Oxygen vacancy self-doped single crystal-like TiO₂ nanotube arrays for efficient light-driven methane non-oxidative coupling

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 (CH4) are the main challenges for this reaction. Here, single crystal-like TiO2 nanotubes (VO-p-TNTs) with oxygen vacancies (VO) 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 VO. The preferential orientation of VO-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, VO provides abundant coordination unsaturated sites for CH4 chemisorption and also acts as electron traps to hinder the recombination of electrons and holes, establishing an effective electron transfer channel between the adsorbed CH4 molecule and photocatalyst, thus weakening the C–H bond. In addition, the introduction of VO broadens the light absorption range. As a result, VO-p-TNT exhibits excellent PNOCM performance and provides new insights into catalyst design for CH4 conversion.