氯对苯氧化过程影响机制的实验研究

针对高含氯垃圾气化-燃烧工艺中焦油的氧化裂解过程,利用均相管流反应器配合傅里叶红外光谱仪,以C_6H_6为焦油模型化合物,对比研究了氯参与前后,裂解产物组成和氧化完全程度随温度和当量比的变化,探索了氯对C_6H_6氧化裂解过程的影响机制。结果表明,低温下氯对C_6H_6的氧化有明显的激发作用,但由于氯对OH的消耗,对裂解产物进一步转化为完全氧化产物CO_2又存在抑制作用。此外,在高温低当量比条件下氯对聚合反应也有促进作用。因此,在工程应用中,高含氯垃圾气化产物的燃烧可适应更低的温度,但应避免高温低当量比反应环境的形成以避免聚合产物。此外,还应控制垃圾原料中的氯元素比例,以保障氧化反应的充分进行。     

Investigation of field emission and photoemission properties of high-purity single-walled carbon nanotubes synthesized by hydrogen arc discharge

Single-walled carbon nanotubes (SWCNTs) were directly synthesized by a hydrogen arc-discharge method by using only Fe catalyst. The synthesized carbon materials indicated high-purity SWCNTs without amorphous carbon materials from SEM observation. The SWCNTs had diameters of 1.5-2.0 nm from TEM and Raman observation. After a simple purification, TGA indicated that SWCNTs had a purity of ca. 90.1 wt %. Field emission from the SWCNT emitters which were fabricated by using a spray method was measured by a diode structure. The vertically aligned SWCNT emitters showed the low turn-on voltage of 0.86 V/microm and a high emission-current density of 3 mA/cm2 at an applied field of about 3 V/microm. From a Fowler-Nordheim plot, the vertically aligned SWCNT revealed a high field enhancement factor of 2.35 x 10(4). The photoemission measurements, excited by a photon energy of 360 eV, showed significantly delocalized graphite-pi states at the purified SWCNTs. Here, we investigated that the field-emission properties of SWCNTs would be attributed to the high electronic density of states near Fermi energy, including the delocalized graphite-pi states.     

Surface reactions of chlorine molecules and atoms with water and sulfuric acid at low temperatures

Reactions of chlorine-containing species are of great current interest, particularly in reference to possible stratospheric ozone depletion. We have been investigating the potential role of heterogeneous reactions of these species with stratospheric aerosols. Here we wish to report on the results of a study of the interactions of Cl atoms and Cl₂ with H₂SO₄ and H₂O, the dominant components of stratospheric aerosols, at low temperature using X-ray photoelectron spectroscopy (XPS). It appears that chlorine atoms and molecules form chloride ion and higher oxidation states of chlorine upon reacting with cooled surfuric acid surfaces while only chloride ion forms with ice. To test the validity of the chlorine oxidation assignment, an XPS study was also made of chlorine in its various oxidation states as found in the chlorides, hypochlorites, chlorites, chlorates, and perchlorates of sodium, potassium, and calcium. Possible mechanisms by which chlorine changes its oxidation state on contact with H₂SO₄ glasses are discussed.     

Controlled assembly of Ag nanoparticles and carbon nanotube hybrid structures for biosensing

Here we report a chemical-free, simple, and novel method in which a part from a silver-based anode is controllably used in a straightforward manner to produce silver nanoparticles (Ag NPs) in order to fabricate a controlled assembly of Ag NPs and single walled carbon nanotube (SWCNT) hybrid structures. The attachment and distribution of Ag NPs along SWCNTs have been investigated and characterized by field emission scanning electron microscopy (FESEM). We have achieved the decoration of SWCNTs with different densities of Ag NPs by changing the deposition time, the applied voltage, and the location of carbon nanotubes with respect to the anode. At low voltage, single silver nanoparticle is successfully attached at the open ends of SWCNTs whereas at high voltage, intermediate and full coverage densities of Ag NPs are observed. As voltage is further increased, fractals of Ag NPs along SWCNTs are observed. In addition, a device based on a Ag NPs-SWNT hybrid structure is used for the label-free detection of ssDNA molecules immobilized on it. We believe that the proposed method can be used to decorate and/or assemble metal nanoparticles or fractal patterns along SWCNTs with different novel metals such as gold, silver, and copper and can be exploited in various sensitive applications for fundamental research and nanotechnology.     

