Effect of pretreatment of black carbon on electrocatalytic activity of Pt/C catalyst for methanol oxidation

Direct methanol fuel cell (DMFC) has attracted wide attention due to its many advantages. However, its practical application is limited by the low electrocatalytic activity of the anodic Pt/C catalyst usually used for the methanol oxidation. In this paper, in order to increase the electrocatalytic performance of the Pt/C catalyst for the methanol oxidation, the black carbon, usually used as the supporter, was pretreated with CO2, air, HNO3 or H2O2. The cyclic voltarnmetric results indicated that the current densities of the anodic peak of methanol oxidation at the Pt/C catalysts with the black carbon pretreated with CO2,air, HN03, H202 and untreated black carbon were 39, 33, 32, 20 and 18 mA center dot cm(-2), respectively, illustrating that among the above five kinds of the Pt/C catalysts, the Pt/C catalyst with the black carbon pretreated with CO2 shows the best electrocatalytic activity and stability for the methanol oxidation. Its main reason is that the CO2 pretreatment could reduce the content of the oxygen-containing groups on the surface of the black carbon and increase the content of graphite in the black carbon, leading to the low resistance of the black carbon and the increase in the dispersion extent of the Pt particles in the Pt/C catalyst.

Highly enhanced luminescence from single-crystalline C-60 center dot 1m-xylene nanorods

Single-crystalline C-60 center dot 1m-xylene nanorods with a hexagonal structure were successfully synthesized by evaporating a C-60 solution in m-xylene at room temperature. The ratio of the length to the diameter of the nanorods can be controlled in the range of approximate to 10 to over 1000 for different applications. The photoluminescence (PL) intensity of the nanorods is about 2 orders of magnitude higher than that for pristine C-60 crystals in air. Both UV and Raman results indicate that there is no charge transfer between C-60 and m-xylene. It was found that the interaction between C-60 and m-xylene molecules is of the van der Waals type. This interaction reduces the icosahedral symmetry of C-60 molecule and induces strong PL from the solvate nanorods.

Fabrication and electrochemical behavior of a sol-gel-derived carbon ceramic composite electrode entrapping 2 : 18-molybdodiphosphate

A new type of inorganic-organic hybrid material incorporating carbon powder and alpha -type 2:18-molybdodiphosphate (P2Mo18) in a methyltrimethoxysilane (MTMOS) based gel has been produced by a sol-gel process and used to fabricate a chemically modified electrode. The P2Mo18-doped carbon ceramic composite electrode was characterized using SEM and cyclic voltammetry. Square-wave voltammetry with an excellent sensitivity was exploited to conveniently investigate the dependence of current and half-wave potential (E-1/2) on pH. The chemically modified electrode has some advantages over the modified film electrodes constructed by the conventional methods, such as long-term stability, reproducibility, and especially repeatability of surface-renewal by simple polishing in the event of surface fouling or dopant leaching. In addition, the modified electrode shows a good catalytic activity for the electrochemical reduction of bromate in an acidic aqueous solution. (C) 2000 Elsevier Science B.V. All rights reserved.

Synthesis and crystal structure of a new supermolecular compound: [C12H24O6][H3PMo12O40]center dot 22H(2)O (C12H24O6=18-crown-6)

The title compound, [C12H24O6][H3PMo12O40]. 22H(2)O, was synthesized by the self-assembly of 18-crown-6 (abbreviated as C12H24O6 or 18C6) and H3PMo12O40 in the mixed solvent of CH3OH and CH3CN, and was characterized by IR, H-1 NMR and Xray diffraction for the first time. Crystal data: Triclinic, P (1) over bar, a = 13.428(3) Angstrom, b = 13.557(3)A, c = 14.642(3) Angstrom, a = 105.39(3)degrees, beta = 90.06(3)degrees, gamma = 119.56(5)degrees, V = 2207.5(8) Angstrom(3), Z = 1, R1 = 0.0719, wR2 = 0.1990. It has a disordered alpha-Keggin PMo12O403- anion, which contains the strong alternating short (mean 1.844 Angstrom) and long (mean 1.958 Angstrom) Mo-O-Mo bonds. In the unit cell, crown ethers and molybdophosphates are alternatively arranged in good order along c-axis. An oxonium ion is located at the center of a crown ether molecule., Oxonium ion interacts with 18C6 by the means of hydrogen bonds (mean 2.7771 Angstrom), which are electrostatic or resonant. The observations show the existence of [H3O(C12H24O6)](+) (C) 2000 Elsevier Science B.V. All rights reserved.

