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Application of Experimental Design for Synthesis and Controlling Aspect Ratio of Metallic Nanorods

Robatjazi, Hossein | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 42742 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Jalali-Heravi, Mehdi; ormozi Nezhad, Mohammad Reza
  7. Abstract:
  8. Aspect ratio dependant optical properties of silver and gold nanorods is responsible for great attention toward controlling the aspect ratio of this class of the nanostructure for their application in variety of area, such as medical diagnosis, drug delivery, biosensing and treatment. In this research, gold and silver nanorods have been synthesized using chemical reducation and growth based on seed mediated method, which is the newest and one of the best methods with less difficulty for producing silver and gold nanorods. Absorption of the visible light by gold and silver nanorods results in appearing the longitudinal and transverse Plasmon bands in their absorption spectra which is related to the absorption of the incident light along the longitudinal and transverse axis, respectively. Increasing the aspect ratio of the nanorods would reduce the frequency of absorption along the longitudinal axis, and as a result, the longitudinal Plasmon band will shift towards the red region of visible spectra. Therefore, the place of the longitudinal Plasmon peak can be an appropriate criterion to determine the aspect ratio of the nanorods. The first part of this research focuses on the optimization of the silver nanorads’ aspect ratio using face centered central composite design based on response surface methodology (RSM). Silver ions were, first, reduced with sodium borohydride in the presence of sodium citrate dehydrate, as stabilizer. Then, the prepared seeds were added to a solution containing more metal salt,a weak reducing agent (ascorbic acid) and a rod like micellar template (cetyltrimethylammonium bromide, CTAB). Three factors of ratio of metal seed to metal salt, amount of ascorbic acid and the concentration of CTAB were selected as main factors affecting the aspect ratio and their values were optimized using RSM. Mathematical models were proposed for the prediction of transverse and longitudinal Plasmon band wavelength and the optimized condition was obtained for the synthesis of the silver nanorods with highest aspect ratio. It is found that the ratio of metal seeds to metal salt is the most important factor controlling the aspect ratio of the silver nanorads. The optimum values for the factors were found to be 0.06 mL of seed, 7.2 × 10-3 M of ascorbic acid and 0.05 M of the CTAB in the final solution. The optimum predicted value for the longitudinal plasmon band is 653.9 nm, which is in agreement with the experimental value of 655.0 nm.In the second part of the research, short gold nanorods with average aspect ratio ranging from 1(spherical particle) to 5.1 and corresponding tunable surface Plasmon absorption maxima between 514 and 880 nm were synthesized, in high yield and with minimum amount of by product, such as cube or spherical shaped nanoparticles. Based on the systematically variation of the synthetic parameters involved in rods formation, including molar ratio of reducing agent to metal salt, concentration of silver ion, CTAB and CTAB-capped seed in the growth solution; and subsequently by using central composite design (CCD) based on the response surface methodology (RSM), the relation between independent variables and how they impact the aspect ratio of developing NRs was explored, in order to find the appropriate conditions to prepare high yield short gold nanorods with desire aspect ratio, especially for Surface-Enhanced Raman Scattering (SERS) applications. The resulting Au nanorods were characterized using UV-visible spectrometry, transmission electron microscopy (TEM), and measuring the zeta potential
  9. Keywords:
  10. Aspect Ratio ; Experimental Design ; Response Surface Methodology ; Silver Nanorods ; Gold Nanorods ; Plasmon Peak

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