Thermal Decomposition Of Co Research Articles

Mesoporous nano-Co 3O 4: A potential negative electrode material for alkaline secondary battery

A potential negative electrode material (mesoporous nano-Co 3O 4) is synthesized via a simple thermal decomposition of precursor Co(OH) 2 hexagonal nanosheets in the air. The structure and morphology of the samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is found that the nano-Co 3O 4 is present in mesoporous hexagonal nanoparticles. The average size of holes is about 5–15 nm. The electrochemical performances of mesoporous nano-Co 3O 4 as the active starting negative electrode material for alkaline secondary battery are investigated by galvanostatic charge–discharge and cyclic voltammetry (CV) technique. The results demonstrate that the prepared mesoporous nano-Co 3O 4 electrode displays excellent electrochemical performance. The discharge capacity of the mesoporous nano-Co 3O 4 electrode can reach 436.5 mAh g −1 and retain about 351.5 mAh g −1 after 100 cycles at discharge current of 100 mA g −1. A properly electrochemical reaction mechanism of mesoporous nano-Co 3O 4 electrode is also constructed in detail.

Chelating agent assisted heat treatment of carbon supported cobalt oxide nanoparticle for use as cathode catalyst of polymer electrolyte membrane fuel cell (PEMFC)

Cobalt-based catalysts for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cell (PEMFC) have been successfully incorporated cobalt oxide (Co 3O 4) onto Vulcan XC-72 carbon powder by thermal decomposition of Co–ethylenediamine complex (ethylenediamine, NH 2CH 2CH 2NH 2, denoted en) at 850 °C. The catalysts were prepared by adsorbing the cobalt complexes [Co(en)(H 2O) 4] 3+, [Co(en) 2(H 2O) 2] 3+ and [Co(en) 3] 3+ on commercial XC-72 carbon black supports, loading amount of Co with respect to carbon black was about 2%, the resulting materials have been pyrolyzed under nitrogen atmosphere to create CoO x /C catalysts, donated as E1, E2, and E3, respectively. The composite materials were characterized using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). Chemical compositions of prepared catalysts were determined using inductively-coupled plasma-atomic emission spectroscopy (ICP-AES). The catalytic activities for ORR have been analyzed by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The electrocatalytic activity for oxygen reduction of E2 is superior to that of E1 and E3. Membrane electrode assemblies (MEAs) containing the synthesized CoO x /C cathode catalysts were fabricated and evaluated by single cell tests. The E2 cathode performed better than that of E1 and E3 cathode. This can be attributed to the enhanced activity for ORR, in agreement with the composition of the catalyst that CoO co-existed with Co 3O 4. The maximum power density 73 mW cm −2 was obtained at 0.3 V with a current density of 240 mA cm −2 for E2 and the normalized power density of E2 is larger than that that of commercial 20 wt.% Pt/C-ETEK.

Decoration of Carbon Nanotubes with CoO and Co Nanoparticles

Multiwall carbon nanotubes (MWNTs) decorated with CoO nanocrystals were synthesized by in-situ thermal decomposition of Co(acac)2 in oleyl amine under reflux conditions open in the air. The CoO/MWNTs composite material can be easily converted to metallic Co/MWNTs through annealing under reducing atmosphere (4% H2) at 500°C without any significant sintering effect. The composite materials characterized by X-ray diffraction, transmission electron microscopy, and Nuclear Magnetic Resonance (NMR) spectroscopy. The structural and morphological characterization shows that the CoO has cubic face (fcc) and the particles deposited uniformly on the external surface of the carbon nanotubes. In the annealed materials, the NMR shows that the fcc and hcp metallic Co phases coexist with a significant percentage of stacking faults. The magnetic measurements indicated that the CoO/MWNTs composite is largely composed of CoO nanoparticles with uncompensated surface spins. The fluctuations of spins persist in partially reduced CoO grains as shown by nuclear spin-lattice relaxation measurements.

Synthesis of nanosized mesoporous Co–Al spinel and its application as solid base catalyst

A novel mesoporous Co–Al spinel catalyst with high surface area and suitable basicity was prepared by the thermal decomposition of Co–Al hydrotalcite-like compound. The properties of the solid base catalyst were characterized by XRD, FTIR, TEM, nitrogen sorption and CO 2-TPD. The formation mechanism of the mesopores and the Co–Al spinel structure was also investigated by TG/DTA and mass-spectrometer, respectively. This is due to the partial oxidation of Co 2+ ions and the dehydration of the interface OH groups in precursor. The formed Co 3+ ions collapsed into the interlayer space, coordinated with the adjacent oxygen atoms (tetrahedral or octahedral), worked as pillars between layers and made the interlayer space to be almost opened (mesopores formed). The partial oxidation of Co 2+ ions plays a critical role in the phase transformation and the formation of mesopores. The as-obtained mesoporous Co–Al spinel-type solid base catalyst was first used in the aldol condensation of furfural with acetone and the self-condensation of acetone and found that it had good activity and excellent selectivity in both reactions. The stability studies showed that the catalyst can be completely regenerated easily by calcination.

