Ozone, UV, and Nanoparticles Mort Sternheim STEM Education Institute STEM ED/CHM Nanotechnology 2011.
Presentation on theme: "Ozone, UV, and Nanoparticles"— Presentation transcript:
1 Ozone, UV, and Nanoparticles Mort SternheimSTEM Education Institute6/29/2008
2 Ozone, UV, and Nanoparticles Today’s agendaOzone and ultraviolet lightNanoparticles and sunscreenHands on activitySunscreen PowerPoint and activities based onNanoSense web site:Ozone and ultraviolet lightNanoparticles and sunscreenHands on activitySunscreen PowerPoint and activities based onNanoSense web site:
3 Ozone, UV, and Nanoparticles The big ideasUltraviolet light causes skin damage and cancerOzone in the stratosphere blocks UVSunscreen blocks UV, partlyNanoparticles in sunscreen improve blocking
4 Ozone, UV, and Nanoparticles 1. What is ozone?Ordinary oxygen gas: O2 (2 oxygen atoms)Ozone: O3 (3 oxygen atoms)Polar molecule, like waterOzone is much more reactive, unstablePale blue, poisonous gas Bad!Absorbs ultraviolet radiation! Good!
5 The Sun’s radiation spectrum Ozone, UV, and NanoparticlesThe Sun’s radiation spectrumMost 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 NanoparticlesSome types of electromagnetic radiationThe sun emits several kinds of electromagnetic radiation: Visible (Vis), Infrared (IR) and Ultra Violet (UV). Note the split into UVA, UVB, UVCEach kind is distinguished by a characteristic wavelength, frequency and energyHigher energy radiation can damage our skinHigh Energy Low EnergySource:
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 bySince c (the speed of light) is constant, the wavelength and frequency are inversely relatedThis 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 NanoparticlesRadiation energy comes in packets or photonsThe size of an energy packet or photon (E) is determined by the frequency of the radiation (f)E fEfRadiation with a higher frequency has more energy in each packetThe amount of energy in a packet determines how it interacts with our skin
9 Ozone, UV, and Nanoparticles Skin DamageVery high energy radiation (UVC) is currently blocked by the ozone layerHigh energy radiation (UVB) does the most immediate damage (sunburns)But lower energy radiation (UVA) can penetrate deeper into the skin, leading to long term damageSource: 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 Good ozoneIn the stratosphere, absorbs 97+ % of solar UV, protecting life from harmProduced by solar UV light from O2 :O2 + UV (radiation < 240 nm) → 2 OO + O2 → O3Ozone – oxygen cycle:O3 + UV (< 320 nm) → O2 + OThis cycle heats the atmosphere slightly, so ozone is a minor greenhouse gas
11 Ozone, UV, and Nanoparticles Ozone is the Earth’s natural sunscreen10060Thermosphere8050UVc - 100% AbsorptionMesosphereUVb - 90% AbsorptionUVa - 50% Absorption & Scattering4060Altitude (km)Altitude (miles)3040202010Troposphere2468Ozone (parts per million)1111
12 Ozone, UV, and Nanoparticles Ozone layerOzone in stratosphere, 10 to 50 km above surfaceOzone Can be depleted by free radical catalysts – NO, OH, Cl, Br – from natural sourcesAlso from chlorofluorocarbons (CFCs) (freons) and bromofluorocarbons (halons)UV light produces free Cl, Br radicalsCl, Br catalyze chain reactions destroying ~100,000 ozone moleculesUsed in aerosols, refrigerators, air conditioners, fire extinguishers
