Photocatalytic ozonation mechanism of gaseous n-hexane on MOx-TiO2-foam nickel composite (M = Cu, Mn, Ag): unveiling the role of OH and O2-

Nanocomposites of MOx-TiO2 (M = Cu, Mn, Ag) supported on foam nickel (MOx/ TiFN) were successfully applied in the photocatalytic ozonation of gaseous alkane. All MOx samples presented nanoflake structures with two metal oxides, corresponding to Cu2O and CuO in CuOx, Mn2O3 and MnO2 in MnOx, and Ag and Ag2O in AgOx. These binary metal oxides composited with TiFN displayed 1.3 to 2.0 times higher degradation and mineralization efficiencies toward 350 ppmv of n-hexane than TiFN. The promoted (OH)-O-center dot and O-center dot(2)- from O-3 conversion on MOx were responsible for the enhanced efficiency. And O-center dot(2)- made a higher contribution to the enhancement, since the relative amount of O-center dot(2)- increased by 3.2 to 7.9 times more than (OH)-O-center dot after MOx composition. Our experimental and theoretical mechanism results further confirmed that both (OH)-O-center dot and O-center dot(2)- were important for the epoxidation transformation of n-hexane on MOx/TiFN, while (OH)-O-center dot dominated in the conversion of alcohol intermediates to corresponding radicals, and O-center dot(2)- determined the subsequent epoxidation transformations of these radicals to four epoxides with 3, 5 and 6 membered rings. The present work could provide deep insight into an enhanced mechanism for nanomaterial photocatalytic ozonation technology, and efficiently replenish alkane atmospheric transformation mechanisms.