Template-free synthesis of polymer-derived mesoporous SiOC/TiO2 and SiOC/N-doped TiO2 ceramic composites for application in the removal of organic dyes from contaminated water

Mesoporous SiOC/TiO2 and SiOC/N-doped TiO2 (nitrogen-doped TiO2) ceramic composites were prepared by the incorporation of TiO2 (containing 65 wt.% anatase and 35 wt.% rutile) and N-doped TiO2 powders into vinyl-functionalized polysiloxane polymer followed by pyrolysis at 700-900 degrees C for 2 h in argon atmosphere. The N-doped TiO2 powders were obtained by ammonolysis of commercial TiO2 nanopowders. The resulting samples were characterized by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and nitrogen physisorption. The specific surface area (S-BET) values of the as-prepared SiOC ceramic and SiOC/TiO2 and SiOC/N-doped TiO2 ceramic composites decreased with increasing the pyrolysis temperature due to a gradual collapse of small pores. A transformation from microporous SiOC ceramic (pore-size < 2 nm) to mesoporous SiOC/TiO2 and SiOC/N-doped TiO2 ceramic composites (pore-size similar to 4 nm) was analyzed. Adsorption and photocatalytic activity of the resulting samples were evaluated by measuring the decrease in concentration of methylene blue (MB) after adsorption in the dark and photodegradation reaction under UV-vis light irradiation, respectively. Pure microporous SiOC ceramic showed no significant adsorption as well as photocatalytic activity for MB because of its high microporosity and low solid acidity, respectively, whereas mesoporous SiOC/TiO2 and SiOC/N-doped TiO2 ceramic composites exhibited higher adsorption and photocatalytic activities. The photodegradation rate constant k( x 10(-3) min(-1)) of the samples increased in the following order: 1.3 for SiOC ceramic < 2.2 for SiOC/TiO2 < 3.4 for SiOC/N-doped TiO2. The highest k for the SiOC/N-doped TiO2 ceramic composite is discussed in terms of the change of the electronic structures and crystallinity of N-doped TiO2 if compared with pure TiO2. These polymer-derived ceramic composites can be applied for the purification of water contaminated with organic dyes without the need for hydrogen peroxide. (C) 2011 Elsevier B.V. All rights reserved.