Effects of solvent on the in situ preparation of CdS quantum dots using PAMAM dendrimer templates

In order to study the effects of non-coordinated solvents on the in situ preparation of CdS quantum dots (QDs) using poly(amidoamine) (PAMAM) dendrimer templates, well-dispersed CdS QDs were synthesized using PAMAM dendrimers of generation 4.5 (G4.5, 64 terminal ester groups) as templates in following solvents: methanol, water, the mixture of methanol and water (VCH₃OH:VH₂O=2:1). CdS QDs prepared in methanol are single crystals and the average diameter is 2.7 nm, and besides, their size-distribution is the narrowest and photoluminescence (PL) is the strongest. While CdS QDs prepared in water are polycrystals and the average diameter is as large as 5.7 nm, furthermore, their size-distribution is the broadest and PL intensity is the weakest. However, CdS QDs prepared in the mixed solvent are composed of single crystals and polycrystals, the average diameter is 4.1 nm, and the size-distribution and PL intensity are middling. These differences were attributed to the different template effects of the PAMAM dendrimers. The branches of the dendrimers can extend freely in methanol, which makes the dendrimers inner templates. While in water, the dendrimer-water cross-linked structures built through double hydrogen bonds prevent Cd2+from coordinating with the inner groups of the dendrimers, which makes the dendrimers exterior templates mainly. Therefore, dendrimers act as inner templates and exterior templates simultaneously in the mixed solvent.