Flexible Nanofibers Research Articles

Porous Carbon Nanofiber Flexible Membranes via a Bottlebrush Copolymer Template for Enhanced High-Performance Supercapacitors.

We report a method to construct ordered hierarchical porous structures in carbon nanofiber membranes using poly(ethylene oxide)-block-polydimethylsiloxane bottlebrush block copolymers (BBCPs) as templates. The BBCPs self-assemble into a spherical morphology driven by small-molecule hydrogen bond donors which act as bridges between carbon precursors and templates to promote uniform dispersion of the templates. We successfully obtained flexible, self-supporting, and porous carbon nanofiber membranes (PCNFs) with high porosity. Then, a supercapacitor electrode was independently prepared using PCNFs as an active substance without infiltrating any conductive agents or binders. The PCNFs exhibit excellent performance with a capacitance of 234.1 F g-1 at a current density of 1 A g-1 owing to the abundant hierarchical porous structures and high content of nitrogen and oxygen elements internally. The aqueous symmetric supercapacitor prepared using PCNFs electrodes maintains more than 95% capacitance retention after 55,000 charge-discharge cycles. Furthermore, the capacitance retention reaches up to 67.72% at a current density of 50 A g-1 (compared to 1 A g-1), exhibiting excellent cycling stability and rate capability. Based on the excellent electrochemical performance and flexible self-supporting ability of PCNFs, this work is expected to facilitate the development of flexible displays, flexible sensors, wearable devices, and electrocatalysis.

Multifunctional nanofiber mat for high temperature flexible sensors based on electrospinning

The application environment and scenarios of flexible sensors are limited by the low temperature tolerance of the flexible substrate and the lack of protection of the sensitive layer surface. A flexible alumina-silicon oxide composite nanofiber mat (Al2SiO5) with high-temperature resistance is obtained based on electrospinning technique. The maximum tensile strength of the nanofiber mat reach 3.09 MPa and the maximum withstanding temperature exceeds 973 °C through parameter optimization. The patterned functional thin films are successfully prepared on the flexible Al2SiO5 nanofiber mat by using magnetron sputtering technology, vacuum vapor deposition technology and ink jet printing technology and other coating processes. Meanwhile, the process characteristics of the nanofiber mat prepared by electrospinning technique are fully utilized to realize flexible packaging of the high-temperature flexible sensors. Multifunctional nanofiber mats prepared based on electrospinning have great prospects for future applications in the field of flexible sensors.

Flexible and robust nanofiber sponge with superior capacity to transport water for efficient and sustained solar-driven interfacial evaporation

Solar-driven interfacial evaporation is an emerging route for desalination and wastewater treatment with great potential to alleviate freshwater shortages. However, the current solar-driven interfacial evaporation systems generally suffer from complex design, poor customization and salt accumulation issues. Design and preparation of solar-driven interfacial evaporation systems with excellent comprehensive performance and capable of being mass-produced remains a great challenge. Herein, we demonstrate a novel electrospun nanofiber sponge for efficient and sustained solar-driven interfacial evaporation. The nanofibrous structure of its surface can promote the absorption of light, and its interconnected pore structure is conducive to the diffusion of water vapor, thereby improving the evaporation effect. Under 1 sun irradiation (1 kW·m−2), the nanofiber sponge interfacial evaporation system showed an outstanding water evaporation rate (1.57 kg·m−2·h−1) with 95.6 % evaporation efficiency. The hierarchical porous structure, super-hydrophilic properties and integrated design of evaporation and mass transfer make it have superior water transport capacity and excellent salt self-discharge performance. Simultaneously, the excellent strength, flexibility, and processability of the nanofiber sponge can realize the customized fabrication of solar interfacial evaporation systems. This work is expected to advance the development of solar-driven interfacial evaporation systems toward compact, independent and portable.

Flexible Janus-structured porous fluorescent nanofibers with white-light emission

Flexible porous Janus-structured fluorescent nanofibers with efficient white-light emission and excellent hydrophobicity are obtained via a side-by-side electrospinning technique.

