Efficiency of TiO2 photocatalytic degradation of HHCB (1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethylcyclopenta[γ]-2-benzopyran) in natural aqueous solutions by nested experimental design and mechanism of degradation

The present paper deals with the photocatalytic transformation of HHCB (1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethylcyclopenta[γ]-2-benzopyran, trade name Galaxolide), under simulated solar irradiation using titanium dioxide as a photocatalyst. The investigation has involved a study of HHCB decomposition under a variety of experimental conditions, the identification of intermediate compounds, as well as the assessment of mineralization. A fully nested experimental design was applied to study the effect of various matrices (i.e. distilled water, surface water and wastewater) as well as the initial HHCB concentration on the variation of the photocatalytic efficiency. GC/MS and LC/MS were brought to bear in assessing the temporal course of the photocatalyzed process. A first pathway involves the hydroxylation, that is confined to the benzopyran moiety. Another route proceeds through the detachment of the hexamethylpentacycle moiety, with the formation of the ketoderivative. A parallel transformation involves benzopyran moiety with the ring cleavage. All the identified transformation products are degraded themselves until 2 h of irradiation, while complete mineralization is achieved until 8 h.

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• Nested experimental design approach showed that HHCB photocatalytic efficiency depends on both the aqueous matrix and the initial concentration of the substrate involved.
• The benzopyran moiety was involved in hydroxylation and the ring cleavage, while another route proceeds through the detachment of the hexamethylpentacycle moiety, with the formation of the ketoderivative.
• The identified compounds are easily degraded within 2 h of irradiation and complete mineralization is accomplished within 8 h.