Template synthesis and photocatalytic properties of porous metal oxide spheres formed by nanoparticle infiltration

Porous polymeric beads have been used as templates for the fabrication of porous metal oxide spheres. The beads were soaked in sols of titanium dioxide, zirconium dioxide, iron oxide, aluminum oxide, indium oxide, tin oxide, and cerium oxide. Successful infiltration and templating was obtained for titania, zirconia, tin oxide, and ceria giving monodisperse, nonaggregated spheres with a porous surface and inner structure. The use of iron and aluminum oxide sols resulted in cracked spheres with excess oxide material on the sphere surfaces, and in the case of indium oxide, broken, hollow, shell-like structures were produced. Combining the iron, aluminum, or indium oxide sols with the titania sol, at a 1:1 weight ratio, and impregnating the template produced inorganic spheres containing the two metal oxides. The photocatalytic properties of the titania and mixed titania/indium oxide spheres were studied by monitoring the decomposition of 2-chlorophenol as a function of time and solution pH. Both the porous titania and mixed titania/indium oxide spheres were more efficient photocatalysts than Degussa P25 titania, a commercial standard. Optimum solution pH for the photocatalytic reaction was determined to be pH 6 for the titania spheres and pH 4 for the titania/indium oxide sample. Pyridine adsorption on the mixed titanium/indium oxide spheres showed FTIR peak shifts similar to those of the indium oxide spheres, which indicated the presence of stronger Lewis acid sites compared with the titania spheres.