Exploration of Blood Coagulation of N-Alkyl Chitosan Nanofiber Membrane in Vitro.

N-Alkylated chitosan (NACS) may improve the blood clotting efficiency of chitosan (CS). To study its blood coagulation capability, a series of NACSs with various carbon chain lengths and degrees of substitution (DS) of alkyl groups were synthesized and characterized by FTIR, NMR, elemental analysis, and X-ray diffraction (XRD). The corresponding NACS nanofiber membranes (NACS-NM) were subsequently fabricated by electronic spinning technique. SEM, XRD, DSC, surface area, porosity, contact angle, blood absorption, and mechanical properties were used to characterize the CS-NM/NACS-NM. Moreover, cytotoxicity, coagulation, activated partial thromboplastin time, plasma prothrombin time, thrombin time, and platelet aggregation tests were performed to evaluate the biocompatibility and blood coagulation properties of NACS-NM. The results showed that NACS-NM was not cytotoxic. NACS-NM with DS of 19.25% for N-hexane CS (CS6b), 17.87% for N-dodecane CS (CS12b), and 8.97% for N-octadecane CS (CS18a) exhibited good blood clotting performance. Moreover, NACS-NMs favored the activation of coagulation factors and platelets. In addition, intracellular Ca2+ was not related to platelet activation. The above results suggested that NACS-NM would be an effective hemostatic agent.

Hierarchical fibrous microfiltration membranes by self-assembling DBS nanofibrils in solution-blown nanofibers.

A novel hierarchical nanofibrous membrane was demonstrated via in situ self-assembly of 1,3:2,4-dibenzylidene-d-sorbitol (DBS) supramolecular fibrils in solution-blown polyacrylonitrile (PAN) nanofibers. The formed DBS fibrils were interconnected into networks and anchored onto the PAN nanofibers, which decreased the pore sizes and enhanced the mechanical properties, the filtration efficiency, and particularly the flux.

Bimetallic metal-organic framework aerogels supported by aramid nanofibers for efficient CO2 capture.

The excessive CO2 emission has gained global attentions due to its potential effects on climate change, plant nutrition deterioration, and human health and safety. Metal-organic frameworks (MOFs) featured with high specific surface area, adjustable pore size, and tailorable morphology have been widely applied for CO2 capture. However, some drawbacks of poor mechanical stability and uneven distribution of mesopores limit their further applications. Herein, we demonstrate a one-step synthesis of bimetallic center framework (OSSBCF) and pore reconstruction (PRC) strategy to prepare the hierarchical porous Zn/Co-ZIF@ANF aerogels. This unique design achieves the construction of efficient gas transfer channels and creates massive micropores with abundant Lewis basic adsorption sites. Benefiting from theses merits, the bimetallic Zn/Co-ZIF@ANF aerogels demonstrate high MOFs loading mass of 47.51 wt%, high specific surface area of 686.39 m2g-1, and large porosity of 99.31 %. Moreover, the bimetallic Zn/Co-ZIF@ANF aerogels exhibit an enhanced CO2 adsorption capacity of 5.99 mmol/g and CO2/N2 adsorption selectivity of 35 at 25 °C and 1 bar. The CO2 capacity of bimetallic Zn/Co-ZIF@ANF aerogels keep up to 95.19 % after ten cycles of CO2 adsorption, indicating the excellent long-term recycle stability. Therefore, this study provides a promising strategy to engineer hierarchical porous bimetallic MOF aerogels toward practical CO2 capture.

High-performance, breathable and flame-retardant moist-electric generator based on asymmetrical nanofiber membrane assembly.

