Pulse deposition of large area,patterned manganese oxide nanowires in variable aspect ratios without templates

Manganese oxide nanowires with β-MnOOH in core and Mn₃O₄ in shell were successfully plated onto various conductive substrates from a Mn(CH₃COO)₂ solution by anodic deposition under a two-electrode, pulse-rest mode. The aspect ratio of uniform nanowire morphologies in cm² scale is controllable by varying the deposition variables. Patterned MnO_x nanowire arrays were obtained by combining lithographic and electroplating techniques demonstrated to be a powerful method for preparing MnO_x nanowires in the field emission (FE) array cathodes with a low turn-on voltage (∼3.4 V/μm at 1 μA/cm²).     

Highly ordered MnO2 nanowire array thin films on Ti/Si substrate as an electrode for electrochemical capacitor

AAO/Ti/Si substrate was successfully synthesized by a two-step electrochemical anodization of the aluminum film on the Ti/Si substrate and then used as template to grow nanowire arrays. The ordered MnO₂ nanowire arrays with about 40 nm diameters had been directly fabricated on AAO/Ti/Si substrate by direct current (DC) electrodeposition. The microstructure of the nanowire arrays was investigated by field-emission scanning electron microscopy, transmission electron microscopy and X-ray diffraction. Their electrochemical characterization was performed using cyclic voltammetry in 0.5 M Na₂SO₄ aqueous solution. The synthesized MnO₂ nanowires had amorphous nature until 400 °C. The deal capacitive behavior was obtained when the as-prepared sample was heat-treated at 200 °C. The specific capacitance of the electrode was about 254 F/g.     

Electrodeposition of MnO2 nanowires on carbon nanotube paper as free-standing,flexible electrode for supercapacitors

MnO₂ nanowires were electrodeposited onto carbon nanotube (CNT) paper by a cyclic voltammetric technique. The as-prepared MnO₂ nanowire/CNT composite paper (MNCCP) can be used as a flexible electrode for electrochemical supercapacitors. Electrochemical measurements showed that the MNCCP electrode displayed specific capacitances as high as 167.5 F g⁻¹ at a current density of 77 mA g⁻¹. After 3000 cycles, the composite paper can retain more than 88% of initial capacitance, showing good cyclability. The CNT paper in the composite acted as a good conductive and active substrate for flexible electrodes in supercapacitors, and the nanowire structure of the MnO₂ could facilitate the contact of the electrolyte with the active materials, and thus increase the capacitance.     

3D hierarchical MnO2 aerogels with superhydrophobicity for selective oil–water separation

Inorganic nanowire aerogel with low density, high specific surface area and high porosity has received increasing attention in the field of materials physics and chemistry because of not only the unique structural and physical features of metallic oxide but also low cost, environmental friendliness and earth abundant of precursor materials. In this work, MnO₂ nanowire aerogels (MNA) with ultralow density, and stable 3D hierarchical structures was successfully fabricated by freeze‐drying processes using MnO₂ nanowire as building blocks. The length of MnO₂ nanowires exceeds 100 μm, making it easier to cross‐link and self‐assemble into a 3D network of aerogels, and the acid and alkali resistance of MnO₂ enables it to adapt to extreme environments. Simultaneously, the monodispersed MnO₂ nanowire was prepared by the hydrothermal method, followed by acid treatment. To obtain superhydrophobic properties and achieve selective oil adsorption, the surfaces of nanowire aerogels were grafted the hydrophobic groups with low surface energy via vapor deposition. It is indicated that the obtained 3D hierarchical MNA show both superhydrophobic and super‐lipophilic properties simultaneously with a high‐water contact angle of 156°  ±  2° and an oil contact angle of 0°. And the MNA exhibited a high oil adsorption capacity of 85–140 g/g, thereby indicating its potential applications in oil/water separation. More importantly, the resulting MNA can be recycled ten cycles without loss of oil absorption capacity (more than 120 g/g). The results presented in this work demonstrate that the as‐prepared nanowire aerogel may find applications in chemical separation and environmental remediation for large‐scale absorption of oils from water.     

