SERS and XPS observation of the adsorption behavior of NO and NO2 on a silver powder surface

The influence of H₂O on the adsorption behavior of NO or NO₂ on a silver powder surface was studied by SERS and XPS at room temperature. Water vapor was found to be responsible for the adsorption of NO on the silver powder surface. When surface species such as Ag₂O are present on the surface, some of the NO₂ molecules are adsorbed on the surface species to produce NO^-₃, whereas NO molecules are adsorbed on a different site to produce NO^-₂.     

SERS observation of the effects of pressure and water on the absorbed state of nitrogen dioxide on a silver powder surface

The effects of pressure and water on the adsorbed state of nitrogen dioxide on silver powder produced from an aqueous solution of AgNO₃ were studied by SERS. NO₂ of 10² Pa was added to the silver powder in the sample chamber and then pressure was raised up to ∼10⁵ Pa with dry Ar, N₂ or O₂. The observed surface species are NO₃⁻ and NO₂⁻ ions under atmospheric pressure. When the total pressure decreases, NO₂⁻ is transformed into NO₃⁻ and NO⁺. This reaction is reversible with the total pressure variation of dry gases regardless of kind. Once the silver powder adsorbing nitrogen oxides is exposed to moistened gas or air of ∼10⁵ Pa, the reversible variation was interrupted, and NO₃⁻ and NO₂⁻ ions are observed on the silver surface.     

Study on Adsorption States by Surface-Enhanced Raman Spectroscopy

Abstract

SERS has been used as a state-resolving probe to study the adsorption states. in the case of pyridine (Py) adsorbed on the Ag electrode surface, the equilibrium and transition between two adsorbed states, i.e., the perpendicular mode adsorbed through the nitrogen lone-pair electrons and the flat mode through the π electrons of the aromatic ring, were studied. It was found that in the low pyridine concentration or the initial stage of adsorption, the flat mode was favored. While the concentration became higher and the adsorption tended to equilibrium, the adsorbed molecules would transit to the perpendicular mode. The similar phenomenon was also observed when changing the applied electric potential and the pH value of the solution. In the case of the adsorption of Methylene Blue (MB) on the HNO₃-etched silver surface, the influence of Cl^? ions on the adsorption states of MB was investigated. It showed that MB molecules adsorbed on the silver surface tended to transform from the “lying-down” state to the “end-on” state while adding Cl^? ions.     

甲基橙在银镜上的表面增强拉曼光谱研究

利用表面增强拉曼光谱(SERS)技术研究了甲基橙的(MO)的SERS谱,对拉曼峰进行了指认,并给出了甲基橙在银镜上的吸附状态。     

Effects of Cl, NO3 and SO4 anions on the anodic behavior of carbon steel in deaerated 0.50 M NaHCO3 solutions

The effects of Cl⁻, NO₃⁻ and SO₄²⁻ aggressive anions on the corrosion and passivation behavior of carbon steel electrode in deaerated 0.50 M NaHCO₃ solutions were studied using potentiodynamic anodic polarization and SEM techniques. It was found that the presence of Cl⁻, NO₃⁻ and SO₄²⁻ anions stimulates the anodic dissolution rate in both the active and the pre-passive potential regions. Moreover, significantly great effects were observed in both the passive and the trans-passive potential regions. Pitting corrosion was observed only in the presence of Cl⁻ anions, while the presence of NO₃⁻ and SO₄²⁻ anions facilitate only passivation by oxygen of water without themselves participating in the cathodic process. Also, it was observed that the effect of NO₃⁻ anion, which is a strong oxidizing agent acting “primarily” as stimulator of the cathodic process and then its reaction product acts “indirectly” retarding the anodic process. On the other hand, the effect of SO₄²⁻ anion, which is a non-oxidizing agent, exerts an “indirect” effect on the cathodic reaction increasing its rate and then “directly” influence on the anodic reaction, retarding it.     

