Facile Synthesis of Hollow Porous Silica Micro- and Nanospheres and Their Application

The unique properties of both amorphous silica (SiO2) and silver nanoparticles (Ag NPs) make them quintessential for extensive range of applications. The high melting point of SiO2 along with its chemical and mechanical stability as well as the biocompatibility, makes it an exclusive candidate as a fire retardant filler and a drug carrier. The optical and antibacterial properties of Ag NPs have experienced a growth on demands for industrial applications. Interestingly, Ag-SiO2 nanocomposite combines disparate advantages of both materials and are found applicable in coating and biomedical industries. Furthermore, due to the surface plasmon resonance of Ag NPs and low dielectric constant of silica, the Ag-SiO2 nanocomposite is promoting the usages in emerging technologies, such as, in surface enhanced fluorescence. This research work was initiated from real problems in fire protection coating on polymers as well as the dilemma of aggregation and oxidation from Ag NPs in both academy and industries. Despite the existing studies on forming variable sizes and forms of silica and Ag-SiO2 composite using different physical and chemical methods, the research on finding the correlation between reaction parameters and properties of obtained products demand intensive investigation, particularly for aiming a simple and cost-effective approach. This thesis focuses on improving the existing sol-gel based synthesis techniques for producing hollow and/or hollow porous SiO2 micron powders with low thermal conductivity, and core-shell silver@mesoporous silica nanoparticles (Ag@MSN) powders for use as encapsulating materials. This research work contributes the knowledges to the sol-gel filed in four aspects: (i) The relation between synthesis time, mechanical stirring speed and volume of 1-octanol and properties of obtained hollow and hollow porous SiO2 were found; (ii) The synthesis process was flexibly customized to meet the requirements on forming SiO2 with various size and morphologies; (iii) Tunable Ag@MSN were achieved via a facile and cost-effective one-pot synthesis based on a modified Stöber method. This approach significantly avoids the drawbacks of complication and reduces the costs in comparison with a multi-steps approach; (iv) The importance on the impact of ethanol on the properties of both Ag cores and SiO2 shells are studied. In addition, the core-shell structure with tunable thickness and porosity of SiO2 shell is essential in metal-enhanced fluorescence (MEF) and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) studies, and the release of Ag cores from obtained powders at acidic condition provides good bases for antibacterial uses