Electrochemical Fabrication of Pd-Ag Alloy Nanowire Arrays in Anodic Alumina Oxide Template

The synthesis of Pd-Ag alloy nanowires in nanopores of porous anodic aluminum oxide （AAO） template by electrochemical deposition technique was reported. Pd-Ag alloy nanowires with 16%-25% Ag content are expected to serve as candidates of useful nanomaterials for the hydrogen sensors. Scanning electron microscopy （SEM） and energy dispersed X-ray spectroscopy （EDX） were employed to characterize the morphologies and compositions of the Pd-Ag nanowires. X-ray diffraction （XRD） was used to characterize the phase properties of the Pd-Ag nanowires. Pd-Ag alloy nanowire arrays with 17.28%-23.76% Ag content have been successfully fabricated by applying potentials ranging from -0.8 to -1.0 V （vs SCE）. The sizes of the alloy nanowires are in agreement with the diameter of AAO nanopores. The underpotential deposition of Ag＋ on Pd and Au plays an important role in producing an exceptionally high Ag content in the alloy. Alloy compositions can still be controlled by adjusting the ion concentration ratio of Pd^2＋ and Ag＋ and the electrodeposition processes. XRD shows that nanowires obtained are in the form of alloy of Pd and Ag.     

Quantificational Etching of AAO Template

Ni nanowires were prepared by electrodeposition in porous anodized aluminum oxide （AAO） template from a composite electrolyte solution. Well-ordered Ni nanowire arrays with controllable length were then made by the partial removal of AAO using a mixture of phosphoric acid and chromic acid （6 wt pct H3PO4：1.8 wt pct H3CrO4）. The images of Ni nanowire arrays were studied by scanning electron microscopy （SEM） to determine the relationship between etching time and the length of Ni nanowire arrays. The results indicate that the length of nanowires exposed from the template can be accurately controlled by controlling etching time.     

One-dimensional iridium-based nanowires for efficient water electrooxidation and beyond

The sluggish reaction kinetics of oxygen evolution reaction(OER)has largely lowered the efficiency of electrochemical water splitting.Ir represents one of the state-of-the-art electrocatalysts for promoting OER especially in acidic electrolytes.However,it remains a formidable challenge to synthesize high-quality one-dimensional(1D)Ir-based nanostructures for improved electrocatalytic performance.Herein,a template-assisted synthesis method is reported wherein 1D porous Ir-Te nanowires(Ir-Te NWs)are synthesized with Te NWs serving as the template.The Ir-Te NWs exhibit highly enhanced OER performance compared to commercial IrO₂ and Ir/C.In detail,the overpotentials to reach 10 mA cm^-2 are 248 and 284 mV in 1 M KOH and 0.5 M H2S04,respectively,much lower than those of commercial catalysts.The Ir-Te NWs also show smaller Tafel slopes than commercial IrO₂ and Ir/C,signifying faster reaction kinetics.Besides,much more durable OER activity can be maintained for Ir-Te NWs with negligible decay during 25 and 20 h stability tests in 1 M KOH and 0.5 M H₂SO₄,respectively.Further analysis indicates that the significantly improved OER performance of Ir-Te NWs could be ascribed to the larger electrochemical surface area and smaller electrical resistance.More significantly,the templated synthesis of Ir-Te NWs can be facilely extended to the fabrication of other metal-Te NWs including Ru-Te,Rh-Te and Pt-Te NWs.The design and synthesis of 1D metal-based NWs in this work provide important inspiration for the synthesis of diversified 1D metallic nanostructures with distinctly enhanced catalytic performance and beyond.     

