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Synthesis of Nobel Metal Nanoparticles in Spherical Polymer Brushes and Their Catalytic Activities

Author: ZhuYuanQing
Tutor: GuoXuHong；LiGongSheng
School: East China University of Science and Technology
Course: Chemical Engineering
Keywords: emulsion polymerization spherical polymer brushes nanoreactor nanometal catalyst catalytic activity
CLC: TB383.1
Type: Master's thesis
Year: 2012
Downloads: 62
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Abstract

Spherical polymer brushes (SPBs)are nanoparticles with a core-shell structure which constitute of polymer spherical core and linear polymer chains fixed on core surface by chemical bond. With different kind of polymers, the spherical polymer brushes exhibit unique physical and chemical properties:pH-sensitivity and thermosensitivity, for instance. Spherical polymer brushes have potential applications in wastewater treatment, bio-microreactor, preparation of nano-metal catalysts, controlled drug release and so on.In this thesis, new spherical polymer brushes were synthesized by using polybutadiene(PB) colloidal particles as core and chemically grafted linear poly(acrylic acid) (PAA) or poly(N-isopropyl acrylamide) (NIPA)as a shell. Transmission electron microscopy (TEM) was used to study the microstructure of spherical polymer brushes and dynamic light scattering (DLS) to determine the size of spherical polymer brushes under different conditions.Nobel metal nanoparticles with various size and morphology were obtained by reduction of nobel metallic ions adsorbed in spherical polymer brushes (PB-PAA). PB-PAA loaded with nobel metals remained stimuli-responses to pH and ionic strength. This new nanocomposites containing nobel metal catalysts were used to catalytze the reduction of p-nitrophenol into p-aminopheno by NaBH4.(1) New spherical polymer brushes consisted of a PB core with size of 112 nm and linear PAA shell chemically grafted onto the core were synthesized by emulsion polymerization. The thickness and grafting density of PAA chains could be controlled. Optimal reaction conditions were:s olid content of PBwas 1.0 wt%, KPS was 2 wt% of PB, reaction temperature was 80℃. Spherical PB-PAA brushes prepared under optimal conditions were of polydisperse index (P.D.I.)0.001. Based on improved Daoud-Cotton model, the graft density of PB-PAA brush synthesized by emulsion polymerization was 0.02 nm-2.(2) Temperature-sensitive PB-PNIPA spherical polymer brushes were prepared by emulsion polymerization. It consisted of a PB core and a linear N-isopropyl acrylamide shell.The thickness and grafting density of PNIPA brushes could be controlled. The emulsion was stable for 6 months without precipitation and agglomeration. Results showed that the morphology, size and size distribution were affected by monomer concentration and reaction temperature.(3) Ni @ PB-PAA brush, Ag @ PB-PAA brush and Co @ PB-PAA brush were successfully synthesized. Composite particles were monodispersed. The emulsion was homogeneous and stable. Different metals had different average particle sizes. Ni nanoparticle size was 9-18 nm, Ag nanoparticle size was 3-6 nm, Co nanoparticle size was 1-4 nm in diameter. Spherical polymer brushes with metal particles remained their ionic strength response and pH-sensitivity. The morphology, size and size distribution of metal nanoparticles in spherical polymer brushes were various in different temperatures. The sizes of Co, Ag, and Ni nanoparticles prepared at temperature 5℃were 1.5 nm,4.2 nm, and 9 nm. And the size increased to 4 nm,5.4 nm, and 17.5 nm prepared at 25℃.(4) The Ni @ PB-PAA, Ag @ PB-PAA, and Co @ PB-PAA brushes were used as catalysts in the reduction reaction of p-nitrophenol. All of them had a high catalytic activity.Their catalytic activities increased with concentration of nanocomposites.and reduced at lower temperature.

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