Preparation Of A New Type Of Hybrid Silica Composite Microspheres

The silica composite particles have attracted significant attention in the last few decades, due to their wide applications in different fields. Silica/titania core/shell composite microspheres have demonstrated their broad potential in various fields such as water splitting, removing organic pollutants from environment and eliminating bacteria and fungi in water. However, current preparation methods either suffer from the difficulty in the formation of regular shell layer of titania due to the high reactivity of titania precursor, or from the complex and labrous synthesis steps to achieve dense and conformal shell layer. In another application, hollow silica composite particles are a promising carrier for drug and other organic or inorganic molecules, as a result from its special stereo structure that shows high stability, good biology compatibility and large cavity capacity. Nevertheless, the synthesis of hollow structure mostly need sacrifice template, which was neither efficient in economics nor environment friendly. Moreover, the procedures required to prepare highly controllable homogeneous hollow silica composite particles were tedious and effort-taking. In order to solve all these problems, also based on a new-type preparation of hybrid silica sub-microspheres, here we systematically studied the preparation and modification of these hybrid silica sub-microspheres. Afterwards, different coating was introduced to form organic/inorganic or inorganic/inorganic composite particles. The well-defined multi-responsive capsules also could be prepraed based on the method. The main summary is listed as below:1) The monodispersed hybrid silica particles (h-SiO2) were firstly prepared by a modified sol-gel process and the surface was modified in situ with double bonds, then abundant carboxyl moieties were introduced onto the surface of the silica core via thiol-ene click reaction. Afterward, the h-SiO2/TiO2 core/shell microspheres were prepared by hydrolysis of titanium tetrabutoxide (TBOT) via sol-gel process in mixed ethanol/acetonitrile solvent, in which the activity of TBOT could be easily controlled. The carboxyl groups on the surface of silica particles promote the formation of a dense and smooth titania layer under well control, and the layer thickness of titania could be tuned from 12 to 100 nm. The well-defined h-SiO2/TiO2 core/shell structures have been confirmed by electron microscopy and X-ray photoelectron spectroscopy studies. After calcination at 500℃for 2 hours, the amorphous TiO2 layer turned into anatase titania. These anatase titania coated silica particles showed good photocatalytic performance in degradation of methyl orange aqueous solution under UV light.2) Using the same hybrid silica particles (h-SiO2) as self-template, the mono-dispersed silica hollow sub-microspheres were prepared by initiating the vinyl groups that were located on the surface of the silica particles to polymerize in different solvent with different initiator, which was followed by an etching process in HF water solution. The uncross-linked silica core was removed to form an identical hollow structure, which was confirmed by TEM and FT-IR. The size of the resulting hollow particles resembles that of the original ones, while the shell thickness could be altered from 10nm to 20nm by changing the solvent from water to ethanol.3) In the dispersion of silica particles with vinyl groups located on the surface, 8wt%-12wt% NIPAM (N-Isopropyl acrylamide) was added to copolymerize to form the PNIPAM/silica composites particles with hairy PNIPAM chains. The polymer shell thickness increase with the increasing amount of the monomer added. After etching, thermal responsive organic/inorganic capsules were obtained, which was demonstrated by TEM, FTIR and DLS with a temperature trend program. The transit temperature of low cross-linking hairy PNIPAM located on the surface of the resulting capsule is around 32℃, which is in accordance to that of the pure un-crosslinked PNIPAM. Furthermore, acrylic acid (12wt%-14wt%to total monomer content) was introduced to the system so that the resulting capsules could possess both thermal and pH responsive (a broad pH responsive range from pH=3.5 to pH=7.5), which was characterized by DLS with both temperature trend and pH titrator.