Electrochemical processing of discrete nanoparticle ions

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High quality, purified nanoparticles are required for both fundamental scientific studies and technological applications in a variety of (hierarchical) functional materials. Carbon nanotubes are an archetypical nanoparticle with enormous promise if the remaining processing hurdles can be overcome. One recent route addresses this challenge by using chemical charging in metal-ammonia solutions to form "nanotubide" anions. Charging uniquely provides an approach to true thermodynamic equilibrium solutions of single walled nanotubes, and has proved to offer a means both to remove amorphous carbon and to separate metallic from semiconducting fractions; this technology has already been licensed commercially and is the subject of a new venture. However, having developed this methodology, we realised that the challenging alkali metal-ammonia solution can be avoided by using pure electrochemical charging. This approach represents an entirely new strategy for nanoparticle processing, through electrochemical dissolution and subsequent electrodeposition of discrete nanoparticle ions. We believe that the approach will be general and may be applicable to a variety of electrochemically stable, conductive nanoparticles, likely including noble metal systems, graphene, and some transition metal chalcogenides; it offers unrivalled control of charge density and chemical potential. The results raise fundamental scientific questions about the possibility of discrete nanoparticle electrochemistry and potential analogies to traditional atomic/ionic systems. They also suggest opportunities for new large scale manufacturing processes involving nanoparticles, particularly purification (fractionation), functional coatings or co-deposition of composites/hybrids. It is worth noting that many large scale industrial processes rely on electrochemical approaches, including the purification of copper, and electrowinning of aluminium. The nanoparticle ions themselves offer opportunities for further chemical reactions or assembly. As an example, nanotubide anions are reactive to electrophiles, offering a means to generate functionalised individual species in high yield. The ability to manipulate charge density and potential accurately, coupled with an understanding of the complex density of states of these materials, will allow this new chemistry to be understood, controlled and exploited.In short, this project will explore a new direction: the scientific challenges and technological opportunities enabled by the formation of well-defined discrete ions through electrochemical processing.