Photooxidation of bisphenol A (BPA) in water in the presence of ferric and carboxylate salts

In this work, the photooxidation of bisphenol A (BPA), a suspected endocrine disruptor (ED), in water in the presence of ferric and oxalate ions was investigated in a concentric reactor under a 125 W high-pressure mercury lamp (λ 365 nm). The photooxidation efficiencies were dependent on the pH values and ferric/oxalate concentration ratios (Fe(III)/Ox) in the water, with higher efficiency at pH 3.50±0.05 and Fe(III)/Ox 10.0/120.0 μmol l−1. The initial rate of photooxidation increases with increasing the initial concentration of BPA from 2.0 to 5.0 mg l−1 while do not change at 5.0 and 10.0 mg l−1. However, higher removal efficiency of BPA is archived at lower BPA initial concentration over range of 2.0 to 10.0 mg l−1. For 2.0 mg l−1 BPA, the initial rate of photooxidation is 0.06 mg l−1 min−1. By using UV–Vis spectrum and LC–MS techniques, the predominant photooxidation product BPA-o-catechol was identified and the mechanisms for the oxidative degradation were proposed. When BPA reacted with OH radicals, C atoms in 3-position were added with OH radicals followed by O2 peroxidation and HO2 radical escape. Then catechol derivatives were produced. After that, the two H atoms on the hydroxy group were extracted in two individual steps to form intermediates semiquinone radical and o-quinone. The intermediates underwent further oxidation, benzene ring cleavage and decarboxylation, up to mineralization ultimately.