Nanocrystalline CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> powders prepared by egg white solution route: synthesis,characterization and its giant dielectric properties

Nanocrystalline CaCu₃Ti₄O₁₂ powders with particle sizes of 50–90 nm were synthesized by a simple method using Ca(NO₃)₂·4H₂O, Cu(NO₃)₂·4H₂O, titanium(diisoproproxide) bis(2,4-pentanedionate) and freshly extracted egg white (ovalbumin) in aqueous medium. The synthesized precursor was characterized by TG-DTA to determine the thermal decomposition and crystallization temperature which was found to be at above 400 °C. The precursor was calcined at 700 and 800 °C in air for 8 h to obtain nanocrystalline powders of CaCu₃Ti₄O₁₂. The calcined CaCu₃Ti₄O₁₂ powders were characterized by XRD, FTIR, SEM and TEM. Sintering of the powders was conducted in air at 1100 °C for 16 h. The XRD results indicated that all sintered samples have a typical perovskite CaCu₃Ti₄O₁₂ structure and a small amount of CuO, although the sintered sample of the 700 °C calcined powders contained some amount of CaTiO₃. SEM micrographs showed the average grain sizes of 12.0±7.8 and 15.5±8.9 μm for the sintered CaCu₃Ti₄O₁₂ ceramics prepared using the CaCu₃Ti₄O₁₂ powders calcined at 700 and 800 °C, respectively. The sintered samples exhibit a giant dielectric constant, ε^′ of ∼ 1.5–5×10⁴. The dielectric behavior of both samples exhibits Debye-like relaxation, and can be explained based on a Maxwell–Wagner model. PACS 77.22.Gm; 81.05.Je; 81.07.Wx; 81.20.Ev     

Synthesis of NiCo2S4 nanospheres/reduced graphene oxide composite as electrode material for supercapacitor

The NiCo₂S₄ nanospheres arrayed on the surface of reduced graphene oxide (rGO) was fabricated via one-step hydrothermal method. The effect of initial feeding mass of Ni(NO₃)₂·6H₂O and Co(NO₃)₂·6H₂O to rGO on the microstructure and electrochemical performance of the as-prepared composites was studied. The results indicated that the specific capacitances of the composites were first increased and then reduced due to the aggregation of NiCo₂S₄ nanospheres. NiCo₂S₄ nanospheres/rGO composites exhibited a remarkable specific capacitance of 1406 F/g and excellent cyclic stability of 82.36% at the current density of 1 A/g, which were better than those of individual NiCo₂S₄ (792 F/g and 64.77%) counterpart. These results showed that the as-prepared NiCo₂S₄ nanospheres/rGO composites were outstanding candidate for electrode material of supercapacitors.     

Preparation and application of core–shell Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/polythiophene nanoparticles

The Fe₃O₄/polythiophene nanoparticles, possessing core–shell structure, were prepared by two-step method. In the first step, the Fe₃O₄ particles were synthesized via co-precipitation of FeCl₃ and FeSO₄, using the NH₃·H₂O and N₂H₄·H₂O as precipitant system. In the second step, the thiophene adsorbed and polymerized on the surface of the Fe₃O₄ in the solvent of chloroform. Raman, FTIR, EDS, XRD, TEM, Zeta potential measurement and TG-SDTA were employed to characterize the composition and structure of the products. The results showed that the Fe₃O₄/polythiophene nanoparticles were successfully synthesized with good dispersion and stable core–shell structure, provided with average particle size of approximately 20 nm, in which the diameter of Fe₃O₄ core was approximately 14 nm and the thickness of polythiophene shell was approximately 3–4 nm. Then, the nanoparticles were added into alkyd varnish to prepare a composite coating. The neutral salt spray test, paraffin control test and mechanical test were carried out to identify the properties of the composite coating. It was found that the composite coating had good performances of anticorrosion and paraffin controlling when the mass fraction of the nanoparticles was 0.8–1 wt% in alkyd varnish. As a multifunctional material, the Fe₃O₄/polythiophene nanoparticles can be used in the internal coating of pipeline and have great potential application in crude oil pipeline transportation.     

