Síntesis de materiales mesoporosos compuestos sílice/carbono y su empleo como plataforma para la fabricación de materiales con propiedades avanzadas

Resumen

[EN] The design of nanomaterials has attracted widespread interest in recent years and it is constantly growing in the search for novel materials whose properties fulfil the requirements of increasingly demanding applications. The use of composite materials which embody both the characteristics of each individual component and new properties arising from their combination, will act as a further stimulus to progress in this field. The present thesis focuses on the design and fabrication of mesoporous silica-carbon composites. In the first part of the thesis, mesostructured silica-carbon composites with well-defined textural properties were synthesized by the incorporation of a carbon film over the internal surface of the silica materials. The resulting materials exhibited, on one hand, the characteristics typical of mesostructured silica, such as a high surface area (500 700 m2•g-1), a large pore volume (~ 1 cm3•g-1) and a porosity made up of uniform mesopores. On the other hand, the generated carbon layer uniformly covers the porosity of the silica material independently of the carbon precursor used (i.e. the surfactant used in synthesis of the silica or an external carbon precursor). In specific cases, the chemical properties of the composites were modified by the functionalization of the carbon layer. Functionalization was performed following two procedures: i) the post-synthesis incorporation of oxygen and sulfonic functional groups; and ii) direct introduction via the use of nitrogen or sulphur rich carbon precursors. The combination of specially tailored textural and chemical properties gave rise to high-performance sorbents for dyes and heavy metals in aqueous solution as well as to excellent solid acid catalysts for esterification reactions. In the second part of the manuscript, mesoporous silica-carbon composites with a spherical morphology were designed and synthesized. By means of the porogen agent used in the synthesis of silica nanospheres or by adding a carbon precursor, it was possible to prepare composites consisting of a solid silica core covered by a porous silica shell whose porosity was partially occupied by a layer of carbon. Subsequent etching of the silica generated nanorattles which are composed of tunable silica spherical nanoparticles confined inside mesoporous carbon shells (~ 40-50 nm thick). The diameter of the silica core was tuned (between 330 and 160 nm) by varying the etching time. Finally, complete dissolution of the silica led to mesoporous carbon capsules with a high surface area (1620 m2•g-1), a large pore volume (2.3 cm3•g 1), a central macroporous core of diameter ~ 350 nm and a carbon shell thickness of ~ 50 nm. Magnetic composites were prepared by incorporating magnetic inorganic nanoparticles inside the pores of the carbon capsule shell. The potential of these composites as nano-containers of biomolecules and as bio-catalysts for dye degradation was demonstrated. The recovery of the materials from the liquid medium was achieved quickly and efficiently by using a simple conventional magnet.