Effect of the Exposure to Air in the morphology of water soluble Silver Nanoparticles Coated with MUA

LISANDRO J. GIOVANETTI; J. M. RAMALLO-LOPEZ; CRISTINA E. HOPPE; F.G. REQUEJO

Campinas

Congreso; LNLS 26th Annual Users? Meeting (RAU); 2016

CNPEM

Metallic nanoparticles exhibit size and shape-dependent properties that are of interest for applications ranging from catalysts and sensing to optics, antibacterial activity and data storage [1-3]. For instance, the antibacterial activity of different metal nanoparticles such as silver colloids is closely related to their size; that is, the smaller the silver nuclei, the higher itsantibacterial activity. Moreover, the catalytic activity of these nanoparticles is also dependent on their size as well as their structure, shape, size distribution, and chemical?physical environment. Thus, control over thesize and size distribution is an important task. Generally, specific control of shape, size, and size distribution is often achieved by varying the synthesis methods, reducing agents and stabilizers. One important point for the use of metallic nanoparticles in technological applications is the possibility to stabilize them in nontoxic solvent (water, DMSO, etc) by surface modification using different types of capping agents. A large variety of experimental techniques has been developed in recent years to synthesize metal NPs coatedwith different stabilizing thiols. Recently Hoppe et. al. reported a new route of synthesis that gives as result Ag nanoparticles (AgNPs) of a well-controlled size and soluble in water in one step[4]. In this work the local atomic structure and chemical nature of this newly synthesized AgNPs functionalized with MUA have been probed combining TEM, UVvis, X-ray absorption fine structure spectroscopy (XAFS) and Small Angle X-ray scattering. Complementary information about chemical and electronic structure was obtained combining XAFS data obtained at the SXS beamline at the Ag-L3 and S-K edges. Ag-K edge EXAFS data obtained at the XDS beamline was also measured in order to obtain the average Ag atoms local structure. In order to study the effect of the exposition to air all samples were measured dry and in its original solvent (water), in order to avoidmodifications of the surface morphology and chemistry produced by the exposure to atmosphere. In this contribution we discuss the role of the exposure to air in the physicochemical sate of the MUA molecules attached to the NP surface. The combination of all of these techniques shows that Ag atoms in the AgNP are in metallic form and also are bonded to S atoms from the capping. A discussion about the type of Sulfur species in the AgNP is also presented.