## 5 Noble Nanofluids
### Bimetallic Nanofluids  
The bimetallic nanoparticles composed of two different metals have attracted considerable attention due to their unique properties relevant for several applications including catalysis, sensing, optics, electronic devices, and medicine [83]. The bimetallic nanoparticles have also been applied to design bio sensors, to fabricate targeted drug delivery carriers and to increase the luminescence of the nanoparticles. The bimetallic nanoparticles of copper have also received much attention because of their novel properties and applications [84]. For instance, the copper-palladium nanoparticles have been prepared by several methods and because of many potential applications [85]. These studies confirm that copper-palladium bimetallic nanoparticles are easy to fabricate and relatively cheaper catalysts. The preparation and characterization of the metallic nanoparticles with diverse configurations, thermophysical properties, sizes and shapes have been the focus of the research community in the field. Also, considerable emphasis has been given to the production of colloidal bimetallic nanoparticles because of their improved optical, magnetic, electric, and catalytic properties over those of the single metallic nanoparticles. The bimetallic counterparts can be applied in a broad range of purposes including catalysts, sensors, biomedical imaging, drug delivery, and quantum dots [85]. The inclusion of a second metal alters the physicochemical properties of the individual constituents and offers synergistic-driven features derived from the interactions between the components [86]. As an example, the researchers [PERSON] et al. [87] evaluated the catalytic activity of nickel-palladium nanoparticles. The research team observed a high hydrogen selectivity of more than 80% for the decomposition of hydrodrazine at 50 \({}^{\circ}\)C. The corresponding monometallic counterparts were either have poor activity like the nickel nanoparticles or were inactive including the palladium nanoparticles. Moreover, the authors [PERSON] et al. [88] verified an appreciably higher catalytic activity when gold-platinum nano-sized dendrites were used in the methanol oxidation in respect to that of the commercially available catalyst of platinum-carbon. The authors interpreted the result based on the enhanced electronic interaction among the constituents of the nanoparticles. Furthermore, the researchers [PERSON] et al. [89] synthesized gold-silver bimetallic nanoparticles with pomergnate fruit juice and observed an increased catalytic activity and nitric oxide and hydroxyl radical scavenging activity with the developed nanoparticles. Besides, the pairing of gold and platinum was already frequently explored by the researchers. The gold nanoparticles possess an large application spectrum due to the inherent wide absorption band over the visible region in, for instance, plasmonic photothermal therapies, photovoltaics, therapeutic agents, and electronic conductors [90]. A feature of great relevance of the gold nanoparticles is the adjustable optoelectronic ability that can be tuned according to the morphology and agglomeration degree of the nanoparticles [91]. The platinum nanoparticles exhibit enhanced antioxidant and catalytic characteristics usually employed in the petrochemical cracking and electrocatalytic processes [92]. The platinum nanoparticles due to inherent favorable Fermi level positioning and superior electron interactions are very suitable to be applied in the hydrogen evolution and oxygen reduction reactions as electrocatalysts. Nonetheless, the bimetallic gold-platinum nanoparticles have shown superior performance in different purposes as compared to either of their constituents. Also, the authors [PERSON] et al. [93] reported the preparation of gold-platinum core-shell nanorods for catalytic and medical applications. Moreover, the authors [PERSON] et al. [94] reported the formation of hollow gold-platinum and gold-palladium nanoparticles through galvanic replacement reactions.