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 (V_O-p-TNTs) with oxygen vacancies (V_O) 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_O. The preferential orientation of V_O-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_O 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 V_O broadens the light absorption range. As a result, V_O-p-TNT exhibits excellent PNOCM performance and provides new insights into catalyst design for CH₄ conversion.