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2006 Volume 22 Issue 12
2006, 22(12): 1435-1440
doi: 10.1016/S1872-1508(06)60073-9
Abstract:
Micellization of a series of newly synthesized dialkyl benzene sulfonates was studied using proton chemical shift changes, spin-lattice, and spin-spin relaxation NMR spectroscopy, and two-dimensional nuclear Overhauser enhancement spectroscopy (2D NOESY). The o-substituted chains are normal alkyl chains with varying lengths, and the m-substituted ones are branched alkyl chains. The results showed that the longer the o-substituted normal alkyl chain, protons of more methylene groups participated in the formation of the rigid surface layer of the hydrophobic micellar core. Consequently, the larger was the area per molecule adsorbed on the interface between oil and water at saturation. The branched m-substituted alkyl chains of the dialkyl benzene sulfonates were less tightly packed than the o-substituted normal alkyl chains in the hydrophobic micellar cores. The shorter the m-substituted branched alkyl chains, the looser they were packed in the hydrophobic micellar core. The relative arrangement of the surfactant molecules in the micelles was elucidated.
Micellization of a series of newly synthesized dialkyl benzene sulfonates was studied using proton chemical shift changes, spin-lattice, and spin-spin relaxation NMR spectroscopy, and two-dimensional nuclear Overhauser enhancement spectroscopy (2D NOESY). The o-substituted chains are normal alkyl chains with varying lengths, and the m-substituted ones are branched alkyl chains. The results showed that the longer the o-substituted normal alkyl chain, protons of more methylene groups participated in the formation of the rigid surface layer of the hydrophobic micellar core. Consequently, the larger was the area per molecule adsorbed on the interface between oil and water at saturation. The branched m-substituted alkyl chains of the dialkyl benzene sulfonates were less tightly packed than the o-substituted normal alkyl chains in the hydrophobic micellar cores. The shorter the m-substituted branched alkyl chains, the looser they were packed in the hydrophobic micellar core. The relative arrangement of the surfactant molecules in the micelles was elucidated.
2006, 22(12): 1441-1444
doi: 10.3866/PKU.WHXB20061202
Abstract:
The dilational viscoelasticity properties of octane-water interface containing three sodium alkyl benzene sulfonates with straight chain (C8phSO3Na and C16phSO3Na) and branch chain (7-8-1) respectively were investigated. The influences of alkyl chain length and hydrophobic branched-chain structure on interfacial dilational properties were expounded. It showed that the increase of alkyl chain length resulted in the enhancement of molecular interaction and the increase of interfacial dilational elasticity. The slow relaxation processes were caused by the rearrangement and entanglement of branched-chains at interface and resulted in relative higher interfacial dilational modulus.
The dilational viscoelasticity properties of octane-water interface containing three sodium alkyl benzene sulfonates with straight chain (C8phSO3Na and C16phSO3Na) and branch chain (7-8-1) respectively were investigated. The influences of alkyl chain length and hydrophobic branched-chain structure on interfacial dilational properties were expounded. It showed that the increase of alkyl chain length resulted in the enhancement of molecular interaction and the increase of interfacial dilational elasticity. The slow relaxation processes were caused by the rearrangement and entanglement of branched-chains at interface and resulted in relative higher interfacial dilational modulus.
2006, 22(12): 1445-1450
doi: 10.3866/PKU.WHXB20061203
Abstract:
The electrochemical characteristics and pseudocapacitive effects of Fe3+/Fe2+ ion pair were investigated in an electrochemical capacitor (EC) system using porous carbon as electrode material and with H2SO4 solution containing Fe3+/Fe2+ ion pair as electrolyte. The cyclic voltammetric results indicated that highly reversible electrochemical redox reactions of Fe3+/Fe2+ ion pair occurred within the nano-pore structures of the porous carbon electrodes. Symmetrical charge/discharge cycles were achieved due to the existence of Fe3+/Fe2+ ion pair, which effectively improved the capacity of the electrochemical capacitor system. Apart from its excellent cyclic stability, the specific capacitance of the single electrode system reached 174 mAh•g−1, which is 109 mAh•g−1 higher than that obtained for H2SO4 as the electrolyte. The charge/discharge mechanism of Fe3+/Fe2+ ion pair in the EC systems was discussed and a new type of redox electrolyte electrochemical capacitor was suggested.
The electrochemical characteristics and pseudocapacitive effects of Fe3+/Fe2+ ion pair were investigated in an electrochemical capacitor (EC) system using porous carbon as electrode material and with H2SO4 solution containing Fe3+/Fe2+ ion pair as electrolyte. The cyclic voltammetric results indicated that highly reversible electrochemical redox reactions of Fe3+/Fe2+ ion pair occurred within the nano-pore structures of the porous carbon electrodes. Symmetrical charge/discharge cycles were achieved due to the existence of Fe3+/Fe2+ ion pair, which effectively improved the capacity of the electrochemical capacitor system. Apart from its excellent cyclic stability, the specific capacitance of the single electrode system reached 174 mAh•g−1, which is 109 mAh•g−1 higher than that obtained for H2SO4 as the electrolyte. The charge/discharge mechanism of Fe3+/Fe2+ ion pair in the EC systems was discussed and a new type of redox electrolyte electrochemical capacitor was suggested.
