Hands-on Activity Engineering Silver Nanoparticles

Learning Objectives

After this activity, students should be able to:

• Discuss how nanotechnology and silver nanoparticles can be used in water treatment.
• Explain the current process for creating silver nanoparticles and issues with cost of use of energy to make them.
• Describe how plants can be used as a reducing agent when added to silver nitrate to make silver nanoparticles.
• Explain the results of their experiment and make recommendations for what plant(s) to use to make silver nanoparticles.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

Common Core State Standards - English

International Technology and Engineering Educators Association - Technology

State Standards

Materials List

Each group needs:

• whiteboards (one per pair of students in group of four)
• dry erase markers and erasers
• plant material for students to test (See Before the Activity below for suggestions)
• 15 m conical tube
• mortar and pestle
• 400 ml beaker with 200 ml of water
• funnel
• filter papers
• hot plate
• 10 ml of 0.1 M AgNO₃ (silver nitrate) from teacher’s stock solution; extract with a pipette
• scale
• gloves
• goggles
• razor blade
• internet access via laptop or cellular device
• Engineering Silver Nanoparticles Student Worksheet

Teacher materials to make 0.1 M silver nitrate:

• scale
• weigh boat or weigh paper
• scoopula
• 250 ml brown bottle with lid
• distilled water
• label tape
• gloves
• goggles

To share with the entire class:

• Engineering Silver Nanoparticles PowerPoint Presentation
• 200 ml of 0.1 M of AgNO₃ stock solution
• gallon Ziploc bags with plant materials

Worksheets and Attachments

Pre-Req Knowledge

Students should know the basic structure of an atom, including the concept that electrons are found in orbitals surrounding the nucleus. The students should know that an ion is an atom with an unequal amount of protons and electrons.

Introduction/Motivation

Silver (Ag) is an element that has many practical applications. Silver is used to make silverware, mint coins and currency, or fashioned into jewelry. Its versatility means we can also use it to help us with many of our problems. Scientists and engineers found that nanoparticles derived from silver can be used as a type of cleaning agent, from used gym shoes water sanitation. Silver nanoparticles have antimicrobial properties that can kill small microbes. They can be attached to water filters and columns to kill microbes and help remove other harmful products from the water, such byproducts of disinfection.  

There are two main methods used to synthesize silver nanoparticles. Engineers can use a “top-down” approach that requires mechanical grinding of bulk silver metals or they can use a “bottoms-up” method which includes using chemical reactions. Both methods can be expensive, and the materials used to make silver nanoparticles are toxic and hazardous. Plants, however, contain unique reducing agents that can synthesize silver nanoparticles without creating toxic waste. Plant extracts can reduce silver ions because of the combination of biomolecules they contain, such as proteins, enzymes, amino acids, tannins, and many more. Our task as environmental engineers will be to determine which plant may effectively reduce silver and produce the most silver nanoparticles, so we may use them in a filters design for a water treatment facility.

Procedure

Background

Metallic nanoparticles are used in engineering and medical fields due to their unique properties and size. Silver nanoparticles have been receiving special interest in the medical field for their antimicrobial properties, and in the environmental field for their ability to remove disinfection byproducts from water. They can also prevent biofouling on water filter membranes. Biofouling can occur when there is a buildup of microorganisms on a filter that is used to clean water. Silver nanoparticles are produced two ways: top to bottom and bottom to top. In the top to bottom method, nanoparticles are produced using evaporation-condensation in a tube furnace at atmospheric pressure. This process requires a lot of space for equipment, energy to heat the substances up, and time to occur. The bottom to top process produces nanoparticles chemically by using reducing agents. Reduction is a chemical process by which one of the atoms involved gains electrons from the other. Plant extracts are used as reducing agents because they gain an electron from the silver ion to make it a silver nanoparticle with no charge. In the reaction, you can see that silver initially has a charge of +1, and afterwards has no charge.

Ag⁺ _(aq)   ----->    Ag _(s)

One of the most common reducing agents is sodium borohydride (NaBH₄₎. The full chemical reaction is shown below:

AgNO₃(aq) + NaBH₄(aq) → Ag(s) + 1/2H₂(g) + 1/2B₂H₆(g) + NaNO₃(aq)

Unfortunately, this process is toxic and not environmentally friendly. As a solution, scientists are looking to plants. Plants contain natural reducing agents that turn silver ions (Ag⁺) to silver nanoparticles (Ag⁰). Biomass and microorganisms are also being engineered as a green way to synthesize silver nanoparticles. The silver nanoparticles that are produced can be added to a water filter or granulated activated carbon in a water column to help remove disinfection byproducts and reduce biofouling.

Before the Activity

• Teacher needs to prepare 200 ml of 0.1 M of AgNO₃ solution that the whole class will use.
• Using a scale, measure out 3.4 g of AgNO₃ by using a scoopula to transfer the AgNO₃ from the stock bottle to a weigh boat or weigh paper on the scale.
• Add 100 ml of distilled water to a brown 250 ml bottle and add the 3.4 g of AgNO₃.
• Stir the solution and then add more distilled water until you reach the 250 mL mark.
• Mix the solution and label the bottle “0.1 M of AgNO₃ “ Note: Silver nitrate is light sensitive and should be stored in a brown bottle. Gloves and goggles should be worn when preparing the solution because silver nitrate can stain skin.
• Collect a gallon size zip lock bag of different plants for students to use in the lab.
• Some suggestions for plants to use: ficus (leaves), banana (peel), aloe vera, orange (peel), lemongrass (leaves), tea extract, lotus (leaves), onion (leaves), and grapes (fruit).
• Set materials on 8 lab tables for student groups of four (maximum).

