Correlating oxygen vacancies and phase ratio/interface with efficient photocatalytic activity in mixed phase TiO2

The photocatalytic activity is a result of the synergy of a succession of phenomena-photogeneration, separation, and participation of the charge carriers in redox reaction at the catalyst surface. While the extent of photogeneration is assessable in terms of absorption spectrum (band gap), the redox reaction can be correlated to specific surface area. However the respective change in the photocatalytic activity has not been rationally and consistently correlated with the above mentioned parameters. A satisfactory explanation of suppression of recombination based on separation of carriers due to differential mobility/diffusivity in the material phase(s) and/or intrinsic potential barrier exists but its correlation with common identifiable parameter/characteristics is still elusive. This paper attempts to address this issue by correlating the carrier separation with the phase ratio (phase interface) in mixed phase titania and generalizing it with the presence of oxygen vacancy at the phase interface. It essentially appears to complete the quest for identifiable parameters in the sequence of phenomena, which endow a photocatalyst with an efficient activity level. It has been done basically using photoluminescence; X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy in addition to other characterization tools such as X-ray diffraction (XRD), transmission electron microscope (TEM), UV-Vis absorption (UV-Vis DRS), and Fourier transform infrared (FTIR) studies. (C) 2015 Elsevier B.V. All rights reserved.