Metal Oxide Nanofibers Research Articles

Self-Assembled Conductive Metal-Oxide Nanofiber Interface for Stable Li-Metal Anode.

Li-metal anodes promise to build high-energy-storage systems, but they suffer from safety problems from severe dendrite growth. Here, we develop a thin and conformal hybrid ionic and electronic conducting metal-oxide nanofiber interface to stabilize Li-anodes without forming dendrites. The thin ionic-conductive Li0.33La0.56TiO3 (LLTO) nanofiber film is first fabricated by electrospinning followed by pyrolysis. After connecting with the electrolytes-wetted Li-metal anodes, due to the self-driven chemical reactions, LLTO is reduced, and a hybrid conducting interface is developed. The interface can act as a reservoir to redistribute the nonuniform Li-ion flux above the anode surface and reduce the driving force of dendrite formation by leveling electric potential distribution, enabling a stable Li plating-stripping with a low overpotential of 80 mV over 800 h at a high current of 5 mA/cm2. More practically, the Li-LiNi0.8Co0.15Al0.05O2 cells deliver a high capacity of 147 mA h/g at 1 C with a Coulombic efficiency of 99% over 150 cycles, offering prospects to achieve reliable Li-metal batteries.

ZnO Nanostructures and Electrospun ZnO-Polymeric Hybrid Nanomaterials in Biomedical, Health, and Sustainability Applications.

ZnO-based nanomaterials are a subject of increasing interest within current research, because of their multifunctional properties, such as piezoelectricity, semi-conductivity, ultraviolet absorption, optical transparency, and photoluminescence, as well as their low toxicity, biodegradability, low cost, and versatility in achieving diverse shapes. Among the numerous fields of application, the use of nanostructured ZnO is increasingly widespread also in the biomedical and healthcare sectors, thanks to its antiseptic and antibacterial properties, role as a promoter in tissue regeneration, selectivity for specific cell lines, and drug delivery function, as well as its electrochemical and optical properties, which make it a good candidate for biomedical applications. Because of its growing use, understanding the toxicity of ZnO nanomaterials and their interaction with biological systems is crucial for manufacturing relevant engineering materials. In the last few years, ZnO nanostructures were also used to functionalize polymer matrices to produce hybrid composite materials with new properties. Among the numerous manufacturing methods, electrospinning is becoming a mainstream technique for the production of scaffolds and mats made of polymeric and metal-oxide nanofibers. In this review, we focus on toxicological aspects and recent developments in the use of ZnO-based nanomaterials for biomedical, healthcare, and sustainability applications, either alone or loaded inside polymeric matrices to make electrospun composite nanomaterials. Bibliographic data were compared and analyzed with the aim of giving homogeneity to the results and highlighting reference trends useful for obtaining a fresh perspective about the toxicity of ZnO nanostructures and their underlying mechanisms for the materials and engineering community.

Facile Synthesis of Carbon Supported Porous Metal Oxide Nanofibers for Prospective Supercapacitor Electrodes

Supercapacitors (SCs) have received great attention due to their rapid charging-discharging rate and long life cyclic stability. Transition metal oxides (TMOs) have been widely investigated as electrode materials for their theoretically higher specific capacitance. Here, a facile and effective synthesis route of metal oxide embedded in porous carbon nanofiber support has been developed. First, the corresponding metal salts were dissolved in a homogenous polyacrylonitrile (PAN) and cellulose diacetate (CDA) polymer solution. Fresh fibers were obtained by electrospinning the polymer solution. Then it was annealed at high temperature in N2 atmosphere to obtain the carbonized samples. During the thermal treating process, metal salts are converted to less oxidation states or even only metal, while PAN forms carbon backbone and CDA as the sacrificial polymer is burned to form pores. For samples with only metal formed, the hydrothermal treatment is subsequently performed for further oxidation. When tested for supercapacitors, the 3D connected porous nanofiber structure can provide transport channel for electrolyte during charging-discharging process. In detail, porous TMOs/carbon fibers including cheap and high performance TMOs, such as NiO, Co3O4, MnO2 and ZnO based materials, or even multiple metal TMOs will be systematically investigated. The effects of different annealing temperature on the compositions, porous structure and electrochemical performance will also be investigated. The preliminary results show that TMOs supported by the porous carbon fiber demonstrated greatly improved electrochemical performance, indicating that this facile synthesis method can be a promising alternative to prepare TMOs electrode materials with high performance.

