University of Alabama, Shanlin Pan, Karen Boykin, Dawen Li, Dee Goldston
Clean Energy: Nanoparticles, Chemical Reactions, and Light
Key Concepts: In this module, students are expected to learn:
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How light interacts with matter such as chemicals;
How light interacts differently with nanomaterials than other materials; and
How energy is involved in light-matter interactions.
Alabama Standards: 8th Grade
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Describing how waves travel through media
Describing the electromagnetic spectrum in terms of frequency
e.g. electromagnetic spectrum in increasing frequencies-microwaves, infrared
light, visible light, ultraviolet light, X rays
National Science Education Standards: Grades 5-8
Abilities necessary to do scientific inquiry
Transfer of Energy
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Light transmission, absorption, and scattering.
Energy as a property of many substances and its association with heat,
light, electricity, mechanical motion, sound, atomic, nuclei, and the nature of a
chemical
Energy transfer
Materials:
Titanium dioxide (TiO2) nanoparticles, water containing silver ions, clean white paper, handheld
UV lamp, Methanol, dropper pipet, spot plate with three depressions, 2 ml microcentrifuge tubes,
self-clean TiO2 coated glass slides, gloves, black rubberized fabric, safety goggles, stop watch or
some type of timing device (optional toothpicks for stirring).
ENGAGE:
The module begins with a question, “Scientists say the coal, natural gas, and oil are important
energy sources. How do we use these resources? We use them to power our cars, heat and cool
our houses to name a few. However, scientists suggest that we will run out of many of these fuels
in 150 years. Now think for a moment. Is there an energy resource that won’t run out for a long
time? The sun is such a source of energy. Scientists say that sunlight can be used as a
sustainable clean energy source to replace these three expensive energy sources. Ask students if
they agree or disagree with this statement. Have them discuss their views using prompts such as
how are coal, oil and natural gas and light similar? How are they different? Transition to the
activity below by asking students to create a concept web of their ideas about the following:
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University of Alabama, Shanlin Pan, Karen Boykin, Dawen Li, Dee Goldston
Ask: What do you know about light and its interactions with various forms of matter? How
does light behave when interacting with various surfaces?
Have students work in teams or create a class chart to develop a concept web of their ideas about
light and the way it interacts with surfaces.
Figure 1.
Light and how it
interacts with
various surfaces
EXPLORE:
Following the class discussion of the engage on light and its interactions with typical forms of
matter, students will conduct an activity to learn how light, a form of clean energy, interacts with
nanomaterials and visualize the reaction. Nanomaterials, by definition, are any materials with a
dimension less than a micrometer, or materials with a size smaller than 1/50 of the diameter of a
human hair. 1 nanometer is 1/1,000 of a micrometer, and 1/1,000,000,000 of a meter. It’s a very
small size unit and is tens of thousands of times smaller than living cells and human hair.
Investigation: How does light, a form of clean energy, behave when it interacts with Ti02
nanoparticles?
(Teacher Background) Ultraviolet (UV) light can degrade methanol from water in the presence
of TiO2 nanoparticles with a size of about 25 nanometers and this degradation process can be
dramatically enhanced in the presence of silver ions. The enhanced reaction can be visualized by
the presence of black/grey silver nanoparticles in a very short period of time (less than ten
seconds).
Activity 1.
Teacher Note: Before beginning, identify the names of the materials that will be used in the
activity. Students may not be familiar with some of the materials.
Students will work in teams. An assigned team leader will operate the UV lamp powered
by AA batteries. The team member operating the lamp will need to wear safety goggles for
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University of Alabama, Shanlin Pan, Karen Boykin, Dawen Li, Dee Goldston
UV light protection. All team members are required to wear gloves and safety goggles for
the following activities!
Procedures:
A. Fill a microcentrifuge tube with 0.5 mLof water containing silver ions using dropper pipet.
B. Using another new pipet, transfer 0.5 ml of methanol into the microcentrifuge tube with the
water solution from A. Mix the solution by gently shaking the tube, or you can stir the solution
with a toothpick.
C. Using another new pipet, transfer three drops of above solution from step B (methanol and
silver solution) into each of the three depressions of the provided spot plate.
D. Now, using another new dropper pipet, transfer two drops of the nanoparticle solution
(TiO2) into the second depression of the spot plate. Then transfer two drops of the nanoparticle
(TiO2) solution to the third depression of the spot plate. Shake the spot plate gently to mix the
solution in each of the depression. Then use the provided black rubberized fabric to cover the
third depression.
E. Place the second depression under a handheld UV lamp with its surface facing the lamp
Place the UV lamp about 2-3 cm or about an inch above the surface of the solution. Switch
on the UV lamp. Record the color of the solution you observe at 20 second intervals for 80
seconds in the chart below. (Have one student time, one student record and one student hold
the lamp. There should be no time elapse between readings)
Black Fabric
1
2
3
M/S
M/S
M/S
TiO₂
TiO₂
Complete the following time vs color of the solution in the second depression using the coded
color scale bellow. Please turn off UV light when checking the color of the solution.
