Login In
2012 Volume 28 Issue 5
2012, 28(05):
Abstract:
2012, 28(05): 993-1011
doi: 10.3866/PKU.WHXB201203023
Abstract:
This review summaries the syntheses and applications of magnetic iron oxide nanocrystals that have been published worldwide. In particular, it discusses the future applications of magnetic iron oxide nanoparticles in molecular imaging of tumors.
This review summaries the syntheses and applications of magnetic iron oxide nanocrystals that have been published worldwide. In particular, it discusses the future applications of magnetic iron oxide nanoparticles in molecular imaging of tumors.
2012, 28(05): 1012-1020
doi: 10.3866/PKU.WHXB201203052
Abstract:
This review summarizes the current status of the evolution and observation of oxygen vacancies in CeO2-doped solid solutions as characterized by Raman spectroscopy. Three Raman peaks at 465, 560, and 600 cm-1 are ascribed to the F2g symmetrical stretching vibration mode of CeO2 in a fluorite structure, oxygen vacancies, and a MO8-type complex, respectively. The presence of oxygen vacancies was related to the ionic valence states of the dopant, while the MO8-type complex was associated with the ionic radii of the dopant. The oxygen vacancy concentration correlated with the sample absorbance and the surface enrichment of oxygen vacancies. The in situ Raman spectroscopic investigations show that the atmospheric composition and temperature had a large influence on the absorbance of the samples, which in turn alters the detection depth of the Raman laser and the observed oxygen vacancy concentration.
This review summarizes the current status of the evolution and observation of oxygen vacancies in CeO2-doped solid solutions as characterized by Raman spectroscopy. Three Raman peaks at 465, 560, and 600 cm-1 are ascribed to the F2g symmetrical stretching vibration mode of CeO2 in a fluorite structure, oxygen vacancies, and a MO8-type complex, respectively. The presence of oxygen vacancies was related to the ionic valence states of the dopant, while the MO8-type complex was associated with the ionic radii of the dopant. The oxygen vacancy concentration correlated with the sample absorbance and the surface enrichment of oxygen vacancies. The in situ Raman spectroscopic investigations show that the atmospheric composition and temperature had a large influence on the absorbance of the samples, which in turn alters the detection depth of the Raman laser and the observed oxygen vacancy concentration.
2012, 28(05): 1021-1029
doi: 10.3866/PKU.WHXB201202271
Abstract:
A series of oxides in the Mn3O4-Fe2O3 system have been synthesized at 1200 ℃ in air, followed by quenching to room temperature. Three solid solutions, Mn3-3xFe3xO4 (0.00≤x≤0.278), Mn3-3xFe3xO4(0.291≤x≤0.667), and Mn2-2xFe2xO3 (0.89≤x≤1.00), have been identified by powder X-ray diffraction (XRD). Rietveld refinement of the XRD data show that the solids belong to the hausmannite phase with the space group I41/amd, the spinel phase with the space group Fd3m, and the hematite phase with the space group R3c, respectively. Between these are two-phase regions. 57Fe Mössbauer spectra indicate that the valence state of Fe in the three solid solutions is +3; in addition, there are two crystallographically independent Fe3+ ions in the unit cells of the hausmannite and spinel phases, and one Fe3+ in the hematite phase. Analyses of 57Fe Mössbauer spectra and X-ray photoelectron spectra (XPS) revealed that a formula of Mn1-x2+Fex3+[Mnx3+Fex3+Mn2-3x3+]O4 describes the cation distribution of both the hausmannite and spinel phases, but that for the hematite phase is Mn2-2x3+Fe2x3+O3.
A series of oxides in the Mn3O4-Fe2O3 system have been synthesized at 1200 ℃ in air, followed by quenching to room temperature. Three solid solutions, Mn3-3xFe3xO4 (0.00≤x≤0.278), Mn3-3xFe3xO4(0.291≤x≤0.667), and Mn2-2xFe2xO3 (0.89≤x≤1.00), have been identified by powder X-ray diffraction (XRD). Rietveld refinement of the XRD data show that the solids belong to the hausmannite phase with the space group I41/amd, the spinel phase with the space group Fd3m, and the hematite phase with the space group R3c, respectively. Between these are two-phase regions. 57Fe Mössbauer spectra indicate that the valence state of Fe in the three solid solutions is +3; in addition, there are two crystallographically independent Fe3+ ions in the unit cells of the hausmannite and spinel phases, and one Fe3+ in the hematite phase. Analyses of 57Fe Mössbauer spectra and X-ray photoelectron spectra (XPS) revealed that a formula of Mn1-x2+Fex3+[Mnx3+Fex3+Mn2-3x3+]O4 describes the cation distribution of both the hausmannite and spinel phases, but that for the hematite phase is Mn2-2x3+Fe2x3+O3.
