Porous Fiber Research Articles

Boosting pH-universal electrosynthesis of hydrogen peroxide by regulating three-phase interface of carbon gas penetration electrode

Electrochemical oxygen reduction is a sustainable method for onsite H2O2 production. However, pH-universal H2O2 electrosynthesis still suffered from low kinetics and efficiency. Here carbon nanotube hollow fiber (CNT-HF) with porous fiber wall is designed to enhance H2O2 electrosynthesis via tailoring the three-phase interface. The CNT-HF gas penetration electrode with enhanced local electric field is favorable for boosting oxygen mass transfer and regulating catalyst-electrolyte interfacial protons, resulting in significantly enhanced H2O2 production performance in comparison with CNT planar gas diffusion electrode under pH-universal media. Its H2O2 production efficiency is 98.1% at pH 13. Meanwhile, H2O2 production efficiency of 96.1% and high H2O2 concentration of 46.4 g L-1 are achieved at pH 1 with 20 mM K+. Experimental and simulation results reveal the boosted H2O2 electrosynthesis on CNT-HF is mainly contributed from its significantly reduced diffusion layer thickness, enhanced local electric field and interfacial proton regulation by K+ enriched at electrode surface.

Porous Spindle-Knot Fiber by Fiber-Microfluidic Phase Separation for Water Collection and Nanopatterning.

Porous spindle-knot structures have been found in many creatures, such as spider silk and the root of the soybean plant, which show interesting functions such as droplet collection or biotransformation. However, continuous fabrication of precisely controlled porous spindle-knots presents a big challenge, particularly in striking a balance among good structural controllability, low-cost, and functions. Here, we propose a concept of a fiber-microfluidics phase separation (FMF-PS) strategy to address the above challenge. This FMF-PS combines the advantages of a microchannel regulated Rayleigh instability of polymer solution coated onto a fiber with the nonsolvent-induced phase separation of the polymer solution, which enables continuous and cost-effective production of porous spindle-knot fiber (PSKF) with well-controlled size and porous structures. The critical factors controlling the geometry and the porous structures of the spindle-knot by FMF-PS have been systematically investigated. For applications, the PSKF exhibited faster water droplet nucleation, growth, and maximum water collection capability, compared to the control samples, as revealed by in situ water collection growth curves. Furthermore, high-level fabrics of the PSKFs, including a two-dimensional network and three-dimensional architecture, have been demonstrated for both large-scale water collection and art performance. Finally, the PSKF is demonstrated as a programmable building block for surface nanopatterning.

Multifunctional Bionic Periosteum with Ion Sustained-Release for Bone Regeneration.

In this study, a novel bionic periosteum (BP)-bioactive glass fiber membrane (BGFM) is designed. The introduction of magnesium ion (Mg2+) and zinc ion (Zn2+) change the phase separation during the electrospinning (ES) jet stretching process. The fiber's pore structure transitions from connected to closed pores, resulting in a decrease in the rapid release of metal ions while also improving degradation via reducing filling quality. Additionally, the introduction of magnesium (Mg) and zinc (Zn) lead to the formation of negative charged tetrahedral units (MgO4 2- and ZnO4 2-) in the glass network. These units effectively trap positive charged metal ions, further inhibiting ion release. In vitro experiments reveal that the deigned bionic periosteum regulates the polarization of macrophages toward M2 type, thereby establishing a conducive immune environment for osteogenic differentiation. Bioinformatics analysis indicate that BP enhanced bone repair via the JAK-STAT signaling pathway. The slow release of metal ions from the bionic periosteum can directly enhance osteogenic differentiation and vascularization, thereby accelerating bone regeneration. Finally, the bionic periosteum exhibits remarkable capabilities in angiogenesis and osteogenesis, demonstrating its potential for bone repair in a rat calvarial defect model.

N-Vacancy Enriched Porous BN Fibers for Enhanced Polysulfides Adsorption and Conversion in High-Performance Lithium-Sulfur Batteries.

