Metal Oxide Nanofibers Research Articles

(IMCS Third Place Best Paper Award) Highly Selective and Sensitive Trimethylamine Gas Sensors Using Patterned Metal Oxide Nanofibers Prepared By Near-Field Electrospinning

IntroductionOxide nanofibers consisting of nanoparticles are excellent nanostructures for designing high performance gas sensors. To date, randomly tangled oxide nanofiber networks prepared by far-field electrospinning process (FFES) have been widely explored as the sensing materials. When the distance between spinneret needle and substrate is very short, the straight configuration of nanofibers can be directly written on the substrate without whipping. This is referred as near-field electrospinning (NFES), which can be applied to well-defined patterning of one-dimensional nanofibers for various new applications such as sensors, optoelectronic circuits, and functional nanoelectronics. The patterning of polymeric nanofibers has been demonstrated over a decade ago. In contrast, the fabrication of one-dimensional (1D) metal oxide nanopatterns remains challenging because it becomes difficult to control the chaotic whipping motion of the jet due to the acceleration of metal ions under the electric field. In the present study, grids, diamonds, and hexagrams composed of In2O3, Co3O4, and NiO nanofibers were prepared by NFES and their potential applications as gas sensors were investigated. The sensor using In2O3 nanofiber pattern exhibited an unprecedentedly high response (resistance ratio = 239) to 5 ppm trimethylamine (TMA) with negligible cross-responses to ubiquitous ethanol and other interference gases. Method Transparent solution containing 7 g of methanol (99 %), polyvinylpyrrolidone (PVP, 17.4 wt%, Mw = 1,300,000) and metal nitrates (indium nitrate hydrate, 1.4 wt%, 99.999%; cobalt nitrate hexahydrate, 1.7 wt%, 99.99%; nickel nitrate hexahydrate, 1.7 wt%, 99.99%) were stirred for 24 h at room temperature. The prepared clear solution was transferred to a glass syringe (1000 μL) with a 21-gauge needle, and electrospun onto a 4-inch Si/SiO2 wafer containing 76 sensor substrates (size: 1 × 1 cm2) in which Pt interdigitated electrodes (electrode width: 50 μm, electrode spacing: 5 μm) above a metallic collector. The flow rate is fixed as 0.005 μL min−1 at an applied voltage of 50 V and the distance between the tip and the collector is 1 mm. During electrospinning, the loader and collector moved toward x- and/or y-axis at a controlled moving velocity of 800 mm s−1, leading to the fabrication of precursor fiber patterns, for example, grids, diamonds, and hexagrams. The precursor patterns were annealed at 600 °C for 5 h in an air atmosphere, and converted into the corresponding patterns of In2O3, Co3O4, and NiO pattern sensors, respectively. The sensors were placed in a quartz tube furnace and heated at sensing temperature (In2O3: 350 °C; Co3O4: 225 °C; NiO: 300 °C). The dc-probe resistance of the sensor was measured using an electrometer interfaced with a computer. Results and Conclusions The well-defined patterns of continuous and cylindrical oxide nanofibers could be prepared by using highly volatile solvent (methanol) and by controlling the viscosity and electrical conductivity of spray solution, the distance between spinneret needle and substrate, and the moving velocity of spinneret needle. All the parameters had an optimum window, indicating that the sophisticated control or tuning of the parameters is essential to prepare well-organized and continuous precursor and/or metal oxide fibers via NFES. It is worthwhile to note that the longstanding problem of preparing elaborate nano-architectures consisting of 1D metal oxides has been solved for the first time by investigating the interrelations of the solution/working parameters in NFES systematically. Interestingly, the sensor using In2O3 nanofiber pattern on Pt electrodes exhibited unprecedented high selectivity and responses to TMA compared with other metal oxide nanostructures reported in the literature, whereas random networks of In2O3 nanofibers and dense thin In2O3 film with negligible Pt electrode exposure showed low response and selectivity to TMA. The intriguing trimethylamine sensing characteristics are explained in relation to the promotion of gas sensing reaction by catalytic Pt electrode, which is supported again by the high TMA selectivity of the sensors using the patterns of Co3O4 and NiO nanofibers. In addition, the highly increased sensitivity to analyte gases compared with thin film sensors can be attributed by the increased gas accessibility due to the sensor structures, which is composed of mono-layered In2O3 nanofibers with 200 nm diameter. The NFES-assisted patterning of metal oxide nanofibers can provide a new platform to design high performance gas sensors for a range of emerging applications.

