Oxide Nanowires Research Articles

Virtual Work Principle for Piezoelectric Semiconductors and Its Application on Extension and Bending of ZnO Nanowires

This paper presents the principle of virtual work (PVW) for piezoelectric semiconductors (PSs), which extends the piezoelectric dielectrics to involve the semiconducting effect. As an application of the PVW, a one-dimensional (1D) approximation theory for the extension and bending of PS nanowires is established by directly applying the PVW and Bernoulli–Euler beam theory with the aid of the second-order approximation of electrostatic potential. To illustrate the new model, the mechanical displacement, electrostatic potential, and concentration of electrons for extension and bending deformation of n-type ZnO nanowires are analytically determined. Additionally, numerical results show that, for n-type Zinc Oxide nanowires, the distribution of electrostatic potential is anti-symmetric along the thickness direction for extension deformation. In contrast, the bending deformation causes a symmetric distribution of electrostatic potential characterized by the zeroth-order and the second-order electrostatic potential. Furthermore, these two different deformations result in the redistribution of electrons. The electrostatic potential can be tuned by adjusting the amplitude of the applied mechanical load. Moreover, we find that the increase in doping level will reduce the magnitude of electrostatic potential due to the screening effect. The presented PVW provides a general approach to establishing structural theories and an effective way of implementing numerical methods.

Defect-dependent mechanical and electrical properties of laser-processed CuO nanowires

Narrow bandgap p-type semiconducting metal oxide nanowires (NWs), such as copper oxide (CuO), have gained significant attention for their potential in the development of electrical nano-devices. Tailoring the mechanical and electrical properties of CuO NWs is crucial for optimizing their functionality in specific applications. In this study, we employ nanosecond laser irradiation to precisely modify the properties of individual CuO NWs by inducing point and line defects, including oxygen vacancies and dislocations. Through controlled laser irradiation, we observe a gradual enhancement in the concentration of oxygen vacancies within CuO NWs until reaching a saturation point. The accumulation of vacancies leads to a substantial residual stress, resulting in lattice distortion and misfit. This high residual stress serves as a catalyst for the nucleation of dislocations, subsequently leading to a meaningful enhancement in plasticity. Remarkably, the density of dislocations demonstrates a strong correlation with the duration of laser irradiation. Prolonged irradiation leads to a thermally activated restoration process, where the dislocation configuration transitions from a random distribution to ordered dislocation loops. Mechanical characterization tests indicate that pristine CuO NWs exhibit brittleness, while laser irradiation renders them ductile with improved plasticity. Furthermore, the laser processing of CuO NWs demonstrates an enhancement in their electrical conductivity and optical absorbance.

Electrical Activity and Extremes of Individual Suspended ZnO Nanowires for 3D Nanoelectronic Applications.

We explored the electrical activity and extremes inside individual suspended zinc oxide (ZnO) nanowires (NWs) (diameter: 50-550 nm, length: 5-50 μm) subjected to high forward bias-induced Joule heating using two-terminal current-voltage measurements. NWs were isolated using a reproducible nanometrology technique, employing a nanomanipulator inside a scanning electron microscope. Schottky behavior is observed between installed tips and ZnO NW. The suspended ZnO NWs exhibited an average electrical resistivity ρ (approximately 2.3 × 10-2 Ω cm) and a high electron density n (exceeding 1.89 × 1018 cm-3), comparable to that of InP NWs, GaN NWs, and InAs NWs (1018∼1019 cm-3), suggesting the potential to drive advancements in high-performance NW devices. A maximum breakdown current density (JBD) of ∼0.14 MA/cm2 and a maximum breakdown power density (PBD) of 6.93 mW/μm3 were obtained, both of which are higher than substrate-bound ZnO NWs and consistent with previously reported results obtained from probed ZnO NWs grown vertically on the substrate. Moreover, we discovered that NWs experienced thermal breakdown due to Joule heating and exploited this breakdown mechanism to further investigate the temperature distribution along the ZnO NWs, as well as its dependence on the electrical properties and thermal conductance of contact electrodes. Thermal conductance was determined to be ∼0.4 nW K-1 and ∼1.66 pW K-1 at the tungsten(W)-ZnO NW and platinum(Pt)-ZnO NW contacts, respectively. In addition, we measured the elastic modulus (130-171 GPa), which closely approximated bulk values. We also estimated the nanoindentation hardness to be between 5 and 10 GPa. This work provides valuable insights into the electrical activity and extreme mechanisms, thus providing a better understanding of the potentials and limitations associated with utilizing suspended NWs in 3D nanodevices.

