title: Photoinduced Hydrodefluorination Mechanisms of Perfluorooctanoic Acid by the SiC/Graphene Catalyst.
abstract: Cleavage of the strong carbon-fluorine bonds is critical for elimination of perfluorooctanoic acid (PFOA) from the environment. In this work, we investigated the decomposition of PFOA with the SiC/graphene catalyst under UV light irradiation. The decomposition rate constant (k) with SiC/graphene was 0.096 h(-1), 2.2 times higher than that with commercial nano-TiO2. Surface fluorination on SiC/graphene was analyzed by X-ray photoelectron spectroscopy (XPS), revealing the conversions of Si-H bonds into Si-F bonds. A different route was found to generate the reactive Si-H bonds on SiC/graphene, substituting for silylium (R3Si(+)) to activate C-F bonds. During the activation process, photogenerated electrons on SiC transfer rapidly to perfluoroalkyl groups by the medium of graphene, further reducing the electron cloud density of C-F bonds to promote the activation. The hydrogen-containing hydrodefluorination intermediates including (CF3(CF2)2CFH, CF3(CF2)3CH2, CF3(CF2)4CH2, and CF3(CF2)4CFHCOOH) were detected to verify the hydrodefluorination process. The photoinduced hydrodefluorination mechanisms of PFOA can be consequently inferred as follows: (1) fluorine atoms in perfluoroalkyl groups were replaced by hydrogen atoms due to the nucleophilic substitution reaction via the Si-H/C-F redistribution, and (2) generation of CH2 carbene from the hydrogen-containing perfluoroalkyl groups and the C-C bonds scission by the Photo-Kolbe decarboxylation reaction under UV light excitation. This photoinduced hydrodefluorination provides insight into the photocatalytic decomposition of perfluorocarboxylic acids (PFCAs) in an aqueous environment.
authors.affiliation: State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University , Beijing 100875, P.R. China.
authors.forename: Dahong
authors.initials: D
authors.lastname: Huang
authors.affiliation: State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University , Beijing 100875, P.R. China.
authors.forename: Lifeng
authors.initials: L
authors.lastname: Yin
authors.affiliation: State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University , Beijing 100875, P.R. China.
authors.forename: Junfeng
authors.initials: J
authors.lastname: Niu
mesh_terms: D002384:Catalysis; D006108:Graphite; D056951:Photoelectron Spectroscopy; D014466:Ultraviolet Rays; D018508:Water Purification
chemical_list: D006108:Graphite