Formation of sulfur oxide groups by SO2 and their roles in mercury adsorption on carbon-based materials.

The presence of SO2 display significant effect on the mercury (Hg) adsorption ability of carbon-based sorbent. Yet the adsorption and oxidation of SO2 on carbon with oxygen group, as well as the roles of different sulfur oxide groups in Hg adsorption have heretofore been unclear. The formation of sulfur oxide groups by SO2 and their effects on Hg adsorption on carbon was detailed examined by the density functional theory. The results show that SO2 can be oxidized into SO3 by oxygen group on carbon surface. Both C-SO2 and C-SO3 can improve Hg adsorption on carbon site, while the promotive effect of C-SO2 is stronger than C-SO3. Electron density difference analyses reveal that sulfur oxide groups enhance the charge transfer ability of surface unsaturated carbon atom, thereby improving Hg adsorption. The experimental results confirm that surface active groups formed by SO2 adsorption is more active for Hg adsorption than the groups generated by SO3.

DFT and Experimental Studies on the Mechanism of Mercury Adsorption on O2-/NO-Codoped Porous Carbon.

The utilization of O2 and NO in flue gas to activate the raw porous carbon with auxiliary plasma contributes to an effective mercury (Hg)-removal strategy. The lack of in-depth knowledge on the Hg adsorption mechanism over the O2-/NO-codoped porous carbon severely limits the development of a more effective Hg removal method and the potential application. Therefore, the generation processes of functional groups on the surface during plasma treatment were investigated and the detailed roles of different groups in Hg adsorption were clarified. The theoretical results suggest that the formation of functional groups is highly exothermic and they preferentially form on a carbon surface, and then affect Hg adsorption. The active groups affect Hg adsorption in a different manner, which depends on their nature. All of these active groups can improve Hg adsorption by enhancing the interaction of Hg with a surface carbon atom. Particularly, the preadsorbed NO2 and O3 groups can react directly with Hg by forming HgO. The experimental results confirm that the active groups cocontribute to the high Hg removal efficiency of O2-/NO-codoped porous carbon. In addition, the mercury temperature-programmed desorption results suggest that there are two forms of mercury present on O2-/NO-codoped porous carbon, including a carbon-bonded Hg atom and HgO.