Metal and Metal Oxide Nanostructures Prepared by Electrical Arc Discharge Method in Liquids

In this review, the importance of electrical arc discharge technique in liquids in synthesis of various nanostructures from carbon based materials to metal and metal oxide nanostructures with their general and specific properties, especially the photocatalytic performance of metal oxide nanostructures is studied. The effect of arc current on size distribution, morphology and physicochemical properties of metal and semiconductor nanostructures was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray photoelectron spectroscopy (XPS) and UV–Vis spectroscopy. WO₃ Cubic nanostructures with 30 nm mean particle size were formed during the discharge process in water. Discharge between zinc electrodes in water leads to formation of rod like and semi spherical ZnO nanostructures with 15–20 nm diameter range. ZrO₂ nanoparticles were formed using zirconium electrodes in water. Photodegradation of Rhodamine B (Rh. B) shows that the as prepared nanostructures in this method have potential ability for environmental purifications. Also, using silver electrodes in water leads to formation of silver nanoparticles with 8–15 nm average particle size. Moreover, a novel method for synthesis of gold nanoparticles without using gold electrodes is presented. Finally, the future outlook of this technique in synthesis of various nanocrystalline materials is presented.     

Structural transition to electrolyte-water solvent and changes in the molecular dynamics of water and properties of solutions

A model of concentration transition “ions and complexes in a water structure → ionic and ionicaqueous clusters → polymer structures of salt and crystal hydrate melts” is suggested. The appearance of cluster nanostructures outside the first zone of a waterlike structure is regarded as a general characteristic of solutions. The characteristics of solutions, phase equilibria, and salts of complex composition are interpreted based on this model. Investigation of the complex dielectric constant of electrolytic solutions in the SHF and EHF bands (7–119 GHz) at high concentrations showed that there are two dispersion regions in which the relaxation times differ by a factor of 5–10. Relaxation processes are separated, the numbers of molecules in hydration shells are calculated, and relaxation times are determined for bulky tetrahedral water with hydration shells of ions, for clusters, and for ionicaqueous polymer chains. It is shown that the two structure subsystems of water molecules in concentrated solutions may be described using the limited rotator/generalized diffusion molecular model. Translated fromZhumal Strukturnoi Khimii, Vol. 39, No. 5, pp. 851–863, September–October, 1998.     

Low-voltage anodized TiO<Subscript>2</Subscript> nanostructures studied by alternate current electrochemical microscopy and photoelectrochemical measurements

This paper presents the characterization of TiO₂ nanostructures obtained by low-voltage anodization using alternate current electrochemical microscopy (AC-SECM) and photoelectrochemical (PEC) measurements. TiO₂ nanostructures were obtained from the exposure of titanium foils to several aqueous acidic solutions of hydrofluoric acid + phosphoric acid at potentials of 1 to 3 V. Scanning electron microscopy, X ray diffraction, and atomic force microscopy studies evidence the formation of a thin porous amorphous layer (<600 nm) with pore size in the range of 200–1,000 nm. By AC-SECM studies at different bias, we were able to confirm the unambiguous semiconducting properties of as-obtained porous titania films, as well as differences in surface roughness and conductivity in specimens obtained at both potentials. The difference in conductivity persists in air annealed samples, as demonstrated by electrochemical impedance spectroscopy and PEC measurements. Specimens obtained at 3 V show lower photocurrent and dark current than those obtained at 1 V, regardless of their larger conductivity, and we proposed it is due to differences on the oxide layer formed at the pore bottom.     

Synthesis, characterization, and electrochemical properties of self-assembled leaf-like CuO nanostructures

A simple hydrothermal process was used to synthesize the assembled leaf-like copper oxide (CuO) from copper hydroxide and urea in aqueous solution. The field emission scanning electron microscopy revealed that the individual CuO leaf-like nanostructure has a dimension of about 0.5–1.5 μm in length, 50–70 nm in thickness, and 80–110 nm in width, respectively. These CuO nanostructures were structurally characterized by X-ray diffraction and Raman spectroscopy, which showed that the CuO nanostructures prepared from the hydrothermal process have high crystalline properties with a monoclinic structure. X-ray photoelectron spectroscopy studies confirmed that the as-prepared sample is composed of CuO, which is consistent with X-ray diffraction patterns. The CuO nanostructures were used as electrode materials for lithium-ion batteries, demonstrating electrochemical properties of a high initial discharge capacity of approximately 1,028 mAh/g along with good cycle stability.     