Performance of flexible ZnO nanowire piezoelectric generators enhanced by bifacial superposition

High performance piezoelectric nanogenerators have important applications in many fields. In this work, we report a bifacial superposed zinc oxide piezoelectric nanogenerator that shows better performance than a single unit. A stainless steel substrate with both front and back zinc oxide nanowire arrays is an elementary unit. Then we engage in an alternating superposition of two elementary units with a carbon-contained polyurethane foil. Multiple units can be similarly assembled by adding alternating structures to further enhance the piezoelectric output performance. Nanogenerators obtained by the above bifacial method are flexible and stability with high output. The method can be used to increase the overall piezoelectric performance and is expected to have a wide application in self-powered device fields.

Self‐Assembled Asymmetric Electrodes for High‐Efficiency Thermogalvanic Cells

AbstractThe thermogalvanic cell (TGC) is considered a promising thermoelectric device for directly converting low‐grade waste heat into electricity due to its low‐cost and scalable properties. However, the low output and conversion efficiency limit its practical application. Herein, record‐high thermoelectric conversion performances are achieved in the aqueous ferri/ferrocyanide ([Fe(CN)6]3−/[Fe(CN)6]4−) based TGC by using the electrode of cobaltous oxide nanowires array on carbon cloth fiber. Because of the temperature‐dependence reaction activity between CoO with [Fe(CN)6]4−, the asymmetric electrodes of Co2Fe(CN)6 and CoO nanowires array on carbon cloth fiber are constructed at the hot anode and cold cathode, respectively. These self‐assembled asymmetric electrodes exhibit specific catalysis toward electrode reactions at both ends of TGC, leading to a significant reduction in electronic activation energy. It is demonstrated that the electrodes have high catalytic activity and high specific surface area, enabling the construction of a high‐efficiency TGC with a Carnot‐relative efficiency (ηr) of 14.8% and a maximum output power density (Pmax) of 24.5 W m−2. This work offers an asymmetric electrode engineering pathway for the continuous evolution of TGCs.

A Transparent Photodetector Based on a Composite of Silver and Tungsten Oxide Nanowires

This work presents the development of a transparent photodetector based on a composite of tungsten trioxide (WO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) and silver nanowires (Ag NWs). A uniform transparent conducting film with a resistance of 64 Ω and a transparency of 89 % (at 550 nm) is obtained via spin coating followed by annealing at 120 °C. The device exhibits negative photo-conductance, which can be attributed to the Schottky junction formation at the silver and tungsten oxide interface. The device shows a sensitivity of 25.6 mAW <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and detectivity of 3.38 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> Jones at a low bias voltage of 1 V at room temperature. The low annealing temperature makes the composite compatible with conventional flexible substrates.

Detection of hemoglobin concentration in human blood samples using a zinc oxide nanowire and graphene layer heterostructure based refractive index biosensor

Detection of hemoglobin concentration in human blood samples using a zinc oxide nanowire and graphene layer heterostructure based refractive index biosensor

Investigation of Trap Density Effect in Gate-All-Around Field Effect Transistors Using the Finite Element Method

Trap density refers to the density of electronic trap states within dielectric materials that can capture and release charge carriers (electrons or holes) in a semiconductor channel, affecting the transistor’s performance. This study aims to investigate the influence of trap density on the electrothermal behavior of nanowire gate-all-around GAAFET devices. The numerical solution of Poisson’s equations and continuity equations, coupled with the heat conduction model, has been used to predict the temperature inside the GAAFET device. The finite element method has been used to discretize the semiconductor equations. Investigations have been carried out on a number of physical and geometric parameters, such as oxide thickness, nanowire radius, and gate length. Their effects on output characteristics and device temperature have been discussed. A thinner oxide thickness, lower device radius, and longer channel length led to a higher current flow. Results also reveal that high trap densities can have significant impacts on the degradation of electronic devices, particularly in the context of semiconductor devices like transistors.