Expanding cyclitol structural diversity by biocatalysis and metalocatalysis. A click chemistry approach

The palladium catalyzed cross-coupling reaction of phenyltrifluoroborate with a chemoenzymatically derived bromoazidoconduritol, combined with 1,3-dipolar cycloaddition, with a variety of alkynes is described. Fourteen new compounds were synthesized in moderate to good yields. The click chemistry reaction can be effected by using sodium ascorbate and CuSO₄ · 5H₂O as catalyst in toluene–H₂O at room temperature.     

One-pot synthesis of hybrid nanospheres with multistructure for selective adsorption of Hg<Superscript>2+</Superscript>

Novel complex nanospheres with core/shell structure for selective adsorption of Hg²⁺ have been prepared by a simple one-pot method. Scanning electron microscopy (SEM) and transmission electron microscope (TEM) images showed the nanospheres had perpendicularly thiol-functionalized mesoporous SiO₂ hybrid shell and Fe₃O₄@SiO₂ core (Fe₃O₄@nSiO₂@mSiO₂–SH). XRD patterns of as-synthesized nanospheres confirmed the observation of the SEM and TEM. The size of the nanospheres is about 100 nm. Based on the analysis of N₂ sorption–desorption isotherm, the surface area and pore volume of the adsorbent are 861 m²/g and 0.48 cm³/g, respectively. The saturation magnetization value for Fe₃O₄@nSiO₂@mSiO₂–SH is as high as 6.87 emu g⁻¹. The nanospheres showed more accessible active sites and high dispersibility in water, exhibited excellent performance for selective Hg²⁺ adsorption, had a stable structure, and could be recycled easily with magnet.     

Langmuir-Blodgett self-assembly and electrochemical catalytic property of FePt magnetic nano-monolayer

Dispersed-well FePt nanoparticles with particle size ~5 nm have been prepared by hydrazine hydrate reduction of H₂PtCl₆·6H₂O and FeCl₂·4H₂O in ethanol–water system. By employing as-synthesized FePt nanoparticles, the monolayer can be formed by LB Technique. The structural, magnetic properties and electrochemical properties of FePt monolayer were respectively studied by XRD, TEM, VSM and CHI 820 electrochemical workstation. The as-synthesized particle has a chemically disordered fcc structure and can be transformed into chemically ordered fct structure after annealing treatment above 400°C. The coercivity of ordered fct FePt phase can be up to 2515Oe. CVs of 0.5 M H₂SO₄/0.5M CH₃OH on GCE modified with FePt nanoparticles monolayer films illustrate that the as-synthesized FePt is a kind of active electrochemical catalyst.     

Fabrication of magnetic gold nanorod particles for immunomagnetic separation and SERS application

The preparation and application of rod-shaped core–shell structured Fe₃O₄–Au nanoparticles for immunomagnetic separation and sensing were described for the first time with this study. To synthesize magnetic gold nanorod particles, the seed-mediated synthetic method was carried out and the resulting nanoparticles were characterized with transmission electron microscopy (TEM), ultraviolet visible spectroscopy (UV–Vis), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD). Magnetic properties of the nanoparticles were also examined. Characterization of the magnetic gold nanorod particles has proven that the resulting nanoparticles were composed of Fe₃O₄ core and the gold shell. The rod-shaped gold-coated iron nanoparticles have an average diameter of 16 ± 2 nm and an average length of about 50 ± 5 nm (corresponding aspect ratio of 3). The saturation magnetization value for the magnetic gold nanorod particles was found to be 37 emu/g at 300 K. Rapid and room temperature reaction synthesis of magnetic gold nanorod particles and subsequent surface modification with E. coli antibodies provide immunomagnetic separation and SERS application. The analytical performance of the SERS-based homogenous sandwich immunoassay system with respect to linear range, detection limit, and response time is also presented.     