Fabrication of high‐efficiency anatase TiO2 photocatalysts using electrospinning with ultra‐violet treatment

AbstractIn metal oxide nanofiber fabrication using the electrospinning method, heat treatment is performed at temperatures of 500°C or higher for crystallization and polymer desorption. Therefore, it is difficult to fabricate low‐temperature phase metal oxides that crystallize at low temperatures. TiO2, a representative metal oxide often used as photocatalysts, is known to have higher photocatalytic activity in the low‐temperature phase (anatase structure) than in the high‐temperature phase (rutile structure). Studies on the fabrication of TiO2 anatase nanofibers using conventional electrospinning have reported disadvantages such as the partial expression of rutile structures and low crystallinity. This study developed an anatase TiO2 nanofiber as a high‐efficiency catalyst based on the electrospinning method and a residual organic matter cleaning method that employs ultra‐violet (UV) light. We fabricated nanofibers using the electrospinning method and implemented TiO2 nanofibers with the anatase structure through heat treatment at 260°C. Residual organics remaining after heat treatment of the fabricated crystalized TiO2 nanofibers were removed by exposing them to UV light, thereby improving photocatalytic efficiency. The photocatalytic efficiency of the fabricated TiO2 nanofibers was confirmed through a methylene blue (MB) decomposition experiment under visible light irradiation. The photocatalytic efficiency (time taken for the concentration of the MB solution to reach 50%) of the UV‐treated TiO2 nanofibers was approximately six times higher than of P25 and the heat‐treated nanofibers.

Chemiresistive acetylene sensor fabricated from Ga-doped ZnO nanofibers functionalized with Pt catalysts

Herein, we demonstrate a sensitization strategy via solid-solution doping and catalytic metal nanoparticles (NPs) onto porous metal oxide nanofibers (NFs) for superior acetylene (C2H2) sensing capabilities. The introduction of dopants and catalysts not only increases the inherent reactivity of metal oxides, but also induces the spillover of C2H2 onto metal oxides, significantly improving the sensing properties. We elucidate that the high porosity of the metal oxide NFs, prepared by electrospinning and utilizing saponin as a sacrificial template, is the key to achieving high gas permeability and numerous active sites. Consequently, Ga-doped ZnO porous NFs functionalized with Pt catalysts exhibited the highest C2H2 sensing responses among the current state-of-the-art C2H2 sensors (Ra/Rg = 26.2 at 400 °C) with a fast response time (10.2 s), at a particularly low concentration of 5 ppm. Moreover, these NFs showed excellent selectivity against the interfering gas (H2, C7H8, CO, CH4, C8H10, CH3COCH3, HCHO and C2H5OH) and outstanding stability up to 20 sensing cycles to 0.4 ppm of C2H2. These results provide an efficient strategy to tailor composites of metal oxide nanostructures, dopants, and catalysts for highly sensitive gas sensors.

Highly conductive and transparent electrospun indium tin oxide nanofibers calcined by microwave plasma

In this work, indium tin oxide (ITO) nanofibers have been prepared by electrospinning of polymers and post-growth microwave plasma calcination (MPC). Interestingly, compared to traditional calcination in furnace, MPC can accelerate the degradation of high polar polymers and improve adhesion of ITO nanofibers to the sapphire substrate. Further characterizations reveal that the ITO nanofibers with diameters of 100–150 nm prepared by MPC at 600 °C can reach a low sheet resistance of 269 Ω/sq and a high transmittance of 90.7% at 550 nm simultaneously, which has not been previously reported by others. Our results show that the efficient MPC method has great potential in preparation of metal-oxide nanofibers for electrical and optical applications.

