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The rapid recombination of carriers on plasmon metal nanoparticles leads to relatively low efficiency of traditional photocatalysts. The combination of a metal and a semiconductor allows to the separation of hot electrons and holes to improve photocatalytic efficiency. In this study, Au nanoparticles were integrated with semiconductor TiO2 nanoparticles of different sizes to improve the photocatalytic activity. Various techniques have been developed to study the mechanism of catalytic activity, the significance of band bending in the space-charge region within metal–semiconductor nanocomposites, and the built-in electric field. The results provide theoretical and experimental evidence for the design of a high-performance surface plasmon resonance (SPR) photocatalyst. To reveal the interface band structure, surface-enhanced Raman spectroscopy (SERS) was employed to analyze the band structure of the TiO2–metal composites. This approach was based on the electrochemical Stark effect and a molecular probe strategy, combined with X-ray photoelectron spectroscopy (XPS), Electrochemical impedance spectroscopy (EIS), and other techniques at the molecular level. The results demonstrated that charge transfer occurred spontaneously between the Au nanoparticles and TiO2, and that the TiO2–metal interface constitutes a Schottky barrier. Moreover, the size of the TiO2 nanoparticles affects the degree of band bending. Optimal state matching was achieved with TiO2 (60 nm)–Au, improving the photocatalytic activity of the nanocomposite. The photocatalytic coupling reaction of p-aminothiophenol (PATP) acted as a probe to study the catalytic performance of TiO2–metal nanocomposites. The results revealed that the introduction of TiO2 improves the SPR catalytic activity of Au, mainly through the efficient separation of electrons and holes at the TiO2–metal interface.

Discharging of aprotic sodium-oxygen (Na-O

One hexanuclear Cu(I) cluster of 4,6-dimethylpyrimidine-2-thiolate efficiently catalyzes the dehydrogenative cross-coupling of secondary and primary alcohols to α-alkylated ketones with high selectivity. This transformation proceeds through a one-pot sequence of dehydrogenation of alcohols, condensation of aldehydes and ketones, hydrogenation of the resulting α,β-unsaturated ketones, and dehydrogenation of the α-alkylated alcohols to generate α-alkylated ketones. This catalytic system also displays high activity for the annulation reaction of secondary alcohols with γ-amino- and 2-aminobenzyl alcohols to yield pyridines and quinolines, respectively.

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Silicon nanowire arrays (SiNWAs) are under extensive investigation for solar cells and biomedical applications. This study reports for the first time that hydrogen fluoride-treated (H)-SiNWAs are an efficient catalyst for the reduction of nitrobenzene derivatives. We show that SiNWAs, after hydrogen fluoride treatment, have a high catalytic activity in p-nitrophenol (PNP) reduction. The conversion rate of PNP by H-SiNWAs increases with time and is almost complete within 30 min, which thus indicates catalytic activity comparable to that of platinum nanoparticles. The catalytic activity of SiNWAs is closely related to the chemical composition and specific morphology of the surface. SiH bonds on the surface are essential for activity, and arrays with longer nanowires showed a higher catalytic activity. Moreover, the activity can be easily regenerated by hydrogen fluoride treatment. It was also found that H-SiNWAs exhibit a similar catalytic activity for the reduction of other nitrobenzene derivatives such as p-nitroaniline and sodium m-nitrobenzenesulfonate. It is concluded that H-SiNWAs may be considered as an environmentally friendly alternative to noble-metal-based catalysts for the reduction of nitrobenzene derivatives.

Traditional "sandwich" structure immunoassay is mainly based on the self-assembly of "antibody on solid substrate-antigen-antibody with nanotags" architectures, and the sensitivity of this strategy is critically depended on the surface enhanced Raman scattering (SERS) activities and stability of nanotags. Therefore, the rational design and fabrication on the SERS nanotags attracts the common interests to the bio-related detecting and imaging. Herein, silica encapsulated Au with mercaptobenzoic acid (MBA) core-shell nanoparticles (Au-MBA@SiO

The fabrication and characteristics of spindle Fe2O3@Au core/shell particle were investigated, and the effect of the core/shell nanoparticles as the surface enhanced Raman spectroscopy (SERS)-active substrates was studied. By using the seed-catalyzed reduction technique, anisotropic Fe2O3@Au core/shell particles with spindle morphology were successfully prepared. The Fe2O3 particles with spindle morphology were initially prepared as original cores. The Au nanoparticles of 2 nm were attached onto the Fe2O3 particles through organosilane molecules. Uniform Au shell formed onto Fe2O3 core modified by Au nanoparticles through the in-situ reduction of HAuCl4. The shell thickness was controlled through regulating the concentration of HAuCl4 solution. The results of TEM, XRD and UV-vis characterization show that the core/shell particles with the original shape of the Fe2O3 particles are obtained and these surfaces are covered by Au shell completely. The surface enhanced Raman spectrum of the probe molecules adsorbed on these core/shell substrates is strong and the intensity is enhanced with the increase of the thickness of Au shell or the aspect ratio of particles. The spindle Fe2O3@Au core/shell particles exhibit optimum (SERS) activity.