Towards chemical analysis of nanostructures in biofilms I: imaging of biological nanostructures

Due to their direct influence on the stability of bacterial biofilms, a better insight into the nanoscopic spatial arrangement of the different extracellular polymeric substances (EPS), e.g., polysaccharides and proteins, is important for the improvement of biocides and for process optimization in wastewater treatment and biofiltration. Here, the first application of a combination of confocal laser-scanning microscopy (CLSM) and atomic force microscopy (AFM) to the investigation of river-water biofilms and related biopolymers is presented. AFM images collected at selected areas of CLS micrographs dramatically demonstrate the heterogeneity of biofilms at the nanometer scale and the need for a chemical imaging method with nanoscale resolution. The nanostructures (e.g., pili, flagella, hydrocolloids, and EPS) found in the extracellular matrix are classified according to shape and size, which is typically 50–150 nm in width and 1–10 nm in thickness, and sets the demands regarding spatial resolution of a potential chemical imaging method. Additionally, thin layers of the polysaccharide alginate were investigated. We demonstrate that calcium alginate is a good model for the EPS architecture at the nanometer scale, because of its similar network-like structure. Figure CLSM-AFM allows imaging of nanometer-sized extracellular structures     

Equilibrium locations for nested carbon nanocones

Potentially, carbon nanostructures are very important as ideal components to create many novel nano-devices. Such devices including nano-oscillators, ultra-fast optical filters and nano-bearings, are based on the unique mechanical and electronic properties of carbon nano-structures. Common carbon nanostructures used are usually C₆₀-fullerenes, carbon nanotubes, carbon nano-bundles and carbon nanotori. In the synthesis and production of carbon nanostructures, carbon nanocones tend to occur less frequently, and it is known that five different size cones may occur, depending on the number of pentagons in the atomic network. However, the simple geometric structure of carbon nanocones certainly facilitates calculations for their potential energy. Here, the Lennard–Jones potential energy function and the usual continuum approximation are employed to determine the energy for two such nested carbon nanocones which are located co-axially. We show graphically the energy profiles for any two carbon nanocones arising from the five possible structures. For both two distinct cones and two identical cones, we find that the equilibrium location moves further away from the vertex as the number of pentagons is increased. However, we observe that the equilibrium position occurs such that one cone is always inside the other, and therefore, we might expect that nested double-cones are formed according to these results.      

Formation and properties of the nanocluster structure of iron oxides

Nanostructures based on iron oxide clusters 1–300 nm in size were synthesized and studied. Thermodynamic models of nanocluster nucleation resulting in the formation of both primary nanoclusters and nanocluster aggregates with the sizes up to 70–80 nm were considered. Models of heat capacity of the nanoclusters were examined, and the twofold increase in the heat capacity of the iron oxide clusters 2–3 nm in size compared to that of the bulk iron oxide samples was found. The size of the primary nanoclusters and the intercluster interaction make it possible to vary the magnetic properties of the nanostructures in a wide range from paramagnetic to magnetically ordered α-Fe₂O₃-γ-Fe₂O₃ nanostructures with the first-order magnetic phase transitions, magnetic twinning, and a strong magnetic field (10 Oe) effect on the magnetization increase at low temperatures. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1693–1704, October, 2006.     

“Perfect” structure regions in amorphous argon

The structure of molecular dynamic models of amorphous argon is investigated by the Voronoi-Delaunay method. It is shown that the majority of Delaunay simplices (determined by quadruplets of the nearest atoms) are “perfect,” i.e., close in their shape either to the ideal tetrahedron or to the ideal quartoctahedron. These two types of structural elements are positioned in a correlated manner relative to each other, forming regions of a “perfect” structure which, however, is not crystalline. The regions themselves are separated by sections of an “imperfect” structure in which the shape of simplicial atomic configurations differs from the mentioned ideal forms. Institute of Chemical Kinetics and Combustion, Siberian Branch, Russian Academy of Sciences. Novosibirsk State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 1, pp. 53–63, January–February, 1994. Translated by L. Chernomorskaya     

Analysis of organomercuric species in soils from orchards and wheat fields by capillary gas chromatography on-line coupled with atomic absorption spectrometry after in situ hydride generation and headspace solid phase microextraction

