Preparation of Dense and Porous Silicon Oxycarbide Submicrometer-Sized Spheres Using a Modified Stober Process

Dense and highly porous silicon oxycarbide (Si–O–C) submicrometer-sized spheres, with diameters in the range 100–400 nm are synthesized through pyrolysis of sol–gel-derived hybrid precursors. A modified Sto¨ ber process is used for the synthesis of silsesquioxane submicrometer-sized particles from different organotriethoxysilanes RTES, R=CH3, C5H11, and C6H5. The hybrid particles are transformed into dense inorganic Si–O–C submicrometer-sized spheres through a pyrolysis process in controlled atmosphere and the spherical morphology is kept provided that the glass transition temperature of the silsesquioxane network is higher than the onset of the polymerto-ceramic transformation. The Si–O–C spheres are stable up to 1400°C. By HF etching the silica nanodomains present in the silicon oxycarbide structure, the dense Si–O–C particles can be further engineered and transformed into highly porous Si–O–C submicrometer-sized spheres with specific surface area up to 564 m2 g-1 and pore volume up to 0.7 cm3 g-1.