Ladder-like metal oxide nanowires: Synthesis,electrical transport,and enhanced light absorption properties

Transparent metal oxide nanowires （NWs） have attracted intense research interest in recent years. We report here the synthesis of interesting ladder-like metal oxide NWs, including In2O3, SnO2, ZnO, and Ga2O3, via a facile chemical vapor deposition （CVD） method. Their structural features and growth mechanism are demonstrated in detail by using the ladder-like In2O3 NWs as an example. Single ladder-like NW-based field-effect transistors （FETs） and photodetectors （PDs） of SnO2 were fabricated in order to investigate their electrical transport and light absorption properties. Compared with straight NW-based FETs which operate in an enhancement mode （E-mode）, FETs build on ladder-like NWs operate in a depletion mode （D-mode）. The ladder-like NWs also give higher carrier concentrations than conventional single nanowires. Finite-difference time-domain （FDTD） simulations have been performed on the ladder-like NWs and the results reveal a great enhancement of light absorption with both transverse-electric （TE） and transverse-magnetic （TM） polarization modes, which is in good agreement with the experimental results.     

Hierarchical porous metal ferrite ball-in-ball hollow spheres: General synthesis,formation mechanism,and high performance as anode materials for Li-ion batteries

High yields of CoFe204, NiFe204 and CdFe204 hierarchical porous ball-in-ball hollow spheres have been achieved using hydrothermal synthesis followed by calcination. The mechanism of formation is shown to involve an in situ carbonaceous-template process. Hierarchical porous CoFe2O4 hollow spheres with different numbers of shells can be obtained by altering the synthesis conditions. The electrochemical properties of the resulting CoFe2O4 electrodes have been compared, using different binders. The as-obtained CoFe2O4 and NiFe2O4 have relatively high reversible discharge capacity and good rate retention performance which make them promising materials for use as anode materials in lithium ion batteries.     

Porous CuO nanowires as the anode of rechargeable Na-ion batteries

We report the preparation of porous CuO nanowires that are composed of nanoparticles （-50 nm） via a simple decomposition of a Cu（OH）2 precursor and their application as the anode materials of rechargeable Na-ion batteries. The as-prepared porous CuO nanowires exhibit a Brunauer-Emmett-Teller （BET） surface area of 13.05 m^2.g^-1, which is six times larger than that of bulk CuO （2.16 m^2.g^-1）. The anode of porous CuO nanowires showed discharge capacities of 640 mA.h.g^-1 in the first cycle and 303 mA.h.g^-1 after 50 cycles at 50 mA.g^-1 The high capacity is attributed to porous nanostructure which facilitates fast Na-intercalation kinetics. The mechanism of electrochemical Na-storage based on conversion reactions has been studied through cyclic voltammetry, X-ray diffraction （XRD）, Raman spectroscopy, and high resolution transmission electron microscopy （HRTEM）. It is demonstrated that in the discharge process, Na＋ions first insert into CuO to form a CuⅡ1-x CuⅠ x O1-x/2solid and a Na2O matrix then CuⅡ1-xCu Ⅰ xO1-x/2 reacts with Na＋ to produce Cu2O, and finally Cu2O decompose into Cu nanoparticles enclosed in a Na2O matrix. During the charge process, Cu nanopartides are first oxidized to generate Cu2O and then converted back to CuO. This result contributes to the design and mechanistic analysis of high-performance anodes for rechargeable Na-ion batteries.     

Effect of Oxide Assisted Metal Nanoparticles on Microstructure and Morphology of Gallium oxide Nanowires

Several researches have been reported about the characteristic of β-Ga2O3 nanowires which was synthesized on nickel oxide particle. But indeed, recent researches about synthesis of β-Ga2O3 nanowires on oxide-assisted transition metal are limited to nickel or cobalt oxide catalyst. In this work, Gallium oxide (β-Ga2O3 ) nanowires were synthesized by a simple thermal evaporation method from gallium powder in the range of 700 - 1000℃ using the iron, nickel, copper, cobalt and zinc oxide as a catalyst, respectively. The β-Ga2O3 nanowires with single crystalline without defects were successfully synthesized at the reaction temperature of 850, 900 and 950℃ in all the catalysts. But optimum experimental condition in synthesis of nanowires varied with the kind of catalyst. As increasing synthesis temperature,the morphology of gallium oxide nanowires changed from nanowires to nanorods, and its diameter increased. From these results, we could be proposed that the growth mechanism of β-Ga2O3 nanowires was changed with synthesis temperature of nanowires. Microstructure and morphology of Synthesized nanowire was characterized by HR-TEM, FE-SEM, EDX and XRD.     

