A novel ultrasound assisted method in synthesis of NZVI particles

This research is about a novel ultrasound assisted method for synthesis of nano zero valent iron particles (NZVI). The materials were characterized using TEM, FESEM, XRD, BET and acoustic PSA. The effect of ultrasonic power, precursor/reductant concentration (NaBH₄, FeSO₄·7H₂O) and delivery rate of NaBH₄ on NZVI characteristics were investigated. Under high ultrasonic power the morphology of nano particles changed from spherical type to plate and needle type. Also, when high precursor/reductant and high ultrasonic power was used the particle size of NZVI decreased. The surface area of NZVI particles synthesized by ultrasonic method was increased when compared by the other method. From the XRD patterns it was found also the crystallinity of particles was poor.     

Ultrafine anatase TiO2 nanoparticles produced in premixed ethylene stagnation flame at 1 atm

Nano-sized titanium oxide particles were synthesized in a stationary, laminar, premixed, stagnation flame burning an ethylene–oxygen–argon mixture at an equivalence ratio of 0.36 under the atmospheric pressure. The titanium precursor, titanium tetraisopropoxide (TTIP), was fed into the flame by a carrier argon flow through a heated TTIP bath. Particles synthesized in this flame were characterized for their size distribution, morphology, phase purity, and crystal structure, by scanning mobility particle sizer, transmission electron microscopy, and X-ray diffraction. It was found that the mean diameter of the particles was highly controllable and ranged from 3 to 6 nm depending on TTIP loading. The particle size was nearly uniform, and particles appeared to be single crystals without excessive aggregation. XRD analyses show that particles directly synthesized in the flame are pure anatase. Upon sintering and size growth on the flame stabilizer, a notable portion of particles transformed into rutile with much larger crystal sizes.     

Production of cobalt and nickel particles by hydrogen reduction

Cobalt and nickel nanoparticles were produced by hydrogen reduction reaction from cobalt or nickel chloride precursor vapour in nitrogen carrier gas. This aerosol phase method to produce nanoparticles is a scalable one-step process. Two different setups were introduced in particle production: a batch type reactor and a continuously operated reactor. Common feature in these setups was hydrogen mixing in a vertical flow reactor. The process was monitored on-line for particle mass concentration and for gas phase chemical reactions. Tapered element oscillating microbalance measured the particle mass concentration and Fourier transform infrared spectroscopy was used to monitor relevant gas phase species. The produced cobalt and nickel particles were characterised using transmission electron microscopy and x-ray diffraction. The produced cobalt and nickel particles were crystalline with cubic fcc structure. Twinning was often observed in cobalt particles while nickel particles were mostly single crystals. The cobalt particles formed typically long agglomerates. No significant neck growth between the primary particles was observed. The primary particle size for cobalt and nickel was below 100 nm.     

Synthesis and morphology of silicon oxide nanowires from a free jet activated by electron-beam plasma

Silicon oxide nanowires were synthesized from monosilane–argon–hydrogen mixture by the gas-jet electron-beam plasma chemical deposition method with simultaneous oxygen injection into the vacuum chamber. The synthesis was performed on monocrystalline silicon substrates covered with micron and nanometer tin catalyst particles. The nanowires are formed the via vapor–liquid–solid mechanism in the “catalyst-on-bottom” mode, in which many nanowires grow from one catalyst particle. The process of synthesizing nanowires on a substrate with catalyst consists of three stages: heating to synthesis temperature, hydrogen plasma treatment, and nanowire growth. In the substrate region corresponding to the jet axis, different structures are formed depending on the catalyst particle size. For catalyst particles under 100 nm, there are formed structures of chaotically oriented and interlaced bundles of silica nanowires. For catalyst particles of 0.3–1 micron, there are formed oriented arrays of cylindrically shaped nanowire bundles (“microropes”). Cocoon-like structures are formed for catalyst particles of more than 1 micron.We propose a model of nanowire growth by this method, which is based on nonuniform heating of a catalyst particle by a directed plasma flow. It was found that for synthesis of oriented microrope arrays the initial tin film thickness should be less than 100 nm and the synthesis process should include a hydrogen plasma treatment stage.     

