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Remediation and Mitigation • Soil and Groundwater become contaminated due to industrial manufacturing processes • Industries have contaminated lakes, streams, groundwater, air and soil • Abandoned mines • Landfills • Underground storage tanks • Pollutants include • Heavy metals (cadmium, mercury, lead) • Organic compounds (benzene, chlorinated solvents, creosote) • Clean up of these sites are expensive, labor intensive, and time consuming.
Remediation and Mitigation • The use of nanotechnology allows for cleanup to occur in situ (where the contamination is) • More thorough because it can reach places standard remediation processes can’t (crevices and aquifers) • Allows for the treatment costs to be reduced. • Example: traditionally treating an aquifer (large underground water source) requires removal of the water (pump) and external treatment (treat) or “pump and treat” Nanotechnology would allow the water to be treated in the aquifer rather than pump and treat. • Allows treatment to be specific to a certain pollutant • Increases selectivity and sensitivity
Remediation and Mitigation • Drinking water contamination • Drinking water expected to be the “oil” of the 21st century • From pollutants such as • Arsenic • Mercury • Both are heavy metals that pose high health risks. • Nanotechnology can introduce methods that are fast, cheap, and effective. • Some remediation methods currently under investigation • Iron and bi-metallic nanoparticles • Semiconductor nanoparticles • Magnetic nanoparticles • dendrimers
Remediation • Remediation using metal Nanoparticles • Uses “non-valent” iron nanoparticles to remediate contaminated ground water. • Iron normally are charged and have either a +2 or +4 charge associated with them. Non-valent, or zero valent iron has no charge. • When iron rusts in the presence of certain toxic pollutants, it causes them to degrade into far less toxic pollutants. • PCB’s, Dioxins, tricholoethylene(TCE), Carbon tetrachloride • This works for new pollutants (recently produced) but not pollutants that have soaked into soil or groundwater. • Industry has tried remediating by using iron powder, however some of those pollutants don’t fully degrade and their byproducts are equally hazardous.
Remediation • This is because regular iron reacts slowly. • Over time these iron powder particles lose their ability to react with other substances as the surfaces become covered with layers of products from the reactions • Nanoparticles result in an increase in surface area that increases the reactivity of the particles as compared to larger particles. • 10-1000 times more effective than commonly used • More mobile, so easily transportable, remain in suspension longer • Effective against chlorinated organic solvents organochloride pesticides and PCB’s
Remediation using semiconductors • Uses semiconductor materials like TiO2 and ZnO2 (Titanium and Zinc oxides) in a Photocatalytic reaction. • Semiconductor materials can act as both conductors, or insulators. • Photocatalytic reaction is a reaction where sunlight speeds up or enables the reaction to occur.
Remediation using semiconductors • Both oxides are capable of transferring charge to pollutants which allows the pollutants to react to form less harmful byproducts like CO2, or H2O • Both oxides are plentiful (aka cheap!) • Both oxides absorb UV sunlight in order to cause the reaction with pollutants. However, their efficiency is limited because they only absorb UV light.
Remediation using semiconductors • Nanosizedparticles • would increase the surface area available to react with pollutants. • When attached to nanosized gold or platinum particles, the reaction is accelerated. • Using organic dyes, scientists are trying to make the particles responsive to visible light as well. • These particles have also been shown to remove toxic metal contaminates from air • Could be used in industrial smoke stacks to reduce the mercury produced.
Remediation using dendrimers • Dendrimer is a highly branched polymer with nanoscale dimensions whose shape and form can be easily manipulated. • These dendrimers can form “cages” to trap metal ions making them soluble or causing them to bind to certain surfaces.
Remediation using magnetic nanoparticles • Nanoparticles of rust have been shown to remove arsenic from water using a magnet • Arsenic sticks to rust, and rust responds to magnets • Nanosized rust particles (about 10nm diameter) have high surface area, and reduce the amount of material used. • Useful since many arsenic contaminated sites are in locations with limited access to power. • Process is suitable for both in situ and ex situ remediation.
Pollution Prevention • Materials • By engineering materials on the nanoscale to have a structure more optimal for degradation, we can create environmentally friendly materials that can more easily biodegrade • Examples: • Polymers (think of plastic bags that can biodegrade) • A non-toxic nanocrystalline structure to replace Lithium- graphite electrodes in rechargeable batteries • Materials can be made self cleaning • Example: • Activ Glass: http://www.pilkington.com/products/bp/bybenefit/selfcleaning/activ/default.htm • Coated with TiO2 nanocrystals break down organic dirt and rainwater washes it away.