Metal–metal bonding and structures of trinickel and tricobalt dipyridylamido complexes from surface‐enhanced Raman spectra

We recorded surface‐enhanced Raman scattering (SERS) spectra of metal‐string complexes Co₃(dpa)₄ Cl₂ [di(2‐pyridyl)amido (dpa)], Ni₃(dpa)₄ Cl₂ and the oxidized form of the Ni₃ complex to determine their vibrational wavenumbers and to investigate their structures. For SERS measurements these complexes were adsorbed on silver nanoparticles in aqueous solution to eliminate the constraint of a crystal lattice and the complexes remain in thermal equilibrium. From our analysis of the vibrational normal modes we assigned the SERS lines at 242 and 276 cm⁻¹ to Ni₃ and Co₃ symmetric‐stretching modes of the symmetric form. For Co₃ (dpa)₄Cl₂ a Raman line at 383 cm⁻¹ was assigned to the Co Co stretching mode of the unsymmetric form. The wavenumber of the Ni₃ symmetric‐stretching mode of the oxidized form [Ni₃(dpa)₄]³⁺ is 274 cm⁻¹, greater than that for neutral Ni₃(dpa)₄Cl₂, in agreement with a prediction of delocalized molecular‐orbital theory that an electron is removed from an antibonding orbital after oxidation. The experimental data show that the SERS technique serves as an excellent tool to observe the variation of metal–metal bonding during an oxidation or reduction reaction. Copyright © 2010 John Wiley & Sons, Ltd.     

少量KCl引起水杨酸表面增强喇曼散射谱的异常变化

本文报道KCl引起的银胶中水杨酸(C₇H₄O₃)表面增强喇曼散射谱(SERS)的异常变化。发现KCl造成水杨酸分子中某些结构的SERS强度急剧而迅速下降,但同时又造成3436cm^-1附近v(—OH)振动的SERS信号的进一步增强。还研究了KCl对一系列含—COOH结构的分子(例如苯甲酸、对氨基苯甲酸等)SERS信号的影响,发现Cl^-对v(—COO^-)振动的SERS强度有明显的 关键词：     

Role of Cl ions in photooxidation of propylene on TiO2 surface

The effect of Cl⁻ ions on photooxidation of propylene on TiO₂ semiconductor was investigated. Cl⁻/TiO₂ catalysts were prepared by annealing Degussa P25 TiO₂ in the gas flow of N₂ and Cl₂ under 100-400 °C. The photocatalytic oxidation of propylene was carried out in a continuous flow system, with the chromatograph to analyze the products on line. The experimental results showed that the activity of Cl⁻/TiO₂ catalysts increased as heat-treated temperature decreased. The activity of the sample heat-treated at 100 °C was about two times higher than that of pure TiO₂. Moreover, as to TiO₂, the main product of the propylene photocatalytic oxidation was CO₂, but with Cl⁻/TiO₂ catalysts, not only CO₂ but also trace CO was determined. The adsorbed species on TiO₂ surface before and after reaction were analyzed by X-ray photoelectron spectroscopy (XPS) and thermogravimetric/differential thermal analyses (TG-DTA) coupled to a mass spectrometer (MS). XPS analysis showed that there was Cl⁻ absorbed on the Cl⁻/TiO₂ surface, and the absorption amount of Cl⁻ decreased after the photooxidation reaction of propylene. TG-DTA-MS analysis confirmed chlorine absorbed on the surface of TiO₂ in the form of Cl⁻ ion. These results illuminated that absorbed Cl⁻ on the surface of TiO₂ formed a weak physical absorption on TiO₂ at low temperature, and subsequently participated in the photooxidation of propylene, finally removed from TiO₂ surface.     

Enhancement in SERS intensities of azo dyes adsorbed on ZnO by plasma treatment

Surface‐enhanced Raman scattering (SERS) spectra of azo dyes (methyl orange and p‐methyl red) adsorbed on ZnO nanoparticles were observed. Hydrothermally synthesized ZnO nanoparticles were characterized by powder X‐ray diffraction and X‐ray photoelectron spectroscopy. The ZnO nanoparticle size, monitored with X‐ray diffraction, was tuned by calcination to optimize SERS intensities. The observed SERS effect of azo dyes adsorbed on ZnO can be ascribed to charge‐transfer resonance effect. Time‐dependent density functional theory was used to calculate the optical spectra and interpret the chemical enhancement observed in the experiment. The SERS enhancement factors for methyl red on ZnO were boosted by nearly four times and twice with O₂ plasma and H₂ plasma, respectively. However, plasma treatment showed no effect on the enhancement factors of methyl orange on ZnO. We conclude that plasma‐induced defect formation and band gap shift in ZnO and the coupling of energy levels between ZnO and azo dye molecules are responsible for the observed enhancement of SERS intensities. Copyright © 2014 John Wiley & Sons, Ltd.     

pH‐dependent surface‐enhanced Raman scattering observation of sulfanilamide on the silver surface

