Silver-based Nanocomposites As SERS Substrate:Fabrication And Detection Of Aromatic Dyes

The rapid and sensitive detection of toxic and harmful substances in the environment has important practical significance for the protection of life and health,and the maintenance of ecological security.Aromatic dye molecules,such as Crystal Violet(CV),Malachite Green(MG),Rhodamine 6G(R6G),Methylene Blue(MB),and so on,are high carcinogenicity,toxicity,vestigital and teratogenicity,so it is important to detect the aromatic dye molecules in the environment.Surface enhanced Raman scattering spectroscopy(SERS)has been widely used for environmental monitoring due to its advantages of high sensitivity,selectivity and no requirement for pretreatment of samples.Moreover,preparing highly efficient SERS substrates is always one of the main research direction.Therefore,in this thesis,three SERS enhancement substrates were synthesized to detect the dye molecules by SERS technique.The main contents as follows:In the first work,a simple wet-chemical approach is proposed to prepare spinous silver@gold(Ag@Au)or silver@gold@silver(Ag@Au@Ag)nanostructures as highly active substrates for SERS dectetion.Using silver nanostructures with different shapes(nano-spheres,nano-rods or nano-sheets)as precursors to prepear spiny Ag@Au or Ag@Au@Ag nanostructures which have similar shapes with precursors.These spinous products display a broad and enhanced absorption spectrum in the visible light region,and high enhancement ability as SERS substrate.For probing CV,all spiny Ag@Au@Ag with different shapes display much stronger SERS signal than those of corresponding Au@Ag precursors.Among these products,the spiny Ag@Au@Ag with spherical shape shows the highest enhancement ability.The synthetic method has the advantages of low cost,simple operation and high yield,and the obtained products may have a good prospects for application in other fields.In the second work,reduced graphene oxide-silver nano-particle composite(rGO-Ag)wrapped by a thin layer of poly-dopamine(PDA)to prepare a highly active substrate for surface enhanced Raman scattering detection of aromatic dyes.In the reduced of graphene silver@poly-dopamine(rGO-Ag@PDA)complex,rGO-Ag was obtained by one-pot citrate reduction and the PDA was prepared by self-polymerization of dopamine.As a result of wrapping a layer of dopamine molecules,the synthesized rGO-Ag@PDA composite had a stronger adsorption ability to dye molecules.Therefore,it possess stronger SERS signal of dyes molecules than rGO-Ag.The prepared rGO-Ag@PDA composite served as SERS substrates and achieved highly sensitive detection of CV,MG and MB.Moreover,the rGO-Ag@PDA also displayed enhanced stability and improved recyclability than those of rGO-Ag.In the third work,silver nano-sheets(AgNSs)were grown on a three-dimensional macroporous substrate for molecule sensing by SERS.Interlaced silver nano-sheets(AgNSs)growed on three dimensional macroporous carbon foam(3D-CF)which decorated by poly-aniline(PANI)nano-bars to prepare AgNSs@PANI/3D-CF composite.The 3D-CF obtained from the carbonization of melamine foam was used as the framework,and PANI was grown as a reduced agent.Controlling the silver growth time and introduction of succinic acid were the key factors for preparing the interlaced silver nano-sheets which fully covered on the 3D scaffold surface.The porous structure and large surface area of the hybrid possessed a high adsorption ability to dye molecules.And interlaced AgNSs endow the hybrid with dense hots spot for highly efficient SERS detection.AgNSs@PANI/3D-CF as SERS substrate can detect 4-MBA,Nile blue(NB),MB and show high enhanced ability.Using NB as a probe molecule can detect the actual water sample.The proposed hybrid with special structure,high Raman enhancement ability and good reproducibility may find promising applications in environment monitoring,optical sensing and so on.