Substrate assisted electrochemical deposition of patterned cobalt thin films

The patterned Co layers deposited on the scratched Cu surfaces were investigated with the use of the scanning electron microscopy. Patterned cobalt thin films were electrochemically deposited from the cobalt sulfate bath at room temperature. Pattering of cobalt was carried out by simple means of substrate scratching. Gentle scratching induces a direct pattering of cobalt from vertical to horizontal. The prepared pattered films were characterized for their structural, surface morphological and compositional properties by means of X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. X-ray diffraction studies reveal that the films are of cobalt. From the SEM images fabrication of patterns of cobalt is apparent. This work demonstrates a novel approach for obtaining patterned cobalt for many technological applications.     

Soft‐Chemical Exfoliation Route to Layered Cobalt Oxide Monolayers and Its Application for Film Deposition and Nanoparticle Synthesis

A colloidal suspension of exfoliated, layered cobalt oxide nanosheets has been synthesized through the intercalation of quaternary tetramethylammonium ions into protonated lithium cobalt oxide. According to atomic force microscopy, exfoliated nanosheets of layered cobalt oxide show a plateau‐like height profile with nanometer‐level height, underscoring the formation of unilamellar 2D nanosheets. The exfoliation of layered cobalt oxide was cross‐confirmed by X‐ray diffraction, UV/Vis spectroscopy, and transmission electron microscopy. The maintenance of the hexagonal in‐plane structure of the cobalt oxide lattice after the exfoliation process was evidenced by selected‐area electron diffraction and Co K‐edge X‐ray absorption near‐edge structure analysis. The zeta‐potential measurements clearly demonstrated the negative surface charge of cobalt oxide nanosheets. Adopting the nanosheets of layered cobalt oxide as a precursor, we were able to prepare the monodisperse CoO nanocrystals with a particle size of ≈10 nm as well as the heterolayered film composed of cobalt oxide monolayer and polycation.     

Preparation and characterization of a Mexican organo clinoptilolite-heulandite mineral and its evaluation for the sorption of cadmium and cobalt

The preparation and characterization of a Mexican organo clinoptilolite-heulandite mineral as well as the evaluation of its sorption properties for cadmium and cobalt are presented. The mineral was modified with different concentrations of hexadecyltrimethyl-ammonium bromide (HDTMA), the resulting materials were characterized by electron microscopy, IR spectroscopy, BET surface analysis, X-ray diffraction and their cation exchange capacities were determined. The cobalt and cadmium uptake was carried out in different concentrations. Neutron activation was used to measure the sorption of cobalt and cadmium. Organo zeolitic mineral samples were obtained with different surface characteristics compared with the original material and it was found that the retention of cobalt and cadmium by the organo zeolite diminishes due to the presence of HDTMA.     

Nitrogen-doped carbon nanotubes: growth, mechanism and structure

Nitrogen-doped bamboo-structured carbon nanotubes have been successfully grown using a series of cobalt/molybdenum catalysts. The morphology and structure of the nanotubes were analysed by transmission electron microscopy and Raman spectroscopy. The level of nitrogen doping, as determined by X-ray photoelectron spectroscopy, was found to range between 0.5 to 2.5 at.%. The growth of bamboo-structured nanotubes in the presence of nitrogen, in preference to single-walled and multi-walled nanotubes, was due to the greater binding energy of nitrogen for cobalt in the catalyst compared to the binding strength of carbon to cobalt, as determined by density functional theory.     

The effect of cobalt addition on sintering and microstructural behaviour of silver–tungsten (Ag–W) composite

The present investigation has been revealed that homogeneous silver-tungsten (Ag–W) composite powders doped with cobalt as sinter aid can be produced by the two-stage reduction of co-precipitated tungstate. The sintering of the powders has been studied using dilatometry and the results showed that the critical level for activated sintering is of the order of 0.3 mass percent cobalt with respect to the tungsten content of the compact powder. This critical level is equivalent to approximately six to seven atomic layer coverage of the tungsten particles by cobalt. The levels of cobalt addition above the critical amount leads to the formation of cobalt tungsten (CoW₃) intermetallic compound precipitates, which become trapped within the silver phase in the sintered composite material. Microstructural evaluation of sintered specimens has been carried out using optical and electron microscopy. Transmission electron microscopy results revealed the neck formation between adjacent tungsten particles along with the presence of silver around the tungsten particles. Energy dispersive X-ray (EDX) analysis also confirmed that amounts of cobalt was 0.3 mass percent, in the region containing the silver at the tungsten particle interface which agreed with the level of activated sintering.     

