Elemental Mercury Capture from Simulated Flue Gas by Graphite-Phase Carbon Nitride
Dongjing Liu, Zhen Zhang, Feijun Luo, Jiang Wu
Abstract
Graphite-phase carbon nitrides (g-C3N4), composed of only C, N, and some impurity H, have been synthesized by direct thermal polymerization of urea in air and employed to capture elemental mercury (Hg0) from simulated flue gas. The performance and kinetic behavior of g-C3N4 toward Hg0 adsorption are investigated. Its optimal polymerization temperature and ramping rate are 550 °C and 5 K/min, respectively. It shows extraordinary affinity with elemental mercury associated with an Hg0 removal efficiency >77% at 40–240 °C under a nitrogen atmosphere, which is probably attributed to its unique electronic structure property and fluffy tremella-like morphology with ample exposed adsorption sites. The Hg0 may be captured on the sp2-bonded carbon atoms in g-C3N4 by producing carbon–mercury (C–Hg) covalent bonds via Lewis acid–base interaction. The presence of O2 slightly reduces the mercury capture efficiency, while the Hg0 removal efficiency greatly decreases by nearly a half in the presence of H2O, NO, and SO2, which is plausibly owing to the competitive adsorption or deletion of active sites on the g-C3N4 surface. The process of Hg0 adsorption on g-C3N4 is controlled by both intraparticle diffusion and chemisorption processes.