Circular dichroism and resonance Raman comparative studies of wild type cytochrome c and F82H mutant

The UV-visible, circular dichroism (CD), and resonance Raman (RR) spectra of the wild type yeast iso-1-cytochrome c (WT) and its mutant F82H in which phenylalanine-82 (Phe-82) is substituted with His are measured and compared for oxidized and reduced forms. The CD spectra in the intrinsic and Soret spectral region, as well as RR spectra in high, middle, and low frequency regions, are discussed. From the analysis of the spectra, it is determined that in the oxidized F82H the two axial ligands to the heme iron are His-18 and His-82 whereas in the reduced form the sixth ligand switches from His-82 to Met-80 providing the coordination geometry similar to that of WT. Based on the spectroscopic data, the conclusion is that the porphyrin macrocycle is less distorted in the oxidized F82H compared to the oxidized WT. Similar distortions are present in the reduced form of the proteins. Frequency shifts of Raman bands, as well as the decrease of the or-helix content in the CD spectra, indicate more open conformation of the protein around the heme. (C) 2000 John Wiley & Sons, Inc.

Electrochemical and in situ spectroelectrochemical behavior of 2,3,7,8,12,13,17,18-octakis(hexyl-thio) tetraazaporphyrin (H(2)OHTTAP) and (Zn(II)OHTTAP)

The characterization of free base porphyrin 2,3,7,8,12,13,17,18-octakis(hexyl-thio) tetraazaporphyrin (H(2)OHTTAP) and its zinc(II) complexes [Zn(II)OHTTAP] containing eight thioether groups at the beta -pyrrole positions of the macrocycle was reported. Results obtained by cyclic voltammetry and differential pulse voltammetry indicated a five-electron reduction in five steps for each complex. They were oxidized in two single-electron-transfer steps to yield pi -cation radicals and dications and reduced in three single-electron-transfer steps to yield pi -anion radicals, dianions and trianions, respectively. The redox property of H(2)OHTTAP was unusual as compared to porphyrins (PPs) and phthalocyanines (Pcs). Each process was monitored by in situ thin-layer spectroelectrochemistry, which indicated that only the Ligand was electroactive. The existence of the eight hexylthio groups was responsible for the intrastack interactions and enhanced intracolumnar and intercolumnar electron motions, resulting in improved conductivity. Copyright (C) 2001 John Wiley & Sons, Ltd.

16-and 18-electron Cp*Rh complexes with 1,2-dicarba-closo-dodecabofane(12)-1,2-dichalcogenolato ligands, as studied by multinuclear magnetic resonance

The reaction of [Cp*RhCl2](2) 1 with dilithium 1,2-dicarba-closo-dodecaborane(12)-1,2-dithiolate (a) and -diselenolate (b) afforded the 16-electron rhodium(III) half-sandwich complexes Cp*Rh[E2C2(B10H10)] [E=S (3a), Se (3b)]. The 18-electron trimethylphosphane rhodium(III) half-sandwiches Cp*Rh(PMe3)[E2C2(B10H10)] 4a-c were prepared from the reaction of Cp*RhCl2(PMe3) 2 with the same dichalcogenolates, including the ditelluride (c). The complexes 4a,b could also be obtained from the reaction of 3a,b with trimethylphosphane. The molecular geometry of 4b was determined by X-ray structural analysis. The 16-electron complexes 3 an monomeric in solution as shown by multinuclear magnetic resonance (H-1-, B-11-, C-13-, P-31- Se-77-, Rh-103-, Te-125-NMR). also in comparison with the data for the trimethylphosphane analogues 4a-c and for 6a in which the rhodium bears the eta(5)-1,3-C5H3 Bu-t(2) ligand. The Rh-103 nuclear shielding is reduced by 831 ppm (3a) and 1114 ppm (3b) with respect to the 18-electron complexes 4a,b. Similarly, the Se-77 nuclear shielding in 3b is reduced by 676.4 ppm with respect to that in 4b. (C) 1999 Elsevier Science S.A. All rights reserved.

Synthesis and x-ray structure of a highly symmetrical selenium-centered hexanuclear neodymium complex, [(Cp6Nd6Se13)-Nd-t](-) (Cp-t=eta(5)-(BuC5H4)-C-t)

The half-sandwich tert-buthylcyclopentadienyl neodymium complex [(CpNdCl2)-Nd-t(THF)(2)](2) (1) reacts with Na2Se5 to give organoneodymium polyselenide complex [Na(THF)(6)][(Cp6Nd6)-Nd-t(mu(6)-Se)(mu(2)-Se-2)(6)] (2) which has been characterized by X-ray crystallography.