胶束辅助的酞菁给体-碳纳米管受体超分子自组装及光诱导长寿命电荷分离态

利用十二烷基硫酸钠(SDS)阴离子胶束能够稳定分散单壁碳纳米管(SWCNT)和解聚富集四磺酸锌酞菁(ZnPcS₄)的能力, 组装了ZnPcS₄-SWCNT的电子给体-受体对来模拟光合作用的原初电子转移过程. 用稳态和时间分辨荧光法研究了相应的给体-受体分子间和分子内的光诱导电子转移速率, 用激光闪光光解技术检测了生成的电荷分离态. ZnPcS₄-SWCNT的电子给体-受体组装体在707 nm处出现了基态特征吸收峰, 但是复合体不产生荧光, 这主要归因于有效的分子内光诱导电子转移过程. 瞬态吸收光谱检测到相应的离子对, 动力学衰减结果表明, 电荷分离态的寿命长达42 μs. 这一长寿命电荷分离态的形成, 主要是因为ZnPcS₄是良电子给体(低氧化电位), SWCNT是好的电子受体, 使得三重态电子转移能够发生, 生成三重态电荷分离态.     

The interaction of CH<Subscript>3</Subscript>Cl,CH<Subscript>2</Subscript>Cl<Subscript>2</Subscript>, CHCl<Subscript>3</Subscript>, and CCl<Subscript>4</Subscript> with ozone on the surface of ice under stratospheric conditions

The interaction of ozone with chlorinated methanes adsorbed on a thin ice film was studied over the temperature range 77–292 K. Ozone was shown to oxidize chlorinated methanes starting with 210 K to produce chlorine oxides of various compositions. The products formed in the oxidation of chlorinated methanes with ozone over the temperature range 77–292 K were analyzed by IR Fourier transform spectroscopy. Along with carbon dioxide and water, chlorine oxides in high oxidation states were predominantly formed.     

W-Fe-MgO催化分解CH4制备单壁碳纳米管

使用“柠檬酸法”制备了一系列较高比表面的W-Fe-MgO催化剂,在较易放大的流化床反应器中,1 100 ℃ H2气流中分解CH4,制得SWCNTs管束,单管直径在1～3 nm,最高碳产率36 mg/100 mg催化剂.经TEM、微区Raman、程序升温氧化(TPO)测量表明,产物中无定形碳、MWCNTs均较少,为纯度较高、缺陷较少的SWCNTs.从EDAX结果并参考W-Fe相图推测SWCNTs生长的催化剂活性相可能为W、Fe的金属间化合物或富Fe的固溶体.     

单壁纳米碳管的纯化及表征

利用微孔膜及空气氧化法逐步除去电弧放电法制备的单壁纳米碳管(SWCNTs)中的金属催化剂粒子、碳纳米粒子、无定形碳等杂质,并利用热重分析（TGA）、高分辨透射电子显微镜（HRTEM）及拉曼（Raman）光谱,对每一步得到的产物进行分析表征.实验证明,该方法对单壁纳米碳管的纯化是比较有效的,可以得到纯度在90％以上的单壁纳米碳管.     

Studies on the role of oxidation states of the platinum surface in electrocatalytic oxidation of small primary alcohols

The role of the oxidation state of a platinum polycrystalline surface in the electrocatalytic oxidation of C₁ to C₄ primary alcohols has been studied by using electrochemical techniques, in situ FTIR spectroscopy and X-ray photoelectron spectroscopy. The results revealed that the oxidation state of the Pt surface plays a key role in the oxidation of primary alcohols, and demonstrated that the oxidation of C₁ to C₄ primary alcohols on a Pt electrode is controlled by the formation of surface oxides on the Pt electrode at different potentials. It was found that the dependence of the reaction process on the oxidation states of the platinum surface yielded similar features in the cyclic voltammogram for oxidation of different primary alcohols at a Pt electrode. According to the effects in the oxidation of primary alcohols, the surface oxides of platinum may be classified as active and poison species. The Pt surface oxides of higher oxidation states (Pt(OH)₃ and PtO₂) formed at potentials above 1.0 V (SCE) were identified as poison species, while other lower oxidation states of Pt surface oxides such as PtOH, Pt(OH)₂ and PtO may be identified as the possible active species for primary alcohol oxidation.     

What spectroscopy reveals concerning the Mn oxidation levels in the oxygen evolving complex of photosystem II: X-ray to near infra-red

