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2008 Volume 24 Issue 1
2008, 24(01):
Abstract:
2008, 24(01): 1-7
doi: 10.1016/S1872-1508(08)60001-7
Abstract:
On the basis of the calculated band structure of EuB6 with a higher accuracy, the optical conductivity and energy-loss function spectra were calculated, and the results were in od agreement with the experiments. All possible interband electronic transitions, the k points in the first Brillouin zone where the transitions took place, and the transition probability were figured out through specific calculations. The wave functions of the initial and final states related to individual transitions were obtained as well. The calculated results were used to analyze, indetail, the correlation between the spectral peaks and the interband electronic transitions. On the basis of this, the experimental spectra were assigned, confirming the reasonable part of the empirical assignments given by Kimura et al. and pointing out the inaccurate part, and also supplying some electronic transitions, which made an important contribution to the spectral peaks, but had not been considered by Kimura et al.
On the basis of the calculated band structure of EuB6 with a higher accuracy, the optical conductivity and energy-loss function spectra were calculated, and the results were in od agreement with the experiments. All possible interband electronic transitions, the k points in the first Brillouin zone where the transitions took place, and the transition probability were figured out through specific calculations. The wave functions of the initial and final states related to individual transitions were obtained as well. The calculated results were used to analyze, indetail, the correlation between the spectral peaks and the interband electronic transitions. On the basis of this, the experimental spectra were assigned, confirming the reasonable part of the empirical assignments given by Kimura et al. and pointing out the inaccurate part, and also supplying some electronic transitions, which made an important contribution to the spectral peaks, but had not been considered by Kimura et al.
2008, 24(01): 8-12
doi: 10.3866/PKU.WHXB20080102
Abstract:
The density functional theory and ab initio molecular dynamic method were applied on the radical initiated chain reaction of unsaturated 1-alkene molecules on H-terminated Si(100)-2×1 surface. The results showed that the crucial step of the surface chain reaction, namely, the abstraction of a H atom from a nearby surface hydride unit, had a somewhat smaller activation energy from the nearest silicon site than that from the next nearest silicon site. Ab initio molecular dynamics showed that the H-abstraction on Si(100)-2×1 surface bound organic group with a carbon-centered radical was very easy to be obtained from the transition state, and a new silicon dangling bond was produced to lead to a surface chain reaction.
The density functional theory and ab initio molecular dynamic method were applied on the radical initiated chain reaction of unsaturated 1-alkene molecules on H-terminated Si(100)-2×1 surface. The results showed that the crucial step of the surface chain reaction, namely, the abstraction of a H atom from a nearby surface hydride unit, had a somewhat smaller activation energy from the nearest silicon site than that from the next nearest silicon site. Ab initio molecular dynamics showed that the H-abstraction on Si(100)-2×1 surface bound organic group with a carbon-centered radical was very easy to be obtained from the transition state, and a new silicon dangling bond was produced to lead to a surface chain reaction.
2008, 24(01): 13-19
doi: 10.1016/S1872-1508(08)60002-9
Abstract:
Activated carbon (AC) samples as electrode materials were prepared by means of simultaneous physical-chemical activation using walnut shells as precursors. The porosity and surface chemistry of the resultant AC samples were studied by the nitrogen adsorption at 77 K and FTIR spectrum. The testing supercapacitors were assembled with resultant carbon electrode and electrolyte of 6 mol·L-1 KOHsolution. Their electrochemical properties were investigated by charge-discharge of constant current, cyclic voltammogram, impedance spectrumand so on. The results showed that the capacitor had low inner resistance, low leakage current, high stability, and capacitance retainability. The specific capacitance of AC increased with increasing BET specific surface area. The specific capacitance of the AC sample with a specific area of 1197 m2·g-1 could be as high as 292 F·g-1. At a discharge current of 80 mA, the corresponding specific energy density, power density, and maximum power of the supercapacitor are 7.3 Wh·kg-1, 770 W·kg-1, and 5.1 W·g-1, respectively.
Activated carbon (AC) samples as electrode materials were prepared by means of simultaneous physical-chemical activation using walnut shells as precursors. The porosity and surface chemistry of the resultant AC samples were studied by the nitrogen adsorption at 77 K and FTIR spectrum. The testing supercapacitors were assembled with resultant carbon electrode and electrolyte of 6 mol·L-1 KOHsolution. Their electrochemical properties were investigated by charge-discharge of constant current, cyclic voltammogram, impedance spectrumand so on. The results showed that the capacitor had low inner resistance, low leakage current, high stability, and capacitance retainability. The specific capacitance of AC increased with increasing BET specific surface area. The specific capacitance of the AC sample with a specific area of 1197 m2·g-1 could be as high as 292 F·g-1. At a discharge current of 80 mA, the corresponding specific energy density, power density, and maximum power of the supercapacitor are 7.3 Wh·kg-1, 770 W·kg-1, and 5.1 W·g-1, respectively.
2008, 24(01): 20-24
doi: 10.3866/PKU.WHXB20080104
Abstract:
The influence of electromagnetic fields on conductivity of aqueousNaCl solution at microwave frequency was studied. The Langvin equation was performed by using an asymmetrical double-well and periodic potential. All runs were started from describing the average hydrogen-bond of cluster configuration in aqueous NaCl solution under the constant temperature conditions. The relation between the conductivity and the probability of hydrogen bonding formation was established by using Bertolini function. When the intensity of microwaves was above 10 kV·m-1, the calculation indicated that microwave energies were partly transformed to intermolecular energies of cluster, which made conductivity interrelated with intensity of microwave. The results agreed well with experiments. The strongly nonlinear change was cate rized as one of microwave nonthermal effects.
The influence of electromagnetic fields on conductivity of aqueousNaCl solution at microwave frequency was studied. The Langvin equation was performed by using an asymmetrical double-well and periodic potential. All runs were started from describing the average hydrogen-bond of cluster configuration in aqueous NaCl solution under the constant temperature conditions. The relation between the conductivity and the probability of hydrogen bonding formation was established by using Bertolini function. When the intensity of microwaves was above 10 kV·m-1, the calculation indicated that microwave energies were partly transformed to intermolecular energies of cluster, which made conductivity interrelated with intensity of microwave. The results agreed well with experiments. The strongly nonlinear change was cate rized as one of microwave nonthermal effects.
2008, 24(01): 25-31
doi: 10.3866/PKU.WHXB20080105
Abstract:
Molecularly imprinted polymer (MIP) against dropropizine was synthesized using dropropizine as template, α-methyl acrylic acid as functional monomer, and trimethylolpropane trimethacrylate as crosslinking agent. Its application for separation and enrichment in solid phase extraction was investigated. It was found that, the imprinted polymer exhibited satisfactory performance in recognition and enrichment towards template, but it was not the case with non-imprinted polymer. The retention and separation of imprinted molecule with its structural analogues were also studied. The selectively separation was proved to be successful. The mechanism of imprinted recognition was also discussed here. With the help of PM3 semi-empirical method, the possible MIP system was simulated and compared with experimental results.
Molecularly imprinted polymer (MIP) against dropropizine was synthesized using dropropizine as template, α-methyl acrylic acid as functional monomer, and trimethylolpropane trimethacrylate as crosslinking agent. Its application for separation and enrichment in solid phase extraction was investigated. It was found that, the imprinted polymer exhibited satisfactory performance in recognition and enrichment towards template, but it was not the case with non-imprinted polymer. The retention and separation of imprinted molecule with its structural analogues were also studied. The selectively separation was proved to be successful. The mechanism of imprinted recognition was also discussed here. With the help of PM3 semi-empirical method, the possible MIP system was simulated and compared with experimental results.
