Solution Reduction Method Research Articles

新素材：環境・エネルギー材料の新展開 水溶液中における金属微粉末の合成と形態制御

Metal powders were prepared by precursor—thermal decomposition method and chemical reduction method in aqueous solutions. In precursor—thermal decomposition method, the morphology and size of nickel powder were controlled via the thermal decomposition of nickel oxalate powder, that was prepared by mixing a solution containing oxalic acid ion with some kinds of nickel sources such as nickel ion, ammoniacal nickel complex ion, and nickel hydroxide. Needle-like nickel oxalate powder with high aspect ratio, [Ni(NH3)2]C2O4 2H2O, was synthesized by using ammoniacal nickel complex ion, and rectangular parallelepiped shape of nickel oxalate powder, NiC2O4 2H2O, was by nickel hydroxide. As for the chemical reduction method in aqueous solution, ascorbic acid (vitamin C) at pH 3 reacts with copper ion as a reducing agent, and copper metal particle in size of 100 nm was obtained. Under the condition of pH > 3, reduction property is weakened, and precipitates consisted of copper powder with cuprous oxide. Ti3+ ion (Ti2(SO4)3 solution) also has a reducing property for copper ion and acts as a new reducing agent in liquid phase reduction process.

Facile synthesis of stable, water-soluble magnetic CoPt hollow nanostructures assisted by multi-thiol ligands

We report the synthesis of CoPt hollow nanostructures using a simple reduction method in aqueous solution in the presence of poly(methacrylic acid) pentaerythritol tetrakis (3-mercaptopropionate) (PMAA-PTMP) polymer or a mixture of O-[2-(3-mercaptopropionyl-amino)ethyl]-O′-methylpolyethylene glycol (PEG-SH) polymer and cysteine-cysteine-alanine-leucine-asparagine-asparagine (CCALNN) peptide ligands. The presence of the multi-thiol functional group of the ligands is essential for the formation of the hollow nanostructures and their perimeter size can be tuned within the range of 7–54 nm by changing peptide concentration or length of polymer. These hollow nanostructures are water-soluble and superparamagnetic at room temperature. They are stable in a wide range of pH from 1 to 10, high electrolyte concentration up to 2 M NaCl, and in cell culture medium which makes them have great potential to be utilised in biomedical applications.

Magnetic nanocomposite multilayers using layer-by-layer assembly in nonpolar and polar solvent

Magnetic nanoparticles have recently attracted a great deal of attentions due to a number of potential applications such as MRI contrast agents, magnetic separation, nonvolatile memory devices or magnetic cards as well as a fundamental scientific interest. The effective use of magnetic nanoparticles in a given application is based on two important factors: the inherent properties of nanoparticles (magnetization, size, etc.) and the ability to tailor their adsorbed amount onto the substrates. It has been reported by several research groups that high temperature decomposition of iron precursors in the presence of capping ligands can induce the high quality particles with facile size control, size uniformity and crystalline in comparison with more traditional coprecipitation/dextran methods or the reduction method in aqueous solution. These nanoparticles obtained from thermal decomposition can be well dispersed in nonpolar solvent due to hydrophobic property of the used stabilizers. Additionally, the particles with negatively charged stabilizers can allow the multiple depositions (i.e., layerby-layer assembled deposition) between particles and oppositely charged components and resultantly can enhance the intensity of their inherent properties such as magnetization. However, to the best of our knowledge, the facile and efficient method fully satisfying these two factors has not been introduced up to date. Herein, we introduce the novel and simple method for the fabrication of magnetic nanocomposite multilayers, including the high quality γ-Fe2O3 nanoparticles (MP) by thermal decomposition method and allowing the tailored magnetic properties. 2-bromo-2-methylpropionic acid (BMPA)-stabilized MP in toluene solvent was prepared by exchanging oleic acid with BMPA after initially synthesizing the oleic acid-stabilized MP (OA-MP). The bromo (-Br) groups of BMPA-MP can be covalently bonded with amine (-NH2) groups. Based on this high affinity, it is demonstrated that the magnetic nanocomposite multilayers can be fabricated using BMPA-MP dispersed in toluene and poly(allyamine hydrochloride) (PAH) in water.

