共查询到20条相似文献,搜索用时 15 毫秒
1.
An analysis using the formalism of crystalline orbitals for extended systems with periodicity in one dimension demonstrates that any antiferromagnetic and half-metallic spin-polarization of the edge states in n-acenes, and more generally in zigzag graphene nanoislands and nanoribbons of finite width, would imply a spin contamination S(2) that increases proportionally to system size, in sharp and clear contradiction with the implications of Lieb's theorem for compensated bipartite lattices and the expected value for a singlet (S = 0) electronic ground state. Verifications on naphthalene, larger n-acenes (n = 3-10) and rectangular nanographene islands of increasing size, as well as a comparison using unrestricted Hartree-Fock theory along with basis sets of improving quality against various many-body treatments demonstrate altogether that antiferromagnetism and half-metallicity in extended graphene nanoribbons will be quenched by an exact treatment of electron correlation, at the confines of non-relativistic many-body quantum mechanics. Indeed, for singlet states, symmetry-breakings in spin-densities are necessarily the outcome of a too approximate treatment of static and dynamic electron correlation in single-determinantal approaches, such as unrestricted Hartree-Fock or Density Functional Theory. In this context, such as the size-extensive spin-contamination to which it relates, half-metallicity is thus nothing else than a methodological artefact. 相似文献
2.
Electrochemical synthesis of copper nanoparticles on nafion–graphene nanoribbons support for the synthesis of diaryl ethers via Ullmann type coupling is reported. The catalyst showed excellent performance for C–O cross coupling reactions under ligand free condition. The catalyst was characterized by various techniques such as SEM, TEM, XRD, EDX, BET, TGA, and UV spectrophotometry. It was recycled several times without significant loss in its catalytic activity. 相似文献
3.
Nipapan Ruecha Nadnudda Rodthongkum David M. Cate John Volckens Orawon Chailapakul Charles S. Henry 《Analytica chimica acta》2015
This work describes the development of an electrochemical sensor for simultaneous detection of Zn(II), Cd(II), and Pb(II) using a graphene–polyaniline (G/PANI) nanocomposite electrode prepared by reverse-phase polymerization in the presence of polyvinylpyrrolidone (PVP). Two substrate materials (plastic film and filter paper) and two nanocomposite deposition methods (drop-casting and electrospraying) were investigated. Square-wave anodic stripping voltammetry currents were higher for plastic vs. paper substrates. Performance of the G/PANI nanocomposites was characterized by scanning electron microscopy (SEM) and cyclic voltammetry. The G/PANI-modified electrode exhibited high electrochemical conductivity, producing a three-fold increase in anodic peak current (vs. the unmodified electrode). The G/PANI-modified electrode also showed evidence of increased surface area under SEM. Square-wave anodic stripping voltammetry was used to measure Zn(II), Cd(II), and Pb(II) in the presence of Bi(III). A linear working range of 1–300 μg L−1 was established between anodic current and metal ion concentration with detection limits (S/N = 3) of 1.0 μg L−1 for Zn(II), and 0.1 μg L−1 for both Cd(II) and Pb(II). The G/PANI-modified electrode allowed selective determination of the target metals in the presence of common metal interferences including Mn(II), Cu(II), Fe(III), Fe(II), Co(III), and Ni(II). Repeat assays on the same device demonstrated good reproducibility (%RSD < 11) over 10 serial runs. Finally, this system was utilized for determining Zn(II), Cd(II), and Pb(II) in human serum using the standard addition method. 相似文献
4.
Caetano EW Freire VN Dos Santos SG Galvão DS Sato F 《The Journal of chemical physics》2008,128(16):164719
Results of classical force field geometry optimizations for twisted graphene nanoribbons with a number of twists N(t) varying from 0 to 7 (the case N(t)=1 corresponds to a half-twist M?bius nanoribbon) are presented in this work. Their structural stability was investigated using the Brenner reactive force field. The best classical molecular geometries were used as input for semiempirical calculations, from which the electronic properties (energy levels, HOMO, LUMO orbitals) were computed for each structure. CI wavefunctions were also calculated in the complete active space framework taking into account eigenstates from HOMO-4 to LUMO+4, as well as the oscillator strengths corresponding to the first optical transitions in the UV-VIS range. The lowest energy molecules were found less symmetric than initial configurations, and the HOMO-LUMO energy gaps are larger than the value found for the nanographene used to build them due to electronic localization effects created by the twisting. A high number of twists leads to a sharp increase of the HOMO-->LUMO transition energy. We suggest that some twisted nanoribbons could form crystals stabilized by dipolar interactions. 相似文献
5.
