SERS observation of the adsorption behavior of SO2 on silver powder surfaces at nearly real environmental conditions

The influence of O₂ and H₂O on the adsorption behavior of SO₂ on surfaces of silver powders was studied by surface enhanced Raman scattering (SERS) at room temperature. The presence of H₂O (∼10³ Pa) and of O₂ (∼10⁴-10⁵ Pa) is necessary to observe SERS peaks of surface species such as SO^2-₃ and SO^2-₄. These peaks disappeared on evacuation.     

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.     

An XPS and UPS investigation of the adsorption of ethylene on the (111) surface of silver

Monolayer adsorption of pure ethylene on the (111) surface of saver at 80 K has been studied by X-ray (hv = 1486.6 eV) and ultraviolet (hv = 21.2 and 40.8 eV) photoelectron spectroscopy. The density of the adlayer is approximately 5 × 10¹⁴ molecules/cm² at saturation, multilayer formation being prohibited by the ultrahigh vacuum of the spectrometer. The molecular orbitals designated σ¹_CH, σ_CC, σ_CH and 2ss¹ by Demuth are observed at 7.0, 9.0, 10.3 and 13.6 eV below the Fermi level, respectively, but the higher lying π level is obscured by the silver d-band emission. The data are consistent with an undistorted molecule, adsorbed with the molecular axis parallel to the surface. Desorption occurs below 200 K without significant decomposition products remaining on the surface in agreement with the conventional notion that clean silver is relatively inert with respect to olefin adsorption.     

Synchrotron XPS and desorption study of the NO chemistry on a stepped Pt surface

The interaction of NO with Pt(4 1 0) was studied using high-energy resolution fast XPS and temperature programmed desorption/reaction mass spectroscopy. LEED studies show that the surface in the clean state restructures, which results in the formation of some larger {1 0 0} terraces. STM measurements show, that most terraces are small, ∼1 nm. Two different binding energy (BE) components were observed in the N 1s region of the core level spectra, both assigned to molecular forms of NO. NO dissociation starts between 350 and 400 K. This is a significantly higher temperature than previous literature reports suggested. This difference is thought to be caused by the restructuring of the surface used in our experiments. The reaction of NO with H₂, NH₃ and CO was also studied. The onset of these NO reduction reactions is determined by the NO_ad dissociation temperature (between 350 and 400 K) and NO_ad dissociation is the rate limiting step for all the reactions that were studied. Reaction with H₂ yields NH₃ below 600 K, but the selectivity shifts towards N₂ at higher temperatures. We did not find any indication that reaction between NO_ad and NH_3 ad proceeds via a special NO-NH₃ intermediate. A new surface species was detected during the reaction between NO and CO, both in the N 1s and the C 1s spectrum. It is tentatively assigned to either CN or CNO. The reactivity of NO on Pt(4 1 0) is compared with the reactivity that was observed for Pt(1 0 0) and other noble metal surfaces, such as Pd and Rh.     

NO adsorption on the Rh(110) surface: kinetics and composition of the adlayer studied by fast XPS

The adsorption and dissociation of NO on the Rh(110) surface were studied by synchrotron radiation X-ray photoemission spectroscopy at temperatures in the range 210–370 K. The O 1s or N 1s spectra were collected every 14 s while the surface was continuously exposed to a steady NO gas pressure. The difference in the binding energies for the atomic oxygen (O 1s ≤530.2 eV), atomic nitrogen (N 1s 397.2 eV) and molecular upright bonded NO molecules (O 1s ≥531.0 eV and N 1s 400 eV) allowed us to distinguish these surface species and to follow the evolution of the adsorbate layer. In addition to these dominating surface species a new species, characterized by O 1s binding energy of 530.7 eV and N 1s binding energy similar to that of the atomic nitrogen, was detected within a narrow coverage range. This state is tentatively assigned to a “lying down” NO bonding configuration, detectable at the timescale of the measurements. The uptake plots, constructed using the integrated intensity of the deconvoluted O 1s and N 1s spectra, are used to elucidate the effect of the reaction temperature and surface coverage and composition on the kinetics of dissociative and molecular NO adsorption of Rh(110).     