(Invited) Polymer-Ceramic Composite Electrolytes for All-Solid-Sate Lithium-Ion Batteries

This talk will present our effort to develop the polymer-ceramic composite electrolytes for all-solid-sate lithium-ion batteries. Li-ion conducting metal oxide nanofibers are fabricate with electrospinning techniques. The electrospun nanofibers serve as the three-dimensional scaffold for in-situ polymerization of matrix. The electrochemical performance of the Li-ion battery with the polymer-ceramic composite electrolyte is tested in terms of energy density, rate capability and cyclic stability.

Field Effect Transistors Based on One-Dimensional, Metal-Oxide Semiconducting Nanofiber Mats

Metal-oxide semiconductors are very promising alternatives to amorphous and polycrystalline Si semiconductors. In addition to thin-film metal-oxide semiconductors, nanostructured metal-oxide semiconductors have also attracted considerable attention due to their interesting physical properties for versatile potential applications. Here, we report on metal-oxide semiconducting (InZnO and HfInZnO) nanofiber mats prepared by electrospinning. Thermal gravimetric analyses (TGA) and X-ray diffraction (XRD) measurements were carried out so as to investigate the phase transition from as-spun metal precursor/polymer matrix composite nanofibers mats to metal-oxide nanofiber mats. We fabricated field effect transistor (FETs) based on InZnO and HfInZnO nanofiber mats, and both FETs showed proper n-type transfer and output characteristics. FETs based on InZnO nanofiber mats-based FETs exhibited superior device performance: negligible hysteresis, a decent electron mobility of 5.49 cm2/Vs, and a good on/off current ratio of 107.

Electrospun metal oxide nanofibrous mat as a transparent conductive layer

The fabrication of low cost conductive transparent layers with appropriate flexibility is a major challenge for developing the next generation of optoelectronic devices. Metal oxide nanofibers with aligned and random orientation, as conductive and high transparent layers, were fabricated through electrospinning method followed by the calcination process. The prepared samples were characterized with scanning electron microscopy (SEM), four-point probe device, and diffuse transmittance Spectroscopy (DTS) for evaluating their conductivity and transparency properties. The diameter of the as-spun fibers is in the range of 270 nm- 1 μm and annealed fibers have diameter about 60 nm–300 nm with mesoporous structure. Optimized electrospun CuO nanostructure mats showed high transparency in the range of 70%–90% and the sheet resistance of 0.38 MΩ/sq to 5.41MΩ/sq. The results show the potential of metal oxide nanostructures as transparent conductive layers for applications such as touch screens which need high resistivity and transparency. • Metal oxide nanostructures as transparent conductive layers with high resistivity and transparency were successfully produced. • Optimized electrospun CuO nanostructure mats showed high transparency in the range of 70%–90% and the sheet resistance of 0.38 MΩ/sq to 5.41MΩ/sq. • The transparency of the layers could be adjusted by changing the fibers orientation and thickness in the fibrous structure.

Thermal properties of electrospun polyvinylpyrrolidone/titanium tetraisopropoxide composite nanofibers

In this work, polyvinylpyrrolidone/titanium tetraisopropoxide (PVP/TTIP) composite nanofibers were prepared by electrospinning from alcoholic solutions. The morphology and the properties of the fibers were investigated by SEM, Raman spectroscopy, and XRD. The thermal properties and the evolved gases were studied in detail by TG/DTA-MS. The as-spun 800–900-nm-thick PVP/TTIP fibers were then, respectively, annealed in different atmospheres (air and nitrogen) and at different temperatures (550 °C, 900 °C) in order to obtain anatase and rutile TiO2 nanofibers. The investigation of the thermal properties was important before the preparation of the oxide nanofibers, because based on them the crystallinity and the composition of the TiO2 nanofibers could be controlled. Metal oxide nanofibers with a slightly smaller diameter, made up mostly by anatase TiO2, were successfully prepared when the annealing was done at 550 °C, while at 900 °C, rutile TiO2 fibers were obtained. If nitrogen atmosphere was applied, the nanofibers contained some carbon residue as well.