Preparation of Ni-GDC Powders by the Solution Reduction MethodUsing Hydrazine and Its Electrical Properties

Ni-GDC (gadolinia-doped ceria) composite powders, the anode material for the application of solid oxide fuel cells, were prepared by a solution reduction method using hydrazine. The distribution of Ni particles in the composite powders was homogeneous. The Ni-GDC powders were sintered at 1400˚C for 2 h and then reduced at 800˚C for 24 h in 3% H2. The percolation limit of Ni of the sintered composite was 20 vol%, which was significantly lower than these values in the literature (30-35 vol%). The marked decrease of percolation limit is attributed to the small size of the Ni particles and the high degree of dispersion. The hydrazine method suggests a facile chemical route to prepare well-dispersed Ni-GDC composite powders.

Synthesis and application of DNA-templated silver nanowires for ammonia gas sensing

The DNA-templated silver nanowires have been synthesized by a simple chemical reduction method in solution and used for gas detection of ammonia. Lactic acid as a stabilizer in reduction bath can effectively decrease the nonspecific deposition of metallic silver by slowing down the reaction. In the present experiments, the highly conductive DNA-templated silver nanowires consisting of grains improve the surface area/volume ratio, which can increase the adsorption of ammonia gas molecules. The results of gas sensing measurements indicate that these nanowires show a high selectivity to ammonia, a quick gas response (~ 10 s) and a fast recovery (~ 7 s). Moreover, the possible gas sensing mechanism has been discussed in this paper. Therefore, we found that the DNA-templated silver nanowires reported here might be a potential candidate of gas sensing materials for ammonia gas detection.

SnO₂Two-dimensional Nanostructures Prepared by Solution Reduction Method and Their Gas Sensing Characteristics

SnO nanosheets were prepared at room temperature through a reaction between an aqueous solution of <TEX>$SnCl_2$</TEX>, <TEX>$N_2F_4$</TEX>, and NaOH and were converted into <TEX>$SnO_2$</TEX> nanosheets without a morphological change. The SnO nanosheets were formed through a dissolution-recrystallization mechanism. Uniform and well-dispersed SnO nanosheets with the round-shape morphology were attained when the solution was treated by ultrasonic sound immediately after the addition of NaOH. The <TEX>$SnO_2$</TEX> nanosheets prepared by means of solution reduction under the ultrasonic treatment, and subsequent oxidation at <TEX>$600^{\circ}C$</TEX> showed a high level of gas sensitivity to <TEX>$C_2H_5OH$</TEX> and <TEX>$CH_3COCH_3$</TEX>.

Large scale synthesis and characterization of Ni nanoparticles by solution reduction method

Ni nanoparticles were mass synthesized by solution reduction process successfully. The influence of the parameters on the particle size of Ni nanoparticles were studied and the referential process parameters were obtained. The morphology and structure of the synthesized Ni nanoparticles were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area analysis and infrared spectroscopy (IR). The results show that Ni nanoparticles are of high purity and are covered by hydroxyethyl carboxymethyl cellulose (HECMC) layer and the mean size being about 31 nm. The magnetic measurement revealed that Ni nanoparticles are ferromagnetic.

Ultrafine LiFePO 4 cathode materials synthesized by chemical reduction and lithiation method in alcohol solution

The Olivine-type LiFePO 4, which is one of the most attractive cathode materials for lithium ion batteries, was synthesized via calcining amorphous LiFePO 4 obtained by chemical reduction and lithiation of FePO 4 using Vitamin C as reducer and lithium acetate as lithium source in alcohol solution. The prepared LiFePO 4 was characterized by XRD and SEM. The results showed that the LiFePO 4 powder has good crystallinity and spherical morphology with an average diameter of about 150 nm. Electrochemical measurement results indicated that the material exhibited high-rate characteristic and delivered a stable discharge capacity of 159 mAh g − 1 at 0.1 C rate.

