Study of benzylparaben photocatalytic degradation by TiO2

The photocatalytic degradation of benzylparaben in TiO2 suspension under UV irradiation was investigated and different experimental parameters were optimized. The degradation apparently followed a Langmuir–Hinshelwood kinetic relationship and the apparent first order rate constant was found equal to kapp = 0.017 min−1. It was found that alkaline pH was beneficial for benzylparaben photocatalysis, and the highest degradation efficiency was obtained at pH 9. A TiO2 loading of 2.5 g L−1 was enough to reach an optimal conversion rate while a higher loading (3.0 g L−1) had obvious inhibition phenomenon. The pseudo first order kinetic constant increased from 0.0043 to 0.025 min−1 while oxygen concentration increased from 0 to 36 mg L−1. In addition, the removal efficiency decreased while initial benzylparaben concentrations increased from 5 to 25 mg L−1. Light intensity is a quite important parameter influencing benzylparaben photocatalysis since for photonic flux ranging from 1.2 to 5.0 × 1015 photons s−1 cm−2, the rate constant was directly proportional to the photonic flux, while for higher intensity (from 5.0 to 5.8 × 1015 photons s−1 cm−2) the rate of degradation varied as a square root of the photonic flux. Different intermediates of benzylparaben photocatalysis were identified or characterized by GC–MS and HPLC and total organic carbon (TOC) analyses showed an almost total mineralization. These observations suggest that photocatalysis may be envisaged as an efficient method for treatment of diluted waste waters containing emerging paraben pollutants.

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► We choose benzylparaben, an emerging pharmaceutical and personal care products, as environmental pollutant to research its photocatalysis phenomenon.
► We study effects of several important parameters, such as pH values, TiO2 loading, dissolved oxygen concentration, initial benzylparaben concentration and light intensity, on benzylparaben photocatalysis.
► The optimal experimental condition for benzylparaben photocatalysis is obtained.
► We identify photocatalytic intermediates using GC–MS and HPLC-DAD, and propose a tentative reaction pathway.