Severe shuttle effect of soluble polysulfides and sluggish redox kinetics have been thought of as the critical issues hindering the extensive applications of lithium-sulfur batteries (LSBs). Herein, one-dimensional boron nitride (1D BN) fibers with abundant pores and sufficient N-vacancy defects were synthesized using a thermal crystallization following a pre-condensation step. The 1D structure of BN facilitates unblocked ions diffusion pathways during charge/discharge cycles. The embedded pores within the polar BN strengthen the immobilization of polysulfides via both physical confinement and chemical interaction. Moreover, the highly exposed active surface area and intentionally created N-vacancy sites substantially promote reaction kinetics by lowering the energy barriers of the rate-limiting steps. After incorporating with conductive carbon networks and elemental S, the as-prepared S/Nv-BN@CBC cathode of LSBs deliver an initial discharge capacity of up to 1347 mAh g-1 at 200 mA g-1, while maintaining a low decay rate of 0.03 % per cycle over 1000 cycles at 1600 mA g-1. This work offers an effective strategy to mitigate the shuttle effect and highlights the significant potential of defect-engineered BN in accelerating the reaction kinetics of LSBs.

Cobalt-ions pre-intercalation MnO2 nanosheet arrays on nickel foam achieving boosted electrochemical pseudocapacitance for supercapacitors

Metal oxide have attracted much attention as a pseudocapacitive electrode for high energy density supercapacitors (SCs). However, the battery-like charge storage mechanism based on ions diffusion and valence change for metal oxide would lead to a poor cycling stability and unsatisfied rate performance. Herein, cobalt ions pre-intercalation MnO2 nanosheet arrays on Ni foam (Co-MnO2/NF) was prepared as the cathode for SCs. The capacitive behavior of MnO2 was enhanced via cobalt introduction. The optimized Co-MnO2/NF-2 demonstrated improved pseudocapacitance and stability, with a specific capacitance of 405.6 mF cm−2 at 1 mA cm−2. It retained 90.5 % of its initial capacitance at 10 mA cm−2 after 5000 cycles, which was superior to that of pristine MnO2 (222.4 mF cm−2, 65.0 % after 1000 cycles), Co-MnO2/NF-1 (295.2 mF cm−2, 85.9 % after 1000 cycles), and Co-MnO2/NF-3 (349.9 mF cm−2, 84.9 % after 1000 cycles). The asymmetric aqueous supercapacitor consisted of Co-MnO2/NF-2 and N-doped porous carbon fiber (NPCF) electrodes with an operating potential of 2.0 V reaches a high areal energy density of 0.06 mWh cm−2 at a power density of 0.5 mWh cm−2.

Boosting the H2/CO2 and H2/N2 selectivities of a graphene oxide membrane by shrinking the membrane interlayer spacing via thermal treatment

Graphene oxide (GO) membranes have been widely studied and used for gas separation processes, but some structural changes are necessary to guarantee high membrane selectivities. The thermal reduction process stands out for reducing the interlayer channel size of the GO nanosheets to improve the molecular sieving mechanism. Herein, thermally annealed GO layers were deposited on the outer surface of porous alumina hollow fiber substrates and the produced composite membranes were tested for selective hydrogen (H2) separations. The influence of the thermal annealing process at different mild temperatures (80 and 160 °C) on the characteristics of the GO structure was investigated towards the improvement of the membrane efficiency for H2 separation. ATR-FTIR results confirmed the elimination of oxygenated groups, and XRD analyses showed the GO interlayer space decreased from 8.71 to 7.38 Å after the thermal annealing process at 160 °C. The GO thermally annealed membrane presented an H2 permeance of 2032.47 ± 101.69 GPU and an H2/N2 selectivity of 12.16 ± 0.30, which is 315% greater than the selectivity of the pristine GO membrane. Hence, the application of the thermal reduction method to produce GO membranes with greater selectivities is a viable alternative to deal with gas separation processes.

Dynamical Adsorption Behavior Prediction of Dried Tobacco Leaf Heterogeneous Interfaces through Simulation and Image Recognition Techniques.