2012, 28(05): 1030-1036
doi: 10.3866/PKU.WHXB201203025
Abstract:
UV-visible electronic absorption spectra of methyl red aqueous solutions are characterized by the overlap of a principal peak at λmax ((520±15) nm) with a shoulder peak at λmax ((435±20) nm), which are assigned to acidic species (HMR) and basic species (MR-) of methyl red, respectively. In this study, the spectra and the integrated absorbance of the MR- and HMR peaks (denoted A1 and A2, respectively) were interpreted using a new multi-peaks Gaussian fitting method. From the absorbance ratio A1/A2 and the concentration ratio cMR-/cHMR, the average acid dissociation constant (pKa) was determined as 4.76 at 298.15 K. The odness is high and the values of R2 (degree of fitting) and χ2 (chi-square test for odness of fit) were 0.998 and below 10-5, respectively. The effects of aggregation behavior of sodium dodecyl sulfate (SDS) and cetylammonium bromide (CTAB) on pKa were also investigated via this method. The multi-peaks Gaussian fitting method was shown to determine pKa more reliably and simply than traditional spectrophotometric techniques.
UV-visible electronic absorption spectra of methyl red aqueous solutions are characterized by the overlap of a principal peak at λmax ((520±15) nm) with a shoulder peak at λmax ((435±20) nm), which are assigned to acidic species (HMR) and basic species (MR-) of methyl red, respectively. In this study, the spectra and the integrated absorbance of the MR- and HMR peaks (denoted A1 and A2, respectively) were interpreted using a new multi-peaks Gaussian fitting method. From the absorbance ratio A1/A2 and the concentration ratio cMR-/cHMR, the average acid dissociation constant (pKa) was determined as 4.76 at 298.15 K. The odness is high and the values of R2 (degree of fitting) and χ2 (chi-square test for odness of fit) were 0.998 and below 10-5, respectively. The effects of aggregation behavior of sodium dodecyl sulfate (SDS) and cetylammonium bromide (CTAB) on pKa were also investigated via this method. The multi-peaks Gaussian fitting method was shown to determine pKa more reliably and simply than traditional spectrophotometric techniques.
2012, 28(05): 1037-1044
doi: 10.3866/PKU.WHXB201203072
Abstract:
Quasi-elastic neutron scattering (QENS) spectroscopy as an important tool can be used to extract the molecular dynamic properties. However, the validity of the dynamical models and the decoupling approximation used in QENS spectral analysis is a topic of on ing debate. In this paper, the self-intermediate scattering function FS(Q, t) and the decoupling approximation function FP(Q, t) of the hydroxyl hydrogen in pure water and in 1-propanol/water mixture, and certain dynamic properties predicted by three translation models, are derived from molecular dynamics simulations to assess their reasonability. The results suggest that the decoupling approximations for the water hydrogen in pure water and in mixture are reasonable at low momentum transfer Q. The contribution from the translation-rotation coupling term is small for the pure water. The coupling effect is strengthened for the water hydrogen when 1-propanol is added to the water. Under these conditions, the coupling and rotation terms both increase with the momentum transfer Q and largely cancel each other. For the hydroxyl hydrogen of 1-propanol in the mixture, the translational diffusion constant cannot be directly derived from the experimental spectrum, due to large deviation between FS(Q, t) and the center-of-mass translational function FCM(Q, t). The translational diffusion constants by the three translation models used in our current work are consistent with experimental results and a little higher than those predicted by the Einstein method. The jump rotation, as opposed to continuous rotation, is observed for the water molecule in both bulk water and mixture. For the 1-propanol molecule, rotations are anisotropic, being continuous along the axis from the hydroxyl hydrogen to the center-of-mass, and jumping along the hydroxyl bond vector. Simulations indicate that neither the rotational diffusion constant nor the relaxation time at high momentum transfer Q are adequately determined by the decoupling models, since the coupling effects become significant. Within the low momentum transfer range, the translation properties can be reasonably derived, due to the negligible contributions from the rotation and the coupling terms, as well as the canceling effect between them.
