## 3 Result and Discussion
After increasing the amount of FeCl\({}_{3}\cdot\)6H\({}_{2}\)O to 5 mmol, the hollow structure of as-obtained Fe\({}_{3}\)O\({}_{4}\) NPs (S2) is more apparent, and the mean particle size is 222 nm (Figure 2B,F). The average particles size of S3 is 116 nm, and the internal mesoporous structure could be observed in Figure 2C,G. Moreover, with the increasing of FeCl\({}_{3}\cdot\)6H\({}_{2}\)O, the flower-like Fe\({}_{3}\)O\({}_{4}\) NPs without hollow and mesoporous structure are presented in Figure 2D,H. These results indicated that the morphology could be influenced by the amount of FeCl\({}_{3}\cdot\)6H\({}_{2}\)O greatly. Moreover, the XRD patterns of these Fe\({}_{3}\)O\({}_{4}\) (S1-S4) are shown in Figure 3. The XRD is conducted to confirm the crystal structure and composition of these samples. As shown in Figure 3, the peaks at 20 = 25.7\({}^{\circ}\), 30.4\({}^{\circ}\), 35.7\({}^{\circ}\), 43.2\({}^{\circ}\), 57.3\({}^{\circ}\) and 62.8\({}^{\circ}\) are evidently observed in these curves, and these peaks could index to the crystal planes of (111), (220), (311), (400), (511) and (440) of Fe\({}_{3}\)O\({}_{4}\) (JCPDS PDF: 01-1111, \(\alpha\) = 8.393 A), respectively. There are no other impurity peaks in these curves, it indicates that the as-prepared Fe\({}_{3}\)O\({}_{4}\) NPs possess inverse spinel phase. Meanwhile, the intensities of S1-S4 is increasing gradually. It indicates that the FeCl\({}_{3}\cdot\)6H\({}_{2}\)O could influence the crystal performance of as-prepared Fe\({}_{3}\)O\({}_{4}\) NPs. Figure 1: SEM images of Fe\({}_{3}\)O\({}_{4}\) with different molar quantity of FeCl\({}_{3}\cdot\)6H\({}_{2}\)O, (**A**) 0.4 mmol; (**B**) 5 mmol; (**C**) 10 mmol; (**D**) 20 mmol. Finally, the magnetic performances of as-obtained Fe\({}_{3}\)O\({}_{4}\) NPs are investigated by VSM. The magnetization curves of the Fe\({}_{3}\)O\({}_{4}\) NPs are shown in Figure 4A,B. The magnetic saturation _M_s values of the as-obtained Fe\({}_{3}\)O\({}_{4}\) NPs in Figure 4A (a: S1, b: S2, c: S4) are 79.80, 62.50 and 53.43 emu-g\({}^{-1}\), respectively. The present coercivity (\(H_{c}\)) values in Figure 4B are about 100 Oe (A/m), indicating a very good soft magnetic property. Obviously, the _M_s values of Fe\({}_{3}\)O\({}_{4}\) NPs increase gradually with the decreasing of FeCl\({}_{3}\)\(\cdot\)6H\({}_{2}\)O. Figure 3C shows the photographs of the suspension of Fe\({}_{3}\)O\({}_{4}\) NPs with an external magnet application. The Fe\({}_{3}\)O\({}_{4}\) NPs can be easily dispersed in ethyl alcohol solution to form a black suspension, and it could also be drawn from the solution to the sidewall of the vial by an external magnetic field. The aggregate NPs could further re-dispersed in solution by removing the external field and slightly shaking. Figure 3: XRD patterns of Fe\({}_{3}\)O\({}_{4}\) obtained with different molar ratio of FeCl\({}_{3}\)\(\cdot\)6H\({}_{2}\)O, A: 0.4 mmol, B: 5 mmol, C: 10 mmol, D: 20 mmol. Figure 2: TEM images and size distribution patterns of Fe\({}_{3}\)O\({}_{4}\) with different molar ratio of FeCl\({}_{3}\)\(\cdot\)6H\({}_{2}\)O, (**A**) 0.4 mmol; (**B**) 5 mmol; (**C**) 10 mmol; (**D**) 20 mmol, the insets are the corresponding size distribution patterns. (**E–H**) is the corresponding magnification images. Morphology, Crystal Structure, and Magnetic Property of Fe\({}_{3}\)O\({}_{4}\) NPs with Different Amount of NaAc  
The amount of anhydrous NaAc could be the another factor to influence the morphologies and performances of Fe\({}_{3}\)O\({}_{4}\) NPs. Five experimental groups with different anhydrous NaAc adding (5 mmol (S5), 10 mmol (S6), 20 mmol (S7), 40 mmol (S8), 60 mmol (S9)) are carried out for discussion the effect. Other synthetic conditions in each of these experiments are kept the same as those in the typical experiment, and the specific parameters are presented in Table 1. In the first place, the SEM images of S5-S9 are presented in Figure 5. As shown in these SEM images, the floccule is observed when 5 mmol NaAc is added.