2008, 24(01): 32-36
doi: 10.3866/PKU.WHXB20080106
Abstract:
Using B3LYP functional with 6-311+G** basis set, the structures, stabilities and vibrational frequencies of a kind of novel diboron organic compound C9B2H6 containing a planar tetracoordinated carbon (ptC)were investigated. The results showed that there was a significant relationship between the stability and the positions of the two boron atoms, and boron atoms played a σ-donating and π-accepting role. The most stable structure was isomer (1,5) with C2v symmetry, in which the two boron atoms connected with the ptC atom and located on a same six-membered ring. Analysis of occupied πorbitals of isomer (1,5) indicated that it satisfied 4n+2 rule (10π electrons). And the calculated NICS (nucleus-independent chemical shift) values of isomer (1,5) showed that the high aromaticity located at the two three-membered rings, rather than the six-membered rings.
Using B3LYP functional with 6-311+G** basis set, the structures, stabilities and vibrational frequencies of a kind of novel diboron organic compound C9B2H6 containing a planar tetracoordinated carbon (ptC)were investigated. The results showed that there was a significant relationship between the stability and the positions of the two boron atoms, and boron atoms played a σ-donating and π-accepting role. The most stable structure was isomer (1,5) with C2v symmetry, in which the two boron atoms connected with the ptC atom and located on a same six-membered ring. Analysis of occupied πorbitals of isomer (1,5) indicated that it satisfied 4n+2 rule (10π electrons). And the calculated NICS (nucleus-independent chemical shift) values of isomer (1,5) showed that the high aromaticity located at the two three-membered rings, rather than the six-membered rings.
2008, 24(01): 37-40
doi: 10.1016/S1872-1508(08)60003-0
Abstract:
Theoretical study on the geometries and electronic properties of new conjugated compounds based on thiophene and phenylene was carried out. The theoretical ground-state geometries and electronic structures of the studied molecules were obtained using the density functional theory (DFT) method at B3LYP level with 6-31G(d) basis set. The electronic properties were determined by ZINDO/s, CIS/3-21G(d), and TD//B3LYP/3-21G(d) calculations performed on the B3LYP/6-31(d) optimized geometries. The effects of the ring structure and the substituents on the geometries and electronic properties of these materials were discussed. The results of this study indicate how the electronic properties can be tuned by the backbone ring or side group and suggest these compounds as od candidates for opto-electronic applications.
Theoretical study on the geometries and electronic properties of new conjugated compounds based on thiophene and phenylene was carried out. The theoretical ground-state geometries and electronic structures of the studied molecules were obtained using the density functional theory (DFT) method at B3LYP level with 6-31G(d) basis set. The electronic properties were determined by ZINDO/s, CIS/3-21G(d), and TD//B3LYP/3-21G(d) calculations performed on the B3LYP/6-31(d) optimized geometries. The effects of the ring structure and the substituents on the geometries and electronic properties of these materials were discussed. The results of this study indicate how the electronic properties can be tuned by the backbone ring or side group and suggest these compounds as od candidates for opto-electronic applications.
2008, 24(01): 41-46
doi: 10.1016/S1872-1508(08)60004-2
Abstract:
Sound velocity, density, and viscosity values were measured at 303Kin four binary systems of benzene + 1-, 2-, tert-, or iso-butanol. From these data, acoustical parameters, such as adiabatic compressibility, free length, free volume, and internal pressure were estimated using the standard relations. The results are interpreted in terms of molecular interaction between the components of the mixtures. Observed excess value in all the mixture indicates that the molecular symmetry existing in the system is highly disturbed by the nonpolar benzene molecules. Interaction energy terms of the statistical mixing are also verified for these binary systems and the dipole-dipole interactions are found to be predominantly present and are sharply affected by the isomeric forms of butanol.
Sound velocity, density, and viscosity values were measured at 303Kin four binary systems of benzene + 1-, 2-, tert-, or iso-butanol. From these data, acoustical parameters, such as adiabatic compressibility, free length, free volume, and internal pressure were estimated using the standard relations. The results are interpreted in terms of molecular interaction between the components of the mixtures. Observed excess value in all the mixture indicates that the molecular symmetry existing in the system is highly disturbed by the nonpolar benzene molecules. Interaction energy terms of the statistical mixing are also verified for these binary systems and the dipole-dipole interactions are found to be predominantly present and are sharply affected by the isomeric forms of butanol.
2008, 24(01): 47-54
doi: 10.1016/S1872-1508(08)60005-4
Abstract:
The densities (ρ), ultrasonic speeds (v), and refractive indices (n) of binary mixtures of styrene (STY) with m-, o-, or p-xylene, including those of their pure liquids, were measured over the entire composition range at the temperatures 298.15, 303.15, 308.15, and 313.15 K. The excess volumes (VE), deviations in isentropic compressibilities (⊿ks), acoustic impedances (⊿Z), and refractive indices (⊿n) were calculated from the experimental data . Partial molar volumes (V0φ,2) and partial molar isentropic compressibilities (K0φ,2) of xylenes in styrene have also been calculated. The derived functions, namely, VE, ⊿ks, ⊿Z, ⊿n, V0φ,2 , and K0φ,2 were used to have a better understanding of the intermolecular interactions occurring between the component molecules of the present liquid mixtures. The variations of these parameters suggest that the interactions between styrene and o-, m-, or p-xylene molecules follow the sequences: p-xylene>o-xylene>m-xylene. Apart from using density data for the calculation of VE, excess molar volumes were also estimated using refractive index data. Furthermore, several refractive index mixing rules have been used to estimate the refractive indices of the studied liquid mixtures theoretically. Overall, the computed and measured data were interpreted in terms of interactions between the mixing components.
The densities (ρ), ultrasonic speeds (v), and refractive indices (n) of binary mixtures of styrene (STY) with m-, o-, or p-xylene, including those of their pure liquids, were measured over the entire composition range at the temperatures 298.15, 303.15, 308.15, and 313.15 K. The excess volumes (VE), deviations in isentropic compressibilities (⊿ks), acoustic impedances (⊿Z), and refractive indices (⊿n) were calculated from the experimental data . Partial molar volumes (V0φ,2) and partial molar isentropic compressibilities (K0φ,2) of xylenes in styrene have also been calculated. The derived functions, namely, VE, ⊿ks, ⊿Z, ⊿n, V0φ,2 , and K0φ,2 were used to have a better understanding of the intermolecular interactions occurring between the component molecules of the present liquid mixtures. The variations of these parameters suggest that the interactions between styrene and o-, m-, or p-xylene molecules follow the sequences: p-xylene>o-xylene>m-xylene. Apart from using density data for the calculation of VE, excess molar volumes were also estimated using refractive index data. Furthermore, several refractive index mixing rules have been used to estimate the refractive indices of the studied liquid mixtures theoretically. Overall, the computed and measured data were interpreted in terms of interactions between the mixing components.
2008, 24(01): 55-60
doi: 10.1016/S1872-1508(08)60006-6
Abstract:
First-principle pseudopotential plane wave calculations and the Nudged Elastic Band method based on the density functional theory (DFT) were used in this article to study the dissociation of molecular hydrogen on a Mg(0001) surface and the subsequent diffusion of atomic hydrogen into the magnesiumsubstrate. First, the dissociation pathway of H2 and the relative barrier were investigated. It was shown that physical adsorption rather than chemisorption of molecular hydrogen was observed in the calculation of the dissociation process of molecular hydrogen. Also, the diffusion process of atomic hydrogen on Mg(0001) was presented. The surface effect, which affected the diffusion of hydrogen obviously, was observed. Finally, comparing the values of the activation energies for the steps of dissociation, diffusion, and desorption, our calculation further showed that the dissociation of H2 and desorption of hydride were the rate-limiting steps.