Synthesis of wide band gap nanocrystalline NiO powder via a sonochemical method

A sonochemistry-based synthesis method was used to produce nanocrystalline nickel oxide powder with ∼20 nm average crystallite diameter from Ni(OH)₂ precursor. Ultrasound waves were applied to the primary solution to intensify the Ni(OH)₂ precipitation. Dried precipitates were calcined at 320 °C to form nanocrystalline NiO particles. The morphology of the produced powder was characterized by transmission electron microscopy. Using sonochemical waves resulted in lowering of the size of the nickel oxide crystallites. FT-IR spectroscopy and X-ray diffraction revealed high purity well-crystallized structure of the synthesized powder. Photoluminescence spectroscopy confirmed production of a wide band-gap structure.     

Formation of two-dimensional ordered magnetic nanolattices in opal structures

A method of forming a two-dimensional ordered superlattice of magnetic nanoparticles in close-packed opal structures of silica (SiO₂) spheres has been developed. Nickel nanopowder with an average particle size of about 70 nm is used as a source of magnetic particles. Atomic-force and magnetic-force microscopy studies show that all magnetic particles are located in the interstices of the opal lattice, while the magnetization vectors of neighboring nickel particles can have different magnitudes and directions.     

Effects of atomization conditions on morphology and SOFC anode performance of spray pyrolyzed NiO–Sm0.2Ce0.8O1.9 composite particles

NiO–Sm_0.2Ce_0.8O_1.9 (NiO–SDC) composite particles were synthesized by spray pyrolysis (SP). SP resulted in composite particles of NiO enveloped with SDC and these capsule-type composite particles would reduce aggregation of Ni during the reduction from NiO to Ni metals. SOFC anode microstructures and morphologies of NiO–SDC composite precursor particles much affects on SOFC power densities or anode polarization. Therefore, we focused on atomizing conditions of SP process. Relationship between ultrasonic atomization conditions and morphologies of NiO–SDC composites were investigated by controlling temperatures of atomization vessels. The atomizing temperature changed concentration of mists in the vessel, and mean particle size and particle size distribution were increased with an increase in temperature of the atomization vessels. Some extremely large particles were observed by synthesizing at higher atomization temperatures. Large particles contained voids in the particles. The voids in the composite particles would play a role of pore-formers. SOFC measurement showed the synthesis at the atomizing temperature of 30 °C resulted in the high-performance anode. The atomizing process of SP much affected morphology of anode precursor particles, and the atomizing conditions were important to improve anode performance.     

Properties of nanocrystalline TiO2 synthesized in premixed flames stabilized on a rotating surface

The properties of TiO₂ nanoparticles synthesized using the flame stabilized on a rotating surface method (FSRS) are investigated. The method uses a laminar, premixed, stagnation flame, combining particle synthesis and film deposition in a single step. The current study examines the effects of flame properties on particle characteristics. Synthesized particles were characterized using X-ray diffractometry, Transmission Electron Microscopy and UV–vis spectrometry in order to quantify the effects of equivalence ratio and precursor loading on particle size, crystallinity and optical band-gap. Results show that flame stoichiometry significantly affects crystal phase, but it has little to no effect on particle size and light absorption band edge. In addition, precursor loading impacts both the particle size and the crystal phase. The study demonstrates the potential of the FSRS method for producing tailored nanoscale TiO₂ particles for a variety of applications.     

The effect of oxidation on the structure of nickel nanoparticles

The structural properties of nickel nanoparticles which are prepared by means of DC sputtering in argon and subsequently oxidized in ambient air are reported. Ex situ structural and chemical investigations utilizing (high resolution) transmission electron microscopy and electron energy loss spectroscopy reveal that the particles consist of a metallic core surrounded by an oxide shell. The lattice constant of the nickel core is found to increase significantly with decreasing particle size. This widening of the nickel lattice is attributed to an interfacial stress that originates from the lattice mismatch between nickel and nickel oxide. Received 21 December 2000     

Nanoscale synthesis and optical features of nickel nanoparticles

Nickel nanoparticles have been synthesized by chemical reduction method. By the analysis of X-ray diffraction, the resultant particles are characterized and found to be pure crystalline nickel with a face-centered cubic (FCC) structure. The morphology and size of the nanoparticles are studied by scanning electron microscopy (SEM) and micrographs reveal that the nanoparticles are mostly spherical. The compositional analysis has been carried out by using EDAX. The quantum size confinement of the crystallites is evident from the blue-shift of the absorption edge in the UV–vis absorption spectrum.     

