Gold nanoparticles (Au-NPs) were reproducibly obtained by thermal, photolytic, or microwave-assisted decomposition/reduction under argon from Au(CO)Cl or KAuCl4 in the presence of n-butylimidazol dispersed in the ionic liquids (ILs) BMIm+BF4-, BMIm+OTf-, or BtMA+NTf2- (BMIm+=n-butylmethylimidazolium, BtMA+=n-butyltrimethylammonium, OTf-=-O3SCF3, NTf2-=-N(O2SCF3)2).

The ultra small and uniform nanoparticles of about 1–2 nm diameter were produced in BMIm+BF4- and increased in size with the molecular volume of the ionic liquid anion used in BMIm+OTf- and BtMA+NTf2-. Under argon the Au-NP/IL dispersion is stable without any additional stabilizers or capping molecules. From the ionic liquids, the gold nanoparticles can be functionalized with organic thiol ligands, transferred, and stabilized in different polar and nonpolar organic solvents.

Au-NPs can also be brought onto and stabilized by interaction with a polytetrafluoroethylene (PTFE, Teflon) surface. Density functional theory (DFT) calculations favor interactions between IL anions instead of IL cations. This suggests a Au···F interaction and anionic Aun stabilization in fluorine-containing ILs. The 19F NMR signal in BMIm+BF4- shows a small Au-NP concentration-dependent shift. Characterization of the dispersed and deposited gold nanoparticles was done by transmission electron microscopy (TEM/HRTEM), transmission electron diffraction (TED), dynamic light scattering (DLS), UV/Vis absorbance spectroscopy, scanning electron microscopy (SEM), electron spin resonance (ESR), and electron probe micro analyses (EPM, SEM/EDX).

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