Insights into the mechanism of mechanically treated Fe/Mn-N doped seed meal hydrochar for efficient adsorption and degradation of tetracycline

Abstract Tetracycline (TC), which is widely employed in agriculture, constitutes a serious source of environmental pollution. In this study, mechanical ball-milling (B) treated iron/manganese-nitrogen (Fe/Mn-N) doped hydrochars (Fe/Mn-BNHT) synthesized using saponin-containing seed meal (T) as a carbon source, showed excellent removal ability of tetracycline with a removal efficiency 95%. The Fe/Mn-BNHT showed superior performance in batch experiments with solution pH (3–9), coexisting ions, and after 5 cycles of application. Further analysis showed that Fe/Mn-BNHT mediated the degradation of adsorbed tetracycline with a degradation efficiency 87%. Surface complexation, electrostatic interactions, and hydrogen bonding facilitated the adsorption of tetracycline. ·OH induced by oxygen vacancy (O V ) was identified as the main reactive oxidation species in tetracycline degradation. Fe(III)- tetracycline complexes gained electrons through graphitic N, leading to tetracycline degradation and Fe(III) reduction. The degradation pathways for tetracycline are shown through density functional theory calculation and intermediate identification, and the ecological toxicity risk of 10 degradation intermediates is evaluated. This research provides a new perspective on the development of environmentally friendly materials that can simultaneously adsorb and degrade pollutants. Graphical Abstract