2006, 22(12): 1451-1455
doi: 10.1016/S1872-1508(06)60074-0
Abstract:
Interfacial tensions of the aqueous two-phase systems formed by cationic-anionic surfactant mixtures were measured using spinning drop method. The effects of surfactant structure, molar ratio of cationic surfactants to anionic surfactants, surfactant concentration, salt, and temperature on the interfacial tensions were investigated. It was shown that the values of the interfacial tensions of the aqueous two-phase were in the scale of ultra-low interfacial tensions at certain molar ratios of cationic to anionic surfactants. Three types of interfacial tension curves were observed. The first curve comprised two curves that were located on either side of 1:1 molar ratio, and the interfacial tension decreased with the increase of excessed surfactant component. The second one was a saddle-shaped curve that strode over the 1:1 molar ratio. The third type was a saddle-shaped curve that was located beside the 1:1 molar ratio. The types of interfacial tension depended on the molecular structure of the surfactants such as the hydrophilic groups and the lengths and symmetry of hydrophobic chains.
Interfacial tensions of the aqueous two-phase systems formed by cationic-anionic surfactant mixtures were measured using spinning drop method. The effects of surfactant structure, molar ratio of cationic surfactants to anionic surfactants, surfactant concentration, salt, and temperature on the interfacial tensions were investigated. It was shown that the values of the interfacial tensions of the aqueous two-phase were in the scale of ultra-low interfacial tensions at certain molar ratios of cationic to anionic surfactants. Three types of interfacial tension curves were observed. The first curve comprised two curves that were located on either side of 1:1 molar ratio, and the interfacial tension decreased with the increase of excessed surfactant component. The second one was a saddle-shaped curve that strode over the 1:1 molar ratio. The third type was a saddle-shaped curve that was located beside the 1:1 molar ratio. The types of interfacial tension depended on the molecular structure of the surfactants such as the hydrophilic groups and the lengths and symmetry of hydrophobic chains.
2006, 22(12): 1456-1459
doi: 10.3866/PKU.WHXB20061205
Abstract:
The binding reaction between topotecan hydrochloride (THC) and human serum albumin (HSA) was studied by fluorescence and UV-Vis absorption spectra. The binding equilibrium constant, number of binding site and thermodynamic parameters were calculated. The distance between the binding site and tryptophan residue is 3.63 nm. The study of molecular simulation indicated that topotecan hydrochloride bound within the subdomain IIA of human serum albumins and the interaction between topotecan hydrochloride and HSA was dominated by hydrophobic force. In addition, both the residues Ala-291 and Asp-256 of HSA formed hydrogen bonds with topotecan hydrochloride, respectively.
The binding reaction between topotecan hydrochloride (THC) and human serum albumin (HSA) was studied by fluorescence and UV-Vis absorption spectra. The binding equilibrium constant, number of binding site and thermodynamic parameters were calculated. The distance between the binding site and tryptophan residue is 3.63 nm. The study of molecular simulation indicated that topotecan hydrochloride bound within the subdomain IIA of human serum albumins and the interaction between topotecan hydrochloride and HSA was dominated by hydrophobic force. In addition, both the residues Ala-291 and Asp-256 of HSA formed hydrogen bonds with topotecan hydrochloride, respectively.
2006, 22(12): 1460-1465
doi: 10.3866/PKU.WHXB20061206
Abstract:
A free energy density functional theory (DFT) has been used to investigate the density profiles of binary hard-core repulsive Yukawa (HCRY) mixtures under the influence of various external fields. The representation of the excess Helmholtz free energy functional was based on the perturbation theory, where a weighted density approximation (WDA) theory, proposed by Kierlik and Rosinberg, was applied for the hard-core repulsive interaction and a mean field theory (MFT) was used for the long-range dispersion one. To test the validity of the DFT, the grand canonical ensemble Monte Carlo (GCMC) simulations were carried out to obtain the density profiles of binary HCRY mixtures under different bulk densities, hard-core diameters, and energy parameter ratios. The DFT calculations are in quite od agreement with the GCMC simulations.
A free energy density functional theory (DFT) has been used to investigate the density profiles of binary hard-core repulsive Yukawa (HCRY) mixtures under the influence of various external fields. The representation of the excess Helmholtz free energy functional was based on the perturbation theory, where a weighted density approximation (WDA) theory, proposed by Kierlik and Rosinberg, was applied for the hard-core repulsive interaction and a mean field theory (MFT) was used for the long-range dispersion one. To test the validity of the DFT, the grand canonical ensemble Monte Carlo (GCMC) simulations were carried out to obtain the density profiles of binary HCRY mixtures under different bulk densities, hard-core diameters, and energy parameter ratios. The DFT calculations are in quite od agreement with the GCMC simulations.
2006, 22(12): 1466-1472
doi: 10.1016/S1872-1508(06)60075-2
Abstract:
The interaction between 2,2′-p-phenylenebis (5-phenyloxazol) (POPOP) and cyclodextrins (CDs) was investigated using UV-Vis absorption, steady-state fluorescence, and dynamic light scattering (DLS). The results indicated that POPOP could form the 1:2 (guest:host) inclusion complex with β-CD at lower concentrations, which could further form the extended nanotube at higher concentrations. POPOP could also induce the formation of the nanotube of γ-CD. The fluorescence emission of POPOP in aqueous solution of γ-CD showed obvious red shift accompanied by the disappearance of fine structure compared with that in aqueous solution of β-CD, which could be attributed to the formation of the excimer of POPOP in the larger cavity of γ-CD. It was found that at pH greater than 12, the hydrogen bond between the neighboring CDs was destroyed, which led to the collapse of the nanotubular structure. The results also showed that the nanotube structure was not stable at temperatures above 331 K.
