Photodegradation of 4-alkylphenols using BiVO4 photocatalyst under irradiation with visible light from a solar simulator

A visible-light-driven photocatalyst, BiVO4, has been applied for degradation of a series of linear 4-n-alkylphenols under irradiation from a solar simulator. Degradation rates become faster with increasing alkyl chain length. Half-life of 4-n-nonylphenol (4-n-NP) is 18 min, which is about eight times shorter than that of phenol. The rate law of disappearance for heptyl-, octyl- and nonylphenols exhibits zero-order kinetics. The amount of adsorption on BiVO4 surface is much larger for longer hydrophobic alkylphenols. It is thus concluded that BiVO4 is suitable for degradation of hydrophobic alkylphenols such as nonyl- and octylphenols nominated as endocrine disruptors. Degradation of branched 4-nonylphenol (mixture of isomers) has also been examined, and disappearance of its estrogenic activity was confirmed by means of the yeast two-hybrid assay. A gas chromatography–mass spectroscopy (GC–MS) analysis after solid-phase extraction indicates that the major product is cis,cis-4-alkyl-6-oxo-2,6-hexadienoic acids, and the minor products are 4-alkylcatechols and 4-(1-alkenyl)phenols.