Hollow microspheres of porous silica prepared starting from a hybrid containing chitosan

The combination of sols containing silica polymers, prepared by the sol-gel method under conditions of nearly linear chain growth, with solutions of the biopolymer chitosan has allowed us to obtain hybrid materials in the form of films or particles. In these hybrid nanocomposites, the organic and inorganic phases are associated through hydrogen bonds. In this work we present the preparation of hybrid xerogels of spherical morphology and their transformation into hollow spherical particles of silica with high specific area (276 m²/g) and a pore volume of 0.23 cm³/g. The xerogel particles were obtained by precipitation and subsequent drying. Thereafter, chitosan was extracted partially with acetic acid (5%) and finally the product was calcined at 550°C for two hours. The SEM micrograph shows that the silica particles were obtained as hollow spheres with size in the range between 10 and 100 μm. By using larger magnification, it was found that much smaller spheres of about 0.01 μm constitute the surface of these hollow spheres. Porosimetry shows the presence of micropores as well as mesopores. The observed morphology is discussed on the basis of a coprecipitation process conditioned by an association of both organic and inorganic phases in the precursor hybrid sol.