Based on the first-principles calculations, we investigate the magnetic and electronic properties of α-graphyne nanoribbons (NRs). We show that all the armchair α-graphyne NRs are nonmagnetic semiconductors with band gaps as a function of ribbon widths. The zigzag α-graphyne NRs are found to have magnetic semiconducting ground state with ferromagnetic ordering at each edge and opposite spin orientation between the two edges. Under the application of transverse electric field, we further predict the existence of half-metallicity in the zigzag NRs which strongly depends on the width of the ribbon. 相似文献
6.
The performances of graphene oxide (GO) and graphene–platinum hybrid nanoparticles (Gr-Pt hybrid NPs) were compared for biofuel cell (BFC) systems. This is the first study that constitutes these nanomaterials in BFC systems. For this purpose, fabricated bioanodes were combined with laccase modified biocathode in a single cell membraneless BFC. Power and current densities of these systems were calculated as 2.40 μW cm− 2 and 211.90 μA cm− 2 for GO based BFC and 4.88 μW cm− 2 and 246.82 μA cm− 2, for Gr-Pt hybrid NPs based BFC. As a result, a pioneer study which demonstrates the effective performances of combination of graphene with Pt was conducted. 相似文献
7.
Mohammad Reza Pourjavid ;Ali Akbari Sehat ;Majid Haji Hosseini ;Mohammad Rezaee ;Masoud Arabieh ;Seyed Reza Yousefi ;Mohammad Reza Jamali 《中国化学快报》2014,25(5):791-793
A simple and selective method using a column packed with graphene oxide(GO) as a solid phase extractant has been developed for the multi-element preconcentration of Fe(Ⅲ),Ni(Ⅱ),Cu(Ⅱ) and Zn(Ⅱ)ions prior to flame atomic absorption spectrometric determinations.The method is based on the sorption of mentioned ions on synthesized GO using 2-(tert-butoxy)-N-(3-carbamothioylphenyl)acetamide as a chelating agent.Several parameters on the extraction and complex formation were optimized.Under the optimized conditions(pH 6,flow rate 9 mL/min),metal ions were retained on the column,then quantitatively eluted by HNO3solution(5 mL,3.0 mol/L).The preconcentration factor was calculated as250.The detection limits for the analyte ions of interest were found in the range of 0.11 ng/mL(Ni2+) to0.63 ng/mL(Cu2+).The column packed with GO was adequate for metal ions separation in matrixes containing alkali,alkaline earth,transition and heavy metal ions. 相似文献
8.
Analytical and Bioanalytical Chemistry - 相似文献
9.
Singh Nand K. Kushawaha Surendra K. Ayyagari Archana 《Transition Metal Chemistry》2001,26(1-2):140-146
A new ligand, N-phenyl-N
-2-furanthiocarbohydrazide (HPhfth), and its complexes with VOIV, MnIII, FeIII, CoII, NiII, CuII and ZnII have been prepared and characterized by elemental analyses, magnetic susceptibility measurements, i.r., n.m.r., u.v.–vis., mass and FAB mass spectral data. The room temperature e.s.r. spectra of the VOIV, FeIII and CuII complexes yield <g> values characteristic of square pyramidal VOIV, octahedral FeIII and square planar CuII, respectively. The NiII and CuII complexes semiconduct, but the ZnII complex is an insulator at room temperature. However, the conductivity increases as the temperature increases from 303–383 K, with a band gap of 0.21–1.01 eV. HPhfth and its soluble complexes have been screened against several bacteria and fungi. 相似文献
10.
