Chemistry of the unusually high uptake and recovery of gas-phase Hg⁰ by TiO₂ even under household fluorescent lights

Reaction mechanisms for the removal of Hg⁰ by a TiO₂ photocatalyst in the presence of O₂, the main electron acceptor for the photocatalyst, were proposed. The Hg⁰ removal efficiency was over 90%, and the desorption efficiency was approximately 70%. As the photocatalyst reacted with Hg⁰, TiO₂ was activated, forming OH radicals on the surface that oxidized Hg. HgO was formed in the first layer, and Hg⁰ was captured. Then, oxidized Hg acted as an electron acceptor. Physical adsorption between Hg⁰ molecules was realized by the reaction of Hg⁰ and HgOH. The adsorption of Hg⁰ was analyzed by various surface analysis methods, and the results proved that physical and chemical adsorption occurred. After this adsorption, desorption with alcohol was performed. Hg⁰ was desorbed, and HgO was reduced by the simultaneous illumination by light and addition of alcohol. The analytical and calculated values were compared for quantitative confirmation.