A novel polyol method to synthesize colloidal silver nanoparticles by ultrasonic irradiation

A polyol synthesis of silver nanoparticles in the presence of ultrasonic irradiation was compared with other configurations (at ambient temperature, 120 °C, and 120 °C with injected solutions) in the absence of ultrasonic irradiation in order to obtain systematic results for morphology and size distribution. For applying ultrasonic irradiation, rather fine and uniform spherical silver particles (21 ± 3.7 nm) were obtained in a simple (at ambient temperature without mechanical stirring) and fast (within 4 min, 3.61 × 10⁻³ mol min⁻¹) manner than other cases (at ambient temperature (for 8 h, 0.03 × 10⁻³ mol min⁻¹): 86 ± 16.8 nm, 120 °C (for 12 min, 1.16 × 10⁻³ mol min⁻¹): 64 ± 14.9 nm, and 120 °C with injected solutions (during 12 min): 35 ± 6.8 nm; all other cases contained anisotropic shaped particles). Even though the temperature of polyol reaction reached only at 80 °C (<120 °C) in the presence of ultrasonic irradiation, a uniform mixing (i.e. enhanced collision between silver particle and surrounding components) by ultrasonic irradiation might induce a better formation kinetics and morphological uniformity.     

Polystyrene-co-maleic acid/CdS nanocomposites: Preparation and properties

Composites of CdS nanoparticles confined in a polystyrene-co-maleic acid (PS-co-MAc) matrix have been prepared and characterized. It was shown that the acid groups of the co-polymer could be successfully used to control the aggregation of the nanoparticles, because they act as coordinate sites for Cd ions. UV-VIS measurements showed a blue shift of the absorption threshold, proving the presence of nanoparticles. An average size of the nanoparticles of about 4 nm is estimated from the change in band gap energy. Although the FTIR spectrum of the nanocomposite showed the presence of C-S bonds, a broad emission originating from surface recombination sites are noticed. DSC and TGA measurements revealed changes in thermal properties upon incorporation of nanoparticles. No thermal transition was observed in the nanocomposite, while the pure co-polymer exhibits a glass transition at 190 °C. In the presence of nanoparticles the onset of the thermal decomposition of the matrix is also shifted by 50 °C towards a higher temperature.     

Ultrasound assisted co-precipitation synthesis and catalytic performance of mesoporous nanocrystalline NiO-Al2O3 powders

Mesoporous nanocrystalline NiO-Al₂O₃ powders with high surface area were synthesized via ultrasound assisted co-precipitation method and the potential of the selected samples as catalyst was investigated in dry reforming reaction for preparation of synthesis gas. The prepared samples were characterized by N₂ adsorption (BET), X-ray diffraction (XRD), Temperature programmed reduction and oxidation (TPR, TPO) and scanning electron microscopy (SEM) techniques. The effects of pH, power of ultrasound irradiation, aging time and calcination temperature on the textural properties of the catalysts were studied. The sample prepared under specified conditions (pH10, 70 W, without aging time and calcined at 600 °C) exhibited the highest surface area (249.7 m² g⁻¹). This catalyst was calcined at different temperature and employed in dry reforming of methane and the catalytic results were compared with those obtained over the catalysts prepared by impregnation and co-precipitation methods. The results showed that the catalyst prepared by ultrasound assisted co-precipitation method exhibited higher activity and stability with lower degree of carbon formation compared to catalysts prepared by co-precipitation and impregnation methods.     

ZnSe、ZnS量子点的可控合成与表征

采用改进后的合成方法,以Se和ZnO粉末为原料,在十六胺(HDA)、月桂酸(LA)和三辛基膦(TOP)有机溶剂体系中合成了胶体ZnSe和ZnS量子点。主要研究了溶剂配比、反应温度及生长时间对ZnSe量子点粒径和光学性质的影响。结果表明:制得的ZnSe和ZnS量子点均是纤锌矿型结构,且具有较好的尺寸均匀性、分散性及荧光特性。粒子直径可控制在4.5~8 nm范围内。采用参数n(ZnO) : n(HDA) : n(LA)=1 : 2.1 : 5.2,c(TOPSe)=1 mol/L,在280 ℃成核,240 ℃生长条件下合成的ZnSe量子点具有最佳的尺寸范围,并且随着生长时间的延长,粒径变大,荧光发射峰明显红移。     

Synthesis and characterization of nanostructured strontium hexaferrite thin films by the sol–gel method

Nanostructured single phase strontium hexaferrite, SrFe₁₂O₁₉, thin films have been synthesized on the (100) silicon substrate using a spin coating sol–gel process. The thin films with various Fe/Sr molar ratios of 8–12 were calcined at different temperatures from 500 to 900 °C. The composition, microstructure and magnetic properties of the SrFe₁₂O₁₉ thin films were characterized using Fourier transform infrared spectroscopy, differential thermal analysis, thermogravimetry, X-ray diffraction, electron microscopy and vibrating sample magnetometer. The results showed that the optimum molar ratio for Fe/Sr was 10 at which the lowest calcination temperature to obtain the single phase strontium hexaferrite thin film was 800 °C. The magnetic measurements revealed that the sample with Fe/Sr molar ratio of 10, exhibited higher saturation magnetization (267.5 emu/cm³) and coercivity (4290 Oe) in comparison with those synthesized under other Fe/Sr molar ratios.     

