Clean Modification of Carbon-Based Materials Using Hydroxyl Radicals and Preliminary Study on Gaseous Elemental Mercury Removal

Carbon-based materials (e.g., activated carbon and biomass carbons) are widely used porous materials for adsorbing gaseous Hg0 as a result of the developed porous structure. However, scarcity of active sites on the carbon-based material surface impedes its application. Existing mainstream modification methods (acid/alkaline substances, halides, sulfides, metal oxides, etc.) have deficiencies relating to high energy consumption, extreme working conditions, and/or secondary pollution. In this work, hydroxyl radicals (center dot OH) produced by the photochemical advanced oxidation process (UV/H2O2 AOP) are used to modify three kinds of carbon-based materials (activated carbon, wheat straw biochar, and corn straw biochar) to form more oxygen-containing functional groups on carbon surfaces, and then these modified carbon-based materials are used to adsorb gaseous Hg0. The interaction between free radicals and the carbon surface, modification mechanism, and adsorption principle of Hg0 are preliminarily explored. The UV/H2O2 AOP can significantly raise the quantity of oxygen-containing functional groups on carbon surfaces, further resulting in the improvement of the Hg0 removal performance. The average Hg0 removal efficiencies of the three modified samples (WSW-UV/H2O2 AOP, MSW-UV/H2O2 AOP, and AC-UV/H2O2 AOP) are up to 90.59, 87.55, and 91.46%, respectively, which are significantly higher than those samples modified by UV or H2O2 alone (a new synergistic effect for modification is discovered). Chemically adsorbed oxygen (O*) and a C-O functional group are proven to play a vital important function in the adsorbing removal process of Hg0 over the tested modified samples.

Automated summary

In this study, hydroxyl radicals (•OH) generated by the photochemical advanced oxidation process are used to modify different carbon-based materials to enhance their ability to adsorb gaseous Hg0. The modified materials show significantly improved Hg0 removal efficiency compared to samples modified with UV or H2O2 alone. Chemically adsorbed oxygen (O*) and C-O functional groups play a crucial role in the adsorption process.