Aluminum (Al) nanoparticles have unique optical, physical, and chemical properties that make them candidates for use in a variety of applications, ranging from nanophotonics and catalysis, to the preparation of high energy composites. Through precise control of the synthetic process, nanoComposix has the ability to fabricate a variety of shapes and sizes and to optimize plasmonic properties for your application. Below are just some examples of the diversity of aluminum nanoparticle configurations achievable at nanoComposix—including nanospheres, silica-shelled nanocubes, and faceted nanoparticles.
Aluminum Plasmonics: Tunable from the UV to the NIR
Aluminum nanoparticles absorb and scatter light with extraordinary efficiency due to a strong interaction of light with conduction electrons on the metal surface of the nanoparticle. When excited by light of a specific wavelength, these conduction electrons undergo a collective oscillation known as surface plasmon resonance (SPR) and this oscillation causes the absorption and scattering intensities of aluminum nanoparticles to be much higher than identically sized non-plasmonic nanoparticles.
Gold and silver are common examples of plasmonic nanoparticles used in nano-enabled technologies because the optical properties of these materials can be tuned throughout the visible and near-infrared (NIR) portions of the spectrum, providing a useful response for diagnostics, therapeutics, display technologies, and more. Aluminum-based nanomaterials offer additional capabilities, with an optical response that extends into the ultraviolet (UV) region. This extension of the SPR peak into the UV region is appreciable when compared against silver and gold, as shown in the graph below.
Depending on the size and shape of the aluminum nanoparticles, their extinction can also be tuned to provide broad absorbance from the UV, across the visible, and into the near-infrared as shown by the spectra of various sizes of aluminum nanoparticles below.
Surface Oxide Passivation and Particle Reactivity
Aluminum nanoparticles naturally form a self-limiting oxide shell that provides long-term stability and enables a host of surface modifications for specific applications. Although the surface oxide of aluminum nanoparticles is chemically distinct from bulk alumina, its chemistry is characteristic of metal oxides, enabling rational ligand design for optimal dispersibility and functionality. The surface oxide also serves as a dielectric spacer, which is ideal for nanophotonic applications.
Chemically synthesized aluminum nanoparticles provide the highest purity aluminum with nanoscale dimensions. The active aluminum content ranges from 75 to 95%, depending on the aluminum nanoparticle size. The native surface oxide of the aluminum nanoparticles accounts for the remainder of the sample weight. The thin oxide layer provides long-term stability in ambient conditions, though water can penetrate the shell and oxidize the aluminum nanoparticles into extremely high-surface area aluminum oxide hydride nanoparticles. Enhanced aqueous stability is accomplished by passivation of the aluminum nanoparticles with organic polymers, metal-organic-frameworks, or other metal oxide shells. Unpassivated aluminum nanoparticles will exothermically oxidize when heated above the melting point of aluminum (600 °C), which is suitable for use in high-energy density composites.
Applications of Aluminum Nanoparticles
Aluminum nanoparticles are novel plasmonic materials with optical properties that extend into the UV, making them distinct from gold and silver nanoparticles that have plasmonic properties in the visible and NIR. Control of the shape and crystal structure of aluminum nanoparticles thereby enables fundamental investigations in UV plasmonics and nanophotonics. Directing the shape of aluminum nanoparticles toward cube and concave-cube morphologies enables light energy to be concentrated onto the sharp corners and tips of the particles, creating strong localized field enhancements that are useful for sensing and photocatalysis. The surface oxide imparts unique functionality in sensing applications and is a built-in dielectric spacer for studying and utilizing plasmon-enhanced phenomena.
The surface of aluminum nanoparticles can be decorated with small transition metal nanoparticle islands to produce “antenna-reactor” bimetallic nanoparticle photocatalysts. When illuminated, the plasmonic aluminum core forces the excitation of plasmons in the transition metal islands increasing their ability to harness light to drive chemical transformations. Modular synthesis of transition metal decorated aluminum nanoparticles enables the rational fabrication of nanoparticle photocatalysts specific to industrially relevant chemical reactions.
High-Energy Density Composites
Low-purity aluminum nanoparticles made by physical methods have been intensively investigated for their use in explosives, fuels, and other high-energy density composites. Chemically fabricated aluminum nanoparticles are high-purity alternatives with superior physical and optical properties that are easily tuned based on control of the aluminum nanoparticle synthesis. For example, small aluminum nanoparticles are strong UV absorbers while larger particles are strong optical scatterers. Further tuning of the morphology can produce large aluminum nanowires, which gives rise to material that can strongly absorb both UV and near-infrared light due to their thin diameters and high aspect ratios. Precise control of aluminum nanoparticle size, shape and related optical responses enables the investigation of size- and shape-dependent combustion kinetics to maximize the energy released by aluminum nanoparticle oxidation.
Custom synthesis of Aluminum Nanoparticles at nanoComposix
While many other manufacturers use “top-down” synthesis methods to break down bulk aluminum into nanoparticles, nanoComposix uses colloidal synthesis methods to fabricate aluminum nanoparticles, yielding high purity particles with precise control of morphology and size. Contact us today to inquire about aluminum nanoparticles for your development needs.
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