Transcript Ozone, UV and nanoparticles

STEM ED/CHM Nanotechnology 2011
Ozone, UV, and Nanoparticles
Mort Sternheim
STEM Education Institute
[email protected]
Today’s agenda
1. Ozone and ultraviolet light
2. Nanoparticles and sunscreen
3. Hands on activity (brief)
Sunscreen PowerPoint and activities based on
NanoSense web site:
http://nanosense.org/activities/clearsunscreen
The big ideas
•
•
•
•
Ultraviolet light causes skin damage and cancer
Ozone in the stratosphere blocks UV
Sunscreen blocks UV, partly
Nanoparticles in sunscreen improve blocking
1. Ozone and Ultraviolet Light
What is ozone?
• Ordinary oxygen gas:
O2 (2 oxygen atoms)
• Ozone: O3 (3 oxygen
atoms)
• Polar molecule, like
water
• Ozone is much more
reactive, unstable
• Pale blue, poisonous
gas Bad!
• Absorbs ultraviolet
radiation! Good!
The Sun’s radiation spectrum
Most of the sun’s radiation is Ultraviolet (UV),
Visible & Infrared (IR) :
• ~ 43% is in the visible
range
• ~ 49% is in the near
infrared range
• ~ 7% is in the
ultraviolet range
.
• < 1% is x-rays, gamma
rays, radio waves
Source: Adapted from http://www.ucar.edu/learn/imgcat.htm
Some types of electromagnetic radiation
• The sun emits several kinds of electromagnetic
radiation: Visible (Vis), Infrared (IR) and Ultra
Violet (UV). Note the split into UVA, UVB, UVC
High Energy
Low Energy
• Each kind is distinguished by a characteristic
wavelength, frequency and energy
• Higher energy radiation can damage our skin
Source: http://www.arpansa.gov.au/is_sunys.htm
What is Radiation?
• Light radiation is often thought
of as a wave with a wavelength
(l), speed (c), and frequency (f)
related by
• Since c (the speed of light) is constant, the
wavelength and frequency are inversely related
• This means that light with a short wavelength will
have a high frequency and visa versa.
Source: http://www.pueblo.gsa.gov/cic_text/health/sun_uv/sun-uv-you.htm
Radiation energy comes in packets or
photons
•
The size of an energy packet or photon (E) is
determined by the frequency of the radiation
(f)
E
•
•
Radiation with a higher
frequency has more energy in
each packet
The amount of energy in a
packet determines how it
interacts with our skin
Ef
f
Skin Damage
• Very high energy
radiation (UVC) is
currently blocked by the
ozone layer
• High energy radiation
(UVB) does the most
immediate damage
(sunburns)
• But lower energy
radiation (UVA) can
penetrate deeper into the
skin, leading to long term
damage
Source: N.A. Shaath. The Chemistry of Sunscreens. In: Lowe NJ, Shaath NA, Pathak MA, editors. Sunscreens, development,
evaluation, and regulatory aspects. New York: Marcel Dekker; 1997. p. 263-283.
