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

Abstract

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.