The SiO2 shell with the thickness of 4 nm was attached onto high surface enhanced Raman spectroscopy (SERS) active Au core nanoparticles to obtain Au@SiO2 core shell nanoparticles by the hydrolysis of sodium silicate solution with the boiling water bath. The inert shell of SiO2 isolated the direct interaction of Au nanoparticles and probe molecules. The stable, compact and uniform monolayer nanoparticles film was self assembled at water/oil interface, and one to six monolayers film was transferred to Si wafer as SERS substrates through layer by layer technique. The relationship between the SERS activities and layers of the monolayer nanoparticles film on Si surface was investigated. The SERS mapping was developed to determine the layers of the Au@SiO2 film. The coupling effect among the Au@SiO2 films was explored by changing the adsorption location of the probe on the multilayer films. The result revealed that the monolayer film was a favourable candidate with high-quality performances for the SERS application. The SERS signal was distributed on the surface with high uniformity at the same monolayer film, and it was enhanced in the intensity with the increase in film layers. It reached the maximun intensity as the film was over five layers. It indicated that the SERS signal was contributed mainly by the first five monolayers. The probe molecules were immobilized onto the first monolayer nanoparticles film, and the SERS signal from the probe approached to the maximum as the second monolayer covered the probe modified first nanoparticles film. It was dominated by the coupling effect ("hot spots") of the adjacent layers. The SERS signal decreased in intensity when the third layer was transferred onto the second layer, and it disappeared after the fouth layer was covered, mainly duo to the shield of the nanoparticles film to the incident laser and Raman signal. The preliminary results provided guidance for fabricating optimal SERS substrates.

A new approach was developed for the magnetic separation of copper(II) ions with easy operation and high efficiency. p-Mercaptobenzoic acid served as the modified tag of Fe2O3@Au nanoparticles both for the chelation ligand and Raman reporter. Through the chelation between the copper(II) ions and carboxyl groups on the gold shell, the Fe2O3@Au nanoparticles aggregated to form networks that were enriched and separated from the solution by a magnet. A significant decrease in the concentration of copper(II) ions in the supernatant solution was observed. An extremely sensitive method based on surface-enhanced Raman spectroscopy was employed to detect free copper(II) ions that remained after the magnetic separation, and thus to evaluate the separation efficiency. The results indicated the intensities of the surface-enhanced Raman spectroscopy bands from p-mercaptobenzoic acid were dependent on the concentration of copper(II) ions, and the concentration was decreased by several orders of magnitude after the magnetic separation. The present protocol effectively decreased the total amount of heavy metal ions in the solution. This approach opens a potential application in the magnetic separation and highly sensitive detection of heavy metal ions.

Magnetic nanoparticles as well as core-shell magnetic nanocomposites are of great interest for researchers due to their potential applications in lots of areas. In the present review, the authors summarized several universal synthetic methods of nanocomposites and their specific properties. In the following, the authors focused on the applications of functionalized magnetic nanoparticles in separation and spectral detection, along with the introduction of some work in the authors' lab. At last, the questions remaining in magnetic nanoparticles and the application perspectives of magnetic nanocomposites were discussed.

Gold nanoparticles were homogeneously coated with silica using the silane coupling agent (3-aminopropyl)-trimethoxysilane to functionalize the gold surface and sodium silicate solution as the precursor of silica. The shell thickness could be well controlled by changing the amount of sodium silicate, reaction temperature and time. The Au@SiO2 core-shell nanoparticles with a suitable silica shell thickness exhibited optimal SERS activity and were self-assembled onto an ITO substrate in order to get a stable and reproducible SERS substrate. The conditions for preparing SERS substrates can be optimized by investigating the relationship between the intensity of SERS signals and the thickness of silica shell. The reproducible SERS measurements were performed by using 1,4-BDT and 4,4'-bipyridine as probe molecules. Within a certain concentration range, the linear relationship between the SERS intensities and the logarithm of concentration was obtained. The results revealed that the Au@SiO2 substrate assembled on ITO surface could be developed as a reproducible substrate for the quantitative analysis.

