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Citation: Ajeet Kumar (2015) Silver flower: Synthesis and the mechanism of formation in homogeneous solutions1:100112
Copyrights: Â© 2015 Ajeet K,
Uniform, well-dispersed flower shaped silver particles have been prepared by reducing silver nitrate solutions in acidic medium with sodium ascorbate in the presence of a guar gum as a dispersing agent. The flowerlike silver microstructure is self-assembled by thin and uniform fiber like structure with a thickness of approximately 30nm. X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) are used to characterize the structure and morphology. The possible growth mechanism is carefully proposed based on the reaction process.
Keywords: Silver Flower; ascorbic acid; Guar gum; precipitation; catalysis; self-assembly.
The extensive research in three-dimensional (3D) nanoscale materials have received considerable attention due to their remarkable properties as applied in electronic1,2, solar cells3,4, surface Enhanced Raman scattering (SERS)5, Antennas6, field emission displays7, catalysis8,9, and gas sensors10 and other surface plasmon resonance techniques11,12. In this regard, silver has received much research attention, since it has the highest electrical and thermal conductivities of all metals, and also it has been observe that its performance can be often enhanced many fold in one-dimensional structures13. In order to prepare particles of desired morphology, most precipitation processes are directed in the presence of templates1, 14–17. The formation of uniform anisotropic particles by chemical precipitation in solutions remains a more challenging task.
In this paper, flower like silver particles are prepared by a simple homogeneous chemical solution approach in the presence of guar gum as dispersing agent in aqueous solution. We observed that the process is convenient, inexpensive and environmental friendly.
Materials and characterization techniques
All chemicals were of the highest purity grade. The dispersing agent guar gum was obtained from Frutarom, North Bergen/New Jersey, USA. The resulting metallic particles were characterized by scanning and field emission electron microscopies and their structure was determined by X-ray diffraction.
Preparation of Silver Flower
A volume of 140 ml HNO3 was rapidly added under mechanical stirring to 1000 ml of a 1.1mol dm−3 AgNO3 solution maintained at temperature 60 ± 1 ◦C containing 1 wt% guar gum. Then, a 50 wt% ascorbic acid aqueous solution was added at the rate of 1.5 cm3 min−1 for the first 1 min, After 2 min of discontinued introduction of ascorbic acid the color changed to dark green, and then the rest of the ascorbic acid was added, in 15 min. The resulting dispersions were kept overnight in a thermo stated oven maintained at 60 ◦C. The off white precipitate was filtered with DI water and purified, dried at 60˚C to obtain silver flower shape particles (Figure 1 a-c)
Figure 1: Field Emission electron micrograph of silver flower at different magnification (a) 15KX (b) 20KX (c) 1000X
The Morphology of silver particles was assessed by Field emission scanning electron microscopy (FE-SEM) Figure 1 a-c. The flower shaped silver particles showed X-ray patterns characteristic of silver as illustrated in Figure 2.
Figure 2: X-ray diffraction patterns of flower shaped silver particles
Ascorbic acid is a powerful reducing agent in acidic conditions, having the ability to completely convert silver ions into metallic silver even in concentrated solutions. However, at sufficiently high concentration of nitric acid, the freshly formed silver nanosize particles will re-dissolve, at elevated temperatures. For this reason, the role of protecting agent becomes important otherwise reaction in such concentrated acidic system cannot advance. While many organic molecules could provide such protection, guar gum not only is very effective in preventing dissolution, but they are also extremely powerful dispersants in highly acidic aqueous solutions. The protecting effect of this dispersant was attributed to the strong interaction of guar gum with the surface of silver. Figure 3 shows the schematic growth diagram of the silver flowers formed by the homogeneous solution precipitation process.
Figure3: The Schematic growth diagram of the silver flowers fabricated by the homogeneous solution precipitation process solution process
Silver particles having flower like structure have successfully been synthesized by a simple chemical precipitation approach using guar gum as a dispersing
Agent The simple synthesis method brings new dimension on the controllable assembly of novel 3D silver architectures.
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