Localized Partial Oxidation of Acetic Acid at the Dual Perimeter Sites of the Au/TiO(2) Catalyst-Formation of Gold Ketenylidene

Chemisorbed acetate species derived from the adsorption of acetic acid have been oxidized on a nano-Au/TiO(2) (～3 nm diameter Au) catalyst at 400 K in the presence of O(2)(g). It was found that partial oxidation occurs to produce gold ketenylidene species, Au(2)═C═C═O. The reactive acetate intermediates are bound at the TiO(2) perimeter sites of the supported Au/TiO(2) catalyst. The ketenylidene species is identified by its measured characteristic stretching frequency ν(CO) = 2040 cm(-1) and by (13)C and (18)O isotopic substitution comparing to calculated frequencies found from density functional theory. The involvement of dual catalytic Ti(4+) and Au perimeter sites is postulated on the basis of the absence of reaction on a similar nano-Au/SiO(2) catalyst. This observation excludes low coordination number Au sites as being active alone in the reaction. Upon raising the temperature to 473 K, the production of CO(2) and H(2)O is observed as both acetate and ketenylidene species are further oxidized by O(2)(g). The results show that partial oxidation of adsorbed acetate to adsorbed ketenylidyne can be cleanly carried out over Au/TiO(2) catalysts by control of temperature.     

S-oxygenation of thiocarbamides IV: Kinetics of oxidation of tetramethylthiourea by aqueous bromine and acidic bromate

The kinetics and mechanism of oxidation of tetramethylthiourea (TTTU) by bromine and acidic bromate has been studied in aqueous media. The kinetics of reaction of bromate with TTTU was characterized by an induction period followed by formation of bromine. The reaction stoichiometry was determined to be 4BrO(3)(-) + 3(R)(2)C═S + 3H(2)O → 4Br(-) + 3(R)(2)C═O + 3SO(4)(2-) + 6H(+). For the reaction of TTTU with bromine, a 4:1 stoichiometric ratio of bromine to TTTU was obtained with 4Br(2) + (R)(2)C═S + 5H(2)O → 8Br(-) + SO(4)(2-) + (R)(2)C═O + 10H(+). The oxidation pathway went through the formation of tetramethythiourea sulfenic acid as evidenced by the electrospray ionization mass spectrum of the dynamic reaction solution. This S-oxide was then oxidized to produce tetramethylurea and sulfate as final products of reaction. There was no evidence for the formation of the sulfinic and sulfonic acids in the oxidation pathway. This implicates the sulfoxylate anion as a precursor to formation of sulfate. In aerobic conditions, this anion can unleash a series of genotoxic reactive oxygen species which can explain TTTU's observed toxicity. A bimolecular rate constant of 5.33 ± 0.32 M(-1) s(-1) for the direct reaction of TTTU with bromine was obtained.     

Synthetic nanocrystalline diamond as a third-generation biosensor support

Horseradish peroxidase (HRP) has been immobilized on the surface of functionalized nanocrystalline diamond (NCD) thin films. The structure of the modified NCD surface as well as the electrochemical behavior of the whole system was characterized by impedance spectroscopy and cyclic voltammetry. The proximity of HRP heme groups to the NCD surface allowed direct electron transfer between them, resulting in two separated one-electron-transfer peaks at 0.05 V and 0.29 V vs Ag/AgCl, corresponding to the cathodic and anodic process, respectively. The heterogeneous electron-transfer constant for both processes was calculated to be 0.066 s(-1), the charge-transfer coefficient alpha = 0.49, and the immobilized enzymatic layer about 2.10(-10) mol/cm2. The modified NCD electrode was used as a third-generation biosensor for hydrogen peroxide determination showing a linear response in the 0.1-45 mM H2O2 range, at +0.05 V vs Ag/AgCl.     

A new strategy for the preparation of maleimide-functionalised gold surfaces

We have developed and investigated a new route to functionalise Au surfaces using maleimide groups. This functionalisation has been performed by grafting aminophenyl (AP) via an electrochemical reduction of 4-aminophenyldiazonium salt in acetonitrile solution and the subsequent chemical binding of N-(2-carboxyethyl) maleimide (NCEM). The resulting maleimide functionalised surface was interacted with a cysteine-modified peptide. The grafting of AP was monitored by the occurrence of NH₂ and aryl ring vibrations, whereas the binding of the NCEM led to a strong and sharp peak because of the C═O stretching mode. The immobilisation of the peptide was identified by the appearance of the amide I band. Half of the maleimide surface groups reacted with the peptide because of steric hindrance. The charge efficiency for the AP layer formation was about 45% at a thickness of about 6–8 nm.     

