Influence of the preparation temperature on the photocatalytic activity of 3d-ordered macroporous anatase formed with an opal polymer template

Even if many aspects of three-dimensionally ordered macroporous (3DOM) titania have been extensively studied, the interplay between the amorphous and crystalline components of their skeleton wall has not attracted too much attention, although it should strongly influence the properties of these materials. In order to gain new insight on this interplay, we have studied in detail the wall structure of three 3DOM titania samples prepared by heating the 3DOM titania precursor at 673, 773, and 873 K by X-ray diffraction, thermogravimetric analysis, differential thermal analysis, N₂ adsorption/desorption, pore-size distribution, high-resolution transmission electron microscopy, and ¹H magic-angle-spinning NMR. In addition, their photoreactivity toward the partial oxidation and mineralization of 4-methoxybenzyl alcohol was determined and compared with that of commercial anatase and P25 samples. The results show that when the 3DOM sample heated at 673 K, whose skeleton wall is formed by very small anatase nanoparticles covered by relatively thick layers of amorphous titania, is heated at 773 K, most amorphous titania is eliminated, leaving a very thin amorphous titania layer covering the slightly grown anatase nanoparticles. The photoreactivity results show that the sample heated at 773 K has the highest overall photoreactivity, which was lower than those of commercial anatase and P25 samples; however, its reactivity toward the alcohol partial oxidation was the highest compared with those obtained with all of the other samples. These results indicate that amorphous titania negatively affects the overall photocatalytic activity; however, its particular distribution in the 3DOM samples enhances the partial oxidation reaction.