Synthesis of cobalt-containing nanoparticles by cobalt formate thermolysis in hydrocarbon oil without stabilizing ligands

A simple and available method is proposed for the synthesis of cobalt-containing nanoparticles. This method comprises cobalt formate thermolysis in hydrocarbon oil without extra stabilizing ligands. The size, composition, and structure of the nanoparticles are determined by transmission electron microscopy, X-ray powder diffraction, and electron diffraction. The average particle size is 10–14 nm. The major components are cobalt oxides CoO and Co₃O₄. Apart from these oxides, the particles contain minor metallic cobalt.     

Light‐Triggered Release of Trapped Charges in Molecular Assemblies

We demonstrate the mediation of charge transport and release in thin films and devices by shifting the redox properties of layers of metal complexes by light. The nanoscale surface arrangement of both photo‐ and electrochemically‐active components is essential for the function of the thin films. Layers of well‐defined ruthenium complexes on indium‐tin‐oxide electrodes provide electron‐transport channels that allow the electrochemical addressing of layers of isostructural cobalt complexes. These cobalt complexes are electrochemically inactive when assembled directly on transparent metal‐oxide electrodes. The interlayer of ruthenium complexes on such electrodes allows irreversible oxidation of the cobalt complexes. However, shifting the redox properties of the ruthenium complexes by excitation with light opens up an electron‐transport channel to reduce the cobalt complexes; hence releasing the trapped positive charges.     

Synthesis and characterisation of cobalt hydroxy carbonate Co2CO3(OH)2 nanomaterials

In an attempt to make nanofibres based upon cobalt oxides, a novel compound hydrated cobalt hydroxy carbonate was formed. This compound is related to the minerals of the rosasite mineral group. X-ray diffraction (XRD) showed that the formed compound was a cobalt hydroxy carbonate, and scanning electron microscopy (SEM) displayed bundles of fibres on the micron scale in length and nanoscale in width. The morphology was compared with that of the rosasite mineral group. X-ray photoelectron spectroscopy (XPS) proved two bond energies for cobalt and three for oxygen in the compound. The compound was characterised by vibrational spectroscopy and the spectra related to minerals of the rosasite mineral group. The stability of the synthetic mineral was limited to temperatures below 200°C.     

多级孔ZSM-5负载的钴催化剂的费-托合成催化性能

采用水蒸气辅助转晶(SAC)法合成了粒径均一(180 nm)的纳米ZSM-5颗粒,颗粒间堆积形成大量的开放介孔,与ZSM-5的微孔共同形成多级孔结构。以该材料为载体采用满孔浸渍法制备了负载量为15%(质量分数)的钴催化剂。采用XRD、SEM、TEM、N_2物理吸附-脱附等表征技术对多级孔ZSM-5载体及其负载催化剂的形貌和结构进行了表征,并对催化剂的费-托合成催化性能进行了测试。结果表明,相比于大颗粒的ZSM-5和商业ZSM-5,多级孔ZSM-5负载的钴催化剂的费-托合成活性最高,CH_4选择性最低,C_(5-20)产物的选择性高达68.9%,这归因于多级孔ZSM-5的介孔孔道有效地促进反应过程中产物的传质扩散以及ZSM-5微孔骨架上的酸中心促进了长链烃产物的二次加氢裂解。     

Magnetic characteristics of LnCo5ThCo5 pseudobinary systems

Magnetic characteristics of Ln_1?xTh_xCo₅ ternaries, with Ln = Gd, Ho or Er, are reported. Th is introduced into the lattice in an effort to achieve ferromagnetic coupling. It is observed that the antiferromagnetic LnCo coupling, which exists in the LnCo₅ binaries, also persists in the ternaries. The cobalt moment and Curie temperature are reduced as the Th content of the sample is increased. The decreased cobalt moment is ascribed to electron transfer from Th to the cobalt d-shell. Failure to achieve ferromagnetism in the ternaries is ascribed to electron capture by cobalt, which prevents a rise in electron concentration as Th replaces Ln in the lattice.     