The interaction between 2,2′-p-phenylenebis (5-phenyloxazol) (POPOP) and cyclodextrins (CDs) was investigated using UV-Vis absorption, steady-state fluorescence, and dynamic light scattering (DLS). The results indicated that POPOP could form the 1:2 (guest:host) inclusion complex with β-CD at lower concentrations, which could further form the extended nanotube at higher concentrations. POPOP could also induce the formation of the nanotube of γ-CD. The fluorescence emission of POPOP in aqueous solution of γ-CD showed obvious red shift accompanied by the disappearance of fine structure compared with that in aqueous solution of β-CD, which could be attributed to the formation of the excimer of POPOP in the larger cavity of γ-CD. It was found that at pH greater than 12, the hydrogen bond between the neighboring CDs was destroyed, which led to the collapse of the nanotubular structure. The results also showed that the nanotube structure was not stable at temperatures above 331 K.
2006, 22(12): 1473-1477
doi: 10.3866/PKU.WHXB20061208
Abstract:
X-ray absorption near-edge structure (XANES) spectrum of thermal and tribochemical films of alkyl polysulfides with different sulfur contents was determined. It was found that the chemical nature of these films was strongly dependent on the operating environment for the additives. That was, the thermal films of the serial polysulfides were composed of FeSO4 or Fe2(SO4)3 under 70 ℃ and 150 ℃, the thickness of thermal films increased with the increasing of the temperature and additives′ sulfur content. Tribochemical films were composed of different forms of sulfur rather than iron sulfate observed in the thermo-oxidative films. They were mixtures of iron sulfate, pyrite and sulfoxide, and the rise of sulfur content led to the increase of thickness in the tribochemical films.
X-ray absorption near-edge structure (XANES) spectrum of thermal and tribochemical films of alkyl polysulfides with different sulfur contents was determined. It was found that the chemical nature of these films was strongly dependent on the operating environment for the additives. That was, the thermal films of the serial polysulfides were composed of FeSO4 or Fe2(SO4)3 under 70 ℃ and 150 ℃, the thickness of thermal films increased with the increasing of the temperature and additives′ sulfur content. Tribochemical films were composed of different forms of sulfur rather than iron sulfate observed in the thermo-oxidative films. They were mixtures of iron sulfate, pyrite and sulfoxide, and the rise of sulfur content led to the increase of thickness in the tribochemical films.
2006, 22(12): 1478-1483
doi: 10.3866/PKU.WHXB20061209
Abstract:
The strength that the nucleus attracts the valence electrons in alkane molecules can be scaled by the eigenvalues of the bond orbital-connection matrices of C—C and C—H bonds. Using the above two kinds of eigenvalues, the branching parameter of alkane molecules and temperature parameter, a four-parameter equation was developed to fit the thermal conductivity λ of a training set with 45 alkanes bearing 5 to 24 carbon atoms: λ=0.7568−0.2728(ΣX1CC)/NC—C+1.5171(ΣX1CH)/NC—H+7.4×10−5ΣSij+2.0966T −0.4 The standard error between the estimation values by above equation and the experimental values is only 0.0033 W•m−1•K−1 and the relative average error is only 2.11%. Further, the thermal conductivities of 9 another alkanes excluded in the training set were predicted with the obtained model, and the predicted relative average error is only 1.64%, which is within the experimental uncertainties. Therefore it is expected that this model can be used to estimate and predict the thermal conductivity of liquid alkanes whose λ values have not been measured by experiments.
The strength that the nucleus attracts the valence electrons in alkane molecules can be scaled by the eigenvalues of the bond orbital-connection matrices of C—C and C—H bonds. Using the above two kinds of eigenvalues, the branching parameter of alkane molecules and temperature parameter, a four-parameter equation was developed to fit the thermal conductivity λ of a training set with 45 alkanes bearing 5 to 24 carbon atoms: λ=0.7568−0.2728(ΣX1CC)/NC—C+1.5171(ΣX1CH)/NC—H+7.4×10−5ΣSij+2.0966T −0.4 The standard error between the estimation values by above equation and the experimental values is only 0.0033 W•m−1•K−1 and the relative average error is only 2.11%. Further, the thermal conductivities of 9 another alkanes excluded in the training set were predicted with the obtained model, and the predicted relative average error is only 1.64%, which is within the experimental uncertainties. Therefore it is expected that this model can be used to estimate and predict the thermal conductivity of liquid alkanes whose λ values have not been measured by experiments.
2006, 22(12): 1484-1488
doi: 10.1016/S1872-1508(06)60076-4
Abstract:
Kinetics of complexation reaction of Co2+ with 2-benzoylpyridine-4-phenyl-3-thiosemicarbazone (BPPT) was spectrophotometrically examined at 421 nm. The ligand that is developed for a simple kinetic-spectrophotometric determination of Co2+ is based on 1:2 complex formation between Co2+ and BPPT. The complexation reaction was carried out in ethanol-water medium at 25 ℃. Kinetic and activation parameters of the complexation reaction were calculated, and the rate equation and the reaction mechanism were proposed. The calibration graph is linear in the concentration range of 0.10～2.91 mg•L−1 for the tangent method. The species that caused interference were investigated.
