# Fabrication of Novel CeO2/GO/CNTs Ternary Nanocomposites with Enhanced Tribological Performance
## 3 Results and Discussion
The aggregation of CeO\({}_{2}\) nanoparticles on CNTs was observed in Figure 2 and the CeO\({}_{2}\)/CNTs additives were prone to precipitate because of its poor compatibility with the lubricant base oil, which led to slightly influencing the improvement of tribological properties. Therefore, all these additives were effective for enhancing the tribological property of paraffin oil. In particular, the paraffin oil filled with CeO\({}_{2}\)/GO/CNTs-d nanocomposites displayed excellent tribological properties. This can be explained by the fact that the two-dimensional lamellar structure of GO, the one-dimensional tubular CNTs, and the zero-dimensional spherical CeO\({}_{2}\) were uniformly compounded and achieved the synergistic lubrication effect [42] that the improvement of tribological properties of CeO\({}_{2}\)/GO/CNTs-d nanocomposites was far superior to the single-component nanomaterials. Figure 5: Digital photos of dispersion stability of 1 wt% CeO\({}_{2}\)/GO/CNTs-d nanocomposites in paraffin oil at 30 \({}^{\circ}\)C.  
Figure 6: (**a**) Typical friction coefficient curves using the base oil and the oil with 1 wt% GO nanosheets, CeO\({}_{2}\) nanoparticles, CeO\({}_{2}\)/CNTs nanocomposites, and CeO\({}_{2}\)/GO/CNTs-d nanocomposites; and (**b**) comparisons of average friction coefficient and average WSD of steel disks using these oils over the entire duration of the test (load of 10 N, rotating speed of 300 rpm, test duration of 30 min). Considering the effect of different weight ratios of CeO\({}_{2}\), GO, and CNTs in the nanocomposite on the friction properties of paraffin oil, the tribological behaviors of CeO\({}_{2}\)/GO/CNTs nanocomposites with a content of 1 wt% in paraffin oil were investigated as lubricant additives in pure paraffin oil. In Figure 7a, the paraffin oil filled with CeO\({}_{2}\)/GO/CNTs nanocomposites using different weight ratios of raw materials gave different tribological properties. Therein, the friction coefficients of paraffin oil filled with the CeO\({}_{2}\)/GO/CNTs-a and CeO\({}_{2}\)/GO/CNTs-e nanocomposites presented large fluctuations and tended to rise slowly. In contrast to the instability of friction coefficients of paraffin oil filled with CeO\({}_{2}\)/GO/CNTs-a and CeO\({}_{2}\)/GO/CNTs-e nanocomposites, paraffin oil filled with CeO\({}_{2}\)/GO/CNTs-(b-d) nanocomposites not only expressed the better stability but also had the lower friction coefficients. From the curve of friction coefficient and WSD shown in Figure 7b, it can be observed that CeO\({}_{2}\)/GO/CNTs-d nanocomposites had the lowest friction coefficient and the narrowest WSD compared with other additives. The comprehensive analysis signifies that GO/CNTs hybrids decorated with uniform CeO\({}_{2}\) nanoparticles were achieved at a proper mass ratio of GO/CNTs and Ce(NO\({}_{3}\))\({}_{3}\cdot\)6H\({}_{2}\)O, which is an important point to reduce the wear rate of base oil. Therefore, CeO\({}_{2}\)/GO/CNTs-d possessed the superior lubricating performance owing to the uniform distribution of CeO\({}_{2}\) nanoparticles on surface of hybrids and no obvious aggregation of among CeO\({}_{2}\), CNTs, and GO, which is consist with the TEM images shown in Figure 2.  
In order to obtain the appropriate content of CeO\({}_{2}\)/GO/CNTs-d nanocomposites as a lubricant additive that improves the friction resistance of paraffin oil, the tribological performance of paraffin oil with different contents of CeO\({}_{2}\)/GO/CNTs-d nanocomposites were investigated, as shown in Figure 8a,b. From the curve of friction coefficient with time in Figure 8a, it can be found that the CeO\({}_{2}\)/GO/CNTs-d nanocomposites lubricant with a content of 0.5 wt% and 1 wt% were relatively stable. In particular, in Figure 7b, CeO\({}_{2}\)/GO/CNTs-d nanocomposites with a content of 1 wt% manifested the lowest friction coefficient and the smallest WSD compared with other concentrations of additives.