Moist-electric generators (MEGs), which are capable of spontaneously generating energy from ubiquitous moisture, are considered as a potential power supply candidate for wearable electronics. However, the application of the MEGs in the wearable field is still challenging due to the low electric output and the lack of wearable attributes such as breathability and flame retardancy. Herein, we demonstrated a wearable MEG with high power-output, breathability and flame retardancy, which was fabricated by designing an asymmetrical nanofiber assembly using hydrophilic polyvinyl alcohol/phytic acid (PVA/PA) and hydrophobic polyvinylidene difluoride (PVDF) nanofiber membranes. Owing to the synergistic effects of strong water absorption, enhanced ion release and numerous micro-nano transport channels, a single MEG of 1 cm2 could constantly generate high direct-current (DC) power, i.e., a voltage of 1.0 V, a current of 15.5 µA, and a power density of 3.0 µW cm-2, outperforming other reported nanofiber-based MEGs. More importantly, the asymmetric nanofiber structure ensured the moisture circulation inside MEG and thus produced a sustained voltage output for 7 days without any deterioration. The MEG also showed good flexibility, air/moisture permeability and flame retardancy, which give it necessary wearable attributes. Furthermore, large-scale integration of MEG units could be readily realized to fabricate a power source device for driving different portable electronics, while the moisture sensitivity made the MEG well used for sensing applications (e.g., respiration monitoring, fire warning).

NaBiS2 decorated polysaccharide sponges for adsorption-photocatalytic degradation of dye under visible light illumination.

Dye is emissions aggravating aquatic ecosystem pollution, and photocatalysis is considered the most appealing option to remove dyes by degradation. However, the current photocatalysts suffer from agglomeration, large bandgaps, high mass transfer resistance, and high operation cost. Herein, we present a facile hydrothermally induced phase separation and in situ synthesis strategy for fabrication of sodium bismuth sulfide (NaBiS2)-decorated chitosan/cellulose sponges (NaBiCCSs). The NaBiCCSs demonstrate unique polysaccharide cellular structure (150-500 µm), uniformly immobilized NaBiS2 nanoparticles (70-90 nm), narrow bandgap (1.18 eV), high photocurrent (0.74 µA/cm2), and outstanding compressibility. Benefiting from the characteristics and the high affinity to dyes, the NaBiCCSs provide innovative synergistic adsorption-photocatalytic degradation model for dye removal, attaining a superior methylene blue removal rate of 98.38 % under visible light illumination and offering good reusability. This study offers a sustainable technical solution for dye contaminant removal.

Aramid nanofibers supported metal-organic framework aerogel for protection of chemical warfare agent.

Protective fabrics containing Zr-Based Metal-Organic Frameworks (Zr-MOFs) show great potential in the detoxification of chemical warfare agents (CWAs). However, the current studies still face the challenges of complicated fabrication processes, limited MOF loading mass, and insufficient protection. Herein, we developed a lightweight, flexible and mechanical robust aerogel by in situ growth of UiO-66-NH2 onto aramid nanofibers (ANFs) and assembly of UiO-66-NH2 loaded ANFs (UiO-66-NH2@ANFs) into 3D hierarchically porous architecture. The UiO-66-NH2@ANF aerogels feature high MOF loading of 261 %, high surface area of 589.349 m2 g-1, open and interconnected cellular structure, which provide efficient transfer channels and promote catalytic degradation of CWAs. As a result, the UiO-66-NH2@ANF aerogels demonstrate high 2-chloroethyl ethyl thioether (CEES) removal rate at 98.9 % and a short half-life of 8.15 min. Moreover, the aerogels present good mechanical stability (recovery rate of 93.3 % after 100 cycles under 30 % strain), low thermal conductivity (λ of 25.66 mW m-1 K-1), high flame resistance (LOI of 32 %) and good wearing comfortableness, indicating promising potential in multifunctional protection against CWAs.

Flexible nanofibrous membranes of dual metallic metal-organic framework with enhanced Lewis basic sites and high loading mass for efficient CO2 capture.

