PALLADIUM NANO PARTICLES

PRESENTED BYP.VINUTHA,CA14M004.

What are nano particles?

Nano particles range between 1nm to 100nm It is originated from the greek word meaning

“dwarf”. The properties of many materials change

when they are prepared from nano particles. The important feature of nano materials are

that they have high surface area to volume ratio and can be extensively used as catalytic materials.

why nano particles are different from bulk? Meltingpoint, color,Ionization potential ,electron

affinity which for bulk amount of matter do not depend upon size becomes size independent when size falls below a certain limit(100nm ).

On this basis properties of materials can be tuned to their desired values by adjusting the size of nano particles.

The important fact is that even the atom sitting on the surface of small particle has different properties when compared to the atom sitting on the surface of large particle.

When particle size is reduced to nano ,the particle behaves like in individual atoms due to formation of discrete energy levels rather than the continuum in energy levels.

The no of surface atoms increase in the case of nano materials when compared to bulk as the surface atoms possess more energy nano particles are more reactive .

Surface structure of metal

Quantum dots are tiny paricles or nano crystals with size ranging from 2-10 nm.

Due to therir small size the electrons in the quantum dots are restricted in a small place and when the radii of semiconductor nano crystal is less than the exciton bohr radius(the average distance between the electron in the conduction band and the hole it leaves in the valence band there is quantization of energy levels.

The discrete energy levels of them relate them closely to the atoms than bulk materials and they are nicknamed as “ARTIFICIAL ATOMS”.

As the size of the crystal decreases the difference in energy between highest valence band and lowest conduction band increases.

More energy is then needed to excite the dot and consequently more energy is released when it reaches to ground state resulting from shift in color from red to blue in the emitted light.

As a result quantum dots can emit any color of light from the same material by changing the dot size.

ALLOYED QUANTUM DOTS:

Multi component quantum dots offer an alternative method to tune properties without changing its crystallite size.

By changing the composition of internal structure optical properties can be changed.

For example alloyed quantum dots of compostions CdSxSe1-x/ZnS of 6nm diameter emits of colors of different colors by varying the compositions.

Alloyed quantum dots of two different semiconducting materials of different band gaps energies gives distinctive properties not only from their bulk materials but also from their parent semiconducting materials.

Photoluminescence of alloyed CdSxSe1-xZnS of varying composition:

Palladium: Atomic number 46 Group,Period 10,5 Block d State at solid Electronic configuaration [Kr] 4d10

Melting point 1554.8°C Boiling point 2963°C Density 12 gm /cm3 Atomic mass 106.42

Why palladium nano materials

Palladium nano particles have been extensively studied in wide range of catalytic applications such as oxidation, dehydrogenation, formation of c-c bond and electro chemical reaction in fuel cells.

They have ablity to absorb hydrogen and so can be used in its storage and sensing applications and also in purification.

Main advantage:

A Hydrogen based economy is one potential approach towards maintaining our standard of living by reducing CO2 Emissions.

Palladium has the ability to absorb large amount of hydrogen at room temperature and pressure and subsequently form palladium hydride.

On palladium surfaces the dissociative adsorption of hydrogen takes place with little or no activation energy.

Palladium hydride is metallic palladium that contain substantial amount of palladium in its crystal lattice.

Hydrogen absorption on palladium produces two different phases alpha and beta. Pure alpha phase exists for x<0.017where as pure beta phase is recognized when x rises above 0.58 intermediate values corresponds to alpha –beta mixtures.

At low x valves crystal lattice expands from 3.889-3.995Å. at high valves of x it expands to 4.025Å.metallic conductivity is reduced as hydrogen gets absorbed it becomes semiconductor around PdH0.5 .

Thus incorporation of hydrogen plays a crucial role in optical properties of palladium.

TEM OF 1%Pd on polymorphs of TiO2

Methds invoved in preparation of nano particles:

Gas phase evaporation method Sol gel processing :It involves

combination of chemical reactions which turns a homogeneous solution of reactants into an infinite molecular weight polymer. This polymer is a three dimension interconnected pores.

On further filtration and calcination gives nano structure.

Metal salts+reducing agent+capping agent on heating if required give metal nano colloids.

Capping agents Ex: thiols,citrates. Reducing agents Ex: sodium citrate, NaBH4

The nucleation and growth of particles are the crucial factors for controlling the size of nano particles formed.

This is suitably achieved by choice of suitable capping agents and also their functionality,

Their hydrophobic and hydrophilic parts interacting suitably with particles formed and thus preventing growth mechanism.

Recent development in the synthesis of palladium nano particles is by irradiating a solid liquid system consisting of palladiumoxide-alcohol with micro waves.

The obtained suspension is observed using scanning electron microscopy and the average diameter is measured by dynamic light scaterring.

A Non chemical method of synthesis of palladium nano particles is sputtering a thin layer of palladium on fused silica. Subsequent annealing resulted in the formation of palladium nano particles with diameters in the range of 20-200 nm.

Nothing is ever perfect Problems may arise when this particles

are inhaled. Atomic weapons can become more

powerful and accessible Fossilfuels may lose their value.

References Nano sciences and nano

technologies,why nano is different-enil roduner.

Nanomaterial based catalyst –wikipedia. Nano materials by B.Viswanathan. Quqntum dots by Sigma-Aldrich. Research paper in Springer by Micheal

kracker.

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