Oxygen vacancy self-doped single crystal-like TiO 2 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 are the main challenges for this reaction. Here, single crystal-like TiO₂ nanotubes (V_O-p-TNT) 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 [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 methane chemisorption and also acts as electron traps to hinder the recombination of electrons and holes, establishing an effective electron transfer channel between adsorbed CH₄ molecule and photocatalyst, thus weakening 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.