Kinetics of complexation reaction of Co2+ with 2-benzoylpyridine-4-phenyl-3-thiosemicarbazone (BPPT) was spectrophotometrically examined at 421 nm. The ligand that is developed for a simple kinetic-spectrophotometric determination of Co2+ is based on 1:2 complex formation between Co2+ and BPPT. The complexation reaction was carried out in ethanol-water medium at 25 ℃. Kinetic and activation parameters of the complexation reaction were calculated, and the rate equation and the reaction mechanism were proposed. The calibration graph is linear in the concentration range of 0.10～2.91 mg•L−1 for the tangent method. The species that caused interference were investigated.
2006, 22(12): 1489-1494
doi: 10.3866/PKU.WHXB20061211
Abstract:
The geometry structures and the energy barriers for the ground-state isomerization reactions of nitromethane, nitroethylene, nitrobenzene, and trans-β-nitrostyrene were computed using B3LYP/6-31G* level of theory. Their electronic transition energies were obtained using B3LYP-TD/6-31G* calculations. The results indicated that the C—N bond lengths of trans-β-nitrostyrene and nitrobenzen were significantly shorter than that of nitromethane, meanwhile the isomerization energy barriers of trans-β-nitrostyrene and nitrobenzen were somewhat lower than that of nitromethane. The energy difference (ΔE) between the vertical electronic transition energy and the transition state of the ground-state isomerization decreased dramatically with the increase of the molecular unsaturation as the molecule went from trans-β-nitrostyrene to nitrobenzene and to nitromethane. This suggests that as the unsaturation degree of the substituent R increases for R—NO2, the curve crossing between the excited state and the ground isomerization potential energy surface increases and this greatly favors the isomerization exit channel. The calculated first transition-allowed absorption band (also called A-band absorption) was assigned to a π→π* transition for these molecules. While the A-band electronic transition of nitromethane is mainly localized on the NO2 group, those of trans-β-nitrostyrene, nitrobenzene and nitroethylene are largely delocalized over the molecules, which causes the intramolecular charge-transfer processes to take place between the NO2 group and the C6H5—C=C group, the C6H5 group as well as the C=C group. Thus the localization or delocalization of the A-band electronic transition of nitroalkanes or nitroaromatics plays an important role in manipulating its photodissociation channel or photoisomerization channel.
The geometry structures and the energy barriers for the ground-state isomerization reactions of nitromethane, nitroethylene, nitrobenzene, and trans-β-nitrostyrene were computed using B3LYP/6-31G* level of theory. Their electronic transition energies were obtained using B3LYP-TD/6-31G* calculations. The results indicated that the C—N bond lengths of trans-β-nitrostyrene and nitrobenzen were significantly shorter than that of nitromethane, meanwhile the isomerization energy barriers of trans-β-nitrostyrene and nitrobenzen were somewhat lower than that of nitromethane. The energy difference (ΔE) between the vertical electronic transition energy and the transition state of the ground-state isomerization decreased dramatically with the increase of the molecular unsaturation as the molecule went from trans-β-nitrostyrene to nitrobenzene and to nitromethane. This suggests that as the unsaturation degree of the substituent R increases for R—NO2, the curve crossing between the excited state and the ground isomerization potential energy surface increases and this greatly favors the isomerization exit channel. The calculated first transition-allowed absorption band (also called A-band absorption) was assigned to a π→π* transition for these molecules. While the A-band electronic transition of nitromethane is mainly localized on the NO2 group, those of trans-β-nitrostyrene, nitrobenzene and nitroethylene are largely delocalized over the molecules, which causes the intramolecular charge-transfer processes to take place between the NO2 group and the C6H5—C=C group, the C6H5 group as well as the C=C group. Thus the localization or delocalization of the A-band electronic transition of nitroalkanes or nitroaromatics plays an important role in manipulating its photodissociation channel or photoisomerization channel.
2006, 22(12): 1495-1500
doi: 10.1016/S1872-1508(06)60077-6
Abstract:
Silicoaluminophosphate (SAPO)-11 molecular sieve was modified by rare earth La and Ce using impregnating and ion-exchanging methods. The RE-modified SAPO-11 samples were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), pore-size distribution (PSD), in-situ Fourier transform infrared spectroscopy (FTIR), and temperature-programmed desorption of ammonia (NH3-TPD), and compared with unmodified SAPO-11 sample. The XRD patterns indicated that after RE modification, especially for the La-exchanged sample, the composition of molecular sieve was changed and the crystallinity decreased. The normalized surface area (NSA) of ion-exchanged samples proved that the unsubstituted metal oxides accumulated inside the SAPO-11 pores. Because of the RE cations that were loaded onto the surface of molecular sieve, which could be regarded as the Lewis acid sites, there was an increase in the amount of Lewis acid sites and decrease in the Brønsted acid/Lewis acid (B/L) ratio. The ability of RE cations to acquire electrons was weaker than that of Al3+; therefore, the bond strength of bridged hydroxyl decreased after modification. The total acidity of SAPO-11 decreased after RE modification.
