Visible-light activation of TiO2 by dye-sensitization for degradation of pharmaceutical compounds

Abstract

This work reports the improvement in the photon absorption and degradation of acetaminophen (ACF) and diclofenac (DFC) by photosensitizing TiO₂ with two types of dyes Eosin Y (Ey) and Rhodamine B (RhB). Experimental tests were carried out in a solar simulator for three hours for different systems and both pollutants. The influences of the TiO₂ concentration (100, 200 and 800 mg L⁻¹) and the catalyst–dye ratio (2%, 5% and 10%) were investigated. The degradation of the compounds was higher in the presence of TiO₂-Ey compared to the TiO₂-RhB and TiO₂ for both pharmaceutical compounds, which was attributed to the anionic nature of Ey. DFC total degradation was achieved using 100 mg L⁻¹ of catalyst loading and 10% of catalyst–dye ratio and the highest ACF degradation (71%) was obtained at 800 mg L⁻¹ of catalyst loading and 5% of catalyst–dye ratio. The photon absorption was studied for both dyes using the six-flux absorption scattering model (SFM) for estimating the LVRPA (local volumetric rate of photon absorption). This was done by modifying the apparent optical thickness equation. It was found that the presence of dye in the photocatalytic systems considerably increases the LVRPA. The rate coefficients for the degradation of pharmaceutical compounds in the presence of the organic dyes were also obtained.