## 3 Results  
### Characterization of CoSN@C  
The SEM data allow for the observation of the material's surface morphology (Figure 1a,b). Figure 1a,c are SEM images of the CoN@C carbon-derived material used as the control. The pyrolyzed CoN@C nanoparticles retain their homogeneous dodecahedral morphology and structure, with an average diameter of around 500 nm and a wrinkled surface. Figure 1b,d are SEM images of the CoSN@C carbon-derived materials after sulfur modification. Moreover, Figure 1b demonstrates that the majority of the CoSN@C nanoparticles after pyrolysis still have dodecahedral morphology and structure with an average diameter of about 600 nm, with a certain degree of aggregation and fragmentation and obvious pores, most likely due to the high-temperature pyrolysis. The high-temperature pyrolysis of allylthiourea employed for sulfur modification may result in structural fragmentation and the formation of pores, which makes it possible for a larger area to adsorb pollutants, and is advantageous for PMS activation. The elements of S, Co, C, N, and O were uniformly distributed in the catalysts, according to the EDS mapping data (Figure 1g,h). TEM was used to explore the material's structure in further detail (Figure 1e,f). The nanoparticles were contained in the carbon layer, according to the TEM image. The nanoparticles were dispersed on the carbon layer's surface and were contained in it, according to TEM pictures. By using XRD, the produced material's crystal structure was examined. According to prior investigations, ZIF-67 was present in the unpyrolyzed catalysts as evidenced by the XRD patterns of the unpyrolyzed material ZIF-67 and ZIF-67-S, which exhibited three diffraction peaks of ZIF-67 at 7.19\({}^{\circ}\), 10.34\({}^{\circ}\), and 12.82\({}^{\circ}\), respectively (Figure 2a) [24; 25; 26]. Compared to pure ZIF-67, the XRD patterns of ZIF-67-S exhibited broader diffraction peaks and decreased intensity of diffraction peaks. The direct synthesis of thiourea-functionalized organic frameworks (S-MOFs), as described in the literature, can influence the porosity, crystallinity, and stability of the materials via various types of secondary interactions [27; 28]. In this study, the crystallinity of ZIF-67-S decreased following sulfur doping modification by thiourea-functionalized MOFs, as determined by a combination of XRD and SEM data. Both CoN@C and CoSN@C are derived by pyrolysis in an inert gas atmosphere. The XRD patterns of the CoN@C and CoSN@C catalysts represented a diffraction peak located at 44\({}^{\circ}\), 52\({}^{\circ}\), and 76\({}^{\circ}\), corresponding, respectively, to the (111), (200), and (220) planes of metal Cobalt, implying the reduction in cobalt monomers dispersed in the carbon frameworks after pyrolysis at 900 \({}^{\circ}\)C (Figure 1b) [29; 30], thus verifying that the small particles on the surface of the samples shown by SEM results are metallic cobalt monomers. Comparatively, the XRD pattern of CoN@C and CoSN@C revealed the presence of g-N3C4 (JCPDS PDF#87-1525) (Figure 2b), which indicates a high degree of graphitization [31], which is advantageous for the activation of PMS [32; 33]. Figure 1: SEM images of CoN@C (**a**,**c**); SEM images of CoSN@C (**b**,**d**); TEM images of CoSN@C (**e**,**f**); SEM image of CoSN@C and corresponding elemental mappings of C, N, O, S, and Co elements (**g**); EDS of CoSN@C and X-ray maps of C, N, O, S, and Co (**h**). The nitrogen adsorption-desorption isotherm (Figure 2c) showed that when p/p\({}_{0}\)\(>\) 0.2, the amount of nitrogen adsorbed by the aforementioned materials increased gradually, whereas CoN@C and CoSN@C showed a hysteresis loop in the adsorption isotherm, indicating the presence of mesopores. According to the results of nitrogen sorption, SN@C exhibits type I isotherms. Additionally, the nitrogen adsorption isotherm of CoN@C and CoSN@C were comparable to type-IV(H\({}_{2}\)) and type-IV, respectively (H4).