Monolayers of sulfanilamide on metallic surface can serve as an ideal model for understanding the interaction mechanism between the metal and the sulfanilamide molecule. In the present paper, the surface‐enhanced Raman scattering (SERS) technique was employed to obtain the SERS spectra of sulfanilamide monolayers formed on the silver surface under different pH values. Assignments of the spectra were carried out with the aid of density functional theory (DFT) calculations (BLYP/6‐311G). It can be found that the adsorption function of sulfanilamide on the silver surface was influenced by the pH value. The fully protonated sulfanilamide molecule adsorbed on the silver surface through N¹³H₂ group and the benzene ring anchored in a relatively perpendicular manner leading to N⁷H₂ and S¹⁰O₂ groups near the surface, while the completely deprotonated sulfanilamide molecule attached on the silver surface via N⁷H₂ and the benzene ring was perpendicular to, and the N¹³H₂ and S¹⁰O₂ groups were far from the silver surface. Copyright © 2009 John Wiley & Sons, Ltd.     

Sers measurement of oxidation-reduction reactions of adsorbates on gold microstructures

The use of surface enhanced Raman scattering (SERS) to study oxidation-reduction and complexation chemical reactions on Au surfaces is illustrated by: (1) the reaction of Au(CN)₂^? adsorbed on a Au colloid (2140 cm^?) to form Au(CN)₃^2? (2131 cm^?1) on the surface in excess CN^?; (2) the oxidation of Au(CN)₂^? by HNO₃, Cl₂, or Br₂ solutions to form Au(CN)₄^? (2190 cm^?) on a Au colloid; and (3) the dissolution of Au in excess CN^? with O₂. Unlike with Ag surfaces, no SERS is observed when Au powder is exposed to NO, NO₂, SO₂, CO, or CO₂ gases. The surface chemistry of Au is discussed in the light of these reactions.     

Positioning of cationic silver nanoparticle by using AFM lithography and electrostatic interaction

One-dimensional metal lines of silver nanoparticles with a nano-sized width were generated onto silicon surface by using a nano-level lithography technique, field induced oxidation (FIO) by AFM, on self-assembled monolayer-modified Si wafers. This FIO technique provided SiO₂ lines a width of less than 100 nm. Short-time immersion of partially anodized silicon surface which is covered by a cationic silanol surfactant ((CH₃O)₃SiCH₂CH₂CH₂N(CH₃)₃⁺Cl⁻)-monolayer into quaternary ammonium (HSCH₂CH₂N(CH₃)₃⁺Br⁻)-covered silver nanoparticles readily and reproducibly gave nano-metal lines of silver onto silicon wafers. Hydrophilicity of the whole wafer surface was indispensable for homogeneously wetting the anodized SiO₂ area with a nanodimensional width.     

Surface-enhanced Raman scattering of methyl <Emphasis Type="Italic">p</Emphasis>-hydroxy benzoate: A molecular orientational study

The surface geometry of a methyl p-hydroxy benzoate (MPHB) molecule was studied by analysis of the SERS spectra adsorbed on silver colloid surfaces. For a reliable analysis of the SERS spectrum, we also performed density functional theoretical calculations. The large enhancement of the in-plane ring-stretching and ring-stretching modes in the surface-enhanced Raman scattering spectrum indicates that the molecule is adsorbed on the silver surface in a stand on orientation of MPHB on a silver surface.     

Electrochemical and AFM characterization of the electropolimerization of pyrrole over a graphite-epoxy resin solid composite electrode, in the presence of different anions

This work studied the process of electrochemical formation of polypyrrole, Ppy, over a graphite-epoxy resin composite electrode in the presence of different anions: DS⁻, NO₃⁻ and Cl⁻. It was shown by means of AFM that the morphological characteristics and the formation kinetics of the Ppy deposit, from analysis of experimental current density transients, are strongly dependent on the nature of the anion present. It was found that for all cases, the formation mechanism involves the simultaneous presence of adsorption and 3D nucleation, limited by diffusion of the different pyrrole oligomer species, processes.     