Modulating the Transport Properties of Metal Oxide Nanofibers Transistors by Controlling the Grain Size

Although SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanofibers (NFs) are one of the good candidates as active materials for next-generation consumable electronics, these NFs based devices still suffer from insufficient on-off current ratios, large and negative threshold voltages ( V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><b>TH</b></sub> ), leading to high energy consumption and rather complicated circuit design. Here, SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> NFs field-effect transistors (FET) were fabricated by an electrospinning technique. The device performance can be precisely manipulated by controlling the crystal grain size in the NFs. This is done by simply adjusting the annealing holding time to achieve high-performance enhancement mode. For the optimal annealing holding time of 60 min, the grain size of NFs is about 11 nm, and the devices exhibit the best electrical performance, including a small and positive V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> (≈ 2.2 V), a large switching current ratio (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> ≥ 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> ), and proper carrier mobility ( μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FE</sub> ) (≈ 2.3 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ). Moreover, this approach is universal and can be applied to optimize other metal oxide semiconductors such as ZnO NFs. This simple and facile method indicates that adjusting annealing holding time is a potential way to control the grain size to achieve low voltage operation and enhancement mode 1D metal oxide FETs.

Effect of two-step calcination on the formation of nickel oxide hollow nanofibers

1D (one-dimensional) hollow nanofibers are of great technological interest. Their formation can be controlled by tuning the calcination process. However, the formation mechanism through the control of the burning stage is still debated in the literature. Herein, the influence of calcination in two steps on the morphology of hollow nanofibers of nickel oxide (NiO), prepared by solution blow spinning (SBS) technique, was investigated. A systematic study using a variety of characterization techniques suggests that a prolonged residence time in the initial step of calcination produces nanofibers with a better definition of the hollow region with better control of tubular wall thickness. Statistically, the calcination methodology studied here does not affect the outer diameter of nanofibers, as shown by Analysis of Variance (ANOVA) and Tukey’s method. According to our findings, the formation mechanism is influenced by gas diffusion and phase separation during fiber spinning and heat treatment, which suggests that neither the Kirkendall effect nor the Ostwald ripening process can be solely responsible for the formation hollow fibers. These findings contribute to a better understanding of the formation of metal-oxide hollow nanofibers induced by heat treatment.

Reduced Graphene Oxide (rGO)-Loaded Metal-Oxide Nanofiber Gas Sensors: An Overview.

Reduced graphene oxide (rGO) is a reduced form of graphene oxide used extensively in gas sensing applications. On the other hand, in its pristine form, graphene has shortages and is generally utilized in combination with other metal oxides to improve gas sensing capabilities. There are different ways of adding rGO to different metal oxides with various morphologies. This study focuses on rGO-loaded metal oxide nanofiber (NF) synthesized using an electrospinning method. Different amounts of rGO were added to the metal oxide precursors, and after electrospinning, the gas response is enhanced through different sensing mechanisms. This review paper discusses rGO-loaded metal oxide NFs gas sensors.

MOFs-derived Co3O4 loaded hollow In2O3 nanofibers with greatly enhanced acetone sensing performance

In this paper, metal-organic frameworks (MOFs)-derived Co3O4 were easily functionalized on In2O3 nanofibers (NFs) by electrospinning followed a calcination at 600 °C in air. The influences of doping content, morphology, and operating temperature on the acetone sensing performances of In2O3 based NFs were comprehensively studied. Our results showed that the 20 wt% Co3O4-In2O3 NFs exhibited outstanding acetone sensing properties at 300 °C. Exactly, it showed a high response to acetone (S∼43.67 @ 100 ppm acetone), which was ∼22 times larger than that of pristine In2O3 NFs. On the same time, it exhibited a short response time (∼13 s). The excellent acetone sensing properties of MOFs-derived Co3O4-In2O3 NFs can be explained by the formation of p-n junction between Co3O4 and In2O3. Our work offers a facile and cost-effective approach to load MOFs-derived Co3O4 on other metal oxides based NFs as a promising gas sensing material and shows the prospects of MOFs-derived metal oxides loaded in metal oxide NFs used for gas sensors.

Highly Selective and Sensitive Trimethylamine Gas Sensors Using Patterned Metal Oxide Nanofibers Prepared By Near-Field Electrospinning

