ScholarWorks@숙명여자대학교

초록

Titanium dioxide has been the most popular environmental photocatalyst of which role critically depends on the generation of OH radicals. In particular, the mobile free OH racial ((OHf)-O-center dot) generation and the subsequent diffusion from the surface are critical in achieving the mineralization of non-adsorbing substrates by extending the reaction zone from the surface to the solution bulk. Here the origin of the crystalline phase-dependent generation of (OHf)-O-center dot was investigated using tetramethylammonium (TMA) cation as a main probe compound for (OHf)-O-center dot in a UV/TiO2 photocatalytic system. We found a clear evidence that the mobile free OH radical is generated through a reductive conversion of dissolved O-2 on anatase only (O-2 -> H2O2 -> (OHf)-O-center dot. The surface trapped holes are not involved in (OHf)-O-center dot formation, but lead to the generation of surface-bound OH radical ((OHs)-O-center dot) on both anatase and rutile. The generation of (OHf)-O-center dot is favorable on anatase because more H2O2 are evolved (via dioxygen reduction) and adsorbed on the anatase surface. Rutile showed little sign of (OHf)-O-center dot formation. The generation of O-18-labelled p-hydroxybenzoic acid on anatase only (not rutile) from benzoic acid oxidation under O-18(2)-saturated condition provides a solid evidence that the (OHf)-O-center dot generation mechanism on anatase involves the reductive pathway. Better understanding of (OHf)-O-center dot production pathway in photocatalysis will provide a new insight leading to an engineering solution for how the production of (OHf)-O-center dot can be maximized, which is critically important in achieving the efficient photocatalytic oxidation of various pollutants.

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