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Photoluminescence and PhotocatalyticPhotoluminescence and Photocatalytic
studies of doped and capped ZnO andstudies of doped and capped ZnO and
CeOCeO22 nanomaterialsnanomaterials
Ph.D
Proposal
By
Manish Mittal
Roll No. 950912008
Under the Supervision of
Dr. O.P Pandey
Professor
School of Physics and Materials Science
THAPAR UNIVERSITY, PATIALA(PUNJAB)-147004
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PRESENTATION OUTLINE
Nanotechnology
Need of capping
Literature review
Gaps
Objective
Methodology
Experimental work done so far Results and Discussion
References
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Nanotechnology
Deals with various structures of matter having dimensions of the order of a billionth of a meter.
Different types of nanostructures compared with bulk
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Band Gap comparisonWhen the radius of nanoparticle approaches the size of the exciton Bohr radius,the motionof electrons and holes become confined in the nanoparticle. A created electron-hole pair can only fit into the nanoparticle when the charge carriers are in the state of higher energy.As a result the band-gap increases with decreasing particle size.
Here the kinetic energy becomes quantized and the energy bands will split into discrete
levels and phenomena is known as quantum size effect. These structures have very highsurface to volume ratio & hence surface defects play an important role in their study.
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Quantum confinement effects
It is possible to engineer the electronic structure of a material,
by reducing the crystal size.
Quantum confinement effects are observed when the nano-
crystallite size is less than the exciton Bohr radius
nanocrytal bulk g g bulk g l nanocrysta g MR
E E E E 2
22
)()()( 2
TJ!(!
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What extraordinary at nano-scale?
Physical, Chemical, Biological .........propertiesdrastically change
Why????
* Surface to volume ratio increases
* Confinement of electron-hole pairs
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Need for Capping
Surface passivation
Control agglomeration
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Various Techniques for the
preperation of nanoparticles
1. Thermal Decomposition Method
2. Chemical Vapor Deposition Method
3. Sol-Gel Method
4. Spray Pyrolysis Method
5. Co-Precipitation Method
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Advantages of Co-Precipitation Method
1. Simple growth process for large scale production
2. Efficient
3. Inexpensive
4. Homogeneous distribution of doped ions in the
host matrix
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Scientist Name/Year/Sample/Route Work Done Gaps
Reddy et al.(2011)/ ZnO:Cu/Wet
chemical method(1)
XRD shows 40nm of undoped
and37nm for Cu doped ZnO
nanoparticles having wurtzite
structure. PL studies shows decrease
in green emission and increase of UVemission due to decrease in
defects.TEM shows 40-50nmof
particle size.
Concentration of defects responsible
for deep level emission could be
reduced with Cu doping and it is
possible to tune UV emission but the
percentage of dopant required for defect reduction is not reported.
Chauhan et al. (2010)/ZnO:Cu/Co-
Precipitation /(2)
XRD shows increase in particle size
with doping than undoped ZnO NPs.
However, the particle size reduceswith increase in dopant concentration
but still greater than undoped ZnO
NPs. UV shows decrease in band gap
from 3.15-2.92eV of undoped and Cu
doped ZnO.
Reddy et al.(1) reported decreaes in
particle with doping but here the
particle size increase with doping.
Literature Review«
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Literature Review«
Scientist Name/Year/Sample/Route Work Done Gaps
Rana et al. (2010)/ZnO:Cu/ Wet
chemical /(3)
XRD results shows decreaes in
particle with doping than undoped
ZnO NPs. SEM and EDS shows
single phase NPS of doped and
undoped ZnO and no other element
except Zn and O respectively.
Here again the decrease in particle
size is reported with doping which is
contradictory to as reported by Reddy
et al.
PL and UV-vis spectra is not done.
Ullah et al. (2007)/ ZnO: Mn/Wetchemical/(13)
Showed that Mn doped ZnO bleachesMB much faster than undoped ZnO
upon its exposure to UV light.
The doping concentration proposed to be 1% for faster degradation of MB.
Different dopant concentrations were
not tried.
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Literature Review«
Scientist Name/Year/Sample/Route Work Done Gaps
Tsuzuki et al.(2009)/ZnO:Mn/Sol-
gel/(14)
XRD shows 10nm particle size. UV
is done. 3% Mn doping of 3% is
reported for photocatalytic
degradation of Rh-B dye.
Variation in dopant concentration is
required for getting optimum dopant
conc. For degradation of dye.
Singh et al.(2009)/Capped
ZnO/Chemical method(6)
XRD- 12-20nm Paricle size.TG has
been found to be more efficientcapping agent than TEA(
triethnolamine) , and Oleic acid.