Introduction Oxide nanofibers consisting of nanoparticles are excellent nanostructures for designing high performance gas sensors. To date, randomly tangled oxide nanofiber networks prepared by far-field electrospinning process (FFES) have been widely explored as the sensing materials. When the distance between spinneret needle and substrate is very short, the straight configuration of nanofibers can be directly written on the substrate without whipping. This is referred as near-field electrospinning (NFES), which can be applied to well-defined patterning of one-dimensional nanofibers for various new applications such as sensors, optoelectronic circuits, and functional nanoelectronics. The patterning of polymeric nanofibers has been demonstrated over a decade ago. In contrast, the fabrication of one-dimensional (1D) metal oxide nanopatterns remains challenging because it becomes difficult to control the chaotic whipping motion of the jet due to the acceleration of metal ions under the electric field. In the present study, grids, diamonds, and hexagrams composed of In2O3, Co3O4, and NiO nanofibers were prepared by NFES and their potential applications as gas sensors were investigated. The sensor using In2O3 nanofiber pattern exhibited an unprecedentedly high response (resistance ratio = 239) to 5 ppm trimethylamine (TMA) with negligible cross-responses to ubiquitous ethanol and other interference gases. Method Transparent solution containing 7 g of methanol (99 %), polyvinylpyrrolidone (PVP, 17.4 wt%, Mw = 1,300,000) and metal nitrates (indium nitrate hydrate, 1.4 wt%, 99.999%; cobalt nitrate hexahydrate, 1.7 wt%, 99.99%; nickel nitrate hexahydrate, 1.7 wt%, 99.99%) were stirred for 24 h at room temperature. The prepared clear solution was transferred to a glass syringe (1000 μL) with a 21-gauge needle, and electrospun onto a 4-inch Si/SiO2 wafer containing 76 sensor substrates (size: 1 × 1 cm2) in which Pt interdigitated electrodes (electrode width: 50 μm, electrode spacing: 5 μm) above a metallic collector. The flow rate is fixed as 0.005 μL min−1 at an applied voltage of 50 V and the distance between the tip and the collector is 1 mm. During electrospinning, the loader and collector moved toward x- and/or y-axis at a controlled moving velocity of 800 mm s−1, leading to the fabrication of precursor fiber patterns, for example, grids, diamonds, and hexagrams. The precursor patterns were annealed at 600 °C for 5 h in an air atmosphere, and converted into the corresponding patterns of In2O3, Co3O4, and NiO pattern sensors, respectively. The sensors were placed in a quartz tube furnace and heated at sensing temperature (In2O3: 350 °C; Co3O4: 225 °C; NiO: 300 °C). The dc-probe resistance of the sensor was measured using an electrometer interfaced with a computer. Results and Conclusions The well-defined patterns of continuous and cylindrical oxide nanofibers could be prepared by using highly volatile solvent (methanol) and by controlling the viscosity and electrical conductivity of spray solution, the distance between spinneret needle and substrate, and the moving velocity of spinneret needle. All the parameters had an optimum window, indicating that the sophisticated control or tuning of the parameters is essential to prepare well-organized and continuous precursor and/or metal oxide fibers via NFES. It is worthwhile to note that the longstanding problem of preparing elaborate nano-architectures consisting of 1D metal oxides has been solved for the first time by investigating the interrelations of the solution/working parameters in NFES systematically. Interestingly, the sensor using In2O3 nanofiber pattern on Pt electrodes exhibited unprecedented high selectivity and responses to TMA compared with other metal oxide nanostructures reported in the literature, whereas random networks of In2O3 nanofibers and dense thin In2O3 film with negligible Pt electrode exposure showed low response and selectivity to TMA. The intriguing trimethylamine sensing characteristics are explained in relation to the promotion of gas sensing reaction by catalytic Pt electrode, which is supported again by the high TMA selectivity of the sensors using the patterns of Co3O4 and NiO nanofibers. In addition, the highly increased sensitivity to analyte gases compared with thin film sensors can be attributed by the increased gas accessibility due to the sensor structures, which is composed of mono-layered In2O3 nanofibers with 200 nm diameter. The NFES-assisted patterning of metal oxide nanofibers can provide a new platform to design high performance gas sensors for a range of emerging applications.

