Crystal phase-dependent generation of mobile OH radicals on TiO2: Revisiting the photocatalytic oxidation mechanism of anatase and rutile
- Authors
- Hwang, Ji Young; Moon, Gun-hee; Kim, Bupmo; Tachikawa, Takashi; Majima, Tetsuro; Hong, Seungwoo; Cho, Kangwoo; Kim, Wooyul; Choi, Wonyong
- Issue Date
- 5-Jun-2021
- Publisher
- ELSEVIER
- Keywords
- Anatase; Hydroxyl radicals; Photocatalytic oxidation mechanism; Rutile; TiO2
- Citation
- APPLIED CATALYSIS B-ENVIRONMENTAL, v.286, pp 1 - 8
- Pages
- 8
- Journal Title
- APPLIED CATALYSIS B-ENVIRONMENTAL
- Volume
- 286
- Start Page
- 1
- End Page
- 8
- URI
- https://scholarworks.sookmyung.ac.kr/handle/2020.sw.sookmyung/146538
- DOI
- 10.1016/j.apcatb.2021.119905
- ISSN
- 0926-3373
1873-3883
- Abstract
- 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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