Insight into the Role of TiO<sub>2</sub> Facets in Photocatalytic Selective Oxidation of <i>p</i>-Xylene
Xiaowen Sun, Zhendong Feng, Shengyang Wang, Qing‐Nan Wang, Pengfei Zhang, Rengui Li, Can Li
Abstract
The crystal facets of semiconductors often have critical effects on photocatalytic reactions. The spatial charge separation between different facets in TiO 2 reveals a preferential accumulation of photogenerated holes on the {001} facet; thereby, the activation of the C–H bond predominantly occurs on the {001} facet. However, the dissociative adsorption of initially generated p -methylbenzyl alcohol ( p -MBY) forms alcoholate species, which impedes the interaction between p -xylene and the {001} facet, and thus blocks the photocatalytic reaction of p -xylene oxidation on {001}-72%. On the other hand, H 3 PO 4 predominantly adsorbs on the {001} facet, with an adsorption energy higher than p -MBY (−5.15 vs −3.90 eV). Therefore, adding H 3 PO 4 can prevent the dissociative adsorption of p -MBY on the {001} facet. The addition of H 3 PO 4 also significantly improves the injection efficiency of photogenerated holes into p -xylene and suppresses the generation of ·O 2 2–, thereby enhancing the conversion and selectivity. Consequently, the addition of H 3 PO 4 obtains a selectivity as high as 94.8% to the primary products at 15.2% conversion on {001}-72%. The results demonstrate that facet engineering for a semiconductor-based photocatalyst can regulate the charge separation, charge injection, and adsorption behavior of intermediates, which is an effective strategy to accomplish high performance of photocatalytic reactions.