Synthesis, Characterization and Photocatalytic Activity of Nanocrystalline First Transition-Metal (Ti, Mn, Co, Ni and Zn) Oxisde Nanofibers by Electrospinning

In this work, five nanocrystalline first transition-metal (Ti, Mn, Co, Ni and Zn) oxide nanofibers were prepared by electrospinning and controlled calcination. The morphology, crystal structure, pore size distribution and specific surface area were systematically studied by scanning electron microscope (SEM), transmission electron microscope (TEM), surface and pore analysis, and thermo gravimetric analyzer (TGA). The results reveal that the obtained nanofibers have a continuously twisted three-dimensional scaffold structure and are composed of neat nanocrystals with a necklace-like arrangement. All the samples possess high specific surface areas, which follow the order of NiO nanofiber (393.645 m2/g) > TiO2 nanofiber (121.445 m2/g) > ZnO nanofiber (57.219 m2/g) > Co3O4 nanofiber (52.717 m2/g) > Mn2O3 nanofiber (18.600 m2/g). Moreover, the photocatalytic degradation of methylene blue (MB) in aqueous solution was investigated in detail by employing the five kinds of metal oxide nanofibers as photocatalysts under ultraviolet (UV) irradiation separately. The results show that ZnO, TiO2 and NiO nanofibers exhibit excellent photocatalytic efficiency and high cycling ability to MB, which may be ascribed to unique porous structures and the highly efficient separation of photogenerated electron-hole pairs. In brief, this paper aims to provide a feasible approach to achieve five first transition-metal oxide nanofibers with excellent performance, which is important for practical applications.

NiO and Co3O4 nanofiber catalysts for the hydrogen evolution reaction at liquid/liquid interfaces

The development of the non-precious, earth abundant and inexpensive catalysts with high catalytic efficiency for the electrocatalytic hydrogen evolution reaction acts an essential role in sustainable energy conversion and storage. Herein, we report that hydrogen evolution in two-phase systems by an organic soluble electron donor decamethylferrocene (DMFc) has been efficiently catalyzed by Co3O4 and NiO nanofiber catalysts, which are fabricated by the low-cost and simple electrospinning method. The catalytic activities of these metal oxide nanofibers have been examined by two-phase reactions and four-electrode cyclic voltammetry methods at water/1,2 dichloroethane interface. The hydrogen evolution reaction rate of nanofiber catalysts is also compared to the bulk forms of these metal oxide catalysts. The reaction rate is increased 74, 152, 284 and 384 times by using bulk and nanofiber forms of Co3O4 and NiO, respectively, when compared to an uncatalyzed reaction. The higher catalytic activity of the metal oxide nanofibers can be ascribed to the enhanced surface to volume ratio revealed from the fibrous structures.

A systematic comparative study of the efficient co-catalyst-free photocatalytic hydrogen evolution by transition metal oxide nanofibers

The efficiencies of a series of hydrogen evolving catalysts based on metal oxide nanofibers (NiO, Co3O4, Mn3O4) are investigated for the photocatalytic hydrogen evolution from water without using any co-catalyst under the visible light irradiation by using triethanolamine (TEOA) as an electron donor and Eosin-Y (EY) dye as a photosensitizer. It is found that the photocatalytic hydrogen evolution activities follow the order as: Mn3O4<Co3O4<NiO (196 μmolg−1h−1, 5552 μmolg−1h−1, 7757 μmolg−1h−1, respectively). Moreover, the catalytic behavior of these nanofibers on the hydrogen production has been also compared to bulk forms of NiO, Co3O4 and Mn3O4 by producing hydrogen 937 μmolg−1h−1, 901 μmolg−1h−1 and 135 μmolg−1h−1, respectively. The nanofiber structures demonstrated much higher photocatalytic activity than bulk forms due to the effect of the increased surface to volume ratio deduced from the fibrous character. The photocatalytic plausible pathway for the hydrogen production is also discussed.

Nature-Inspired Capillary-Driven Welding Process for Boosting Metal-Oxide Nanofiber Electronics.