Synthesis and characterization of mesoporous ZnS with narrow size distribution of small pores

Pure, nanocrystalline cubic ZnS forming a stable mesoporous structure was synthesized at room temperature by a non-toxic surfactant-assisted liquid–liquid reaction, in the 9.5–10.5 pH range of values. The appearance of an X-ray diffraction (XRD) peak in the region of very small angles (∼ 2°) reveals the presence of a porous material with a narrow pore size distribution, but with an irregular arrangement of the pores, a so-called worm hole or sponge-like material. The analysis of the wide angle XRD diffractograms shows the building blocks to be ZnS nanocrystals with cubic structure and average diameter of 2 nm. Transmission electron microscopy (TEM) investigations confirm the XRD results; ZnS crystallites of 2.5 nm with cubic (blende) structure are the building blocks of the pore walls with pore sizes from 1.9 to 2.5 nm, and a broader size distribution for samples with smaller pores. Textural measurements (N₂ adsorption–desorption isotherms) confirm the presence of mesoporous ZnS with a narrow range of small pore sizes. The relatively lower surface area of around 100 m²/g is attributed to some remaining organic molecules, which are filling the smallest pores. Their presence, confirmed by IR spectroscopy, seems to be responsible for the high stability of the resulting mesoporous ZnS as well. PACS  61.46.Df; 68.37.Lp; 78.67.-n; 81.05.Ea; 81.07.Bc     

The direct precipitation of rhabdophane (REEPO<Subscript>4</Subscript>·<Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O) nano-rods from acidic aqueous solutions at 5–100 °C

The precipitation of lanthanum and neodymium phosphate phases from supersaturated aqueous solutions at pH ~1.9 was studied at 5, 25, 50, and 100 °C in batch reactors for up to 168 h. Crystalline La and Nd–rhabdophane phases precipitated immediately upon mixing of the initial aqueous La or Nd and PO₄ solutions. Changes in aqueous PO₄ and Rare Earth Element (REE) concentrations during the experiments were determined by ICP-MS and UV–Vis spectrophotometry, while the resulting solids were characterized via powder XRD, SEM, TEM, and FTIR. All precipitated crystals exhibited a nano-rod morphology and their initial size depended on temperature and REE identity. At 5 °C and immediately after mixing the La and Nd–rhabdophane crystals averaged ~44 and 40 nm in length, respectively, while at 100 °C lengths were ~105 and 94 nm. After 168 h of reaction, the average length of the La and Nd rhabdophanes increased by 23 and 53% at 5 °C and 11 and 59% at 100 °C, respectively. The initial reactive solutions in all experiments had activity quotients for rhabdophane precipitation: \textREE ³⁺ + \textPO₄^{3 -} + n\textH₂ \textO = \textREEPO₄ ·  n\textH₂ \textO {\text{REE}}^{ 3+ } + {\text{PO}}_{4}^{3 - } + n{\text{H}}_{2} {\text{O}} = {\text{REEPO}}_{4} \cdot\;n{\text{H}}_{2} {\text{O}} of ~10^−20.5. This activity quotient decreased with time, consistent with rhabdophane precipitation. The rapid equilibration of rhabdophane supersaturated solutions and the progressive rhabdophane crystal growth observed suggests that the REE concentrations of many natural waters may be buffered by rhabdophane precipitation. In addition, this data can be used to guide crystallization reactions in industrial processes where monodisperse and crystalline La or Nd rhabdophane materials are the target.     