Large-scale recovery of C-phycocyanin from Spirulina platensis using expanded bed adsorption chromatography

C-phycocyanin was purified on a large scale by a combination of expanded bed adsorption, anion-exchange chromatography and hydroxyapatite chromatography from inferior Spirulina platensis that cannot be used for human consumption. First, phycobiliproteins were extracted by a simple, scaleable method and then were recovered by Phenyl-Sepharose chromatography in an expanded bed column. The purity (the A(620)/A(280) ratio) of C-phycocyanin isolated with STREAMLINE (TM) Column was up to 2.87, and the yield was as high as 31 mg/g of dried S. platensis. After the first step, we used conventional anion-exchange chromatography for the purification steps, with a yield of 7.7 mg/g of dried S. platensis at a purity greater than 3.2 and with an A(620)/A(650) index higher than 5.0. The fractions from anion-exchange chromatography with a level of purity that did not conform to the above standard were subjected to hydroxyapatite chromatography, with a C-PC yield of 4.45 mg/g of dried S. platensis with a purity greater than 3.2. The protein from both purification methods showed one absolute absorption peak at 620 nm and a fluorescence maximum at 650 nm, which is consistent with the typical spectrum of C-phycocyanin. SDS-PAGE gave two bands corresponding to 21 and 18 kDa. In-gel digestion and LC-ESI-MS showed that the protein is C-phycocyanin. (c) 2006 Elsevier B.V. All rights reserved.

Benthic foraminifera and bottom water evolution in the middle-southern Okinawa Trough during the last 18 ka

A piston sediment core E017 from the middle-southern Okinawa Trough was investigated. A preliminary study of the deep-water evolution since 18 cal. ka BP was performed based on the quantitative census data of benthic foraminiferal fauna, together with planktonic foraminiferal oxygen and carbon isotope, AMS(14)C dating, and the previous results achieved in the southern Okinawa Trough. The result shows that the benthic fauna was dominated by Bulimina aculeata (d'Orbigny), Uvigerina peregrina (Cushman), Hispid Uvigerina and Uvigerina dirupta (Todd) during the glaciation-deglaciation before 9.2 cal. ka BP, while Epistominella exigua (Brady), Pullenia bulloides (d'Orbigny), Cibicidoides hyalina (Hofker), Sphaeroidina bulloides (d'Orbigny) and Globocassidulina subglobosa (Brady) predominated the fauna in the post-glacial period after 9.2 cal. ka BP. The benthic foraminifera accumulation rate (BFAR), paleoproductivity estimates and benthic foraminiferal assemblage conformably indicate that surface water paleoproductivity and organic matter flux during the glaciation-deglaciation were higher than those of the post-glacial period in the middle-southern Okinawa Trough, and gradually enhanced from the southern to the central Okinawa Trough during the glaciation-deglaciation, which could be caused by the discrepancy of the terrigenous nutrients supply. High abundances of E exigua, an indicator of pulsed organic matter input, after 9.2 cal. ka. BP may indicate that the intensity of seasonally riverine pulsed flux during the post-glacial period was stronger than that of the glaciation-deglaciation period, and the seasonal influx in the central trough might be stronger than in the south. The temporal distributions of the typical species indicating bottom water oxygen content and ventilation condition show that the ventilation of the bottom water during the post-glacial period is more active than the glaciation-deglaciation, which reflects that the evolution of the intermediate and deep waters of the northwestern Pacific during the last glaciation has no evident influence on the deep-water of the middle-southern Okinawa Trough. Additionally, the variations in agglutinated benthic foraminiferal abundance and other carbonate dissolution proxies indicate that carbonate dissolution gradually increased since the last 18 ka in the Okinawa Trough and rapidly enhanced at 9.2 cal. ka BP. The modern shallow carbonate lysocline could form at 3 cal. ka BP.

云南会泽超大型铅锌矿床C、O同位素地球化学

云南会泽超大型铅锌矿床规模大、品位富、伴生有用元素多，预示其成矿环境较为特殊。本文分析该矿床矿石中脉石矿物方解石和赋矿碳酸盐地层的C、O同位素组成，结果表明矿石中脉石矿物方解石的C、O同位素组成相对均一，不同矿体(不同标高)、不同产状以及相同矿体不同产状方解石的C、O同位素组成不具明显差别，其δ^13CPDB值和δ^18 OSMOW值分别为-2．1‰～-3．5‰(均值-2．8‰)和16．7‰～18．6‰(均值17．7‰)，在δ^13CPDB-δ^18OSMOW图上集中于岩浆碳酸岩与海相碳酸盐岩之间的狭小范围内。多方面的证据表明：矿床成矿流体为壳一幔混合流体，其中壳源组分可能主要由矿区(或区域)碳酸盐地层提供，而幔源组分则可能与区域大面积峨眉山玄武岩岩浆活动过程中的去气作用有关。

