Visible light degradation of tetracycline and bisphenol A by a hybrid photocatalyst composed of orange peel biochar, clay, and C/N-doped titania

A new photoactive nitrogen-doped hybrid clay photocatalyst based on orange peel, titania, and melamine is highly effective for the degradation of tetracycline (TET) and bisphenol A (BPA) from aqueous solution. The photocatalysts were synthesized using a simple low cost approach and characterized by powder X-ray diffraction, scanning electron microscopy, nitrogen sorption, thermogravimetric analysis, UV-visible diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy (XPS). The titania present in the material is C/N-doped and plays a key role in the photocatalytic process, influencing the bandgap and the overall optical properties of the hybrid photocatalyst. Notably, XPS confirms the successful incorporation of nitrogen into the TiO2 lattice. This N-doping induces a red shift in the absorption edge of the photocatalysts, which significantly improves the photocatalytic efficiency under visible light irradiation relative to pristine TiO2. The photocatalysts also exhibit an increased specific surface area, reaching up to 180 m2 g-1. Under visible light irradiation at 25 °C and neutral pH, the photocatalysts achieve complete degradation of TET in aqueous solutions within 30 min. Similarly, 82% degradation of BPA in 10 mg L−1 BPA aqueous solutions is achieved within 120 min. Total organic carbon analysis reveals moderate mineralisation of 46 to 50% for both pollutants and radical trapping experiments identify superoxide radicals (˙O2-) as the primary reactive species responsible for pollutant degradation. Furthermore, the catalysts show an excellent performance in the degradation of TET in river water, clearly demonstrating an applicability in practical water treatment. Finally, the photocatalysts can effectively be recycled without significant loss of efficiency.