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Summary Nanomaterials and their spectroscopic characterization
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Nanomaterials and their spectroscopic characterization
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Chemistry (18BSCH03) Jan-June 2020Module 4
Nanomaterials and their spectroscopic characterization
S.No Questions Marks
1 Discuss the optical properties of nano materials. 4
Nanomaterials exhibit a different optical property from their bulk
material,
It depends on their size, shape and diameter which causes
difference in extinction of light.
EXTINCTION - the reduction of the intensity of transmitted
light as a result of absorption and scattering.
When light is incident on nanoparticle we observe extinction.
At diameter less than 20nm, extinction involves only absorption.
At diameter between 20-100nm, extinction involves both
absorption and scattering.
And the size above 200nm extinction is mainly due to scattering.
These changes causes difference in the colour between Bulk and
nanoparticle.
Eg., Gold spheres of 2-5nm exhibit yellow color.
Gold spheres of 10-20nm exhibit red color.
Gold spheres of >20nm exhibit purple color
2 Describe the electrical properties of nano materials 4
This property depends on surface scattering of electrons and
change In crystal structure,
The property may vary depending on the following conditions:
Conducting nanoparticles: Reduction in size will increase in
crystal defects like frenkel defect and schotky defect, which
, creates a hole in the crystal. Also conduction can be improved by
adding impurity to it.
Insulating nanoparticles: Reduction in size results in reduction of
structure leading to widening of band gap.
Because of these variations some material undergo transition
from insulator to semiconductor, conductor to semiconductor,
insulator to conductor etc.,
3 Explain the magnetic properties of nano materials 4
It depends on the size and structure of the material.
Size ranging from 1-100nm show supermagnetism.
These acts as single magnets.
this makes us to control the tiny magnets by removing or
applying the field
4 Discuss the principle and instrumentation of UV-VIS Spectrophotometer 8
Principle:
Spectrophotometry is a technique that uses the absorbance of light
by an analyte at a certain wavelength to determine the analyte
concentration. UV-Vis spectrophotometry uses liquid in UV
(190-400nm) and Visible (400-765nm) part of the
electromagnetic spectrum.
UV−Vis spectrophotometer measures absorbance or transmittance
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