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121.
Evaluation of catalytic properties of tungsten carbide for the anode of microbial fuel cells 总被引:5,自引:0,他引:5
Miriam Rosenbaum Feng Zhao Marion Quaas Harm Wulff Uwe Schrder Fritz Scholz 《Applied catalysis. B, Environmental》2007,74(3-4):261-269
In this communication we discuss the properties of tungsten carbide, WC, as anodic electrocatalyst for microbial fuel cell application. The electrocatalytic activity of tungsten carbide is evaluated in the light of its preparation procedure, its structural properties as well as the pH and the composition of the anolyte solution and the catalyst load. The activity of the noble-metal-free electrocatalyst towards the oxidation of several common microbial fermentation products (hydrogen, formate, lactate, ethanol) is studied for microbial fuel cell conditions (e.g., pH 5, room temperature and ambient pressure). Current densities of up to 8.8 mA cm−2 are achieved for hydrogen (hydrogen saturated electrolyte solution), and up to 2 mA cm−2 for formate and lactate, respectively. No activity was observed for ethanol electrooxidation.
The electrocatalytic activity and chemical stability of tungsten carbide is excellent in acidic to pH neutral potassium chloride electrolyte solutions, whereas higher phosphate concentrations at neutral pH support an oxidative degradation. 相似文献
122.
Mitochondrial cardiolipin synthase catalyzes the transfer of a phosphatidyl moiety from phosphatidyl-CMP PtdCMP) to phosphatidylglycerol
(PtdGro) in the presence of specific divalent cations. The synthase was solubilized fromSaccharomyces cerevisiae mitochondria and purified about 300-fold. The partially purified enzyme was part of a medium-size, mixed micelle which had
to bind to a foreign substrate/detergent micelle before catalysis could occur. The kinetics of cardiolipin synthase were studied
by changing the molar fraction of substrate in the micelles. The enzyme obeyed Michaelis-Menten kinetics in relation to PtdCMP
with aK
m of 0.03 mol%. PtdGro caused sigmoidal kinetics with a low apparent affinity. it is speculated that it was involved in docking
the enzyme to the substrate/detergent micelle. Cardiolipin synthase did not catalyze isotope exchange between [14C]CMP and PtdCMP, virtually excluding a ping-pong catalytic mechanism. Mg2+stimulated the activity by increasing the turnover number rather than the substrate affinity, a mechanism which was also found
for the Co2+-activation of rat liver cardiolipin synthase. It is concluded that a direct association of the metal ion and the enzyme forms
the active cardiolipin synthase which has a very high affinity for PtdCMP and a lower affinity for PtdGro. 相似文献
123.
Pranav Nawani Matt Lundwall Benjamin S. Hsiao Miriam Rafailovich Andy H. Tsou Syed Khalid 《Polymer》2007,48(3):827-840
A unique class of nanocomposites containing organoclays modified with catalytically active transition metal ions (TMI) and ethylene vinyl acetate (EVA) copolymers was prepared. The morphology, thermal and rheological properties of these nanocomposites were studied by thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), extended X-ray absorption fine structure (EXAFS) spectroscopy, X-ray scattering/diffraction and oscillatory shear rheometry. TMI-modified organoclays were thought to possess pillaring of multivalent TMI in the interlayer silicate gallery, leading to a notable reduction of the interlayer d-spacing. The resulting nanocomposites exhibited significantly improved thermal stability and fire retardation properties, but similar morphology (i.e., an intercalated-exfoliated structure) and rheological properties comparable with EVA nanocomposites containing unmodified organoclays. It appears that the compressed organic component in the TMI-modified organoclay can still facilitate the intercalation/exfoliation processes of polymer molecules, especially under extensive shearing conditions. The improved fire retardation in nanocomposites with TMI-modified organoclays can be attributed to enhanced carbonaceous char formation during combustion, i.e., charring promoted by the presence of catalytically active TMI. 相似文献
124.
Laboratory studies with live and frozen Maladera matrida female and male beetles showed that males were attracted to chemical substances emanating from the females at dusk. Beetles exhibited sexual activity (including mating) at dusk towards frozen females but not towards frozen males. Frozen females that had been extracted with methanol together with either hexane or dichloromethane or with a mixture of all three solvents did not elicit male sexual activity. Activity was fully restored when a concentrate of the extract was applied to the previously extracted frozen females. Males also responded with vigorous sexual activity to frozen males to which female extract had been applied. Deterrent chemicals appear to be absent from the male body. Males exposed to females that had been frozen during the morning displayed weak sexual activity, indicating that females lack active semiochemicals. Differences between dusk and morning extracts were found with respect to more than 20 compounds, some of which were present in much higher concentrations at dusk than in the morning, while others were not detected in the morning extract. The active component(s) of the short-range sex pheromone of female M. matrida is (are) presumably to be found among these compounds. 相似文献
125.
