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2006 Volume 22 Issue 6
2006, 22(06): 649-652
doi: 10.3866/PKU.WHXB20060601
Abstract:
T-jump/FTIR spectroscopy was used to study thermal decomposition of energetic material [Co(CHZ)3](ClO4)2 and [Ni(CHZ)3](ClO4)2 in thin film with rapid heating rate. During the exothermic decomposition process, the major gas products were identified as CO2, H2O, HCN, HNCO, and HONO. Time-to-exotherm (tx) kinetics method derived from the control voltage trace of T-jump/FTIR spectroscopy was introduced to resolve kinetics of the exothermic decomposition reaction of flash pyrolysis of the title compounds. In the temperature range of 613～653 K under 0.1 MPa Ar atmosphere the Arrhenius activation energy of the exothermic decomposition reaction of [Co(CHZ)3](ClO4)2 was determined to be Ea=39.42 kJ•mol−1 and lnA=5.93. The Arrhenius activation energy of [Ni(CHZ)3](ClO4)2 was determined to be Ea=60.44 kJ•mol−1 and lnA=9.40 in the temperature range of 618~678 K under 0.1 MPa Ar atmosphere.
T-jump/FTIR spectroscopy was used to study thermal decomposition of energetic material [Co(CHZ)3](ClO4)2 and [Ni(CHZ)3](ClO4)2 in thin film with rapid heating rate. During the exothermic decomposition process, the major gas products were identified as CO2, H2O, HCN, HNCO, and HONO. Time-to-exotherm (tx) kinetics method derived from the control voltage trace of T-jump/FTIR spectroscopy was introduced to resolve kinetics of the exothermic decomposition reaction of flash pyrolysis of the title compounds. In the temperature range of 613～653 K under 0.1 MPa Ar atmosphere the Arrhenius activation energy of the exothermic decomposition reaction of [Co(CHZ)3](ClO4)2 was determined to be Ea=39.42 kJ•mol−1 and lnA=5.93. The Arrhenius activation energy of [Ni(CHZ)3](ClO4)2 was determined to be Ea=60.44 kJ•mol−1 and lnA=9.40 in the temperature range of 618~678 K under 0.1 MPa Ar atmosphere.
2006, 22(06): 653-656
doi: 10.1016/S1872-1508(06)60024-7
Abstract:
The unsaturated silylenoid H2C=SiNaF was studied by using the DFT B3LYP method in conjunction with the 6-31+G(d, p) basis set. Geometry optimization calculations indicate that H2C=SiNaF has four equilibrium configurations, in which the p-complex has the lowest energy and is the most stable structure. Three transition states for isomerization reactions of H2C=SiNaF are located and the energy barriers are calculated. For the most stable one, vibrational frequencies and infrared intensities have been predicted.
The unsaturated silylenoid H2C=SiNaF was studied by using the DFT B3LYP method in conjunction with the 6-31+G(d, p) basis set. Geometry optimization calculations indicate that H2C=SiNaF has four equilibrium configurations, in which the p-complex has the lowest energy and is the most stable structure. Three transition states for isomerization reactions of H2C=SiNaF are located and the energy barriers are calculated. For the most stable one, vibrational frequencies and infrared intensities have been predicted.
2006, 22(06): 657-660
doi: 10.3866/PKU.WHXB20060603
Abstract:
A novel and efficient method was applied to prepare gallium nitride (GaN) powder. Hexa nal gallium nitride (GaN) powder was successfully synthesized by means of a combination of sol-gel process with high temperature ammoniation using Ga(OC2H5)3 as a precursor. Ammoniation of Ga2O3 gel was conducted in the flow of NH3 gas at 950 ℃ for 20 min. Measurement results by XRD, FTIR, TEM, and SAED indicate that the synthesised GaN is of a single-phase hexa nal wurtzite structure, and the granularity of the GaN powder has a od uniformity. In addtion, the FTIR shows a distinct peak broadening.
A novel and efficient method was applied to prepare gallium nitride (GaN) powder. Hexa nal gallium nitride (GaN) powder was successfully synthesized by means of a combination of sol-gel process with high temperature ammoniation using Ga(OC2H5)3 as a precursor. Ammoniation of Ga2O3 gel was conducted in the flow of NH3 gas at 950 ℃ for 20 min. Measurement results by XRD, FTIR, TEM, and SAED indicate that the synthesised GaN is of a single-phase hexa nal wurtzite structure, and the granularity of the GaN powder has a od uniformity. In addtion, the FTIR shows a distinct peak broadening.
2006, 22(06): 661-665
doi: 10.1016/S1872-1508(06)60025-9
Abstract:
First order mean spherical approximation (FMSA) equation of state (EOS) with two parameters for Lennard- Jones (L-J) fluid proposed by Tang has been studied in this article. This equation was used to predict the vapor-liquid phase coexisting diagrams, saturated pressure profiles, and PVT properties of real fluids. The results of prediction were compared with literature data and thaose from three-parameter FMSA EOS. The two parameters of L-J potential model were determined with vapor-liquid phase coexisting data of the corresponding fluid at the reduce d temperature Tr<0.95. For approximate spherical and non-polar molecular fluids, the equation can predict PVT properties of real fluids perfectly in wide ranges of temperature and pressure except for near the critical region. The deviations of the predicted results were not sensitive to the sizes of the spherical molecules. The two-parameter FMSA EOS should not be applied to strong polar fluids. Calculations show that this function is superior to Peng-Robinson (P-R) equation at high density. For nonspherical molecular fluids, the results showed some evident deviations and were sensitive to the shape of molecules which can be taken into consideration in the three-parameter FMSA EOS.
