Preparation And Catalytic Properties Of Nano-Silver Coated Dendrimer-Modified Polymer Microsphere

Recently, the hierarchial nanocomposites have drawn a considerable interest in chemistry and materials science due to their potential applications in photoelectronic devices, antibacterial materials, biosensing, drug delivery and catalysts. Among these types of nanocomposites, the binding of metal catalysts to inorganic or organic polymer supports was widely used. This research was focused on the study of PAMAM-metal grafted magnetic polymer microsphere and PAMAM-metal grafted cross-linked polymer microsphere. The recoverable catalytic activity of the magnetic nanocomposites was analyzed and PAMAM-metal grafted cross-linked polymer microspheres were packed in catalytic column. The catalytic performance of packed column and how to improve the life of the catalysts were studied. The detailed information are shown as follows:1. The magnetic supports were prepared by coating Fe3O4nanoparticles with polystyrene (PS) in this paper. The target nanocomposites were based on growing polyamidoamine (PAMAM) dendrimer on magnetic polymer supports with carboxylic groups and then silver nanoparticles were embedded into the PAMAM dendrimer shell. Therefore, the recoverable Fe3O4@PS@PAMAM-Ag nanocomposites were successfully prepared. Moreover, the magnetic nanocatalysts were characterized by FTIR spectra, scanning electron microscope and X-ray photoelectron spectroscopy. The results demonstrate that the PAMAM dendrimer shell immobilized on the magnetic supports is beneficial to disperse and stabilize the silver nanoparticles. The catalytic activity of the Fe3O4@PS@PAMAM-Ag nanocomposites is proved using the reduction of4-nitrophenol as a model catalytic reaction. The nanocomposites could be readily separated by magnetic separation and reused for the next reduction with high efficiency. After the nanocatalysts was recycled at least six times, the catalytic activity was remained completely.2. The polymer nanoparticles with dendrimer-Ag shell were prepared and their application in column for the catalytic reduction of4-nitrophenol (4-NP) was also investigated. The cross-linked polystyrene (PS) microspheres were prepared through dispersion copolymerization of styrene, acrylic acid and crosslinking monomer1,2-divinylbenzene. The PS microspheres with average size of450nm and narrow size distribution were used as supports for the immobilization of dendrimer-Ag shell. The polyamidoamine (PAMAM) dendrimer shell was grafted on the surface of PS microsphere through repetitive Michael addition reaction of methyl acrylate (MA) and amidation of the obtained esters with a large excess of ethylenediamine (EDA) successively. The silver nanoparticles directly formed inside the PAMAM shell through reduction with NaBH4. When the obtained PS@PAMAM-Ag nanoparticles are packed in a stainless steel column, it can be used successfully for catalytic reduction of4-NP. This technique for packing catalytic polymer particles in column improves the efficiency of application for metal catalysts and reduces the tedious separation processes in catalytic reaction.3. The polymer particles with dendrimer@SiO2-Ag hierarchial shell were prepared and their application in the catalytic column for the reduction of4-nitrophenol (4-NP) was also investigated. The PS microspheres with the carboxyl group were used as the supports for the immobilization of dendrimer@SiO2-Ag shell. The polyamidoamine (PAMAM) dendrimer was grafted on the surface of PS microsphere through repetitive Michael addition reaction of methyl acrylate (MA) and amidation of the obtained esters with a large excess of ethylenediamine (EDA) successively. The silver nanoparticles formed inside the PAMAM shell. Then, the silver nanoparticles, which were used as center of nucleation, were coated with SiO2shell through improved Stober method. Moreover, the more silver nanoparticles were dispersed on the surface of SiO2shell. The contents of silver element were measured using inductively coupled plasma (ICP-MS). When the obtained PS@PAMAM@SiO2-Ag nanoparticles were packed in stainless steel column, it is used effectively for the catalytic reduction of4-NP. Under column pressures, the rigid SiO2shell plays a better role in immobilization of silver nanoparticles than the soft PAMAM shell. This technique for packing catalytic nanoparticles in column improves the efficiency of application with metal catalysts as well as reduces the tedious separation processes in catalytic reaction.4. The SiO2particles with SiO2-Ag hierarchial shell were prepared and their application in the catalytic column for the reduction of4-nitrophenol (4-NP) was also investigated. The SiO2particles modified with APS silicane coupling agent were used as the supports for the immobilization of SiO2-Ag shell. The silver nanoparticles formed inside the APS shell. Then, the silver nanoparticles, which were used as center of nucleation, were coated with SiO2shell through improved Stober method. Moreover, the more silver nanoparticles were dispersed on the surface of SiO2shell. The contents of silver element were measured using inductively coupled plasma (ICP-MS). When the obtained SiO2@SiO2-Ag nanoparticles were packed in stainless steel column, it is used effectively for the catalytic reduction of4-NP.