Preparation of magnetic N-doped iron sludge based biochar and its potential for persulfate activation and tetracycline degradation

The widespread use of tetracycline (TC) is a non-negligible cause of environmental pollution , such as antibiotic resistance genes (ARGs). Economical, green and efficient treatment methods are urgently needed. In this study, the magnetic N-doped iron sludge based biochar (N-BCFe) was prepared by a one-step pyrolysis method using the iron-containing sludge from groundwater treatment plants, sycamore leaves and urea as raw materials to active persulfate (PS) for TC degradation . The results show that under the optimal experimental conditions, the removal rate of 10 mg/L TC in the N-BCFe/PS system could reach 86.56% (120 min), accompanied by a 59.9% reduction in total organic carbon (TOC), and still 63.34% of TC was removed in the third recycle experiment. Combined with EPR, free radical quenching experiments and XPS spectra, it is confirmed that there are free radicals ( S O 4 · − $\text{S}{\text{O}}_4^{·-}$ , ·OH) and non-radical ( 1 O 2 ) pathways in N-BCFe/PS system. And the former is related to Fe doping, while the latter is attributed to N doping (nitrogen-containing functional groups). Seventeen TC intermediates were identified by LC-MS technology, and three TC degradation pathways were established accordingly. Generally, this study illustrates the considerable catalytic potential of N-BCFe and provides valuable insights into the synthesis of catalysts prepared from iron-containing sludge as feedstock.