Experiment 10: Growing Silver Nanoprisms
CH3500: Inorganic Chemistry, Plymouth State University
Adapted from "Synthesis of Silver Nanoprisms," Video Lab Manual, Interdisciplinary Education group, Materials Research
Science and Engineering Center, University of Wisconsin at Madison
(http://mrsec.wisc.edu/Edetc/nanolab/silver/index2.html), D. Aherne, D. M. Ledwith, M. Gara, and J. M. Kelly, "Optical
Properties and Growth Aspects of Silver Nanoprisms Produced by a Highly Reproducible and Rapid Synthesis at Room
Temperature", Adv. Funct. Mater., 18, 2005-2016, (2008), and McElhinny, K., Cadwell, K.D., Eversage, J., Benitez, S.M., .
Lisensky, G.C., Zenner, G.M. "Observing progressive color change through the growth of silver nanoprisms ," article in
perparation..
Introduction:
The term "nanomaterials" refers to a class of synthetic materials with features in the nanoscale
(roughly 1-100 nm). The size of the nanoscale is between that of atoms / molecules (which exhibit
properties governed by quantum mechanics) and bulk materials (which exhibit colligative properties
associated more with classical mechanics). Nanomaterials thus often exhibit unique or interesting
properties related to their size, which enables us to change the properties by changing the size.
A common example of nanomaterials exhibiting unique properties is their color. For example,
certain metals, when synthesized as nanoscale particles, yield a range of colors depending on the size,
which are very different from the expected metallic luster of the bulk metal. Silver--the material
chosen for study in this lab--is one such metal.
Nanotechnology--the field concerned with the study and synthesis of nanomaterials--is a recent and
rapidly developing field integrating numerous disciplines, including chemistry, engineering, and
biology. The reason for the recent (i.e. last 15-20 years) development of nanotechnology is the
relatively recent development of tools needed to synthesize and analyze materials of such small size.
One of the initial challenges in synthesizing many nanomaterials is the ability control crystal growth to
limit their size. Two techniques are often employed, many times simultaneously: 1) the use of a
"capping agent" (often a long chained molecule) to cover the surface of the particle and prevent
addition of further atoms to the crystal, and 2) the use of seed-crystals that are then added onto in a
controlled fashion until the desired size is obtained.
In this lab, you will grown nanoscale silver prisms using a combination of seed crystals and
capping agent. The growth of the crystals will be followed using UV-Vis spectroscopy. The color of
the nanoprisms changes due to a nanoscale phenomenon known as "plasmon resonance." In laymen's
terms, this is the result of electrons on the surface of the particles being confined to orbitals the size of
the particle. The absorbance of the light is therefore akin to absorbance of light by an electron in an
atomic orbital followed by promotion to an orbital of higher energy. In the nanoparticle, the ground
and excited state "orbitals" exist over the entire particle, not a single atom. Thus, the size and energies
of the orbitals are changed by changing the size of the particle. It has been empirically determined that
the length (L, in nm) of the silver nanoprisms can be determined by UV-Vis spectroscopy with the
equation:
 peak −418.8
(Eqn 1)
L=5.5nm[
]
33.8
Safety Considerations:
• Sodium borohydride (NaBH4) is a strong reducing agent, is flammable and explosive in its solid
form, and liberates hydrogen gas when dissolved in water. Handle it with care.
© Copyright Plymouth State University and Jeremiah Duncan. May be distributed freely for education purposes only.
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•
Although bulk silver is generally considered "safe" (people wear it on a regular basis), the
environmental, health, and safety research on the nanoscale version indicates that it is likely
toxic in certain situations. Nanoscale particles are incredibly small, with the ability to cross
through the skin and be transported through the body. Limited contact with the material will
likely result in nothing more than a dark stain on your skin remaining for days or weeks, but
you should take precautions and treat nanosilver as a toxic material nonetheless.
Procedure
• You will work with a partner for this lab.
• Remember to record what you do (including exact masses weighted out), data collected, and
observations at each step in the procedure.
