Oxygen evolution on Ru1 − x Ni x O2 − y nanocrystalline electrodes

Nanocrystalline Ru_1 − x Ni _x O_2 − y with 0.02 < x < 0.30 were prepared by a sol–gel approach at temperatures between 300 and 600 °C. XRD patterns of the prepared materials indicate a single-phase character conforming to a tetragonal syngony. All prepared materials are sufficiently stable in acid media and show activity towards oxygen evolution. The activity towards oxygen evolution reaction of the materials with constant chemical composition decreases with increasing particle size. The increasing Ni content enhances the electrocatalytic activity in a stepwise manner with abrupt changes for materials containing approximately 5% or 15% of the cationic sites substituted by Ni.     

DNA-modified electrodes (Ⅶ)——Preparation and characterization of DNA-bonded and DNA-adsorbed SAM/Au electrodes

Two kinds of DNA-modified electrodes were prepared by covalent and adsorptive immobilization of DNA onto self-assembled monolayers of 2, 2'-dithiodiethanol on gold electrodes and characterized by cyclic voltammetry, Xray photoelectron spectroscopy and scanning tunneling microscopy. The results suggest that the methods are satisfactory for the immobilization of DNA on electrodes.     

Synthesis and characterization of nano-structured Th1?x Ce x O2 mixed oxide

GEL combustion technique was applied to obtain oxides of thorium and cerium from their respective nitrate solutions using citric acid as the gelating agent. The dried samples were characterized by IR and TG studies. Intermediate and final products during TG studies have been isolated and characterized by XRD studies. All the TG runs during heating of thorium and cerium nitrate with citric acid dried Gels showed a two step process. The weight loss at each step and the X-ray data of the product at each step, helped in suggesting a possible mechanism. Kinetic study was carried out independently for each step. The reaction mechanism as observed during interactive procedure was found to be diffusion controlled. The kinetic parameters (activation energy and pre-exponential factor) for each step in all reactions have been calculated. Observations from XRD studies show that with increase in cerium concentration in the oxides, the lattice parameter values have shown a decreasing trend for all the five compositions studied. It was observed that in TG studies with increase in cerium concentration, the final temperature of the reactions have shown a decreasing trend. SEM studies of the powders reveal that synthesized oxides have a tendency to form agglomerate of varying size ranging from 50 to 100 μm in case of mixed oxides but the size of thorium oxide powder so synthesized have pore size 10–100 μm. SEM images shows that GEL combustion may result in agglomeration, if the temperature is not properly controlled to the desired value. SEM studies also reveal that each agglomerate contains approximately 10–100 individual particles. Surface area of the mixed oxide powders were determined using Gas adsorption technique. The surface area was found to be in the range of 3–17 m²/g in all cases. Specific surface area of thorium oxide was found to be lesser than cerium oxide but in case of mixed oxides surface area decreases with increase in cerium content. Majority of pores, indicating the particle size are in the range of 0.01–0.04 cm³/g.     

Electrochemical testing of composite electrodes of (La1?x Sr x ) s MnO3 and doped ceria in NO-containing atmosphere

The possibility of using electrochemical cells for removal of NO _x from an exhaust gas with excess O₂ has been examined. (La_1−x Sr _x ) _s MnO₃ (LSM) and ceria doped with Pr or Gd were selected as electrode materials and investigated in three-electrode cells. The electrodes were characterised electrochemically with electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV), and the gas composition monitored while the electrodes were polarised. The electrodes of (La_0.5Sr_0.5)_0.99MnO₃ (LSM50) and Ce_0.8Pr_0.2O_2−δ exhibit higher current densities in 0.1% NO in Ar than in air at 300 to 400 °C during CV. This indicates some apparent selectivity towards NO compared to O₂. The electrodes can remove NO, when polarised to at least −0.6 V vs. Pt/Air at 600 °C, and EIS measurements under polarisation indicate that the kinetics of the electrodes change, when the electrode potential gets below −0.6 V vs. Pt/Air.     

