Formation of RuO2 nanoparticles by thermal decomposition of Ru(NO)(NO3)3

A simple one-pot synthesis of RuO₂ nanoparticles by the thermal decomposition of ruthenium nitrosyl nitrate [Ru(NO)(NO₃)₃] up to 800 °C was investigated. The RuO₂ phase was characterized by XRD, SAXS, FE SEM/EDS, Raman, DTA/TGA and FT-IR techniques. Broadening of prominent diffraction lines (110), (101) and (211) was used to estimate nanocrystallite sizes in RuO₂ particles. FE SEM showed the formation of RuO₂ plates at 400 °C which consisted of RuO₂ nanoparticles of about 15–25 nm in size. At 800 °C RuO₂ nanoparticles showed the sintering effect and some of them increased in size to about 200 nm. Raman and FT-IR spectra consolidated the findings. Moreover, DTA curves showed the decomposition and release of NO and NO₃⁻ groups to be a stepwise process.     

葡萄糖辅助热分解法制备CdS纳米粒子

通过葡萄糖辅助热分解法制备出CdS纳米粒子,对产品进行了表征。在反应过程中葡萄糖可以阻止产物团聚,进而有效地降低产物尺寸。根据前驱体热分解过程的热重分析仪和差热分析仪测试结果,提出了葡萄糖的形貌控制机理。最后研究了葡萄糖加入量和辅助剂种类对产物形貌的影响。     

Microwave-assisted synthesis of layered basic zinc acetate nanosheets and their thermal decomposition into nanocrystalline ZnO

We have developed a low-cost technique using a conventional microwave oven to grow layered basic zinc acetate (LBZA) nanosheets (NSs) from a zinc acetate, zinc nitrate and HMTA solution in only 2 min. The as-grown crystals and their pyrolytic decomposition into ZnO nanocrystalline NSs are characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), X-ray diffraction (XRD) and photoluminescence (PL). SEM and AFM measurements show that the LBZA NSs have typical lateral dimensions of 1 to 5 μm and thickness of 20 to 100 nm. Annealing in air from 200°C to 1,000°C results in the formation of ZnO nanocrystalline NSs, with a nanocrystallite size ranging from 16 nm at 200°C to 104 nm at 1,000°C, as determined by SEM. SEM shows evidence of sintering at 600°C. PL shows that the shape of the visible band is greatly affected by the annealing temperature and that the exciton band to defect band intensity ratio is maximum at 400°C and decreases by a factor of 15 after annealing at 600°C. The shape and thickness of the ZnO nanocrystalline NSs are the same as LBZA NSs. This structure provides a high surface-to-volume ratio of interconnected nanoparticles that is favorable for applications requiring high specific area and low resistivity such as gas sensing and dye-sensitized solar cells (DSCs). We show that resistive gas sensors fabricated with the ZnO NSs showed a response of 1.12 and 1.65 to 12.5 ppm and 200 ppm of CO at 350°C in dry air, respectively, and that DSCs also fabricated from the material had an overall efficiency of 1.3%.

PACS

81.07.-b; 62.23.Kn; 61.82.Fk     

Surfactant-free dispersion of silver nanoparticles into MWCNT-aqueous nanofluids prepared by one-step technique and their thermal characteristics

This paper reports a significant enhancement in the thermal conductivity of silver-nanoparticle-based aqueous nanofluids with the addition of negligible amounts of multi-walled carbon nanotubes (MWCNTs). The present work was conducted using purified MWCNTs/water nanofluids prepared by a wet grinding method. Silver nanoparticles were dispersed into the MWCNT/water nanofluids via a one-step method using pulse power evaporation, which was observed to improve the dispersibility and thermal conductivity of the nanofluids. A particle sizing system (PSS) and transmission electron microscopy (TEM) were used to confirm the size of silver nanoparticles in base fluids. The PSS measurement results reveal that the size of the silver nanoparticles was approximately 100 nm, which is in good agreement with the results obtained from TEM and SEM. The maximum absorbance (2.506 abs at a wavelength of 264 nm) and highest thermal conductivity enhancement (14.5% at 40 °C) were achieved by a fluid containing ‘0.05 wt% MWCNTs–3 wt% Ag’ composite.     

