Preparation And Applications Of Noble Metal Nanoparticle/agarose Composite Gels

Noble metal nanomaterials have received broad interests due to their excellent physical/chemical features, such as optical, electrical, magnetic properties, and catalytic and antibacterial capabilities. Herein, a brief introduction is made concerning the synthesis, structure, properties and applications of noble metal nanomaterials. In general, metal nanoparticles are synthesized through the reduction of the corresponding metal ions. To avoid the agglomeration in the nanoparticle preparation, stabilizing agent is always added. In this thesis, noble metal based nanoparticle/agarose composite gel is prepared, using agarose both as the reducing agent and stabilizing agent.Gold nanoparticle/agarose and silver nanoparticle/agarose composite gel were produced through a one-step reduction process, using chloroauric acid, silver nitrate and agarose as the starting materials. The size and structure of obtained nanoparticles were characterized by UV-Vis spectrophotometer(UV-Vis), transmission electron microscopy(TEM), dynamic light scattering. The effects of the reaction conditions and the post-treatment methods on the size and morphology of prepared nanoparticles were investigated. The results show that the obtained gold and silver nanoparticles present a size of 1~10nm and 1~50 nm, respectively, with a narrow size distribution dispersion. The amount of obtained nanoparticles increases with the increasing content of agarose and the increasing concentration of chloroauric acid/silver nitrate. The particles size, however, decreases with the increasing concentration of the starting materials. In addition, the amount of nanoparticles also increases with the reaction time in the preparation process.The stability of gold nanoparticle/agarose composite gel was investigated in the presence of acid/basic solution with varing ion concentration, in order to understand the proper condition for its applications. The results show that, the ionic strength does not obviously affect the stability of the composite gel. The maximum temperature for the practical use of the composite gel is about 40 ?, and the appropriate pH value of the solution is less than 10. In the applicable solution condition, the gold nanoparticle/ agarose composite shows significant catalytic activity in the reduction reaction of p-nitrophenol. The time for complete conversion of p-nitrophenol to p-aminophenol is about 30 min, and the catalytic activity of the composite gel declines a little in the recycling assay.The antibacterial activities of silver nanoparticle/agarose composite gel were studied against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. The results show that with the increase of the concentration of silver nitrate or agarose in the preparation process, the antibacterial activity of the composite gel is enhanced.In summary, the preparation procedure of gold/silver nanoparticle/agarose composite gel presented in this thesis has the advantages of facile synthesis, easy handling, and convenient recycling, and paves a new way for the design, synthesis and applications of active catalysts/antibacterial agent based on metal nanoparticles.