Introduction Water shortage and pollution become serious due to the improvement of economic and the acceleration of industrialization. Water bodies contain a large number of pollutants, affecting the environment and human-being health. Heterogeneous catalyst activation of peroxymonosulfate (PMS) is an effective degradation technology for organic pollutants, but SO4-· is difficult to effectively activate due to the high redox potential. It is thus necessary to develop catalytic materials that can activate PMS efficiently. The metal organic frame materials based on Prussian blue have the typical physical and chemical characteristics of metal-organic framework (MOFs) materials, adjustable and controllable chemical composition, high specific surface area and porosity, and diversified structure and function, etc., which become the hot materials in various fields. The conversion of Prussian blue analogue (PBA) into nitrogen-doped carbon materials with a high specific surface area, a high porosity and a high nitrogen content through high-temperature calcination or inert gas carbonization is of great significance for improving the catalytic performance of the catalyst. In this paper, a nitrogen-doped carbon nanosheet supported FeMnO catalyst was prepared by a high-temperature carbonization method. Its catalytic degradation performance was analyzed. The effects of different systems, pH value of solution, Rhodamine B (RhB) initial mass concentration, PMS mass concentration and catalyst mass concentration on the RhB degradation were investigated. In addition, the possible mechanism of RhB degradation was also proposed.Methods Fe-Mn PBA and colloides were prepared by a co-precipitation method. After grinding, the catalyst was heated in nitrogen atmosphere at 750 ℃ at 2 ℃/min for 2 h to synthesize transition bimetal oxide (i.e., Fe0.099Mn0.9010/FeMn2O4) N-doped carbon nanosheets. Compared with FeMnO and graphite C, the degradation properties of FeMnO@C in different systems and under different factors were characterized by ultraviolet-visible spectroscopy (UV-Vis). The structure and morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR). Results and discussion Heterogeneous catalyst activation of PMS can inhibit the dissolution of metal ions and it is not easy to cause secondary pollution. An efficient nitrogen-doped carbon catalyst FeMnO@C was obtained based on Fe-Mn PBA, which has a high specific surface area and provides a high density of active sites for catalytic reactions, and can effectively activate PMS to rapidly degrade organic pollutants. FeMnO@C has good magnetic properties, which can be conducive to recycling. The interaction between different metals in the double transition metal materials makes the metals difficult to be dissolved, greatly reducing the concentration of toxic metal ions in the system. The redox cycle between Mn and Fe ions on the surface of FeMnO@C catalyst and a series of free radicals generated after the self-decomposition of PMS make FeMnO@C have a superior catalytic degradation performance. The effects of PMS amount, initial concentration of RhB, catalyst amount and initial pH value of RhB solution on the catalytic performance were analyzed. The optimal reaction conditions were PMS concentration of 0.15 g/L, concentration of RhB solution of 20 mg/L, catalyst concentration of 0.1 g/L and pH value of 7. The possible degradation mechanism was proposed based on capture experiments and EPR spectra. Conclusions A transition bimetallic oxide catalyst supported by nitrogen-doped carbon nanosheets was synthesized by a high-temperature carbonization method, which could be used as an efficient PMS activated heterogeneous catalyst to degrade the target pollutant RhB. In the PMS activation system, the FeMnO@C catalyst could degrade 95.5% of RhB within 10 min. The redox cycling between Mn and Fe ions on the surface of the FeMnO@C catalyst and a series of free radicals generated after the self-decomposition of PMS could make the FeMnO@C have a superior catalytic degradation performance. The capture experiments showed that 1O2 was the main contributing radical. In addition, FeMnO@C catalyst also had a magnetic property and a good cyclic stability. 84.7% RhB removal rate could be obtained after five consecutive cycles. The results indicated that FeMnO@C had a good magnetic property, which could be easy to be recycled, having a promising potential in treating organic wastewater.