Hierarchical Porous Nanofibers Research Articles

Hierarchical porous nanofibers comprising N-doped graphitic C and ZIF-8 derived hollow N-doped C nanocages for long-life K-ion battery anodes

Hierarchical porous carbon nanofibers (NFs) are designed via electrospinning, followed by simple carbonization, and applied as the anode for K-ion batteries (KIBs). The carbonization process is optimized to simultaneously satisfy sufficient graphitization of polyacrylonitrile (PAN)-derived soft carbon and complete conversion of zeolitic imidazolate framework-8 (ZIF-8) to hollow N-doped C nanocages. The prepared NFs through an optimized carbonization consists of porous and hollow N-doped C nanocages, which are encapsulated within the conductive graphitic carbon (GC) matrix, that acts as an efficient electron transport pathway. Moreover, the interconnected porous and hollow nanocages ensure a high contact area between the electrode and electrolyte and reduces the K-ion diffusion length. The N-doped GC with high electrical conductivity in the structure demonstrates reinforcing structural integrity as well as providing additional transport pathways for the unique electron transport. Therefore, the hierarchical porous carbon NFs show outstanding energy storage properties, such as stable cycle performance up to 10,000 cycles at the high current density of 1.0 A g-1 with high areal loading mass (1.8–1.9 mg cm−2) of the active material, which clearly suggests the structural advantages of the nanostructure introduced in this study.

An efficient atmospheric pollution control using hierarchical porous nanofibers containing zeolitic-imidazolate-frameworks and hydroxyapatite nanoparticles

Air pollution due to contaminants such as particulate matter (PM) and bacteria has become a global atmospheric pollution issue. Identifying effective methods for removing PM and other contaminants such as bacteria is an important challenge, and several efforts are being made to resolve it. In this study, we introduced a polystyrene (PS) hierarchical porous nanofiber (HAP/ZIF-8 @PS HPNF) containing a zeolitic imidazolate framework (ZIF-8) and hydroxyapatite (HAP) for PM (PM2.5, PM10) filtration and antibacterial applications. HAP/ZIF-8 @PS HPNF was manufactured by electrospinning of ZIF-8, which has a synergistic effect on the adsorption of PM and HAP that have antibacterial properties. The modified nanofibers improved the filtration performance and antibacterial activity by adsorbing PM (efficiency = 96.68% for PM2.5 and 96.98% for PM10) and reducing microbial populations (S. aureus and E. coli.). Thus, the well-dispersed ZIF-8 and HAP on the nanofibers, the multifunctional nanofibers are appropriate for use in environments with harmful PM as well as bacteria.

Hierarchical porous nanofibers containing thymol/beta-cyclodextrin: Physico-chemical characterization and potential biomedical applications.

As an effective natural antibacterial component, the low water solubility of thymol (THY) has stemmed its potential in biomedical application. Here, β-cyclodextrin (β-CD) and THY were self-assembled to form water-soluble inclusion complex (IC). The successful formation of IC was confirmed via 1H NMR. As an antibacterial agent, the resultant IC was then incorporated into cellulose acetate (CA) fibrous matrix with hierarchical structure (nanopores on porous fibrous webs) via electrospinning (CA/THY/β-CD), and the pure THY was also encapsulated into CA for comparison (CA/THY). In vitro dissolution tests demonstrated that CA/THY/β-CD fibrous membrane exhibited sustained drug release, which abided by non-Fickian diffusion. Besides, the CA/THY/β-CD fibrous membrane exhibited more effective and long-lasting antibacterial activity against S. aureus. Furthermore, the combination of hierarchical porous structure with sustained drug release endowed the CA/THY/β-CD fibrous membrane with good cytocompatibility. Taken together, the CA/THY/β-CD fibrous membrane could be an attractive candidate for wound dressing material.

Manganese dioxide-filled hierarchical porous nanofiber membrane for indoor air cleaning at room temperature

Indoor air pollution, including atmospheric particular matter 2.5 (PM2.5) and chemical gaseous pollutants (HCHO), has been an ongoing concern. Seeking a practical strategy for protection of the indoor air quality (IAQ) remains a challenge. Herein, we demonstrated a hierarchical porous membrane consisting of the birnessite-type MnO2 that was filled in the polystyrene porous nanofibers (MnO2/PS HPNM) fabricated by a versatile electrospinning method. The effective air cleaning of both PM2.5 and HCHO at remarkably low resistance was achieved by dominating the hierarchical porous structure. The HCHO gas could easily permeate through the mesopores of the PS nanofibers and contact MnO2, thereby resulting in an excellent HCHO removal efficiency of 88.2% after the initial run and 74% after five cycles. In addition, the pore-filling MnO2 with the layered structure increased the nanofiber membrane surface area, thus enhancing its PM capture performance (99.77%). Moreover, the macropores from the interwoven nanofibers ensured clean air penetration leading to a low airflow resistance of 82 Pa. The hierarchical multifunction porous structure membrane provided a new approach for the IAQ protection.

