Controllable growth of gold nanowires and nanoactuators via high-frequency AC electrodeposition

An electrochemical deposition method using high-frequency alternating current (AC) signal is reported here for the in situ synthesis and assembly of Au nanowires and nanoactuators on microelectrodes without using any masks or templates. High conductivity of 3.79 ± 0.14 × 10⁷ Ω^− 1 m^− 1 is achieved on the Au nanowires assembled between electrodes. Au nanoactuators with expansion ratio of more than 500% can be fabricated at higher frequency. The actuators can act as claws to grab SiO₂ nanoparticles in a water solution when driven by an alternating electric field. Disconnected nanowires and nanoparticles which self-aligned around the electrodes were also obtained at lower gold ion concentration, indicating a different current transfer mode in AC electrodeposition.     

Synthesis,structure and magnetic properties of 2-D and 3-D [cation]{M[Au(CN)2]3} (M = Ni, Co) coordination polymers

In order to study the templating effect of the cation and the resulting impact on the magnetic properties, reactions of M(II) salts with [cation][Au(CN)₂] were conducted, yielding a series of coordination polymers of the form [cation]{M[Au(CN)₂]₃} (cation = ⁿBu₄N⁺, PPN⁺ (bis(triphenylphosphoranylidene)ammonium); M = Ni(II) and Co(II)). The structures of ⁿBu₄N{M[Au(CN)₂]₃} and PPN{M[Au(CN)₂]₃} (M = Ni and Co) contain two distinct 3-D anionic frameworks of {M[Au(CN)₂]₃}⁻, hence the framework was sensitive to the cation, but not to the identity of the metal center. In ⁿBu₄N{M[Au(CN)₂]₃}, the metal centers are connected by [Au(CN)₂] units to form six 2-D (4, 4) rectangular grids that are fused through the M centers to yield a complex three-dimensional framework which accommodates the ⁿBu₄N⁺ cations. In PPN{M[Au(CN)₂]₃}, the framework adopts a simpler non-interpenetrated Prussian-blue-type pseudo-cubic array, with the PPN⁺ cations occupying each cavity; no reduction in dimensionality occurs despite the large cation size. In the presence of water, {Co(H₂O)₂[Au(CN)₂]₂} · ⁿBu₄N[Au(CN)₂] was obtained, a 2-D layered polymer that contains neutral sheets of {Co(H₂O)₂[Au(CN)₂]₂} which are separated by ⁿBu₄N[Au(CN)₂] layers; aurophilic interactions of 3.4250(13) Å and hydrogen-bonding connect the layers. The magnetic properties of all compounds were investigated by SQUID magnetometry. The Ni(II) polymers have similar magnetic behaviour, which are dominated by zero-field splitting with very weak antiferromagnetic interactions at low temperature (D ∼ 2–3 cm⁻¹, zJ < 1 cm⁻¹). The magnetic behaviour of all of the Co(II) polymers were found to be very similar, and dominated by single-ion effects (i.e. a large first-order orbital contribution). No significant magnetic coupling is observed in any of these coordination polymers, suggesting that the [Au(CN)₂] bridging unit behaves as a poor mediator of magnetic exchange in these high-dimensionality systems.     

Design and application of a magnetic field gradient electrode

A platinum coated electrode, which creates a magnetic field of 25 mT and a field gradient of order 10⁵ T m⁻¹ within 100 nm of the electrode surface is produced by embedding an array of CoPt nanowires in an alumina membrane. There is an enhancement by up to a factor of three for a model oxygen reduction reaction in an alkaline medium when the nanowires in the electrode are in a magnetized state. We suggest that the enhancement of the oxygen reduction current is associated with an increase of concentration of ${\text{HO}}_2^{-}$ on the surface of the electrode by the magnetic field gradient.     