A series of competitive metal-ion transport experiments has been performed.Each involved transport from an aqueous source phase across an organic membrane phase into an aqueous receiving phase.The source phase contained equimolar concentration of Co(Ⅱ),Ni(Ⅱ),Zn(Ⅱ),Cd(Ⅱ),Ag(Ⅰ),Cu(Ⅱ) and Mn(Ⅱ) metal cations.The transport experiments of metal cations were carried out by 2,2’-dithio(bis)benzothiazole(DTB) in chloroform(CHCl3).The source phase being buffered at range pH of 4-6.5 and receiving phase being buffered at pH 3.The obtained results show that the selectivity and the efficiency of Ag(I) transport from aqueous solutions are observed in this investigation.The effect of concentration of palmitic acid in the transport efficiency of Ag(Ⅰ) ion was also conformed. 相似文献
11.
Two nondissociative processes, a Bailar twist that proceeds through a transition state of D3h symmetry and a Ray-Dutt twist mechanism that proceeds through a transition state of C(2v) symmetry, as well as dissociative/associative processes are potential mechanisms by which the enantiomeric forms of chiral metal trischelates can be interconverted. We have applied density functional theory to locate the stationary points for metal trischelates of a beta-diketonate ligand analogue that interconvert Delta and Lambda forms via one or both of these nondissociative pathways. Although many two-dimensional static representations of the Bailar and Ray-Dutt twist mechanisms can be found in the chemical literature (of the type shown in Figure 1), in this communication, we present our results in the form of interactive three-dimensional animations as a means of enhancing the scientific perception of these fluxional processes. 相似文献
12.
Guseva G. B. Antina E. V. Berezin M. B. V'yugin A. I. 《Russian Journal of Coordination Chemistry》2004,30(1):30-33
Thermodynamics of complexation reactions between Zn(II), Ni(II), Hg(II), Co(II), and Cu(II) acetates and 3,35,5-tetramethyl-4,4-dibutyldipyrrolylmethene in DMF at 298.15 K is studied by calorimetric and spectrophotometric methods. The replacement of Zn2+, Ni2+, and Hg2+ ions by Co2+ and Cu2+ ions was found to increase the equilibrium constants of reactions of complex formation with dipyrrolylmethene by more than two orders of magnitude. The role of solvation interactions in coordination of dipyrrolylmethene by d-metal ions is established. 相似文献
13.
Minsoo Koo Jong-Seong Bae Seong Eun Shim Dongmin Kim Dae-Geun Nam Jae-Won Lee Gang-Woo Lee Jeong Hyun Yeum Weontae Oh 《Colloid and polymer science》2011,289(13):1503-1509
Polyimide–graphene composites (PIG) were prepared with variable amounts of graphene, and their thermal properties were analyzed
in films on substrates or sheet states. The thermal conductivities of PIG composite sheets gradually moved upwards with increase
of graphene loading. Coefficient of thermal expansion of composite sheet was higher in out-of-plane mode than in-plane mode.
The residual stress of a composite film was monotonously changed in accordance with the variation of temperature and lowered
with increase of graphene. In addition, the residual stress of a composite film reached to the initial stress value during
cooling process after heating. The stress profiles on further heating and cooling runs closely followed the stress profile
during the first cooing run. 相似文献
14.
I. A. Baidina G. I. Zharkova N. V. Pervukhina S. A. Gromilov I. K. Igumenov 《Journal of Structural Chemistry》2004,45(4):678-687
Synthesis of volatile complexes based on -ketoimine pivalyltrifluoroacetone, C(CH3)3C(NH)CH2COCF3, is described. The general formula of the complexes is M(L)2, where M = Cu, Ni, Pd. Complexes of this kind with Ni and Pd were obtained for the first time. The Cu and Pd complexes were found to be isostructural. A comprehensive crystal-chemical study showed that all structures are molecular and built of trans-complexes. The central atom has a square plane environment. The average M-O and M-N distances are nearly equal in all compounds: 1.84 , 1.92 , and 1.98 for Ni, Cu, and Pd complexes, respectively; the mean values of the O-M-N chelate angles are 93.4°, 91.9°, and 92.7°, respectively.Original Russian Text Copyright © 2004 by I. A. Baidina, G. I. Zharkova, N. V. Pervukhina, S. A. Gromilov, and I. K. IgumenovTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 713–722, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date. 相似文献
15.
