Hierarchical Cobalt Research Articles

Synthesis of three-dimensional hierarchical cobalt hydroxide microstructures

α-Co(OH)2 with three-dimensional (3-D) structures was prepared by a simple hydrothermal method. It was found that the amount of cetyltrimethylammonium bromide (CTAB), the pH value, and the reaction time all had an important influence on the formation of this morphology. The products were characterized by X-ray diffraction, energy-dispersive X-ray analysis, and scanning electron microscopy. A possible mechanism of the formation of the 3-D microstructures of β-Co(OH)2 was proposed.

Hierarchical porous cobalt oxide array films prepared by electrodeposition through polystyrene sphere template and their applications for lithium ion batteries

Hierarchical porous cobalt oxide (Co 3O 4) array films are successfully prepared by electrodeposition through polystyrene sphere monolayer template. The as-prepared Co 3O 4 array films exhibit three typical porous structures from non-close-packed bowl array to close-packed bowl array and hierarchical two layer array structures. These Co 3O 4 array films have a hierarchical porous structure, in which the skeleton is composed of ordered arrays possessing nanoporous walls. A possible growth mechanism of porous Co 3O 4 array films is proposed. As anodes for Li ion batteries, the as-prepared Co 3O 4 array films exhibit quite good cycle life and high capacity. The first discharge capacity for the three Co 3O 4 array films is 1511, 1475, 1463 mAh g −1, respectively, and their initial coulombic efficiencies are as high as 72%. The specific capacity after 50 cycles for the three electrodes is 712, 665 and 640 mAh g −1 at 1 C rate, corresponding to 80%, 75%, 72% of the theoretical value (890 mAh g −1), respectively.

A facile route to prepare hierarchical magnetic cobalt–silica hollow nanospheres with tunable shell thickness

Magnetic nanoshells composed of close-packed cobalt–silica nanoparticles have been successfully fabricated on silica spheres. The synthesis is facile and no high pressure, high temperature, or other severe reaction conditions were required. TEM images showed that two batches of the hollow-structured products have a good spherical morphology with an average diameter of 380 and 550 nm, respectively. The surface area and magnetic properties of cobalt–silica nanoshells are measured. By varying the times of the precipitation procedure, the shell thickness is successfully controlled within the 5–30 nm range and each time of procedure might increase the thickness about 5 nm. It is expected that the in situ reaction method can be extended to the synthesis of other hollow metal spheres. The prepared microcapsule with controllable shell thickness and interspaces has the potential to be used for controlled release applications.

Structure and magnetic properties of hierarchical cobalt dendrites

Hierarchical cobalt dendrites with ferromagnetic properties have been synthesized by using the in situ produced cobalt carbonate together with cobalt oxalate as precursor and hypophosphite (H 2PO 2 −) as the reducing agent in mixed solutions at 160 °C. XRD and SAED patterns reveal that the as-prepared cobalt dendrites have a single-crystalline structure with a [001] growth orientation. The shape evolution of the hierarchical cobalt dendrites was investigated.

Hierarchical Three-Dimensional Cobalt Phosphate Microarchitectures: Large-Scale Solvothermal Synthesis, Characterization, and Magnetic and Microwave Absorption Properties

Novel hierarchical cobalt phosphate (alpha- and beta-Co2P2O7) and cobalt hydrogen phosphate hydroxide [Co-11(HPO3)(8)(OH)(6)] three-dimensional (3D) architectures with different morphologies were synthesized under a solvothemal condition. The form and shape of cobalt phosphate can be readily tuned by adjusting experimental parameters of the reaction system. The novel hierarchical alpha-CO2P2O7 microcrystals with basketry-like microstructures were obtained with a molar ratio of Co2+/H3PO4/CH3NH2/HO(CH2)(2)0OH of 1:1.2:1:108, the reaction temperature of 180 degrees C, and the reaction time of 5 days; dumbbell-like beta-Co2P2O7 microspheres were formed with the same reaction temperature and time but the molar ratio of 1: 1.2:1:54, and Co-11(HPO3)(8)(OH)(6) with peony-like nanostructures was prepared with the same molar ratio and reaction time as beta-Co2P2O7 but the reaction temperature of 120 degrees C. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectra (FT-IR) technologies, a Quantum Design superconducting quantum interference device (SQUID) magnetometer, and a network analyzer. The formation mechanism of cobalt phosphate microstructures was investigated in detail.

Synthesis of Micrometer-Sized Nanostructured Magnesium Oxide and Its High Catalytic Activity in the Claisen−Schmidt Condensation Reaction.

Micrometer-sized nanostructured flowerlike MgO nanostructures were synthesized by an ethylene-glycol-mediated self-assembly process. The synthesized samples were studied systematically by X-ray powder diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Fourier-transform IR, and energy-dispersive X-ray analysis. The results show that the flowerlike MgO have uniform morphologies with an average diameter of 600 nm for micrometer-sized spheres and 16 nm for the ribbonlike nano building blocks. Compared to hierarchical structured cobalt oxide, a new morphology evolution process is observed for the MgO precursor, indicating a new kinetic control mechanism for morphology evolution. Because of its micrometer-sized nanostructure, the as-obtained MgO shows high catalytic activity, high stability, and easy recovery for the Claisen−Schmidt condensation between benzaldehyde and acetophenone.

Synthesis of Micrometer-Sized Nanostructured Magnesium Oxide and Its High Catalytic Activity in the Claisen−Schmidt Condensation Reaction

Micrometer-sized nanostructured flowerlike MgO nanostructures were synthesized by an ethylene-glycol-mediated self-assembly process. The synthesized samples were studied systematically by X-ray powder diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Fourier-transform IR, and energy-dispersive X-ray analysis. The results show that the flowerlike MgO have uniform morphologies with an average diameter of 600 nm for micrometer-sized spheres and 16 nm for the ribbonlike nano building blocks. Compared to hierarchical structured cobalt oxide, a new morphology evolution process is observed for the MgO precursor, indicating a new kinetic control mechanism for morphology evolution. Because of its micrometer-sized nanostructure, the as-obtained MgO shows high catalytic activity, high stability, and easy recovery for the Claisen−Schmidt condensation between benzaldehyde and acetophenone.