Quasi-elastic neutron scattering (QENS) spectroscopy as an important tool can be used to extract the molecular dynamic properties. However, the validity of the dynamical models and the decoupling approximation used in QENS spectral analysis is a topic of on ing debate. In this paper, the self-intermediate scattering function FS(Q, t) and the decoupling approximation function FP(Q, t) of the hydroxyl hydrogen in pure water and in 1-propanol/water mixture, and certain dynamic properties predicted by three translation models, are derived from molecular dynamics simulations to assess their reasonability. The results suggest that the decoupling approximations for the water hydrogen in pure water and in mixture are reasonable at low momentum transfer Q. The contribution from the translation-rotation coupling term is small for the pure water. The coupling effect is strengthened for the water hydrogen when 1-propanol is added to the water. Under these conditions, the coupling and rotation terms both increase with the momentum transfer Q and largely cancel each other. For the hydroxyl hydrogen of 1-propanol in the mixture, the translational diffusion constant cannot be directly derived from the experimental spectrum, due to large deviation between FS(Q, t) and the center-of-mass translational function FCM(Q, t). The translational diffusion constants by the three translation models used in our current work are consistent with experimental results and a little higher than those predicted by the Einstein method. The jump rotation, as opposed to continuous rotation, is observed for the water molecule in both bulk water and mixture. For the 1-propanol molecule, rotations are anisotropic, being continuous along the axis from the hydroxyl hydrogen to the center-of-mass, and jumping along the hydroxyl bond vector. Simulations indicate that neither the rotational diffusion constant nor the relaxation time at high momentum transfer Q are adequately determined by the decoupling models, since the coupling effects become significant. Within the low momentum transfer range, the translation properties can be reasonably derived, due to the negligible contributions from the rotation and the coupling terms, as well as the canceling effect between them.
2012, 28(05): 1045-1053
doi: 10.3866/PKU.WHXB201203061
Abstract:
Photodissociation of CH2BrCl was investigated around 265 nm using resonance-enhanced multiphoton ionization technique combined with velocity map ion-imaging detection. The ion images of Br (2P1/2) and Br (2P3/2) were analyzed to obtain the corresponding velocity distributions and total translational energy distributions. Using an impulsive model invoking angular momentum conservation, the vibrational internal energy distributions of chloromethyl radical (·CH2Cl) formed by the photodissociation of CH2BrCl, were derived from the total translational energy distributions. In the CH2BrCl+hv→Br (2P1/2)+CH2Cl channel, v4, v3+v4, v2+v4 and v2+v6 vibrational modes were found to be excited in the radical; while in the CH2BrCl+hv→ Br (2P3/2)+CH2Cl channel, the excited vibrational modes were v2+v6, v1+v3, v2+v5, v2+v3+v5, and v1+v5. The results further implied that, following absorption of one photon by the parent molecule CH2BrCl, other vibrational modes besides v5 (CBr stretch) mode, such as v7 (CH2 a-stretch) mode, are excited in the parent molecule.
Photodissociation of CH2BrCl was investigated around 265 nm using resonance-enhanced multiphoton ionization technique combined with velocity map ion-imaging detection. The ion images of Br (2P1/2) and Br (2P3/2) were analyzed to obtain the corresponding velocity distributions and total translational energy distributions. Using an impulsive model invoking angular momentum conservation, the vibrational internal energy distributions of chloromethyl radical (·CH2Cl) formed by the photodissociation of CH2BrCl, were derived from the total translational energy distributions. In the CH2BrCl+hv→Br (2P1/2)+CH2Cl channel, v4, v3+v4, v2+v4 and v2+v6 vibrational modes were found to be excited in the radical; while in the CH2BrCl+hv→ Br (2P3/2)+CH2Cl channel, the excited vibrational modes were v2+v6, v1+v3, v2+v5, v2+v3+v5, and v1+v5. The results further implied that, following absorption of one photon by the parent molecule CH2BrCl, other vibrational modes besides v5 (CBr stretch) mode, such as v7 (CH2 a-stretch) mode, are excited in the parent molecule.