With the Students

1. Introduce the activity using the Engineering Silver Nanoparticles PowerPoint Presentation. Have students brainstorm the different uses of silver nanoparticles on their whiteboard with a partner. Students share what they came up with for the class.
2. Ask students: “Have you ever thought of using silver to clean water?”
3. (Slide 3) Use the “Nanosilver and Biofouling” video in the presentation to introduce how silver nanoparticles are being used to clean water.
4. (Slide 4) Have students do individual research using the internet on laptops or cellular devices to get some background information on nanotechnology, and silver nanoparticles. You may split this part up per pair of students and have them share what they learned with their partner. Students will put their findings from their research on the Engineering Silver Nanoparticles Student Worksheet.
5. (Slides 5-9) Use the PowerPoint to help explain to students that the traditional way of producing silver nanoparticles requires using harsh chemicals that are bad for our environment. Explain that plants have chemicals in them that can reduce the silver to a nanoparticle form.
6. Have students use the instructions on their Engineering Silver Nanoparticles Student Worksheet to make their plant extract (See Figure 1 for set up).
7. Instruct students to analyze their solution to see if they created silver nanoparticles (See Figure 2 for an example of silver nanoparticle formation).

1. The solution should turn a light yellow to brown color if silver nanoparticles formed. Students record their qualitative observations in the Engineering Silver Nanoparticles Student Worksheet. The browner the solution, the less likely they made small silver nanoparticles. As groups complete their analyses, display Slide 11 of the PowerPoint.

8. (Slide 11) Have students fill out the “Class Results” table and whether they had a color change or not. Have each group talk about their experience in making the plant extract and silver nanoparticles. Have them share their results and any possible errors. The less color change, the smaller the nanoparticles formed. The greater the color change, the larger the nanoparticles. Smaller silver nanoparticles are ideal because they take up less space and will allow for more silver nanoparticles in water filters and columns. If students did not clean their plant well enough before making the extract, silver precipitate may form in their solution.
9. (Slide 12) Students can retest their plants by changing the amount of plant material used to make the extract, or changing their plant to another plant (or plants) to see if they get better results.
10. (Slide 13) Allow students to make a decision of what plant (or plants) they would use to make silver nanoparticles to add to the water filters. At the end of the activity, tell students write a letter to a water plant foreman with their recommendation for how to improve their filter using data from their experiment and information from their research to justify their recommendation.

Vocabulary/Definitions

nanotechnology: Technology that deals with dimensions and tolerances of less than 100 nanometers, such as the manipulation of individual atoms and molecules.

reducing agent : A substance that tends to bring about reduction by being oxidized and losing electrons.

reduction: Chemical reaction involving the gaining of electrons by one of the atoms involved in the reaction; refers to the element that accepts electrons, as the oxidation state of the element that gains electrons is lowered.

silver nanoparticles: Nanoparticles of silver of between 1 nm and 100 nm in size.

Assessment

Pre-Activity Assessment

What are the uses of silver? Ask the students to write down the different things they know that silver is used for. For example, silverware, jewelry, coins, etc.

Activity Embedded Assessment

Student Worksheet: Have students work through the Engineering Silver Nanoparticles Student Worksheet.

1. Explain where all materials are located in the lab area and begin with identifying the materials needed for the experiment, safety materials, safety hazards and proper procedures for the lab protocol.
2. Explain the purpose of the experiment and have students choose which plant or plants they want to test.

• Which plant will produce the most silver nanoparticles?

3. Students will write down qualitative and quantitative data on the Engineering Silver Nanoparticles Student Worksheet.
4. Have students share their results with the class and fill out the post-lab questions on the Engineering Silver Nanoparticles Student Worksheet. It is important to reiterate that failures are okay and that there is always something that can be learned from a failure.
5. Have students create a list of “What Ifs…” and come up with a list of uses for their silver nanoparticles.

Post-Activity Assessment

Letter to Water Plant: Students write a letter to a water plant foreman recommending the use of silver nanoparticles and why they should be used on the water filter and columns. Students describe the process of making silver nanoparticles from plants and make a suggestion for the best plant(s) to use.

Investigating Questions

How can silver nanoparticles clean water? (Answer: Silver nanoparticles have antimicrobial properties. When silver is chemically coated onto the surface of a membrane filter, the nanoparticles kill and prevent the growth of microbes. Silver-coated filters last longer and produce more clean water.)

How can plants be used to make silver nanoparticles? (Answer: Plants can act as reducing agents in the reaction that turns silver ions (Ag⁺) to silver nanoparticles (Ag⁰). Plant extract replaces common reducing agents like sodium borohydride (NaBH₄), which leads to a more environmentally-friendly reaction with less harmful byproducts.)

Safety Issues

Students should wear goggles and globes during the lab experiment. Students must use caution if they need to use a razor blade to slice up their plant.

Troubleshooting Tips

A precipitate may form as a byproduct once students add the plant extract. This may occur if the plant is not cleaned with distilled water beforehand.

Activity Scaling

• For higher grades, have students make suggestions for how they could improve their silver nanoparticle production with plants.

References

Copyright

Contributors

Supporting Program

Acknowledgements

This curriculum was based upon work supported by the National Science Foundation under Rice University Engineering Research Center for Nanotechnology Enabled Water Treatment Systems (NEWT) RET grant no.1449500. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.

Special thanks to Christina Crawford.