Two kinds of nanoparticles (gold nanoparticles and Au core Pt shell nanoparticles) on silicon surfaces which were silanization were electrostatically self-assembled. The density of nanoparticles was controlled by changing the time of the substrate immersed in colloids. The substrate was characterized by scanning electron microscope (SEM), and the results indicated that Au and Au@Pt particles were dispersed on the substrate with mono/submonolayers. The authors used pyridine (Py) as a probing molecule, and surface enhanced Raman spectroscopy (SERS) effect was investigated on pure Au and Au-Au@Pt mixed nanoparticle surfaces under the excitation line of 632.8 nm. The results revealed that there is a significant shift of the two characteristic peaks of Py, but the enhancement factors of Au dropped off precipitously with the introduction of the Au@Pt nanoparticles. The authors attributed this effect to the introduction of metal d-states from the metal, which would serve effectively to quench the surface plasmon excitation necessary for large (electromagnetic) enhancements in Raman spectroscopy.

Labelled immunoassay by surface enhanced Raman scattering (SERS) has great research and application value. It combines SERS which has the high sensitivity and high selectivity with specific adsorption in immunology. The present paper mainly studies the regeneration about SERS labelled immunoassay, striving to develop the recycling value of it. The authors used glycine-HCl eluent for the sandwich structure including solid matrix antibody, antigen and labelled immuno-gold colloids, then the authors had got expected result. The complex of antibody and antigen would be separated by changing the pH scale. It could elute the most antigen and the labelled immuno-gold colloids. Also the authors could assemble it again and distinguish the characteristic SERS spectrum of the reporter molecules. Under this condition, we researched the stability and reusing of this technology. The authors found that it has better stability and it retained activity after 10 recycles of applications.

Surface-enhanced infrared absorption spectroscopy (SEIRAS) in attenuated total reflection (ATR) configuration has been extended to the Fe electrode/electrolyte interface in neutral and weakly acidic solutions for the first time. The SEIRA-active Fe film electrode was obtained through a potentiostatic electrodeposition of a virtually pinhole-free 40 nm-thick Fe overfilm onto a 60 nm-thick Au underfilm chemically predeposited on the reflecting plane of an ATR Si prism. The infrared absorption for CO adlayer at the Fe film electrode measured with ATR-SEIRAS was enhanced by a factor of larger than 34, as compared to that at a Fe bulk electrode with external infrared absorption spectroscopy in the literature. More importantly, the unipolar band shape enabled the reliable determination of the Stark tuning rates of CO adlayer at Fe electrode. In situ ATR-SEIRAS was also applied to study the electrosorption of a typical corrosion inhibitor benzotriazole (BTAH) on Fe electrode as a function of potential, providing additional spectral information at positive potentials in support of the formation of a polymer-like surface complex Fe(II)(m)(BTA)(n) as the corrosion-resistant layer.

Various roughening methods for the bare Ti electrode such as mechanical roughening, electrochemical oxidation-reduction method and chemical etching were tried to obtain surface-enhanced Raman spectra (SERS) successfully for the first time. The results of the experiments proved that mechanical roughening and electrochemical oxidation-reduction method could be successfully employed in roughening titanium electrode, however, surfaces roughened in such ways showed no SERS-activity in Raman detection. Finally, chemical etching with hydrofluoric acid was proved to be an effective way to get SERS-active titanium surface, and surface-enhanced Raman spectra of pyridine adsorbed on a titanium surface was observed for the first time. In order to get the most effective titanium surface, roughening conditions, including concentration of the acid, the time of etching and the external potential, were investigated. As illustrated, Raman activity varies with conditions changing in roughening processes and the most reasonable condition for roughening was indicated. The result showed that at the concentration of hydrofluoric acid 0.33% (Wt) and 5 min for etching, the most SERS-active rough titanium surface could be obtained. In addition, with an external potential to speed up corrosion, the surface of titanium electrode tended to form a thin film of oxide, which prevented further corrosion and caused SERS-activity decrease. Thus, in this paper, the surface-enhanced Raman spectra of pyridine (pyridine 0.01 mol L(-1), and electrolyte KCl 0.1 mol L(-1)) adsorbed on bare roughed Ti electrode were observed at open circuit potential. Referring to the calculations of enhancement factor of pyridine on electrode, the enhancement factor is about 102 on the roughened titanium electrode.

