Nanomaterials

I- Purpose/Objective:

The purpose of this laboratory is to enable you to understand the principles related to design, synthesis, and characterization of nanomaterials. We will conduct CdSe nanoparticle synthesis and characterization of their photophysical properties. We also synthesize gold nanoparticle and analyze the relationship between their optical properties and the size. Transmission Electro Microscopy will be used to investigate the size of the nanoparticles.

This lab involves five major tasks, which we have scheduled in a sequence in order to minimize waiting time:

  • Chemical synthesis and purification of CdSe quantum dots
  • Photophysical characterization of the CdSe quantum dots
  • Chemical synthesis and purification of gold nanoparticles
  • Optical characterization of the gold nanoparticles
  • TEM analysis of the CdSe and gold nanoparticles (GSI will conduct the TEM study)

II - Experimental Procedure:

CdSe Nanoparticles (Quantum Dots)

A. Synthesis and Purification

CdO (0.308 g, 2.40 mmol), tetradecylphosphonic acid (1.336 g, 4.80 mmol) and trioctylphosphine oxide (4. 36 g) will loaded into the reaction flask and heated up to 100°C under argon and degassed for 20 min. The mixture will be heated to 300°C under argon. After the solution became clear, trioctylphosphine (2.25 g) will be added. The solution should be stirred for 5-10 min and selenium solution in trioctylphosphine (15 wt%, 1.263 g, 2.40 mmol of Se) will be then injected very quickly at 300°C. The temperature of the mixture will be lowered down to 290°C and the mixture will be kept at 290°C for a given period of time (Three different teams will use three different reaction times, 30 seconds, 2 minutes, and 10 minutes) to control the size of the nanoparticles. The mixture should be cooled down quickly by the flow of air to the flask wall. Toluene (5 ml) will be added into the flask at around 60°C, and the mixture will be transferred into a vial under argon atmosphere in a glove box. The minimum amount of 2-propanol (about 5-7 ml) will be added dropwise to the vial under vigorous stirring, and the mixture should be centrifuged for 5 min immediately after the addition of 2-propanol. The supernatant solution should be quickly removed with a pipette. The precipitate will be re-dissolved in the minimum amount of toluene (about 1 ml) and re-precipitated with minimum amount of 2- propanol (about 0.5 to 1 ml). Nanocrystals will be obtained as wet precipitates.

B. Characterization

The prepared CdSe quantum dots will be examined by UV-Vis spectroscopy, fluorescence spectroscopy, and fluorescence microscopy. Additionally, TEM analysis will be conducted.

  • UV-Vis spectroscopy: This analysis will reveal the absorption λmax of the prepared CdSe nanoparticles. The results combined with the TEM results will give us the correlation between the size of the nanoparticles and their absorption property.
  • Fluorescence spectroscopy:  The emission property of the prepared CdSe nanoparticles will be analyzed by means of fluorescence spectroscopy. The results combined with the TEM analysis will give us the correlation between the size of the nanoparticles and their emissive property. Observe the correlation between the absorption λmax and the emission λmax of the CdSe quantum dots
  • Fluorescence microscopy: The size of the prepared CdSe nanoparticles will be too small to be visualized the individual quantum dot. However, it will be possible to show the emissive color of a thin layer of the prepared CdSe quantum dots by using fluorescence microscopy.


Gold Naoportiles

A. Synthesis and Purification


Preparation of Octadecanethiol-Functionalized Gold Nanoparticles. A 235mg (0.82 mmol) sample of dodecanthiol will be added under vigorous stirring to a solution of 0.9 mmol of hydrogen tetrachloroaureate(III) trihydrate (H[Au- (Cl4)]•3H2O) in 10 mL of freshly distilled, anhydrous THF (about 1:1 ratio between dodecanthiol and hydrogen tetrachloroaureate(III) trihydrate). We also try 0.5:1 and 2:1 ratios. The reaction mixture will be stirred for 20 minutes at room temperature, before a 1.0 M solution of lithium triethylborohydride in THF is added dropwise. The mixture should turn to dark red-brown immediately. The addition of the reducing agent will be continued at increasingly slower rate, until no more gas evolution could be observed.

B. Characterization

The prepared gold nanoparticles will be examined by UV-Vis spectroscopy and optical microscopy. Additionally, TEM analysis will be conducted.

  • UV-Vis spectroscopy: This analysis will reveal the absorption λmax of the prepared Au nanoparticles. The results combined with the TEM results will give us the correlation between the size of the nanoparticles and their absorption property.
  • Optical microscopy: The size of the prepared Au nanoparticles will be too small to be visualized the individual nanoparticle. However, it will be possible to show the color of a thin layer of the prepared Au nanoparticles by using optical microscopy.

III - Theory/Background Information:


IV - Theory/Background References:


V- Activity Schedule:


VI -Format and Important Questions for Lab Report:

You should know the answers of the following important questions

  1. This laboratory experiment consists of several separate but related tasks. List the five major tasks and describe briefly what will be done in each
  2. Why does the size of the nanomaterials influence on their optical property?
  3. Gold nanoparticles have their unique color depending on their size. What is the origin of the color?
  4. How does UV-Vis spectroscopy work?
  5. How does fluorescence spectrophotometer work?
  6. What is the difference between an optical microscope and a fluorescence microscope?