Hydrogen adsorption on single-walled carbon nanotubes studied by core-level photoelectron spectroscopy and Raman spectroscopy

We have investigated the adsorption of atomic hydrogen on vertically aligned carbon nanotube (CNT) films using in situ synchrotron-radiation-based core-level (CL) photoelectron spectroscopy and Raman spectroscopy. From C 1s CL spectra, we identified a CL peak component due to C-H bonds of carbon atoms in single-walled carbon nanotubes (SWCNTs). We also found the suppression of π-plasmon excitation, indicating that the hydrogen adsorption deforms the bonding structure. Raman spectra of the SWCNT film indicated that the radial-breathing-mode intensities of SWCNTs decreased due to the adsorption-induced bonding-structure deformation. Moreover, the decrease for small-diameter SWCNTs was more severe than that for large-diameter SWCNTs. Our results strongly suggest that the hydrogen adsorption, which induces the structure deformation from sp² to sp³-like bonding, depends on the diameter of SWCNTs.     

Multiple depositions of Ag nanoparticles on chemically modified agarose films for surface-enhanced Raman spectroscopy

A facile and cost-effective approach for the preparation of a surface-enhanced Raman spectroscopy (SERS) substrate through constructing silver nanoparticle/3-aminopropyltriethoxysilane/agarose films (Ag NPs/APTES/Agar film) on various solid supports is described. The SERS performance of the substrate was systematically investigated, revealing a maximum SERS intensity with four layers of the Ag NP deposition. The enhancement factor of the developed substrate was calculated as 1.5 × 10(7) using rhodamine 6G (R6G) as the probe molecule, and the reproducibility of the SERS signals was established. A high throughput screening platform was designed, manufactured and implemented which utilised the ability to cast agarose to assemble arrays. Quantitative analysis of 4-aminobenzoic acid (4-ABA) and 4-aminothiophenol (4-ATP) was achieved over a ～0.5 nM-0.1 μM range.     

Doublet of D and 2D bands in graphene deposited with Ag nanoparticles by surface enhanced Raman spectroscopy

Surface enhanced Raman spectrum of graphene was obtained by modifying graphene with Ag nano-particles. The doublet of D band and 2D band was observed due to surface enhanced Raman scattering (SERS) enhancement and relaxation of the selection rules originated from the interaction of Ag nano-particles and graphene. The difference in the doublet of D band in which the separation between the two peaks is 11 cm⁻¹ is close to the theoretical value of 9 cm⁻¹ and can be attributed to the disorder and edge effect. The doublet of 2D band can be assigned to the asymmetry of dispersion relation along KM and KГ respectively. The phonon mode at 1510 cm⁻¹ can be associated with the iTO phonon near ГK/4. This confirms the phonon dispersion based on double resonance (DR) theory in iTO branch.     

N-氧化-2-巯基吡啶锌盐的合成

以2-氯吡啶为起始原料，在冰醋酸介质中用质量分数为30％H2O2直接氧化，再与NaSH进行巯基化，然后同ZnSO4螯合成盐得到吡啶硫酮锌(ZPT)。同时还研究了溶剂的回收套用、不同催化剂对氧化反应的影响及不同pH值对巯基化反应的影响，优化条件下ZPT总收率可达78．0％。通过对溶剂的循环使用，减少了溶剂(冰醋酸)用量66．7％，反应收率也提高了10％左右，巯基化反应的pH值控制在9～10。产品经熔点、含量、pH值和IR的测试，达到了出口标准的要求。     

The dynamic surface chemistry during the interaction of CO with ceria captured by Raman spectroscopy

The interaction of CO with ceria under conditions typically used to measure the oxygen storage capacity (OSC) of automotive three way catalysts (TWC) has been investigated by in situ Raman spectroscopy. During exposure of the ceria to CO at 623 K vibrational bands at 1582–1600 and 1331–1340 cm⁻¹ appeared; these bands increased with increasing time of exposure to CO. The band positions are consistent with phonon modes of carbon; however, assignment to carboxylate species or carbonate species cannot be excluded. Subsequent exposure to O₂ at room temperature resulted in a decrease in the intensities of the 1582–1600 and 1331–1340 cm⁻¹ bands by more than 90%. As well, exposure to O₂ at room temperature also resulted in the appearance of Raman modes characteristic of formate and peroxide surface species. The mechanism by which formate forms upon room temperature O₂ exposure is discussed in the context of the assignment of the 1582–1600 and 1331–1340 cm⁻¹ bands to carbon phonon modes which result from the disproportionation of CO on reduced ceria.     

