# Magnetic and Hydrophobic Composite Polyurethane Sponge for Oil-Water Separation
## 3 Results and Discussion  
The morphologies of magnetic Fe3O4 nanoparticles scanned by TEM are exhibited in Figure 2. The diameter of magnetic Fe3O4 nanoparticles is between 10-20 nm, and the particle size reaches the nanoscale. The magnetic Fe3O4 nanoparticles are spherical and dispersed. As shown in Figure 3, the magnetic Fe3O4 nanoparticles are firmly attracted to the glass wall by magnets, which shows that the magnetic Fe3O4 nanoparticles have excellent magnetism. The magnetic Fe3O4 nanoparticles which can be used in magnetic composite sponge were successfully prepared by chemical coprecipitation. Figure 4 compares the magnetic properties of the original sponge and the magnetic composite sponge by testing with magnets. Obviously, unlike the original PU sponge, the magnetic composite sponge can be easily attracted by magnets, indicating that the magnetic Fe3O4 nanoparticles are successfully filled into the original PU sponge. Figure 2: TEM images of magnetic Fe3O4 nanoparticles. The chemical composition of the coating on the sponge was identified by FT-IR, demonstrating the existence of magnetic Fe\({}_{3}\)O\({}_{4}\) nanoparticles, expanded graphite and stearic acid in composite sponge. As showed in the Figure 5, the absorption bands at \(\sim\)3297 cm\({}^{-1}\), \(\sim\)2867 cm\({}^{-1}\), \(\sim\)2275 cm\({}^{-1}\), \(\sim\)1721 cm\({}^{-1}\), \(\sim\)1106 cm\({}^{-1}\), and \(\sim\)1542 cm\({}^{-1}\) of line iv in FT-IR spectra are attributed to the characteristic peak of polyurethane sponge [43]. The N\(-\)H peak at 3297 cm\({}^{-1}\), the peak at 2928 cm\({}^{-1}\) is attributed to the C\(-\)H stretching of \(-\)CH\({}_{3}\) and \(-\)CH\({}_{2}\), and the peak at 2275 cm\({}^{-1}\) is due to the asymmetric stretching of \(-\)NCO. The peaks at 1721 cm\({}^{-1}\) and 1106 cm\({}^{-1}\) are associated with C=O stretching in the amide, urea and ether groups respectively, and the peak at 1542 cm\({}^{-1}\) is attributed to the amide II band. As for the line v, the FT-IR spectra of magnetic composite sponge, the absorption bands at \(\sim\)2919 cm\({}^{-1}\), \(\sim\)2849 cm\({}^{-1}\), \(\sim\)1703 cm\({}^{-1}\), and \(\sim\)1466 cm\({}^{-1}\) are due to the characteristic peak of stearic acid [44]. The peaks at \(\sim\)2919 cm\({}^{-1}\) and \(\sim\)2849 cm\({}^{-1}\) are due to the anti-symmetry and symmetric stretching vibration of \(-\)CH\({}_{2}\), the peak at \(\sim\)1703 cm\({}^{-1}\) is due to the stretching vibration of C=O and the peak at \(\sim\)1466 cm\({}^{-1}\) is ascribed to the scissoring vibration of \(-\)CH\({}_{2}\). The absorption bands at \(\sim\)565 cm\({}^{-1}\) and \(\sim\)3446 cm  
Figure 4: Digital photographs of magnetic test by magnet for (**a**) the original polyurethane sponge and (**b**) the composite sponge. Figure 3: Digital photographs (**a**) Fe\({}_{3}\)O\({}_{4}\) nanoparticles (**b**) the magnetic test by magnet for Fe\({}_{3}\)O\({}_{4}\) nanoparticles. are associated with the characteristic peak of magnetic Fe\({}_{3}\)O\({}_{4}\) nanoparticles and expanded graphite, respectively [45; 46; 47]. The results of FT-IR spectra indicates that the expanded graphite, Fe\({}_{3}\)O\({}_{4}\) magnetic nanoparticles and stearic acid were dispersed successfully into the original PU sponge and there is no new bond created on magnetic composite sponge surface. The surface morphological evolution of sponge sample 1 and 2 were investigated by SEM. Figure 6(a1-a4) and Figure 6(b1-b4) shows the morphology of sample 1 not modified by stearic acid and sample 2 modified by stearic acid, respectively, which demonstrate sponge samples both have a three dimensional porous structure with pore sizes in the range of 100-500 \(\upmu\)m and the surface are rough and the skeleton coated with expanded graphite at the range of 10-30 \(\upmu\)m. Obviously, the surface of sample 2 looks brighter than that of sample 1, indicating stearic acid coated at the surface skeleton of sponge sample 2 successfully.