title: DFT studies on the heterogeneous oxidation of SO2by oxygen functional groups on graphene.
abstract: The heterogeneous oxidation of SO2has been the subject of intense scrutiny in atmospheric chemistry because of the adverse effects of sulfate particles. Although it has been found that the soot particles with a graphene-like structure play an important role in the oxidation of SO2, little is known about the atomic-level mechanism involved. Here, we studied the oxidation of SO2on oxygen-functionalized graphene using density functional theory (DFT) calculation. The results showed that SO2is oxidized by the epoxide group via a two-step mechanism, where the C-O bond away from the SO2is broken first, followed by the breaking of the other C-O bond and the synchronous formation of a new S-O bond. The energy barriers are significantly decreased when solvation free energies are involved, suggesting that humidity is favorable for promoting the oxidation by reducing the reaction barrier. The energy barriers for H2SO3oxidation are much higher than that for SO2oxidation, indicating that the direct conversion of SO2to SO3is the main pathway for the oxidation of SO2by oxygen-functionalized graphene sheets in both the gas phase and solution. The reduced density gradient (RDG) analysis showed that the hydrogen bond formed between H2SO3and epoxide groups enhances the stability of the reaction complex, and is responsible for the high energy barrier that has to be overcome for the reaction to proceed. These atomistic studies proposed a two-step mechanism for the oxidation of SO2on the oxygen-functionalized graphene-like carbonaceous surfaces under ambient conditions.
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. honghe@rcees.ac.cn.
authors.forename: Guangzhi
authors.identifier: http://orcid.org/0000-0003-1770-3522
authors.initials: G
authors.lastname: He
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. honghe@rcees.ac.cn and Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China and University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Hong
authors.initials: H
authors.lastname: He