Incorporation of Reduced Graphene Oxides for Enhancing the Gas Sensing Characteristics

Incorporation of Reduced Graphene Oxides for Enhancing the Gas Sensing Characteristics

Single Atom Catalysts-Anchored Carbon Nitride: Dual Sensitisation and Morphological Control of Metal Oxide Nanofibers

Reducing the size of noble metal catalysts is one of the key goals in designing catalytic systems with maximum efficiency. Sensitisation of metal oxides with noble metals in a form of single-atoms or a few-atoms-cluster is hence of great interest in various fields including photocatalysis and catalytic conversions [1][2]. With this respect, we employed single atom-anchored shredded carbon nitride nanosheets (Pt-MCN) as a catalyst that can work as both dual-sensitizer and a morphological modifier of tin oxide nanofibers (SnO2 NF). Through electrospinning followed by a calcination process, it is possible to synthesize metal oxide nanofibers uniformly functionalized with Pt-MCN. Thermally stable carbon nitride survives through the calcination step and forms heterojunctions with tin oxide, hence acts as a dual-sensitizer together with the atomic scale Pt, and at the same time, induces the formation of peculiar nano-fiber-in-tubes (FIT) instead of nanofibers. Atomic scale Pt strongly bound on MCN experiences only a minor degree of agglomeration even after calcination, and the majority remains in singly dispersed state, as confirmed by HAADF-STEM analysis. This structure demonstrates an excellent sensing performance toward formaldehyde gas, and in particular, showing an extremely low experimentally determined limit of detection (LOD = 50 ppb).

Dual-Sensitization of Cocatalysts on Elliptical Metal Oxide Nanofiber to Enhance Sensitivity and Selectivity of Acetylene Gas Sensor

Detection of flammable hydrocarbons in power transformer oil has garnered great attention to prevent leakage and explosion, and to maintain safe working environment. Particularly, acetylene which readily dissolves in transformer oil is hazardous for its fast burning property and low explosive limit (2.4 %). Thus, it is of importance to develop highly sensitive chemiresistive materials entailing fast response time. Even if zinc oxide (ZnO) has been recognized as a selective acetylene sensing material [1],it has suffered from several limitations: high resistivity, higher limit of detection and sluggish sensing kinetics. Thus, to overcome such limitations, we designed a novel sensing platform by combining gallium (Ga) doping and co-catalyst decoration.We, herein, introduce highly sensitive and selective acetylene gas sensor through facile morphology tuning with following strategies: 1) Bi-functional Ga doping, 2) morphology control toward elliptical nanofiber, and 3) in-situ coupling of rhodium (Rh) and platinum (Pt) catalysts. The bi-functional Ga dopant does not only lower resistance by forming more free electrons, but also inhibits grain growth. Next, the elliptical nanofiber morphology directed by saponin and H2O-EtOH co-solvent is readily accessible by gas molecules compared to bulk materials, taking advantages of point-to-point contact, a large aspect ratio, a high surface-to-volume ratio, large porosity and high surface area (Fig. 1) [2]. Lastly, the in-situ coupling of Rh and Pt co-catalysts promotes heterogeneous sensitization toward acetylene. The different catalytic behaviors—electronic sensitization of Rh [3] and chemical sensitization of Pt—significantly enhanced the sensitivity and selectivity toward acetylene and achieved a remarkably low limit of detection compared to both bare and mono-metallic catalyst decorated Ga-doped ZnO (Response of bare Ga-doped ZnO to 5 ppm C2H2 > 8). Furthermore, our sodium iodide-templated catalyst synthesis enables small noble metal nanoparticles, facilitating gas penetration and adsorption and numerous p-n heterojunctions, and thereby improving gas sensing performance. These results open a new channel of tailoring highly sensitive and selective acetylene gas sensor. Reference [1] P. Y. Qiao, L. X. Zhang, M. Y. Zhu, Y. Y. Yin, Z. W. Zhao, H. N. Sun, J. Y. Dong, L. J. Bie, Acetylene sensing enhancement of mesoporous ZnO nanosheets with morphology and defect induced structural sensitization, Sensors and Actuators B, 250 (2017) 189-197; doi: 10.1016/j.snb.2017.04.158[2] X. Ren, H. Hou, Z. Liu, F. Gao, J. Zheng, L. Wang, W. Li, P. Ying, W. Yang, T. Wu, Shape‐Enhanced Photocatalytic Activities of Thoroughly Mesoporous ZnO Nanofibers, Small, 12 (2016) 4007-4017; doi: 10.1002/smll.201600991[3] A. Staerz, I. Boehme, D. Degler, M. Bahri, D. E. Doronkin, A. Zimina, H. Brinkmann, S. Herrmann, B. Junker, O. Ersen, J.-D. Grunwaldt, U. Weimar, N. Barsan, Rhodium Oxide Surface-Loaded Gas Sensors, Nanomaterials, 8 (2018) 892; doi:10.3390/nano8110892 Figure 1

