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Bimetallic nanoparticles have recently generated a lot of interest in the scientific community. It is a relatively new scientific study area with a wide range of applications across various science and technology fields.
Bimetallic nanoparticles, as the name suggests, are synthesized by combining two different metallic nanoparticles. The properties of a bimetallic nanoparticle are dependent on their constituent metallic nanoparticles and their nanometric size.
Scientists are currently experimenting with synthesizing these nanoparticles using different innovative methods. They are also focusing on developing bimetallic nanoparticles of different forms, such as core-shell, alloys, and contact aggregate. The reason why these nanoparticles have invoked much interest in the scientific community is that an extra degree of freedom can be introduced through bimetallization.
Properties of Bimetallic Nanoparticles
The properties of bimetallic nanoparticles can be significantly different from those of the elemental monometallic nanoparticles. Some of these properties are discussed below:
Catalytic properties
Combination of different metal nanoparticles results in the formation of bimetallic nanoparticle with higher catalytic properties. Such properties are incredibly advantageous for scientific and technological developments. For example, the combination of equal atomic concentration of gold nanoparticles and silver nanoparticles is used in different catalytic reactions for its enhanced surface area and decreased density.
Optical properties
Plasmonic coupling between nanoparticles draws interesting optical properties. The excited surface electrons display characteristic absorption that leads to a colored nanoparticle dispersion. The surface plasmon resonance (SPR) absorption wavelength is dependent on the individual elements. SPR of bimetallic nanoparticles reveals the internal distribution of the elements.
Antibacterial properties
The most important characteristic feature of nanoparticles is that they can penetrate the cells and release bioactive ions. Gold-silver bimetallic nanoparticles reveal superior-quality antibacterial activity against pathogenic bacteria such as Staphylococcus aureus and Klebsiella pneumoniae.
Thermal conductivity
Nanofluids, consisting of silver-gold bimetallic nanoparticles in water, enhance the thermal conductivity of fluids.
Examples of Bimetallic Nanoparticles
Scientists are developing novel bimetallic nanoparticles of desired properties. Some of the examples of such nanoparticles are discussed below:
Platinum-based bimetallic nanoparticles
Platinum (Pt) nanoparticles are critical catalysts that are widely used commercially. These are especially used in an automotive catalytic converter for their high surface to volume ratio. However, to increase its efficiency of platinum-based electrodes, researchers have developed Pt-based bimetallic nanoparticle catalysts. Pt-X alloys (X- gold, silver, copper, etc.) have a very high catalytic efficiency.
Nickel-based bimetallic nanoparticles
Nickel nanoparticles are used for their low-cost, high stability and magnetic and catalytic properties. Many fascinating properties are obtained when nickel is associated with other metals. Researchers have found that the efficiency of various reactions can be significantly improved by varying the stoichiometric ratios of nickel and metals in a nickel-based bimetallic nanoparticle, such as nickel-tin and nickel-copper.
Gold-based bimetallic nanoparticles
Gold nanoparticles are extensively used as a biosensor and catalyst. Recently, gold-palladium bimetallic nanoparticles have shown promising electrochemical, catalytic, and structural properties. Gold-copper nanoparticles help develop various medical sensors and biomedicines. Gold-silver bimetallic nanoparticles are used to detect glucose in the blood level and reveal chemiluminescence property.
Iron-based bimetallic nanoparticles
Iron-copper bimetallic catalyst shows high catalytic activity.
Applications of Bimetallic Nanoparticles
Biomedical applications
Controlled drug delivery system plays a vital role in treating various diseases that include cancer. The main focus of such a drug delivery process is the maintenance of biocompatibility during the therapeutic process and specificity.
Magnetic bimetallic nanoparticles are used for controlled drug delivery. These nanoparticles offer high specificity.
When the magnetic bimetallic nanoparticles are administered to the body, they reach the target site under the influence of an external magnetic field that involves eliminating infected cells.
The addition of specific proteins or antibodies to the bimetallic nanoparticle surface provides greater specificity and immunologically directed targeting.
Iron-based bimetallic nanoparticles can be used for improving MRI of cancerous cells. Bimetallic nanoparticles containing gold and silver are used in vitro and in vivo photothermal cancer therapies.
In pharmaceutical sciences, these nanoparticles are also used to reduce the toxicity and side effects of the drugs.
Mechanical Applications
Bimetallic nanocomposites offer different mechanical properties compared to monometallic nanoparticles. They provide an effectual method for surface modification that enhances the quality of nanofabrication and nanomanufacturing.
Bimetallic nanocomposites that are prepared under the influence of external force offer anti-corrosion properties and induce other new properties.
The mechanical properties of these nanoparticles depend upon the chemical composition, size of particles, hardness, the arrangement of atoms, interfacial adhesion, friction, and elastic modulus.
Electronics
Bimetallic nanoparticles are used in the production of electrical devices. This is because of the small size of nanoparticles that provides a larger surface area, which, in turn, offers high conductivity.
The high surface area helps in the construction of super-capacitors. The main advantages of utilizing bimetallic nanoparticles in electronics include reduced weight and thickness, reduction in the size of transistors used in integrated circuits, increased density of memory chips, improved display screens, reduced power consumption, low cost, and easy availability.
Dechlorination
Bimetallic nanoparticles containing nickel and iron help in the dechlorination of monochlorobenzene.
Electrochemical sensing
Platinum/Iridium-Carbon (Pt/Ir-C) nanocomposites are utilized for the electrochemical sensing of hydrogen peroxide.
Cosmetics
Bimetallic nanoparticles are used in many sunscreens.
Environmental remediations
Bimetallic nanoparticles are used as catalysts in environmental remediations.
References and Further Readings
Loza, L. et al. (2020) Synthesis, Structure, Properties, and Applications of Bimetallic Nanoparticles of Noble Metals. Advanced Functional Material. 30, 1909260 https://doi.org/10.1002/adfm.201909260
Sharma, G. et al. (2019). Novel development of nanoparticles to bimetallic nanoparticles and their composites: A review. Journal of King Saud University - Science, 31,2, 257-269, https://doi.org/10.1016/j.jksus.2017.06.012.
Nasrabadi, H. T. et al. (2016). Bimetallic nanoparticles: Preparation, properties, and biomedical applications, Artificial Cells, Nanomedicine, and Biotechnology. 44:1, 376-380, DOI: 10.3109/21691401.2014.953632
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