Quantiflcational Etching of AAO Template

Ni nanowires were prepared by electrodeposition in porous anodized aluminum oxide (AAO) template from a composite electrolyte solution. Well-ordered Ni nanowire arrays with controllable length were then made by the partial removal of AAO using a mixture of phosphoric acid and chromic acid (6 wt pct H3PO4: 1.8 wt pct H3CrO4). The images of Ni nanowire arrays were studied by scanning electron microscopy (SEM) to determine the relationship between etching time and the length of Ni nanowire arrays. The results indicate that the length of nanowires exposed from the template can be accurately controlled by controlling etching time.     

Understanding Formation Mechanism of Titanate Nanowires through Hydrothermal Treatment of Various Ti-Containing Precursors in Basic Solutions

Titanate nanowires prepared by hydrothermal treatment of TiO₂ in NaOH solution have attracted intensive attentions,but the formation mechanism is still under debate.Herein,we report an in-depth study on the formation mechanism through investigating the hydrothermal behavior of various Ti-containing precursors in basic solutions,including Ti,TiN,TiO₂,Ti₂SnC and Ti₂AlN.Based on the results by means of X-ray diffraction（XRD）,transmission electron microscopy（TEM） and Raman spectroscopy,it is demonstrated that the crystal structure of the hydrothermal products is irrespective to the structure of the precursors or the types of basic solution（NaOH or KOH） in use.Alkali ions play an important role in the formation of titanate nanowires.The formation mechanism of the resultant titanate nanowires was proposed to be dissolution-crystallization mechanism.     

Preparation of Silver Nanowires via a Rapid,Scalable and Green Pathway

Rapid synthesis of silver nanowires(Ag NWs) with high quality and a broad processing window is challenging because of the low selectivity of the formation of multiply twinned particles at the nucleation stage for subsequent Ag NWs growth.Herein we report a systematic study of the water-involved heterogeneous nucleation of Ag NWs with high rate(less than 20 min) in a simple and scalable preparation method.Using glycerol as a reducing agent and a solvent with a high boiling point,the reaction is rapidly heated to 210 ℃ in air to synthesize Ag NWs with a very high yield in gram level.It is noted that the addition of a small dose of water plays a key role for obtaining highly pure Ag NWs in high yield,and the optimal water/glycerol ratio is0.25%.After investigating a series of forming factors including reaction temperature and dose of catalysts,the formation kinetics and mechanism of the Ag NWs are proposed.Compared to other preparation methods,our strategy is simple and reproducible.These Ag NWs show a strong Raman enhancement effect for organic molecules on their surface.     

Induced structural modifications in ZnS nanowires via physical state of catalyst:Highlights of 15R crystal phase

Peculiar and unique growth mechanisms involved in semiconductor nanowires(NWs)pave the way to the achievement of new crystallographic phases and remarkable material properties,and hence,studying polytypism in semiconductor NWs arouses a strong interest for the next generation of electronic and photonic applications.In this context,the growth of ZnS nanowires has been investigated,as bulk ZnS compound exhibits numerous unstable polytypes at high temperatures,but their stable occurrence is highly anticipated in a nanowire due to its special quasi-dimensional shape and growth modes.In this work,the idea is to provide a change in the growth mechanism via the physical state of catalyst droplet(liquid or solid)and hence,study the induced structural modifications in ZnS nanowires.The HRTEM images of VLS(via liquid alloyed catalyst)grown ZnS NWs show periodic stacking faults,which is precisely identified as a stacking sequence of cubic or hexagonal individual planes leading to an astonishing 15R crystal polymorph.This crystallographic phase is observed for the first time in nanowires.Contrastingly,NWs grown with VSS(via solid catalyst)show crystal polytypes of zinc blende and wurtzite.We calculate and discuss the role of cohesive energies in the formation of such ZnS polytypes.Further,we present the selection rules for the crystallization of such 15R structure in NWs and discuss the involved VLS and VSS growth mechanisms leading to the formation of different crystal phases.     

