Structure and Electrochemical Properties of Carbon Nanotubes Synthesized with Catalysts Obtained by Decomposition of Co,Ni, and Fe Polyoxomolybdates Supported by MgO

Carbon nanotubes (CNTs) were synthesized by thermal decomposition of methane at 900 °C using Co–Mo/MgO, Fe–Mo/MgO, and Ni–Mo/MgO catalysts. To obtain metallic nanoparticles, polyoxomolybdate clusters of Co, Ni, and Fe deposited on MgO were thermally decomposed at 700 °С, and the obtained oxides were heated in a carbon-containing atmosphere. The method of transmission electron microscopy (TEM) testified formation of one to ten walled CNTs with the average outer diameter depending on the catalyst used. Raman spectroscopy data confirmed the presence of single-walled CNTs in the samples obtained with Co–Mo/MgO and Fe–Mo/MgO catalysts. The electrochemical properties demonstrated by the obtained materials in supercapacitors are shown to be functions of their structural and compositional features.     

Improvement of Fe/MgO catalysts by calcination for the growth of single- and double-walled carbon nanotubes

Calcination at 900-1000 degrees C for 8-12 h of an Fe/MgO catalyst prepared by impregnation was found to result in a uniform MgFe2O4/MgO solid solution that showed a successful settling of well-dispersed iron species into the MgO lattice. During methane reduction, many iron-containing particles with a diameter of about 4 nm were formed on the catalyst surface to provide numerous active sites for the growth of single- and double-walled carbon nanotubes. There was a significant improvement of the Fe/MgO catalyst that resulted in a high yield of impurity-free nanotubes. Using C2H4 cracking at 600 degrees C and transmission electron microscope observations, the Fe species distribution in the catalysts and microscope images of nanotube growth were described in detail. H2 reduction of the calcined Fe/MgO catalyst was found to cause the formation of iron layers on the catalyst surface, which resulted in the growth of only carbon layers. The results are useful for understanding changes in the metal species distribution in the catalysts and the nanotube growth mechanism, and they provide a simple method to improve Fe/MgO catalysts.     

Adsorbability and photocatalytic degradability of humic substances in water on Ti-modified silica

From the viewpoint of development of a removal agent for humic substances, we prepared Ti-modified silica gel, SiO2-Ti, from titanium alkoxide and microsized silica gel. The prepared silica agent was investigated in adsorption and photocatalytic degradation of humic substances in water. In these experiments, four humic substances, commercially available Wako humic acid (Wako-HA), Nordic aquatic humic acid (Nordic-HA), Nordic aquatic fulvic acid (Nordic-FA), and Suwannee river fulvic acid (Suwannee-FA), were used, and Freundlich constants (KF and 1/n) and photodegradation rates were evaluated. Wako-HA, which has the highest aromaticity ratio [Ar-OH]/[COOH] and molecular weight, had the highest adsorbability (KF=17.5 (mg/g)(L/mg)(1/n), 1/n=0.67) but the lowest photodegradability (<80%). On the other hand, Suwannee-FA, which has the lowest aromaticity, [Ar-OH]/[COOH] ratio, and molecular weight, afforded lesser adsorbability (KF=7.1 (mg/g)(L/mg)(1/n), 1/n=0.39) but the highest photodegradability (>99%). Nordic-HA and Nordic-FA afforded adsorbabilities similar to that for Suwannee-FA, and medium photodegradabilities between those for Wako-HA and Suwannee-FA. Adsorption and photodegradation capacities of SiO2-Ti were improved with increased Ti content and phosphorescence emission amount, respectively. From XRD analysis, we found that the structure of anatase-type TiO2 features the Ti modifiers of SiO2-Ti. Therefore, humic substance molecules effectively interact with the Ti modifiers and are decomposed by OH radicals generated in situ. We hope that SiO2-Ti will be used as a photodegradation catalyst in water purification plants.     

Adsorption of humic substances by macro weakly basic ion-exchange resin and their effects on removal of Cu2+ and Pb2+

<正>Adsorption ofhumic,tannic and gallic acids by a macro weakly basic ion-exchange resin JN-01 was studied.The adsorption capacity of this resin for gallic and tannic acids is much higher than that for humie acid,which can be explained on the basis of both their molecular size and ionization degree.Furthermore,humic acid is separated into different components with molecular weight in the range from 2000 Da to 100000 Da by ultra-filter,and their adsorption isotherms on resin JN-01 indicate that humic acid's molecular weight is an important factor which makes significant influence on adsorption.Finally,changes in the amount of Cu~(2+) and Pb~(2+) adsorbed on resin JN-01 as a function of the concentration of each of these three acids were studied.A large increase in the heavy metal ions uptake is observed in the presence of humic substance,such advantages are due to the interactions between the heavy metal ions and the unbound functional groups of the adsorbed organic acids.     

