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May 28 2015: Au Nanoparticle Synthesis Part 2
A 1%(w/v) stock solution of sodium citrate was prepared for this experiment. 1.053 g of sodium citrate was weighed in a plastic weigh boat on a scale and transferred into a 50 mL beaker. The weigh boat was rinsed with water and emptied into the 50 mL beaker to ensure maximum sodium citrate transfer. Water was added to the 50 mL beaker and was stirred to dilute the solvent. The solution was then transferred into a 100 mL volumetric flask. The remaining space in the flask was filled with water and stirred. This solution was emptied from the volumetric flask into a sealed container and labeled.
This .001 mM stock solution was modified to use HAuCl4 in place of HAuClr*3H2O (see calculations 1). 0.17 g of HAuCl4 was weighed in a plastic weigh boat on a scale and transferred into a 50 mL beaker. The weigh boat was rinsed with water and emptied into the 50 mL beaked to ensure maximum transfer. Water was added to the 50 mL beaker and was stirred to dilute the solvent. The solution was then transferred into a 500 mL volumetric flask. The remaining space in the flask was filled with water and stirred. This solution was emptied from the volumetric flask into a sealed container and labeled.
1) A hot plate was obtained and placed under the fume hood, with heat set to level 4 and stirring set to level 2.
2) A 50 mL beaker and stirring rod were obtained. After placing stirring rod in beaker, 22 mL of water was measured using a graduated cylinder and transferred into the beaker. The water line was then marked, and the water was disposed. Using a graduated cylinder, 20 mL of the stock gold solution was measured and transferred into the beaker containing the stirring rod. This beaker was then placed on the hot plate in the fume hood and a timer was set.
3) When the solution in the beaker began to boil, the time since placement was recorded. Using a P1000 micro-pipette, 4 mL of the stock sodium citrate solution was added into the beaker. The time of color change from light yellow to purple was then recorded.
4) Water was added to the solution using a transfer pipette to keep water line at marked level.
5) Solution was left to change into a dark red color, which it was then removed and the time recorded.
The first table shows raw data calculations, with an average size of 12.95 nm and a standard deviation of 12.488 nm. The second table shows baselined data calculations, with an average size of 30.75 nm and a standard deviation of 15.655 nm. The third table shows the times at which the sodium citrate was added to the gold solution, the time of color change from light yellow to dark purple, and the time removed from the hot plate when the color appeared dark red. The average time for color change was approx 55 seconds after the addition of sodium citrate, and the average time of removal was after 12 minutes and 29 seconds.
The purpose of this experiment was to synthesize gold nanoparticles using sodium citrate as a reducing agent. Citrate anions are absorbed to the surface of the gold nanoparticles, which creates an electrostatic repulsion. This prevents the nanoparticles from aggregating. Our procedure was modified from a lab performed at the Department of Chemistry of Northwestern University. Instead of using 38.8 mM sodium citrate, we substituted our 1%w/v stock solution, and used 4 mL instead of 2 mL. We did not perform trials with NaCl or sucrose, as was done in the original. It is important to note the differences between the results of the raw data in comparison to those of the baselined data. It is interesting that the average size and standard deviation from the raw and baselined data were strikingly similar. The average concentration from the raw data greatly differed from that of the baselined data, however the standard deviations for concentration were similar in the baselined data and the raw data. The difference in average concentration may be due to outliers. This procedure was modeled after a study done at the University of Liverpool. Our results were determined from tabular material provided by the study in order to determine the size of the gold nanoparticles. However, our experiment did not include the use of NaBH4 or hydroxylamine-hydrochloride solution, as was used in the original study.
McFarland, Adam D., Christy L. Haynes, Chad A. Mirkin, Richard P. Van Duyne, and Hilary A. Godwin. "Color My Nanoworld." JCE Classroom Activities (n.d.): n. pag. ACSeBooks. Web. 27 May 2015