Photodegradation of bisphenol Z by UV irradiation in the presence of β-cyclodextrin

In this work, the formation of the inclusion complex of bisphenol Z (1,1-bis(4-hydroxyphenyl)cyclohexane, abbreviated as BPCH) with β-cyclodextrin (β-CD) has been studied, 1:1 inclusion complex can be obtained, the formation constant of the β-CD/BPCH complex is 5.94 × 103 M−1. The photodegradation behavior of BPCH was investigated under monochromatic UV irradiation (λ = 254 nm). The photodegradation rate constant of BPCH in aqueous solutions with β-CD showed a 9.0-fold increase, and simultaneously the mineralization of BPCH can be enhanced by β-CD. The influence factors on photodegradation of BPCH were also studied and described in details, such as concentration of β-CD, initial concentration of BPCH, organic solvent and pH. The photodegradation of BPCH in the presence of β-CD includes the direct photolysis and the photooxidation of BPCH during the photochemical process. Some predominant photodegradation products are 4-(2,4,5-trihydroxy-phenyl)-4-(4-hydroxyphenyl) butanoic acid, 5,5-bis(4-hydroxyphenyl)pentanoic acid, meta-hydroxylated BPCH, ortho-hydroxylated BPCH and 4-(1-(4-hydroxyphenyl)pentyl)phenol respectively. The enhancement of photodegradation of BPCH mainly results from moderate inclusion depth of BPCH molecule in the β-CD cavity. This kind of inclusion structure allows BPCH molecule sufficient proximity to secondary hydroxyl groups of the β-CD cavity, and these hydroxyl groups could be activated and converted to hydroxyl radicals under UV irradiation, which can enhance the photooxidation of BPCH.