Electrochemical oxidation of 2-mercaptopyridine N-oxide on mercury electrodes in aqueous solutions

The oxidation mechanism of 2-mercaptopyridine N-oxide (NOS) is studied in aqueous media. Polarographic, classical and differential pulse, and voltammetic studies were made. The effect of pH, reactant concentration and scan rate on the electrochemical parameters is studied. The results indicate that the anionic form of NOS is oxidized at the mercury electrode to yield a radical. At pH 2 > 4.5 the dissociation of NOS precedes the electrochemical process.At low concentration values the reversible oxidation of NOS to yield the strongly adsorbed radical takes place, whereas at high concentrations this process is accompanied by the diffusional reversible oxidation. Both processes appear at different potentials due to the contribution of ΔG_ads, which has been determined from polarographic and voltammetric measurements, having a value of −7.7 kJ mol⁻¹. The oxidation potential of the NOS⁻/NOS redox couple has been also calculated as E ° = 274 ± 5 mV vs. the Ag/AgCl/KCl_sat electrode.     

Electrochemical and surface-enhanced Raman spectroscopy studies of 4-phenylpyridine adsorption at the gold/solution interface

The adsorption of 4-phenylpyridine (4-PhPy) on the Au electrode was examined using conventional electrochemical techniques: cyclic voltammetry and impedance measurements and also by surface enhanced Raman spectroscopy (SERS) in a wide range of electrode potentials. Electrochemical results indicate the strong adsorption of 4-Phpy molecules, particularly at the positively charged Au electrode. The wide shoulder of capacity close to the pzc suggests that the composition and/or the structure of 4-Phpy monolayer change with the sign of the surface charge on the electrode. Investigation of integrity of adsorbed layer, however, indicates that adsorbed molecules do not form tight, compact monolayer even in the case of adsorption from saturated solution. SERS spectra provided evidence for gradual, potential-induced reorientation of the molecular plane with respect to the surface, from nearly vertical in the negatively charged electrode, to more flat at the positively charged metal surface.     

Raman spectroscopy of carbon nanohoops

We present the Raman spectra for [n]Cycloparaphenylenes ([n]CPPs) of different sizes. A plethora of Raman modes are observed in these spectra, including modes that are analogous to those of the carbon nanotubes (CNTs) such as G-band, as well as Raman peaks that are unique for carbon nanohoops. In addition, we have calculated the theoretical Raman spectra of [n]CPPs for n = 4–20 using density functional theory (DFT), which are then compared to the experimental results for the assignment of different modes. The Raman peak positions are seen to be dependent on the size of the nanohoop from both the experimental and the calculated results.     

Raman spectroscopy of mesophase pitches

Raman spectra have been measured for mesophase pitches prepared from different starting materials. The spectra exhibited the two major absorption peaks characteristic of other carbonaceous materials. The relative intensities of these peaks have been related to molecular size and to the degree of order in the mesophase. A comparison of Raman data for carbonaceous materials shows that the absorption frequency of the longer wavelength band is related to the degree of graphitization.     

