Preparation of Silver Nanoparticles Loaded Photoresponsive Composite Microgels and Their Light-Controllable Catalytic Activity

A new type of smart composite microgels, which are able to control the catalytic activity of their loaded silver nanoparticles by light, was designed and fabricated based on the idea of function transfer between their constituent components. First, the surfaces of monodisperse gold nanorods (AuNRs) with strong photothermal effect were coated with poly(N-isopropyl-acrylamide) (PNIPAM) hydrogel by seed precipitation polymerization to prepare the two-component composite microgels with core shell structure (AuNR@PNIPAM microgels). Then, Ag+ ions coordinated into the shell of AuNR@PNIPAM microgels were in situ reduced by sodium borohydride to produce silver nanoparticles (AgNPs) loaded three-component composite microgels (AuNR@(AgNPs/PNIPAM) microgels). The characterization results obtained by transmission electron microscopy show that the gold nanorod is located at the center of the three-component composite microgels and AgNPs with the average particle diameters of 6-10 nm are evenly distributed within its shell. The hydrodynamic diameters of the composite microgels, measured by dynamic light scattering before or after exposure of their aqueous dispersion to near-infrared (NIR) laser of 808 nm wavelength, indicate that they have photoresponsive property. The AgNPs and AuNR inside AuNR@(AgNPs/PNIPAM) microgels hold their respective localized surface plasmon resonance (LSPR) optical property, and the longitudinal LSPR wavelength of the latter is blue-shifted with increasing content of the former. Moreover, the LSPR efficiency of the AgNPs and the longitudinal LSPR wavelength of the AuNR are capable of being changed in response to the NIR illumination, and the stimulus-responsive behavior is reversible. AuNR@(AgNPs/PNIPAM) microgels are able to be used as the smart microreactor for reducing 4-nitrophenol by NaBH4, and the reaction rate can be modulated by power density of the NIR light, demonstrating that the three-component composite microgels have light-controllable catalytic activity.