Thermal Oxidation of a Carbon Condensate Formed in High-Frequency Carbon and Carbon–Nickel Plasma Flow

We have reported on the comparative characteristics of thermal oxidation of a carbon condensate prepared by high-frequency arc evaporation of graphite rods and a rod with a hollow center filled with nickel powder. In the latter case, along with different forms of nanodisperse carbon, nickel particles with nickel core–carbon shell structures are formed. It has been found that the processes of the thermal oxidation of carbon condensates with and without nickel differ significantly. Nickel particles with the carbon shell exhibit catalytic properties with respect to the oxidation of nanosized carbon structures. A noticeable difference between the temperatures of the end of the oxidation process for various carbon nanoparticles and nickel particles with the carbon shell has been established. The study is aimed at investigations of the effect of nickel nanoparticles on the dynamics of carbon condensate oxidation upon heating in the argon–oxygen flow.     

A simple route to the synthesis of high-quality NiO nanoparticles

Dispersed nickel oxide nanoparticles were obtained by a simple and low-cost method using a mixture of gelatin as organic precursor and NiCl₂ · 6H₂O as Ni source. The average particle size was estimated from X-ray powder diffraction (XRPD) peaks using the Rietveld refinement. The values ranged from 3.2 to 79 nm. We observed that the particle size changes as a function of synthesis time, with a notable decrease after the addition of NaOH to the solution. Field emission scanning electron microscopy (FE-SEM) measurements show that particles have well defined shapes and are dispersed in an organic matrix. X-ray absorption near edge spectroscopy (XANES) shows also the formation of fcc NiO nanoparticles structures.     

Elementary processes at nanoparticulate photocatalysts

The paper is a mini review on the authors own work related to laser induced processes at metal nanoparticle/oxidic support systems. A number of aspects will be addressed ranging from the nano particle size dependence on the efficiency of the photochemical process, the influence of low coordination sites of the nano particles and dynamical processes such as energy transfer between adsorbates, light induced particle changes or spill over processes. The paper reviews nano and femtosecond laser experiments as well as quantum state resolved experiments. Results will be compared to typical findings from simple oxidic supports and metal single crystals. This review may be of interest for future photocatalyst development for applications such as solar fuel synthesis and related problems.     

Superparamagnetic nickel nanoparticles obtained by an organometallic approach

Nickel nanoparticles were prepared by decomposition of the organometallic precursor Ni(COD)₂ (COD=cycloocta-1,5-diene) dissolved in organic media in the presence of anthranilic acid as stabilizer. Transmission electron microscopy revealed nickel nanoparticles with a mean size of 4.2 ± 1.1 nm and selected area electron diffraction showed the formation of fcc nickel. FTIR spectroscopy confirmed the presence of modified anthranilic acid on the surface of the Ni nanoparticles suggesting that it is able to interact with the metal particles. The magnetic response of the nanoparticles was established as being of superparmagnetic character, for which a detailed quantitative analysis resulted in a mean magnetic moment of 2652 μ_B per particle together with a blocking temperature of 32 K.     

Exciton polaritons of nano-spherical-particle photonic crystals in compound lattices

Nonlocal investigations are presented for exciton-photon coupling in three-dimensional nano-spherical-particle photonic crystals in compound lattices for a tailored dielectric environment to optimize the optical properties of nano particles. The photonic band structure can be modified by tuning the nano particle size and the distance between two interlacing identical face-centered sub-lattices making up the photonic crystal lattice. A complete photonic band gap with a gap-midgap ratio as large as 40.82% has been found in the wurzite structure under the current investigation.     

