Preparation Of Nano Ag Composites By Poly(dopamine) Functionalization And In Situ Chemical Reduction

As one kind of nanomaterials, silver （Ag） nanoparticles exhibit uniqueoptical, electronic, magnetic, catalytic and sensitive properties since they notonly show excellent properties on electrical and thermal conductivity,sterilization, catalytic, but also have unique effects of metal nanoparticles.Polystyrene/silver core-shell microspheres and carbon nanotubes/silvernanocomposites prepared by immobilizing silver nanoparticles on the surfaceof PS microspheres and CNTs respectively have a wide application on thelow-temperature superconductor, catalysts, biosensors, surface-enhancedRaman scattering, antibacterial and so on. Poly（dopamine）（PDA）, a kind ofenvironment friendly biopolymer, could be formed on a wide range ofinorganic and organic materials by in situ spontaneous oxidativepolymerization of dopamine. PDA could improve the dispersion ofhydrophobic substrates in aqueous solution because of its hydrophilicity. Moreimportantly, the PDA layer could be used as a versatile platform for secondaryreactions. Especially, the metal-binding ability of catechol andnitrogen-containing groups present in the PDA structure was exploited to absorb [Ag（NH3）2]+ions onto various PDA coated surface, and the weakreducibility of PDA was used to reduce the absorbed [Ag（NH3）2]+ions intosilver nanoparticles immobilized onto various substrates. In this work, nanoAg composites were prepared by poly（dopamine） functionalization and in situchemical reduction, and the details are as follows:（1） A novel method to prepare PS-PDA/Ag core-shell microspheres bypoly（dopamine） fictionalization and in situ chemical reduction wasdemonstrated. PS microspheres were coated by PDA. The catechol andnitrogen-containing groups present in the PDA were exploited to absorb[Ag（NH3）2]+ions, and the weak reducibility of PDA was used to reduce theseabsorbed [Ag（NH3）2]+ions into silver nanoparticles immobilized on thePS-PDA surfaces. The silver nanoparticles on the PS-PDA surface could beused as catalytic sites, and make the new silver nanoparticles grow on them inorder to form continuous and dense silver layer. The effect of dopamineconcentration on the thickness of PDA layer, and the effect of the thickness ofPDA layer and AgNO₃concentration on the silver nanaoparticles wereinvestigated. The as-prepared samples were characterized by TGA, SEM,XRD, XPS, contact angle, and electrical conductivity. The results showed thatthe thickness of PDA layer increased with the increment of dopamineconcentration. The diameter of silver nanoparticles decreased with theincrement of PDA thickness, and increased with the increment of AgNO₃concentration. The amount of silver nanoparticles on the PS-PDA microsphere surface increased with the increment of PDA thickness and AgNO₃concentration. When the dopamine concentration reached to2g·L1and theAgNO₃concentration reached to10g·L1, silver nanoparticles could formcontinuous and dense layer on the surface of PS-PDA microspheres to getPS-PDA/Ag core-shell microspheres with electrical conductivity of10S·cm1and effective density of1.8g·cm3.（2） Immobilization of Ag nanopartilces on the surface of CNT-PDA wascarried out to prepare CNT-PDA/Ag nanocomposites. The surface of CNTswas functionalized by PDA layer. The catechol and nitrogen-containinggroups present in the PDA structure were exploited to absorb [Ag（NH3）2]+ions, and the weak reducibility of PDA was used to reduce these absorbed[Ag（NH3）2]+ions into siver nanoparticles immobilized on the CNT-PDAsurfaces. The effect of dopamine concentration on the thickness of PDA layer,and the effect of PDA layer on dispersion of CNTs in the aqueous solutionwere investigated. The as-prepared samples were characterized by HR-TEM,TGA, XRD, and XPS. The results showed that the thickness of PDA layerincreased with the increment of dopamine concentration, and the PDA layercould improve the dispersion of CNTs in the aqueous solution because of itshydrophilicity. When the dopamine concentration was2g·L1and the AgNO₃concentration was10g·L1, spherical silver nanoparticles with3–4nm wereimmobilized homogeneously on the surface of CNT-PDA, and the spacebetween silver nanopartilces was less than10nm. The thickness of PDA layer, the diameter of silver nanoparticles, and theamount of silver nanoparticles could be controlled by changing reactionconditions such as dopamine concentration, AgNO₃concentration, and so on.The method used in this work provides the advantages of simple operation,mild reaction condition, and enviorment friendly, no special requirements onequipment, no special requirments on the type and the shape of materials, andso on.