Dr. Vishnumurthy K A

UNIT IV

NANO material chemistry

 

 

 

 

Introduction to Nanomaterials
Materials are composed of grains, which in turn comprise of many atoms. These grains can be visible or invisible to the naked eye, depending on their size. Conventional materials have grains varying in size anywhere from hundreds of microns to centimeters. Nanomaterials are commonly defined as materials with an average grain size less than 100 nanometers. The word "nano" originates from the Greek word "nanos" which means "dwarf". However, in scientific language it is a prefix which has a value equal to "one billionth, i.e. 10 9 Therefore, one nanometer is one billionth of a meter (1 nm = 10 9 m). Following examples helps to understand a sense of nano scaled objects and figure 1 gives qualitative idea Solution combustion

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Mimicking the nature

 

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Application of nano materials

Energy:
1) Hydrogen storage materials synthesized at nanoscale have high H2 storage capacity. Ex: Carbon nano tubes , Metal hydrides (MgH2, CaH2, LiAlH2)
(The Hydrogen Economy offers a potential solution to satisfying the global energy requirements while reducing (and eventually eliminating) carbon dioxide and other greenhouse gas emissions and improving energy security. Hydrogen is a very attractive alternative energy vector)
2) Nanomaterials for batteries :LiFePO4
3) Nanomaterials for solar cells: ZnO, TiO2, Thin film of Si, CdSe, CdTe etc
Environmental:
1) Electrochemical sensors based nanomaterials (Fe2O3, SnO2, ZnO, silica, carbon nanotubes,) for environmental monitoring/sensing CO2, NOx, CO gasses.
2) Nanocrystalline MgO, CaO, TiO2 and Al2O3 adsorb polar organics such as aldehydes and ketones, industrial waste etc
3) Nanocrystalline metal oxides are highly effective adsorbents towards a broad range of environmental contaminants ranging from acids, chlorinated hydrocarbons, organophosphorus and organosulfur compounds to chemical warfare agents. These materials do not merely adsorb, but actually destroy many chemical hazards by converting them to much safer byproducts under a broad range of temperatures. Ex: TiO2 based nanomaterials for photo catalytic dye degradation.
Electronics:
The most revolutionary application in nanotechnology is in the semiconductor area. Electrically conducting nanowires are developed by lithography; which reduces the size and increases the conductivity of electrical contacts; The width of the nanowire can be controlled by the size of the cluster that is chosen. The decrease in size and increase in efficiency of Computers, Laptops, LEDs, Mobile phones etc is result of usage of nanomaterials in their construction. Ex: use of nanotechnology in the design of printed circuit boards (PCBs)
Medicine:
The use of nanotechnology in medicine and more specifically drug delivery is set to spread rapidly. Currently many substances are under investigation for drug delivery and more specifically for cancer therapy. Ex: Nanostructured silica materials, carbon nanotubes, grapheme oxide etc.
Catalysis:
Nanomaterial-based catalysts are usually heterogeneous catalysts. The extremely small size of the particles maximizes surface area exposed to the reactant, allowing more reactions to occur. Ex: Nano TiO2 for photocatalytic activity dye degradation, Co/ZrO2 catalysts in CO hydrogenation, Nano MgO, CaO for biodiesel production, etc.

 

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Synthesis of Nanomaterials: SCS for metal oxide, Sol-Gel- for TiO2 nanoparticles Carbon Nano materials Researchers are active worldwide developing new preparation methods for functionally and technologically useful nanoparticles and nanostructures. Nature efficiently builds nanostructures by relying on chemical approaches. There are many methods developed to prepare nanomaterials, they are listed as chemical methods (bottom up) and physical methods (top down)

Low temperature solution combustion (SCS) method
This method was discovered by Prof. K. C Patil when the mixture of Al(NO3)3·9H2O and urea solution, rapidly heated around 500 ºC in a muffle furnace. The author observed that the solution mixture undergoes vaporization followed by vigorous ignition with an incandescent flame yielding voluminous white product which was identified as -Al2O3. Combustion method: is a low temperature, time saving, energy efficient, self
propagating method, involving spontaneous exothermic redox reaction between metal nitrate and organic fuel, used to prepare nanomaterials.
Principle: The method is based on the utilization of heat energy produced during the exothermic spontaneous redox reaction between an oxidizer (metal nitrate) and a reducing agent (organic fuel). The oxidizer can be of any metal nitrates and reducing agents may be organic fuels, such as glycine, oxalic acid, urea, hexamine, sugar, EDTA, Detrose etc.