Mechanism for sonochemical reduction of Au(III) in aqueous butanol solution under Ar based on the analysis of gaseous and water-soluble products

When an aqueous Au(III) solution containing 1-butanol was sonicated under Ar, Au(III) was reduced to Au(0) to form Au particles. This is because various reducing species are formed during sonication, but the reactivity of these species has not yet been evaluated in detail. Therefore, in this study, we analyzed the effects of Au(III) on the rates of the formation of gaseous and water-soluble compounds (CH₄, C₂H₆, C₂H₄, C₂H₂, CO, CO₂, H₂, H₂O₂, and aldehydes), and the rate of Au(III) reduction as a function of 1-butanol concentration. The following facts were recognized: 1) for Au(III) reduction, the contribution of the radicals formed by the pyrolysis of 1-butanol was higher than that of the secondary radicals formed by the abstraction reactions of 1-butanol with ·OH, 2) ·CH₃ and CO acted as reductants, 3) the contribution of ·H to Au(III) reduction was small in the presence of 1-butanol, 4) aldehydes and H₂ did not act as reductants, and 5) the types of species that reduced Au(III) changed with 1-butanol concentration.     

Complexation between variable-valency uranium and organic ligands in solutions,their photostability and spectral identification

We discuss possible directions for searching for prospective materials based on low-valency uranium (III–V) as detection media for hard electromagnetic radiation. We have studied the processes of formation of tetravalent and pentavalent uranium complexes from UO₂(NO₃)₃·6H₂O and UO₂Cl₂·H₂O in DMF and with addition of CCl₄, including when the systems are exposed to radiation in the visible range (400–450 nm). In the first case (UO₂(NO₃)₃·6H₂O solutions in DMF), upon irradiation we observe stable complexes of pentavalent uranium, and when CCl₄ is added to the solution we observe complexes of tetravalent uranium. In the system UO₂Cl₂·3H₂O in DMF, we do not observe the appearance of new forms of uranium; but when CCl₄ is added, then complexes of tetravalent uranium are formed. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 184–187, March–April, 2007.     

Synthesis, crystal structure, thermal and dielectric properties of bis(p-phenylenediammonium) chloride hexachlorobismuthate(III) monohydrate [C6H4(NH3)2]2ClBiCl6.H2O

Synthesis, crystal structure, and dielectric properties of [C₆H₄(NH₃)₂]₂ClBiCl₆.H₂O are reported. The compound crystallizes in the monoclinic system with space group P2₁/n. The unit cell dimensions are a = 9.836(5), b = 19.582(5), c = 13.082(5) ?, β = 104.731(5)° with Z = 4. The atomic arrangement can be described by an alternation of organic and inorganic layers. The anionic layer is built up of octahedral of [BiCl₆]^3- arranged in sandwich between the organic layers. The crystal packing is governed by means of the ionic N–H···Cl hydrogen bonds, forming a three-dimensional network. The dielectric properties have been investigated at temperature range from 297 to 410 K at various frequencies (10 Hz–100 kHz). Dielectric studies were performed to confirm results obtained with thermal analysis. The evolution of dielectric constant as a function of temperature and frequency of single crystal has been investigated in order to determine some related parameters.     

Electrocatalytic activity of a Gd2Ti0.6Mo1.2Sc0.2O7-δ anode towards hydrogen and methane electro-oxidation in a solid oxide fuel cell

Mixed conducting oxide anodes are being considered for the direct utilisation of natural gas in high temperature fuel cells. This work refers to the electrochemical characterization of the pyrochlore Gd₂Ti_0.6Mo_1.2Sc_0.2O_7-δ (GTMS) as anode in a solid oxide fuel cell running in low humidity hydrogen or methane. The electro-oxidation reaction was investigated using impedance spectroscopy, potentiostatic measurements and cyclic voltammetry. Kinetic data were obtained for different fuels in the temperature range 845–932 °C. In a methane-fuelled cell, steam reforming appears to be the rate-limiting step. The overall polarisation resistance of the anode under open circuit conditions at 932 °C was 6.86 Ω·cm² in 97% H₂/3% H₂O, and 43 Ω·cm² in 97% CH₄/3% H₂O. For a 97% fuel-3% H₂O/GTMS//YSZ-Al₂O₃//Pt/air cell, the maximum power output at 932 °C was 9.5 mW/cm² and 1.8 mW/cm² in hydrogen and methane, respectively. First investigations on this type of electrode material show unidentified peaks on XRD spectra after electrochemical test, which indicate GTMS instability under experimental conditions. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Co<Subscript>3</Subscript>O<Subscript>4</Subscript> @ PFR cube-like core–shell nanocomposite prepared via a facile one-step hydrothermal approach