Complexed sol-gel synthesis of improved Pt-Ru-Os-based anode electro-catalysts for direct methanol fuel cells

A high specific surface area (SSA) Pt-Ru-Os-based anode catalyst synthesized by a novel complexed sol-gel (CSG) process shows better catalytic activity in comparison to pure equi-atomic compositions of Pt-Ru anode catalysts synthesized by similar sol-gel processes. A homogeneous amorphous gel was successfully synthesized by complexing platinum(II) acetylacetonate, ruthenium(III) acetylacetonate and osmium(III) chloride with tetramethylammonium hydroxide (TMAH) used as a complexing agent. Phase-pure Pt(Ru,Os) and Pt(Ru) solid solutions possessing high specific surface area (∼110-120 m²/g) were successfully synthesized by controlled removal of carbonaceous species present in the as-prepared precursor generated from the CSG process. This has been successfully achieved by precise thermal treatments of the precursor using controlled oxidizing atmospheres. Results indicate that the nano-crystalline Pt(Ru,Os) solid solution of nominal composition 50 at%-Pt-40 at% Ru-10 at% Os possesses good chemical homogeneity, and reveals excellent catalytic activity, thus demonstrating the potential of the novel CSG process for synthesizing high-performance Pt-Ru-Os-based catalysts for direct methanol fuel cells.     

Characterization of new-layered Cr(III)-doped chlorocadmiumphosphate, Cd(HPO4)Cl·[H3N(CH2)6NH3]0.5 crystal by EPR and optical studies

Cr(III)-doped Cd(HPO₄)Cl·[H₃N(CH₂)₆NH₃]_0.5, a new-layered cadmium phosphate, is synthesized in acidic condition at room temperature. EPR and optical studies are carried out at room temperature. Polycrystalline EPR spectrum reveals the presence of two sites of Cr(III) ions in this layered phosphate lattice with zero-field splitting values of 24.24 and 7.65 mT, indicating that Cr(III) ions are in distorted octahedral sites. The optical absorption spectrum of the sample indicates near octahedral symmetry for the dopant ions. Crystal field, inter-electronic and bonding parameters are evaluated by collaborating EPR and optical data. The evaluated parameters suggest the mode of entry of Cr(III) ion into the layered phosphate as interstitial site, and bonding between the metal and ligand is partially covalent.     

Nucleation and growth mechanism for flame synthesis of MoO2 hollow microchannels with nanometer wall thickness

The growth and morphological evolution of molybdenum-oxide microstructures formed in the high temperature environment of a counter-flow oxy-fuel flame using molybdenum probes is studied. Experiments conducted using various probe retention times show the sequence of the morphological changes. The morphological row begins with micron size objects exhibiting polygonal cubic shape, develops into elongated channels, changes to large structures with leaf-like shape, and ends in dendritic structures. Time of probe–flame interaction is found to be a governing parameter controlling the wide variety of morphological patterns; a molecular level growth mechanism is attributed to their development. This study reveals that the structures are grown in several consecutive stages: material “evaporation and transportation”, “transformation”, “nucleation”, “initial growth”, “intermediate growth”, and “final growth”. XRD analysis shows that the chemical compositions of all structures correspond to MoO₂.     

Electrochemically induced oxidative cyclization of 2,3‐dihydroxypyridine. Synthesis of a novel highly oxygenated heterocyclic compound

Electrochemical oxidation of 2,3‐dihydroxypyridine in aqueous phosphate buffer solution at a glassy carbon electrode has been studied using cyclic voltammetry and controlled potential coulometry. The results indicate that oxidation of 2,3‐dihydroxypyridine on glassy carbon electrode shows an irreversible feature in aqueous solution. This data indicates that the electrochemically generated pyridindione is unstable and via an oxidative conversion pathway converts to a novel highly oxygenated heterocyclic compound. By means of the obtained electrochemical data, an efficient, one‐pot method for the synthesis of this heterocyclic compound based on the oxidative cyclization of 2,3‐dihydroxypyridine under green conditions, and in a good yield and purity is described. Copyright © 2011 John Wiley & Sons, Ltd.     

Bimodal Nanoparticle Size Distributions Produced by Laser Ablation of Microparticles in Aerosols

Silver nanoparticles were produced by laser ablation of a continuously flowing aerosol of microparticles in nitrogen at varying laser fluences. Transmission electron micrographs were analyzed to determine the effect of laser fluence on the nanoparticle size distribution. These distributions exhibited bimodality with a large number of particles in a mode at small sizes (3–6-nm) and a second, less populated mode at larger sizes (11–16-nm). Both modes shifted to larger sizes with increasing laser fluence, with the small size mode shifting by 35% and the larger size mode by 25% over a fluence range of 0.3–4.2-J/cm². Size histograms for each mode were found to be well represented by log-normal distributions. The distribution of mass displayed a striking shift from the large to the small size mode with increasing laser fluence. These results are discussed in terms of a model of nanoparticle formation from two distinct laser–solid interactions. Initially, laser vaporization of material from the surface leads to condensation of nanoparticles in the ambient gas. Material evaporation occurs until the plasma breakdown threshold of the microparticles is reached, generating a shock wave that propagates through the remaining material. Rapid condensation of the vapor in the low-pressure region occurs behind the traveling shock wave. Measurement of particle size distributions versus gas pressure in the ablation region, as well as, versus microparticle feedstock size confirmed the assignment of the larger size mode to surface-vaporization and the smaller size mode to shock-formed nanoparticles.