Nitrogen-Doped Carbon-Encapsulated Co–Fe Catalyst for Efficient Peroxymonosulfate Activation Toward Rhodamine B Degradation

A nitrogen-doped carbon-confined cobalt–iron bimetallic catalyst (CFNC) was fabricated through high-temperature pyrolysis of a ZIF-67-modified CoFe2O4 precursor and employed as a heterogeneous activator for peroxymonosulfate (PMS)-mediated Rhodamine B (RhB) degradation. The physicochemical properties of the as-prepared catalyst were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) analysis. These analyses demonstrated that Co–Fe bimetallic species were successfully embedded within the nitrogen-doped carbon framework, forming a confined carbon-supported catalytic structure. Under optimized conditions (CFNC dosage of 20 mg L−1, PMS concentration of 150 mg L−1, and initial pH of 7), the CFNC/PMS system achieved 99.45% RhB removal within 10 min. Moreover, the catalyst retained 78.91% degradation efficiency after five successive cycles, indicating its satisfactory reusability and structural stability. Mechanistic investigations based on radical scavenging experiments and electron paramagnetic resonance (EPR) analysis revealed that PMS activation over CFNC involved the coexistence of radical and non-radical oxidation pathways, in which singlet oxygen (1O2) played a predominant role. The defect-rich nitrogen-doped carbon matrix facilitated PMS adsorption and activation, promoting the selective formation of 1O2, while the confined Co–Fe bimetallic sites contributed to efficient electron transfer during the catalytic process. The synergistic coupling between the Co–Fe active centers and conductive carbon framework accounted for the enhanced catalytic performance, suppressed metal leaching, and long-term stability of CFNC. This work presents a promising approach for constructing robust bimetallic carbon-based catalysts and advances the application of PMS-driven advanced oxidation processes for wastewater remediation.