Performance and Mechanism of Monolithic Co-Doped Nickel–Iron Foam Catalyst for Highly Efficient Activation of PMS in Degrading Chlortetracycline in Water

Metal–organic framework (MOF) materials were extensively studied in the removal of pollutants in wastewater. However, catalysts in the powder form usually suffered from the strong tendency to agglomerate and the intricate operation for recycling, which significantly limited their practical application. In comparison, monolithic catalysts with their high macroscopic operability and recoverability as well as impressive specific surface area have attracted tremendous attention in recent years. To address these issues, a monolithic Fe-based catalyst was prepared via in situ synthesis, using nickel–iron foam (NFF) as the substrate with cobalt (Co) incorporation. XPS analysis showed that Co doping enhanced the synergistic interaction among Fe, Ni, and Co, accelerating the redox cycle among species, thus improving electron transfer and laying a kinetic foundation for efficient peroxymonosulfate (PMS) activation. Quenching experiments and EPR indicated singlet oxygen (1O2) as the main reactive species; Co doping shifted the degradation pathway from radicals to non-radicals. Under optimized conditions (PMS: 0.08 mmol/L; catalyst: 1 cm2; initial Chlortetracycline (CTC): 50 mg/L), 95.7% CTC degradation was achieved within 60 min, and efficiency only dropped to 90.5% after 5 cycles. This catalyst provided theoretical and technical support for the application of monolithic MOF-derived catalysts and highly efficient PMS activators.