Variation in concentration of capping
agent is required to study their effectson PL. Energy transfer mechanism is
required for tunable emission.
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Sample and
Synthesis route
Dopants
and
Concentra
tion
Excitation Emission UV(Band
Gap)(eV)
XRD &
ParticleSize
TEM Remarks
CeO2
[20]
(2010) (microwave)
-------------
---
---------- --------- 3.1 Cubic
9nm
10nm SEM and Propylene glycol
usedas stabilizing agent
CeO2
[21] (2001)
Combustion
Er ----------- 550nm
(Green)&
660nm
(Red)
------ 18,38 &
70nm
Dark and White
clouds appeard.
Dark clouds are
crystallne & white
are amorphous.
18nm are more
amorphous than
38nm.
PAS is done.
CeO2
[22] (2002)
Soft solution chemical
Calcia
20mol%
----------- --------- 300(Trans
mittance)
Fluorite 50nm(Pure),
5-10nm
(doped)
pH-7,11 Doping CaO with
CeO2 reduce the particle
size and increase UV
shielding and transparency
to visible light.
Comprehensive Study of Literature
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Sample and Synthesis
route
Dopants
and
Concentrat
ion
Excitation Emission UV(Band
Gap)(eV)
XRD &
Particle Size
(nm)
TEM Remarks
CeO2
[6]
(2002)
Chemical Precipitation
------------ ------------ ----------- 3.15 Calculated
Lattice
parameter
from (h,k,l)
6nm and bigger Lattice parameters increases
upto 0.45% as particle size
reduces to 6nm.
CeO2
[9]
(2006)
Co-precipitation method
Ca(10,20,3
0,
40& 50%)
315nm
( pure),
250-330nm
(doped)
-------- 3.20
( pure),3.36
& 3.51
(doped)
Fluorite type
cubic
9.3nm( pure),
5.7nm
(50%doped)
8.3nm( pure) 5.9 &
6.3nm(20 & 50%
doped)
Above30mol% Ca doping,
sample contain CaCo3-
secondary phase and is not
suitable for cosmetic
products.
CeO2
[23]
(2006)
Sol-Gel
PtAu
(Bimetallic
catalyst),Pt & Au
--------- -------- ------- CeO2-16.18,
1%PtAu-
15.14,0.5% PtAu-
30.77,
2%Pt-13.65,
1%Pt-13.65,
1%Au-13.64
5-10nm Catalytic studies are done
with PtAu, Pt & Au doped
CeO2
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Sample and
Synthesis route
Dopants and
Concentration
Excitation Emission UV(Band
Gap)(eV)
XRD&
Particle Size
(nm)
TEM Remarks
CeO2
[24]
(2006)
Soft solution
chemical
Calcia doped
silica coated
---------- --------- 300(Trans
mittance)
----------- 10-15nm
Calcia doped
Non coated calcia doped
ceria shows better UV
shielding ability and
transparency to visible light
region than calcia doped
coated ceria
CeO2
[13]
(2006)
Composite-
hydroxide-mediated
------------- -------------- -------- ----- Cubic lattice
constant-
5.411A0
2-3nm at
1650C(0h),5-7nm at
1900C(48h),
2-4nm at 2200C (0h)
and 6-8nm at 2200C
(120h)
The ceria particle with sizeless than 6nm display a very
strong agglomeration to
minimize the interface
energy.
CeO2
[31]
(2007)
Hydrothermal
Synthesis
--------- ---------- -------- ------ Cubic
15.5nm
5-6nm
(cerium hydroxide),
10-15nm
(Cerium acetate)
Study Lattice type and lattice
constant at 500 and 10000C.
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Sample and
Synthesis route
Dopants and
Concentration
Excitation Emission UV(Band
Gap)(eV)
XRD &
Particle Size
(nm)
TEM Remarks
CeO2
[20]
(2008) Precursor
growth calcinations
Sm3+ 369nm Two
bands
325-
430nm &
260-
290nm
------ Fluorite
Small particle
size
----------- Rod like structure without
PVP and spherical particles
100nm size with PVP
reported by SEM
CeO2
[22]
(2009)
Silver (0.1,
0.25, 0.5, 0.75
& 1.0mol %)
---------- ------- ------- Cubic 5-6nm
( pure CeO2), 7-8nm
(Doped CeO2)
SEM and EDS studies
CeO2
[32]
(2009)
Homogeneous
Precipitation
----------- ------ --------- ------- Cubic
13-20nm
------------ Study the variation of particle
size with temp.
CeO2
[27]
(2010) precipitation
method
Fe(0,10,40,50,6
0,90,100%)--------- --------- 342
(3.62)
Concludes the
formation of
mixed oxides
10-20nm Degrade dyes like MB & CR.