Good ozone
• In the stratosphere, absorbs 97+ % of solar UV,
protecting life from harm
• Produced by solar UV light from O2 :
– O2 + UV (radiation < 240 nm) → 2 O
– O + O2 → O3
• Ozone – oxygen cycle:
– O3 + UV (< 320 nm) → O2 + O
• This cycle heats the atmosphere slightly, so
ozone is a minor greenhouse gas
Ozone is the Earth’s natural sunscreen
100
60
Thermosphere
UVc - 100% Absorption
Mesosphere
UVb - 90% Absorption
UVa - 50% Absorption & Scattering
50
40
60
30
40
20
20
10
Troposphere
0
0
2
4
6
Ozone (parts
per million)
11
8
0
Altitude (miles)
Altitude (km)
80
Ozone layer
• Ozone in stratosphere, 10 to 50 km above
surface
• Ozone Can be depleted by free radical catalysts –
NO, OH, Cl, Br – from natural sources
• Also from chlorofluorocarbons (CFCs) (freons)
and bromofluorocarbons (halons)
– UV light produces free Cl, Br radicals
– Cl, Br catalyze chain reactions destroying
~100,000 ozone molecules
• Used in aerosols, refrigerators, air conditioners,
fire extinguishers
Chemicals that Destroy
Stratospheric Ozone
Other gases
Methyl chloroform (CH3CCl 3)
HCFCs (e.g., HCFC-22 = CHClF 2)
CFC-113 (CCl 2FCClF 2)
1%
4%
5%
7%
3400
3000
Other halons
20
Carbon tetrachloride
(CCl 4)
12%
14%
Halon-1301 (CBrF3)
Halon-1211 (CBrCIF 2)
15
CFC-11 (CCl 3F)
20%
5-20%
2000
23%
4%
Methyl bromide (CH3Br)
10
CFC-12 (CCl 2F2)
1000
5
32%
0
Natural
sources
16%
27-42%
Methyl chloride (CH3Cl)
0
Very-s hort live d gas e s
(e.g., bromoform = CHBr 3)
15%
• Cl is much more abundant than Br
• Br is about 50 times more effective at O3 destruction
From Ozone FAQ - see http://www.unep.org/ozone/faq.shtml
Ozone depletion
• Stratospheric ozone levels decreasing ~4% per
year since ’70’s
• More skin cancer?
• Larger seasonal decrease in lower altitudes
(troposphere) in polar regions: the ozone hole
• CFC’s phased out globally by 1996 (Montreal
Protocol, 1987) – will take decades to leave
atmosphere
• Ozone levels have stabilized
• Recovery will take decades
2. Nanoparticles and sunscreen
• Nanoparticles: 1 to 100 nm in diameter, or about
10 to 1000 atomic diameters
• Number of products using nanomaterials is
growing very rapidly
– Doubling every year?
• Clothing, food and beverages, sporting goods,
coatings, cosmetics, personal care
• Sunscreens: many use nanomaterials
– Some labeled as containing nanoparticles
– Some not labeled
http://www.masspolicy.org/p
df/workshop/rejeski.pdf
http://www.nanotechproject.org/inventories/consumer/analysis_draft/
Why Use Sunscreen?
Too much unprotected sun exposure
leads to:
•
Premature skin aging (e.g. wrinkles)
•
Sunburns
•
Skin cancer
Sources: http://www.oasishospital.org/previousnews.html; http://wohba.com/archive/2005_03_01_archive.html
Skin Cancer Rates are Rising Fast
Probability of
getting skin cancer:
1930 : 1 in 5,000
2004 : 1 in 65
2050 : 1 in 10…
Skin cancer:
• Is ~50% of all cancer
cases
• Has > 1 million cases
diagnosed each year
• Causes 1 person to die
every hour
Causes of the increase:
• Decreased ozone protection
• Increased time in the sun
• Increased use of tanning beds
Sources: http://www.msnbc.msn.com/id/8379291/site/newsweek/ ;
http://www.skincarephysicians.com/skincancernet/whatis.html; http://www.msu.edu/~aslocum/sun/skincancer.htm
Sun Radiation Summary
Radiation
Type
Characteristic
Wavelength (l)
Energy per
Photon
% of
Total Radiation
Reaching Earth
Effects on
Human Skin
Visible
to
Human
Eye?
UVC
~200-290 nm
(Short-wave UV)
Increasing
Energy
~0%
DNA Damage
No
High Energy
(<1% of all UV)
Sunburn
DNA Damage
Skin Cancer
No
Tanning
Skin Aging
DNA Damage
Skin Cancer
No
UVB
UVA
~290-320 nm
(Mid-range UV)
~320-400 nm
(Long-wave UV)
Vis
~400-700 nm
IR
~700-120,000 nm
Increasing
Wavelength
Medium Energy
~.35%
(5% of all UV)
~6.5%
Low Energy
Lower Energy
Lowest Energy
(95 % of all UV)
~43 %
Yes
~49%
No
Which Sunscreen Should You Use???