Preparation of La0.67Ca0.33MnO3:Ag x polycrystalline by sol–gel method

La_0.67Ca_0.33MnO₃:mol%Ag _x (LCMO:Ag _x , x = 0, 0.04, 0.08, 0.10 and 0.20) ceramics were prepared by sol–gel method. The X-ray diffraction studies of the LCMO:Ag _x samples confirm the pure phase of the LCMO composites with Pbnm space group. With the increase of Ag doping from x = 0 to 0.20, the normalized resistivity (ρ/ρ _300K ) of the samples around the metal–insulator transition temperature (T _p ) reduced in sequence. Both T _p and the peak of temperature coefficient of resistance (T _k ) improved 5–8 K. Energy dispersive X-ray spectroscopy analysis showed that the composition of La, Ca and Mn of the obtained LCMO composites was in accordance with the composition of the precursor. The results indicated that the improvement of grain boundaries and crystallization were responsible for the enhancements of ρ, T _p and T _k of LCMO:Ag _x composites. The fitted curves of electrical resistivity for LCMO:Ag _x composites indicated that the mechanisms of grain/domain boundary, electron–electron and magnon scattering and adiabatic small polaron hopping are proposed to explain the phase transition of ferro-magnetic metallic region (T < T _p ) and the para-magnetic insulating region (T > T _p ), respectively.     

Preparation and characterization of AgSt/AgC1 composite grains

AgSt/AgC1 composite gains were prepared by adding chloride ions to a mixed solvent in which silver stearate （AgSt） grains were dispersed under the condition of controlled pH value and characterized by SEM, XRD, UV and DSC. The results showed that AgSt/AgC1 composite grains were composed of plateqike AgSt grains with small face-centered cubic AgC1 particles formed on the surface of AgSt. UV spectra displayed a red shift of absorption for AgSt/AgC1 relative to pure AgSt or AgC1. DSC showed a new thermal phase transition of AgSt/AgC1 grains.     

Sol-gel formation and properties of nanocrystals of solid solutions Y1 − x Ca x FeO3

Nanopowders of ferrites Y_{1 ? x} Ca _x FeO₃ (x = 0.1, 0.2, and 0.3) were prepared by chemical coprecipitation of cations Y³⁺, Ca²⁺, and Fe³⁺ by an aqueous sodium carbonate solution. It was found that an increase in the calcium content leads to a decrease in the size of nanocrystals, the average size of which is 25–50 nm. Doping of yttrium orthoferrite with the doubly charged calcium ion enhances magnetization and decreases coercivity in samples.     

Preparation and characterization of crosslinked chitosan-based nanofibers

Crosslinked chitosan-based nanofibers were successfully prepared via electrospinning technique with heat mediated chemical crosslinking followed.The structure,morphology and mechanical property of nanofibers were characterized by attenuated total reflection-Fourier transform infrared spectroscopy(ATR-FTIR),scanning electron microscopy(SEM),Instron machine,respec- tively.The results showed that,nanofibers exhibited a smooth surface and regular morphology,and tensile strength of nanofibers improved with increasing of triethylene glycol dimethacrylate(TEGDMA)content.     

Preparation and properties of highly conductive La1−x M x MnO3−y thin film showing magnetic effect from sol-gel process

The sol-gel synthesis of Sr-doped-LaMnO₃ thin film was investigated. The optimum condition was obtained when strontium, lanthanum and manganese nitrates were used as raw materials and diethylene or propylene glycol was used as solvent. An alumina plate was used as a substrate. The film thickness was about 0.2 m for one dip coating. The conductivity of Sr-substituted-LaMnO₃ increased with increasing Sr content and showed ferromagnetic properties. The conduction mechanism was a hopping conduction due to the small polaron. The metal-semiconductor transition at around room temperature was considered to be caused by the Jahn-Teller effect.     

Forms of oxygen in La1 − x Ca x MnO3 + δ (x = 0–1) perovskites and their reactivities in oxidation reactions

The effects of substitution in the cationic sublattice and of the synthesis procedure on the reactivity of different forms of oxygen in La_{1 ? x} Ca _x MnO_{3 + δ} perovskites synthesized by mechanochemical and ceramic processing was studied by temperature-programmed reduction (TPR) with hydrogen. As the calcium content of the perovskite is raised, the maxima of the TPR peaks shift to lower temperatures and the extent of reduction of the perovskite increase, implying an increase in the reactivity of the system. Conversely, raising the calcination temperature or extending the calcination time shifts the maxima of the peaks to higher temperatures and diminishes the extent of reduction of the sample. TPR data for the intermediate-composition samples can be explained in terms of the dependence of microstructure on the synthesis procedure (near-surface calcium segregation in the mechanochemically synthesized samples and the microheterogeneous structure of the ceramic samples). The reduction process Mn⁴⁺ → Mn²⁺ takes place in the low- and medium-temperature regions. According to the literature, the bulk reduction process Mn³⁺ → Mn²⁺ occurs at high temperatures. The activity of the system in CO oxidation is correlated with the amount of the most reactive surface oxygen, which is eliminated in hydrogen TPR runs below 250–300°C.     

