Spontaneous Bulk-Surface Charge Separation of TiO₂-{001} Nanocrystals Leads to High Activity in Photocatalytic Methane Combustion

Photocatalytic methane combustion is a promising strategy to eliminate methane at ambient condition, but efficient photocatalysts are still lacking. Herein, we report that uniform anatase TiO 2 nanocrystals predominantly enclosed with the {001} facets exhibit high activity in photocatalytic catalyzing methane combustion at RT in a flow-bed reactor. The photocatalytic methane reaction rate is 17.6 mmol CH 4 ·h –1 ·g catalyst –1, which is about 6 and 7 times of those catalyzed by TiO 2 nanocrystals predominantly enclosed with the {100} facets or with the {101} facets. The valence band maximum and conduction band minimum were found to locate space-separately for TiO 2 -{001} nanocrystals terminated with the reconstructed (001)-(1 × 4) surface, at the surface and in the bulk, respectively. Meanwhile, the HOMO of methane adsorbed at the 4-fold-coordinated Ti 4c site of reconstructed TiO 2 (001)-(1 × 4) surface is located at the valence band maximum of TiO 2 . Upon UV light illumination, TiO 2 -{001} nanocrystals exhibit spontaneous bulk-surface charge separation of photoexcited holes and electrons, leading to large concentrations of photoexcited holes on the surface, and subsequent facile interfacial hole transfer from TiO 2 (001) surface to adsorbed methane, leading to efficient methane combustion reaction.