CdS Nano Particles Embedded in Zeolites

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CdS Nano Particles Embedded in Zeolites

• Nano Technology
• Course
• Supervisor Dr. Taghavinia
• (Physics Department)
• Student A. Izadbakhsh
• Chemical Eng. Dep., Sharif University of
  Technology, Tehran, Iran

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Introduction

• In the second half of this century, zeolitic
  materials doped with polymers and metals with
  interesting properties have been obtained.
• In the same time, semiconducting materials
  researchers have been directed towards the study
  and synthesis of semiconductor nanostructures
  deposited into different kind of matrices.

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Continued

• Nanosize semiconductor particles exhibit novel
  physical properties such as
• blue shifts of optical absorption spectra,
• nonlinear optical properties
• Technological applications of semiconductor
  embedded in zeolites include
• Photocatalyst
• Nonlinear optics
• Flat panel display
• Sensors

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Continued

• The nanocomposite material properties can be
  varied either by
• using different kind of zeolites, (notable)
• or, by changing the type of semiconductor
  cluster.
• Different type of Zeolite such as Y,A (LTA) and
  MOR have been used as the host to generate CdS
  nanoclusters.

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zeolite may be better than others porous media
for nanosize particle generation.

• So many zeolites are available now.
• Crystalline framework, in order regular
  channels.
• Fixed cavity size which may cause to produce
  sharp nano cluster size distribution.

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Zeolite Framework
Mordenite
A (LTA)
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nano clusters generation in zeolites

• zeolite powder is slurreid in distilled water.
• Solution PH is adjusted to acidic usually by
  nitric based acid.
• Ionic exchange with cadmium
• Filtration, washing, drying calcination of
  Cd(2)-exchanged zeolite.
• Sulfidation by sulphide flow or Na2S solution
• Filtration, washing, drying calcination of CdS
  loaded zeolite.

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Experiments

• N2 Absorption
• Raman Spectroscopy (argon laser, line 488 nm)
• Reflection Absorption Spectra, ABS
• Positron Annihilation Spectroscopy, PAS
• PAS is a kind of nuclear technique, which is
  capable of investigating the microvoids and
  inner-surface properties of porous materials
  because positronium is easily formed in these
  materials. Its annihilation is sensitively
  affected by the physical-chemical properties of
  the environment.

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N2 AbsorptionData Results
Doped zeolite
zeolite

• zeolite losses its specific surface by CdS doping
  due to pore volume decreasing by CdS clusters
  formation.
• So CdS Clusters have been formed in zeolite
  channels.

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Continued

• M8 has a large pore size dis. centered about 60
  nm.
• Pore mean diameter evolution reveals the losses
  of crystallinity by CdS clusters formation.

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Raman Spectroscopy Data Results

• band at 304 cm(-1) correspond to the first order
  vibrations of CdS.

• band around 600 cm(-1) related to the second
  order vibrations of CdS.

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Reflection Absorption SpectraData Results

• Eg (M8) 3.40 ev
• Eg (M11)2.63 ev
• Eg (M13)2.59 ev
• Eg (bulk CdS) 2.53 ev
• Calculated band gap for M8 reflects a blue
  shifting in the emission spectra.

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Continued

• not a great difference between M11 M13 optical
  behavior in the visible range.
• M13 band gap is very near to that of the bulk
  CdS.
• So there is a critical CdS loading on zeolite
  that higher values dont change optical
  properties of CdS clusters

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Sulfidation Temperature Effect
SEM images of (a) unloaded zeolite, (b) CdS/A
sample prepared at 30 C and (c) CdS/A sample
prepared at 70 C.
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Continued

• higher Temp., higher size of CdS clusters formed
  outside the cages, shifting absorption edge from
  the blue to the red.

Absorption spectra of the five samples measured
by diffuse reflectance spectroscopy.
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Building up zeolite structures
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P.A. Spectroscopy Data Results
Positron annihilation data resolved into 4
component in zeolite Y CdS/Y. T1 (shortest life
time)? P.A. in the bulk of zeolite. T2 decrease
shows CdS clusters form in Sodalite cages
Super cages
Super clusters are formed.
Sodalite cage
Positron lifetime t2, t3, t4 in CdS/Y composites
as a function of CdS loading concentration.
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summery

• CdS nanoclusters have been formed in zeolite
  channels even smaller than 60 nm.
• Calculated band gap for CdS nanoclusters
  corresponds to a blue shifting in the emission
  spectra due to quantum size effect and higher
  loading results in smaller band gap.
• higher Temp., higher size of CdS clusters formed
  outside the cages, shifting absorption edge from
  the blue to the red.

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References

• 1-H. Peng and others,"Growing process of CdS
  nanoclusters in zeolite Y studied by positron
  annihilation",Journal of Crystal Growth, Vol.
  224, 2001.
• 2-H. Villavicencio Garcia,and others,"CdS
  doped-MOR type zeolite characterization",
  Solid-State Electronics, vol. 43, 1999.
• 3-R. Ochoa-Landin and others, "Characterization
  of Cds clusters in zeolite-A grown in alkaline
  solution", Journal of Physics and Chemistry of
  Solids, vol. 64, 2003.
• 4-M.M. Garcia and others, "Hydrothermal growth of
  CdS and ZnS Nanoparticles in MOR-type zeolites",
  Materials Science and Engineering, vol. 15, 2001.
• 5-Internet search results on zeolite.