First-principle pseudopotential plane wave calculations and the Nudged Elastic Band method based on the density functional theory (DFT) were used in this article to study the dissociation of molecular hydrogen on a Mg(0001) surface and the subsequent diffusion of atomic hydrogen into the magnesiumsubstrate. First, the dissociation pathway of H2 and the relative barrier were investigated. It was shown that physical adsorption rather than chemisorption of molecular hydrogen was observed in the calculation of the dissociation process of molecular hydrogen. Also, the diffusion process of atomic hydrogen on Mg(0001) was presented. The surface effect, which affected the diffusion of hydrogen obviously, was observed. Finally, comparing the values of the activation energies for the steps of dissociation, diffusion, and desorption, our calculation further showed that the dissociation of H2 and desorption of hydride were the rate-limiting steps.
2008, 24(01): 61-66
doi: 10.3866/PKU.WHXB20080111
Abstract:
The electronic structures of pure and N-doped wurtzite ZnO were calculated using first-principle ultrasoft pseudo-potential approach of the plane wave based upon the density functional theory, and the structure change, bandstructure, density of state, the difference charge density, and the influence of p-type ZnO by H atom and N2 molecule were studied.
The electronic structures of pure and N-doped wurtzite ZnO were calculated using first-principle ultrasoft pseudo-potential approach of the plane wave based upon the density functional theory, and the structure change, bandstructure, density of state, the difference charge density, and the influence of p-type ZnO by H atom and N2 molecule were studied.
2008, 24(01): 67-73
doi: 10.3866/PKU.WHXB20080112
Abstract:
Twenty-three possible steady isomers of N5H5 were optimized at 6-311++G** level using the density functional B3LYP method, and tautomerisms between them were discussed. To discuss the possibility of N5H5 isomers as candiate of energetic materials, energies and heats of formation were calculated by the G3B3 method. The results indicated that chain isomers were the most stable isomers and the isomer containing a tetrazetinyl group was the most unstable isomer. The existence of N=N double bonds were beneficial to their stabilities. The formation heats of all conformers were positive, and isomer E1 had the highest formation heat. In addition, at 6-311++G** level by the B3LYP method the molar volume of N5H5 was estimated, and from the density formula: ρ=MT/Vmol, we could know that the density of E1 was the largest.
Twenty-three possible steady isomers of N5H5 were optimized at 6-311++G** level using the density functional B3LYP method, and tautomerisms between them were discussed. To discuss the possibility of N5H5 isomers as candiate of energetic materials, energies and heats of formation were calculated by the G3B3 method. The results indicated that chain isomers were the most stable isomers and the isomer containing a tetrazetinyl group was the most unstable isomer. The existence of N=N double bonds were beneficial to their stabilities. The formation heats of all conformers were positive, and isomer E1 had the highest formation heat. In addition, at 6-311++G** level by the B3LYP method the molar volume of N5H5 was estimated, and from the density formula: ρ=MT/Vmol, we could know that the density of E1 was the largest.
2008, 24(01): 74-78
doi: 10.3866/PKU.WHXB20080113
Abstract:
In order to study the homogeneous nucleation temperature of intracellular solution during cooling, an iteration method has been presented to calculate nucleation temperature of system with changeable concentrations. Glycerol was chosen for a cryoprotective agent (CPA) during cooling of mouse oocytes. The equilibriummelting points of intracellular solutions were calculated using an empirical equation determined by the phase diagram of glycerol-sodium chloride-water ternary system. The widely used cell dehydration equation was numerically solved and the concentrations of intracellular solutions as a function of time were calculated. The assumption that the homogeneous nucleation temperature depression was directly proporlianal to the equilibrium melting point depression has been used. The homogeneous nucleation temperatures of intracellular solutions as a function of concentrations were then calculated using the new proposed method coupling with the equilibrium melting points and the concentrations of intracellular solutions. It was found that for glycerol-sodium chloride-water ternary system, depression of the homogeneous nucleation temperature and depression of the equilibrium melting point followed the relation: ⊿Th=1.17⊿Tm . The result proved that the assumption was reasonable and showed that homogeneous nucleation temperatures of aqueous solutions depended on solutes. This research can provide convincing data to support the further study of intracellular ice formation and growth during cooling.
In order to study the homogeneous nucleation temperature of intracellular solution during cooling, an iteration method has been presented to calculate nucleation temperature of system with changeable concentrations. Glycerol was chosen for a cryoprotective agent (CPA) during cooling of mouse oocytes. The equilibriummelting points of intracellular solutions were calculated using an empirical equation determined by the phase diagram of glycerol-sodium chloride-water ternary system. The widely used cell dehydration equation was numerically solved and the concentrations of intracellular solutions as a function of time were calculated. The assumption that the homogeneous nucleation temperature depression was directly proporlianal to the equilibrium melting point depression has been used. The homogeneous nucleation temperatures of intracellular solutions as a function of concentrations were then calculated using the new proposed method coupling with the equilibrium melting points and the concentrations of intracellular solutions. It was found that for glycerol-sodium chloride-water ternary system, depression of the homogeneous nucleation temperature and depression of the equilibrium melting point followed the relation: ⊿Th=1.17⊿Tm . The result proved that the assumption was reasonable and showed that homogeneous nucleation temperatures of aqueous solutions depended on solutes. This research can provide convincing data to support the further study of intracellular ice formation and growth during cooling.
2008, 24(01): 79-84
doi: 10.3866/PKU.WHXB20080114
Abstract:
Nanocrystalline TiO2 electrode as well as Zn(II) tetracarboxy phthalocyanine (ZnPcTc) doped mesoporous nanocrystalline TiO2 electrode were fabricated. Electrochemical impedance spectrum (EIS) measurement was used to investigate the electron transfer characters in electrodes and the interface characters. Arcs of EIS and corresponding electrode processes were discussed. Dynamic parameters of the electrodes were evaluated through proper calculation model. On the basis of experimental data, we confirmed that the doping of ZnPcTc into the pure mesoporous nanocrystalline TiO2 electrode could largely decrease the electron transfer resistance, and increase the electrode-electrolyte interface capacity which was benefit to develop the performance of dye-sensitized solar cell (DSSC).
Nanocrystalline TiO2 electrode as well as Zn(II) tetracarboxy phthalocyanine (ZnPcTc) doped mesoporous nanocrystalline TiO2 electrode were fabricated. Electrochemical impedance spectrum (EIS) measurement was used to investigate the electron transfer characters in electrodes and the interface characters. Arcs of EIS and corresponding electrode processes were discussed. Dynamic parameters of the electrodes were evaluated through proper calculation model. On the basis of experimental data, we confirmed that the doping of ZnPcTc into the pure mesoporous nanocrystalline TiO2 electrode could largely decrease the electron transfer resistance, and increase the electrode-electrolyte interface capacity which was benefit to develop the performance of dye-sensitized solar cell (DSSC).
