Nanocrystalline Cobalt Oxide Research Articles

Hydrothermal synthesis of carbon nanotube/cobalt oxide core-shell one-dimensional nanocomposite and application as an anode material for lithium-ion batteries

Carbon nanotube/cobalt oxide core-shell one-dimensional nanostructures were prepared via a hydrothermal synthesis method, in which nanosize cobalt oxide crystals were homogeneously coated on the surface of carbon nanotubes. The morphologies and crystal structures of the as-prepared core-shell nanocomposites were analysed by X-ray diffraction, field emission gun scanning electron microscopy, and transmission electron microscopy. When applied as anodes in lithium-ion cells, carbon nanotube/cobalt oxide core-shell nanostructures exhibited an initial lithium storage capacity of 1250 mAh/g and a stable capacity of 530 mAh/g over 100 cycles. The good electrochemical performance could be attributed to the nanocrystalline cobalt oxide and the unique core-shell one-dimensional nanostructures.

Total oxidation of propane using nanocrystalline cobalt oxide and supported cobalt oxide catalysts

Supported and unsupported nanocrystalline cobalt oxides have been shown to be extremely efficient catalysts for the total oxidation of propane. Total conversion with a high stability has been achieved at reaction temperatures as low as 250°C. In the present work, a comparison between the catalytic performance of bulk and alumina-supported nanocrystalline cobalt oxide catalysts has been made. The influence of crystallite size, nature of the support (alpha, gamma and mesoporous alumina) and cobalt loading, has been probed. Unsupported cobalt oxide catalysts were more active than any supported cobalt oxide catalysts. The catalytic activity was mainly dependent on the crystallite size, decreasing with an increase in the crystallite size. Whilst the TOF of supported catalysts increases with both a decrease in the surface area of the support and an increase of the cobalt content. Only those catalysts with a cobalt content of 50wt% achieve a catalytic activity per cobalt atom similar to that of unsupported Co3O4 prepared under similar conditions. High surface area alumina was shown to be a less efficient support especially at low Co-loadings due to the dispersion of cobalt on the surface leading to the formation of inactive Co–O–Al species. The low surface area support (α-Al2O3) presents a low capacity to isolate the cobalt oxide species resulting in a lower concentration of inactive Co–O–Al species and, therefore, the highest activity among supported catalysts. In conclusion, two parameters seem to determine the catalytic activity of nanocrystalline cobalt oxide: these are the presence of inactive Co–Al bonds (prevalent in supported catalysts) and also the size of the active Co3O4 particles.

A mechanistic study of the low-temperature conversion of carbon monoxide to carbon dioxide over a cobalt oxide catalyst

A nanocrystalline cobalt oxide (Co 3O 4)-based catalyst formed by heating a basic cobalt(II) carbonate precursor in air at 250–300 °C has been shown to exhibit much greater catalytic activity than Co 3O 4 calcined at higher temperatures. In a highly exothermic reaction, the properly calcined catalyst rapidly oxidizes carbon monoxide to carbon dioxide at room temperature. X-ray diffraction, X-ray photoelectron spectrometry, Brunauer–Emmett–Teller surface area measurements, and two FT-IR techniques were used to investigate the mechanism of the CO oxidation reaction. Diffuse reflection (DR) infrared spectrometry of the catalyst was used to monitor the gases adsorbed on the catalyst surface. The observation of a CO band at 2006 cm −1 indicates that CO is adsorbed onto cobalt atoms in a low oxidation state. The highest catalytic activity appears to be achieved when a specific ratio of Co(II) to Co(III) is found on the surface and the particle size is small (i.e., the surface area is large). Poisoning of the catalyst is evidenced in the DR spectra by the geminal adsorption of two CO molecules onto a cobalt atom in a high oxidation state, giving rise to a doublet at ∼2180 cm −1. A strong band at 2343 cm −1 indicates that CO 2 is physisorbed onto the catalyst when it is poisoned. A unique ultra-rapid scanning FT-IR spectrometer was used to measure the concentration of the CO 2 formed, as well as that of the unreacted CO within 5 ms after the gas was passed through the catalyst. The spectra indicate that CO 2 is formed in a vibrationally excited state.

La 0.67Ce 0.03Sr 0.3MnO 3-coupled microwave assisted ultra-fast synthesis of nanocrystalline Cobalt oxide and Bismuth oxide

Bismuth hydroxide and Cobalt hydroxide gels were freshly prepared by adding aqueous sodium hydroxide to their corresponding nitrates under basic conditions. Then they were oven dried at 373 K and found to be amorphous in X-ray diffraction (XRD) study. They crystallized into their respective oxides by microwave irradiation (2.45 GHz) in merely 2 min using La 0.67Ce 0.03Sr 0.3MnO 3 (LCSMO) as couplant in a microwave domestic oven (~ 100 W). This is the lowest temperature treatment and synthesis time so far reported in the literature for the formation of these systems. Formation of nanocrystallites of Bi 2O 3 (10 nm) and Co 3O 4 (15 nm) has been confirmed by XRD. Normally these hydroxides produce oxides only on heating at temperature > 673 K or digesting them at 373 K for 4 – 6 hours as reported by us earlier. Microwave assisted heating proves to be a novel technology whose applications can be carefully harnessed due to its unique effects compared to the conventional heating, such as rapid volumetric heating, shortened reaction time and energy saving.

