# Study on the Tribological Properties of F-T DS/ZnFe-LDH Composite Lubricating Material
## 3 Results and Discussion  
### FTIR and XPS Analysis  
As we can see from the infrared spectra of the three lubricating materials in Figure 1 that the characteristic peaks of ZnFe-LDH and FS/ZnFe-LDH are very similar. However, FS is very different from ZnFe-LDH and FS/ZnFe-LDH, which indicates that the functional groups of ZnFe-LDH and FS/ZnFe-LDH are basically the same but distinct from FS. The hydroxyl C-OH was associated with the characteristic peak near 3400 cm in Figure 1. For the two materials FS and FS/ZnFe-LDH, the peaks of -CH\({}_{2}\) bond were found at 2930 cm\({}^{-1}\) and 2850 cm\({}^{-1}\) separately. Moreover, for FS, the peak at 1725 cm\({}^{-1}\) and 1613 cm\({}^{-1}\) corresponded with the C=O bond (1725 cm\({}^{-1}\)) and the C=O bond on the aromatic ring (1613 cm\({}^{-1}\)). In the FS infrared spectrum, the peak that appears at 1384 cm\({}^{-1}\) was caused by the C-H bond. The characteristic peak at 1044 cm\({}^{-1}\) was assigned to the ether bond C-O-C. In the infrared spectra of ZnFe-LDH and FS/ZnFe-LDH these two materials, the peak of the O-C-O bond is observed, which is in the range of 1500-1636 cm\({}^{-1}\). The peak at 1395 cm\({}^{-1}\) (1392 cm\({}^{-1}\)) was caused by the symmetrical stretching vibration of carbonate O-C-O in the v3 modes [22], and a peak that confirmed the presence of zinc hydroxylation (Zn-OH) was found near 950 cm\({}^{-1}\)[23]. The three peaks appearing in the range of 835-1048 cm\({}^{-1}\) were carbonate stretching vibrations. The two peaks at 465-549 cm\({}^{-1}\) are related to the metal-oxygen bond [24; 25]. To investigate the differences in the elemental composition of the above three lubricating materials, the elemental valence composition of the three lubricating materials prepared was analyzed through XPS. Figure 2 shows the full spectrum of the three lubricating materials, FS, ZnFe-LDH, and FS/ZnFe-LDH, all discovered two elements of C and O. It is worth noting that, among them, ZnFe-LDH and FS/ZnFe-LDH detected the two elements Zn and Fe. To further distinguish them, the fine spectra of the above elements were fitted. Figure 3a,c,g shows the carbon element spectra of FS, ZnFe-LDH, and FS/ZnFe-LDH, respectively. The C-C bond, which is used for charge correction, is shown by the peak at 284.8 eV. The characteristic peak of 286.28 eV in the carbon element spectrum of FS is attributed to C-O-C or C=O; For the carbon spectra of ZnFe-LDH and  
Figure 1: Fourier transform infrared spectrometer(FTIR) spectra of Zinc-iron hydrotalcite(ZnFe-LDH), FS/ZnFe-LDH, and F-T diesel soot (F-T DS, FS). FS/ZnFe-LDH, in Figure 3c,g, the peaks appearing at 289.47 eV and 289.33 eV are related to carbonate hydroxides [26]. Figure 3b,d,h shows the oxygen element spectra of the three lubricating materials, respectively. For FS, the peaks of C-O and C=O appear at 531.8 eV and 533.81 eV, respectively. The characteristic peaks appearing at around 529.6 eV in the oxygen spectrum of ZnFe-LDH and FS/ZnFe-LDH are assigned to metal oxides (Zn-O, Fe-O) [27]. In Figure 4d,h, the peak at about 531.7 eV corresponds to the existence of surface defects in ZnFe-LDH and FS/ZnFe-LDH, in the form of oxygen vacancies [28]. Figure 3e,i shows the zinc element spectra of ZnFe-LDH and FS/ZnFe-LDH, respectively. In Figure 3e,i, the two peaks corresponding to Zn2p3/2 and Zn2p1/2 appear near 1022 eV and 1045 eV, respectively [29]. Figure 3f,g shows the iron element spectra of ZnFe-LDH and FS/ZnFe-LDH, respectively. In the figure, characteristic peaks around 721 eV and 725 eV belong to Fe3+, the peaks around 718 eV belong to the satellite peaks of Fe2p3/2 [30]. The result of XPS analysis corresponds to the result of infrared spectrogram analysis. Figure 3: XPS fine spectra of ZnFe-LDH, FS/ZnFe-LDH, and FS. (**a**,**b**) FS; (**c**–**f**) ZnFe-LDH; (**g**–**j**) FS/ZnFe-LDH. Figure 2: X-ray photoelectron spectroscopy(XPS) survey spectra of ZnFe-LDH, FS/ZnFe-LDH, and FS. Figure 4: Scanning electron microscope(SEM) diagram of ZnFe-LDH, FS/ZnFe-LDH, and FS.