Self-assembed Fe-doped tobacco straw rich in lignin biochar towards efficient activation of peroxymonosulfate for...

In this study, biochars derived from different crop straws rich in lignin were prepared and used to adsorb the transition metal Fe³⁺ from wastewater. Among these biochars, ball-milled tobacco straw biochar (BTBC) exhibited a greater adsorption capacity. Subsequently, BTBC saturated with Fe³⁺ was pyrolysed to prepare self-assembled Fe-doped BTBC (Fe@BTBC), which exhibited excellent catalytic ability for peroxymonosulfate (PMS). The degradation rate of sulfadiazine (SDZ) in Fe@BTBC/PMS system was 92.4 % within 60 min. Solution pH and co-existing HCO₃^- and CO₃^2- were the undeniable environmental factors influencing the degradation rate/efficiency of sulfonamides (SAs). Characterization analysis showed that abundant defects, oxygenated groups of -OH/C=O, and grafted Fe(II) on Fe@BTBC were the main catalytic sites. Surface-bound radicals and ¹O₂ were the primary contributors for SAs oxidation, and SO₄^•- and ^•OH were additional participants. Five degradation pathways were proposed based on intermediate authentication and density functional theory (DFT) calculations, and pathway II was speculated to be the primary pathway. In addition, the Fe@BTBC/PMS system exhibited excellent detoxification capacity for SAs, as the toxicity of the intermediates was lower than that of SAs. Additionally, the Fe@BTBC/PMS system could efficiently remove SAs from real waters, and Fe@BTBC exhibited favourable security over a wide pH range.