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Sol-gel method
It is a wet chemical technique widely used for the fabrication of nano-structured ceramic materials and thin films. Sol-gel process involves the conversion of precursor solution (usually metal salts or metal alkoxide) into a nano-structured inorganic solid through inorganic polymerization reactions catalyzed by water. In general, metal alkoxides (M-OR) are widely used as precursors, because they readily react with water.

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Carbon nanotubes:
A promising group of nanostructured materials is the nanotubes, which are currently fabricated from various materials such as boron nitride, molybdenum, carbon (carbon nanotube), etc. However, at the moment, carbon nanotubes seem to be superior and most important due to their unique structure with interesting properties, which suit them to a tremendously diverse range of applications in micro or nanoscale electronics, biomedical
devices, nanocomposites, gas storage media, scanning probe tips, etc. In 1970, Morinobu Endo, First carbon filaments of nanometer dimensions was prepared, as part of his PhD studies at the University of Orleans in France. He grew carbon fibers about 7 nm in diameter using a vapor-growth technique. Filaments were not recognized as nanotubes and were not studied.
 

 

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Graphene: Introduction, Preparation, properties and applications.
Graphene is an allotrope of carbon made of a single layer of carbon atoms that are bonded together in a repeating pattern of hexagons. It is one million times thinner than paper; so thin that it is actually considered two dimensional. Its most frequent form in nature is graphite, a mere stack of graphene layers held together by Van der Waals interactions. It is also the basic structural element of other allotropes, including charcoal, carbon nanotubes and fullerenes. Carbon nanomaterial which has made big news (in the last few years) in physics, chemistry and materials science is graphene, a two dimensional nano-material. We know that the graphite consists of layers of six membered carbon rings. Suppose, if you lift of one layer from graphite, one can get graphene sheet. Graphene is a very thin sheet with a thickness of few nanometers. Spherical carbon nanomaterials are referred to as fullerenes, while cylindrical ones are called carbon nanotubes. Carbon nanotubes can be broadly classified into two types, namely singlewalled carbon nanotube (SWCNT) and multi-walled carbon nanotube (MWCNT). SWCNT contains one graphene sheet that rolls up to form a cylinder. MWCNT consist of several grapheme sheets rolled up together to form concentric cylinders with large annular space at centre. Graphene is a purely carbon-based, honeycomb-structured, one-atom thick layer of carbon atoms (two dimensional sheet), bonded to one another by sp2 hybridization. The novel material has generated great interest throughout the scientific and technological community because of its remarkable properties and numerous potential applications. This novel material is atomically thin, chemically inert, consists of light atoms, and possesses a highly ordered
structure.
A single sheet of graphite is called graphene It is sp2 hybridized covalently bonded The bonding between the graphene sheets in graphite is of van der Walls type.

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Nano materials for Energy conversion devices:

 

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Nanomaterials for LED:
inorganic/organic LED with nanomaterials. Parallel to energy generation, energy saving is another route to tackle the global energy challenge. Energy-efficient applications include any technology or route that consumes less energy without compromising their functions. They cover a wide range of technologies, for example, solid state lighting based on light-emitting diodes (LED), low-power electronics based on nanoelectronics or spintronics, waste heat recycling based on thermoelectric effect, self-powered devices, and so forth. Nanomaterials open up tremendous opportunities towards energy saving in these fields, as the photon emission, electron transport, spin configuration, and transport, as well as phonon scattering change drastically as the size of the materials shrinking to nanometer scale. The light-emitting diode (LED) is a semiconductor device that converts electrical energy into light, have attracted much more attention in recent years because of several advantages over the common illumination technologies like incandescent lamps, halogen lamps, and high quantum efficiency, high light emitting efficiency, long lifetime, energy saving,
environmental protection, and so on. Therefore, LEDs are considered as a potential candidate of the next generation lighting source. LED bulbs have a very long life, almost 50 times more than ordinary bulbs, and 8-10 times that of CFLs, and therefore provide both energy and cost savings in the medium term. The LED lighting device anatomy primarily consisting of i) LED semiconductor p-n junction chip ii) heat sink slug iii) encapsulant iv) anode lead & cathode lead v) plastic lens vi) phosphor etc. The Fig.1 represents the typical anatomy of the LED lighting device

Construction and working of LED

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