Research On The Preparation, Characterization And Properties Of Silver / Graphene Nano Hybrid Materials

With the alteration of the surface electronic structure and crystal structure, nano materials produced a series of specific properties which conventional materials do not possess, including the small size effect, the quantum size effect, the macroscopic quantum tunnel effect, the surface effect and the dielectric confinement effect. Compared with conventional materials, nano materials with the above specific effects, have wide potential application in various fields.Matrix assisted laser desorption/ionization mass spectrometry(MALDI MS) has become an prominent technology of biological analysis, which has played an significant part in the analysis of biological molecules, especially for the quality of biological macromolecules inlcuding protein, DNA and polysaccharide. It has advantage of using a small amount of sample and the ability of determining the sequences of nucleotide or peptides and high sensitivity and no longer need markers, which is suitable especially for high throughput screening. But it is rarely used for the analysis of small molecules(<700 Da), because MALDI mass spectra suffer from high chemical background noise in the low-mass region(<700 Da) due to the formation of clusters of matrix ions or matrix degradation products. With the use of nanomaterial-coupled MS techniques, the detectable mass range of Surface-assisted laser desorption/ionization mass spectrometry(SALDI-MS) has been extended from the low- to the high-mass region for the analysis of large molecules including proteins and synthetic polymers as well as small biomolecules, pharmaceuticals, peptides, carbohydrates, and nonpolar compounds.With the small size effect, the surface and interface effect and the quantum size effect, the nanoparticles has many superiorities in catalysis compared with the traditional catalysts, including the better catalytic activity, reproducibility and selectivity.Surface-enhanced Raman scattering(SERS) technique has verified to be a striking analytical approach due to its outstanding sensitivity, superior selectivity, and the property of fluorescence-quenching, which is a nondestructive tool that provides rich molecular information about molecules and molecular structures in the close district of noble metal surfaces such as gold and silver. With the facility of single molecule detection sensitivity, it has become a prominent technique for the characterization and determination of a variety of molecules. One highly promising approach for the design of SERS substrates involves the positioning or fabrication of nearly adjacent metallic nanostructures with nanoscale gaps.According to the mentioned background, we mainly have done the following three studies in this paper.1. We report the design and construction of an Ag NP/graphene-assembled porous nanostructure for the effective SALDI MS analysis of small molecules including amino acids, fatty acids and other small molecules. The nanoporous material with large surface area is derived from layer-by-layer assemblies of the negatively charged silver nanoparticles and graphene and the positively polymers on an underlying silicon wafer, which provides superior biocompatibility for biomolecules surface analysis. The nanoporous structure was characterized by scanning electron microscopy(SEM), in which Ag NPs and graphene can be observed.2. Graphene oxide-supported double shell hollow Au-Ag nanocages(Au Ag NC/GO) were in situ fabricated by employing a galvanic replacement reaction between HAu Cl4 and Ag nanoparticles loading on the graphene oxide nanosheets(Ag NP/GO). Ag NPs on the graphene oxide nanosheets were firstly synthesized as sacrificial templates by the microwave method. The as-obtained hybrid materials were characterized by transmission electron microscopy(TEM), energy dispersive X-ray spectroscopy(EDX) and X-ray photoelectron spectroscopy(XPS). In the well-known reaction system of 4-nitrophenol(4-NP) reduction to 4-aminophenol(4-AP) with the presence of excess borohydride, Au Ag NC/GO as a solid phase heterogeneous catalyst has been investigated, which exhibited perfect catalytic activity and good stability against agglomeration for the reduction.3. An effortless, stable, and repeatable method for the aggregation of Ag NPs in aqueous solutions without any aggregation agents has been proposed. The procedure of this method consists of centrifugation, water washing and following ultrasonication. The information of the components and structure of as-obtained aggregation has been identified by UV visible spectroscopy and TEM. We have proposed the mechanism of the as-obtained aggregation, which is devised from the asymmetric distribution of capping agents. Further, on the as-obtained silver nanoparticle aggregations, the SERS signals of the residual citrate with the low concentration and the single-molecule R6 G were obtained. Drip a drop of the as-obtained silver nanoparticle aggregations on the Si substrate. After the drying process, the signals of citrate or R6 G could also be observed respectively besides the marked red- or blue-shifts.