Stabilization of Intrazeolitic Cadmium Telluride Nanoclusters by Ion Exchange

Citations Over Time

Abstract

Cadmium telluride nanoclusters were prepared by vapor-phase deposition of elemental tellurium in Na+−zeolite A, followed by partial exchange of the zeolite with aqueous Cd(NO3)2, and reduction with hydrogen at 450 °C. The stability of the nanoclusters in environments that normally cause rapid Ostwald ripening or oxidation (air, water, and Br2/MeOH) was greatly enhanced by exchanging the Na+−zeolite with K+ after the Te0 deposition and hydrogen reduction steps. Exchange of K+ for Na+ narrows the effective pore diameter of zeolite A from 4.0 to 3.3 Å, inhibiting the diffusion of larger atoms, ions, and molecules (Te0, Te2-, and Br2). Distinct absorption maxima in diffuse reflectance UV−visible spectra and sharp exciton peaks in low-temperature excitation spectra verified the presence of quantum-confined CdTe. These spectral features are largely unchanged when the material, in its K+-exchanged form, is exposed to air and water for periods of months. Under the same conditions, materials in the Na+ form are rapidly degraded. TEM micrographs of the K+-exchanged materials show 20−50 Å diameter nanoclusters dotted throughout the zeolite matrix. The partial loss of host crystallinity observed in X-ray diffraction patterns suggests that the process of cluster formation involves aggregation within the large cages of the zeolite and local destruction of the pore network.

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