Synthesis and reactions of heterodinuclear organopalladium–cobalt complexes acting as copolymerization catalyst for aziridine and carbon monoxide

A series of heterodinuclear acylpalladium–cobalt complexes having a bidentate nitrogen ligand, L₂(RCO)Pd–Co(CO)₄ (L₂ = bpy, R = Me (5), Ph (6); L₂ = tmeda, R = Me (7), Ph (8); L₂ = phen, R = Me (9), Ph (10)) are prepared by metathetical reactions of PdRIL₂ with Na⁺[Co(CO)₄]⁻ followed by treatment with CO. These complexes are characterized by NMR and IR spectroscopies and elemental analyses, and the molecular structures of 6, 8, and 9 are determined by X-ray structure analysis. Geometry at Pd is essentially square planar and the Co atom is considered to have d¹⁰ tetrahedral structure, where cobalt(-I) anion coordinates to palladium(II) cation. Heterodinuclear organopalladium–cobalt complexes are shown to catalyze copolymerization of aziridines and CO under mild conditions. Reaction of (dppe)MePd–Co(CO)₄ (1) with aziridine gives a cationic (aziridine)palladium(II) complex with [Co(CO)₄]⁻ anion, [PdMe(aziridine)(dppe)]⁺[Co(CO)₄]⁻ (13).     

Solid-state high-resolution NMR studies on spin fluctuation associated with valence tautomerism of metal–benzoquinone system: Cobalt complex in the stable and meta-stable phases

Equilibrium between low-spin [Co^III(SQ)(Cat)(N–N)] and high-spin [Co^II(SQ)₂(N–N)] redox isomers, where SQ is semiquinonate (charge: −1, spin: 1/2), Cat is catecholate (charge: −2, spin: 0) and N–N is chelating nitrogen donor ligand, respectively, is a representative valence tautomeric phenomenon. To elucidate independently the spin state of the cobalt ion and that of benzoquinone-derived ligands in the solid state, we measured ¹³C MAS NMR spectrum of 3,5-di-t-butyl-1,2-benzoquinone and ²H MAS NMR spectrum of deuterated 2,2′-bipyridine for [Co(3,5-di-t-butyl-1,2-benzoquinone)₂(2,2′-bipyridine)] · x(C₆H₅CH₃) and its deuterated analogue in a temperature range of 200–350 K. Irreversible change of an effective magnetic moment μ_eff of a virgin sample was observed around 370 K due to a partial loss of crystal solvent and a change of crystal structure, whereas the sample annealed at 390 K showed a crystal structure different from the reported one and a reversible change of μ_eff, which is ascribed to equilibrium between Co(III)-form (S = 1/2) and Co(II)-form (S = 3/2). Based on the shifts and the number of NMR peaks for the annealed sample, we concluded that (1) interconversion between redox isomers occurs faster than NMR time scale (>10⁴ s⁻¹) in the solid state, (2) intraconversion between SQ and Cat in Co(III)-form also occurs much faster than 5 × 10⁴ s⁻¹ even at 198 K and (3) electron spins on SQ ligands in Co(II)-form are quenched probably due to a strong antiferromagnetic coupling between the two SQ ligands. The enthalpy and the entropy of the interconversion were estimated to be 17 kJ/mol and 54 J/(K mol), respectively. For the virgin metastable phase, SQ and Cat were clearly distinguished by ¹³C MAS NMR spectrum. The solid-state high-resolution NMR spectrum is useful to detect independently the change of spin states of benzoquinone-derived radical and metal ion.     

Li2ZnTi3O8 nanorods: A new anode material for lithium-ion battery

Spinel Li₂ZnTi₃O₈ nanorods were first synthesized using titanate nanowires as a precursor. The synthesized nanorods are highly crystalline and used as an anode material in a rechargeable Li-ion battery. A large capacity of 220 mA h g^? 1 was kept after 30 cycles at a current density of 0.1 A g^? 1, which is close to the theoretic capacity. The electrochemical measurements indicate that the anode material made of spinel Li₂ZnTi₃O₈ nanorods displayed a highly reversible capacity and excellent cycling stability.     

Facile hydrothermal-thermal conversion synthesis of CaSiO3 nanowires as promising structure and function integrated photoluminescent host candidate

A facile green hydrothermal-thermal conversion method was developed for the uniform high aspect ratio CaSiO₃ nanowires as promising structure and function integrated photoluminescent host, without any organic additive.     

