Preparation and characterization of titania-entrapped silica hollow particles: effective dye removal and evidence of selectivity.

A titania-entrapped silica hollow nanostructure was prepared using two consecutive coating processes, followed by calcination. The hydrothermal treatment of D-glucose assisted by polyethylene glycol was used to form a carbon layer over the titania surface. The resulting composite was used to fabricate a silica layer on top by hydrolyzing tetraethyl orthosilicate in strong base. The titania nanoparticles were then released but still trapped inside the silica hollow after calcination. Scanning and transmission electron microscopic techniques were employed to determine the morphology of the obtained product; nitrogen gas adsorption and X-ray diffraction methods were also used. Photocatalytic studies on five organic dyes showed that efficient dye-removal due to photocatalysis and adsorption with selectivity based on the charge-charge interaction between the dye and silica surface was possible. Other factors including the structures of the dyes and their molecular interaction also influenced the observed removal efficiency.