Electrochemical characterization of vertical arrays of tin nanowires grown on silicon substrates as anode materials for lithium rechargeable microbatteries

Vertical arrays of one-dimensional tin nanowires on silicon dioxide (SiO₂)/silicon (Si) substrates have been developed as anode materials for lithium rechargeable microbatteries. The process is complementary metal-oxide-semiconductor (CMOS) compatible for fabricating on-chip microbatteries. Nanoporous anodized aluminum oxide (AAO) templates integrated on SiO₂/Si substrates were employed for fabrication of tin nanowires resulting in high surface area of anodes. The microstructure of these nanowire arrays was investigated by scanning electron microscopy and X-ray diffraction. The electrochemical tests showed that the discharge capacity of about 400 mA h g⁻¹ could be maintained after 15 cycles at the high discharge/charge rate of 4200 mA g⁻¹.     

Preparation of Ag2Se and Ag2Se1 − xTex nanowires by electrodeposition from DMSO baths

We have developed a novel electrochemical route to fabricate highly ordered stoichiometric Ag₂Se nanowire arrays by electrodeposition from non-aqueous dimethyl sulfoxide (DMSO) solutions. Cyclic voltammetry technique was used to study this cathodic deposition process. X-ray energy dispersion analysis shows that stoichiometric Ag₂Se nanowires can be obtained in a wide range of deposition condition. X-ray diffraction and electron diffraction patterns demonstrate that the as-deposited nanowires are [0 0 2] oriented orthorhombic β-Ag₂Se. Furthermore, ternary Ag₂Se_1 − xTe_x nanowires have been electrodeposited in mixed SeCl₄–TeCl₄ DMSO solutions.     

Template synthesis and characterization of PbTiO3 nanowire arrays from aqueous solution

Highly ordered PbTiO₃ nanowire arrays were first reported by fabricating within the pores of anodic aluminum oxide (AAO) template in the aqueous solution by liquid-phase deposition method. The structure and morphology of PbTiO₃ nanowire arrays were characterized by SEM and TEM, respectively. The XRD result shows that desired stoichiometric composition could be easily obtained preparing the treatment solution during post-annealing in order to crystallize the nanowires. TEM analyses confirmed that the obtained nanowires composed of large crystals than others made by sol-gel methods. Finally, a possible growth mechanism of the PbTiO₃ nanowires is discussed.     

Facile preparation of α-MnO2 nanowires for assembling free-standing membrane with efficient Fenton-like catalytic activity

Assembling MnO₂ nanowires into macroscopic membrane is a promising engineered technology for catalyst separation and enhancement of Fenton-like reaction activity, yet its development is limited by the deficiencies in preparation and property modulation of the MnO₂ nanowires. In this work, we developed a facile method using C₂H₅OH and CH₃COOK as reductive and vital control reagents to react with KMnO₄ by hydrothermal reaction at 140 °C for 12 h, to prepare the ultralong α-MnO₂ nanowires up to tens of micrometers with high purity and aspect ratio. Such strategy not only had the advantages of being mild, easily controlled and environmental pollution-free, but also endowed α-MnO₂ nanowires with excellent ability as a Fenton catalyst when assembled into free-standing membrane for degrading phenolic compounds (k_obs = 0.0738 ～ 0.1695 min^?1) in a continuous flow reaction. The reactive oxygen species (i.e., ^?OH) from Fenton-like reaction were enriched within this α-MnO₂ nanowire membrane via nanoconfinement effect, which further enhanced the mass transportation of ^?OH available for phenolic contaminants. MnO₂ nanowire membrane using our method possessed the high practical potential for water purify due to its easy-preparation and enhanced catalytic performances.     

