Hydrophobicity Of Sio <sub> 2 </ Sub> Aerogels By Sol - Gel Synthesis And Its Performance Study

Silica aerogels are a kind of light mesoporous materials with high porosity and high surface area. In order to simplify the preparation process, lower costs, shorten production cycle, and improve production safety, in this paper teraethoxysilane (TEOS) was used as precursor and absolute alcohol as solvent. Hydrophobic silica aerogels had been synthesized by a two-step acid-base catalyzed sol-gel method with hexamethylidislazane (HMDZ) for the surface chemical modification, under ambient pressure.The stability of sol, density of aerogels, microstructure, specific surface area and contact angle were considered as standards for preparing silica aerogels. The amount of absolute alcohol, oxalic acid concentration, stirring time, hydrolysis time, ammonia concentration, amount of surface modification, surface modified time and other parameters influencing the structures and properties of silica aerogels were investigated, respectively, by single factor experiment and orthogonal experiment of four factors and three levels. The influences on the stability of sol, density of silica aerogels and contact angle among various factors were investigated comparatively. The result showed that the amount of absolute alcohol had the greatest effects on stability of sol and density of aerogels, and the amount of ammonia had the greatest effects on contact angle. The results showed that the most optimal molar ratio of TEOS, absolute alcohol, oxalic acid, ammonia, HMDZ were 1:7:3:2:0.75 respectively, the hydrolysis time was 18 hours and the surface modified time was 24 hours.The surface group, thermal stability, morphology and microstructure of silica aerogels had been investigated by FT-IR, DSC-TG, XRD, SEM, BET specific surface area and other analysis methods. The results showed that the density of silica aerogels was 98kg/m3, specific surface area was 898.62m2/g, porosity was 95.4%, and average pore diameter was 13.48nm. The obtained samples had higher purity. The particles which constituted the continual net structure of aerogels were spherical and dispersed evenly. The samples were non-crystallized, porous and light nanometer materials with higher purity, higher stability and higher specific surface area.The adsorb ability of organic solvents chloroform etc for silica aerogels was investigated. Silica aerogels are capable of adsorbing organic solvents chloroform etc effectivelly, and the properties such as high specific surface area and porosity of aerogels did not change after adsorption. Thus silica aerogels can be used repetitiously, and the application future is promising in the aspect of waste water treatment and organic substance adsorption.