Carbon supported PdCo catalysts in varying atomic ratios of Pd to Co, namely 1 : 1, 2 : 1 and 3 : 1, were prepared. The oxygen reduction reaction (ORR) was studied on commercial carbon-supported Pd and carbon-supported PdCo nanocatalysts in aqueous 0.1 M KOH solution with and without methanol. The structure, dispersion, electrochemical characterization and surface area of PdCo/C were determined by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Cyclic Voltammetry (CV), respectively. The electrochemical activity for ORR was evaluated from Linear Sweep Voltammograms (LSV) obtained using a rotating ring disk electrode. The catalysts were evaluated for their electrocatalytic activity towards oxygen reduction reaction (ORR) in Alkaline Polymer Electrolyte Membrane Fuel Cells (APEMFCs). PdCo(3 : 1)/C gives higher performance (85 mW cm(-2)) than PdCo(1 : 1)/C, PdCo(2 : 1)/C and Pd/C. The maximum electrocatalytic activity for ORR in the presence of methanol was observed for PdCo(3 : 1)/C. First principles calculations within the framework of density functional theory were performed to understand the origin of its catalytic activity based on the energy of adsorption of an O(2) molecule on the cluster, structural variation and charge transfer mechanism. 相似文献
A sensitive spectrophotometric method for the determination of trace amounts of cobalt based on the complex formation with nitrosochromotropic acid in ammoniacal medium is described. After its extraction as thiocyanate complex into isobutylmethyl ketone, cobalt is stripped into nitrosochromotropic acid in ammonia buffer. The method has been applied to the determination of cobalt in mild steel, ferrous alloys and multivitamin preparations. 相似文献
In this work, composite samples were prepared using Borassus fibers and a high-density polyethylene matrix. Alternatively, a chemically modified matrix (maleic anhydride grafted HDPE) was also used to improve fiber-matrix compatibility. The effect of fiber loading on the mechanical properties was investigated. Borassus fiber/modified HDPE composites exhibited improved mechanical performance as compared to pure HDPE composites. SEM studies on the fractured specimens of unmodified HDPE fiber composites reveal the poor fiber-matrix interaction, whereas the interaction is strong with enhanced mechanical properties for modified HDPE fiber composites. This is due to an improvement of the chemical bonding between the modified HDPE matrix and the Borassus fiber as also supported by Fourier transform infrared spectroscopy results. Thermal stability was also found to be enhanced slightly for modified HDPE composites. 相似文献
In analogy with the definition of resonant or quasi-bound states used in three-dimensional quantal scattering, we define the
quasi-bound states that occur in one-dimensional transmission generated by twin symmetric potential barriers and evaluate
their energies and widths using two typical examples: (i) twin rectangular barrier and (ii) twin Gaussian-type barrier. The
energies at which reflectionless transmission occurs correspond to these states and the widths of the transmission peaks are
also the same as those of quasi-bound states. We compare the behaviour of the magnitude of wave functions of quasi-bound states
with those for bound states and with the above-barrier state wave function. We deduce a Breit-Wigner-type resonance formula
which neatly describes the variation of transmission coefficient as a function of energy at below-barrier energies. Similar
formula with additional empirical term explains approximately the peaks of transmission coefficients at above-barrier energies
as well. Further, we study the variation of tunnelling time as a function of energy and compare the same with transmission,
reflection time and Breit-Wigner delay time around a quasi-bound state energy. We also find that tunnelling time is of the
same order of magnitude as lifetime of the quasi-bound state, but somewhat larger. 相似文献
