Photocatalytic removal of NO and Hg⁰ using microwave induced ultraviolet irradiating H₂O/O₂ mixture

We developed a novel method, microwave (MW) induced ultraviolet (UV) irradiating H₂O/O₂, to cooperatively remove NO and Hg⁰, with the efficiencies of 89.3% and 99.5%. It also can remove 97% SO₂. O₂ at a content of 2-8% was sufficient to conduct a good removal of NO and Hg⁰. Ozone (O₃) and hydroxyl radical (HO•) were proved to be the major oxidants for the removal of Hg⁰ and NO, respectively. High temperature facilitated NO removal but impaired Hg⁰ removal. SO₂ greatly promoted the removal of NO and Hg⁰ due to the formation of SO₄•^-. The presence of Cl^{- and Br}suppressed NO removal but promoted Hg⁰ removal, because Cl^- and Br^-quenched HO• to produce Cl- and Br-radicals. The produced NO₂ could be totally absorbed by the Na₂SO₃ solution that followed the main reactor. The O₃ yield and the formation of HO• under different conditions were determined using iodine quantity method and electron spin resonance (ESR). The distributions of anion concentration and mercury proportion were obtained using ion chromatography (IC) and cold atom fluorescence spectrometry (AFS), and the main products were identified to be SO₄^2-, NO₃^- and HgO. The mechanisms of removal of SO₂, NO and Hg⁰ were speculated.