Sulfur Dioxide Adsorption on TiO₂ Nanoparticles: Influence of Particle Size, Coadsorbates, Sample Pretreatment, and Light on Surface Speciation and Surface Coverage

Abstract

The adsorption of sulfur dioxide (SO 2 ) on titanium dioxide (TiO 2 ) nanoparticle surfaces at 296 K under a wide range of conditions has been investigated. X-ray photoelectron spectroscopy is used to investigate the surface speciation and surface coverage of sulfur-containing products on ca. 4 nm TiO 2 anatase particles that remain on the surface following adsorption of SO 2 . The effects of various environmental conditions of relative humidity, molecular oxygen, and broadband UV/vis irradiation as well as sample pretreatment were found to impact the speciation of adsorbed SO 2 as well as the saturation coverage. In particular, in the absence of light, the majority surface species upon SO 2 adsorption is found to be adsorbed sulfite. Broadband UV/vis irradiation during sulfur dioxide adsorption leads to an increase (nearly 2-fold) in the amount of adsorbed sulfur species, as compared to experiments with no light, and results in the formation of adsorbed sulfate. The formation of sulfate was quantitative in the presence of molecular oxygen. New surface species including chemisorbed molecular SO 2 were observed on samples that have been reduced in vacuum through argon ion sputtering. The total amount of adsorbed sulfur was impacted by surface hydroxyl group coverage and molecularly adsorbed water layer. Additionally, comparison of sulfur dioxide adsorption on 4 versus 32 nm sized anatase nanoparticles showed that surface saturation coverages of adsorbed sulfite on the 4 nm particles was almost twice that of 32 nm particles as measured by the S2p:Ti2p peak area ratios, thus showing an increase in the inherent adsorption capacity of the smaller particles. Proposed adsorption sites and mechanisms to account for the observed experimental data are discussed.

Photocatalytic removal of SO2 over Mn doped titanium dioxide supported by multi-walled carbon nanotubes

“…It was reported in the research of Li et al [25] that NO was mainly adsorbed to the hydroxyl groups on the surface of photocatalyst due to strong bonding NO to TiO 2 induced by charge transfer. However, the hydroxyl groups are also important for SO 2 chemisorbed on TiO 2 in the form of sulfite [26]. Therefore, competition for the surface hydroxyl groups between SO 2 and NO is inevitable while introducing SO 2 and NO into simulated flue gas simultaneously.…”

SiC–FET based SO2 sensor for power plant emission applications

“…There was also a difference in the size of the response since humidity increased the size of the response to SO 2 . Most likely this was caused by a surface reaction between SO 2 and water forming HSO 3 - [30,31], which might adsorb on the sensor surface and thereby contribute to the response of by the sensor. In Figure 10(b) shows a close up of the sensor signal.…”

Mineral dust photochemistry induces nucleation events in the presence of SO2

“…During advection, mineral dust particles interact with sulfur dioxide (SO 2 ) and other atmospheric trace gases. Current knowledge shows that sulfur dioxide adsorbs onto many of the components of mineral dust as adsorbed sulfite, which can be oxidized to sulfate (3), for example, by ozone (4), by surface defect sites, or by photooxidation (5)(6)(7)(8). These previous studies (and references therein) clearly demonstrated that particulate sulfate is the end product of the SO 2 chemistry on dust surfaces (9).…”