Synthesis, Gas Sensing and Photocatalytic Properties of Manganese-Doped and Potassium-Doped Hexagonal Tungsten Trioxide Nanowires

On account of its unique and variable lattice structure and stoichiometric ratio, tungsten oxide is suitable for material modification; for example, doping is expected to improve its catalytic properties. However, most of the doping experiments are conducted by hydrothermal or multi-step synthesis, which is not only time-consuming but also prone to solvent contamination, having little room for mass production. Here, without a catalyst, we report the formation of high-crystallinity manganese-doped and potassium-doped tungsten oxide nanowires through chemical vapor deposition with interesting characterization, photocatalytic, and gas sensing properties. The structure and composition of the nanowires were characterized by transmission electron microscopy and energy-dispersive spectroscopy, while the morphology and chemical valence were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. Electrical measurements show that the single nanowires doped with manganese and potassium had resistivities of 1.81 × 10−5 Ω·m and 1.93 × 10−5 Ω·m, respectively. The doping contributed to the phase transition from monoclinic to metastable hexagonal for the tungsten oxide nanowires, the structure of which is known for its hexagonal electron channels. The hexagonal structure provided efficient charge transfer and enhanced the catalytic efficiency of the tungsten oxide nanowires, resulting in a catalytic efficiency of 98.5% for the manganese-doped tungsten oxide nanowires and 97.73% for the potassium-doped tungsten oxide nanowires after four hours of degradation of methylene blue. Additionally, the gas sensing response for 20 ppm of ethanol showed a positive dependence of doping with the manganese-doped and potassium-doped responses being 14.4% and 29.7%, respectively, higher than the pure response at 250 °C. The manganese-doped and potassium-doped tungsten oxide nanowires are attractive candidates in gas sensing, photocatalytic, and energy storage applications, including water splitting, photochromism, and rechargeable batteries.

(Invited) Coupling Metal-Organic Framework with Oxide Photocatalyst for Selective Photoredox Reactions

Oxide photocatalyst is one of the major groups of photoactive semiconductors capable of facilitating useful photoredox reactions for a variety of energy and environmental-related applications. The intrinsic optical and electronic properties of oxide photocatalysts encounter a number of limitations. Often, the wide band gap and inferior photoexcited charge transportation within oxide semiconductors are highlighted. Wide band gap limits the light absorption while inadequate charge transport properties such as low charge mobility and short lifetime can only afford mild photoactivities. Strategies have been formulated to improve the performance of these semiconductors in order to bridge the gap for practical use. Among many existing strategies, coupling oxide photocatalysts with metal-organic framework (MOF) has gained attention in the community as one potential method to improve performance (e.g. higher light absorption, better product yield, prolonged stability and etc). Attaching photoactive MOFs onto or “doping” metallic element into oxide photocatalyst may extend the light absorption of the composite materials. Improved product yield is, more often, attributed to the adsorption capacity of MOFs towards reactant, which bring about the localised concentration of reactants adjacent to active sites of photocatalyst. Encapsulation of oxide photocatalyst by MOFs can suppress the undesirable side reactions (such as preventing Cu2O from direct contact with moisture) to prolong the stability of oxide photocatalyst.In this presentation, in addition to the above mentioned advantages of MOFs, the role of MOFs in tuning the selectivity of product formation will also be examined and discussed. Figure 1 shows an example of improved selective oxidation of ethanol to form acetaldehyde using ZIF-8 encapsulated ZnO. Selectivity towards acetaldehyde has been improved from ~79% to ~92% with stable photocatalytic activity.1 In another work, Cu2O covered by Cu-MOF has afforded selective CO2 photoreduction to CH4.2 We believe there is charge interaction between the oxide photocatalyst and the adjacent MOF structure. Transfer of photoexcited electrons from the conduction band of Cu2O to the LUMO level of non-excited wide band gap Cu-MOF has been indicated using time-resolved photoluminescence. Because photocatalytic reactions are the results of electron transfer between photocatalyst and reactants, the presence of photocharge interplay between oxide photocatalyst and MOFs may provide new room for exploration as it has demonstrated significant influence in the selectivity of product formation. Figure 1. Example of improved product selectivity by incorporating MOFs to oxide photocatalyst. The left figure indicates the improved formation of acetaldehyde from photocatalytic ethanol oxidation. The right figure shows the reasonable stability of the MOF-oxide photocatalyst under illumination. Reference: H. Wu, T. H. Tan, R. Liu, H. -Y. Hsu, Y. H. Ng, Selective Ethanol Oxidation to Acetaldehyde on Nanostructured Zeolitic Imidazolate Framework-8-wrapped ZnO Photothermocatalyst Thin Films, Solar RRL 2021, 5, 2000423.H. Wu, X. Y. Kong, X. Wen, S. –P. Chai, E. C. Lovell, J. Tang, Y. H. Ng, Metal-Organic Framework Decorated Cuprous Oxide Nanowires for Long-lived Charges Applied in Selective Photocatalytic CO2 Reduction to CH4. Angew. Chem. Int. Ed. 2021, 60, 8455-8459. Figure 1

