Photocatalytic degradation of parabens in aquatic environment: Kinetics and degradation pathway

Parabens are p -hydroxybenzoic acid ester compounds widely used as preservatives in foods, cosmetics, toiletries and pharmaceuticals. These compounds exert a weak estrogenic activity as determined by in vitro estrogen receptor assay and in vivo uterotrophic assay. The photocatalytic degradation of parabens (butylparaben and ethylparaben), as a function of pH and initial concentration of parabens, was investigated in the presence of TiO 2 photocatalyst (P-25, “Degussa”). Experiments conducted at pH 4 with O 2 -sparged concentration of 15 mg/L showed that in terms of the photocatalytic efficiency the catalysts were slightly superior to those tested at pH 6-11. The intrinsic reaction rates of 2.08 × 10 2 and 1.81 × 10 2 μmol L −1 min −1 were estimated, and Langmuir-Hinshelwood model adsorption constants K were calculated as 0.05 and 0.06 L/μmol for butylparaben and ethylparaben, respectively. Ten organic intermediates appeared during the photocatalytic degradation of parabens, and were identified by LC/MS/MS. In addition, a tentative reaction pathway was proposed.