A convenient procedure for the determination of organomercuric compounds in soils from orchards and wheat fields is described based on the aqueous derivatization of the polar organomercuric halides in 0.1 M HAc-NaAc (pH 4) buffer into their hydrides by addition of 1 mL of 6% KBH₄ with subsequent headspace solid phase microextraction (SPME) of the volatile derivatives. The volatile derivatives are separated by gas chromatography (GC) with a Supelco SPB-1 capillary column and on-line detected by electric heated quartz furnace atomic absorption spectrometry (AAS). The relative standard deviations for ten replicate measurements are 2.1%, 2.8% and 3.5% for methyl-, ethyl- and phenylmercury with absolute detection limits of 16 ng, 12 ng and 7 ng, respectively. This method is applied to the analysis of organomercuric compounds in soil samples and 0.04–0.64 μg/g of organomercuric species are detected in soils from different sites. The recoveries after standard addition are between 93–106%.     

Properties of Zinc alloy electrodeposits produced from acid and alkaline electrolytes

Zinc–cobalt (Zn–Co) and zinc–nickel (Zn–Ni) alloy electrodeposits each prepared from acid and alkaline formulations were compared for their properties. Compared to alkaline baths, acid baths offer higher metal percent of the alloying element and higher current efficiency. In alkaline baths, the variation of metal percent in deposit with current density is less significant, but that of current efficiency with current density is more. Electrolyte pH does not change significantly in alkaline solutions compared to acid solutions. X-ray diffraction evaluation of Zn–Co deposits from both electrolytes indicated their presence in the η-phase, while Zn–Ni shows pure γ-phase for deposits obtained from alkaline solutions and the existence of γ-phase with traces of η-phase of zinc for deposits obtained from the acid electrolytes. Scanning electron microscope examination shows finer grain structure for deposits obtained from alkaline solutions, and atomic force microscope studies confirm their nanostructure with reduced surface roughness. Deposits obtained from the alkaline baths exhibited higher corrosion resistance probably due to their nanostructure.     

Photocatalytic production of hydrogen in systems based on Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>S/Ni<Superscript>0</Superscript> nanostructures

A relation was established between the composition of Cd _x Zn_1–x S nanoparticles and their ability to accumulate excess negative charge during irradiation. The rate of expenditure of the accumulated charge depends on the composition of the nanoparticles and is determined by their electric capacitance. A correlation was found between the photocatalytic activity of the Cd _x Zn_1–x S nanoparticles in the release of hydrogen from solutions of Na₂SO₃, their composition, and their capacity for photoinduced accumulation of excess charge. It was shown that Ni⁰ nanoparticles photodeposited on the surface of Cd _x Zn_1–x S are effective cocatalysts for the release of hydrogen. It was found that Zn^II additions in photocatalytic systems based on Cd _x Zn_1–x S/Ni⁰ nanostructures have a promoting action on the release of hydrogen from water–ethanol mixtures. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 1, pp. 8–16, January-February, 2009.     

SIMS Investigations on the Distribution of Trace Elements in Modified Aluminium–Silicon–Magnesium Alloys

 Strontium modified aluminium–silicon cast alloys are well known for their outstanding mechanical properties as they combine excellent strength with good ductility that is due to a modification of brittle Si in the eutectic with traces of Sr (0.3–0.5 wt%). Although the level of Sr addition is very low, formation of ternary AlSiSr phases with deleterious effects on the ductility can take place. Consequently, there is a certain need of alternative modifying elements. Following the theory of Lu and Hellawell which predicts an optimal atomic size for good modification, Eu, which has an atomic radius close to that optimal size, was additionally used as a modifying element. This study presents SIMS (secondary ion mass spectrometer) investigations of the 3D-distributions of the main alloying and trace elements in Al–Si feedstock alloys for thixocasting modified with Sr and Eu, respectively. Received October 1, 2001; accepted May 21, 2002     

Colloidal synthesis of new silver-based nanostructures with tailored localized surface plasmon resonance

Silver-based nanostructures with tailored localized surface plasmon resonance are of interest for a number of practical applications. They can conventionally be divided into three main groups: (1) anisotropic silver particles, (2) particles of alloys of silver with other metals, and (3) composite particles with dielectric or magnetic cores and silver shells. Fine “tuning” of plasmon resonance of these particles is ensured by changes in their shapes, composition, and/or structure. Procedures for the colloidal synthesis of nanostructures of all these groups and some fields of their application are described, with the main attention focused on core/shell composite particles.     

