Adsorption and oxidation of SO2 on the surface of TiO2 nanoparticles: the role of terminal hydroxyl and oxygen vacancy–Ti3+ states. Issue 18 (28th April 2020)

• Record Type: Journal Article
• Authors: Wang, Bing; Li, Xue; Liang, Shanshan; Chu, Runxuan; Zhang, Dan; Chen, Hanqing; Wang, Meng; Zhou, Shuang; Chen, Wei; Cao, Xingzhong; Feng, Weiyue
• Is Part Of: Physical chemistry chemical physics. Volume 22:Issue 18(2020)
• Page Start: 9943
• Page End: 9953
• Publication Date: 2020-04-28
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/d0cp00785d
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : The absorption and oxidation reactions of SO2 on TiO2 nanoparticles were investigated by using a flow chamber, synchrotron X-ray absorption near-edge structure and high resolution synchrotron X-ray photoelectron spectroscopy techniques. Abstract : Herein, the absorption and oxidation reactions of SO2 on TiO2 nanoparticles (TiO2 NPs) at 296 K under various environmental conditions (humidity, UV irradiation, and ozone copresence) were investigated by using a 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 oxidation of SO2 to sulfate via TiO2 NP catalysis happened at a very rapid rate. The appropriate relative humidity, UV irradiation and co-presence of ozone all markedly promoted SO2 oxidation on TiO2 NPs. High resolution XPS unraveled that the terminal hydroxyl (OHt ) and oxygen vacancy (VO )–Ti 3+ states on TiO2 NPs were the active sites for SO2 adsorption and oxidation. The data of XPS measurements suggest that SO2 was adsorbed on a OHt next to a Ti 3+ VO and reacted to form HSO3 − . HSO3 − can then transform into SO3 2− via transfer of a proton. The resulting adsorbed SO3 2− could bind to a surface bridging O (Ob ) atom and transform into SO4 2− . A H2 O molecule could dissociate on VO –Ti 3+ into two bridging hydroxyl (OHb ) groups, subsequently forming new Ob, which provides an active O site for the adsorbed HSO3 − /SO3 2− and oxidizes them into HSO4 − /SO4 2− on the surface of the TiO2 NPs. The copresence of O3 could promote H2 O dissociation into OHb, promoting the formation of Ob . The copresence of O3 may also promote the dissociation of adsorbed H2 O into TiO2 –O2 − and hydroxyl radicals (˙OH) on VO s, facilitating the oxidation of adsorbed HSO3 − /SO3 2− . Under UV irradiation, new VO s were created via oxidation of lattice O by photo-generated holes, resulting in increased Ob and subsequently enhanced oxidation of adsorbed HSO3 − /SO3 2− on TiO2 NPs.