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University of Alabama, Shanlin Pan, Karen Boykin, Dawen Li, Dee Goldston
Time vs Color Change of TiO2 Solution in depression 2
Record the color changes by using the code number shown in above color scale.
0 sec
20 sec
40 sec
60 sec
80 sec
If the color is not on the scale, place NOS (Not On Scale) in the box.
F. Place the first depression under a handheld UV lamp with its surface facing the lamp. Switch
on the UV lamp. Record the color of the solution you observe at 20 second intervals for 80
seconds the chart below.
Complete the following time vs color of the solution in the first depression using the coded color
scale bellow. Please turn off UV light when checking the color of the solution.
Time vs Color change of TiO2 Solution in depression 1
Record the color changes by using the code number shown in above color scale.
0 sec
20 sec
40 sec
60 sec
80 sec
G. Remove the black rubberized fabric on top of the third depression. What’s the color of the
solution in this depression? _________________________
What do you expect will happen if you turn the UV lamp on top of the third depression for ten
seconds? ______________________________
EXPLAIN:
Begin discussion of the investigation with the questions from the activity.
1. What was the purpose of irradiating the methanol and silver solution in the first
depression of the spot plate?
2. What variables were the same in all three spot plate depression solutions? Why was the
third depression covered with black rubberized fabric?
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University of Alabama, Shanlin Pan, Karen Boykin, Dawen Li, Dee Goldston
3. What changes did you observe when looking at the solution in the second depression
which includes TiO2, silver water solution, and methanol under UV light? How does it
compare to the silver ion water and methanol solution under UV light in the first
depression?
4. What do you think caused the changes you found in the second depression solution on
spot plate?
5. What questions do you have about the results you found? What do you think would
happen if you took the solutions out into sunlight? How would you develop an
investigation to answer that and other question(s) you may have?
Looking at the Time vs Color Change Data above. What do you notice about the changes in
color for each solution over the two minute time period?
Questions are asked of students so that they explain what they did and learned from the
activities. Using questions derived from the activities the students conducted, the teacher then
introduces the terminology associated with the concepts of the activities (e.g., visible light,
spectrum, matter, etc.). Develop student’s understanding of the unique interaction of light and
matter, the variations of how matter is constructed, and unique properties of nanoparticles.
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Spectral Radiation (W m nm )
Teacher Background: TiO2 nanoparticles only
absorb ultraviolet (UV) light with wavelengths
Absorption of TiO2
less than 400 nm as shown in the shadowed
2.0
region in above figure. When light in this short
Solar Spectrum
1.5
wavelength is absorbed by TiO2, the electrons in
TiO2 are excited to higher energy levels. Since
1.0
the excited electrons have very negative energy
level they can reduce silver ions to produce silver
0.5
nanoparticles on TiO2 surface. Small silver
clusters and nanoparticles have a grey and/or
0.0
200
400
600
800 1000 1200 1400
black color depending on their size. Meanwhile,
Wavelength (nm)
TiO2 nanoparticles becomes so positively charged
due to the removal of electrons that they can
Figure 2
interact with water to produce super active
species (form) that can interact with methanol molecules and degrade them. Therefore, the color
changing process of the solution in the presence of TiO2 nanoparticles can only take place under
UV light. However, the UV light only accounts a small fraction of the overall solar radiation
spectra as shown in above figure. All the light from sunlight will be wasted when we use solar
energy to work with TiO2 to degrade any organic complex in water, yielding poor efficiency of
the TiO2 photocatalyst. One would expect much higher efficiency if the nanoparticles can absorb
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University of Alabama, Shanlin Pan, Karen Boykin, Dawen Li, Dee Goldston
visible light up to 600 nm. It should be noticed that it is one of the biggest challenges scientists
are facing to develop visible-light sensitive nanomaterials that can be used to produce clean
energy at high efficiency using sun light.
Use the 3 D Simulation for the Module in conjunction with the discussion.
In addition, because TiO2 is a semi-conductor with interesting photochemical properties as
discussed above, it is used as a white pigment. When used as a pigment or as a UV absorber in
sunscreens, these small oxide nanoparticles can help clean contaminates on its surface under sun
light, therefore they can be used to form self-cleaning glass window.
Meanwhile, there are disadvantages when TiO2 is used in the destruction of pollutants because
when bare TiO2 is irradiated with UV light in solution, it completely destroys any organic
compounds close to its surface. As a result, any organic pollutants present are completely
mineralized to carbon dioxide, water and ammonium and chloride ions. CO2 is released to air
and as such it may contribute to the causes the global warming.
Teacher Note: After discussion of the activity’s concepts return to the concept web created
during the engage. Have students change, add or delete their earlier ideas based on what they
have learned in the activities to make a revised web. You may want them to do webs at their
tables in partners or do this as a whole class activity.
