Stabilization of Intrazeolitic Cadmium Telluride Nanoclusters by Ion Exchange

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• 作者：Elaine S. Brigham ; Carl S. Weisbecker ; Walter E. Rudzinski ; and Thomas E. Mallouk
• 刊名：Chemistry of Materials
• 出版年：1996
• 出版时间：August 1996
• 年：1996
• 卷：8
• 期：8
• 页码：2121 - 2127
• 全文大小：409K
• 年卷期：v.8,no.8(August 1996)
• ISSN：1520-5002

文摘

Cadmium telluride nanoclusters were prepared byvapor-phase deposition of elementaltellurium in Na⁺-zeolite A, followed by partialexchange of the zeolite with aqueous Cd(NO₃)₂, and reduction with hydrogen at 450 s/entities/deg.gif">C.The stability of the nanoclusters inenvironments that normally cause rapid Ostwald ripening or oxidation(air, water, and Br₂/MeOH) was greatly enhanced by exchanging the Na⁺-zeolitewith K⁺ after the Te⁰ depositionand hydrogen reduction steps. Exchange of K⁺ forNa⁺ narrows the effective pore diameterof zeolite A from 4.0 to 3.3 Å, inhibiting the diffusion of largeratoms, ions, and molecules(Te⁰, Te^2-, and Br₂).Distinct absorption maxima in diffuse reflectance UV-visiblespectraand sharp exciton peaks in low-temperature excitation spectra verifiedthe presence ofquantum-confined CdTe. These spectral features are largelyunchanged when the material,in its K⁺-exchanged form, is exposed to air and water forperiods of months. Under thesame conditions, materials in the Na⁺ form are rapidlydegraded. TEM micrographs of theK⁺-exchanged materials show 20-50 Å diameternanoclusters dotted throughout the zeolitematrix. The partial loss of host crystallinity observed in X-raydiffraction patterns suggeststhat the process of cluster formation involves aggregation within thelarge cages of the zeoliteand local destruction of the pore network.