Synthesis and characterization of Fe3O4@Cs@Ag nanocomposite and its use in the production of magnetic and antibacterial nanofibrous membranes

Electrospinning is a promising technique to produce polymeric as well as metal oxide nanofibers in diverse domains. In this work, different weight ratios (5%, 7.5% and 10%) of Fe3O4@Cs@Ag magnetic nanoparticles were added in PVP (polyvinylpyrrolidone) polymer and fabricated via electrospinning method to produce magnetic nanofibers (MNFs). Structural, magnetic, morphological, spectroscopic and thermal properties of produced nanofibers were characterized. Furtheremore, antibacterial effects of Fe3O4@Cs@Ag nanofibrous membrane was investigated. Obtained SEM images showed that produced nanofibers were uniform and defect free. Moreover, crystallinity and magnetic moment of fibers was tested by using X-ray diffraction and a vibrating sample magnetometer. The results showed that produced nanofibrous membranes exhibited good antibacterial activity versus Staphylococcus aureus, Bacillus subtilis, Enterococcus faecalis, Escherichia coli, Proteus mirabilis and Pseudomonas aeruginosa.

Li-ion battery cathode performance from the electrospun binary LiCoO2 to ternary Li2CoTi3O8

Metal oxide nanofibers are prepared by electrospinning and are developed to be the electrodes for lithium-ion batteries (LIBs). The effect of calcination temperature and the Li:Co mole ratio of LiCoO2 nanofibers was investigated on the electrochemical cathode performance in a coin cell battery. The higher temperature calcination and Li:Co mole ratio have improved the electrochemical performance of the nanofibers. Lithium cobalt oxide (LiCoO2) nanofibers obtained at 400 and 700 °C retain 65% and 90% of the initial capacity, respectively, after the high-current test and the C-rate reverted to 0.1 C. When doubling the mole ratio of Li:Co (2:1), an increase in specific capacity values from 78 to 148 mAh g−1 has been provided. Additionally, colloidal titania nanoparticles (TiO2 NPs)-doped LiCoO2 nanofibers were obtained and investigated as a cathode material. While the increment in calcination temperature results in higher crystallinity and stability of the LiCoO2 phase, in the presence of the TiO2 NPs causes a transformation of binary (LiCoO2/TiO2) to ternary Li-based transition metal oxide (Li2CoTi3O8/TiO2). An initial discharge capacity of 82 mAh g−1 was found at 0.1 C for the Li2CoTi3O8/TiO2 nanoparticles and the capacity retention was 83% when returned to 0.1 C after 25 cycles.

Understanding the synergy between MgO-CeO2 as an effective promoter and ionic liquids for high dimethyl carbonate production from CO2 and methanol

Direct conversion of carbon dioxide (CO2) to dimethyl carbonate (DMC) using methanol (MeOH) is an attractive approach to utilize CO2. However, this reaction is limited by low CO2 solubility and large amount water formation. For now, dehydrating agents are used to solve this problem. Our goal is to substitute to these dehydrating agents with more abundant porous metal oxide/ionic liquids (ILs) hybrid catalysts. Herein, we have prepared a glycol-based symmetrical cation with different anions assisted ILs combined with electrospun MgO-CeO2 metal oxide nanofiber sponge-500 (EMCMONS-500). The hybrid catalyst displays excellent performance towards DMC synthesis. Notably it showed 98.9% selectivity, and 73.1 mmol g−1 cat DMC yield within 3 h reaction time, 3 MPa CO2 pressure, 120 °C, and 1.12 mmol catalyst loading. In addition, the catalyst shows there is no change in yield and selectivity after several recycles. Furthermore, due to a sponge-like morphology of the EMCMONS-500 catalyst, in which the creation of strong heterojunction takes place which is confirmed by electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) measurements. On the other hand, ILs give tunable acidic properties, high thermal stability, less viscosity, and low vapor pressure. Therefore, EMCMONS-500 easily mixed into ILs and form a highly porous network which gives a huge surface to volume ratios to form a nanoconfinement structure which is helpful to capture more CO2. Considering these advantages of ILs-EMCMONS-500 can be suitable catalyst for CO2 utilization.

