Cooperative Catalytic Activity of á-Cyclodextrin and Ag Nanoparticles in Spherical Polyelectrolyte Brushes

Spherical poly(acrylic acid) brushes (SPB) were prepared by photo-emulsion polymerization. Positive silver ions were absorbed and concentrated in SPB due to the Donnan effect. Silver nanoparticles (Ag-NP) were synthesized in-situ by reduction of Ag⁺ upon addition of NaBH₄. The nano-composite particles were characterized using TEM, DLS, ICP-AES and UV-vis spectroscopy. While the size distribution of the Ag-NP synthesized at a given temperature is quite uniform this distribution varies with change in synthesis temperature. The lower temperature results in smaller silver nanoparticles. The Ag-NP loaded in SPB have a strong catalytic effect on the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by NaBH₄. The addition of α-cyclodextrin (α-CD) further accelerates this 4-nitrophenol reduction and modifies the associated activation parameters. This is attributed to α-CD complexing 4-nitrophenol in the vicinity of the Ag-NP surface and thereby aiding the catalysis. This work opens a new way to prepare metal nano-particles and to improve their catalysis by addition of CD.