Nanocatalysis on tailored shape supports: Au and Pd nanoparticles supported on MgO nanocubes and ZnO nanobelts

Active gold and palladium nanoparticles supported on MgO nanocubes and ZnO nanobelts and transition-metal-containing MgO nanobelts were synthesized by combining evaporation and deposition-precipitation techniques. The high activity and stability of the Au/CeO2 and Pd/CeO2 nanoparticle catalysts deposited on the MgO cubes are remarkable and imply that a variety of efficient catalysts can be designed and tested using this approach. The significant increase in the concentration of corner and edge sites in MgO nanocubes make them well-defined supports to study the detailed mechanism of the catalytic activity enhancement.     

Preparation of ZnO nanoparticles in a reverse micellar system and their photoluminescence properties

ZnO nanoparticles with spherical morphology and narrow size distribution were obtained by calcination of Zn(OH)2 nanoparticles, which were prepared in a polyethylene glycol mono-4-nonylphenyl ether (NP-5)/cyclohexane reverse micellar system and incorporated into polyurea (PUA) via an in situ polymerization of hexamethylene diisocyanate (HDI). The resulting ZnO nanoparticles demonstrated a near-UV emission and a green emission, the intensity ratio of which depended on calcination conditions. For the nanoparticles studied, the calcination atmosphere influenced remarkably the photoluminescence properties such as intensity ratio of the near-UV emission to green emission, rather than the size, morphology, and crystallinity of the ZnO nanoparticles. The green emission decreased by calcination in O2 flow but increased by calcination in N2 flow, as compared with the case calcined in air flow. This finding suggests that the green emission is enhanced with the increase of the number of oxygen vacancies of the ZnO nanoparticles and thus the photoluminescence properties of the nanoparticles were successfully controlled by the calcination condition, without changing the size and morphology.     

Synthesis of ZnO and TiO2 nanoparticles

We report on the synthesis of ZnO and TiO₂ nanoparticles by solution-phase methods, with a particular focus on the influence of experimental parameters on the kinetics of nucleation and coarsening. The nucleation rate of ZnO from the reaction between ZnCl₂ and NaOH in ethanol was found to increase with increasing precursor concentration, while the coarsening rate is independent of precursor concentration up to a threshold concentration. The nucleation rate of ZnO from Zn(OOC-CH₃)₂ and NaOH in n-alkanols was found to decrease with decreasing chain length, which is explained by the increase of the dielectric constant of the solvent. Due to the larger solubility of ZnO, nucleation is significantly slower than that observed in the case of TiO₂. TiO₂ nanoparticles coarsen according to the Lifshitz-Slyozov-Wagner model for Ostwald ripening. We also show that using amorphous titania as a base material, pure anatase and brookite nanoparticles can be synthesized.     

Synthesis of ZnO nanomaterials with controlled morphology and their photoelectrochemical properties

Three morphologies of ZnO nanomaterials (ZnO-hand grenade, ZnO-rod and ZnO-particle) were synthesized via a facile hydrothermal method. The as prepared ZnO nanomaterials were used as photoelectrodes to fabricate dye sensitized solar cells (DSSCs). Of the three samples, ZnO-particle displays the highest photovoltaic conversion efficiency which can be attributed to the high surface area to absorb light more efficiently. Intensity modulated photocurrent spectroscopy (IMPS), and intensity-modulated voltage spectroscopy (IMVS) indicate that ZnO-rod provides superior electron transfer kinetics: fast electron transfer and long electron lifetimes with suppressed recombination.     

Synthesis of 2,5-diaryl-4-halo-1,2,3-triazoles and comparative study of their fluorescent properties

A convenient method for arylation of mono- and disubstituted 1,2,3-triazoles by copper-catalyzed Chan-Lam coupling was developed. The method is applicable for the regioselective synthesis of fluorescent 4-halogen-substituted (Hal?=?F, Cl, Br) 2,5-diaryl-1,2,3-triazoles in high yields. Comparative study of their fluorescent properties revealed that 4-fluorosubstituted triazoles possess the highest quantum yield (up to 0.69) among halogenated triazoles possessing Cl and Br in the position 4.     