First order mean spherical approximation (FMSA) equation of state (EOS) with two parameters for Lennard- Jones (L-J) fluid proposed by Tang has been studied in this article. This equation was used to predict the vapor-liquid phase coexisting diagrams, saturated pressure profiles, and PVT properties of real fluids. The results of prediction were compared with literature data and thaose from three-parameter FMSA EOS. The two parameters of L-J potential model were determined with vapor-liquid phase coexisting data of the corresponding fluid at the reduce d temperature Tr<0.95. For approximate spherical and non-polar molecular fluids, the equation can predict PVT properties of real fluids perfectly in wide ranges of temperature and pressure except for near the critical region. The deviations of the predicted results were not sensitive to the sizes of the spherical molecules. The two-parameter FMSA EOS should not be applied to strong polar fluids. Calculations show that this function is superior to Peng-Robinson (P-R) equation at high density. For nonspherical molecular fluids, the results showed some evident deviations and were sensitive to the shape of molecules which can be taken into consideration in the three-parameter FMSA EOS.
2006, 22(06): 666-671
doi: 10.3866/PKU.WHXB20060605
Abstract:
An account on the application of solid-state CD on chiral metal complexes is briefly reviewed. Special focus is on the methods to record solid-state CD spectra of chiral solid sample, and then we switch to the comparison between solid-state and solution CD spectra of four pairs of chiral M(II) (M = Ni, Cu) Schiff base complexes. The solid-state CD spectra reveal that the chiral complexes mantain the same handeness found in solution states. But it is notable that there are some differences between the solid-state and solution CD spectra for the selective chiral complexes, which may be ascribed to some subtle tetrahedral distortion or conformational distinctions of the complexes between the two states.
An account on the application of solid-state CD on chiral metal complexes is briefly reviewed. Special focus is on the methods to record solid-state CD spectra of chiral solid sample, and then we switch to the comparison between solid-state and solution CD spectra of four pairs of chiral M(II) (M = Ni, Cu) Schiff base complexes. The solid-state CD spectra reveal that the chiral complexes mantain the same handeness found in solution states. But it is notable that there are some differences between the solid-state and solution CD spectra for the selective chiral complexes, which may be ascribed to some subtle tetrahedral distortion or conformational distinctions of the complexes between the two states.
2006, 22(06): 672-678
doi: 10.1016/S1872-1508(06)60026-0
Abstract:
PtSnNa/ZSM-5 catalysts with different amounts of Na were prepared by the sequential impregnation method on HZSM-5 zeolites, and their catalytic activities and stabilities in propane dehydrogenation were investigated. The effect of the addition of sodium on the physicochemical properties was studied by means of XRD (X-ray diffration), IR spectrum of adsorbed pyridine, NH3-TPD, H2 chemisorption, TPR (temperature-programmed reduction), etc. The results indicated that the addition of Na had an obvious impact on the catalytic performance of the PtSn/ZSM-5 catalyst. A suitable concentration of Na could not only reduce the Brönsted acid sites and moderate/strong Lewis acid sites, thus preventing the catalyst from coking and improving the catalytic stability, but also increase the fraction of bare metallic Pt on the surface of the catalyst, thus increase the catalytic activity. It was found that the propene selectivity and yield could reach the maximum, when the Na content was 1.0%(w). After reaction for 30 h, the propane conversion was still high (36.4%). However, the continuous addition of Na increased the weak Lewis acid sites and promoted the tin species to be reduced to metallic tin. In this instance, the cracking and hydrogenolysis of propane could be carried out easily, which was disadvantageous to the dehydrogenation.
PtSnNa/ZSM-5 catalysts with different amounts of Na were prepared by the sequential impregnation method on HZSM-5 zeolites, and their catalytic activities and stabilities in propane dehydrogenation were investigated. The effect of the addition of sodium on the physicochemical properties was studied by means of XRD (X-ray diffration), IR spectrum of adsorbed pyridine, NH3-TPD, H2 chemisorption, TPR (temperature-programmed reduction), etc. The results indicated that the addition of Na had an obvious impact on the catalytic performance of the PtSn/ZSM-5 catalyst. A suitable concentration of Na could not only reduce the Brönsted acid sites and moderate/strong Lewis acid sites, thus preventing the catalyst from coking and improving the catalytic stability, but also increase the fraction of bare metallic Pt on the surface of the catalyst, thus increase the catalytic activity. It was found that the propene selectivity and yield could reach the maximum, when the Na content was 1.0%(w). After reaction for 30 h, the propane conversion was still high (36.4%). However, the continuous addition of Na increased the weak Lewis acid sites and promoted the tin species to be reduced to metallic tin. In this instance, the cracking and hydrogenolysis of propane could be carried out easily, which was disadvantageous to the dehydrogenation.
