Synthesis and photocatalytic properties of hollow microparticles of titania and titania/carbon composites templated by Sephadex G-100

Hollow titania microparticles about 20-60 mu m in size and hollow titania/carbon composite microparticles about 30-90 mu m in size were prepared by employing commercial Sephadex G-100 beads as the template as well as the carbon precursor. The cross-linked dextran gel template was first immersed in aqueous TiCl4 solution to allow the surface mineralization of titania, resulting in the formation of hollow microparticles of titania/G-100 hybrids. Hollow titania microparticles with a shell thickness adjustable from 1 mu m to 2.5 mu m were fabricated by calcination of the hollow titania/G-100 hybrid microparticles at temperatures from 400 to 700 degrees C in air. On the other hand, hollow titania/carbon composite microparticles similar to 2.6 mu m in shell thickness, which consisted of anatase nanocrystals and amorphous carbon, were obtained by carbonization of the hollow titania/G-100 hybrid microparticles at temperatures from 500 to 700 degrees C in flowing nitrogen. For the titania/carbon composites, the phase transformation from anatase to rutile was suppressed; moreover, the crystallinity of anatase was decreased and the surface area was increased with increasing calcination temperature, in contrast to the case of hollow titania microparticles. The photocatalytic activity of the obtained hollow microparticles of titania and titania/carbon composites was investigated by monitoring the photodegradation of Rhodamine B. In both cases, the product calcined at an intermediate temperature exhibited the highest photocatalytic activity possibly because of a compromise between the anatase crystallinity and the surface area. Compared with the hollow titania microparticles, the hollow titania/carbon composite microparticles exhibit remarkably enhanced photocatalytic activity.