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2006 Volume 22 Issue 9
2006, 22(09): 1043-1046
doi: 10.3866/PKU.WHXB20060901
Abstract:
The temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) were used to study the adsorption and thermal decomposition of 2-iodoethanol on clean Ni(100). The results show that 2-iodoethanol adsorbs molecularly at 100 K in two ways, either just by iodine atom or by both iodine and hydroxyl ends of the molecule. A thermal decomposition starts around 140 K with the production of small amounts of ethylene and water. The bulk of the 2-iodoethanol decomposes at about 150 K via a carbon-iodine scission to form −O(H)CH2CH2− and 2-hydroxyethyl intermediates. Around 160 K the −O(H)CH2CH2− dehydrogenates to an oxametallacycle species (−OCH2CH2−). The two intermediates further decompose to acetaldehyde, at around 210 K and above 250 K, respectively, and some of the acetaldehyde desorbs while the rest decomposes to hydrogen and carbon monoxide.
The temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) were used to study the adsorption and thermal decomposition of 2-iodoethanol on clean Ni(100). The results show that 2-iodoethanol adsorbs molecularly at 100 K in two ways, either just by iodine atom or by both iodine and hydroxyl ends of the molecule. A thermal decomposition starts around 140 K with the production of small amounts of ethylene and water. The bulk of the 2-iodoethanol decomposes at about 150 K via a carbon-iodine scission to form −O(H)CH2CH2− and 2-hydroxyethyl intermediates. Around 160 K the −O(H)CH2CH2− dehydrogenates to an oxametallacycle species (−OCH2CH2−). The two intermediates further decompose to acetaldehyde, at around 210 K and above 250 K, respectively, and some of the acetaldehyde desorbs while the rest decomposes to hydrogen and carbon monoxide.
2006, 22(09): 1047-1051
doi: 10.1016/S1872-1508(06)60045-4
Abstract:
A systemic theoretical study on the decomposition of 2,2-dimethoxypropane (DMP) and 2,2-diethoxy- propane (DEP) in condensed phase has been carried out. The four-center cyclic transition state is studied using the B3LYP method in DFT, using the PCM and COSMORS models within the self-consistent reaction filed (SCRF) theory. The results indicate that the solvent effect and tunneling effect must be taken into account in determining the rate constant of the decomposition reaction in the condensed phase.
A systemic theoretical study on the decomposition of 2,2-dimethoxypropane (DMP) and 2,2-diethoxy- propane (DEP) in condensed phase has been carried out. The four-center cyclic transition state is studied using the B3LYP method in DFT, using the PCM and COSMORS models within the self-consistent reaction filed (SCRF) theory. The results indicate that the solvent effect and tunneling effect must be taken into account in determining the rate constant of the decomposition reaction in the condensed phase.
2006, 22(09): 1052-1055
doi: 10.3866/PKU.WHXB20060903
Abstract:
A new representation technique for peptide sequences, namely SZOTT(scores vector of zero dimension, one dimension, two dimension, and three dimension), was derived from 1369 parameters of 20 coded amino acids using principle components analysis (PCA). It was then employed to express 71 peptide sequences with different lengths. Quantitative structure-retention modelings (QSRMs) were constructed by support vector machine (SVM) and partial least square (PLS). The results indicated that 71 peptide sequences could be preferably represented by SZOTT with many advantages, such as plentiful structural information and easy manipulation. Also simulative power for interior samples and predictive power for exterior samples by SVM were superior to those from PLS. SZOTT and SVM can be applied to develop QSRMs.
2006, 22(09): 1056-1060
doi: 10.3866/PKU.WHXB20060904
Abstract:
A series of photosensitive monomers, including hexafluorobiphenol A dicinnamate ester (6F-BADE) and fluorinated dicinnamate esters (FDE-n, n=2, 3, 4), were synthesized. These monomers could be crosslinked under irradiation of linearly polarized ultraviolet light. FTIR spectra and GPC spectra were used to measure the results in real time. The results indicated that the crosslinking reaction was [2+2] cycloaddition. The photoalignment films formed by monomers under the ultraviolet light could induce different types of liquid crystal (LC) alignments: 6F-BADE and FDE-n films resulted in vertical and parallel alignments, respectively. AFM images of the surfaces of the alignment showed no obvious anisotropy on the surfaces of these films. Finally, it was found that, using semiempirical method AM1 of quantum mechanics, the difference of the polarities among different monomer molecules was large, which was considered to be the main cause resulting in different LC alignments.
A series of photosensitive monomers, including hexafluorobiphenol A dicinnamate ester (6F-BADE) and fluorinated dicinnamate esters (FDE-n, n=2, 3, 4), were synthesized. These monomers could be crosslinked under irradiation of linearly polarized ultraviolet light. FTIR spectra and GPC spectra were used to measure the results in real time. The results indicated that the crosslinking reaction was [2+2] cycloaddition. The photoalignment films formed by monomers under the ultraviolet light could induce different types of liquid crystal (LC) alignments: 6F-BADE and FDE-n films resulted in vertical and parallel alignments, respectively. AFM images of the surfaces of the alignment showed no obvious anisotropy on the surfaces of these films. Finally, it was found that, using semiempirical method AM1 of quantum mechanics, the difference of the polarities among different monomer molecules was large, which was considered to be the main cause resulting in different LC alignments.
2006, 22(09): 1061-1064
doi: 10.3866/PKU.WHXB20060905
Abstract:
A new approach for the acquisition of in situ Raman spectra of Langmuir monolayers at air-water interface with minimal interference was presented. An in situ Raman instrument was designed, which comprises a Raman spectrometer (JY-U1000), a micro Langmuir-Blodgett trough, and a CCD imaging system. By lowering the subphase slowly until Langmuir monolayer deposited on a surface-enhanced Raman scattering (SERS) substrate that was placed under subphase in advance, Raman spectra of Langmuir monolayers of octadecylamine (ODA) and dipalmitoylphosph-atidylcholine (DPPC) have been acquired with od signal-to-noise ratio. These spectra present informations of the headgroup interaction and the ordering degree of alkane chains at different surface pressures. This new method could expand SERS application in the study of Langmuir monolayers at the air-water interface.
