Amphiphilic polymer-Ag composite microgels with tunable catalytic activity and selectivity

Environmentally sensitive polymer microgels are increasingly being used to enhance the catalytic activity of supported metal nanoparticles. Herein, we synthesized composite polymer microgels composed of the core-shell structure poly(styrene-N-isopropylacrylamide)/poly(N-isopropylacrylamide-co-methacrylic acid) (P(St-NIPAM)/P(NIPAM-co-MAA)). Ag nanoparticles (AgNPs) were loaded onto/into the network chains of the polymer microgels through a facile method. The prepared composite microgels were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray powder diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, and ultraviolet-visible spectroscopy. The catalytic selectivity of P(St-NIPAM)/P(NIPAM-co-MAA)-Ag composite microgels for the reduction of hydrophilic 4-nitrophenol (4-NP) and hydrophobic nitrobenzene (NB) by NaBH4 was investigated. The results indicated that the introduction of PMAA segments into the microgel networks caused the poly(N-isopropylacrylamide) (PNIPAM) chains to separate into a shell layer and prevented the aggregation of AgNPs. The separated PNIPAM segments not only favor the mass transfer, but also possess thermosensitive function to modulate the catalytic activity of AgNPs. These structural features of the prepared composite microgels could enhance the selectivity and mass transfer of the reactants for catalytic reduction of 4-NP and NB through temperature modulation.