Orange peel biochar/clay/titania composites: low cost, high performance, and easy-to-reuse photocatalysts for the degradation of tetracycline in water†

Abstract

New orange peel biochar/clay/titania nanocomposites (NCs) were studied for photocatalytic degradation of tetracycline (TET) under both UV and natural solar irradiation by variation of NC dose, initial TET concentration, ionic strength, and competing anions. Total organic carbon (TOC) reduction was used to assess mineralization. Intermediate product formation during TET degradation was characterized using liquid chromatography-mass spectrometry and agar-based diffusion assays. The as-synthesized material prepared with biochar obtained at 600 °C (C600KT) exhibits the best TET degradation performance under UV light exposure and solar irradiation with up to 92 and 89% after 2 h, respectively. Especially under UV exposure, C600KT exhibits the highest apparent rate constant of 2.9 × 10⁻² min⁻¹ and a half-life of 23.9 min. About 60 and 50% TOC are removed after 2 h under UV and solar irradiation, respectively. Quenching experiments confirm that superoxide and hydroxyl radicals are the major reactive species involved in the degradation process. Furthermore, the treated effluents are harmless to both Escherichia coli and Staphylococcus xylosus, indicating that no intermediate products with higher toxicity are produced during the photocatalytic degradation. Additionally, the results show that the main fraction of TET is degraded within the first 15 min of irradiation. The C600KT composite is recyclable and retains its performance over at least four cycles, proving its stability and reusability. Overall, the new NCs are therefore highly attractive for the remediation of TET pollution in water.