13 Chemicals that Destroy Stratospheric Ozone Ozone, UV, and NanoparticlesChemicals that Destroy Stratospheric OzoneCl is much more abundant than BrBr is about 50 times more effective at O3 destructionFrom Ozone FAQ - seeFrom Ozone FAQ - see13
14 Ozone, UV, and Nanoparticles Ozone depletionStratospheric ozone levels decreasing ~4% per year since ’70’sMore skin cancer?Larger seasonal decrease in lower altitudes (troposphere) in polar regions: the ozone holeCFC’s phased out globally by 1996 (Montreal Protocol, 1987) – will take decades to leave atmosphereOzone levels have stabilizedRecovery will take decades
15 2. Nanoparticles and sunscreen Ozone, UV, and Nanoparticles2. Nanoparticles and sunscreenNanoparticles: 1 to 100 nm in diameter, or about 10 to 1000 atomic diametersNumber of products using nanomaterials is growing very rapidlyDoubling every year?Clothing, food and beverages, sporting goods, coatings, cosmetics, personal careSunscreens: many use nanomaterialsSome labeled as containing nanoparticlesSome not labeled
17 Ozone, UV, and Nanoparticles Why Use Sunscreen?Too much unprotected sun exposure leads to:Premature skin aging (e.g. wrinkles)SunburnsSkin cancerSources:
18 Skin Cancer Rates are Rising Fast Ozone, UV, and NanoparticlesSkin Cancer Rates are Rising FastProbability of getting skin cancer:1930 : 1 in 5,0002004 : 1 in 652050 : 1 in 10…Skin cancer:Is ~50% of all cancer casesHas > 1 million cases diagnosed each yearCauses 1 person to die every hourCauses of the increase:Decreased ozone protectionIncreased time in the sunIncreased use of tanning bedsSources: ;
19 Ozone, UV, and Nanoparticles Sun Radiation SummaryRadiationTypeCharacteristicWavelength (l)Energy per Photon% ofTotal RadiationReaching EarthEffects on Human SkinVisible to Human Eye?UVC~ nm(Short-wave UV)High Energy~0%(<1% of all UV)DNA DamageNoUVB~ nm(Mid-range UV)Medium Energy~.35%(5% of all UV)SunburnSkin CancerUVA~ nm(Long-wave UV)Low Energy~6.5%(95 % of all UV)TanningSkin AgingVis~ nmLower Energy~43 %YesIR~ ,000 nmLowest Energy~49%IncreasingEnergyIncreasingWavelength
20 Which Sunscreen Should You Use??? Ozone, UV, and NanoparticlesWhich Sunscreen Should You Use???New and ImprovedNow with Nano-ZBroadband ProtectionSafe for ChildrenSPF 50Goes on Clear
21 A Brief History of Sunscreens: The Beginning Ozone, UV, and NanoparticlesA Brief History of Sunscreens: The BeginningFirst developed for soldiers in WWII (1940s) to block “sunburn causing rays”These were called UVB raysWWII soldier in the sunShorter wavelengths (more energy) called UVCLonger wavelengths (less energy) called UVASources:
22 A Brief History of Sunscreens: The SPF Rating Ozone, UV, and NanoparticlesA Brief History of Sunscreens: The SPF RatingSunscreens first developed to prevent sunburnIngredients were good UVB blockersSPF (Sunscreen Protection Factor) NumberMeasures the strength of UVB protection onlyHigher SPF # = more protection from UVBDoesn’t tell you anything about protection from UVASources: and
23 A Brief History of Sunscreens: The UVA Problem Ozone, UV, and NanoparticlesA Brief History of Sunscreens: The UVA ProblemUVA rays have no immediate visible effects but cause serious long term damageCancerSkin agingSunscreen makers working to find UVA blockersNo official rating of UVA protection yetTwenty different skin cancer lesionsSource:
