capacity of 51 mg/g at 25 °C and 1 bar.•The PEI-loaded PA/CNT exhibited excellent regenerability and stability.Particle-shaped sorbent materials have great potential for energy-efficient carbon dioxide (CO2) capture and separations, but a major hurdle is the lack of mechanical strength and flexibility. The ability to solve this problem would have broad technological implications for CO2 capture; despite of many past efforts, it remains a great challenge to achieve alternative adsorption materials for stabilized CO2 capture. Herein, we develop an effective spider-web-like fibrous sorbent via electrospinning and subsequent impregnation approach. Polyamide-6/carbon nanotube (PA/CNT) nano-fiber/nets composite membrane comprising of common electrospun nanofibers and two-dimensional (2D) spider-web-like nano-nets has been used as porous substrate for polyethylenimine (PEI) impregnation, which exhibits several fundamental characteristics, such as open porosity and good interconnectivity. The physicochemical properties are characterized by N2 adsorption/desorption, scanning electron microscopy (SEM), thermal gravimetric analysis (TGA) and fourier transform infrared spectroscopy (FT-IR) techniques. The optimal PEI loading on PA/CNT nano-fiber/nets composite is determined to be 75 wt% with a CO2 adsorption capacity of 51 mg/g-sorbent at 25 °C. In addition, the developed adsorbent can be regenerated easily at 105 °C, and it exhibits excellent regenerability and stability. These results indicate that this PEI impregnated PA/CNT nanofibrous sorbent has a good potential for CO2 capture in the future.

•We firstly created stable electret membranes towards moisture and oily molecules.•We firstly coupled high dielectric constant Si3N4 and high resistivity PVB.•The charge dissipation mechanism under moisture and oil condition was revealed.•Self-designed FPU was included to enhance the electret stability to water and oil.The fabrication of electret air filter with robust charge stability towards moisture and oily molecules is becoming increasingly essential due to the severe haze pollution, which is featured with high relative humidity (80–90%) and contains oily components (30–40%); however, this remains an ongoing challenge. Herein, a nanofibrous electret membrane able to enduringly capture PM2.5 with high efficiency and low air resistance under the surroundings containing moisture and oily components is successfully designed via electrospinning. Benefiting from the high electrical resistivity of polyvinyl butyral (PVB) and high dielectric constant of silicon nitride nanoparticles (Si3N4 NPs), PVB/Si3N4 nanofibrous membranes are endowed with improved stable surface potentials from 1610 to 2010 V when the content of charge enhancer (Si3N4) increases from 0 to 1 wt%. More importantly, the charge dissipating mechanism under water and oil condition is revealed. Moreover, by further introducing hydro-oleophobic fluorinated polyurethane (FPU), the stable surface potentials of PVB/Si3N4-FPU membranes are elevated by 62.8% under high relative humidity (85%) and 48.4% towards oily components, compared with PVB/Si3N4 membranes. The resultant membranes achieve a high filtration efficiency of 99.950%, low air resistance of 55.0 Pa, and robust durability, providing a guidance for the design of electret air filtration materials used in haze environment.

•The sharp rise of pressure drop under high humidity is addressed.•Resonance effect of FIR and water was firstly introduced to air filtration field.•The effect of FIR emissivity on the stability of pressure drop is revealed.•The resultant membranes exhibited excellent performance.Air filters have attracted increasing attention due to the lethal danger of haze pollution worldwide. However, it remains challenging to fabricate air filtration materials that can remove particles efficiently and especially allow air flowing easily under the high relative humidity (RH) of haze environment. Here we designed an air filter exhibiting low and stable resistance towards moisture by taking advantage of the resonance effect between far infrared ray (FIR) and water molecules. Polyacrylonitrile (PAN) fibers were endowed with high FIR emissivity via optimizing the content of far infrared nanoparticles (FIPs) and the typical multi-level rough structure of fibrous membranes. Significantly, benefitting from the improved FIR emissivity, the rising rate of pressure drop declined from 20 to 8.9% under high RH of 85%. The stabilization mechanism of pressure drop was revealed by means of low field nuclear magnetic resonance. Furthermore, a high filtration efficiency of 99.998%, low pressure drop of 79.5 Pa, and particularly low rising rate of pressure drop (6%) were achieved simultaneously by obtaining the balance of pore size (2.1 μm) and FIR emissivity (87%). The resultant membranes exhibited a rapid PM2.5 removal rate (~15 min) after 10 h, and a robust stability of low pressure drop (increased by 8.7% after 25 h) in the field test in Shanghai. The fabrication of such a promising material may provide a new insight to design air filtration materials with durable high performance.

•Self-standing Ag2O@YSZ-TiO2 p-n nanofibrous photocatalyst membrane was firstly designed and fabricated by electrospinning technique and precipitation process.•Ag2O@YSZ-TiO2 photocatalytic nanofibrous membranes exhibit superior photocatalytic activity and robust reversibility in degrading methylene blue.•This work shows a new insight to development of flexible and high-efficiency nanoheterojunction nanocrystalline photocatalyst membrane.Study of high-efficiency and free secondary pollution TiO2 based photocatalyst has become the one of the most urgent problems in improving the decolorization effect of the waste water from printing and dyeing mill. In this work, a novel self-standing Ag2O@YSZ-TiO2 p-n nanoheterojunction nanofibrous membrane was designed for ultraviolet (UV) photocatalyst by a facile combination of electrospinning technique and precipitation process. Moreover, the UV photocatalytic performance of the flexible AZT p-n nanoheterojuction nanofibrous membranes with a band gap energy of 2.89 eV and good reversibility of 5 cycles, was superior to the commercial catalyst P25 for photocatalytic degradation of methylene blue. Furthermore, the photocatalytic mechanism of the flexible Ag2O@YSZ-TiO2 nanofibrous photocatalyst was proposed by the electron transition in Ag2O/TiO2 p-n nanoheterojunction, which showed a new insight to development of flexible and high-efficiency nanoheterojunction nanocrystalline photocatalytic membranes.Novel self-standing Ag2O@YSZ-TiO2 p-n nanoheterojunction hierarchical composite nanofibrous membranes with excellent reversibility were designed for high-efficiency ultraviolet photocatalyst.Download high-res image (256KB)Download full-size image

•A humidity-resisting TENG is proposed to harvest energy from human movements for wearable electronics.•The electrospun nanofibrous membranes are rationally tailored to eliminate the adverse effects of water vapor on the electrical output.•With human biomechanical motions, the HR-TENG can respectively deliver a power density up to 1.3 W/m2.•It can sustainably power an electronic watch, a commercial calculator, a thermal meter and light up about 400 LEDs.With the rapid advancement of modern technology, wearable electronic devices become more and more indispensable to daily life. However, powering them in a stable and sustainable manner remains a challenge and highly desired. In this work, we proposed a humidity-resisting triboelectric nanogenerator (HR-TENG) to harvest energy from human biomechanical movements for wearable electronics. The electrospun nanofibrous membranes were rationally tailored to eliminate the adverse effects of water vapor on the electrical output and construct a high-performance humidity-resisting triboelectric nanogenerator. It could work with improved adaptability to the environmental humidity caused by human perspiration during sport. With human biomechanical motions, such as hand tapping, the wearable HR-TENG can respectively deliver a current and voltage output up to 28 µA and 345 V, corresponding to a power density of 1.3 W/m2 under a relative humidity 55%. It was also demonstrated to sustainably power an electronic watch, a commercial calculator, a thermal meter and light up about 400 LEDs by harvesting the biomechanical energy from human movements under different ambient humidity. And its electrical output was still at a relatively high level when the relative humidity was increased from 30% to 90%. Given a collection of compelling features of being wearable, flexible and cost-effective, the HR-TENG could be utilized as a sustainable power source to drive wearable electronics during human sport even with heavy perspiration.A humidity-resisting triboelectric nanogenerator is proposed to harvest energy from human biomechanical movements for wearable electronics. The electrospun nanofibrous membranes are rationally tailored to eliminate the adverse effects of water vapor on the electrical output and it could work with improved adaptability to the environmental humidity caused by human perspiration during sport.Download high-res image (273KB)Download full-size image

The separation of oil and water is a worldwide challenge due to the ever-increasing amount of oily industrial wastewater and polluted oceanic waters, as well as the increasing frequency of oil spill accidents. As the leader of advanced fibrous materials, electrospun nanofibers combine the properties of tunable wettability, large surface area, high porosity, good connectivity, fine flexibility, and ease of scalable synthesis from various materials (polymer, ceramic, carbon, etc.), and they hold great potential for many emerging environmental applications, including the separation of oily wastewater. In this review, the recent progress in the design and fabrication of electrospun nanofibrous materials with tunable surface wettability for oil/water separation applications is summarized and highlighted. This review covers the research and development starting from the design concepts and the synthesis of nanofibrous sorbents, nanofibrous membranes, and nanofibrous aerogels for effective oil/water separation. The review concludes with a brief forecast of challenges and future directions in this rapidly expanding field.

Creating porous carbonaceous membranes with durable mechanical properties and designed functionality is critical for the next generation of soft electronic devices; however, it has been proven extremely challenging. Herein, we report a facile strategy to fabricate highly porous carbon nanofibrous membranes with enhanced mechanical elasticity and intriguing functionality based on polybenzoxazine via combining multicomponent electrospinning and in situ polymerization. Tin oxide nanoclusters with diameters of 20–40 nm are homogenously distributed in the carbon matrix and on the surface of carbon nanofiber (CNF). A plausible plasticizing effect of the heterogeneous nanotextures endows the SnO2/CNF membrane with robust mechanical elasticity and durability, which can maintain its original shape after serious deformation. Moreover, the elastic SnO2/CNF membrane possesses a high surface area of 1415 m2 g−1 with a pore volume of 0.82 cm3 g−1. With their integrated properties of extraordinary mechanical properties, high porosity, large surface area, and good electrochemical properties, the as-prepared SnO2/CNF membranes exhibited a satisfactory capacitive performance with high energy density, ultralong cycling properties, and robust electrochemical stability against bending deformation, suggesting a promising usage as soft electrodes for flexible energy storage devices, and also opened up an avenue to the design of functional CNF materials with fine elasticity for various applications.

Effective air filtration proposed for fibers requires their assembly into a porous structure with small pore size, low packing density, and controllable macro-structure; however, creating such filtration media has proved to be a grand challenge. Here, we introduce a strategy to create microwave structured polyamide-6/poly(m-phenylene isophthalamide) nanofiber/net (PA-6/PMIA NFN) membranes for effective air filtration by combining the electro-spinning/netting (ESN) and staple fiber intercalating process. Our approach causes the PA-6 NFN membrane composed of one-dimensional (1D) nanofibers and 2D Steiner-tree nanonets, and the embedded PMIA staple fibers, to assemble into a stable filtration medium with tunable pore size, packing density, and microwave fluctuation by facilely optimizing binary fiber construction and extrinsic staple fiber intercalation. By virtue of the integrated structural properties of small pore size (∼0.32 μm), high porosity (91.3%), and extended surface area, the resulting PA-6/PMIA NFN filter can effectively filter ultrafine airborne particles, mainly using physical sieving, with high filtration efficiency of 99.995%, low pressure drop of 101 Pa, desirable quality factor of 0.1 Pa−1, and large dust-holding capacity of >50 g m−2, which match well with the requirements for treating the real particulate matter (PM) pollutions. This work would not only provide great potential for PM2.5 governance, but also open new avenues for the design and development of stable porous membranes with controllable macro-structures for various applications.

Flexible membranes created from porous carbon nanofibers (CNFs) hold great promise in the next generation wearable energy storage devices, but challenges still remain due to the poor mechanical properties of porous carbon nanofibers. Here, we report a facile strategy to fabricate elastic and hierarchical porous CNF membranes with NiFe2O4 nanocrystals embedded via multicomponent electrospinning and nano-doping methods. Benefiting from the scattering effect of NiFe2O4 nanocrystals and graphitized carbon layers for the condensed stress, the resultant CNF membranes exhibit an enhanced elasticity with a bending radius <12 μm, rapid recovery from the deformations, and a superior softness. Quantitative pore size distribution and fractal analysis reveal that the CNFs possessed tunable porous structures with a high surface area of 493 m2 g−1 and a pore volume of 0.31 cm3 g−1. Benefiting from the robust mechanical stability, hierarchical porous structures and good electrochemical properties, the NiFe2O4 doped CNF membranes demonstrate a high electrical capacitance of 343 F g−1, and good reversibility with a cycling efficiency of 97.4% even after 10000 cycles. The successful synthesis of elastic porous CNF membranes also provided a versatile platform for the design and development of functional CNF based materials for various applications.

The demand of water-resistant and breathable materials applied to a separation medium and protective garments is steadily increasing. Typical approaches to obtain these functional materials are based on hydrophobic agents and porous substrates with small fiber diameter, tiny pore, and high porosity. However, a fluorinated hydrophobic finishing agent usually employed in providing effective waterproofness is limited with respect to their environmental persistence and toxic potential. Herein, with the aim to keep a balance between the water-resistance and breathability as well as mechanical properties, we fabricate a novel fluoride-free functional membrane by electrospun polyacrylonitrile (PAN) nanofibers modified with polydimethylsiloxane (PDMS). As determined by morphological, DSC, and FT-IR analyses, the curing reaction of PDMS macromolecules formed an abundance of hydrophobic adhesive structures, which improved the waterproof performance dramatically and imparted relative good breathability at the same time. By systematically tuning the curing temperature as well as the concentration of PDMS, the modified PAN membranes with 4 wt % PDMS possessed good water-resistance (80.9 kPa), modest vapor permeability (12.5 kg m–2 d–1), and air permeability (9.9 mm s–1). Compared with pristine PAN membranes, the modified membranes were endowed with enhanced tensile stress of 15.7 MPa. The good comprehensive performance of the as-prepared membranes suggested their potential applications in protective clothing, membrane distillation, self-cleaning materials, and other medical products. Furthermore, the proposed relationship between porous structure and waterproof/breathable property as one considerable principle is applicable to designing functional membranes with different levels of protective and comfortable performance.Keywords: electrospinning; poly(dimethylsiloxane); polyacrylonitrile; surface modification; waterproof/breathable

Airborne particle filtration proposed for fibers requires their assembly into porous structures with small pore size and low packing density. The ability to maintain structural stability upon deformation stress in service is essential to ensure a highly porous packing material that functions reliably; however, it has proven extremely challenging. Here, we report a strategy to create anti-deformed poly(ethylene oxide)@polyacrylonitrile/polysulfone (PEO@PAN/PSU) composite membranes with binary structures for effective air filtration by combining multijet electrospinning and physical bonding process. Our approach allows the ambigenous fiber framework including thin PAN nanofibers and fluffy PSU microfibers, through which run interpenetrating PEO bonding structures, to assemble into stable filtration medium with tunable pore size and packing density by facilely optimizing the bimodal fiber construction and benefiting from the PEO inspiration. With the integrated features of small pore size, high porosity, and robust mechanical properties (8.2 MPa), the resultant composite membrane exhibits high filtration efficiency of 99.992%, low pressure drop of 95 Pa, and desirable quality factor of 0.1 Pa–1; more significantly, it successfully gets rid of the potential safety hazards caused by unexpected structural collapsing under service stress. The synthesis of PEO@PAN/PSU medium would not only make it a promising candidate for PM2.5 governance but also provide a versatile strategy to design and develop stable porous membranes for various applications.Keywords: air filtration; anti-deformed; binary structure; composite membrane; high filtration efficiency; low pressure drop