Flocculation of humic substances with metal ions as followed by capillary zone electrophoresis

Humic and fulvic acids from various sources have been shown to give different electropherograms by capillary zone electrophoresis (CZE), depending on the pH of the electrolyte. This CZE work is extended here through investigations involving the titration of humic and fulvic acids with Fe(III) and Cu(II) cations. As increasing amounts of these cations were added to the humic substances (HUS), flocculation of metal-humic complexes occurred. This is believed to be caused by binding of the metal cations with negative carboxyl and phenolic sites on the HUS, resulting in a decrease of the repulsive forces that keep the HUS in a conformation more suitable for water solubility. The flocculated complexes were separated from the supernatant by centrifugation, and the supernatants were characterized as to total organic carbon (TOC) content, molecular weight (MW) using gel permeation chromatography, and average electrophoretic mobility (AEM) using CZE. The extent of flocculation correlated with both TOC and quantitative CZE measurements. The MW of the HUS remaining in solution actually decreased, presumably because of precipitation of larger molecules as they became insoluble because of reactions with the metals. Humic acids showed total precipitation of TOC with both metals at a concentration equivalent to their measured acidity. CZE demonstrated that certain fulvic acid fractions (low molecular weight phenolic acids) remained in solution even at high metal concentrations. In summary, changes in electrophoretic behavior of the soluble HUS could be related to changes in charge-to-mass ratios (charge densities) of both humic and fulvic acids with increasing metal cation concentration (neutralization). The copper treated HUS showed changes in their electrophoretic behavior even at low metal concentrations before flocculation, whereas the iron treated HUS flocculated uniformally over the range of added iron without significant changes in AEM. Thus these changes in CZE patterns illustrate different specific binding sites of the HUS for each metal.     

Flocculation of humic substances with metal ions as followed by capillary zone electrophoresis

Humic and fulvic acids from various sources have been shown to give different electropherograms by capillary zone electrophoresis (CZE), depending on the pH of the electrolyte. This CZE work is extended here through investigations involving the titration of humic and fulvic acids with Fe(III) and Cu(II) cations. As increasing amounts of these cations were added to the humic substances (HUS), flocculation of metal-humic complexes occurred. This is believed to be caused by binding of the metal cations with negative carboxyl and phenolic sites on the HUS, resulting in a decrease of the repulsive forces that keep the HUS in a conformation more suitable for water solubility. The flocculated complexes were separated from the supernatant by centrifugation, and the supernatants were characterized as to total organic carbon (TOC) content, molecular weight (MW) using gel permeation chromatography, and average electrophoretic mobility (AEM) using CZE. The extent of flocculation correlated with both TOC and quantitative CZE measurements. The MW of the HUS remaining in solution actually decreased, presumably because of precipitation of larger molecules as they became insoluble because of reactions with the metals. Humic acids showed total precipitation of TOC with both metals at a concentration equivalent to their measured acidity. CZE demonstrated that certain fulvic acid fractions (low molecular weight phenolic acids) remained in solution even at high metal concentrations. In summary, changes in electrophoretic behavior of the soluble HUS could be related to changes in charge-to-mass ratios (charge densities) of both humic and fulvic acids with increasing metal cation concentration (neutralization). The copper treated HUS showed changes in their electrophoretic behavior even at low metal concentrations before flocculation, whereas the iron treated HUS flocculated uniformally over the range of added iron without significant changes in AEM. Thus these changes in CZE patterns illustrate different specific binding sites of the HUS for each metal.     