Preparation and characterization of nitrogen-doped titanium dioxides

A type of high visible-light active titanium oxinitride(TiO2-xNx) powder was prepared by a simple proc-ess:the calcination of the hydrated titanium dioxide at the atmosphere of ammonia-argon using a tu-bular electric furnace at high temperatures. The hydrated titanium dioxide was synthesized as the precursor of TiO2-xNx using titanic acid as raw material,which came from sulfate technique of produc-ing titanium white. The effects of temperature and reaction time on the nitrogen content,grain size and crystal structure were studied. The visible-light activity and photocatalysis capability of the powder were also investigated.     

Preparation, characterization, and catalysis of mecro-catalysts

Because catalysis by metals is a surface phenomenon, many technological catalysts contain small (typically nanometre-sired) supported metal particles with a large fraction of the atoms exposed. Many reactions, such as hydrocarbon hydrogenations, are structure-insensitive, proceeding at approximately the same rates on metal particles of various sizes provided that they are larger than 1 nm and show bulk-like metallic behavior. But the catalytic properties are not known when metal particles become so small that their sizes are indium clusters consisting of several indium atoms. Here the catalytic behavior of precisely defined clusters of just four and six indium atoms on solid supports is shown. It is found that the Ir4 and Ir6 clusters differ in catalytic activity both from each other and from metallic Ir particles.     

Preparation and characterization of polyacrylamide–silver nanocomposites

Polyacrylamide–silver nanocomposites are successfully prepared by irradiating the aqueous solution of AgNO₃ and acrylamide monomer with ⁶⁰Co γ-ray. The composites are found to contain nanometer silver particles with a narrow size distribution and a homogeneous dispersion. The existing of isopropanol (as a hydroxyl radical scavenger and chain transfer agent) in system affects the properties of both the dispersed phase and matrix of the nanocomposites. The fast-formed polymer chains probably play a key role in preventing the aggregation of silver particles which are reduced later.     

LaNi1 − x Cu x O3 (x = 0.05, 0.10, 0.30) coated electrodes for oxygen evolution in alkaline medium

LaNi_1???x Cu _x O₃ (x?=?0.05, 0.10, 0.30) coated electrodes were prepared by brush painting using Ni foam substrates in order to increase its active surface area. For comparison, coatings with x?=?0.05 were also prepared using vitreous carbon substrates. Cyclic voltammetry was used to evaluate the coating roughness (R _f). Values between 5,145?±?148 and 6,334?±?277 were obtained, depending on the x value, for the coatings on Ni foam. These results show that the electrodes prepared with LaNi_1???x Cu _x O₃ powder, obtained at 600 °C, lead to a big increase on the oxide electrode roughness when compared with LaNiO₃ electrodes prepared by a similar method. Much lower values were obtained for the coatings on vitreous carbon indicating that the substrate nature is also a key factor for the preparation of high surface area electrodes. The calculated kinetic parameters for the oxygen evolution reaction (OER) show that the partial replacement of Ni by Cu has no beneficial effect on the intrinsic catalytic activity of the coatings. On the other hand, a big increase on the active area is observed even for small amounts of Cu (x?=?0.05), leading to a better overall OER performance for the LaNi_0.95Cu_0.05O₃ coating on Ni foam. For this composition, the activity is dominated by geometric effects.     

Enhancement of temperature coefficient of resistance (TCR) and Magneto-resistance (MR) in La1–x Ca x MnO3:Ag0.2 polycrystalline composites

La_1?x Ca _x MnO₃ (x ranges from 0.28 to 0.34) ceramics with Ag addition were synthesized by sol–gel method using methanol as solvent. The EDS elemental mapping shows that Ag element was detected dominantly on the sample surface. The sample of x?=?0.28 has almost no pore and bigger grain size, which indicated that it has better crystallization and high density. Temperature dependence of resistivity shows that the samples for all Ca content exhibit sharp metal–insulator transition, and the corresponding metal–insulator temperature shift toward higher temperature with increasing Ca content. The temperature coefficient of resistance value for x?=?0.28 reaches its the highest value, 71.8%·K^?1. This temperature coefficient of resistance value is even higher than the previously reported for LCMO films and single crystals, and it shows a very promising application for the infrared and bolometric detectors. The high magnetoresitance for x?=?0.28 reaches up to 69.3% in magnetic field of 1?T near room temperature. It was concluded that it improved the properties of LCMO:Ag composites are attributed to its improved crystallization by Ag addition, homogeneity and Mn⁴⁺/Mn³⁺ ratio. Different theoretical models are employed to analyze the resistance behaviors in different temperature regions, which give good agreements with experimental results.

