Mechanistic and Kinetic Understanding of the UV254 Photolysis of Chlorine and Bromine Species in Water and Formation of Oxyhalides
- 15 September 2020
- journal article
- research article
- Published by American Chemical Society (ACS) in Environmental Science & Technology
- Vol. 54 (18), 11546-11555
- https://doi.org/10.1021/acs.est.0c02698
Abstract
This study investigated the UV254 photolysis of free available chlorine and bromine species in water. The intrinsic quantum yields for (OH)-O-center dot and X-center dot (X = Cl or Br) generation were determined by model fitting of formaldehyde formation using a tert-butanol assay to be 0.61/0.45 for HOCl/OCl- and 0.32/0.43 for HOBr/OBr-. The steady-state (OH)-O-center dot concentration in UV/HOX was higher than that in UV/OX- by a factor of 23.3 and 7.8 for Cl and Br, respectively. This was attributed to the different (OH)-O-center dot consumption rate by HOCl versus OCl-, while for HOBr/OBr-, both the (OH)-O-center dot formation and consumption rates were implied. This was supported by a k of 1.4 x 10(8) M-1 s(-1) for the (OH)-O-center dot reaction with HOCl, which was >14 times less than the k for (OH)-O-center dot reactions with OCl-, HOBr, and OBr-. Formation of ClO3- and BrO3- was found to be significant with apparent quantum yields of 0.12-0.23. A detailed mechanistic study on the formation of XO3- including a new pathway involving XO center dot is presented, which has important implications as the level of XO3- can exceed the regulation (BrO3-) or guideline (ClO3-) values during UV/halogen oxidant water treatment. Our new kinetic models well simulate the experimental results for the halogen oxidant decomposition, probe compound degradation, and formation of ClO3- and BrO3-.Funding Information
- National Research Foundation of Korea (NRF-2017M3A7B4042273)
- Gwangju Institute of Science and Technology
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