Degradation of Tetracycline Hydrochloride by Peroxymonosulfate Activation Using Cu/N Co-Doped Biochar

With the rapid development of industrialization and technology, antibiotic wastewater pollution has become a serious environmental problem facing human beings. Conventional physical and biological techniques are often ineffective in removing antibiotic residues from water. Sulfate radical-based advanced oxidation processes (SR-AOPs) are considered among the most promising methods for antibiotic removal in practical applications due to their strong degradation performance and fast reaction rates. In this study, the NH4Cl-modified Cu/N co-doped biochar (Cu-N5) was prepared via a two-step calcination process and used to activate peroxymonosulfate (PMS) for the degradation of tetracycline hydrochloride (TCH) in water. This modification was designed to overcome the limitations of pristine biochar (BC), which lacks metal active sites and has inherent physicochemical properties that are insufficient for handling increasingly complex antibiotic wastewater. Compared with BC, Cu-Np, and Cu-N4, Cu-N5 exhibited the best defect structure and morphology characteristics. The high-temperature modification using NH4Cl facilitated more effective Cu and N doping onto the biochar surface, providing a greater abundance of active sites and N-containing functional groups. Degradation experiments demonstrated that Cu-N5 exhibited superior PMS activation efficiency compared with BC, Cu-Np and Cu-N4. After a 60-minute degradation experiment, the TCH degradation efficiency reached approximately 78.95%, representing a 29.09% increase compared to pristine BC, with minimal contribution from adsorption. In the analysis of influencing factors, the effect of acid washing was negligible, and the Cu-N5/PMS system functioned effectively within a broad pH range (3 to 9). Cu-N5 also exhibited the fastest reaction rate (k = 0.02588 min−1), as calculated using the first-order reaction kinetic constant. When [TCH] = 10 mg/L, the most economical experimental conditions were determined to be [Cu-N5] = 0.2 g/L, [PMS] = 1.0 mmol/L, and pH = 7. Further investigations confirmed that the Cu-N5/PMS system possessed good anti-interference capability and high practical applicability, maintaining high degradation activity even in the presence of various anions and humic acids. Moreover, Cu-N5 demonstrated removal efficiency for other common pollutants, including Rhodamine B (RhB), Methylene Blue (MB), Ciprofloxacin (CIP), and Carbamazepine (CBZ), indicating its broad applicability. Radical quenching experiments revealed that the free radical pathway was nearly inactive in the Cu-N5/PMS/TCH system, while non-radical mechanisms, primarily singlet oxygen 1O2 and high-valence Cu(Ⅲ) species, dominated TCH degradation. This work provides valuable insights for the rational design of modified biochar and its application in PMS activation for antibiotic degradation.