Effect of polar solvents on the optical properties of water-dispersible thiol-capped cobalt nanoparticles

We were able to stabilize cobalt nanoparticles dispersible in water by optimizing the synthetic procedure using small polar thiol containing compounds as the capping agents. The nanoparticles were found to be spherical. The optical properties of the cobalt nanoparticles were investigated by monitoring the changes in the surface plasmon resonance (SPR) spectrum in various polar solvents. The extent of solvent dependence of the SPR spectrum was found to be dependent on the nature of the capping agent, the size of the cobalt nanoparticles, as well as the nature of the solvent. The Drude model was applicable for the particles capped with mercaptopropionic acid, while the effect of variations in the free electron density in the particles at different solvents became predominant in the nanoparticles capped with mercaptoethanol. The absorption spectra of the Co nanoparticles were simulated with the help of the classical Mie theory, and the results supported the effect of free electron density due to different capping agents on the spectra of the particles.     

Facile Non‐enzymatic Lactic Acid Sensor Based on Cobalt Oxide Nanostructures

In this study, we have investigated the effect of counter anions on the morphology of cobalt oxide nanostructures. The nanostructures of cobalt oxide are prepared by a low temperature aqueous chemical growth method. The morphology of cobalt oxide nanostructure material was investigated by scanning electron microscopy and the crystalline structure was studied by powder X‐ray diffraction technique. The cobalt oxide nanostructures exhibit the nanowire, lump, bundle of the nanowire and flower‐like morphologies. The XRD study has revealed a cubic phase of cobalt oxide nanostructures. The electro‐catalytic properties of cobalt oxide nanostructures were explored through cyclic voltammetry and amperometric techniques by sensing of lactic acid in the alkaline media. The cobalt oxide nanostructures prepared from cobalt nitrate have shown a well‐resolved redox peak. The proposed mechanism for the non‐enzymatic lactic acid sensor is elucidated by considering the morphology and cyclic voltammetry response. The limit of detection for the sensor was found to be 0.006 mM and it exhibits a linear range from 0.05–3 mM of lactic acid as shown by cyclic voltammetry. The amperometric response has shown the excellent current‐concentration response and the linear range of sensor was found to be 0.1 mM to 5.5 mM. The lactic acid sensor is stable, selective and can be used for practical applications. This study provides an excellent alternative analytical tool for the determination of lactic acid.     

Effect of catalyst confinement and pore size on Fischer-Tropsch synthesis over cobalt supported on carbon nanotubes

This paper studies the impact of structure of cobalt catalysts supported on carbon nanotubes(CNT) on the activity and product selectivity of Fischer-Tropsch synthesis(FTS) reaction.Three types of CNT with average pore sizes of 5,11,and 17 nm were used as the supports.The catalysts were prepared by selectively impregnating cobalt nanoparticles either inside or outside CNT.The TPR results indicated that the catalyst with Co particles inside CNT was easier to be reduced than those outside CNT,and the reducibility of cobalt oxide particles inside the CNT decreased with the cobalt oxide particle size increasing.The activity of the catalyst with Co inside CNT was higher than that of catalysts with Co particles outside CNT.Smaller CNT pore size also appears to enhance the catalyst reduction and FTS activity due to the little interaction between cobalt oxide with carbon and the enhanced electron shift on the non-planar carbon tube surface.     

Aerobic Epoxidation of Alkenes Catalysed by Cobalt(II) 1,1,1,5,5,5-Hexafluoroacetylacetonate or Cobalt(II) Benzoylacetonate

The aerobic epoxidation of terminal or electron deficient alkenes with an aldehyde does not proceed with cobalt(II) acetylacetonate but goes to completion with the cobalt(II) benzoylacetonate and cobalt(II) 1,1,1,5,5,5-hexafluoroacetylacetonate complexes.     