Hierarchical porous nanofibers of carbon@nickel oxide nanoparticles derived from polymer/block copolymer system

The triblock copolymer (PAA-b-PAN-b-PAA) is prepared by reversible addition-fragmentation chain-transfer polymerization, and then blended with polymer (PAN) and metal hydroxide (Ni(OH)2) as a precursor for heat-treatment. A composite material of hierarchical porous nanofibers and nickel oxide nanoparticles (HPCF@NiO) is prepared by electrospinning combined with high-temperature carbonization. The effects of the ratio of PAA and PAA-b-PAN-b-PAA on the internal structure of nanofibers and their electrochemical properties as positive electrode materials are investigated. The experimental results show that when the ratio of PAA to PAA-b-PAN-b-PAA is 1.3 to 0.4, it has good pore structure and excellent electrochemical performance. At the current density of 1 A/g, the specific capacitance is 188.7 F/g and the potential window is −1 V to 0.37 V. The asymmetric supercapacitor assembled with activated carbon as the negative electrode materials has a specific capacitance of 21.2 F/g in 2 mol/L KOH and a capacitance retention of 85.7% after 12,500 cycles at different current density.

Zeolitic-imidazolate-framework filled hierarchical porous nanofiber membrane for air cleaning

Severe environmental impact caused by particulate matters (PM) and chemical gaseous pollutants (SO2, NOx, VOCs) has become a global atmospheric issue. Seeking an effective way for both PM removal and other pollutants is urgent and remains a challenge. Herein, we introduced a zeolitic imidazolate framework (ZIF-67) trap-in polystyrene hierarchical porous nanofiber membrane (ZIF-67/PS HPNFM) for both PM and SO2 filtration. By controlling the hierarchical porous structure we achieve highly-effective and multi-functional air cleaning membrane that has remarkably low resistance. The macropores interwoven by nanofibers offer high gas permeance of 1489 m3 m−2 h−1 kPa−1 which ensure a low pressure drop of 91 Pa. Meanwhile, the filled ZIF-67 enhanced the PM capture so that the ZIF-67/PS HPNFM showed a very high PM (<0.3 μm) removal efficiency of 99.921%. The mesopores in each nanofiber provided the gas permeating channels that direct SO2 to ZIF-67. Further, the micropores from ZIF-67 dramatically enhanced the surface area (236 m2 g−1) and porosity (0.259 cm3 g−1) which resulted in a good SO2 adsorption capacity (1362 mg g−1) at room temperature and humidity of 55%. The hierarchical porous structure membrane with multifunction provides a new concept for synergistic removal of various air contaminants.

One-dimensional porous nanofibers of Co3O4 on the carbon matrix from human hair with superior lithium ion storage performance.

One-dimensional (1D) hierarchical porous nanofibers of Co3O4 possessing of (220) facets on the carbon matrix from human hair (H2@Co3O4) with 20–30 nm in width and 3–5 μm in length are prepared by a facile solvothermal and calcination approach. The well crystallized small Co3O4 particles with the diameter of about 8–12 nm were closely aggregated together in the nanofibers. Electrochemical analyses show that the first discharge capacity of H2@Co3O4 electrode is 1368 mAh g−1 at the current density of 0.1 A g−1 based on the total mass of composite. A high reversible capacity of 916 mAh g −1 was obtained over 100 cycles at 0.1 A g−1, presenting a good cycling stability. When cycled at a high current density of 1 and 2 A g−1, the specific capacity of 659 and 573 mAh g−1 could be still achieved, respectively, indicating a superior power capability.

Superior lithium storage performance of hierarchical porous vanadium pentoxide nanofibers for lithium ion battery cathodes

The hierarchical V2O5 nanofibers cathode materials with diameter of 200–400nm are successfully synthesized via an electrospinning followed by annealing. Powder X-ray diffraction (XRD) pattern confirms the formation of phase-pure product. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) obviously display the hierarchical porous nanofibers constructed by attached tiny vanadium oxide nanoplates. Electrochemical behavior of the as-prepared product is systematically studied using galvanostatic charge/discharge testing, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). It turns out that in comparison to the commercial V2O5 and other unique nanostructured materials in the literature, our V2O5 nanofibers show much enhanced lithium storage capacity, improved cyclic stability, and higher rate capability. After 100 cycles at a current density of 800mAg−1, the specific capacity of the V2O5 nanofibers retain 133.9mAhg−1, corresponding to high capacity retention of 96.05%. More importantly, the EIS at various discharge depths clearly reveal the kinetics process of the V2O5 cathode reaction with lithium. Based on our results, the possible approach to improve the specific capacity and rate capability of the V2O5 cathode material is proposed. It is expected that this study could accelerate the development of V2O5 cathode in rechargeable lithium ion batteries.

Tuning porous silica nanofibers by colloid electrospinning for dye adsorption

Porous silica nanofibers were prepared by electrospinning alkoxide precursors and sacrificial polystyrene nanoparticles (PSNs). The multi-compartmented fibers were electrospun from a mixed solution of colloidal particles and poly (vinyl pyrrolidone), added with tetraethyl orthosilicate and acetic acid. The colloidal particles were embedded into the resultant fibers with a close-packing structure. After air calcination, the removal of polymeric particles created porous silica nanofibers. The pore size of the silica nanofibers ranges from micropores (∼3 nm) to mesopores (∼50 nm), and can be precisely controlled by changing the weight ratio of the PSNs. Such hierarchical porous nanofibers have been demonstrated as a promising candidate for dye adsorption. The dye absorption ability was enhanced as more mesopores were created, although the specific surface area simultaneously decreased with the decrease of micropores.