A. Preparation of Stock Solutions
Your group will be assigned to prepare one of the solutions below. All solutions should be prepared
using ultra-pure water and volumetric flasks:
1. 2.5 mM trisodium citrate: Dissolve 0.037 g trisodium citrate in 50 mL water. Fill a buret with
this solution. Note what is in the buret on a piece of paper nearby.
2. 0.5 g/L poly(sodium styrenesulfonate): Dissolve 0.025 g in 50 mL water.
3. 10 mM sodium borohydride: Dissolve 0.019 g NaBH4 in 50 mL water.
4. 0.50 mM silver nitrate (AgNO3). Dissolve 0.021 g AgNO3 in 25 mL water. Dilute 10 mL of
this up to 100 mL. Fill a buret with this solution. Note what is in the buret on a piece of paper
nearby.
5. 0.75 mM ascorbic acid: Dissolve 0.065 g of ascorbic acid in 5 mL distilled water. Dilute 5 mL
of this up to 50 mL total.
B. Preparation of Seed Solution
1. Add 2.5 mL of 2.5 mM trisodium citrate (TSC) from a buret to a 25-mL Erlenmeyer flask.
2. Using autopipets, add 0.125 mL of 0.5 g/L poly(sodium styrenesulfonate) and 0.15 mL of 10
mM sodium borohydride to the flask. Add a magnetic stir bar.
3. While stirring the solution, add 2.5 mL of 0.50 mM silver nitrate (AgNO3) at a rate of 2 mL/min
from a buret. The rate of addition is very important to the quality of the seed solution.
C. Growing Silver Nanoprisms
1. To a 10 mL beaker, add 5.0 mL of deionized water (graduated cylinder), 0.50 mL of silver seed
solution (graduated pipet), 1.0 mL of 0.75 mM ascorbic acid (graduated pipet), and a stir bar.
Stir for at least one minute.
2. Measure out 5.0 mL of 0.50 mM AgNO3 into a graduated cylinder. This is the total amount of
silver nitrate you will need, and you will add it to the solution with a disposable pipet.
3. Begin by adding one drop of silver nitrate solution. Allow the color to stabilize by stirring for
at least 30 second. In a table, record the number of drops added and the color of the solution.
© Copyright Plymouth State University and Jeremiah Duncan. May be distributed freely for education purposes only.
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4. Continue the process of adding silver nitrate, allowing the color to stabilize, and recording the
color. In the beginning, the addition of just one drop will result in a noticeable change in color.
Eventually you will need to add more drops each time.
5. At five different times during the course of your reaction--including one near the beginning and
one near the end--record the UV-Vis spectrum of the solution. Be sure to note how many drops
were added total at that point.
Analysis (Lab Notebook)
1. Calculate the length of the nanoprisms for each of the four solutions you analyzed with UV-Vis
spectroscopy. Record these numbers in a table that includes the drops of silver nitrate added to
that point.
2. Calculate the energies of the photons absorbed at the λpeak of your UV-Vis spectra. Record these
in that same table used in Question 1.
3. Did the energies of the photons absorbed by the silver nanoprisms increase or decrease as the
reaction progressed? How is this consistent or inconsistent with what you know to be
happening in the reaction?
Analysis and Conclusions (Lab Report)
Your lab report is due by lecture on Wednesday, . Your report must be handed in BOTH
electronically (via Moodle) and in hard copy form. See the document "InorgChemLabReportGuide.pdf" on the course website
(http://oz.plymouth.edu/~jsduncan/courses/2010_Fall/InorganicChemistry) for guidelines on writing
your report.
In addition to the Analysis performed in your notebook, include the following in your report:
1. Provide all the UV-Vis spectra overlaid in the same graph.
2. Make a plot of the length of the silver nanoprisms versus drops of AgNO3 added. Comment on
the shape of this curve (is it linear, curved, etc.), and what they implies about the growth of the
silver nanoprisms as silver nitrate is added.
© Copyright Plymouth State University and Jeremiah Duncan. May be distributed freely for education purposes only.
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