Silicoaluminophosphate (SAPO)-11 molecular sieve was modified by rare earth La and Ce using impregnating and ion-exchanging methods. The RE-modified SAPO-11 samples were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), pore-size distribution (PSD), in-situ Fourier transform infrared spectroscopy (FTIR), and temperature-programmed desorption of ammonia (NH3-TPD), and compared with unmodified SAPO-11 sample. The XRD patterns indicated that after RE modification, especially for the La-exchanged sample, the composition of molecular sieve was changed and the crystallinity decreased. The normalized surface area (NSA) of ion-exchanged samples proved that the unsubstituted metal oxides accumulated inside the SAPO-11 pores. Because of the RE cations that were loaded onto the surface of molecular sieve, which could be regarded as the Lewis acid sites, there was an increase in the amount of Lewis acid sites and decrease in the Brønsted acid/Lewis acid (B/L) ratio. The ability of RE cations to acquire electrons was weaker than that of Al3+; therefore, the bond strength of bridged hydroxyl decreased after modification. The total acidity of SAPO-11 decreased after RE modification.
Effect of NaBr on the Ability of C12-s-C12•2Br Reverse Micelles for Solubilizing Water in Chloroform
2006, 22(12): 1501-1505
doi: 10.3866/PKU.WHXB20061213
Abstract:
Near-infrared (NIR) spectroscopy technique can be used to characterize the ability of reverse micelles for solubilizing water in chloroform. For C12-s-C12•2Br (s=2, 3, 4, 5, 6, 8) homologue, no matter whether adding NaBr in water, the ability of the reverse micelles for solubilizing water reduces with increasing spacer length since the surfactant with shorter spacer trends to form larger reverse micelles. Compared with the system without NaBr, the ability of the reverse micelles for solubilizing water decreases when adding NaBr in water.
Near-infrared (NIR) spectroscopy technique can be used to characterize the ability of reverse micelles for solubilizing water in chloroform. For C12-s-C12•2Br (s=2, 3, 4, 5, 6, 8) homologue, no matter whether adding NaBr in water, the ability of the reverse micelles for solubilizing water reduces with increasing spacer length since the surfactant with shorter spacer trends to form larger reverse micelles. Compared with the system without NaBr, the ability of the reverse micelles for solubilizing water decreases when adding NaBr in water.
2006, 22(12): 1506-1510
doi: 10.3866/PKU.WHXB20061214
Abstract:
Nanostructured platinum is prepared by electrochemical deposition from the lamellar lyotropic liquid crystalline phase, composed of the nonionic triblock copolymer EO106PO70EO106 (F127), n-butanol and H2PtCl6 aqueous solution. Observations from the transmission or scanning electron microscopes illustrate that the deposit is of bunchy nanostructure, clustered by nanowires with high aspect ratio. Analysis on energy dispersion spectrum and the electrode potentials suggests the platinum metal nature of the deposit. The results of cyclic voltammetry show a high specific surface area (about 53 m2•g−1) for the deposit. The factors influencing the deposit morphology and the possible deposition mechanism are discussed.
Nanostructured platinum is prepared by electrochemical deposition from the lamellar lyotropic liquid crystalline phase, composed of the nonionic triblock copolymer EO106PO70EO106 (F127), n-butanol and H2PtCl6 aqueous solution. Observations from the transmission or scanning electron microscopes illustrate that the deposit is of bunchy nanostructure, clustered by nanowires with high aspect ratio. Analysis on energy dispersion spectrum and the electrode potentials suggests the platinum metal nature of the deposit. The results of cyclic voltammetry show a high specific surface area (about 53 m2•g−1) for the deposit. The factors influencing the deposit morphology and the possible deposition mechanism are discussed.
2006, 22(12): 1511-1515
doi: 10.3866/PKU.WHXB20061215
Abstract:
Ti-doped NaAlH4 complex hydride can be prepared by hydrogenation of the ball-milled (NaH/Al+Ti) composite using NaH and pre-treated Al powder as raw materials, and Ti powder as a dopant. The influence of preparation parameters (ball-milling atmosphere, milling time, and hydrogenation pressure) on its hydrogen storage characteristic has been investigated. It is found that the hydrogen storage properties are affected greatly by the preparation methods. The hydrogen storage properties of the composite ball-milled under hydrogen atmosphere are better than that of the composite ball-milled under ar n atmosphere. With extending the milling time from 6 h to 24 h under hydrogen atmosphere, the hydrogen absorption capacity and rate increase first and then decrease, and the maximum values are obtained at 12 h, while the hydrogen desorption capacity and speed increase gradually. The particles of the composite will agglomerate when prolonging the milling-time over 12 h, which deteriorates the hydrogen absorption properties. As the hydrogenation pressure increases from 7.5 MPa to 13.5 MPa, the hydrogen absorption storage capacity (mass fraction) increases from 2.83% to 4.21%. The appearance of intermediate Na3AlH6 hydride phase in the ball-milled composite indicates that the Ti-doped (NaH/Al) composites ball-milled under hydrogen atmosphere can catalyze the hydrogenation reaction of NaH and Al.