The process of spraying water and flavorings on dry tobacco is an important factor in the industrial environment and product quality. Tobacco as a complex porous fiber material, the interfacial transfer process of water is complex. In this study, machine learning and image recognition techniques were utilized to quickly obtain the structural parameters of the tobacco surface and construct a cellular structure model of the tobacco surface. In situ observation of the droplet impact spreading process was carried out using a high-speed camera to explore the droplet dissipation dynamics on different surfaces. And the competing processes of droplet wetting and evaporation under the influence of surface microstructure were determined by combining experimental studies and finite element simulation calculations. Based on the characteristics of tobacco pore size distribution, the infiltration under gas-liquid two-phase action was transformed into single-phase flow transfer under capillary force, and the continuous droplet infiltration process was simulated. A parallel artificial membrane permeability measurement method of bionic tobacco waxy layer was constructed for the screening of spray dosing copenetrant. This study brings new insights into the wetting of porous fibrous materials and is important for exploring the wetting process and additive development process influenced by the microstructure.

Controllable synthesis of porous boron nitride fibers modified by cobalt and nickel oxides for efficient ceftriaxone sodium adsorption from aqueous solution.

Antibiotics can easily enter the water environment through direct or indirect approach, causing environmental pollution and endangering the health of organisms. Therefore, development of highly efficient adsorbent materials to adsorb and remove antibiotics is necessary. Here, cobalt oxide and nickel oxide are uniformly and tightly bonded on the surface of porous boron nitride fibers (PBNFs-NiCo), significantly increasing the number of functional groups (B-O and N-H) and hydrogen bond receptors within PBNFs. The total pore volume and specific surface area of resulting PBNFs-NiCo can reach up to 0.48 cm3/g and 720.3 m2/g, respectively. Encouraged by the unique micromorphology and chemical composition mentioned above, PBNFs-NiCo exhibits excellent ceftriaxone sodium (CS) adsorption ability, showing the adsorption capacity and removal efficiency up to 410.9 mg/g and 96.5%, respectively. Chemical adsorption plays an important role in their adsorption behavior, abiding by Langmuir adsorption theory and pseudo-second-order kinetic equation. Importantly, PBNFs-NiCo exhibits fascinating adsorption effects in surroundings with pH ranging from 4 to 6, 25 °C and varying salt concentrations. This work would establish a practical and feasible foundation for the practical application of PBNFs-NiCo for CS adsorption in aqueous solution.

Preparation of cellulose-based porous carbon fibers and their methylene chloride adsorption/desorption behaviors

Methylene chloride is a type of volatile organic compounds for which effective and economical treatment and recovery technologies need to be developed because it is impossible to reburn. In this study, a cellulose-based porous carbon fibers were prepared for the adsorption/desorption of methylene chloride. From the results, the specific surface area and total pore volume of cellulose-based porous carbon fibers were determined to be 1700–2220 m2/g and 0.69–1.03 cm3/g, respectively, and the micropore ratio was observed to be high. As the activation time increased, methylene chloride activity and methylene chloride retentivity increased from 51.75 % to 58.07 % and from 9.08 % to 14.92 %, respectively. Methylene chloride adsorption/desorption showed a high correlation with pore volume, Especially, methylene chloride retentivity had a linear relationship between the mesopore volume and mesopore ratio.

Semi-analytical framework for modelling of surface heating and its impact on nonlinear stability of nanotube reinforced doubly curved porous fiber composite panels

