Synergistic Adsorption and Degradation of Tetracycline by Municipal Sludge-Based Biochar

Tetracycline (TC), a widespread aquatic contaminant, poses significant ecological risks. In this study, municipal sludge-based biochar (BC) was prepared by high-temperature pyrolysis to assess its efficiency and mechanism for TC removal. Various sources of BC exhibited effective TC removal, with BC pyrolyzed at 800 °C demonstrating the highest adsorption capacity at 173.42   mg/g (K800). Quenching and Electron Paramagnetic Resonance (EPR) analysis confirmed that persistent free radicals (PFRs) in BC facilitate the generation of superoxide radical (⸱O 2 - ) and singlet oxygen ( 1 O 2 ), promoting efficient oxidative degradation of TC. Brunauer-Emmett-Teller (BET), X-ray Photoelectron Spectroscopy (XPS), and Fourier Transform Infrared (FTIR) characterization identified the mesoporous structure, C-O, C=O groups, graphitic/pyridine nitrogen, and the Si-O-Si framework as key active sites. In summary, BC effectively removes TC through a synergistic process combining adsorption and degradation, offering a promising remediation strategy.