Preparation Of Micro-nano Materials Of Gold And Composite Silver Salts And Their Surface Enhanced Raman Scattering And Catalytic Performance

Due to the unique surface-dependent particle properties, size-dependent particle properties and size-dependent quantum effects of nanoparticles, the optical, electronic/electrical, magnetic, and catalytic properties of nanomaterials are different from those of the corresponding bulk materials, making nanomaterials very attractive in diverse fields including energy, electronic, medicine, chemical engineering and biological engineering. Au and Ag are two important noble metals. Au is the most stable metal and Au nanoparticles (NPs) are catalytically active, nontoxic and biological compatible, which have been widely applied in biosensing and catalysis. Silver halides and doped silver oxides were proven to be photocatalytic activity. Moreover, Ag and Au nanomaterials are the most used and effective surface enhanced Raman scattering (SERS) substrates. In this thesis, several novel and convenient approaches have been developed to fabricate gold or silver salts based functional micro/nanomaterials. We systemically investigated the SERS performance on several SERS-active Au substrates, the electrocatalytic oxidation of HCOOH on AuPt bimetallic electrocatalysts, the enzyme-free detection of glucose on nanoporous Au film and the photocatalytic activities of several Ag2SO3based composite particles. The main points of this thesis are summarized as follows:1. Literature about the preparation and application of micro-nanostructured materials, SERS effect, nonenzymatic glucose sensors, the electrocatalytic oxidation of HCOOH and semiconductor photocatalysis have been systematically reviewed.2. A unique one-step anodic potential step strategy has been developed to fabricate a three-dimensional (3D) nanoporous gold film (NPGF) within one minute as an efficient SERS active substrate. The SERS performances of the NPGFs fabricated in electrolytes of KCl and HCl were compared for the first time, using pyridine as a test molecule. Equivalent SERS intensities can be obtained on the3D NPGFs prepared in these two electrolytes under respectively optimum conditions. The results indicated that H+had subtle influences on the size of nanogaps between Au NPs. Subnanometer gaps between two NPs and crevices within fused NPs were produced in situ in HCl electrolyte due to the dissolution of protective gold oxide coatings, which significantly promoted the electromagnetic filed enhancement. For NPGF prepared in KCl electrolyte, wider nanogaps were presumably created in the follow-up acidic treatment. Accordingly, the electromagnetic filed enhancement effect was somewhat weaker than the former. However, NPGF prepared in1M KCl had larger surface area to adsorb more analyte molecules, which compensated the smaller electromagnetic filed enhancement in some extent, showing comparable SERS intensity as that of NPGF prepared in2M HCl.3. Clean dendritic gold (DG) was directly fabricated on a smooth gold electrode via square wave potential pulses (SWPPs) in a blank H2SO4solution containing no Au(III) species and additives. The effects of potential range, frequency and duration time of SWPPs and H2SO4concentration on the construction of DG were systematically investigated. The formation and evolution of DG were characterized by scanning electron microscopy (SEM). The growth of DG was believed to be nanoparticle-aggregated self-organization involving diffusion transport process of soluble Au species in H2SO4solution and deposited Au atoms at surface. The whole process was templateless and surfactantless, and therefore effectively avoided possible contaminations that occurred in other synthetic routes. Further, the morphological effect of DG under different development stage on SERS performance was investigated and discussed using rhodamine B as probe molecule.4. Ordered arrays of polystyrene (PS) spheres dissymmetrically decorated with gold nanoparticles (NPs) were facilely assembled at air/liquid interface by the combination of colloidal crystal templating method and modified conventional electroless plating technique. Sn2+ions served as the reductant, stabilizer and sensitizer. Colloidal Au NPs spontaneously aggregated onto the sensitized portion of PS spheres due to oxygen-induced ligand replacement of SnCl3-with Cl-, forming asymmetric PS/Au composite particle arrays. Moderate heating accelerated the assembly process. The method presented here is