Flexible Nanofibrous Membranes Research Articles

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 (70.23wt%), high specific surface area (379.63 m2g-1), large porosity (92.34%), high CO2 adsorption capacity (4.43mmol/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.

Liquid metal integrated PU/CNT fibrous membrane for human health monitoring.

Wearable flexible sensors are widely used in several applications such as physiological monitoring, electronic skin, and telemedicine. Typically, flexible sensors that are made of elastomeric thin-films lack sufficient permeability, which leads to skin inflammation, and more importantly, affects signal detection and consequently, reduces the sensitivity of the sensor. In this study, we designed a flexible nanofibrous membrane with a high air permeability (6.10mm/s), which could be effectively used to monitor human motion signals and physiological signals. More specifically, a flexible membrane with a point (liquid metal nanoparticles)-line (carbon nanotubes)-plane (liquid metal thin-film) multiscale conductive structure was fabricated by combining liquid metal (LM) and carbon nanotubes (CNTs) with a polyurethane (PU) nanofibrous membrane. Interestingly, the excellent conductivity and fluidity of the liquid metal enhanced the sensitivity and stability of the membrane. More precisely, the gauge factor (GF) values of the membrane is 3.0 at 50% strain and 14.0 at 400% strain, which corresponds to a high strain sensitivity within the whole range of deformation. Additionally, the proposed membrane has good mechanical properties with an elongation at a break of 490% and a tensile strength of 12MPa. Furthermore, the flexible membrane exhibits good biocompatibility and can efficiently monitor human health signals, thereby indicating potential for application in the field of wearable electronic devices.

Enhancement of Piezoelectric Properties of Flexible Nanofibrous Membranes by Hierarchical Structures and Nanoparticles.

Piezoelectric nanogenerators (PENGs) show superiority in self-powered energy converters and wearable electronics. However, the low power output and ineffective transformation of mechanical energy into electric energy l limit the role of PENGs in energy conversion and storage devices, especially in fiber-based wearable electronics. Here, a PAN-PVDF/ZnO PENG with a hierarchical structure was designed through electrospinning and a hydrothermal reaction. Compared with other polymer nanofibers, the PAN-PVDF/ZnO nanocomposites not only showed two distinctive diameter distributions of uniform nanofibers, but also the complete coverage and embedment of ZnO nanorods, which brought about major improvements in both mechanical and piezoelectric properties. Additionally, a simple but effective method to integrate the inorganic nanoparticles into different polymers and regulate the hierarchical structure by altering the types of polymers, concentrations of spinning solutions, and growth conditions of nanoparticles is presented. Further, the designed P-PVDF/ZnO PENG was demonstrated as an energy generator to successfully power nine commercial LEDs. Thus, this approach reveals the critical role of hierarchical structures and processing technology in the development of high-performance piezoelectric nanomaterials.

Photo and thermal crosslinked poly(vinyl alcohol)-based nanofiber membrane for flexible gel polymer electrolyte

Novel dual crosslinked nanofibrous membranes (DCNMs) were fabricated by a combination of UV-photocrosslinking and thermal sol-gel crosslinking procedures and used as a matrix for gel polymer electrolytes for lithium-ion batteries (LIBs). Flexible nanofibrous membranes were obtained from the solution of poly(vinyl alcohol) (PVA), maleated PVA (PVA-MA), polyethylene glycol diacrylate (PEGDA), and tetraethyl orthosilicate (TEOS) by electrospinning technique. As a matrix for gel polymer electrolyte (GPE), it showed significantly higher ionic conductivity of 1.98 × 10−3 S cm−1 than the commercial separators and pure PVDF based GPE. Incorporation of TEOS into the membrane composition, and formation of siloxane bonds (Si–O–Si) greatly increased the conductivity providing excellent mechanical and thermal stability. The assembled lithium metal cell with LiFePO4 cathode exhibited excellent cycling performance and delivered a high reversible capacity of 133 mA h g−1 at 0.1 C and retained 87% of the initial discharge capacity after 150 cycles with a stable coulombic efficiency near 100%. The GPE could substantially suppressed the growth of Li dendrites during the stably cycles up to 1000 h, while the cell with the commercial separator failed within 800 h. In consequence, this novel DCNM possesses a potential for application in flexible and safe Li-ion and Li-metal batteries.

Electrospun flexible nanofibrous membranes for oil/water separation

This review focuses on electrospun flexible nanofibrous membranes with tunable wettability for oil/water separation, and future perspectives are discussed.

Ultrahigh Metal-Organic Framework Loading and Flexible Nanofibrous Membranes for Efficient CO2 Capture with Long-Term, Ultrastable Recyclability.

