## 2 Results and Discussion  
### Synthesis and Characterization of DETA-MPs-GO  
Fe\({}_{3}\)O\({}_{4}\) microspheres were prepared by solvothermal synthesis. It was observed that the synthesized Fe\({}_{3}\)O\({}_{4}\) microspheres showed good spherical shape, with a coarse surface and narrow size distribution of around \(\sim\)320 nm from the TEM photograph, as shown in Figure 1a. Then, well-defined core-shell Fe\({}_{3}\)O\({}_{4}\)@poly(GMA-co-DVB) was prepared via modified precipitation polymerization. In the polymerization process, DVB and GMA were chosen as two polymeric monomers since DVB showed a fast reaction rate, while GMA holds many epoxy groups. Furthermore, GMA was easy to locate outside the surface of the co-polymer microspheres in acetonitrile [25]. Hence, the amino groups were easily modified on the Fe\({}_{3}\)O\({}_{4}\)@poly(GMA-_co_-DVB) microspheres by a ring-opening reaction toward the outside reactive epoxy groups. As was observed in Figure 1b, the polymeric component was regularly coated outside the Fe\({}_{3}\)O\({}_{4}\) core, and well-defined core-shell Fe\({}_{3}\)O\({}_{4}\)@poly(GMA-_co_-DVB) was achieved since the black core and gray shell could be clearly observed. Moreover, the Fe\({}_{3}\)O\({}_{4}\)@poly(GMA-_co_-DVB) also had a spherical shape but with a smooth surface. There is no significant difference between DETA-MPs and Fe\({}_{3}\)O\({}_{4}\)@poly(GMA-_co_-DVB) in terms of shape (Figure 1c). Figure 1d listed the last DETA-MPs-GO material, where DETA-MPs were immobilized on the GO sheet.  
Figure 1: Transmission electron microscopy (TEM) images of: (**a**) magnetic Fe\({}_{3}\)O\({}_{4}\) microspheres; (**b**) magnetic core-shell polymer (Fe\({}_{3}\)O\({}_{4}\)@poly(GMA-_co_-DVB)); (**c**) DETA-MPs; (**d**) DETA-MPs-GO; (**e**) Fourier-transformed infrared spectroscopy (FTIR); and (**f**) X-ray diffraction (XRD) spectra of synthesized materials. EDTA-MPs: diethylenetriamine-functional magnetic core-shell polymer, GO: graphene oxide.  
FTIR spectra were also conducted to further validate the success of grafting DETA-MPs onto the GO sheet. As could be observed in Figure 1e, the characteristic absorption of -NH\({}_{2}\) groups occurred at \(\sim\)3425 cm\({}^{-1}\). Compared with DETA-MPs, a new characteristic absorption at \(\sim\)1638 cm\({}^{-1}\) arose after linking to the GO sheet, implying that DETA-MPs was covalently modified on the GO sheet through an amidation reaction. Finally, the XRD technique was also carried out to further demonstrate the structure and components of DETA-MPs-GO, and the as-synthesized Fe\({}_{3}\)O\({}_{4}\), DETA-MPs and GO were tested, as exhibited in Figure 1f. It could be seen that the diffraction peaks at 2\(\theta\) = 30.25\({}^{\circ}\), 35.58\({}^{\circ}\), 43.21\({}^{\circ}\), 54.39\({}^{\circ}\), 57.09\({}^{\circ}\), and 62.92\({}^{\circ}\) could be owing to (220), (311), (400), (422), (511), and (440) reflections, respectively, confirming the cubic spinel crystal structure of Fe\({}_{3}\)O\({}_{4}\). Figure 1f(ii) presents a sharp diffraction peak located at 2\(\theta\) = 11.28\({}^{\circ}\), which could be attributed to the (002) reflection of the GO sheet [26]. For DETA-MPs-GO (Figure 1f(iii)), the above six peaks of Fe\({}_{3}\)O\({}_{4}\) could also been observed, but the (002) reflection absorption of the GO sheet could not be discovered. This was because the GO sheets can't stack with each other anymore to form crystalline structures after being covered with magnetic polymer microspheres [27].