UMass Nanotechnology Summer Institute
Lau & Nguyen
Gold Nanoparticles-Electrolyte Experiment Worksheet
1. Gold in its bulk form has a metallic yellow coloration. What color(s) would you expect gold
nanoparticles to be? If not metallic yellow, hypothesize why the color changes.
Pre-Activity:
Post-Activity:
2.
Nanoparticles in the environment can be potentially harmful. What are some ways we can
remove them from streams, rivers, and lakes?
Pre-Activity:
Post-Activity:
3.
What do you expect to happen to nanoparticles when electrolytes (e.g., NaCl) are added into
solution? Draw a rough sketch explaining your reasoning.
Pre-Activity:
Post-Activity:
4. What do you expect to happen to nanoparticles when organic matter (remains of organisms) is
added into solution along with electrolytes? Draw a rough sketch explaining your reasoning.
Pre-Activity:
Post-Activity:
UMass Nanotechnology Summer Institute
Lau & Nguyen
Gold Nanoparticles-Electrolyte Experiment Worksheet
1. Gold in its bulk form has a metallic yellow coloration. What color(s) would you expect gold
nanoparticles to be? If not metallic yellow, hypothesize why the color changes.
Answer: The coloration of gold nanoparticles depends on their degree of aggregation or size. Gold
nanoparticles can be yellow, red, purple or blue. Color is a function of the size of a nanoparticle’s
electron cloud; the size of the cloud determines the wavelength of light that is absorbed and reflected.
Our eyes see the reflected portions of visible light.
2. Nanoparticles in the environment can be potentially harmful. What are some ways we can remove
them from streams, rivers, and lakes?
Answer: Nanoparticles can be used as adsorbents and/or photocatlysts to improve water quality, but at
the same time, they have the potential to become a contaminant of concern. Nanoparticles can be
removed using conventional and/or advanced treatment technologies. The efficiency of specific
treatment process (e.g., filtration) depends greatly on the environmental conditions such as pH, ionic
strength, and organic matter concentration of the system.
3. What do you expect to happen to nanoparticles when electrolytes (e.g., NaCl) are added into
solution? Draw a rough sketch explaining your reasoning.
Answer: Nanoparticles generally have a charged
surface. The charged particles repel one another
and prevent aggregation. The addition of
electrolytes introduces charged cations, which are
attracted to the surface of the nanoparticles to cause
charge neutralization and subsequently aggregation.
4. What do you expect to happen to nanoparticles when organic matter (remains of organisms) is added
into solution along with electrolytes? Draw a rough sketch explaining your reasoning.
Answer: The addition of organic matter stabilizes the
nanoparticles by modifying the surface of the
particles. The organic matter provides greater
repulsion forces for nanoparticles to repel each other.
As a result, a higher concentration of electrolytes
would be needed to remove the energy barrier that
prevents aggregation to occur.