A new approach for the acquisition of in situ Raman spectra of Langmuir monolayers at air-water interface with minimal interference was presented. An in situ Raman instrument was designed, which comprises a Raman spectrometer (JY-U1000), a micro Langmuir-Blodgett trough, and a CCD imaging system. By lowering the subphase slowly until Langmuir monolayer deposited on a surface-enhanced Raman scattering (SERS) substrate that was placed under subphase in advance, Raman spectra of Langmuir monolayers of octadecylamine (ODA) and dipalmitoylphosph-atidylcholine (DPPC) have been acquired with od signal-to-noise ratio. These spectra present informations of the headgroup interaction and the ordering degree of alkane chains at different surface pressures. This new method could expand SERS application in the study of Langmuir monolayers at the air-water interface.
2006, 22(09): 1065-1070
doi: 10.1016/S1872-1508(06)60046-6
Abstract:
The inclusion of 2′-ethylhexyl-4-(N, N-dimethylamino)-benzoate (EHDAB) into methylated β-cyclodextrin (M-CD) and 2′-hydroxypropyl-β-cyclodextrin (HP-CD) was examined using molecular spectra. Both the flexible 2′-ethylhexyl chain and the rigid aromatic moiety of EHDAB were encapsulated within the cavity of M-CD and HP-CD, respectively. EHDAB was stabilized within the 2:1 cage-type host-guest inclusion complexes. The hydrophobic 2′-ethylhexyl tail greatly contributes to the extraordinarily stable complexes. M-CD and HP-CD increased the water solubility of EHDAB. The enhanced absorbance of EHDAB was obtained, and the photo-induced twisted intramolecular charge transfer of EHDAB was greatly suppressed by the restricted shape and size of the cavity. The photodegradation of EHDAB was markedly reduced in aqueous solution. EHDAB was still stable in alkaline solutions of M-CD and HP-CD. Anti-oxidation and thermal stability were appreciably promoted at the same time.
The inclusion of 2′-ethylhexyl-4-(N, N-dimethylamino)-benzoate (EHDAB) into methylated β-cyclodextrin (M-CD) and 2′-hydroxypropyl-β-cyclodextrin (HP-CD) was examined using molecular spectra. Both the flexible 2′-ethylhexyl chain and the rigid aromatic moiety of EHDAB were encapsulated within the cavity of M-CD and HP-CD, respectively. EHDAB was stabilized within the 2:1 cage-type host-guest inclusion complexes. The hydrophobic 2′-ethylhexyl tail greatly contributes to the extraordinarily stable complexes. M-CD and HP-CD increased the water solubility of EHDAB. The enhanced absorbance of EHDAB was obtained, and the photo-induced twisted intramolecular charge transfer of EHDAB was greatly suppressed by the restricted shape and size of the cavity. The photodegradation of EHDAB was markedly reduced in aqueous solution. EHDAB was still stable in alkaline solutions of M-CD and HP-CD. Anti-oxidation and thermal stability were appreciably promoted at the same time.
2006, 22(09): 1071-1074
doi: 10.3866/PKU.WHXB20060907
Abstract:
The indexing for experimental X-ray diffraction powder patterns of polycrystalline sample was performed on N-(1-naphthyl)-succinimide compound by using Materials Studio software, and the important information on crystal system, space group, and crystal lattice parameters was provided via the powder refinement and space searching processes. The simulated X-ray diffraction pattern of the calculated crystal unit cell agrees with the experimental XRD powder data. The theoretical crystal prediction of structure using the minimum energy conformation obtained by density-functional theory calculation as the input molecular structure, can afford a series of the hypothetical crystal structures in P212121 space group. It can be found that the parameters of the crystal unit cell, agreeing with both the result from powder indexing calculation and the single-crystal data, have been obtained by the refinement against experimental powder X-ray diffraction data of the polycrystalline sample of N-(1-naphthyl)-succinimide.
The indexing for experimental X-ray diffraction powder patterns of polycrystalline sample was performed on N-(1-naphthyl)-succinimide compound by using Materials Studio software, and the important information on crystal system, space group, and crystal lattice parameters was provided via the powder refinement and space searching processes. The simulated X-ray diffraction pattern of the calculated crystal unit cell agrees with the experimental XRD powder data. The theoretical crystal prediction of structure using the minimum energy conformation obtained by density-functional theory calculation as the input molecular structure, can afford a series of the hypothetical crystal structures in P212121 space group. It can be found that the parameters of the crystal unit cell, agreeing with both the result from powder indexing calculation and the single-crystal data, have been obtained by the refinement against experimental powder X-ray diffraction data of the polycrystalline sample of N-(1-naphthyl)-succinimide.
2006, 22(09): 1075-1078
doi: 10.1016/S1872-1508(06)60047-8
Abstract:
The viscoelastic behavior and the ability of dissipating energy of fumed silica dispersions in ethylene glycol, propylene glycol and butylene glycol have been studied under oscillation stress shear. The systems show linear viscoelastic, shear thinning, and shear thickening behaviors as the shear stress (σ) increasing. In linear viscoelastic region, the storage modulus (G′) and loss modulus (G′′) remain unchanged； in shear thinning region, G′ decreases and the sequence of the decreasing degree of G′ is EG/SiO2>PG/SiO2> BG/SiO2; however G′′ remains unchanged with σ increasing； in shear thickening region, both G′ and G′′ increase as σ increases. The magnitude of G′′ is larger than the magnitude of G′ over the studied range of stress, indicating that the dispersions mainly possess viscous property, and the energy dissipated is larger than the energy stored. The dissipated energies (Ed) of EG/SiO2, PG/SiO2, and BG/SiO2 dispersions increase with the maximum strain (γ0) in a second power relation under low shear stress; however, in the shear thickening region, the Ed of EG/SiO2, PG/SiO2, and BG/SiO2 dispersions show an exponential increase with γ0 by the exponents of n=2.79, 4.93, and 4.88, respectively.
