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.