New and Improved
Now with Nano-Z
Broadband Protection
Safe for Children
SPF 50
Goes on Clear
A Brief History of Sunscreens:
The Beginning
• First developed for soldiers
in WWII (1940s) to block
“sunburn causing rays”
These were called UVB rays
WWII soldier in the sun
Shorter wavelengths
(more energy) called UVC
Longer wavelengths
(less energy) called UVA
Sources: http://www.bbc.co.uk/wiltshire/content/articles/2005/05/05/peoples_war_feature.shtml
http://www.arpansa.gov.au/is_sunys.htm
A Brief History of Sunscreens:
The SPF Rating
• Sunscreens first developed to prevent sunburn
– Ingredients were good UVB blockers
• SPF (Sunscreen
Protection Factor)
Number
– Measures the strength of
UVB protection only
– Higher SPF # = more
protection from UVB
– Doesn’t tell you anything
about protection from UVA
Sources: http://www.shop.beautysurg.com/ProductImages/skincare/14521.jpg and
http://www.shop.beautysurg.com/ProductImages/skincare/14520.jpg
A Brief History of Sunscreens:
The UVA Problem
• UVA rays have no
immediate visible effects
but cause serious long
term damage
– Cancer
– Skin aging
• Sunscreen makers
working to find UVA
blockers
– No official rating of UVA
protection yet
Source: http://www.cs.wright.edu/~agoshtas/fig8.jpg
Twenty different skin cancer lesions
How do you know if your
sunscreen is a good UVA blocker?
Proposed UVA Ratings (2010)
• Label will state whether
there is UVA protection,
but not how much
• There is no present
standard for UVA
• Proposed 1 to 4 star
system for UVA protection
for “low protection” to
“highest protection”
• Debate: is this dual system
confusing or helpful?
• Plan has been scrapped
New FDA UVA Ratings (2012)
• The phrase “broad
spectrum” is meant to
indicate protection
against UVA
• Products labeled
“broad spectrum” will
have to provide equal
protection against
UVB and UVA
• Bathing suits: 3 tbsp
every 2 hours
Clothing
• Ordinary clothing provides a good sun shield
when dry (the tighter the weave, the better) but
little or no protection when wet
• Special sun-protective clothing is costly but
works well wet or dry; it is a wise investment for
children who tend to stay in or around water for
hours.
Know Your Sunscreen:
Look at the Ingredients
• UV blocking agents suspended in a lotion
– “Colloidal suspension”
• Lotion has “inactive
ingredients”
– Don’t block UV light
• UV blocking agents are
“active ingredients”
– Usually have more than
one kind present
• Two kinds of active ingredients
– Organic ingredients and inorganic ingredients
Source: Original Image
Organic Ingredients: The Basics
• Organic = Carbon Atoms
– Hydrogen, oxygen & nitrogen
atoms are also often involved
• Structure
– Covalent bonds
– Exist as individual molecules
• Size
– Molecular formula determines
size
– Typical a few to several dozen
Å (<10 nm)
Sources: http://www.3dchem.com/molecules.asp?ID=135# and original image
Octyl methoxycinnamate (C18H26O3)
an organic sunscreen ingredient
Organic Ingredients: UV Absorption
1. Electrons capture
the energy from UV
rays
2. They jump to
higher energy
levels
hf=2.48 eV
3. The energy is
released as infrared
rays which are
harmless (each ray
is low in energy)
3hf=2.48 eV
Source: Adapted from http://www.3dchem.com/molecules.asp?ID=135#and http://members.aol.com/WSRNet/tut/absorbu.htm
Organic Ingredients: Absorption Range
• Organic molecules only absorb UV rays whose
energy matches difference between electron
energy levels
– Different kinds of molecules have different peaks
and ranges of absorption
– Using more than one kind of ingredient (molecule)
gives broader protection
One Ingredient
Two Ingredients
Three Ingredients
Source: Graphs adapted from http://www.aims.gov.au/pages/research/projects/sunscreens/pages/sunscreens02.html
Organic Ingredients:
Absorption Range cont.
• Most organic ingredients that are currently used
were selected because they are good UVB
absorbers
– The FDA has approved 15 organic ingredients
• Sunscreen makers are trying to develop organic
ingredients that are good UVA blockers
– Avobenzone (also known as Parasol 1789) is a new
FDA approved UVA blocker
Source: http://jchemed.chem.wisc.edu/JCEWWW/Features/MonthlyMolecules/2004/Oct/JCE2004p1491fig4.gif
How are inorganic sunscreen
ingredients different from organic
ones?