The viscoelastic behavior and the ability of dissipating energy of fumed silica dispersions in ethylene glycol, propylene glycol and butylene glycol have been studied under oscillation stress shear. The systems show linear viscoelastic, shear thinning, and shear thickening behaviors as the shear stress (σ) increasing. In linear viscoelastic region, the storage modulus (G′) and loss modulus (G′′) remain unchanged； in shear thinning region, G′ decreases and the sequence of the decreasing degree of G′ is EG/SiO2>PG/SiO2> BG/SiO2; however G′′ remains unchanged with σ increasing； in shear thickening region, both G′ and G′′ increase as σ increases. The magnitude of G′′ is larger than the magnitude of G′ over the studied range of stress, indicating that the dispersions mainly possess viscous property, and the energy dissipated is larger than the energy stored. The dissipated energies (Ed) of EG/SiO2, PG/SiO2, and BG/SiO2 dispersions increase with the maximum strain (γ0) in a second power relation under low shear stress; however, in the shear thickening region, the Ed of EG/SiO2, PG/SiO2, and BG/SiO2 dispersions show an exponential increase with γ0 by the exponents of n=2.79, 4.93, and 4.88, respectively.
2006, 22(09): 1079-1084
doi: 10.1016/S1872-1508(06)60048-X
Abstract:
Equilibrium geometries of cis-HOOOH and trans-HOOOH have been investigated using the density functional theory (DFT), complete active space self-consistent-field (CASSCF), and coupled cluster with single and double replacement (CCSD) approaches. The harmonic vibrational frequencies on the optimized geometries were calculated using the DFT theory. The potential energy curve of the isomerization between the trans-HOOOH and cis-HOOOH was obtained by DFT calculations. Time-dependent density functional theory (TD-DFT) and complete active space perturbation theory of second order (CASPT2) calculations have been performed to obtain the vertical excitation energies of selected low-lying singlet and triplet excited states. Computed results show that: (1) trans-isomer is more stable than cis-isomer; (2) there are two pathways of the conversion between the trans-HOOOH and cis-HOOOH; (3) the vertical excitation energies of the lowest singlet and triplet excited states in trans-HOOOH are lower than those in cis-isomer; (4) in the singlet excited states, 21A state in trans-HOOOH and 21A′′ state in cis-HOOOH have the longest lifetimes of 2.07×10−5 s and 1.44×10−5 s with the excitation energies of 165.52 and 167.43 nm, respectively.
Equilibrium geometries of cis-HOOOH and trans-HOOOH have been investigated using the density functional theory (DFT), complete active space self-consistent-field (CASSCF), and coupled cluster with single and double replacement (CCSD) approaches. The harmonic vibrational frequencies on the optimized geometries were calculated using the DFT theory. The potential energy curve of the isomerization between the trans-HOOOH and cis-HOOOH was obtained by DFT calculations. Time-dependent density functional theory (TD-DFT) and complete active space perturbation theory of second order (CASPT2) calculations have been performed to obtain the vertical excitation energies of selected low-lying singlet and triplet excited states. Computed results show that: (1) trans-isomer is more stable than cis-isomer; (2) there are two pathways of the conversion between the trans-HOOOH and cis-HOOOH; (3) the vertical excitation energies of the lowest singlet and triplet excited states in trans-HOOOH are lower than those in cis-isomer; (4) in the singlet excited states, 21A state in trans-HOOOH and 21A′′ state in cis-HOOOH have the longest lifetimes of 2.07×10−5 s and 1.44×10−5 s with the excitation energies of 165.52 and 167.43 nm, respectively.
2006, 22(09): 1085-1089
doi: 10.1016/S1872-1508(06)60049-1
Abstract:
The charge and relaxation effects on the C 1s core ionization energies of halomethanes CHnY4−n−mZ (Y, Z=F, Cl, Br, I) were evaluated based on the atomic electronegativity χP and the polarizability α. The charge effect was scaled using the electronegativity discrepancy between C and H or the halogen atom in the C—H or C—Y(Z) bond. The relaxation effect (induced dipole) was scaled using the charge on the carbon atom together with the polarizabiliy of the H and halogen atoms. Furthermore, the electrostatic-relaxation shielding ΔSi of the C 1s electron in the halomethane was expressed by the charge effect in combination with the relaxation effect. By introducing the ΔSi into the Slater model, a Slater-like model was obtained for calculating the C 1s core ionization energy E1,C of halomethane, whose correlation coefficient r was 0.99987, and the average absolute error was only 0.038 eV between the calculated and the experimental C 1s core ionization energies for 27 halomethanes. Moreover, the cross-correlation was tested using the leave-one-out (LOO) cross-validation method, and the obtained model had od predictive ability and stability (the correlation coefficient rcv was 0.99977, the average absolute error between the predicted and the experimental values was only 0.049 eV). The proposed model probably laid a od foundation for computing the core ionization energies of various atoms in more complex molecules.
The charge and relaxation effects on the C 1s core ionization energies of halomethanes CHnY4−n−mZ (Y, Z=F, Cl, Br, I) were evaluated based on the atomic electronegativity χP and the polarizability α. The charge effect was scaled using the electronegativity discrepancy between C and H or the halogen atom in the C—H or C—Y(Z) bond. The relaxation effect (induced dipole) was scaled using the charge on the carbon atom together with the polarizabiliy of the H and halogen atoms. Furthermore, the electrostatic-relaxation shielding ΔSi of the C 1s electron in the halomethane was expressed by the charge effect in combination with the relaxation effect. By introducing the ΔSi into the Slater model, a Slater-like model was obtained for calculating the C 1s core ionization energy E1,C of halomethane, whose correlation coefficient r was 0.99987, and the average absolute error was only 0.038 eV between the calculated and the experimental C 1s core ionization energies for 27 halomethanes. Moreover, the cross-correlation was tested using the leave-one-out (LOO) cross-validation method, and the obtained model had od predictive ability and stability (the correlation coefficient rcv was 0.99977, the average absolute error between the predicted and the experimental values was only 0.049 eV). The proposed model probably laid a od foundation for computing the core ionization energies of various atoms in more complex molecules.