Fabrication of nanocrystalline cobalt oxide via sol–gel coating

Nanocrystalline cobalt oxide thin films were fabricated by sol–gel processing method. The effect of cobalt salt amount in sol–gel mixture on film properties was investigated by means of Raman spectroscopy and atomic force microscopy. Micropatterns of these sol–gel mixtures were fabricated by spin coating followed by a lift-off method. It is generally known that sol–gel processed films are difficult to etch or remove by chemical and plasma techniques. In this novel process, cobalt oxide microstructures could be fabricated by transformation of pre-fabricated nanocrystalline cobalt oxide particles in a sol–gel process. Also, the growth of carbon nanotubes on fabricated cobalt oxide films was investigated. It was found that different size multiwall carbon nanotubes could be grown on the cobalt oxide films depending on the concentration of cobalt salt in sol–gel mixtures.

Complete oxidation of short chain alkanes using a nanocrystalline cobalt oxide catalyst

Exceptionally high activity for the complete oxidation of propane is reported for the first time using a nanocrystalline cobalt oxide catalyst. The catalyst shows stable activity for prolonged time on stream and when the reaction temperature is cycled. Furthermore, the nanocrystalline catalyst demonstrates considerably higher activity than an alumina supported palladium catalyst, which is recognised as one of the most active reported. The high activity of the cobalt oxide catalyst is associated with the nanocrystalline nature of the material, which gives rise to new catalytically active surface sites. A broader comparison with other reported high activity catalysts emphasises the high efficacy of nanocrystalline cobalt oxide for total oxidation and demonstrates that it has significant potential for important applications, such as control of emissions from liquid petroleum gas powered vehicles and alkane volatile organic emissions from stationary sources.

Nanocrystalline cobalt oxide immobilized on titanium dioxide nanoparticles for the heterogeneous activation of peroxymonosulfate

Recently, sulfate radical-based advanced oxidation technologies have shown significant implications for environmental remediation to decompose water pollutants. In this study, we evaluated the performance of heterogeneous activation of peroxymonosulfate (PMS) to generate sulfate radicals using cobalt catalyst immobilized on titanium dioxide nanoparticles (Co/TiO2). The Co/TiO2 catalyst was prepared via an incipient wetness impregnation method employing Degussa P-25 TiO2 and Co(NO3)·6H2O. The activity of Co/TiO2 system was compared with those of Co(NO3)2 solution for homogeneous PMS activation and neat Co3O4 for heterogeneous PMS activation. More emphasis was given to the effect of cobalt loading and heat treatment on the physicochemical properties of Co/TiO2 and cobalt leaching. The results showed that heat treatment of Co/TiO2 at 500°C, where cobalt existed as Co3O4, induced negligible Co leaching and enhanced catalytic activity to decompose 2,4-dichlorophenol. The Co/TiO2 catalyst at Co/Ti molar ratio of 0.1 showed the highest activity via heterogeneous PMS activation. On the other hand, Co/TiO2 catalysts with Co/Ti molar ratio of above 0.2 exhibited rather much lower activity which was initiated predominantly via a homogeneous pathway from leached cobalt, although they contained considerable amounts of Co3O4. The formation of CoOH complexes at the surface of Co/TiO2 nanoparticles, due to the ability of TiO2 to dissociate H2O for the formation of surface hydroxyl groups, was proposed to facilitate the heterogeneous PMS activation. However, high cobalt loading covering the TiO2 surface diminished the beneficial role of TiO2 due to the reduction in the concentration of surface hydroxyl groups and thus decreased the heterogeneous PMS activation. The activity of Co3O4 in Co/TiO2 catalysts was much higher than that of neat Co3O4 due to the presence of surface hydroxyl groups and uniform distribution of well-defined 10−15nm nanocrystalline Co3O4 particles at the surface of 30−40nm TiO2 nanoparticles.

Nanocrystalline cobalt oxide: a catalyst for selective alkane oxidation under ambient conditions

Nanocrystalline cobalt oxide activates propane, yielding propene at room temperature and pressure.

Hierachically porous nanocrystalline cobalt oxide monoliths through nanocasting.

Nanocrystalline cobalt oxide, Co(3)O(4), monoliths exhibiting hierarchical bimoidal porosity have been prepared by nanocasting of porous silica monoliths.

Fabrication and characterization of nanocrystalline cobalt oxide thin films

A simple solution growth route has been employed to synthesize nanocrystalline cobalt oxide thin films on glass substrates. The obtained films were characterized by X-ray diffraction and FTIR spectroscopy. The as-deposited films were identified as a mixture of different phases of Co(OH) 2, while the annealed ones as Co 3O 4. The absorption of the annealed films gradually decreases with an increase of the wavelength in the 310–820 nm region. Upon annealing, the absorption coefficient decreases. The calculated band gap energy from optical absorption data for annealed films is 2.2 eV. The as-deposited thin films are dielectric, while the post-deposition heat-treated ones are characterized by resistivity of several MΩs/cm 2 at room temperature.