Elemental Mercury Capture from Simulated Flue Gas by Graphite-Phase Carbon Nitride

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 (Hg-0) from simulated flue gas. The performance and kinetic behavior of g-C3N4 toward Hg-0 adsorption are investigated. Its optimal polymerization temperature and ramping rate are 550 degrees C and 5 K/min, respectively. It shows extraordinary affinity with elemental mercury associated with an Hg-0 removal efficiency >77% at 40-240 degrees 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 Hg-0 may be captured on the sp(2)-bonded carbon atoms in g-C3N4 by producing carbon-mercury (C-Hg) covalent bonds via Lewis acid-base interaction. The presence of O-2 slightly reduces the mercury capture efficiency, while the Hg-0 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 Hg-0 adsorption on g-C3N4 is controlled by both intraparticle diffusion and chemisorption processes.