How might this affect the way
they absorb UV light?
Inorganic Ingredients: The Basics
• Atoms involved
– Zinc or Titanium
– Oxygen
• Structure
– Ionic molecules: ZnO, TiO2
– Cluster of ions
– Formula unit doesn’t dictate
size
• Cluster (particle) size
– Varies with # of ions in cluster
– ~10 nm – 300 nm
Detail of the ions in
one cluster
Group of TiO2 particles
Source: http://www.microspheres-nanospheres.com/Images/Titania/TIO2%20P7.jpg and image adapted from
http://www.cse.clrc.ac.uk/msi/projects/ropa.shtml
Inorganic Ingredients: Cluster Size
• Inorganic ingredients come in different cluster
sizes (sometimes called “particles”)
– Different number of ions can cluster together
– Must be a multiple of the formula unit
• ZnO always has equal numbers of Zn and O atoms
• TiO2 always has twice as many O as Ti atoms
~100 nm TiO2 particle
Source: Images adapted from http://www.cse.clrc.ac.uk/msi/projects/ropa.shtml
~200 nm TiO2 particle
Inorganic Ingredients: UV Absorption
• Inorganics have a
different absorption
mechanism than
organics
• Absorb consistently
through whole UV
range up to ~380nm
Source: Graph adapted from http://www.aims.gov.au/pages/research/projects/sunscreens/pages/sunscreens02.html
Why not use inorganics?
• Appearance Matters
• Traditional inorganic
sunscreens have appear
white on our skin
• Many people don’t like
how this looks, so they
don’t use sunscreen with
inorganic ingredients
• Of the people who do use
them, most apply too little
to get full protection
Source: http://www.4girls.gov/body/sunscreen.jpg
Why Do They Appear White?
• Traditional ZnO and TiO2
clusters are large
– (> 200nm)
• Large clusters scatter
visible light
– (400-700 nm)
– Maximum scattering occurs
for wavelengths twice as
large as the clusters
• The scattered light is
reflected to our eyes,
appearing white
Source: Original image
Organic Sunscreen Molecules
are Too Small to Scatter Light
~200 nm TiO2 particle
Methoxycinnamate
(Inorganic)
(Organic)
(Note that these images are not drawn to scale)
Source: Images adapted from http://www.cse.clrc.ac.uk/msi/projects/ropa.shtml and http://www.3dchem.com/molecules.asp?ID=135#
Waves and obstacles
• Waves go around small obstacles
• Waves scatter all around from obstacles of sizes
comparable to a wavelength
• Water wave (ripple tank) simulation:
http://www.falstad.com/ripple/
What could we do to inorganic
clusters to prevent them from
scattering visible light?
Source: Adapted from http://www.loc.gov/rr/scitech/mysteries/images/sunscreen2.jpg
Nanosized Inorganic Clusters
• Maximum scattering occurs for wavelengths
twice as large as the clusters
– Make the clusters smaller (100 nm or less) and they
won’t scatter visible light
Source: Graph adapted from http://www.aims.gov.au/pages/research/projects/sunscreens/pages/sunscreens02.html
In Summary…
• Nanoparticle sunscreen ingredients are small
inorganic clusters that:
– Provide good UV protection by absorbing both UVB
and UVA light
– Appear clear on our skin because they are too small
to scatter visible light
Source: http://www.smalltimes.com/images/st_advancednanotech_inside_.jpg
Essential Questions: Time for Answers
1. What are the most important factors to consider
in choosing a sunscreen?
2. How do you know if a sunscreen has “nano”
ingredients?
3. How do “nano” sunscreen ingredients differ
from other ingredients currently used in
sunscreens?
3. Testing sunscreen activity
• Use UV sensitive beads
• Compare opacity/
transparency of
samples for visible
light and UV light
•
Beads absorb UV from
300 nm to 360 nm
(UV A is 320 – 400 nm,
UV B is 280 – 320 nm)
• Make UV detector
necklaces