Sulfidation of magnetic CoFeAl-layered double hydroxide material as peroxymonosulfate activator for efficient degradation of norfloxacin

Abstract

A magnetic CoFeAl-layered double hydroxide (LDH) material was synthesized via a hydrothermal method, followed by sulfidation treatment with sodium sulfide, and the obtained S/CoFeAl-LDH nanocomposite was used as a peroxymonosulfate (PMS) activator for efficient degradation of antibiotics in water by using norfloxacin (NOR) as a model. Through sulfidation modification, the proportion of low-valent metal ions in the composites was increased. Therefore, the S/CoFeAl-LDH displayed a higher performance of NOR degradation via the activation of PMS than the CoFeAl-LDH. Within 6 min, 0.10 g per L S/CoFeAl-LDH and 0.20 g per L PMS could degrade 98.3% NOR (20 mg L⁻¹). S/CoFeAl-LDH, as a heterogeneous catalyst, could efficiently activate PMS and degrade NOR in the pH range of 4–9. Since the synthesized material was a composite of magnetic CoFe₂O₄ and LDH, it could be recycled by magnetism after the reaction. After 4 cycles, the NOR degradation rate still reached 84.3%, indicating the good stability of the catalyst. During the degradation of NOR by S/CoFeAl-LDH/PMS, both free radical pathway and non-free radical pathway played a role, among which SO₄˙⁻, O₂˙⁻ and ¹O₂ were the main active species. The Co²⁺ and Fe²⁺ in the composites reacted with PMS to generate active species. The synergistic effect of metals and the reducibility of sulfur further promoted the cyclic regeneration of Co²⁺ and Fe²⁺, which was conducive to the activation of PMS to generate free radicals. In addition, the intermediate products of the degradation reaction were analyzed by LC-MS, and the possible degradation paths were put forward. This study revealed that the S/CoFeAl-LDH was a heterogeneous catalyst with good application prospect, which provides a new method for removing antibiotics from water.