Formation of bamboo-like conducting carbon nanotubes decorated with Au nanoparticles by the thermal decomposition of sucrose in an AAO template

An easy method is reported for the preparation of bamboo-like conducting carbon nanotubes decorated with Au nanoparticles (Au-CNT), by carbonization of sucrose inside of anodic aluminum oxide (AAO) nanochannels (～80 nm and ～30 μm in diameter and length, respectively). First, the AAO membrane nanochannels were coated with Au nanoparticles (～10 nm in diameter) and the carbon nanotubes were then formed in the same channels below 973 K. Electron microscopy shows long bamboo-like carbon nanotubes, ～30 μm in length, decorated with crystalline gold nanoparticles, ～50 nm in diameter. The coalescence of the precoated small Au nanoparticles inside the channel results in the attached large Au nanoparticles. The apparent resistivity of the Au-CNT prepared at 973 K, was ～16.8 Ω cm. The electrical conductivity of the structure is discussed with relation to electrochemical and micro Raman experiments.     

Immobilization of palladium nanoparticles on latex supports and their potential for catalytic applications

Palladium nanoparticles were reduced in the presence of several latex dispersions possessing different hydrophobicities. Various reduction methods were investigated, specifically the slower methods of refluxing the alcoholic solution and the more rapid reduction by potassium tetrahydridoborate. In several cases the latexes showed the ability to adsorb and immobilize the palladium nanoparticles on their surface. Transmission electron microscopy was employed to show the immobilization of the metal nanoparticles on the latex surfaces, and their nanosize dimensions. The latex-metal dispersions showed catalytic activity for the hydrogenation of cyclohexene as a model reaction. A selection of water-soluble protective polymers was included to explore whether the metal nanoparticles were still immobilized. In the case of the more hydrophobic latexes, the accumulation and immobilization of the metal nanoparticles was preserved both before and after their use as hydrogenation catalysts.     

Removal of sulfuroxyanions by magnesium aluminium oxides and their thermal decomposition

The behaviour of the removal of the sulfuroxyanions, SO^2?₄, S₂O^2?₃, S₂O^2?₆ and S₄O^2?₆, in aqueous solutions by Mg_0.61Al_0.26□_0.13O (□:vacancy) was investigated at 40–80°C. All the sulfuroxyanions were removed from solution competitively with OH^? to form the hydrotalcite-like compounds. The rate of the removal was first order with respect to the concentration of the sulfuroxyanion in the solution, and the apparent activation energy was about 60 kJ mol^?1. All the sulfuroxyanions intercalated in the interlayer of hydrotalcite structure decomposed to SO^2?₄ at 100–300°C.     

Synthesis of CeO2 nanoparticles by rapid thermal decomposition using microwave heating

Abstract

This article describes the synthesis of a CeO₂ fine powder by thermal decomposition of cerium oxalate and cerium nitrate powders using a microwave furnace. Plate-like crystalline CeO₂ particles were obtained using the cerium oxalate precursor powder. Using the cerium nitrate powder as a precursor, spherical crystalline CeO₂ particles were obtained with a primary particle diameter of 30?nm and secondary particle size of 550?nm.     

Kinetic modelling of the thermal decomposition of ettringite into metaettringite

Despite recent insights into thermal stability of ettringite and structural changes during decomposition, a lack of knowledge on nucleation and growth mechanisms of metaettringite remained. Therefore, a better understanding of the kinetic modelling of this heterogeneous reaction was proposed. Thanks to an experimental approach allowing to check the validity of kinetic assumptions (rate-determining step, expression of the rate as dα/dt = kf(α)…), a good agreement was found between the calculated and experimental α vs. t and dα/dt vs. t kinetic curves. The reaction area of the region in which the rate-limiting step occurs was also elucidated. Finally, we demonstrated that the rate-limiting step of the growth process follows an Arrhenius law in non-isothermal conditions.     

Methanol decomposition over supported palladium and platinum

Methanol decomposition over supported Pt and Pd catalysts was investigated in the temperature range from 453 to 573 K with the partial pressure of methanol up to 0.8 arm. The specific activity of Pd was higher than that of Pt, and alumina-supported Pd was more active than silicasupported Pd, although aluminasupported catalysts produced dimethyl ether as a by-product. A silica-supported Pd catalyst prepared from a tetraamine salt solution with a proper pH exhibited higher activity than the other silica-supported Pd catalysts. Dependence of the decomposition rate on the partial pressure of methanol was similar regardless of the metal, the support or the preparation method. The apparent reaction orders were near 0.3 at low pressures below about 0.4 atm and became near zero or slightly negative at higher pressures. The apparent activation energies were about the same for most of the catalysts and were in the range from 66 to 77 kJ/g-mol.     

