Study On The Peformance Of Nanoporous Hollow Silica Microspheres

Nanoporous hollow silica microspheres have been found potential applications in thefields of separation, adsorption, drug delivery, catalyst support and packaging due to structuraland performance advantages such as small specific gravity, high surface area, large porevolume, internal hollow space. In this work, the nanoporous hollow silica microspheres withdifferent structures have been prepared using template approaches combined with sol-geltechnique. The synthesized samples were characterized by small angle XRD, N₂-sorption, SEM,TEM, IR and TG-DTA. The adsorption of rhodamine6G of the obtained samples to （R6G） andthe loading of ferric acetylacetonate were studied. Thin layer chromatography plates wereprepared using synthesized hollow silica microsphers with different microstructures asstationary phase. The separating effiency of these plates towards a mixture of methyl red anddimethyl yellow has been compared.Nanoporous hollow silica microspheres with single, double and three silica coating layerswere synthesized. The synthesized hollow microspheres have good monodispersity, smoothsurface and uniform particle size. The specific surface area and pore size of the hollowmicrospheres prepared by multiple single silica coatings gradually increase with increasingsurfactant alkyl chain length, which leads to the increase in the adsorption rate and capacity ofR6G into the hollow microspheres. If the surfactant alkyl chain length used in the outer silicacoatings is decreasing, the samples show samller pore parameters than in the case when thesurfactant chain length is increasing. The sample whose outer layer was formed withoutsurfactant has small surface area, pore size and low adsorption capacity. The adsorption of R6Gon all the nanoporous hollow silica microspheres complies with the quasi-second-order kineticadsorption model.Thin layer chromatography plates prepared using nanoporous hollow silica microspheresas stationary phase were used to separate the mixture. Comparisons show that distilled water isthe best mixing agent, the separation effect of the plates prepared using ethanol or starchsolution as mixing agents was poor. The separation effect of activated plates is superior to thenon-activated plates. When using the mixtures of cyclohexane/toluene（3:4（v:v））andcyclohexane/toluene/ethanol （1.5:5:0.5（v:v:v）） as mobile phases the mixture could be separated easily; but it failed when using the mixture of toluene/ethanol （5:2（v:v）） as mobile phase. Theseparation efficiency of hollow microspheres with three silica coating layers is better than thehollow microspheres with single or double silica layer. The the separation efficiency of thehollow microspheres with a single silica coating increases with increasing the alkyl chainlength of the surfactant used. The organic mixture was not separated when using uncalcinedcomposite microspheres as the stationary phase. The results evidence that the enhancement ofthe thin layer separation efficiency is due to the nanoporous and hollow structure of thehollow silica microspheres.Iron can be laoded in the nanoporous hollow silica microspheres. After the loading, thespecific surface area and pore volume of the samples are reduced. The specific surface area andpore volume of the sample loaded iron was increased after calcination, suggesting that iron ismainly loaded inside the pores. The hollow microspheres with a single silica coating has thelargest iron loading, wheras the sample that no surfactant was used in the outer silica coatinghas the smallest iron loading. The amount of iron laoding increase with increasing the specificsurface area, pore volume, pore size of the hollow silica microspherews and the initial Fe3+concentration, and reduces with the thickness of silica shells.