13C NMR STUDY OF SUBSTITUENT EFFECTS IN 1,2,4-OXADIAZOLE AND 1,2,4-THIADIAZOLE DERIVATIVES

¹³C chemical shifts of C═N, C═O and C═S carbons of 3,4-disubstituted-1,2,4-oxadiazole-5-ones(thiones) and 3,4-disubstituted-1,2,4-thiadiazole-5-ones have been determined in CDCl₃ solution. Exceptionally good Hammett correlations of ¹³C NMR chemical shifts of these carbons with σ were obtained. The negative ρ values observed (inverse substituent effects) indicate π-polarization of the C═N, C═O and C═S bonds. As expected, the long distance C═O and C═S ¹³C chemical shifts were found less susceptible to substituent-induced electronic changes.     

XPS法研究煤表面碳官能团的变化及硫迁移行为

采用XPS对六枝（Liuzhi）和遵义（Zunyi）原煤及其固定床热解半焦表面的含碳官能团和硫迁移行为进行了研究。在氮气气氛下,在400℃～700℃遵义煤焦表面O=C－O, C－H 和 C－C含量与原煤相比,呈现下降趋势,而C=O和O－C－O、C－O含量却呈现增加趋势; 六枝煤焦表面的O=C－O、C=O和O－C－O、C－O含量的变化规律与遵义煤相似,而C－H和C－C含量的变化却与遵义煤相反。在氢气气氛下, 遵义煤焦表面不仅O=C－O含量与原煤相比下降, 而且C=O和O－C－O、C－O含量也下降,但C－H和C－C含量却增加; 六枝煤除了C=O 和O－C－O含量下降外, 其他官能团的变化与其在氮气气氛下相似。两种煤焦表面S/C比在氮气气氛下随着温度的升高而升高,氢气气氛下在400℃~600℃随着温度的升高却下降,700℃又显著升高。这说明在热解过程中硫在两种气氛下都能从体相向表面迁移,但是氢气能够和含硫自由基反应,所以氢气气氛下煤焦表面的S/C比率低于其氮气气氛下的。     

电解质溶液对聚吡咯电聚合中过氧化行为的影响

分别以硫酸/水和高氯酸锂/乙腈为电解质溶液, 采用循环伏安法在铂基底电极上电聚合制备了聚吡咯, 研究了电解质溶液对聚吡咯电聚合过程中过氧化行为的影响. 与硫酸/水溶液相比, 在高氯酸锂/乙腈溶液中电聚合制备的聚吡咯发生过氧化的峰电位正移了0.42 V. 采用原位傅里叶变换红外(in situ FTIR)光谱技术检测, 结果表明, 电聚合制备的聚吡咯在2种电解质溶液中均发生了过氧化反应, 其β-C经氧化生成C-OH或CO. 在硫酸/水溶液中, 部分聚吡咯发生电氧化降解生成CO₂, 致使其共轭结构被破坏, 电导率迅速下降. 而在高氯酸锂/乙腈溶液中, 在更高的电位范围内, 聚吡咯并没有氧化降解成CO₂.     

Surface Modification of Vapor-grown Carbon Nanofibers in Radio Frequency Plasma

"Vapor-grown carbon nanofibers (VGCNFs) were treated in radio frequency (RF) plasma to activate their surface and thus to improve the compatibility with the matrix in polymer composites. The surface of VGCNFs was modified in atmospheres containing different ratios of O2 and Ar. Fourier transform infrared spectroscopy and thermogravimetric measurement shows that when the O2 content in mixture gases was 5%, C-O and O-H functional groups were produced abundantly in the surface of the VGCNFs. When O2 content increased to 8%, most of the surface of carbon fibers was severely oxidized, resulting in defects in structures of the inner layers of VGCNFs."     

