Gold Nanoparticles Stabilized by δ-Cyclodextrin in Aqueous Media: Characterization and Evaluation of their Catalytic Properties in the Reduction of 4-Nitrophenol

The synthesis of gold nanoparticles stabilized by cyclomaltononaose (δ-CD) in aqueous phase was performed. Protection of the gold nanoparticles by standard native cyclodextrins such as α-CD, β-CD and γ-CD has also been considered for comparison. All of these colloidal suspensions were fully characterized by FT-IR, DLS, UV-Vis spectroscopy, TEM, XPS and also NMR experiments. Finally, their catalytic activity was evaluated in the reduction of 4-nitrophenol to 4-aminophenol in the presence of an excess of sodium borohydride. Gold nanoparticles stabilized by δ-CD presented good activity and exhibited better long-term stability. This study highlighted the fact that the obtention of the best catalytic activity corresponds to not only a compromise between the size of the nanoparticles and the interaction of the substrate with the metal nanoparticles surface, but also the supramolecular interactions between the substrate and the cyclodextrin.