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2008 Volume 24 Issue 8
2008, 24(08):
Abstract:
2008, 24(08): 1329-1334
doi: 10.1016/S1872-1508(08)60054-6
Abstract:
Apparatus integrating a Fourier transform-infrared (FT-IR) spectrometer and a mid-infrared difference frequency generation (DFG) laser pectrometer was built for the study of the matrix isolation spectrumin solid molecular hydrogen. A 3-cm-long molecular hydrogen crystal was grown in a liquid-helium Dewar and its infrared absorption spectrum in the 1-5 μm region was recorded to test the system. The W0(0) (v=0→0, J=6→0) line around 2410 cm-1 of solid hydrogen was investigated with the DFG laser spectroscopy. High-resolution matrix isolation spectrum of CO2 co-deposited with hydrogen on a BaF2 cold plate at liquid-heliumtemperature was studied.
Apparatus integrating a Fourier transform-infrared (FT-IR) spectrometer and a mid-infrared difference frequency generation (DFG) laser pectrometer was built for the study of the matrix isolation spectrumin solid molecular hydrogen. A 3-cm-long molecular hydrogen crystal was grown in a liquid-helium Dewar and its infrared absorption spectrum in the 1-5 μm region was recorded to test the system. The W0(0) (v=0→0, J=6→0) line around 2410 cm-1 of solid hydrogen was investigated with the DFG laser spectroscopy. High-resolution matrix isolation spectrum of CO2 co-deposited with hydrogen on a BaF2 cold plate at liquid-heliumtemperature was studied.
2008, 24(08): 1335-1341
doi: 10.1016/S1872-1508(08)60055-8
Abstract:
C—Br bond dissociation mechanisms of 2-bromothiophene and 3-bromothiophene at 267 nm were investigated using ion velocity imaging technique. Translational energy distributions and angular distributions of the photoproducts, Br(2P3/2) and Br*(2P1/2), were obtained and the possible dissociation channels were analyzed. For these two bromothiophenes, the Br fragments were produced via three channels: (i) the fast predissociation following the intersystemcrossing fromthe excited singlet state to repulsive triplet state; (ii) the hot dissociation on highly vibrational ground state following the internal conversion of the excited singlet state; and (iii) dissociation following the multiphoton ionization of the parent molecules. Similar channels were involved for photoproduct Br* of the 2-bromothiophene dissociation at 267 nm; while for the photoproduct Br* of 3-bromothiophene, the dissociation channel via internal conversion from the excited singlet state to highly vibrational ground state became dominating and the fast predissociation channel via the excited triplet state almost disappeared. Informations about the relative contribution, energy disposal, and the anisotropy of each channel were quantitatively given. It was found that with the position of Br atom in the thienyl being far from S atom, the relative ratios of products from channels (i) and (ii) decreased obviously and the anisotropies corresponding to each channel became weaker.
C—Br bond dissociation mechanisms of 2-bromothiophene and 3-bromothiophene at 267 nm were investigated using ion velocity imaging technique. Translational energy distributions and angular distributions of the photoproducts, Br(2P3/2) and Br*(2P1/2), were obtained and the possible dissociation channels were analyzed. For these two bromothiophenes, the Br fragments were produced via three channels: (i) the fast predissociation following the intersystemcrossing fromthe excited singlet state to repulsive triplet state; (ii) the hot dissociation on highly vibrational ground state following the internal conversion of the excited singlet state; and (iii) dissociation following the multiphoton ionization of the parent molecules. Similar channels were involved for photoproduct Br* of the 2-bromothiophene dissociation at 267 nm; while for the photoproduct Br* of 3-bromothiophene, the dissociation channel via internal conversion from the excited singlet state to highly vibrational ground state became dominating and the fast predissociation channel via the excited triplet state almost disappeared. Informations about the relative contribution, energy disposal, and the anisotropy of each channel were quantitatively given. It was found that with the position of Br atom in the thienyl being far from S atom, the relative ratios of products from channels (i) and (ii) decreased obviously and the anisotropies corresponding to each channel became weaker.
2008, 24(08): 1342-1346
doi: 10.1016/S1872-1508(08)60056-X
Abstract:
Ce0.65Zr0.25Y0.1O1.95 oxides were prepared by oxidation-coprecipitation method using ammonia and salvolatile as precipitators. The as-prepared samples were thermally treated at different temperatures and characterized by thermogravimetry-differential scanning calorimetry (TG-DSC), Fourier transform-infrared (FT-IR) spectrometry, X-ray diffraction (XRD), and specific surface area measurements (BET). The results showed that the hydroxyl and carboxyl groups coexisted in the precipitate and a perfect solid solution was gradually formed with an increase in calcination temperature. The physisorbed water was lost from 100 to 170 ℃, hydroxyl groups were removed from 250 to 300 ℃, and the carboxyl groups were eliminated from420 to 500 ℃. A structure model was further proposed to understand the Ce0.65Zr0.25Y0.1O1.95 structure evolution process in depth.
Ce0.65Zr0.25Y0.1O1.95 oxides were prepared by oxidation-coprecipitation method using ammonia and salvolatile as precipitators. The as-prepared samples were thermally treated at different temperatures and characterized by thermogravimetry-differential scanning calorimetry (TG-DSC), Fourier transform-infrared (FT-IR) spectrometry, X-ray diffraction (XRD), and specific surface area measurements (BET). The results showed that the hydroxyl and carboxyl groups coexisted in the precipitate and a perfect solid solution was gradually formed with an increase in calcination temperature. The physisorbed water was lost from 100 to 170 ℃, hydroxyl groups were removed from 250 to 300 ℃, and the carboxyl groups were eliminated from420 to 500 ℃. A structure model was further proposed to understand the Ce0.65Zr0.25Y0.1O1.95 structure evolution process in depth.
2008, 24(08): 1347-1352
doi: 10.1016/S1872-1508(08)60057-1
Abstract:
A series of double-chain sulfobetain zwitterionic surfactants with varying carbon number of the intercharge group (spacer), (C16H33)2NCH3(CH2)nSO3, where n=2, 3, 4, and 6, referred to as (C16)2NCnS, were synthesized. The influence of the spacer length on the thermal behaviors of (C16)2NCnS in their pure state was studied using thermogravimetry (TG), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD). Thermogravimetric analysis (TGA) showed that the thermal stability of (C16)2NCnS lowered with increasing the spacer length. All compounds showed a complex polymorphism. Only for (C16)2NC4S and (C16)2NC6S thermotropic liquid crystals were observed using POM. The former exhibited a smectic A (SmA) phase, whereas the latter formed a hexa nal columnar phase. These liquid crystals obtained both in the cooling and the second heating scans provided compelling evidence for the thermal stability of these compounds.
A series of double-chain sulfobetain zwitterionic surfactants with varying carbon number of the intercharge group (spacer), (C16H33)2NCH3(CH2)nSO3, where n=2, 3, 4, and 6, referred to as (C16)2NCnS, were synthesized. The influence of the spacer length on the thermal behaviors of (C16)2NCnS in their pure state was studied using thermogravimetry (TG), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD). Thermogravimetric analysis (TGA) showed that the thermal stability of (C16)2NCnS lowered with increasing the spacer length. All compounds showed a complex polymorphism. Only for (C16)2NC4S and (C16)2NC6S thermotropic liquid crystals were observed using POM. The former exhibited a smectic A (SmA) phase, whereas the latter formed a hexa nal columnar phase. These liquid crystals obtained both in the cooling and the second heating scans provided compelling evidence for the thermal stability of these compounds.
2008, 24(08): 1353-1358
doi: 10.1016/S1872-1508(08)60058-3
Abstract:
Density functional theory (DFT) and time-dependent density functional theory (TDDFT) with hybrid functional B3LYP were used to investigate several physical and chemical properties of [6,6]-phenyl-C61 butyric acid methyl ester (PCBM), including the geometry, electron structure, charge population, bond properties, as well as IR, Raman and electronic absorption spectra. The analysis of the natural bond orbital (NBO) suggested that there were about 0.11 electrons transferred from the moiety phenyl and butyric acid methyl ester group of PCBMto fullerene cage. The strongest IR and Raman peaks came from different modes with the frequencies of 1773 and 1492 cm-1, respectively. The calculated isotropic polarizability, polarizability anisotropy invariant, and hyperpolarizability were 577.7, 96.9, and -22.8 a.u., respectively. Based on TDDFT, the electronic absorption spectra of PCBM were calculated and analyzed. The calculated absorption band near 349 nmagreed well with the experimental measurement.