Surface ozonation and photooxidation of polyethylene film

High-density polyethylene (HDPE) and low-density polyethylene (LDPE) films were oxidized by treatment with ozone and by photooxidation with a low-pressure mercury lamp. The changes that resulted in the surfaces of the films were followed by ESCA. On ozonation, the surface of LDPE initially is oxidized more rapidly than that of HDPE; however, extended ozonation produces a surface composition that corresponds to C₈O for HDPE and to C₁₈O for LDPE. The surface oxidation products are mainly carboxyl groups, with lower levels of carbonyl and C? O groups. For both polymers photooxidation provides more extensively oxidized surfaces than ozonation, although the surface of HDPE oxidizes slightly faster than that of LDPE treated under identical conditions. In both cases the surface stoichiometry after extensive photoxidation is C₆O. The functional groups formed are mainly carboxyl and C? O. The effects of ozonation and photooxidation on the polyethylene surfaces are compared with those produced by several other means of surface oxidation.     

Wettability and surface free energy of electrolytically oxidized graphite fibers

Wettability of electrolytically oxidized graphite fibers has been investigated by contact angle measurements employing the Wilhelmy method. The atomic ratio of oxygen to carbon, O/C, in the surface layer of the graphite fiber increased with increasing electric specific charge. Contact angle hysteresis was not observed for the untreated graphite fiber (O/C=0.01). The contact angles decreased with increasing O/C, especially for the receding angle, and approached constant for O/C>0.2. The nondispersive and dispersive surface free energies of the oxidized graphite fibers were calculated from the experimentally determined contact angles. The nondispersive surface free energy increased by the oxidation, whereas the dispersive one decreased. From the results of surface analysis, it was found that the changes in the nondispersive and dispersive surface free energies were caused by the increase in O/C ratio and the decrease in surface crystallinity, respectively.     

The oxidation of diamond: the geometry and stretching frequency of carbonyl on the (100) surface

Microwave plasma deposited (100) diamond films have been thermally oxidized in dry O2 between 500 and 723 degrees C. The roughness of a single crystalline grain following oxidation is consistent with a layer-by-layer mechanism for the removal of carbon monoxide. The resulting surface exhibits infrared absorption bands at 1731 and 905 cm-1, attributed to the stretching and bending modes of a surface bonded carbonyl group. The former is within 1 cm-1 of the structurally analogous molecule 2-adamantanone. These data are consistent with the carbonyl groups being present on diamond (100) terraces.     

Influence of combustion conditions on hydrophilic properties and microstructure of flame soot

Previous studies suggest that structure and reactivity of soot depend on combustion conditions like the fuel/oxygen ratio and nature of fuels. However, the essence of how combustion conditions affect physical and chemical properties of soot is still an open question. In this study, soot samples were prepared by combusting toluene, n-hexane, and decane under controlled conditions, and their hydrophilic properties, morphology, microstructure, content of volatile organic compounds, and functional groups were characterized. The hydrophilicity of n-hexane and decane flame soot increased with decreasing fuel/oxygen ratio, while it almost did not change for toluene flame soot. Fuel/oxygen ratio had little effect on the morphology of aggregates and the graphite crystallite size. The primary particle size and the content of volatile organic compounds on soot decreased with decreasing fuel/oxygen ratio. Less hydrophobic groups (C-H) and more hydrophilic groups (C═O) were observed on lean n-hexane and decane flame soot than that on the corresponding rich flame soot. Volatile organic compounds had little effect on the hydrophilicity of soot while the hydrophilicity correlated linearly with the ratio of C═O content to C-H content. The hydrophilic functional groups were found to be mainly located at graphene layer edges and on surface graphene layers in soot.     

Heat-induced alterations in the surface population of metal sites in bimetallic nanoparticles

The ability to alter the surface population of metal sites in bimetallic nanoparticles (NPs) is of great interest in the context of heterogeneous catalysis. Here, we report findings of surface alterations of Pt and Ru metallic sites in bimetallic carbon-supported (PtRu/C) NPs that were induced by employing a controlled thermal-treatment strategy. The thermal-treatment procedure was designed in such a way that the particle size of the initial NPs was not altered and only the surface population of Pt and Ru was changed, thus allowing us to deduce structural information independent of particle-size effects. X-ray absorption spectroscopy (XAS) was utilized to deduce the structural parameters that can provide information on atomic distribution and/or extent of alloying as well as the surface population of Pt and Ru in PtRu/C NPs. The PtRu/C catalyst sample was obtained from Johnson Matthey, and first the as-received catalyst was reduced in 2 % H2 and 98 % Ar gas mixture at 300 degrees C for 4 h (PtRu/C as-reduced). Later this sample was subjected to thermal treatment in either oxygen (PtRu/C-O2-300) or hydrogen (PtRu/C-H2-350). The XAS results reveal that when the as-reduced PtRu/C catalyst was exposed to the O2 thermal-treatment strategy, a considerable amount of Ru was moved to the catalyst surface. In contrast, the H2 thermal-treatment strategy led to a higher population of Pt on the PtRu/C surface. Characterization of the heat-treated PtRu/C samples by X-ray diffraction and transmission electron microscopy reveals that there is no significant change in the particle size of thermally treated samples when compared to the as-received PtRu/C sample. The electrochemical properties of the as-reduced and heat-treated PtRu/C catalyst samples were confirmed by cyclic voltammetry, CO-adsorption stripping voltammetry, and linear sweep voltammetry. Both XAS and electrochemical investigations concluded that the PtRu/C-H2-350 sample exhibits significant enhancement in reactivity toward methanol oxidation as a result of the increased surface population of the Pt when compared to the PtRu/C-O2-300 and PtRu/C as-reduced samples.     