CO adsorption on supported and promoted Ag epoxidation catalysts

CO was used to probe the nature of adsorption sites on Ag/α-Al₂O₃ epoxidation catalysts and to investigate the effect of Cs and Cl promoters by employing diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and chemisorption measurements. In contrast to previous studies, IR absorption bands for CO chemisorbed on reduced, supported Ag crystallites were observed; however, CO adsorption occurred on only 3–7% of the total Ag surface at 300 K and coverage depended on both the pretreatment and CO pressure utilized. No irreversible CO adsorption occurred on the alumina, whereas linearly bonded CO was the dominant species on the metallic Ag sites. After a 30-min purge, the bands due to these chemisorbed forms of CO decreased in intensity while a band due to bridge-bonded CO increased in intensity, which implies that CO reoriented as the surface concentration of CO decreased. In the presence of Cs, similar behavior was observed and the band intensity of the bridge-bonded CO increased. After reduction at 673 K, cesium suboxides appeared to be formed based on the formation of carbonyl complexes at 2028, 1950, and 1869 cm⁻¹. On reduced Ag catalysts, electronic effects of Cs and Cl were observed and adsorbed CO gave a lower frequency, i.e., 2018 and 2009 cm⁻¹ for Cs-promoted samples reduced at 473 and 673 K, respectively, due to an increase in the electron density on surface Ag atoms, while this band occurred at a higher frequency of 2129 cm⁻¹ with a CsCl-promoted Ag catalyst due to a net decrease in the electron density on surface Ag atoms. After CO adsorption on O-covered Cs-promoted and CsCl-promoted catalysts, a band between 1520 and 1491 cm⁻¹ existed which was assigned to a COO⁻ stretching mode in a carbonate species formed on composite AgCs_xO_y sites. These studies with CO provide evidence that reduction at 673 K following a calcination step can lead to redistribution of Cs atoms.     

气体与煤表面吸附作用的量子化学研究

选用褐煤、次烟煤、高挥发分烟煤、低挥发分烟煤和无烟煤5种煤表面结构模型,采用量子化学半经验方法INDO,从分子水平描述了CO、O₂、H₂O(g)、CO₂、CH₄和H₂等6种气体在煤表面的吸附作用,计算了气体在煤表面的吸附能、吸附距离、吸附作用键级和净电荷变化等微观参数,用Morse函数拟合了气体与煤表面的结合能曲线,得到了气体吸附作用强弱次序为：CO和O₂最强,H₂O和CO₂次之,CH₄和H₂最弱。     

Raman spectroscopy and nitrogen vapour adsorption for the study of structural changes during purification of single-wall carbon nanotubes

Raman spectroscopy and nitrogen adsorption measurements were combined to study the surface features of semi-conducting and metallic single-wall nanotubes (SWNTs). The nanotubes were treated chemically and with heat under moderate conditions that more than doubled the mesopore volume of the tested samples, which consistently led to a significant rise in the total surface area of up to 1550 m²/g. The large increase in the number of micropores of less than 1 nm in diameter was associated with the loosening of nanotube bundles as well as the creation of structural flaws on the surface of individual SWNTs due to chemical treatment. Micropores in the 1.0-1.8 nm range were associated with the holes created on the surface of individual tubes. Heating at 1000 °C was shown to restore nanotube diameter to their initial pre-chemical treatment levels with the change in the chirality of SWNTs and diminish the porosity by closing small holes. It was assumed that the intermediate frequency range (500-1100 cm⁻¹) was associated with the degree of imperfection of HiPco SWNTs crystalline structures, and therefore provided information about the degree of tube surface damage due to the presence of functional groups. A hypothesis explaining the transformation of SWNT porous structure during heat treatment is proposed.     

Resonant Raman spectroscopy on enriched C carbon nanotubes

Isotopically enriched single-wall carbon nanotubes with different ¹³C concentrations were investigated by resonant Raman spectroscopy. Linear reductions of the Raman frequencies with an increase of ¹³C concentration are observed for the different nanotube Raman modes, and the effect of the reduced mass variation of the isotope mixture on the phonon frequencies is described through a simple harmonic oscillator model. In addition to the frequency dependence, the Raman linewidths as a function of the ¹³C concentration were also investigated and an expression describing this is presented. We observe an increase in the G band linewidth, as the ¹³C:¹²C ratio approaches unity. Measurements with different excitation energies were performed and the frequency dispersions of the D and G′ bands with laser energy were observed to be the same for ¹²C and ¹³C nanotubes, suggesting no changes in the electronic structure after isotope enrichment. Through analysis of the radial breathing modes in the Raman spectra obtained with different excitation energies, a relation between these modes frequency and the ¹³C nanotubes diameter was also established.     

