▎ 摘　　要

Graphitic carbon nitride (g-C3N4) has attracted increasing interest owing to its unique electronic property, facile synthesis, chemical and thermal stability. In this work, a graphene-like g-C3N4 is synthesized by direct thermal polymerization of environmentally benign guanidine thiocyanate. The graphene-like g-C3N4 is further modified with NH4Br via incipient-wetness impregnation approach and applied to remove Hg-0 from coal-fired flue gas. The results indicate that the optimal polymerization temperature is 700 degrees C. The Hg-0 removal performance of g-C3N4 is enhanced by NH4Br modification. The optimal NH4Br content and reaction temperature range are 3 wt% and 120-180 degrees C, respectively. NO exerts a promotional effect on mercury removal, while SO2 displays a dual impact on Hg-0 adsorption. Low concentration of SO2 is beneficial for mercury removal, whereas high concentration of SO2 restrains Hg-0 removal to some extent. The edge carbons of g-C3N4 may function as the principal reactive sites for Hg-0 removal. The Hg-0 might be captured on the armchair edge carbons of the g-C3N4 by forming covalent carbon-mercury bonds via Lewis acid-base conjugation. Loading NH4Br onto g-C3N4 may produce carbenium bromine ion pairs at the zigzag edge carbons that represent as oxidation sites, which convert Hg-0 into HgBr2. Besides, the adsorbed Hg-0 may also be oxidized into HgO by the chemisorbed oxygen.