Adsorption and oxidation of ciprofloxacin by a novel layered double hydroxides modified sludge biochar.

[Display omitted] • A novel adsorbent and oxidant (CoFe-LDH@SBC) was synthesized. • The removal rates of ciprofloxacin, total organic carbon and total nitrogen were improved. • Oxygen-centered radicals were verified as dominant environmental persistent free radicals (EPFRs). • A possible working mechanism and ciprofloxacin degradation pathway were proposed. • CoFe-LDH@SBC exhibited good stability and EPFRs had a long lifetime. In this study, biochar derived from municipal sludge (SBC) was modified by CoFe-Layered double hydroxides (CoFe-LDH), and used as adsorbent and oxidant for the removal of ciprofloxacin (CIP) for the first time. Under the optimal conditions, the CIP removal rate is increased by 24% compared with the single SBC, while the removal rates of total organic carbon and total nitrogen in the modified one are increased by 24% and 27%, respectively. Mechanism investigation suggested that the specific surface area and adsorption sites of modified biochar increased, and more CIP was adsorbed to the composite surface and then oxidized by more environmental persistent free radicals contained in the CoFe-LDH@SBC, when the adsorbed CIP molecules was oxidized and degraded, the adsorption sites can be freed and thus new CIP could be adsorbed to the CoFe-LDH@SBC. In addition, the plausible degradation pathways of CIP were proposed according to high-performance liquid chromatography-mass spectrometry and density functional theory calculation. It not only reveals that CoFe-LDH@SBC has the high ability of adsorption and oxidation for CIP removal but also sheds novel insight into the application of biochar. [ABSTRACT FROM AUTHOR]