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.

Selective Removal of Perfluorooctanoic Acid Using Molecularly Imprinted Polymer-Modified TiO2Nanotube Arrays

“…According to a previous study [13], the concentration of fluoride ions generated in the degradation samples was monitored with an ion chromatography system (Dionex ICS-2000) equipped with a degasser, an autosampler, a guard column (IonPac AG11-HC), a separation column (IonPac AS11-HC), a column heater (30 ∘ C), and a conductivity detector with a suppressor. The mobile phase was an aqueous solution of KOH (30 mmol/L) with a flow rate of 1.0 mL/min.…”

“…Therefore, the development of affinity media that selectively removes PFCs from water and wastewater is of significant interest. Some researchers have reported that TiO 2 alone displays low degradation capacity for organic compounds [9,13]. Many studies seek to hybridize TiO 2 with selective adsorbents leveraging the advantages of both materials.…”

“…The unmodified TiO 2 NTs showed no significant absorptions (curve (a)). After the surface modification of the TiO 2 NTs, a N-H bending mode at around 1612 cm −1 , C=O amide stretching mode at around 1672 cm Among the characteristic peaks of PFOA, signals in the range of 1300-1100 cm −1 are attributed to C-F stretching [6,13]. These characteristic peaks were not present in the spectra of the MIP-and NIP-TiO 2 NTs (curves (c) and (d)), which confirmed that PFOA was removed after the rinsing of the samples with CH 3 OH solution.…”

What is the effect of phasing out long-chain per- and polyfluoroalkyl substances on the concentrations of perfluoroalkyl acids and their precursors in the environment? A systematic review protocol

“…Engineering solutions using oxidants and catalysts have been developed to degrade PFCAs on a small scale in the lab. For example, UV photo-oxidation with indium oxide (In 2 O 3 ) as the catalyst is effective for PFOA degradation [11], but these processes will not occur in the natural environment.…”

Temperature effect on photolysis decomposing of perfluorooctanoic acid

“…Indium oxide (In 2 O 3 ) exhibits remarkable photocatalytic activity for PFOA decomposition. The tightly bidentate compound or the bridging configuration of PFOA molecule to the In 2 O 3 surface enhances the direct decomposition of PFOA by photogenerated holes in In 2 O 3 under UV irradiation (Li et al, 2012a). Nanostructured In 2 O 3 with greater oxygen vacancy defects shows higher photocatalytic activity (Li et al, 2012b(Li et al, , 2013.…”