In elevated temperatures, the stiffness of the panel deteriorates and can lead to loss of stability of structures. Hence, the stability analysis of thin-walled structures is a critical investigation in the thermal environment. Finding such criticality, the present semi-analytical study investigated the nonlinear stability behaviour of porous doubly curved thin-walled panels subject to surface heating like dome heating and localised heating. To improve the stiffness of the panel, the matrix is reinforced with carbon nanotubes (CNTs). Improper mixing of such nanoparticles can lead to agglomeration or bundling effect, which may reduce the structure's stiffness. Still, its investigation in surface heating can be an essential aspect that is found to be untouched by researchers for porous shell panels. The effective material properties of the three-phase composite panel are determined using the Eshelby-Mori-Tanaka (E-M-T) approach and the Chamis homogenisation technique. Using the variational principle, governing equations are derived and further simplified to non-linear algebraic equations using the Galerkin technique. Gibson and Ashby foam model is used to model cell structure. It is observed that a complete agglomerated state results in higher post-buckling strength, a continuous deformation path due to biaxial compression and curved geometry, and porosity of cellular structure distribution and cell walls are the important parameters to study the stability of panel in a thermal environment are the major conclusions drawn from the current study. Current investigation can be an important contribution towards modelling aircraft structure in supersonic airflow and furnace walls of thermal power plants subjected to localised heating.

Experimental study on the performance of various porous water-absorbing fiber materials for indoor humidification

To increase the relative humidity in heating rooms in winter, a new humidification method is proposed. The capillary water absorption performance of porous fiber materials is utilized to compose a bottom water-absorbing component, and the spray device of the traditional direct evaporative cooling system is eliminated, which can be used for miniaturized heating humidification devices. To compare the heating and humidification performance of various fiber materials, an experimental system was designed and constructed with fiber materials arranged in parallel as humidification components. The experimental materials include nonwoven fabric (Sample A), polyester fiber (Sample B) and fiber cotton (Sample C). The experimentally obtained temperature drop is lower than the conventional evaporative cooling system, and the relative humidity enhancement is between 6 % and 15 %. Sample B had a maximum temperature drop of 6.83 °C, a maximum relative humidity increment of 14.07 %, a maximum humidification capacity of 272.4 g/h, and a maximum humidification capacity per unit area of material of 972.86 g/(m2·h). The maximum humidification capacity of Sample B was 13.8 % higher than that of Sample A and 18.5 % higher than that of Sample C. The cooling energy density of the three samples was only within 330 J/m3 under all working conditions. Applying sample B to the fan coil unit increased the relative humidity by 33.8 % with only 0.3 °C temperature drop, providing humidification while heating the indoor air. This paper provides a theoretical basis for a fiber material humidification, which to some extent can meet the heating and humidification integration in winter.

Hierarchical Bi2O3 nanosheets and ZIF-8 derived porous nitrogen-doped carbon fibers as novel assembled nanocomposites for high-performance flexible supercapacitors

The unique design of the core–shell heterostructure is significant for obtaining electrode materials with excellent electrochemical properties. In this paper, porous carbon nanofibers (NPC@PPZ) embedded with N-doped porous carbon nanoparticles are used to construct flexible electrodes (NPC@PPZ@Bi2O3). Zeolite imidazole skeleton (ZIF)-8 and poly(methyl methacrylate) (PMMA) derived porous carbon fibers and Bi2O3 nanosheets, were utilized as the porous core and multilayer shell, respectively. The unique core and shell result in abundant pores and channels for fast ion transport and storage, high specific surface area, and additional electroactive sites. This perfect structural design enables the NPC@PPZ@Bi2O3 composite electrode to have excellent electrochemical performance. The results show that this electrode can obtain a high specific capacitance of 697 F g−1 at a current density of 1 A g−1 and a stable cycling performance at a high current density of 5 A g−1. The strategy developed in this study provides a new approach for the design and fabrication of flexible supercapacitors by electrostatic spinning combined with hierarchical porous structures.

