Nanotechnology and Its applications in energy sector

Vipin Sharma

Department of Physics, Govt. College, Bhoranj

*Corresponding Author Email:

ABSTRACT:

The introduction of new materials every decade has paved the way for the advancement of knowledge in science, Nanomaterials appear to have taken this development in science to new heights and these materials are expected to revolutionize the application. If science in every sector of human endeavor. It has become necessary that this topic is introduced in our educational curriculum at an early stage. This will be possible only when appropriate text book materials made available to our teaching and taught community. Present effort is to satisfy this need. Present presentation is made to reflect the many sectors of human endeavor where the nanomaterials can be expected to play a significant role in near future. It has been envisaged that the famous silicon material can be substituted by appropriate nanomaterials, in addition to conventional applications like catalysis and optical properties where the modern nanomaterials can be expected to influence enormously.

Materials in the nanometer size range commonly exhibit fundamentally new behavior. Nanomaterials include clusters of atoms, grains that are less than 100nm in size, fibres that are less than 100nm in diameter, films that are less than 100nm in thickness, nanoholes and composite that are combination of these, composition can be any combination of naturally occurring elements with the more important composition being silicates, carbides, nitrides, oxides metals, organic polymers and composites. Nanomatrerials will have good energy implication but considerable challenges existing regarding the integration of basic research and commercialization.

KEYWORDS:

1. INTRODUCTION:

When Neil Armstrong stepped onto the moon, he called it a small step for man and a giant leap for mankind. Nano may represent another giant leap for mankind, but with a step so small that it makes Neil Armstrong look the size of a solar system.

The prefix “Nano” means one billionth. One nanometer (abbreviated as 1nm) is 1/1,000,000,000 of a meter, which is close to 1/1,000,000,000 of a yard. To get a sense of the nano scale, a human hair measures 50,000 nanometers across, a bacterial cell measures a few hundred nanometers across, and the smallest features that are commonly etched on a commercial microchip as of February 2002 are around 130 nanometers across. The smallest things seeable with the unaided human eye are 10,000 nanometers across. Just ten hydrogen atoms in a line make up one nanometer. It’s really very small indeed.

This image show the size of the nanoscale relative to some things we are more familiar with. Each image is magnified 10 times from the image before it. As you can see, the size difference between a nanometer and a person is roughly the same as the size difference between a person and the orbit of the moon.

Nanoscience is at its simplest, the study of the fundamental principles of molecules and structures with at least on dimension roughly between 1 to 100 nanometers. These structures are known, perhaps uncreatively, as nanostructures. Nanotechnology is the application of these nanostructures into useful nanoscale devices. That isn’t a very sexy or fulfilling definition, and it is certainly not one that seems to explain the hoopla. To explain that it’s important to understand that the nanoscale isn’t just small, it’s a special kind of small.

Anything smaller than a nanometer in size is just a loose atom or small molecule floating in space as a little dilute speck of vapour. So nanostructures aren’t just smaller than anything we’ve made before, they are the smallest solid things it is possible to make. Additionally the nanoscale is unique because it is the size scale where the familiar day-to-day properties of materials like conductivity, hardness, or melting point meet the more exotic properties of the atomic and molecular world such as wave-particle duality and quantum effects. At the nanoscale, the most fundamental properties of materials depend on their size in a way they don’t at any other scale.

NOTE ON MEASURES
Meter(m)	Approximately three feet
Centimeter(cm)	1/100 of a meter
Millimeter(mm)	1/1000 of a meter
Micrometer	1/1000000 of a meter
Nanometer(nm)	1/1000000000 of a meter

A Different kind of small

Imaging something we would all like to have a cube of gold that is 3 feet in each side. Now take the imaginary cube and slice it in half along its length, width, and height to produce eight little cubes, each 18 inches (50 centimeters) on a side. The properties (excepting cash value) of each of the eight smaller cubes will be exactly the same as the properties of the big one; each will still be gold, yellow, shiny, and heavy. Each will still be a soft electrically conductive metal with the same melting point it had before you cut it. Aside from making your gold a bit easier to carry, you won’t have accomplished much at all.

Now imagine taking one of the eight 18-inch (50- centimeter) cubes and cutting it the same way. Each of the eight resulting cubes will now be 9 inches (25-centmeter) on a side and will have the same properties as the parent cube before we started cutting it. If we continue cutting the gold in this way and proceed down in size from feet to inches, from inches to centimeters, from centimeters to millimeters, and from millimeters to microns, we will still notice no change in the properties of the gold. Each time, the gold cubes will get smaller. Eventually we will not be able to see them with the naked eye and we’ll start to need some fancy tools to keep cutting. Still, all the gold bricks’ physical and chemical properties will be unchanged. This much is obvious from our real;-world experience-at the macro scale chemical and physical properties of materials are not size dependent. It doesn’t matter whether the cubes are gold, iron

When we reach the nanoscale, though, everything will change, including the gold’s color, melting point and chemical properties. The reason for this change has to do with the nature of the interactions among the atoms that make up the gold, interactions that are averaged out of existence in the bulk material, Nano gold doesn’t act like bulk gold.

