Preparation Of Silica Hollow Spheres And Their Properties

Silica-based hollow spheres have attracted much attention since the discovery of hollow structures because they have large capacity, low density, thermal stability, low toxicity, and are prepared under mild synthetic conditions and have easily controllable morphology. And more importantly, they have tremendous applications in biomedical materials, catalysis, composite materials, environmental technologies and electronic devices. Many interesting approaches have been developed for the fabrication of silica hollow spheres, such as hard-template method and soft-template method. The hollow spheres were synthesized by removing of template through etching or calcination, but this may be time and energy consuming. while soft template were usually thermodynamically unstable and easily influenced by factors such as the solvent polarity, the pH value, and the ionic strength of the solution.The silica hollow hybrid spheres were fabricated via a sol-gel procedure involving the hydrolysis and condensation reactions of VTMS and TEOS. The particle size with 390.4nm and 644.5nm could be successfully synthesized. Transmission electron microscopy (TEM showed that the particles were spheres with inner cavity. The maximum Brunauer-Emrnett-Teller (BET) surface area calculated through the Brunauer-Joyner-Halenda (BJH) method was 238.99m2/g. The Fourier transform infrared spectra (FTIR) spectrum showed that the strong peak at 1602cm-1 is related to the vibration of C=C groups. In Raman spectrum the stretching modes of C=C groups were also observed at 1604cm-1 which showed that these silica hollow spheres had been effectively functionalized by vinly group.These spheres were used to load fragrances such as Thyme, Maltol, Vanillin and Phenethanol which could enhanced the thermal stability of fragrances; the maximum loading efficiency of Phenethanol was 94.20%, and more than 95% components of Thyme could be effectively encapsulated. The release of Phenethanol at 45 ℃ well fitted to the pseudo-second-order model.The as-synthesized hybrid hollow spheres were used as adsorbents for the removal of methylene blue (MB) and Cd (II) from aqueous solutions. The experimental data of the silica hybrid hollow spheres isotherms for Cd (II) and MB followed the Langmuir isotherm model. The hybrid hollow spheres exhibited the adsorption capacities as high as 54.703 and 25.421 mg/g for Cd (Ⅱ) and MB, respectively. The adsorption kinetics of Cd (Ⅱ) and MB onto the hybrid hollow spheres can be well fitted to the pseudo-second-order model. The adsorption processes of Cd (Ⅱ) and MB onto the hybrid hollow spheres at 298,318 and 338 K could be carried out spontaneously. At the same time, these obtained silica spheres showed high adsorption capacity to Pb(Ⅱ)、 Zn(Ⅱ)、 Cu(Ⅱ), and the maximum adsorption capacities were 75.6mg/g,71.5mg/g,54.7mg/g respectively.