The chemical and physical properties of metal nanoparticles are strongly dependent on their size and morphology. This aspect is particularly relevant in the field of catalysis, plasmonics, bio-imaging and a number of healthcare applications. While the use of stabilising ligands such as PVP, PVA, citrates, etc. have enabled an exquisite control of particle size, size tuneability, specially &lt; 5nm is still highly challenging, setting back progress in the field. Herein, we present a novel strategy for the synthesis of ultra-small (1-2 nm) gold nanoparticles by replacing the conventional use of external reducing agents by deep eutectic solvents (DES), a new generation of non-toxic, eco-friendly and biodegradable designer solvents. Within the framework of green chemistry, deep eutectic solvents (DESs) are solvent systems discovered by Abbott et al in 2001. These DESs offer many interesting chemical properties such as templating action, supramolecular catalyst etc. We demonstrate that reline, a eutectic mixture of urea and choline chloride, can actively form gold nanoparticles by reducing a salt precursor and simultaneously stabilize the nuclei, delaying their growth, leading to highly monodispersed small gold particles without the addition of any external capping ligands, surfactants or stabilizers. These results also demonstrate the stability of Au(I) in reline. Au(I) species are quite unstable in aqueous systems as these rapidly disproportionate to Au(III) and Au(0). Au(I) species are highly catalytic towards homogeneous reactions for e.g. hydration of alkynes. The stabilisation of such species in the reline system will open up new avenues in the use of Au(I) in colloidal catalysis.

Elucidating the role of deep eutectic solvents (reline) towards the synthesis of gold nanoparticles

2019 Fall National Meeting

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