Silver nanoparticles: Ultrasonic wave assisted synthesis, optical characterization and surface area studies
Introduction
Nanostructured materials are fascinating the world of science due to their unusual optical, chemical, photoelectrochemical, and electronic properties [1], [2]. The applications of nanoparticles as catalysts are rapidly growing because of their size-dependent electronic structure and extremely large surface area [3]. Ultrafine nanoparticles of silver and gold have been the key to many important applications in catalysis [4], optics [5] and surface enhanced Raman spectroscopy [6]. Silver nanoparticles can also be used as an antimicrobial agent in various bio-medical applications [7]. Numerous processes have been used in the literature for the synthesis of silver nanoparticles such as sol–gel [8], reverse micelle [9] and inert gas condensation [10]. Several reports are also available in the literature on silver nanoparticles using sonochemistry, viz. silver nanoparticles in Y-zeolite substrates [11], nanorods by the reduction of aqueous silver nitrate [12], highly fluorescent silver nanoclusters [13] and polyaniline/Ag nanocomposites using H2O2 [14]. Sonochemically synthesized silver nanoparticles also have number of applications for photocatalytic activity [15], coating on stainless steel plate [16] and surface enhanced Raman spectroscopy (SERS) [17]. Recently we have reported [18] the large scale synthesis (yield of 98.5%) of silver nanoparticles having an average size of ~ 5 nm using the solvothermal method. In this paper, we report the effect of reducing agents on the size and shape of silver nanoparticles using the sonochemical method. The silver nanoparticles have been characterized by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), UV–Visible spectroscopy and BET surface area analysis.
Section snippets
Experimental
Silver nanoparticles were synthesized by reducing AgNO3 (Thomas Baker, India, 99.8%) with strong as well as weak reducing agents in the presence of ultrasonic waves. In a typical synthesis, 50 ml of 0.1 M silver nitrate (AgNO3) was taken in a conical flask assembled within an ultrasonic cleanser (operating at a frequency of 20 kHz and with a power of 2.5 W/cm2). 50 ml of 0.1 M sodium borohydride (Spectrochem. India, 96%) was added dropwise to the aqueous solution of AgNO3 in the presence of
Results and discussion
The X-ray diffraction patterns of the silver nanoparticles synthesized by the sonochemical method using sodium borohydride and sodium citrate as the reducing agents are shown in Fig. 1. All the reflections correspond to pure silver metal with face centered cubic symmetry. The reflections were indexed as (111), (200) and (220) with the corresponding 2θ values of 38.116, 44.277 and 64.426 respectively (JCPDS 07-0783). The intensity of peaks reflected the high degree of crystallinity of the silver
Conclusions
Silver nanoparticles have been successfully synthesized using the sonochemical route with two different reducing agents. The size and morphology of the nanoparticles are dependent on the strength of the reducing agent. The strong reducing agent (NaBH4) produced spherical nanoparticles with an average particle size of 10 nm, however the weak reducing agent (sodium citrate) resulted in smaller silver nanoparticles of narrow size distribution. The citrate stabilized silver nanoparticles have higher
Acknowledgements
TA thanks the Department of Science and Technology (DST), India for financial support (SR/FTP/CS-120/2006). The authors thank Professor Ashok K. Ganguli for the use of HRTEM facility (funded by DST, Nano Mission) at IIT Delhi. IAW, AG and JA thank UGC and CSIR for their research fellowships.
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