The Synthesis And Characterization Of Silica Nanomaterials

In recent years, the studies on silica nanomaterials become one of the hotspots and focuses in the nanomaterials researching fields. Silica nanometermaterials can be widely used in various fields, such as medicine, catalyst, and the military field, etc. Preparation of smaller, better dispersed silica nanomaterials with tailored morphologies has attracted much attention. The preparation strategies of silica nanomaterials generally fall into either of the following two types: the dry or the wet one. Among these methods, the sol gel method owns the advantage of preparing pure samples, but with larger sizes. While in the gas-phase preparing techniques, the prepared silica has good dispersibility, high purity and less surface hydroxyl groups, but with high cost, complex methodology, high energy consumption, and disapplicability for mass production.At present, the smallest particle size of silica available can be up to 5 nm, prepared by using chemical precipitation method. Silica nanomaterials with sizes below 10 nm may exhibit better biological compatibility. However, the preparation typically involves complex processes and requires rigorous conditions.This paper described a simple preparation method of silica nanomaterials, with high purity, large output, and low cost. The main research results were as follows:(1) With oleic acid as the solvent, TEOS was employed as the silicon source to react with anhydrous methanol, ethanol, propanol, and isopropanol under different temperatures. The prepared samples were characterized by XRD,TEM and SEM. The resulting samples mainly consisted of silica nano-spheres that conglomerated into chain-like structures. Using ethanol as the precursor, with the reaction time of 24 h, the resulting silica nanoparticles were uniform with the particle size of around 500 nm, with extremely good dispersibility.(2) It was found that the selection of alcohols and the reaction times will affect the particle sizes of silica nanoparticles. When anhydrous isopropanol was used as the precursor, the size of silica nanoparticles is the smallest, between 20 nm ~ 40 nm. When anhydrous methanol was used as the precursor, the size is the largest, between the 0.5 μ m~1.5 μm.(3) When the reaction time was changed with other experimental conditions remained constant, it was found that the reaction time also can influence the features of the prepared samples. Along with the prolonging of reaction time, the size of the sample became larger at first and then grew smaller at certain periods. When methanol was used as the precursor, the critical reaction time was 24 h, and the resulting silica nanoparticles is the largest around 1.5 μm. When isopropanol was used as the precursor, the critical reaction time is 48 h, and the resulting silica nanoparticles is the largest around 40 nm. When the reaction time is short, the hydroxyl groups were mainly provided by alcohols. When the reaction time is prolonging, the alcohols were exhausted and the reactions between oleic acids and the produced silica became prevalent. That should be the reason why the size became smaller when the reaction time was long.(4) To study the effects of surfactants, a set of control experiments with the addition of SDBS as the surfactant were carried out. The experimental results showed that the surfactant under the above conditions can make the surface of the prepared silica more smooth. In the control experiment with ethanol as the precursor and the reaction time of 24 h, the samples also conglomerated together into chain-like structures.(5) Silicon tetrachloride(Si Cl4) is a common toxic waste in the silicon industry. In this paper, Si Cl4 was used as the silicon source to prepare non-toxic silica nanometer materials. By using different alcohols(ethanol, normal propyl alcohol, isopropyl alcohol) as precursors, and changing the reaction times(from 24 h to 96 h), the influences of different alcohols and the reaction time on the morphologies of the prepared silica were explored. The sizes of the samples prepared by using Si Cl4 as the silicon source are larger, between 200 nm ~2 μm. With isopropyl alcohol as the precursor, the size of the prepared samples reached a minimum of about 200 nm. with ethanol as the precursor, the size of the prepared samples can reach 2 μm. When the precursor was ethanol, with the reaction time of 24 h, the prepared samples consisted mainly of nano-flakes assembled into hollow nano-spheres. When the reaction time was increased, the sample grew further into solid sphere.