Diola Marina Núhez-Ramirez Aquiles Solis-Soto Javier López-Miranda Benito Perevra-Alférez Miriam Rutiaga-Quihónes Luis Medina-Torres Hiram Medrano-Roldán 《北京科技大学学报(英文版)》2011,18(5):523-526
The iron concentrate from Hercules Mine of Coahuila,Mexico,which mainly contained pyrite and pyrrhotite,was treated by the bioleaching process using native strain Acidithiobacillus ferrooxidans(A.ferrooxidans)to determime the ability of these bacteria on the leaching of zinc.The native bacteria were isolated from the iron concentrate of the mine.The bioleaching experiments were carried out in shake flasks to analyze the effects of pH values,pulp density,and the ferrous sulfate concentration on the bioleaching process.The results obtained by microbial kinetic analyses for the evaluation of some aspects of zinc leaching show that the native bacteria A.ferrooxidans,which is enriched with a 9K Silverman medium under the optimum conditions ofpH 2.0,20 g/L pulp density,and 40 g/L FeSO4,increases the zinc extraction considerably observed by monitoring duringl 5 d,i.e.,the zinc concentration has a decrease of about 95% in the iron concentrate. 相似文献
126.
127.
Dynamics of metal availability and toxicity in historically polluted floodplain sediments 总被引:2,自引:0,他引:2
Many floodplains contain high concentrations of sediment associated contaminants that might be subjected to large changes in terms of mobility, transformation and bioavailability. Therefore, this study describes 1) changes in the redox conditions and the mobility of metals in artificially uncovered polluted floodplain sediments, 2) metal uptake by organisms and 3) colonization, succession and functioning of benthic algae on these sediments. Flooding caused long term changes in redox potential (Eh) profiles. In top layers strong gradients in redox potential established quickly, while in deeper layers changes occurred more gradually. The availability of copper as measured by Diffusive Gradients in Thinfilms (DGT) showed a consistent relationship with fluctuations in Eh. However, this relationship was restricted to deeper layers in the sediment. Within 1 week high amounts of total copper were immobilized. Differences in total copper concentrations between polluted and clean sediments became only partially apparent when comparing the available copper fraction (DGT-Cu). Introduced Tubifex shows only marginal differences in levels of accumulated Cu. Colonization, growth and succession of algal communities on polluted sediments was not impaired, most likely due to low bioavailability. It is concluded that changing environmental conditions, such as flooding, can result in stable chemical conditions with low a availability of metals and hence in a diminution of actual ecological risks. 相似文献
128.
The ability to control the conductance of single molecules will have a major impact in nanoscale electronics. Azobenzene, a molecule that changes conformation as a result of a trans/cis transition when exposed to radiation, could form the basis of a light-driven molecular switch. It is therefore crucial to clarify the electrical transport characteristics of this molecule. Here, we investigate, theoretically, charge transport in a system in which a single azobenzene molecule is attached to two carbon nanotubes. In clear contrast to gold electrodes, the nanotubes can act as true nanoscale electrodes and we show that the low-energy conduction properties of the junction may be dramatically modified by changing the topology of the contacts between the nanotubes and the molecules, and/or the chirality of the nanotubes (that is, zigzag or armchair). We propose experiments to demonstrate controlled electrical switching with nanotube electrodes. 相似文献
129.
Ehrensaft Miriam K.; Langhinrichsen-Rohling Jennifer; Heyman Richard E.; O'Leary K. Daniel; Lawrence Erika 《Canadian Metallurgical Quarterly》1999,13(1):20
Spouses in maritally happy nonaggressive (H; n?=?21), distressed nonaggressive (DNA; n?=?16), and distressed aggressive (DA; n?=?20) marriages were interviewed about their perceptions of their spouse as controlling. Four areas of spousal control were assessed: involvement in decision making, relationships with family and friends, freedom to plan activities independently, and sense of competence and self-respect. Overall, as expected, spouses in happy marriages reported feeling less controlled than spouses in the 2 distressed groups. Few gender differences were obtained, with the exception that wives in aggressive marriages were more likely to report that their husbands controlled their sense of competence and self-respect. Differences between the DA and DNA groups depended on the specific area of control. Wives in the aggressive couples were significantly more likely than their husbands to state that their spouse's aggression was an attempt to control them. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
130.