Formation mechanism of barium titanate by thermal decomposition of barium titanyl oxalate

This study examined the formation mechanism of BaTiO₃ from the thermal decomposition of barium titanyl oxalate. A significant amount of O₂ evolution near 357 and 720 °C was observed by gas chromatography/mass spectroscopy, except for the previously known H₂O, CO₂, CO evolution. The metastable Ba₂Ti₂O₅CO₃(CO₂) intermediate phase seemed to be transformed mainly to Ba₂Ti₂O₅CO₃, while a certain amount of crystalline BaCO₃ and amorphous Ti-rich phase were formed simultaneously at 450-600 °C in air. A modification of the decomposition mechanism reported by Gopalakrishnamurthy et al. was proposed based on the experimental findings.     

Formation of nanosize ZnO particles by thermal decomposition of zinc acetylacetonate monohydrate

Formation of ZnO particles by thermal decomposition of zinc acetylacetonate monohydrate in air atmosphere has been investigated using XRD, DTA, FT-IR, and FE-SEM as experimental techniques. ZnO as a single phase was produced by direct heating at ≥200 °C. DTA in air showed an endothermic peak at 195 °C assigned to the ZnO formation and exothermic peaks at 260, 315 and 365 °C, with a shoulder at 395 °C. Exothermic peaks can be assigned to combustion of an acetylacetonate ligand released at 195 °C. ZnO particles prepared at 200 °C have shown no presence of organic species, as found by FT-IR spectroscopy. Particles prepared for 0.5 h at 200 °C were in the nanosize range from ∼20 to ∼40 nm with a maximum at 30 nm approximately. The crystallite size of 30 nm was estimated in the direction of the a₁ and a₂ crystal axes, and in one direction of the c-axis it was 38 nm, as found with XRD. With prolonged heating of ZnO particles at 200 °C the particle/crystallite size changed little. However, with heating temperature increased up to 500 or 600 °C the ZnO particle size increased, as shown by FE-SEM observation. Nanosize ZnO particles were also prepared in two steps: (a) by heating of zinc acetylacetonate monohydrate up to 150 °C and distillation of water and organic phase, and (b) with further heating of so obtained precursor at 300 °C.     

通过一水乙酰丙酮锌的热分解形成纳米级ZnO颗粒

采用X-射线粉料衍射、差热分析、傅里叶变换红外线光谱以及热场发射扫描电子显微镜,研究了在大气气氛中通过一水乙酰丙酮锌的热分解来形成ZnO颗粒.通过在≥200℃的直接加热,生成了单相ZnO.分2个步骤制备了纳米级ZnO:(a)将一水乙酰酮锌加热到150℃,对水和有机相进行蒸馏;(b)进一步加热在300℃时获得先质.     

Formation of gold nanoparticles on multiwalled carbon nanotubes by thermal evaporation

Multiwalled carbon nanotubes (MWCNTs) were grown on W substrates by chemical vapor deposition and modified with Au nanoparticles by thermal evaporation. The resulting hybrid structures were investigated by TEM to determine the effects of evaporation rate, nominal film thickness, and substrate temperature on the nanoparticle size and distribution. The results demonstrate that as-grown MWCNTs can be used as a support for well distributed Au nanoparticles, with the size and distribution on the carbon nanotubes being primarily influenced by the nominal film thickness. The observed structures ranged from small 4 nm diameter spherical particles to 150 nm long wire-like structures. Depositions with substrates at 25 °C and 400 °C resulted in similar particle structures, except for the highest amount of deposited Au.     