Effect of Ni+2-substituted Fe2TiO5 on the H2-reduction and CO2 Catalytic Decomposition Reactions at 500℃

CO2 is a major component of the greenhouse gases, which causes the global warming. To reduce CO2 gas, high activity nanosized Ni＋2 substituted Fe2TiO5 samples were synthesized by conventional ceramic method. The effect of the composition of the synthesized ferrite on the H2-reduction and CO2-catalytic decomposition was investigated. Fe2TiO5 （iron titanate） phase that has a nanocrystallite size of -80 nm is formed as a result of heating Fe2O3 and TiO2 while the addition of NiO leads to the formation of new phases （-80 nm） NiTiO3 and NiFe2O4, but the mixed solid of NiO and Fe2O3 results in the formation of NiFe2O4 only. Samples with Ni^＋2=0 shows the lowest reduction extent （20%）; as the extent of Ni＋2 increases, the extent of reduction increases. The increase in the reduction percent is attributed to the presence of NiTiO3 and NiFe2O4 phases, which are more reducible phases than Fe2TiO5. The CO2 decomposition reactions were monitored by thermogravimetric analysis （TGA） experiments. The oxidation of the H2-reduced Ni＋2 substituted Fe2TiO5 at 500℃ was investigated. As Ni^＋2 increases, the rate of reoxidation increases. Samples with the highest reduction extents gave the highest reoxidation extent, which is attributed to the highly porous nature and deficiency in oxygen due to the presence of metallic Fe, Ni and/or FeNi alloy. X-ray diffraction （XRD） and transmission electron microscopy （TEM） of oxidized samples show also the presence of carbon in the sample containing Ni＋2〉0, which appears in the form of nanotubes （25 nm）.     

Synthesis of α-Mo_2C by Carburization of α-MoO_3 Nanowires and Its Electrocatalytic Activity towards Tri-iodide Reduction for Dye-Sensitized Solar Cells

Nanowire-shaped α-Mo O3 was synthesized on a large scale by hydrothermal route.Nanocrystalline α-Mo2 C phase was obtained by the carburization of α-Mo O3 nanowires with urea as a carbon source precursor.The phase purity and crystalline size of the synthesized materials were ascertained by using powder X-ray diffraction.The shape and morphology of synthesized materials were characterized by field-emission scanning electron microscopy(FE-SEM) and high resolution transmission electron microscopy(HR-TEM).The electrocatalytic activity of α-Mo2 C for I-/I3-redox couple was investigated by the cyclic voltammetry.The synthesized α-Mo2 C was subsequently applied as counter electrode in dye-sensitized solar cells to replace the expensive platinum.     

Ultrahigh quantum efficiency photodetector and ultrafast reversible surface wettability transition of square In<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires

Due to a large surface-to-volume ratio,the optoelectronic performance of low-dimensional semiconductor nanostructure-based photodetectors depends in principle on chemisorption/photodesorption at the exposed surface,but practical examples that show such an effect are still unavailable.Some theoretical calculations have predicted that the {001} facets of In2O3 can effectively accumulate photogenerated holes under irradiation,providing a model material to examine whether the facet cutting of nanowires (NWs) can boost their optoelectronic performance.Herein,we present the design and construction of a novel nanowire-based photodetector using square In2O3 NWs with four exposed {001} crystal facets.The photodetector delivers excellent optoelectronic performance with excellent repeatability,fast response speed,high spectral responsivity (Rλ),and high external quantum efficiency (EQE).The Rλ and EQE values are as high as 4.8 x 106 A/W and 1.46 x 109％,respectively,which are larger than those of other popular semiconductor photodetectors.In addition,the square In2O3 NWs show hydrophobic wettability as manifested by a contact angle of 118° and a fast photoinduced reversible switching behavior is observed.     

