Spray-dried mesoporous silica microspheres with adjustable textures and pore surfaces homogenously covered by accessible thiol functions

Abstract

Micrometric mesoporous spheres with textures possessing a relative high degree of ordering and incorporating up to 0.1 thiol function per siloxane unit have been synthesised through sol–gel, self-assembly and—for the first time—spray-drying processes. The sol preparation was optimised as a function of the final properties: morphology, texture, and proportion of thiol functions. A two step synthesis allows the positioning of these functions at the pore surface as proven in particular by ¹H solid state NMR. From Ag⁺ sorption experiments, we have shown that the thiol functions are also homogenously distributed in the sphere's volume and fully accessible to external chemical species. So these materials could be used for environmental remediation or metallic nano-particle syntheses. In order to increase the stability and applicability of the materials, different post-synthesis treatments have been studied. A thermal treatment under mild conditions is enough to preserve most of the properties. From the hydrothermal treatments tested, the use of ammonia is shown to be quite interesting for the modulation of the properties. In particular, hierarchical porosities and high specific surface areas have been created. The high degree of ordering observed for the smaller pores is accompanied by a re-ordering of the surfactant polar head groups as deduced from ¹⁴N NMR. Lastly, the synthesis can be extended under some conditions to other functions or to higher proportions of thiol functions (up to 0.2).