Electrochemical synthesis of ordered alumina nanowire arrays

Ordered Al₂O₃ nanowire arrays embedded in the nanochannels of anodic alumina membranes (AAMs) were synthesized by electrodepostion at room temperature. Our synthetic route yielded large quantities of Al₂O₃ nanowires of uniform size and shape that are ~40 μm long with diameters of 70 nm. The Al₂O₃ nanowire structures were characterized by scanning and transmission electron microscopies, high-resolution transmission electron microscopy, energy dispersive spectroscopy and X-ray photoelectron spectroscopy. Electronic Publication     

Epitaxial Growth and Thermoelectric Measurement of Bi2Te3/Sb Superlattice Nanowires

Superlattice nanowires are expected to show further enhanced thermoelectric performance compared with conventional nanowires or superlattice thin films. We report the epitaxial growth of high density Bi₂Te₃/Sb superlattice nanowire arrays with a very small bilayer thickness by pulse electrodeposition. Transmission electron microscopy, selected area electron diffraction and high resolution transmission electron microscopy were used to characterize the superlattice nanowires, and Harman technique was employed to measure the figure of merit (ZT) of the superlattice nanowire array in high vacuum condition. The superlattice nanowire arrays exhibit a ZT of 0.15 at 330 K, and a temperature difference of about 6.6 K can be realized across the nanowire arrays.     

Poly(3,4-ethylenedioxithiophene)/MnO2 composite electrodes for electrochemical capacitors

Composite electrodes of poly(3,4-ethylenedioxithiophene) and manganese oxide (PEDOT/MnO₂) have been prepared by electrodeposition of manganese oxide over PEDOT-modified titanium substrate. The PEDOT layers are deposited on titanium by potentiostatic deposition at 1.4 V and at two different temperatures: 5 and 25 °C (named PEDOT₍₅₎ and PEDOT₍₂₅₎, respectively). The electrodes are characterized by field emission gun scanning electron microscopy (FEG-SEM) and their electrochemical performances are evaluated by using cyclic voltammetry (CV) in 1 molL⁻¹ Na₂SO₄. The results show an improvement in the specific capacitance (C_s) of the oxide due to the presence of the polymer layer. Considering only the MnO₂ mass, the C_s values of the electrodes Ti/MnO₂, Ti/PEDOT₍₅₎/MnO₂ and Ti/PEDOT₍₂₅₎/MnO₂, estimated by the CV technique, are 151, 159 and 199 Fg⁻¹ at 10 mVs⁻¹ respectively. The micrographies of electrodes show that the polymer layer leads to very significant changes in the morphology of the oxide layers, which in turn generates the improvement observed in the capacitive property.     

Carbon nanotube arrays supported manganese oxide and its application in electrochemical capacitors

Manganese oxide (MnO_x) has been coated on carbon nanotubes (CNTs) and fabricated as the electrodes for electrochemical capacitors (ECs) by cathodic electrodeposition. In the process, randomly oriented CNT arrays are grown directly onto the Ti/Si substrates by chemical vapor deposition method. Potentiostatic method has been utilized for cathodic electrodeposition of MnO_x onto the surface of CNTs while immersed in KMnO₄ solution. The highly porosity and fibrous microstructure of the as-prepared MnO_x/CNT electrode is beneficial for the electrolyte access to the active material, whereas CNTs provide improved electronic conductivity. Electrochemical investigations show that the increase in the loading mass of MnO_x results in a significant reduction in the specific capacitances (SCs) of the MnO_x/CNT electrodes. The MnO_x/CNT electrode with MnO_x loading mass of 50 μg shows a high SC of 400 F g⁻¹ with good long cycle stability at a current density of 10 A g⁻¹, suggesting its potential application in ECs.     