ELABORATE: Self-cleaning glass by definition is the glass that can
remove dirt from its surface under sunlight. First, let students
determine which side of the self-cleaning sample is coated with TiO2.
Students can check the light reflection properties of the glass surfaces
and compare with each other to see which side is more reflective. The
more reflective side should be the TiO2 side because of the high
reflection index of the surface coating layer. Ask students why the
glass can take care of itself under sunlight and is much cleaner than a
regular glass window as shown in above image. Teachers can also ask
students why the self-cleaning takes a long time to happen. What can
students do to improve the self-cleaning efficiency and quality of the
glass?
Image borrowed from selfcleaning-glass.com
Activity 2 (Optional). Which side is coated with TiO2
The teacher will distribute 1 piece of 22 cm2 square self-cleaning glass sample coated with
TiO2 to every group of students. The students will be asked to identify the side of the glass that
is coated with TiO2. One can identify the TiO2 side by looking at the light reflectivity at the
edges of the sample. The more reflective side is coated with TiO2. However, it isn’t easy to tell.
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University of Alabama, Shanlin Pan, Karen Boykin, Dawen Li, Dee Goldston
Have student figure out what side is the coated side by looking at the glass. Alternative method
is to find the TiO2 coating layer by using the knowledge from activity 1.
Hint: Guessing which side is coated and then adding two drops of silver solution and methanol
from step B of activity 1 and exposing it to UV lamp. It doesn’t matter which side they use
because if there is no change they know it is the other side and if there is a color change they
have the coated side up. Students will need to remove the droplets after irradiating it with UV
lamp for 30 sec and dry the glass before observing the color change because the surface area of
TiO2 is much smaller than the one of TiO2 nanoparticles in activity 1.
Ask the following:
By doing this investigation, how can you identify the coated self-cleaning side of the glass?
________________________________________________________________________
Here students will discuss and think about new ideas to extend their knowledge of optical
properties of light. These include, but are not limited to: (1) Students will discuss light
properties cleaning a dirty glass window in their classroom using TiO2 and sun light; (2)
Students will discuss how to use visible light to drive chemical reaction as TiO2 absorbs only in
UV region; and (3) Students will how to remove methanol, metal ions from contaminated water
using sunlight.
Evaluate:
Post-test content specific information for the module includes:
1. What wavelengths of light were used to excite TiO2?
2. What is the electromagnetic spectrum?
3. Compare the electromagnetic spectrum to UV light used in the investigation.
4. What is a control?
4. What happens to the methanol and silver ions?
5. What is responsible for the change on the self-clean glass surface? Explain
6. Describe properties of light.
7. Given a choice, would you select sunlight or electricity for cleaning up waste? Why?
8. What other natural phenomenon do you think may be related to light?
Safety: Use safety goggles when an UV lamp is used. Use gloves with chemicals. All
students use safety goggles.
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University of Alabama, Shanlin Pan, Karen Boykin, Dawen Li, Dee Goldston
Additional information and Q&A for teachers:
1. If nano particles interact differently than what we would expect in a normal chemical
reaction, then what is different about TiO2 nanoparticles with respect to the chemical
oxidation of methanol and silver removal procedure?
First, the methanol degradation reaction would not take place effectively in pure
water without TiO2 nanoparticles. Now, the question- how does the small size of
TiO2 make a difference when compared to TiO2 film or blocks. The answer is that
small particles provide a large surface area to interact with more methanol
molecules so one expects more efficiency from small nanoparticle. Secondly, one
would have a stable suspension of such small TiO2 in water to avoid
agglomeration. Last, light travels through small particle solutions easily. Large
particles will scatter the light and make the solution cloudy, so less TiO2 absorbs
light. Small particles can also change the electronic structure so it will cause
differences in the reaction efficiency and light absorption efficiency as well.
Better understanding of the system requires deep understanding of advanced
physics.
2. What exactly takes place on the surface of TiO2 at the microscopic scale when the
methanol is removed by TiO2?
When we talk about nanoparticles, their size is thousands of times smaller than
that of a molecule which are participating the reaction. The microscopic chemical
reaction will take place at the surface of individual nanoparticles. Such
nanoparticle scale and molecular scales would not be obvious to students as we
demonstrate the module, therefore we need to use animation and 3D
demonstration.
3. Useful terms and concepts associated with this module:
a. Nanometer, nanoparticles: particles with their size in the range of nanometer
scale.
b. UV light: light with wavelength from 200 nm to 400 nm, can cause skin cancer
and damage to cell and protein. Sunlight has small portion of UV light.
c. Photocatalyst: substances that can improve chemical reaction efficiency under
light without changing their own stability and properties.
d. Catalyst: substances that can enhance chemical reaction without changing their
own properties.
e. Electron: smallest unit in a molecule and atom with negative charge and smallest
mass in atom.
f. Charges: can be positive and negative and can move in electrical field.
g. Photoexcitation: illumination with light
h. Efficiency: yield of product per reactant provided.
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