Lotus Effect • Sometimes associated with the idea of self cleaning since lotus leaves are self cleaning • Due to superhydrophobia which prevents the absorption of water into a substance and allows water to roll off. • Would prevent the absorption of staining substances like juice and mud. • http://www.spillcontainment.com/everdry
Pollution Prevention • Superhydrophobicity being explored in textiles • NanoTex creating fabrics by creating nanosized whiskers on the surface of the fabrics • Adding TiO2 to fabrics to break down organic dirt • Lotusan is an exterior paint that reduces the attack of dirt on the outside of a building, allowing rainwater to wash it away.
Pollution Prevention • Antimicrobial coatings • Silver has antimicrobial properties. • Romans knew it. • Used it to clean wounds • Prevents bacteria and fungi respiration • Relatively harmless to humans • In rare cases can cause change in skin color and possibly death!
Pollution Prevention • Concerns: • Silver nanoparticles are one of the most common used in consumer products including • Utensils, personal wear, outerwear & sportswear, bedding, appliances
Energy • Currently, the world gets most of their energy from combustible materials • Coal • Oil • Natural Gas • Only about 11% of world energy resources come from non combustible materials like fission and hydroelectric, and very little from renewables like wind and solar.
Energy • The use of fossil fuels results in the increase in greenhouse gases in the atmosphere which leads to global climate change. By the end of the century, at the current rate, average global temperatures are expected to climb as much as 5 degrees and our most aggressive attempts to control it expect to only limit it to about 3.8 degrees. • The results of this change are: • Stronger, more frequent tropical storms • Rise of sea levels • Change in ecosystems • Change in weather patterns. • Massive extinctions.
Energy • By 2050, it is estimated emerging 3rd world countries could double current energy needs to approximately 14 Terrawatts. • There is a need to find ways to increase energy output and to shift to cleaner methods of producing energy. • Shifting to a non-petroleum based economy means looking into other sources of energy production • Solar • Wind • Geothermal • Fusion
Energy • These are not the least of the concerns with fossil fuels. The world’s supply of fossil fuels is dwindling. • The world’s supply of oil is expected to reach its peak within the next 50 years, at which point, the price is expected to skyrocket as ever increasing demand drives the price up on a quickly shrinking supply.
Energy • Solar Energy • Most abundant source of energy available. • Not constant • Geographically uneven
Energy • Some parts of the world receive enough sunlight to provide all the worlds energy needs. The problem is storing and transporting it. • How do we get the energy from the places where the sun shines a lot (the desert, the tropical rain forests etc) to the places where the people live? • How do we store the extra energy we produce when the sun is shining for use when it isn’t?
Energy • Photovoltaics • A device which converts Solar energy into electricity • Conventional cell is composed of two separate material layers: • One with a reservoir of electrons (negatively charged) • The other with a lack of electrons ( Called holes) (positively charged) • Sunlight provides the energy necessary to allow the electrons to electrons to jump the gap and move to the positive material, which is electrical current.
Energy • Problem with PV: • Made of semiconductor materials which only absorb a fraction of the solar energy available. Most commonly used material is crystalline Silicon • Expensive to produce • Other materials are cheaper but use less of the EM spectrum (5%) • Efficiency is only about 15-20% on a conventional PV solar cell • Efficiency is limited by the size and structure of the silicon crystals
Energy • Nanotechnology can improve PV cells: • By engineering silicon nanocrystals to absorb a broader spectrum of light • By shrinking the size of the crystals, we can increase the percentage of the EM spectrum that the silicon absorbs and converts to electricity. • Engineer a new generation of solar panels that mimic photosynthesis to produce energy. • Uses an antenna with chlorophyll pigment to absorb a large part of the visible light spectrum • Researchers have been able to use the photosynthetic processes of spinach to power electronic devices. Created by layering a conducting layer on top of on top of semiconducting material, a layer of biomaterial, on top of conducting material
Energy • Hydrogen Society • Using sunlight to produce hydrogen by splitting water • Hydrogen could then be used in fuel cells to power homes and cars. • First introduced in 1839 by Sir William Grove who thought the reverse process of electrolysis could be used to produce electricity. • Hydrogen is the most abundant element in the universe, so it will never run out • Byproduct is only water.