Electrospun flexible magnesium-doped silica bioactive glass nanofiber membranes with anti-inflammatory and pro-angiogenic effects for infected wounds.

Antibacterial, anti-inflammatory, and pro-angiogenic properties are prerequisites for dressing materials that accelerate the healing process of infected wounds. Herein, we report a magnesium-doped silica bioactive glass (SiO2/MgO) nanofiber membrane prepared by electrospinning. Our results demonstrate that this SiO2/MgO nanofiber membrane has good flexibility and hydrophilicity, which give it intimate contact with wound beds. In vitro assessments illustrate its good cytocompatibility and bioactivity that contribute to its robust cell proliferation and angiogenesis. It shows capacity in modulating the cellular inflammatory response of murine macrophages. In addition, in vitro assays prove its good antibacterial activity against both Gram-positive and Gram-negative strains. In a full-thickness skin defect inoculated with Staphylococcus aureus in mice, it effectively inhibits bacterial infection. Both gene expression and histological/immunohistochemical analyses confirmed the down-regulated pro-inflammatory factors, up-regulated anti-inflammatory factors, and enhanced angiogenesis. Taken together, these desirable properties work in concert to contribute to the rapid healing of infected wounds and make it a good candidate for wound dressing materials.

One-step synthesis of CePO4 nanoparticle-decorated cerium-doped ultralong flexible hydroxyapatite nanofibers

Ultralong flexible CePO4/Ce–HA nanofibers were synthesized via a solvothermal method, combining exceptional advantages of Ce ions and nanofibers.

Hierarchically porous networks structure based on flexible SiO2 nanofibrous aerogel with excellent low frequency noise absorption

Environmental noise has been regarded as major noise pollution with severe hazards to human physical and mental health. The common commercial fiber sound-absorption materials have insufficient low frequencies wave absorbing and fire-resistant ability, limiting their wide application. To solve these problems, a novel strategy combining flexible nanofibers and rGO/MXene nanosheets was proposed to fabricate rGO/MXene/SiO2 nanofibers composite aerogel with hierarchically porous structure, which possessed an extremely low density of 9.8 mg/cm3 and superior low-frequency sound absorption ability (NRC value of 0.51). The obtained composite aerogel possessed a large deformation up to 80% (corresponding compressive stress of 17 kPa) and quickly recovered. In addition, the as-prepared aerogel could be easily produced on a large scale, providing a reference for the development of new generation of sound-absorbing products.

Improving Flexibility and Capacitive Charge Storability in Free-Standing Carbon Nanofiber Electrodes

Energy storage devices with higher volumetric energies and power densities are crucial in delivering high electrochemical performances without being bulky. Herein, a flexible free-standing carbon nanofiber (CNF) electrode with and without graphene is derived from electrospun polyacrylonitrile nanofiber mesh. The embedded graphene enhanced the conductivity of the polymeric solution, generating significant “whipping” motion to create better fiber cross-linking that enhances the flexibilities of CNFs. Besides, the presence of graphene reduced the population of surface oxygenated functional groups when compared to the pristine CNF. Raman spectroscopy demonstrated lower defect states in graphene-embedded CNFs, favorable for better electrical conductivity. Both the reduced surface functional group and reduced impedance (1.0 Ω compared to 1.1 Ω of pristine CNF) show that a graphene-embedded CNF recorded improved rate capability compared to a pristine CNF. When fabricated into a symmetry supercapacitor, a volumetric energy density of ∼4 mWh cm–3 at a power density of ∼63 mW cm–3 was achieved, which is one of the highest reported values based on our knowledge.

