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

Abstract

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 SO42-, NO3− and HgO. The mechanisms of removal of SO2, NO and Hg0 were speculated.