2008, 24(01): 85-90
doi: 10.3866/PKU.WHXB20080115
Abstract:
A filtering method based on empirical mode decomposition (EMD) for coulostatically-induced transients (CITs) was presented. The effect of EMD filtering was evaluated from different simulation systems. To boost the applicable solution for EMD filtering and reduce the subjectivity of filtering, discussions of the simulating noises were mainly focused on white noise, high frequency noise, 50 Hz noise from commercial power and blend of above-mentioned noises. To illustrate the most importance of EMD filtering for the odness of fit of CIS, one real corrosion system involving multi-time constant was simultaneously investigated by electrochemical impedance spectrum (EIS) and coulostatically-induced spectrum (CIS). The results reported here demonstrate that EMD de-noising is applicable for CITs. The proposed method shows od performance of de-noising and is an alternative de-noising method for the CITs analysis. CIS with EMD filtering are in od agreement with EIS. For practical application of EMD, removal of the first two items of intrinsic mode function (IMF) and 50 Hz element in forth IMF will be generally satisfactory for CIS analysis.
A filtering method based on empirical mode decomposition (EMD) for coulostatically-induced transients (CITs) was presented. The effect of EMD filtering was evaluated from different simulation systems. To boost the applicable solution for EMD filtering and reduce the subjectivity of filtering, discussions of the simulating noises were mainly focused on white noise, high frequency noise, 50 Hz noise from commercial power and blend of above-mentioned noises. To illustrate the most importance of EMD filtering for the odness of fit of CIS, one real corrosion system involving multi-time constant was simultaneously investigated by electrochemical impedance spectrum (EIS) and coulostatically-induced spectrum (CIS). The results reported here demonstrate that EMD de-noising is applicable for CITs. The proposed method shows od performance of de-noising and is an alternative de-noising method for the CITs analysis. CIS with EMD filtering are in od agreement with EIS. For practical application of EMD, removal of the first two items of intrinsic mode function (IMF) and 50 Hz element in forth IMF will be generally satisfactory for CIS analysis.
2008, 24(01): 91-96
doi: 10.3866/PKU.WHXB20080116
Abstract:
The dielectric constants (D) for aqueous solutions of D-(-)-fructose, D-(+)-glucose, D-(+)-galactose, D-(+)-xylose, and D-(-)-ribose were measured at 278.15, 283.15, 288.15, 293.15, 298.15, 303.15, 308.15, and 313.15 K. Molalities of saccharides are at 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 mol·kg -1. The results indicated that the logarithmic values of dielectric constants for these saccharide-water solutions decreased with increasing molalities of saccharides and decreased also as the temperature rising. At given molalities, the relationship between dielectric constants and temperatures can be expressed by lgD=A1-B1(T-298.15) for fructose-water, glucose-water, galactose-water, and xylose-water solutions, and by lgD=A2-B2(T-298.15)+C2(T-298.15)2 for ribose-water solution. At given temperatures, dependence of the dielectric constants on the mole fraction (x) can be described by lg(D/D0)=-B3x for all five saccharide-water solutions. At given temperatures and molalities, the dielectric constants are mostly in the order: water>galactose-water>fructose-water>glucose-water≥xylose-water (there is not the order for ribose).
The dielectric constants (D) for aqueous solutions of D-(-)-fructose, D-(+)-glucose, D-(+)-galactose, D-(+)-xylose, and D-(-)-ribose were measured at 278.15, 283.15, 288.15, 293.15, 298.15, 303.15, 308.15, and 313.15 K. Molalities of saccharides are at 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 mol·kg -1. The results indicated that the logarithmic values of dielectric constants for these saccharide-water solutions decreased with increasing molalities of saccharides and decreased also as the temperature rising. At given molalities, the relationship between dielectric constants and temperatures can be expressed by lgD=A1-B1(T-298.15) for fructose-water, glucose-water, galactose-water, and xylose-water solutions, and by lgD=A2-B2(T-298.15)+C2(T-298.15)2 for ribose-water solution. At given temperatures, dependence of the dielectric constants on the mole fraction (x) can be described by lg(D/D0)=-B3x for all five saccharide-water solutions. At given temperatures and molalities, the dielectric constants are mostly in the order: water>galactose-water>fructose-water>glucose-water≥xylose-water (there is not the order for ribose).
2008, 24(01): 97-102
doi: 10.3866/PKU.WHXB20080117
Abstract:
Coating carbon nanotube surface with TiO2 as anatase was performed by sol-gel method using Ti(OBu)4. The morphological structure of the photocatalyst particles was characterized by XRD and TEM. Absorbency was analyzed by the UV-Vis diffuse reflection spectra of TiO2 and CNT-TiO2 photocatalysts. The photocatalytic activities of the materials heat-treated at different reaction temperatures have been tested on decomposable substrate methyl orange solution under UV-light illumination. The results showed that the nanocomposites had excellent photocatalytic ability. When the wavelength was between 200 -800 nm, CNT-TiO2 nanocomposites had od absorbency. TEM micrographs showed that TiO2 was closely coated on the surface of carbon nanotubes. The best heat treatment temperature of CNT-TiO2 nanocomposites was 450 ℃. The crystal formof TiO2 was anatase and the diameter of crystal was 7.3 nm. The photodegradation rate of CNT-TiO2 nanocomposites was better than that of pure TiO2 under sunlight.
Coating carbon nanotube surface with TiO2 as anatase was performed by sol-gel method using Ti(OBu)4. The morphological structure of the photocatalyst particles was characterized by XRD and TEM. Absorbency was analyzed by the UV-Vis diffuse reflection spectra of TiO2 and CNT-TiO2 photocatalysts. The photocatalytic activities of the materials heat-treated at different reaction temperatures have been tested on decomposable substrate methyl orange solution under UV-light illumination. The results showed that the nanocomposites had excellent photocatalytic ability. When the wavelength was between 200 -800 nm, CNT-TiO2 nanocomposites had od absorbency. TEM micrographs showed that TiO2 was closely coated on the surface of carbon nanotubes. The best heat treatment temperature of CNT-TiO2 nanocomposites was 450 ℃. The crystal formof TiO2 was anatase and the diameter of crystal was 7.3 nm. The photodegradation rate of CNT-TiO2 nanocomposites was better than that of pure TiO2 under sunlight.
2008, 24(01): 103-108
doi: 10.3866/PKU.WHXB20080118
Abstract:
The electrochemical behaviors of ferrocene (Fc)-containing ionic liquid [BMIm]BF4 were investigated in a system, which used ferrocene-containing ionic liquid as electrolyte, porous carbon as electrode materials. The cyclic voltammetry and constant current charge-discharge results indicated that redox reaction of Fc happened in the porous carbon, and which was a diffusion-controlled, highly reversible redox reaction. The average specific capacitance of 0.01 mol·L-1 [BMIm]BF4/Fc at a current density of 1 mA·cm-2 was 163 F·g-1, 63% higher than that of pure [BMIm]BF4. The increase of average specific capacitance indicates that the faradic pseudocapacitance associated with Fc species in the redox reactions has a considerable contribution to the total capacitance of ECs (electrochemical capacitors). At the same time, it shows a power density of 400 W·kg-1 as well as energy density of 37.5 Wh·kg-1 approaching the level of a practical battery.
The electrochemical behaviors of ferrocene (Fc)-containing ionic liquid [BMIm]BF4 were investigated in a system, which used ferrocene-containing ionic liquid as electrolyte, porous carbon as electrode materials. The cyclic voltammetry and constant current charge-discharge results indicated that redox reaction of Fc happened in the porous carbon, and which was a diffusion-controlled, highly reversible redox reaction. The average specific capacitance of 0.01 mol·L-1 [BMIm]BF4/Fc at a current density of 1 mA·cm-2 was 163 F·g-1, 63% higher than that of pure [BMIm]BF4. The increase of average specific capacitance indicates that the faradic pseudocapacitance associated with Fc species in the redox reactions has a considerable contribution to the total capacitance of ECs (electrochemical capacitors). At the same time, it shows a power density of 400 W·kg-1 as well as energy density of 37.5 Wh·kg-1 approaching the level of a practical battery.