2006, 22(06): 679-683
doi: 10.3866/PKU.WHXB20060607
Abstract:
A series of titanic-silica mesoporous materials have been synthesized by using the Gemini surfactant [C16H33(CH3)2N+(CH2)6N+(CH3)2C16H33]•2Br− (GEM16-6-16) as a template. The XRD patterns and TEM images provide the evidence that the mesoporous phases are changed according to the following path by varying the molar ratio of n(Ti)/n(Si): hexa nal mesoporous structures are obtained when n(Ti)/n(Si)≤0.20; cubic when n(Ti)/n(Si)=0.30; lamellar when n(Ti)/n(Si)=0.50; and amorphous when n(Ti)/n(Si)=1.0. The FT-IR spectra suggest that the amount of Ti—O—Si bonds in the framework increases with increasing n(Ti)/n(Si) initially, and reaches to a limit when n(Ti)/n(Si)≥0.20. Additionally, the ethanol and butanol have been approved that they can control the evolvement of silica mesoporous phase transition. Following that, the process of titanic-silica mesoporous phase transition has been elucidated by the aggregation of Ti—O—Si bonds and the effect of butanol produced from the hydrolysis of tetrabutyl titanate(TBOT).
A series of titanic-silica mesoporous materials have been synthesized by using the Gemini surfactant [C16H33(CH3)2N+(CH2)6N+(CH3)2C16H33]•2Br− (GEM16-6-16) as a template. The XRD patterns and TEM images provide the evidence that the mesoporous phases are changed according to the following path by varying the molar ratio of n(Ti)/n(Si): hexa nal mesoporous structures are obtained when n(Ti)/n(Si)≤0.20; cubic when n(Ti)/n(Si)=0.30; lamellar when n(Ti)/n(Si)=0.50; and amorphous when n(Ti)/n(Si)=1.0. The FT-IR spectra suggest that the amount of Ti—O—Si bonds in the framework increases with increasing n(Ti)/n(Si) initially, and reaches to a limit when n(Ti)/n(Si)≥0.20. Additionally, the ethanol and butanol have been approved that they can control the evolvement of silica mesoporous phase transition. Following that, the process of titanic-silica mesoporous phase transition has been elucidated by the aggregation of Ti—O—Si bonds and the effect of butanol produced from the hydrolysis of tetrabutyl titanate(TBOT).
2006, 22(06): 684-690
doi: 10.1016/S1872-1508(06)60027-2
Abstract:
The structures of the (BCO)n(n=1~12) compounds were studied by HF(Hartree-Fock)/3-21G and B3LYP of density functional theory (DFT) with a basis set of 6-31G*. By discussing the geometries, electron structures, vibrational frequencies, B—C average bonding energies, nucleus independent chemical shifts (NICS), and energy secondary differences of the most stable structures at the B3LYP/6-31G* level, the stability information of the (BCO)n(n=1~12) compounds was obtained. The carbonyls of ground state of the (BCO)n(n=1~12) are μ1-CO. The most stable structures are linear or planar for the compounds (BCO)n(n=1~3, 5, 6), and polyhedron cages for (BCO)n(n=4, 7~12). Analyses of the B—C average binding energies and energy secondary differences of the most stable structures at the B3LYP/6-31G* level provides theoretic interpretation for experiment results.
The structures of the (BCO)n(n=1~12) compounds were studied by HF(Hartree-Fock)/3-21G and B3LYP of density functional theory (DFT) with a basis set of 6-31G*. By discussing the geometries, electron structures, vibrational frequencies, B—C average bonding energies, nucleus independent chemical shifts (NICS), and energy secondary differences of the most stable structures at the B3LYP/6-31G* level, the stability information of the (BCO)n(n=1~12) compounds was obtained. The carbonyls of ground state of the (BCO)n(n=1~12) are μ1-CO. The most stable structures are linear or planar for the compounds (BCO)n(n=1~3, 5, 6), and polyhedron cages for (BCO)n(n=4, 7~12). Analyses of the B—C average binding energies and energy secondary differences of the most stable structures at the B3LYP/6-31G* level provides theoretic interpretation for experiment results.
2006, 22(06): 691-695
doi: 10.1016/S1872-1508(06)60028-4
Abstract:
The adsorption of four β-dicarbonyl derivatives on highly oriented pyrolytic graphite (HOPG) surface was studied by scanning tunneling microscopy (STM) in an ambient environment. All the molecules include π-conjugated part and alkyl chains in their chemical structures. The molecules were dissolved in toluene and a drop of the solution was deposited on HOPG to form self-assembled adlayer. The characteristic stripe-like structure in the self-assembled monolayer (SAM) on the high-resolution STM images of the compounds was observed. Different molecular structures led to different SAMs. It was found that noncovalent interactions such as hydrogen bonds and dipole-dipole interactions played an important role in the formation of different SAMs.
The adsorption of four β-dicarbonyl derivatives on highly oriented pyrolytic graphite (HOPG) surface was studied by scanning tunneling microscopy (STM) in an ambient environment. All the molecules include π-conjugated part and alkyl chains in their chemical structures. The molecules were dissolved in toluene and a drop of the solution was deposited on HOPG to form self-assembled adlayer. The characteristic stripe-like structure in the self-assembled monolayer (SAM) on the high-resolution STM images of the compounds was observed. Different molecular structures led to different SAMs. It was found that noncovalent interactions such as hydrogen bonds and dipole-dipole interactions played an important role in the formation of different SAMs.
