Stabilization and prolonged reactivity of aqueous-phase ozone with cyclodextrin

Abstract

Recalcitrant organic groundwater contaminants, such as 1,4-dioxane, may require strong oxidants for complete mineralization. However, their efficacy for in-situ chemical oxidation (ISCO) is limited by oxidant decay and reactivity. Hydroxypropyl-β-cyclodextrin (HPβCD) was examined for its ability to stabilize aqueous-phase ozone (O) and prolong oxidation potential through inclusion complex formation. Partial transformation of HPβCD by O was observed. However, HPβCD proved to be sufficiently recalcitrant, because it was only partially degraded in the presence of O. The formation of a HPβCD:O clathrate complex was observed, which stabilized decay of O. The presence of HPβCD increased the O half-life linearly with increasing HPβCD:O molar ratio. The O half-life in solutions increased by as much as 40-fold relative to HPβCD-free O solutions. Observed O release from HPβCD and indigo oxidation confirmed that the formation of the inclusion complex is reversible. This proof-of-concept study demonstrates that HPβCD can complex O while preserving its reactivity. These results suggest that the use of clathrate stabilizers, such as HPβCD, can support the development of a facilitated-transport enabled ISCO for the O treatment of groundwater contaminated with recalcitrant compounds.

An integrated approach using ozone nanobubble and cyclodextrin inclusion complexation to enhance the removal of micropollutants

“…S7), which has been reported previously with other guest molecules and has been explained in terms of a change in the environment of the molecule as it is included within the CD cavity (Hendy and Breslin, 2011;Lin et al, 2020). Usually, O3 would have been completely degraded after 1-3 hour in DI water (Dettmer et al, 2017), however in this study, absorption peaks were still observed even after 12 h in the presence of HPβCD (Fig 5a and Fig. S7).…”

“…2a and Table 1). As the hydroxypropyl group of HPβCD could be oxidised, the ring in glycosides remains stable in the presence of oxidants, including O3 (Manhas et al, 2007;Dettmer et al, 2017). Addition of small amounts of HPβCD, e.g.…”

“…Nevertheless, these acidic effluents would need further treatment before discharge, which would incur considerable hidden costs for the application. Another promising method was through use of cyclodextrins (CDs), which contain doughnut-shaped molecular structures with a hydrophilic outer shell and a hydrophobic inner cavity (Cai et al, 2015;Dettmer et al, 2017;Khan et al, 2018). This low polarity cavity can encapsulate dissolved size-matched guest compounds via coordination through various weak interactions (e.g.…”

“…sorption or degradation) (Cheirsilp and Rakmai, 2016;Zhou et al, 2018;Zhou et al, 2020). According to this concept, Dettmer et al (2017) initially investigated the hydroxypropyl-β-cyclodextrin (HPβCD):O3 clathrate complex as an ozone stabilizer. The addition of HPβCD has been further proven to significantly enhance the ozonation of 1,4-Dioxane, Trichloroethylene and 1,1,1-Trichloroethane (Khan et al 2019).…”

Solution Density Models as Functions of Sodium Chloride, Hydroxypropyl-β-cyclodextrin, and Temperature (278.15–333.15 K) via Progressive Linear and Stepwise Regression

“…This unique arrangement gives CDs the ability to form inclusion complexes with low-polarity molecules of appropriate size and shape . CDs have been utilized in an increasingly wide range of applications such as drug carriers, − oil recovery, cosmetics, , agriculture, analytical chemistry, and aquifer remediation. − …”