Fabrication of Hollow and Porous Tin-Doped Indium Oxide Nanofibers and Microtubes via a Gas Jet Fiber Spinning Process.

We report the morphologies of tin-doped indium oxide (ITO) hollow microtubes and porous nanofibers produced from precursor solutions of polyvinylpyrrolidone (PVP), indium chloride (InCl3), and stannic chloride (SnCl4). The polymer precursor fibers are produced via a facile gas jet fiber (GJF) spinning process and subsequently calcined to produce ITO materials. The morphology shows strong dependence on heating rate in calcination step. Solid porous ITO nanofibers result from slow heating rates while hollow tubular ITO microfibers with porous shells are produced at high heating rates when calcined at a peak temperature of 700 °C. The mechanisms of formation of different morphological forms are proposed. The ITO fibers are characterized using several microscopy tools and thermogravimetric analysis. The concentration of inorganic salts in precursor solution is identified as a key factor in determining the porosity of the shell in hollow fibers. The data presented in this paper show that GJF method may be suitable for fabrication of hollow and multi-tubular metal oxide nanofibers from other inorganic precursor materials.

A novel self-assembly approach for synthesizing nanofiber aerogel supported platinum single atoms

A new self-assembling methodology of incorporating Pt single atoms into metal oxide nanofiber is presented with controlled structural formation over the entire range of length scales. The Pt single atoms substantially enhance the oxygen reduction reaction performance.

Electrospun nanofibers with surface oriented lamellar patterns and their potential applications.

This work shows conclusively that lamellar surface patterns can be obtained with diverse ceramic compositions during electrospinning. The lamellar structure formation is governed by the creation of an outer shell during the thermal treatment of initially uniform cylindrical fibers, consisting of polymer and pre-ceramic compounds. By changing the polymer to pre-ceramic ratio in the electrospinning solution, we demonstrate for the first time a facile way to control the obtained surface structure and the orientation of the lamellas. Furthermore, the lamellar morphology was illustrated in seven different compositions. This report provides a new pathway to obtain unique surface patterns in metal-oxide nanofibers and demonstrates their utilization in different applications. Specifically, we demonstrate the prospect of utilizing Ni-Al-O fibers with lamellar structures as alternative Li-ion battery anodes. In addition, we show the potential of Fe-Al-O fibers as an effective catalyst material.

Self-Welding and Low-Temperature Formation of Metal Oxide Nanofiber Networks and its Application to Electronic Devices

Electrospinningtechnique is considered to be one of the most powerful approaches for the preparation of one-dimensional (1D) metal oxide nanofiber networks (NFNs). In this report, In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> NFNs were fabricated by electrospinning using polymethyl methacrylate (PMMA) as polymer and epoxy resin as additive. Benefiting from the excellent chemical properties of PMMA, In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> NFNs with impact stacking were prepared at a relatively low annealing temperature by a welding process. The welded In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> NFNs were characterized by various techniques and the electrical performance of the field-effect transistors (FETs) based on the welded In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> NFNs were systematically investigated. It is observed that the FET based on In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> NFNs annealed at 320 °C, with a nanofiber density of 0.4 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> exhibits high electrical performance,including an I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> of ~5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> , a μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FE</sub> of 1.27 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V s, an on voltage of -8 V and a hysteresis of 5 V. A device array with 4×5 units was fabricated and tested, confirming the excellent reliability and reproducibility of the FET.

Electrospun ZnSnO Nanofibers for Neuromorphic Transistors With Ultralow Energy Consumption

Emulating the essential synaptic working principles using a three-terminal synaptic transistor has been an important research field in recent years. Electrospun metal oxide nanofibers have been regarded as promising blocks for large-area, low-cost, and one-dimensional (1D) electronic devices. In this letter, zinc-tin oxide (ZnSnO) nanofibers were fabricated by electrospinning, and the synaptic transistors based on ZnSnO nanofibers were integrated. To mimic the synaptic behavior of human brain, LiClO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> dissolved in polyethylene oxide was used as the gate electrolyte in the synaptic transistors. The plasticities, including short term and long term, are mimicked with the help of electrolyte ion dynamics under low and large bias voltage, and an energy consumption of as low as 0.44 pJ per event is observed. This work demonstrates a new approach for establishing the large-scale, energy-efficient 1D artificial synapses for neuromorphic networks.