2006, 22(06): 696-700
doi: 10.1016/S1872-1508(06)60029-6
Abstract:
Two new methods were developed for characterizing the kinetics of the complexation and oxidation processes of the thin films by using transmission spectrum and sheet resistance. Ag/TCNQ (7, 7, 8, 8-tetracyanoquino-dimethane) bi-layer films and copper films were prepared on glass substrate by vacuum deposition. The complex kinetics of Ag/TCNQ bi-layer thin films was studied via the transmission spectrum. The oxidation kinetics of the copper thin films was studied via sheet resistance, which increased during the process. The results suggested that these two methods can be used to characterize the kinetics of the reaction process of thin films.
Two new methods were developed for characterizing the kinetics of the complexation and oxidation processes of the thin films by using transmission spectrum and sheet resistance. Ag/TCNQ (7, 7, 8, 8-tetracyanoquino-dimethane) bi-layer films and copper films were prepared on glass substrate by vacuum deposition. The complex kinetics of Ag/TCNQ bi-layer thin films was studied via the transmission spectrum. The oxidation kinetics of the copper thin films was studied via sheet resistance, which increased during the process. The results suggested that these two methods can be used to characterize the kinetics of the reaction process of thin films.
2006, 22(06): 701-705
doi: 10.3866/PKU.WHXB20060611
Abstract:
The electronic structural properties of Cn (n=3~10) molecular wires are investigated systemically using the B3LYP density functional method under the basis set 6-311++g** level. By the analysis about the calculated results, it can be found that because of the effect of delocalization, the ground state of carbon molecular wires Cn is singlet as n is odd number, whereas the triplet is the stable ground state of carbon molecular wires Cn as n is even number. Meanwhile, based on the obtained equilibrium structures in ground state, the polarizability, charge distribution and energy level distribution of carbon molecular wires have been investigated. At the same time, the relationship between high occupied molecular orbits EH (HOMO), low virtual molecular orbits EL(LOMO) and the number n of carbon molecular wires is determined, i. e., EHn－2 < EHn < EHn+2, ELn－2 > ELn > ELn+2. Therefore, the fermi levels of carbon molecular wires display their own brand of odd-even alternation properties. The reason for these properties of carbon molecular wires is explained in present work.
The electronic structural properties of Cn (n=3~10) molecular wires are investigated systemically using the B3LYP density functional method under the basis set 6-311++g** level. By the analysis about the calculated results, it can be found that because of the effect of delocalization, the ground state of carbon molecular wires Cn is singlet as n is odd number, whereas the triplet is the stable ground state of carbon molecular wires Cn as n is even number. Meanwhile, based on the obtained equilibrium structures in ground state, the polarizability, charge distribution and energy level distribution of carbon molecular wires have been investigated. At the same time, the relationship between high occupied molecular orbits EH (HOMO), low virtual molecular orbits EL(LOMO) and the number n of carbon molecular wires is determined, i. e., EHn－2 < EHn < EHn+2, ELn－2 > ELn > ELn+2. Therefore, the fermi levels of carbon molecular wires display their own brand of odd-even alternation properties. The reason for these properties of carbon molecular wires is explained in present work.
2006, 22(06): 706-711
doi: 10.3866/PKU.WHXB20060612
Abstract:
The mechanism for the gas phase ion-molecule reaction of BH2+ with H2O has been investigated by using the B3LYP/6-311+G(d, p) and CCSD/6-311+G(d, p) methods. The geometries of reactants, intermediates, transition states, and products are optimized, and the topological properties of electron density of the chemical bonds are analysed. A ring-type and a T-type structure transition states as well as an energy transition state are found in the reaction (I).
The mechanism for the gas phase ion-molecule reaction of BH2+ with H2O has been investigated by using the B3LYP/6-311+G(d, p) and CCSD/6-311+G(d, p) methods. The geometries of reactants, intermediates, transition states, and products are optimized, and the topological properties of electron density of the chemical bonds are analysed. A ring-type and a T-type structure transition states as well as an energy transition state are found in the reaction (I).
2006, 22(06): 712-715
doi: 10.3866/PKU.WHXB20060613
Abstract:
The structure and catalytic properties of supported Pd/TiO2 and Pd-Ag/TiO2 catalysts for selective hydrogenation of acetylene have been studied by using microreactor tests combined with temperature-programmed reduction (TPR), X-ray diffraction (XRD), infrared spectroscopy of adsorbed carbon monoxide (CO-IR), and electronic paramagnetic resonance (EPR). The results indicate that the Pd/TiO2 catalyst exhibits better catalytic performance than Pd/γ-Al2O3 catalyst for selective hydrogenation of acetylene, which can be correlated to the strong metal-support interaction (SMSI) between Pd and TiO2 in the Pd/TiO2 catalyst. Adding Ag component to Pd/TiO2 catalyst results in formation of Pd-Ag alloy, leading to an increase in selectivity of acetylene hydrogenation to ethylene, but a decrease in the activity of acetylene hydrogenation.
