Hydrogenated nanotubes/nanowires assembled from TiO2 nanoflakes with exposed {111} facets: excellent photo-catalytic CO2 reduction activity and charge separation mechanism between (111) and () polar surfaces

Abstract

Nanotubes/nanowires assembled from TiO₂ nanoflakes with exposed {111} facets were prepared via heating a mixture of titanium(IV) oxysulfate–sulfuric acid hydrate, glacial acetic acid and water. The photocatalytic CO₂ reduction activity of the as-prepared TiO₂ nanoflake based nanotubes/nanowires was remarkably increased through hydrogenation. The apparent quantum yield for CH₄ evolution of the hydrogenated TiO₂ nanotubes/nanowires is as high as 17.4%, which is higher than that of all the TiO₂ based photocatalysts reported until now. The excellent photocatalytic performance is ascribed to the exposed clean TiO₂ {111} facets and enhanced solar absorption. On the basis of the polar structure of the exposed TiO₂ {111} crystal facets, we proposed a separation mechanism of photocreated electrons and holes. A spontaneous electric field (Es) is created between polar TiO₂ (111) and () planes. Under Es, the photocreated electrons and holes transit to TiO₂ (111) and () surfaces, respectively. Redox reactions selectively take place at the Ti–TiO₂ (111) and O–TiO₂ () polar planes. The charge separation mechanism provides a clear insight for understanding the photocatalysis of high performance semiconductor nanocrystals and offers guidance for the design of high performance photocatalysts for CO₂ reduction.