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 TiO2 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 mmolCH4·h–1·gcatalyst–1, which is about 6 and 7 times of those catalyzed by TiO2 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 TiO2-{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 Ti4c site of reconstructed TiO2(001)-(1 × 4) surface is located at the valence band maximum of TiO2. Upon UV light illumination, TiO2-{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 TiO2(001) surface to adsorbed methane, leading to efficient methane combustion reaction.