2006, 22(09): 1090-1094
doi: 10.3866/PKU.WHXB20060911
Abstract:
The non-close-packed photonic crystal gels (NCPPCGs) with the range of Bragg diffractive peaks from 700 nm to 800 nm were fabricated. The relation between the swelling-shrinking of NCPPCGs and the shifts of the Bragg diffractive peaks was studied by their dehydrating in air and immersing in ethanol solutions with different concentrations and buffers with different pHs. When they were dehydrated in air, the Bragg diffractive peaks of the NCPPCGs blue-shifted; when they were immersed in water, the Bragg diffractive peaks of the dehydrated NCPPCGs red-shifted to the original position rapidly. The volume of the NCPPCGs varied when they were immersed in ethanol solutions with different concentrations, and their Bragg diffractive peaks blue-shifted proportionally with the concentrations of ethanol. The hydrolyzed NCPPCGs were pH-sensitive, and their Bragg diffractive peaks red-shifted in the pH range from 2.2 to 9.6, but blue-shifted in the pH range from 9.6 to 10.6. The Bragg diffractive peak positions of the prepared NCPPCGs can cover the entire visible region of light.
The non-close-packed photonic crystal gels (NCPPCGs) with the range of Bragg diffractive peaks from 700 nm to 800 nm were fabricated. The relation between the swelling-shrinking of NCPPCGs and the shifts of the Bragg diffractive peaks was studied by their dehydrating in air and immersing in ethanol solutions with different concentrations and buffers with different pHs. When they were dehydrated in air, the Bragg diffractive peaks of the NCPPCGs blue-shifted; when they were immersed in water, the Bragg diffractive peaks of the dehydrated NCPPCGs red-shifted to the original position rapidly. The volume of the NCPPCGs varied when they were immersed in ethanol solutions with different concentrations, and their Bragg diffractive peaks blue-shifted proportionally with the concentrations of ethanol. The hydrolyzed NCPPCGs were pH-sensitive, and their Bragg diffractive peaks red-shifted in the pH range from 2.2 to 9.6, but blue-shifted in the pH range from 9.6 to 10.6. The Bragg diffractive peak positions of the prepared NCPPCGs can cover the entire visible region of light.
2006, 22(09): 1095-1100
doi: 10.1016/S1872-1508(06)60050-8
Abstract:
The reaction mechanism between atomic oxygen radical anion and benzene has been investigated using the density functional theory (DFT). Geometries of the reactants, products, complexes and transition states involved have been optimized at the B3LYP/6-31+G(d, p) level, and their vibrational frequencies and zero-point energies (ZPEs) have been calculated subsequently at the same level. The multichannel pathways, e.g. the H-atom abstraction, oxide-ion formation, H2+ transfer, and proton transfer, are confirmed by calculated potential energy surface of this reaction described in this study. Based on the G2MP2 energies, a reasonable description has been proposed qualitatively to explain the inconsistency of previous experimental conclusions.
The reaction mechanism between atomic oxygen radical anion and benzene has been investigated using the density functional theory (DFT). Geometries of the reactants, products, complexes and transition states involved have been optimized at the B3LYP/6-31+G(d, p) level, and their vibrational frequencies and zero-point energies (ZPEs) have been calculated subsequently at the same level. The multichannel pathways, e.g. the H-atom abstraction, oxide-ion formation, H2+ transfer, and proton transfer, are confirmed by calculated potential energy surface of this reaction described in this study. Based on the G2MP2 energies, a reasonable description has been proposed qualitatively to explain the inconsistency of previous experimental conclusions.
2006, 22(09): 1101-1105
doi: 10.3866/PKU.WHXB20060913
Abstract:
Based on the density-functional theory(DFT) and the first-principle method, the electronic distribution and the density of states(DOS) of the armchair (5, 5) and zigzag (8, 0) single-walled carbon nanotubes (SCNTs) grafted by hydroxyl were calculated. First a geometry optimization of SCNTs is performed by using BLYP function in DMol3 program, then the variations of electronic distribution and DOS are calculated by adopting the CASTEP program. It has been found that the electronic structure of the SCNTs due to the graft changes significantly, namely, the electron density of states near Fermi level, the delocalized degree of the highest occupied molecular orbital (HOMO), and accordingly the transport properties of SCNTs decrease as the number of grafted hydroxyl groups increase.
Based on the density-functional theory(DFT) and the first-principle method, the electronic distribution and the density of states(DOS) of the armchair (5, 5) and zigzag (8, 0) single-walled carbon nanotubes (SCNTs) grafted by hydroxyl were calculated. First a geometry optimization of SCNTs is performed by using BLYP function in DMol3 program, then the variations of electronic distribution and DOS are calculated by adopting the CASTEP program. It has been found that the electronic structure of the SCNTs due to the graft changes significantly, namely, the electron density of states near Fermi level, the delocalized degree of the highest occupied molecular orbital (HOMO), and accordingly the transport properties of SCNTs decrease as the number of grafted hydroxyl groups increase.