convenient, cost-effective and can be extended to prepare asymmetric composite particle arrays of PS/Pd and PS/AuPd. Furthermore, the SERS performance of the ordered arrays of asymmetric PS/Au composite particle array was examined. It was found that the SERS performances of PS/Au composite particles were dependent on the aggregation state of Au NPs on PS spheres, where effective nanometer and sub-nanometer gap between two close Au NPs formed. Local electromagnetic field enhancement from the closely packed Au NPs assembled on the PS spheres and from the aggregation of PS/Au particles was believed to be responsible for the strong SERS signals. Besides, nanojets would be formed when a laser passed through the bare top of asymmetric PS/Au structures, which led to the highly localized electromagnetic field. The method described in this work provided a new and much simple route to prepare ordered SERS-active substrates.5. A nonenzymatic amperometric method was established for glucose detection using a nanoporous gold film (NPGF) electrode by a rapid one-step anodic potential step method within5min in1M KCl. The prepared NPGF was characterized by SEM and cyclic voltammetry. The NPGF has a large roughness over200and thus possesses high electrocatalytic activity toward the direct oxidation of glucose with good stability. Electrochemical responses of the as-prepared NPGF to glucose in0.1M PBS (pH7.4) with or without Cl-were discussed. In amperometric studies carried out at-0.15V in the absence of Cl-, the NPGF electrode exhibited a high sensitivity of232μA mM-1cm-2and gave a linear range from1mM up to14mM with a detection limit of53.2μM (with a signal-to-noise ratio of3). The interferences from ascorbic acid (AA) and uric acid (UA) at physiological levels can be completely eliminated at such a low applied potential. On the other hand, the quantification of glucose in0.1M PBS (pH7.4) containing0.1M NaCl offered an extended linear range from10μM to11mM with a sensitivity of66.0μA mM-1cm-2and a low detection limit of8.7μM (signal-to-noise ratio of3) at a detection potential of0.2V.6. By controlling the electrodeposition time, we successfully fabricated Pt-decorated dendritic Au electrode (Pt-DG), Pt-decorated nanoporous Au electrode (Pt-NG) and Pt-decorated smooth Au electrode (Pt-SG). The morphologies and composition of the three Pt-decorated Au electrodes and dendritic AuPt alloy for HCOOH oxidation were systematically investigated and compared. The low Pt loading Pt-DG demonstrated different electrochemical behavior from that on Pt-NG, Pt-SG and on Pt-decorated Au NPs because of more defect sites like steps and edges on the DG surface. The defect sites with low coordinated atoms on DG for depositing Pt clusters were supposed to contribute to the enhanced electrocatalytic activity for the oxidation of HCOOH. Ensemble effect, as well as electronic effect, account for the improved electrocatalytic activity of low Pt loading Pt-DG. 7. Ag2SO3based composites, ASO/Ag2S (ASO=Ag2SO3/Ag2SO4) and ASO/AgX (X=Cl, Br), were prepared by a simple and mild gas-liquid reaction and ion-exchange method. SEM, energy-dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD) and UV-vis diffuse reflectance absorption spectra were performed to characterize the as-synthesized materials. The photocatalytic performances of Ag2SO3, ASO, ASO/Ag2S and ASO/AgX (X=Cl, Br) were evaluated by the photodegradation of Rhodamine B (RhB) under simulated visible light. The formation of photo-reduced Ag nanoparticles (NPs) during visible light illumination resulted in plasmon-induced photodegradation of RhB.8. Density functional theory (DFT) and conceptual/chemical DFT study were carried out in this work for the normal electron demand Diels-Alder reaction between isoprene and acrolein to compare chemical reactivity and regioselectivity of the reactants in the absence and presence of Lewis acid (LA) catalysts. Catalytic activities of different LAs have been estimated via frontier molecular orbitals and found to be consistent with experiments. Linear relationships have been discovered among the bond order, bond length, catalytic activation, and chemical reactivity for the systems concerned. The validity and applicability of maximum hardness principle (MHP), minimum polarizability principle (MPP), and minimum electrophilicity principle (MEP) were examined for the systems and discussed in the prediction of the major regioselective isomer and the preferred reaction pathway for the reactions in the present study.