A novel synthesis of ultrathin CoPt3 nanowires by dealloying larger diameter Co99Pt1 nanowires and subsequent stress-induced crack propagation

A novel approach to the fabrication of ultrathin CoPt₃ nanowires with a diameter of a few nanometers has been developed, by taking advantage of the volume shrinkage and formation of nanoporous structures upon dealloying electrodeposited Co₉₉Pt₁ nanowires (28 nm in diameter), followed by an ultrasonication treatment. The as-produced ultrathin CoPt₃ nanowires have an average diameter of 5 nm and lengths of up to 10 μm, and are found to be ferromagnetic at room temperature.     

Radiotracer and analytical evidences proving the reduction of ClO4− ions at the cobalt/electrolyte solution interface

The occurrence of the reduction of ClO₄⁻ ions in the course of the dissolution (corrosion) of Co was indicated through the study of the adsorption of radio labelled (³⁶Cl) Cl⁻ ions. A detailed analytical study determining the Co²⁺ and Cl⁻ content of the solution phase furnished firm evidences that under suitable chosen experimental conditions the 4Co + ClO₄⁻ + 8H⁺=4Co²⁺ + Cl⁻ + 4H₂O reaction could be as important as the Co + 2H⁺=Co²⁺ + H₂ reaction considered in the literature as the only reaction path.     

Electronic transport and magnetic properties of the perovskites La0.8Sr0.2Co1−xFexO3; x ≤ 0.3

Transport and magnetic properties of LaCoO₃-based compounds, doped with 20% Sr and 2.5, 5, 10, 15, 20 and 30% Fe, were investigated by means of magnetization, resistivity and magnetoresistance measurements as well as by ⁵⁷Fe Mössbauer spectroscopy. While the temperature dependence of the dc and ac magnetic susceptibilities reveals the presence of magnetic phase separation accompanied by spin-glass and cluster-glass behavior, the electrical resistivity and magnetoresistance characteristics indicate that the mesoscopic structure of the present compounds is rather well described as consisting of ferromagnetic, metallic grains embedded in an insulating matrix. The effect of the partial Co → Fe substitution on the bulk magnetic and transport properties, as well as on the local state of Co and Fe ions is discussed.     

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).     

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.     

Electrochemical deposition of (Mn, Co)-codoped ZnO nanorod arrays without any template

(Mn, Co)-codoped ZnO nanorod arrays were successfully prepared on Cu substrates by electrochemical self-assembly in solution of 0.5 mol/l ZnCl₂–0.01 mol/l MnCl₂–0.01 mol/l CoCl₂–0.1 mol/l KCl–0.05 mol/l tartaric acid at a temperature of 90 °C, and these nanorods were found to be oriented in the c-axis direction with wurtzite structure. Energy dispersive X-ray spectroscopy and x-ray diffraction show that the dopants Mn and Co are incorporated into the wurtzite-structure of ZnO. The concentrations of the dopants, and the orientations and densities of nanorods can easily be well controlled by the current densities of deposition or salt concentrations. Magnetization measurement indicates that the prepared (Mn, Co)-codoped ZnO nanorods with a coercivity of about 91 Oe and a saturation magnetization (M_s) of about 0.23 emu/g. The anisotropic magnetism for the (Mn, Co)-codoped ZnO nanorod arrays prepared in solution of 0.5 mol/l ZnCl₂–0.01 mol/l MnCl₂–0.01 mol/l CoCl₂–0.1 mol/l KCl–0.05 mol/l tartaric acid with current density of 0.5 mA/cm² was also investigated, and the crossover where the magnetic easy axis switches from parallel to perpendicular occurs at a calculated time of about 112 min. The anisotropic magnetism, depending on the rod geometry and density, can be explained in terms of a competition between self-demagnetization and magnetostatic coupling among the nanorods.     