Using citrate as protector, Au-Ag alloy nanoparticles with different molar ratios were prepared with hydrazine as the reducer. One plasmon band between monometallic Ag and Au was observed in their UV-Vis spectra. And the peak of alloy shifted linearly with the ratio of Au changing in the alloy. By UV-Vis spectra, the course of reaction of the alloy colloid with HAuCl4 was studied. The result shows that the UV-Vis spectra of the alloy colloid changed regularly with the adding volume of HAuCl4 increasing. And there is a linear interval in it with the change in the calculated ratio of Au. With the former studies, the course can be attributed to the dealloy of Au/Ag alloy.

Ag and Au nanoparticles were self-assembled on a silicon substrate simultaneously. The density of Ag and Au nanoparticles was controlled by changing the volume ratio of Au to Ag colloids. The substrate was characterized by UV-Vis diffuse reflectance and SEM, and the results indicated that Ag and Au nanoparticles were dispersed on the substrate with mono/submono layers. Using SCN as a probing molecule, surface enhanced Raman spectroscopic (SERS) effect was investigated on pure Au, pure Ag and Au-Ag mixed nanoparticle surfaces. After a series of calibration, the results revealed that the SERS spectral features of SCN from the mixture system were similar to those from the pure Ag nanoparticles, indicating the coupling effect between the Ag and Au nanoparticles, which results in the property of Au inclining to Ag.

In the present paper, the authors reported the assembly and SERS studies of a simple device unit of a metal nanowire-molecule-metal nanoparticles junction in an anodic aluminum oxide (AAO) template. The AAO template was fabricated by two-step electrochemical oxidation. Metals were filled into the pores by AC deposition. Then the AAO template with metal nafiowires was immersed into the solution of 1,4-benzenedithiol (1,4-BDT), which was followed by the immersion into silver nanoparticles with appropriate diameter. 1,4-BDT served as the probe molecule for SERS detection as well as the molecule for linking the metal nanowires and metal nanoparticles. The simple junction of metal-molecule-metal embedded in AAO template was built successfully. The SERS effect of the junction was investigated through the dissolution of AAO template to expose the junctions in the same orientation (standing on the substrate vertically). The giant enhancement from the former junction might be attributed to the coupling effect in the junction. The authors' preliminary results revealed that SERS might be a characteristic tool for the junction and the construction on the junction will be beneficial to the investigation of the complex SERS mechanism.

The adsorption behavior and coadsorption of N-methylimidazole (NMIM) and 2,2'-bipyridine(2,2'-bipy) at copper electrode were investigated by in situ electrochemical surface enhanced Raman spectroscopy (SERS) in the acetonitrile solution. In situ SERS studies revealed that NMIM can adsorb stably onto Cu electrode in a quite different potential range, but the potential range for adsorbing 2,2'-bipy is narrow. With the introduction of 2,2'-bipy into the solution, the SERS could be divided into three parts: (a) under -0.8 V, NMIM molecule adsorption, (b) near the open potential, 2,2'-bipy molecule adsorption with cis-conformation, (c) at positive potential region, both NMIM and 2,2'-bipy were coadsorbed at Cu surface, and the SERS data also suggested that the NMIM bound to copper surface with a tilted orientation, while the 2,2'-bipy was adsorbed through cis-conformation to the surface.

Using citrate as protector, Au-Ag alloy nanoparticles with different molar ratios were prepared by using hydrazine as the reducer, One plasmon band between that of monometallic Ag and Au observed in their UV-Vis spectra indicated the formation of Au-Ag alloy nanoparticles. TEM results showed diameters about 25 nm and homogeneous color of the alloy nanoparticles without clear core-shell contrast. By using Pyridine as the probe molecules, SERS studies were performed. The results indicated the spectra of Pyridine adsorbed on alloy is different from that of Ag and Au.

Ag-Au alloy seeds were prepared by the simultaneous reduction of Ag and Au salts. The seeds were grown via NH2OH x HCl-growth method to obtain novel Ag-Au alloy nanoparticles with diameters of 40-60 nm. The nanoseeds and novel nanoparticles were characterized by UV-Vis spectroscopy and TEM respectively. The observation of one surface plasma resonance absorption band, the redshift in their frequencies, and the uniform color of the nanoparticles shown in TEM images indicated the formation of alloy structure for both the nanoseeds and the novel nanoparticles. By using thiophenol (TP) as probe molecules, SERS studies were performed on the novel nanoparticles. The absorption bands of the nanoparticles red shifted with the addition of TP, and new bands were detected in the near infrared region, which were attributed to the aggregation of TP covered nanoparticles. With the excitation line of 632. 8 nm, the SERS intensity of TP on Au was most largely enhanced, and that on alloy nanoparticles were increased as X(Au) increased.