Density functional theory (DFT) and time-dependent density functional theory (TDDFT) with hybrid functional B3LYP were used to investigate several physical and chemical properties of [6,6]-phenyl-C61 butyric acid methyl ester (PCBM), including the geometry, electron structure, charge population, bond properties, as well as IR, Raman and electronic absorption spectra. The analysis of the natural bond orbital (NBO) suggested that there were about 0.11 electrons transferred from the moiety phenyl and butyric acid methyl ester group of PCBMto fullerene cage. The strongest IR and Raman peaks came from different modes with the frequencies of 1773 and 1492 cm-1, respectively. The calculated isotropic polarizability, polarizability anisotropy invariant, and hyperpolarizability were 577.7, 96.9, and -22.8 a.u., respectively. Based on TDDFT, the electronic absorption spectra of PCBM were calculated and analyzed. The calculated absorption band near 349 nmagreed well with the experimental measurement.
2008, 24(08): 1359-1365
doi: 10.3866/PKU.WHXB20080806
Abstract:
The nano TiO2 photocatalytic oxidation method combined with immunity and electroporation techniques performed high efficiency for photokilling LoVo cancer cells even at very low concentration (3.12 μg·mL-1). In this method, the LoVo cells could be killed completely within 30 min under the irradiation of UV light (wavelength 253.7 nm, 4 mW·cm-2). The mechanism of this process was investigated using confocal florescent microscopy, TEM, and comet assay methods. The results demonstrated that the antibody modified nano TiO2 particles could adsorb on the cell membrane, after electroporation it could enter the inside of LoVo cells and located around the karyon. Under the irradiation of UV light, the cell’s structure, organelle, and DNA were destroyed seriously, which caused the necroses of LoVo cells. Because the photocatalysis effect of nano TiO2 took place inside of cells, so the photokilling efficiency enhanced strongly.
The nano TiO2 photocatalytic oxidation method combined with immunity and electroporation techniques performed high efficiency for photokilling LoVo cancer cells even at very low concentration (3.12 μg·mL-1). In this method, the LoVo cells could be killed completely within 30 min under the irradiation of UV light (wavelength 253.7 nm, 4 mW·cm-2). The mechanism of this process was investigated using confocal florescent microscopy, TEM, and comet assay methods. The results demonstrated that the antibody modified nano TiO2 particles could adsorb on the cell membrane, after electroporation it could enter the inside of LoVo cells and located around the karyon. Under the irradiation of UV light, the cell’s structure, organelle, and DNA were destroyed seriously, which caused the necroses of LoVo cells. Because the photocatalysis effect of nano TiO2 took place inside of cells, so the photokilling efficiency enhanced strongly.
2008, 24(08): 1366-1370
doi: 10.3866/PKU.WHXB20080807
Abstract:
The adsorption of the species(CH3, NH2, and CH3NH2) on clean and carbon(nitrogen or oxygen) modified
Mo(100) surfaces has been investigated by the first-principles DFT-GGA calculations with the slab model. The calculated results showed that the adsorption energies of the adsorbed species(CH3, NH2 and CH3NH2) changed a little with the coverage of θ=1/6 ML (monolayer); but an obvious change could be observed at the relative higher coverage (θ=1/4 ML). In addition, it was found that the adsorption energies were lower on the modified Mo(100) surface as compared with the results on clean Mo(100) surface, and the activity of the Mo(100) surface decreased in the presence of the pre-adsorbed C(N, O) atoms with the order of C>N>O. It may be due to the reason that these electronegative atoms reduce the capability of electron donation of the metal, which results in the downshift of the surface metal atom d-band center. By the analysis of the density of state(DOS) projected onto Mo d-band, it can be found that d-band center only account for the diversification of the surface caused by the pre-adsorbed atoms, whereas the dz2-center can explain the changing trend of the adsorption energies more exactly.
The adsorption of the species(CH3, NH2, and CH3NH2) on clean and carbon(nitrogen or oxygen) modified
Mo(100) surfaces has been investigated by the first-principles DFT-GGA calculations with the slab model. The calculated results showed that the adsorption energies of the adsorbed species(CH3, NH2 and CH3NH2) changed a little with the coverage of θ=1/6 ML (monolayer); but an obvious change could be observed at the relative higher coverage (θ=1/4 ML). In addition, it was found that the adsorption energies were lower on the modified Mo(100) surface as compared with the results on clean Mo(100) surface, and the activity of the Mo(100) surface decreased in the presence of the pre-adsorbed C(N, O) atoms with the order of C>N>O. It may be due to the reason that these electronegative atoms reduce the capability of electron donation of the metal, which results in the downshift of the surface metal atom d-band center. By the analysis of the density of state(DOS) projected onto Mo d-band, it can be found that d-band center only account for the diversification of the surface caused by the pre-adsorbed atoms, whereas the dz2-center can explain the changing trend of the adsorption energies more exactly.
2008, 24(08): 1371-1377
doi: 10.3866/PKU.WHXB20080808
Abstract:
Thermal behavior under pressures of 0.1, 4, and 7MPa and non-isothermal decomposition reaction kinetics under pressures of 4 and 7MPa of the composite modified double base propellant containing hexanitrohexaazaisowurtzitane (CL-20-CMDB propellant) were investigated by differential scanning calarimetry (DSC) and thermogravimetry (TG). The results showed that there were three exothermic peaks on DSC curve and three mass loss stages on TG curve under 0.1 MPa. There was only one exothermic peak on the DSC curve under 4 and 7 MPa. The exothermic peak temperatures under 4 and 7 MPa increased with increasing the heating rate. The exothermic decomposition reaction mechanism and kinetic parameters of the propellant changed little with testing surroundings. The reaction mechanism was randomnucleation and then growth. The kinetic equations of exothermical decomposition reaction can be expressed as, dα/dt=1014.5(1-α)[-ln(1-α)]1/3e-17981.7/T (under 4 MPa) and dα/dt=1014.7(1-α)[-ln(1-α)]1/3e-18138.1/T (under 7 MPa).
Thermal behavior under pressures of 0.1, 4, and 7MPa and non-isothermal decomposition reaction kinetics under pressures of 4 and 7MPa of the composite modified double base propellant containing hexanitrohexaazaisowurtzitane (CL-20-CMDB propellant) were investigated by differential scanning calarimetry (DSC) and thermogravimetry (TG). The results showed that there were three exothermic peaks on DSC curve and three mass loss stages on TG curve under 0.1 MPa. There was only one exothermic peak on the DSC curve under 4 and 7 MPa. The exothermic peak temperatures under 4 and 7 MPa increased with increasing the heating rate. The exothermic decomposition reaction mechanism and kinetic parameters of the propellant changed little with testing surroundings. The reaction mechanism was randomnucleation and then growth. The kinetic equations of exothermical decomposition reaction can be expressed as, dα/dt=1014.5(1-α)[-ln(1-α)]1/3e-17981.7/T (under 4 MPa) and dα/dt=1014.7(1-α)[-ln(1-α)]1/3e-18138.1/T (under 7 MPa).
2008, 24(08): 1378-1382
doi: 10.3866/PKU.WHXB20080809
Abstract:
Heat capacities of the complex of rare-earth element with valine [Sm(Val)Cl3·6H2O] were measured with a high-precision automatic adiabatic calorimeter over the temperature range from 80 to 376 K, and the thermodynamic unctions (HT-H298.15 and ST-S298.15) were calculated. A large step in heat capacity was detected around 308Kand this may be attributed to a glass transition corresponding to freezing of structural disorder. Thermal decomposition of this complex as studied by thermogravimetric (TG) technique and a possible mechanism for the decomposition was suggested.
Heat capacities of the complex of rare-earth element with valine [Sm(Val)Cl3·6H2O] were measured with a high-precision automatic adiabatic calorimeter over the temperature range from 80 to 376 K, and the thermodynamic unctions (HT-H298.15 and ST-S298.15) were calculated. A large step in heat capacity was detected around 308Kand this may be attributed to a glass transition corresponding to freezing of structural disorder. Thermal decomposition of this complex as studied by thermogravimetric (TG) technique and a possible mechanism for the decomposition was suggested.