2008, 24(01): 109-114
doi: 10.3866/PKU.WHXB20080119
Abstract:
Algal eucheuma striatumsulfated polysaccharide (ESPS) collected from Indonesian sea was degraded by hydrogen peroxide (H2O2).After degradation the averagemolecularweight of ESPSwas decreased from1410000 to 4819, and the content of sulfate (OSO2-3) was lightly decreased from 16.0%to 15.2% (w). The effect of ESPS before and after degradation on the growth of calcium oxalate crystal was investigated in vitro by using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. Compared with the undegraded ESPS, the size and number of calcium oxalatemonohydrate (COM) crystal induced by the degraded ESPS weremuch smaller.With increasing the concentration of degraded ESPS from0.006 g·L-1 to 0.010 and 0.050 g·L-1, the average size of COMcrystals decreased from 11.5 μm×2.9 μm to 9.2 μm×2.9 μm and 6.0 μm×2.5 μm, respectively, and the number of COM crystals decreased from 3357 per mm2 to 2298 and 1532 per mm2, and the diffraction peak intensity ratio of the (101) plane to (010) plane of COM crystals (I(101)/I(020)) increased from5.54 to 16.2 and 20.0. The result showed that the inhibition efficiency of the degraded ESPS with a low-molecular-weight on the nucleation and growth of CaOxa crystal was obviously superior to that of the undegraded ESPS.
Algal eucheuma striatumsulfated polysaccharide (ESPS) collected from Indonesian sea was degraded by hydrogen peroxide (H2O2).After degradation the averagemolecularweight of ESPSwas decreased from1410000 to 4819, and the content of sulfate (OSO2-3) was lightly decreased from 16.0%to 15.2% (w). The effect of ESPS before and after degradation on the growth of calcium oxalate crystal was investigated in vitro by using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. Compared with the undegraded ESPS, the size and number of calcium oxalatemonohydrate (COM) crystal induced by the degraded ESPS weremuch smaller.With increasing the concentration of degraded ESPS from0.006 g·L-1 to 0.010 and 0.050 g·L-1, the average size of COMcrystals decreased from 11.5 μm×2.9 μm to 9.2 μm×2.9 μm and 6.0 μm×2.5 μm, respectively, and the number of COM crystals decreased from 3357 per mm2 to 2298 and 1532 per mm2, and the diffraction peak intensity ratio of the (101) plane to (010) plane of COM crystals (I(101)/I(020)) increased from5.54 to 16.2 and 20.0. The result showed that the inhibition efficiency of the degraded ESPS with a low-molecular-weight on the nucleation and growth of CaOxa crystal was obviously superior to that of the undegraded ESPS.
2008, 24(01): 115-120
doi: 10.3866/PKU.WHXB20080120
Abstract:
The anticorrosion and inhibiting mechanism for the self-assembled monolayers (SAMs) of 3-amino-1,2,4-triazole (ATA) on the surface of brass had been investigated by electrochemical method, as well as its adsorption behavior. The results indicated that ATA was liable to interact with brass forming SAMs on the surface of brass. The SAMs changed the structure of the electric-double layer. The SAMs restrained the process of anodic oxidation and had well anticorrosion effect. It was in od agreement with the results by EIS and polarization curve methods. The results from electrochemical measurements indicated that the corrosion resistance for brass electrode was improved by the ATASAMs. Adsorption of the ATASAMs was found to followthe Langmuir’s adsorption isotherm, and the adsorption mechanismwas typical chemisorption.
The anticorrosion and inhibiting mechanism for the self-assembled monolayers (SAMs) of 3-amino-1,2,4-triazole (ATA) on the surface of brass had been investigated by electrochemical method, as well as its adsorption behavior. The results indicated that ATA was liable to interact with brass forming SAMs on the surface of brass. The SAMs changed the structure of the electric-double layer. The SAMs restrained the process of anodic oxidation and had well anticorrosion effect. It was in od agreement with the results by EIS and polarization curve methods. The results from electrochemical measurements indicated that the corrosion resistance for brass electrode was improved by the ATASAMs. Adsorption of the ATASAMs was found to followthe Langmuir’s adsorption isotherm, and the adsorption mechanismwas typical chemisorption.
2008, 24(01): 121-126
doi: 10.3866/PKU.WHXB20080121
Abstract:
Pt nano clusters were produced by the laser vaporization of bulk metal and were deposited on the surface of carbon nanotubes (CNTs) to produce carbon nanotubes supported Pt catalyst (Pt/CNTs). Transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) showed that Pt nanoparticles had a narrow size distribution and the Pt content was connected with the preparation condition. X-ray diffraction (XRD) analysis showed that the Pt/CNTs had crystalloid structure which related to the catalytic performance. X-ray photoelectron spectroscopy (XPS) was used to measure core level binding energy shifts of Pt 4f7/2 and Pt 4f5/2. Its catalytic performance was evaluated by liquid-phase hydrogenation of o-chloronitrobenzene (o-CNB). The results showed that the Pt/CNTs catalyst exhibited higher conversion and selectivity. The most favorable preparation condition was obtained as follows: T=25 ℃, V=250 V, and p=300 Pa. It was found that the highest conversion of o-chloronitrobenzene could reach 99.7% while the selectivity to o-chloroaniline could reach 98.2% in alcohol at 60 ℃ under 1.0 MPa of hydrogen, showing od potential application.
Pt nano clusters were produced by the laser vaporization of bulk metal and were deposited on the surface of carbon nanotubes (CNTs) to produce carbon nanotubes supported Pt catalyst (Pt/CNTs). Transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) showed that Pt nanoparticles had a narrow size distribution and the Pt content was connected with the preparation condition. X-ray diffraction (XRD) analysis showed that the Pt/CNTs had crystalloid structure which related to the catalytic performance. X-ray photoelectron spectroscopy (XPS) was used to measure core level binding energy shifts of Pt 4f7/2 and Pt 4f5/2. Its catalytic performance was evaluated by liquid-phase hydrogenation of o-chloronitrobenzene (o-CNB). The results showed that the Pt/CNTs catalyst exhibited higher conversion and selectivity. The most favorable preparation condition was obtained as follows: T=25 ℃, V=250 V, and p=300 Pa. It was found that the highest conversion of o-chloronitrobenzene could reach 99.7% while the selectivity to o-chloroaniline could reach 98.2% in alcohol at 60 ℃ under 1.0 MPa of hydrogen, showing od potential application.
2008, 24(01): 127-132
doi: 10.3866/PKU.WHXB20080122
Abstract:
First-principle calculations were performed on the geometric structure and adsorption properties of CO monolayer on Cu(001) surface by using USPP and FLAPWmethods. Relaxed geometry structure suggested that top was the most stable site. The distance between C and Cu atoms was about 0.1868 nm on top site, compared with 0.1975 nm on bridge sites and 0.2231 nm on hollow sites. The bond length of CO molecules on top, bridge and hollow sites were estimated to be 0.1154, 0.1165 and 0.1175 nm, respectively. From the structure of adsorbed surface, it was found that the bond length of COwas enlarged by the nearest copper atoms. PDOS (partial orbital of density of state) of COshowed that the interaction between adsorbent and adsorbate was mainly induced by the hybridization of molecule 5σ orbital and copper 3d orbital. The hybridization was mainly induced by the symmetry of orbital and sites. The result of orbital charge indicated that the s orbital charge of carbons reduced and the p orbital charge of carbons increased, when CO molecules were adsorbed on the top sites. At last, the work functions for three adsorbed surfaces were investigated, which were calculated to be 5.51 eV on top, 6.00 eV on bridge, and 6.23 eV on hollow, in contrast to 4.57 eV in clean surface. The work function and DOS indicated that CO layer was insulating.
