Surface Properties And SERS Effects Of Nanostructures And Roughed Electrodes Of Noble Metals

The synthesis and properties of noble metallic nanomaterials have aroused a lot of attention in the scientific field. Great success has been achieved in the designing the mono- and multi-component nanostructures, fabricating methods, as well as the applications in optics, electronics, catalysis, biology. These specific applications are based on the controlled synthesis and the exact growth mechanisms of nanostructures. Therefore, design and synthesis of new nanomaterials with novel properties offer experimental basis for expanding their various applications.Optical properties and catalytic activities are the two specific characteristics of the noble metallic nanostructures. Particularly, surface enhanced Raman scattering （SERS） is a novel optical phenomenon in the nanoscale. It results in the significant enhancement of Raman signal, which is related to the material nature, morphologies, sizes, and the nanostructure aggregation. Fine SERS substrates can be prepared by adjusting the morphologies and sizes. They act as the substrates for molecular absorption and/or reaction, as well as the model materials for the investigation on the SERS mechanisms. Moreover, majority of nanomaterials exhibit excellent catalytic performance due to their high specific surface area. As a result, the noble metallic nanostructures can serve as functional materials in both SERS and catalytic fields.This dissertation is focused on the four facets: synthesis of specific nanostructure morphologies, the growth mechanism of nanomaterials, applications in catalysis, electrocatalysis, sensor, and the molecular adsorption on the rough electrodes, respectively. The main results are listed as follows:（1） Stacking faults enriched Ag nanowires with high yield were prepared by the sodium polyacrylate（PAANa） combined with the seed-mediate（Fe₂O₃/Au） method. Control experiments were performed to identify the effects of the seeds, AgNO3 and PAANa by tuning the adding volumes. A model catalytic reduction of p-nitrophenol by NaBH4 was conducted due to the rich stacking faults in the twist Ag nanowires, The catalytic efficiency of our Ag nanowires is 170 times superior than that of five-fold twinned Ag nanowires prepared by polyol reduction approach. Besides, lots of“hot spot”can be formed originated from their twist characteristics. The excellent SERS performances were proved by the probing molecule, 1,4-BDT. The detection limit was as low as 10-7 mol·dm^-3.（2） It was reported that Ag microplates with controlled morphology were synthesized and applied in fabrication of H₂O₂ sensors. In the presence of PAANa and mixed solvent （water/THF）, a convenient and rapid synthetic method for Ag microplates were sequentially developed. Various approaches, such as the SERS experiments, were employed to determine the crystal pattern and the possible growth mechanisms. It was concluded that the Ag microplates are mesocrystal. Then H₂O₂ sensors were fabricated based on the Ag microplates and their performances were estimated by response linear region, response time, detection limit, as well as selectivity and stability. It was resulted that the Ag microplate sensors have terrific response performances. Their detection linear region is 50μmol·dm^-3 25 mmol·dm^-3, and detection limit is as low as 13.8μmol·dm^-3. High selectivity and stability were also proved by the experiments. There are several advantages of the non-enzymatic sensor, one of the vivid examples is its high sensitivity and wide detection region properties with low construction cost..（3） Rapid synthesis of Pd nanoparticles with controllable morphologies by tunable conditions was performed, as well as their SERS and electrocatalytic properties. Various additives were utilized to prepare the Pd nanomaterials with different morphologies, such as pentacle, concave cube, thorn, waxberry, and large waxberry. The as-prepared Pd nanomaterials were applied in the HCOOH electrochemical oxidation experiments. It was summarized that thorn and waxberry particles were outstanding among these Pd nanomaterials by comparison of the catalytic activities, efficiency, and stability. Therefore, the two materials are the potential anodic catalysts for direct formic acid fuel cells. At the same time, SERS experiments were also carried out to identify the best SERS substrate based on the Pd nanomaterials. It was demonstrated that the strongest SERS signal was from the substrate fabricated by the concave cube. This was relevant to the SERS favored structure and the observed SPR band in the UV-vis spectrum. （4） In situ SERS technology was employed to the systematic investigation of molecular adsorption and/or reaction on various electrodes. It offers the basis of exploring the nanostructures / solutions surfaces at molecular level. Molecules with triple bonds were intentionally selected due to their sensitivity towards the surface structures and electric fields. A series of these molecules, such as 2, 3, 4-CP isomers, 2-amino-5-cyanopyridine, 4-aminobenzonitrile, and phenylacetylene were investigated by SERS combining with electrochemical cyclic voltammetry method. Adsorption information was obtained from the surfaces of the noble metals and transition metals, for instance, Au, Pt, and Pd. It was found that the adsorption of these molecules was heavily depended on the electrodes, potentials, positions of substituted group, and the number of functional groups. Surface reactions of phenylacetylene and 4-aminobenzonitrile were also shown in the extreme negative potentials. In a word, molecules with rings and triple bonds render rich spectral information for resolving the surface behavior in the electrochemical field.