Chemical Synthesis Of Silver Nanoparticles With Various Morphologies And Its Application In Fluoresence Enhancement

The progress of nanomaterials suggests its great potential foreground in the fields of synthetic chemistry and materials science,especially for metal nanoparticles with unique chemical and physical properties,which have extensive applications in optics,optoelectronics,sensor and bioassays.Their properties are strongly depended on the size and shape of metal nanoparticles.Therefore,it is believed that property-controllable metal nanoparticles will be conveniently produced by tuning their sizes,dimensionalities,compositions and morphologies,and expected to be fabricated into functional nanodevices.Although there have been a lot of reports on the synthesis of nanomaterials,the shape-controllable synthesis is still a challenge for materials and chemistry researchers.Based on the development of metallic silver nanoparticles in the world,this dissertation presents a facile chemical solution-method to prepare silver nanoparticles with various morphologies and obtain novel silver nanostructures.This dissertation also investigates application of silver nanoparticles in metal-enhanced fluorescence(MEF).The main results and conclusions of this dissertation are outlined as follows:Chapter 2 presents a seed-mediated method to synthesize triangular silver nanoparticles in solution and on the glass.The nanoparticles synthesized in solution showed size of 50±5 nm and thickness of 27±4 nm.They exhibited different morphologies in transmission electron microscopy(TEM)and atomic force microscopy(AFM),respectively.The most suitable temperature for preparation of seed solution was 35℃.Triangle-like silver nanoparticles could also be obtained on the glass by the seed-mediated method.The formation of the triangular nanoparticles was due to the modification in growth rates of crystalline planes by CTAB.Chapter 3 demonstrates a soft template method to prepare zigzag silver nanowires and gleditschia horrida-like silver nanoparticles.Zigzag nanowires showed uniform diameter of 20±5 nm,length of 600 nm and angles range of 74～151°.These nanowires with interesting shape were developed from end-to-end nanorods,and the interface could be observed between two nanorods.With the reaction time extended, the interface gradually disappeared,and zigzag nanowires finally formed.If the reaction temperature was elevated to 150℃and time was reduced to 6 h,the gleditschia horrida-like nanoparticles with size of 60～70 nm could be obtained.In Chapter 4,we demonstrate a solvothermal route to the shape-controllable synthesis of mono-dispersed triangular/hexagonal silver nanoplates,chain-like silver nanoplate assemblies and silver nanobelts in the presence of PVP,using DMF as solvent and reducing reagent.The strong interaction between PVP and Ag⁺ ions could be favorable for slowing down the reaction of DMF and AgNO₃.A slow and moderate reduction rate was advantageous for the formation of the nanoplates at higher yields,and the outline of silver nanoplates was determined by the ratio between AgNO₃ and PVP.The formation of novel chain-like nanoplate assemblies could be explained according to the secondary growth of the nanocrystals.If the reaction was continuously lasted for 7 h after the chain-like assemblies shaped, belt-like nanostructures with uniform aspect ratio could be obtained,showing diameter of 40～100 nm and length of several,even tens of micrometers.In Chapter 5,we investigate the effects of silver nanoparticles and silver nanoparticles coated-films on the fluorescent properties of dye Rhodamine B.Silver nanoparticles could largely enhance the fluorescence intensity of Rhodamine B and partially release its self-quenching effect.With the increase in the concentration of silver nanoparticles,the fluorescence intensity of Rhodamine B firstly enhanced up to a maximum,and then decreased.Among triangular nanoplates,hexagonal nanoplates, chain-like nanoplate assemblies and nanobelts,the maximal fluorescence enhancement of Rhodamine B solution could be obtained in the presence of silver nanobelts.The fluorescence intensity of Rhodamine B could also be enhanced in the presence of silver nanoparticles coated-films,and dye could exhibit higher emission intensity than that in the presence of silver nanoparticles.