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چکیده
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Metal Nanoparticles have been successfully used in photonic, biological imaging, surface-enhanced Raman scattering, and catalysis [1]. Utilization of simple and nontoxic chemicals, environmentally compatible solvents, and renewable materials are some of pivotal issues in the nanotechnology field [2]. The silver (Ag) nanoparticles (NPs) were synthesized by reduction of Ag+ ions in the aqueous soluble starch at 80 ºC and at different pH in the ranges of 5-12. The soluble starch was acted both as reducing and stabilizing agent for the preparation of Ag NPs. The surface Plasmon maximum absorption spectra of Ag NPs (λmax) shift to a higher value with the increase of the pH of solution, as evidenced for increasing in the size of Ag NPs. Thus it is easy to deduce that the lower pH (pH ≤ 7.0) can be more effective the capping function of the soluble starch and the nucleation sites of the starch provide to finally result in smaller silver nanoparticles. The average size of Ag NPs is observed 26.5 nm (SD=3.4 nm) from the TEM image. The catalytic function of starch-capped Ag NPs on the reduction of 4-nitrophenol was investigated. In the absence of catalyst of Ag NPs, the strong reducing agent NaBH4 itself enable to reduce 4-nitrophenol to 4-aminophenol. Whereas, the addition of an aliquot of Ag NPs dispersion to the reaction system caused a fast fading in the color of 4-nitrophenol in aqueous solution, suggested the occurrence of the reduction reaction. The kinetic reaction rate constant is estimated to be 4.32×10-4 s-1.
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