First-principle calculations were performed on the geometric structure and adsorption properties of CO monolayer on Cu(001) surface by using USPP and FLAPWmethods. Relaxed geometry structure suggested that top was the most stable site. The distance between C and Cu atoms was about 0.1868 nm on top site, compared with 0.1975 nm on bridge sites and 0.2231 nm on hollow sites. The bond length of CO molecules on top, bridge and hollow sites were estimated to be 0.1154, 0.1165 and 0.1175 nm, respectively. From the structure of adsorbed surface, it was found that the bond length of COwas enlarged by the nearest copper atoms. PDOS (partial orbital of density of state) of COshowed that the interaction between adsorbent and adsorbate was mainly induced by the hybridization of molecule 5σ orbital and copper 3d orbital. The hybridization was mainly induced by the symmetry of orbital and sites. The result of orbital charge indicated that the s orbital charge of carbons reduced and the p orbital charge of carbons increased, when CO molecules were adsorbed on the top sites. At last, the work functions for three adsorbed surfaces were investigated, which were calculated to be 5.51 eV on top, 6.00 eV on bridge, and 6.23 eV on hollow, in contrast to 4.57 eV in clean surface. The work function and DOS indicated that CO layer was insulating.
2008, 24(01): 133-137
doi: 10.3866/PKU.WHXB20080123
Abstract:
Two light emissive organic light-emitting diodes (OLEDs) of high performance were prepared by vacuum thermal evaporation using two kinds of silole derivatives 1,2-bis (1-methyl-2,3,4,5-tetraphenyl-1H-silole-1-yl)ethane (BMPSiE) and 1,1’-dimethyl-3,3’,4,4’-tetraphenyl-2,2’,5,5’-tetra(thiophen-2-yl)-1,1’-bi(1H-silole) (BMPThSi) as emitting materials, N, N’-diphenyl-N,N’-bis(3-methylphenyl)-1,1’-biphenyl-4,4’-diamine(NPB) and tris(8-hydroxyquinolinolato) aluminum(Alq3) as hole transporting layer (HTL) and electron transporting layer (ETL), respectively. The luminance-voltage and current density-voltage characteristics of devices were investigated, and the difference between their performances was discussed. The results demonstrate that at a bias voltage of 20 V, the device consisting of novel emissive material BMPSiE had a maximum luminance of 9991.9 cd·m-2 and the device of BMPThSi had a maximumluminance of 15261.5 cd·m-2. The peaks of electroluminescence (EL) spectra were located at 483 and 495 nm, respectively, which were in od accordance with the photoluminescent characteristics. The Commissions International d’Eclairage (CIE) coordinates were located at (0.202, 0.337) and (0.246, 0.419), which were independent on the variation of forward bias.
Two light emissive organic light-emitting diodes (OLEDs) of high performance were prepared by vacuum thermal evaporation using two kinds of silole derivatives 1,2-bis (1-methyl-2,3,4,5-tetraphenyl-1H-silole-1-yl)ethane (BMPSiE) and 1,1’-dimethyl-3,3’,4,4’-tetraphenyl-2,2’,5,5’-tetra(thiophen-2-yl)-1,1’-bi(1H-silole) (BMPThSi) as emitting materials, N, N’-diphenyl-N,N’-bis(3-methylphenyl)-1,1’-biphenyl-4,4’-diamine(NPB) and tris(8-hydroxyquinolinolato) aluminum(Alq3) as hole transporting layer (HTL) and electron transporting layer (ETL), respectively. The luminance-voltage and current density-voltage characteristics of devices were investigated, and the difference between their performances was discussed. The results demonstrate that at a bias voltage of 20 V, the device consisting of novel emissive material BMPSiE had a maximum luminance of 9991.9 cd·m-2 and the device of BMPThSi had a maximumluminance of 15261.5 cd·m-2. The peaks of electroluminescence (EL) spectra were located at 483 and 495 nm, respectively, which were in od accordance with the photoluminescent characteristics. The Commissions International d’Eclairage (CIE) coordinates were located at (0.202, 0.337) and (0.246, 0.419), which were independent on the variation of forward bias.
2008, 24(01): 138-142
doi: 10.3866/PKU.WHXB20080124
Abstract:
Laboratory investigations (polarization and electrochemical impedance spectroscopy) were performed in order to assess the effectiveness and the inhibition mechanism of new synthesized imidazoline derivative inhibitor to prevent corrosion of steel in saltwater saturated with carbon dioxide. The inhibitor efficiencies and thermodynamic parameters were calculated. The inhibition efficiency increased with the increase in inhibitor concentration, but increased then decreased with temperature. It was seen that the adsorption of imidazoline derivative on steel fitted the Langmuir isothermequation. The electrochemical results have also been supplemented by quantumchemical analysis.
Laboratory investigations (polarization and electrochemical impedance spectroscopy) were performed in order to assess the effectiveness and the inhibition mechanism of new synthesized imidazoline derivative inhibitor to prevent corrosion of steel in saltwater saturated with carbon dioxide. The inhibitor efficiencies and thermodynamic parameters were calculated. The inhibition efficiency increased with the increase in inhibitor concentration, but increased then decreased with temperature. It was seen that the adsorption of imidazoline derivative on steel fitted the Langmuir isothermequation. The electrochemical results have also been supplemented by quantumchemical analysis.
2008, 24(01): 143-146
doi: 10.3866/PKU.WHXB20080125
Abstract:
A new synthetic way of magnesium tetraphenyl porphyrin (MgTPP) was presented, by which MgTPP was synthesized with tetraphenyl porphyrin and magnesium acetate, and purified by chromatography. The purified sample was confirmed as MgTPP by UV-Vis spectral method, 1H-NMR method, and matrix assisted laser desorption ionization time of filight mass spectrometry (MALDI-TOF-MS) method. The sample’s Soret band was shown at 424 nm, and Q band was shown at 563 nm and 602 nm in UV-Vis spectra. In addition, the spectral characters of MgTPP were studied after irradiating with incandescent light by UV-Vis spectral method and fluorescence spectral method. The results showed that the Soret band of MgTPP decreased remarkably with the increasing of irradiation time in the UV-Vis spectra, and fluorescence quenching was observed in the fluorescence spectra with 550 nm as excitation wavelength. Meanwhile, a new molecular ion peak 668 (m/z) in the MALDI-TOF-MS was shown, indicating that the coordinated complex of MgTPP-O2 may be formed by the photochemical interaction between MgTPP molecules and oxygen molecules under the illumination condition.