Heat of solution of polyhalite and its analogues at T = 298.15 K

Calorimetric measurements have been performed to determine the heat of dissolution of polyhalite K₂SO₄ · MgSO₄ · 2CaSO₄ · 2H₂O and its analogues K₂SO₄ · MSO₄ · 2CaSO₄ · 2H₂O (M = Mn, Co, Ni, Cu, and Zn) at T = 298.15 K. The dissolution experiments were carried out in NaClO₄ solution with varying concentrations (0.5 to 2.0) mol kg^?1. All polyhalites dissolve exothermically. Exothermicity increases with concentration of NaClO₄. An extrapolation to infinite dilution was done using the SIT model.Within the limits of experimental uncertainty, the enthalpies of dissolution for the triple salts K₂MgCa₂(SO₄)₄ · 2H₂O with M = Mg, Mn, Ni, and Zn coincide. The value for the cobalt salt is noticeably less exothermic. Dissolution enthalpy of leightonite K₂CuCa₂(SO₄)₄ · 2H₂O, which does not crystallize in the polyhalite structure, deviates considerably within the series.     

Crystal and magnetic structures of electrochemically delithiated Li1−xCoPO4 phases

Precise structural data have been determined from a combined Rietveld refinement, based on neutron and X-ray powder diffraction data simultaneously, for the three phases LiCoPO₄, Li_zCoPO₄ with a specific intermediate Li-content z = 0.60(10) and CoPO₄, which are obtained by electrochemical Li-extraction from LiCoPO₄. All three phases are isopointal. Therefore, the transitions between these phases are necessarily of first order, in agreement with their observed coexistence. The same collinear antiferromagnetic structures with magnetic moments nearly parallel to the [010] direction are observed for LiCoPO₄ and Li_zCoPO₄, but with a significantly higher Néel temperature of 76 K for the latter compound in comparison with 23 K for LiCoPO₄. Olivine-type CoPO₄ can only be prepared from LiCoPO₄ by delithiation and its physical properties were investigated for the first time. An antiferromagnetic arrangement along the [100] direction is observed for CoPO₄ with an additional weak ferromagnetic component along the [001] direction (magnetic space group Pn′m′a and T_C = 45 K). The magnetic moment of 3.1(2) μ_B per Co-ion indicates a mainly high-spin state for Co³⁺ in the octahedral coordination of CoPO₄, which is exceptional and probably the first example in a phosphate. The easy axes and the magnetic exchange interactions between Co-ions change dramatically with the Co²⁺ ? Co³⁺ transition. A continuous change of the formal oxidation state of a transition element by electrochemical Li-extraction and a quasi-continuous in situ observation of the resulting magnetic structure by neutron diffraction appear feasible.     

Synthesis and magneto-optical properties of a series of bis(β-diketonato) Co(II) complexes with imino nitroxide radical chelate

A series of bis(4,4,4-trifluoro-1-R-1,3-butanedinato) Co(II) complexes with imino nitroxide radical(IM2py), [Co(Rtfc)₂(IM2py)] (R = trifluoromethyl, phenyl, naphthyl, thienyl), was prepared and characterized by the X-ray analysis which demonstrated the stereospecific formation of the trans(CF₃)-isomer with the trans disposition of the CF₃ groups. The significant substituents effect on the UV–Vis spectra and magnetic properties were discussed in consideration of the inversion of the d_π(t_2g) orbital levels leading to the orbital orthogonality or overlap with the SOMOπ¹ of IM2py in terms of the AOM parametrizations or spin-paring energy.     

Prospects for a widely applicable reference potential scale in ionic liquids based on ideal reversible reduction of the cobaltocenium cation

Oxidation of ferrocene, Fe(cp)₂ or reduction of the cobaltocenium cation, [Co(cp)₂]⁺ represent reversible processes that are widely used to provide a voltammetric potential reference scale. However, the [Fe(cp)₂]^0/+ process has been reported to exhibit complexities which may restrict its usefulness for this purpose in ionic liquids. In this study, the reduction of [Co(cp)₂]⁺ in the ionic liquids, [bmpyr][Ntf₂], [emim][Ntf₂], and [bmim][PF₆] (bmpyr = 1-butyl-1-methylpyrrolidinium, emim = 1-ethyl-3-methylimidazolium, bmim = 1-butyl-3-methylimidazolium, Ntf₂ = bis(trifluoromethanesulfonyl)amide) is reported at macro, micro, and rotating disk electrodes. Reversible behaviour, after allowance for ohmic drop, and linear current–concentration relationships are attained over wide concentration ranges for all electrode configurations. Results support the use of the [Co(cp)₂]^+/0 process for reference potential purposes, with non-idealities of the kind reported for ferrocene not being detected.     