Surface-Engineered Li4Ti5O12 Nanostructures for High-Power Li-Ion Batteries

Materials with high-power charge–discharge capabilities are of interest to overcome the power limitations of conventional Li-ion batteries.In this study,a unique solvothermal synthesis of Li4Ti5O12 nanoparticles is proposed by using an off-stoichiometric precursor ratio.A Li-deficient off-stoichiometry leads to the coexistence of phaseseparated crystalline nanoparticles of Li4Ti5O12 and TiO2 exhibiting reasonable high-rate performances.However,after the solvothermal process,an extended aging of the hydrolyzed solution leads to the formation of a Li4Ti5O12 nanoplate-like structure with a self-assembled disordered surface layer without crystalline TiO2.The Li4Ti5O12 nanoplates with the disordered surface layer deliver ultrahighrate performances for both charging and discharging in the range of 50–300C and reversible capacities of 156 and 113 mAh g−1 at these two rates,respectively.Furthermore,the electrode exhibits an ultrahigh-charging-rate capability up to 1200C(60 mAh g−1;discharge limited to 100C).Unlike previously reported high-rate half cells,we demonstrate a high-power Li-ion battery by coupling Li4Ti5O12 with a high-rate LiMn2O4 cathode.The full cell exhibits ultrafast charging/discharging for 140 and 12 s while retaining 97 and 66% of the anode theoretical capacity,respectively.Room-(25℃),low-(−10℃),and high-(55℃)temperature cycling data show the wide temperature operation range of the cell at a high rate of 100C.     

Fabrication and Characterization of Porous Sintered Ti--Ag Compacts for Biomedical Application Purpose

Porous sintered Ti—Ag compacts with different Ag content were fabricated by powder metallurgy.The associated hydrothermal treatment and the effect on the apatite formation were studied.The results suggested that TiO was generated under the condition of low vacuum(1×10^-2 Pa) during the process of burning out the spacer-holding particles.After hydrothermal treatment,a sub-microscale porous layer was formed at the pore wall surface of the samples.The apatite-inducing ability of hydrothermal treated porous sintered Ti—Ag compacts with different Ag content was evaluated in modified simulated body fluid（SBF）.And the results proved that there is a clear correlation between the apatite-inducing ability and Ag content.The higher Ag content in porous leads to the decrease of Na⁺ ions and basic hydroxyl（OH）_b amount,resulting in the decline of apatite-inducing ability in the first stage.However,their apatite-inducing ability was not significantly different from that of Ti after two weeks SBF immersing.Hence,the ionic activity should restore with the processing of SBF soaking,as the saturation of Ag effect.     

Preparation and Characterization of Some Ferrites from CuO-ZnO-Fe_2O_3 Mixtures

The ferrites of Cuo-ZnO-Fe2o3 solid solution series near the molar ratio of ZnxCu1-x were prepared by direct heating of their coprecipitated hydroxides using NH4OH as precipitating agent where x=0.0, 0.2, 0.5, 0.8 and 1.0. Additional amounts of Cu and Zn sulphates were added to compensate the loss during the coprecipitation of the hydroxides. The ferritized samples were characterized by chemical analysis, XRD. DTA, TGA and SEM. XRD of both Zn0.2Cu0.8Fe2O4 and Zn0.5Cu0.5 Fe2O4 that indicates the formation of a heterogeneous ferrite material of ZnFe2O4 and CuFe2O4 mixed with variable amounts of α-Fe2O3. Zn and Cu ferrites were observed only in Zn0.8Cu0.2Fe2O4.From TGA-time relation, the activation energy of the different transformation phases were calculated. It is found that, the activation energy of ZnFe2O4 is slightly equal to 3/2 of that for CuFe2O4. Dielectric measurements show that the electrical behaviour depends on the ordering and disordering of the phases.     