High loading MnO2 nanowires on graphene paper: Facile electrochemical synthesis and use as flexible electrode for tracking hydrogen peroxide secretion in live cells

Recent progress in flexible and lightweight electrochemical sensor systems requires the development of paper-like electrode materials. Here, we report a facile and green synthesis of a new type of MnO₂ nanowires–graphene nanohybrid paper by one-step electrochemical method. This strategy demonstrates a collection of unique features including the effective electrochemical reduction of graphene oxide (GO) paper and the high loading of MnO₂ nanowires on electrochemical reduced GO (ERGO) paper. When used as flexible electrode for nonenzymatic detection of hydrogen peroxide (H₂O₂), MnO₂–ERGO paper exhibits high electrocatalytic activity toward the redox of H₂O₂ as well as excellent stability, selectivity and reproducibility. The amperometric responses are linearly proportional to H₂O₂ concentration in the range 0.1–45.4 mM, with a detection limit of 10 μM (S/N = 3) and detection sensitivity of 59.0 μA cm⁻² mM⁻¹. These outstanding sensing performances enable the practical application of MnO₂–ERGO paper electrode for the real-time tracking H₂O₂ secretion by live cells macrophages. Therefore, the proposed graphene-based nanohybrid paper electrode with intrinsic flexibility, tailorable shapes and adjustable properties can contribute to the full realization of high-performance flexible electrode material used in point-of-care testing devices and portable instruments for in-vivo clinical diagnostics and on-site environmental monitoring.     

Conducting Polyaniline Nanowire Arrays Modified Electrode for High Performance Supercapacitor and Enhanced Catalysis of Nitrite Reduction

Vertically aligned conducting polymer nanowire arrays had great potential applications in supercapacitor electrode material and exhibited enhanced electrocatalytic behavior towards the reduction of nitrite. In this paper, a facial template‐free approach to synthesize large arrays of vertically aligned polyaniline (PANI) nanowires on electrochemically pretreated glassy carbon electrodes was reported by using a galvanostatic current method. The as‐prepared large arrays of PANI nanowires had very narrow diameters and were oriented perpendicular to the substrate, which was a benefit to the ion diffusion when being used as the supercapacitor electrode. The highest specific capacitance of PANI nanowire arrays was measured and kept high at a large charge‐discharge current density. Furthermore, it also can detect nitrite with ultrahigh sensitivity of 62.99 µA mM^?1 cm^?2 and a remarkable fast response time of less 1 s. The results indicated that the vertically aligned PANI nanowires could dramatically enhance the electrochemical performance.     

Enhanced specific energy of silver-doped MnO2/graphene oxide electrodes as facile fabrication symmetric supercapacitor device

The present work is about the preparation of silver (Ag)-doped manganese oxide (MnO₂)/graphene oxide (GO) composite thin films are deposited by a facile and binder-free successive ionic layer adsorption and reaction (SILAR) method for the first time. The Brunauer-Emmett-Teller (BET) study revealed the nanosheets of MnO₂–Ag3/GO exhibit high specific surface area of 192 m² g^?1. The tailored flower-like morphology and interconnected nanosheets of MnO₂–Ag3/GO electrodes achieved high electrochemical performance. The maximum specific capacitance (Cs) of 877 F g^?1 at the scan rate of 5 mV s^?1 is obtained for MnO₂–Ag3/GO electrode tested in 1 M sodium sulfate (Na₂SO₄) electrolyte with capacity retention of 94.57% after 5000 cycling stability. The MnO₂–Ag3/GO composite-based flexible solid state symmetric supercapacitor (FSS-SSC) device delivered Cs as 164 F g^?1 with specific energy of 57 Wh kg^?1 at specific power of 1.6 kW kg^?1 and capacitive retention of 94% after 10,000 cycles.     

