TEM and HRTEM Characterization of Water–Soluble Au Nanoparticles and Their Modification with Ag.

CORTHEY, G.; FONTICELLI, M. H.; SALVAREZZA, R. C.; ZELAYA, E.

Rosario

Congreso; 10 Inter-American Congress of Electron Microscopy 2009 (CIASEM 2009).; 2009

Bimetallic nanoparticles have been extensively studied because the small size, the great surface to volume ratio and the intrinsic properties of bimetallic surfaces enhance the chemical reactivity minimizing the material cost. In fact, bimetallic Ag/Au NPs have been used to transform toxic carbon monoxide (CO) to less toxic carbon dioxide (CO2).A new method for the synthesis of these systems was recently published. This method is based on two well established electrochemical concepts: the underpotential deposition (UPD) phenomena and the ability of a redox couple to control the interfacial potential. Although the proposed strategy is based on thermodynamic aspects already proved, it has been applied to NPs which can not be dispersed in water. In order to prepare large volumes of water-dispersible bimetallic NPs, a hydrophilic capping agent is required.Here we show the results obtained using AuNPs protected with mercaptosuccinic acid (MSA) synthesized by a modified Brust method. Despite the AuNPs were characterized by different methods, the structural and microstructural characterization is of singular interest. Moreover, due to the low dimensionality of the nanoparticles, TEM offers a highly efficient technique to reveal the morphological, structural and microstructural characteristics.In Fig. 1 a. and Fig. 2 it can be observed a circular morphology of the nanoparticles. In Fig. 1 b. a ring diffraction pattern which can be indexed with a FCC Au structure is shown. The size distribution histogram of nanoparticles was achieved counting a total of 4500 units using iTEM software. A Lorentzian distribution with a maximum in 2.78 (0.02) nm was obtained.In Fig. 3 a HRTEM micrograph of an AuNP is shown. This micrograph and the ring diffraction pattern (Fig. 1 b.) show the crystalline character of the NPs.The AuNPs were modified with Ag using the mentioned method of synthesis and then characterized by different techniques (TEM, XPS, UV/Vis).