## 5 Noble Nanofluids
### Palladium Nanofluids
[76] studied the possibility of using palladium nanofluids in the hyperthermia therapy. The authors highlighted that the palladium nanoparticles can be explored for hyperthermia therapy to increase the localized absorption of energy by external sources, to eliminate tumor cells be only heating them and with only little thermal damages imposed on the adjacent healthy cells. The palladium nanoparticles can also play the role of drug carriers acting on the tumor when heated to provide a localized antioxidant action and decrease cancer cells viability. Consequently, the palladium hydride nanoparticles can be adopted as promising materials for hyperthermia therapeutic processes. The PdCeO\({}_{2}\) nanoparticles and palladium nanocubes were synthesized and the nanofluids prepared with them were hydrogenated. The nanofluid having palladium nanocubes showed significant temperature increases of more than 30 \({}^{\circ}\)C after 3 min of diode-laser irradiation. Also, the nanofluids having PdCeO\({}_{2}\)H nanoparticles showed temperature increases of approximately 11 \({}^{\circ}\)C under similar irradiation conditions. The behavior of the PdCeO\({}_{2}\)H nanofluids was because of the ion H\({}^{+}\) in reducing the ion Ce\({}^{4+}\) to Ce\({}^{3+}\). The palladium nanocubes were produced through chemical precipitation with the addition of the CTAB surfactant. The mechanical grinding and internal oxidation were also employed to fabricate a nanostructured PdCeO\({}_{2}\) alloy that displayed the formation of nano-scaled ceria in the palladium matrix. The temperature changes verified in the nanofluids were much greater than those verified with the distilled water alone, demonstrating the superior photothermal performance of the employed nanoparticles, including those that were hydrogenated. Moreover, the authors [PERSON] et al. [77] investigated diverse palladium nanoparticles modified by octadecanthiol, octadecylamine, and a mixture of them were prepared, which are named herein by Pd-S, Pd-N, and Pd-S+N, respectively. The size of the palladium nanoparticles was from 1 nm to 3 nm and they were well-dispersed in kerosene. The researchers verified that the Pd-S+N was the most promising additive for the hydrocarbon fuel for preparing a highly stable propellant, thermal conductivity, and cooling ability. The investigation team found that the viscosity of the nanofluids containing palladium nanoparticles with concentrations inferior to 0.2% wt. had no appreciable increase in respect to the viscosity of the kerosene. Besides, the researchers reported that the thermal conductivities of the nanofluids were considerably enhanced at 0.2% wt. of palladium nanoparticles. The stability trend of the nanofluids were as follows: Pd-S+N > Pd-S > Pd-N. The pyrolysis of decalin in the absence/presence of palladium nanoparticles was carried out from 440 \({}^{\circ}\)C to 470 \({}^{\circ}\)C. The order of the catalytic ability for the palladium nanoparticles was as follows: Pd-N > Pd-S+N > Pd-S. The catalytic activities of the surface-modified nanoparticles for pyrolysis of decalin were attributed to the synergistic effects of palladium and its ligands. Hence, it was concluded that the functional nanoparticles could be synthesized by adjusting the relative content of the core palladium and its ligands in the nanoparticles. The researchers verified that the Pd-S+N was the most promising additive for the hydrocarbon fuel for preparing a highly stable propellant, thermal conductivity, and cooling ability. Figure 10 schematically illustrates a typical green synthesis method for palladium nanoparticles obtained from the _Origanum vulgare_ plant. Figure 10: Typical green preparation method to synthesize palladium nanoparticles from _Origanum vulgare_ plant. Figure 9: Fundamental methods to produce palladium nanoparticles.