Ag-Au bimetallic nanocomposites stabilized with organic-inorganic hybrid microgels: synthesis and their regulated optical and catalytic properties.

Herein, we present the synthesis of Ag-Au bimetallic nanocomposites stabilized with organic-inorganic hybrid microgels. The aim is to get both the surface plasmon resonance (SPR) and catalytic performance of the composite material can be changed in response to external stimuli. Ag@poly(-isopropylacrylamide--3-methacryloxypro-pyltrimethoxysilane) (Ag@P(NIPAM--MAPTMS)) hybrid microgels were synthesized by seed-emulsion polymerization using Ag nanoparticles (NPs) as the core and NIPAM/MAPTMS as monomers. Ag-Au@P(NIPAM--MAPTMS) bimetallic hybrid microgels were prepared by a galvanic replacement (GR) reaction between Ag NPs and HAuCl, with the composition and structure of these bimetallic nanocomposites being determined by the amount of added HAuCl. The highly porous organic-inorganic microgel layer provided confined space for the GR reaction, effectively preventing the aggregation of Ag-Au NPs. The shell layer of P(NIPAM--MAPTMS) three-dimensional network chains not only enhanced nanocomposite dispersity and stability, but also provided highly porous gel microdomains that could increase the diffusion of the substrate and hence enhanced catalytic activity. Additionally, the SPR and catalytic properties of Ag-Au@P(NIPAM--MAPTMS) are reversibly sensitive to external temperature. With increase of temperature, the maximum absorption peak of bimetallic nanocomposites shifted to longer wavelengths, and the catalytic activity of these composites for the reduction of 4-nitrophenol by NaBH remarkably increased. The features above mentioned are related to presence of the thermosensitive PNIPAM chains and the highly porous structure constructed by rigid MAPTMS segments intersected between NIPAM chains.