Ti-doped NaAlH4 complex hydride can be prepared by hydrogenation of the ball-milled (NaH/Al+Ti) composite using NaH and pre-treated Al powder as raw materials, and Ti powder as a dopant. The influence of preparation parameters (ball-milling atmosphere, milling time, and hydrogenation pressure) on its hydrogen storage characteristic has been investigated. It is found that the hydrogen storage properties are affected greatly by the preparation methods. The hydrogen storage properties of the composite ball-milled under hydrogen atmosphere are better than that of the composite ball-milled under ar n atmosphere. With extending the milling time from 6 h to 24 h under hydrogen atmosphere, the hydrogen absorption capacity and rate increase first and then decrease, and the maximum values are obtained at 12 h, while the hydrogen desorption capacity and speed increase gradually. The particles of the composite will agglomerate when prolonging the milling-time over 12 h, which deteriorates the hydrogen absorption properties. As the hydrogenation pressure increases from 7.5 MPa to 13.5 MPa, the hydrogen absorption storage capacity (mass fraction) increases from 2.83% to 4.21%. The appearance of intermediate Na3AlH6 hydride phase in the ball-milled composite indicates that the Ti-doped (NaH/Al) composites ball-milled under hydrogen atmosphere can catalyze the hydrogenation reaction of NaH and Al.
2006, 22(12): 1516-1519
doi: 10.3866/PKU.WHXB20061216
Abstract:
The potential energy curves and stability of PdYn± (n=0, 1, 2, 3) were calculated using density functional theory B3LYP method with relativistic effective core potential and SDD basis for Pd and Y atoms. PdY molecular, PdY−, PdY2−, PdY3−, and PdY+ molecular ions could be stable with the ground states X2Σ, X1Σ, X2Σ, X2Σ, X1Σ, respectively. Their Murrell-Sorbie analytic potential energy functions were derived to be fitted with ab initio data, and force constants and spectroscopic data were derived. PdY2+ and PdY3+ molecular ions could be metastable with the ground states X2Σ and X2Σ, PdY3+ molecular ion could not be stable with a repulsive character.
The potential energy curves and stability of PdYn± (n=0, 1, 2, 3) were calculated using density functional theory B3LYP method with relativistic effective core potential and SDD basis for Pd and Y atoms. PdY molecular, PdY−, PdY2−, PdY3−, and PdY+ molecular ions could be stable with the ground states X2Σ, X1Σ, X2Σ, X2Σ, X1Σ, respectively. Their Murrell-Sorbie analytic potential energy functions were derived to be fitted with ab initio data, and force constants and spectroscopic data were derived. PdY2+ and PdY3+ molecular ions could be metastable with the ground states X2Σ and X2Σ, PdY3+ molecular ion could not be stable with a repulsive character.
2006, 22(12): 1520-1525
doi: 10.3866/PKU.WHXB20061217
Abstract:
The geometry and electronic structure of C(6,0)@BN(n,0) system were studied by density functional theory method with DMol3 code. It was found that the favorable BN(n,0) nanotubes for C(6,0) to form C(6,0)@BN(n,0) were BN(15,0), and BN(16,0) nanotubes. In C(6,0)@BN(15,0) and C(6,0)@BN(16,0), the interwall distances between the inner C tube and outer BN tube were 0.36 and 0.40 nm, respectively. In the most stable C(6,0)@BN(16,0), the conductivity of C nanotube was not affected by outer BN tube while the bandgap of BN nanotube was reduced about 0.5 eV. The analysis of orbitals of C(6,0)@BN(16,0) indicated that the interaction between C and BN nanotube was typical van der Waals interaction.
The geometry and electronic structure of C(6,0)@BN(n,0) system were studied by density functional theory method with DMol3 code. It was found that the favorable BN(n,0) nanotubes for C(6,0) to form C(6,0)@BN(n,0) were BN(15,0), and BN(16,0) nanotubes. In C(6,0)@BN(15,0) and C(6,0)@BN(16,0), the interwall distances between the inner C tube and outer BN tube were 0.36 and 0.40 nm, respectively. In the most stable C(6,0)@BN(16,0), the conductivity of C nanotube was not affected by outer BN tube while the bandgap of BN nanotube was reduced about 0.5 eV. The analysis of orbitals of C(6,0)@BN(16,0) indicated that the interaction between C and BN nanotube was typical van der Waals interaction.
2006, 22(12): 1526-1531
doi: 10.3866/PKU.WHXB20061218
Abstract:
The full geometry optimizations for the π-type halogen-bond systems, C2H4(C2H2)-XY(XY=F2, Cl2, Br2, ClF, BrF, BrCl) were carried out using MP2 and DFT at 6-311++G(d, p) and aug-cc-pvdz levels. T-shaped halogen-bonded complexes were obtained. The calculated results indicated that MP2(full)/6-311++G(d, p) was the better method. After the corrections of ZPE and BSSE (basis set superposition error) by the counterpoise method, the interaction energies of the halogen-bonded complexes were calculated at the MP2 level. The topological properties were investigated by the topological analysis of electron density.
The full geometry optimizations for the π-type halogen-bond systems, C2H4(C2H2)-XY(XY=F2, Cl2, Br2, ClF, BrF, BrCl) were carried out using MP2 and DFT at 6-311++G(d, p) and aug-cc-pvdz levels. T-shaped halogen-bonded complexes were obtained. The calculated results indicated that MP2(full)/6-311++G(d, p) was the better method. After the corrections of ZPE and BSSE (basis set superposition error) by the counterpoise method, the interaction energies of the halogen-bonded complexes were calculated at the MP2 level. The topological properties were investigated by the topological analysis of electron density.
2006, 22(12): 1532-1536
doi: 10.1016/S1872-1508(06)60078-8
Abstract:
On the basis of the approximation of harmonic oscillation between SC and S for the symmetric stretching vibration of the CS2+ ions, the Franck-Condon factors for the C2Σg+←B2Σu+ transitions of CS2+ ions have been calculated using the potential curves and wavefunctions of the harmonic oscillator. The calculation results have been used for comparison with the photodissociation spectra via the C2Σg+←B2Σu+ transition, and to estimate the validity of the rotation constants and the bond length of C2Σg+ state given in the previous studies. The photodissociation mechanism via the C2Σg+←B2Σu+transitions of CS2+ ions has also been discussed.