Highly flexible all-inorganic nanofiber networks with stress-accommodating microstructure for light-activated wearable chemiresistive sensor

Inorganic semiconductor chemiresistors have been the mainstream of well-explored gas sensing technology. However, the intrinsic fragile and rigid nature seriously impedes their future application in the thriving wearable sensing devices. Herein, we demonstrate a flexible all-inorganic semiconductor-based chemiresistive sensor through in-situ anchoring nanosheets-assembled SnO2/SnS2 sensing layer on flexible yttria-stabilized zirconia (YSZ) ceramic nanofiber networks. It is revealed that the flexible YSZ ceramic substrate possesses low section modulus in bending and good toughness that is mainly derived from its unique nanofiber structure (300 nm in diameter) and ultrafine grain size (16 nm). It is first demonstrated that nanosheets-assembled sensing layer characterized by abundant void spaces plays a pivotal role in affecting the flexibility of inorganic nanofiber networks. The void spaces between SnO2/SnS2 nanosheets, acting as stress-accommodating microstructures, could effectively releasing stress concentration, enabling abnormal mechanical flexibility of inorganic YSZ/SnO2/SnS2 network. In addition, to achieve more compatibility with wearable application and realize room-temperature gas sensing function, visible light rather than traditional high heat is employed as excitation source to activate the flexible YSZ/SnO2/SnS2 chemiresistor. This work shows the possibility of inorganic semiconductor chemiresistor for application in wearable sensing device and offers a valuable guidance for constructing flexible room-temperature inorganic chemiresistor.

Construction of self-supporting ultra-micropores lignin-based carbon nanofibers with high areal desalination capacity

Lignin is a renewable biomacromolecule that can be used as precursors for carbon materials. In this work, highly flexible lignin-based carbon nanofibers with abundant ultra-micropores are constructed via electrospinning, oxidative stabilization and carbonization. The results indicate that replacing PAN with 80 % lignin is feasible in regulating ultra-micropores. The synthesized L4P1-CNFs possess many attractive properties (e.g., pore size distribution, electrochemical and deionization property) compared with that produced from other non-renewable precursors or more-complexed processes. It shows excellent electrochemical double-layer capacitance in 6 M KOH (233 to 162 F g−1 at 0.5 to 5 A g−1) and 1 M NaCl (158 to 82 F g−1 at 0.5 to 5 A g−1) electrolytes. Upon assembling into CDI cells, the average salt adsorption rate could reach 1.79 mg g−1 min−1 at 1.2 V and 3.32 mg g−1 min−1 at 2 V in 500 mg L−1. Benefiting from the excellent flexibility, we innovatively stack four layers of L4P1-CNFs to improve the areal electrosorption capacity to 0.0817 mg cm−2 at 500 mg L−1, significantly higher than that of traditional carbon-based electrodes. The good desalination property makes lignin-based carbon nanofibers ideal for practical, low-cost capacitive deionization applications.

Hierarchical ZIF-67 of dodecahedral structure on binder-free carbon nanofiber for flexible supercapacitors

Binder-free, highly flexible carbon nanofibers decorated with ZIF-67 dodecahedral structures are synthesized via electrospinning and impregnation for use in supercapacitor applications. Because cobalt ions from ZIF-67 are highly attracted to carbon rings and the oxygen functional groups of polyvinylpyrrolidone (PVP), the concentration of PVP is varied to tune the morphology of ZIF-67. Accordingly, morphology tuning via PVP inclusion enhances the electron transfer within the ZIF-67-derived CoOx dodecahedral structure. Parametric studies are conducted to investigate the effect of PVP concentration on the electrochemical performance of carbon nanofibers decorated with ZIF-67. The optimal sample yields a capacitance of 444 mF⋅cm−2 at a current rate of 5 mA⋅cm−2. The corresponding capacitance retention is 94 % after 30,000 cycles with a potential window of 1 V. Furthermore, the energy density increases by 262.7 % when the potential window is increased from 1 to 1.5 V. These results confirm the long-term stability and outstanding energy-storage capabilities of the fabricated supercapacitor electrodes.