2006, 22(09): 1106-1110
doi: 10.3866/PKU.WHXB20060914
Abstract:
Photodissociation dynamics of n-C7H15Br molecule was investigated at different wavelengths of 231 to 239 nm by an ion imaging spectrometer operated under optimal conditions for velocity mapping , where the ions were generated from (2+1) resonance enhanced ionization (REMPI) of the photofragments Br(2P3/2) and Br*(2P1/2) at the same wavelength as that of the photolysis laser. The released kinetic energies and the angular distributions of both fragments at different photolysis wavelengths were derived from the three-dimensional velocity images. The probabilities of the individual pathways of the fragments at 234 nm were calculated from the relative quantum yield and angular distribution. The total translational energy distributions were interpreted using soft impulsive model. The anisotropy parameter for Br* is sensitive to the photolysis wavelength. This fact can be explained by the adiabatic and non-adiabatic dissociation processes in the electronically excited states of n-C7H15Br.
Photodissociation dynamics of n-C7H15Br molecule was investigated at different wavelengths of 231 to 239 nm by an ion imaging spectrometer operated under optimal conditions for velocity mapping , where the ions were generated from (2+1) resonance enhanced ionization (REMPI) of the photofragments Br(2P3/2) and Br*(2P1/2) at the same wavelength as that of the photolysis laser. The released kinetic energies and the angular distributions of both fragments at different photolysis wavelengths were derived from the three-dimensional velocity images. The probabilities of the individual pathways of the fragments at 234 nm were calculated from the relative quantum yield and angular distribution. The total translational energy distributions were interpreted using soft impulsive model. The anisotropy parameter for Br* is sensitive to the photolysis wavelength. This fact can be explained by the adiabatic and non-adiabatic dissociation processes in the electronically excited states of n-C7H15Br.
2006, 22(09): 1111-1115
doi: 10.1016/S1872-1508(06)60051-X
Abstract:
Nanocomposite of LiF-Ni with a highly heterogeneous mixture was fabricated using pulsed laser deposition (PLD) method, and it exhibited remarkable electrochemical activity. The electrochemical reaction of LiF-Ni nanocomposite thin-film electrode with Li was firstly investigated by the discharge/charge and cyclic voltammetry. The initial charge capacity of the LiF-Ni/Li cell was found to be 107 mAh•g−1. The process of releasing Li from the as-deposited LiF-Ni nanocomposite thin films was confirmed by ex-situ high-resolution transmission electron microscopy and by the selected area electron diffraction measurements. These results provided a direct experimental evidence to support the electrochemical decomposition of LiF driven by the transition metal Ni in the potential range from 1.0 V to 4.0 V. LiF-Ni nanocomposite electrodes could be a novel candidate that could be used as an appropriate for Li storage material.
Nanocomposite of LiF-Ni with a highly heterogeneous mixture was fabricated using pulsed laser deposition (PLD) method, and it exhibited remarkable electrochemical activity. The electrochemical reaction of LiF-Ni nanocomposite thin-film electrode with Li was firstly investigated by the discharge/charge and cyclic voltammetry. The initial charge capacity of the LiF-Ni/Li cell was found to be 107 mAh•g−1. The process of releasing Li from the as-deposited LiF-Ni nanocomposite thin films was confirmed by ex-situ high-resolution transmission electron microscopy and by the selected area electron diffraction measurements. These results provided a direct experimental evidence to support the electrochemical decomposition of LiF driven by the transition metal Ni in the potential range from 1.0 V to 4.0 V. LiF-Ni nanocomposite electrodes could be a novel candidate that could be used as an appropriate for Li storage material.
2006, 22(09): 1116-1120
doi: 10.3866/PKU.WHXB20060916
Abstract:
Gallium atoms had been introduced into the framework of Y zeolite by treatment of zeolites with an aqueous solution of ammonium hexafluoro gallate. At ambient conditions and space velocity of 7 h−1, desulfurization of various model fuel, containing about 500 μg•g−1 sulfur was studied over the synthesized Y zeolite. Every gram adsorbent could adsorb 7.7, 17.4, 14.5 mg sulfur from thiophene, tetrahydrothiophene, 4,6-dimethyldibenzothiophene (4,6-DMDBT), respectively. The charge on S atom of thiophene, 4,6-DMDBT, and tetrahydrothiophene, calculated by using density functional theory (DFT), were −0.159, −0.214, and −0.298 respectively, implying that the S—M bond between the adsorption site and thiophene was much weaker than that between the adsorption site and tetrahydrothiophene or 4,6-DMDBT. The synthesized Y zeolites were evaluated for the adsorptive desulfurization of the FCC gasoline (sulfur content：299 μg•g−1) supplied by the No.2 Refinery in Fushun. After 2.1 mL gasoline being treated in one gram adsorbent, the sulfur content was 54.8 μg•g-1.
Gallium atoms had been introduced into the framework of Y zeolite by treatment of zeolites with an aqueous solution of ammonium hexafluoro gallate. At ambient conditions and space velocity of 7 h−1, desulfurization of various model fuel, containing about 500 μg•g−1 sulfur was studied over the synthesized Y zeolite. Every gram adsorbent could adsorb 7.7, 17.4, 14.5 mg sulfur from thiophene, tetrahydrothiophene, 4,6-dimethyldibenzothiophene (4,6-DMDBT), respectively. The charge on S atom of thiophene, 4,6-DMDBT, and tetrahydrothiophene, calculated by using density functional theory (DFT), were −0.159, −0.214, and −0.298 respectively, implying that the S—M bond between the adsorption site and thiophene was much weaker than that between the adsorption site and tetrahydrothiophene or 4,6-DMDBT. The synthesized Y zeolites were evaluated for the adsorptive desulfurization of the FCC gasoline (sulfur content：299 μg•g−1) supplied by the No.2 Refinery in Fushun. After 2.1 mL gasoline being treated in one gram adsorbent, the sulfur content was 54.8 μg•g-1.