The size-dependent properties of the nanostructures cannot be sustained when we climb again to the macro scale. We can have a macroscopic spread of gold nanodots that looks red because of the size of the individual nanodots, but the nanodots will rapidly start looking yellow again if we start pushing them back together and let them join. Fortunately, if enough of the nanodots are close to each other but not close enough to combine, we can see the red color with the naked eye, That’s how it works in the glass and glaze.

To understand why this happens, nanoscientists draw on information from many disciplines. Chemists are generally concerned with molecules; important molecules have characteristic sizes that can be measured exactly on the nanoscale: they are larger than atoms and smaller than microstructures. Physicists care about the properties of matter, and since properties of matter at the nanoscale are rapidly changing and often size-controlled, nanoscale physics is a very important contributor.

The Fundamental Science Behind Nanotechnology

ELECTRONS:

The electron was discovered early in 20^th Century. Electrons are very light (2,000 times lighter than the smallest atom, hydrogen) and have a negative charge. Protons, which make up the rest of the mass of hydrogen, have law. This force can be expressed by a simple equation that is sometimes called Coulomb’s law.

ATOMS AND IONS:

The simplest picture of an atom consists of a heavy nucleus with a positive charge surrounded by a group of electrons that orbit the nucleus and that (like all electrons) have negative charges. Since the nucleus and the electrons have opposite charges, electrical forces hold the atom together in much the same way that gravity holds planets around the sun. The nucleus makes up the vast majority of the mass of the atom-it is around 1,999/2,000 of the mass in hydrogen, and an even greater percentage in other atoms.

MOLECULES:

When atoms are brought in a fixed structure, they form molecules. This construction resembles the way the parts are put together in children’s building sets.

METALS:

Most if the 91 naturally occurring atoms like cluster with others of the same kind. This process can make huge molecule-like structures containing many billions of billions of atoms of the same sort. In most cases, these become hard, shiny, ductile structure called metals. In metals, some of the electrons can leave their individual atoms and flow through the bulk of the metal. These flowing electrons comprise electrical currents; therefore, metals conduct charge.

Other Materials:

The most common polymers are plastics. They are sometimes called macromolecules to convey the sense that they are extremely large by molecular standards (though generally not big enough for a human to see individually, as the prefix “macro” would normally suggest). Most polymers are based on carbon because carbon has an almost unique ability to bond to itself. Polymers are single molecules formed of repeating patterns of atoms (called monomers) connected in a chain. In a sample such as a polystyrene drinking cup, there will be many different structures, and the chains will be different.

Size dependent properties of nanomaterials:

It is evident that nanomaterials and nanotechnology dependent properties as recognized as follows:

1. Chemical properties – reactivity, catalysis

2. Thermal properties- melting temperature

3. Mechanical properties – adhesion, capillary forces

4. Optical properties – absorption and scattering of light

5. Electrical properties – tunneling of current

6. Magnetic properties – super para magnetic effect

This list can be extended to include many other sensing and biochemical properties and functions. Normally the size of nanometer of compared to human hair which is 80000nm wide.

Alternate approaches for the preparation of nanomaterials:

Nanochemistry, as opposed to nanophysics is an emerging constituent of solid state chemistry. It emphasized the synthesis rather than engineering aspect of preparing minute pieces of matter with nanometer size in one or two or three dimension. Chemists strive towards this objective from the “atom up” while nanophysicists operate from the “bulk down”. Building and organizing nano objects under mild and controlled conditions, one atom at a time instead of manipulating the bulk in principle provide the chemist with simple reproducible and cost effective synthetic approaches to materials of perfect atom sizes and shapes rather than having to use the complex and sophisticated instrumental techniques of the engineering physicist. The evolving nanophysics fabrication methods include molecular beam epitaxy, scanned optical, x-ray, ion and electron beam lateral engineering techniques (lithographic) which could produce sub micrometer scale objects with any desired architecture.

Chemists pride themselves in being able to synthesize small and perfect molecular size. However to prepare routinely and reproducibly, atomically perfect nanostructures, chemist have to develop new type of synthetic approaches that have the ability to assemble and position these tiny particles in appropriately organized arrays with uniform size and space distribution. Two exemplary approaches involve “pattering and templating” principles. In patterning, nanolithography is used to spatially define physically or chemically active foundation sites usually on planer substrates on which subsequent site-specific chemical synthesis allows the growth of the nanoscale objects. Templating on the other hand exploits the preexisting perfectly periodic. Single size and single shape voids space found in porous materials for performing host and guest inclusion chemistry.

Applications of nanomaterials in energy sector:

The promising application fields for the energy sector are

· Photovoltaics

· Hydrogen production and conversion

· Thermoelectricity

· Rechargeable batteries

· Super capacitors

· Hydrogen storage

Solar cells (photo voltaics):

Primary source of clean abundant energy is the sun. Sunlight or solar energy can be used to generate electricity, provide hot water and to heat to cool and to light buildings.