The reactions of the ligand 2-(2-pyridyl)benzthiazole (pbt) with CuBr 2 and ZnCl 2 in acetonitrile produce the complexes [Cu(pbt)Br 2] ( 1) and [Zn(pbt)Cl 2] ( 3), respectively. When complex 1 is dissolved in DMF, complex 2 is obtained as light-green crystals. The reaction of pbt with CuBr 2 in DMF also yields the complex [Cu(pbt)Br 2(dmf)] ( 2) (dmf = dimethylformamide). Complexes 1- 3 were characterized by X-ray crystallography. Complexes 1 and 3 have distorted tetrahedral coordination environments, and complex 2 is constituted of two slightly different copper centers, both exhibiting distorted trigonal bipyramidal geometries. Complexes 1 and 2 cleave phiX174 phage DNA, both in the presence and the absence of reductant. The free ligand pbt does not show any DNA-cleaving abilities. The poor solubility of complex 3 makes it not applicable for biological tests. The occurrence of DNA breaks in the presence of various radical scavengers suggests that no diffusible radicals are involved in the DNA cleavage by complex 1, as none of the scavengers inhibit the cleavage reaction. The DNA-cleavage products are not religated with the enzyme T4 DNA ligase, which is an additional proof that the cleavage is nonhydrolytic. Most probably the cleaving reaction involves reactive oxygen species, which could not be trapped, leading to an oxidative mechanism. An easy oxidation of Cu (II)(pbt)Br 2 to Cu (III) in DMF and the reduction of the same to Cu (I), under similar electrochemical conditions may lead to the in situ activation of molecular oxygen, resulting in the formation of metal solvated nondiffusible radicals able to prompt the oxidative cleavage of DNA. Complex 1 and the pure ligand exhibit remarkable cytotoxic effects against the cancer cell lines L1210 and A2780 and also against the corresponding cisplatin-resistant mutants of these cell lines. 相似文献
A metal-free, regioselective strategy for the synthesis of 3-arylimidazo[1,2-a]pyridines from β-nitrostyrenes and 2-aminopyridines using triethylamine as the catalyst and H2O2 (30% aq.) as the oxidant is reported. The use of an inexpensive base and facile reaction conditions make this strategy a practical alternative for the synthesis of 3-arylimidazo[1,2-a]pyridines. 相似文献
The authors describe an amperometric biosensor for the determination As(III) and Cd(II) based on the inhibition of the enzyme acetylcholineesterase (AChE). A platinum electrode was modified with ruthenium(II)-tris(bipyridyl), graphene oxide and AChE and then showed redox peaks at 0.06 and 0.2 V vs Ag/AgCl in the presence of acetylthiocholine chloride (ATChCl). Amperometry unveiled a steady-state turnover rate with the release of thiocholine. In the presence of arsenic(III) and cadmium(II), AChE showed an inhibitive response at 0.214 and 0.233 V vs Ag/AgCl, respectively. The electrode exhibits a detection limit and linear range of 0.03 μM and 0.05–0.8 μM for As(III) and 0.07 μM and 0.02–0.7 μM for Cd(II), respectively. Type of inhibition and inhibition constants induced by As(III) and Cd(II) on the catalytic sites of AChE were determined from Dixon and Lineweaver-Burk plots. The modified electrode was applied to the determination of As3+ and Cd2+ in river, tap and waste water, and the results proved that the method is sensitive and can be an alternative to chromatographic and spectroscopic techniques.
The siliceous frustules of diatom algae contain complex proteins known as silaffins, which consist of a peptide chain with grafted polyamine chains. These polyamines contain twenty or more nitrogen atoms with trimethylene groups between the nitrogens. We synthesized a set of polymers containing grafted long-chain polyamine fragments by using acryloyl chloride(ACh) polymers and activated acrylic acid copolymers as the starting materials. The new polymers contained 0.05 mol%-3.2 mol% of polyamine chains, which corresponded to 0.06-3.56 mmol·g~(-1) amine groups. The new amine-containing polymers formed complexes with short(19-21-mer)deoxyribonucleic acid(DNA) and ribonucleic acid(RNA) strands, and these complexes penetrated into model yeast cells and A549 lung cancer cell. This study demonstrates the potential of these species based on long-chain polyamines to serve as novel gene delivery systems. 相似文献