土壤胡敏酸的^13C核磁共振研究

胡敏酸(HA)是土壤有机质的重要组分,其结构性质与土壤形成和肥力特性有密切关系,长期以来一直是土壤化学研究的难点和重点之一。NMR是研究HA结构的有效手段。自Bar-ton和Schnitzer(1963)首次用~1H NMR研究土壤有机质以来,国外已先后应用~1H、~(13)C NMR和CP-MAS-~(13)C NMR等对土壤及其它来源的HA进行了许多研究,并取得引人注目的进展。但在国内,这方面研究还刚刚开始。本文应用~(13)C NMR方法对东北几种主要耕作土壤以及泥炭和猪粪的HA进行了结构表征,为土壤腐殖酸化学的基础研究提供了资料。     

CVD growth of single-walled carbon nanotubes with narrow diameter distribution over Fe/MgO catalyst and their fluorescence spectroscopy

Single-walled carbon nanotubes (SWNTs) with a narrow diameter distribution are synthesized by thermal chemical vapor deposition (CVD) of methane over Fe/MgO catalyst on the basis of parametric study considering Fe loading, reaction temperature and time, methane concentration, and structure of a support material. We found that the porous MgO support gives the SWNTs with a narrow diameter distribution with the mean diameter and standard deviation of 0.93 and 0.06 nm, respectively, only when the Fe loading and reaction temperature are relatively low. The higher Fe loading and/or the higher reaction temperature enlarged the nanotube diameter, forming double-walled carbon nanotubes (DWNTs) in addition to SWNTs. This result indicates that only the diameter of Fe nanoparticles determines the growth of either SWNTs or DWNTs on the MgO support. The fluorescence and absorption spectra of the nanotube dispersion in D(2)O solution with sodium dodecyl sulfate (SDS) were studied to identify their chirality distribution. The fluorescence of the uniform-diameter SWNTs indicates the formation of the near armchair structures. On the other hand, the SWNTs synthesized over the catalyst with a high Fe loading, 3 wt %, showed a wide chirality distribution including the near zigzag structure. The synthesis of the SWNTs with a narrow diameter distribution could be applied to the selection of SWNTs with a specific chirality based on postsynthesis separation.     

POLYMERIZATION OF BUTYL METHACRYLATE BY IRON PYRIDINEBISIMINE COMPLEXES

Fe(Ⅱ)pyridinebisimine complexes activated with trialkylaluminium or modified methylaluminoxane(MMAO)ascatalysts were employed for the polymerization of butyl methacrylate(BMA).Polymer yields,catalytic activities andmolecular weights as well as molecular weight distributions of BMA can be controlled over a wide range by varying thereaction parameters such as cocatalyst,Al/Fe molar ratio,monomer/catalyst molar ratio,monomer concentration and reactiontemperature used in the polymerization.The catalytic activity of Fe(Ⅱ)complex was 11.1 kg_(polym)/mol_(Fe)h and the highestyield could reach 99.1% under optimum condition.     

Multistep flow-membrane filtration,gel-permeation chromatography,and spectrophotometric determination of polydisperse compounds

To determine the molecular weight distribution of natural polydisperse compounds (peat humic acids) and synthetic substituted polyvinyls, membrane filtration, gel-permeation chromatography, and spectrophotometric determination procedures were developed. The determination limit of polyvinyls was 0.1–0.2 mg/mL. The absorbance of polyvinyl solutions was a linear function of the concentration over the range 0.1–6.0 mg/mL. It was found that the size-fraction distributions of both humic substances and substituted polyvinyls depended not only on the molecular weight, but also the molecular conformation.     

固定床反应器中Ti-MWW催化H2O2分解

在固定床反应器中,H2O2与Ti-MWW分子筛的接触时间越长,其分解率越高.结果表明,分子筛骨架Ti和其拥有的酸性位是造成H2O2在分子筛上分解的主要原因,非骨架Ti对H2O2分解的影响弱于骨架Ti.H2O2的无效分解直接影响反应物的转化效率.了解H2O2无效分解的原因,有利于设计出高活性钛硅分子筛.同时在固定床中研究钛硅分子筛催化分解H2O2的反应有可能成为一种评价钛硅分子筛催化活性的新方法.     

Synthesis of glycerol carbonate from glycerol and dimethyl carbonate catalyzed by K2CO3/MgO

A series of M/MgO (M?=?CaO, KNO₃, KOH, K₂CO₃) catalysts were prepared by a dry impregnation method and used for synthesis of glycerol carbonate from glycerol and dimethyl carbonate. It was found that K₂CO₃/MgO was the most efficient catalyst, with a glycerol carbonate yield of approximately 99% under the conditions: DMC/glycerol molar ratio 2.5:1, catalyst/raw material weight ratio 1%, reaction time 2?h, and reaction temperature 80?°C. FTIR, BET, TEM, and XRD were used for characterization of the catalyst and showed that the active sites seemed to be K₂O formed on the K₂CO₃/MgO catalyst. Finally, a recycling experiment showed that the catalyst was relatively stable and could be reused up to four times, at least, by regeneration.     

