Gold Nanoparticles Formal Lab

Gold Nanoparticles Formal Lab - Analysis of Colloid...

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Analysis of Colloid Characteristics: Observations on Gold Nanoparticles Michael J. Parrott ABSTRACT: We use visible absorption spectroscopy to measure the changes in the colloid by measuring the absorbed wavelengths (the change in color of the colloid) as gold nanoparticles precipitate out of solution. First, we mix hydrogen tetrachloroaurate (III) trihydrate and sodium citrate to form the gold nanoparticles. We will analyze the affects of the addition of NaCl, HCl, NaOH, and glucose to the nanoparticles. Visual observations and UV-Vis spectrum analysis via a HP spectrophotometer revealed that addition of electrolytes to the nanoparticles alters their characteristics such that their peak absorbance is shifted to different wavelengths. Acids and bases work on an additional level in that they are electrolytic and also alter the pH of the solution. Changes in wavelength absorption describe alterations of the charges surrounding the gold atoms. These changes are not true in the physical world however, as having many gold coins would not make the coins appear a color. INTRODUCTION: The National Nanotechnology Initiative defines nanotechnology as “the understanding and control of matter at dimensions of roughly 1 to 100 nanometers, where unique phenomena enable novel applications” [1]. Norio Taniguchi coined the term “nanotechnology” in a paper saying “'Nano-technology' mainly consists of the processing of, separation, consolidation, and deformation of materials by one atom or one molecule” [2]. A nanometer is defined as one billionth of a meter [3]. Nanoparticles can be synthesized by chemical reactions. In particular photosynthesis can be used, to make SilverN for example [4]. Nanoparticles can take the shape of 1
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prisms (see Figure 1 ) or spheres (see Figure 2 ) [4]. Particles can be anywhere from 40 to 100 nm in diameter (with exceptions of course) [4]. Every physical and chemical property (including color) is dependent on size [3]. In this lab we will see that aggregation of nanoparticles can cause similar affects in varying colors. For gold colloids, the absorbtion wavelength is directly related to preparation (the size and shape of the particles). Larger asymetric particles absorb longer wavelengths than smaller, spherical particles. Each wavelength absorbed has a complementary wavelength located across the color wheel (you see the complementary wavelength). Nanoparticles
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Gold Nanoparticles Formal Lab - Analysis of Colloid...

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