## 3 Results and Discussion  
### Sample Characterizations  
Figure 1a displays the SEM image of PC, in which typical 3D carbon nanosheets are observed. The microstructural morphology of the MPC was determined by TEM. It is observed that the MPC surface is covered with large quantities of well-dispersed spherical particles (5.2 nm in diameter) through the solvothermal process (Figure 1b-c). The HRTEM image in Figure 1d further confirms the synthesis of MPC via observing the typical (400) facet of Fe\({}_{3}\)O\({}_{4}\) with a d-spacing of 0.21 nm. The corresponding elemental mapping analysis clearly shows that the O, Fe and C elements are homogeneously distributed on the surface of the PC (Figure 1e-h). TEM results have demonstrated that the nano-sized Fe\({}_{3}\)O\({}_{4}\) has been successfully synthesized and anchored on the PC matrix. XRD characterization was employed to determine the chemical structure of PC and MPC. As shown in Figure 2a, two diffraction peaks situated at 20 = 26.2\({}^{\circ}\) and 44.4\({}^{\circ}\) are detected in XRD pattern of PC, corresponding the (002) and (101) facets of the graphitic carbon [12]. In addition, seven new peaks at 30.1\({}^{\circ}\), 35.5\({}^{\circ}\), 43.1\({}^{\circ}\), 53.5\({}^{\circ}\), 57.0\({}^{\circ}\), 62.6\({}^{\circ}\), and 65.8\({}^{\circ}\) are obtained in the XRD pattern of MPC, which are assigned to the (220), (311), (400), (422), (511), (440), and (531) reflections of Fe\({}_{3}\)O\({}_{4}\) (JCPDS No. 65-3107). XRD results have shown that the MPC is successfully prepared by the one-pot solvothermal process, consistent with the TEM results. Figure 2b illustrates the magnetic hysteresis loops of MPC composite. The material exhibits a saturation magnetization of 20.73 emu g\({}^{-1}\), benefiting for its separation and recycling. Figure 1: (**a**) SEM image of PC; (**b**) TEM image of MPC; (**c**) Particle size distribution of MPC; (**d**) HRTEM images of the MPC and (**e–h**) STEM-EDS mapping images of MPC. An XPS survey scan was conducted to analyze the surface compositions of MPC. The XPS signals corresponding to C, O, and Fe elements were distinctively observed in the sample (Figure 2c), consistent with the EDS mapping results. High-resolution spectra of each element were recorded to identify their chemical states. Figure 2d shows the high-resolution O1s spectrum of MPC, in which the typical peaks indexed to Fe-O-C [13], -OH [14], and C-O [15] bonds are detected, respectively. These results verify the strong chemical interaction between the Fe\({}_{3}\)O\({}_{4}\) and PC matrix, which allows the tight attachment of Fe\({}_{3}\)O\({}_{4}\) nanoparticles, and thereby greatly improves the stability and recyclability of the MPC adsorbent. The Fe 2p spectrum in Figure 2e can be deconvoluted into two predominant peaks at 710.60 [16] and 712.49 eV [17] corresponding to the Fe\({}^{2+}\) and Fe\({}^{3+}\) species, suggesting the formation of Fe\({}_{3}\)O\({}_{4}\) phase in the composite [1]. Regarding the C1s spectrum (Figure 2f), the fitted peaks corresponding to C-C, C-OH, C (epoxy and alkoxy), and HO-C=O bonds are observed, respectively [18; 19; 20; 21; 1]. Moreover, the presence of oxygen-containing groups on MPC can enhance the hydrophilicity of MPC, benefitting its dispersion in aqueous solution. Figure 3a,b shows the N\({}_{2}\) sorption isotherms of PC and MPC, in which the typical type IV isotherms are observed [22]. According to the calculation results, it is discovered that the attachment of Fe\({}_{3}\)O\({}_{4}\) NPs on the PC surface leads to a decrease of BET specific surface area from 1174.1 to 622.2 m\({}^{2}\) g\({}^{-1}\), accompanying by the decline of pore volume from 0.75 to 0.54 cm\({}^{3}\) g\({}^{-1}\). This could be ascribed to the deposition of the relatively small Fe\({}_{3}\)O\({}_{4}\) NPs and the overlap of the PC surface by Fe\({}_{3}\)O\({}_{4}\) NPs [23; 24; 25; 10].