Excessive CO2 emissions and the resultant global warming present significant environmental challenges, posing threats to human health and public safety. Metal-organic frameworks (MOFs), known for their high specific area and large porosity, hold the promise for CO2 capture. However, a major obstacle is the low loading mass of MOFs and the limited interface affinity and compatibility between MOFs and substrates. In this study, we present an electrospinning-assisted in-situ synthesis dual metallic framework strategy for preparing flexible Zn/Co-ZIF nanofibrous membranes (NFMs). This method achieves the high loading mass of MOFs and introduces abundant Lewis basic sites, thereby enhancing the CO2 adsorption. The dual metallic Zn/Co-ZIF NFMs exhibit remarkable features, including high MOF loading mass (70.23 wt%), high specific surface area (379.63 m2g-1), large porosity (92.34 %), high CO2 adsorption capacity (4.43 mmol/g), high CO2/N2 adsorption selectivity (37), and high CO2/CH4 adsorption selectivity (31). Moreover, the dual metallic Zn/Co-ZIF NFMs demonstrate robust structural stability and durability attributed to the excellent interface affinity between MOFs and NFMs, retaining 96.56 % of their initial capacity after 10 adsorption-desorption cycles. This work presents a prospective direction for developing flexible dual metallic MOF NFMs for the efficient capture of CO2.

Hierarchically Structured Carbon Nanofiber-Enabled Skin-Like Strain Sensors with Full-Range Human Motion Monitoring and Autonomous Self-Healing Capability.

Flexible strain sensors that mimic the properties of human skin have recently attracted tremendous attention. However, integrating multiple functions of skin into one strain sensor, e.g., stretchability, full-range motion response, and self-healing capability, is still an enormous challenge. Herein, a skin-like strain sensor was presented by the construction of hierarchically structured carbon nanofibers (CNFs), followed by encapsulation of elastic self-healing polyurethane (PU). The hierarchical sensing structure was composed of diversified CNFs with orientations from highly aligned to randomly oriented, and their different fracture mechanisms enabled the resultant strain sensor to successfully integrate key sensing properties including high sensitivity (gauge factor of 90), wide sensing range (∼80% strain), and fast response (52 ms). These properties, combined with high stretchability (870%) and excellent stability (>2000 cycles), allowed the sensor to precisely detect full-range human motions from large joint motions to subtle physiological signals. Moreover, the strain sensor had spontaneous self-healing capability at room temperature with high healing efficiencies of 97.7%, while the healing process could substantially be accelerated by the natural sunlight (24 h → 0.5 h). The healed sensor possessed comparable stretchability, sensing performance, and accurate monitoring ability of subtle body signals with the original sensor. The biomimetic self-healing functionality along with skin-like sensing properties makes it attractive for next-generation wearable electronics.

In situ synthesis of ZnS nanoparticles onto cellulose/chitosan sponge for adsorption-photocatalytic removal of Congo red.

Developing an efficient and sustainable approach for removing dyes from wastewater remains a challenge. Herein, we report a facile and reliable strategy to create ZnS nanoparticles (NPs) supported by cellulose/chitosan sponge (ZnCCSs) via hydrothermal decomposition of xanthates and in situ synthesis of ZnS NPs. ZnCCSs demonstrate high porosity, low bulk density, outstanding compressibility, and uniformly immobilized ZnS NPs. Benefiting from the affinity sites of polysaccharide sponge skeleton and highly exposed ZnS NPs, ZnCCSs show an excellent synergistic effect of adsorption and photocatalytic degradation performances in removing Congo red pollutants. By regulating the structure through the ratio of components, ZnCCSs show a high removal ratio of 96.53% and excellent stability after reusability cycles. The adsorption and degradation behavior and the photodegradation mechanism are also investigated through trapping experiments. This study provides a promising way of removing dye contaminants through a combination of various mechanisms.

Hybrid nanofibrous aerogels for all-in-one solar-driven interfacial evaporation.

Solar-driven interfacial evaporation is an emerging technology to obtain fresh water using solar energy. However, the complicated system and the corresponding fabrication process severely restrict its large-scale and cost-effective production. Herein, an all-in-one solar-driven interfacial evaporator was fabricated via a hybrid nanofibrous aerogel of aramid nanofibers (ANFs), carbon nanotubes (CNTs), and gold nanoparticles (AuNPs). Assisted by the reprotonation of the ANFs, CNTs are assembled into the nanofibrous network for through-body light-to-heat activity, and AuNPs are set on the surface layer to enhance solar absorption. The aerogel also features low thermal conductivity to suppress heat losses and high capillary action to wick and confine water within the aerogels. Benefitting from the synergistic effect, the aerogel shows a high evaporation rate of 1.53 kg m-2h-1 and an evaporation efficiency of 91.3% under 1 sun irradiation. Simultaneously, the evaporator demonstrates high purification capacity for wastewaters with dyes and heavy metal ions. The integrated structure design and facile fabrication process would make the hybrid nanofibrous aerogel-based all-in-one evaporators promising for cost-effective and large-scale application under ambient solar irradiance.