2006, 22(09): 1121-1125
doi: 10.3866/PKU.WHXB20060917
Abstract:
Three dimensional ordered macroporous (3DOM) zirconium dioxides with pore diameters of about 500 nm are successfully prepared via a direct calcining step, using a methanol solution of ZrOCl2•8H2O as filling precursor and polystyrene sphere (PS) colloid crystals as templates. The method of synthesis is simple, quicker than other synthesis, and based on readily available precursors. Precursor concentration and a second filling of the 3D packed polystyrene spheres are important parameters in fine tuning the mechanical properties of the walls and achieving long range ordered materials. Low calcination temperature (≤500 ℃) introduces impurities in the wall structure of zirconia and crystallite phase transformation in the crystal structure. Excess high calcination temperature (≥ 800 ℃) leads the 3D wall structure destroyed and collapse. The BET behaviour of 3DOM-ZrO2 shows that pore wall has a non-porous structure, which agrees with the TEM results.
Three dimensional ordered macroporous (3DOM) zirconium dioxides with pore diameters of about 500 nm are successfully prepared via a direct calcining step, using a methanol solution of ZrOCl2•8H2O as filling precursor and polystyrene sphere (PS) colloid crystals as templates. The method of synthesis is simple, quicker than other synthesis, and based on readily available precursors. Precursor concentration and a second filling of the 3D packed polystyrene spheres are important parameters in fine tuning the mechanical properties of the walls and achieving long range ordered materials. Low calcination temperature (≤500 ℃) introduces impurities in the wall structure of zirconia and crystallite phase transformation in the crystal structure. Excess high calcination temperature (≥ 800 ℃) leads the 3D wall structure destroyed and collapse. The BET behaviour of 3DOM-ZrO2 shows that pore wall has a non-porous structure, which agrees with the TEM results.
2006, 22(09): 1126-1131
doi: 10.1016/S1872-1508(06)60052-1
Abstract:
The adsorption and dissociation of two NO molecules on Cu2O(111) surface have been studied with periodic slab model by DFT method using the generalized gradient approximation(GGA) with the Perdew-Burke-Emzerhof(PBE) exchange-correlation functional. Three kinds of structures, Cu+(NO)(NO), Cu+(NO)(ON), and Cu+(ON)(ON), with singlet and triplet states, were considered. Their corresponding adsorption energies and Mulliken charges were calculated. The calculated results indicate that in the optimized Cu+(ON)(ON) configuration, two adsorbed NO molecules form a dimeric species with a much shorter N—N bond length (about 124.4 pm). Such a configuration contributes to the dissociation of NO to Cu-O surface species, with elimination of N2 or N2O.
The adsorption and dissociation of two NO molecules on Cu2O(111) surface have been studied with periodic slab model by DFT method using the generalized gradient approximation(GGA) with the Perdew-Burke-Emzerhof(PBE) exchange-correlation functional. Three kinds of structures, Cu+(NO)(NO), Cu+(NO)(ON), and Cu+(ON)(ON), with singlet and triplet states, were considered. Their corresponding adsorption energies and Mulliken charges were calculated. The calculated results indicate that in the optimized Cu+(ON)(ON) configuration, two adsorbed NO molecules form a dimeric species with a much shorter N—N bond length (about 124.4 pm). Such a configuration contributes to the dissociation of NO to Cu-O surface species, with elimination of N2 or N2O.
2006, 22(09): 1132-1136
doi: 10.3866/PKU.WHXB20060919
Abstract:
The surficial characters and charge effects of the modified K2CO3/MoS2 catalysts with different Ni content were investigated by XRD, BET, XPS. The results suggested that two types of Ni-contained species were formed in Ni/K2CO3/MoS2 catalysts, namely, pure phases of NiSx and Ni-Mo-S mixed phase. With lower Ni loading (nNi/nMo＜1/3), the main Ni species was Ni-Mo-S and Ni content on the surface was lower than that of the bulk. With the increasing of Ni content, the coordination between Ni and MoS2 became saturation and NiSx phases were formed gradually. The formation of NiSx phases resulted in the enrichment of Ni on the surface as well as S and K and a favorable chemical environment for the formation of alcohols but not hydrocarbons. As a donor promoter, the Ni-Mo-S structures corresponded to a strong electron transition between Ni and Mo, however, the electron effect between NiSx and MoS2 was weaker. The regularly decline of electron interaction between Ni and Mo with the increasing of Ni content indicated that the saturation of coordination betweenNi and MoS2 and the formation of NiSx phase.
The surficial characters and charge effects of the modified K2CO3/MoS2 catalysts with different Ni content were investigated by XRD, BET, XPS. The results suggested that two types of Ni-contained species were formed in Ni/K2CO3/MoS2 catalysts, namely, pure phases of NiSx and Ni-Mo-S mixed phase. With lower Ni loading (nNi/nMo＜1/3), the main Ni species was Ni-Mo-S and Ni content on the surface was lower than that of the bulk. With the increasing of Ni content, the coordination between Ni and MoS2 became saturation and NiSx phases were formed gradually. The formation of NiSx phases resulted in the enrichment of Ni on the surface as well as S and K and a favorable chemical environment for the formation of alcohols but not hydrocarbons. As a donor promoter, the Ni-Mo-S structures corresponded to a strong electron transition between Ni and Mo, however, the electron effect between NiSx and MoS2 was weaker. The regularly decline of electron interaction between Ni and Mo with the increasing of Ni content indicated that the saturation of coordination betweenNi and MoS2 and the formation of NiSx phase.
