Fe-doped biochars prepared via hydrothermal treatment and low-temperature air calcination to activate peroxymonosulfate for efficient tetracycline degradation

In this study, a new sludge-based biochar loaded with Fe species (Fe/SSBC) was prepared by a two-step process involving hydrothermal treatment and low-temperature air calcination, and used to degrade tetracycline (TC) by activating peroxymonosulfate (PMS). After 30 min reaction, more than 98 % TC (50 mg/L) could be removed by optimized Fe/SSBC/PMS system (k = 0.166 min⁻¹), which was 2.18 times compared with individual hydrothermal treatment (k = 0.076 min⁻¹). Besides, it also exhibited good stabilization. Detailed characterizations revealed the effect of hydrothermal treatment on the Fe–O coordination of the biochar surface and the change of the Fe valence state by air calcination. The electron paramagnetic resonance (EPR), electrochemical analysis and quenching experiments confirmed that singlet oxygen (¹O₂) was the main active substance. We further elucidated the influence of grafting Fe–O on the surface electron distribution of biochar by DFT calculations. Moreover, two possible pathways were proposed based on LC-MS analysis. In this study, a method of preparing high catalytic performance sludge-based carbon materials under low energy consumption has been proposed, which provides a new strategy for sludge recycling.