LAUSR

Abstract 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 Hg0 from coal-fired flue gas. The results indicate that the optimal polymerization temperature is 700 °C. The Hg0 removal performance of g-C3N4 is enhanced by NH4Br modification. The optimal NH4Br content and reaction temperature range are 3 wt% and 120–180 °C, respectively. NO exerts a promotional effect on mercury removal, while SO2 displays a dual impact on Hg0 adsorption. Low concentration of SO2 is beneficial for mercury removal, whereas high concentration of SO2 restrains Hg0 removal to some extent. The edge carbons of g-C3N4 may function as the principal reactive sites for Hg0 removal. The Hg0 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 Hg0 into HgBr2. Besides, the adsorbed Hg0 may also be oxidized into HgO by the chemisorbed oxygen.