Syntheses and electrochemical behaviour of novel dmit or dmio (dithiolato) cobalt(iii) complexes with a η5-cyclopentadienyl or η5-pentamethylcyclopentadienyl ring

Four novel cobalt(III) complexes with a cyclopentadienyl or pentamethylcyclopentadienyl ring and dmit or dmio ligands were synthesized, and their electrochemical behaviour was investigated. All these complexes exhibited three one-electron transfer steps: one reduction and two oxidation steps. In addition, a novel organosulphur compound was afforded by electrochemical oxidation of dmit cobalt complex. Thus, these complexes may have considerable synthetic potential as precursors for electron reservoirs and organosulphur compounds.     

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.     

PHOTOPRODUCTION OF HYDROGEN FROM LINKED CHROMOPHORES

Abstract On irradiation of solutions of anthryl-substituted cobalt(III) cage complexes, [(l-(anthryl-9-methylamino)-8-methyl-3,6,10,13,16,19-hexaazabicyclo [6.6.6] eicosane) cobalt(III)]³⁺ or [(l-(4-an-thryl-9)-3-aza-butyl-l-amino)-8-methyl-3,6,10,13,16,19-hexaazabicyclo [6.6.6] eicosane)cobalt (III)]³* in the presence of ethylenediaminetetraacetic acid and platinum catalysts hydrogen was produced. These complexes act as coupled photosensitizers (anthracene moiety) and electron relays (cobalt cage) to produce H₂ via energy trapping and intramolecular electron transfer initially. The intensity of fluorescence and the photochemical reactivity favour the latter complex and the excited singlet state of the anthracene chromophore is invoked as the intermediate state leading to the reduction of Co(III) to Co(II).     

Effects of Substituents on the Electrocatalytic Activity of Cobalt Phthalocyanines when Conjugated to Graphene Quantum Dots

We report on the π–π interactions between graphene quantum dots (GQDs) and the following cobalt phthalocyanine derivatives: cobalt monocarboxyphenoxy phthalocyanine (complex 1 ), cobalt tetracarboxyphenoxyphthalocyanine (complex 2 ), and cobalt tetraaminophenoxy phthalocyanine (complex 3 ). The conjugates (conj) with GQDs are represented as 1 @GQDs(conj), 2 @GQDs(conj) and 3 @GQDs(conj), respectively. The resulting phthalocyanine/GQDs conjugates were adsorbed on containing a glassy carbon electrode (GCE) using the drop and dry method. We explore the electrochemical properties of phthalocyanines functionalized with both electron withdrawing groups and electron donating groups when non‐covalently linked to the π‐electron rich graphene quantum dots. GCE/ 3, GCE/ 2 @GQDs(conj) and GCE/ 1 @GQDs(conj) had the lowest limits of detection (LOD). Sequentially modified electrodes showed less favourable detection limits compared to the conjugates.     

含Fe、Co、Ni的LDHs为催化剂前体生长碳纳米管

分别以具有相似Fe、Co、Ni含量的层状双金属氢氧化物（LDHs）为催化剂前体,用化学气相沉积的方法生长碳纳米管（CNTs）。 催化剂由LDHs焙烧还原得到。 通过X射线衍射（XRD）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）及拉曼光谱（Raman）测试技术对LDHs及其焙烧产物的结构、CNTs的形貌和结构进行了研究。 结果表明,3种催化剂生长的CNTs均为多壁结构;其中Co催化剂活性较低,生长CNTs的管径较细、石墨化程度较高;Ni催化剂的活性较高,生长CNTs的密度较大、管壁较厚、石墨化程度较差;Fe催化剂的活性介于Co和Ni之间。 催化剂活性及CNTs的密度可以由生长CNTs的结构来解释。     

Synthesis and crystal structure of a rare square-planar Co(II) complex of a hydroxyamidinate ligand

Novel hydroxyamidinate complexes of cobalt(II) are presented, together with their electrochemical and spectroscopic properties. An unusual d(7) square-planar coordination around the cobalt(II) center exists and was confirmed by chemical oxidation to its Co(III) species. The Co(II) complex is difficult to reduce, but its facile oxidation suggests that it may be useful as an electron donor in photoredox reactions.