Synthesis, structures and magnetic properties of carbon-encapsulated nanoparticles via thermal decomposition of metal acetylide

A new low-temperature synthetic method for carbon-encapsulated metal and metal carbide nanoparticles was developed, where the metal cation M²⁺ is reduced by . In this method, metal cations form clusters at the beginning, followed by neutralization and segregation. Formations of metallic tin and cobalt, and metastable carbides of cobalt, palladium and nickel are evidenced by powder X-ray diffractions. TEM observation reveals that the nanoparticles are encapsulated in carbon shells despite the low temperature treatment. The formation of the metastable carbides and carbon shells can be explained by the carbon-rich precursor, acetylide clusters. Surplus carbon atoms tend to be excluded from the metal-carbon cores even at low temperature, automatically forming carbon shells.     

Preparation of carboxyl group-modified palladium nanoparticles in an aqueous solution and their conjugation with DNA

The use of nanomaterials in biomolecular labeling and their corresponding detection has been attracting much attention, recently. There are currently very few studies on palladium nanoparticles (Pd NPs) due to their lack of appropriate surface functionalities for conjugation with DNA. In this paper, we thus firstly present an approach to prepare carboxyl group-modified Pd NPs (with an average size of 6 nm) by the use of 11-mercaptoundecanoic acid (MUDA) as a stabilizer in the aqueous solution. The effect of the various reducing reaction conditions on the morphology of the Pd NPs was investigated. The particles were further characterized by TEM, UV-vis, FT-IR and XPS techniques. DNA was finally covalently conjugated to the surface of the Pd NPs through the activation of the carboxyl group, which was confirmed by agarose gel electrophoresis and fluorescence analysis. The resulting Pd NPs-DNA conjugates show high single base pair mismatch discrimination capabilities. This work therefore sets a good foundation for further applications of Pd NPs in bio-analytical research.     

Size dependence of the magnetic properties of Ni nanoparticles prepared by thermal decomposition method

By means of thermal decomposition, we prepared single-phase spherical Ni nanoparticles (23 to 114 nm in diameter) that are face-centered cubic in structure. The magnetic properties of the Ni nanoparticles were experimentally as well as theoretically investigated as a function of particle size. By means of thermogravimetric/differential thermal analysis, the Curie temperature T_C of the 23-, 45-, 80-, and 114-nm Ni particles was found to be 335°C, 346°C, 351°C, and 354°C, respectively. Based on the size-and-shape dependence model of cohesive energy, a theoretical model is proposed to explain the size dependence of T_C. The measurement of magnetic hysteresis loop reveals that the saturation magnetization M_S and remanent magnetization increase and the coercivity decreases monotonously with increasing particle size, indicating a distinct size effect. By adopting a simplified theoretical model, we obtained M_S values that are in good agreement with the experimental ones. Furthermore, with increase of surface-to-volume ratio of Ni nanoparticles due to decrease of particle size, there is increase of the percentage of magnetically inactive layer.     

Preparation and characterization of CaO nanoparticles from Ca(OH)2 by direct thermal decomposition method

CaO is an important material because of its application as catalyst and effective chemisorbents for toxic gases. In this research CaO nanoparticles were prepared via direct thermal decomposition method using Ca(OH)₂ as a wet chemically synthesized precursor. Nanocrystalline particles of Ca(OH)₂ have been obtained by adding 1 and 2 M NaOH aqueous solutions to 0.5 M CaCl₂·2H₂O aqueous solutions at 80 °C. The precursor [Ca(OH)₂] was calcined in N₂ atmosphere at 650 °C for 1 h. Samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), infrared spectrum (IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunaure–Emett–Teller (BET). SEM images showed that CaO nano-particles were nearly spherical in morphology. TEM images illustrated that produced CaO nano-particles had the mean particle size of 91 and 94 nm for 1 and 2 M NaOH concentration, respectively. As a result, this method could be used for production of CaO nano-particles on large-scale as a cheap and convenient way, without using any surfactant, organic medium or complicated equipment.     

Hydrogenation activity and selectivity behavior of supported palladium nanoparticles

Enhancement in activity and selectivity of catalytic hydrogenation using supported nanosize palladium catalyst has been investigated. Pd/C catalyst prepared in the presence of polyvinyl pyrrolidone (PVP) as a stabilizer gave Pd particle size in a narrow range of 3–5 nm. While, evaluating for hydrogenation of 2-butyne-1,4-diol, the rate enhancement was found to be 10 times higher as compared to the conventional (bulk) Pd catalysts. A proper choice of stabilizer (PVP) giving small particle size as well as highly dispersed nature of nano particles were the major factors for such a dramatic enhancement of activity.