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Amino acids are important constituents of microorganisms and organic matter in water and may contribute to generation of nitrogenous disinfection by-products (N-DBPs) during chlorination and chloramination. The photocatalytic oxidation of amino acids has thus been carried out to seek their mineralization and to understand their interactions with solid TiO2 surfaces, which have a wide range of applications in biological and environmental fields. In the present study, the photodecomposition of amino acids (R-CH(NH3+)COO-) onto TiO2 aqueous suspension was examined using Hammett correlations to enhance understanding the mechanism of the mineralization of amino acids to NH4+, NO 3-, and CO2. Amino acids, except Ser, Asp, and Glu, had reasonable linear Hammett correlations. The deviation of alcoholic and dicarboxylic groups containing amino acids (Ser, Asp, and Glu) from the Hammett correlations suggests that not only steric and inductive factors, but also other processes such as adsorption behavior of amino acids onto solid surface also contributed to mineralization of amino acids to oxidized species. The rate constants for the release of NH4+ and CO2 were also correlated with the second-order rate constants for the reactions of hydrated electron and OH, respectively. Correlations had negative relationships, which indicate that the nature of reactive species, reaction pathways and intermediates, involved in mineralization of amino acids under illuminated aqueous TiO2 suspensions, differs from the redox species (e.g. e aq-, O2-, and OH) in homogeneous reactions. Mechanism in light of correlations was briefly discussed. 2014 Elsevier B.V.
author list (cited authors)
Sharma, V. K., Zhao, J., & Hidaka, H.