Controllable Hydrocarbon Formation from the Electrochemical Reduction of CO2 over Cu Nanowire Arrays

In this work, the effect of Cu nanowire morphology on the selective electrocatalytic reduction of CO₂ is presented. Cu nanowire arrays were prepared through a two‐step synthesis of Cu(OH)₂ and CuO nanowire arrays on Cu foil substrates and a subsequent electrochemical reduction of the CuO nanowire arrays to Cu nanowire arrays. By this simple synthesis method, Cu nanowire array electrodes with different length and density were able to be controllably synthesized. We show that the selectivity for hydrocarbons (ethylene, n‐propanol, ethane, and ethanol) on Cu nanowire array electrodes at a fixed potential can be tuned by systematically altering the Cu nanowire length and density. The nanowire morphology effect is linked to the increased local pH in the Cu nanowire arrays and a reaction scheme detailing the local pH‐induced formation of C₂ products is also presented by a preferred CO dimerization pathway.     

The particle dimension controlling synthesis of α-MnO2 nanowires with enhanced catalytic activity on the thermal decomposition of ammonium perchlorate

Hydrothermal method synthesis of α-MnO₂ nanowires has been achieved at different temperatures in this work. X-ray diffraction and transmission electron microscopy confirmed the pure phase of the α-MnO₂ nanowires. All of the samples crystallized in a single-phase nanowires shape. The α-MnO₂ nanowires diameter increased from 11 nm to 21 nm with the increase in hydrothermal temperature from 120 °C to 200 °C. The α-MnO₂ catalytic activity on the decomposition of ammonium perchlorate (AP) was characterized through thermogravimetric analysis. The decomposition rate of AP with the addition of α-MnO₂ was size relative. The 11 nm MnO₂ nanowires exhibited the best catalytic activity, which lowered the high-temperature peak of AP by 130 °C.     

MnS纳米线阵列上MnS花状球的水热合成

通过水热处理的方法,在氧化铝模板表面生成的MnS纳米线阵列上合成了六方相MnS花状球。利用场发射扫描电镜,透射电子显微镜,高分辨透射电子显微镜,选区电子衍射和X射线衍射对制备的样品进行了分析与表征。结果表明MnS花状球是在MnS纳米线阵列上生长的,纳米线的直径为70～80nm,与氧化铝模板的孔径一致且结晶性较好。随着阳极氧化氧化铝模板(AAO)的孔洞长度的减少,MnS花状球的数量快速增加。提出了MnS复合纳米结构可能的生长机制:氧化铝模板和反应中硫脲分解产生的H2S气体对产物的最终形貌有很重要的影响。室温光致发光光谱显示在420nm处存在一个很强的MnS带边发射峰。     

Tl_2O_3/聚-N-乙烯基咔唑复合纳米线的研究

微型化是纳米科技发展的关键驱动力之一，然而使用现行的光刻技术生产大规模集成电路器件的技术已经接近极限尺寸（～0．8μm）．1982年STM的研制成功使得在纳米尺寸上进行操作成为可能[1－3]同时，LB技术正在应用于纳米粒子薄膜的制备中[4]．进一步利用Iangmuir单层膜诱导控制     

Tl2O3/聚-N-乙烯基咔唑复合纳米线的研究

Stable monolayers of electropolymerized poly-N-vinylcarbazole (EPVK) and arachidic acid(AA) are obtained on a subphase of alkaline Tl2O3 colloidal solutions. As revealed by the atomic force microscope, there is phase separation in the mixed LB monolayers. Transmission electron microscopic observations reveal that ordered arrays of composite Tl2O3/Epvk nanowires are formed in the mixed monolayers. Formation of the composite nanowire arrays is attributed to the ordered adsorption of Tl2O3 colloidal particles along the polycationic EPVK chains. The composite nanowire array is 3.2nm wide with a spacing of 2.7nm.The composite nanowire arrays can also be formed when pure EPVK is used. Composite LB multilayers of Tl2O3/EPVK nanowire arrays are prepared. The bilayer spacing is 5.54nm.The present study is of importance to the fabrication of inorganic semiconductor/functional polymer composite nanowires.