TiO2表面氧空位对NO分子吸附的作用

采用程序升温热脱附(TPD)实验方法测定了NO在TiO2表面吸附后的脱附谱，利用分子轨道理论研究了TiO2吸附NO的原子簇模型及吸附前后的原子簇能级变化．结果表明，NO在TiO2表面吸附后可在两个峰值温度450和980K脱附出N2．TiO2表面经预覆氧处理后，N2的脱附量降低．吸附时NO中的O能够占据TiO2表面氧空位并与N脱离，而N原子则相互结合成为N2脱附．分子轨道理论计算证明在TiO2(110)表面能够存在氧空位并具备吸附NO的结构条件．     

A study of the competitive adsorption of pyridine and monosubstituted pyridines on a silver electrode by the SERS method

The dependency of the SERS intensity on the concentration of pyridine and various monosubstituted stituted pyridines at competitive adsorption on a silver electrode was investigated by varying the concentration of bulk pyridine and monosubstituted pyridines. This co-adsorption behavior was found to be well approximated by Langmuir isotherms for binary systems, and the substituents of 2-substituted-pyridine strongly inhibited the adsorption due to their steric hindrance.     

汞在Ti2NO2 MXene表面吸附氧化的第一性原理计算

汞是一种有毒的重金属,在生产生活中以各种形式排放的汞对生态及人类健康都存在一定程度的威胁.因此,寻找高效的汞吸附剂具有十分重要的意义.本文基于密度泛函理论的第一性原理计算方法,研究了汞在Ti₂NO₂(MXene)和具有一个氧空位缺陷的Ti₂NO₂(Ov-Ti₂NO₂)上的吸附和氧化机理.计算结果表明Hg⁰在Ti₂NO₂表面的吸附为物理吸附,在Ov-Ti₂NO₂表面为化学吸附. Ti₂NO₂表面氧空位的存在可以改善HgO与Ov-Ti₂NO₂之间的相互作用,从而使吸附能提高116 kJ/mol. Hg⁰在Ov-Ti₂NO₂表面氧化为HgO的反应能垒为92.55 kJ/mol,小于其在Ti_2<...     

CuAg纳米结构表面共存和Ag表面对甘氨酸的新吸附行为

在异质纳米结构表面发生的新现象是当前研究的热点.最近发现，尽管甘氨酸在纯Ag表面只 能作物理吸附，蒸镀在Cu表面的单层Ag岛却能在Cu的帮助下，出现对甘氨酸作化学吸附的能力，这种现象是溢流效应的一种反映.蒸镀在Ag表面的Cu岛也能帮助附近裸露的Ag表面获得 化学吸附甘氨酸的能力，虽然这里已不是单原子层的银了.结果说明这种溢流现象来源于CuA g在表面的纳米结构共存，而不只是这种共存的某个结构所特有的.但是，由于Cu的表面能大 于Ag，所以即使是在室温下，Cu岛也会逐渐地被一单层Ag原子完全覆盖，从而失去溢 关键词： 溢流 甘氨酸 Cu Ag(111)     

MoSi_2(001)表面的氧吸附行为

运用第一原理密度泛函理论方法,首先计算了MoSi_2各清洁表面的表面能,(001)Si-|-Si断面具有较低的表面能,是MoSi_2最可能的解理面;通过生成能及键布居分析研究了单氧原子、双氧原子及氧分子在(001)Si-|-Si断面的吸附行为,发现单氧原子在空位处吸附最稳定,此时O极易与Si结合,得到的Si-O-Si键长及键角与SiO_2的非常接近,表明低浓度下O极易与表面的Si结合生成SiO_2;双氧原子发生空位+顶位吸附时O原子除与Si有强作用外,可与Mo有一定相互作用;氧分子以平行的方式接近空位最有利于吸附,此时氧分子最易分解为氧原子,发生氧原子在空位的吸附.     

First-principles study on anatase TiO2（101） surface adsorption of NO

In this paper, the stable structure and the electronic and optical properties of nitric oxide （NO） adsorption on the anatase TiO2 （101） surface are studied using the plane-wave ultrasoft pseudopotential method, which is based on the density functional theory. NO adsorption on the surface is weak when the outermost layer terminates on twofold coordinated oxygen atoms, but it is remarkably enhanced on the surface containing O vacancy defects. The higher the concentration of oxygen vacancy defects, the stronger the adsorption is. The adsorption energies are 3.4528 eV （N end adsorption）, 2.6770 eV （O end adsorption）, and 4.1437 eV （horizontal adsorption）. The adsorption process is exothermic, resulting in a more stable adsorption structure. Furthermore, O vacancy defects on the TiO2 （101） surface significantly contribute to the absorption of visible light in a relatively low-energy region. A new absorption peak in the low-energy region, corresponding to an energy of 0.9 eV, is observed. However, the TiO2 （101） surface structure exhibits weak absorption in the low-energy region of visible light after NO adsorption.     

