Characterization of Oxygen Vacancy Associates within Hydrogenated TiO2: A Positron Annihilation Study

This paper introduces a novel method for characterizing the oxygen vacancy associates in hydrogenation-modified TiO2 by using a positron annihilation lifetime spectroscopy (PALS). It was found that a huge number of small neutral Ti3+–oxygen vacancy associates, some larger size vacancy clusters, and a few voids of vacancy associates were introduced into hydrogenated TiO2. The defects blurred the atomic lattice high-resolution transmission electron microscopy (HRTEM) images and brought about the emergence of new Raman vibration. X-ray photoelectron spectroscopy (XPS) measurement indicated that the concentration of oxygen vacancies was 3% in the TiO2 lattice. The photoluminescence (PL) spectroscopy, photocurrent, and degradation of methylene blue indicated that the oxygen vacancy associates introduced by hydrogenation retarded the charge recombination and therefore improved the photocatalytic activity remarkably.