## 3 Results and Discussion  
XRD patterns of TiO\({}_{2}\), Fe\({}_{3}\)O\({}_{4}\), Fe\({}_{3}\)O\({}_{4}\)@SiO\({}_{2}\), and FS-NT (0, 2, 3, 4, and 5 mL) are shown in Figure 1. The prepared TiO\({}_{2}\) displayed good crystallinity: the diffraction peaks of TiOwere exhibited at 25.2\({}^{\circ}\), 38.7\({}^{\circ}\), 48\({}^{\circ}\), 54\({}^{\circ}\), 55.14\({}^{\circ}\), and 62.5\({}^{\circ}\), corresponding to the (101), (004), (200), (105), (211), and (204) lattice planes of TiO\({}_{2}\) (JCPDS No. 65-3369) [18]. The results suggest that TiO\({}_{2}\) has anatase crystals. The diffraction peaks of Fe\({}_{3}\)O\({}_{4}\) were exhibited at 30.1\({}^{\circ}\), 35.5\({}^{\circ}\), 43.1\({}^{\circ}\), 53.4\({}^{\circ}\), 56.9\({}^{\circ}\), and 62.5\({}^{\circ}\), corresponding to the (220), (311), (400), (422), (511), and (440) lattice planes of the magnetite phase (JCPDS No. 02-0387) [19]. Fe\({}_{3}\)O\({}_{4}\)@SiO\({}_{2}\) maintained the characteristic diffraction peaks of Fe\({}_{3}\)O\({}_{4}\) in Figure 1a. XRD patterns of FS-NT (0 mL) are shown in Figure 1a. It can be seen that compared with Fe\({}_{3}\)O\({}_{4}\)@SiO\({}_{2}\), the peak intensity of Fe\({}_{3}\)O\({}_{4}\) in FS-NT decreased due to the thickness of the TiO\({}_{2}\) coating, and the characteristic diffraction peaks of TiO\({}_{2}\) appeared at 20 = 25.2\({}^{\circ}\), 38.7\({}^{\circ}\), 48.1\({}^{\circ}\), 54.1\({}^{\circ}\), and 62.5\({}^{\circ}\), corresponding to (101), (004), (200), (211), and (204) crystal planes, which indicates that TiO\({}_{2}\) on the surface of FS-NT (0 mL) has anatase crystal TiO\({}_{2}\). The XRD patterns of FS-NT (2-5 mL) are shown in Figure 1b. The intensity of the Fe\({}_{3}\)O\({}_{4}\) characteristic diffraction peaks was still high, which suggests that the prepared FS-NT (2-5 mL) can provide a strong magnetic response for the subsequent magnet recovery samples. The characteristic diffraction peaks of TiO\({}_{2}\) appeared at 20 = 25.2\({}^{\circ}\) and 48.1\({}^{\circ}\), corresponding to the (101) and (200) planes of TiO\({}_{2}\), respectively. Compared with FS-NT (0 mL), the diffraction peaks of FS-NT (2 and 3 mL) shifted slightly toward the small-angle direction. The reason for this is that N ions are larger than O ions, and both substitutional and interstitial N ions can result in an increase in the lattice parameters of TiO\({}_{2}\)[20]. The possible reason for the insignificant shift of FS-NT (4 and 5 mL) is that the addition of 4 or 5 mL of NH\({}_{4}\)OH can increase the pH of the solution and accelerate the hydrolysis of tetraethyl titanate [21], so that N ions do not or rarely enter into the lattice structure. The TEM micrographs of FS-NT (0 mL) and FS-NT (3 mL) are shown in Figure 2a,b, where it can be seen that the nanocomposite samples clearly have a core-shell structure. The HRTEM image of FS-NT (0 mL) is shown in Figure 2c. The observed lattice spacings of 0.355 nm could be indexed to the (101) plane of TiO\({}_{2}\)[22], whereas those of 0.176 nm corresponded to the (422) plane of Fe\({}_{3}\)O\({}_{4}\)[23]. The HRTEM image of FS-NT (3 mL) is shown in Figure 2d. The observed lattice spacings of 0.355 nm could be indexed to the (101) plane of TiO\({}_{2}\)[22], whereas those of 0.263 nm corresponded to the (311) plane of Fe\({}_{3}\)O\({}_{4}\)[23]. Moreover, the corresponding selected-area electron diffraction (SAED) pattern (Figure 2e,f) displayed diffuse diffraction rings that were well indexed to the characteristic planes of TiO\({}_{2}\) and Fe\({}_{3}\)O\({}_{4}\). The lattice spacings of (101) and (200) planes of FS-NT (3 mL) in Figure 2f were larger than those of FS-NT (0 mL) in Figure 2e, which may be due to the fact that N ions were larger than O ions in the lattice structure. The results are consistent with those of XRD. Figure 3a,b show the UV-VIS DRS spectra of FS-NT (0 mL) and FS-NT (2-5 mL), respectively.