Graphitic Carbon Nitride for Gaseous Mercury Emission Control: A Review
Dongjing Liu, Lingtao Yang, Yang Ling, Jiang Wu, Bin Li, Chaoen Li
Abstract
Mercury emissions from combustion of coal, biomass, and solid waste threaten human life and the environment. As the principal mercury species in flue gas, elemental mercury (Hg0) can easily escape from available air pollution control instruments because of its chemical inertness, high volatility, and aqueous insolubility. Recently, graphitic carbon nitride (g-C3N4) seems to be an intriguing candidate for Hg0 emission control. This review highlights the latest advances in adsorptive and photocatalytic removal of Hg0 by g-C3N4-based composites. Metal oxide (MeOx)- and halide-modified g-C3N4 can effectively capture Hg0 from simulated flue gas. Nonetheless, acidic flue gas components can degrade the performances of MeOx/g-C3N4 adsorbents, while halide-modified g-C3N4 suffers from release of halogen and potential leaching risk of mercury. Metal sulfide (MeSx)-modified g-C3N4 appears to be the best candidate for Hg0 capture owing to its superior tolerance to sulfur dioxide, fast adsorption rate, and high mercury capacity. Combining bismuth oxyhalides (BiOX) with g-C3N4 can promote photocatalytic oxidation of elemental mercury under visible light irradiation; nonetheless, the Hg0 removal efficiency is still unsatisfactory, and the underlying photocatalysis mechanism is not yet clear.