Effect of water on the behavior of semiconductor quantum dots in zeolite Y: Aggregation with framework destruction with H-Y and disaggregation with framework preservation for NH ₄-Y

Treatment of dry M ²⁺-exchanged zeolite Y (M ²⁺ = Cd ²⁺, Mn ²⁺, and Zn ²⁺) with dry H ₂S leads to the formation of isolated, ligand-free, subnanometer MS quantum dots (QDs) in zeolite Y with no framework destruction and with H ⁺ as the countercation. Treatment of the dry H ⁺/CdS QD-incorporating zeolites Y with dry NH ₃ leads to the neutralization of H ⁺ to NH ₄ ⁺. During this process, the framework structure remains intact. However, small amounts of interconnected CdS QDs were formed within the zeolite Y by coalition of isolated CdS QDs at the windows. With H ⁺ as the countercation, isolated CdS QDs rapidly aggregate into interconnected and mesosized QDs with accompanying destruction of ∼50% of sodalite cages leading to the framework rupture. With NH ₄ ⁺ as the countercation, however, the isolated QDs and zeolite framework remain intact even after exposure to the moist air for 4 weeks. Interestingly, the interconnected QDs that were formed during neutralization of H ⁺ with NH ₃ disintegrate into isolated QDs in the air. Similar results were obtained from ZnS and MnS QDs generated in zeolite Y. Thus, ligand-free, naked, subnanometer QDs can now be safely preserved within zeolite pores under the ambient conditions for long periods of time. This finding will expedite the generation and dispersion of various QDs in zeolite pores, their physicochemical studies, and applications.