In the global transition to a sustainable low-carbon economy, CO2 capture and storage technology plays a key role in reducing emissions. Metal-organic frameworks (MOFs) are crystalline materials with ultrahigh porosity, tunable pore size, and rich functionalities, holding the promise for CO2 capture. However, the intrinsic fragility and depressed processability of MOF crystals make the fabrication of the flexible MOF nanofibrous membrane (NFM) rather challenging. Herein, we demonstrate an effective strategy for the versatile preparation of self-supported and flexible HKUST-1 NFM with ultrahigh HKUST-1 loading (up to 82 wt %) and stable and uniform HKUST-1 growth through the combination of electrospinning, multistep seeded growth, and activation process. The loading rate of MOF is the highest level among the reported analogues. Significantly, the HKUST-1 NFM exhibits a prominent CO2 adsorption capacity of 3.9 mmol g-1, good CO2/N2 selectivity, and remarkable recyclability. The CO2 capacity retains ∼95% (3.7 mmol g-1) of the initial value after 100 adsorption-desorption cycles, indicating that the HKUST-1 NFM has long-term and ultrastable recyclability and a significant practical value. Thus, the low-cost and scalable production pathway is able to convert MOF particles into self-supported and flexible NFMs, and thereby, they are better applied to the efficient postcombustion CO2 capture.

Facile preparation of super-hydrophobic nanofibrous membrane for oil/water separation in a harsh environment

Oil removal or oil/water separation from the industrial waste water especially under harsh environment such as acid and alkali solutions have now been becoming an urgent task for human being. Here, flexible nanofibrous membrane with super-hydrophobicity/super-oleophilicity was prepared through a facile one-step solution-immersion approach, i.e., the poly(vinylidene fluoride) nanofiber mat modified with methyltrichlorosilane (MTS). The nanostructured polysiloxane with different morphologies including the ultrathin cylindrical wires and particles, were present on the nanofiber surface after MTS hydrolysis and subsequent condensation, which significantly enhanced the surface roughness and hence the hydrophobicity of the membrane. The influence of MTS concentration in the n-hexane solution and the hydrolysis time of MTS on the morphology of polysiloxane decorated nanofiber and hence the super-hydrophobicity was investigated in detail. The super-hydrophobic nanofibrous membrane could repel hot water and corrosive solutions, and the contact angle maintained around 150° with a pH ranging from 1 to 13. It was found that the oil/water separation with a high flux and efficiency was achieved by using the nanofibrous membrane that could not only separate the oil with the pure water and hot water but also the corrosive solution including the salt, acid and alkali solution. The organic/inorganic hybrid nanofibrous membrane may have find its potential applications in oil/water separation under a harsh environment.

Separation of organic liquid mixture by flexible nanofibrous membranes with precisely tunable wettability

Separation of liquid mixtures, especially organic liquid mixtures, is widely used in industrial processes but still faces challenges with respect to separation in a high-efficiency, low-energy mode. In this work, we report a flexible wettability-tunable nanofibrous membrane composed of a high-performance fluoro-polymer as the matrix and fluorosilane as a surface energy regulator that can be successfully applied in immiscible organic liquid mixture separation. The separation is achieved by tuning the surface energy of a membrane to a value between the surface tensions of two organic liquids. Moreover, for use in different mixed liquid systems, we programmatically designed nanofibrous membranes with the proper surface energy that could intercept the relatively high surface tension liquid and allow the low surface tension liquid to pass through. These membranes are expected to become a competitive candidate for complex organic chemical product separation, resource recycling, and environmental protection. Polymer nanofibre membranes with tunable wetting properties can match the surface tension of complex liquids and separate them. Purifying organic liquids with similar physical properties often requires energy-intensive methods. However, a membrane developed by Yong Zhao from Beihang University in China and colleagues offers high-throughput separation, thanks to incorporate of ‘dopants’ made from long silicon fluorocarbon chains, which repel both water and oil, into electrospun nanofibres made from poly(vinylidene fluoride-co-hexafluoropropylene enabled the team to selectively adjust membrane wetting to match organic liquid targets. With organic liquids having slightly different surface tensions, such as propylene glycol and benzene solutions, the membranes intercepted the high-surface tension liquid while the other passed through spontaneously. The flexible membrane offers improved mechanical properties over conventional ceramic membranes and is promising for cleaning oil spills and treating other environmental problems. Organic liquid separation is currently an important but troublesome issue, which closely related to resource recycling and environmental protection. Here we reported a wettability-tunable nanofibrous membrane that can be used for efficient separation of wide ranges of immiscible organic liquid mixtures.

Effect of constrained annealing on the mechanical properties of electrospun poly(ethylene oxide) webs containing multiwalled carbon nanotubes

ABSTRACTIn this work, flexible nanofibrous membranes (mats) of poly(ethylene oxide) (PEO) with and without multiwall carbon nanotubes (MWNTs) were fabricated by electrospinning. The effects of annealing and MWNT concentration on mat morphology, MWNT dispersion within the nanofibers, and the mechanical properties of electrospun mats were studied. Annealing temperatures ranged from 60 °C to 64 °C [near the melting temperature (64 °C via differential scanning calorimetry)] for 4 minutes. Samples were annealed with and without applied tension (constrained and unconstrained annealing). Annealing at the highest temperature (64 °C), before the loss of fibrous morphology, significantly improved fiber–fiber bonding and therefore the tensile strength of the mats. Compared with unconstrained annealing, constrained annealing introduced fiber alignment (and therefore molecular orientation) along the tensile axis (direction of constraint) during annealing and resulted in a significant increase in modulus for all samples (with and without MWNTs). The use of constrained annealing may be a facile approach to enhance modulus in nanofibrous mats while maintaining high porosity. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 787–796

Nickel Ferrite Nanoparticles Anchored onto Silica Nanofibers for Designing Magnetic and Flexible Nanofibrous Membranes.

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.