2006, 22(09): 1137-1142
doi: 10.1016/S1872-1508(06)60053-3
Abstract:
Molecular dynamics (MD) is used to investigate the structural and diffusive properties of interlayer species, namely water and counterion speciations of Na-montmorillonite and Na/Mg-montmorillonite. It is found that Na/Mg-montmorillonite exhibits a higher swellability compored with that of Na-montmorillonite for given water content, especially with 48～72 water molecules of interlayer, the expansion of layer spacings of Na/Mg-montmorillonite is greater than those of Na-montmmorillonite. Interlayer water molecules have a stronger tendency to solvate Mg2+ compared to that of Na+. Inner-sphere complexes and outer-sphere complexes of Mg2+ with water are observed, whereas only planar inner-sphere complexes of Na+ with water are found for two-layer Na/Mg-montmorillonite hydrates. The results also indicate the different diffusion modes of Na+ and Mg2+ for Na/Mg montmorillonite: Na+ remains close to the surfaces of the sheets, whereas Mg2+ is easily hydrated and is located in the middle of the interlayer. Comparatively, Na+ has a wider diffusion range and higher self-diffusion coefficient than Mg2+. Moreover, self-diffusion coefficient of interlayer water is higher for Na-montmorillonite than that for Na/Mg-montmorillonite at the same water content. Most of the results obtained in this study can be understood in terms of the strong solvation of Mg2+ with water molecules, and Mg2+ and Na+ have different influences on the structure of interlayer. It can therefore be assumed that the replacement of a relatively small amount of interlayer Na+ cations by Mg2+ in Na-montmorillonite during the initial stage can substantially change the swelling and diffusion properties of interlayer species.
Molecular dynamics (MD) is used to investigate the structural and diffusive properties of interlayer species, namely water and counterion speciations of Na-montmorillonite and Na/Mg-montmorillonite. It is found that Na/Mg-montmorillonite exhibits a higher swellability compored with that of Na-montmorillonite for given water content, especially with 48～72 water molecules of interlayer, the expansion of layer spacings of Na/Mg-montmorillonite is greater than those of Na-montmmorillonite. Interlayer water molecules have a stronger tendency to solvate Mg2+ compared to that of Na+. Inner-sphere complexes and outer-sphere complexes of Mg2+ with water are observed, whereas only planar inner-sphere complexes of Na+ with water are found for two-layer Na/Mg-montmorillonite hydrates. The results also indicate the different diffusion modes of Na+ and Mg2+ for Na/Mg montmorillonite: Na+ remains close to the surfaces of the sheets, whereas Mg2+ is easily hydrated and is located in the middle of the interlayer. Comparatively, Na+ has a wider diffusion range and higher self-diffusion coefficient than Mg2+. Moreover, self-diffusion coefficient of interlayer water is higher for Na-montmorillonite than that for Na/Mg-montmorillonite at the same water content. Most of the results obtained in this study can be understood in terms of the strong solvation of Mg2+ with water molecules, and Mg2+ and Na+ have different influences on the structure of interlayer. It can therefore be assumed that the replacement of a relatively small amount of interlayer Na+ cations by Mg2+ in Na-montmorillonite during the initial stage can substantially change the swelling and diffusion properties of interlayer species.
2006, 22(09): 1143-1146
doi: 10.3866/PKU.WHXB20060921
Abstract:
CdTe quantum dots (QDs) stabilized by mercaptopropionic acid (MPA) with strong fluorescence were prepared in aqueous solution at low temperature. A series of hybrid nanocomposites of CdTe/2,4,6-tri[N-(4-hydroxyphenyl)maleimide] triazine (TMT) were successfully prepared at room temperature based on the existence of strong hydrogen-bond interactions between the CdTe quantum dots and TMT. The photophysical properties of these nanocomposites were systematically investigated by UV-Vis and PL spectra, which indicated that energy transfer (ET) occurred between CdTe QDs and TMT. In addition, the morphologies of these nanocomposites were also observed by transmission electronic microscopy, showing that there was an extraordinary enhancement of the dispersibility of CdTe quantum dots.
CdTe quantum dots (QDs) stabilized by mercaptopropionic acid (MPA) with strong fluorescence were prepared in aqueous solution at low temperature. A series of hybrid nanocomposites of CdTe/2,4,6-tri[N-(4-hydroxyphenyl)maleimide] triazine (TMT) were successfully prepared at room temperature based on the existence of strong hydrogen-bond interactions between the CdTe quantum dots and TMT. The photophysical properties of these nanocomposites were systematically investigated by UV-Vis and PL spectra, which indicated that energy transfer (ET) occurred between CdTe QDs and TMT. In addition, the morphologies of these nanocomposites were also observed by transmission electronic microscopy, showing that there was an extraordinary enhancement of the dispersibility of CdTe quantum dots.
2006, 22(09): 1147-1150
doi: 10.3866/PKU.WHXB20060922
Abstract:
Large-scale silicon nanowires (SiNWs), which consist of a crystalline silicon core and a thick oxide shell with a length of tens of micrometers, were synthesized by evaporation of silicon monoxide (SiO) using a ld-coated silicon wafer as substrate in a low vacuum CVD system. The morphology and structure of the nanowires were inspected and analyzed by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected electron diffraction (SAED), and Raman spectroscopy. The experimental results indicated the quality of silicon nanowires (SiNWs) varied with different growth temperatures, and it was found that the SiNWs produced at 700 ℃ zone had a well-crystallized structure. Compared with the Raman peak of the first-order transverse optical phonon mode (TO) at 520.3 cm−1 for bulk silicon, the corresponding peak for as-grown SiNWs redshifted to 514.8 cm−1.
Large-scale silicon nanowires (SiNWs), which consist of a crystalline silicon core and a thick oxide shell with a length of tens of micrometers, were synthesized by evaporation of silicon monoxide (SiO) using a ld-coated silicon wafer as substrate in a low vacuum CVD system. The morphology and structure of the nanowires were inspected and analyzed by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected electron diffraction (SAED), and Raman spectroscopy. The experimental results indicated the quality of silicon nanowires (SiNWs) varied with different growth temperatures, and it was found that the SiNWs produced at 700 ℃ zone had a well-crystallized structure. Compared with the Raman peak of the first-order transverse optical phonon mode (TO) at 520.3 cm−1 for bulk silicon, the corresponding peak for as-grown SiNWs redshifted to 514.8 cm−1.