Proton Donor-Regulated Mechanically Robust Aramid Nanofiber Aerogel Membranes for High-Temperature Thermal Insulation.

High-performance thermal insulators are urgently desired for energy-saving and thermal protection applications. However, the creation of such materials with synchronously ultralow thermal conductivity, lightweight, and mechanically robust properties still faces enormous challenges. Herein, a proton donor-regulated assembly strategy is presented to construct asymmetric aramid nanofiber (ANF) aerogel membranes with a dense skin layer and a high-porous nanofibrous body part. The asymmetric structure originates from the otherness of the structural restoration of deprotonated ANFs and the resulting ANF assembly due to the diversity of available proton concentrations. Befitting from the synergistic effect of the distinct architectures, the resulting aerogel membranes exhibit excellent overall performance in terms of a low thermal conductivity of 0.031 W·m-1·K-1, a low density of 19.2 mg·cm-3, a high porosity of 99.53%, a high tensile strength of 11.8 MPa (16.5 times enhanced), high heat resistance (>500 °C), and high flame retardancy. Furthermore, a blade-scraping process is further proposed to fabricate the aerogel membrane in a continuous and scalable manner, as it is believed to have potential applications in civil and military fields.

In situ loading MnO2 onto 3D Aramid nanofiber aerogel as High-Performance lead adsorbent.

Fabricating a high-performance adsorbent as a desirable candidate for removing Pb2+ from aqueous water remains a challenge. Aramid nanofibers (ANFs) are promising building blocks that have realized multifunctional applications due to their intrinsic mechanical and chemical stability. Herein, an in situ loading strategy for preparing nanofiber composite aerogel was proposed by assembling ANFs into a 3D aerogel and applying it as host media for the in situ polymerization of pyrrole followed by facile redox reaction between the polypyrrole (PPy) and MnO4-1 to load manganese dioxide (MnO2). The idea was to fully exploit the structural advantages of ultra-low bulk density, large specific surface area, and high porosity of ANFs, and the possible chemical adsorption characteristics of MnO2 on the basis of ion exchange reaction. The adsorption capacity of 3D ANF/MnO2 composite aerogel was as large as 554.36 mg/g for Pb2+. The adsorption mechanism based on an exchange reaction between Pb2+ and protons on the surface of MnO2 was also investigated. The desorption results showed that the adsorption performance could remain up to 90% after five times of usage. In conclusion, this research provides promising insights into the preparation of high-performance lead adsorbent for water treatment.

Hot-Pressed Wet-Laid Polyethylene Terephthalate Nonwoven as Support for Separation Membranes.

In this work, a polyethylene terephthalate (PET) nonwoven support was prepared by wet-laid and hot-press technology and used as support for separation membranes. The properties of the PET nonwoven support were studied to determine the effect of hot-pressing parameters and PET fiber ratio, and were optimized by response surface methodology. Result showed that the PET nonwoven support with 62% low melting point PET (LPET-180) fibers obtained satisfactory properties and structure after hot pressing at 220 °C under the pressure of 9 MPa for 20 s. The response surface analysis indicated that the temperature and time of hot pressing and the fiber ratio were the most important factors affecting the strength and air permeability of the PET nonwoven support. After hot pressing, the PET nonwoven support exhibited interconnected structure, small pore size, low porosity, and high strength. Then phase inversion technique was applied to prepare a polysulfone (PSF) layer on the PET nonwoven support and an ultra-thin polyamide (PA) active layer was prepared by interfacial polymerization on the PSF layer. The practicality of PET nonwoven support was verified by testing the pure water flux and retention of the PA composite membrane and the structural change of the PA composite membrane before and after use. The results proved the feasibility and remarkable application prospects of hot-pressed wet-laid PET nonwoven support as support for separation membranes.