Hetero-Structured Palladium-Coated Zinc Oxide Photocatalysts for Sustainable Water Treatment

Hetero-structured catalysts have recently attracted considerable interest from researchers in various fields, including electronics, sensing, energy, and photocatalysis. Treated water contains many harmful microorganisms and organic contaminants, which can be effectively removed through an advanced photocatalytic oxidation process. Photocatalysts with wide band gaps, such as semiconductor oxides like titanium dioxide (TiO2) and zinc oxide (ZnO), are typically utilized to decompose these organic pollutants. These generate a charge when exposed to UV-A light irradiation and produce oxidation radicals that cause the decomposition of the organic matter present in water. Metals such as Pd, Ag, Au, Cu, and Ni are being studied as photocatalysts. Semiconducting oxides and metals with appropriate band gaps and Fermi levels can effectively capture the charge generated by the oxide owing to the Moss–Burstein effect. These reactions can enhance the photocatalytic effect by hindering the recombination of the generated holes and electrons, thereby increasing the probability of charge survival.In this study, the performance of zinc oxide nanowires (ZnO NWs) decorated with Pd nanoparticles was evaluated as photocatalysts for sustainable water treatment. To maximize the number of active sites on the surface of the ZnO nanowires, Pd nanoparticles were uniformly deposited via atomic layer deposition (ALD). In ALD, a very thin film that can be deposited in one cycle is created with less than one atomic layer owing to the precursor oxidation reaction. Additionally, the ALD process provides all the surfaces with sufficient time and chemical sources to react, resulting in a uniform amount of deposited material. This unique technology is suitable for the large-area deposition of atomic-level thickness surface materials. Therefore, ALD was used to deposit Pd onto the catalyst surface. The ZnO nanowires were initially fabricated in the form of seeds by ALD and grown via a hydrothermal method. Subsequently, ALD Pd nanoparticles with an average particle size of 3.75 nm were deposited on the enlarged ZnO nanowires. The prepared hetero-structured ALD Pd-deposited ZnO nanowires were analyzed using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and valence band X-ray photoelectron spectroscopy. A new Fermi level of the Pd-ZnO hetero-structure was formed, which was lower than the conduction band energy level of ZnO. The new Fermi level suppresses the recombination of the conduction band and valence band electron holes under UV-A irradiation. The enhanced charge separation enhances the photocatalytic activity. In addition, compared to ZnO NWs, ALD Pd-deposited ZnO NWs produced higher amounts of reactive oxygen species and improved the decomposition rate of organic pollutants in water. To evaluate the performance of the prepared photocatalyst, the decomposition rates of 4-chlorophenol (4-CP), 4-chlorobenzoic acid, and furfuryl alcohol were measured. Regarding the decomposition rate of 4-CP, the photocatalytic performance increased significantly from 42.5 % to 62.8 % when the ZnO nanowires were decorated with Pd nanoparticles. Figure 1