Low Pt content Pt–Ru–Ir–Sn quaternary catalysts for anodic methanol oxidation in DMFC

In this communication we report our research work on low Pt content Pt–Ru–Ir–Sn quaternary catalysts for use in DMFC anodes. The carbon-supported quaternary metal alloy catalyst was synthesized according to the solution reduction method and was deposited onto a carbon fiber paper or a carbon aerogel nanofoam to form the anode for direct methanol fuel cells. The Pt loading of the electrode is 0.1 mg/cm 2. The testing results from a three-electrode electrochemical cell show that the simultaneous use of higher Ir (25–35 wt.%) and Sn (10 wt.%) content gives satisfactory stability and higher activity for methanol oxidation than the commercially available E-TEK anode (80%[0.5Pt 0.5Ru]/C on carbon cloth). Energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), scanning electron microscope (SEM), and Bruner–Emmett–Teller method (BET) measurements were carried out to characterize the composition, structure, morphology, and surface area of the developed catalysts.

Synthesis of Mono-Dispersed Fine Spherical Silver Powders by Chemical Reduction Method

The synthesis of spherical silver powders by chemical reduction method was investigated. Conductive metal pastes to have good properties in adhesion, stability, and conductivity, it is very important to control the purity, size, and shape of metal particles. In the present study, proper methods to control the properties of micron sized metal powders for conductive pastes are investigated. Chemical reduction method in aqueous solution was adapted to produce silver powder. The effects of reaction time, concentration of reductant and additives, and stirring speed were investigated, in experimental. Fine spherical silver powder of 0.5 to 3 ㎛ were synthesized from silver nitrate solution with hydroquinone as a reducing additive by liquid phase method, and some variables and reaction mechanism in conjunction with the particle morphology and size were studied.

Hydrazine 법에 의한 CuO 미분말의 합성 및 가스 감응성 평가

CuO is an important transition metal oxide with many practical applications such as catalysts, p-type semiconductor, solar cells, magnetic storage media and cathode materials. In this contribution, nanocrystalline CuO powders were prepared by solution reduction method using copper chloride (), hydrazine () and NaOH and subsequent heat treatment. The gas sensor using nanocrystalline CuO powders showed high sensitivities to acetone and ethanol.

Room temperature preparation of carbon supported Pt-Ru catalysts

A carbon supported Pt-Ru (Pt-Ru/C-T) catalyst can be prepared by a chemical reduction method in an aqueous solution with tetrahydrofuran (THF) at room temperature. The Pt-Ru particles possess high alloying, small average size and a low relative crystallinity. The electrocatalytic activity of the prepared Pt-Ru/C catalyst for methanol oxidation is much higher than that of commercial Pt-Ru/C (Pt-Ru/C-E) catalysts which have a similar average size and relative crystallinity, but the alloying extent is much lower than that in our Pt-Ru/C-T catalyst. The results illustrate that the alloying extent of Pt and Ru in the Pt-Ru/C catalyst plays an important role in the electrocatalytic activity of the Pt-Ru/C catalyst for methanol oxidation.

Preparation of Ge nanocrystals via ultrasonic solution reduction

Germanium nanocrystals, ranging from 3 to 10 nm with a narrow size distribution, can be synthesized by an inexpensive, simple ultrasonic solution reduction method. This is based on the reduction of GeCl4 by metal hydride or alkaline in ambient condition. Effects of reduction agent, reaction condition and the concentration of GeCl4 on the formation of germanium nanocrystals were investigated. The morphology and the crystal structure of Ge nanocrystals obtained at different conditions were characterised by transmission electron microscope and selected area electron diffraction. Possible mechanisms for the formation of Ge nanocrystals were discussed.