In Situ Synthesis of Au Nanoparticles on Viscose Cellulose Sponges for Antibacterial Activities.

Antibacterial viscose cellulose sponges (VCSs) were fabricated by heating cellulose xanthogenate (viscose) containing HAuCl4·nH2O. Viscose was used as the reducing agent and stabilizer for the in situ synthesis of Au nanoparticles (AuNPs) onto the VCSs. The morphology, structures, thermal properties, mechanical performance, and antibacterial activities of the sponges were investigated. Results indicate that AuNPs were uniformly immobilized in the VCSs, and the resulting complexes (AuNPs@VCSs) showed enhanced thermal stability and mechanical properties. Additionally, the AuNPs@VCSs exhibited remarkable antibacterial activities, with zone of inhibition diameter of 35.7 and 37.1 mm for Staphylococcus aureus and Escherichia coli, respectively. The process is simple and applicable at the industrial level and can be applied to the fields of cleaning and sanitation.

Solution Blown Nylon 6 Nanofibrous Membrane as Scaffold for Nanofiltration.

In this work, a nylon 6 nanofibrous membrane was prepared via solution blowing technology and followed hot-press as scaffold for nanofiltration. The structure and properties of the hot-pressed nylon 6 nanofibrous membrane (HNM) were studied the effect of hot-pressing parameters and areal densities. Then an ultra-thin polyamide (PA) active layer was prepared by interfacial polymerization on HNM. The effects of nanofibrous scaffolds on the surface properties of ultra-thin nanofiltration membranes and their filtration performance were studied. Results showed that the nylon 6 nanofibers prepared at a concentration of 15 wt % had a good morphology and diameter distribution and the nanofibers were stacked more tightly and significantly reduced in diameter after hot pressing at 180 °C under the pressure of 15 MPa for 10 s. When the porous scaffold was prepared, HNM with an areal density of 9.4 and 14.1 g/m² has a better apparent structure, a smaller pore size, a higher porosity and a greater strength. At the same time, different areal densities of HNM have an important influence on the preparation and properties of nanofiltration membranes. With the increase of areal density, the uniformity of HNM increased while their surface roughness and pore size decreased, which is beneficial to the establishment of PA barrier layer. With areal density of 9.4 and 14.1 g/m², the as-prepared nanofiltration membrane has a smoother surface and more outstanding filtration performance. The pure water flux is 13.1 L m-2 h-1 and the filtration efficiencies for NaCl and Na2SO4 are 81.3% and 85.1%, respectively.

Proton-Conducting Poly-γ-glutamic Acid Nanofiber Embedded Sulfonated Poly(ether sulfone) for Proton Exchange Membranes.

Development and fabrication of novel proton exchange membranes (PEMs) with excellent performance have a great significance to the commercial application of PEM fuel cell. Inspired from the proton-conducting mechanism, γ-poly(glutamic acid) (γ-PGA) nanofibers (NFs) are first fabricated by solution blowing with the help of polylactic acid (PLA) and designed to form amino acid arrays as efficient proton channels for PEMs. The NFs with 50% γ-PGA exhibit a high proton conductivity of 0.572 S cm-1 at 80 °C/50% relative humidity (RH), and 1.28 S cm-1 at 40 °C/90% RH. Density functional theory is carried out to explain the mechanisms of proton hopping in γ-PGA, and the activation energy barriers from NH to COO- for trans and cis conformations under anhydrous conditions are only 0.64 and 0.62 eV, respectively. Then the γ-PGA/PLA NFs are incorporated into sulfonated poly(ether sulfone) to prepare PEMs, which show remarkable performance compared with the Nafion membrane. The composite membrane with 30 wt % NFs exhibits the highest proton conductivity (0.261 S cm-1 at 80 °C/100% RH). The direct methanol fuel cells with this membrane show a maximum power density (202.3 mW cm-2) among all of the PEMs, showing great application potential in the field of PEMs.

Magnetic field alignment of stable proton-conducting channels in an electrolyte membrane.