Effects of electrochemical and plasma treatments on carbon fibre surfaces

This paper summarizes the chemical changes induced on carbon fibre surfaces (examined by X-ray photoelectron spectroscopy, XPS) by a variety of electrochemical treatment in aqueous electrolytes together with the improvements in fibre/resin bonding in the corresponding composite materials. It was found that there was no correlation between the amount of chemical functionality introduced onto the fibre surface and the fibre/resin bond strength, i.e. chemical bonding does not play a major role in fibre resin adhesion. This does not rule out the possibility of chemical bonding between the fibre and resin—it simply implies that it is not the governing factor. It is suggested that the immediate surface concentration of chemical groups is too low to make a significant contribution. To tailor interfacial properties it would be desirable to promote chemical bonding between fibre and matrix. The use of a specially designed plasma treatment cell has led to an increase in the surface concentration of chemical groups ( C OH, hydroxyl) that have the potential to react chemically with the resin. By exploiting grazing angle data taken from XPS analysis, it is shown that changes in the chemical nature of the fibres only occurs in the outermost layers, whereas the electrochemical reaction proceeds well into the fibre sublayers. Selective introduction of nitrogen-containing functionality (such as amines,  NH₂) has been achieved. The reactivity towards a particular plasma is shown to be largely dependent on the structure of the fibre surface. The number of C/N groups produced on higher modulus fibres was undesirably low. Their concentration was increased by biasing the fibres to a negative potential (10–30 V) during plasma exposure.     

Donor-acceptor-stabilized silicon analogue of an acid anhydride

A stable silicon analogue of an acid anhydride {PhC(Bu(t)N)(2)}Si{═O·B(C(6)F(5))(3)}O-Si(H){═O·B(C(6)F(5))(3)}{(NBu(t))(HNBu(t))CPh} (4) with a O═Si-O-Si═O core has been prepared by treating monochlorosilylene PhC(Bu(t)N)(2)SiCl (1) with H(2)O·B(C(6)F(5))(3) in the presence of NHC (NHC = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene). Compound 4 has been characterized by elemental analysis and multinuclear NMR spectroscopic investigations. The molecular structure of 4 has been established by single-crystal X-ray diffraction studies, and DFT calculations support the experimental results.     

Glycolaldehyde as a probe molecule for biomass derivatives: reaction of C-OH and C═O functional groups on monolayer Ni surfaces

Controlling the activity and selectivity of converting biomass derivatives to syngas (H(2) and CO) is critical for the utilization of biomass feedstocks as renewable sources for chemicals and fuels. One key chemistry in the conversion is the selective bond scission of the C-OH and C═O functionalities, which are present in many biomass derivatives. Because of the high molecular weight and low vapor pressure, it is relatively difficult to perform fundamental surface science studies of C6 sugars, such as glucose and fructose, using ultrahigh vacuum techniques. Glycolaldehyde (HOCH(2)CH═O) is the smallest molecule that contains both the C-OH and C═O functional groups, as well as the same C/O ratio as C6 sugars, and thus is selected as a probe molecule in the current study to determine how the presence of the C═O bond affects the reaction mechanism. Using a combination of density functional theory calculations and experimental measurements, our results indicate that the reaction pathway of glycolaldehyde to produce syngas can be enhanced by supporting monolayer Ni on a Pt substrate, which shows higher activity than either of the parent metals. Furthermore, the Pt substrate can be replaced by tungsten monocarbide to achieve similar activity and selectivity, indicating the possibility of using Ni/WC to replace Ni/Pt as active and selective catalysts with higher stability and lower cost.     