Recently, semiconducting nanofiber networks (NFNs) have been considered as one of the most promising platforms for large-area and low-cost electronics applications. However, the high contact resistance among stacking nanofibers remained to be a major challenge, leading to poor device performance and parasitic energy consumption. In this report, a controllable welding technique for NFNs was successfully demonstrated via a bioinspired capillary-driven process. The interfiber connections were well-achieved via a cooperative concept, combining localized capillary condensation and curvature-induced surface diffusion. With the improvements of the interfiber connections, the welded NFNs exhibited enhanced mechanical property and high electrical performance. The field-effect transistors (FETs) based on the welded Hf-doped In2O3 (InHfO) NFNs were demonstrated for the first time. Meanwhile, the mechanisms involved in the grain-boundary modulation for polycrystalline metal-oxide nanofibers were discussed. When the high-k ZrO x dielectric thin films were integrated into the FETs, the field-effect mobility and operating voltage were further improved to be 25 cm2 V-1 s-1 and 3 V, respectively. This is one of the best device performances among the reported nanofibers-based FETs. These results demonstrated the potencies of the capillary-driven welding process and grain-boundary modulation mechanism for metal-oxide NFNs, which could be applicable for high-performance, large-scale, and low-power functional electronics.

High-performance field-effect transistors based on gadolinium doped indium oxide nanofibers and their application in logic gate

One-dimensional metal oxide nanofibers have been regarded as promising building blocks for large area low cost electronic devices. As one of the representative metal oxide semiconducting materials, In2O3 based materials have attracted much interest due to their excellent electrical and optical properties. However, most of the field-effect transistors (FETs) based on In2O3 nanofibers usually operate in a depletion mode, which lead to large power consumption and a complicated integrated circuit design. In this report, gadolinium (Gd) doped In2O3 (InGdO) nanofibers were fabricated by electrospinning and applied as channels in the FETs. By optimizing the doping concentration and the nanofiber density, the device performance could be precisely manipulated. It was found that the FETs based on InGdO nanofibers, with a Gd doping concentration of 3% and a nanofiber density of 2.9 μm−1, exhibited the best device performance, including a field-effect mobility (μFE) of 2.83 cm2/V s, an on/off current ratio of ∼4 × 108, a threshold voltage (VTH) of 5.8 V, and a subthreshold swing (SS) of 2.4 V/decade. By employing the high-k ZrOx thin films as the gate dielectrics in the FETs, the μFE, VTH and SS can be further improved to be 17.4 cm2/V s, 0.7 V and 160 mV/decade, respectively. Finally, an inverter based on the InGdO nanofibers/ZrOx FETs was constructed and a gain of ∼11 was achieved.

Electrospinning to Prepare Nanostructured Photocatalysts and Photoelectrodes

Electrospinning is a well-known, simple and fast method to prepare polymer fibers with diameters of 100-500 nm and lengths up to several micrometers.[1] Since for many semiconductor materials the charge carrier diffusion length is a critical parameter restricting photocatalytic or photoelectrochemical performance, we use the electrospinning approach to prepare nanostructured metal oxide nanofibers.[2] Directly after electrospinning, such nanofibers still contain spinning polymer, after calcination crystalline metal oxide nanofibers with diameter of 100-200 nm can be prepared.[3] Using the electrospinning technique, it is also possible to prepare fibrous photoelectrodes directly onto conducting substrates in a one step process.[4,5] Nanofibers of the (111)-layered perovskite materials Ba5Ta4O15 are built up from small single crystals, and are able to generate hydrogen without any co-catalyst in photocatalytic reformation of methanol. After photodeposition of Rh-Cr2O3 co-catalysts, the nanofibers show better activity in overall water splitting compared to sol–gel-derived powders.[3] Hollow a-Fe2O3 nanofibers and core–shell-like a-Fe2O3/indium-tin oxide (ITO) nanofiber composites were utilized as a photoanode for solar water splitting, the latter showing a doubled photocurrent compared to the hollow fiber photoanodes. This can be most likely be attributed to fast interfacial charge carrier exchange between the highly conductive ITO nanoparticles and a-Fe2O3, thus inhibiting the recombination of the electron–hole pairs in the semiconductor by spatial separation.[4] CuO photocathodes were directly prepared via electrospinning onto FTO, and calcination studies were performed to systematically characterize their crystallographic and structural evolution.[5] The higher the annealing temperature, the more developed are the crystalline domains of the nanofibers, which results in better conductivity and less defect sites serving as trap states for the photo-excited charge carriers. Hence, the CuO nanofiber photocathodes annealed at 800 °C showed the highest photoresponse and stability. No decrease in the photocurrent density after prolonged operation in aqueous electrolyte was observed.

