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

Abstract

This paper introduces a novel method for characterizing the oxygen vacancy associates in hydrogenationmodified TiO 2 by using a positron annihilation lifetime spectroscopy (PALS). It was found that a huge number of small neutral Ti 3+ −oxygen vacancy associates, some larger size vacancy clusters, and a few voids of vacancy associates were introduced into hydrogenated TiO 2 . 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 TiO 2 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.

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“…3A. The oxidation state of Ti in the materials (Ti (2p 3/2 ), binding energy 458.6 eV; Ti (2p 1/2 ), binding energy 464.3 eV) was identical to that of Ti 4+ , as reported previously (Pillai et al, 2007;Jiang et al, 2012). The O (1s) line in TiO 2 was composed of two or three components.…”

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“…T-2 6.6% T-3 2.2% 700 Temperature (K) 800 900 ARTICLE located on the surface of the samples, respectively 45,46 . The lifetime t 1 and t 2 of T-1 is comparable with that of T-3, which indicates the similar nature of surface and bulk defects in both samples, as the nature of defects can influence the local electron density and subsequently influence the positron lifetime 47 .…”

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“…11,21 For the samples determined over multiple measurements in the present work, the results were resolved into components by the PATFIT program with good reduced x 2 around unity, and the best-fitting parameter ranged from 0.95 to 1.1 after subtraction of the source contribution and a constant background. 12,21 Fig . 1 illustrates the typical positron lifetime spectra from four samples.…”

“…The τ 1 components were also straight lines, but they were closed to the time resolution. 12,23 For the shorter component τ 1 , it is usually denote to annihilation of positrons at the defect free sits, and positrons at the defects such as individual vacancies or small vacancy at grain boundaries. 11,19,21,24 In general, the thermalized positrons annihilate from the perfect lattice with electrons.…”

“…In addition, our previous work demonstrated that the oxygen vacancies were introduced into hydrogenated TiO 2 lattice from the PALS analysis, which increased the electron-hole separation and improved the photocatalytic activity of TiO 2 . 12 Moreover, it has been known that there exists a lot of lattice changes during TiO 2 photocatalysis. [13][14][15] The urgency for the mechanism drives cutting-edge researches to the relationship between the lattice changes and photocatalytic activity of TiO 2 .…”