Photosystem II (PS II), found in oxygenic photosynthetic organisms, catalyses the most energetically demanding reaction in nature, the oxidation of water to molecular oxygen and protons. The water oxidase in PS II contains a Mn(4)Ca cluster (oxygen evolving complex, OEC), whose catalytic mechanism has been extensively investigated but is still unresolved. In particular the precise Mn oxidation levels through which the cluster cycles during functional turnover are still contentious. In this, the first of several planned parts, we examine a broad range of published data relating to this question, while considering the recent atomic resolution PS II crystal structure of Umena et al. (Nature, 2011, 473, 55). Results from X-ray, UV-Vis and NIR spectroscopies are considered, using an approach that is mainly empirical, by comparison with published data from known model systems, but with some reliance on computational or other theoretical considerations. The intention is to survey the extent to which these data yield a consistent picture of the Mn oxidation states in functional PS II - in particular, to test their consistency with two current proposals for the mean redox levels of the OEC during turnover; the so called 'high' and 'low' oxidation state paradigms. These systematically differ by two oxidation equivalents throughout the redox accumulating catalytic S state cycle (states S(0)S(3)). In summary, we find that the data, in total, substantially favor the low oxidation proposal, particularly as a result of the new analyses we present. The low oxidation state scheme is able to resolve a number of previously 'anomalous' results in the observed UV-Visible S state turnover spectral differences and in the resonant inelastic X-ray spectroscopy (RIXS) of the Mn pre-edge region of the S(1) and S(2) states. Further, the low oxidation paradigm is able to provide a 'natural' explanation for the known sensitivity of the OEC Mn cluster to cryogenic near infra-red (NIR) induced turnover to alternative spin/redox states in S(2) and S(3).     

Cavitand-functionalized SWCNTs for N-methylammonium detection

Single-walled carbon nanotubes (SWCNTs) have been functionalized with highly selective tetraphosphonate cavitand receptors. The binding of charged N-methylammonium species to the functionalized SWCNTs was analyzed by X-ray photoelectron spectroscopy and confirmed by (31)P MAS NMR spectroscopy. The cavitand-functionalized SWCNTs were shown to function as chemiresistive sensory materials for the detection of sarcosine and its ethyl ester hydrochloride in water with high selectivity at concentrations as low as 0.02 mM. Exposure to sarcosine and its derivative resulted in an increased conductance, in contrast to a decreased conductance response observed for potential interferents such as the structurally related glycine ethyl ester hydrochloride.     

Element speciation analysis by capillary electrophoresis

An overview of recent developments in the application of capillary electrophoresis to simultaneous separation and determination of different chemical forms of an inorganic element is presented, with particular emphasis placed on metal speciation analysis. Examples of species analysis are addressed, covering metal ions in different oxidation states, metal complexes with inorganic and organic ligands, metalloid oxoanions, organometallic compounds, ionic non-metal species, etc. The speciation performance of capillary electrophoresis is illustrated by a number of practically relevant applications. The method's strengths and current limitations with regard to chemical speciation studies are critically discussed.     

Application of an amperometric sensor to in-line monitoring of pulp bleaching with chlorine dioxide

Chlorine dioxide is replacing chlorine as the active compound in pulp bleaching in order to reduce the amount of chlorine used in the process and hence also in the waste waters. In bleaching with chlorine dioxide part of the effective bleaching chemical is usually chlorite. The electrochemistry of chlorine dioxide and chlorite at solid electrodes was studied by cyclic voltammetry at different pH values. The observed voltammograms indicated that reduction of chlorine dioxide gives chlorite and oxidation of chlorite gives chlorine dioxide. Both voltammograms were well developed, indicating a reversible process. Both platinum and glassy carbon were used as the working electrode. The dependence of the limiting current of chlorine dioxide and chlorite on pH was studied at both electrodes. The method was tested in the chlorine dioxide bleaching stage D1 in a typical bleaching process. A good correlation was found between the concentrations of chlorine dioxide and chlorite measured by the in-line amperometric method and a standard titrimetric method.     

Fermi level engineering of single-walled carbon nanotubes by AuCl3 doping

We investigated the modulation of optical properties of single-walled carbon nanotubes (SWCNTs) by AuCl 3 doping. The van Hove singularity transitions (E 11 (S), E 22 (S), E 11 (M)) in absorption spectroscopy disappeared gradually with an increasing doping concentration and a new peak appeared at a high doping concentration. The work function was downshifted up to 0.42 eV by a strong charge transfer from the SWCNTs to AuCl 3 by a high level of p-doping. We propose that this large work function shift forces the Fermi level of the SWCNTs to be located deep in the valence band, i.e., highly degenerate, creating empty van Hove singularity states, and hence the work function shift invokes a new asymmetric transition in the absorption spectroscopy from a deeper level to newly generated empty states.     

Determination of S(IV) Oxoanions at Poly[Ru(5‐NO2‐Phen)2Cl] Tetrapyridylporphyrin Glassy Carbon Modified Electrode

Glassy carbon electrodes modified with conducting polymers of Ni(II), Zn(II) and metal free tetraruthenated porphyrin were evaluated for reduction and oxidation processes of S(IV) oxoanions in Na₂SO₃/water‐ethanol at pH 1.0 and 3.5, showing electrocatalytic activity. A Ni(II) film was able to reduce the S(IV) oxoanions selectively in presence of high concentration of gallic acid. The Ni(II) film was also used as an amperometric sensor toward S(IV) oxoanions reduction in white wine samples showing a detection and quantification limit of 1.40 mg L^?1 and 4.68 mg L^?1, respectively. These results are promising for the electrochemical determination of S(IV) using conducting polymers from these macrocycles.     