特定碱性MgO纳米晶暴露晶面上铁基催化剂及其费-托合成反应的研究

本研究采用等量浸渍法、化学沉淀法和超声浸渍法合成了一系列具有良好外露晶面的Fe/MgO催化剂。采用X射线粉末衍射、高分辨透射电子显微镜、CO₂程序升温脱附、H₂程序升温还原、X射线光谱学和N₂物理吸附等物理化学方法对催化剂进行了表征。MgO纳米晶载体的碱性会影响费-托合成产物的选择性。在超声浸渍过程中,MgO纳米晶载体的碱性得到了保持。研究结果显示,Fe/MgO催化剂的碱性会提高CO解离速率和产物中烯烃的选择性。此外,相比于MgO（100）晶面,MgO（111）晶面负载铁基催化剂具有更高的活性（TOF）和烯烃选择性。MgO（111）晶面上更有利于CO的吸附,抑制二次加氢反应,提高产物中烯烃的收率。     

Cu-Fe-MgO/AlPO_4-5对甲醇水蒸气重整制氢的催化性能研究

以AlPO_4-5分子筛为载体,采用浸渍法制备Cu-Fe-MgO/AlPO_4-5催化剂,用于催化甲醇和水蒸气重整反应制氢气。采用XRD、N2吸附-脱附、H2-TPR、CO2-TPD和NH3-TPD等对催化剂进行表征。结果表明,加入Fe可以明显提高甲醇的转化率,但副产物二甲醚的选择性也增加,添加MgO对降低二甲醚具有明显的作用,但不能提高甲醇的转化率。AlPO_4-5负载Cu、Fe和MgO的质量分数分别为15%、6%和1%时具有较高的催化活性,在反应温度300℃、水醇物质的量比为1.1∶1和质量空速2.51 h~(-1)的条件下,对甲醇的转化率为93.08%,二氧化碳和氢气的选择性分别为95.80%和96.93%,对副产物一氧化碳和二甲醚的选择性分别为1.70%和2.51%。表征结果表明,Cu-Fe-MgO/AlPO_4-5同时含有弱酸弱碱和强酸强碱中心,适量的MgO增加了强碱中心的量,降低弱酸中心的强度,但对强酸中心影响不大。     

Modification of the(SiO_2/MgO/MgCl_2)·TiCl_x Ziegler-Natta Polyethylene Catalysts Using the Third Metal Elements

Various(SiO_2/MgO/MgCl_2)·Ti Clx Ziegler-Natta catalysts modified by the third metal elements were synthesized by the co-impregnation of water-soluble magnesium and the third metal salts. Several key factors including the electronegativity of the third metal elements, catalyst performances in ethylene homo-polymerization, ethylene/1-hexene copolymerization and hydrogen response were systematically investigated. Both the catalyst performance and the polymer properties are influenced by the introduction of the third metal elements. Compared with the unmodified(SiO_2/MgO/MgCl_2)·Ti Clx Ziegler-Natta catalyst, activity and 1-hexene incorporation are enhanced by the introduction of zirconium, vanadium, aluminum and chromium, while deteriorated by the addition of ferrum, nickel, molybdenum and tungsten. Correlations of the catalyst activities and 1-hexene incorporation ability with the electronegativity of the third metal elements are discovered. It is found that the lower electronegativity of the third metal elements leads to the catalyst with higher activity and higher α-olefin co-polymerization ability. The polyethylene produced by a nickel modified catalyst showed broad molecular weight distribution(MWD) and the lowest average molecular weight(MW), while by using a ferrum modified catalyst, the resulting polyethylene had the highest MW, reaching the ultra-high MW area. Vanadium and chromium modified catalysts demonstrated the best hydrogen response.     

