| Abstract
| - Here we report on the synthesis, physical and chemical properties, and stability of Pdnanoparticles encapsulated within poly(amidoamine) (PAMAM) dendrimers. Specifically,amine- and hydroxyl-terminated PAMAM dendrimers ranging in generation from 4 to 8were studied. Under appropriate conditions, addition of K2PdCl4 results in covalentattachment of the PdCl3- hydrolysis product of this complex to tertiary amines within thedendrimers. Reduction with NaBH4 results in conversion of dendrimer-encapsulated PdCl3-to nearly size monodisperse, encapsulated, zerovalent Pd nanoparticles. Details regardingthe Pd species present in solution and within the dendrimer prior to reduction are reported,as is the maximum Pd2+ loading of the dendrimers. Dendrimer-encapsulated Pd nanoparticlesundergo oxidation in air, but this process is slowed significantly when coordinating ions areremoved from solution. In the absence of O2, dendrimer-encapsulated Pd nanoparticles arestable indefinitely. The oxidation product is not PdO, but rather Pd ions coordinated to thedendrimer interior. Dendrimer generation does not affect the rate of Pd oxidation. Thedendrimer itself undergoes irreversible oxidation in the presence of O2. Finally, the oxidationof dendrimer-encapsulated Pd nanoparticles is reversible. Specifically, H2 gas can be usedto re-reduce partially oxidized Pd nanoparticles without changing their average size.
- The synthesis, characterization, and oxidative stability of dendrimer-encapsulated Pd nanoparticles are examined. Air oxidation of these nanoparticles yields Pd2+ ions that remain coordinated within the dendrimer, allowing the nanoparticles to be reactivated.
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