Controlled Synthesis Of Cobalt Oxide Nanocrystals Self-assembly

The spinel structure CO3O4 is an important magnetic p-type semiconductor known by its applications in many fields such as heterogeneous catalysts, anode material in Li-ion rechargeable batteries, solid-state sensors, electrochromic devices, solar energy absorbers, pigments, and so on. The controlled synthesis of nanocrystals with a single size and shape is important for constructing nanostructured materials by bottom-to-top techniques. Liquid-phase synthesis is a good approach for preparation of inorganic nanoparticles. The controlled synthesis of metal oxide nanocrystals through liquid-phase chemistry routes are investigated in the paper. The contents include designing a novel route for the control over the nucleation and growth of nanocrystals, the investigation of the controlling mechanism for the size, shape and dispersibility of nanocrystals. Monodispersed CO3O4 nanocrystals with different size are synthesized by controlling reaction conditions in the solvothermal method, which can be self-assembled into 1D, 2D, 3D superstructure on the copper grid. 1. A solubility-controlled nucleation and growth of nanocrystals A metathetical reaction between cobalt nitrate and sodium dodecyl benzene-sulfonate (SDBS) in long-carbon-chain alcohol occurs to precipitate sodium nitrate. When a polar solvent such as water, methanol or dimethylsulfoxide (DMSO) is added sodium nitrate is re-dissolved, and the solubility of the precipitated sodium nitrate is altered by changing the content of the polar solvent in the system. As a result the thermodynamic and kinetics of the thermo-decomposition reaction of cobalt nitrate can be controlled by controlling the solubility of the precipitated sodium nitrate. Based on LaMer's theory of burst nucleation-slow growth of colloid particles, the separation between nucleation and growth of nanocrystals are accomplished when the solubility of the precipitated sodium nitrate is limited at an appropriated value, and monodispersed nanocrystals with a particle size of 2nm, 2.5nm and 4.7nm are obtained. In order to reveal the solubility-controlled mechanism for nucleation and growth, XRD, UV-visible absorption spectrum characterizations and a series of designed experiments are carried out. The surface structures of the nanocrystals are...