Dual‐Fiber Approach toward Flexible Multifunctional Hybrid Materials

AbstractMultifunctional paper‐like materials containing metal oxide nanofibers are important for flexible electronics and other redox‐based applications, but are often prone to mechanical failure. This work presents the coassembly of V2O5 nanofibers (VNFs) in a dual‐fiber approach together with cellulose nanofibers to produce tough (0.26 MJ m−3), but strong (250 MPa) flexible hybrid materials. Indeed, nanotensile tests reveal a significant increase in toughness (200%) and strength (85%) of the hybrid films as compared to pristine VNF films. The microstructure of the films shows a transition from an anisotropic texture for the single‐component films to an isotropic, entangled network in case of the hybrid films, which facilitates effective fracture resistance mechanisms. The flexible hybrid films display high electrical conductivity (0.2 S cm−1) and elastic properties originating from V2O5 nanofibers with excellent toughness and transparency endowed by the cellulose nanofibers. The self‐supported hybrid films show reversible electrochromic behavior without the need for common substrates such as conducting indium tin oxide glass. It is conceivable that these self‐supported films can be exploited in the future in smart, flexible optoelectronic devices.

Electrospun p-type CuO nanofibers for low-voltage field-effect transistors

One-dimensional metal-oxide nanofibers show great promise as the basis for nano-device platforms due to their large surface to volume ratio and unique electrical properties. Here, we represent the facile fabrication of p-type CuO nanofibers utilizing the electrospinning technique for field-effect transistors (FETs), which incorporate CuO nanofibers as a channel and high-κ Al2O3 as a dielectric layer. The FETs exhibit typical p-type characteristics with a high hole mobility of 3.5 cm2/Vs at a low operating voltage of 4 V, fast switching speed, and modulation of light emission over the external light-emitting diode.

Facile synthesis of metal oxide nanofibers and construction of continuous proton-conducting pathways in SPEEK composite membranes

In this study, a facile approach was used to prepare hydrophilic TiO2 nanofibers (TiNFs) by calcining electrospun polyacrylonitrile nanofibers embedded with titanium precursors. A high-performance proton exchange membrane (PEM) was achieved by incorporating the TiNFs into a sulfonated poly(ether ether ketone) (SPEEK) matrix. The high aspect ratios of the inorganic nanofibers permitted interconnecting of ion-conducting channels, thereby significantly improving proton conductivity in the membrane. In addition, the TiNFs provided tortuous pathways for methanol transport, suppressing the methanol permeability coefficient. The maximum power density of the SPEEK/TiNFs-1.0 composite membrane was 1.4 times higher than that of the pristine SPEEK membrane at 100% relative humidity and 60 °C. Furthermore, the stable fiber skeleton improved the mechanical stability of the composite membrane. The SPEEK/TiNFs-1.0 membrane exhibited superior mechanical properties with the tensile strength of 40.4 MPa and maximum elongation at break of 76%.

Recent Advances in Electrospun Nanofiber Interfaces for Biosensing Devices.

Electrospinning has emerged as a very powerful method combining efficiency, versatility and low cost to elaborate scalable ordered and complex nanofibrous assemblies from a rich variety of polymers. Electrospun nanofibers have demonstrated high potential for a wide spectrum of applications, including drug delivery, tissue engineering, energy conversion and storage, or physical and chemical sensors. The number of works related to biosensing devices integrating electrospun nanofibers has also increased substantially over the last decade. This review provides an overview of the current research activities and new trends in the field. Retaining the bioreceptor functionality is one of the main challenges associated with the production of nanofiber-based biosensing interfaces. The bioreceptors can be immobilized using various strategies, depending on the physical and chemical characteristics of both bioreceptors and nanofiber scaffolds, and on their interfacial interactions. The production of nanobiocomposites constituted by carbon, metal oxide or polymer electrospun nanofibers integrating bioreceptors and conductive nanomaterials (e.g., carbon nanotubes, metal nanoparticles) has been one of the major trends in the last few years. The use of electrospun nanofibers in ELISA-type bioassays, lab-on-a-chip and paper-based point-of-care devices is also highly promising. After a short and general description of electrospinning process, the different strategies to produce electrospun nanofiber biosensing interfaces are discussed.