2008, 24(08): 1383-1386
doi: 10.3866/PKU.WHXB20080810
Abstract:
Titania nanotubes (TNTs) were synthesized by hydrothermal treatment of rutile-phase TiO2 nanoparticles in 10 mol·L-1NaOHsolution at 110 ℃ for 24 h. The Ag loaded titania nanotubes (Ag/TNTs) were obtained by chemical deposition method with the TNTs suspending in the AgNO3 solution (pH=8) at 50 益. The characterizations of the as-synthesized samples were performed by TEM, EDS, XRD, XPS, and UV-Vis spectra. The photocatalytic performance of the Ag/TNTs was investigated by UV-light induced photocatalytic decomposition of methyl orange(MO). The results showed that the inner/outer diameters of TNTs were about 6/10 nm and the length was several hundred nanometers. Both the shape and the crystalline of the nanotubes were not changed after the modification. The zero oxidation state Ag quantumdots, about 4 nmin diameter, were well dispersed on the external surface of the nanotubes. Ag/TNTs exhibited enhanced absorption at the visible range in the UV-Vis spectra. The Ag nanoparticles were found to significantly enhance the photocatalytic activity of TiO2 nanotubes, and the catalyst system was demonstrated to be highly efficient for the UV-light induced photocatalytic decomposition of MO compared to both rutile-phase TiO2 nanoparticles and pure TNTs. After irradiation for 60 min, the decomposition rates of MO solution in rutile-phase TiO2 nanoparticles, TNTs, and Ag/TNTs systemwere 46.8%, 57.2%, and 92.2%, respectively.
Titania nanotubes (TNTs) were synthesized by hydrothermal treatment of rutile-phase TiO2 nanoparticles in 10 mol·L-1NaOHsolution at 110 ℃ for 24 h. The Ag loaded titania nanotubes (Ag/TNTs) were obtained by chemical deposition method with the TNTs suspending in the AgNO3 solution (pH=8) at 50 益. The characterizations of the as-synthesized samples were performed by TEM, EDS, XRD, XPS, and UV-Vis spectra. The photocatalytic performance of the Ag/TNTs was investigated by UV-light induced photocatalytic decomposition of methyl orange(MO). The results showed that the inner/outer diameters of TNTs were about 6/10 nm and the length was several hundred nanometers. Both the shape and the crystalline of the nanotubes were not changed after the modification. The zero oxidation state Ag quantumdots, about 4 nmin diameter, were well dispersed on the external surface of the nanotubes. Ag/TNTs exhibited enhanced absorption at the visible range in the UV-Vis spectra. The Ag nanoparticles were found to significantly enhance the photocatalytic activity of TiO2 nanotubes, and the catalyst system was demonstrated to be highly efficient for the UV-light induced photocatalytic decomposition of MO compared to both rutile-phase TiO2 nanoparticles and pure TNTs. After irradiation for 60 min, the decomposition rates of MO solution in rutile-phase TiO2 nanoparticles, TNTs, and Ag/TNTs systemwere 46.8%, 57.2%, and 92.2%, respectively.
2008, 24(08): 1387-1392
doi: 10.1016/S1872-1508(08)60059-5
Abstract:
Interfacial behavior of cysteine (Cys) between mild steel and sulfuric acid solution as a corrosion inhibitor has been studied with electrochemical AC (alternating current) and DC (direct current) techniques at (25.0±0.1) ℃. The AC impedance results were evaluated using equivalent circuits in which a constant phase element (CPE) has been replaced with double layer capacitance (Cdl) to represent the frequency distribution of experimental data. Changes in impedance parameters (charge transfer resistance and double layer capacitance) indicated that cysteine molecules acted by accumulating at the metal/solution interface. The fractional coverage of the metal surface (θ) was determined using AC impedance results and it was found that the adsorption of cysteine on the mild steel surface followed a Langmuir isothermmodel with a standard free energy of adsorption (⊿G0ads) of -35.1 kJ·mol-1. To clarify the type of interaction between mild steel surface and cysteine molecules with a molecular orbital approach, electronic properties, such as, the highest occupied molecular orbital (HOMO) energy, the lowest unoccupied molecular orbital (LUMO) energy, and the frontier molecular orbital coefficients have been calculated. Energy gaps for the interaction of mild steel surface and cysteine molecules (ELUMOFe-EHOMOCys and ELUMOCys-EHOMOFe) were used to determine whether cysteine molecules acted as electron donors or electron acceptors when they interacted with the mild steel surface. The local reactivity was evaluated through the condensed Fukui indices. Theoretical calculations were carried out using the density functional theory (DFT) at B3LYP level with the 6-311++G(d,p) basis set for all atoms by Gaussian 03W program.
Interfacial behavior of cysteine (Cys) between mild steel and sulfuric acid solution as a corrosion inhibitor has been studied with electrochemical AC (alternating current) and DC (direct current) techniques at (25.0±0.1) ℃. The AC impedance results were evaluated using equivalent circuits in which a constant phase element (CPE) has been replaced with double layer capacitance (Cdl) to represent the frequency distribution of experimental data. Changes in impedance parameters (charge transfer resistance and double layer capacitance) indicated that cysteine molecules acted by accumulating at the metal/solution interface. The fractional coverage of the metal surface (θ) was determined using AC impedance results and it was found that the adsorption of cysteine on the mild steel surface followed a Langmuir isothermmodel with a standard free energy of adsorption (⊿G0ads) of -35.1 kJ·mol-1. To clarify the type of interaction between mild steel surface and cysteine molecules with a molecular orbital approach, electronic properties, such as, the highest occupied molecular orbital (HOMO) energy, the lowest unoccupied molecular orbital (LUMO) energy, and the frontier molecular orbital coefficients have been calculated. Energy gaps for the interaction of mild steel surface and cysteine molecules (ELUMOFe-EHOMOCys and ELUMOCys-EHOMOFe) were used to determine whether cysteine molecules acted as electron donors or electron acceptors when they interacted with the mild steel surface. The local reactivity was evaluated through the condensed Fukui indices. Theoretical calculations were carried out using the density functional theory (DFT) at B3LYP level with the 6-311++G(d,p) basis set for all atoms by Gaussian 03W program.
2008, 24(08): 1393-1399
doi: 10.3866/PKU.WHXB20080812
Abstract:
The reaction mechanism of hydroxyl anion and benzene has been theoretically studied at the G3MP2B3 level of theory. All possible thermodynamic product channels are considered and investigated. The [C6H6…OH]- complex formation has been found on the most favorable reaction pathway, which is consistent with the previous experimental studies. The proton transfer and hydrogen replacement pathways are endothermic and difficult to occur in the case of the lower experimental collision energy. Additionally, the H2 formation as an exothermal product channel of this reaction system by -119.5 kJ·mol -1 hardly happens because of a high energy barrier. The proton transfer processes of hydroxyl anion, oxygen anion, and fluorine anion from benzene have been compared in the present computation, and the electron transfers in these processes were investigated by the Mulliken charge population analysis as well. Furthermore, the reaction mechanism between hydroxyl anion or hydroxyl radical and benzene, has been also compared and analyzed.
2008, 24(08): 1400-1404
doi: 10.3866/PKU.WHXB20080813
Abstract:
Electron energy distribution functions for N2/O2/H2O/HCHO dielectric barrier discharge plasma were obtained by numerically solving the Boltzmann equation. The electron-molecule reaction constants were calculated using the computed electron energy distribution function. A space averaged chemical kinetics model in dielectric barrier discharge was reported. The evolution of·OH, HO2·and electron as functions of time were studied. The influences of H2O and O2 molar ratios on the generations of·OH and HO2·were also discussed. The calculated results were in od agreement with our experiments result.
Electron energy distribution functions for N2/O2/H2O/HCHO dielectric barrier discharge plasma were obtained by numerically solving the Boltzmann equation. The electron-molecule reaction constants were calculated using the computed electron energy distribution function. A space averaged chemical kinetics model in dielectric barrier discharge was reported. The evolution of·OH, HO2·and electron as functions of time were studied. The influences of H2O and O2 molar ratios on the generations of·OH and HO2·were also discussed. The calculated results were in od agreement with our experiments result.
