Colloidal Synthesis of Gold Nanoparticles

City University of Hong Kong

Department of Applied Physics and Material Science

AP 4178

Nanostructure and Nanotechnology

Lab Report of

Lab 1. Colloidal synthesis of gold nanoparticles

Date of Exp.: 14/10/2015

Liu Tsz Kwan

Objective

When we complete this laboratory, we are able to:

1. Applicate the concept of light scattering on particles in colloid suspension.
2. Differentiate the difference between reflection and absorption of UV.
3. Applicate the concept of reduction and oxidation we had learnt.
4. Compare effect of the color change and wavelength absorption on the different time and density of stock solution of the gold salt (HAuCl4).

Introduction

In this experiment we are going to mix the citrate stock solution (trisodium citrate, Na3C6H5O7H2O) with the stock solution of gold salt (HAuCl4). With two different amount of citrate stock solution add in and heated up into around 100 degree Celsius there will be color change (Figure 1). And we will also add the mixed solution into a small container and add in different amount of water by the pipet (Figure 2), in order to provide different density of the solution. Then put the solution into the Perkin Elmer Lambda 2 machine (Figure 3) to find out the absorption and reflection of the UV of the solutions. Also, we will heated up the solution in a longer period of time and find out the difference in the result between the solutions.

[pic 1][pic 2][pic 3]

Figure 1. Color change         Figure 2. Pipet                  Figure 3. Perkin Elmer Lambda                    

of the solutions                                                                2 machine

In this experiment we need to do some safety precaution too, we need to wear gloves to do the experiment and we can take off the gloves when we put the small container in the Perkin Elmer Lambda 2 machine.

Materials used in the experiment:

• Glass cylinder
• 2 flask
• Magnetic stir bar
• Heater
• Stock solution of the gold salt (HAuCl4)
• Water
• Citrate stock solution (trisodium citrate, Na3C6H5O7H2O)
• Pipet
• 4 container
• Perkin Elmer Lambda 2

Theory

In this experiment the stock solution of gold salt (HAuCl4) are mixed with the citrate stock solution (trisodium citrate, Na3C6H5O7H2O), a reducing agent. So that the gold ions will be reduced to neutral gold particles. In the heating process the mixture of the solution was stirred vigorously, in order to make sure the gold particles in precipitate forms will be in similar size and will not stick together, also the heating process is to enhance the solutions’ stability.

Almost any types of amalgamation of single material can form a mixture of particles called Colloid. The mixtures of particles are smaller than the bare eye discrete through alternative substance.

Also Colloids will show the Tyndall effect, which is an effect of the tiny particles reflect the light in some kind of. This effect happens in a colloid since the small particles was scattered by the beam of light.

Procedure

• 1)  Add 20 mL of 1.0 mM HAuCl4 to a 50 mL Erlenmeyer flask clamped to a ring stand and place it on a stirring hot plate. Add a magnetic stir bar to the flask. Turn on the hot plate and the stirring function and bring the solution to a boil. Note: The stirring function should be set between a medium to fast setting for vigorous stirring.  
• 2)  When boiling make sure there is adequate volume of liquid left in the flask.  
• 3)  Slowly add 2 ml of 1% trisodium citrate dehydrate Na3C6H5O7.2H2O to the 50 ml flask, allowing the solution to continue stirring and boiling on the hot plate until a  deep red color appears. The color will first appear as a dark purple, but over time  will take on a deep red hue that is a little darker than the color of beets.  
• 4)  When the color is achieved, carefully remove the flask from the hot plate and  place on wire gauze. Once it is cool enough to handle, pour contents of flask into  a 50 ml beaker.  
• 5)  Take a laser pointer and wrap a rubber band around the on­switch so it is on  continuously. Place the laser pointer to the edge of the beaker and pass the light  

through the solution. Record your observations. Now rotate the laser pointer at 90° intervals and record any new observations.

• 6)  Take two test tubes or disposable cuvettes. Place 4 ml of the colloidal gold into each one. To one tube add 5­10 drops of NaCl until the color of the liquid changes. What is the color change that is observed?  
• 7)  Record the UV absorption spectrum of both of the cuvettes. Attach spectrum to lab.  

Result and Analysis

The color of the mixed solution

In the experiment we need to add 0.2ml and 2ml citrate stock when we start boiling the gold solution into two separate flask. By eyes observation, we can see that the color change we add the citrate stock into the gold solution.(Figure4)

When we start the experiment, we can see that the gold solution was light yellow in color, but after we add the 0.2ml of citrate stock into the gold solution the mixture of the solutions has some color change. The mixture of the solutions turn into dark purple in a short period of time, while the other, which add 2ml citrate stock turn colorless, just like pure water.