Professional Education


  • Doctor of Philosophy, Johns Hopkins University (2017)

All Publications


  • Aqueous Chlorination Kinetics of Cyclic Alkenes-Is HOCI the Only Chlorinating Agent that Matters? ENVIRONMENTAL SCIENCE & TECHNOLOGY Lau, S. S., Reber, K. P., Roberts, A. 2019; 53 (19): 11133–41

    Abstract

    Although Cl2 and Cl2O have been recognized as highly reactive constituents of free available chlorine (FAC), robust rate constants for Cl2 and Cl2O remain scarce in the environmental literature. In this work, we explored the chlorination kinetics of three structurally related alkenes (α-ionone, β-ionone, and dehydro-β-ionone), a class of compounds whose reactivities with Cl2 and Cl2O have not been previously investigated. Second-order rate constants for Cl2, Cl2O, and HOCl were computed from experimental rate constants obtained at various pH values, [Cl-], and [FAC]. Our results show that while HOCl is the predominant chlorinating agent for the most reactive alkene, Cl2 and Cl2O can dominate the chlorination kinetics of the less reactive alkenes at high [Cl-] and high [FAC], respectively. The tradeoff between overall reactivity with FAC and selectivity for Cl2 and Cl2O previously observed for aromatic compounds also applies to the alkenes examined. In laboratory experiments in which high [FAC] may be used, omission of Cl2O in data modeling could yield second-order rate constants of dubious validity. In chlorinating real waters with elevated [Cl-], formation of Cl2 may enhance the formation kinetics of chlorinated disinfection byproducts (DBPs) and exacerbate the burden of DBP control for water utilities.

    View details for DOI 10.1021/acs.est.9b01171

    View details for Web of Science ID 000488993500010

    View details for PubMedID 31478649

  • 1,3,5-Trimethoxybenzene (TMB) as a new quencher for preserving redox-labile disinfection byproducts and for quantifying free chlorine and free bromine ENVIRONMENTAL SCIENCE-WATER RESEARCH & TECHNOLOGY Lau, S. S., Dias, R. P., Martin-Culet, K. R., Race, N. A., Schammel, M. H., Reber, K. P., Roberts, A., Sivey, J. D. 2018; 4 (7): 926–41

    View details for DOI 10.1039/c8ew00062j

    View details for Web of Science ID 000436569400003

  • Chlorination Revisited: Does Cl- Serve as a Catalyst in the Chlorination of Phenols? ENVIRONMENTAL SCIENCE & TECHNOLOGY Lau, S. S., Abraham, S. M., Roberts, A. 2016; 50 (24): 13291–98

    Abstract

    The aqueous chlorination of (chloro)phenols is one of the best-studied reactions in the environmental literature. Previous researchers have attributed these reactions to two chlorine species: HOCl (at circum-neutral and high pH) and H2OCl+ (at low pH). In this study, we seek to examine the roles that two largely overlooked chlorine species, Cl2 and Cl2O, may play in the chlorination of (chloro)phenols. Solution pH, chloride concentration, and chlorine dose were systematically varied in order to assess the importance of different chlorine species as chlorinating agents. Our findings indicate that chlorination rates at pH < 6 increase substantially when chloride is present, attributed to the formation of Cl2. At pH 6.0 and a chlorine dose representative of drinking water treatment, Cl2O is predicted to have at best a minor impact on chlorination reactions, whereas Cl2 may contribute more than 80% to the overall chlorination rate depending on the (chloro)phenol identity and chloride concentration. While it is not possible to preclude H2OCl+ as a chlorinating agent, we were able to model our low-pH data by considering Cl2 only. Even traces of chloride can generate sufficient Cl2 to influence chlorination kinetics, highlighting the role of chloride as a catalyst in chlorination reactions.

    View details for DOI 10.1021/acs.est.6b03539

    View details for Web of Science ID 000390620900015

    View details for PubMedID 27993072