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

The widespread use of tetracycline (TC) severely damages the aquatic environment. Economical, green and efficient treatment methods are urgently needed. In this study, a 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 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 · − , ·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. • A magnetic N-doped iron sludge based BC was successfully prepared by a one-step pyrolysis method. • Fe and N were involved in the free radical and non-radical pathways of TC degradation, respectively. • N–BCFe showed good separation and reusability.