A double-sided coating paper antibacterial indicator card based on polyvinyl alcohol/sodium carboxymethyl cellulose-anthocyanins and chitosan-halloysite nanotubes loaded essential oil to monitor fish freshness

This study developed a multifunctional paper-based freshness antibacterial indicator card by dual-sided coating on conventional filter paper. The indicator coating was composed of anthocyanins from purple cabbage, and polyvinyl alcohol and sodium carboxymethyl cellulose as substrates while the antibacterial coating contained halloysite nanotubes for loaded thyme essential oil and chitosan. FT-IR, XRD, and SEM analyses revealed that the components were well-mixed, and the paper was tightly bound to the coatings through hydrogen bonds. Additionally, the coating effectively filled the porous fiber gaps in the paper, significantly enhancing the mechanical properties of the paper. The tensile strength of the coated paper was enhanced from 14.28 MPa to a range of 42.25–47.71 MPa, and the bending resistance was increased from 0.35 N·mm to a range of 1.72–1.99 N·mm compared to the uncoated paper. The addition of anthocyanins provided excellent sensitivity to pH and ammonia for the indicator card. Furthermore, the coating including halloysite nanotubes for loaded thyme essential oil exhibited antimicrobial resistance against Escherichia coli and Staphylococcus aureus. When used on fresh carp, the antibacterial indicator card not only indicated the freshness of the carp but also extended the best before date of the fish meat by 1–2 days. The indicator exhibited the most pronounced color transformation and optimal freshness indication performance when the mass fraction of anthocyanins was 2 %.

Porous Structure Fibers Based on Multi-Element Heterogeneous Components for Optimized Electromagnetic Wave Absorption and Self-Anticorrosion Performance.

The excellent performance of electromagnetic wave absorbers primarily depends on the coordination among components and the rational design of the structure. In this study, a series of porous fibers with carbon nanotubes uniformly distributed in the shape of pine leaves are prepared through electrospinning technique, one-pot hydrothermal synthesis, and high-temperature catalysis method. The impedance matching of the nanofibers with a porous structure is optimized by incorporating melamine into the spinning solution, as it undergoes gas decomposition during high-temperature calcination. Moreover, the electronic structure can be modulated by controlling the NH4F content in the hydrothermal synthesis process. Ultimately, the Ni/Co/CrN/CNTs-CF specimen (P3C NiCrN12) exhibited superior performance, while achieving a minimum reflection loss (RLmin) of -56.18dB at a thickness of 2.2mm and a maximum absorption bandwidth (EABmax) of 5.76GHz at a thickness of 2.1mm. This study presents an innovative approach to fabricating lightweight, thin materials with exceptional absorption properties and wide bandwidth by optimizing the three key factors influencing electromagnetic wave absorption performance.

Graphene modified Sb2O3/porous carbon nanofibers via electrospinning treated in air for potassium-ion batteries with enhanced cycling stability

Sb2O3 is regarded as an ideal anode material for potassium-ion batteries for its high theoretical specific capacity. However, the potassiation and depotassiation during cycling causes large volume change which will result in cracking of the electrode and irreversible loss of capacity. Here, we prepared graphene-modified Sb2O3 porous carbon nanofiber by electrospinning and subsequent annealing in air as anode material of potassium-ion batteries. The mechanical properties of the electrode materials are greatly enhanced owing to the introduction of graphene with the Young's modulus increased to 3045.5 MPa from 1367.9 MPa. Ultimately, the as-prepared Sb2O3@GPCN-100 porous fibers delivered a high specific capacity of 327 mAh g−1 after 300 cycles at a current density of 500 mA g−1. Even at a high current density of 1000 mA g−1, the electrode exhibits a specific capacity of 292 mAh g−1 after 600 cycles, showing excellent reversible stability and high specific capacity. This graphene modification strategy can also provide a feasible solution for the modification of other anode materials for potassium-ion batteries.

Fabrication of a high-performance MOF-COP-based porous hollow fiber membrane for carbon dioxide separation

A thin-film nanocomposite (TFNC) hollow fiber membrane with high CO2 permeability and selectivity was synthesized for the separation of carbon dioxide, a major greenhouse gas. A highly porous polyethersulfone (PES) hollow fiber membrane support with a porous structure was first fabricated using heat and pressure treatments, and a thin film was prepared via interfacial polymerization by reacting polyethylenimine (PEI) with 1,3,5-benzenetricarbonyl trichloride (TMC) on the surface of the PES support. A metal–organic framework (MOF)-covalent organic polymer (COP) complex, obtained via polycondensation between an UiO-66-NH2 based MOF and a piperazine- and cyanuric chloride-based COP, was then added to the TFNC to prepare the mixed matrix membrane. The complex contributed to reducing defects between the porous support and the coating layer and additionally led to high CO2 permselectivity by providing a CO2 permeation pathway within the support. The newly prepared TFNC hollow fiber membrane contributed to its excellent separation performance, as evidenced by a CO2 permeability of 352 GPU and a CO2/N2 ideal selectivity of 75 after optimization of the MOF-COP content.