24 Ozone, UV, and Nanoparticles How do you know if your sunscreen is a good UVA blocker?
25 Know Your Sunscreen: Look at the Ingredients Ozone, UV, and NanoparticlesKnow Your Sunscreen: Look at the IngredientsUV blocking agents suspended in a lotion“Colloidal suspension”Two kinds of active ingredientsOrganic ingredients and inorganic ingredientsLotion has “inactive ingredients”Don’t block UV lightUV blocking agents are “active ingredients”Usually have more than one kind presentSource: Original Image
26 Organic Ingredients: The Basics Ozone, UV, and NanoparticlesOrganic Ingredients: The BasicsOrganic = Carbon AtomsHydrogen, oxygen & nitrogen atoms are also often involvedStructureCovalent bondsExist as individual moleculesSizeMolecular formula determines sizeTypical a few to several dozen Å (<10 nm)Octyl methoxycinnamate (C18H26O3)an organic sunscreen ingredientSources: and original image
27 Organic Ingredients: UV Absorption Ozone, UV, and NanoparticlesOrganic Ingredients: UV AbsorptionElectrons capture the energy from UV raysThey jump to higher energy levelsThe energy is released as infrared rays which are harmless (each ray is low in energy)hf=2.48 eV3hf=2.48 eVSource: Adapted from
28 Organic Ingredients: Absorption Range Ozone, UV, and NanoparticlesOrganic Ingredients: Absorption RangeOrganic molecules only absorb UV rays whose energy matches difference between electron energy levelsDifferent kinds of molecules have different peaks and ranges of absorptionUsing more than one kind of ingredient (molecule) gives broader protectionOne Ingredient Two Ingredients Three IngredientsSource: Graphs adapted from
29 Organic Ingredients: Absorption Range cont. Ozone, UV, and NanoparticlesOrganic Ingredients: Absorption Range cont.Most organic ingredients that are currently used were selected because they are good UVB absorbersThe FDA has approved 15 organic ingredientsSunscreen makers are trying to develop organic ingredients that are good UVA blockersAvobenzone (also known as Parasol 1789) is a new FDA approved UVA blockerSource:
30 Ozone, UV, and Nanoparticles How are inorganic sunscreen ingredients different from organic ones?How might this affect the way they absorb UV light?
31 Inorganic Ingredients: The Basics Ozone, UV, and NanoparticlesInorganic Ingredients: The BasicsAtoms involvedZinc or TitaniumOxygenStructureIonic molecules: ZnO, TiO2Cluster of ionsFormula unit doesn’t dictate sizeCluster (particle) sizeVaries with # of ions in cluster~10 nm – 300 nmDetail of the ions in one clusterGroup of TiO2 particlesSource: and image adapted from
32 Inorganic Ingredients: Cluster Size Ozone, UV, and NanoparticlesInorganic Ingredients: Cluster SizeInorganic ingredients come in different cluster sizes (sometimes called “particles”)Different number of ions can cluster togetherMust be a multiple of the formula unitZnO always has equal numbers of Zn and O atomsTiO2 always has twice as many O as Ti atoms~100 nm TiO2 particle ~200 nm TiO2 particleSource: Images adapted from
33 Inorganic Ingredients: UV Absorption Ozone, UV, and NanoparticlesInorganic Ingredients: UV AbsorptionInorganics have a different absorption mechanism than organicsAbsorb consistently through whole UV range up to ~380nmSource: Graph adapted from
34 Ozone, UV, and Nanoparticles Why not use inorganics?Appearance MattersTraditional inorganic sunscreens have appear white on our skinMany people don’t like how this looks, so they don’t use sunscreen with inorganic ingredientsOf the people who do use them, most apply too little to get full protectionSource:
35 Why Do They Appear White? Ozone, UV, and NanoparticlesWhy 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 clustersThe scattered light is reflected to our eyes, appearing whiteSource: Original image
36 Organic Sunscreen Molecules are Too Small to Scatter Light Ozone, UV, and NanoparticlesOrganic 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 and
37 Ozone, UV, and Nanoparticles Waves and obstaclesWaves go around small obstaclesWaves scatter all around from obstacles of sizes comparable to a wavelengthWater wave (ripple tank) simulation:
38 Ozone, UV, and Nanoparticles What could we do to inorganic clusters to prevent them from scattering visible light?Source: Adapted from
39 Nanosized Inorganic Clusters Ozone, UV, and NanoparticlesNanosized Inorganic ClustersMaximum scattering occurs for wavelengths twice as large as the clustersMake the clusters smaller (100 nm or less) and they won’t scatter visible lightSource: Graph adapted from
40 Ozone, UV, and Nanoparticles In Summary…Nanoparticle sunscreen ingredients are small inorganic clusters that:Provide good UV protection by absorbing both UVB and UVA lightAppear clear on our skin because they are too small to scatter visible lightSource:
41 Essential Questions: Time for Answers Ozone, UV, and NanoparticlesEssential Questions: Time for AnswersWhat are the most important factors to consider in choosing a sunscreen?How do you know if a sunscreen has “nano” ingredients?How do “nano” sunscreen ingredients differ from other ingredients currently used in sunscreens?
42 3. Testing sunscreen activity Ozone, UV, and Nanoparticles3. Testing sunscreen activityUse UV sensitive beadsCompare opacity/ transparency of samples for visible light and UV light
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