Synthesis,properties, and applications of fractionated nanodiamonds

The methods for dispersing nanodiamond powders of different purity grades and preparing nanodiamond powder suspensions suitable for fractionation are analyzed. The main physicochemical properties of fractions separated from the synthesis products (blends) and purified nanodiamonds are investigated. It is found that the size distribution of nanodiamonds in the blend is inhomogeneous: an increase in the particle size leads to a decrease in the fraction of these particles. The advantages of nanodiamonds fractionated in size are demonstrated for different applications.     

Microstructure, magnetic and transport properties of magnetoresistive Cu80Fe x Ni20?x (x?=?5, 10 and 15 at.%) ribbons

The generation of copper nanoparticles in an arc furnace by the evaporation/condensation method is systematically investigated. The evaporation/condensation process is advantageous because it allows direct synthesis using pure metals as starting materials avoiding reactions of expensive and potentially poisonous precursors. In the presented system, a transferred direct current arc provides the energy for evaporation of the metal target. In order to prevent an oxidation of the particles in the process, the synthesis is conducted in an atmosphere of inert gases (purity grade 5.0). The arc stability and its effect on particle synthesis are investigated. The experiments reveal excellent long-term arc stability for at least 8?h continuous operation delivering aerosols with high reproducibility (±10?% of average particle size). The influences of the arc current and length, the flow rates of the applied gases and the injection of hydrogen in the plasma zone on the particle size distributions and the agglomerate structure are studied. The produced copper nanoparticles are characterized by scanning mobility particle sizing and scanning electron microscopy. The average particle size could be well controlled in a size range 4?C50?nm by selecting appropriate operating parameters.     

纳米金属粉对高氯酸铵热分解动力学的影响

用TG和DSC研究了普通级和纳米级的铝、镍金属粉对普通高氯酸铵热分解特性的影响 .结果表明 ,普通级和纳米级铝粉对普通高氯酸铵热分解几乎没有影响 ,纳米镍粉对普通高氯酸铵的热分解 ,特别是高温阶段的促进作用最明显 .这种促进作用随着纳米镍粉含量的减少而逐渐减弱 .利用Coats Redfern积分法计算了超细高氯酸铵热分解的动力学参数 ,结果显示纳米镍粉使超细高氯酸铵热分解的表观活化能从 15 7.9kJ/mol下降为134.9kJ/mol,而其热分解的机理函数都同属于“成核和核成长”的Avrami Erofeev方程系列的函数 ,同时还探讨了纳米镍粉对高氯酸铵热分解促进作用的机理 .     

Interfacial Reactions and Cubic Neodymium Oxide Formation in Low Dispersed Nd2O3-SiO2 System by Wet Chemical Method

Neodymium (binary oxide) powders are synthesized by a solgel technique. Prepared powders are heat treated under different temperature for different time duration and obtained nanostructure of Nd. Metal particle have diameters in the range 7.8-21.6nm. It is found that the heat treatment plays an important role to produce different structure of Nd-doped silica matrix. The peak position shifts to lower angle as the size of the nano metal oxide particles size increases.     

电化学阴极沉积制备氧化镍/碳纳米管复合电极的准电容特性

采用催化裂解的方法制备了碳纳米管,其比容量为12F/g.采用碳纳米管作为电极基体,采用阴极电化学还原Ni(NO3)2的方法在碳纳米管基体表面均匀的沉积了纳米氧化镍颗粒并由此制备了氧化镍碳纳米管复合电极材料.采用循环伏安、恒流充放电、交流阻抗及扫描电镜等方法考察了复合电极材料的容量特性、阻抗特性、自放电特性以及电极表观特征.实验表明复合电极具有良好的电化学特性,碳纳米管基体在明显降低氧化镍材料的阻抗的同时还提高了电极材料的电化学容量并拓宽了电极材料的有效工作电位窗,复合电极在6mol/LKOH电解液中比容量达到25F/g且表现了良好的电化学可逆性.与碳纳米管基电容器相比,采用氧化镍复合电极材料组装的电容器具有较低的自放电率.