Hollow, Porous, and Flexible Co3O4‐Doped Carbon Nanofibers for Efficient CO2 Capture

Hollow and porous fibrous materials have huge potential for gas filtration applications. However, synthesizing such carbonaceous materials is still a critical job owing to their inherent fragile nature. Herein, a facile strategy to fabricate porous, hollow, and flexible carbon nanofibers (CNF) for enhanced CO2 adsorption via biaxial electrospinning is reported. Polymethylmethacrylate (PMMA) is used in core as sacrificial precursor owing to its easy decomposition at relatively low temperature. Polyacrylonitrile (PAN) is opted as shell because of its tendency to produce high carbon yield. Co3O4 nanoparticles (NPs) are embedded in PAN shell to increase roughness and surface area through in situ synthesis from cobalt salt. Besides, uniform presence of Co3O4 NPs adds flexibility to the resultant hollow CNF (HCNF‐Co) by serving as a plasticizer for single‐fiber‐crack connection and provides additional vacant oxygen sites to improve CO2 adsorption capacity. The optimized HCNF‐Co nanofibers exhibit exceptional CO2 capture performance of 3.28 mmol g−1 at 25 °C. Experimental results suggest that synthesized HCNF‐Co also offers extremely high CO2 gas selectivity (S = 26) than N2 gas. Meaningfully, porous, hollow, and flexible HCNF‐Co nanofibers with exceptional structural stability overcome the limitations of annihilation and collapse of structures, making them a suitable candidate for the applications of CO2 capture.

Electrospun Bi-decorated BixTiyOz/TiO2 flexible carbon nanofibers and their applications on degradating of organic pollutants under solar radiation

Presently, photocatalytic degradation has emerged as an attractive and efficient technology for wastewater treatment. In order to avoid hurdles, such as difficulty in the suspended photocatalyst segregation from the aqueous system and low reutilization rate, the strategy of immobilizing photocatalysts with electrospun fibers has been widely studied. However, those methods usually require multi-step preparation and complex operations. Considering this, a novel metallic Bi-decorated flexible multiphase BixTiyOz/TiO2 electrospun carbon nanofibers (Bi/BixTiyOz-TiO2/CNFs) with high photocatalytic efficiency, good mechanical property, good stability, easy separation, and recovery were synthesized via a one-step approach of pre-oxidation and carbonization treatment. The as-prepared Bi/BixTiyOz-TiO2/CNFs with multiphase BixTiyOz, anatase TiO2, and metallic Bi particles embedded not only enhance the harvest of light but also provide more separation paths for photogenerated carriers, which improve photocatalytic efficiency greatly. The Bi/BixTiyOz-TiO2/CNFs (S3) exhibited excellent photocatalytic performance and the degradation rate of 10 mg L–1 Rhodamine B (RhB) was up to 97% in only 30 min under simulated sunlight irradiation. Also, S3 exhibited stable activity during 5 cycles of experiments since the degradation rates remained at about 97% in 30 min. The mechanism of degradation of RhB by Bi/BixTiyOz-TiO2/CNFs in the photocatalytic process was also proposed based on active species trapping experiments. The work in this paper shows that Bi/BixTiyOz-TiO2/CNFs are easy to prepare and have high photocatalytic ability and stability, thereby offering a new strategy in catalyst immobilization and wastewater treatment.

Highly conductive and flexible porous carbon nanofibers cloth for high-performance supercapacitor

Porous carbon nanofibers combine the superiorities such as good electrical conductivity, intrinsic and structural flexibility, as well as potential mass production, rendering it an important material for flexible and wearable electronics. Nonetheless, the influence of porous carbon nanofiber's nanostructure on electrochemical performances and mechanical flexibility remains an important open question in the design of high-performance and flexible supercapacitors. To address this matter, herein, we report a systematic study to fabricate the porous carbon nanofibers cloth with both high electrical conductivity and flexibility. Our results indicate that the stress concentration during the bending of porous carbon nanofibers can be efficiently relieved through reducing the size of graphite microcrystals and introducing pores between graphite microcrystals, resulting in good flexibility. Meanwhile, the fabricated porous carbon nanofiber achieves high electrical conductivity (Max. 1600 S/m), which can be directly used as flexible supercapacitor electrode material without introducing a conductive agent and binder. Finally, the flexible supercapacitor electrode based on this porous carbon nanofiber exhibits a high specific capacitance of 184 F/g at a current density of 0.5 A/g. Our win-win strategy provides new insight into the fabrication of flexible porous carbon nanofiber materials, showing great application prospects in the field of flexible supercapacitors.

