Nature of surface oxygen intermediates on TiO2 during photocatalytic splitting of water

Titanium dioxide (TiO2) is the most widely studied solid photocatalyst, but when applied to photocatalytic splitting of water to H-2 and O-2, the evolution rate of H-2 is low and decreases with reaction time. The origin of the decreasing evolution rate for the photocatalytic splitting of water was investigated for the first time by directly monitoring the surface species on TiO2 during water photocatalysis with in situ attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectroscopy. The in situ ATR-FTIR spectroscopic analysis during UV illumination of TiO2 immersed in water reveals that surface dioxygen and hydroxyl species are formed on TiO2: charged Ti-OOH-, peroxo Ti(O-2)(2-), and bridging Ti-(OH+)-Ti groups. The accumulation of these surface oxygenated species on the TiO2 photocatalyst blocks the activation of H2O on the surface titania sites and is responsible for the decreasing H-2 evolution rate and absence of O-2 evolution. (C) 2017 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.