Chrysotile Acid Leaching And The Preparation Of Silicon Oxide Nanowires

As a one-dimensional nanostructure material, silica nanowires, which have special blue light emission, will have good potential application in many fields. Considering from the nanotube structure of natural chrysotile, we report the production of silica nanowires with high-purity, low diameter, large scale of length to diameter and well-dispersion using a chemical dispersing and acid leaching route with chrysotile as a source material in this paper. The main points and content of the paper are indicated as following:(1) The chemical dispersal of chrysotileChrysotile was dispersed with anionic surfactant Aerosol OT (AOT). The dispersal effect was characterized by FTIR, XRD and SEM. The results show that AOT is absorbed onto the chrysotile surface effectively and chrysotile is dispersed into single fibers. The interspace between fibers is obvious.(2) Chrysotile was leached in hydrochloric acidThe optimum leaching conditions were obtained by separate factor conditional experiments. Then we build the overall kinetic model for the fibrous particle in liquid-solid reaction. Based on the model the apparent activation energy of the reaction is 24.4kJ/mol, which is consistent with the 23.6kJ/mol obtained by subsequent leaching. The kinetic result shows that the reaction rate is determined by diffusion.The change of chrysotile structure during the leaching process in hydrochloric acid was researched by XRF, XRD, FTIR and N₂ adsorption-desorption techniques. The results show that Fe mostly in the form of Fe²⁺ ions occupies octahedral sites to subtitute Mg²⁺, and Al ions are mainly in the tetrahedral sites in place of Si⁴⁺. Chrysotile reacted with acid mainly through its cylinder. As leaching, Mg and Fe ions are dissolved, but Si becomes non-crystal silica. The brucite-like sheet disappeares gradually and the silica-like sheet experiences a distortion. The amorphous silica is obtained at last. A continous enhancement of the specific surface area and total pore volume is observed as leaching. The characteristic of hysteresis loop indicates mainly slit-shaped pores. (3) Preparation of silica nanowires from chrysotile by acid leachingBy chemical dispersion and acid leaching, high-purity silica nanowires were prepared from chrysotile. The chemical composition of silica nanowires is SiO_1.8·0.6H₂O. The silica is amorphous. The structure unit of silica nanowires is a SiO₄ tetrahedron, which retains six-member silicon-oxygen rings. The silica nanowires are well-dispersed and have columned morphology and a smooth surface, with lengths over 10μm and diameters of 25～55 nm.