Gas-Phase Mercury Removal by Modified Activated Carbons Treated with Ar-O2 Non-Thermal Plasma under Different O2 Concentrations

During the plasma modification process on activated carbon surface, reactive gas of O2 in the plasma field dominates the formation of oxygen-containing groups on activated carbon surface, which is a key factor that affects the mercury adsorption. Previous studies showed that change the O2 concentration would influence the generation of oxygen-containing groups and thus affect the mercury adsorption. It is important to investigate the effects of O2 concentration in the non-thermal plasma field on the mercury adsorption characteristic of modified activated carbon. This work presents the results of the novel use of non-thermal plasma in Ar-O2 gas to increase surface oxygen functionality on the surface of a commercially available biomass carbon. The volume fraction of O2 in the Ar-O2 mixture was varied from 10 % to 100 %. The surface physical and chemistry properties of modified activated carbon were analyzed by using BET, FT-IR and XPS techniques. Results showed that activated carbon modified by Ar-O2 non-thermal plasma showed significantly better mercury removal performance compared with the original activated carbon. Moreover, increase O2 concentration in the plasma field can further increase the mercury removal efficiency of modified activated carbon. Higher O2 concentration can produce more O radicals during plasma system and facilitated the formation of carbonyl and ester groups on activated carbon surface and thus enhanced the mercury removal. Temperature programmed desorption (TPD) results indicated that mercury reacted with ester groups were prior to carbonyl groups. When O2 concentration increased to 100 %, the ester groups of modified activated carbon dominated the mercury adsorption process.