The structure and catalytic properties of supported Pd/TiO2 and Pd-Ag/TiO2 catalysts for selective hydrogenation of acetylene have been studied by using microreactor tests combined with temperature-programmed reduction (TPR), X-ray diffraction (XRD), infrared spectroscopy of adsorbed carbon monoxide (CO-IR), and electronic paramagnetic resonance (EPR). The results indicate that the Pd/TiO2 catalyst exhibits better catalytic performance than Pd/γ-Al2O3 catalyst for selective hydrogenation of acetylene, which can be correlated to the strong metal-support interaction (SMSI) between Pd and TiO2 in the Pd/TiO2 catalyst. Adding Ag component to Pd/TiO2 catalyst results in formation of Pd-Ag alloy, leading to an increase in selectivity of acetylene hydrogenation to ethylene, but a decrease in the activity of acetylene hydrogenation.
2006, 22(06): 716-720
doi: 10.3866/PKU.WHXB20060614
Abstract:
Manganese dioxide was synthesized by a spray pyrolysis method and Ni-MnO2 film-type electrode was prepared by a spray-coating approach as well. SEM and AFM in combination with electrochemical measures were employed to characterize the microstructure, electrocatalytic properties, and the correlation between electroreduction of oxygen and electrocatalysis of the Ni-MnO2 electrode. A reductive process of intermediate particle was discovered by fast cyclic voltammograms. The concentration of the intermediate particle could be cumulated and its life could be up to about 200 cycles. The reduction of the intermediate particle was the main reason of highly electrocatalytical activity for oxygen reduction reaction.
Manganese dioxide was synthesized by a spray pyrolysis method and Ni-MnO2 film-type electrode was prepared by a spray-coating approach as well. SEM and AFM in combination with electrochemical measures were employed to characterize the microstructure, electrocatalytic properties, and the correlation between electroreduction of oxygen and electrocatalysis of the Ni-MnO2 electrode. A reductive process of intermediate particle was discovered by fast cyclic voltammograms. The concentration of the intermediate particle could be cumulated and its life could be up to about 200 cycles. The reduction of the intermediate particle was the main reason of highly electrocatalytical activity for oxygen reduction reaction.
2006, 22(06): 721-725
doi: 10.3866/PKU.WHXB20060615
Abstract:
A newly developed three-dimensional holographic vector of atomic interaction field (3D-HoVAIF) was used to describe the chemical structure of anti-HIV drug-34 1-[(2-hydroxyethoxy)-methyl]-6-(phenylthio) thymine (HEPT). After the structural characterization, the descriptors obtained were screened by stepwise multiple regression (SMR). The cumulative multiple correlation coefficient(R2cum), cumulative leave-one-out cross-validated(Q2cum, and standard error (SD) were R2cum=0.928, Q2cum =0.883, and SD= 0.43, respectively, which were all better than previous report (R2cum=0.911, Q2cum =0.863, and SD= 0.45). The result showed that the model had favorable stability and od prediction capability and the 3D-HoVAIF was applicable to the molecular structural characterization and biological activity prediction.
A newly developed three-dimensional holographic vector of atomic interaction field (3D-HoVAIF) was used to describe the chemical structure of anti-HIV drug-34 1-[(2-hydroxyethoxy)-methyl]-6-(phenylthio) thymine (HEPT). After the structural characterization, the descriptors obtained were screened by stepwise multiple regression (SMR). The cumulative multiple correlation coefficient(R2cum), cumulative leave-one-out cross-validated(Q2cum, and standard error (SD) were R2cum=0.928, Q2cum =0.883, and SD= 0.43, respectively, which were all better than previous report (R2cum=0.911, Q2cum =0.863, and SD= 0.45). The result showed that the model had favorable stability and od prediction capability and the 3D-HoVAIF was applicable to the molecular structural characterization and biological activity prediction.
2006, 22(06): 726-731
doi: 10.3866/PKU.WHXB20060616
Abstract:
Using the B3LYP(Becke-3-parameter-Lee-Yang-Parr) method of density functional theory(DFT), the geometries and electronic structures of boron-doped carbon clusters of the type B2Cn+(n=1～9) have been optimized at 6-311G* basis set level. Frequency calculations at the same level of theory were performed to characterize the nature of the optimized structures. The calculation results show that most of the ground state structures for B2Cn+(n=1～9) clusters are planer except that for B2C2+ and B2C3+ are linear structure with D∞h symmetry and three-dimensional monocycle with Cs symmetry for B2C7+. The preference order for the bonding in the ground state of B2Cn+(n=1～9) clusters is C—C ＞ B—C ＞ B—B. In addition, the total energy(ET), zero point energy(EZ), molar heat capacity(Cp), standard entropy(S0) and atomization energy(ΔEn+) of B2Cn+(n=1～9) clusters are also obtained. The ET, EZ, Cp and S0 values tend to increase with increasing n, in which the increasing zero point energy(EZ) has an approximately constant gradient. The vertical electron affinities of the most stable B2Cn+(n=1～9) clusters indicate that B2Cn+ with odd n is more stable than that with even n.
