Hwang, Ji Young Moon, Gun-hee Kim, Bupmo Tachikawa, Takashi Majima, Tetsuro Hong, Seungwoo Cho, Kangwoo Kim, Wooyul Choi, Wonyong 2024-01-19T14:32:44Z 2024-01-19T14:32:44Z 2021-09-05 2021-06 0926-3373 https://pubs.kist.re.kr/handle/201004/116934 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. English Elsevier BV Crystal phase-dependent generation of mobile OH radicals on TiO2: Revisiting the photocatalytic oxidation mechanism of anatase and rutile Article 10.1016/j.apcatb.2021.119905 1 Applied Catalysis B: Environmental, v.286 Applied Catalysis B: Environmental 286 N scie scopus 000621626700005 2-s2.0-85099951209 Chemistry, Physical Engineering, Environmental Engineering, Chemical Chemistry Engineering Article Anatase Hydroxyl radicals Photocatalytic oxidation mechanism Rutile TiO2