2008, 24(08): 1405-1410
doi: 10.1016/S1872-1508(08)60060-1
Abstract:
Barium strontium titanate (Ba0.6Sr0.4TiO3, BST) nano-powders were prepared using Ba(NO3)2, Sr(NO3)2, oxalic acid dehydrate, and tetrabutyl titanate (Ti(OC4H9)4) as precursors by the chemical co-precipitation method. The product was characterized by thermogravimetry-differential scanning calorimetry (TG-DSC) thermal analyses, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The experimental results indicated that the resulting Ba0.6Sr0.4TiO3 nano-powders were homogeneous with agglomerated nature. The Ba0.6Sr0.4TiO3-MgTiO3 (BST-MT) bulk composite ceramics doped by Mn were obtained by the traditional solid phase method. The XRD patterns demonstrated that Mn-doped BST was unable to change the perovskite crystalline structure of BST materials. SEM photographs revealed that the crystalline grains became larger with increasing the content of doping Mn (<1.5% (x, molar fraction)) and then the size of grains decreased after the Mn content exceeded 1.5%in the BST ceramics, suggesting the effect of Mn doping on the morphologies of BST-MT composites. The dielectric properties of BST-MT composite ceramics doped with 0.1%-2.0% (x)Mn were investigated systematically. Two effects of Mn doping on the dielectric properties of the BST-MT composite ceramics were observed. At low Mn doping concentrations (<1.5%), Mn mainly acted as an acceptor dopant to replace Ti at the B site of ABO3 perovskite structure, leading to a diffused phase transition. It was also observed that the grain size increased drastically as the Mn content increased and thus caused the decrease of dielectric loss. At higherMn doping concentrations (>1.5%), the grain size decreased and the suppression of permittivity and the drastic increase of the dielectric losses were observed, which indicated a“composite”mixing effect.
Barium strontium titanate (Ba0.6Sr0.4TiO3, BST) nano-powders were prepared using Ba(NO3)2, Sr(NO3)2, oxalic acid dehydrate, and tetrabutyl titanate (Ti(OC4H9)4) as precursors by the chemical co-precipitation method. The product was characterized by thermogravimetry-differential scanning calorimetry (TG-DSC) thermal analyses, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The experimental results indicated that the resulting Ba0.6Sr0.4TiO3 nano-powders were homogeneous with agglomerated nature. The Ba0.6Sr0.4TiO3-MgTiO3 (BST-MT) bulk composite ceramics doped by Mn were obtained by the traditional solid phase method. The XRD patterns demonstrated that Mn-doped BST was unable to change the perovskite crystalline structure of BST materials. SEM photographs revealed that the crystalline grains became larger with increasing the content of doping Mn (<1.5% (x, molar fraction)) and then the size of grains decreased after the Mn content exceeded 1.5%in the BST ceramics, suggesting the effect of Mn doping on the morphologies of BST-MT composites. The dielectric properties of BST-MT composite ceramics doped with 0.1%-2.0% (x)Mn were investigated systematically. Two effects of Mn doping on the dielectric properties of the BST-MT composite ceramics were observed. At low Mn doping concentrations (<1.5%), Mn mainly acted as an acceptor dopant to replace Ti at the B site of ABO3 perovskite structure, leading to a diffused phase transition. It was also observed that the grain size increased drastically as the Mn content increased and thus caused the decrease of dielectric loss. At higherMn doping concentrations (>1.5%), the grain size decreased and the suppression of permittivity and the drastic increase of the dielectric losses were observed, which indicated a“composite”mixing effect.
2008, 24(08): 1411-1416
doi: 10.1016/S1872-1508(08)60061-3
Abstract:
A simple acid treatment method was applied to functionalize the surface and to modify the structures of multi-walled carbon nanotubes (CNTs) grown on silicon substrates using a mixed solution of chromic trioxide (CrO3) and nitric acid (HNO3). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and energy dispersive spectrometer (EDS) were employed to investigate the mechanismcausing the modified field emission (FE) properties of the CNT films. After 20 min of CrO3+HNO3 treatment, the emitted currents were enhanced by more than one order of magnitude compared with those of the untreated CNTs. This large increases in emitted current can be attributed to the favorable surface morphologies, open-ended structures, and highly curved CNT surfaces in the CNT films. These factors altogether caused an increase in the field enhancement factors of CNTs. We also demonstrated that using a mixed solution of CrO3+HNO3 post-treatment exhibited a higher emission current and a lower turn-on electric field than in the CNTs treated with HNO3. The method provides a simple, economical, and effective way to enhance the CNT field emission properties.
A simple acid treatment method was applied to functionalize the surface and to modify the structures of multi-walled carbon nanotubes (CNTs) grown on silicon substrates using a mixed solution of chromic trioxide (CrO3) and nitric acid (HNO3). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and energy dispersive spectrometer (EDS) were employed to investigate the mechanismcausing the modified field emission (FE) properties of the CNT films. After 20 min of CrO3+HNO3 treatment, the emitted currents were enhanced by more than one order of magnitude compared with those of the untreated CNTs. This large increases in emitted current can be attributed to the favorable surface morphologies, open-ended structures, and highly curved CNT surfaces in the CNT films. These factors altogether caused an increase in the field enhancement factors of CNTs. We also demonstrated that using a mixed solution of CrO3+HNO3 post-treatment exhibited a higher emission current and a lower turn-on electric field than in the CNTs treated with HNO3. The method provides a simple, economical, and effective way to enhance the CNT field emission properties.
2008, 24(08): 1417-1424
doi: 10.3866/PKU.WHXB20080816
Abstract:
The crosslinking microspheres of poly (glycidyl methacrylate) (PGMA) were modified chemically with aminating agents, hexanediamine and three kinds of multi-ethylene multi-amine. The effects of various factors, such as the chemical structures of the aminating agents, pH values of the medium, ionic strength, and temperature, on the adsorption property of the functional microsphers for bilirubin were examined. The adsorption mechanism of the aminated microspheres towards bilirubin was studied deeply. The experimental results showed that the aminated microspheres had strong adsorption ability for bilirubin and the adsorption capacity could reach 17.80 mg·g -1; the isotherm adsorption could be fitted by Freundlich equation satisfactorily. There were three acting forces between the aminated microspheres and bilirubin molecules, i.e., electrostatic, hydrogen bonding and hydrophobic interactions. Among them, the electrostatic interaction was dominative, and the latter two kinds exert cooperating action. As pH=6, there was the strongest electrostatic interaction between the aminated microspheres and bilirubin molecules, leading to the highest adsorption capacity. The higher ionic strength was disadvantageous to the electrostatic interaction, and salinity conduces to the weakening of the electrostatic interaction and the decreasing of the adsorption capacity. The rising of temperature was advantageous to the hydrophobic interaction, whereas unfavorable to hydrogen bonding, and the predominated one of themdominates the effect of temperature on the adsorption capacity. The adsorption ability of the aminated microspheres modified with hexanediamine was stronger than that of those aminated microspheres modified with multi-ethylene multi-amine owing to enhancement of the hydrophobic interaction and smaller steric hindrance which came fromlonger spacer arm.
The crosslinking microspheres of poly (glycidyl methacrylate) (PGMA) were modified chemically with aminating agents, hexanediamine and three kinds of multi-ethylene multi-amine. The effects of various factors, such as the chemical structures of the aminating agents, pH values of the medium, ionic strength, and temperature, on the adsorption property of the functional microsphers for bilirubin were examined. The adsorption mechanism of the aminated microspheres towards bilirubin was studied deeply. The experimental results showed that the aminated microspheres had strong adsorption ability for bilirubin and the adsorption capacity could reach 17.80 mg·g -1; the isotherm adsorption could be fitted by Freundlich equation satisfactorily. There were three acting forces between the aminated microspheres and bilirubin molecules, i.e., electrostatic, hydrogen bonding and hydrophobic interactions. Among them, the electrostatic interaction was dominative, and the latter two kinds exert cooperating action. As pH=6, there was the strongest electrostatic interaction between the aminated microspheres and bilirubin molecules, leading to the highest adsorption capacity. The higher ionic strength was disadvantageous to the electrostatic interaction, and salinity conduces to the weakening of the electrostatic interaction and the decreasing of the adsorption capacity. The rising of temperature was advantageous to the hydrophobic interaction, whereas unfavorable to hydrogen bonding, and the predominated one of themdominates the effect of temperature on the adsorption capacity. The adsorption ability of the aminated microspheres modified with hexanediamine was stronger than that of those aminated microspheres modified with multi-ethylene multi-amine owing to enhancement of the hydrophobic interaction and smaller steric hindrance which came fromlonger spacer arm.
