Oxygen vacancy self-doped TiO2 nanotube arrays for efficient methane non-oxidative coupling

What is it about?

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.

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Photo by Jim Witkowski on Unsplash

Photo by Jim Witkowski on Unsplash

Why is it important?

In this work, oxygen vacancy self-doped VO-p-TNT photocatalysts were synthesized on Ti foil by a novel and robust method to achieve an efficient and reliable solar energy-mediated NOCM process. The photocatalyst is able to effectively activate the inert CH4 C–H bond, resulting in an excellent photocatalytic activity with stable, high conversion, and high selectivity, which are difficult to achieve simultaneously in thermal catalysis. In addition, an in-depth assessment of the photocatalytic mechanism through the DFT calculations reveals the great potential of VO in C–H activation and conversion.

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