Nanotech 2010

Green Chemistry Used in the Synthesis and Characterization of Silver and Gold Nanoparticles

R. Vallejo, P. Segovia, N. Elizondo, O. Vázquez, V. Coello, V. Castaño
Universidad Autonoma de Nuevo Leon, MX

Keywords: green synthesis, nanoparticles, gold, silver


Gold (Au) and silver (Ag) nanoparticles have a diversity of interesting properties between which they emphasize the electrical ones, optical, catalytic and the applications in biomedicine like antibacterial and antiviral, same that depend on their morphology and size. The nanoparticles were synthesized using polyol and green methods. We made a comparison of these methods in order to investigate the influence of reaction parameters on the resulting particle size and its distribution. In the first method we use polyol process with poly (vinylpyrrolidone) (PVP) acting as a stabilizer and ethylenglycol as a reductor [1, 2]. Such procedure yield different morphologies of metal nanoparticles (including gold and silver) [3-5]. The green method is an ecological synthesis technique. There, we made use of chemical compounds of plants like rosa berberifolia and geranium manculatum in order to obtain ascorbic acid as redactor agent. Ascorbic acid (C6H8O6) is an abundant component of plants which reaches a concentration of over 20 milimols in chloroplasts and occurs in all cell compartments including the cell wall. Additionally the acid has functions in photosynthesis as an enzyme cofactor (including synthesis of ethylene, gibberellins and anthocyanins) and in the control of cell growth [6]. We use for the synthesizes other kinds of plants also with compounds that have surfactant properties like saponins. Here, we show that green method reduces the temperature requirement which is in contrast to the obtained with the polyol method. The use of these natural components allows synthesize metallic nanoparticles. In this study, gold and silver nanoparticles were prepared by the reduction of HAuCl4 and AgNO3 respectively using ascorbic acid as reducing agent obtained from geranium manculatum leaves and rosa berberifolia petals. The reaction time for the polyol method was around 3 hours and the nanoparticles were synthesized at 190oC. In this green method the reaction time is reduced from 3 hours to 30 minutes until 1 hour at 60oC. The synthesis of colloidal metallic nanoparticles was carried out taking into account the optimization of the conditions of nucleation and growth. For this reason the variation of parameters like the concentration of the metallic precursors, reductor agent, amount of stabilizer, temperature and time of synthesis was realized. The effects of the size and composition on the optical, electronic and structural properties are investigated using different techniques from characterization: UV-Visible spectroscopy, TEM, SEM, DRX, EDX, and others optical characterizations. In accordance with the studies of UV visible spectroscopy, the results shown an absorption energy in 547 nm and 415 nm for Au and Ag synthesized nanoparticles respectively. The TEM characterization reveal the formation of nanoparticles of these metals, independent of the employed method, with a size distribution between 20 and 120 nm for gold and between 10 and 27 nm for the silver. References [1]. G. Cao, Nanostructures and Nanomaterials, synthesis, properties and applications, Imperial College Press (2004). [2]. Y. Xia, P. Yang, Y. Sun, Y. Wu, B. Mayers, B. Gates, Y. Yin, F. Kim, H.Yan, Adv. Mater., 15, 353 (2003). [3]. C. Burda, X. Chen, R. Narayanan and M. A. El-Sayed, Chem. Rev., 2005, 105, 1025. [4]. Y. Xia and N. J. Halas, Mater. Res. Soc. Bull., 2005, 30, 338. [5]. N. L. Rosi and C. A. Mirkin, Chem. Rev., 2005, 105, 1547. [6]. Nicholas Smirnoff, Glen L. Wheeler, Critical Reviews in Biochemistry and Molecular Biology, 2000, Vol 35, No. 4, Pages 291-314.
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