A versatile cooperative template-directed coating method to synthesize hollow and yolk-shell mesoporous zirconium titanium oxide nanospheres as catalytic reactors

The design of hollow mesoporous nanostructures for cascade catalytic reactions can inject new vitality into the development of nanostructures. In this study, we report a versatile cooperative template-directed coating method for the synthesis of hollow and yolk-shell mesoporous zirconium titanium oxide nanospheres with varying compositions （ZrO2 content from 0 to 100%）, high surface areas （465 m2·g-1） and uniform mesopores. In particular, the hexadecylamine （HDA） used in the coating procedure serves as a soft template for silica@mesostructured metal oxide core-shell nanosphere formation. By a facile solvothermal treatment route with an ammonia solution and calcination in air, the silica@mesostructured zirconium titanium oxide spheres can be converted into highly uniform hollow zirconium titanium oxide spheres. By simply replacing hard template silica nanospheres with core-shell silica nanocomposites, the synthesis approach can be further used to prepare yolk-shell mesoporous structures through the coating and etching process. The approach is similar to the preparation of mesoporous silica nanocomposites from the self-assembly of the core, the soft template cetyltrimethylammonium bromide （CTAB） and a silica precursor and can be extended as a general method to coat mesoporous zirconium titanium oxide on other commonly used hard templates （e.g., mesoporous silica spheres, mesoporous organosilica ellipsoids, polymer spheres, and carbon nanospheres）. The presence of highly permeable mesoporous channels in the zirconium titanium oxide shells has been demonstrated by the reduction of 4-nitrophenol with yolk-shell Au@mesoporous zirconium titanium oxide as the catalyst. Moreover, a cascade catalytic reaction including an acid catalyzed step and a catalytic hydrogenation to afford benzimidazole derivatives can be carried out very effectively by using the accessible acidity of the yolk-shell structured mesoporous zirconium titanium oxide spheres containing a Pd core as a bifunctional catalyst, which mak     

Vertical α-FeOOH nanowires grown on the carbon fiber paper as a free-standing electrode for sensitive H<Subscript>2</Subscript>O<Subscript>2</Subscript> detection

Highly sensitive,selective,and stable hydrogen peroxide (H2O2) detection using nanozyme-based catalysts are desirable for practical applications.Herein,vertical α-FeOOH nanowires were successfully grown on the surface of carbon fiber paper (CFP) via a low-temperature hydrothermal procedure.The formation of vertical α-FeOOH nanowires is ascribed to the structure-directing role of sodium dodecyl sulfate.The resulting free-standing electrode with one-dimensional (1D)nanowires offers oriented channels for fast charge transfer,excellent electrical contact between the electrocatalyst and the current collector,and good mechanical stability and reproducibility.Thus,it can serve as an efficient electrocatalyst for the reduction and sensitive detection of H2O2.The relation of the oxidation current of H2O2 with the concentration is linear from 0.05 to 0.5 mM with a sensitivity of-0.194 mA/(mM.cm2) and a low detection limit of 18 μM.Furthermore,the portability in the geometric tailor and easy device fabrication allow extending the general applicability of this free-standing electrode to chemical and biological sensors.     

Effect of Sn precursor on the synthesis of SnO2 and Sb-doped SnO2 particles via polymeric precursor method

SnO2 and Sb-doped SnO2 particles were synthesized using the polymeric precursor method with different Sn salt precursors： SnCl2.2H2O, SnCl4.5H20, or Sn citrate. Sb2O3 was used as the precursor of Sb, and the molar ratio of nsn：nsb was held constant. FTIR and TGA/DTA were used to examine the influence of the Sn precursor on the formation and thermal decomposition of the Sn and Sn-Sb complexes. The calcination products obtained from heating the Sn and Sn-Sb complexes at 500℃ in air were analyzed using XRD and TEM analysis. The results revealed that the SnO2 and Sb-doped SnO2 formation temperatures depended on the nature of the Sn precursor. The calcination products were found to be SnO2 and Sb-doped SnO2 particles, which crystallized in a tetragonal cassiterite structure with a highly preferred （110） planar orientation. The Sn precursor and the presence of Sb in the SnO2 matrix strongly influenced the crystallinity and lattice parameters.