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.