Sodium Borohydride Synthesis of Silver Nanoparticles
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).
Ag+ + BH4- + 3 H2O → Ag0 + B(OH)3+ 3.5 H2
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 until sodium chloride is added.
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 metal nanoparticles can be detected by their interaction with a beam of light since the oscillating electric field causes quantized light emission from the particles. Can you see a laser beam as it passes through the solution?
The light from a laser pointer may be polarized with the electric field oscillation in only in one plane. Is your laser pointer polarized? In so the plasmon emission would occur only in one plane. Shine the laser through the solution and rotate the laser. What fraction of a full rotation separates the maximum and minimum observed brightness?
Record the visible spectrum of the solution. You will need data from 375 nm and longer wavelengths. What is the peak width at half height?
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.
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.