A new synthetic way of magnesium tetraphenyl porphyrin (MgTPP) was presented, by which MgTPP was synthesized with tetraphenyl porphyrin and magnesium acetate, and purified by chromatography. The purified sample was confirmed as MgTPP by UV-Vis spectral method, 1H-NMR method, and matrix assisted laser desorption ionization time of filight mass spectrometry (MALDI-TOF-MS) method. The sample’s Soret band was shown at 424 nm, and Q band was shown at 563 nm and 602 nm in UV-Vis spectra. In addition, the spectral characters of MgTPP were studied after irradiating with incandescent light by UV-Vis spectral method and fluorescence spectral method. The results showed that the Soret band of MgTPP decreased remarkably with the increasing of irradiation time in the UV-Vis spectra, and fluorescence quenching was observed in the fluorescence spectra with 550 nm as excitation wavelength. Meanwhile, a new molecular ion peak 668 (m/z) in the MALDI-TOF-MS was shown, indicating that the coordinated complex of MgTPP-O2 may be formed by the photochemical interaction between MgTPP molecules and oxygen molecules under the illumination condition.
2008, 24(01): 147-151
doi: 10.3866/PKU.WHXB20080126
Abstract:
The semiconductor properties of anodic oxide film formed on commercial pure aluminum were analyzed usingMott-Schottky theory and point defect model (PDM). The donor density, oxygen vacancy diffusion coefficient and flat-band potential were measured for the oxide films sealed by boiling water and K2Cr2O7, respectively. The results indicated that the anodic oxide films showed the n-type semiconductor property and the donor density decreased exponentially with the voltage elevating. The value of oxygen vacancy diffusion coefficient is about (1.12-5.53)伊10-14 cm-2·s-1. The flat-band potential of anodic oxide filmdeclined after sealing.
The semiconductor properties of anodic oxide film formed on commercial pure aluminum were analyzed usingMott-Schottky theory and point defect model (PDM). The donor density, oxygen vacancy diffusion coefficient and flat-band potential were measured for the oxide films sealed by boiling water and K2Cr2O7, respectively. The results indicated that the anodic oxide films showed the n-type semiconductor property and the donor density decreased exponentially with the voltage elevating. The value of oxygen vacancy diffusion coefficient is about (1.12-5.53)伊10-14 cm-2·s-1. The flat-band potential of anodic oxide filmdeclined after sealing.
2008, 24(01): 152-156
doi: 10.3866/PKU.WHXB20080127
Abstract:
Nanocrystalline Ni-coated Al composite powders were prepared by a fast, simple and quantitative method. The morphology and oxidation ability of both raw Al powders and nano Ni-coated Al composite powders were investigated by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). The results showed that the weight growth rate of raw Al powders at 1050 ℃ was 122% and could be increased to 135% when covering the raw Al powders with 0.75%(w) nano-sized Ni particles. More covering content of Ni powders will further increase the weight growth rate of Al powders. The ignition and combustion behaviors of composite powders were observed at ca 1000 ℃ when the covering content of Ni went up to 8.93%(w). Due to its oxygen transfer ability, the nano Ni powders play a crucial role in enhancing the oxidation of superfine Al powders.
Nanocrystalline Ni-coated Al composite powders were prepared by a fast, simple and quantitative method. The morphology and oxidation ability of both raw Al powders and nano Ni-coated Al composite powders were investigated by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). The results showed that the weight growth rate of raw Al powders at 1050 ℃ was 122% and could be increased to 135% when covering the raw Al powders with 0.75%(w) nano-sized Ni particles. More covering content of Ni powders will further increase the weight growth rate of Al powders. The ignition and combustion behaviors of composite powders were observed at ca 1000 ℃ when the covering content of Ni went up to 8.93%(w). Due to its oxygen transfer ability, the nano Ni powders play a crucial role in enhancing the oxidation of superfine Al powders.
2008, 24(01): 157-160
doi: 10.3866/PKU.WHXB20080128
Abstract:
CdS nanowires were successfully synthesized via a solvothermal route with the assistance of poly(vinyl alcohol) (PVA). The prepared sample was characterized by XRD, TEM, HRTEM, UV-Vis, and PL(photoluminescence) emission spectrum. The results indicated that the wurtzite CdS nanowires, with typical diameter of 70 nmand length up to 10 μm, had a preferential growth direction of [001] and showed a quantumconfinement effect. Based on the results of comparative experiments, a PVA-assisted growth mechanismwas proposed.
CdS nanowires were successfully synthesized via a solvothermal route with the assistance of poly(vinyl alcohol) (PVA). The prepared sample was characterized by XRD, TEM, HRTEM, UV-Vis, and PL(photoluminescence) emission spectrum. The results indicated that the wurtzite CdS nanowires, with typical diameter of 70 nmand length up to 10 μm, had a preferential growth direction of [001] and showed a quantumconfinement effect. Based on the results of comparative experiments, a PVA-assisted growth mechanismwas proposed.
2008, 24(01): 161-164
doi: 10.3866/PKU.WHXB20080129
Abstract:
The binding of alkaline earth metal ions with 18-crown-6 was studied by microcalorimetry. Equilibrium constant and changes of enthalpy, entropy, Gibbs free energy can be obtained from titration analysis. In the process of binding, the free metal ions bind to oxygen atom of 18-crown-6 by static force. The binding causes both energy and entropy in system to decrease, so reaction process was accompanied by release of heat and reduction of freedom. Having the similar size to ion radii (138 pm) of Ba2+, the cycle of 18-crown-6 can surround Ba2+ tightly. Metal ions with a smaller size have a weaker force to bind oxygen atom because of size effect. From Be2+, Mg2+, Ca2+, Sr2+ to Ba2+, more heat releases and equilibriumconstant increases in the process of the binding reaction.
The binding of alkaline earth metal ions with 18-crown-6 was studied by microcalorimetry. Equilibrium constant and changes of enthalpy, entropy, Gibbs free energy can be obtained from titration analysis. In the process of binding, the free metal ions bind to oxygen atom of 18-crown-6 by static force. The binding causes both energy and entropy in system to decrease, so reaction process was accompanied by release of heat and reduction of freedom. Having the similar size to ion radii (138 pm) of Ba2+, the cycle of 18-crown-6 can surround Ba2+ tightly. Metal ions with a smaller size have a weaker force to bind oxygen atom because of size effect. From Be2+, Mg2+, Ca2+, Sr2+ to Ba2+, more heat releases and equilibriumconstant increases in the process of the binding reaction.
2008, 24(01): 165-170
doi: 10.3866/PKU.WHXB20080130
Abstract:
5 V cathode materials LiNi0.5Mn1.5O4-xFx (x=0, 0.1) for lithium ion battery were synthesized via sol-gel method combined with high temperature treatment. The synthesized samples were characterized by X-ray diffractrometry (XRD), scanning electron microscopy (SEM) and specific surface area measurements (BET). Coin cells were assembled using these cathode materials, followed by storage at an elevated temperature (85 ℃) for 24 h, and then a series of electrochemical measurements were conducted to examine the changes of the electrochemical properties before and after cell storage at the elevated temperature. The experimental results showed that the open-circuit voltage of the cell declined quickly during high temperature storage because of self-discharge. The voltage retention was significantly influenced by specific surface area of the powder material and fluorine doping. The larger the specific surface area is, the shorter the voltage retention time becomes. Fluorine doping was favorable for stabilizing the cell voltage at elevated storage temperature and could improve the interfacial property between the electrode and electrolyte. Therefore, the charge and discharge performance was enhanced.