2006, 22(09): 1151-1154
doi: 10.3866/PKU.WHXB20060923
Abstract:
The average value of hydrogen diffusion coefficient in metal hydride (MH) electrode was measured by constant current discharge method. The relationship between hydrogen diffusion coefficient and state of charge (SOC) was determined by potentiostatic method. According to the MH electrode model, the fast charging performance of MH electrode can be improved by increasing hydrogen diffusion coefficient or decreasing the particle size of hydrogen storage alloy. The time when the surface hydrogen atom concentration on the MH electrode reaches maximum value under different initial states of charge and charge rates also can be calculated.
The average value of hydrogen diffusion coefficient in metal hydride (MH) electrode was measured by constant current discharge method. The relationship between hydrogen diffusion coefficient and state of charge (SOC) was determined by potentiostatic method. According to the MH electrode model, the fast charging performance of MH electrode can be improved by increasing hydrogen diffusion coefficient or decreasing the particle size of hydrogen storage alloy. The time when the surface hydrogen atom concentration on the MH electrode reaches maximum value under different initial states of charge and charge rates also can be calculated.
2006, 22(09): 1155-1158
doi: 10.3866/PKU.WHXB20060924
Abstract:
A bipolar pulse current charge method was developed to charge lithium metal electrode in 1 mol•L−1 LiPF6/ethylene carbonate (EC):dimethyl carbonate (DMC) (1:1, V/V) electrolyte. The surface variations of lithium electrode during charge processes were investigated by in situ optical microscopic observation and impedance measurement. It was observed that lithium dendrites formed on lithium electrode during direct current (DC) charge process, but it was inhibited by bipolar pulse charge method. The results of the impedance measurement show that the surface area increases much slower in bipolar pulse current charge process than that in DC charge process. This technique may be useful for the rechargeable lithium battery.
A bipolar pulse current charge method was developed to charge lithium metal electrode in 1 mol•L−1 LiPF6/ethylene carbonate (EC):dimethyl carbonate (DMC) (1:1, V/V) electrolyte. The surface variations of lithium electrode during charge processes were investigated by in situ optical microscopic observation and impedance measurement. It was observed that lithium dendrites formed on lithium electrode during direct current (DC) charge process, but it was inhibited by bipolar pulse charge method. The results of the impedance measurement show that the surface area increases much slower in bipolar pulse current charge process than that in DC charge process. This technique may be useful for the rechargeable lithium battery.
2006, 22(09): 1159-1162
doi: 10.3866/PKU.WHXB20060925
Abstract:
Far-infrared absorption spectra of D-, L-, and DL- penicillamines have been measured by terahertz time-domain spectroscopy (THz-TDS) in the frequency range from 0.2 THz to 1.8 THz. The experimental results show large difference among absorption spectra of enantiomers (D- and L- penicillamines) and their racemic compound (DL-penicillamine), which probably originated from the difference of crystal structure and vibration modes of crystal lattice. The study indicates that THz-TDS can be used for discrimination of D-, L-, and DL- penicillamines. The absorption spectra of their mixtures have been fitted by the absorption spectra of D- and L- penicillamines, and we have demonstrated the feasibility of this method to determine quantitatively the mixture ratios of penicillamine enantiomers. These will not only give a new experimental method to distinguish chiral medicine, but also provide a suggestion for further comprehending the interaction of chiral medicine and target biomolecule.
Far-infrared absorption spectra of D-, L-, and DL- penicillamines have been measured by terahertz time-domain spectroscopy (THz-TDS) in the frequency range from 0.2 THz to 1.8 THz. The experimental results show large difference among absorption spectra of enantiomers (D- and L- penicillamines) and their racemic compound (DL-penicillamine), which probably originated from the difference of crystal structure and vibration modes of crystal lattice. The study indicates that THz-TDS can be used for discrimination of D-, L-, and DL- penicillamines. The absorption spectra of their mixtures have been fitted by the absorption spectra of D- and L- penicillamines, and we have demonstrated the feasibility of this method to determine quantitatively the mixture ratios of penicillamine enantiomers. These will not only give a new experimental method to distinguish chiral medicine, but also provide a suggestion for further comprehending the interaction of chiral medicine and target biomolecule.
2006, 22(09): 1163-1167
doi: 10.3866/PKU.WHXB20060926
Abstract:
According to the phenomena that inorganic salt may deposit on biological cell membrane and the biomineralization theory, under the man-made culture conditions, one kind of SiO2 nanostructured material with special shape was biominerally synthesized successfully by means of the cell templates of lower eukaryote-yeast and by tetraethyl orthosilicate(TEOS) as Si nutrition. In the yeast cell wall, the shell-like nanostructured SiO2 was synthesized, and its thickness was 150 nm. The samples were investigated by TEM, SEM, EDX, FT-IR, XPS, TGA, etc., and massive experimental data were obtained.
According to the phenomena that inorganic salt may deposit on biological cell membrane and the biomineralization theory, under the man-made culture conditions, one kind of SiO2 nanostructured material with special shape was biominerally synthesized successfully by means of the cell templates of lower eukaryote-yeast and by tetraethyl orthosilicate(TEOS) as Si nutrition. In the yeast cell wall, the shell-like nanostructured SiO2 was synthesized, and its thickness was 150 nm. The samples were investigated by TEM, SEM, EDX, FT-IR, XPS, TGA, etc., and massive experimental data were obtained.
2006, 22(09): 1168-1174
doi: 10.3866/PKU.WHXB20060927
Abstract:
Popular computational methods were reviewed, such as first-principle calculations, molecular dynamics simulation, and Monte Carlo simulation. Novel results and important progress were introduced to exhibit the great roles of the above methods utilized in simulating lithium ion battery and hydrogen storage materials. The wide use of material simulation and design is prospected for the future material innovation in the field of energy storage.
Popular computational methods were reviewed, such as first-principle calculations, molecular dynamics simulation, and Monte Carlo simulation. Novel results and important progress were introduced to exhibit the great roles of the above methods utilized in simulating lithium ion battery and hydrogen storage materials. The wide use of material simulation and design is prospected for the future material innovation in the field of energy storage.