Redox transitions of chromium, manganese, iron, cobalt and nickel protoporphyrins in aqueous solution

The electrochemical redox behavior of immobilized chromium, manganese, iron, cobalt, and nickel protoporphyrins IX has been investigated over the pH 0-14 range. In the investigated potential domain the metalloporphyrins were observed in four different oxidation states (M(I), M(II), M(III) and M(IV)). The metalloporphyrins differ in the potentials at which the redox transitions occur, but the observed pH dependence of the redox transitions was similar for the different metalloporphyrins and revealed that the M(II)/M(III) and M(III)/M(IV) transitions were accompanied by a hydroxide transfer at high pH. The fact that the metalloporphyrins are immobilized on graphite does not seem to have a large influence on their redox behavior, as can be deduced from the comparable behavior of immobilized metalloporphyrins on gold and of watersoluble metalloporphyrins in solution. We also performed density functional theory (DFT) calculations on the metalloporphyrins in different oxidation states. The geometries and spin states predicted by these calculations agree well with experimentally determined values; the calculations were also able to predict the electrochemical potentials of the [M(II)]/[M(III)-OH] redox transition to within about 300 mV.     

The production of a high loading of almost monodispersed Pt nanoparticles on single-walled carbon nanotubes for methanol oxidation

Pt/single-walled carbon nanotube (SWCNT) composites have been prepared by mixing surfactant-assisted solubilized SWCNTs and Pt carbonyl complexes. Pt nanoparticles that are nearly monodispersed with a diameter of ca. 2.2 nm are formed on the surface of the SWCNTs and broadly dispersed (even at 60 wt.% loading) on individual and/or small bundles. Formation of the composite does not lead to a change in the structure of SWCNTs, and the composite exhibits significantly enhanced electrocatalytic activity for methanol oxidation. The enhancement in catalytic activity may result from the unique 1-D structures of SWCNTs, the uniform dispersion of Pt nanoparticles, and the interactions between the Pt nanoparticles and the SWCNTs. The SWCNT-supported Pt can serve as a high surface area support for fuel cell applications and a co-catalyst for methanol oxidation.     

Influence of air oxidation on the surfactant-assisted purification of single-walled carbon nanotubes

Arc discharge single-walled carbon nanotube (SWCNT) soot was treated under different experimental conditions including gas- and liquid-phase oxidation, heat treatment in an inert gas, and hydrogen gasification. Afterward, the samples were dispersed in a surfactant and centrifuged at a moderately high speed. Near-infrared spectra of all the dispersions were compared with that of raw SWCNT soot. The relative intensity of SWCNT characteristic spectral bands strongly increased for air-oxidized samples after centrifugation, while it did not substantially change for samples oxidized with nitric acid or reduced with hydrogen. The relative SWCNT spectral intensity was associated to the sample purity through the so-called purity index, which was calculated from the S(22) band transition of semiconducting SWCNTs. Air-oxidized samples experienced a 7-fold increase in the purity index during centrifugation, while it increased by only 2-3 times for nonoxidized samples. Air oxidation specifically improves the preferential stability of SWCNTs over carbonaceous impurities in the dispersions, leading to the highest purity index values reported so far.     

Controlling the Oxidation State of Pt Single Atoms for Maximizing Catalytic Activity

Single-atom catalysts (SACs) have emerged as promising materials in heterogeneous catalysis. Previous studies reported controversial results about the relative level in activity for SACs and nanoparticles (NPs). These works have focused on the effect of metal atom arrangement, without considering the oxidation state of the SACs. Here, we immobilized Pt single atoms on defective ceria and controlled the oxidation state of Pt SACs, from highly oxidized (Pt⁰: 16.6 at %) to highly metallic states (Pt⁰: 83.8 at %). The Pt SACs with controlled oxidation states were then employed for oxidation of CO, CH₄, or NO, and their activities compared with those of Pt NPs. The highly oxidized Pt SACs presented poorer activities than Pt NPs, whereas metallic Pt SACs showed higher activities. The Pt SAC reduced at 300 °C showed the highest activity for all the oxidations. The Pt SACs with controlled oxidation states revealed a crucial missing link between activity and SACs.     

Selective oxidation of semiconducting single-wall carbon nanotubes by hydrogen peroxide

Selective oxidation of single-wall carbon nanotubes (SWCNTs) by H2O2 was conducted at varying heating times and monitored by UV-vis-NIR spectroscopy. A major increase in the relative absorption intensity indicated a higher than 80% concentration of metallic SWCNTs in the final product. Here, it is suggested that semiconducting SWCNTs are more reactive than metallic SWCNTs because of hole-doping by H2O2, resulting in faster oxidation.