The simplest inorganic nanomaterials are metallic with a wide range of metals already produced in nano form. These include aluminium, copper, nickel, cobalt, iron, silver and gold with a wide range of potential applications including land remediation, batteries and explosives. Metal nanoparticles have been prepared for some time, but several have found significant commercial application. These include aluminium, iron, cobalt and silver.

3.3.1 Aluminium. Aluminium nanoparticles have been used for their pyro-phoric characteristics in explosives.32 Aluminium is a highly reactive metal when produced as a nanopowder and when in formulations such as metastable intermolecular composites (MIC) reacts to produce a large amount of heat energy. Aluminium powder is air stable due to a thin oxide shell that forms during production and protects the inner core from further oxidation.

3.3.2 Iron. Nanoscale iron particles have large surface areas and high surface reactivity and research has shown32,33 that these particles are very effective for the transformation and detoxification of a wide variety of contaminants, such as chlorinated solvents, organochloric pesticides and polychlorinated bi-phenyls. Thus they have been used for remediation of soil and groundwater, which contains such contaminants.

3.3.3 Cobalt. Cobalt nanoparticles exhibit magnetic behaviour,34 37 which may find application in medical imaging.38

3.3.4 Silver. Silver nanoparticles, which demonstrate antimicrobial and antibacterial activity,39,40 have been used in a number of applications including medical dressings and non-smelling socks!41

3.3.5 General. Special shaped metal nanometals hold promise for the miniaturisation of electronics, optics and sensors42 where, for example, studies have shown that the conductance of copper nanowires is determined by the absorption of organic molecules.43 Electrochemical deposition of palladium nano-structured films has led to potential application as calorimetric gas sensors for combustible gases.44 In the biological sciences, many applications for metal nanoparticles are being explored, including biosensors,39 labels for cells and biomolecules45 and cancer therapeutics.46

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