Synthesis of Metal Nanoparticles
Title: Synthesis of Nanoparticles
Objective: Synthesis of silver nanoparticles using sodium borohydride in the presence of
polyvinylpyrrolidone (PVP) as a stabilizer.
Theory: A nanoparticle is a small particle with at least one dimension in the range of 1 to 100
nanometers (nm). These particles have physical and chemical properties compared to their bulk
counterparts due to their small size and high surface area. This size allows them to interact with
materials in ways that are not possible for larger particles.
Nanoparticles can be prepared from various materials such as metals (like gold or silver),
carbon (like carbon nanotubes or graphene), and polymers. Their unique properties make them
highly versatile for a wide range of applications.
There are two ways to prepare nanoparticles –
1. Top-down approach – This method refers to constructing something by starting with a
larger, more general structure and progressively breaking it down into smaller, more detailed
components. In the context of nanotechnology, this approach involves creating nanoparticles
by breaking down bulk materials into smaller particles, typically using mechanical, chemical,
or physical methods.
Fig 1. Top-down approach
2. Bottom-up approach – The method refers to constructing nanoparticles or nanostructures
by starting with basic building blocks such as atoms, molecules, or simple units that selfassemble into more complex structures. In nanotechnology, the bottom-up approach is often
used to build nanoparticles, nanowires, and other nanoscale materials from molecular or atomic
scale components. It typically involves chemical or biological processes to create nanoscale
materials with precise control over their structure and properties.
Fig.2 Bottom-up approach
Silver is currently used to control bacterial growth in a variety of applications, including dental
work and burn wounds. Ag ions and Ag-based compounds are highly toxic to the environment,
health, and aquatic life. Reducing the particle size of materials is an efficient and reliable tool
for improving their biocompatibility. The extremely small size of nanoparticles exhibits
different properties when compared with the bulk material. As a result, nanoparticles with very
large surface area relative to their volume have become possible. These particles easily interact
with other particles and increase their antibacterial efficiency.
Chemical synthesis of silver nanoparticles involves the reduction of a silver salt such as silver
nitrate with a reducing agent like sodium borohydride in the presence of a colloidal stabilizer.
Sodium borohydride has been used with Polyvinylpyrrolidone (PVP) which is used as a
stabilizing agent. A large excess of sodium borohydride is needed to reduce the ionic silver
nanoparticles. and PVP is used to stabilize the formed nanoparticles. Polyvinylpyrrolidone
(PVP) prevents aggregation. Polyvinylpyrrolidone (PVP) is a polymer that binds strongly to
the silver nanoparticle surface. It provides greater stability than citrate or tannic acid but is
more difficult to displace. PVP is used to protect the silver nanoparticles from growing and
agglomerating.
A sodium borohydride solution was added dropwise (about 1 drop second) to silver nitrate
solution. The reaction mixture was stirred vigorously on a magnetic stir plate. The solution
turned light brown after the addition of very few drops of sodium borohydride and red wine
color when all of the reducing agents had been added. The entire addition took about three
minutes, after which the stirring was stopped and the stir bar removed. The clear wine-colored
silver is stable at room temperature and stored in a transparent vial for as long as several weeks
or months.
The chemical reaction is the sodium borohydride reduction of silver nitrate:
AgNO3 + NaBH4 → Ag + ½ H2+½ B2H6 +NaNO3
Chemicals required: Silver nitrate (AgNO3), Sodium
Polyvinylpyrrolidone (PVP), double distilled water (H2O).
Borohydride
(NaBH4),
Apparatus required: 250 ml beaker, 50 ml beaker, magnet, magnetic stirrer, pipette,
micropipette, UV-Visible Spectrophotometer.
Procedure:
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Prepare100 ml approx. (N/2) sodium borohydride solution
Prepare 100 ml of 0.01(M) polyvinylpyrrolidone solution
Prepare 100 ml of 0.001(M) silver nitrate solution
Take 20-30 ml of PVP solution in a 50 ml beaker
Stir the solution with a magnetic stirrer
Add 5-10 ml of silver nitrate solution dropwise in the PVP solution with stirring
condition
After 10 mins of stirring, add sodium borohydride solution dropwise and continue the
stirring
Observe color change immediately after adding the sodium borohydride solution. A
light yellow to brown color should be found. To get a deeper colored solution add more
sodium borohydride solution dropwise. Finally, the reddish-brown color solution
should appear.
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Perform UV-Visible Spectroscopy: Take the prepared solution and measure
absorbance using a UV-vis spectrophotometer.
Observation:
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The yellow / brown color of the solution should appear
UV-Visible spectroscopy should show an absorption peak in the range of 400–450
nm
Results:
• The yellow / brown color of the solution confirms the formation of silver
nanoparticles
• UV-Visible spectroscopy should show an absorption peak in the range of 400–450
nm confirming the presence of silver nanoparticles.
Precaution:
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Neat and clean apparatus should be used.
Before use, the beaker should be rinsed properly.
Colour change should be observed properly.
Application:
Silver nanoparticles (AgNP) have various applications in diverse fields
Antimicrobial property: Silver nanoparticles (AgNPs) are used in antimicrobial drug
development. They have high reactivity and antibacterial activity against microorganisms.
They have been proved that the antibacterial effect of silver nanoparticles is due to the sustained
release of free silver ions from the nanoparticles.
Cancer treatment: Silver nanoparticles are used in anticancer therapy.
Biosensor: Peptide-capped silver nanoparticles for colorimetric sensing have been mostly
studied in past years, which focus on the nature of the peptide and silver interaction and the
effect of the peptide on the formation of the silver nanoparticles. Besides, the efficiency of
silver nanoparticle-based fluorescent sensors can be very high and overcome the detection
limits.
Catalyst: Silver nanoparticles have been demonstrated to present catalytic redox properties for
biological agents such as dyes, as well as chemical agents such as benzene. The chemical
environment of the nanoparticle plays an important role in their catalytic properties. In addition,
it is important to know that complicated catalysis takes place by adsorption of the reactant
species to the catalytic substrate. When polymers, complex ligands, or surfactants are used as
stabilizers or to prevent coalescence of the nanoparticles, the catalytic ability is usually
decreased due to reduced adsorption ability.