One Pot Synthesis of Crystalline Silver Nanoparticles

Veiw figure View Figure

2.3. Characterization

The UV-Vis spectra were recorded on a Varian Cary 100 dual beam spectrophotometer. Transmission Electron Microscopy (TEM) images were taken on Philips Morgagni 268, 200 KV electron microscopes by using carbon coated copper grids as substrates. For TEM analysis a drop of silver particles dispersed in water was put onto a carbon coated copper grid and dried naturally. The X-ray diffraction measurements were carried out by Rigaku RU 200 B X-ray Diffractometer using Ni filtered CuKα radiation. FTIR spectra were recorded at room temperature on Perkin Elmer FTIR Spectrophotometer Spectrum 2000 in the scan range of 400-4000 cm^-1.

Figure 1. UV-Visible Absorption spectra of Silver Nanoparticle

Download as

Veiw figure View Figure

3. Results and Discussion

3.1. UV-Visible Spectroscopy

The solid crystalline powder of silver was dispersed in water and UV-Visible spectra were recorded. A peak at wavelength 405 nm was observed in UV-Visible absorption spectra as shown in Figure 1, signifying the surface plasmon resonance () band of silver nanoparticles ^{[17, 18]}.

3.2. FTIR Study

In order to ensure the presence of acetate as an integral part of silver particles, FTIR spectra have been recorded. Figure 2 (a) and Figure 2 (b) represents the IR spectra of crystalline silver nanoparticle and that of sodium acetate respectively. IR spectra of sodium acetate shows 2 peaks at 1560 cm^-1 and 1413 cm^-1 corresponding to the stretching frequency of carbonyl, however in the IR spectra of silver nanoparticle it is clearly observed that there is no peak at the carbonyl frequency region. This confirms that acetate is not present with silver particles. Absence of acetate with silver particle is also been supported by thermal analysis. TGA profile does not show any step corresponding to decomposition of acetate. This indicates, the acetate is not adsorbed to silver particle as happens usually in other capping agents. Again the experiment conducted without addition of acetate led to aggregation of particles to big particles of silver metal, instead of crystalline powders, confirms the role of acetate as stabilizing agent. But FTIR and TGA analysis provides no clue on the presence of acetate with silver particles. It can be inferred, that the acetate is playing as a role of stabilizer, preventing the aggregation of silver particles, only in the chemical bath and gets removed through washing. In chemical bath, addition of reducing agent, hydrazine hydrate into the aqueous solution containing both silver and acetate ions, leads to formation of small silver metallic particles. These particles are surrounded by acetate ions present in solution. Due to ionization of acetate in water, there is an electrostatic repulsion between adjacent acetate ions that keeps silver particles separated and prevents from aggregation, which is happening otherwise in absence of acetate. However the acetate is not bound to silver and ultimately washed away, leaving silver powders only. Unlike other stabilizing agents, here acetate does not remain an integral part of silver nanoparticles. This report provides a simple and convenient route for one pot synthesis of crystalline silver nanoparticles free from stabilizing agent.

Figure 2. (a) FTIR Spectra of Sodium acetate, (b) FTIR Spectra of Crystalline Silver Nanoparticles

Download as

Veiw figure View Figure

3.3. X-Ray Diffraction Studies

Figure 3 shows the X-ray diffraction pattern of synthesized crystalline silver nanoparticles. The diffraction pattern shows four sharp and well defined diffraction lines at 2θ = 38.15°, 44.34°, 64.5° and 77.46°, which can be assigned to the (111), (200), (220) and (311) reflections of the face centered cubic (fcc) structure of metallic silver, respectively. The lattice parameter calculated from XRD pattern is a = b = c = 4.082975 A° in agreement with the literature value a = 4.086 A°. The diffraction pattern is in well agreement with the literature report JCPDS File No. 04-0783. The well defined intense peaks in diffraction pattern confirm excellent crystallinity of silver nanoparticles.

Figure 3. X-ray Diffraction pattern of crystalline silver nanoparticle

Download as

Veiw figure View Figure

3.4. Thermogravimtric Analysis (TGA)

Figure 4 illustrates the TGA profile of silver nanoparticles. TGA profile reveals that, there is no mass loss and confirms the absence of acetate as an integral part of silver nanoparticles.

Figure 4. TGA profile of crystalline silver nanoparticles

Download as

Veiw figure View Figure

3.5. Transmission Electron Microscopy (TEM)

Figure 5 shows the Transmission electron micrograph of silver nanoparticles. The average particle size is found as 100 to 150 nm. As shown from the TEM image the particles are well separated from the neighboring nanoparticles. Also it is clearly visible in TEM image that, the particles are cubic in shape. This is also supported by the observation made from XRD pattern, which suggests the FCC pattern of silver particles.

Figure 5. Trasmission Electron Micrograph of crystalline silver particles. Scale bar corresponds to 200 nm

Download as

Veiw figure View Figure