CO 2 gas-activated sintering of carbonated hydroxyapatites

Sintering compacts of carbonated hydroxyapatite (CHA) nanoparticles (3.4 wt% CO 3 2−) in a CO 2 flow (4 mL/min) proceeded at a temperature which was more than 200 °C lower than that for hydroxyapatite in air (1150 °C). During heating from RT to 1200 °C (5 K/min) the rate of shrinkage of the CHA compacts showed a maximum thrice as high as that in air at about 929 °C. The shrinkage correlates with a mass loss caused by the release of CO 2 due to the thermal decomposition of CO 3 2− ions that substitute PO 4 3− ions in the CHA lattice. Firing the compacts in the CO 2 flow at 800 and 900 °C for 2 h resulted in an additional carbonatation on the B-sites and a further decrease in the sintering temperature to 890 °C. The compacts fired in the 900–1000 °C range became almost complete ceramics with high densities and mechanical properties close to those of medical implants. Firing at temperatures above 1000 °C resulted in an additional carbonatation on the A-sites. However, this led to a material with low densities and poor mechanical properties. A supposition has been proposed that the effect of CO 2 gas-activated sintering is a result of the intensification of the diffusion in the nanoparticles caused by CO 2 molecules entering the bulk from the CO 2 atmosphere and (or) releasing from the bulk due to the decomposition of carbonates on the B-sites in the lattice.

Enhanced magnetic properties of cobalt nanoparticles on FeMn films

Monodisperse cobalt nanoparticles are synthesized by the thermal decomposition of Co 2(CO) 8 in phenyl ether and subsequently deposited on antiferromagnetic (AFM) FeMn films and glass substrates, respectively. Magnetic measurement shows that the as-prepared Co nanoparticles are superparamagnetic and can be transformed into ferromagnetic (FM) through thermal treatment. While keeping monodisperse, the annealed FM Co nanoparticles on AFM FeMn films show a much larger coercivity than the ones on glass substrates due to FM/AFM exchange coupling. Accordingly, we propose a convenient method to enhance magnetic properties of nanoparticles.

Synthesis and self-assembly of monodisperse CoxNi100−x (x=50,80) colloidal nanoparticles by homogenous nucleation

Self-assembled monodisperse fcc Co(50)Ni(50) and Co(80)Ni(20) alloy nanoparticles with the average size of 25 and 8 nm respectively are synthesized by reductive thermal decomposition of Co(II)(acac)(2) and Ni(II)(acac)(2) in the presence of surfactants such as oleic acid, oleylamine and trioctylphosphine. The mechanism for formation of colloidal CoNi alloy nanoparticles is explored in this work. The CoNi nanoparticles with high atomic percentage of nickel are found to be more stable and non-interacting. The Co(50)Ni(50) nanoparticles are superparamagnetic at room temperature and exhibit superparamagnetic to ferromagnetic transition at the blocking temperature (T(b)) ∼130-160 K, whereas Co(80)Ni(20) nanoparticles are ferromagnetic at room temperature with low coercivity (∼20 Oe). The magnetization value of Co(80)Ni(20) nanoparticles is found to be high as compared to Co(50)Ni(50) nanoparticles due to high atomic percentage of cobalt. Interestingly, size of CoNi alloy nanoparticles with high nickel content is found to be large, which indicates that nickel nuclei act as catalysts for the growth of CoNi alloy nanoparticles in the reaction.

Directing oxidation of cobalt nanoparticles with the capping ligand

The oxidation of Co nanoparticles stabilized with various ligands has been studied in an autoclave. Tridodecylamine stabilized Co nanoparticles with different sizes (8 nm, 22 nm and 36 nm) were prepared by thermal decomposition of Co 2(CO) 8 in dodecane. The oxidation of the particles was studied by introducing oxygen into the autoclave and following the oxygen consumption with a pressure meter. Tridodecylamine capped particles were initially oxidized at a high rate, however, the oxidation layer quickly inhibited further oxidation. The thickness of the oxide layer estimated from the oxygen consumption was 0.8 nm for all three particle sizes showing that the oxidation is size independent in the studied particle size range. The tridodecylamine ligand was exchanged for various long chain carboxylic acids and the oxidation was studied. While the carboxylic acids give a slower initial oxidation rate, the formed oxide layer does not inhibit further oxidation as effectively as in the case of tridodecylamine. TEM studies show that tridodecylamine capping leads to particles with a metal core surrounded by an oxide layer, while particles capped with long chain carboxylic acids form hollow cobalt oxide shells.

