Download presentation
Presentation is loading. Please wait.
1
STEM ED/CHM Nanotechnology 2012
Ozone, UV, and Nanoparticles Mort Sternheim STEM Education Institute
2
Ozone, UV, and Nanoparticles
Today’s agenda Ozone and ultraviolet light Nanoparticles and sunscreen Hands on activity Sunscreen PowerPoint and activities based on NanoSense web site: Ozone and ultraviolet light Nanoparticles and sunscreen Hands on activity (brief) Sunscreen PowerPoint and activities based on NanoSense web site:
3
Ozone, UV, and Nanoparticles
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
4
1. Ozone and Ultraviolet Light What is ozone?
Ozone, UV, and Nanoparticles 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!
5
The Sun’s radiation spectrum
Ozone, UV, and Nanoparticles 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
6
Some types of electromagnetic radiation
Ozone, UV, and Nanoparticles 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 Each kind is distinguished by a characteristic wavelength, frequency and energy Higher energy radiation can damage our skin High Energy Low Energy Source:
7
Ozone, UV, and Nanoparticles
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:
8
Radiation energy comes in packets or photons
Ozone, UV, and Nanoparticles 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 f E f 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
9
Ozone, UV, and Nanoparticles
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; p
10
Ozone, UV, and Nanoparticles
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 / human sources (CFC’s) 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
11
Ozone, UV, and Nanoparticles
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
12
2. Nanoparticles and sunscreen
Ozone, UV, and Nanoparticles 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 Clothing, food and beverages, sporting goods, coatings, cosmetics, personal care, electronics Sunscreens: many use nanomaterials Some labeled as containing nanoparticles Some not labeled
13
Ozone, UV, and Nanoparticles
14
Ozone, UV, and Nanoparticles
Why Use Sunscreen? Too much unprotected sun exposure leads to: Premature skin aging (e.g. wrinkles) Sunburns Skin cancer Sources:
15
Skin Cancer Rates are Rising Fast
Ozone, UV, and Nanoparticles 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: ;
16
A Brief History of Sunscreens: The Beginning
Ozone, UV, and Nanoparticles 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:
17
A Brief History of Sunscreens: The SPF Rating
Ozone, UV, and Nanoparticles 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 UVA causes cancer, skin aging No official UVA ratings until now Sources: and
18
Ozone, UV, and Nanoparticles
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
19
How much UV is there today
Ozone, UV, and Nanoparticles How much UV is there today EPA UV index 1 = low risk, 11+ = extreme risk Sometimes included in weather reports Reflective surfaces (concrete, sand, snow, water) may make actual level higher than reported Free Smartphone App: myUV Alert
20
Ozone, UV, and Nanoparticles
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.
21
Know Your Sunscreen: Look at the Ingredients
Ozone, UV, and Nanoparticles Know Your Sunscreen: Look at the Ingredients UV blocking agents suspended in a lotion “Colloidal suspension” Two kinds of active ingredients Organic ingredients and inorganic ingredients Lotion has “inactive ingredients” Don’t block UV light UV blocking agents are “active ingredients” Usually have more than one kind present Source: Original Image
22
Organic Ingredients: The Basics
Ozone, UV, and Nanoparticles 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 Typically < 10 nm Octyl methoxycinnamate (C18H26O3) an organic sunscreen ingredient Sources: and original image
23
Organic Ingredients: UV Absorption
Ozone, UV, and Nanoparticles Organic Ingredients: UV Absorption Electrons capture the energy from UV rays They jump to higher energy levels The energy is released as infrared rays which are harmless (each ray is low in energy) hf=2.48 eV 3hf=2.48 eV Source: Adapted from
24
Organic Ingredients: Absorption Range
Ozone, UV, and Nanoparticles 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 & ranges of absorption; usually in UVB region Using more than one kind of ingredient (molecule) gives broader protection One Ingredient Two Ingredients Three Ingredients Source: Graphs adapted from
25
Inorganic Ingredients: The Basics
Ozone, UV, and Nanoparticles Inorganic Ingredients: The Basics Atoms: 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 Absorb thru whole UV spectrum up to 380 nm Detail of the ions in one cluster Group of TiO2 particles Source: and image adapted from
26
Ozone, UV, and Nanoparticles
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:
27
Why Do They Appear White?
Ozone, UV, and Nanoparticles Why Do They Appear White? Traditional ZnO and TiO2 clusters are large (> 200nm) Large clusters scatter visible light ( 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
28
Ozone, UV, and Nanoparticles
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: Organic sunscreen molecules are too small to scatter light ( < 10 nm) How does absorption of light by inorganic compounds differ from absorption by organic molecules?
29
Inorganic Compounds: Energy Levels
29 Inorganic Compounds: Energy Levels Inorganic ingredients exist as particle clusters Very large number of atoms involved Electrons’ energy depends on their position in relation to all of them Huge number of different energy levels possible ~200 nm TiO2 particle Source: Images adapted from
30
Inorganic Compounds: Absorption I
30 Inorganic Compounds: Absorption I Because the energy levels are so closely spaced, we talk about them together as energy “bands” Normal energy band for electrons (ground states) is called the “valence band” Higher energy band (electrons are more mobile) is called the “conduction band” In each band, there are many different energies that an electron can have The energy spacing between the two bands is called the "energy gap” or "band gap“ Source: Original Image
31
Inorganic Compounds: Absorption II
31 Inorganic Compounds: Absorption II Electrons can “jump” from anywhere in the valence band to anywhere in the conduction band Inorganic Compounds are able to absorb all light with energy equal to or greater than the band gap energy Source: Original Images
32
Inorganic Compounds: Absorption Curve
32 Inorganic Compounds: Absorption Curve This is the same as saying that all light absorbed must have a wavelength equal to or less than the wavelength corresponding to the band gap energy Absorption curves have sharp cutoffs at this l Cutoff l is characteristic of the kind of compound Doesn’t depend on size of the cluster Source: Graph adapted from
33
Inorganic Compounds: UV Protection
33 Inorganic Compounds: UV Protection Inorganic Compounds with cut off wavelengths around 400 nm (ZnO and TiO2) are able to absorb almost the whole UV spectrum Can be the only active ingredient in a sunscreen Can also be combined with other ingredients for reasons such as appearance or cost True for both nano and traditional forms (not dependant on size) Source: Graph adapted from
34
Absorption Summary Atoms Organic Molecules Inorganic Compounds
34 Absorption Summary Atoms Organic Molecules Inorganic Compounds Energy Levels Absorption Spectrum
35
Nanosized Inorganic Clusters
Ozone, UV, and Nanoparticles 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
36
Ozone, UV, and Nanoparticles
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:
37
3. Testing sunscreen activity
Ozone, UV, and Nanoparticles 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
38
Teacher note highlights
Ozone, UV, and Nanoparticles Teacher note highlights Safety. Do not look directly at the UV lamp Liquids. Apply directly to bead or to clear plastic strips Purchasing. See teacher notes handout Making the testers. Melt beads in oven, glue to sticks
39
Ozone, UV, and Nanoparticles
Available documents Handouts More on the website This PowerPoint Teacher guide Student write-up Consumer Reports sunscreen ratings UV violet color guide Controlled Experiment On The Transmission Of Ultra-Violet Radiation (Jennifer) Web links UVA standards articles Sunscreen clothing – does it work?
Similar presentations
