Two-approach study for preparing stable colloidal gold nanoparticles in organic solvents by using 1-dodecyl-3-methylimidazolium bromide as an efficient capping and phase transfer agent

• Phase transfer of IL-capped AuNPs from aqueous phase into chloroform phase.
• Obtaining narrower size distribution of AuNPs upon phase transfer.
• Preparation of AuNPs in chloroform after transfer of AuCl4−into chloroform phase.
• Entrapment of AuNPs at water/chloroform interface as 2-D film.

Efficient preparation of stable gold nanoparticles in an organic solvent has been studied. To do this, two approaches have been performed. In the first approach, AuCl4− and sodium borohydride were used, respectively, as precursor and reducing agent in the presence of ionic liquid 1-dodecyl-3-methylimidazolium bromide ([C12mim]Br) as the capping agent in the aqueous phase. Extraction into different organic solvents showed that the phase transfer efficiency of the gold nanoparticles into chloroform was higher than dichloromethane, toluene and n-heptane. The nanoparticles were stable in chloroform for more than three months. The effect of different experimental conditions on phase transfer efficiency of the nanoparticles has been checked by UV–vis spectroscopy, dynamic light scattering and transmission electron microscopy. In the second approach, the complex of [C12mim]Br with AuCl4−, after formation in aqueous phase (upper phase), was extracted into chloroform. Sodium borohydride solution was injected into the aqueous phase followed by vigorous stirring. The result was production of dispersed gold nanoparticles in the chloroform phase through reduction of the extracted complex by sodium borohydride. Both approaches were compared with each other in terms of reproducibility, procedure time, nanoparticles size and effect of ionic liquid. A solution of gold nanoparticles in chloroform (prepared by the second approach) was brought into contact with either cysteine or homocysteine aqueous solution in order to form a thin film of the gold nanoparticles at the water/chloroform interface.

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