On the basis of the approximation of harmonic oscillation between SC and S for the symmetric stretching vibration of the CS2+ ions, the Franck-Condon factors for the C2Σg+←B2Σu+ transitions of CS2+ ions have been calculated using the potential curves and wavefunctions of the harmonic oscillator. The calculation results have been used for comparison with the photodissociation spectra via the C2Σg+←B2Σu+ transition, and to estimate the validity of the rotation constants and the bond length of C2Σg+ state given in the previous studies. The photodissociation mechanism via the C2Σg+←B2Σu+transitions of CS2+ ions has also been discussed.
2006, 22(12): 1537-1541
doi: 10.3866/PKU.WHXB20061220
Abstract:
The three-dimensional reticular Sn-Co alloy deposits were prepared by electroplating. The structure and electrochemical performance of the electroplated three-dimensional reticular Sn-Co alloys have been investigated in detail. Experimental results show that the Sn-Co alloy film is of hexa nal solid solution, with Sn as the solvent, Co as the solute. Electrochemical tests show that the three-dimensional reticular Sn-Co alloy coating electrodes can deliver a discharge capacity of 493.4 mAh•g−1 in the first cycle. At the 50th cycle the charge was 329.6 mAh•g−1. The three-dimensional reticular structure in Sn-Co alloy electrode was beneficial in reducing the irreversible capacity of Sn-Co alloy electrode at initial charge-discharge, and in relaxing the volume expansion during cycling, which improved the cyclability of Sn-Co alloy electrode. They are also beneficial to diffusion of Li into /out of macroporous materials, and improve coulomb efficiency in charge-discharge cycle.
The three-dimensional reticular Sn-Co alloy deposits were prepared by electroplating. The structure and electrochemical performance of the electroplated three-dimensional reticular Sn-Co alloys have been investigated in detail. Experimental results show that the Sn-Co alloy film is of hexa nal solid solution, with Sn as the solvent, Co as the solute. Electrochemical tests show that the three-dimensional reticular Sn-Co alloy coating electrodes can deliver a discharge capacity of 493.4 mAh•g−1 in the first cycle. At the 50th cycle the charge was 329.6 mAh•g−1. The three-dimensional reticular structure in Sn-Co alloy electrode was beneficial in reducing the irreversible capacity of Sn-Co alloy electrode at initial charge-discharge, and in relaxing the volume expansion during cycling, which improved the cyclability of Sn-Co alloy electrode. They are also beneficial to diffusion of Li into /out of macroporous materials, and improve coulomb efficiency in charge-discharge cycle.
2006, 22(12): 1542-1546
doi: 10.3866/PKU.WHXB20061221
Abstract:
Carbon nanotubes (CNTs) were employed to remove toxic hexavalent chromium ions from aqueous solution. Effects of concentration of hexavalent chromium, solution pH, coexistent trivalent chromium in the solution on the Cr(VI) adsorption were examined. The results show that the adsorption capacity of Cr(VI) on CNTs increased with increase of Cr(VI) concentration, and then reach a plateau between 300~700 mg•L−1 of Cr(VI); the maximum value of 532.215 mg Cr(VI) per g CNTs was achieved at the Cr(VI) concentration of 493.557 mg•L−1, and followed by a decrease at still higher concentration of Cr(VI). The capacity was also significantly affected by the pH value of the solution between 2 and 7, and little change was observed above pH value of 7. Addition of Cr(III) into the Cr(VI) solution could decrease the Cr (VI) removal capacities because of their competitive adsorption on CNTs. Under the same experimental conditions, CNTs showed an adsorption capacity of Cr(VI) 6 times as large as the commercial activated carbon at 190 mg•L−1 of the concentration of Cr(VI).
Carbon nanotubes (CNTs) were employed to remove toxic hexavalent chromium ions from aqueous solution. Effects of concentration of hexavalent chromium, solution pH, coexistent trivalent chromium in the solution on the Cr(VI) adsorption were examined. The results show that the adsorption capacity of Cr(VI) on CNTs increased with increase of Cr(VI) concentration, and then reach a plateau between 300~700 mg•L−1 of Cr(VI); the maximum value of 532.215 mg Cr(VI) per g CNTs was achieved at the Cr(VI) concentration of 493.557 mg•L−1, and followed by a decrease at still higher concentration of Cr(VI). The capacity was also significantly affected by the pH value of the solution between 2 and 7, and little change was observed above pH value of 7. Addition of Cr(III) into the Cr(VI) solution could decrease the Cr (VI) removal capacities because of their competitive adsorption on CNTs. Under the same experimental conditions, CNTs showed an adsorption capacity of Cr(VI) 6 times as large as the commercial activated carbon at 190 mg•L−1 of the concentration of Cr(VI).