Fabricating protein adsorbents with high adsorption capacity and appreciable throughput is extremely important and highly desired for the separation and purification of protein products in the biomedical and pharmaceutical industries, yet still remains a great challenge. Herein, we demonstrate the synthesis of a novel protein adsorbent by in situ functionalizing eletrospun ethylene-vinyl alcohol (EVOH) nanofibrous membranes (NFM) with critic acid (CCA). Taking advantage of the merits of large specific surface area, highly tortuous open-porous structure, abundant active carboxyl groups introduced by CCA, superior chemical stability, and robust mechanical strength, the obtained CCA-grafted EVOH NFM (EVOH–CCA NFM) present an excellent integrated protein (take lysozyme as the model protein) adsorption performance with a high capacity of 284 mg g–1, short equilibrium time of 6 h, ease of elution, and good reusability. Meanwhile, the adsorption performance of EVOH–CCA NFM can be optimized by regulating buffer pH, ionic strength, and initial concentration of protein solutions. More importantly, a dynamic binding efficiency of 250 mg g–1 can be achieved driven solely by the gravity of protein solution, which matches well with the demands of the high yield and energy conservation in the actual protein purification process. Furthermore, the resultant EVOH–CCA NFM also possess unique selectivity for positively charged proteins which was confirmed by the method of sodium dodecyl sulfate polyacrylamide gel electrophoresis. Significantly, the successful synthesis of such intriguing and economic EVOH–CCA NFM may provide a promising candidate for the next generation of protein adsorbents for rapid, massive, and cost-effective separation and purification of proteins.Keywords: citric acid; electrospinning; ethylene-vinyl alcohol nanofibers; protein adsorption and purification; surface modification

Rational structural design involving controlled pore size, high porosity, and particle-targeted function is critical to the realization of highly efficient air filters, and the filter with absolute particle-screen ability has significant technological implications for applications including individual protection, industrial security, and environmental governance; however, it remains an ongoing challenge. In this study, we first report a facile and scalable strategy to fabricate the highly integrated polysulfone/polyacrylonitrile/polyamide-6 (PSU/PAN/PA-6) air filter for multilevel physical sieving airborne particles via sequential electrospinning. Our strategy causes the PSU microfiber (diameter of ∼1 μm) layer, PAN nanofiber (diameter of ∼200 nm) layer, and PA-6 nanonets (diameter of ∼20 nm) layer to orderly assemble into the integrated filter with gradually varied pore structures and high porosity and thus enables the filter to work efficiently by employing different layers to cut off penetration of particles with a certain size that exceeds the designed threshold level. By virtue of its elaborate gradient structure, robust hydrophobicity (WCA of ∼130°), and superior mechanical property (5.6 MPa), our PSU/PAN/PA-6 filter even can filtrate the 300 nm particles with a high removal efficiency of 99.992% and a low pressure drop of 118 Pa in the way of physical sieving manner, which completely gets rid of the negative impact from high airflow speed, electret failure, and high humidity. It is expected that our highly integrated filter has wider applications for filtration and separation and design of 3D functional structure in the future.Keywords: air filtration; integrated filter; microfiber; nanofiber; nanonets

•Chicken eggshell membrane is used as a skeleton to load CuInS2 nanocrystals.•CESM-CuInS2 composite shows a 3D macroporous submicron fiber network structure.•N-doped CESM loaded CuInS2 nanocrystals show better electrocatalytic activity.•DSSC fabricated using CESM-CuInS2 counter electrode exhibit an efficiency of 5.8%.A domestic waste, chicken eggshell membrane (ESM), is used as a raw material to fabricate carbonized ESM loaded with chalcopyrite CuInS2 nanocrystals (denoted CESM-CuInS2) by a simple liquid impregnation and carbonization method. The CESM-CuInS2 composite possesses a natural three-dimensional macroporous network structure in which numerous CuInS2 nanocrystals with a size of about 25 nm are inlaid in carbon submicron fibers that form a microporous network. The CESM-CuInS2 composite is used as the counter electrode in a dye-sensitized solar cell (DSSC) and its photoelectric performance is tested. The DSSC with a CESM-CuInS2 counter electrode exhibits a short-circuit current density of 12.48 mA cm−2, open-circuit voltage of 0.78 V and power conversion efficiency of 5.8%; better than the corresponding values for a DSSC with a CESM counter electrode, and comparable to that of a reference DSSC with a platinum counter electrode. The favorable photoelectric performance of the CESM-CuInS2 counter electrode is attributed to its hierarchical structure, which provides a large specific surface area and numerous catalytically active sites to facilitate the oxidation of the electrolyte. This new composite material has many advantages, such as low cost and simple preparation, compared with Pt and pure CuInS2 counter electrodes.

•Successful cross-linking of PEGDA decreases packing density and average pore size.•Introduction of x-PEGDA improves the affinity, wettability and ionic conductivity.•x-PEGDA coated PEI/PVdF membranes show superior thermostability and nonflammability.•x-PEGDA coated PEI/PVdF fibers demonstrate higher rate capability than Celgard.The x-polyethylene glycol diacrylate (x-PEGDA) coated polyetherimide/polyvinylidene fluoride (PEI/PVdF) membranes are obtained by the facile combination of dip-coating and free radical polymerization of PEGDA on the electrospun PEI/PVdF fiber membranes. Successful cross-linking of PEGDA increases the average fibers diameter from 553 to 817 nm and reduces the packing density, which not only increases the tensile strength of x-PEGDA coated PEI/PVdF membranes, but also decreases the average pore diameter. Besides, the x-PEGDA coated PEI/PVdF membranes are endowed with good wettability, high electrolyte uptake, high ionic conductivity and improved electrochemical stability window because of the good affinity of PEI and PEGDA with liquid electrolyte. Benefiting from the synergetic effect of PEI and PVdF, the x-PEGDA coated PEI/PVdF membranes exhibit excellent thermal stability and nonflammability, which are beneficial for enhancing the safety of lithium ion batteries. More importantly, the x-PEGDA coated PEI/PVdF membranes based Li/LiFePO4 cell exhibits comparable cycling stability with capacity retention of 95.9% after 70 cycles and better rate capability compared with the Celgard membrane based cell. The results clearly demonstrate that the x-PEGDA coated PEI/PVdF membranes are the promising separator candidate with improved wettability and safety for next-generation lithium ion batteries.

•A 3D NiCo2O4/CNTs carbon nanofibers (CNFs) membrane for supercapacitors and CO2 adsorption is produced.•The membrane possess high flexibility and good conductivity.•NiCo2O4/CNTs CNFs show high CO2 capture of 1.54 mmol/g at 25 °C and 1.0 bar.•Supercapacitors electrodes showed high capacitance of 220 F/g (in 1 M KOH) at a current density of 1 A/g.Controllable synthesis of carbon nanofibers (CNFs) with hierarchical porosity and high flexibility are extremely desirable for CO2 adsorption and energy storage applications. Herein, we report a nickel cobaltite/carbon nanotubes doped CNFs (NiCo2O4/CNTs CNFs) mesoporous membrane that shows well-developed flexibility, tailored pore structure, hydrophobic character, and high stability. Ascribed to these unique features, NiCo2O4/CNTs CNFs membrane shows high CO2 capture of 1.54 mmol/g at 25 °C and 1.0 bar, and electrochemical measurements for supercapacitors exhibit good performance with specific capacitances of 220 F/g (in 1 M KOH) at a current density of 1 A/g. The successful synthesis of such hybrid membrane provides new insight into development of various multifunctional applications.A multifunctional membrane that shows high CO2 adsorption and good capacitance.

A surprising brittle to flexible transition in ZrMxOy (M = Na, Mg, Al) nanofibrous membranes was found by varying the undersized dopant species and content. The fiber morphology, crystalline structure, and pore structure of the ZrMxOy nanofibrous membranes can be significantly modulated by varying the dopant valence from +1 to 3 and the dopant content from 1 to 20 mol%, respectively. Meanwhile, a classical Hall-Petch effect was revealed for the ZrMxOy nanofibrous membranes systems, which corresponded to a nanocrystalline size of 22.8 nm and an enhanced flexibility of 23 mN. Moreover, the substitutional solid solution and interstitial solid solution dissolution processes of Na, Mg, and Al into ZrO2 were analyzed using vacancy compensation and dopant interstitial compensation mechanisms, respectively. Most importantly, the flexible Al doped zirconia nanofibrous membranes exhibit a low infrared emissivity of 0.589 and 0.703 in the 3–5 μm and 8–14 μm wavebands, respectively, which suggests them to be a promising candidate for infrared stealth materials in the confrontation strategy field for personnel, aircraft, missiles, satellites, etc.

The study of nanocrystalline inorganic nanofibrous membranes (NINMs) with flexibility is one of the most active academic research areas in advanced functional nanofibrous materials. Nonetheless, the role of nanocrystallinity in flexibility has remained uninvestigated until now, according to typical Hall–Petch effects of nanocrystalline metals. Here, we show a surprising brittle-to-flexible-to-brittle transition of zirconia and yttria stabilized zirconia (YSZ) nanofibrous membranes as the grain size and pore size reduce below 26 and 13 nm, respectively. Moreover, classical and inverse Hall–Petch effects were revealed in nanocrystalline zirconia and YSZ nanofibrous systems, which correspond to intragranular and intergranular deformation mechanisms, respectively. Most importantly, the bending deformation mechanism of the flexible nanocrystalline YSZ nanofibrous membranes was proposed from macroscopical membranes to microscopic unit cells, including the slip of fibers, bending of fibers, grain activity, and dislocation motions, which was given for the first time in electrospun flexible NINM materials. Our discovery is fundamentally important for understanding deformation behavior and designing various flexible NINMs as promising candidates in the field of catalysis, supercapacitors, biomaterials, etc.

•Waterproof-breathable membranes were prepared by electrospinning and heat treatment.•FPU enriched the PAN/FPU macroporous membranes with superhydrophobicity.•Heating induced inter-fiber adhesion structure and decreased pore size.•Heat treatment enhanced the waterproof-breathable and mechanical properties.•High hydrostatic pressure (114.6 kPa) and WVTR (10.1 kg m−2 d−1).Macroporous membranes with robust waterproofness, breathability and mechanical properties have attracted a great deal of attention. However, great challenges still remained in developing an effective and cost-efficient method to fabricate such materials. In this study, polyacrylonitrile (PAN)/fluorinated polyurethane (FPU) nanofibrous composite membranes with enhanced waterproof and breathable performance were fabricated by combination of electrospinning and heat post-treatment. The introduction of FPU enriched the nanofibrous membranes with superhydrophobic surface with water contact angle of 151°, optimized pore size and porosity. Moreover, the relationship among hydrostatic pressure, pore structure and surface wettability has proven to be in accordance with Young–Laplace equation. By employing the heat post-treatment, the pristine PAN/FPU composite membranes were endowed with physically adhesion structure, thereby significantly improved the waterproof-breathable performance as well as the mechanical property. Owing to these effects, the resulting thermal treated PAN/FPU composite membranes exhibited the integrated properties of high hydrostatic pressure (114.6 kPa), water vapor transmission rate (10.1 kg m−2 d−1) and good tensile strength (9.4 MPa). Furthermore, the reinforced PAN/FPU nanofibrous composite membranes have great potential to be used as functional materials for fabricating separation media, filter, outdoor sportswear, chemical protective clothing, and army combat uniforms.

Metal organic–frameworks (MOFs) with intriguing structural motifs and unique properties are potential candidates for carbon dioxide (CO2) storage. Although structures with the single functional constructions and micropores were demonstrated to capture CO2 with high capacities at low temperature, their feeble interactions still limit practical applications at room temperature. Herein, we report in situ growth observation of hierarchical pores in copper(II) benzene-1,3,5-tricarboxylate (Cu-BTC) doped MOFs which gives high adsorption and enhances the CO2 binding ability. Thus, understanding this CO2-capturing mechanism, which has been causing controversy, is crucial for further development toward advanced study. The doped MOFs exhibit high specific surface areas of 1180 m2 g−1 and show good capacity to store CO2, which is mainly due to the presence of acid and amine functionalized CNTs and a large amount of narrow micropores (<1.0 nm).

Electrospun nanofibrous membranes with thin fiber diameter, small pore size, and high porosity have attracted a great deal of attention in the waterproof and breathable field. However, great challenges still remain in simultaneously reinforcing the mechanical and waterproof-breathable performance of such materials. In this study, a new type of fluorinated polyurethane/polyacrylonitrile/polyvinyl butyral nanofibrous membranes (FPU/PAN/PVB NFM) with a blocked isocyanate prepolymer (BIP) as chemical cross-linking agent were fabricated. The composite NFM, with robust mechanical, waterproof and breathable performance, has been prepared using an innovation strategy combining electrospinning with thermally induced physical bonding and chemical cross-linking. By systematically tuning the cross-linked temperature and time as well as the concentration of PVB and BIP, large breaking elongation (81.5%), good hydrostatic pressure (110 kPa) and modest WVTR (9.6 kg m−2 d−1) of the membranes were achieved. Meanwhile, the physically bonded structure and chemically cross-linked networks between PVB and BIP endowed the composite NFM with the robust tensile strength of 32.8 MPa, which was three times higher than that of pristine FPU/PAN membranes. Considering the excellent performance of the as-prepared membranes, this simple and intriguing approach may provide a versatile platform for exploring the applications of the bonded and cross-linked membranes in separation processes, membrane distillation, self-cleaning materials, and protective clothing.

Introducing flexibility and high porosity into carbon nanofibers (CNFs) is one of the critical challenges for the next generation of multifunctional energy storage and CO2 adsorption materials. Herein, we developed an efficient strategy for the controllable fabrication of a flexible and mechanically robust Co3O4 nanoparticles (NPs) doped CNFs (CNFs-Co) hybrid membrane via electrospinning and subsequent carbonization treatment. The quantitative pore size distribution and fractal analysis revealed that the CNFs-Co possessed a tunable porous structure with high surface area of 483 m2 g−1. Therefore, it exhibited exceptional performance in CO2 capture, i.e. a high CO2 adsorption capacity of 5.4 mmol g−1 at 1 bar and room temperature. Electrochemical measurements performed on CNFs-Co for supercapacitor applications demonstrated very high capacitance of up to ∼911 F g−1 at 5 mV s−1 (76% capacitance retention after 1000 cycles) in 1 M H2SO4 solution. The successful synthesis of this hybrid membrane may also provide new insights towards the development of materials for various multifunctional applications.