On the Effect of the Nature of Carbon Nanostructures on the Activity of Bifunctional Catalysts Based on Manganese Oxide Nanowires

Manganese oxide nanowires (MONW) combined with carbon nanostructures were synthesized using three different carbon materials, and their effect on the activity towards Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER) was investigated in alkaline electrolytes. The carbon structures were carbon nanofibers (CNF), multiwall carbon nanotubes (CNT) and reduced graphene oxide (rGO). Both MONW and carbon nanostructures were characterized by X-ray diffraction, scanning and transmission electron microscopy, N2 physisorption and X-ray photoelectron spectroscopy. The electrochemical activity was assessed in a three-electrode cell. Composite MONW/CNF showed the best activity towards ORR, and MONW/rGO exhibited the highest activity towards OER of the series. The addition of the carbon nanostructures to MONW increased the number of electrons transferred in the ORR, indicating a synergistic effect between the carbon and manganese oxide structures due to changes in the reaction pathway. The analysis of Tafel slopes and electrochemical impedance spectroscopies showed that carbons and MONW catalyze different steps of the reactions, which explains the better activity of the composites. This led us to synthesize a MONW/rGO-CNF composite, where rGO-CNF is a hybrid carbon material. Composite MONW/rGO-CNF showed an improved activity towards ORR, close to the benchmark Pt/C catalyst, and activity towards OER, close to MONW/rGO, and better than the benchmark IrO2 catalyst. It also showed remarkable stability in challenging operation conditions.

Dual Lewis Acid-Base Sites Regulate Silver-Copper Bimetallic Oxide Nanowires for Highly Selective Photoreduction of Carbon Dioxide to Methane.

Highly selective photoreduction of CO2 to valuable hydrocarbons is of great importance to achieving a carbon-neutral society. Precisely manipulating the formation of the Metal1 ⋅⋅⋅C=O⋅⋅⋅Metal2 (M1 ⋅⋅⋅C=O⋅⋅⋅M2 ) intermediate on the photocatalyst interface is the most critical step for regulating selectivity, while still a significant challenge. Herein, inspired by the polar electronic structure feature of CO2 molecule, we propose a strategy whereby the Lewis acid-base dual sites confined in a bimetallic catalyst surface are conducive to forming a M1 ⋅⋅⋅C=O⋅⋅⋅M2 intermediate precisely, which can promote selectivity to hydrocarbon formation. Employing the Ag2 Cu2 O3 nanowires with abundant Cu⋅⋅⋅Ag Lewis acid-base dual sites on the preferred exposed {110} surface as a model catalyst, 100 % selectivity toward photoreduction of CO2 into CH4 has been achieved. Subsequent surface-quenching experiments and density functional theory (DFT) calculations verify that the Cu⋅⋅⋅Ag Lewis acid-base dual sites do play a vital role in regulating the M1 ⋅⋅⋅C=O⋅⋅⋅M2 intermediate formation that is considered to be prone to convert CO2 into hydrocarbons. This study reports a highly selective CO2 photocatalyst, which was designed on the basis of a newly proposed theory for precise regulation of reaction intermediates. Our findings will stimulate further research on dual-site catalyst design for CO2 reduction to hydrocarbons.

Dual Lewis Acid‐Base Sites Regulate Silver‐Copper Bimetallic Oxide Nanowires for Highly Selective Photoreduction of Carbon Dioxide to Methane