A Comparative study on synthesis, characterization and photocatalytic activities of MgO and Fe/MgO nanoparticles

MgO and Fe/MgO particles in the nanometer-size regime have been successfully synthesized by a hydrothermal crystallization process using dodecyl benzenesulphonic acid as a surfactant. The prepared catalysts were characterized in details by multiform techniques: XRD, SEM, TEM, UV-DRS, TGA-DSC, BET surface area, and EPR spectroscopy. Comparative photocatalytic activity of the samples was evaluated through the photodegradation of Acid Blue 80 dye under sunlight. The results of the photocatalytic degradation of Acid Blue 80 dye in aqueous solution demonstrated that Fe ions doping greatly improved the photocatalytic efficiency of MgO nanoparticles. Most interestingly, this is the first time that it has been observed that the Fe/MgO system is quite an effective visible light active catalyst.     

The methylation of inorganic tin by humic materials in an aquatic environment

This paper presents a study of methylation of inorganic tin (SnCl₄·5H₂O) by humic materials (humic and fulvic acids) isolated from the sediment of Tianjin Harbor, Tianjin, China, and the effects of pH, salinity, and the concentration of inorganic tin on the production of methyltin were investigated. These humic materials could methylate inorganic tin, and the methyltin product was mainly monomethyltin. Low molecular weight compounds of the humus fraction (i.e. fulvic acid) were more active in the methylation, which could be facilitated by salinity and affected by pH.     

Study on the influence of humic acid of different molecular weight on basic ion exchange resin's adsorption capacity

In this paper, humic acid (HA) was ultra-filtered into different molecular weight sections and was characterized by multi-element analysis, UV₂₅₄/TOC, FT-IR and three-dimensional fluorescence spectrometric. Since humic acids of different molecular weights have different hydrophilic and molecular size, the maximum adsorption capacity of basic ion exchange resins appears on the humic acid whose molecular weight ranges from 6000 to 10,000 Da.     

Insights into colloid-mediated trace element release at the soil/water interface

Organic or inorganic colloids play a major role in the mobilization of trace elements in soils and waters. Environmental physicochemical parameters (pH, redox potential, temperature, pressure, ionic strength, etc.) are the controlling factors of the colloidal mobilization. This study was dedicated to follow the colloid-mediated mobilization of trace elements through time at the soil/water interface by means of an experimental approach. Soil column experiments were carried out using percolating synthetic solutions. The percolated solutions were ultrafiltrated with various decreasing cutoff thresholds to separate the different colloidal phases in which the dissolved organic carbon and trace element concentrations were measured. The major results which stem from this study are the following: (i) The data can be divided into different groups of organic compounds (microbial metabolites, fulvic acids, humic acids) with regard to their respective aromaticity and molecular weight. (ii) Three groups of elements can be distinguished based on their relationships with the colloidal phases: the first one corresponds to the so-called "truly" dissolved group (Li, B, K, Na, Rb, Si, Mg, Sr, Ca, Mn, Ba, and V). The second one can be considered as an intermediate group (Cu, Cd, Co, and Ni), while the third group gathers Al, Cr, U, Mo, Pb, Ti, Th, Fe, and rare earth elements (REE) carried by the organic colloidal pool. (iii) The data demonstrate that the fulvic acids seem to be a major organic carrier phase for trace elements such as Cu, Cd, Co, and Ni. By contrast, the trace elements belonging to the so-called colloidal pool were mostly mobilized by humic acids containing iron nanoparticles. Lead, Ti, and U were mobilized by iron nanoparticles bound to these humic acids. Thus, humic substances allowed directly or indirectly a colloidal transport of many insoluble trace elements either by binding trace elements or by stabilizing a ferric carrier phase. (iv) Finally, the results demonstrated also that REE were mostly mobilized by humic substances. The REE normalized patterns showed a middle REE downward concavity. Therefore, as previously shown elsewhere humic substances are a major control of REE speciation and REE fractionation patterns as well since the humic substance/metal ratio was the key parameter controlling the REE pattern shape.     

2-硝基-10-羟基-5,10-二氢磷杂吖嗪-10-氧化物的还原研究

10-羟基-5,10-二氢磷杂吖嗪-10-氧化物硝基衍生物的还原反应研究报道始见于1978年.尹志刚等进一步对2-硝基-10-羟基-5,10-二氢磷杂吖嗪-10-氧化物进行了催化加氢研究,结果发现,催化剂用量达到底物质量的7.5%以上,反应介质为中性或弱碱性,该化合物能够被顺利还原[1].该还原方法缺点是Pd/C催化剂不能够回收利用,还原成本高,需要较高氢气压力,危险性大,从而不利于该染料中间体工业化生产.