Flexible and hydrophobic nanofiber composites with self-enhanced interfacial adhesion for high performance strain sensing and body motion detection

Flexible and electrically conductive fibric (fiber) composite (CFC) strain sensors are promising in smart wearable electronics. Challenges remain to develop CFC with strong interfacial interaction and excellent durability. Here, a facile and cost-efficient method is proposed to fabricate flexible and hydrophobic CFCs with self-enhanced interfacial adhesion based on ultrasonication induced carbon black nanoparticles (CBNPs) embedded onto the swelled polyurethane (PU) nanofiber membranes immersed in a mixed solvent. CBNPs were tightly decorated onto the nanofiber surface, while the electrical conductivity keeps stable during cyclic durability tests. The CBNPs improve the Young’s modulus and tensile strength while maintain the outstanding stretchability of PU membrane. The CBNPs also endow the CFCs with hydrophobicity and photo-thermal conversion property. The stretchable CFC strain sensors show controllable sensitivity and cyclic stability, and can monitor various body motions. This work provides a new route to fabricate low-cost and high-performance strain sensors without using interfacial bonding agents.

A flexible carbon nanofiber and conjugated polymer-based electrode for glucose sensing

Herein, a specific and stable biosensor for glucose using a flexible, modified electrode with a carbon nanofiber (CNF) and a novel conjugated polymer including three moieties of benzotriazole, benzodithiophene, and benzenediamine (P-BDT-BTz:BDA) as a platform was designed. For this purpose, polyacrylonitrile (PAN) nanofiber mats were obtained by a solution-based electrospinning method. PAN nanofiber mats were stabilized and carbonized to turn into carbon nanofibers and the sensing platform was formed by combining the nanofibers on a defined area of a flexible polyethylene terephthalate (PET) substrate. In addition, a random conjugated polymer, P-BDT-BTz:BDA, was synthesized, characterized, and used as a modifier of a CNF-coated transducer surface for glucose detection. The effect of each parameter on biosensor response was evaluated. Under optimized conditions, the electrode responded to glucose in a linear concentration range of 20 µM to 500 µM with a detection limit of 8.5 µM. In addition, it was observed that the designed biosensor has a good sensing ability for glucose in beverages. The results of our study show that the proposed amperometric glucose oxidase (GOx)-based biosensor has high specificity, a low limit of detection, and an extended range of linear detection for glucose.

Flexible Electrospun strawberry-like structure SiO2 aerogel nanofibers for thermal insulation

Herein, a novel flexible SiO2 aerogel composite nanofiber membrane with strawberry-like structure and excellent thermal insulation properties, in which SiO2 aerogel particles act as thermal insulation filler, was prepared by electrospinning technology. With the addition of nano-pore structure SiO2 aerogel particles, the heat transfer path of the fibers inside the membrane became discontinuous, endowing the as-prepared membrane an ultra-low thermal conductivity of 30.3 mW/(m⋅K) and large surface area of 240 m2/g. Moreover, the nanofibers membrane also possesses the combined merits of excellent fire resistance, high-temperature stability, and temperature-invariant flexibility, rendering it a promising in the application of insulation and gas adsorption. The successful preparation of this flexible nanofiber membrane paves a new way to design materials with excellent thermal insulation and adsorption properties.

