Bimetallic zeolitic imidazolate framework-derived nitrogen-doped porous carbon-coated CoFe2O4 core–shell composite with high catalytic performance for peroxymonosulfate activation in Rhodamine B degradation

The rational design and development of a highly efficient and sustainable heterogeneous catalyst has become a limiting factor for the practical application of persulfate-based advanced oxidation processes in organic dye degradation. Herein, a nitrogen-doped porous carbon-coated CoFe2O4 core–shell composite (CoFe2O4 @NPC) was synthesized by in-situ growth of cobalt/iron bimetallic zeolitic imidazolate framework-9 (Co/Fe-ZIF-9) on graphene oxide (GO) nanosheets followed by one-step calcination of the bimetallic ZIF-GO composite in nitrogen. The textural, chemical, and magnetic properties of the composites were comprehensively characterized using various analytical techniques. The catalytic performances of the as-prepared CoFe2O4 @NPC in activating PMS to decompose Rhodamine B (RhB) were then systematically evaluated. The composite calcined at 600 °C exhibited the highest catalytic activity. The maximum RhB degradation efficiency of 99.05% and pseudo-second-order kinetic constant of 0.0766 L/(mg·min) were achieved after 20 min at 25 °C. Moreover, CoFe2O4 @NPC displayed excellent recyclability and stability with negligible leaching of Co and Fe ions into the solution. Subsequently, electron spin resonance, reactive oxygen species quenching, and X-ray photoelectron spectroscopy were conducted to clarify the PMS activation mechanisms. Results suggested that SO4•− and •OH were generated during PMS activation and that SO4•− was the predominant radical involved in RhB degradation. In addition, Co(II), Fe(III), and structured nitrogen, especially pyridinic and graphitic N groups, participated in the PMS activation. Some insights into possible mechanisms of RhB degradation were also attained from spectral analyses. All these results suggested that CoFe2O4 @NPC had excellent potential as a PMS activator for application in dye-contaminated wastewater treatment.