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An Unexpected Fluctuating Reactivity for Odd and Even Carbon Numbers in the TiO 2 ‐Based Photocatalytic Decarboxylation of C2‐C6 Dicarboxylic Acids
Author(s) -
Sun Yiran,
Chang Wei,
Ji Hongwei,
Chen Chuncheng,
Ma Wanhong,
Zhao Jincai
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201303236
Subject(s) - denticity , photocatalysis , decarboxylation , reactivity (psychology) , chemistry , chelation , dicarboxylic acid , aqueous solution , carbon fibers , degradation (telecommunications) , medicinal chemistry , catalysis , inorganic chemistry , organic chemistry , photochemistry , materials science , metal , medicine , telecommunications , alternative medicine , pathology , composite number , computer science , composite material
Abstract The degradation behaviours of five straight‐chain dicarboxylic acids (from ethanedioic acid to hexanedioic acid) were compared in aqueous TiO 2 ‐based photocatalysis. When all other conditions were identical, the degradation rates were found to fluctuate regularly with the parity of the number of carbon atoms. Dicarboxylic acids with an even number of carbon atoms (e‐DAs) always degraded more slowly than those acids with an odd number of carbon atoms (o‐DAs). This unusual fluctuation in the reactivity for the degradation of dicarboxylic acids by TiO 2 ‐based photocatalysis is very closely related to the different pre‐coordination modes of the acids with the photocatalyst. Attenuated total reflection FTIR (ATR‐FTIR) of e‐DAs labelled with 13 C showed that both carboxyl groups of the acid coordinate to TiO 2 through bidentate chelating forms. In contrast, only one carboxyl group of the o‐DAs coordinated to TiO 2 in a bidentate chelating manner, whereas the other formed a monodentate binding linkage. The bidentate chelating form with bilateral symmetric coordination did not favour degradation. Isotope‐labelling experiments were performed with 18 O 2 to observe the different ways in which incorporated oxygen entered the initial decarboxylated products of e‐ and o‐DAs. For the degradation of butanedioic acid, (45.9±0.5) % of the oxygen in the formed propanedioic acid came from H 2 O, whereas for pentanedioic acid, (97.4±0.2) % of the oxygen in the formed butanedioic acid came from H 2 O. Our results demonstrate that in TiO 2 ‐based photocatalysis, the reactivity of active species, such as . OH/h vb + , is far from non‐selective and that the attacks of these active species on organic substrates are significantly affected by the coordination patterns of the substrates on the TiO 2 surface.