2008, 24(08): 1425-1431
doi: 10.3866/PKU.WHXB20080817
Abstract:
In order to improve the electrochemical performance of zinc electrodes in alkaline batteries, several sonochemically modified zinc powders were successfully prepared in different concentrations of Y(NO3)3 solutions by means of ultrasonic immersion. Moreover, the formation of Y(OH)3/Y2O3 on modified zinc powder, the corrosion inhibition and cyclic performance of corresponding zinc electrodes were investigated through scanning electron microscopy (SEM), X-ray diffraction (XRD), electrochemical and other techniques. The results showed that Y(OH)3/Y2O3 particles were uniformly distributed on sonochemically modified zinc powder with 0.036 mol·L-1 Y(NO3)3 solution. Simultaneously, the yttrium compounds grew preferentially on the defect sites of zinc powder surface, and prevented the dissolution and diffusion of zincate anions into alkaline electrolyte during the electrochemical process. All these results contributed to the facts that the inhibition efficiency of zinc electrode achieved 79.6%, and differential value between anodic and cathodic peak potentials decreased by 285 mV at the 20th cyclic voltammogram. Simulated silver-zinc batteries were assembled using bare zinc powder and the zinc powder modified with 0.036 mol·L-1 Y(NO3)3 solution. According to the detections of the batteries at a high discharge current density of 250 mA·cm-2, capacity loss of zinc electrode containing the modified zinc powder reached only 62.7 mAh·g-1 from the 1st to 30th cycles, and discharge capacity of 322.6 mAh·g -1 was still reserved after 50 cycles. Therefore, a conclusion was drawn that discharge capacity and cycle life of zinc electrodes were obviously enhanced owing to the application of sonochemically modified zinc powder.
In order to improve the electrochemical performance of zinc electrodes in alkaline batteries, several sonochemically modified zinc powders were successfully prepared in different concentrations of Y(NO3)3 solutions by means of ultrasonic immersion. Moreover, the formation of Y(OH)3/Y2O3 on modified zinc powder, the corrosion inhibition and cyclic performance of corresponding zinc electrodes were investigated through scanning electron microscopy (SEM), X-ray diffraction (XRD), electrochemical and other techniques. The results showed that Y(OH)3/Y2O3 particles were uniformly distributed on sonochemically modified zinc powder with 0.036 mol·L-1 Y(NO3)3 solution. Simultaneously, the yttrium compounds grew preferentially on the defect sites of zinc powder surface, and prevented the dissolution and diffusion of zincate anions into alkaline electrolyte during the electrochemical process. All these results contributed to the facts that the inhibition efficiency of zinc electrode achieved 79.6%, and differential value between anodic and cathodic peak potentials decreased by 285 mV at the 20th cyclic voltammogram. Simulated silver-zinc batteries were assembled using bare zinc powder and the zinc powder modified with 0.036 mol·L-1 Y(NO3)3 solution. According to the detections of the batteries at a high discharge current density of 250 mA·cm-2, capacity loss of zinc electrode containing the modified zinc powder reached only 62.7 mAh·g-1 from the 1st to 30th cycles, and discharge capacity of 322.6 mAh·g -1 was still reserved after 50 cycles. Therefore, a conclusion was drawn that discharge capacity and cycle life of zinc electrodes were obviously enhanced owing to the application of sonochemically modified zinc powder.
2008, 24(08): 1439-1444
doi: 10.3866/PKU.WHXB20080819
Abstract:
A gel-like paste was made by mixing 1:1 (w/w) carboxylic group-functionalized short single-walled carbon nanotubes (S-SWNTs) and a kind of room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6). The composite film was modified on the glassy carbon electrode (GCE) to prepare the S-SWNT&RTIL/GCE. The modified electrode showed an attractive electrocatalytic ability and could enhance the current response of electro-active molecules by employing potassium ferricyanide, ascorbic acid and methylene blue as probes. In the B-R buffer solution, ssDNA had a sensitive voltammetric response at the S-SWNT&RTIL/GCE and the oxidative peak potentials of guanine base and adenine base were 0.532 and 0.808 V, respectively. The mechanism of electrode reaction was studied and the results showed that the heterogeneous electron transfer rate constants (k’s) for the two bases were 1.84×10-2 and 3.69×10-2 s-1, respectively. Under the optimal conditions, the differential pulse voltammetric peak current of guanine base vs the concentration of ssDNA was linear in the range of 40 μg·L-1-5.0 mg·L-1 with a detection limit of 5 μg·L-1 (S/N=3, signal/noise).
A gel-like paste was made by mixing 1:1 (w/w) carboxylic group-functionalized short single-walled carbon nanotubes (S-SWNTs) and a kind of room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6). The composite film was modified on the glassy carbon electrode (GCE) to prepare the S-SWNT&RTIL/GCE. The modified electrode showed an attractive electrocatalytic ability and could enhance the current response of electro-active molecules by employing potassium ferricyanide, ascorbic acid and methylene blue as probes. In the B-R buffer solution, ssDNA had a sensitive voltammetric response at the S-SWNT&RTIL/GCE and the oxidative peak potentials of guanine base and adenine base were 0.532 and 0.808 V, respectively. The mechanism of electrode reaction was studied and the results showed that the heterogeneous electron transfer rate constants (k’s) for the two bases were 1.84×10-2 and 3.69×10-2 s-1, respectively. Under the optimal conditions, the differential pulse voltammetric peak current of guanine base vs the concentration of ssDNA was linear in the range of 40 μg·L-1-5.0 mg·L-1 with a detection limit of 5 μg·L-1 (S/N=3, signal/noise).
2008, 24(08): 1445-1450
doi: 10.3866/PKU.WHXB20080820
Abstract:
The electron transport properties of diphenylacetylene molecular wires with various conformations were studied by the first-principles density functional theory (DFT) and the non-equilibriumGreen function (NEGF) technique. The electron transport properties were discussed in terms of the spatial distributions of molecular orbitals and the transmission spectra of the molecular wires under various applied voltages. The results demonstrated that with the increase of molecular torsion, the LUMO-HOMO gap increased and transmission spectrum decreased. Under the influence of applied voltage, the HOMO and LUMO tended to move to low and high potential sides of the molecule, respectively. Current -voltage calculations revealed that the planar molecule was the most conductive. With the increasing torsional angle, the molecular conductance decreased and the perpendicular molecule conductance was the worst. Quantitative relationship between molecular torsion and molecular conductance was given.
The electron transport properties of diphenylacetylene molecular wires with various conformations were studied by the first-principles density functional theory (DFT) and the non-equilibriumGreen function (NEGF) technique. The electron transport properties were discussed in terms of the spatial distributions of molecular orbitals and the transmission spectra of the molecular wires under various applied voltages. The results demonstrated that with the increase of molecular torsion, the LUMO-HOMO gap increased and transmission spectrum decreased. Under the influence of applied voltage, the HOMO and LUMO tended to move to low and high potential sides of the molecule, respectively. Current -voltage calculations revealed that the planar molecule was the most conductive. With the increasing torsional angle, the molecular conductance decreased and the perpendicular molecule conductance was the worst. Quantitative relationship between molecular torsion and molecular conductance was given.
2008, 24(08): 1451-1458
doi: 10.3866/PKU.WHXB20080821
Abstract:
The vibrational energy transfer of I2 in ar n solution confined in a nano-spherical cavity has been simulated by the equilibriummolecular dynamics (EMD) approach. The solute vibrational energy relaxation time T1, as a function of the radius of the spherical cavity and the solvent density, is calculated and discussed. According to the analysis of intermolecular interactions at atomic and molecular level, the reason of T1 increasing with the cavity radius decreasing is explored. The results showed that the geometry confinement and surface effect played an important role in the solvent distribution, which would influence the vibrational relaxation significantly. In addition, the simulations of bulk system indicated the values of T1 obtained by EMD and non-equilibrium molecular dynamics (NEMD)
were in od agreement for I2/Ar system.