Physical properties of suspension ZnO nanoparticles prepared by wet chemical method: Comparison study

In this work a suspension of Nano-crystalline of ZnO particle is prepared by wet chemical at different temperature and concentration. From FTIR spectral exhibit present of Zn–O bond which indicate to formation ZnO particles. While all suspension and nano films exhibit a high transmittance in visible region about 90% which falls sharply in the UV region. The particle size is measured by using effective mass approximation (EMA), which was approximation (1.7–1.96 nm), and the band gap changes from 3.95 to 4.52eV for nanoparticles in suspension, and change from 3.76 to 3.94 eV for nanoparticles in ZnO film, which is change as function of concentration, temperature and aging time. Hall Effect measurements for ZnO films exhibit n-type conductivity for films deposited with activation energy 0.742eV at high temperature and 0.178eV at low temperature which is different as prepared sample conditions. Also the nanoparticle suspension and nanoparticle film could be implemented as a filter with variable cut off (8.9 × 10¹⁴–1.28 × 10¹⁵) H_Z.     

Synthesis of anisotropic silver nanoparticles and investigation of their sensory properties

A simple procedure has been proposed for synthesis of planar triangular silver nanoparticles. Optimal conditions have been determined for particles to form, and the particles have been characterized by physicochemical methods. The halide-ion-sensory properties of sols of anisotropic silver nanoparticles prepared in different ways have been studied; sensitivity to halide ions is based on the changes in positions and intensities of longitudinal surface plasmon resonance (SPR) peaks in the range 500–800 nm in the optical absorption spectra of solutions.     

Mesoporous MgO: Synthesis,physico-chemical,and catalytic properties

Mesoporous MgO was obtained via the hydrothermal synthesis using both ionogenic and non-ionogenic surfactants as structure-directing templates. The materials prepared were characterized by SEM, BET-N₂, XRD, and TG-DTA techniques. MgO particles are spherical 20-μm aggregates of primary oxide particles well shaped as rectangular parallelepipeds. Magnesium oxide samples have the specific surface area of 290–400 m²/g and pore sizes of 3.3–4.1 nm. Their mesoporous structure remained unchanged after calcination up to 350°C. Catalytic activity of mesoporous MgO was studied in acetone condensation reaction.     

A Comparative study on synthesis, characterization and photocatalytic activities of MgO and Fe/MgO nanoparticles

MgO and Fe/MgO particles in the nanometer-size regime have been successfully synthesized by a hydrothermal crystallization process using dodecyl benzenesulphonic acid as a surfactant. The prepared catalysts were characterized in details by multiform techniques: XRD, SEM, TEM, UV-DRS, TGA-DSC, BET surface area, and EPR spectroscopy. Comparative photocatalytic activity of the samples was evaluated through the photodegradation of Acid Blue 80 dye under sunlight. The results of the photocatalytic degradation of Acid Blue 80 dye in aqueous solution demonstrated that Fe ions doping greatly improved the photocatalytic efficiency of MgO nanoparticles. Most interestingly, this is the first time that it has been observed that the Fe/MgO system is quite an effective visible light active catalyst.     

Synthesis of composite of ZnO spheres with polyaniline and their microwave absorption properties

Three-dimensional (3D) ZnO microspheres with the composite of polyaniline (PANI) have been successfully synthesized by one-pot solvothermal and in-suit polymerization method. The obtained microspheres were uniform having the diameter of 4 μm–7 μm. These microspheres, inside cushion of PANI polymer, exhibit excellent microwave absorption properties. Composite of ZnO microspheres with PANI increased the complex permeability and enhanced the dielectric loss. Thus, the microwave absorption properties of the composite have been intensified. Despite the fact that the composite of ZnO with PANI herein dissipate the microwaves by dielectric loss, their performance is admirable compared to most of PANI-based composites reported. The morphological, structural and spectral properties have been investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and the Fourier transform infrared (FT-IR). It is found that the maximum reflection loss value of [email protected] reaches ?41 dB at 14 GHz with a thickness of 3.5 mm that is superior to the previously reported composite of PANI with other materials.     

Small-size ZnO/MgO quantum systems with zinc oxide nanoparticles of controlled size

A method is proposed for the preparation of nanosized ZnO/MgO systems by the deposition of previously formed zinc oxide nanoparticles onto a support from a colloidal solution and for determination of the size of the deposited ZnO particles from the electronic spectra. The morphology of composites containing zinc oxide nanoparticles was investigated by electronic spectroscopy and transmission electron microscopy. The possibility of synthesizing solid-phase ZnO/MgO quantum systems with controllable size characteristics was demonstrated. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 3, pp. 183–188, May–June, 2007.     

