Disinfection byproducts (DBPs) such as trihalomethanes (THMs), haloacetic acids (HAAs) etc. are mostly generated from chlorination methods to disinfect drinking water. Natural occurring organic matters will be reacted to form DBPs which are potentially toxic. These products are sensitive to UV irradiation and their subsequent photochemical reactions contribute to the transformation of contaminants and goes into environmental aquatic systems. Tribromoacetic acid (TBAA), one of the typically HAAs, is widespread in the drinking water. Since they have the −CBr3 chromophore, they have high reactivity under UV irradiation. This property can be utilized to effectively remove the toxic compound in water. However, the mechanisms of the photochemical reactions of TBAA in aqueous solution have not been fully understood because of the short lifetime of Br radical intermediates and the extreme difficulty in the detection of these species experimentally. In this study, with the aid of ultrafast transient absorption spectroscopy, we can examine the chemical reaction of TBAA with H2O under 266 nm laser excitation. Our results indicate that isomerization of TBAA lead to the formation of HOOCCBr2−Br and reacts with H2O to produce OH adduct. The reaction kinetics between the isomer product of TBAA and water is about ~109M-1s-1. We also carried out DFT calculations for the UV-initiated photodegradation of TBAA. The profile of the potential energy surface was constructed, and the possible channels involved in the reaction are discussed. Several energetically favorable reaction pathways are revealed for the first time. The calculated results were compared with the available experimental observations. Two product pathways are energetically feasible for HOOCCBr2−Br degradation and are consistent with the experimentally observed products CO2 and CO, and the additional products oxalic acid also predicted.

UV-initiated photooxidation process of disinfection byproducts: mechanism of the degradation of tribromoacetic acid by femtosecond transient absorption spectroscopy and density functional theory study

2019 Spring National Meeting

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