2006, 22(12): 1547-1550
doi: 10.3866/PKU.WHXB20061222
Abstract:
The size-consistency of the single reference perturbation series corresponding to two Hamiltonian partitions has been studied theoretically using an N hydrogen molecular model. One perturbation series corresponding to the so-called Epstein-Nesbet partition was found to be size consistent up to the fourth order, and another perturbation series (Chen, F.; Davidson, E. R.; Iwata, S. Int. J. Quantum Chem., 2002, 86: 256, see the discussions about Eq.(24)) was found to be not size consistent starting from the second order. However, when its denominator was expanded in a Taylor series, a size consistent perturbation expansion was obtained, for the size inconsistent terms turned out to be cancelled out.
The size-consistency of the single reference perturbation series corresponding to two Hamiltonian partitions has been studied theoretically using an N hydrogen molecular model. One perturbation series corresponding to the so-called Epstein-Nesbet partition was found to be size consistent up to the fourth order, and another perturbation series (Chen, F.; Davidson, E. R.; Iwata, S. Int. J. Quantum Chem., 2002, 86: 256, see the discussions about Eq.(24)) was found to be not size consistent starting from the second order. However, when its denominator was expanded in a Taylor series, a size consistent perturbation expansion was obtained, for the size inconsistent terms turned out to be cancelled out.
2006, 22(12): 1551-1554
doi: 10.3866/PKU.WHXB20061223
Abstract:
Pt-Au/MWCNTs (multi-wall carbon nanotubes) electrocatalyst was prepared by microwave method, and characterized by SEM, TEM, and EDS techniques. The results showed that the Pt-Au nanoparticles were small and well dispersed on the surface of MWCNTs. The electrochemical behaviors were studied by rotating disk electrode (RDE) technique in 0.1 mol•L−1 HClO4 solution. The linear sweeping voltammetry (LSV) results indicated that Pt-Au/MWCNTs with mPt:mAu of 1:2 exhibited the highest catalytic activity for oxygen reduction.
Pt-Au/MWCNTs (multi-wall carbon nanotubes) electrocatalyst was prepared by microwave method, and characterized by SEM, TEM, and EDS techniques. The results showed that the Pt-Au nanoparticles were small and well dispersed on the surface of MWCNTs. The electrochemical behaviors were studied by rotating disk electrode (RDE) technique in 0.1 mol•L−1 HClO4 solution. The linear sweeping voltammetry (LSV) results indicated that Pt-Au/MWCNTs with mPt:mAu of 1:2 exhibited the highest catalytic activity for oxygen reduction.
2006, 22(12): 1555-1559
doi: 10.3866/PKU.WHXB20061224
Abstract:
FeSb2 nanorods, as a potential anode material for lithium-ion batteries, were prepared by solvothermal method in the present work. High-resolution transmission electron microscopy (HRTEM) observations show that the FeSb2 nanorods are 20～40 nm in diameter and 0.2～1.0 μm in length. The charge-discharge measurements and cyclic voltammetry tests reveal that the FeSb2 nanorods exhibit the high initial reversible capacity of 543 mAh•g−1 and an approving cycling stability with 353 mAh•g−1 after 10 cycles. Although the initial coulomb efficiency of the FeSb2 nanorods is only 64%, it is better than that of FeSb2 nano-particles and maintains at 90% after 10 cycles. However, the FeSb2 nanorods could be pulverized and cracked during the cyclic voltammetry test resulting in the failure of the electrode.
FeSb2 nanorods, as a potential anode material for lithium-ion batteries, were prepared by solvothermal method in the present work. High-resolution transmission electron microscopy (HRTEM) observations show that the FeSb2 nanorods are 20～40 nm in diameter and 0.2～1.0 μm in length. The charge-discharge measurements and cyclic voltammetry tests reveal that the FeSb2 nanorods exhibit the high initial reversible capacity of 543 mAh•g−1 and an approving cycling stability with 353 mAh•g−1 after 10 cycles. Although the initial coulomb efficiency of the FeSb2 nanorods is only 64%, it is better than that of FeSb2 nano-particles and maintains at 90% after 10 cycles. However, the FeSb2 nanorods could be pulverized and cracked during the cyclic voltammetry test resulting in the failure of the electrode.
2006, 22(12): 1560-1562
doi: 10.1016/S1872-1508(06)60079-X
Abstract:
The hydrogen bonding interactions between N-methylformamide and primary, secondary, and tertiary alcohols have been studied using the FTIR spectroscopic method. The most likely association complex between alcohol and N-methylformamide is the 1:1 stoichiometric complex formed between the hydroxyl group of alcohol and the carbonyl group of N-methylformamide. The formation constant of the 1:1 complexes has been calculated using the Nash method. It appears that the primary alcohols have larger formation constant compared with the secondary and tertiary alcohols. The results showed that the proton-donating ability of the alcohols decreased in the order: primary>secondary>tertiary, and that the association constant increased with the increase in carbon chain of the alkyl group of alcohols.
The hydrogen bonding interactions between N-methylformamide and primary, secondary, and tertiary alcohols have been studied using the FTIR spectroscopic method. The most likely association complex between alcohol and N-methylformamide is the 1:1 stoichiometric complex formed between the hydroxyl group of alcohol and the carbonyl group of N-methylformamide. The formation constant of the 1:1 complexes has been calculated using the Nash method. It appears that the primary alcohols have larger formation constant compared with the secondary and tertiary alcohols. The results showed that the proton-donating ability of the alcohols decreased in the order: primary>secondary>tertiary, and that the association constant increased with the increase in carbon chain of the alkyl group of alcohols.
2006, 22(12): 1563-1584
Abstract:
2006, 22(12): 1585-1594
Abstract:
