Synthesis of thermo- and pH-responsive Ag nanoparticle-embedded hybrid microgels and their catalytic activity in methylene blue reduction

Abstract

Ag nanoparticles (AgNPs)-containing hybrid microgels were prepared by in situ reduction of Ag+ ions pre-dispersed in copolymer microgels of poly (N-isopropylacrylamide-co-2-(dimethylamino)ethyl methacrylate) (P(NIPAM-co- DMA)). The prepared hybrid microgels possess excellent thermo- and pH-responsive properties and exhibit a responsive swelling and shrinking behavior. The increase in pH can induce a decrease in the absorption intensity and a blue shift of the surface plasmon band of AgNPs, which is attributed to a reduction in the polarity of AgNPs surroundings as a result of the conformational change of PDMA segments. Furthermore, the hybrid microgel was found to be an active catalyst for the reduction of methylene blue by NaBH4 in aqueous solution. The effects of temperature and the amount of catalyst on the reduction rate were investigated using UV–vis spectrophotometry. Kinetic studies indicate that the apparent reaction rate constant kapp follows the typical Arrhenius-type dependence on temperature in the range of 25 ∼ 40 °C and the activation energy is 62.0 kJ mol−1. The AgNPs embedded in hybrid microgels show good thermal and chemical stability and the catalytic activity remains unchanged after storage for 40 days at room temperature. Such hybrid microgels, with the merits of good thermal and chemical stability as well as the catalytic activity, have a potential application in the field of heterogenous catalysis.