•The PAN/PU based separators were prepared by multi-needle electrospinning technique.•The electrospun separators displays good mechanical properties and thermal stability.•These separators exhibit good wettability with liquid electrolyte, high ion conductivity and internal short-circuit protection.•Nanofibrous composite nonwoven possesses stable cyclic performance which give rise to acceptable battery performances.Lithium ion batteries (LIBs) for high performance require separators with auspicious reliability and safety. Keeping LIBs reliability and safety in view, microporous polyacrylonitrile (PAN)/polyurethane (PU) nonwoven composite separator have been developed by electrospinning technique. The physical, electrochemical and thermal properties of the PAN/PU separator were characterized. Improved ionic conductivity up to 2.07 S cm−1, high mechanical strength (10.38 MPa) and good anodic stability up to 5.10 V are key outcomes of resultant membranes. Additionally, high thermal stability displaying only 4% dimensional change after 0.5 h long exposure to 170 °C in an oven, which could be valuable addition towards the safety of LIBs. Comparing to commercialized polypropylene based separators, resulting membranes offered improved internal short-circuit protection function, offering better rate capability and enhanced capacity retention under same observation conditions. These fascinating characteristics endow these renewable composite nonwovens as promising separators for high power LIBs battery.

•A novel strategy to mimic the hierarchical collagen fibril in bone is proposed by electrospinning and conventional textile technology.•The tensile strength of the woven scaffold was nearly 4-fold larger than that of nonwoven mats.•The nanofiber woven scaffolds show excellent cytocompatibility and accelerate osteoblast differentiation.•The composite scaffold significantly enhanced formation of new bone in damaged condyles in rabbit femur.To engineer bone tissue, a scaffold with good biological properties should be provided to approximate the hierarchical structure of collagen fibrils in natural bone. In this study, we fabricated a novel scaffold consisting of multilayer nanofiber fabrics (MLNFFs) by weaving nanofiber yarns of polylactic acid (PLA) and Tussah silk fibroin (TSF). The yarns were fabricated by electrospinning, and we found that spinnability, as well as the mechanical properties of the resulting scaffold, was determined by the ratio between polylactic acid and Tussah silk fibroin. In particular, a 9:1 mixture can be spun continuously into nanofiber yarns with narrow diameter distribution and good mechanical properties. Accordingly, woven scaffolds based on this mixture had excellent mechanical properties, with Young's modulus 417.65 MPa and tensile strength 180.36 MPa. For nonwoven scaffolds fabricated from the same materials, the Young's modulus and tensile strength were 2- and 4-fold lower, respectively. Woven scaffolds also supported adhesion and proliferation of mouse mesenchymal stem cells, and promoted biomineralization via alkaline phosphatase and mineral deposition. Finally, the scaffolds significantly enhanced the formation of new bone in damaged femoral condyle in rabbits. Thus, the scaffolds are potentially suitable for bone tissue engineering because of biomimetic architecture, excellent mechanical properties, and good biocompatibility.

Safety remains a practical concern in lithium ion batteries (LIBs), which is closely associated with the internal shorting caused by the poor dimensional thermostability at elevated temperature and the flammability of separators. Here, we report a novel strategy to fabricate thermostable and nonflammable silica–polyetherimide–polyurethane (SiO2–PEI–PU) nanofibrous membranes via an electrospinning process. Benefiting from the high porosity, interpenetrating network structure and synergetic effect of silica nanoparticles, PEI and PU, the as-prepared SiO2–PEI–PU membranes exhibit uniform pore size distribution, high ionic conductivity (6.25 mS cm−1) and good electrochemical stability up to 4.86 V. Notably, the hot oven and combustion tests reveal that the SiO2–PEI–PU membranes possess improved thermostability displaying 2% dimensional change after exposure to 170 °C for 0.5 h and flame retardant properties, which could be beneficial for improving the safety of LIBs. Significantly, the SiO2–PEI–PU membrane based Li/LiFePO4 cell exhibits more excellent cyclability delivering a discharge capacity of 158.91 mA h g−1 at the 90th cycle and better rate capability compared with the cell based on the Celgard membrane. Meanwhile, the SiO2–PEI–PU membrane based Li/LiFePO4 cell also shows more excellent cell performance even at an elevated temperature of 60 °C. The results clearly demonstrate that the SiO2–PEI–PU membranes are promising separator candidates, which will also pave the way for further application of nanofibrous membranes in high power LIBs.

Creating adsorptive materials for the fast, efficient, and high-throughput adsorption and purification of proteins is critical to meet the great demands for highly purified proteins, yet it has proven to be a highly challenging task. Here, we report that cross-linked and highly carboxylated poly(vinyl alcohol) (PVA) nanofibrous membranes were fabricated by a combination of electrospinning and the in situ graft polymerization of PVA and maleic anhydride (MAH) under mild conditions. Taking advantage of the large surface area available for protein binding, the highly tortuous porous structure, and the robust mechanical properties, the resultant PVA/MAH nanofibrous membranes exhibited a good integrated adsorption performance towards lysozyme, including a superior adsorption capacity of 177 mg g−1, fast adsorption equilibrium within 4 h, good selectivity, and good reversibility. Moreover, the saturation dynamic adsorption amount towards lysozyme reached 159 mg g−1 under 750 Pa driven solely by gravity, which conformed to the specified requirements for high adsorption capacity under relatively low pressure drops. Furthermore, the adsorption performance towards a protein mixture was analyzed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and the resultant PVA/MAH nanofibrous membranes retained excellent stability under depyrogenation conditions. The successful fabrication of such fascinating nanofibrous materials by using this simple and intriguing approach may provide new insights into the design and development of adsorptive materials for the purification of proteins with superior adsorption performance.

Particulate matter (PM) with an aerodynamic diameter of 2.5 micrometers or less (PM2.5), as one of the most hazardous air pollutants, has raised serious concerns for public health. Although individual or environmental protection could be achieved using conventional fibrous media, high performance filters usually rely on energy-intensive and bulky air-filtering media. In this work, an ultra-lightweight nylon 6–polyacrylonitrile nanofibre-nets binary (N6–PAN NNB) structured membrane, consisting of an ambigenous nanofibre framework through which run two-dimensional nano-nets, for sieving-enhanced capture of fine particles was demonstrated. The high coverage N6 nano-nets and low packing density of PAN nanofibres are certified as an efficient property promoter when the fibre spinning jet ratio of N6/PAN reaches 2/2, thereby improving the porosity, filtration efficiency, flow resistance, and stability. Upon exposure to 300 nm NaCl aerosol particles, the N6–PAN2/2 NNB membrane with a low basis weight of 2.94 g m−2 exhibited high filtration efficiency (99.99%) and desirable quality factor (0.1163 Pa−1) even though under a high flow rate (90 L min−1), significantly better results than those of glass fibre and melt-blown polypropylene fibre-based media. Ultimately, three-dimensional computer simulation based on the images of N6-15 and N6–PAN2/2 membranes after particle loading and filtration data via GeoDict were processed statistically through principal component analysis and then used to graphically express the particle deposition pattern change from surface filtration to deep bed filtration. We hope that the methodology and results presented here will encourage different approaches to diminish the negative impact of PM2.5 air pollution, in particular the frequency of haze occurrence in rapidly developing countries.

By virtue of the affinity of pyromellitic dianhydride (PMDA) for lead(II) ion (Pb2+) and the inherent structural merits of electrospun nanofibrous membranes, a novel solid-phase nanofibrous material was facilely fabricated via the modification of deacetylated cellulose acetate membranes with PMDA (DCA-PMDA). The resultant DCA-PMDA can be applied for the simultaneous naked-eye detection and removal of Pb2+ from water matrixes by simple filtration followed by treatment with Na2S solution. Importantly, the color of the DCA-PMDA changes from white to dark yellow-brown due to the formation of PbS, which can be leveraged for the colorimetric detection of Pb2+ by the naked eye with a detection limit of 0.048 μM. Under the same circumstances, the maximum adsorption capacity was determined to be as high as 326.80 mg g−1. Furthermore, the extraction of Pb2+ from DCA-PMDA was possible with HNO3. The regenerated membrane that remained maintained the high sensitivity to Pb2+ and exhibited almost the same adsorption capacity as the original membrane. Therefore, the proposed membrane offers a cost-effective material that can be considered as a viable alternative for effectively detecting and removing toxic Pb2+ from water samples.

With the aim to develop pH-paper-like lead ion (Pb2+) sensing materials, we demonstrate a colorimetric strip, which relies on a SiO2 nanoparticle (NP) decorated polydiacetylene embedded polyacrylonitrile nanofibrous membrane (PAN NFM), that undergoes a brilliant blue-to-red color transition as well as ‘Turn-On’ fluorescence upon incubation with Pb2+. The introduction of an amino acid (glycine) headgroup into a supramolecularly assembled 10,12-pentacosadiynoic acid results in a Pb2+-induced chromic conjugated polymer that is quickly photopolymerizable, rapidly responsive to Pb2+ and specifically identifiable. Moreover, the SiO2 NPs are certified as an efficient sensitivity promoter when their content reaches 0.5 wt% in the strip. With this understanding, the color change that is caused by 0.24 μM Pb2+ at ambient temperature can be easily perceived by the naked eye, which indicates the superiority of our strip compared with previous approaches, and it is also noteworthy that a fluorescent signal could also be produced in 2 min. Furthermore, RGB (red-green-blue) digital parameters obtained from images of the strips and automatic read outs via a smartphone were processed statistically through principal component analysis and then used to elaborate the standard curve and quantify Pb2+ concentration. This methodology for assaying and quantifying Pb2+ avoids time-consuming sample preparation, expensive laboratory techniques, and specialized personnel required to carry out conventional analytical methods.

Construction of nanoparticle modified titanium dioxide nanofibrous membranes (TiNFs) with a mesoporous and stable nanoparticle-nanofiber composite structure would have significant implication for environmental remediation; however, currently nanoparticle-TiNFs are generally brittle with poor structural integrity upon large deformation; thus, creating flexible, robust, and stable nanoparticle-TiNF composites has proven to be extremely challenging. Herein, we report flexible and hierarchical mesoporous TiO2 nanoparticle (TiO2 NP) modified TiNF (TiNFNPs) composites fabricated by the combination of sol–gel electrospinning and in situ polymerization. The electrospun TiNFs served as templates and a synthesized bifunctional benzoxazine (BA-a) was used as a novel carrier and fixative for non-agglomerated growth of TiO2 NPs. Benefiting from the large surface area, high porosity, homogeneity, stable nanofiber–nanoparticle composite structure, and robust mechanical properties, the as-prepared anatase TiNFNPs exhibited excellent photocatalytic activity towards methylene blue including fast degradation within 30 min, good reversibility in 4 cycles, and easiness of recycling. Moreover, the degradation products have been analysed and TiNFNPs exhibited better photodegradation performance towards methylene blue compared with a commercial catalyst (P25). Significantly, the successful synthesis of such fascinating materials may provide a versatile platform for further development of nanofibrous membrane-based photoreactors towards water and air pollutant treatment.

Many applications proposed for magnetic silica nanofibers require their assembly into a cellular membrane structure. The feature to keep structure stable upon large deformation is crucial for a macroscopic porous material which functions reliably. However, it remains a key issue to realize robust flexibility in two-dimensional (2D) magnetic silica nanofibrous networks. Here, we report that the combination of electrospun silica nanofibers with zein dip-coating can lead to the formation of flexible, magnetic, and hierarchical porous silica nanofibrous membranes (SNM). The 290 nm diameter silica nanofibers act as templates for the uniform anchoring of nickel ferrite nanoparticles (size of 50 nm). Benefiting from the homogeneous and stable nanofiber–nanoparticle composite structure, the resulting magnetic SNM can maintain their structure integrity under repeated bending as high as 180° and can facilely recover. The unique hierarchical structure also provides this new class of silica membrane with integrated properties of ultralow density, high porosity, large surface area, good magnetic responsiveness, robust dye adsorption capacity, and effective emulsion separation performance. Significantly, the synthesis of such fascinating membranes may provide new insight for further application of silica in a self-supporting, structurally adaptive, and 2D membrane form.Keywords: electrospinning; flexible membranes; magnetic; nickel ferrite; silica nanofibers

Flexible, magnetic, and hierarchical porous NiFe2O4@SiO2 nanofibrous membranes were prepared by combining the gelatin method with electrospun nanofibers. The membranes exhibited prominent mechanical strength and mesoporosity, as well as multifunctionality of magnetic responsiveness, dye adsorption, and emulsion separation.

Waterproof and breathable macroporous membranes that are both completely resistant to liquid water penetration and easily allowable to vapor transmission would have significant implication for numerous applications; however, fabrication of such materials has proven to be tremendously challenging. Herein, we reported novel electrospun composite fibrous membranes with high waterproof and breathable performance, which consisted of polyurethane (PU), terminal fluorinated polyurethane (FPU), and carbon nanotubes (CNTs). Benefiting from the utilization of FPU and CNTs, the fibrous membranes were endowed with superhydrophobic surface, optimized pores size and porosity, along with enhanced fibers, which resulted in excellent waterproof, breathable and mechanical properties. Significantly, the relationship among waterproofness, pore structure and surface wettability has been confirmed finely accordance with Young–Laplace equation. Ultimately, the resultant membranes presented high waterproofness with hydrostatic pressure up to 108 kPa, good breathability with water vapor transmission rate over 9.2 kg m–2 d–1, as well as robust mechanical properties with bursting strength of 47.6 kPa and tensile strength of 12.5 MPa, suggesting them as promising alternatives for a number of potential applications, such as protective clothing.Keywords: carbon nanotubes; electrospinning; macroporous membrane; terminal fluorinated polyurethane; waterproof and breathable;

Construction of adsorptive materials for simple, efficient, and high-throughput adsorption of proteins is critical to meet the great demands of highly purified proteins in biotechnological and biopharmaceutical industry; however, it has proven extremely challenging. Here, we report a cost-effective strategy to create carbonyl groups surface-functionalized nanofibrous membranes under mild conditions for positively charged protein adsorption. Our approach allows maleic anhydride to in situ graft on cellulose nanofibrous membranes (CMA) to construct adsorptive membranes with large surface area and tortuous porous structure. Thereby, the resultant CMA membranes exhibited high adsorption capacity of 160 mg g–1, fast equilibrium within 12 h, and good reversibility to lysozyme. Moreover, the dynamic adsorption was performed under low pressure-drops (750 Pa), with a relatively high saturation adsorption amount of 118 mg g–1, which matched well with the requirements for proteins purification. Considering the excellent adsorption performance of the as-prepared adsorptive membranes, this simple and intriguing approach may pave a way for the design and development of robust and cost-effective adsorption membranes to meet the great demands for fast and efficient adsorption of positively charged proteins.Keywords: adsorption; electrospun cellulose nanofibrous membranes; lysozyme; maleic anhydride; surface functionalization;

•Electrospinning followed by dip-coating was used to fabricate SiO2/PEI-PU membranes.•Introducing PEI, PU and SiO2 improved safety, tensile strength and ionic conductivity.•Coating SiO2 also restrained the micro-shorting and migrated the self-discharge.•SiO2/PEI-PU membranes based cell exhibited prominent cycling and rate performance.The performance of lithium ion battery based on electrospun nanofibrous membranes has gained a great deal of attention in the past decades, but the intrinsic low mechanical strength and large pore size of electrospun membranes limit their battery performance. To overcome this limitation, a powerful strategy for designing, fabricating and evaluating silica nanoparticles coated polyetherimide-polyurethane (SiO2/PEI-PU) nanofibrous composite membranes is easily developed via electrospinning followed by a dip-coating process. Benefiting from the high porosity, interpenetrating network structure and synergetic effect of PU, PEI and SiO2 nanoparticles, the as-prepared composite membranes exhibit high ionic conductivity (2.33 mS cm−1), robust tensile strength (15.65 MPa) and improved safety (excellent thermal resistance and flame retardant property). Additionally, the as-prepared composite membranes possess relatively narrow pore size distribution with average pore size of 0.58 μm after coating SiO2 nanoparticles, which plays an important role in hindering the micro-shorting and mitigating self-discharge. Significantly, the SiO2/PEI-PU membranes based Li/LiFePO4 cell exhibits more excellent cycling stability with capacity retention of 98.7% after 50 cycles at 0.2 C rate and better rate capability compared with the Celgard membrane based cell. The results clearly demonstrate that this is a promising separator candidate for next-generation lithium ion batteries, which may represent a significant step toward separators with improved performance.

