Nanotechnology in the

Environment

Remediation and MitigationSoil and Groundwater become contaminated

due to industrial manufacturing processesIndustries 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 contaminationDrinking water expected to be the “oil” of the 21st century

From pollutants such as Arsenic

MercuryBoth 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

RemediationRemediation 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.

RemediationThis 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

semiconductorsUses 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

semiconductorsBoth 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

semiconductorsNanosized particles 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 nanoparticlesNanoparticles 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 PreventionMaterials

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 cleaningExample:

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.

Pollution Prevention

Lotus EffectSometimes 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

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

Pollution Prevention

Antimicrobial coatingsSilver has antimicrobial properties.

Romans knew it.Used it to clean wounds

Prevents bacteria and fungi respiration

Relatively harmless to humansIn 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

EnergyCurrently, 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.

EnergyThe 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.

EnergyBy 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

Energy

EnergyThese 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

EnergySolar Energy

Most abundant source of energy available.

Not constant

Geographically uneven

EnergySome 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?

EnergyPhotovoltaics

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.

EnergyProblem 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

EnergyNanotechnology 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

EnergyHydrogen 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.

EnergyAlthough 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.

EnergyExtracting Hydrogen from water still only economically feasible with fossil fuels

EnergyA 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.

EnergyHydrogen 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.

EnergyHow nanotechnology can address these problems

CatalystIf 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

EnergyProton 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

EnergyNanotechnology

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.

EnergyThermoelectrics

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

EnergyProblems:

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