I followed the following procedure for preparing gold seeds for growth of gold nanoparticles of different sizes as reported by Jana et al. I tried this procedure for 7 times but in all the cases I found that on adding adding ice chilled 0.6 mL sodium borohydride into the stirring mixture of gold chloride and sodium citrate, the solution turned clear orange colour (light pink color). But after sometime the color of the solution changes to purple or blackish. I don't know where is the problem. Why the color is changing to purple or blackish? Is there any problem with the temperature?
Preparation of 3.5 nm Gold Seed.
A 20 mL aqueous solution containing 2.5*(exp-4) M HAuCl4 and 2.5*(exp-4)
trisodium citrate was prepared in a conical flask. Next, 0.6 mL of ice-cold, freshly prepared 0.1 M NaBH4 solution was added to the solution while stirring. The solution turned pink immediately after adding NaBH4, indicating particle formation. The particles in this solution were used as seeds within 2-5 h after preparation. Here, citrate serves only as a capping agent since it cannot reduce
the gold salt at room temperature (25 °C)
This change in color of AuNPs is because of agglomeration and change in morphology. Usually the rod shaped AuNPs give purple color. You need to quench the reaction immediately to avoid this process.
Hello, I make a silver seed particle. I use 1mM citrate with 2.5mM AgNO3. It is my impression that this is the minimum citrate that I could use. You may like to try more citrate in your recipe. Also, I have not found it necessary to chill the NaBH4 and I can use the seed directly after synthesis. Good Luck.
Hi Sibasish,
The perfect colour after synthesis is light brown. If you didn't get the same colour then it means quality is not good. Synthesis of Gold seeds is a skill. You need to repeat it many times to get this skill. Please find the attached protocol. I have also included the correct coloured sample. Use it within 2-5 hours after synthesis. if you have any questions then you can ask me.
Hi Aditya,
What were the concentration and volume of gold salt that you used? In your protocol it is marked as xx.
Thank you
hi Aditya sir,
please tell me the size of these gold seeds with your protocol????
Hello,
How to remove sodium borohydride or sodium metaborate from solution after reduction? Thanks.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials Chemistry
- Polymer Chemistry