The vibrational energy transfer of I2 in ar n solution confined in a nano-spherical cavity has been simulated by the equilibriummolecular dynamics (EMD) approach. The solute vibrational energy relaxation time T1, as a function of the radius of the spherical cavity and the solvent density, is calculated and discussed. According to the analysis of intermolecular interactions at atomic and molecular level, the reason of T1 increasing with the cavity radius decreasing is explored. The results showed that the geometry confinement and surface effect played an important role in the solvent distribution, which would influence the vibrational relaxation significantly. In addition, the simulations of bulk system indicated the values of T1 obtained by EMD and non-equilibrium molecular dynamics (NEMD)
were in od agreement for I2/Ar system.
2008, 24(08): 1459-1464
doi: 10.3866/PKU.WHXB20080822
Abstract:
The rust layers formed on upward and downward surfaces of carbon steel exposed to salt lake atmosphere for 25 months were investigated by scanning electron microscopy (SEM), electron probe micro analyzer (EPMA), X-ray diffraction (XRD), infrared transmission spectroscopy (IRS), and electrochemical techniques. The depths of rust layers on upward and downward surfaces were similar to each other. The corrosion products on the two surfaces were mainly composed of β-FeOOH, Fe8(O,OH)16Cl1.3, and a little γ-FeOOH. δ-FeOOH and Fe3O4 were only detected in outer part of the rust layers. The results of electrochemical analysis showed that the rust layer suppressed the corrosion of steel substrate and the corrosion resistance of rust layers increased with time.
The rust layers formed on upward and downward surfaces of carbon steel exposed to salt lake atmosphere for 25 months were investigated by scanning electron microscopy (SEM), electron probe micro analyzer (EPMA), X-ray diffraction (XRD), infrared transmission spectroscopy (IRS), and electrochemical techniques. The depths of rust layers on upward and downward surfaces were similar to each other. The corrosion products on the two surfaces were mainly composed of β-FeOOH, Fe8(O,OH)16Cl1.3, and a little γ-FeOOH. δ-FeOOH and Fe3O4 were only detected in outer part of the rust layers. The results of electrochemical analysis showed that the rust layer suppressed the corrosion of steel substrate and the corrosion resistance of rust layers increased with time.
2008, 24(08): 1465-1470
doi: 10.3866/PKU.WHXB20080823
Abstract:
Chromium (Cr3+) conversion coating was prepared on 6063 aluminium alloy using chromic potassium sulfate and phosphoric acid. Tafel polarization curves and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical properties of the coating formed under different conditions. The optimum conditions were obtained as following: temperature was 30-40 ℃, deposition time 9 min, the pH was adjusted to 2.0-3.0, the KCr(SO4)2 and H3PO4 concentrations were controlled within 15-25 g·L-1 and 10-20 g·L-1, respectively. The polarization result showed that the coating had more positive corrosion potential (Ecorr) and pitting corrosion potential (Epit), and lower corrosion current density (icorr), indicating that the coating formed under the optimum conditions had better corrosion resistance. To explain the electrochemical properties of the coating, a simple equivalent circuit was designed. Electrochemical parameters of EIS, such as the resistance (Rcoat) and capacitance (Ccoat), the charge transfer resistance (Rct) and double layer capacitance (Cdl), were obtained by fitting the EIS plots. The results of EIS were in od agreement with those of Tafel polarization curves.
Chromium (Cr3+) conversion coating was prepared on 6063 aluminium alloy using chromic potassium sulfate and phosphoric acid. Tafel polarization curves and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical properties of the coating formed under different conditions. The optimum conditions were obtained as following: temperature was 30-40 ℃, deposition time 9 min, the pH was adjusted to 2.0-3.0, the KCr(SO4)2 and H3PO4 concentrations were controlled within 15-25 g·L-1 and 10-20 g·L-1, respectively. The polarization result showed that the coating had more positive corrosion potential (Ecorr) and pitting corrosion potential (Epit), and lower corrosion current density (icorr), indicating that the coating formed under the optimum conditions had better corrosion resistance. To explain the electrochemical properties of the coating, a simple equivalent circuit was designed. Electrochemical parameters of EIS, such as the resistance (Rcoat) and capacitance (Ccoat), the charge transfer resistance (Rct) and double layer capacitance (Cdl), were obtained by fitting the EIS plots. The results of EIS were in od agreement with those of Tafel polarization curves.
2008, 24(08): 1471-1476
doi: 10.3866/PKU.WHXB20080824
Abstract:
The influence of substituents on electron transport through single-molecule mercapto-azobenzene were investigated by using density functional theory (DFT) B3LYP/6-31G** to calculate the geometry and electronic structure changes. With the introduction of electron-withdrawing group (—COOH or —NO2) into single-molecule mercapto-azobenzene, the calculation results showed that the electron transporting stability increased, the delocalization effect of LUMO rose, the reactivity of sulfur atomincreased and HOMO-LUMOgap (HLG) decreased evidently; which led to a decrease in the energy gap of electron transport and a rise in the electron transport abilities. Comparing molecular ion with its molecule, it could be found that the HLG of the molecular ion decreased further, S—Au bond was easier to form, and electron transfer took placemore easily through the systemof metal-molecule-metal.
The influence of substituents on electron transport through single-molecule mercapto-azobenzene were investigated by using density functional theory (DFT) B3LYP/6-31G** to calculate the geometry and electronic structure changes. With the introduction of electron-withdrawing group (—COOH or —NO2) into single-molecule mercapto-azobenzene, the calculation results showed that the electron transporting stability increased, the delocalization effect of LUMO rose, the reactivity of sulfur atomincreased and HOMO-LUMOgap (HLG) decreased evidently; which led to a decrease in the energy gap of electron transport and a rise in the electron transport abilities. Comparing molecular ion with its molecule, it could be found that the HLG of the molecular ion decreased further, S—Au bond was easier to form, and electron transfer took placemore easily through the systemof metal-molecule-metal.
2008, 24(08): 1477-1480
doi: 10.3866/PKU.WHXB20080825
Abstract:
The density functional theory (DFT) was used to investigate the geometries, electronic structures, and frequencies of CnAl2 (n=1-10) clusters. At B3LYP/6-311G* level, the ground state of CAl2 was a planar structure while other CnAl2 clusters were linear structures with terminal aluminum atom. The energetic analysis showed that CnAl2 clusters with even n were more stable than those with odd n.
The density functional theory (DFT) was used to investigate the geometries, electronic structures, and frequencies of CnAl2 (n=1-10) clusters. At B3LYP/6-311G* level, the ground state of CAl2 was a planar structure while other CnAl2 clusters were linear structures with terminal aluminum atom. The energetic analysis showed that CnAl2 clusters with even n were more stable than those with odd n.
2008, 24(08): 1482-1486
doi: 10.3866/PKU.WHXB20080826
Abstract:
Three conformations of [M(CO)3(PPh2py)2] (M=Fe, Ru), HH conformation representing that both P atoms on the PPh2py coordinated to M, HT conformation representing that P and N atoms on two different PPh2py coordinated to M, and HH’ representing that two N atoms coordinated to M, were calculated by means of density functional theory (DFT) PBE0 method. The conclusions were drawn as follows: (1) The largest contribution of P atom in PPh2py to HOMO orbital indicated that P atomin PPh2py was easier to coordinate to metal atom as an electron donor thanNatom. (2) The HHconformation was the most stable one, while HH’ was the most unstable according to molecular energies and interaction energies. This conclusion consisted with the result of synthesis experiment, in which the HH conformation products had always been tten. (3) P—Mbonds were stronger thanN—Mbonds by a comparison of their bond lengths and bond indices. There was a σ bond between P and Matoms, while in the case of interaction between N andMatoms, there was only a weak charge transfer between them (nN→n*M or nN→σ*M-P ). (4) The largest negative charge and contribution of metal atom in the HH conformation to HOMO orbital indicated that the HH conformation was the easiest to coordinate to a second metal atom and forma binuclear complex withMas the electron donor.