Adsorption mode of neurotensin family peptides onto a colloidal silver surface: SERS studies

Kinetensin (KN) and its amino acids 1–8 fragment ([des‐Leu⁹]KN), neuromedin N (NMN), and xenopsin (XP) and its two analogs (human XP‐1/xenin‐8 and XP‐2) belong to the neurotensin family of peptides and are known to stimulate the growth of human tumors. In this work, we report surface‐enhanced Raman scattering (SERS) studies of these peptides and discuss their structures, orientation, and mode of adsorption onto a colloidal assembly of apparently randomly adhering Ag spheres with diameters of approximately 20 – 25 nm. We show that small alternations in both the amino acid composition and tertiary structure, which induce striking biological in vitro, were responsible for the observed spectroscopic changes. Copyright © 2012 John Wiley & Sons, Ltd.     

TiO2表面氧空位对NO分子吸附的作用

采用程序升温热脱附(TPD)实验方法测定了NO在TiO₂表面吸附后的脱附谱，利用 分子轨道 理论研究了TiO₂吸附NO的原子簇模型及吸附前后的原子簇能级变化.结果表明， NO在TiO₂表面吸附后可在两个峰值温度450 和980 K脱附出N₂.TiO ₂表面经预覆氧处理后，N₂ 的脱附量降低.吸附时NO中的O能够占据TiO₂表面氧空位并与N脱离，而N原子则 相互结合成 为N₂脱附.分子轨道理论计算证明在TiO₂(110)表面能够存在氧空位 并具备吸附NO的结构条件.     

Magnetic separation and SERS observation of analyte molecules on bifunctional silver/iron oxide composite nanostructures

We report the preparation of bifunctional silver–iron oxide composite nanostructures (Ag@Fe₂O₃) and demonstrate their magnetic separation with an analyte molecule from silver nanoparticles in a mixed solution. Magnetic and non‐magnetic plasmonic nanostructures and their separation are monitored by the surface‐enhanced Raman scattering (SERS) spectra of two different analytes attached to each kind of particles. In general, such separation experiments can provide insight into basic phenomena of adsorption and exchange of adsorbed molecules which are of strong interest in SERS. The formation of stable Ag@Fe₂O₃ nanoparticle–molecule complexes suggests small magnetic SERS labels without additional protective layers for application in analytical assays. The magnetic plasmonic nanostructures have great promise for targeted imaging and sensing in biological structures by directing nanosensors to places of interest using magnetic fields. The option of magnetic separation and collection of plasmonic particles improves the analytical capabilities of SERS. Copyright © 2012 John Wiley & Sons, Ltd.     

Comparative XPS study of surface reduction for nanocrystalline and microcrystalline ceria powder

Nanoscale materials have attracted great interest because of their distinct properties. By means of XPS, the present work investigated the difference of reduction behavior between nanocrystalline and microcrystalline ceria on condition of Ar⁺ bombardment or X-ray irradiation. For the first time, the results indicate that the reduction level of Ce⁴⁺ to Ce³⁺ is lower for nanocrystalline ceria than for microcrystalline ceria although the experimental conditions are identical. These differences have been attributed to the differences in the concentration of oxygen vacancies in the bulk and the diffusion ability of oxygen atoms between them. Besides, the key factor for the reduction of ceria produced by X-ray exposure is discussed.     

High-resolution XPS and NEXAFS study of SO2 adsorption on Pt(111): two surface SO2 species

The adsorption and condensation as well as the temperature-dependent decomposition of SO₂ on Pt(111) have been studied by high-resolution core-level photoemission and near-edge X-ray absorption fine structure. The data analysis shows that SO₂ adsorbs molecularly at 150 K forming a monolayer phase with two SO₂ species of different binding energy and quite different molecular orientation. On increasing the temperature to 210 K only SO₂ molecules of 0.43 monolayer coverage survive with molecular planes being tilted by α = 31° ± 10° with respect to the surface normal. For condensed SO₂ multilayers an SO₄ species is formed close to 300 K.     

Spectral properties of pyrazine adsorbed on silver electrodes and cold silver films from surface enhanced Raman scattering (SERS)

Surface enhanced Raman spectra of molecules adsorbed on electrode surfaces, metal-island films, colloidal particles and UHV-evaporated low-temperature substrates often show considerable differences in mode strength and positions between each other and the bulk molecular spectrum. These differences and their possible origins are discussed for pyrazine adsorbed on silver electrodes and cold silver films.     

