Abstract:

The core-shell type poly(styrene-N-isopropylacrylamide)/poly(N-isopropylacrylamide-co-3-methacryloxypropyltrimethoxysilane) (P(St-NIPAM)/P(NIPAM-co-MPTMS)) composite microgels with thermosensitivity were synthesized by two-step polymerization methods. Using P(St-NIPAM)/P(NIPAM-co-MPTMS) composite microgels modified by (3-mercaptopropyl) trimethoxysilane (MPS) as support material, Ag nanoparticles (AgNPs) were in-situ controllably synthesized using ethanol as a reducing regent. The structure, composition and properties of the prepared P(St-NIPAM)/P(NIPAM-co-MPTMS)-(SH)Ag composite materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fouriertransform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and UV-visible spectroscopy (UV-Vis). Additionally, the catalytic activity of the composite microgels was investigated using the reduction of 4-nitrophenol (4-NP) by NaBH₄ as a model reaction. The results showed that the dispersity of the in situ formed AgNPs was greatly improved because of the confining effect of the organic-inorganic microgel network with mercapto groups. Although the thermosensitivity of the composite microgels decreased because of the PNIPAM segments separated by the inorganic networks formed by MPTMS, the composite microgels still showed excellent catalytic performance and thermosensitivity in modulating the catalytic activity of AgNPs. These findings are related to the following aspects. The separated PNIPAM segments are favorable for mass transfer, and the networks with mercapto groups allow control of the size and local distribution of the in situ formed AgNPs. The present results are significant for construction of functional nanoscale metal catalytic materials.

Key words: Organic-inorganic hybrid microgel, Thermo-sensitivity, Supported catalyst, Silver nanoparticles, 4-Nitrophenol reduction