•Bio-based PA-56 NF/N membrane was fabricated via one-step electrospinning/netting.•2D nanonets (∼20 nm) and stable cavity structures were synchronously constructed.•Superlight weight and mechanical robustness.•High filtration efficiency (99.995%) and low pressure drop (111 Pa).•Surface filtration and dust-cleaning regeneration ability.Nanofibrous media that both possess high airborne particle interception efficiency and robust air permeability would have broad technological implications for areas ranging from individual protection and industrial security to environmental governance; however, creating such filtration media has proved extremely challenging. Here we report a strategy to construct the bio-based polyamide-56 nanofiber/nets (PA-56 NFN) membranes with bimodal structures for effective air filtration via one-step electrospinning/netting. The PA-56 membranes are composed of completely covered two-dimensional (2D) ultrathin (∼20 nm) nanonets which are optimized by facilely regulating the solution concentration, and the bonded scaffold fibers constructed cavity structures which are synchronously created by using the CH3COOH inspiration. With integrated properties of small aperture, high porosity, and bonded scaffold, the resulting PA-56 NFN membranes exhibit high filtration efficiency of 99.995%, low pressure drop of 111 Pa, combined with large dust holding capacity of 49 g/m2 and dust-cleaning regeneration ability, for filtrating ultrafine airborne particles in the most safe manner involving sieving principle and surface filtration. The successful synthesis of PA-56 NFN medium would not only make it a promising candidate for air filtration, but also provide new insights into the design and development of nanonet-based bimodal structures for various applications.Bio-based PA-56 membrane composed of the ultrathin 2D nanonets and stable cavity structures can effectively filtrate ultrafine airborne particles with high filtration efficiency, low air resistance, and long service life.

•Single-step fabrication of electreted fibrous membranes for filtration.•Effect of inorganic electrets on filtration performance was studied.•Self-cleaning property was achieved by tuning the structure of membranes.•Better filtration performance than commercial PP filter media.Development of technologies for air filtration and purification is critical to meet the global challenges of threatened human health and accelerated greenhouse effect, especially for point-of-use applications. Here, we report a novel electreted polyetherimide–silica (PEI–SiO2) fibrous membrane by a single-step strategy to achieve effective filtration of fine particles. The hierarchical structured PEI–SiO2 membranes were endowed with promising superhydrophobicity with a water contact angle of 152°, allowing their better self-cleaning performance compared with commercial polypropylene (PP) filter media. Morphology, electric charge property, porous structure, and filtration performance could be regulated by tuning the type and concentration of electrets as well as the solution properties. Furthermore, unlike the commercial PP-based filter media, the as-prepared membranes can be treated at 200 °C for 30 min without sacrificing filtration efficiency (99.992%) and pressure drop (61 Pa) owing to the combined contribution of polarization and space charges. We anticipate that this promising electreted fibrous medium will act as a core part of numerous air filtration systems, including ultra-low penetration air filters, clean room, respirator, and protective clothing.

Macroporous membranes that could completely resist liquid water penetration and easily permit water vapor transmission would have great significance in numerous areas. However, current fabrication strategies for such materials still suffer from a series of problems. Herein, we reported a kind of waterproof and breathable macroporous membrane fabricated from polyurethane (PU), fluorinated polyurethane (FPU), and lithium chloride (LiCl) via electrospinning. Benefiting from the diversification of conductivity adjusted by LiCl, characteristics of the membranes including fiber diameter, pore size and distribution, even the orientation and aggregation of macromolecules could be simultaneously regulated, which brought about tremendous improvement of waterproof, breathable and mechanical performance. Significantly, the relationship among waterproofness, wettability and pore size has been confirmed to be finely consistent with the Young–Laplace equation. Meanwhile, mechanical performance was investigated on the basis of macromolecular orientation that was evaluated by polarized infrared spectroscopy. Ultimately, the resultant membranes exhibited integrated performance with improved hydrostatic pressure (82.1 kPa) and water vapor transmission rate (10.9 kg m−2 d−1), as well as enhanced tensile strength (11.6 MPa) and bursting strength (8.2 kPa), which would make them promising alternatives for many potential applications, especially in protective clothing fabrication.

To solve the thermal shrinkage, flammability and wettability problems of conventional polyolefin separators, we have prepared the nanonet-structured poly(m-phenylene isophthalamide)–polyurethane (PMIA–PU) nanofibrous membranes with enhanced thermostability and good wettability for high power lithium ion batteries (LIBs) via a one-step electrospinning technique. The as-prepared PMIA–PU membranes demonstrate improved mechanical strength (>15.79 MPa) and high ionic conductivity up to 1.38 mS cm−1 due to the introduction of PU and the formation of the nanonet structure. Benefiting from the introduction of PMIA, the as-prepared PMIA–PU membranes were endowed with not only improved thermostability and non-flammability but also excellent wettability to liquid electrolytes, which could be beneficial for improving the safety and reliability of LIBs. Moreover, the excellent affinity between the carboxy group (PMIA and PU) and the carbonate ester group of the liquid electrolyte endows the PMIA–PU membranes with good anodic stability up to 4.86 V. More importantly, the PMIA–PU membrane based Li/LiFePO4 cell exhibits comparable cycling stability, delivering a discharge capacity of 160 mA h g−1 at the 65th cycle and better rate capability compared with the Celgard membrane based cell. These results indicate a very promising direction for safe and reliable separators, which may make further progress in obtaining the enhanced performance of LIBs.

Novel silica nanofibrous (SNF) membranes with ultra-softness and enhanced tensile strength were prepared for the first time via an electrospinning technique with a sol–gel solution containing NaCl. By employing NaCl incorporation, the bonding structure was formed between silica nanofibers, which significantly enhanced the tensile strength of the SNF membranes from 3.2 to 5.5 MPa. Meanwhile, the morphology and mechanical properties of the SNF membranes can be finely controlled by tuning the calcination temperature and varying the NaCl content in the precursor solution. Additionally, the proposed mechanism of the softness of the SNF membranes was discussed by in situ SEM analysis during the bending and recovery process. Furthermore, the as-prepared SNF membranes with ultra-softness of 40 mN and relative high tensile strength of 5.5 MPa exhibit an ultra-low thermal conductivity of 0.0058 W m−1 K−1, even lower than air, which suggested them to be promising candidates for bunker clothing. This novel method also provides a new insight into the design and development of other soft ceramic nanofibrous membranes with high tensile strength for various applications.

•Sandwich like PA-6/PAN/PA-6 membrane was fabricated via sequential electrospinning.•2D nanonets (∼20 nm) and bead-on-string structures were synchronously constructed.•Extremely small pore size (∼300 nm) and high porosity.•Hybrid vigour and multiple capture manners.•High filtration efficiency (99.9998%) and low pressure drop (117.5 Pa).Air filtration proposed for nanofibers require their adequately thin fiber diameters and porous packing structure. The ability to construct stable and large cavity structures by extremely thin fibers would have broad technological implications for areas ranging from individual protection and industrial security to environmental governance; however, it has proved extremely challenging. Here we report a strategy to design and create sandwich structured polyamide-6/polyacrylonitrile/polyamide-6 (PA-6/PAN/PA-6) composite membrane for effective air filtration via sequential electrospinning. Our approach allows the PAN bead-on-string fibers and two-dimensional (2D) PA-6 nanonets to assemble into stable filtration medium with tunable porous structure and mechanical properties on a large scale, by facilely regulating the solution concentration, applied voltage, combined with weight ratio of PA-6/PAN. With integrated features of ultrathin (∼20 nm) nanonets and bead-on-string fibers supported cavity, the resulting PA-6/PAN/PA-6 composite membrane exhibits robust mechanical properties, high filtration efficiency of 99.9998%, and low pressure drop of 117.5 Pa for filtrating ultrafine airborne particles in multiple capture manners; and it successfully gets rid of the potential safety hazards caused by unexpected electret failure. The successful synthesis of PA-6/PAN/PA-6 medium would not only make it a promising candidate for air filtration, but also provide new insights into the design and development of composite membranes for various applications.Sandwich structured PA-6/PAN/PA-6 membrane composed of the ultrathin 2D nanonets and bead-on-string structures can effectively filtrate ultrafine airborne particles with high filtration efficiency and low air resistance.

Silica aerogels (SA) have well been recognized as one of the most attractive thermal insulation materials, but the inherent brittleness and moisture sensitivity hinder wide applications of these materials. Here, we report the design and fabrication of robust flexible hybrid silica nanofiber (SNF)–SA membranes with super-insulating properties and improved mechanical properties by formation of an interpenetrating network of mesoporous silica within a flexible SNF scaffold. The hybrid SNF/SA membranes were obtained by impregnating electrospun SNF membranes with silica sol, then aging, solvent exchanging, surface modification, and drying at ambient atmosphere. The resultant highly porous (>90%) hybrid SNF/SA membranes exhibit meso- and macroporosity with average pore diameter less than free path of air molecules, improved mechanical strength (224% increase in tensile strength), good flexibility (stiffness < 337.6 mN), hydrophobicity (water contact angle > 144.2°), while maintaining low thermal conductivity (0.021 W m−1 K−1 under ambient conditions). Such a robust hybrid membrane with remarkable integrated performance will have great potential in special thermal management applications under harsh conditions, such as the aerospace field. This success of interpenetrating porous SA in inorganic nanofibrous scaffolds paves a new avenue for the synthesis of multifunctional hybrid aerogels.

Many applications proposed for functional nanofibers require their assembly into a monolithic cellular structure. The ability to maintain structural integrity upon large deformation is essential to ensure a macroscopic cellular material that functions reliably. However, it remains a great challenge to achieve high elasticity in three-dimensional (3D) nanofibrous networks. Here, we report a strategy to create fibrous, isotropically bonded elastic reconstructed (FIBER) aerogels with a hierarchical cellular structure and superelasticity by combining electrospun nanofibers and the freeze-shaping technique. Our approach allows the intrinsically lamellar deposited electrospun nanofibers to assemble into elastic bulk aerogels with tunable porous structure and wettability on a large scale. The resulting FIBER aerogels exhibit the integrated properties of ultralow density (<30 mg cm–3), rapid recovery from 80% compression strain, superhydrophobic-superoleophilic wettability, and high pore tortuosity. More interestingly, the FIBER aerogels can effectively separate surfactant-stabilized water-in-oil emulsions, solely using gravity, with high flux (maximum of 8140 ± 220 L m–2 h–1) and high separation efficiency, which match well with the requirements for treating the real emulsions. The synthesis of FIBER aerogels also provides a versatile platform for exploring the applications of nanofibers in a self-supporting, structurally adaptive, and 3D macroscopic form.Keywords: aerogels; emulsion separation; nanofibers; superelastic; superhydrophobic;

•Two ejection models with critical conditions of Taylor cone apex were developed.•LCST phase diagram of the flying droplets was established.•Method for calculating the concentration sweep paths for the droplets was proposed.•Model predication and experiments validation for nanonet formation.Numerical models that are capable to quantitatively elaborate the formation of novel two-dimensional (2D) nanonets during electrospinning/netting would have broad technological implications for areas ranging from sensing devices and individual protection to industrial filtration and separation; however, creating such models has proved extremely challenging. Here we report novel numerical models for clarifying the origin, evolution, and regulation of the nanonets via combining the ejection modes of Taylor cone apex and the phase separation of charged droplets. Our models propose two critical condition formulas for the generation of jets and droplets, and a LCST phase diagram combined with concentration sweep paths for the nanonets or non-porous films. The resulting model predications exhibit excellent agreement with the experimental results obtained via varying the solution properties and process parameters. The successful model derivation for the nanonets formation may provide new insights into the design and development of 2D multifunctional nanomaterials for various applications.Models for elaborating the origin, evolution, and regulation of 2D nanonets were created via combining the ejection modes of Taylor cone apex and the phase separation of droplets.

Given the dire consequences of accidental lead ion (Pb2+) exposure, a portable, sensitive and robust analytical approach capable of colorimetric visualization is highly desirable. In this study, we demonstrate a colorimetric strip that relies on a novel polydiacetylene (PDA) embedded polyacrylonitrile nanofibrous membrane (PAN NFM). The Pb2+-chromic PDA is prepared from controlled mixtures of 10,12-pentacosadiynoic acid (PCDA) and PCDA-5EG, a PCDA derivative with a pentaethylene glycol headgroup. Moreover, the Pb2+ complexation ability is manipulated by controlling the molar ratio of PCDA to PCDA-5EG. The PAN NFM acting as a three dimensional matrix is designed for PDA immobilization, thereby improving the stability, portability and sensitivity. Upon exposure to a series of metal ions, only Pb2+ could induce a color change, which clearly showed that our strip could act as a highly selective probe to detect Pb2+. Ultimately, the strip with a naked eye detection limit of 0.48 μM undergoes a brilliant color transition, from blue to red, in a concentration-dependent manner and all the color transitions of strips are quantitatively visualized by employing a chromatic framework. The findings indicate that the strip is particularly promising for visual Pb2+ recognition due to its facile functionalization, simple construction, and versatility to empower colorimetric signaling.

Novel, sandwich-structured PVdF/PMIA/PVdF nanofibrous battery separators with robust mechanical strength and thermal stability are fabricated via a sequential electrospinning technique. The nanofibers of the PVdF and the PMIA layers are bonded and interconnected on the interface boundary without any polymer binder or post-treatment. Benefiting from the high porosity of the as-prepared membranes and the introduction of PMIA, the PVdF/PMIA/PVdF composite membranes exhibit high ionic conductivity (2.3 times higher than that of the Celgard membrane), robust tensile strength (13.96 MPa), and excellent thermal stability, sustaining insulation after closing the pores in the PVdF layer. Hot oven testing reveals that the composite membranes exhibit no dimension shrinkage after being exposed to 180 °C for 1 h. Furthermore, the as-prepared-membrane-based Li/LiCoO2 cell shows a higher capacity retention of 93.10% after 100 cycles and better rate performance compared with the cell using the Celgard membrane, providing new insight into the design and development of high-performance rechargeable lithium ion batteries.