AbstractHighly selective photoreduction of CO2 to valuable hydrocarbons is of great importance to achieving a carbon‐neutral society. Precisely manipulating the formation of the Metal1⋅⋅⋅C=O⋅⋅⋅Metal2 (M1⋅⋅⋅C=O⋅⋅⋅M2) intermediate on the photocatalyst interface is the most critical step for regulating selectivity, while still a significant challenge. Herein, inspired by the polar electronic structure feature of CO2 molecule, we propose a strategy whereby the Lewis acid‐base dual sites confined in a bimetallic catalyst surface are conducive to forming a M1⋅⋅⋅C=O⋅⋅⋅M2 intermediate precisely, which can promote selectivity to hydrocarbon formation. Employing the Ag2Cu2O3 nanowires with abundant Cu⋅⋅⋅Ag Lewis acid‐base dual sites on the preferred exposed {110} surface as a model catalyst, 100 % selectivity toward photoreduction of CO2 into CH4 has been achieved. Subsequent surface‐quenching experiments and density functional theory (DFT) calculations verify that the Cu⋅⋅⋅Ag Lewis acid‐base dual sites do play a vital role in regulating the M1⋅⋅⋅C=O⋅⋅⋅M2 intermediate formation that is considered to be prone to convert CO2 into hydrocarbons. This study reports a highly selective CO2 photocatalyst, which was designed on the basis of a newly proposed theory for precise regulation of reaction intermediates. Our findings will stimulate further research on dual‐site catalyst design for CO2 reduction to hydrocarbons.

Boosting the Power of Na0.44MnO2: Unlocking Its Potential for Aqueous Sodium-Ion Storage through Nanostructuring and Hybridization

We report an effective processing route, combining nanostructure formation and hybridization, to improve the rate performance of the tunnel-structure sodium manganese oxide Na0.44MnO2 (NMO) as a cathode material for aqueous sodium ion storage. We use hydrothermal synthesis to prepare an NMO/CNF (Carbon NanoFiber) hybrid, consisting of uniform oxide nanowires with an average width of 70 nm and length in the range of several tenths of µm. The highly dispersed CNFs impart high conductivity to the NMO/CNF electrode, allowing high-rate performance at a C-rate of up to 20 C, with a delivered capacity of more than half the theoretical value in a 1 M Na2SO4 electrolyte. Moreover, the NMO/CNF hybrid shows good electrochemical stability under several hundred cycles at a high C-rate. However, the NMO nanowire electrodes reveal a lower-than-expected capacity, probably as a result of the tendency of nanowires to form bundles, which prevents direct contact with conductive fibers and induce the under-utilization of active material. With this study, we demonstrate a strong improvement of the otherwise inherently low-rate performance of NMO through oxide nanostructuring and hybridization with carbon fibers, paving the way for further research on NMO-based materials for aqueous sodium ion storage.

Bifunctional bimetallic oxide nanowires for high-efficiency electrosynthesis of 2,5-furandicarboxylic acid and ammonia

It is an appealing avenue for electrosyntheis of high-valued chemicals at both anode and cathode by coupling 5-hydroxymethylfurfural (HMF) oxidation and nitrate reduction reactions simultaneously, while the development such bifunctional electrocatalysts is still in its infancy with dissatisfied selectivity and low yield rate. Here, we first report that Zn-doped Co3O4 nanowires array can be served as an efficient and robust dual-functional catalyst for HMF oxidation and nitrate reduction at ambient conditions. Specifically, the catalyst shows a faradaic efficiency of 91 % and a yield rate of 241.2 μmol h−1 cm−2 for 2,5-furandicarboxylic acid formation together with a high conversion of nearly 100 % at a potential of 1.40 V. It also displays good cycling stability. Besides, the catalyst is capable of catalyzing the reduction of nitrate to NH3, giving a maximal faradaic efficiency of 92 % and a peak NH3 yield rate of 4.65 mg h−1 cm−2 at a potential of –0.70 V. These results surpass those obtained using pristine Co3O4 and are comparable to those of state-of-the-art electrocatalysts. Moreover, the catalyst is further employed as the cathode catalyst to assemble a Zn–nitrate battery, giving a peak power density of 5.24 mW cm−2 and a high yield rate of 0.72 mg h−1 cm−2. Theoretical simulations further reveal that Zn-doping favors the adsorption and dissociation of nitrate and HMF species and reduces the energy barrier as well. Our work demonstrates the potential interest of Co3O4-based materials for the highly selective production of valuable feedstocks via ambient electrolysis.