Using the B3LYP(Becke-3-parameter-Lee-Yang-Parr) method of density functional theory(DFT), the geometries and electronic structures of boron-doped carbon clusters of the type B2Cn+(n=1～9) have been optimized at 6-311G* basis set level. Frequency calculations at the same level of theory were performed to characterize the nature of the optimized structures. The calculation results show that most of the ground state structures for B2Cn+(n=1～9) clusters are planer except that for B2C2+ and B2C3+ are linear structure with D∞h symmetry and three-dimensional monocycle with Cs symmetry for B2C7+. The preference order for the bonding in the ground state of B2Cn+(n=1～9) clusters is C—C ＞ B—C ＞ B—B. In addition, the total energy(ET), zero point energy(EZ), molar heat capacity(Cp), standard entropy(S0) and atomization energy(ΔEn+) of B2Cn+(n=1～9) clusters are also obtained. The ET, EZ, Cp and S0 values tend to increase with increasing n, in which the increasing zero point energy(EZ) has an approximately constant gradient. The vertical electron affinities of the most stable B2Cn+(n=1～9) clusters indicate that B2Cn+ with odd n is more stable than that with even n.
2006, 22(06): 732-736
doi: 10.3866/PKU.WHXB20060617
Abstract:
The exfoliation reaction and recombination of the layered hydroxide zinc benzoate compound with a fibrous particle morphology and a basal spacing of 1.44 nm in ethanol, n-propanol and n-butanol were researched. The characteristic, particle morphology and chemical composition of the sample recombined by exfoliated nano-sheets were investigated by using XRD, TG-DTA, SEM, TEM and elementary analysis. The results indicated that the samples obtained by hydrothermal synthesis and recombinated by exfoliated nano-sheets in alcohol solvents have the same layered structures, and their chemical formulas can be written as Zn(OH)1.12(C6H5COO)0.88 and Zn(OH)1.1(C6H5COO)0.9, respectively. The 1.44 nm layered phase can be exfoliated in ethanol, n-propanol and n-butanol solvents, and the exfoliated nano-sheets can be recombined into nano-belt-like and nano-flower-like particles.
The exfoliation reaction and recombination of the layered hydroxide zinc benzoate compound with a fibrous particle morphology and a basal spacing of 1.44 nm in ethanol, n-propanol and n-butanol were researched. The characteristic, particle morphology and chemical composition of the sample recombined by exfoliated nano-sheets were investigated by using XRD, TG-DTA, SEM, TEM and elementary analysis. The results indicated that the samples obtained by hydrothermal synthesis and recombinated by exfoliated nano-sheets in alcohol solvents have the same layered structures, and their chemical formulas can be written as Zn(OH)1.12(C6H5COO)0.88 and Zn(OH)1.1(C6H5COO)0.9, respectively. The 1.44 nm layered phase can be exfoliated in ethanol, n-propanol and n-butanol solvents, and the exfoliated nano-sheets can be recombined into nano-belt-like and nano-flower-like particles.
2006, 22(06): 737-743
doi: 10.1016/S1872-1508(06)60030-2
Abstract:
The hydrophilic silver and hydrophobic ld nanoparticles are doped simultaneously or seperately into different regions of a lyotropic liquid crystal (LLC) with long-range structural order built with the AOT/isooctane/water ternary system. A stable lamellar hybrid is produced under suitable conditions. Polarized optical microscopy and small angle X-ray scattering are used to compare the phase changes upon various doping manners. The interactions between doped particles and surfactant bilayers are analyzed and compared in detail. Factors affecting the stability of inorganic/organic hybrids are also discussed. The doped hydrophobic particles affect the equilibrium of van der Waals and Helfrich interactions between them and the membranes. When hydrophilic particles are incorporated into LLC aqueous region, electrostatic force will be dominant. The results suggest that it is the balance of electrostatic, van der Waals, and Helfrich forces in the lyotropic liquid crystal that determine the hybrid structure.
The hydrophilic silver and hydrophobic ld nanoparticles are doped simultaneously or seperately into different regions of a lyotropic liquid crystal (LLC) with long-range structural order built with the AOT/isooctane/water ternary system. A stable lamellar hybrid is produced under suitable conditions. Polarized optical microscopy and small angle X-ray scattering are used to compare the phase changes upon various doping manners. The interactions between doped particles and surfactant bilayers are analyzed and compared in detail. Factors affecting the stability of inorganic/organic hybrids are also discussed. The doped hydrophobic particles affect the equilibrium of van der Waals and Helfrich interactions between them and the membranes. When hydrophilic particles are incorporated into LLC aqueous region, electrostatic force will be dominant. The results suggest that it is the balance of electrostatic, van der Waals, and Helfrich forces in the lyotropic liquid crystal that determine the hybrid structure.
2006, 22(06): 744-746
doi: 10.3866/PKU.WHXB20060619
Abstract:
The single photon induced reaction of complex Mg+-S2(CH3)2 was studied in the spectral region of 230~440 nm. The mass spectrometry of the photo-induced reaction of the complex Mg+-S2(CH3)2 exhibits the existence of the products Mg+ and Mg+SCH3 throughout the whole wavelength range. The photodissociation spectrum consists of three broad peaks corresponding to the atomic transition of Mg+(32P←32S). The absorption spectrum by using CIS method of quantum chemistry calculation agrees with the experimental spectrum.
The single photon induced reaction of complex Mg+-S2(CH3)2 was studied in the spectral region of 230~440 nm. The mass spectrometry of the photo-induced reaction of the complex Mg+-S2(CH3)2 exhibits the existence of the products Mg+ and Mg+SCH3 throughout the whole wavelength range. The photodissociation spectrum consists of three broad peaks corresponding to the atomic transition of Mg+(32P←32S). The absorption spectrum by using CIS method of quantum chemistry calculation agrees with the experimental spectrum.
