## 3 Results and Discussion
### Structure by XRD, Raman and FTIR
Fe sample depicts vibration modes at around at 190 (T\({}_{\text{2g}}\)), 304 (Eg), 532 (T\({}_{\text{2g}}\)) and 670 (A\({}_{\text{1g}}\)) cm\({}^{-1}\), all of them attributed to the Fe-O bonds of the Fe\({}_{3}\)O\({}_{4}\) crystallographic structures [27; 28]. Accordingly, the A\({}_{\text{1g}}\) represents the symmetric stretch of oxygen atoms along Fe-O bonds while the Eg and T\({}_{\text{2g}}\) are the symmetric and asymmetric bends of oxygen with respect to the FeO\({}_{4}\) tetrahedra lattice-vibration, respectively [28]. As aforesaid, magnetite crystallizes in an inverse cubic Fe\({}^{3+}\)(Fe\({}^{2+}\)Fe\({}^{3+}\))O\({}_{4}\) spinel structure, which contains Fe\({}^{2+}\) and Fe\({}^{3+}\) in the 1:2 ratios and belongs to the _Fd3m_ (O\({}_{7}\)) space group. Although the co-existence of the hematite, goethite, magnetite and maghemite is observed by the XRD patterns, Raman measurements indicate that the aforementioned vibrational modes confirm the predominance of the Fe\({}_{3}\)O\({}_{4}\) particles, in agreement with the XRD observations. Regarding the vibrational modes at high frequencies region, no modes are detected indicating the assignment of the sole magnetite structure [28]. In the case of FeC and Fe/FeC samples (Figure 1b), the vibrational modes broaden and blue shift, suggesting the weakness of the Fe-O bonds. This could be assigned to the presence of the quasi-crystalline forms of single carbon layer as it was the case of core-shell arrangement of the nanostructures [29]. The A\({}_{\text{1g}}\) mode of magnetite splits into two weak modes whereas two new modes near 215 and 276 cm\({}^{-1}\) arise. These modes are indeed totally symmetric, being typical for maghemite as displayed in XRD pattern, because magnetite is isostructural to maghemite with the cubic structure (space group _Fd3m_ (O\({}_{\text{h}}\)\({}^{7}\))). As a defective form of magnetite, \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) has the Fe atoms occupying two crystallographic distinct sites being tetrahedrally [Fe\({}^{2+}\)] and octahedrally [Fe\({}^{3+}\)] coordinated by oxygen anions from an Fe\({}^{3+}\)(Fe\({}^{2+}\)Fe\({}^{3+}\))O\({}_{4}\) structure. At high frequencies, it is evident that the broad band at around 1275 cm\({}^{-1}\) confirms the maghemite presence in Fe/FeC composite probably due to the extra framework \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) specie out of the structure. The defect bands from amorphous carbon, namely D band appears superimposed to that of maghemite and thus, the presence of amorphous carbon layer coated on the structure is likely to appear in Fe/FeC sample. On the contrary, Raman spectrum of FeC composite depicts the D and G modes at 1342 and 1610 cm\({}^{-1}\), respectively. The appearance of the D and G bands in the FeC composite suggests that an increased number of structural defects and disorders in the prepared composite in comparison with Fe sample. Noteworthy, XRD patterns of the FeC and Fe/FeC composites do not show distinct diffraction peak of carbon, which implies in a low degree of crystallinity of carbon content of the sample. These observations are confirmed by electron microscopy measurements. Figure 1c exhibits the FT-IR spectra of the prepared solids. The stretching and bending of the O-H groups from physisorbed water are shown at 3320 and 1615 cm\({}^{-1}\), respectively. It has been reported that Fe\({}_{3}\)O\({}_{4}\) particles has crystallized O-H hydroxyl bonded to the unsaturated surface Fe atoms metals in the same positions mentioned above [30]. Besides, the broad bands appearing in all samples at around 550 cm\({}^{-1}\) are assigned to the Fe-O bonds vibrations in tetrahedral and octahedral sites of magnetite. The above mentioned bands are observable in all solids studied. Importantly, the vibrations at 903 and 800 cm\({}^{-1}\) in Fe sample are attributed to stretching and bendings of O-H groups, respectively from goethite [31]. It confirms the presence of a mixture of iron oxides, as seen by XRD in Fe sample.