TiO_2对Ag/Al_2O_3吸附剂的柴油吸附脱硫性能的影响

采用浸渍法制备不同Ti O2含量的Ag/Ti O2-Al2O3吸附剂,以含硫量为245.36 mg·L-1的商品柴油作为考察对象,常温、常压条件下采用静态评价进行吸附脱硫性能研究。结果表明,经过Ti O2改性的Ag/Al2O3吸附剂柴油吸附脱硫活性有较大幅度提高。通过X射线衍射、N2物理吸附、O2化学吸附和NH3程序升温脱附等研究Ti O2改性剂的影响。关联活性测试和表征结果发现,吸附剂的吸附脱硫活性受吸附剂比表面积、活性金属Ag分散度和吸附剂表面酸协同影响。吸附剂比表面积越大,活性金属Ag分散度越高,吸附剂表面弱酸性位点数量越多,强酸性位点数量越少,吸附剂吸附脱硫活性越高。2%Ag/4%Ti O2-Al2O3的吸附脱硫活性最高,饱和硫容达2.11 mg·g-1。     

Raman spectroscopy on isolated single wall carbon nanotubes

A review is presented on the resonance Raman spectra from one isolated single wall carbon nanotube. The reasons why it is possible to observe the spectrum from only one nanotube are given and the important structural information that is provided by single nanotube spectroscopy is discussed. Emphasis is given to the new physics revealed by the various phonon features found in the single nanotube spectra and their connection to spectra observed for single wall nanotube bundles. The implications of this work on single wall carbon nanotube research generally are also indicated.     

Raman spectroscopy of Kevlar 49 fibre

The Raman spectrum of poly(p-phenylene terephthalate) fibre, Kevlar 49, is reported. Fibre which had been exposed to heat, stress and radiation indicated that within experimental error, no general change takes place in the chemical structure of the material as a whole. However the spectrum of a filament under stress shows that all bands in the spectrum become increasingly polarized with increased stress. The spectral characteristics of the stress fibre lead to a possible explanation of the polymer's response to deformation — opening of the angles in the amide linkage of the polymeric chain and improved alignment of crystallites along the fibre axis.     

Raman spectroscopy of morphology-controlled deposition of Au on graphene

By tuning substrate temperatures in a thermal deposition process, Au nanostructures with different morphologies, such as polygons, dendrites, irregular islands and dense clusters have been obtained on graphene surface. The surface-enhanced Raman scattering (SERS) of graphene caused by gold decoration is systematically investigated. The enhancement factor of graphene G band and the extent of G band splitting are found to be dependent on the morphologies of gold clusters. A maximum enhancement factor as high as ∼270 is obtained for polygonal gold film deposited on monolayer graphene. Furthermore, as a SERS substrate, graphene combined with polygonal gold shows the highest Raman enhancing efficiency for crystal violet (CV) molecules. The mechanisms for the above results are discussed.     

Chemical imaging on the nanoscale-top-illumination tip-enhanced Raman spectroscopy

A top illumination system for tip-enhanced Raman spectroscopy (TERS) in a gap-mode configuration is presented here, which allows chemical analysis of sample surfaces with a lateral resolution beyond the optical diffraction limit and optical detection of very small amounts of analyte molecules (down to single molecule sensitivity). The technique combines the high resolution of an STM with label-free, chemical-rich information of Raman spectra at ambient pressure. In this system, using a special geometry with illumination and detection perpendicular to the sample surface, a lateral resolution of <15 nm was achieved using low laser powers and split second acquisition times per spectrum. This was achieved due to a very high enhancement of the Raman signals in the order of 10(7) by etched metal tips, and allowed the acquisition of 64 x 64 to 200 x 200 pixels chemical Raman maps with full spectral information in every pixel within a reasonable time frame (<25 min for 64 x 64 pixels). The Raman maps give simultaneous information about localization and chemical nature of a sample with high sensitivity and high resolution.