Development of O₂ and NO Co-Doped Porous Carbon as a High-Capacity Mercury Sorbent

In this study, a novel Hg⁰ adsorption strategy based on nonthermal plasma and porous carbon was proposed and tested. The O₂ and NO in flue gas were used to activate porous carbon with auxiliary plasma. The plasma significantly increased the functionalities on the carbon surface, and it has a negligible effect on the textural properties of porous carbon. The O₂/NO co-doped porous carbon was used to remove elemental mercury (Hg⁰). The sample functionalized by plasma in 4% O₂ and 200 ppm NO (balanced with N₂) for 3 min exhibited superior Hg⁰ adsorption ability, which could be assigned to the formation of a large amount of C═O, C-NO, and C-NO₂. O₂, NO, and HCl have a positive effect on Hg⁰ adsorption, whereas SO₂ and H₂O have an inhibitory effect on Hg⁰ removal. The equilibrium Hg⁰ adsorption capacity of optimal O₂/NO co-doped porous carbon was found to be 12315 μg/g, which was far greater than that of brominated activated carbon (1061 μg/g). Density functional theory was used to investigate the mechanism responsible for Hg⁰ adsorption. C═O and C-NO improved the interaction of Hg⁰ with neighboring carbon sites. C-NO₂ could react with Hg⁰ by forming HgO.