Synthesis composit electrospun based gum-resin/polycaprolactone fibers for biomedical application

Electrospun fibers for tissue engineering have recently seen significant advancements. In this study, we created composite fibers by combining Pistacia atlantica Gum-Resin and Poly(ε-caprolactone) (PCL) polymer using the electrospinning method. We examined the morphology, biodegradability, thermal stability, and hydrophilicity of the prepared scaffolds using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermogravimetric (TG) differential scanning calorimetry (DSC), and water contact angle measurements. The results indicated complete integration between the materials and successful synthesis of fibers through the electrospinning method. SEM images demonstrated bead-free fibers with different blending ratios of Gum-Resin and PCL. Fibers with a diameter of 100–200 nm and 1–7 μm were obtained with a 9:1 blending ratio of PCL to Gum-Resin. Additionally, PCL/Gum-Resin fibers with an 8:2 blending ratio exhibited an interwoven and porous fiber network structure with a 1–7 μm fiber diameter. The water contact angle measurements revealed the hydrophilic surface of the fibers, with a WCA of 61.2°. Thermogravimetric (TG) and differential scanning calorimetric (DSC) analysis showed a melting peak at approximately 57°. Cell culture results indicated good cytocompatibility of the fibers. The scaffold sample exhibited inhibitory activity against S. aureus (22 ± 0.26 mm) and E. coli (16.8 ± 0.15 mm) bacteria. These findings suggest that the fabricated fibers could serve as an effective scaffold for wound healing.

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

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

Strength response investigation of defective C/C composite materials based on the Weibull model

In this study, the issue of random fiber strength resulting from initial fiber defects and matrix pore defects in the strength response of C/C composite materials is addressed. A method for generating random numbers following the Weibull distribution is proposed and an improved random sequence adsorption (RSA) algorithm is employed to describe pore defects in the matrix, ultimately leading to the development of a representative volume element (RVE) model for C/C composite materials. The influence of fiber strength distribution and pore defects on the mechanical properties of unidirectional C/C (UD-C/C) composite materials is analyzed. This study offers a new approach to investigate the mechanical behavior of C/C composite materials, taking into account both fiber initial defects and pore defects.

Core-sheath PVDF hollow porous fibers via coaxial wet spinning for energy harvesting

Flexible piezoelectric nanogenerators (PENGs), as a promising sustainable power source in smart electronics, have attracted much attention for their potential applications in the Internet of Things. In this paper, poly(vinylidene fluoride) (PVDF) fibers with core-sheath hollow porous structure were prepared by coaxial wet spinning process, serving as the dielectric layer, which were perfused internally by liquid metal (LM) as the inner electrode layer and wrapped outside by copper-silver nanoparticles (Cu@AgNP) as the outer electrode layer, thus constructing high-performance PVDF/LM/Cu@AgNP composite fibers. The composite PVDF fibers have a layered pore structure and arbitrarily deformable LM electrodes, which can significantly reduce the effective electric constant and thus enhance the piezoelectric properties. The results reveal that PVDF/LM/Cu@AgNP-PENG yields an optimal voltage output of 410 mV, providing a clear advantage over PENG by using alternative fibers. Moreover, the PVDF/LM/Cu@AgNP-PENG shows an excellent charging capability for energy storage devices, being able to charge 1 μF capacitors to 10 V within 30 s and directly power commercial LEDs. This study demonstrates the significant potential for utilizing composite PVDF piezoelectric fibers in flexible wearable electronic devices.