Synthesis of Tailed Porphyrin Modified with Nicotinic Acid and Interactions with Human Serum Albumin
2012, 28(05): 1054-1062
doi: 10.3866/PKU.WHXB201202222
Abstract:
Free porphyrins, namely o-(niacin)C2O-T(3p-OCH3)PP and p-(niacin)C2O-T(3p-OCH3)PP, their complexes, o-(niacin)C2O-T(3p-OCH3)PPZn and p-(niacin)C2O-T(3p-OCH3)PPZn modified with nicotinic acid, were designed, synthesized, and characterized by elementary analysis, and UV-Vis, 1H nuclear magnetic responance (1H NMR), and infrared (IR) spectroscopies. The conformations of the Zn porphyrins were calculated using a quantum- chemical method. The experimental results showed the following. It was found that the nicotinic acid group was on the porphyrin plane in o-(niacin)C2O-T(3p-OCH3)PPZn and Zn― N intramolecular coordination interactions which existed between the N atom of the nicotinic acid group in the side-chain and the Zn2+ in the porphyrin plane. The nicotinic acid group was far from the porphyrin plane in p-(niacin)C2O-T(3p-OCH3)PPZn and Zn ― N intermolecular coordination interactions which existed between the N atom of the nicotinic acid group in one Zn porphyrin and the Zn2+ in the other porphyrin plane. The fluorescence properties of the interactions between Zn porphyrins and human serum albumin (HSA) were studied using fluorescence spectroscopy. There is a large quenching interaction between the Zn porphyrins and human serum albumin. The mechanism of the combination reaction is hydrogen bonding or van der Waals interactions between the Zn porphyrins and human serum albumin. The fluorescence quenching data were analyzed using the Stem-Volmer equation and a double-reciprocal equation, and the quenching constant, binding constant, and thermodynamic parameters were obtained．
Free porphyrins, namely o-(niacin)C2O-T(3p-OCH3)PP and p-(niacin)C2O-T(3p-OCH3)PP, their complexes, o-(niacin)C2O-T(3p-OCH3)PPZn and p-(niacin)C2O-T(3p-OCH3)PPZn modified with nicotinic acid, were designed, synthesized, and characterized by elementary analysis, and UV-Vis, 1H nuclear magnetic responance (1H NMR), and infrared (IR) spectroscopies. The conformations of the Zn porphyrins were calculated using a quantum- chemical method. The experimental results showed the following. It was found that the nicotinic acid group was on the porphyrin plane in o-(niacin)C2O-T(3p-OCH3)PPZn and Zn― N intramolecular coordination interactions which existed between the N atom of the nicotinic acid group in the side-chain and the Zn2+ in the porphyrin plane. The nicotinic acid group was far from the porphyrin plane in p-(niacin)C2O-T(3p-OCH3)PPZn and Zn ― N intermolecular coordination interactions which existed between the N atom of the nicotinic acid group in one Zn porphyrin and the Zn2+ in the other porphyrin plane. The fluorescence properties of the interactions between Zn porphyrins and human serum albumin (HSA) were studied using fluorescence spectroscopy. There is a large quenching interaction between the Zn porphyrins and human serum albumin. The mechanism of the combination reaction is hydrogen bonding or van der Waals interactions between the Zn porphyrins and human serum albumin. The fluorescence quenching data were analyzed using the Stem-Volmer equation and a double-reciprocal equation, and the quenching constant, binding constant, and thermodynamic parameters were obtained．
2012, 28(05): 1063-1069
doi: 10.3866/PKU.WHXB201203021
Abstract:
The reaction mechanism of H2 dissociative adsorption on WO3 surfaces was studied by a first-principles method. Calculations for the clean surface indicated that the c(2×2) reconstruction was the most stable surface geometry. Four H2 dissociative adsorption models were investigated. The optimal configuration was for two H atoms adsorbed at the terminal O1c site, followed by water formation and an oxygen vacancy on the surface. The density of states (DOS) results revealed that H2 dissociative adsorption led to partial filling of the conduction band, which accounted for the increase of WO3 electrical conductivity upon H2 exposure.
The reaction mechanism of H2 dissociative adsorption on WO3 surfaces was studied by a first-principles method. Calculations for the clean surface indicated that the c(2×2) reconstruction was the most stable surface geometry. Four H2 dissociative adsorption models were investigated. The optimal configuration was for two H atoms adsorbed at the terminal O1c site, followed by water formation and an oxygen vacancy on the surface. The density of states (DOS) results revealed that H2 dissociative adsorption led to partial filling of the conduction band, which accounted for the increase of WO3 electrical conductivity upon H2 exposure.
2012, 28(05): 1070-1076
doi: 10.3866/PKU.WHXB201202213
Abstract:
The transport of helium molecules in open and finite-length single-walled carbon nanotubes was studied using non-equilibrium molecular dynamics simulations. We observed that helium molecules were transported through nanotubes with the high mobility characterized by superdiffusion. A transition from superdiffusion to near-ballistic motion occurs when the diameter is larger than a threshold value, and then the transport is again dominated by the superdiffusion. This change is closely related to nanotube ends. Simulations show that molecules are transported rapidly in the nanotubes via ballistic motion, which, however, is dispersed by the potential barrier at the ends of the nanotubes. This blocking effect is jointly determined by the potential barrier and the nanotube diameter.
