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
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.
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
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.
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.
Zeolite Framework A (LTA) Mordenite
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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 clustersformedoutsidethe cages, shifting absorption edge from theblueto thered.
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.