Creating a practical and energy-efficient method with high efficacy to separate oil–water mixtures, especially those stabilized by surfactants, has proven to be extremely challenging. To overcome this challenge, a novel and scalable strategy was developed for the synthesis of superhydrophilic and prewetted oleophobic nanofibrous membranes by the facile combination of in situ cross-linked polyethylene glycol diacrylate nanofibers supported on polyacrylonitrile/polyethylene glycol nanofibrous (x-PEGDA@PG NF) membranes. The as-prepared x-PEGDA@PG NF membranes have shown superhydrophilicity with ultralow time of wetting and promising oleophobicity to achieve effective separation for both immiscible oil–water mixtures and oil-in-water microemulsions solely driven by gravity. These new membranes having a good mechanical strength of 14 MPa and mean pore sizes between 1.5 and 2.6 μm have shown a very high flux rate of 10975 L m−2 h−1 with extremely high separation efficiency (the residual oil content in filtrate is 26 ppm). More importantly, the membranes exhibit high separation capacity, which can separate 10 L of an oil–water mixture continuously without a decline in flux, and excellent antifouling properties for long term use, thus making them important candidates for treating wastewater produced in industry and daily life. Such membranes are also ideal for high viscosity oil purification such as purification of crude oil.

Creating a sensitive and selective method that can provide simple, practical and high-throughput determination of levels of Hg2+ ions in water has proved extremely challenging. This work responds to these challenges by designing, fabricating and evaluating a polyaniline (PANI) based immobilized sensor optimized to exhibit a colorimetric response to trace amount of Hg2+ ions. The sensor design is realized using a leucoemeraldine based PANI as probe, which has a specific interaction with Hg2+ and results in both “off–on” and “color-change” signals. Hierarchical structured nanofibrous sensing membranes within well immobilized probes are fabricated by a bottom-up blending electrospinning nanofabrication method. This sensor shows a vivid colorimetric response specifically to Hg2+ ions (white–yellow/green–green–blue) over other possible interfering metal cations and achieves a low detection limit of 5 nM observed by the naked eye. Additionally, the sensing responses are visualized quantitatively by employing a colorimetric framework that translates measured spectra into numeric color values directly related to color perception. Furthermore, the as-prepared sensors exhibited good reversibility after extended regeneration cycles, which suggests a promising analytical method as an economical alternative to traditional Hg2+ sensors and also provides a new insight into the design and development of a novel colorimetric sensing system based on PANI immobilized materials.

Novel flexible, thermally stable and hierarchical porous silica nanofibrous membranes with superhydrophilicity and underwater superoleophobicity were prepared by a facile in situ synthesis method, which can effectively separate oil-in-water microemulsions solely driven by gravity, with an extremely high flux of 2237 L m−2 h−1.

Novel flexible, mesoporous, and magnetic γ-Fe2O3@SiO2 nanofibrous membranes with high γ-Fe2O3 content and uniform distribution were prepared by a facile in situ growth method, which exhibit prominent mechanical strength and magnetic responsive performance, as well as efficient adsorption for organics in water.

•Novel fabrication of superamphiphobic nanofibrous filtration membranes.•Bonding/non-bonding structured composite membrane were constructed.•Mechanical properties were significantly improved.•Functionalized nanofibrous media showed enhanced air filtration performance.The worldwide demands are rising for an energy-efficient and cost-effective approach that can provide advanced nanofibrous membranes with high filtration performance and superior antifouling properties. Here we report a novel synthesized fluorinated polyurethane (FPU) modified nanofibrous membrane optimized to achieve oil and non-oil aerosol particle filtration. By employing the FPU incorporation, the polyacrylonitrile/polyurethane (PAN/PU) composite membranes were endowed with superhydrophobicity with a water contact angle of 154° and superoleophobicity with an oil contact angle of 151°. Morphology, surface wettability, porous structure, and filtration performance could be manipulated by tuning the solution composition as well as the hierarchical structure. Furthermore, the as-prepared membranes can capture, for the first time, a range of different oil aerosol particles in a single-unit operation, with >99.9% filtration efficiency, by using the combined contribution of fiber diameter and surface roughness acting on the objective particles. Exemplified here by the construction of superamphiphobic nanofibrous membrane, numerous applications of this medium includes high efficiency particulate air filters, ultra-low penetration air filters, and respiratory protection equipment.

•Innovative fabrication of hierarchically structured PSU/TiO2 fibrous membranes.•Fractal dimensional analysis confirmed the irregular rough surface features.•Correlation between hierarchical roughness and filtration performance was proposed.•Two-tier composite medium showed enhanced fine particulate filtration performance.Hierarchically structured, superhydrophobic filter medium exhibiting robust filtration performance to airborne particulate were prepared by a facile deposition of electrospun polysulfone/titania nanoparticles (PSU/TiO2 NPs) on a conventional nonwoven substrate. The air permeability, tensile strength and abrasion resistance of pristine PSU fibrous membranes could be finely controlled by regulating the solvent composition and number ratios of jets. By employing the TiO2 NPs incorporation, the pristine PSU fibers were endowed with promising superhydrophobicity with a water contact angle of up to 152°. The quantitative hierarchical roughness analysis using N2 adsorption method has confirmed the major contribution of TiO2 NPs on enhancing the porous structure and surface fractal features with irregular rough structure. Filtration performance studies have revealed that the filtration efficiency and pressure drop of resultant hybrid membranes could be manipulated by tuning the surface composition as well as the hierarchical structures. Furthermore, the as-prepared PSU/TiO2-5 membrane exhibited improved filtration efficiency (99.997%) and pressure drop (45.3 Pa) compared with pristine PSU membrane, which would make them a promising media for fine particle filtration, and a new insight was also provided into the design and development of high performance filter medium based on hierarchical structured fibers.Graphical abstract

•Innovative fabrication of PAN/SiO2 NPs filter media with multilevel structure.•Correlation between surface roughness and filtration performance was verified.•Non-circular singe fiber filtration mechanism of PAN/SiO2 NPs membranes was proposed.•Multilayer filter media showed high-performance fine particulate air filtration.As engineers strive to develop high-performance filtration membranes with structural alternatives, the challenges and costs of processing often limit creative innovation. Here, we describe a powerful yet economic strategy for fabricating multilevel structured nanofibrous membranes within a single filter medium, which is constructed by the accumulation of bimodal sized and silica nanoparticles (SiO2 NPs) incorporated electrospun polyacrylonitrile (PAN) nanofibrous membranes. By simply varying the composition of precursor solutions and layer-by-layer assisted stacking structure, individual fibers within the medium can conformally be endowed with non-circular cross section, or rough surface to form a skeletal frame-worked membrane with complimentary filtration efficiency (99.989%) and pressure drop (117 Pa) for 300–500 nm NaCl aerosol particles. The results suggested that this cost-effective filter media could be used as promising materials for a variety of potential applications in respiratory protection equipment, high efficiency particulate air filters, and ultra-low penetration air filters.

Creating a facile and efficient method that can provide large-scale, highly aligned, and high strength nanofibers has proved extremely challenging. This work responds to these challenges by designing and evaluating poly(m-phenylene isophthalamide) (PMIA) nanofibrous materials with robust mechanical strength, which can be fabricated on a large scale via a facile combination of relative humidity (RH)-regulated electrospinning and multi-level aggregate reconstructing. The morphology and structure of the PMIA membranes can be finely controlled by regulating the solution concentration and RH during spinning, and a possible RH-regulated alignment mechanism was proposed. Additionally, PMIA nanofibrous aggregates of yarns and subsequent plaits were built up by multi-level reconstructing. During the first-level reconstructing based on twisting, the structure and mechanical properties of the yarns can be facilely optimized by tuning the twist level, and the PMIA yarns with 3000 TPM possess robust tensile strength of 262 MPa. The second-level reconstructing based on yarns braiding endows the corresponding nano-plaits with the highest tensile strength of 330 MPa. This novel method provides a new insight into the design and development of highly aligned nanomaterials for various applications.

Novel zirconia nanofibrous (ZNF) membranes with robust flexibility were prepared for the first time by a facile combination of electrospinning and sol–gel methods. By employing yttrium oxide incorporation, the as-prepared ZNF membranes can be dramatically changed from the extreme fragility to robust flexibility. Meanwhile, the flexibility and mechanical properties of ZNF membranes can be finely controlled by regulating the crystallite phase and crystallite size in zirconia fibers. Additionally, the porous analysis using synchrotron radiation small-angle X-ray scattering measurements have confirmed the correlation between the porous structure and flexibility. Interestingly, the mechanical properties of the ZNF membranes were also controlled by manipulating the precursor composition in hybrid fibers. Furthermore, the as-prepared flexible ZNF membranes exhibit excellent corrosion resistance and high filtration efficiency for zirconia nanoparticles from strong acid and alkaline solutions, which makes them a good candidate as microfiltration membranes in waste water treatment, and new insight also suggested them as a promising candidate for thermal insulation, high temperature filtration, catalyst carriers, etc.

Since 2006, a rapid development has been achieved in a subject area, so called electro-spinning/netting (ESN), which comprises the conventional electrospinning process and a unique electro-netting process. Electro-netting overcomes the bottleneck problem of electrospinning technique and provides a versatile method for generating spider-web-like nano-nets with ultrafine fiber diameter less than 20 nm. Nano-nets, supported by the conventional electrospun nanofibers in the nano-fiber/nets (NFN) membranes, exhibit numerious attractive characteristics such as extremely small diameter, high porosity, and Steiner tree network geometry, which make NFN membranes optimal candidates for many significant applications. The progress made during the last few years in the field of ESN is highlighted in this review, with particular emphasis on results obtained in the author’s research units. After a brief description of the development of the electrospinning and ESN techniques, several fundamental properties of NFN nanomaterials are addressed. Subsequently, the used polymers and the state-of-the-art strategies for the controllable fabrication of NFN membranes are highlighted in terms of the ESN process. Additionally, we highlight some potential applications associated with the remarkable features of NFN nanostructure. Our discussion is concluded with some personal perspectives on the future development in which this wonderful technique could be pursued.

A novel and scalable strategy was developed for the synthesis of in situ polymerized superhydrophobic and superoleophilic nanofibrous membranes for effective separation of water-in-oil microemulsions, which exhibit an extremely high flux of 892 L m−2 h−1 solely driven by gravity, as well as good antifouling properties, thermal stability and durability.

A facile, ultrasensitive, and selective sensor strip utilizing 4-amino-3-penten-2-one (fluoral-p) functionalized electrospun polyacrylonitrile (PAN) (PAN/fluoral-p) nanofibrous membranes has been successfully developed for naked-eye colorimetric assay of formaldehyde. The sensor strips presented a significant reflectance decreasing band at 417 nm which induced a vivid color change from white to yellow and achieved a much lower naked-eye detection limit of 40 ppb compared with the World Health Organization standard (80 ppb). Based on the specific Hantzsch reaction between fluoral-p and formaldehyde, the as-prepared PAN/fluoral-p membranes are highly selective to formaldehyde with little interference from other volatile organic compounds and the proposed mechanism of this reaction is discussed carefully. Moreover, the colorimetric responses were visually quantitative using UV-vis spectra and the color difference calculated from L*, a*, b* values. Furthermore, due to the extremely large surface area and high porosity of the as-spun PAN nanofibrous membranes, the sensitivity of the nanofibrous membranes-based strips is much higher than traditional filter paper-based ones. Hence, such promising portable colorimetric sensor strips could not only potentially allow for assaying gaseous formaldehyde, but also facilitate the design and development of a novel colorimetric sensing system based on nanofibrous membranes.

Two-tier composite filtration medium exhibiting excellent filtration performance to airborne particulate was prepared by a facile deposition of electrospun polyvinyl chloride (PVC)/polyurethane (PU) fibers on a conventional filter paper support. The tortuous structure and composition of resultant fibrous membranes can be finely controlled by regulating the precursor solution composition. By employing the PU incorporation, the pristine PVC fibrous membranes were endowed with robust tensile strength approaching to 9.9 MPa. The plausible correlation between resultant blended fibrous structure and mechanical property of relevant membranes was discussed, and a three-step break mechanism upon the external stress was proposed. Additionally, quantitative pore size and porosity distribution analysis using the capillary flow porometry method has confirmed the tortuous structure of PVC/PU fibrous membranes. Furthermore, the as-prepared membranes with high abrasion resistance (134 cycles) and comparable air permeability (154.1 mm/s) showed fascinating filtration efficiency (99.5%) and low pressure drop (144 Pa) performance for 300–500 nm sodium chloride aerosol particles, suggesting their use as a promising medium for variety of potential applications in air filtration.Graphical abstractHighlights► Innovative fabrication of PVC/PU fibrous membranes with tortuous structure. ► Robust tensile strength has confirmed the interfacial compatibility of PVC and PU. ► A three-step break mechanism of PVC/PU fibrous membranes was proposed. ► Two-tier composite medium showed high-performance fine particulate air filtration.

Superhydrophobic films on glass substrate with robust adhesion and dual pinning to the water droplets were fabricated utilizing a novel in situ polymerized fluorinated polybenzoxazine (F-PBZ) having drooping aliphatic chains and incorporated SiO2 nanoparticles (SiO2 NPs). By employing the F-PBZ/SiO2 NPs modification, the as-prepared composite films possess the robust adhesion to the glass substrate and superhydrophobic pinned state with water contact angle (WCA) of 150° and the non-pinned state with WCA approaching to 165°. Surface morphological studies have indicated that the wettability of the resultant films could be controlled by tuning the surface composition as well as the hierarchical structures. The key role of micro and sub-micro-sized structures and the nanometer sized voids is discussed by the investigation into static contact angle, contact angle hysteresis, droplet evaporation, and propensity for air pocket formation. The as-prepared films exhibited high adhesion toward the glass substrate with considerable durability in corrosive water and proved their simultaneous use in the transportation of micro-droplets, which could be helpful to design large-area and highly scalable superhydrophobic films.Graphical abstractHighlights► Innovative chemical synthesis of flexible fluorinated polybenzoxazine (F-PBZ). ► F-PBZ/SiO2 nanoparticles modification to get dual pinned superhydrophobic films. ► Stability of composite films toward corrosive water covering pH range in totality.

Cellulose fibers deposited with metallic nanoparticles as one kind of renewable, biocompatible and antimicrobial nanomaterials evoke much interest because of their versatility in various applications. Herein, for the first time, a facile, simple and rapid method was developed to fabricate TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) selectively oxidized jute fibers in situ deposited with silver nanoparticles in the absence of reducing reagents. The average size of silver nanoparticles deposited on the fibers is 50.0 ± 2.0 nm by microwave heating for 5 min and 90.0 ± 4.7 nm for 10 min heating sample, respectively. The versatile jute–silver nanoparticles nanocomposites with superior thermal stability and high crystallinity would be particularly useful for applications in the public health care and biomedical fields.Highlights► For the first time, Ag nanoparticles were in situ deposited on TEMPO treated jute fibers. ► Ag nanoparticles were synthesized on jute without any reducing reagents. ► The size distributions of Ag nanoparticles on the jute fibers were narrow. ► Jute/nanosilver nanocomposites exhibited superior thermal stability and high crystallinity. ► Microwave heating provides a promising method for preparation of metallic nanoparticles.