云南会泽铅锌矿田成矿物质来源：Pb、S、C、H、O、Sr同位素制约

云南会泽铅锌矿田是我国著名的超大型特富铅锌矿田之一，由相距3公里的矿山厂和麒麟厂两个独立的矿床组成，Zn＋Pb金属量超过五百万吨，矿石品位在25%至35%之间。为确定矿床成矿流体和成矿金属来源，本文系统研究了矿床的Ph、S、C、O、H和Sr同位素组成特征。矿石硫化物的铅N位素组成均一，^206Pb／^204Pb，^207Pb／^204Pb和。^206Pb／^204Pb的变化范围分别为18．251～18．530，15．663～15．855和38.487～39．433，与围岩碳酸盐岩中浸染状黄铁矿一致，与碳酸盐地层相近，在^208Pb／^204Pb-^206Pb／^204Pb图上显示明显的线性关系，表明铅N位素组成相近的碳酸盐围岩地层提供了成矿物质。矿石硫化物的δ^14S变化范围为10．9‰～17．4‰，多数集中于13‰～17‰，表明还原硫主要来自地层中海相硫酸盐的还原，还原方式为热化学还原，下伏页岩、碎屑岩和泥质岩中的有机质在硫酸盐还原过程中发挥了重要作用。三种不同产状的脉石矿物方解石的碳氧同位素组成均一且没有明显差别，δ^13C变化范围为-2．1‰～-3．5‰, δ^18O为16.8‰～18．6‰。脉石矿物方解石中流体包裹体水的δDFI为-50‰～-60‰，取温度为200℃计算包裹体水的δ^18OH2O值为7．0‰～8.8‰。碳、氧和氢、氧同位素研究结果表明，成矿流体为来自下部上升的变质流体，由于下伏页岩、碎屑岩和泥质岩中有机质的参与，成矿流体具有低的δ^13C和δ^13DFI值，在上升过程中与围岩发生了同位素交换。矿石中黄铁矿、闪锌矿和方解石的初始锶同位素组成（^87Sr／^86Sr）．值的变化范围为0．714～0．717，赋矿围岩中未蚀变白云岩的初始锶同位素组成（^87Sr／^86Sr）．值为0.7083～0．7093，明显低于蚀变白云岩（0．7106），表明成矿流体具有高的（^87Sr／^86Sr），比值。相对围岩碳酸盐岩而言，下伏地层中的页岩、碎屑岩和泥质岩往往具有高得多的^87Sr／^86Sr，因此，流经或者起源于这些地层的流体具有高的锶同位素比值.

湖南香花岭锡多金属矿床C、O、Sr同位素地球化学

对湖南香花岭锡多金属矿床成矿早、晚两期方解石进行了系统的C、O、Sr同位素研究。结果表明，成矿早期方解石具有相对较低的δ^13 CPDB（-5．4‰～-1．4‰）、δ^18 OSMOW（＋6．1‰～＋13．9‰）和较高的^87Sr／^86Sr值（0．7101～0．7230）；而成矿晚期方解石则具有相对较高的δ^13 CPDB（＋0．2‰～＋0．6‰）、δ^18 OSMOW（＋19．4‰～＋21．5‰）和较低的^87Sr／^86Sr值（0．7101）。分析认为，成矿早期方解石为岩浆热液与海相碳酸盐岩相互作用的产物，成矿流体中的碳源于岩浆碳和海相碳酸盐岩；模拟计算结果显示，成矿早期方解石为成矿溶液发生0．05～0．1摩尔分数的CO2去气作用的产物。而成矿晚期方解石主要为矿区碳酸盐岩低温淋滤的产物，流体中的碳主要源于矿区碳酸盐岩围岩。成矿流体中的Sr源于矿区花岗岩和碳酸盐岩，从成矿早期到晚期，岩浆来源的Sr逐渐减少，而碳酸盐岩围岩提供的Sr比例不断增大。

湖北徐家山锑矿床方解石C、O、Sr同位素地球化学

湖北通山的徐家山锑矿床产在上震旦统陡山沱组和灯影组的海相碳酸盐岩中。对该矿床中成矿前和成矿期方解石进行了较系统的C、O、Sr同位素地球化学研究，结果表明，成矿前方解石具相对较高的δ^13CPDB（-0．7‰＋2．0‰）、δ^18OSMOW（＋18．6‰- ＋19．6‰）和Sr含量（2645，8174μg／g，平均5656μg／g），及较低的87Sr／S6Sr比值（0．7096—0．7097）；而成矿期方解石具相对较低的δ^13 CPDB（-3．9‰～-2．1‰）、δ^18OSMOW（＋11．5‰～＋15．3‰）、Sr Rr含量（785～2563μg／g，平均1571μg／g），和较高的^87 Sr／^85 Sr比值（0．7109-0．7154，平均0．7141）。分析认为，成矿前方解石的C、O和绝大部分Sr来源于赋矿围岩——震旦系海相碳酸盐岩；而成矿流体为富H2CO3的溶液，它来自或流经富放射成因。^87 Sr的下伏基底碎屑岩——中元古界冷家溪群浅变质岩；该流体与围岩发生水-岩反应导致成矿期方解石和辉锑矿的沉淀.