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

Abstract

A new photoactive nitrogen-doped hybrid clay material 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 characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), nitrogen adsorption, thermogravimetric analysis (TGA), UV-visible diffuse reflectance spectroscopy (UV-DRS), and X-ray photoelectron spectroscopy (XPS). 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 material. Notably, XPS confirms the successful incorporation of nitrogen atoms from the melamine into the Ti⁴⁺-O lattice.This N-doping induces a red shift in the absorption edge of the photocatalysts, significantly improving their degradation efficiency under visible light relative to pristine TiO₂. The photocatalysts also exhibit a markedly increased specific surface area, reaching up to 180 m 2 .g -1 Under visible light irradiation at 25 °C and neutral pH, the current photocatalyst achieve complete degradation of 10 mg/L TET within 30 minutes (k = 4.91 × 10⁻ 1 min⁻¹) and 82 % degradation of 10 mg/L BPA within 120 min (k = 1.27 × 10⁻² min⁻¹) using 50 mg of catalyst. Total organic carbon analysis reveals moderate mineralization for both pollutants (46 -50 %). Radical trapping experiments identify superoxide radicals (•O₂⁻) as the primary reactive species responsible for pollutant degradation. Furthermore, the catalyst shows an excellent performance in the degradation of TET in river water, clearly demonstrating an applicability in practical water treatment. Overall, the photocatalyst demonstrates promising potential due to its recyclability across multiple cycles without significant loss of efficiency.