Novel inorganic nanofibrous membranes with robust waterproof and breathable performances were prepared by dip-coating of synthesized fluorinated polyurethane (FPU) on free-standing electrospun silica nanofibrous (SNF) membranes. By employing the FPU incorporation, the wettability of the as-prepared SNF/FPU membranes can be dramatically changed from the superamphiphilicity to amphiphobic, meanwhile, a plausible interaction between the water droplets and composite membranes was proposed. Additionally, the mechanical property of SNF/FPU membranes can be finely controlled by regulating FPU concentrations and the diameter of silica nanofibers, and the tensile fracture process of SNF/FPU membranes was discussed. The quantitative porous analysis using the N2 adsorption method has confirmed the correlation between the adhesion structure and wettability for the modified membranes. Furthermore, the SNF/FPU membranes exhibited good air permeability (54.04 mm s−1), high hydrostatic pressure (13.5 kPa), and comparable tensile strength (15.2 MPa), suggesting a promising candidate for protective clothing, bioseparation, water purification, tissue engineering and catalyst carriers, etc.

•Colorimetric strips for Pb2+ assaying with high sensitivity, stability and selectivity.•Electrospun nano-fiber/net (NFN) membranes are utilized as new substrate to immobilize Au probe.•NFN membranes possess high specific surface area and porosity with controllable coverage rate.•Naked-eye detection limit of 0.2 μM, fulfilling the preliminary CDC standard for lead poisoning.A facile, ultrasensitive, reproductive and selective sensor strip utilizing electrospun polyamide-6/nitrocellulose (PA-6/NC) nano-fibers/nets (NFN) membranes assemble bovine serum albumin decorated Au nanoparticles (BAu probe) for naked-eye colorimetric assay of Pb2+ has successfully prepared through dual-component alternate distribution multifluidic electrospinning technique. Benefiting from the extremely large specific surface areas and high porosity of NFN membranes, the stability of BAu probe dramatically increased and the strips presented a significant absorbance decreasing band at 546 nm which induce the visual color changes from deep pink to white after incubated in Pb2+ liquor with a low detection limit of 0.2 μM without any assistance of equipment. Upon exposure to a series of metal ions, only Pb2+ could induce a pink-to-white color change, which clearly exhibited that BAu probe immobilized PA-6/NC membranes could act as highly selective strips to detect Pb2+ with little interference from other metal ions. Additionally, the colorimetric responses are represented in visualized quantitative by calculated color difference from L⁎a⁎b⁎ coordinates which are presented with lightness and chrome values. Furthermore, the sensitivity of NFN membrane-based strips is much higher than that of film-based ones. The results indicate that this promising cost-effective sensing system could potentially allow for assaying of Pb2+ in human urine or blood as preliminary screening of lead poisoning.Graphical abstract

Hierarchical porous, magnetic Fe3O4@carbon nanofibers (Fe3O4@CNFs) comprising graphitic nanofibers and embedded Fe3O4 nanocrystals were prepared by using electrospun polyacrylonitrile/polybenzoxazine (PBZ) nanofibers as composite carbon precursor. By the combination of precursor design and activation process, a series of Fe3O4@CNFs with a tunable porous structure including the surface area, pore volume and micro/mesopore ratio were obtained, and could achieve an extremely high surface area of 1623 m2 g−1 and a pore volume of 1.635 cm3 g−1. Quantitative pore size distribution and fractal analysis were employed to investigate the hierarchical porous structure using N2 adsorption methods and synchrotron radiation small-angle X-ray scattering measurements. The role of the precursor structure and activation treatment for the tuning of the porous structure and surface fractal dimension is discussed, and the relative fraction of closed and open pores in CNFs is confirmed. Furthermore, the as-prepared Fe3O4@CNFs exhibit efficient adsorption for organic dyes in water and excellent magnetic separation performance, which would make them a promising adsorbent for water treatment, and a new insight was also provided into the design and development of functional carbon nanomaterials based on PBZ precursor.

A novel and scalable strategy was developed for the synthesis of one dimensional mesoporous polybenzoxazine-based Fe3O4@carbon nanofibers by using an in situpolymerization method, which exhibit an extremely high surface area of 1885 m2 g−1, as well as efficient adsorption for organic dyes and facilely magnetic separation property.

Hierarchical porous, magnetic Fe3O4@carbon nanofibers (Fe3O4@CNFs) based on polybenzoxazine precursors have been synthesized by a combination of electrospinning and in situ polymerization. The benzoxazine monomers could easily form thermosetting nanofibers by in situ ring-opening polymerization and subsequently be converted into CNFs by carbonization. The resultant fibers with an average diameter of 130 nm are comprised of carbon fibers with embedded Fe3O4 nanocrystals, and could have a high surface area of 1885 m2 g−1 and a porosity of 2.3 cm3 g−1. Quantitative pore size distribution and fractal analysis were used to investigate the hierarchical porous structure using N2 adsorption and synchrotron radiation small-angle X-ray scattering measurements. The role of precursor composition and activation process for the effects of the porous structure is discussed, and a plausible correlation between surface fractal dimension and porous parameter is proposed. The Fe3O4@CNFs exhibit efficient adsorption for organic dyes in water and excellent magnetic separation performance, suggesting their use as a promising adsorbent for water treatment, and also provided new insight into the design and development of a carbon nanomaterial based on a polybenzoxazine precursor.

Cellulose nanowhiskers is a kind of renewable and biocompatible nanomaterials evoke much interest because of its versatility in various applications. Here, for the first time, a novel controllable fabrication of cellulose nanowhiskers from jute fibers with a high yield (over 80%) via a 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)/NaBr/NaClO system selective oxidization combined with mechanical homogenization is reported. The versatile jute cellulose nanowhiskers with ultrathin diameters (3–10 nm) and high crystallinity (69.72%), contains C6 carboxylate groups converted from C6 primary hydroxyls, which would be particularly useful for applications in the nanocomposites as reinforcing phase, as well as in tissue engineering, pharmaceutical and optical industries as additives.Highlights► For the first time, cellulose nanowhiskers are extracted from TEMPO oxidized jute. ► The dimension of the nanowhiskers is 3–10 nm in width and 100–200 nm in length. ► Carboxylate groups formed on cellulose nanowhiskers results in a negative charge. ► It is easily dispersed in water and forms stable and transparent suspension.

A mechanical robust and thermal tolerant nanofibrous membrane with hydrophilicity is presented by one step via electrospinning Nomex® solution. The nanofibrous membrane shows a high specific surface area of 21.46 m2/g, two orders of magnitude larger than that of the commercial Nomex® fibers. The experimental results demonstrate that the membrane has high efficient rejection for nanoparticles from aqueous solution, which reveals its feasibility used in liquid filtration. Additionally, the membrane displays high break strength of 31.34 MPa as well as very excellent thermal resistance, making it as good candidates for applications in reinforced nanomaterials, automobile air filters, template of structure coatings etc., requiring high strength and high thermal resistance.A mechanical robust and thermal tolerant nanofibrous membrane with hydrophilicity was prepared by one step via electrospinning poly(meta-phenylene isophthalamide) fibers solution which was commercialized by Dupont company under the trade name of Nomex®. The membrane exhibits high efficient rejection for nanoparticles from aqueous solution.Highlights► PMIA nanofibrous membrane is prepared by one step via electrospinning Nomex® solution. ► The membrane shows high break strength as well as very excellent thermal resistance. ► The membrane has a high efficient rejection for nanoparticles from aqueous solution.

A novel strategy for highly sensitive colorimetric detection of gaseous formaldehyde was developed based on Methyl Yellow-impregnated electro-spinning/netting (ESN) nylon 6 nano-fiber/nets (NFN). The sensor presented a significant reflectance intensity decreasing band at 550 nm which induce the visual color changes from yellow to red after exposure to formaldehyde and allowed for the detection of formaldehyde with a low detection limit of 50 ppb. Upon exposure to a series of volatile organic compounds (VOCs), only formaldehyde could induce a yellow-to-red color change observable by the naked eye, which clearly exhibited that Methyl Yellow-impregnated nylon 6 NFN membranes could act as highly selective and sensitive strips to detect formaldehyde with minor interference from other VOCs. Additionally, the colorimetric sensor showed good reproducibility under cyclic sensing experiments. Furthermore, the colorimetric responses were visualized quantitative by using a color-differentiation map prepared form converted RGB (red, green and blue) values. As-prepared Methyl Yellow-impregnated nylon 6 NFN sensor strips successfully combined with the visualized detection of color map and fascinating structure of NFN membranes, which indicated promising composite materials as a simple and economical alternative to replace the traditional formaldehyde sensors and facilitated the design and development of other label-free colorimetric sensors toward various analytes based on the NFN template.

A highly sensitive coating comprising 3-mercaptopropionic acid (MPA) monolayer modified electrospun polystyrene (PS) membranes was constructed on the electrode of quartz crystal microbalance (QCM) for Cu2+ detection. The three-dimensional fibrous PS membranes with high specific surface area (SSA) were deposited on the electrode of QCM via electrospinning. The PS membranes were sputter coated with gold, then modified with self-assembled monolayer of MPA. The PS-MPA sensors showed fast response (2–3 s) to Cu2+ and a detection limit down to 100 ppb. Additionally, sensor sensitivity increased concurrently with both increasing PS loading and SSA on QCM electrodes. The response of the PS-MPA sensors with a PS membrane loading of 978 Hz and SSA of 43.31 m2/g was 40 times larger than that without membranes when exposed to 1 ppm of Cu2+. The sensor responses were reproducible toward Cu2+ in the 100–5 ppm concentration range, whereas a linear response was found in the 100–1 ppm concentration range. The sensor response to Cu2+ showed a linear relationship with an increase in pH from 2 to 7. Moreover, the sensors also exhibited chelation selectivity for other transition metal ions in the descending order Cu2+ > Ni2+ > Zn2+ > Fe2+ at concentration between 1 and 5 ppm.

Inspired by the self-cleaning lotus leaf and silver ragwort leaf, here we demonstrate the fabrication of biomimetic superhydrophobic fibrous mats viaelectrospinning polystyrene (PS) solution in the presence of silica nanoparticles. The resultant electrospun fiber surfaces exhibited a fascinating structure with the combination of nano-protrusions and numerous grooves due to the rapid phase separation in electrospinning. The content of silica nanoparticles incorporated into the fibers proved to be the key factor affecting the fiber surface morphology and hydrophobicity. The PS fibrous mats containing 14.3 wt% silica nanoparticles showed a stable superhydrophobicity with a water contact angle as high as 157.2°, exceeding that (147°) of the silver ragwort leaf and approaching that (160°) of the lotus leaf. The superhydrophobicity was explained by the hierarchical surfaces increasing the surface roughness which trapped more air under the water droplets that fell on the fibers.

Two-dimensional (2D) polyacrylic acid (PAA) nano-nets that comprise interlinked ultrathin nanowires with diameters of 10–30 nm are successfully prepared by a facile electro-netting process. Nano-nets feature a clear geometric characteristic with ideal and weighted Steiner networks due to the rapid phase separation process and its obeyed minimal energy principle. The versatile nano-nets create enhanced interconnectivity and additional surface area and facilitate the diffusion of analytes into the membranes, which significantly boost the gas diffusion coefficient and sensing properties. As one example, PAA membranes containing fibers and nano-nets used as sensing materials are deposited by electrospinning/electro-netting on an electrode of a quartz crystal microbalance (QCM) for trimethylamine (TMA) detection, which exhibits a quick response (∼180 s), low detection limit (1 ppm) and ideal selectivity at room temperature.

A uniform electrospun nanofibrous membrane was fabricated from chitosan (CS)–polyvinyl alcohol (PVA)/organic rectorite (OREC) with different mixing ratios by solution-mixing process and eleltrospinning technologies. The morphology, intercalation between polymer and OREC, and bacterial inhibition activity of the electrospun membranes were investigated. Field emission scanning electron microscopy showed uniform fibrous structure generated with the addition of OREC. Energy-dispersive X-ray spectroscopy results confirmed the existence of OREC on the surface of electrospun membranes. Fourier transform infrared spectra and small angle X-ray diffraction results verified that the interlayer of OREC was intercalated by CS and PVA chains successfully. The controllable interlayer distance of OREC was enlarged from 3.68 to 4.28 nm. The membranes had enhanced bacterial inhibition activity with the addition of OREC.

Organic rectorite (OREC) was used to prepare the intercalated composites with chitosan (CS). The negatively charged cellulose nanofibers hydrolyzed from electrospun cellulose acetate fibrous mats were modified with multilayers of the positively charged CS-OREC intercalated composite and the negatively charged sodium alginate (ALG) via layer-by-layer (LBL) technique. The morphology and antibacterial activity of the resultant samples were studied by regulating the number of deposition bilayers, the compositions of dipping solutions and outermost layer of films. Field emission scanning electron microscopy images indicated that the thickness of CS-OREC/ALG bilayer formed on fibers was estimated from 12 to 26 nm. Additionally, the energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy results indicated that CS and OREC were successfully deposited on cellulose fibers. The bacterial inhibition experiments demonstrated that LBL films modified fibrous cellulose mats with the addition of OREC can increase the degree of inhibition on Escherichia coli.

Biomimetics provides a model for developments of functional surfaces with special wettability. Recently, manufacturing bio-inspired superhydrophobic surfaces has become an increasingly hot research topic. The electrospinning technique is a versatile and effective method for manufacturing nanomaterials with controllable compositions and structures, and therefore provides an ideal strategy for construction of superhydrophobic surfaces on a large scale. After a brief description of several superhydrophobic surfaces inspired by nature, we highlighted the recent progresses in design and fabrication of these bio-inspired superhydrophobic surfaces via electrospinning technique. The studies on the switchable wettability of nanofibrous surface brought about by external stimuli are also addressed. We conclude with a summary of current and future research efforts and opportunities in the development of electrospun nanomaterials for superhydrophobic applications.Graphical abstractHighlights► Electrospun superhydrophobic structures inspired by nature were highlighted. ► Surface modification of electrospun nanofibers could introduce rough structure as well as low surface energy materials on pre-formed fibrous surfaces. ► Roughening hydrophobic materials through electrospinning provides a one-step strategy to prepare superhydrophobic surfaces. ► Current research on the reversibly switchable wettability of fibrous surface is briefly addressed. ► Future challenges and perspectives of the development of superhydrophobic micro- and nanofibrous surfaces are concluded.

A novel highly stable and sensitive humidity sensor based on bacterial cellulose (BC) coated quartz crystal microbalance (QCM) has been successfully fabricated. The results showed that the sensors possessed good sensing characteristics by increasing more than two orders of magnitude with increasing relative humidity (RH) from 5 to 97%, and the Log(Δf) showed good linearity (20–97% RH). The sensitivity of sensors coated with BC membranes was four times higher than that of the corresponding cellulose membranes at 97% RH. In addition, the sensor sensitivity is greatly enhanced by increasing the coating load of the BC membranes with more absorption sites in the sensing membranes. Moreover, the experimental results prove that the resultant sensors exhibited a good reversible behavior and good long term stability. Herein, not only a novel and low-cost humidity sensor material was exploited, but also a new application area for BC nanofibrous membranes was opened up.

