Titania and mixed titania/aluminum, gallium, or indium oxide spheres: Sol-gel/template synthesis and photocatalytic properties

Porous polymer beads have been used as templates in which sol-gel chemistry was conducted for the formation of porous titanium dioxide and titania/aluminum, gallium, or indium oxide spheres. The addition of 5, 10, and 15 wt.-% of the second metal oxide to titania was studied, resulting in little variation in the final porous-sphere diameter, but in a decreased titania nanocrystal size and an increased specific surface area of the material. The crystallinity of the samples was observed after heating at 550, 750, and 950 degreesC as anatase to rutile phase transitions became apparent and peaks from the added metal oxide were observed with the increase in temperature. Photocatalytic decomposition of 2-chlorophenol was monitored in the presence of the titania and titania/metal-oxide spheres showing that a 5 wt.-% addition of the second metal oxide gave best photocatalytic results for all the metal oxides studied. At a pH of 6 the pure titania spheres were less photocatalytically active than the Degussa P25 titania, however the mixed titania/5 wt.-% metal-oxide samples were more active than the standard in the order In (least active), Ga, then Al (most active). Variation of the solution pH (between pH 2 and 10) had little influence on the photocatalytic activity of the titania/5 wt.-% aluminum oxide material, more effect on the titanium/5 wt. % gallium oxide, and the most pronounced effect on the titanium/5 wt.-% indium oxide, with increased activity at higher pH values. The adsorption of pyridine to the titania samples containing the second metal oxide indicated the presence of Lewis-acid sites.