SYNTHESIS OF GOLD NANOPARTICLE

A facile (simple) approach involves the reduction of hydrogen Tetrachloroaurate , [HAuCl4] with trisodium citrate dehydrate, [Na3C6H5O7.2H2O], in aqueous solutions at elevated temperatures. The citrate donates electrons to the gold ions producing gold metal and then adsorbs on the surface of the particle preventing growth of large particles. The charges on the citrate molecules help stabilize the gold nanoparticles by electrostatic repulsion and prevent aggregation.

 Au 3+ + 3e → Au (Metallic gold in nm)

Overall reaction:

6Au3+ + C6H5O7 3- + 15OH- → 6 Au + 6CO2 + 10H2O

Procedure 

Dilute solution of HAuCl4 is heated to boil at constant stirring using magnetic stir bar. After the solution begins to boil, 1% solution of trisodium citrate dehydrate, is added continue to boil and stir the solution. The gold nanoparticles will gradually form the citrate reduces the AuCl4. Following color changes observed during reaction which confirms formation of gold nano particle.

YELLOW COLOUR → COLOURLESS → PURPLE → WINE RED

Characterization:
Formation of gold nano particle can be confirmed using tool such as SEM (scanning electron microscope), TEM (transmission electron microscope) and AFM (atomic force microscope). APPLICATIONS:
1. These nanoparticles are used in biomedical nanotechnology for example in cancer therapy.
2. These nanoparticles are used in nanoelectronics.
3. They are used in water purification.