Photocatalytic oxidation removal of elemental mercury from flue gas. A review

Air pollution caused by mercury emissions from combustion and pyrolysis of fossil fuels, biomass, and solid wastes is a major health issue. Elemental mercury (Hg0), the dominant species in flue gas, is poorly captured by actual control equipments because Hg0 has a high volatility and is insoluble in water. Alternatively, photocatalytic processes can oxidize Hg0 into Hg compounds that are easier to remove. Here we review the recent research on oxidative removal of Hg0 by photocatalysts, with focus on titanium dioxide, bismuthides, silver compounds and hybrid photocatalysts. We discuss the Hg0 removal performances and mechanisms of catalytic oxidation. The TiO2 photocatalyst often suffers from low absorption of solar energy and easy recombination of photoinduced electron–hole couples. BiOIO3 appears as a promising photocatalyst due to its high Hg0 oxidation activity under visible light irradiation. Silver carbonates and silver halides are newly developed visible-light-responsive photocatalysts for Hg0 removal. Fast separation and transformation of photogenerated electrons and holes control the performance of Hg0 removal by photocatalysts.