Three conformations of [M(CO)3(PPh2py)2] (M=Fe, Ru), HH conformation representing that both P atoms on the PPh2py coordinated to M, HT conformation representing that P and N atoms on two different PPh2py coordinated to M, and HH’ representing that two N atoms coordinated to M, were calculated by means of density functional theory (DFT) PBE0 method. The conclusions were drawn as follows: (1) The largest contribution of P atom in PPh2py to HOMO orbital indicated that P atomin PPh2py was easier to coordinate to metal atom as an electron donor thanNatom. (2) The HHconformation was the most stable one, while HH’ was the most unstable according to molecular energies and interaction energies. This conclusion consisted with the result of synthesis experiment, in which the HH conformation products had always been tten. (3) P—Mbonds were stronger thanN—Mbonds by a comparison of their bond lengths and bond indices. There was a σ bond between P and Matoms, while in the case of interaction between N andMatoms, there was only a weak charge transfer between them (nN→n*M or nN→σ*M-P ). (4) The largest negative charge and contribution of metal atom in the HH conformation to HOMO orbital indicated that the HH conformation was the easiest to coordinate to a second metal atom and forma binuclear complex withMas the electron donor.
2008, 24(08): 1487-1492
doi: 10.3866/PKU.WHXB20080827
Abstract:
The density profiles in a mixture of bimodal polymer brushes and solvent were simulated with the aid of a self-consistent field theory (SCFT). The results showed that the bimodal brushes in od solvent form two sub-layers, which were in od agreement with those from both experiments and Monte Carlo simulations. And the increase of solubility not only makes the density profiles obtained by SCFT close to the results calculated with strong segregation theory (SST) asymptotically, but also leads to further stretching of polymer chains and sufficient orientation of chain segments. Moreover, the enlargement of grafting densities facilitates the stratification of brushes. In od solvent condition, density profiles with different total grafting densities could fall onto the same master curve. Additionally, polymerization index of long chains plays an important role in stretching of long chains, but it has little effect on density profiles of short chains.
The density profiles in a mixture of bimodal polymer brushes and solvent were simulated with the aid of a self-consistent field theory (SCFT). The results showed that the bimodal brushes in od solvent form two sub-layers, which were in od agreement with those from both experiments and Monte Carlo simulations. And the increase of solubility not only makes the density profiles obtained by SCFT close to the results calculated with strong segregation theory (SST) asymptotically, but also leads to further stretching of polymer chains and sufficient orientation of chain segments. Moreover, the enlargement of grafting densities facilitates the stratification of brushes. In od solvent condition, density profiles with different total grafting densities could fall onto the same master curve. Additionally, polymerization index of long chains plays an important role in stretching of long chains, but it has little effect on density profiles of short chains.
2008, 24(08): 1493-1497
doi: 10.3866/PKU.WHXB20080828
Abstract:
10 metal-organic framework molecules (MOFs) were designed based on the idea that the corners of those MOFs are consistent with that of MOF-5 (the complex with 1,4-benzenedicarboxylate as linker and Zn4O cluster as corner) but their linkers were changed into derivatives of 1,4-benzenedicarboxylate (BDC). Then, methane adsorption of new MOFs was calculated by grand canonicalMonte Carlo (GCMC) method at 298Kand 1-10 MPa, and the adsorption amounts were correlated with different substituent groups. The results show that the isosteric heat of adsorption is the most important factor at 298 K and 3.5 MPa, and the adsorption amount is highest when the linker of MOFs is —NO2. At last, a designed MOF, which has 4 nitro groups on the BDC, was constructed and the corresponding methane adsorption amount was also calculated at the same conditions. The calculated amount of excess adsorption reaches 209 cm3·cm-3 and the calculated total adsorption attains 228 cm3·cm-3, which is 26% higher than the amount of DOE’s requirement for methane storage materials.
10 metal-organic framework molecules (MOFs) were designed based on the idea that the corners of those MOFs are consistent with that of MOF-5 (the complex with 1,4-benzenedicarboxylate as linker and Zn4O cluster as corner) but their linkers were changed into derivatives of 1,4-benzenedicarboxylate (BDC). Then, methane adsorption of new MOFs was calculated by grand canonicalMonte Carlo (GCMC) method at 298Kand 1-10 MPa, and the adsorption amounts were correlated with different substituent groups. The results show that the isosteric heat of adsorption is the most important factor at 298 K and 3.5 MPa, and the adsorption amount is highest when the linker of MOFs is —NO2. At last, a designed MOF, which has 4 nitro groups on the BDC, was constructed and the corresponding methane adsorption amount was also calculated at the same conditions. The calculated amount of excess adsorption reaches 209 cm3·cm-3 and the calculated total adsorption attains 228 cm3·cm-3, which is 26% higher than the amount of DOE’s requirement for methane storage materials.
2008, 24(08): 1498-1502
doi: 10.3866/PKU.WHXB20080829
Abstract:
Mo-doped LiFePO4 was prepared using (NH4)6Mo7O24·4H2O as doping starting material by solid state method under N2 atmosphere. The Mo-doped LiFePO4 samples were characterized by X-ray diffraction, scanning electron microscope, X-ray photoelectron spectrum, extended X-ray absorption fine structure, positron annihilation technique, and electrochemical performance testing at different discharge rates. The results showed that Mo-doped LiFePO4 preserved pure olivine structure. Mo6 + occupied Fe site and Li site simultaneously and the electronic conductivity of LiFePO4 increased. The Mo-doped LiFePO4 had a reversible capacity of 141 mAh·g-1 at 1C discharge rate, and showed od electrochemical properties.
Mo-doped LiFePO4 was prepared using (NH4)6Mo7O24·4H2O as doping starting material by solid state method under N2 atmosphere. The Mo-doped LiFePO4 samples were characterized by X-ray diffraction, scanning electron microscope, X-ray photoelectron spectrum, extended X-ray absorption fine structure, positron annihilation technique, and electrochemical performance testing at different discharge rates. The results showed that Mo-doped LiFePO4 preserved pure olivine structure. Mo6 + occupied Fe site and Li site simultaneously and the electronic conductivity of LiFePO4 increased. The Mo-doped LiFePO4 had a reversible capacity of 141 mAh·g-1 at 1C discharge rate, and showed od electrochemical properties.
2008, 24(08): 1503-1506
doi: 10.3866/PKU.WHXB20080830
Abstract:
The complex structures in the entire composition range of water-methanol mixture were studied by pyrene fluorescence probe. The results showed that the decrease rate of I1/I3, the pyrene scale for solvent polarity, exhibited clear dependence on the mole fraction (xm) range of methanol in the mixture, while the relative quantum yield of pyrene fluorescence showed a remarkable maximum at xm=0.18. These results revealed that in a wide range of 0.18<xm<0.75, the molecules of water and methanol mainly formed water/methanol (W/M) complexes (W5M1-5) and methanol/water (M/W) complexes (M6W2-4, M8W1-3), and a transition of“W/M→M/W”complexes would occur at xm≈0.50. This notion provides a conjuncture to reconcile the two existing formulations about water-methanol complexation.
The complex structures in the entire composition range of water-methanol mixture were studied by pyrene fluorescence probe. The results showed that the decrease rate of I1/I3, the pyrene scale for solvent polarity, exhibited clear dependence on the mole fraction (xm) range of methanol in the mixture, while the relative quantum yield of pyrene fluorescence showed a remarkable maximum at xm=0.18. These results revealed that in a wide range of 0.18<xm<0.75, the molecules of water and methanol mainly formed water/methanol (W/M) complexes (W5M1-5) and methanol/water (M/W) complexes (M6W2-4, M8W1-3), and a transition of“W/M→M/W”complexes would occur at xm≈0.50. This notion provides a conjuncture to reconcile the two existing formulations about water-methanol complexation.
2008, 24(08): 1507-1512
doi: 10.3866/PKU.WHXB20080831
Abstract:
Traditional electrochemical testing technology and atomic force microscopy (AFM) force curve measurement were performed to research the adsorption behavior of corrosion inhibition film on dodecanethiol/ ld electrode and sodiumdodecyl sulfate (SDS)/aluminumelectrode systems. The results showed that the corrosion inhibitor layer obtained at different concentrations presented different micro adhesive force characteristics, being associated with the changing regularity of the electrodes’ electrochemical behavior. The research demonstrated that AFM force curve technology was a successful way to investigate the adsorption behavior of corrosion inhibition film.
