Simple one-step green synthesis of gold nanoparticles with controlled size using imidazolium ionic liquid as ligand

Full text: Synthesis of metallic nanoparticles is an area of ever-growing interest for the scientific community. Gold nanoparticle (AuNP) solutions are very fascinating systems due to their biocompatibility and the possibility to functionalise its surface with various biological molecules. This feature ensures original applications in various fields such as catalysis but also biology [1,2]. We employed a simple method to synthesize AuNP stabilised by different ionic liquids (1-Dodecyl-3-methylimidazolium chloride/bromide) and gold precursors (gold (III) chloride trihydrate and hydrogen bromoaurate (III) hydrate) in water. The study of the interaction between the ionic liquid and the gold solution was performed by both Extended X-ray Absorption Fine Structure (EXAFS) and Ultraviolet-visible (UVvis) spectroscopies ensuring that an ion exchange occurred between the anions of the ionic liquid and the gold solution. A NaBH4 solution was quickly added to the mixture to reduce gold III to stable AuNP. We have used a combination of techniques to study the nucleation and growth processes: UVvis, Small Angle X-ray Scattering (SAXS) and High Resolution Transmission Electron Microscopy (HRTEM). The evolution of the characteristic gold plasmon band as a function of the synthesis conditions was followed by UVvis, while AuNP size and morphology have been characterised by SAXS and HRTEM. It is noticeable that the same concentration of ionic liquid leads to similar size and shape of gold nanoparticles. Spherical AuNP, 2.2-2.4 nm sized according to SAXS results, presenting potential biological and catalysis applications were synthesized. References [1] S.D. Brown, et al, J. Am. Chem. Soc., 132 (2010) 4678–4684. [2] B. Qiao, et al, J. Nano Res., 8 (2015) 2913-2924. (author)