2006, 22(06): 747-751
doi: 10.3866/PKU.WHXB20060620
Abstract:
A series of N-ester appended pyridinium task-specific ionic liquids (TSILs) were synthesized and characterized by 1H NMR, 13C NMR, FTIR, ESI-MS, and DSC. Experimental results showed that pyridinium TSILs containing the same anion had the same miscibility with conventional organic solvents. The miscibility between these N-ester appended pyridinium task-specific ionic liquids and ethyl acetate decreased for the grafted ester group. With increasing the carbon number of the appended ester group, the melt point of the pyridinium TSILs containing the same anion decreases. Pyridinium TSILs containing BF4or PF6anion had better thermal stability and the thermal decomposition temperature was as high as 300 ℃. The physical and chemical properties of TSILs could be adjusted by the modification of the cation with the N-ester appended functional group.
A series of N-ester appended pyridinium task-specific ionic liquids (TSILs) were synthesized and characterized by 1H NMR, 13C NMR, FTIR, ESI-MS, and DSC. Experimental results showed that pyridinium TSILs containing the same anion had the same miscibility with conventional organic solvents. The miscibility between these N-ester appended pyridinium task-specific ionic liquids and ethyl acetate decreased for the grafted ester group. With increasing the carbon number of the appended ester group, the melt point of the pyridinium TSILs containing the same anion decreases. Pyridinium TSILs containing BF4or PF6anion had better thermal stability and the thermal decomposition temperature was as high as 300 ℃. The physical and chemical properties of TSILs could be adjusted by the modification of the cation with the N-ester appended functional group.
2006, 22(06): 752-755
doi: 10.3866/PKU.WHXB20060621
Abstract:
Sn-Sb alloy nanoparticles were prepared by hydrogen plasma-metal reaction. The morphology, crystal structure, and electrochemical action of the nanoparticles were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), and galvanostatic cycling tests. The results show that the particles are spherical in shape, with average particle diameter of 138 nm, and composed of Sn and SnSb phases. Electrochemical cycling tests of model cells show that the specific capacity is far more than that of carbon materials. The lithiation capacity and delithiation capacity in the first cycle reached 930 mAh•g−1 and 701 mAh•g−1, respectively, and it has a od cycling stability. The capacity retention at the 20th cycle is 81%, and the reversible specific capacity is 566 mAh•g−1. The Sn-Sb alloy nanomaterial prepared by hydrogen plasma-metal reaction can be considered as candidate for the anode materials of lithium ion battery.
Sn-Sb alloy nanoparticles were prepared by hydrogen plasma-metal reaction. The morphology, crystal structure, and electrochemical action of the nanoparticles were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), and galvanostatic cycling tests. The results show that the particles are spherical in shape, with average particle diameter of 138 nm, and composed of Sn and SnSb phases. Electrochemical cycling tests of model cells show that the specific capacity is far more than that of carbon materials. The lithiation capacity and delithiation capacity in the first cycle reached 930 mAh•g−1 and 701 mAh•g−1, respectively, and it has a od cycling stability. The capacity retention at the 20th cycle is 81%, and the reversible specific capacity is 566 mAh•g−1. The Sn-Sb alloy nanomaterial prepared by hydrogen plasma-metal reaction can be considered as candidate for the anode materials of lithium ion battery.
2006, 22(06): 756-760
doi: 10.3866/PKU.WHXB20060622
Abstract:
The aggregation effect of yellow silver colloids caused by adding some anions has been investigated with UV-Vis absorption, transmission electron microscopy (TEM), and Raman spectra. It was found that colloidal aggregation and shape changing occurred when anions were added, in addition, an absorption peak at much longer wavelength and an exceptional Raman signals appeared. The experimental results indicated that the effects of various anions were different from each other, and the possible mechanism was discussed.
The aggregation effect of yellow silver colloids caused by adding some anions has been investigated with UV-Vis absorption, transmission electron microscopy (TEM), and Raman spectra. It was found that colloidal aggregation and shape changing occurred when anions were added, in addition, an absorption peak at much longer wavelength and an exceptional Raman signals appeared. The experimental results indicated that the effects of various anions were different from each other, and the possible mechanism was discussed.
2006, 22(06): 761-763
doi: 10.3866/PKU.WHXB20060623
Abstract:
The 266 nm laser photolysis formation and chemical behavior of •HS in aqueous solution have been studied by laser photolysis-transient absorption technique. The 266 nm laser photolysis of H2O2 leads to the formation of •OH, which reacts with H2S to produce •HS, while solutions of HS− can also be directly photolyzed with 266 nm laser pulses to produce •HS radical. The transient UV-Vis absorption spectrum of •HS has been attributed to 220~300 nm with a maximum absorption at 220 nm and a shoulder at 250~270 nm. The chemical behavior of •HS is very active in oxygen saturated aqueous solution:•HS will first react with oxygen to form •SO2−, which further reacts with another oxygen molecule with the production of SO2 and •O2−. In acid solution, •O2− immediately protonates to form •HO2.