Max. Degradation is at 50%
of Fe.
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Sample and
Synthesis route
Dopants and
Concentratio
n
Excitation Emission UV(Band
Gap)(eV)
XRD &
Particle Size
(nm)
TEM Remarks
ZnO
[14] (2006)
Precipitation method
Eu and Eu-Li
codoped
--------- ------ ------- ---------- --------- Particle size of 40nm has
been observed with SEM.
Cathodolumine-scence
spectra
ZnO
[18]
(2008) Chemical
------------- 300-320nm 410&558n
m
262nm Hexagonal
wurtzite
1-3nm Green emission is observed
due to singly ionized oxygen
vacancy.
ZnO
[1
9](2008) Co-
Precipitation
Mn & Cu --------- --------- 3.2 -------- 3-5nm Mn ions affect the absorption
characteristics more than Cuions.
ZnO
[23]
(2009) Wet Chemical
Mn --------- --------- 3.2 ----------- 3-5nm Photocatalytic activity of
doped ZnO is more than pure
ZnO
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Sample and
Synthesis route
Dopants and
Concentration
Excitation Emission UV(Band
Gap)(eV)
XRD &
Particle Size
(nm)
TEM Remarks
ZnO
[31]
(2010) Sol-Gel
Vanadium 325nm &
371nm
-- -- Wurtzite
Zn3(VO4)2
and Zn2V2O7
phases also
appeared, 14-
20nm
15-20nm Defect produced due to
doping of vanadium element
improve the photocatalytic
activity which can further
improve by varing doping
concentration.
ZnO
[33]
(2010) Sol-Gel
Eu, 1,2,3% 320nm -- -- Hexagonal
wurtzite
structure
--- Optical properties can be
significantly improved by Eu
doping.UV emission is
greatly reduced at 3% doping
conc.
ZnO
[34]
(2010) Sol-Gel
Cs -- -- 3.263 Wurtzite --
ZnO
[36]
(2010) Co-
Precipitatio n
Silver (0,1,2,3,4
and 5%)
-------- ------- 3.3 Hexagonal,wu
rtzite,27-
38nm
-------- Temperature variation
300-8000C
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Sample and
Synthesis route
Dopants and
Concentration
Excitation Emission UV(Band
Gap)(eV)
XRD &
Particle Size
(nm)
TEM Remarks
ZnO
[36]
(2011)
Co-Precipitation
Ni(0,1,2,3,4,5
%)
--------- ---------- (Undoped)
300-3.35
400-3.05
500-3.00
800-2.90
(Doped)
300-3.2
400-2.95
500-2.90
800-2.85
Wurtzite
28-37nm
(8000C),
30-42nm
(10000C)
------- The band gap value of
prepared undoped and Ni
doped ZnO Nps reduced as
annealing temp.increased upto
8000C
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Doped and undoped ZnO nanoparticles have been studied for their photoluminescence and photocatalytic applications but capping withemissive polymers like PVP, Thioglycerol, Chitosen etc. on surfacealong with different dopants is not done in detail.
Capping emissive polymers results in tunable emission but their effecton ZnO and doped ZnO nanoparticles is required for their possible useas optoelectronic materials.
From literature survey of doped CeO2 nanoparticles, it appears dopedCeO2 systems have been investigated but the doping effect in ceriananoparticles with well characterized size is not done previously. Thedoping of ceria at that small size can be very beneficial to further improve its catalytic properties.
Doping with various dopants (Ag, Ca, Er, Fe, Pt, Au, CaO, Sm etc.) in
CeO2 has been done but their photocatalytic studies are not available indetail. In some cases dopants concentration increase and sometimes theyreduce the photocatalytic activities. When dopants changes Ce4+ to Ce3+
they are useful for the UV filteration and if they are not transformingCe4+ to Ce3+ then they can be used for degradation of dye. So detailedstudy is needed on the dopant concentration required for UV filterationand degradation of dye.
Gaps in present study
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1. To synthesize Mn and Cu doped and capped ZnO nanomaterials by chemical
pr ecipitation route.
2. To study the effect of capping agents like PVP and Chitosen on UV and PL
properties.
3. To synthesize Ca and Er doped and undoped CeO2 nanomaterials.4. To study effect of dopants on conversion of Ce4+ to Ce3+ which results in
shifting of catalytic properties useful in UV filtration applications.
5. To study their photocatalytic and photoluminescence properties using UV-
visible, PLE and PL spectroscopy.
6. To study morphological studies for structural and size measurement using
XRD, SEM, TEM etc.
Objectives
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ZnO and CeO2 nanostructures will be fabricated using chemical routes.
ZnO will be doped with Mn and Cu whereas CeO2 will be doped with Caand Er respectively.