     

Synthesis and electrochemical properties of nanostructured LiAl x Mn2 − x O4 − y Br y particles

Nanostructured LiAl _x Mn_2 − x O_4 − y Br _y particles were synthesized successfully by annealing the mixed precursors, which were prepared by room-temperature solid-state coordination method using lithium acetate, manganese acetate, lithium bromide, aluminum nitrate, citric acid, and polyethylene glycol 400 as starting materials. X-ray diffractometer patterns indicated that the particles of the as-synthesized samples are well-crystallized pure spinel phase. Transmission electron microscopy images showed that the LiAl _x Mn_2 − x O_4 − y Br _y samples consist of small-sized nanoparticles. The results of galvanostatic cycling tests revealed that the initial discharge capacity of LiAl_0.05Mn_1.95O_3.95Br_0.05 is 119 mAh g⁻¹; after the 100th cycle, its discharge capacity still remains at 92 mAh g⁻¹. The introduction of Al and Br in LiMn₂O₄ bring a synergetic effect and is quite effective in increasing the capacity and elevating cycling performance.     

Preparation and characterization of core-shell structured TiO2–BaCO3 particles

Preparation of core-shell structured TiO₂–BaCO₃ particles as precursor of BaTiO₃ genesis, proceeds using a two step procedure, by first coating the TiO₂ core by Ba(OH)₂ shell followed by conversion of the shell region with CO₂ gas by the formation of BaCO₃. Straightforward experimental results reveal environmental scanning electron microscopy (ESEM) and scanning transmission electron microscopy (STEM) as suitable methods for analytical characterization of the core and shell regions from individual TiO₂–BaCO₃ grains. Evidence of coating the whole ensemble of TiO₂ particles is possible using Photo Electro Motive Force (Photo EMF, PEMF) measurements. This method is able to indicate very sensitively changes of surface properties of TiO₂ after coating with Ba(OH)₂ and BaCO₃, respectively. PEMF measurements were used for the first time with concern to this topic.     

Preparation and characterization of Fe_3O_4/Au composite particles

Colloid gold with different sizes has been widely used in immunoassay and nucleic acid detection mainly because of their properties for immobilization of biomolecules, such as antibodies and oligonucleo-tides, through chemical reactions via active group SH on the biomolecules. Magnetic particles modified with various chemical groups on their surface can not only exhibit good magnetic responsiveness to an external magnetic field but also immobilize biomolecules through these chemical groups. As…     

Ceramic electrolytes based on (Ba1 − x Ca x )(Zr0.9Y0.1)O3 solid solution

The aim of this work was to study the electrical and electrochemical properties of the (Ba_1???x Ca _x )(Zr_0.9Y_0.1)O₃ solid solutions. The powders of different calcium content (x?=?0, 0.05, 0.1, and 1) were prepared by a thermal decomposition of organo-metallic precursors containing ethylenediaminetetraacetate acid. X-ray diffraction analysis showed that a small substitution of calcium for barium caused formation of cubic solid solutions with the decreasing cell parameters. Electrical conductivity measurements were performed by the d.c. four-probe method in controlled gas atmospheres containing Ar, air, H₂, and/or H₂O at temperature from 300 to 800 °C. It was found that the conductivity depended on a chemical composition of the samples and the atmosphere. Overall, the electrical conductivity was higher in wet atmospheres that contained oxygen that was in accordance with the model of a proton transport in perovskite structure which assumed the presence of the oxygen vacancies. The solid solution containing 5 mol% of calcium showed the highest conductivity and the lowest activation energy of conductivity regardless of the atmospheres; this can be attributed to the local changes in the cubic perovskite structure. Test results for CaZr_0.9Y_0.1O₃ used as an electrolyte in solid oxide galvanic cells involving CaCr₂O₄ as a reference electrode are also reported.