The 266 nm laser photolysis formation and chemical behavior of •HS in aqueous solution have been studied by laser photolysis-transient absorption technique. The 266 nm laser photolysis of H2O2 leads to the formation of •OH, which reacts with H2S to produce •HS, while solutions of HS− can also be directly photolyzed with 266 nm laser pulses to produce •HS radical. The transient UV-Vis absorption spectrum of •HS has been attributed to 220~300 nm with a maximum absorption at 220 nm and a shoulder at 250~270 nm. The chemical behavior of •HS is very active in oxygen saturated aqueous solution:•HS will first react with oxygen to form •SO2−, which further reacts with another oxygen molecule with the production of SO2 and •O2−. In acid solution, •O2− immediately protonates to form •HO2.
2006, 22(06): 764-767
doi: 10.3866/PKU.WHXB20060624
Abstract:
Based on the semiclassical model of the charge transfer, kinetic parameters of the charge transfer reaction at the molecular scale in discotic liquid crystals made of the acetylene bridged macrocycle with benzene, acetylene bridged macrocycle with pyridine, butadiyne bridged macrocycle with benzene, butadiyne bridged macrocycle with pyridine have been studied at the level of B3LYP/6-31G(d) and B3LYP/STO-3G. Marcus theory indicates that the rate of charge hopping depends on two main parameters: the reorganization energy λ and the intermolecular transfer integral t. High transfer rates, and hence high charge mobilities, require small values for former and large values for the latter. The transfer integral t between cation and neutral molecule can be approximated by one half of the MO energy-splitting factor between the highest occupied molecular orbital and the next highest occupied molecular orbital at the transition state, where the two molecules adopt the same geometry. Our results prodict that the reorganization energies of the macrocycle molecules are much smaller than that of the triphenylene. The relative hole mobilities at room temperature (T=300 K) in the various macrocycle molecules and triphenylene have been calculated from the ratio of the corresponding transfer rates. Our results prodict that the hole mobility can be increased by up to 3 orders of magnitude when ing from triphenylene to these macrocycle molecules. The significant improvement of the hole mobility in macrocycle molecules is mainly attributable to the smaller recoganization energy. The calculated charge mobility can hardly be predicted at the simple sight of a molecular structure, a theoretical approach has proved useful to design, prior to any chemical synthesis, discotic molecules with potentially high charge carrier mobilities.
Based on the semiclassical model of the charge transfer, kinetic parameters of the charge transfer reaction at the molecular scale in discotic liquid crystals made of the acetylene bridged macrocycle with benzene, acetylene bridged macrocycle with pyridine, butadiyne bridged macrocycle with benzene, butadiyne bridged macrocycle with pyridine have been studied at the level of B3LYP/6-31G(d) and B3LYP/STO-3G. Marcus theory indicates that the rate of charge hopping depends on two main parameters: the reorganization energy λ and the intermolecular transfer integral t. High transfer rates, and hence high charge mobilities, require small values for former and large values for the latter. The transfer integral t between cation and neutral molecule can be approximated by one half of the MO energy-splitting factor between the highest occupied molecular orbital and the next highest occupied molecular orbital at the transition state, where the two molecules adopt the same geometry. Our results prodict that the reorganization energies of the macrocycle molecules are much smaller than that of the triphenylene. The relative hole mobilities at room temperature (T=300 K) in the various macrocycle molecules and triphenylene have been calculated from the ratio of the corresponding transfer rates. Our results prodict that the hole mobility can be increased by up to 3 orders of magnitude when ing from triphenylene to these macrocycle molecules. The significant improvement of the hole mobility in macrocycle molecules is mainly attributable to the smaller recoganization energy. The calculated charge mobility can hardly be predicted at the simple sight of a molecular structure, a theoretical approach has proved useful to design, prior to any chemical synthesis, discotic molecules with potentially high charge carrier mobilities.
2006, 22(06): 768-770
doi: 10.3866/PKU.WHXB20060625
Abstract:
Carbon micro-coils, which have double helix structure, are generally prepared by catalytic chemical vapor deposition of acetylene, using Ni as the catalyst. It is well known that the coils are formed because of the catalytic anisotropy, however the growth process of carbon micro-coils is still unclear. In this paper, it is reported that the fiber constructing the carbon micro-coil is composed of three sub-fibers. Referring to this experimental finding and known facts from the phase diagrams, a vapor-liquid-solid-solid growth mechanism of carbon micro-coils is proposed. In this mechanism every catalyst particle can be divided into two parts, one is liquid while the other is solid. The schematic growth process of the carbon micro-coil is shown. Carbon atoms firstly permeate into the liquid portion from gas, then disperse into the solid portion, and finally deposit from six crystallographic facets of the catalyst to form the carbon micro-coil.
Carbon micro-coils, which have double helix structure, are generally prepared by catalytic chemical vapor deposition of acetylene, using Ni as the catalyst. It is well known that the coils are formed because of the catalytic anisotropy, however the growth process of carbon micro-coils is still unclear. In this paper, it is reported that the fiber constructing the carbon micro-coil is composed of three sub-fibers. Referring to this experimental finding and known facts from the phase diagrams, a vapor-liquid-solid-solid growth mechanism of carbon micro-coils is proposed. In this mechanism every catalyst particle can be divided into two parts, one is liquid while the other is solid. The schematic growth process of the carbon micro-coil is shown. Carbon atoms firstly permeate into the liquid portion from gas, then disperse into the solid portion, and finally deposit from six crystallographic facets of the catalyst to form the carbon micro-coil.