5 V cathode materials LiNi0.5Mn1.5O4-xFx (x=0, 0.1) for lithium ion battery were synthesized via sol-gel method combined with high temperature treatment. The synthesized samples were characterized by X-ray diffractrometry (XRD), scanning electron microscopy (SEM) and specific surface area measurements (BET). Coin cells were assembled using these cathode materials, followed by storage at an elevated temperature (85 ℃) for 24 h, and then a series of electrochemical measurements were conducted to examine the changes of the electrochemical properties before and after cell storage at the elevated temperature. The experimental results showed that the open-circuit voltage of the cell declined quickly during high temperature storage because of self-discharge. The voltage retention was significantly influenced by specific surface area of the powder material and fluorine doping. The larger the specific surface area is, the shorter the voltage retention time becomes. Fluorine doping was favorable for stabilizing the cell voltage at elevated storage temperature and could improve the interfacial property between the electrode and electrolyte. Therefore, the charge and discharge performance was enhanced.
2008, 24(01): 171-175
doi: 10.3866/PKU.WHXB20080131
Abstract:
A sol-gel process was employed to prepare SiC precursors, using tetraethyl orthosilicate (TEOS) and sucrose as raw materials. And oxalic acid, ferric nitrate, and nickel nitrate were added respectively as catalyst for hydrolysis and polymeration reactions. The effects of catalyst, reaction temperature, and reaction time on the gel formation were studied. The results showed that ferric nitrate was optimal for gel formation. SiC of 133 m2·g-1 was obtained by further carbonthermal reduction of the xerogel from the sol-gel system involved ferric nitrate, at 1350 ℃ in an Ar flow for 10 h. Such SiC was then used as catalyst support for CO oxidation. Wet impregnation method was adopted to obtain Pt/SiC catalyst. The as-prepared Pt/SiC catalyst showed od activity and stability for CO oxidation. It was also found that its performance could be improved significantly with the synergistic action of Ni promoter.
A sol-gel process was employed to prepare SiC precursors, using tetraethyl orthosilicate (TEOS) and sucrose as raw materials. And oxalic acid, ferric nitrate, and nickel nitrate were added respectively as catalyst for hydrolysis and polymeration reactions. The effects of catalyst, reaction temperature, and reaction time on the gel formation were studied. The results showed that ferric nitrate was optimal for gel formation. SiC of 133 m2·g-1 was obtained by further carbonthermal reduction of the xerogel from the sol-gel system involved ferric nitrate, at 1350 ℃ in an Ar flow for 10 h. Such SiC was then used as catalyst support for CO oxidation. Wet impregnation method was adopted to obtain Pt/SiC catalyst. The as-prepared Pt/SiC catalyst showed od activity and stability for CO oxidation. It was also found that its performance could be improved significantly with the synergistic action of Ni promoter.
2008, 24(01): 176-178
doi: 10.3866/PKU.WHXB20080132
Abstract:
Crystal structure of ozagrel was determined by X-ray diffraction. The compound was crystallized in the orthorhombic space group P212121. The lattice parameters are, a=0.62522(6) nm, b=0.91897(8) nm, c=1.95789(18) nm, V=1.12492 (18) nm3, Z=4. The ground-and excited-state acid-base properties of ozagrel were studied using UV and emission spectrophotometric pH titrations, and the ground-and excited-state acidity constants were derived. The results showed that ozagrel acted as a pH induced on/off luminescence switch.
Crystal structure of ozagrel was determined by X-ray diffraction. The compound was crystallized in the orthorhombic space group P212121. The lattice parameters are, a=0.62522(6) nm, b=0.91897(8) nm, c=1.95789(18) nm, V=1.12492 (18) nm3, Z=4. The ground-and excited-state acid-base properties of ozagrel were studied using UV and emission spectrophotometric pH titrations, and the ground-and excited-state acidity constants were derived. The results showed that ozagrel acted as a pH induced on/off luminescence switch.
2008, 24(01): 179-182
doi: 10.3866/PKU.WHXB20080133
Abstract:
The Sr2SiO4:Eu3+ phosphor was synthesized by sol-gel method. The excitation and emission spectra were investigated. The emission spectrum of Sr2SiO4:Eu3+ showed several bands, and the main peak value was 618 nm. The excitation spectrumfor 618 nm emission had several excitation bands at 320, 397, 464, and 518 nm. The effect of Eu3+ concentration on the emission spectrum intensity of Sr2SiO4:Eu3+ was investigated, and the results showed that the emission spectrumintensity increased with increasing Eu3+ concentration, and reached the maximumvalue at 7%(x) Eu3+, then decreased. Under the condition of doping 7% Eu3 +, the effect of Li + concentration on the emission spectrum intensity of Sr2SiO4:Eu3+ was studied, and the emission spectrum intensity increased with increasing Li+ concentration, and reached the maximumvalue at 8%(x) Li+, then decreased.
The Sr2SiO4:Eu3+ phosphor was synthesized by sol-gel method. The excitation and emission spectra were investigated. The emission spectrum of Sr2SiO4:Eu3+ showed several bands, and the main peak value was 618 nm. The excitation spectrumfor 618 nm emission had several excitation bands at 320, 397, 464, and 518 nm. The effect of Eu3+ concentration on the emission spectrum intensity of Sr2SiO4:Eu3+ was investigated, and the results showed that the emission spectrumintensity increased with increasing Eu3+ concentration, and reached the maximumvalue at 7%(x) Eu3+, then decreased. Under the condition of doping 7% Eu3 +, the effect of Li + concentration on the emission spectrum intensity of Sr2SiO4:Eu3+ was studied, and the emission spectrum intensity increased with increasing Li+ concentration, and reached the maximumvalue at 8%(x) Li+, then decreased.
2008, 24(01): 183-186
doi: 10.3866/PKU.WHXB20080134
Abstract:
ld crystals are able to self-assemble into multipod-like nanoparticles through reducing HAuCl4 by sodium citrate in the soft template composed of sodium dodecyl sulfate (SDS)-polyvinylpyrrolidone (PVP) clusters assisted by microwave irradiation. TEM image displayed directly that the reduced products possessed multipod-like morphology with equivalent diameter around 50 nm, and electron diffraction (ED) pattern indicated that the ld crystals were polycrystalline. XRD pattern suggested that the multipod-like nanoparticles were self-assembled into tiny pure ld crystals with diameter about 12.7 nm, which were grown preferentially along (111) lattice plane. The cluster of SDS-PVP had great influence on the size and shape of ld nanoparticles. At a fixed level of PVP, as the concentration of SDS increased, the shape of ld nanoparticles changed from sphere to multipod, and UV-Vis absorption spectrum of ld nanoparticles showed that absorption bands at 800 nm became stronger. The preferred multipod-like ld nanoparticles could be obtained easily and quickly by controlling the composition of the soft template of SDS-PVP clusters.
ld crystals are able to self-assemble into multipod-like nanoparticles through reducing HAuCl4 by sodium citrate in the soft template composed of sodium dodecyl sulfate (SDS)-polyvinylpyrrolidone (PVP) clusters assisted by microwave irradiation. TEM image displayed directly that the reduced products possessed multipod-like morphology with equivalent diameter around 50 nm, and electron diffraction (ED) pattern indicated that the ld crystals were polycrystalline. XRD pattern suggested that the multipod-like nanoparticles were self-assembled into tiny pure ld crystals with diameter about 12.7 nm, which were grown preferentially along (111) lattice plane. The cluster of SDS-PVP had great influence on the size and shape of ld nanoparticles. At a fixed level of PVP, as the concentration of SDS increased, the shape of ld nanoparticles changed from sphere to multipod, and UV-Vis absorption spectrum of ld nanoparticles showed that absorption bands at 800 nm became stronger. The preferred multipod-like ld nanoparticles could be obtained easily and quickly by controlling the composition of the soft template of SDS-PVP clusters.