Enhanced supercapacitive behaviors of birnessite

The birnessite type manganese dioxide electrode was prepared by the electrochemical stimulation as we recently described. It showed 190 F g⁻¹ in a Na₂SO₄ aqueous solution between −0.1 and 0.9 V versus Ag/AgCl at 1 A g⁻¹. The specific capacitance of birnessite was decreased by the manganese dissolution when the reduction and oxidation were repeated. By adding small amounts of Na₂HPO₄ or NaHCO₃ into the electrolyte, the capacitance increased to 200–230 F g⁻¹ and the manganese dissolution was successfully suppressed. Thanks to the additives, the birnessite demonstrated the much improved cycleability over >1800 cycles.     

Synthesis and spectroscopic characterization of new tetradentate Schiff base and its coordination compounds of NOON donor atoms and their antibacterial and antifungal activity

New Schiff base (H₂L) ligand is prepared via condensation of o-phthaldehyde and 2-aminobenzoic acid in 1:2 ratio. Metal complexes are prepared and characterized using elemental analyses, IR, solid reflectance, magnetic moment, molar conductance, ¹H NMR, ESR and thermal analysis (TGA). From the elemental analyses data, the complexes were proposed to have the general formulae [MCl(L)(H₂O)]·2H₂O (where M = Cr(III) and Fe(III)); [M(L)]·yH₂O (where M = Mn(II), Ni(II), Cu(II) and Zn(II), y = 1–2) and [M(L)(H₂O)_n]·yH₂O (where M = Co(II) (n = y = 2), Co(II) (n = y = 1), Ni(II) (n = 2, y = 1). The molar conductance data reveal that all the metal chelates were non-electrolytes. IR spectra show that H₂L is coordinated to the metal ions in a bi-negative tetradentate manner with NOON donor sites of the azomethine-N and carboxylate-O. The ¹H NMR spectral data indicate that the two carboxylate protons are also displaced during complexation. From the magnetic and solid reflectance spectra, it was found that the geometrical structure of these complexes are octahedral (Cr(III), Fe(III), Co(II) and Ni(II)), square planar (Cu(II)), trigonal bipyramidal (Co(II)) and tetrahedral (Mn(II), Ni(II) and Zn(II)). The thermal behaviour of these chelates showed that the hydrated complexes losses water molecules of hydration in the first step followed immediately by decomposition of the ligand molecule in the subsequent steps. The biological activity data show that the metal complexes to be more potent/antibacterial than the parent Shciff base ligand against one or more bacterial species.     

Lattice potential energies and thermochemical properties of triethylammonium halides (Et3NHX) (X = Cl,Br, and I)

A series of triethylammonium halides (Et₃NHCl, Et₃NHBr, and Et₃NHI) was synthesized. The crystal structures of the three compounds were characterized by X-ray crystallography. The lattice potential energies and ionic radius of the common cation of the three compounds were obtained from crystallographic data. Molar enthalpies of dissolution of the compounds at various values of molality were measured in the double-distilled water at T = 298.150 K by means of an isoperibol solution-reaction calorimeter. According to Pitzer’s theory, the values of molar enthalpies of dissolution at infinite dilution and Pitzer’s parameters of the compounds were obtained. The values of apparent relative molar enthalpies, relative partial molar enthalpies of the solvent and the compounds at different molalities were derived from the experimental values of molar enthalpies of dissolution of the compounds. Finally, hydration enthalpy of the common cation Et₃NH⁺ was calculated to be ΔH₊ = ?(150.386 ± 4.071) kJ · mol^?1 by designing a thermochemical cycle.