Synthesis of gadolinium-based nanoparticles in a system of direct surfactant micelles and study of their magnetic properties

Synthesis method is suggested and the size and shape of Pt-Gd particles formed in reduction of metal ions in an aqueous system of direct micelles were determined in relation to the concentration of surfactants and reducing agents: hydrazine hydrate, quercetin, and rutin. The magnetic properties of the nanoparticles obtained were studied.     

Li doped and undoped ZnO nanocrystalline thin films: a comparative study of structural and optical properties

Thin films of ZnO were grown by the sol–gel method using spin-coating technique on (0001) sapphire substrates. The effect of doping after annealing on the structural and optical properties has been investigated by means of X-ray diffraction (XRD), cathodoluminescence (CL) spectrum, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The films that were dried at 623 K and then post annealed at 873 K showed (0002) as the predominant orientation. Two emission bands have been observed from CL spectrum. Lithium doped film shows shift in the near band edge UltraViolet emission peak and suppressed defect level emission peak in the visible range. SEM analysis of the films exhibits many spherical shaped nanoparticles. Roughness of the films determined using atomic force microscopy.      

Solvothermal synthesis and properties control of doped ZnO nanoparticles

Indium and gallium doped ZnO nanoparticles have been prepared by a hydrothermal reaction in ethanol and methoxyethanol. A comprehensive study of the preparation process, including a thorough investigation by TG-FTIR and TG-MS of the thermal-purification procedure, is presented. Moreover, the effect of thermal conditions and dopant concentration on the structural and optical properties is discussed on the basis of XRD, TEM and UV-vis-NIR results. Reported data indicated that the use of methoxyethanol as a solvent allows an enhanced control of nanoparticle size and favours dopant incorporation into zinc oxide. Near infrared absorption of these materials can be strongly affected by increasing the doping level and upon treating nanoparticles under reducing atmosphere. Preliminary study indicated that this effect is greatly enhanced for gallium-doped zinc oxide.     

Spectroscopic properties of trapped electrons on the surface of MgO nanoparticles.

To characterise electron-trapping sites on the surface of MgO nanoparticles, surface colour centres were generated using UV light in conjunction with selected hydrogen-based electron sources. Four different colour-centre species, including the characteristic (e-)(H+) or F(S)+(H) centre, were identified due to the distinct shape of the respective electron paramagnetic resonance (EPR) signals. The analysis of the EPR saturation behaviour down to microwave powers of 5 x 10(-3) mW reveals an enhanced spin-relaxation probability of the (e-)(H+) centre compared to all other F(S)+ centres that do not exhibit significant magnetic interactions with hydroxylic protons. Beside the dipolar magnetic interaction in the (e-)(H+) centre observed by EPR, the electronic interaction between the unpaired electron and the proton of a closely spaced OH group produces a redshift of the OH stretching band by about 70 to 170 cm(-1), as observed by infrared spectroscopy. EPR and IR spectroscopic data obtained after the selective address of individual reaction channels for surface colour-centre formation point to the fact that (e-)(H+) centres are formed by trapping electrons from H atoms. Consequently, the underlying surface defect does not belong to the sites of the MgO surface, which chemisorb hydrogen via a heterolytic splitting process.     

N-(取代)-1,3,4-噻二唑基香豆素酰胺类化合物的合成及光谱特性

用6-氯香豆素-3-甲酰氯(Ⅰ)和5-(取代)-2-氨基-1,3,4-噻二唑(Ⅱa-Ⅱi)作用合成了9种新的目标化合物(Ⅲa-Ⅲi),用HRMS,IR和1 H NMR对化合物结构进行了表征,确定了化合物的结构,并对其紫外吸收光谱和荧光光谱进行了分析.研究发现:在紫外光谱中,新化合物(Ⅲa-Ⅲi)和2种原料化合物相比,因共轭链的增长而使其最大吸收波长(λmax)红移;9种化合物表现出比原料化合物(Ⅰ)较强的荧光性能.     

Synthesis and properties of lead nanoparticles

Lead nanoparticles were synthesized by the thermal decomposition of lead stearate in octanol. The nanoparticles were characterized by X-ray powder diffraction, thermal analysis, IR spectroscopy, and electron microscopy. The lead particle size can be controlled by both varying the concentration of lead stearate in octanol and changing the thermolysis time. Lead nanoparticles have an organic coat composed of decomposition products of lead stearate. This coat prevents the particles from oxidation in air and favors their dissolution in organic solvents.