A facile aqueous phase synthesis of cobalt microspheres at room temperature

Solvent dependent morphology and 59Co internal field NMR study of Co-aggregates synthesized by a wet chemical method

Different shapes of Co-aggregates were synthesized via reduction of a Co salt (CoCl2·6H2O) by chemical precipitation using glycerol, ethylene glycol and ethanol as solvents. The effect of solvent on the morphology, fcc or hcp phase-content and the magnetic properties of the synthesized samples were investigated. The Co-aggregates synthesized using glycerol have a dense spherical shape and high saturation magnetization (MS), whereas ethylene glycol leads to formation of flower-shaped spherical aggregates through loose packing of smaller plate-like particles which have a moderate MS value. When ethanol was used as a solvent, a dendritic (leaf like)-shape of the aggregates with the lowest MS value was obtained. The formation of the obtained morphology of the aggregates was explained based on the size of the solvent molecule, the viscosity of the solvent and the number of polar groups (-OH) present in the solvent molecules. The magnetic domain state and domain wall dynamics of all the Co-samples were investigated using 59Co Internal Field Nuclear Magnetic Resonance (IFNMR) spectroscopy at RT and at 77 K. Through the IFNMR spectroscopy, the presence of gain boundaries, single domain particles and multi-domain particles/aggregates with domain walls associated with fcc and hcp phases were identified and quantified. We observed that the use of ethanol facilitates formation of a higher amount of hcp phase in the sample than the use of glycerol or ethylene glycol.

Environmental-Friendly and Facile Synthesis of Co3O4 Nanowires and Their Promising Application with Graphene in Lithium-Ion Batteries

In this work, we developed an eco-friendly strategy for preparing Co₃O₄ nanowires. The process consisted of two steps: controllable synthesis of metal cobalt nanowires followed by a facile air-oxidization step. The 1D nanowire structure with a high aspect ratio was easily achieved via a magnetic-field-assisted self-assembly of cobalt ion complexes during reduction. After air-calcinations, the Co₃O₄ nanowires were prepared in large scale and ready to be used as the anode material for lithium-ion batteries. The Co₃O₄ nanowires, which possessed a length ranging from 3 to 8 μm with the aspect ratio more than 15, exhibited a reversible lithium storage capacity up to ~ 790 mAh/g when using a small amount of defect-free graphene flakes as conductive additives. The superior electrochemical performances were ascribable to the synergistic "flat-on" effect between the 1D nanowires and the 2D graphene. Therefore, the Co₃O₄ nanowire/graphene composite holds promising application for lithium-ion batteries.

Preparation of broccoli-like ferromagnetic cobalt microstructures with superior coercivity via an aqueous reduction strategy

Controlled synthesis of novel hierarchical cobalt (Co) microstructures with extraordinary magnetic performances is a promising strategy for the development of magnetic metals for industrial purposes.