title: Efficient photocatalytic decomposition of perfluorooctanoic acid by indium oxide and its mechanism.
abstract: Perfluorooctanoic acid (C(7)F(15)COOH, PFOA) has increasingly attracted worldwide concerns due to its global occurrence and resistance to most conventional treatment processes. Though TiO(2)-based photocatalysis is strong enough to decompose most organics, it is not effective for PFOA decomposition. We first find that indium oxide (In(2)O(3)) possesses significant activity for PFOA decomposition under UV irradiation, with the rate constant about 8.4 times higher than that by TiO(2). The major intermediates of PFOA were C(2)-C(7) shorter-chain perfluorocarboxylic acids, implying that the reaction proceeded in a stepwise manner. By using diffuse reflectance infrared Fourier transform spectroscopy, (19)F magic angle spinning nuclear magnetic resonance, and electron spin resonance, we demonstrate that the terminal carboxylate group of PFOA molecule tightly coordinates to the In(2)O(3) surface in a bidentate or bridging configuration, which is beneficial for PFOA to be directly decomposed by photogenerated holes of In(2)O(3) under UV irradiation, while PFOA coordinates to TiO(2) in a monodentate mode, and photogenerated holes of TiO(2) preferentially transform to hydroxyl radicals, which are inert to react with PFOA. PFOA decomposition in wastewater was inhibited by bicarbonate and other organic matters; however, their adverse impacts can be mostly avoided via pH adjustment and ozone addition.
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China.
authors.forename: Xiaoyun
authors.initials: X
authors.lastname: Li
authors.forename: Pengyi
authors.initials: P
authors.lastname: Zhang
authors.forename: Ling
authors.initials: L
authors.lastname: Jin
authors.forename: Tian
authors.initials: T
authors.lastname: Shao
authors.forename: Zhenmin
authors.initials: Z
authors.lastname: Li
authors.forename: Junjie
authors.initials: J
authors.lastname: Cao
mesh_terms: D000327:Adsorption / Q000528:radiation effects; D002210:Caprylates / Q000737:chemistry* / Q000528:radiation effects*; D002244:Carbon / Q000032:analysis; D002384:Catalysis / Q000528:radiation effects; D004578:Electron Spin Resonance Spectroscopy; D005461:Fluorine / Q000032:analysis; D005466:Fluorocarbons / Q000737:chemistry* / Q000528:radiation effects*; D007204:Indium / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008968:Molecular Conformation; D017550:Spectroscopy, Fourier Transform Infrared; D013113:Spin Labels; D013997:Time Factors; D014025:Titanium / Q000737:chemistry; D014466:Ultraviolet Rays; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000528:radiation effects
chemical_list: D002210:Caprylates; D005466:Fluorocarbons; D013113:Spin Labels; D014874:Water Pollutants, Chemical; D007204:Indium; C009495:titanium dioxide; D005461:Fluorine; C047711:indium oxide; D002244:Carbon; C023036:perfluorooctanoic acid; D014025:Titanium