Traditional electrochemical testing technology and atomic force microscopy (AFM) force curve measurement were performed to research the adsorption behavior of corrosion inhibition film on dodecanethiol/ ld electrode and sodiumdodecyl sulfate (SDS)/aluminumelectrode systems. The results showed that the corrosion inhibitor layer obtained at different concentrations presented different micro adhesive force characteristics, being associated with the changing regularity of the electrodes’ electrochemical behavior. The research demonstrated that AFM force curve technology was a successful way to investigate the adsorption behavior of corrosion inhibition film.
2008, 24(08): 1513-1518
doi: 10.3866/PKU.WHXB20080832
Abstract:
Ultrafine nickel powders were prepared fromnickel chloride reduced by hydrazine in aqueous solution of sodium dodecyl sulfate (SDS)-polyvinylpyrrolidone (PVP). SEMresults showed that the reduced products were sphere with special needle-like morphology. XRD displayed that the spherical ultrafine nickel powders were self-assembled into by the primary pure crystalline nanonickel of face centric structural (fcc) with the mean crystal size about 10 nm, and grown preferentially along (111) lattice plane. The process that the primary pure crystalline nanonickel self-assembled into the ultrafine nickel powders in virtue of the coupling of PVP chain was clearly observed by TEM. The composition of SDS-PVP mixing system had great influence on the size and shape of ultrafine nickel powders. At a certain concentration, the sizes of the primary pure crystalline nanonickel and the secondary ultrafine nickel powders showed that a decreased trend with increasing the concentration of SDS or PVP revealed a promising possibility of a size and morphology controllable production of the ultrafine nickel particles by adjusting the composition of SDS and PVP.
Ultrafine nickel powders were prepared fromnickel chloride reduced by hydrazine in aqueous solution of sodium dodecyl sulfate (SDS)-polyvinylpyrrolidone (PVP). SEMresults showed that the reduced products were sphere with special needle-like morphology. XRD displayed that the spherical ultrafine nickel powders were self-assembled into by the primary pure crystalline nanonickel of face centric structural (fcc) with the mean crystal size about 10 nm, and grown preferentially along (111) lattice plane. The process that the primary pure crystalline nanonickel self-assembled into the ultrafine nickel powders in virtue of the coupling of PVP chain was clearly observed by TEM. The composition of SDS-PVP mixing system had great influence on the size and shape of ultrafine nickel powders. At a certain concentration, the sizes of the primary pure crystalline nanonickel and the secondary ultrafine nickel powders showed that a decreased trend with increasing the concentration of SDS or PVP revealed a promising possibility of a size and morphology controllable production of the ultrafine nickel particles by adjusting the composition of SDS and PVP.
2008, 24(08): 1519-1523
doi: 10.3866/PKU.WHXB20080833
Abstract:
Highly ordered mesoporous silica materials were synthesized by templating with a nonionic triblock copolymer (Pluronic P104(PEO27-PPO61-PEO27)) via a two-step pathway in mildly acidic conditions. The mechanism of this transformation was also investigated. It was found that a mesostructure transformation could be induced by adjusting acidity from the SBA-15 type 2-dimentional hexa nal channel mesostructure (pH=1.51-2.67) to the MSU-X type with 3-dimentional worm-like mesostructure (pH=3.93-4.56) in the same synthetic system. After modified by γ-(aminopropyl) triethoxysilane (APTES) under the same condition, it was indicated that the MSU-X type was more easily modified by APTES than SBA-15 type.
Highly ordered mesoporous silica materials were synthesized by templating with a nonionic triblock copolymer (Pluronic P104(PEO27-PPO61-PEO27)) via a two-step pathway in mildly acidic conditions. The mechanism of this transformation was also investigated. It was found that a mesostructure transformation could be induced by adjusting acidity from the SBA-15 type 2-dimentional hexa nal channel mesostructure (pH=1.51-2.67) to the MSU-X type with 3-dimentional worm-like mesostructure (pH=3.93-4.56) in the same synthetic system. After modified by γ-(aminopropyl) triethoxysilane (APTES) under the same condition, it was indicated that the MSU-X type was more easily modified by APTES than SBA-15 type.
2008, 24(08): 1524-1528
doi: 10.3866/PKU.WHXB20080834
Abstract:
The methods of the disperse fluorescence, temporal-resolved spectrum and spatial-resolved spectrum were used to study the excited dissociation kinetics of N2/H2O gas in the pulsed streamer discharge plasma at the standared atmospheric pressure (1.013×105 Pa). The main spectra detected in the experiment are assigned to C3∏u→B3∏g for N2, A2∑+→X2∏ for·OH radical, and (n=3→n=2) for H atom, respectively. The temporal-resolved measurements at 337.2, 308.4, 656.5 nm showed that the occurrences of·OH* and H* were 7.4 ns and 17.6 ns later than that of N2* respectively. So the dissociation process of H2O can be described as that H2O is excited to high vibrational level of the first excited state by non-elasticity collision with electron, and then dissociates to·OH* radical at excited state and H atom at ground state. Furthermore, spatial-resolved measurements showed that the densities of active particles reached the maximum at 0.5 mm away from negative electrode corresponding to the negative glow region of streamer discharge, where the maxima of electron temperature and density were helpful to the formation of these active particles.
The methods of the disperse fluorescence, temporal-resolved spectrum and spatial-resolved spectrum were used to study the excited dissociation kinetics of N2/H2O gas in the pulsed streamer discharge plasma at the standared atmospheric pressure (1.013×105 Pa). The main spectra detected in the experiment are assigned to C3∏u→B3∏g for N2, A2∑+→X2∏ for·OH radical, and (n=3→n=2) for H atom, respectively. The temporal-resolved measurements at 337.2, 308.4, 656.5 nm showed that the occurrences of·OH* and H* were 7.4 ns and 17.6 ns later than that of N2* respectively. So the dissociation process of H2O can be described as that H2O is excited to high vibrational level of the first excited state by non-elasticity collision with electron, and then dissociates to·OH* radical at excited state and H atom at ground state. Furthermore, spatial-resolved measurements showed that the densities of active particles reached the maximum at 0.5 mm away from negative electrode corresponding to the negative glow region of streamer discharge, where the maxima of electron temperature and density were helpful to the formation of these active particles.
2008, 24(08): 1529-1534
doi: 10.3866/PKU.WHXB20080835
Abstract:
The novel multilayer nano-composite films consisting of vanadium mono-substituted polyoxometalates (PMo11VO4-40) and a generation-4 poly(amidoamine) (PAMAM) dendrimer were fabricated on quartz and glassy carbon electrode substrates by layer-by-layer self-assembly technique. The incorporation of PMo11VO4-40 and PAMAM into the films was confirmed by XPS. The multilayer films were grew gradually and uniformly in the synthesis process as monitored by UV-Vis and cyclic voltammetry. Four pairs of redox peaks which corresponded to V5+/V4+ and Mo6+/Mo5+ were observed in the cyclic voltammogram of multilayer films. The dependence of peak current on scan rate was indicative of redox surface-confined species and the charge transfer was very quick. The formal potential of the composite films was shifted linearly to negative position at higher pH, which implied that the protons were involved in the redox processes of polyoxometalates. The multilayer films were stable and exhibited od catalytic activities for the reduction of NO-2 , BrO-3, and H2O2.
The novel multilayer nano-composite films consisting of vanadium mono-substituted polyoxometalates (PMo11VO4-40) and a generation-4 poly(amidoamine) (PAMAM) dendrimer were fabricated on quartz and glassy carbon electrode substrates by layer-by-layer self-assembly technique. The incorporation of PMo11VO4-40 and PAMAM into the films was confirmed by XPS. The multilayer films were grew gradually and uniformly in the synthesis process as monitored by UV-Vis and cyclic voltammetry. Four pairs of redox peaks which corresponded to V5+/V4+ and Mo6+/Mo5+ were observed in the cyclic voltammogram of multilayer films. The dependence of peak current on scan rate was indicative of redox surface-confined species and the charge transfer was very quick. The formal potential of the composite films was shifted linearly to negative position at higher pH, which implied that the protons were involved in the redox processes of polyoxometalates. The multilayer films were stable and exhibited od catalytic activities for the reduction of NO-2 , BrO-3, and H2O2.