Proton exchange membranes with short-pathway through-plane orientated proton conductivity are highly desirable for use in proton exchange membrane fuel cells. Magnetic field is utilized to create oriented structure in proton exchange membranes. Previously, this has only been carried out by proton nonconductive metal oxide-based fillers. Here, under a strong magnetic field, a proton-conducting paramagnetic complex based on ferrocyanide-coordinated polymer and phosphotungstic acid is used to prepare composite membranes with highly conductive through-plane-aligned proton channels. Gratifyingly, this strategy simultaneously overcomes the high water-solubility of phosphotungstic acid in composite membranes, thereby preventing its leaching and the subsequent loss of membrane conductivity. The ferrocyanide groups in the coordinated polymer, via redox cycle, can continuously consume free radicals, thus helping to improve the long-term in situ membrane durability. The composite membranes exhibit outstanding proton conductivity, fuel cell performance and durability, compared with other types of hydrocarbon membranes and industry standard Nafion® 212.

Preparation and Properties of sc-PLA/PMMA Transparent Nanofiber Air Filter.

Particulate matter (PM) pollution is a serious concern for the environment and public health. To protect indoor air quality, nanofiber filters have been used to coat window screens due to their high PM removal efficiency, transparency and low air resistance. However, these materials have poor mechanical property. In this study, electrostatic induction-assisted solution blowing was used to fabricate polylactide stereocomplex (sc-PLA), which served as reinforcement to enhance the physical cross-linking point to significantly restrict poly(methyl methacrylate) (PMMA) molecular chain motion and improve the mechanical properties of sc-PLA/PMMA nanofibers. Moreover, the introduction of sc-PLA led to the formation of thick/thin composite nanofiber structure, which is beneficial for the mechanical property. Thus, sc-PLA/PMMA air filters of ~83% transparency with 99.5% PM2.5 removal and 140% increase in mechanical properties were achieved when 5 wt % sc-PLA was added to PMMA. Hence, the addition of sc-PLA to transparent filters can effectively improve their performance.

Self-Assembly DBS Nanofibrils on Solution-Blown Nanofibers as Hierarchical Ion-Conducting Pathway for Direct Methanol Fuel Cells.

In this work, we reported a novel proton exchange membrane (PEM) with an ion-conducting pathway. The hierarchical nanofiber structure was prepared via in situ self-assembling 1,3:2,4-dibenzylidene-d-sorbitol (DBS) supramolecular fibrils on solution-blown, sulfonated poly (ether sulfone) (SPES) nanofiber, after which the composite PEM was prepared by incorporating hierarchical nanofiber into the chitosan polymer matrix. Then, the effects of incorporating the hierarchical nanofiber structure on the thermal stability, water uptake, dimensional stability, proton conductivity, and methanol permeability of the composite membranes were investigated. The results show that incorporation of hierarchical nanofiber improves the water uptake, proton conductivity, and methanol permeability of the membranes. Furthermore, the composite membrane with 50% hierarchical nanofibers exhibited the highest proton conductivity of 0.115 S cm-1 (80 °C), which was 69.12% higher than the values of pure chitosan membrane. The self-assembly allows us to generate hierarchical nanofiber among the interfiber voids, and this structure can provide potential benefits for the preparation of high-performance PEMs.

Cellulose nanofiber-embedded sulfonated poly (ether sulfone) membranes for proton exchange membrane fuel cells.

Cellulose nanofibers were embedded into sulfonated poly (ether sulfone) matrix to heighten the water retention and proton conductivity of proton exchange membranes (PEMs). Cellulose nanofibers were obtained by hydrolyzing cellulose acetate nanofibers, which were prepared via electrostatic-induction-assisted solution blow spinning. Morphology, thermal stability, and mechanical properties of the PEMs were investigated. The results showed that proton conductivity, water uptake, and methanol permeability of the composite membranes were improved. Hydrophilicity of the composite membranes was gradually improved with the addition of nanofibers. When the content of nanofibers was 5 wt%, the highest proton conductivity was 0.13 S/cm (80 °C, 100% RH). Therefore, the cellulose nanofiber could be used as support materials to enhance the performance of proton exchange membranes, the composite membranes have potential application in Direct methanol fuel cells (DMFCs).