Highly effective and recyclable ZnCo₂O₄@NF for peroxymonosulfate activation towards ciprofloxacin degradation: Dual reaction sites and enhanced electron transfer mechanisms

The nano/micro-sized catalysts for peroxymonosulfate (PMS) activation often undergo agglomeration, leading to inevitable loss of active sits and reduced catalytic efficiency. Herein, monolith nickel foam (NF) supported ZnCo₂O₄ nanosheets were constructed, achieving almost complete removal of ciprofloxacin (CIP) within 15 min. ZnCo₂O₄@NF exhibits prominent stability in microstructure and exposed active sites, resulting in high reusability. The unique Zn-O-Co structure and “conducting bridge” of NF could accelerate the electron transfer from ZnCo₂O₄ to PMS and the following O-O bond cleavage. This facilitates Co²⁺/Co³⁺ redox cycle for continuous SO₄^•− generation and endows ZnCo₂O₄@NF with low reaction barrier. The surface hydroxyl groups and the inner-sphere complexation between PMS and catalyst play significant role in the formation of reactive oxygen species (ROS). Furthermore, the quenching test confirmed the dominant role of SO₄^•− and auxiliary role of ^•OH/¹O₂ in ZnCo₂O₄@NF/PMS system. The reaction sites in CIP molecule easily attacked by ROS were determined, and the possible radical/non-radical degradation pathways of CIP were proposed. This work further unveiled the mechanism of the covalency and electronic configuration in ZnCo₂O₄@NF. The distinct advantages of the macroscopic catalyst including outstanding catalytic ability and high structural stability provide great possibility for broad industrial application.