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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

MordeniteA (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

• 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.

Doped zeolite

zeolite

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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 don’t change optical properties of CdS clusters

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Sulfidation Temperature Effect

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

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Continued…

Absorption spectra of the five samples measured by diffuse reflectance spectroscopy.

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

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Building up zeolite structures

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P.A. Spectroscopy Data & Results

Positron lifetime t2, t3, t4 in CdS/Y composites as a function of CdS loading concentration.

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

Sodalite cage

Super clusters are formed.

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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.