## 3 Result and Discussion
It indicates that these Fe\({}_{3}\)O\({}_{4}\) are presented with smaller particle sizes. With increasing the NaAc to 10 mmol, the particle sizes of the Fe\({}_{3}\)O\({}_{4}\) samples are increased obviously with better dispersity, which is observed in Figure 5B. Moreover, nearly monodispersed Fe\({}_{3}\)O\({}_{4}\) NPs with particle sizes between 100 and 200 nm are obtained when the NaAc is increased to 20 mmol (Figure 5C). While the particle sizes of S8 and S9 become larger than S5-S7. These as-prepared Fe\({}_{3}\)O\({}_{4}\) NPs show better dispersity and homogeneity. Additionally, these samples are further characterized by TEM, and these TEM images and the corresponding particle size distribution of the as-prepared Fe\({}_{3}\)O\({}_{4}\) particles are presented in Figure 6. The homogeneity of S5 is very poor when 5 mmol of anhydrous NaAc was added, and the mean particle size of these Fe\({}_{3}\)O\({}_{4}\) NPs (S5) is 85 nm with various morphologies (Figure 6A,F). After 10 mmol of anhydrous NaAc adding, the Fe\({}_{3}\)O\({}_{4}\) (S6) NPs in Figure 6B,G show the unconspicuous hollow structures with uniform size distribution. The average particle size is 122 nm. When increasing the NaAc to 20 mmol, the flower-like Fe\({}_{3}\)O\({}_{4}\) NPs (S7) with average particle size of 103 nm are presented in Figure 6C,H. The mesoporous structure of these Fe\({}_{3}\)O\({}_{4}\) NPs become more apparent. However, the evident hollow structures could be found with the increasing of anhydrous NaAc. The S8 show a better hollow structure in Figure 6D,I with mean particle size of 222 nm, and their surface is smooth. S9 with mean particle size of 256 nm are presented in Figure 6E,J had a similar internal structure. Figure 4: The hysteresis loops at T = 300 K of Fe\({}_{3}\)O\({}_{4}\) (**A**) and corresponding partly amplification images (**B**) with different molar ratio of FeCl\({}_{3}\) 6H\({}_{2}\)O (**a**) 0.4 mmol, (**b**) 5 mmol, (**c**) 20 mmol; (**C**) photograph of magnetic isolation. Moreover, the XRD patterns of Fe\({}_{3}\)O\({}_{4}\) NPs (S5-S9) with different amount of NaAc are shown in Figure 7. The XRD is conducted to confirm the crystal structure and composition of the as-synthesized Fe\({}_{3}\)O\({}_{4}\) NPs. As shown in Figure 7, these peaks at 20 = 25.7\({}^{\circ}\), 30.4\({}^{\circ}\), 357\({}^{\circ}\), 43.2\({}^{\circ}\), 57.3\({}^{\circ}\) and 62.8\({}^{\circ}\) could be evidently observed in all curves, which are corresponding to the crystal planes of (111), (220), (311), (400), (511), (440) in Fe\({}_{3}\)O\({}_{4}\) (JCPDS No. 01-1111, \(\alpha\) = 8.393 A) Only these peaks of Fe\({}_{3}\)O\({}_{4}\) NPs are observed, it indicates that the Fe\({}_{3}\)O\({}_{4}\) NPs show good crystallinity with inverse spinel phase. However, the diffraction peaks of S5 are significantly lower than other samples, indicating the lower crystallization property of S5. These results demonstrate that NaAc show a distinctly influence on the crystallinity of Fe\({}_{3}\)O\({}_{4}\) NPs. S6 show the best crystallization property and smaller particle size, which is facilitated to magnetic targeting drug delivery. Figure 3.0 SEM images of Fe\({}_{3}\)O\({}_{4}\) with different molar ratio of NaAc, (**A**) 5 mmol; (**B**) 10 mmol; (**C**) 20 mmol; (**D**) 40 mmol; (**E**) 60 mmol. Figure 3.1 TEM images and size analysis patterns of Fe\({}_{3}\)O\({}_{4}\) with different molar ratio of NaAc, (**A**) 5 mmol; (**B**) 10 mmol; (**C**) 20 mmol; (**D**) 40 mmol; (**E**) 60 mmol, the insets are the corresponding size distribution patterns; (**F–J**) is the corresponding magnification images, respectively. The magnetization curves of the Fe\({}_{3}\)O\({}_{4}\) NPs (S6, S8 and S9) are shown in Figure 3.2 The magnetic saturation \(M\)s values of the obtained Fe\({}_{3}\)O\({}_{4}\) NPs in Figure 8A (a: S6, b: S8, c: S9) are 49.64, 62.50 and 52.28 emu\(\cdot\)g\({}^{-1}\), respectively. The present coercivity \(H\)\(c\) values in Figure 8B are less than 150 Oe (A/m), it indicates that these NPs show a good soft magnetic property.