Mixing thiols on the surface of silver nanoparticles: preserving antibacterial properties while introducing SERS activity

The purpose of the study was to prepare and characterize nanosuspensions that can maintain high and extended supersaturation to improve the dissolution and absorption of poorly soluble 10-hydroxycamptothecin (10-HCPT). 10-HCPT oral nanosuspensions (HCPT-Nanosuspensions) were produced on a laboratory-scale by microprecipitation- high pressure homogenization method. The particle morphology and the physical state were studied using transmission electron microscopy, X-ray powder diffraction (XRPD), and differential scanning calorimetry (DSC). Supersaturated dissolution tests were carried out with the paddle method. Caco-2 cell experiments were performed to imitate the oral absorption. The in vivo pharmacokinetics studies were undertaken in rats following oral administration. The 10-HCPT nanoparticles were 135 nm in dimension before lyophilization and were claviform or lump in shape. XRPD and DSC both confirmed that a portion of 10-HCPT was present in a crystalline state in nanosuspension. Supersaturated dissolution tests showed HCPT-Nanosuspensions could maintain high supersaturated level for an extended period time. The cell experiment on HCPT-Nanosuspensions showed a significantly higher uptake and greater membrane permeability compared with the other formulations. The pharmacokinetic test exhibited HCPT-Nanosuspensions had a similar pharmacokinetic performance with 10-HCPT solution. In conclusion, highly and extendedly supersaturated HCPT-Nanosuspensions have been prepared which could result in high peak concentration (C _max) and great exposure (AUC) after oral administration.

     

SERS as a probe for adsorbate orientation on silver nanoclusters

Surface‐enhanced Raman scattering (SERS) spectroscopy has been used to characterize multilayers of three isomeric aromatic compounds adsorbed on silver nanoclusters. The three structural isomers, all of which adsorb in the carboxylate form onto the silver nanoclusters, bind in two different geometries to the silver surface. Different molecular configurations correlate to differences in bonding strength of these molecules to the silver surface, which can be probed by SERS. For ortho‐hydroxybenzoic acid (salicylic acid), we observed red shifts of major SERS peaks in comparison to the normal Raman vibrations of nonadsorbed crystalline material. For this molecule the steric hindrance between the adjacent carboxylate and hydroxyl groups causes the carboxylate group to rotate from the common flat geometry of benzene substituents on surfaces and bond directly through one of the oxygen atoms to the surface. In this case, strong coordinative bonding between the carboxylate group and the metal surface causes the red shifts in the SERS peaks. For para‐, and meta‐hydroxybenzoic acid, the steric hindrance is less likely since the two functional groups are not at adjacent positions, and therefore these molecules adsorb on the silver surface in a totally flat geometry. For these molecules, in contrast to the ortho isomer, the CO₂ interacts with the surface through an extended π bond, and these molecules are physically adsorbed in the common flat position. Therefore, for the meta and para substituents, we do not observe significant red shifts in the SERS spectrum. Copyright © 2009 John Wiley & Sons, Ltd.     

Influence of surface plasmon resonance wavelength on SERS activity of naturally grown silver nanoparticle ensemble

We present experimental results to quantify and optimize the surface‐enhanced Raman scattering (SERS) activity of naturally grown silver nanoparticles. Ag nanoparticle ensembles with mean equivalent radii ranging from 10.6 to 20.3 nm were prepared under ultrahigh vacuum conditions by Volmer–Weber growth on quartz plates. A tuning of the localized surface plasmon polariton resonance wavelength from 453 to 548 nm was performed by varying the morphology of the silver nanoparticles. The dependence of the SERS activity on the plasmon resonance wavelength was investigated with a Raman set‐up containing a microsystem light source with an emission line at 488 nm. Shifted excitation Raman difference spectroscopy was applied to remove the fluorescence‐based background from the SERS spectra of pyrene in water using two slightly different emission wavelengths (487.61 and 487.91 nm) of the microsystem light source. We demonstrate that the Raman activities for all SERS substrates are available in the nanomolar range in a water sample. However, the Raman activity crucially depends on the plasmon resonance wavelength of the nanoparticle ensembles. Although for an on‐resonance ensemble the limit of detection for pyrene in water is very low and was estimated to be 2 nmol/L, it increases rapidly to several tens of nanomol for slightly off‐resonance ensembles. Hence, the highest SERS activity was obtained with a nanoparticle ensemble exhibiting a plasmon resonance wavelength at 491 nm, which almost coincides with the excitation wavelengths. Copyright © 2012 John Wiley & Sons, Ltd.