A novel formaldehyde sensor based on nanofibrous polyethyleneimine (PEI)/bacterial cellulose (BC) membranes coated quartz crystal microbalance (QCM) has been successfully fabricated. The nanoporous three-dimensional PEI/BC membranes are composed of nanofibers with diameter of 30–60 nm. The sensor showed high sensitivity with good linearity and exhibited a good reversibility and repeatability towards formaldehyde in the concentration range of 1–100 ppm at room temperature. Moreover, the results showed that the sensing properties were mainly affected by the content of PEI component in nanofibrous membranes, concentration of formaldehyde and relative humidity. Additionally, the nanofibrous PEI/BC membrane coated QCM sensors exhibited a good selectivity to formaldehyde when tested with competing vapors. The simple and feasible method to prepare and coat the PEI/BC sensing membranes on QCM makes it promising for mass production at a low cost.

For the first time, two-dimensional (2D) gelatin nano-nets are fabricated by regulating the solution properties and several process parameters during electrospinning/electro-netting. The spider-web-like nano-nets that comprise interlinked one-dimensional (1D) ultrathin nanowires (10–35 nm) are stacked layer-by-layer and widely distributed in the three-dimensional (3D) porous membranes. The final morphology of the gelatin nano-nets, including nanowire diameter, area density and pore-width of the nano-nets, is highly dependent on the solution concentration, salt concentration, kinds of solvents, applied voltage, ambient temperature and relative humidity (RH). The occurrence of rapid phase separation on the splitting-film and the formation of hydrogen bond among gelatin molecules during electro-netting are proposed as the possible mechanisms for the formation of these spider-web-like nano-nets.Graphical abstractHighlights► Large-scale spider-web-like gelatin nano-nets (∼35 nm) were successfully fabricated via electro-netting. ► The formation of nano-net could be well controlled by regulating the solution properties and several process parameters during electrospinning/electro-netting. ► Nano-nets create enhanced interconnectivity and additional surface area which may have potential application in the field of biomaterials, tissue engineering and ultra-fine filters.

Here we report a novel fabrication approach to highly sensitive formaldehyde sensors by the surface modification of the electrospun nanofibrous membranes. The three-dimensional fibrous membranes comprising nanoporous polystyrene (PS) fibers were electrospun deposition on quartz crystal microbalance (QCM), followed by the functionalization of the sensing polyethyleneimine (PEI) on the membranes. The morphology and Brunauer–Emmett–Teller (BET) surface area of the fibrous PS membranes with fiber diameter of 110–870 nm were controllable by tuning the concentrations of PS solutions. After PEI modification, PEI particles in clusters of varying sizes (50 nm to 1.2 μm) were immobilized onto the surface of the bead-on-string structured nanoporous fibers. The developed formaldehyde-selective sensors exhibited fast response and low detection limit (3 ppm) at room temperature. This high sensitivity is attributed to the high surface-area-to-volume ratio (∼47.25 m2/g) of the electrospun porous PS membranes and efficient nucleophilic addition reaction between formaldehyde molecules and primary amine groups of PEI.

Increasing demands for ever more sensitive sensors for global environmental monitoring, food inspection and medical diagnostics have led to an upsurge of interests in nanostructured materials such as nanofibers and nanowebs. Electrospinning exhibits the unique ability to produce diverse forms of fibrous assemblies. The remarkable specific surface area and high porosity bring electrospun nanomaterials highly attractive to ultrasensitive sensors and increasing importance in other nanotechnological applications. In this review, we summarize recent progress in developments of the electrospun nanomaterials with applications in some predominant sensing approaches such as acoustic wave, resistive, photoelectric, optical, amperometric, and so on, illustrate with examples how they work, and discuss their intrinsic fundamentals and optimization designs. We are expecting the review to pave the way for developing more sensitive and selective nanosensors.

A direct approach for fabricating nanoporous polymer fibers via electrospinning has been demonstrated. Polystyrene (PS) fibers with micro- and nanoporous structures both in the core and/or on the fiber surfaces were electrospun in a single process by varying solvent compositions and solution concentrations of the PS solutions. The porous structures of the fibrous mats were characterized by field emission scanning electron microscopy and Brunauer−Emmett−Teller measurements to confirm that they could be accurately controlled by tuning vapor pressure of tetrahydrofuran (THF) and N,N-dimethylformamide (DMF) solvent mixtures and PS concentrations in the solutions. As the solution concentration decreased, the average fiber diameter decreased, whereas the bead density increased dramatically to show a beads-on-string morphology. Both the specific surface area and pore volume of the fibrous mats showed a unimodal distributions centered at 1/3 THF /DMF mix ratio. Fibers formed from 5 wt % PS in the 1/3 THF and DMF mixtures had the largest specific surface area of 54.92 m2 g−1 and a pore volume of 0.318 cm3g−1, respectively.Keywords: electrospinning; nanoporous fibers; phase separation; polystyrene; solvent evaporation

In this study, we have fabricated the polyacrylonitrile (PAN) reinforced super-hydrophobic fibrous polystyrene (PS) mats via a multi-syringe electrospinning technique. The composition ratio of PS/PAN in the blend mats could be controlled by tuning the number ratios of syringes of PS/PAN. The water contact angles (WCAs) of resultant fibrous mats was decreased from 155° to 143° with the decreasing the number ratios of syringes of PS/PAN from 4/0 to 1/3. The addition of the component of PAN nanofibers in fibrous PS mats significantly improved the mechanical properties of PS mats. At a critical syringe ratio of 3/1 (PS/PAN), the mat surface showed a WCA of 150° with a three times increased tensile strength compared with the pure PS mats. Additionally, the results of field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR), and mechanical properties indicated the multi-syringe electrospinning technique is an effective approach to fabricate the large-scale well-dispersed blend fibrous mats.FE-SEM image of fibrous mat formed with the syringes ratio of 3/1 of PS/PAN. The insets show the larger magnifications and the profile of water droplet on fibrous mat.

In this study, a novel nanocomposite multilayers was deposited on the electrospun nanofibrous mats by an electrostatic layer-by-layer (LBL) self-assembly technique. The positively charged water-insoluble 2,9,16,23-tetraaminophthalocyanine copper (CuTaPc) and the negatively charged water-soluble poly(acrylic acid) (PAA) were alternately deposited on the surface of negatively charged nanofibrous cellulose mats. The cationic CuTaPc was synthesized and characterized by UV–Vis and Fourier transform infrared (FT-IR) spectroscopy. The template nanofibrous cellulose mats were obtained from the alkaline hydrolysis of electrospun nanofibrous cellulose acetate mats. The resultant nanofibrous mats were characterized by scanning electron microscopy (SEM) and FT-IR spectroscopy. The SEM images showed that the composite LBL structured films were homogeneously deposited on the surface of the nanofibers. The diameters of nanofibers increased with the number of deposition bilayers. The average thickness of each CuTaPc/PAA bilayer is about 10 nm. Additionally, the FT-IR spectra results also indicated that the CuTaPc and PAA were coated on the nanofibrous cellulose mats.

For the first time, a novel fibrous polysaccharide scaffold for cell culture was fabricated by the combination of electrospinning and electrostatic layer-by-layer (LBL) self-assembly technique. Oppositely charged chitosan (CS) and alginate (ALG) in aqueous media were alternatively deposited onto the negatively charged cellulose nanofibrous mats which hydrolyzed from electrospun cellulose acetate mats. The morphology and biocompatibility of the resultant scaffolds were investigated by regulating the pH of dipping solutions, the number of deposition bilayers, and the composition of outermost layer. Field emission scanning electron microscopy images indicated that the scaffolds possessed the fibrous structure and the thickness of CS/ALG bilayer formed on fibers was estimated in the range of 8–15 nm. The X-ray photoelectron spectroscopy results verified the existence of nitrogen element of CS on the surface of LBL films. The cell culture experiments demonstrated that the scaffolds have good biocompatibility for Beas-2B human bronchial epithelial cells in vitro.

A novel formaldehyde sensor was fabricated by electrospinning deposition of nanofibrous polyethyleneimine (PEI)/poly(vinyl alcohol) (PVA) membranes as sensitive coatings on quartz crystal microbalance (QCM). The morphology of the porous three-dimensional PEI/PVA membranes comprising fibers with diameter of 40 nm to 1.8 μm was controllable by tuning the compositions of polymers and solvents in PEI/PVA solutions. The resultant sensors showed a fast response to formaldehyde and a linear relationship upon increasing the formaldehyde concentrations due to the reversible interaction between formaldehyde molecules and amine groups of PEI. The sensor responses were reversible and reproducible towards formaldehyde in the concentration range of 10–255 ppm at room temperature. The sensitivity of fibrous membrane coated QCM sensors formed from the cosolvent of water and ethanol was three times higher than that of corresponded flat membrane coated QCM sensors when exposed to 255 ppm of formaldehyde. Relative humidity in testing chamber was proved to be the key parameter to affect the sensor sensitivity. Additionally, the fibrous PEI/PVA membrane coated QCM sensors exhibited a good selectivity to formaldehyde when tested with competing vapors.

In this study, a large-scale superhydrophobic mat surface with an enhanced mechanical property by blending polystyrene (PS) and polyamide 6 (PA6) fibers was fabricated via a four-jet electrospinning technique. The achievement of surface superhydrophobicity of electrospun mat was ascribed to the combination of micro- and nanostructured surface roughness inherent in fibrous PS mats based on the inspiration of self-cleaning silver ragwort leaves. The mechanical properties of PS mats were significantly enhanced with adding the component of PA6 nanofibers in fibrous PS mats and regulated by tuning the number ratios of jets of PS/PA6 in the four-jet electrospinning process. The hydrophobicity of the resulting blend fibrous mats was slightly decreased with decreasing the number ratios of jets of PS/PA6. The fibrous mats formed with the number ratios of jets of 2/2 (PS/PA6) showed a water contact angle of 150° with a three times increased tensile strength compared with that of the pure fibrous PS mats.

•Hierarchical-structured and flexible MnO2@SiO2 nanofibrous membranes were prepared.•The membranes possess morphologies ranged from nanowire, nanoflower to mace-like.•The membranes could cooperate with H2O2 to form the Fenton-like catalyst.•The membrane achieved superb catalytic performance towards organic dyes.Constructing nanostructured catalyst-embedded ceramic fibrous membranes would facilitate the remediation or preliminary treatment of dyeing wastewater, however, most of such membranes are brittle with low deformation resistance, thus, restricting their widely applications. Herein, the flexible and hierarchical nanostructured MnO2-immobilized SiO2 nanofibrous membranes (MnO2@SiO2 NFM) were fabricated by combining the electrospinning technique with hydrothermal method. The morphologies of membranes could be regulated from nanowires and nanoflower to mace-like structure via varying concentration of reactants. The resultant MnO2@SiO2 NFM could cooperate with hydrogen peroxide to form a Fenton-like reagent for the degradation of methylene blue (MB). The resultant membrane exhibited prominent catalytic performance towards MB, including high degradation degree of 95% within 40 min, fast degradation rate of 0.0865 min−1, and excellent reusability in 5 cycles. Moreover, the membranes could be used in a wide pH range of 0 to 14 and the degradation degree reached 76% during dynamic filtration process with a flux of 490,000 L m−2 h−1. The successful fabricating of such membrane with extraordinary catalytic performance would provide a platform for preparing high-performance catalysts for remediation of dyeing wastewater.The flexible MnO2@SiO2 nanofibrous membranes with controllable morphologies, hierarchical mesoporous structure, and enhanced catalytic performance were fabricated via the combination of electrospinning technique and hydrothermal synthesis.Download full-size image

Conventional ultrafiltration (UF) or nanofiltration (NF) filters for water treatments are based on porous membranes, where the torturous porosity usually results in a relatively low flux rate, typically manufactured by the phase immersion method. Electrospun (ES) nanofibrous membranes with a high flux rate evoked a considerable interest in the ultrafiltration or nanofiltration applications, because of their high porosity, good interconnectivity and high specific surface area. Herein, we developed a novel double layers of polyacrylonitrile (PAN) electrospun nanofibrous membranes (with an average fiber diameter of 173 nm) reinforced with TEMPO (2, 2, 6, 6-tetramethylpiperidine-1-oxyl radical) selectively oxidized jute cellulose nanowhiskers (with a diameter in the range of 3–10 nm). From FE-SEM images, the presence of evenly coated thin layer of cellulose nanowhiskers on the PAN ES nanofibers is evident. The versatile PAN/cellulose ES composite membranes with superior mechanical properties and high filtration efficiency of 7–40 nm particles would be particularly useful for applications in the domestic drinking water and industrial waste water treatment.Highlights► Jute cellulose nanowhiskers were evenly coated on PAN ES fiber mats. ► The composite membranes show special good mechanical properties. ► The composite membranes show special efficient removal capability of 7–40 nm particles. ► The composite membrane also could be used for oil/water separation.

A novel superhydrophilic and underwater superoleophobic nanofibrous membrane with a hierarchical structured skin for the separation of oil-in-water emulsions was prepared via electrospinning and electrospraying methods, and was found to exhibit excellent separation efficiency, robust antifouling properties, and extremely high flux solely driven by gravity.

Flexible, magnetic, and hierarchical porous NiFe2O4@SiO2 nanofibrous membranes were prepared by combining the gelatin method with electrospun nanofibers. The membranes exhibited prominent mechanical strength and mesoporosity, as well as multifunctionality of magnetic responsiveness, dye adsorption, and emulsion separation.

Creating porous carbonaceous membranes with durable mechanical properties and designed functionality is critical for the next generation of soft electronic devices; however, it has been proven extremely challenging. Herein, we report a facile strategy to fabricate highly porous carbon nanofibrous membranes with enhanced mechanical elasticity and intriguing functionality based on polybenzoxazine via combining multicomponent electrospinning and in situ polymerization. Tin oxide nanoclusters with diameters of 20–40 nm are homogenously distributed in the carbon matrix and on the surface of carbon nanofiber (CNF). A plausible plasticizing effect of the heterogeneous nanotextures endows the SnO2/CNF membrane with robust mechanical elasticity and durability, which can maintain its original shape after serious deformation. Moreover, the elastic SnO2/CNF membrane possesses a high surface area of 1415 m2 g−1 with a pore volume of 0.82 cm3 g−1. With their integrated properties of extraordinary mechanical properties, high porosity, large surface area, and good electrochemical properties, the as-prepared SnO2/CNF membranes exhibited a satisfactory capacitive performance with high energy density, ultralong cycling properties, and robust electrochemical stability against bending deformation, suggesting a promising usage as soft electrodes for flexible energy storage devices, and also opened up an avenue to the design of functional CNF materials with fine elasticity for various applications.

