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

Ozone (O₃) has been widely used for the elimination of recalcitrant micropollutants in aqueous environments, due to its strong oxidation ability. However, the utilization efficiency of O₃ is constrained by its low solubility and short half-life during the treatment process. Herein, an integrated approach, using nanobubble technology and micro-environmental chemistry within cyclodextrin inclusion cavities, was studied in order to enhance the reactivity of ozonisation. Compared with traditional macrobubble aeration with O₃ in water, nanobubble aeration achieved 1.7 times higher solubility of O_3, and increased the mass transfer coefficient 4.7 times. Moreover, the addition of hydroxypropyl-β-cyclodextrin (HPβCD) further increased the stability of O₃ through formation of an inclusion complex in its molecule-specific cavity. At a HPβCD:O₃ molar ratio of 10:1, the lifespan of O₃ reached 18 times longer than in a HPβCD-free O₃ solution. Such approach accelerated the removal efficiency of the model micropollutant, 4-chlorophenol by 6.9 times, compared with conventional macrobubble ozonation. Examination of the HPβCD inclusion complex by UV-visible spectroscopy and Nuclear Magnetic Resonance analyses revealed that both O₃ and 4-chlorophenol entered the HPβCD cavity, and Benesi-Hildebrand plots indicated a 1:1 stoichiometry of the host and guest compounds. Additionally, molecular docking simulations were conducted in order to confirm the formation of a ternary complex of HPβCD:4-chlorophenol:O₃ and to determine the optimal inclusion mode. With these results, our study highlights the viability of the proposed integrated approach to enhance the ozonation of organic micropollutants.