Preparation and properties of poly(ethylene glycol)-block-poly(acrylic acid)-coated cobalt nanocrystals

Reported in this paper are the preparation and properties of ɛ-Co nanocrystals coated by poly(ethylene glycol)-block-poly(acrylic acid) (PEG-b-PAA). These particles were prepared via the thermal decomposition of Co2(CO)8 at 185°C in 1,2-dichlorobenzene, in the presence of the surfactant PEG-b-PAA and the co-surfactant trioctylphosphine oxide. At a given initial Co2(CO)8 concentration, the size of the particles increased with increasing Co2(CO)8-to-PEG-b-PAA molar ratio, and could be tuned between ∼5 and ∼20nm. The size distribution of the particles narrowed as the Co2(CO)8 concentrations increased. The resultant particles were dispersible in a wide range of solvents, including chloroform, N,N-dimethylforamide, and water, which solubilized PEG. Magnetic measurements revealed that the particles possessed saturation magnetization close to that of bulk Co, suggesting high purity of the particles.

Re-investigation of the thermal decomposition of Co(CO)4SiCl3 adsorbed on silica

Evidence is provided that thermal decomposition of Co(CO)(4)SiCl(3) adsorbed on silica in a hydrogen atmosphere results in the formation of metallic cobalt nanoparticles covered with a Co(2)SiO(4)/CoO shell instead of cobalt silicide nanoparticles, as had been reported previously.

Synthesis and Exchange Bias in γ-Fe2O3/CoO and Reverse CoO/γ-Fe2O3 Binary Nanoparticles

γ-Fe2O3/CoO and reverse CoO/γ-Fe2O3 binary nanoparticles have been prepared by a facile, two-step chemical route through the thermal decomposition of Co(acac)2 and Fe(acac)3 in hot oleyl amine. The synthesis is based on heterogeneous nucleation and growth of the second component on seed nanoparticles of the first one. The binary particles have been characterized by X-ray diffraction, transmission electron microscopy, and cognate techniques. The heteroparticles are very stable in nonpolar organic solvents due the organic coating that is formed in situ. The presence of the antiferromagnetic CoO phase leads to unidirectional anisotropy, which is shown to originate from both magnetically compensated and uncompensated interfaces.

Colloidal Co nanoparticles supported on SiO2: Synthesis, characterization and catalytic properties for steam reforming of ethanol

Colloidal Co nanoparticles with sizes in the 3–8 nm range were obtained by thermal decomposition of Co2(CO)8 in the presence of ligands and impregnated on SiO2 to prepare SiO2-supported Co nanocatalysts. The catalysts showed activity for the steam reforming of ethanol with higher values for smaller Co particles. H2 adsorption results and Fourier transform infrared spectroscopy of adsorbed CO suggested that the fraction of accessible Co sites also depended on the synthesis conditions. Precipitation of the Co nanoparticles with methanol instead of ethanol before impregnation had a positive effect on the density of accessible Co sites to catalysis; similar result was verified by increasing the thermal treatment temperature under H2 flow before the reaction. Based on the distribution of products with temperature of reaction, a mechanism for steam reforming of ethanol on SiO2-supported Co nanocatalysts is suggested.

Optimized molecule supply from nozzle-based gas injection systems for focused electron- and ion-beam induced deposition and etching: simulation and experiment

We simulated and measured near-field distributions of molecules impinging on a flat substrate from tube-based nozzles with varying exit aperture geometries (straight, bevelled and doubly perforated). Simulations were performed with the test-particle Monte Carlo approach taking into account the Knudsen number (molecular/transient flow) at the nozzle exit. Distributions were measured via thermal decomposition of Co2(CO)8 molecules on a homogeneously heated substrate. For all geometries and Knudsen numbers a good match between the simulation and experiment was found. For the first time the maximum accessible molecule flux with respect to the total flux exiting the nozzle could be quantified: it is around 7% for a straight cylindrical tube, around 27% for a bevelled tube and around 32% for a doubly perforated tube, all nozzles being 300 µm distant from the substrate and having a 400 µm aperture. Optimum substrate–nozzle angles were determined and shadow effects quantified.