Chemiresistive room temperature NO2 sensor based on nitrogen doped zinc oxide nanowires

The prevalence of nitrogen dioxide (NO2) in the atmosphere is causing a steady increase in air pollution. As such, there is an urgent need to create a sensitive and energy-efficient NO2 gas sensor to ensure environmental and health safety. In this study, we explore the effectiveness of nitrogen-doped zinc oxide nanowires in detecting harmful NO2 gas. Through the hydrothermal method, we synthesized zinc oxide (NW-0) and nitrogen-doped zinc oxide nanowire sensors (NW-1, NW-2 & NW-4). The introduction of nitrogen induced changes in both the crystallite size and nanowire density in ZnO. Additionally, an increase in oxygen vacancy concentration was observed with nitrogen doping. At room temperature, the NW-2 sensor exhibited exceptional NO2 sensing performance (response of 110) compared to NW-0 sensor (response of 1.9) for 10 ppm of gas. The NW-2 sensor also demonstrated a rapid response/recovery time of 50 s/5 s for a 10 ppm NO2 concentration. Moreover, the sensor showed stability over an extended period, minimal response variation with changes in relative humidity, and selectivity towards NO2 over other gases. Complementing the experimental findings, density functional theory (DFT) calculations were employed to estimate the adsorption energies of NO2 on the sensor surface.

Thickness-Controllable Electrode of Lithium Titanium Oxide Nanowire Sheets with Multiple Stacked Morphology for Ultrahigh Areal Capacity and Stability of Lithium-Ion Batteries

Thickness-Controllable Electrode of Lithium Titanium Oxide Nanowire Sheets with Multiple Stacked Morphology for Ultrahigh Areal Capacity and Stability of Lithium-Ion Batteries

Effect of Hydrogen Plasma Treatment on the Sensitivity of ZnO Based Electrochemical Non-Enzymatic Biosensor.

Information on vitamin C-ascorbic acid (AA)-content is important as it facilitates the provision of dietary advice and strategies for the prevention and treatment of conditions associated with AA deficiency or excess. The methods of determining AA content include chromatographic techniques, spectrophotometry, and electrochemical methods of analysis. In the present work, an electrochemical enzyme-free ascorbic acid sensor for a neutral medium has been developed. The sensor is based on zinc oxide nanowire (ZnO NW) arrays synthesized via low-temperature chemical deposition (Chemical Bath Deposition) on the surface of an ITO substrate. The sensitivity of the electrochemical enzyme-free sensor was found to be dependent on the process treatments. The AA sensitivity values measured in a neutral PBS electrolyte were found to be 73, 44, and 92 µA mM-1 cm-2 for the ZnO NW-based sensors of the pristine, air-annealed (AT), and air-annealed followed by hydrogen plasma treatment (AT+PT), respectively. The simple H-plasma treatment of ZnO nanowire arrays synthesized via low-temperature chemical deposition has been shown to be an effective process step to produce an enzyme-free sensor for biological molecules in a neutral electrolyte for applications in health care and biomedical safety.

Natural convection in vertical solar heat collector nanotextured with reduced graphene oxide and silver nanowires

In this study, a vertical shaft is coated using silver nanowires (AgNWs) together with reduced graphene oxide (rGO) via the supersonic spray-coating technique to enhance the absorption of solar radiative heat for use in solar air heaters. The rGO/AgNW-coated surface induces multiple light reflections, similar to that in a perfect black body inside a Helmholtz jar, thus enhancing the collection of solar radiation. Air fed into the vertical heated shaft ascends owing to buoyancy. The air temperature difference, ΔT, between the outlet and inlet is measured for various mass flow rates to quantify the heat transferred to the air from the solar-heated vertical shaft. The longitudinal air velocity and temperature distributions inside the shaft are numerically simulated using the fire dynamics simulator. Both two- and three-dimensional simulations are performed, and the results are compared with experimental data for various mass flow rates. The results confirm that the trends observed in both the experiments and simulations agree well for all cases. Multiple metal meshes are installed inside the vertical shaft to induce turbulence, which enhances the heat transfer intensity. This turbulence enhancement is confirmed via smoke visualization and infrared images.