Voltammetric detection of synthetic water-soluble phenolic antioxidants using carbon nanotube based electrodes

Glassy carbon electrodes (GCE) modified with carbon nanotubes (CNT) have been created for detection of phenolic compounds—one of the important group of antioxidants in life sciences. The surface of electrode has been characterized by atomic force microscopy. The presence of CNT leads to an at least 20-fold increase in the surface roughness of the electrode. The CNT layer displays closely intertwined vermicular structures with high degree of homogeneity at CNT suspension concentration of 0.2–0.5 mg L⁻¹. Synthetic water-soluble antioxidants (hydroquinone, catechol, pyrogallol, and their derivatives) are electrochemically active on bare GCE and CNT-modified GCE in phosphate buffer solution pH 7.4. Effect of substitutes in molecular structure of phenolic antioxidants has been evaluated. In several cases, oxidation at CNT-modified GCE occurs at potentials that are less positive by 100–200 mV in comparison to bare GCE. The electrodes were studied with respect to their capability of phenols voltammetric sensing. CNT-modified GCE display an enlarged linear range in the calibration graphs and lower detection limits. Voltammetric method for determination of hydroquinone, catechol, pyrogallol, and their derivatives has been developed.     

Selective liquid sorption properties of hydrophobized graphite oxide nanostructures

 Hydrophilic graphite oxide (GO) of lamellar structure was prepared by oxidation of graphite; the thickness of the individual lamellae was 6.1 Å. GO was hydrophobized by n-alkylammonium cations, and the GO-organocomplex nanocomposites were swollen in organic solvents of various polarities (ethanol, toluene, cyclohexane, n-heptane) and their binary mixtures. The binary liquid composition determined the size (15–45 Å) of the lamellar GO nanostructures. Interlamellar swelling was quantitatively characterized by XRD experiments, determination of liquid sorption excess isotherms and flow microcalorimetry. Received: 12 November 1997 Accepted: 12 February 1998     

Molecularly thin nanoparticles from cellulose: isolation of sub-microfibrillar structures

We have succeeded in isolating nanostructures from never-dried cellulose wood pulp, in sheet-form that have sub-microfibril dimensions (single to double digit Å thickness with 100’s of nm in length). A recently developed oxidation procedure by Saito and co-workers (Biomacromolecules 2006, 7:1687–1691) combined with extensive ultrasonication was used to liberate nanoscale cellulose fibrils. We show structures, as determined with atomic force microscopy, that compose the well-known cellulose microfibril, which are tenfold thinner than previous reports on nanoscale celluloses. This work provides indirect evidence in support of, and is consistent with, the hypothesis that the intersheet van der Waals bonding of the cellulose fibril is significantly weaker than the intrasheet hydrogen bonding of the cellulose microfibril. The structures are facile to isolate, contain enormous specific surface area with rich chemical functionality providing potential for numerous novel applications.     

Theory of lineshape in photoelectron and Auger spectra

A theory of lineshape in photoelectron spectra is developed based on the Green’s function calculation of the atomic vacancy structure. It is shown that the broadening of photoelectron lines is always somewhat asymmetrical, and the broadening of satellite lines arising in atomic photoionization is generally strongly asymmetrical and inverse. The approach is generalized to low-energy Auger spectra; it is shown that Auger decay lines of excited atomic states may narrow with respect to the width of the initial level. The results are compared with experimental photoelectron spectra. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 6, pp. 985–991, November–December, 1998.     

Measuring electron sharing between atoms in first-principle simulations

Calculations of large scale electronic structure within periodic boundary conditions, mostly based on solid state physics, allow the modeling of atomic forces and molecular dynamics for atomic assemblies of 100–1000 atoms, thus providing complementary information in material and macromolecular sciences. Nevertheless, these methods lack connections with the chemistry of simple molecules as isolated entities. In order to contribute to establish a conceptual connection between solid state physics and chemistry, the calculation of the extent of electron sharing between atoms, also known as delocalization index, is performed on simple molecules and on complexes with transition metal atoms, using density functional calculations where the Kohn–Sham molecular orbitals are represented in terms of plane waves and in periodic boundary conditions. These applications show that the useful measure of electron sharing between atomic pairs can be recovered from density functional calculations using the same set-up applied to large atomic assemblies in condensed phases, with no projections of molecular orbitals onto atomic orbitals.