Photocatalytic environmental remediation by bismuth oxyhalides-TiO₂ composites: Pharmaceuticals and pollutants degradation

This study investigates the removal of pharmaceutical and industrial pollutants in the presence of bismuth oxyhalides (BiOX, where X = Br, Cl) and BiOX-TiO₂ composites, prepared in different ratios by the ball milling method. The photocatalysts' features were investigated through diffuse reflectance, Raman and luminescence spectroscopy, X-ray diffraction patterns, scanning and transmission electron microscopy, specific surface area determination, electron paramagnetic resonance and electrochemical measurements. Heterogeneous photocatalysis, which is particularly noteworthy among advanced oxidation processes (AOPs), was used to degrade tetracycline, oxytetracycline, and 4-nitrophenol, which are all micropollutants commonly present in wastewater. The photooxidation of these compounds in aqueous solution was performed under both UV and simulated solar light irradiation, even in the absence of a photocatalyst. The homogeneous system proved to be poorly efficient, while for the heterogeneous systems the composites showed both an almost complete conversion of the initial substrates and a higher mineralization degree (up to 76 %) compared to the bare TiO₂ P25 tested for comparison purposes. Selected runs carried out degrading 4-nitrophenol under simulated sunlight irradiation revealed the efficiency of BiOX-TiO₂ composites also under real conditions, encouraging their future use in pilot plant reactors. The higher activity of the coupled photocatalysts has been ascribed to the improved transfer of the photogenerated charges.