# Fabrication of Novel CeO2/GO/CNTs Ternary Nanocomposites with Enhanced Tribological Performance
## 3 Results and Discussion
In Figure 4d, six Ce 3d peaks located at 917.4, 908.4, 901.5, 899.1, 886.3, and 882.9 eV, respectively, were assigned to 3d\({}_{3/2}\) and 3d\({}_{5/2}\) for Ce\({}^{4+}\) final states. Moreover, two weak peaks located at 902.25 and 889.7 eV should be assigned to 3d\({}_{3/2}\) and 3d\({}_{5/2}\) for Ce\({}^{3+}\) final states [33]. In combination with Figure 4b-d, it can be speculated that surfaces of both GO and CNTs were rich in oxygen-containing groups so that CeO\({}_{2}\) can be homogeneously compounded with them using a hydrothermal method. Figure 3: Raman spectra of GO, CeO\({}_{2}\)/CNTs and CeO\({}_{2}\)/GO/CNTs-d nanocomposites. Figure 2: TEM images of (**a**) CeO\({}_{2}\)/CNTs nanocomposites; (**b**) CeO\({}_{2}\)/GO/CNTs-a nanocomposites; (**c**) CeO\({}_{2}\)/GO/CNTs-b nanocomposites; (**d**) CeO\({}_{2}\)/GO/CNTs-c nanocomposites; (**e**) CeO\({}_{2}\)/GO/CNTs-d nanocomposites; and (**f**) CeO\({}_{2}\)/GO/CNTs-e nanocomposites. The dispersion stability of lubricating additive is a significant factor that affects the tribological performance of lubricating oil. Paraffin oil used as the lubricant base oil in this study has a similar structure with petroleum and is more environmentally friendly than petroleum [40]. Figure 5 showed that 1 wt% CeO\({}_{2}\)/GO/CNTs-d nanocomposites were dispersed in paraffin oil under ultrasonic agitation and placed in a water bath at 30 \({}^{\circ}\)C for observation. With the passage of time, the dispersion stability of nanocomposites in base oil was observed using a digital camera. We could clearly see that CeO\({}_{2}\)/GO/CNTs-d nanocomposites possessed excellent dispersion and remained stable in the base oil on the twelfth day. The long-term dispersion stability of the nanocomposites in the base oil resulted from the uniform dispersion of CeO\({}_{2}\) nanoparticles on the GO/CNTs hybrids and the \(\pi\)-\(\pi\) bond interaction and rich oxygen-containing groups on the surface of nanocomposites, which could prevent the agglomeration between nanocomposites [30; 31; 41]. Generally, the friction performances of various nanomaterials used as additives and paraffin oil were characterized by the friction coefficient and wear scar diameters (WSD). Demonstrated in Figure 6 are variation of friction coefficient, average friction coefficient, and WSD of paraffin oil, 1 wt% of GO nanosheets, CeO\({}_{2}\) nanoparticles, CeO\({}_{2}\)/CNTs nanocomposites, and CeO\({}_{2}\)/GO/CNTs-d nanocomposites. Figure 6a shows that the paraffin oils filled with additives have superior stability compared with pure paraffin oil whose friction coefficient was increased with the passage of time. Additionally, the friction coefficient of paraffin oils filled with additives was lower than that of pure paraffin oil. It indicated that the addition of these additives can enhance the tribological performance of pure paraffin oil. Evidently, paraffin oils filled with CeO\({}_{2}\)/GO/CNTs-d nanocomposites manifested the lowest friction coefficient. These results are consistent with average friction coefficient of abovementioned pure paraffin oil and paraffin oils filled with different additives shown in Figure 6b. WSD is of great significance for demonstrating the friction performance of paraffin oils. The trend of WSD of nanocomposites in Figure 6b is the same as the friction coefficient trend wherein the friction coefficient and WSD of paraffin oil filled with CeO\({}_{2}\)/GO/CNTs-d nanocomposites decreased by 31.6%  
Figure 4: XPS survey spectrum for (**a**) C1s of CeO\({}_{2}\)/CNTs nanocomposites; (**b**) C1s; (**c**) O1s; and (**d**) Ce3d spectrum for CeO\({}_{2}\)/GO/CNTs-d nanocomposites. and 37% compared with pure paraffin oil, respectively. The friction coefficient and WSD of paraffin oil filled with CeO\({}_{2}\)/CNTs nanocomposites did not follow the improvement trend.