Preparation and analysis of PVP surface protected

M. V. ROLDÁN; H. TROIANI; M. GRANADA; O. DE SANCTIS; N. PELLEGRI

Rosario, Argentina

Congreso; 10th Inter-American Congress on Electron Microscopy; 2009

CIASEM

Noble metal nanoparticles have been intensely investigated due to their amazing propertiessuch as optical, catalytic and electric ones. These characteristics make them suitable for a variety of potential applications for several devices. Metallic silver particles in particular are technologically important because it shows unique properties normally related to noble metals besides other specific ones that can be controlled depending on the particles size, the size distribution and shape.Several methods have been reported for Ag nanoparticles synthesis, including physical andchemical methods in discrete or continuous media.In this work we present a chemical reduction method of AgNO3 in ethanol, continuous media, toprepare silver nanoparticles of several shapes with PVP (polivinilpirrolidone) as surface modifier,due to their affinity to produce prismatic particles [1]. The use of ethanol as solvent and as reducer agent was crucial for this novel technique, avoiding the surface oxidation of the Ag nanoparticles.We studied the influence of different parameters in the preparation method over the sizeand shape of the nanoparticles: surface modifier influence over the process of nanoparticlesformation, reagents concentration AgNO3 and PVP, processing and irradiation time. Finally weshow the morphological and structural characterization of the nanoparticles by UV-visiblespectroscopy, AFM and TEM.Experimental:The nanoparticles were obtained in a two step process: first the nucleation and second the growing process. In the nucleation step, the reactants were mixed in a vessel at constant temperature. To activate the nucleation the samples were exposed to light irradiation or to reflux with no stirring. To follow the evolution of the reaction media, UV-Vis spectra of the colloids were taken. Results and discussion:In the first step, spherical nanoparticles were obtained, confirmed by an absorption band in the UVVis spectrum at 410 nm (Surface Plasmon Resonance of Ag nanoparticles) of the yellow like color solution and the peak grows with the refluxing time (see Figure 1). The AFM topographic images (see Figure 1) shows 7 nm particles diameter.In the second step the evolution of the nucleus was follow throughout the formation of prismatic nanoparticles. In this work we show the effect of light irradiation with time for the second step: nucleation and growing (see figure 2). Three absorption bands in the Uv-Vis spectra at 332 nm (out plane quadrupole), 415 nm (out plane dipole) and 643 nm (in plane dipole) indicate the formation of prismatic nanoparticles (see figure 2). TEM images confirm the presence of prisms; hexagons and small spherical nanoparticles (see Figure 5). Also the growing process was follow studding the effect of the temperature and time during the reflux, with no stirring. Two absorption bands confirm the presence of prisms, at 344 y 64 nm (see figure 6). TEM images confirm the presence of prisms with a size of 43 nm approximately.Finally in this work PVP protected nanoparticles were obtained using a two step strategy.After the nucleation spherical nanoparticles were conformed and from these the prismatic onescould be obtained in the growing step. The activation of the growing by light irradiation wasconfirmed for specific rates of the reactants. The activation by refluxing also was confirmed andprismatic particles were obtained. These two methods are suitable to reduce the time processconsiderably.