Novel zwitterionic Natural Deep Eutectic Solvents as environmentally friendly media for spontaneous self-assembly of gold nanoparticles

The potential application of some novel zwitterionic Natural Deep Eutectic Solvents, NADESs, based on betaine N, N,N-trimethylglycine and carboxylic acids (glycolic, phenylacetic and oxalic acid), has been evaluated in the synthesis of gold nanoparticles (AuNPs). AuNPs have been successfully obtained by reduction of gold(III) chloride trihydrate by ascorbic acid or sodium borohydride as reducing agents, without the use of any surfactant or capping agent. The effect of the different experimental conditions (nature of the reducing agent, temperature) has been discussed. In the NADES composed of trimethylglycine and oxalic acid, no addition of a reductant was needed because AuNPs start to form immediately after the dissolution of the precursor salt. This result may open new perspectives in fine-tuning smart solvent characteristics and developing the most appropriate NADES for an environmentally friendly metal nanopartide synthesis without using auxiliary chemicals. (C) 2018 Published by Elsevier B.V.