2-Amino-5-(4-pyridinyl)-1,3,4-thiadiazole film at the silver surface: Observation by Raman spectroscopy and electrochemical methods

Surface enhanced Raman scattering (SERS) spectrum of the 2-amino-5-(4-pyridinyl)-1,3,4-thiadiazole (4-APTD) on the silver surface was recorded and assigned with the help of B3LYP/6-311G** method. SERS result explored that 4-APTD molecule with a tilted orientation anchored at the silver surface via N¹², S¹ and C² atoms. In situ SERS spectroelectrochemical experiment indicated 4-APTD molecule experienced an intermediate adsorption process of its thiadiazole ring moiety with the vertical orientation at the surface before the 4-APTD molecule detached completely from the surface as the potential applied at −1.3 V vs. SCE. Electrochemical impedance spectroscopy (EIS) and polarization experiments exhibited the sound anticorrosive effect of the 4-APTD film on silver surface with an efficiency of 89.5%.     

Ni-Al layered double hydroxides modified with citrate, malate, and tartrate: Preparation by coprecipitation and uptake of Cu from aqueous solution

We report on aqueous Cu²⁺ uptake by Ni-Al layered double hydroxides (Ni-Al LDHs) modified with citrate (C₆H₅O₇³⁻), malate (C₄H₄O₅²⁻), and tartrate (C₄H₄O₆²⁻) anions via coprecipitation. Dropwise addition of a mixed aqueous solution of Ni(NO₃)₂ and Al(NO₃)₃ to the respective organic acid solutions at a constant pH of 7.0-9.0 afforded LDHs with intercalated C₆H₅O₇³⁻ and Ni(C₆H₅O₇⁾⁻, C₄H₄O₅²⁻, and C₄H₄O₆²⁻ in their interlayers. The anions were also likely adsorbed on the LDH surface. Citrate·Ni-Al LDH could rapidly take up Cu²⁺ at a constant pH of 5.0, mainly via chelation by the intercalated and adsorbed anions, rather than coprecipitation with dissolved Al³⁺ to form Cu-Al LDH. By contrast, malate and tartrate were not active as chelating agents, probably because they formed bridges between brucite-like layers by direct coordination of the two −COO⁻ groups with Al³⁺ in those layers.     

Adjustment and control of SERS activity of metal substrates by pressure

Metal pellets of silver and copper for surface‐enhanced Raman scattering (SERS) spectroscopy were prepared by compression with different pressures. It was found that the SERS activity of the pellet could be controlled by pressure. Enhanced Raman scattering properties of the metal pellets in the presence of adsorbed 4‐mercaptobenzoic acid (4‐MBA) with excitation at 632.8 or 514 nm could be obtained by choosing proper pressure of pellatization. The SERS peak intensity of the band at ∼1584 cm⁻¹ of 4‐MBA adsorbed on the metal pellets varies as a function of applied pressure, and which is about 1.2–32 times greater than when it is adsorbed on silver and copper particles. The calculated results of three‐dimensional finite‐difference time‐domain method (3D‐FDTD) are in good agreement with the experimental data. Moreover, no spurious peaks appear in the SERS spectra of the samples because no other chemicals are involved in the simple preparation process of the metal pellets, which will facilitate its use as an SERS‐active substrate for analytical purposes. In summary, SERS‐active metal pellets can be produced simply and cost effectively by the method reported here, and this method is expected to be utilized in the development of SERS‐based analytical devices. Copyright © 2009 John Wiley & Sons, Ltd.     

Influence of aliphatic spacer group on adsorption mechanisms of phosphonate derivatives of l-phenylalanine: Surface-enhanced Raman, Raman, and infrared studies

