Electron transfer degradation of ciprofloxacin by peroxydisulfate intercalated MgAlFe-layered double hydroxides: Roles of laminate structure and interlayer peroxydisulfate

Abstract

Peroxydisulfate intercalated MgAlFe-layered double hydroxides (S2O8·LDHs) are synthesized by the one-step co-precipitation method. The Fe content in LDH laminates affects the insertion of S2O82−, and further affects the catalytic activity of S2O8·LDHs. Fe-S2O8·LDH-0.2 with Fe/(Al + Fe) = 0.2 shows superior performance that 1 g/L of dosage leads to 99.55 % degradation of ciprofloxacin (CIP, 10 mg/L) within 60 min. It is fully clarified that electron transfer rather than SO4•−, •OH, O2•− and 1O2 is responsible for CIP degradation. Interlayer S2O82− with longer OO bond length than free S2O82− exists in metastable form, which deprives electrons from the piperazine ring of CIP mainly through the transport of LDH laminates, leading to the degradation of CIP through the cleavage and oxidation of piperazine ring. The efficient degradation of other fluoroquinolones and the modest even negligible influence of Cl−, NO3–, HCO3–/CO32– and natural organic matter on the performance prove the practical application potential of S2O8·LDHs. This work not only provides an in-depth study on the degradation of emerging pollutants by PDS intercalated LDHs, but also provides some new insights into the non-radical mechanism.