The Co₃O₄ @ phenol formaldehyde resin (PFR) cube-like nanocomposites are prepared by one-step hydrothermal process at 120–180 °C for 3–9 h. Co(NO₃)₂·6H₂O, hexamethylenetetramine (HMT), and phenol are used as precursors in water solvent. Any adventitious oxidants and additives are not presented. The transmission/scanning electronic microscope (TEM, SEM) images show as-obtained typical samples are consisted of cube-like Co₃O₄ as core and PFR as shell. The X-ray diffraction (XRD) data indicate the samples are consisted of cube-phase Co₃O₄ with amorphous PFR. Fourier transform infrared spectra (FTIR) further confirm Co₃O₄ and PFR are contained in the samples. Room-temperature vibration magnetic strength measurements (VMS) indicate that the antiferromagnetic properties of core–shell nanocomposites evidently differ from the naked-Co₃O₄ nanoparticles.     

Effect of the concentration of precursors on the microwave absorbent properties of Zn/Fe oxide nanopowders

Zn/Fe oxide compound powders were obtained by the hydrothermal method using ferric nitrate Fe(NO₃)₃·9H₂O and zinc nitrate Zn(NO₃)₂·6H₂O at 200 °C and different precursor molar ratios x = Fe³⁺/Zn²⁺ equal to 2.8/0.2, 2.5/0.5, 1.8/1.2 and 1.5/1.5. The samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive X-ray analysis (SEM–EDAX). Room temperature measurements of the frequency dependence of the complex magnetic permeability and complex dielectric permittivity, over the frequency range from 0.1 to 6 GHz, were performed. For precursor molar ratios x = 2.8/0.2, x = 1.8/1.2 and x = 1.5/1.5 the obtained samples showed a ferromagnetic-like resonance behaviour. This behaviour was assigned to the prevalent compounds in the obtained samples, Fe₂O₃ (for x = 2.8/0.2) and ZnFe₂O₄ (for x = 1.8/1.2 and x = 1.5/1.5). Based on the magnetic and dielectric measurements, the microwave absorbent properties of the four samples were analysed, and the sample containing mostly of ZnFe₂O₄ (for x = 1.8/1.2) was found to be the best electromagnetic absorber in the frequency range 1.36–6 GHz.     

Sonochemical synthesis and characterization of new nanostructures cobalt(II) metal-organic complexes derived from the azo-coupling reaction of 4-amino benzoic acid with anthranilic acid,salicylaldehyde and 2-naphtol

Nanostructures of three new cobalt(II) complexes, (CoL₁)·0.5DMF·1.5MeOH (1), [H₂L₁ = 5-(4-Carboxy phenyl azo) anthranilic acid], (Co(L₂)₂)·1.5MeOH (2), [HL₂ = 5-(4-Carboxy phenyl azo) salicylaldehyde] and (Co(L₃)₂)·0.5 DMF·0.5MeOH (3), [HL₃ = 1-(4-Carboxy phenyl azo) 2-naphtol], have been synthesized by the reaction of H₂L₁, HL₂ and HL₃ with Co(OAc)₂·4H₂O through sonochemical process. Calcination of the nano-sized compounds 1–3 yield Co₃O₄ nanoparticles at 450 °C under air atmosphere. These nanostructures were characterized by X-ray powder diffraction (XRD) and Scanning Electron Microscopy (SEM). Thermal stability of compounds 1–3 was studied by thermogravimetric (TG) and differential thermal analyses (DTA).     