Capping agents like PVP, Merceptoethanol, Thioglycerol, Chitosen etc.
will be tried to passivate the surface. ZnO and CeO2 nanostructures will be characterized by using XRD, TEM,
SAED, Photoluminescence spectroscopy, UV- visible absorption andreflectance spectroscopy, EDS etc.
«Methodology«
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ZnO nanoparticles wer e synthesized by chemical pr ecipitation
technique by adding appropriate amount of zinc acetate and sodium
hydroxide.
0.5 M Zinc acetate sol. In aqueous medium wer e added in 1%
Thioglycerol(TG) and then 0.5 M sodium hydroxide was added dropwise and stirr ed continuously.
The pr ecipitate soon appears after the addition of sodium hydroxide
and they wer e filter ed using Whatman 40 filter paper .
The particles wer e washed several time with ethanol and wer e dried
at 3000C in vacuum.
«Work Done«.
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Characterization
Homogeneous sol.
Capped ZnO nanoparticles
OpticalMorphological
Autoclave
FLOW CHARTWork Done«
Zinc acetate Mixing Capping agent
NaOH
Magnetic stirring
Colloidal Sol.Washing, Filtration ,
Vacuum oven drying
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Results and Discussion
MorphologicalCharacterization and Nano-size confirmation
XRD pattern of and uncapped (a) and (b)TG capped
ZnO nanoparticles
For XRD Rigaku, model D±
maxIIIC diffractometer with
Cu K radiation is used.
Using Scherrer formula
d =0.89 / cos
Average crystallite size of
~13nm and ~16nm for capped
and uncapped ZnO
nanoparticles is obtainedhaving hexagonal wurtzite
structure.
30 40 50 60 70 80
0
500
1000
1500
2000
C o u n t s
Angle(2 U)
Uncapped ZnO NPs
TG capped ZnO NPs
100
002
101
102
110
103
200
112
201
Wurtzite ZnO
(a)
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Excitation spectra of synthesized capped and uncapped
ZnO nanoparticles
Steady state PL spectra recorded using FlouroMax-3 (Jobin-Yvon)spectroflourometer
280 300 320 340 360 380
345nm
Capped ZnO 345nm
Wavelength(nm)
uncapped ZnO
I
n
t e
n
s i t y ( a . u
.
)
Excitation spectra at 460nm emission
Excitation spectra Shows excitonic peak
at 345nm for both capped and uncapped
ZnO Nps.Which is blue shifted than
bulk ZnO which comes at 380nm.
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SEM Analysis of TG capped ZnO
clearly shows the formation of
ZnO Nps
EDX spectrum shows the pr esence of zinc and oxygen ions in larger
amount along with carbon and
nitrogen in less amount which is due
surface adsorbed polymer TG.
SEM and EDX analysis of capped ZnO nanoparticles
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Element Wt. % At%At.At. %
%
CK 13.03 29.90
NK 01.02 02.01
OK 24.45 42.14
ZnK 61.50 25.94
Table I- EDX analysis of TG capped ZnO NPs
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Applications
Since common cells are almost transparent, they can hardly be seen by human eyes
under optical microscope. Researchers often rely on certain fluorescence material, whichattach to the interested biological component, in order to detect cell activities. Althoughorganic fluorescent dye has been widely used to label the cells, their drawbacks, such asnarrow absorption band and high chemical reactivity, are obvious compared to thenanomaterial counterparts, quantum dots (QDs), especially ZnSe, CdSe, ZnS:Mn whoseemission spectra spread most of the visible wavelengths.
Both biocompatibility and aqueous solubility are required for QDs to be used inbiological system. Because CdSe QDs synthesized through metal-organic approach are
hydrophobic, ligands exchange or extra coating are needed for those dots to use inaqueous environment. In addition, highly toxic metalorganic precursors make thiscomplex process much less desirable than the method under development here are,which offers an easy and user-friendly way to prepare high quality CdSeQDs. ZnSe/ZnScore/shell structure QDs can be synthesized to significantly enhance the PL intensityfrom ZnSe so that much less QDs are needed to inject into cells to obtain strong signals.
Silica coatings were also developed on the core/shellQDs to increase chemical stabilityand biocompatibility of the QDs. Silica coatings are also easy to functionalize byconjugating with various molecules, which can be used to track the cell activities orchemical pathways inside cells. It has been reported that PL intensity and peak wavelength of the QDs could change upon chemical bonding events of the functionalmolecules. The electric charges change, among others, is considered to contribute to thisprocess. Therefore, the effect of an applied electric field, known as Stark effect, on thePL intensity and wavelength of the QDs was studied to give preliminary understandingof such phenomenon.
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