On the Reactivity of Silver Electrodes in a Chlorine Radiofrequency Plasma — Plasma Oxidation vs. Thermal Oxidation

The plasma‐electrochemical growth of an ion‐conducting film by the oxidation of a metal in an electronegative plasma is investigated and compared with results from thermal oxidation. As model system we studied the oxidation kinetics of silver electrodes in a Cl₂ rf plasma. The electrochemical control of the reaction by external currents through the product layer using the plasma as a fluid electrode was achieved. Both potentiostatic and galvanostatic control of the reaction was applied. The morphology of the product layer and its temporal evolution was investigated using SEM. A formation of silver chloride surface patterns in the oxidation process takes place if a simple stability criterion is not fulfilled. Specific surface morphologies were found under different experimental conditions. The morphology of the product layer is influenced by the external electric current and the substrate temperature. The influence of the plasma phase on the thermodynamics and kinetics of the oxidation process is discussed. The role of excited plasma species, the electrical charging of the surface and radiation from the plasma are taken into account.     

Plasma-assisted oxidation of Cu(100) and Cu(111)

Oxidized copper surfaces have attracted significant attention in recent years due to their unique catalytic properties, including their enhanced hydrocarbon selectivity during the electrochemical reduction of CO₂. Although oxygen plasma has been used to create highly active copper oxide electrodes for CO₂RR, how such treatment alters the copper surface is still poorly understood. Here, we study the oxidation of Cu(100) and Cu(111) surfaces by sequential exposure to a low-pressure oxygen plasma at room temperature. We used scanning tunnelling microscopy (STM), low energy electron microscopy (LEEM), X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption fine structure spectroscopy (NEXAFS) and low energy electron diffraction (LEED) for the comprehensive characterization of the resulting oxide films. O₂-plasma exposure initially induces the growth of 3-dimensional oxide islands surrounded by an O-covered Cu surface. With ongoing plasma exposure, the islands coalesce and form a closed oxide film. Utilizing spectroscopy, we traced the evolution of metallic Cu, Cu₂O and CuO species upon oxygen plasma exposure and found a dependence of the surface structure and chemical state on the substrate''s orientation. On Cu(100) the oxide islands grow with a lower rate than on the (111) surface. Furthermore, while on Cu(100) only Cu₂O is formed during the initial growth phase, both Cu₂O and CuO species are simultaneously generated on Cu(111). Finally, prolonged oxygen plasma exposure results in a sandwiched film structure with CuO at the surface and Cu₂O at the interface to the metallic support. A stable CuO(111) surface orientation is identified in both cases, aligned to the Cu(111) support, but with two coexisting rotational domains on Cu(100). These findings illustrate the possibility of tailoring the oxidation state, structure and morphology of metallic surfaces for a wide range of applications through oxygen plasma treatments.

A low-pressure oxygen plasma oxidized Cu(100) and Cu(111) surfaces at room temperature. The time-dependent evolution of surface structure and chemical composition is reported in detail for a range of exposure times up to 30 min.     

An ab initio study of electrochemical vs. electromechanical properties: the case of CO adsorbed on a Pt(111) surface

We have studied electrochemical vibrational and energy properties of CO/Pt(111) in the framework of periodic density functional theory (DFT) calculations. We have used a modified version of the previously developed Filhol-Neurock method to correct the unphysical contributions arising from homogeneous background countercharge in the case of thick metallic slabs. The stability of different CO adsorption sites on Pt(111) (Top, Bridge, Hcp, Fcc) has been studied at constant electric field. The energies are dominated by the surface dipole interaction with the external electric field: a strong positive electric field favors the surfaces with the lower dipole moment (that correspond to the ones with the lower coordination). The Stark tuning slope of the CO stretching frequency for a Top site was calculated for different surface coverages in very good agreement with both experimental and other theoretical results. Finally, we have performed an analysis of the origin of Stark shifts showing that the total Stark effect can be split into two competing components. The first one corresponds to the direct effect of charging on the C-O chemical bond: it is referred as an electrochemical effect. The second is the consequence of the surface dipole interaction with the applied electric field that modifies the C-O distance, inducing a change of the C-O force constant because of C-O bond anharmonicity: it is referred as the electromechanical effect. In the CO/Pt(111) case, the dominant contribution is electromechanical. The electrochemical contribution is very small because the electronic system involved in the surface charging is mostly non-bonding as analyzed by looking at the surface Fukui function.