A simple method to tailor spherical nanocrystal hydroxyapatite at low temperature

A simple method, chemical precipitation at low temperature from Ca(NO₃)₂·4H₂O and (NH₄)₂HPO₄ to tailor single phase, highly crystalline nanocrystal hydroxyapatite (HAp) powders was introduced in this paper. HAp powders with controlled morphologies (spherical and rod-like) and different grain sizes have been obtained by varying the reaction temperature, reaction mode, and heat treatment accordingly. X-ray diffraction (XRD) results combined with the Fourier transform-infrared spectroscopy (FT-IR) indicates that the single phase, nanocrystal HAp powder could be obtained in one-step without further heat treatment. At 40 °C with a quick mixing mode, ultra-fine complete spherical HAp particles with diameter range size of 20–50 nm could be obtained.     

Growth and use of metal nanocrystal assemblies on high-density silicon nanowires formed by chemical vapor deposition

In this paper, we describe the growth and potential application of metal nanocrystal assemblies on metal-catalyzed, CVD-grown silicon nanowires (SiNWs). The nanowires are decorated by chemical assembly of closely spaced (1–5 nm) Ag (30–100 nm diameter) and Au (5–25 nm diameter) nanocrystals formed from solutions of AgNO₃ and NaAuCl₄·2H₂O, respectively. The formation and growth of metal nanocrystals is believed to involve the galvanic reduction of metal ions from solution and the subsequent oxidation of available Si-hydride sites on the surfaces of the nanowires. A native oxide layer suppresses formation of metal nanocrystals; adding HF to the ionic solutions significantly increases the density of nanocrystals on the surfaces of the nanowires. The nanocrystals coating the nanowires were characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, and X-ray diffraction. Ag nanocrystals on the nanowires afford sensitive detection of Rhodamine 6G (R6G) molecules in the 100 picomolar–micromolar range by surface enhanced Raman spectroscopy. In addition, Au nanocrystals formed on selected surfaces of a substrate of arbitrary shape can serve as effective nuclei for localized nanowire growth. PACS 81.07.b; 81.15.Gh     

A simple synthesis of SnS nanoflakes at ambient conditions

The present work reports a simple route to prepare tin monosulfide semiconductor nanocrystals at ambient conditions. In the presence of complexant L-tartaric acid, SnCl₂·2H₂O was dissolved in ethylene glycol (EG) solution. After adjusting the solution pH value, sodium sulfide dissolved in EG was added into the solution. The solution changed from colorless into brown immediately and phase-pure SnS, which was confirmed by powder X-ray diffraction (XRD) was produced. The transmission electron microscopic (TEM) investigation shows very thin rectangular flake like SnS crystals of 10∼20 nm in size. PACS 81.05.Hd; 81.07.Bc; 81.16.Be; 81.16.Dn; 81.20.Ka     

Microemulsion-mediated in-situ synthesis and magnetic characterization of polyaniline/Zn<Subscript>0.5</Subscript>Cu<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanocomposite

Polyaniline/Zn_0.5Cu_0.5Fe₂O₄ nanocomposite was synthesized by a simple, general and inexpensive in-situ polymerization method in w/o microemulsion. The effects of polyaniline coating on the magnetic properties of Zn_0.5Cu_0.5Fe₂O₄ nanoparticles were investigated. The structural, morphological and magnetic properties of as-prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectra, scanning electron microscopy (SEM) and magnetic measurements. The morphology analysis confirmed that polyaniline was deposited on the porous surface of magnetic Zn_0.5Cu_0.5Fe₂O₄. It was shown that the saturation magnetization and coercivity of Zn_0.5Cu_0.5Fe₂O₄ decreased after polyaniline coating, which can be interpreted by the interparticle dipole–dipole interactions that contributed to magnetic anisotropy and changed the magnetic properties of the nanoparticles. PACS  74.25.Ha; 81.05.-t; 81.05.Lg