The synthesis procedure shown here was adapted by Steve Ng and Chris Johnson
from a procedure developed by S.D. Solomon, M. Bahadory, A.V. Jeyarajasingam,
S.A. Rutkowsky, C. Boritz, and L. Mulfinger, Journal
of Chemical Education, 84, 322-325, (2007).
The formation of silver nanoparticles can be observed
by a change in color since small nanoparticles of silver are yellow. A layer of absorbed
borohydride anions on the surface of the nanoparticles keep the nanoparticles separated.
When sodium cholride (NaCl) is added the nanoparticles aggregate and the suspension turns
cloudy gray. The addition of a small amount of polyvinyl pyrrolidone will prevent aggregation.
Never look directly into a laser
or shine a laser at another person.
Add 30 mL of 0.002M sodium borohydride (NaBH4) to an Erlenmeyer flask.
Add a magnetic stir bar and place the flask in an ice bath on a stir plate. Stir and
cool the liquid for about 20 minutes.
Drip 2 mL of 0.001M silver nitrate (AgNO3) into the stirring NaBH4
solution at approximately 1 drop per second. Stop stirring as soon as all of the AgNO3
The presence of a colloidal suspension can be detected by the reflection
of a laser beam from the particles.
Transfer a small portion of the solution to a test tube. The addition
of a few drops of 1.5 M sodium chloride (NaCl) solution causes the suspension
to turn darker yellow, then gray as the nanoparticles aggregate.
Transfer a small portion of the solution to a test tube. Add a drop
of 0.3% polyvinyl pyrrolidone (PVP). PVP prevents aggregation. Addition
of NaCl solution then has no effect on the color of the suspension.
Add enough solid polyvinyl alcohol (PVA) to give
a 4% solution. To get the PVA to dissolve you will need to SLOWLY add
it to the strirred, hot, silver colloid solution.
Silver nanoparticles color the yellow stained glass in medieval churches. To make "stained glass" decant the mixture into
a mold leaving air bubbles and undissolved PVA in the beaker.
Evaporate in a toaster oven for 30 minutes. Alternatively the solution can be left to evaporate.
Stock Solutions for 8 batches
0.001M AgNO3: Dissolve 0.017 g of AgNO3 into 100 mL distilled
water. This solution can be kept for later usage.
0.002M NaBH4: Dissolve 0.0189 g of NaBH4 into 250 mL distilled
water. This solution must be made fresh before the experiment.
0.3% PVP solution: Dissolve 0.1 g of PVP into 33 mL distilled water.