Oxygen vacancy self-doped single crystal-like TiO <sub>2</sub> nanotube arrays for efficient light-driven methane non-oxidative coupling
Jinbo Xue, Jinyu Li, Zhe Sun, Huimin Li, Huan Chang, Xuguang Liu, Husheng Jia, Qi Li, Qianqian Shen
Abstract
Photocatalytic non-oxidative coupling of methane (PNOCM) is a mild and cost-effective method for the production of multicarbon compounds. However, the separation of photogenerated charges and activation of methane (CH<sub>4</sub>) are the main challenges for this reaction. Here, single crystal-like TiO<sub>2</sub> nanotubes (V<sub>O</sub>-p-TNTs) with oxygen vacancies (V<sub>O</sub>) and preferential orientation were prepared and applied to PNOCM. The results demonstrate that the significantly enhanced photocatalytic performance is mainly related to the strong synergistic effect between preferential orientation and V<sub>O</sub>. The preferential orientation of V<sub>O</sub>-p-TNT along the [001] direction reduces the formation of complex centers at grain boundaries as the form of interfacial states and potential barriers, which improves the separation and transport of photogenerated carriers. Meanwhile, V<sub>O</sub> provides abundant coordination unsaturated sites for CH<sub>4</sub> chemisorption and also acts as electron traps to hinder the recombination of electrons and holes, establishing an effective electron transfer channel between the adsorbed CH<sub>4</sub> molecule and photocatalyst, thus weakening the C–H bond. In addition, the introduction of V<sub>O</sub> broadens the light absorption range. As a result, V<sub>O</sub>-p-TNT exhibits excellent PNOCM performance and provides new insights into catalyst design for CH<sub>4</sub> conversion.