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Adsorption and Oxidation of SO2 on the Surface of TiO2 Nanoparticles: The Role of Terminal hydroxyl, Oxygen Vacancy-Ti3+ States

Abstract

Herein, the absorption and oxidation reaction of SO2 on TiO2 nanoparticles at 296 K under various environmental conditions (humidity, UV irradiation, and ozone copresence) were investigated by using flow chamber reaction system, synchrotron X-ray absorption near-edge structure (XANES) and high resolution synchrotron X-ray photoelectron spectroscopy (XPS) measurements. The results showed that TiO2NP catalysis SO2 oxidation to sulfate was at an extremely rapid rate. The proper relative humidity, UV irradiation and co-presence of ozone all markedly promoted SO2 oxidation on TiO2NPs. High resolution XPS unraveled that the terminal hydroxyl (OHt) and oxygen vacancy (VO)-Ti3+ states on TiO2NPs were the activate sites for SO2 adsorption and oxidation. The data of XPS measurements suggest that SO2 was adsorbed on OHt at Ti3+ in the vicinity of VOs to form HSO3-/SO32-. The resulted adsorbed-SO32- could bound to surface bridging O (Ob) atom and transformed into SO42-. H2O molecule could dissociate on VOs-Ti3+ into two bridging hydroxyl (OHb), subsequently forms new Ob, which provides activate O sites for the adsorbed-HSO3-/SO32- and oxidized them into SO42- on the surface of TiO2NPs. The co-presence of O3 could promote H2O dissociation into OHb, promoting the formation of Ob. The co-presence of O3 may also promote the adsorbed H2O dissociation into TiO2-O2- and hydroxyl radical (OH) on VOs, facilitating the oxidation of adsorbed HSO3-/SO32-. Under UV irradiation, new VOs were created via oxidation of lattice O by photo-generated hole, resulting in increased Ob and subsequently enhanced oxidation of adsorbed HSO3-/SO32- on TiO2NPs.

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Supplementary files

Article information


Submitted
12 Feb 2020
Accepted
22 Mar 2020
First published
23 Mar 2020

Phys. Chem. Chem. Phys., 2020, Accepted Manuscript
Article type
Paper

Adsorption and Oxidation of SO2 on the Surface of TiO2 Nanoparticles: The Role of Terminal hydroxyl, Oxygen Vacancy-Ti3+ States

B. Wang, X. Li, S. Liang, R. Chu, D. Zhang, H. Chen, M. Wang, S. Zhou, W. Chen, X. Cao and W. Feng, Phys. Chem. Chem. Phys., 2020, Accepted Manuscript , DOI: 10.1039/D0CP00785D

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