Preparation And Applications Of Silica-based Sol-gel Derived Materials

Sol-gel process is a classical wet chemistry synthesis method.It uses metal salts as starting materials.After a series of reactions,including alcoholysis,hydrolysis and condensation,metal oxide sols are produced.And then,after further gelation,aging,drying processes,gels are obtained.Sol-gel process is very versatile.By fine control and tuning of reaction and drying conditions,various types of materials,such as powders,blocks,aerogels,films and fibers etc can all be prepared.Silicon-based sol-gel materials mostly start from orthosilicates to form materials with-Si-O-as the major backbones.By introducing novel organo-functionalized siloxane molecules or other metal alkoxide molecules to copolymerize with orthosilicates,various materials with novel functions or better performance can be obtained.Currently,this is a hot and important topic in the research of sol-gel process.In this thesis,a series of silicon-based sol-gel functional materials were designed and synthesized by introducing different organosiloxanes and zirconium alkoxides as starting materials.The detailed research contents are described as following:（1）The Si-Zr composite porous microspheres were successfully prepared via the sol-gel process,using TEOS as the silicon source and zirconium n-butoxide as the zirconium source.The influences of the content of n-butanol zirconium on the structure and morphology of the composite microspheres were studied.The results show that the Zr is successfully and evenly doped into the silica gel without obvious enrichment or phase separation.When the molar ratio of zirconium n-butoxide and TEOS is 0.1,the composite microspheres obtained are perfectly spherical with an average particle size of 6.55μm and d90/d10 of 4.85.However,the mechanical strength of the composite microspheres needs to be improved for HPLC applications. Porous silica microspheres were prepared with TEOS,during which nano-Si O₂particles were introduced as solid porogen by chemical reaction or physical mixing.The hydrophilic or hydrophobic nature of the nanoparticles and how they were introduced show strong influences on the pore structure of the microspheres.The results show that pore is formed when the hydrophilic nano-Si O₂is added by physical blending.At 4 wt%of addition,best results are achieved with an average particle size of 5.5μm,average pore diameter of 90.43?,pore volume of 0.72 cm³/g,and specific surface area of 298.11 m²/g.（2）Four siloxane-based polymeric sols,including from tetraethyl orthosilicate and other three hybrid siloxane monomers,were prepared by sol-gel process.Their chemical and physical properties and performances as fossil protection materials were examined.Experimental data show that all sols have excellent permeabilities,decent reinforcement abilities,good resistance to light and heat aging.Functional organic moieties can also significantly increase the hydrophobicity of the fossil and reduce gel cracking.The results indicate siloxane-based sols can be very potential protection materials for fossils,among which epoxy modified silica sol shows the best overall performances.（3）Two UV curable silica sols containing acrylate and epoxy groups respectively were prepared by sol-gel process.They were used as 3-D printing materials in DLP and SLA modes.The results show that the precursor with epoxy functional group can be printed better,but the printed product is brittle and easy to crack during storage in air,probably due to inner stress induced by curing.Further studies of post-print treatments and formulation optimizations are required.