A polyaniline supported PtRu nanocomposite anode and a Pd-impregnated nanocomposite Nafion membrane for DMFCs

Nanocomposites of PtRu nanoparticles and polyaniline (an electronically conducting polymer) were synthesized by the borohydride reduction method in an aqueous solution for the anode electrode in direct methanol fuel cells (DMFCs). Due to the high electronic conductivity of polyaniline, the methanol oxidation current for polyaniline supported PtRu nanocomposites was similar to that of carbon supported PtRu catalysts. In addition, Pd-impregnated nanocomposite Nafion membranes were suggested to enhance DMFC performance by blocking or reducing methanol crossover and their characteristics were affected by the impregnation time of Pd-nanoparticles.

용액환원법에 의한 MLCC용 단분산 니켈 미분말의 합성

A mono-disperse Ni powders for multilayer ceramic capacitors were prepared in a large scale by solution reduction method using NiSO₄, N₂H₄, and NaOH. The exothermic reactions such as Ni-complex formation between highly concentrated NiSO₄ and N₂H₄ and the reduction of Ni 2+ into Ni provided thermal energy sufficient for spontaneous solution-reduction. Because well-defined Ni particles could be prepared without external heating, the present method was named as 'auto-thermal method'. The formation of Ni-complex, the precipitation of Ni(OH)₂ gel triggered by NaOH addition, and its reduction into Ni by dissolution-recrystallization route were the reaction mechanism. The preparation of mono-disperse and spherical Ni powder was attributed to uniform distribution of reducing agent (N₂H₄) within Ni(OH)₂ gel due to the decomposition of NiSO₄-N₂H₄ complex.

Zn-doped Ni nanotubes prepared by the chemical reduction method in ethanol solution

Zn-doped Ni nanotubes with wall thickness in the range of 10–20 and 100–200 nm in inner diameter have been synthesized in ethanol via a room-temperature solution synthetic route. Powder X-ray diffraction (XRD) pattern shows that the as-synthesized particles have a chemically disordered fcc structure. The coercivity of the products was investigated to be 515.6 Oe at room temperature. The catalytic property of Zn-doped Ni nanotubes was also conducted.

A posteriori error estimator for Lanczos–Chebyshev reduction method

An accurate and efficient reduction method for solutions of partial differential equations is the Lanczos–Chebyshev reduction method. A posteriori error estimation technique based on a modification of the error of the Lanczos economization is proposed. An upper bound to the error in the solution of the differential equation is also presented.

Self-assembled bismuth nanocrystallites.

Using a high-temperature organic solution reduction method, highly crystalline and single domain bismuth nanoparticles have been synthesized and self-assembled.

A reduction method for periodic solutions of second-order subquadratic equations

The problem of the search for periodic solutions to certain second-order scalar subquadratic equations is reduced, by means of a variational argument, to the study of a real function of one variable, the "reduction function" of the problem. Existence and multiplicity of solutions for the original problem and for its perturbations are linked to the properties of the reduction function. Equivalent conditions for the perturbability of the problem as well as genericity results and descriptions of the range of the differential operator are obtained. Applications cover equations with oscillating or bounded nonlinearities or strongly resonant problems.

A general reduction method for periodic solutions in conservative and reversible systems

We introduce a general reduction method for the study of periodic solutions near equilibria in autonomous systems which are either conservative or reversible. We impose no restrictions on the linearization at the equilibrium, allowing higher multiplicities and all kinds of resonances. It is shown that the problem reduces to a similar problem for a reduced system, which is itself conservative or reversible, but also has an additionalS 1-symmetry. This symmetry allows to immediately write down the bifurcation equations. Moreover, the reduced system can be calculated up to any order by a normal form reduction on the original system. The method of proof combines normal forms with the Liapunov-Schmidt method. A similar approach was already introduced for Hamiltonian systems in [9], and for equivariant systems in [3]; this paper extends the results of these papers to the cases of conservative and reversible systems.