Structural evolution during calcination and sintering of a (La0.6Sr0.4)0.99CoO3−δ nanofiber prepared by electrospinning

Design of three-dimensional metal oxide nanofibers by electrospinning is being widely explored. However, the impacts of calcination and sintering on the resulting morphology remain unknown. For the first time, (La0.6Sr0.4)0.99CoO3−δ (LSC) nanofiber, which is among the most promising electrode materials for solid oxide fuel cells, was synthesized by sol-gel electrospinning. By elevating the temperature in oxygen using in situ transmission electron microscopy, we discovered the structural transitions from nanofibers to nanotubes and then to nano-pearl strings. This facile and up-scalable method can be widely applied to design metal oxide one-dimensional nanomaterials with precise control in both geometry (nanofiber, nanotube and nano-pearl string) and surface area (by varying grain size).

Recent Advances in the Synthesis of Metal Oxide Nanofibers and Their Environmental Remediation Applications

Recently, wastewater treatment by photocatalytic oxidation processes with metal oxide nanomaterials and nanocomposites such as zinc oxide, titanium dioxide, zirconium dioxide, etc. using ultraviolet (UV) and visible light or even solar energy has added massive research importance. This waste removal technique using nanostructured photocatalysts is well known because of its effectiveness in disintegrating and mineralizing the unsafe organic pollutants such as organic pesticides, organohalogens, PAHs (Polycyclic Aromatic Hydrocarbons), surfactants, microorganisms, and other coloring agents in addition to the prospect of utilizing the solar and UV spectrum. The photocatalysts degrade the pollutants using light energy, which creates energetic electron in the metal oxide and thus generates hydroxyl radical, an oxidative mediator that can oxidize completely the organic pollutant in the wastewater. Altering the morphologies of metal oxide photocatalysts in nanoscale can further improve their photodegradation efficiency. Nanoscale features of the photocatalysts promote enhance light absorption and improved photon harvest property by refining the process of charge carrier generation and recombination at the semiconductor surfaces and in that way boost hydroxyl radicals. The literature covering semiconductor nanomaterials and nanocomposite-assisted photocatalysis—and, among those, metal oxide nanofibers—suggest that this is an attractive route for environmental remediation due to their capability of reaching complete mineralization of organic contaminants under mild reaction conditions such as room temperature and ambient atmospheric pressure with greater degradation performance. The main aim of this review is to highlight the most recent published work in the field of metal oxide nanofibrous photocatalyst-mediated degradation of organic pollutants and unsafe microorganisms present in wastewater. Finally, the recycling and reuse of photocatalysts for viable wastewater purification has also been conferred here and the latest examples given.

Micropatterning of metal oxide nanofibers by electrohydrodynamic (EHD) printing towards highly integrated and multiplexed gas sensor applications

Integration of heterogeneous sensing materials in microelectronic devices is essential to accomplish compact and highly integrated environmental sensors. For this purpose, a micro-patterning method of electrospun metal oxide nanofibers based on electrohydrodynamic (EHD) printing process was developed in this work. Several types of metal oxide (SnO2, In2O3, WO3 and NiO) nanofibers that were produced by electrospinning, fragmented into smaller pieces by ultrasonication, and dissolved in organic solvents were utilized as inks for the printing. Constant or pulsed wave bias consisting of base and jetting voltages were applied between a nozzle and a substrate to generate a jetting of nanofiber solutions. Several parameters for EHD printing such as pulse width, inner diameter of the nozzle, distance from the nozzle to the substrate, and stage speed, were optimized for accurate micro-patterning of electrospun nanofibers. By using optimized printing parameters, microscale patterns of electrospun nanofibers with a minimum diameter less than 50μm could be realized. Gas sensors were fabricated by EHD printing on the microelectrodes and then used for the detection of toxic gases such as NO2, CO and H2S. Four kinds of metal oxides could detect down to 0.1ppm of NO2, 1ppm of H2S and 20ppm of CO gases. Also, heterogeneous nanofiber gas sensor array was fabricated by the same printing method and could detect NO2 using the sensor array platform with microheaters. Furthermore, microscale patterns of nanofibers by EHD printing could be applied to the suspended MEMS platform without any structural damage and this sensor array could detect NO2 and H2S gases with 20mW power consumption.