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 Te° 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 (Te°, 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.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)
- Materials Chemistry