Atomic Dual‐Site Ni/Co‐Decorated Carbon Nanofiber Paper for Efficient O2 Electrocatalysis and Flexible Zn‐Air Battery

AbstractThe fabrication of flexible catalytic films with isolated single/dual‐atomic sites and their integration in wearable electronics is challenging. Herein, an efficient method to prepare atomically dispersed binary Ni/Co‐decorated flexible carbon nanofiber (NiCo‐CNF) film using formamide‐derived cyano‐specific NiCo‐NC as nanofillers was developed. The optimized Ni1Co1‐CNF catalytic film, having large‐area, high density of adjacent Ni‐N4 and Co‐N4 active sites, and good mechanical properties under repeated bending and release conditions, possessed high catalytic activity towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The ORR/OER potential difference (ΔE10) for Ni1Co1‐CNF at 10.0 mA cm−2 was highly comparable with the Pt/C+RuO2 mixture. In addition, flexible Ni1Co1‐CNF‐assembled Zn‐air battery displayed very good mechanical robustness and cycling stability. Our work may inspire the fabrication of other atomic metal‐decorated films for membrane electrocatalysis.

Efficient Pathogen Capture and Sensing Promoted by Dynamic Deformable Nanointerfaces.

The M13 bacteriophage (M13 phage)has emerged as an attractive bionanomaterial due to its chemistry/gene modifiable feature and unique structures. Herein, a dynamic deformable nanointerface is fabricated taking advantage of the unique feature of the M13 phage for ultrasensitive detection of pathogens. PIII proteins at the tip of the M13 phage are genetically modified to display 6His peptide for site-specific anchoring onto Ni-NTA microbeads, whereas pVIII proteins along the side of the M13 phage are orderly arranged with thousands of aptamers and their complementary strands (c-apt). The flexible M13 nanofibers with rich recognition sites act as octopus tentacles, resulting in a 19-fold improvement in the capture affinity toward the target. The competitive binding of the target pathogen releases c-apts and initiates rolling circle amplification (RCA). The sway motion of M13 nanofibers accelerates the diffusion of c-apts, thus promoting RCA efficiency. Benefiting from the strengthened capture ability toward the target and the accelerated RCA process, three-orders of magnitude improvement in the sensitivity is achieved, with a detection limit of 8 cfu mL-1 forStaphylococcus aureus. The promoted capture ability and assay performance highlights the essential role of the deformable feature of the engineered interface. This may provide inspiration for the construction of more efficient reaction interfaces.

Design of hierarchical porous carbon nanofibrous membrane for better electrochemical performance in solid-state flexible supercapacitors

The pore structure dramatically influences the electrochemical behavior of carbon nanofibers. The electrochemical performance of flexible carbon nanofibers as electrode materials for supercapacitors can be controlled by changing the size and quantity of pores. Hollow porous carbon nanofibers (HPCNFs) are prepared by coaxial electrostatic spinning and high-temperature carbonization. According to the nitrogen adsorption/desorption curve, HPCNF has a large specific surface area and good pore size distribution. In addition, cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) are used to analyze the electrochemical performance of HPCNF. Results show that the specific capacitance of hollow porous carbon nanofibers is 168.8 F/g at the current density of 1 A/g. Moreover, the specific capacitance retention of HPCNF is 95.61 % after 2000 cycles of charge and discharge at the current density of 5 A/g, exhibiting a stable cycle performance. In addition, solid-state supercapacitors assembled without any adhesives or conductive agents also show good cycle stability and excellent flexibility. As a result, HPCNF with flexibility, high specific surface area, and excellent electrochemical performance has broad prospects as an excellent electrode material for supercapacitors. Therefore, HPCNF has the advantages of good flexibility, high specific surface area, and excellent electrochemical performance. This paper proposes reasonable methods and creates more possibilities for future research and the application of flexible electrode materials for supercapacitors and flexible wearable electronic devices. • Different levels of hierarchical porous carbon nanofibrous membranes are constructed. • The effect of pores in carbon nanofibers on electrochemical performance are deeply studied. • Symmetric solid-state supercapacitors exhibit excellent stability and flexibility. • The charge distribution in supercapacitor are simulated by finite element method.