Synthesis And Characterization Of Ultrafine Amorphous SiO₂ Nanoparticles

Amorphous SiO₂ nanoparticles have been applied in coatings,catalysis,biomedicine,fibers and other fields.The dispersity and size of the particles serverely affect their role in the material.In addition,disperse,fine,spherical amorphous SiO₂nanoparticles with high purity are essential for producing SiO₂ nanoglasses.Herein,the synthesis of disperse,fine,spherical amorphous SiO₂ nanoparticles is of great significance.In this thesis,amorphous SiO₂ nanoparticles were prepared via precipitation and calcination using Na₂SiO₃ as the silicon source.The experimental process of preparing amorphous SiO₂ nanoparticles via precipitation,and the problems of poor dispersity and larger size of the prepared particles were investigated to realize the preparation of completely dispersed,fine,spherical amorphous SiO₂nanoparticles.Besides,the properties of amorphous SiO₂ nanoparticles were simply studied,which established a foundation for broadening the application of amorphous SiO₂ nanoparticles in materials.In the pure water solvent system,the main factors affecting the dispersity,size and shape of SiO₂ nanoparticles including the precipitant type,amount of Na₂SiO₃,concentration of NH₄Cl,amount of surfactant,concentration of electrolyte and pH of reaction system were investigated.The experimental parameters of the preparation of amorphous SiO₂ nanoparticles via precipitation were optimized.The preparation of amorphous SiO₂ nanoparticles with smaller size and better dispersity was achieved.The effects of a series of surfactants（various polyethylene glycol,sodium dodecyl benzene sulfonate and polyvinyl pyrrolidone）on the dispersity,size and shape of SiO₂ nanoparticles were studied.The type and amount of surfactant was optimized.The optimal surfactant for the preparation of amorphous SiO₂nanoparticles by precipitation was explored.The preparation of disperse,fine（average particle size of 8.0 nm）,spherical amorphous SiO₂ nanoparticles was achieved.The effects of different solvent systems on the preparation of SiO₂ nanoparticles were studied.Control of dispersity,size and shape of SiO₂ nanoparticles was achieved by adjusting the solvent volume ratio of ethanol/water and the type of alcohol in the alcohol/water mixed solvent system.The optimal solvent system for the preparation of amorphous SiO₂ nanoparticles by precipitation was obtained.The dispersed,ultrafine,spherical,and high-purity amorphous SiO₂ nanoparticles have the smallest particle size（average particle size of 4.0 nm）,and the largest specific surface area achieved so far.The properties of adsorption,PL and solid UV absorption of the prepared SiO₂nanoparticles with different particle sizes were tested,confirming the decisive relationship between the properties and the particle size.