Porous Co3O4 Nanosheets with Extraordinarily High Discharge Capacity for Lithium Batteries

In this work, we report the simple solid-state formation of porous Co3O4 with a hexagonal sheetlike structure. The synthesis is based on controlled thermal oxidative decomposition and recrystallization of precursor Co(OH)2 hexagonal nanosheets. After thermal treatment, the hexagonal sheetlike morphology can be completely preserved, despite the fact that there is a volume contraction accompanying the process: Co(OH)2-->Co3O4. Because of the intrinsic crystal contraction, a highly porous structure of the product is simultaneously created. Importantly, when evaluated as electrode materials for lithium-ion batteries, the as-prepared porous Co3O4 nanosheets exhibit superior Li-battery performance with good cycle life and high capacity (1450 mAh g(-1)) due to their porous sheetlike structure and small size. As far as we know, the performance of the Co3O4-based anode materials for lithium batteries presented here is the best up to now. Considering the improved performance and cost-effective synthesis, the as-prepared porous Co3O4 nanosheets might be suitable as anode electrodes for next-generation lithium-ion batteries.

Synthesis of functional cobalt nanoparticles for catalytic applications. Use in asymmetric transfer hydrogenation of ketones

Long chain carboxylic acids functionalized at the ω position with chiral amino alcohol fragments have been used to stabilize cobalt nanoparticles prepared by thermal decomposition of Co2(CO)8. The first examples of chirally modified cobalt nanoparticles have been prepared in this manner and used as magnetically decantable ligands in the Ru-catalyzed asymmetric transfer hydrogenation of ketones.

Synthesis and Characterization of Co Nanoparticles by Solventless Thermal Decomposition

Co nanoparticles were synthesized via a solventless thermal decomposition of Co2+-oleate2. The crystalline structure is strongly affected by the thermal treatment of the Co nanoparticles. Further, the annealing also results in the decomposition of surfactant around Co particles. The size of nanoparticles was confirmed by transmission electron microscopy (TEM). The crystal structure of nanoparticles was characterized by X-ray diffraction pattern (XRD). The magnetic properties were characterized by vibrating sample magnetometer (VSM).

Catalytic activity of nanosized Co-Cu oxide systems in the deep oxidation of methane

The effect of the composition of nanosized catalysts, produced by thermal decomposition of Co(II) and Cu(II) formates deposited on ZrO2, SBA-15, and MCM-41, on their activity in the deep oxidation of methane was investigated. It was shown that the activity of the catalyst depends on the nature of the support and on the Co/Cu ratio.

Thermal decomposition of cobalt nitrato compounds: Preparation of anhydrous cobalt(II)nitrate and its characterisation by Infrared and Raman spectra

The thermal decomposition of Co(NO 3) 2·6H 2O ( 1) as well as that one of NO[Co(NO 3) 3] (Co(NO 3) 2·N 2O 4) ( 2) was followed by thermogravimetric (TG) measurements, X-ray recording and Raman and IR spectra. The stepwise decomposition reactions of 1 and 2 leading to anhydrous cobalt(II)nitrate ( 3) were established. In N 2 atmosphere, cobalt oxides are finally formed whereas in H 2/N 2 (10% H 2) cobalt metal is produced. Rapid heating of cobalt(II)nitrate hexahydrate causes melting (formation of a hydrate melt) and therefore side reactions in the hydrate melt by incoupled reactions and evolution/evaporation of different species as, e.g., HNO 3, NO 2, etc. In case of larger amounts in dense packing in the sample container, the formation of oxo(hydoxo)nitrates is possible at higher temperature. For 2, its thermal decomposition to 3 was followed and its decomposition mechanism is proposed.

Phase- and Size-Controlled Synthesis of Hexagonal and Cubic CoO Nanocrystals

Highly crystalline, phase- and size-controlled CoO nanocrystals of hexagonal and cubic phases have been prepared by thermal decomposition of Co(acac)3 in oleylamine under an inert atmosphere. Kinetic and thermodynamic control for the precursor formation leads to two different seeds of hexagonal and cubic phases at higher temperatures. The crystal size of both CoO phases can be easily manipulated by changing the precursor concentration and reaction temperature.

Ultraviolet absorption cross-sections of hot carbon dioxide

The temperature-dependent ultraviolet absorption cross-section for CO 2 has been measured in shock-heated gases between 1500 and 4500 K at 216.5, 244, 266, and 306 nm. Continuous-wave lasers provide the spectral brightness to enable precise time-resolved measurements with the microsecond time-response needed to monitor thermal decomposition of CO 2 at temperatures above 3000 K. The photophysics of the highly temperature dependent cross-section is discussed. The new data allows the extension of CO 2 absorption-based temperature sensing methods to higher temperatures, such as those found in behind detonation waves.