The synergistic effect and underlying mechanism of bimetal and its support in cobalt‑lanthanum doped palygorskite-based catalyst for norfloxacin removal through activating persulfate

CoLaO x @PAL was successfully prepared and had a high effect to activate PMS for NOR removal. • NOR degradation process included free radical pathway ( SO 4 ∙ − ${\mathrm{SO}}_4^{\bullet -}$ and ∙ OH $\bullet \mathrm{OH}$ ) and non-free radical pathway ( O 2 1 ${}^1{\mathrm{O}}_2$ ). • La doping caused oxygen vacancies generation, accelerating the electron transfer during NOR degradation process. • CoLaO x @PAL had a good environmental friendliness and practical applicability for NOR removal. Appropriate catalyst support can effectively alleviate the agglomeration of metal components, and reduce the leaching of metal ions. In this manuscript, CoLaO x was loaded on palygorskite (PAL) to prepare CoLaO x @PAL for norfloxacin (NOR) efficiently removal through persulfate (PMS) activation. Under the optimal experimental conditions (CoLaO x @PAL: 0.5 g/L, PMS dosage: 0.6 mM, pH: 7.7), the removal efficiency and pseudo-first-order rate constant ( k obs $k_{\mathrm{obs}}$ ) of NOR reached 91% and 0.11 min −1 , respectively. The morphology and structure of CoLaO x @PAL were characterized by SEM, XRD and FTIR, which strongly proved that CoLaO x was successfully loaded on the surface of PAL. Quenching experiment and EPR verified the dominant position of O 2 1 ${}^1{\mathrm{O}}_2$ in NOR degradation by CoLaO x @PAL activating PMS. XPS and electrochemical characterization verified that a redox reaction between Co 2+ /Co 3+ promoted the formation of SO 4 ∙ − ${\mathrm{SO}}_4^{\bullet -}$ and ∙ OH $\bullet \mathrm{OH}$ radicals, and La doping introduced oxygen vacancies. These effectively promoted electron transfer, and thus improved the catalytic activity of CoLaO x @PAL. Three possible NOR degradation pathways were proposed through LC-MS analysis. A NOR removal efficiency of over 80% was maintained both after five consecutive cycling experiments and in various real water matrices, which verified the promising practical application potential of CoLaO x @PAL. Finally, the ECOSAR prediction results showed that most of the intermediates were harmless to the environment and had certain environmental stability. The preparation of CoLaO x @PAL broadens the application of rare earth elements, and provides some new insights into naturally occurring mineral-based catalysts for antibiotic wastewater treatment. Download: Download high-res image (240KB) Download: Download full-size image