Charge carrier interfacial transfer pathways from TiO2 and Au/TiO2 nanorod arrays to electrolyte and the association with photocatalysis

In this research, by means of electrochemical cyclic voltammetries (CVs), the pathways of charge carrier interfacial transfer (IT) from TiO₂ and Au/TiO₂ rutile nanorod (NR) arrays to electrolyte were studied. For pure TiO₂, the electron IT to O₂ takes place via both the conduction band (CB) states and the surface states (SS). The UV light illumination increases the electron IT via CB states, but inhibits that via SS pathway. The CV results also evidenced that the Au nanoparticles (NPs) on TiO₂ surface play dual roles of electron storage and electron IT pathway. Our results showed that the Au-induced defects, locating at Au/TiO₂ perimeter, form an important additional pathway for electron IT to O₂. UV light illumination increases the electron IT via Au NPs and Au-induced SS. In addition, we also revealed a special IT pathway of hot holes via the Au/TiO₂ perimeter contributes to the full water oxidation under visible light illumination. Therefore, the Au/TiO₂ perimeter region plays dual roles in the IT of both electrons and holes. Basing on these results, the IT pathways of charge carriers in Au/TiO₂ were illustrated from the viewpoint of energy band diagram. The photocatalytic degradation of methyl orange, photoelectrochemical oxidation of water, and photogeneration of free hydroxyl radicals (OH) were studied under UV and visible light illuminations. The association between the charge carrier IT pathways and the photocatalytic properties was also discussed.