The nature of phosphonopeptides containing N-terminal l-phenylalanine (l-Phe), namely l-Phe-dl-NH-CH(CH(CH₃)₂)-PO₃H₂ (A), l-Phe-l-NH-CH(CH₃)-PO₃H₂ (B), and l-Phe-dl-NH-CH(CH₂CH₂COOH)-PO₃H₂ (C) (Fig. 1 presents molecular structure of these molecules), adsorbed on electrochemically roughened and colloidal silver surfaces has been explored by surface-enhanced Raman spectroscopy (SERS). To reveal adsorption mechanism of these species on the basis of their SERS spectra at first Fourier-transform Raman (FT-RS) and absorption infrared (FT-IR) spectra of non-adsorbed molecules were measured. Examination of enhancement, frequency shifts, and changes in relative intensities of SERS bands due to adsorption and surface roughens variation reveals that the tilted compounds adsorb on the electrochemically roughened silver substrate in similar way, while they behave differently on the colloidal silver surface. A stronger enhancement of in-plane ring vibrations of the l-Phe ring, i.e., ν₃ and ν_18b (B₂), over these of the A₂ symmetry in all SERS spectra on the electrochemically roughened silver substrate suggests that the ring interacts with this surface adopting slightly deflect orientation from the perpendicular one. Also, enhancement of PO and -CH₂-/-CH₃ fragments vibrations points out that they are involved in adsorption process on this substrate. This conclusion was drawn on the basis of the enhancement of 1274-1279 and 1138-1152 (ν(PO)), 1393-1400 (δ(CH) + ρ_b(CNH₂) + ν(C-C_O) + δ(CH₃)), ∼1455 (δ(CCH₃/CCH₂) + ρ_b(CH₃/CH₂), and 1505-1512 cm⁻¹ (δ(CH₂) + Phe(ν_19a)) bands. Although a relative intensity ratio of these bands in the presented SERS spectra is different. On the other hand, on the colloidal silver nanoparticles, the aromatic ring of all molecules is lying flat or takes almost parallel orientation to this surface. Besides, A interacts also via P-terminal group (568, 765, 827, 1040, and 1150 cm⁻¹), whereas B mainly through NH₂-C-(CO)-CNH-(712 and 1255 cm⁻¹). In the case of C, it adsorbs on the silver colloidal surface mainly through the aromatic ring of l-Phe, while other fragments of the molecule are in close proximity to this surface as comes off the weak enhancement of bands due to the aliphatic vibrations.     

Electrochemical and in situ SERS spectroelectrochemical investigations of 4‐methyl‐4H‐1, 2, 4‐triazole‐3‐thiol monolayers at a silver electrode

Electrochemically anticorrosive behavior of 4‐methyl‐4H‐1, 2, 4‐triazole‐3‐thiol (MTTL) self‐assembled monolayers (SAMs) on the silver electrode was studied by means of electrochemical impedance spectroscopy (EIS) and polarization measurements. The promising inhibition effect of the MTTL for silver had been affirmed. Results of surface‐enhanced Raman scattering (SERS) experiments indicated that the MTTL molecule in a tilted orientation was self‐assembled on the silver surface through S⁶ and N² atoms to form monolayers. An in situ electrochemical SERS experiment implied the changes of adsorption fashion of MTTL momolayers on the silver surface with the potential shifted to more negative direction. Copyright © 2009 John Wiley & Sons, Ltd.     

Nitration of phenols in reversed micelle systems and enhanced oxidation ability of dilute nitric acid (less than 2.0 molarity) in concentrated salt solutions

In a previous paper, we have reported that dilute nitric acid in reversed micelle systems can oxidize the Br⁻ ion to Br₂ and proposed that the nitryl (or nitronium) ion NO₂⁺ should be the active species in the oxidation process. Nitration of phenol in reversed micelle systems with dilute nitric acid, CHCl₃/CTAC/H₂O (2.0 mol dm^− 3 HNO₃ in the 1.0% (v/v) H₂O phase), was performed at 35 °C to obtain 2- and 4-nitrophenols, where CTAC represents cetyltrimethylammonium chloride. In similar CTAC and AOT reversed micelle (CHCl₃ or heptane/AOT) systems, 4-methylphenol was converted to 2-nitro-4-methylphenol, where AOT stands for sodium bis(2-ethylhexyl) sulfosuccinate. In aqueous 2.0 mol dm^− 3 HNO₃ solution accompanied by 4.0 mol dm^− 3 LiCl (and a small amount of LiBr as the bromide resource), trans-1,4-dibromo-2-butene was successfully brominated to 1,2,3,4-tetrabromobutane. This result is a good evidence that the Br⁻ ion can be oxidized to Br₂ in dilute nitric acid (2.0 mol dm^− 3) provided that it contains concentrated salts. At 20-40 °C, the apparent oxidation-reaction rate constants (k/s^− 1) of Br⁻ to Br₂ were evaluated in 0.1-2.0 mol dm^− 3 HNO₃ solution accompanied by concentrated LiCl (3.5-9.0 mol dm^− 3). For chloride salts, the cation effects increased as Et₄N⁺ ? Na⁺ < Li⁺ < Ca²⁺ < Mg²⁺. Even the evolution of Cl₂ was demonstrated from < 2.0 mol dm^− 3 HNO₃ solution containing concentrated LiCl, MgCl₂, and CaCl₂ as well as AlCl₃, therefore, an indirect oxidation mechanism of the Br⁻ ion through Cl₂ was proposed as follows: 2Cl⁻ + NO₂⁺ → Cl₂ + NO₂⁻; 2Br⁻ + Cl₂ → Br₂ + 2Cl⁻.