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

Abstract

Nanocomposites of MO_x–TiO₂ (M = Cu, Mn, Ag) supported on foam nickel (MO_x/TiFN) were successfully applied in the photocatalytic ozonation of gaseous alkane. All MO_x samples presented nanoflake structures with two metal oxides, corresponding to Cu₂O and CuO in CuO_x, Mn₂O₃ and MnO₂ in MnO_x, and Ag and Ag₂O in AgO_x. 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 and ˙O₂⁻ from O₃ conversion on MO_x were responsible for the enhanced efficiency. And ˙O₂⁻ made a higher contribution to the enhancement, since the relative amount of ˙O₂⁻ increased by 3.2 to 7.9 times more than ˙OH after MO_x composition. Our experimental and theoretical mechanism results further confirmed that both ˙OH and ˙O₂⁻ were important for the epoxidation transformation of n-hexane on MO_x/TiFN, while ˙OH dominated in the conversion of alcohol intermediates to corresponding radicals, and ˙O₂⁻ 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.