Safety remains a practical concern in lithium ion batteries (LIBs), which is closely associated with the internal shorting caused by the poor dimensional thermostability at elevated temperature and the flammability of separators. Here, we report a novel strategy to fabricate thermostable and nonflammable silica–polyetherimide–polyurethane (SiO2–PEI–PU) nanofibrous membranes via an electrospinning process. Benefiting from the high porosity, interpenetrating network structure and synergetic effect of silica nanoparticles, PEI and PU, the as-prepared SiO2–PEI–PU membranes exhibit uniform pore size distribution, high ionic conductivity (6.25 mS cm−1) and good electrochemical stability up to 4.86 V. Notably, the hot oven and combustion tests reveal that the SiO2–PEI–PU membranes possess improved thermostability displaying 2% dimensional change after exposure to 170 °C for 0.5 h and flame retardant properties, which could be beneficial for improving the safety of LIBs. Significantly, the SiO2–PEI–PU membrane based Li/LiFePO4 cell exhibits more excellent cyclability delivering a discharge capacity of 158.91 mA h g−1 at the 90th cycle and better rate capability compared with the cell based on the Celgard membrane. Meanwhile, the SiO2–PEI–PU membrane based Li/LiFePO4 cell also shows more excellent cell performance even at an elevated temperature of 60 °C. The results clearly demonstrate that the SiO2–PEI–PU membranes are promising separator candidates, which will also pave the way for further application of nanofibrous membranes in high power LIBs.

Given the dire consequences of accidental lead ion (Pb2+) exposure, a portable, sensitive and robust analytical approach capable of colorimetric visualization is highly desirable. In this study, we demonstrate a colorimetric strip that relies on a novel polydiacetylene (PDA) embedded polyacrylonitrile nanofibrous membrane (PAN NFM). The Pb2+-chromic PDA is prepared from controlled mixtures of 10,12-pentacosadiynoic acid (PCDA) and PCDA-5EG, a PCDA derivative with a pentaethylene glycol headgroup. Moreover, the Pb2+ complexation ability is manipulated by controlling the molar ratio of PCDA to PCDA-5EG. The PAN NFM acting as a three dimensional matrix is designed for PDA immobilization, thereby improving the stability, portability and sensitivity. Upon exposure to a series of metal ions, only Pb2+ could induce a color change, which clearly showed that our strip could act as a highly selective probe to detect Pb2+. Ultimately, the strip with a naked eye detection limit of 0.48 μM undergoes a brilliant color transition, from blue to red, in a concentration-dependent manner and all the color transitions of strips are quantitatively visualized by employing a chromatic framework. The findings indicate that the strip is particularly promising for visual Pb2+ recognition due to its facile functionalization, simple construction, and versatility to empower colorimetric signaling.

A novel and scalable strategy was developed for the synthesis of in situ polymerized superhydrophobic and superoleophilic nanofibrous membranes for effective separation of water-in-oil microemulsions, which exhibit an extremely high flux of 892 L m−2 h−1 solely driven by gravity, as well as good antifouling properties, thermal stability and durability.

A novel and scalable strategy was developed for the synthesis of one dimensional mesoporous polybenzoxazine-based Fe3O4@carbon nanofibers by using an in situpolymerization method, which exhibit an extremely high surface area of 1885 m2 g−1, as well as efficient adsorption for organic dyes and facilely magnetic separation property.

Creating adsorptive materials for the fast, efficient, and high-throughput adsorption and purification of proteins is critical to meet the great demands for highly purified proteins, yet it has proven to be a highly challenging task. Here, we report that cross-linked and highly carboxylated poly(vinyl alcohol) (PVA) nanofibrous membranes were fabricated by a combination of electrospinning and the in situ graft polymerization of PVA and maleic anhydride (MAH) under mild conditions. Taking advantage of the large surface area available for protein binding, the highly tortuous porous structure, and the robust mechanical properties, the resultant PVA/MAH nanofibrous membranes exhibited a good integrated adsorption performance towards lysozyme, including a superior adsorption capacity of 177 mg g−1, fast adsorption equilibrium within 4 h, good selectivity, and good reversibility. Moreover, the saturation dynamic adsorption amount towards lysozyme reached 159 mg g−1 under 750 Pa driven solely by gravity, which conformed to the specified requirements for high adsorption capacity under relatively low pressure drops. Furthermore, the adsorption performance towards a protein mixture was analyzed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and the resultant PVA/MAH nanofibrous membranes retained excellent stability under depyrogenation conditions. The successful fabrication of such fascinating nanofibrous materials by using this simple and intriguing approach may provide new insights into the design and development of adsorptive materials for the purification of proteins with superior adsorption performance.

Novel, sandwich-structured PVdF/PMIA/PVdF nanofibrous battery separators with robust mechanical strength and thermal stability are fabricated via a sequential electrospinning technique. The nanofibers of the PVdF and the PMIA layers are bonded and interconnected on the interface boundary without any polymer binder or post-treatment. Benefiting from the high porosity of the as-prepared membranes and the introduction of PMIA, the PVdF/PMIA/PVdF composite membranes exhibit high ionic conductivity (2.3 times higher than that of the Celgard membrane), robust tensile strength (13.96 MPa), and excellent thermal stability, sustaining insulation after closing the pores in the PVdF layer. Hot oven testing reveals that the composite membranes exhibit no dimension shrinkage after being exposed to 180 °C for 1 h. Furthermore, the as-prepared-membrane-based Li/LiCoO2 cell shows a higher capacity retention of 93.10% after 100 cycles and better rate performance compared with the cell using the Celgard membrane, providing new insight into the design and development of high-performance rechargeable lithium ion batteries.

Construction of nanoparticle modified titanium dioxide nanofibrous membranes (TiNFs) with a mesoporous and stable nanoparticle-nanofiber composite structure would have significant implication for environmental remediation; however, currently nanoparticle-TiNFs are generally brittle with poor structural integrity upon large deformation; thus, creating flexible, robust, and stable nanoparticle-TiNF composites has proven to be extremely challenging. Herein, we report flexible and hierarchical mesoporous TiO2 nanoparticle (TiO2 NP) modified TiNF (TiNFNPs) composites fabricated by the combination of sol–gel electrospinning and in situ polymerization. The electrospun TiNFs served as templates and a synthesized bifunctional benzoxazine (BA-a) was used as a novel carrier and fixative for non-agglomerated growth of TiO2 NPs. Benefiting from the large surface area, high porosity, homogeneity, stable nanofiber–nanoparticle composite structure, and robust mechanical properties, the as-prepared anatase TiNFNPs exhibited excellent photocatalytic activity towards methylene blue including fast degradation within 30 min, good reversibility in 4 cycles, and easiness of recycling. Moreover, the degradation products have been analysed and TiNFNPs exhibited better photodegradation performance towards methylene blue compared with a commercial catalyst (P25). Significantly, the successful synthesis of such fascinating materials may provide a versatile platform for further development of nanofibrous membrane-based photoreactors towards water and air pollutant treatment.

Creating a sensitive and selective method that can provide simple, practical and high-throughput determination of levels of Hg2+ ions in water has proved extremely challenging. This work responds to these challenges by designing, fabricating and evaluating a polyaniline (PANI) based immobilized sensor optimized to exhibit a colorimetric response to trace amount of Hg2+ ions. The sensor design is realized using a leucoemeraldine based PANI as probe, which has a specific interaction with Hg2+ and results in both “off–on” and “color-change” signals. Hierarchical structured nanofibrous sensing membranes within well immobilized probes are fabricated by a bottom-up blending electrospinning nanofabrication method. This sensor shows a vivid colorimetric response specifically to Hg2+ ions (white–yellow/green–green–blue) over other possible interfering metal cations and achieves a low detection limit of 5 nM observed by the naked eye. Additionally, the sensing responses are visualized quantitatively by employing a colorimetric framework that translates measured spectra into numeric color values directly related to color perception. Furthermore, the as-prepared sensors exhibited good reversibility after extended regeneration cycles, which suggests a promising analytical method as an economical alternative to traditional Hg2+ sensors and also provides a new insight into the design and development of a novel colorimetric sensing system based on PANI immobilized materials.

By virtue of the affinity of pyromellitic dianhydride (PMDA) for lead(II) ion (Pb2+) and the inherent structural merits of electrospun nanofibrous membranes, a novel solid-phase nanofibrous material was facilely fabricated via the modification of deacetylated cellulose acetate membranes with PMDA (DCA-PMDA). The resultant DCA-PMDA can be applied for the simultaneous naked-eye detection and removal of Pb2+ from water matrixes by simple filtration followed by treatment with Na2S solution. Importantly, the color of the DCA-PMDA changes from white to dark yellow-brown due to the formation of PbS, which can be leveraged for the colorimetric detection of Pb2+ by the naked eye with a detection limit of 0.048 μM. Under the same circumstances, the maximum adsorption capacity was determined to be as high as 326.80 mg g−1. Furthermore, the extraction of Pb2+ from DCA-PMDA was possible with HNO3. The regenerated membrane that remained maintained the high sensitivity to Pb2+ and exhibited almost the same adsorption capacity as the original membrane. Therefore, the proposed membrane offers a cost-effective material that can be considered as a viable alternative for effectively detecting and removing toxic Pb2+ from water samples.

With the aim to develop pH-paper-like lead ion (Pb2+) sensing materials, we demonstrate a colorimetric strip, which relies on a SiO2 nanoparticle (NP) decorated polydiacetylene embedded polyacrylonitrile nanofibrous membrane (PAN NFM), that undergoes a brilliant blue-to-red color transition as well as ‘Turn-On’ fluorescence upon incubation with Pb2+. The introduction of an amino acid (glycine) headgroup into a supramolecularly assembled 10,12-pentacosadiynoic acid results in a Pb2+-induced chromic conjugated polymer that is quickly photopolymerizable, rapidly responsive to Pb2+ and specifically identifiable. Moreover, the SiO2 NPs are certified as an efficient sensitivity promoter when their content reaches 0.5 wt% in the strip. With this understanding, the color change that is caused by 0.24 μM Pb2+ at ambient temperature can be easily perceived by the naked eye, which indicates the superiority of our strip compared with previous approaches, and it is also noteworthy that a fluorescent signal could also be produced in 2 min. Furthermore, RGB (red-green-blue) digital parameters obtained from images of the strips and automatic read outs via a smartphone were processed statistically through principal component analysis and then used to elaborate the standard curve and quantify Pb2+ concentration. This methodology for assaying and quantifying Pb2+ avoids time-consuming sample preparation, expensive laboratory techniques, and specialized personnel required to carry out conventional analytical methods.

Effective air filtration proposed for fibers requires their assembly into a porous structure with small pore size, low packing density, and controllable macro-structure; however, creating such filtration media has proved to be a grand challenge. Here, we introduce a strategy to create microwave structured polyamide-6/poly(m-phenylene isophthalamide) nanofiber/net (PA-6/PMIA NFN) membranes for effective air filtration by combining the electro-spinning/netting (ESN) and staple fiber intercalating process. Our approach causes the PA-6 NFN membrane composed of one-dimensional (1D) nanofibers and 2D Steiner-tree nanonets, and the embedded PMIA staple fibers, to assemble into a stable filtration medium with tunable pore size, packing density, and microwave fluctuation by facilely optimizing binary fiber construction and extrinsic staple fiber intercalation. By virtue of the integrated structural properties of small pore size (∼0.32 μm), high porosity (91.3%), and extended surface area, the resulting PA-6/PMIA NFN filter can effectively filter ultrafine airborne particles, mainly using physical sieving, with high filtration efficiency of 99.995%, low pressure drop of 101 Pa, desirable quality factor of 0.1 Pa−1, and large dust-holding capacity of >50 g m−2, which match well with the requirements for treating the real particulate matter (PM) pollutions. This work would not only provide great potential for PM2.5 governance, but also open new avenues for the design and development of stable porous membranes with controllable macro-structures for various applications.

A surprising brittle to flexible transition in ZrMxOy (M = Na, Mg, Al) nanofibrous membranes was found by varying the undersized dopant species and content. The fiber morphology, crystalline structure, and pore structure of the ZrMxOy nanofibrous membranes can be significantly modulated by varying the dopant valence from +1 to 3 and the dopant content from 1 to 20 mol%, respectively. Meanwhile, a classical Hall-Petch effect was revealed for the ZrMxOy nanofibrous membranes systems, which corresponded to a nanocrystalline size of 22.8 nm and an enhanced flexibility of 23 mN. Moreover, the substitutional solid solution and interstitial solid solution dissolution processes of Na, Mg, and Al into ZrO2 were analyzed using vacancy compensation and dopant interstitial compensation mechanisms, respectively. Most importantly, the flexible Al doped zirconia nanofibrous membranes exhibit a low infrared emissivity of 0.589 and 0.703 in the 3–5 μm and 8–14 μm wavebands, respectively, which suggests them to be a promising candidate for infrared stealth materials in the confrontation strategy field for personnel, aircraft, missiles, satellites, etc.

Particulate matter (PM) with an aerodynamic diameter of 2.5 micrometers or less (PM2.5), as one of the most hazardous air pollutants, has raised serious concerns for public health. Although individual or environmental protection could be achieved using conventional fibrous media, high performance filters usually rely on energy-intensive and bulky air-filtering media. In this work, an ultra-lightweight nylon 6–polyacrylonitrile nanofibre-nets binary (N6–PAN NNB) structured membrane, consisting of an ambigenous nanofibre framework through which run two-dimensional nano-nets, for sieving-enhanced capture of fine particles was demonstrated. The high coverage N6 nano-nets and low packing density of PAN nanofibres are certified as an efficient property promoter when the fibre spinning jet ratio of N6/PAN reaches 2/2, thereby improving the porosity, filtration efficiency, flow resistance, and stability. Upon exposure to 300 nm NaCl aerosol particles, the N6–PAN2/2 NNB membrane with a low basis weight of 2.94 g m−2 exhibited high filtration efficiency (99.99%) and desirable quality factor (0.1163 Pa−1) even though under a high flow rate (90 L min−1), significantly better results than those of glass fibre and melt-blown polypropylene fibre-based media. Ultimately, three-dimensional computer simulation based on the images of N6-15 and N6–PAN2/2 membranes after particle loading and filtration data via GeoDict were processed statistically through principal component analysis and then used to graphically express the particle deposition pattern change from surface filtration to deep bed filtration. We hope that the methodology and results presented here will encourage different approaches to diminish the negative impact of PM2.5 air pollution, in particular the frequency of haze occurrence in rapidly developing countries.

Creating a practical and energy-efficient method with high efficacy to separate oil–water mixtures, especially those stabilized by surfactants, has proven to be extremely challenging. To overcome this challenge, a novel and scalable strategy was developed for the synthesis of superhydrophilic and prewetted oleophobic nanofibrous membranes by the facile combination of in situ cross-linked polyethylene glycol diacrylate nanofibers supported on polyacrylonitrile/polyethylene glycol nanofibrous (x-PEGDA@PG NF) membranes. The as-prepared x-PEGDA@PG NF membranes have shown superhydrophilicity with ultralow time of wetting and promising oleophobicity to achieve effective separation for both immiscible oil–water mixtures and oil-in-water microemulsions solely driven by gravity. These new membranes having a good mechanical strength of 14 MPa and mean pore sizes between 1.5 and 2.6 μm have shown a very high flux rate of 10975 L m−2 h−1 with extremely high separation efficiency (the residual oil content in filtrate is 26 ppm). More importantly, the membranes exhibit high separation capacity, which can separate 10 L of an oil–water mixture continuously without a decline in flux, and excellent antifouling properties for long term use, thus making them important candidates for treating wastewater produced in industry and daily life. Such membranes are also ideal for high viscosity oil purification such as purification of crude oil.