On Oxygen Activation at Rutile- and Anatase-TiO₂

Abstract

The rutile form of titanium dioxide (r-TiO 2 ) usually shows a photocatalytic activity lower than that of anatase-TiO 2 (a-TiO 2 ). Nevertheless, there are numerous examples of sometimes unexpectedly high activity of r-TiO 2 . This material may appear to be particularly useful when a noncomplete and selective photocatalytic oxidation of organic substrates is required. On the basis of literature examples and our own studies, we compare the photocatalytic activities of r-TiO 2 , a-TiO 2 , and r-TiO 2 /a-TiO 2 composites. Because of a significantly better oxygen adsorption at the surface of r-TiO 2 and a lower redox potential of the excited electron, more efficient O 2•− production takes place at the surface of rutile. As a consequence, generation of 1 O 2 (involving O 2 reduction and the subsequent oxidation of superoxide) and reduction of H 2 O 2 to OH − and HO • are also favored with this material. Therefore, r-TiO 2 can be considered to be a particularly good photocatalyst for activation of molecular oxygen. On the other hand, a-TiO 2 appears to be a stronger oxidant. In its presence, efficient HO • generation (the result of water or surface hydroxyl group oxidation) and oxidation of H 2 O 2 to O 2•− are observed.

Photocatalytic CO2 Reduction under Continuous Flow High‐Purity Conditions: Influence of Light Intensity and H2O Concentration

“…On the basis of the former, the participation of H 2 O oxidation in the product formation, and the absence of O 2 in the gas phase of the photoreactor, it might be possible that O 2 or O‐derived species remain on the surface of the photocatalyst instead of being desorbed. Potential O‐derived species could be superoxide or surface peroxyl species . Another likely reason for the absence of O 2 in the gas‐phase of the photoreactor could be incomplete H 2 O oxidation [Equations ] or H 2 O reduction [Equation ].…”

TiO2 Processed by pressurized hot solvents as a novel photocatalyst for photocatalytic reduction of carbon dioxide

“…Recently, we described anatase (a-TiO 2 ) and rutile (r-TiO 2 ) band alignment by using spectroelectrochemical method (−1.14 and −1.53 V vs. Ag/AgCl for a-TiO 2 and r-TiO 2 , respectively) [45]. Using the same method we estimated the potential of brookite band position to −1.2 V vs. Ag/AgCl [46].…”

Photoelectrochemical study of carbon-modified p-type Cu2O nanoneedles and n-type TiO2−x nanorods for Z-scheme solar water splitting in a tandem cell configuration

“…48 Recent studies have also revealed an increase in photoactivity in TiO 2 samples that exhibit a mixture of anatase and rutile TiO 2 phases due to electron transfer from the rutile states to the anatase states which are lower in energy or vice versa. 49 Fig . 3A and B show the respective SEM and TEM images of C/ Cu 2 O NNs synthesized using 10 mg mL À1 dextrose.…”