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Semiconductor clusters in zeolites

We have already seen that photoactive clusters, e.g. CdS, can be introduced into vesicles and BLMs (Sect. 5.2 and 5.3). Similar support interactions are possible with both inorganic and organic polymeric supports. Photoactive colloidal semiconductor clusters can be introduced, for example, into cellulose [164], porous Vycor [165], zeolites [166], or ion exchange resins [167]. The polymer matrix can thus influence the efficiencies of photoinduced electron transfer by controlling access to the included photocatalyst or by limiting the size of the catalytic particle in parallel to the effects observed in polymerized vesicles. As in bilayer systems,... [Pg.94]

Quantization effects have not only been observed with colloidal solutions, but also with nano crystals deposited on Pt or SnOa [38,39] and with semiconductor clusters (CdS,PbS) produced in zeolites [40,41]. The same effect has been found with thin single crystalline semiconductor layers (super lattices) (see e.g. Refs. [42,43]. In this case the quantization occurs only in one dimension, and the shift of energy states is much less, i.e, in the order of 0.1 eV, whereas the shift in a colloidal particle (quantization in 3 dimensions) amounts to several eV. [Pg.114]

Besides cadmium sulfide, other semiconductor particles can also be loaded in zeolite microporous crystals. Moller et al. prepared cadmium sulfide nanoparticles in zeolite Y through a similar approach.[117] Nevertheless, structural analysis indicates that the formed cluster particles are actually rather complex, and apart from cadmium sulfide clusters, there exist other nanoclusters such as Cd404 or Cd202Se in the channels of zeolite Y. These nanoclusters are not isolated, and they strongly interact with the framework oxygen of the zeolite. [Pg.634]

In recent years, molecular sieves have found new uses as hosts for the preparation of small metal- and semiconductor clusters that can be grown in confined zeolite spaces and are envisioned for uses in photo-catalysis, non-linear optics, sensors, flat panel displays, etc..[31] The framework-type structures of zeolites can be described with the presence of the n- rings, e.g., 4-, 6-, 8-, 12-rings or double 5-, 6-, 8- rings, or secondary building units, e.g. the sodalite cavity, super cages, and others. These confined spaces can be used for the preparation of optical and electronic materials with desired properties. [Pg.269]

CdS, PbS, CdSe, and ZnS clusters arc the semiconductor compounds studied most extensively in zeolites.[39,40] In addition, ternary systems such as ZnCdS have attracted the interest of many researchers.[41] An ordered array of cadmium clusters assembled in zeolite A was prepared in an attempt to produce heavy metal clusters with different distributions and gcometries.[42] (Fig. 8)... [Pg.270]

In the present work, we consider the two approaches for synthesis of nanoparticles designed for metal particles and being in the progress for ultraflne semiconductors. They allow to fabricate nanocomposites of the type nanoparticles-in-dielectrics with amorphous and crystalline matrices. The first one is based on the sol-gel technique producing dielectric silica films with nanoparticles incorporated within silica matrix [1]. Nanoparticles provide an optical response of the material due to the plasmon resonance [2] with variable spectral position and band shape. In the second approach nanoparticles are produced within the crystalline zeolite matrices which stabilize both the few-atomic clusters (e.g., Agg) and metal particles in the size range of 1-20 nm [3], Chemical routes of their synthesis admit easy control of size and optical properties. The metal nanoparticles in zeolites can be transformed into semiconductors without destroy of the zeolite matrix and with incorporation of zeolite microcrystals into transparent silica films. This construction... [Pg.342]

Clusters of Metals, Metal Ions and Semiconductors in Zeolite Hosts... [Pg.408]

The semiconductor clusters can then be formed in the zeolite by a ship-in-a-bottle synthesis (Eqs. 4.17 and 4.18). Here, the precursor anchored in the supercages of zeolite is allowed to react with an appropriate reagent e.g. H2S, H2Se, or PH3) at a slightly elevated temperature whereby the remaining methyl groups of the anchored precursor are released as CH4 and a labile spedes is formed (Eq. 4.17, X = S, Se, or P). Condensation reactions then follow (Eq. 4.18). [Pg.357]

Elemental semiconductor clusters encaged in zeolites provide a valuable opportunity for gaining a fundamental understanding of semiconductor clusters because stoichiometry is not a concern in the synthesis. Selenium is of interest because it has an intermediate electrical conductivity and a negative coefficient of resistivity in the dark hence it is markedly photoconductive. It has uses in, for example, photoelectric devices and xerography. When Se is sorbed into a molecular sieve, it gives markedly different optical absorption spectra from those of the bulk material. [Pg.361]

Dramatic advances in molecular synthetic chemistry have led to a high level of control over molecular interactions. However, we are only at the beginning of a more extended design of chemical interactions in two and three dimensions. If we learn how to control the structure, properties, and stability of desired supramolecular assemblies, many areas in materials science and technology, such as microelectronics, optics, sensors, and catalysis, will benefit substantially. Representative areas of research activity include selective monolayer assemblies on electrode surfaces functionalized pillared layered materials and assemblies of conductors, semiconductor clusters, or nonlinear optical materials in three-dimensionally ordered hosts such as zeolites. [Pg.2]

Examples in four different areas of zeolite inclusion chemistry will be discussed in the following. Noble metal and semiconductor clusters, organometallics, and intrazeolite polymer filaments are objects of new and continued research activity. [Pg.279]


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