Electricity from the sunlight:

Photovoltaic cells generally consist of light absorber that will only absorb solar photons above certain minimum photon energy. This minimum threshold energy is called the energy gap or the band gap. Photons with energies below the band gap pass through the absorber while photons with energy above band gap are absorbed; the light absorber PV cell can be either inorganic semiconductor organic molecular structures. In inorganic semiconductor materials such as silicon, electrons have energy that fall within certain energy ranges called bands. All PV cells depend upon the absorption of light the subsequent formation and spatial separation of electrons and holes and the collection of electrons and holes different energies. The efficiency of electrons and hole formation and collection determines the photocurrent and the energy difference between the electrons and holes in their final state before leaving the cell determines the photo voltage. Product of photocurrent and photo voltage is the electrical power generates this product divided by incident irradiant power determines the efficiency of converting solar power to electrical power. Based on interfaces between solar semiconductors and molecules PV cells can be divided into three categories

· Inorganic cells, based on solid state inorganic semiconductors

· Organic cells based on organic semiconductors

· Photo electro chemical cells (PEC)

1. Inorganic PV cells are based on solid state semiconductors for example silicon and gallium arsenide when N type and P type semiconductors are joined together they form so called p-n junction and electric field is created between the two regions. When the cell is illuminated and electrons and holes are thus created, this electric field helps to efficiently separate the negative electrons from positive holes.

Two electrical contacts to the cell then provide a path for the electrons to leave the cell, pass through the external circuit to deliver electrical power and then return to the cell to recombine with the holes to neutralize them and complete the circuit. Semiconductors do not absorb solar photons that have energies lower than the band gap, photons with energies higher than band gaps are absorbed but the extra energies above the band gap is converted to heat rather than to electrical energy. This loss of photon energy to heat is one of the reasons why reasons why the calculated maximum sufficiency of conventional solar cell is limited to about 32%

2. Organic solar cell also operate with junctions, but the n type and p type semiconductor are the organic compounds and photo electrochemical solar cell (PEC) are based on hybrid structures of inorganic semiconductors and molecular structures. Semiconductors can be of n type or P type. Although conventional solar cell based on silicon are produced from abundant raw materials. The high temperature fabrication routes to single crystal and polycrystalline silicon are energy intensive and expensive. The search for alternative solar cells has therefore focused on thin films. The use nanostructures offer an opportunity to circumvent this key limitation and therefore introduce a paradigm shift in the fabrication and design of solar energy conversion devices to produce electricity or fuels. The use of nano structured and possibly nonporous system however refer an opportunity to satisfy the above shortcomings by collecting careers in a direction that is orthogonal to the one in which light is absorbed. In this way such an approach offers the potential for obtaining high energy conversion efficiency from relatively impure and therefore relatively inexpensive photo converters. One important example of such an important structure is provided by mesoscopic dye-sensitized solar cells which generally involve use of a highly porous film of randomly ordered nano particles of a transparent nanocrystalline oxide such as Tio2 coated with an ultra thin layer of light absorber (dye molecules or semiconductors quantum dots.) when photo excited, the absorber injects electrons into the oxide nanoparticles and creates a positive charge in the absorber. After electron injection, positive charge is neutralized by electron transfer to the oxidized dye from a liquid medium that permeates the porous structures, this regenerates the absorber and completes the cycle. An exciting aspect of this approach is that the generic concept of nano structured cell can be extended to a range of noble configurations involving different light absorbers and electron hole conducting phases. A key property of thin nano structured film is that since charge carrier pairs are generated only near the interfaces and are separated in two different obases. Bulk recombination and semiconductor stability are avoided. Current mesoporous nanocrystalline films used in dye-sensitized solar cell consist of a random nanoparticle network and a disordered pore structure.

CONCLUSION:

The main challenge for the application of nano materials in the energy sector to are the improvement of efficiency the reliability and safety and the life time as well as the cost reduction. The most promising application field for the energy conversion domain will be photo voltaic cell (solar cells) by hydrogen conversion (fuels cells) and thermoelectricity. The solar cells will be interesting for the local energy supply. If the cost can be significantly reduced and the electric energy can be efficiently saved. The most promising cost reduction at the solar cells will be expected by Dye Solar Cells and the Organic polymer solar cells. An important breakthrough can be reached with the nanotechnology, The distribution of fuel cells is limited nowadays due to high prices, However the improvements based on the nanotech at membranes, catalysts and electrodes will lower the cost of fuel cells as well as improve the efficiency. For the energy storage domains the most promising application fields will be the rechargeable batteries and super capacitors. In rechargeable batteries nanocrystalline materials and C-Nanotubes as electrode materials have been demonstrated to both energy and power density, lifetime, charging and discharging rates, The miniaturization of the electrode plays a quiet important role. Thereby nanotechnology will open new potential market for batteries and capacitors or combination of both for mobile phones, notebooks and semiconductors.

REFRENCES:

· Nanomaterials-by V Vishwanathan

· http://www.crcpress.com

Received on 18.08.2016 Accepted on 03.09.2016

Int. J. Tech. 2016; 6(2): 87-92.

DOI: 10.5958/2231-3915.2016.00013.4