D. Blach, F. Martinez
Universidad Industrial de Santander,
Keywords: gold nanoparticles, novel reaction media, reverse micelles, ionic liquids
Summary:Nanoparticles (NPs) have been extensively investigated for many application due to their unique properties, particularly gold nanoparticles (AuNPs) stand out because their properties triggered by small changes in their size and morphology. Nowadays, the great challenge is find a way to easy control these properties. In this sense, ionic liquids (ILs) have been shown to be efficient for synthesis and stabilization of nanoparticles, besides they can induce anisotropy and different morphologies on NPs depending on their composition,  although these properties, ILs are still expensive for industrial applications, hence as an alternative we propose a new reaction media entrapping ILs in reverse micelles (RMs). RMs are thermodynamically stable mixtures of polar solvent, surfactant and oil, inside this organized system is possible to entrap different polar solvent including ILs, in addition, polar solvents inside RMs present special properties that might influence the metal NPs size, morphology and stability. Particularly RMs can be used as nanoreactors for synthesis of materials that cannot (or not easily) be made via conventional approaches, entrapped ILs inside these systems allows to decreases the amount of ILs needed to carry out one reaction, and also enhanced the IL properties because of the confinement. As we found, this new system represents a novel reaction media for NPs size and morphology control. Herein, we evaluated by spectroscopic and microscopy technics the effect of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4])/benzyl-n-hexadecyldimethylammonium chloride (BHDC)/Toluene RMs as nanoreactor for AuNPs synthesis in comparison to neat IL and aqueous RMs media. For AuNPs synthesis a typical RMs methodology was used, where A and B RMs interact and the reduction process take place because of the exchange process. We used tetrachloroauric acid (HAuCl4) as precursor and hydrazine (N2H4) and sodium borohydride (NaBH4) as reducing agents. The results suggest a strong interaction between [bmim][BF4] and BHDC interface, [2, 3] we propose this interaction modifies the interface fluidity enhancing the interaction between BHDC RMs droplets, contrary to observed in the analogous aqueous RMs system. Using these RMs as nanoreactors for AuNPs synthesis confirms the importance of reducing agent on NPs morphology, also indicates the fluidity of [bmim][BF4]/BHDC/toluene interface encourage by IL, enhance the material exchange between droplets induced the formation of larger AuNPs in comparison to those formed in aqueous RMs. To the best of our knowledge, this is the first time where [bmim][BF4]/BHDC/toluene RMs is used as nanoreactors for AuNPs synthesis controlling size and morphology. The results show the versatility of this system, where their unique properties can be easily created simply changing the RMs components.  C. Janiak, in: Zeitschrift für Naturforschung B, 2013, pp. 1059.  D. Blach, J.J. Silber, N.M. Correa, R.D. Falcone, Physical Chemistry Chemical Physics, 15 (2013) 16746-16757.  R.D. Falcone, B. Baruah, E. Gaidamauskas, C.D. Rithner, N.M. Correa, J.J. Silber, D.C. Crans, N.E. Levinger, Chemistry – A European Journal, 17 (2011) 6837-6846.  J.A. Gutierrez, M. Alejandra Luna, N. Mariano Correa, J.J. Silber, R. Dario Falcone, New Journal of Chemistry, 39 (2015) 8887-8895.