Energy • Although hydrogen is most abundant, it is not freely available. It is most present in water. The first challenge is getting it from the water, separating is from the oxygen. • Splitting into hydrogen and oxygen is a challenge • Should use renewable energy sources to be a green source. • 500nm light or below (red to infrared) is good to split water, although water is transparent to those frequencies.
Energy • Extracting Hydrogen from water still only economically feasible with fossil fuels
Energy • A major source of the cost for solar lies in the cost of producing silicon for the solar cells • The use of TiO2 instead would be more cost effective • Limited visible light absorption (see PV cells) • Uses the same process to split H2O as PV cell does to create energy. • The use of titanium dioxide nanotube arrays has helped improve the efficiency of PV cells and the water splitting cells.
Energy • Hydrogen storage • Combining hydrogen and oxygen to create more water is a pretty straightforward process, however not without its dangers • Storage and transport need to be both of efficient and safe • Storage: the amount of energy contained in equal volumes of hydrogen and gasoline is about one 10th. So you would need 10 times as much hydrogen as you do gasoline. • That would lead to large, bulky, heavy hydrogen storage tanks installed in your car. • Storing hydrogen and liquid form, would allow for more hydrogen per unit of volume, and therefore more energy per unit of volume • Tanks would need to be strong, lightweight, have high insulating properties, and be able to withstand high pressures • Another option would be metal hydrides. Bonding the hydrogen to a metal substrate or support, would allow the hydrogen to be stored not in gas form but as a compound that can easily be stripped off for use in the cars motor.
Energy • Nanotechnology can improve the efficiency of fuel cells by increasing the substrates ability to hold more hydrogens • The more hydrogens the metal substrate can hold, the larger the fuel cell capacity • Nanotechnology research is looking too create metal substrates that are lightweight, low in volume, bond easily with hydrogen but not so tightly that they require high temperatures to unbond.
Energy • Hydrogen Fuel Cell • Combines oxygen and hydrogen to create water. Process produces electricity and byproduct is water • Oxygen comes from the atmosphere, and hydrogen comes from an onboard storage source. • Problems: • Catalyst uses an electrode made of Platinum • Rare and expensive, and easily damaged due to exposure to carbon monoxide and sulfur products in the atmosphere • The effectiveness of the electrolyte is limited.
Energy • How nanotechnology can address these problems • Catalyst • If the activity the platinum can be increased, then less can be used reducing the cost. • Nanoengineering the platinum to increase the surface area will increase the activity of the platinum meaning needs less to have the same amount of energy produced. • Combined with other nanoengineered materials like carbon can help to disperse the nanoparticles of Platinum, reducing the weight, increasing the surface area and therefore the activity of the platinum
Energy • Proton Exchange Membrane Fuel Cell • Electrolyte used in conventional fuel cells is liquid and operates at about 70ºC which decrease the thermodynamic efficiency of the cell. Solid electrolyte is preferred • Modern fuel cells use a proton permeable membrane made of a polymer. • A platinum anode turns H2 into a stream of protons. The protons move through the membrane to a platinum cathode where it combines with O2 to create water. The electrons are stripped from the H2 at the anode and provide the electricity to power the device. • http://www.sepuplhs.org/high/hydrogen/fuelcell_sim5.html
Energy • Nanotechnology • The membrane is expensive, and degrades at temperatures of 100ºC due to dehydration. • On the hunt for new 3d electrolytes that don’t degrade. • Possibly a ceramic electrolyte, • Nanostructured solid electrolytes • Fillers made to nanoscale specifications. • Modern construction methods result in a non uniform size and distribution of pores on the surface of the membrane, which results in uneven production of energy, and losses. • Nanoengineering of the electrolyte would result in a more even distribution of pores increasing the output of the cell. • Create new fuel cells that are sturdier, more temperature resistant.
Energy • Thermoelectrics • Converts heat energy into electrical energy • A temperature difference across a wire causes electrons to move from high temperature to low temperature. • Increase the efficiency of current power plants by capturing the wasted heat that is currently exhausted • Devices have low conversion rates, 10%. • Have no moving parts, so it can be shrunk down to any size. • No pollutants. • Replace refrigeration
Energy • Problems: • Used only in niche applications • The processes max efficiency depends on high electrical conductivity and low thermal conductivity • Most materials, they are similar and changing one changes the other. • Nanotechnology • Has been found to increase the electrical conductivity and not changing the thermal conductivity when engineered on the nanoscale. • Optimal material has been found to have high symmetry on the nanoscale, and needs to incorporate heavy elements: • Examples: ZrNiSn, Zn4Sb3