The thin films of C60 on Ag electrodes were studied by in situ surface-enhanced Raman spectroscopy (SERS) in acetonitrile solution and water solution respectively. The influence of C60 from bulk solution on the SERS of the adsorbed C60 was removed by pre-forming C60 films on the electrode. The results indicate that the split of some relevant Raman bands was attributed to the loss of vibrational degeneracy due to the lowering of the C60 molecular symmetry. Moreover, the surface selection rule was extended because of the influence of the surface electromagnetic field in which some forbidden modes became Raman-active. The results were similar to that of C60 molecules adsorbed on Ag electrode in the solution of C60. A weak band at about 348 and 311 cm(-1) was observed for the C60 films in acetonitrile solution and in aqueous solution respectively, which could be assigned to the interaction of C60 and Ag electrode surface.

The surface coordination chemistry of benzotriazole (BTAH) at silver electrode was investigated by in situ electrochemical surface enhanced Raman spectroscopy (SERS) and electrochemical synthesis in the acetonitrile solution. In situ SERS studies revealed that BTAH underwent three processes of chemical adsorption of BTAH, formation of compact layer of (AgBTA)n and the loss of SERS activity due to the oxidation of silver. The surface coordination processes of BTAH with Cu, Ag, Zn, Ni and Fe were investigated and the surface complexes prepared by direct electrochemical synthesis method were characterized by microanalysis and Raman spectroscopy. The influence of the neutral ligand of triphenylphosphine (pph3) on the coordination process was deduced. The introduction of pph3 was found to affect the surface processes of BTAH with Cu and Ag, and appeared in the final complex, while it had no influence on the coordination of BTAH with Zn, Ni and Fe.

Two electrochemical methods were used to synthesize Au nanoparticles (AuNPs) with different shapes depending on the applied current. The dumbbell, spheroid and rod-like AuNPs were synthesized by increasing the current with a certain increment, while spheroid and dumbbell AuNPs were obtained by applying constant current. The AuNPs were characterized by TEM, UV-Vis spectrum and surface enhanced Raman spectra (SERS). One absorption band located at near-IR region was observed on the AuNPs, indicating the existence of gold nanorods with the aspect ratio of about 6. The SERS effect from the AuNPs surface was studied by using crystal violet as probe molecules, which adsorbed on AuNPs surface with flat orientation. Meanwhile, the forming mechanism of AuNPs involving crystallization and growth was deduced based on the TEM results.

The electrochemical reduction of benzene on a smooth Pt electrode has been studied by confocal microprobe Raman spectroscopy. The results show that benzene can be reduced directly to cyclohexane, which is insoluble in water, adhered onto the electrode surface to form the third phase. After the drops have been formed on the electrode surface, the relative concentration of benzene to cyclohexane in the drops will rather increase with prolonging the time at a certain electrode potential, although it decreases with the negative shift of the electrode potential at first.

In the non-aqueous acetonitrile solution, recurring to the confocal Raman system, we studied the catalysis and oxidation of carbon monoxide on the surface of platinum electrode utilizing surface-enhanced Raman spectrum (SERS). As the movement of the potential, the process of the catalysis and oxidation interacted with the surrounding molecular. In the present paper, the catalysis and oxidation of carbon monoxide on the surface of platinum electrode was not clearly observed, but also the dissociation of acetonitrile was discovered simultaneously. Results show that acetonitrile decomposition occurs at a certain more negative potential by the appearance of the 2,133 cm-1 bands assigned to CN stretching modes. The bands observed at ca. 502 and 2,055 cm-1 are attributed to the Pt-CO(nu Pt-c) and intramolecular C-O(nu C-O) stretching vibration respectively, suggesting linearly adsorbed CO on platinum. The main product of COads oxidation is confirmed to be carbonate due to the existence of trace water in the double-layer region as a source of oxygen for the reaction.

In the non-aqueous acetonitrile solution, recurring to the confocal Raman system, we studied the intensively chemical adsorption of pyridine(Py) on the surface of platinum electrode utilizing surface-enhanced Raman scattering (SERS). With the change in the potential, the quantity and adsorptive orientation of the adsorbate also change, interacting on the surrounding molecules. In the present paper, the adsorption of Py on the surface of platinum electrode was not only clearly observed, but also the dissociation of acetonitrile was discovered simultaneously. And the more complicated double layer in the non-aqueous solution than in the aqueous one explains the differences of the results between the non-aqueous and aqueous solutions.