Singh Nand K. Kushawaha Surendra K. Thomas Michael J. K. 《Transition Metal Chemistry》2000,25(6):648-658
A new potential tetradentate ligand, N-nicotinoyl-N-2-furanthiocarbohydrazide (H2Nfth), and its complexes with VOIV, MnII, FeII,III, CoII, NiII, CuII and ZnII have been prepared and characterized by elemental analyses, magnetic susceptibility measurements, u.v.–vis, i.r., n.m.r., ES+ and FAB mass spectral data. The room temperature e.s.r spectra of the VOIV and FeIII complexes yield g values, characteristic of octahedral complexes. The Mössbauer spectra of [Fe(HNfth)2] and [Fe2(Nfth)3] at room temperature and at 78 K suggest the presence of high-spin iron(II) and iron(III), respectively. The complexes are electrically insulating at room temperature, however, their conductivities increase as the temperature increases from 333–383 K, with a band gap of 0.46–0.77 eV, indicating their semiconducting behaviour. H2Nfth and its soluble complexes have been screened against several bacteria and fungi. 相似文献
16.
K. Söllner 《Analytical and bioanalytical chemistry》1964,202(1):68-69
17.
G. B. Guseva E. V. Antina A. I. V’yugin A. E. Loginova 《Russian Journal of Coordination Chemistry》2008,34(8):599-605
The reactions of complex formation of Cu(II), Co(II), Zn(II), Ni(II), and Cd(II) acetates with 3,3′,4,4′5,5′-hexamethyl-2,2′-dipyrrolylmethene (HL) in DMF were studied by the electronic spectroscopy and calorimetric titration methods at 298.15 K. The main products of the above reactions are [ML2] chelates. In the case of Cu and Ni salts, the process occurs through the spectrally recorded stage of formation of the heteroligand [ML(AcO)] complexes. The reaction with Cd acetate terminates at the stage of the heteroligand complex formation due to the large radius and decreasing electron affinity of the Cd2+ ion. The effect of the metal nature appears in the increasing thermodynamic stability of single-type complexes in the series [ML2]: Ni(II) < Zn(II) < Co(II) < Cu(II) and [ML(AcO)]: Cd(II) < Ni(II) < Cu(II). 相似文献
18.
19.
A. Czylkowska D. Czakis-Sulikowska A. Kaczmarek M. Markiewicz 《Journal of Thermal Analysis and Calorimetry》2011,105(1):331-339
A novel mixed-ligand complexes with empirical formulae: Ln(4-bpy)1.5(CCl3COO)3·nH2O (where Ln(III) = Pr, Sm, Eu, Gd, Tb; n = 1 for Pr, Sm, Eu and n = 3 for Gd, Tb; 4-bpy = 4,4′-bipyridine) were prepared and characterized by chemical, elemental analysis and IR spectroscopy.
Conductivity studies (in methanol, dimethylformamide and dimethylsulfoxide) were also described. All complexes are crystalline.
The way of metal–ligand coordination was discussed. The thermal properties of complexes in the solid state were studied under
non-isothermal conditions in air atmosphere. During heating the complexes decompose via intermediate products to the oxides:
Pr6O11, Ln2O3 (for Sm, Eu, Gd) and Tb4O7. TG-MS system was used to analyze principal volatile thermal decomposition and fragmentation products evolved during pyrolysis
of Pr(III) and Sm(III) compounds in air. 相似文献
20.
João G. Martins Rui M. Pinto Paula Gameiro M. Teresa Barros Helena M. V. M. Soares 《Journal of solution chemistry》2010,39(8):1153-1167
Divalent metal complexes of N,N′-bis(4-imidazolymethyl)etylenediamine (EMI) have been studied using potentiometric and spectroscopic
techniques (UV-Vis and NMR methods) in aqueous 0.1 mol⋅L−1 KCl supporting electrolyte at 25 °C. Final models and overall stability constants for the complexes of Ca(II), Cd(II), Co(II),
Cu(II), Mg(II), Mn(II), Ni(II), Pb(II) and Zn(II) have been established by potentiometry for all M(II)–EMI systems, except
for Co(II)–EMI. The data revealed that EMI forms ML complexes with all M(II)–EMI systems, which is the dominant species over
a wide range of pH except for the Ca(II)–EMI and Mg(II)–EMI systems. Formation of the MnHL complex was also found for Mn(II)–EMI
solutions. In addition, the UV-Vis and 1H NMR results allowed us establish the coordination modes for the metal complexes between EMI with Cd(II), Cu(II), Ni(II)
and Zn(II). 相似文献