Photocatalytic activities of different well-defined single crystal TiO ₂ surfaces: Anatase versus rutile

The photocatalytic activities of well-defined TiO₂ single-crystal anatase (101) surfaces have been assessed by methanol oxidation and by terephthalic acid hydroxylation evincing the formation of OH ^• radicals and have been compared with that of rutile singlecrystal (001), (100), and (110) surfaces. The results showed that the anatase (101) surface exhibits a higher photocatalytic activity than all investigated rutile surfaces toward the oxidation of methanol and exhibits a comparable activity to that of the rutile (001) surface with respect of terephthalic acid hydroxylation. The rutile (001) surface shows a higher photocatalytic activity than both the rutile (110) and (100) surfaces for both photocatalytic test reactions. Because anatase (101) and rutile (110) are the thermodynamically most stable surfaces, anatase and rutile nanomaterials possess, thus, a large percentage of (101) and (110) surfaces, respectively. This offers a reasonable explanation why anatase nanoparticles usually exhibit higher photocatalytic activities than the respective rutile powders. (Chemical Equation Presented)