The transport of helium molecules in open and finite-length single-walled carbon nanotubes was studied using non-equilibrium molecular dynamics simulations. We observed that helium molecules were transported through nanotubes with the high mobility characterized by superdiffusion. A transition from superdiffusion to near-ballistic motion occurs when the diameter is larger than a threshold value, and then the transport is again dominated by the superdiffusion. This change is closely related to nanotube ends. Simulations show that molecules are transported rapidly in the nanotubes via ballistic motion, which, however, is dispersed by the potential barrier at the ends of the nanotubes. This blocking effect is jointly determined by the potential barrier and the nanotube diameter.
2012, 28(05): 1077-1084
doi: 10.3866/PKU.WHXB201202273
Abstract:
The Boltzmann-Peierls phonon transport equation (BTE) and non-equilibrium molecular dynamics simulation (NEMD) are used to investigate the thermal transport properties of boron nitride nanotubes (BNNTs). First, the thermal-mechanical coupling is explored using NEMD. Then, by combining BTE and NEMD, the influence of temperature and length is investigated. Quantum correction is used to extend the range over which NEMD can be used. The results demonstrate that under low-strain conditions, the thermal conductivity decreases with increasing tensile or compressive strain. Then the phonon density of state (PDOS) is used to analyze the trends in thermal transport properties theoretically; it is found that the variations in thermal transport properties under tension are caused by changes in the phonon modes, and that under compression changes are induced by the flection of the BNNT structure. The BNNT thermal conductivity increases linearly with increasing temperature because of the quantum effect at low temperatures, and it decreases significantly as the temperature reaches a certain value. When the BNNT length is less than 120 nm, the BNNT's ballistic characteristics weaken with increasing length, but it also performs ballistic characteristic mainly, and thermal conductivity (κ) and length (L) obey the relationship κ ∝ Lα.
The Boltzmann-Peierls phonon transport equation (BTE) and non-equilibrium molecular dynamics simulation (NEMD) are used to investigate the thermal transport properties of boron nitride nanotubes (BNNTs). First, the thermal-mechanical coupling is explored using NEMD. Then, by combining BTE and NEMD, the influence of temperature and length is investigated. Quantum correction is used to extend the range over which NEMD can be used. The results demonstrate that under low-strain conditions, the thermal conductivity decreases with increasing tensile or compressive strain. Then the phonon density of state (PDOS) is used to analyze the trends in thermal transport properties theoretically; it is found that the variations in thermal transport properties under tension are caused by changes in the phonon modes, and that under compression changes are induced by the flection of the BNNT structure. The BNNT thermal conductivity increases linearly with increasing temperature because of the quantum effect at low temperatures, and it decreases significantly as the temperature reaches a certain value. When the BNNT length is less than 120 nm, the BNNT's ballistic characteristics weaken with increasing length, but it also performs ballistic characteristic mainly, and thermal conductivity (κ) and length (L) obey the relationship κ ∝ Lα.
2012, 28(05): 1085-1093
doi: 10.3866/PKU.WHXB201203024
Abstract:
Meso-substituted porphyrin derivatives have demonstrated great potential as sensing materials for toxic gas detection. In this paper, density functional theory (DFT) and its time-dependent DFT approach (TD-DFT) were employed to investigate the ultraviolet-visible (UV-Vis) or the near-ultravioletvisible (near-UV-Vis) absorption spectra of Meso-tetra (o-nitrophenyl/o-aminophenyl) porphyrins (NO2PP, NH2PP) and their corresponding zinc derivatives, NO2ZnPP and NH2ZnPP. The geometry optimizations for these four molecules were obtained from two different exchange-correlation functionals, the generalizedgradient approximation functional PBE (Perdew-Burke-Ernzerhof) and the hybrid functional B3LYP (Becke, three-parameter, Lee-Yang-Parr). The excitation energies and oscillation strengths were obtained from TD-DFT calculations. Calculations show that the optical absorptions are associated with numerous electronic transitions. In addition, the PBE-predicted wavelengths of the B and Q bands are more consistent with experiment than those predicted by B3LYP. The B band of NO2-substituted derivative exhibits a bathochromic shift different from that of NH2-containing material, also consistent with experimental results. In addition, at the PBE/6-31G(d) level of theory, the calculated energies of the lowest triplet excited states of NO2PP, NH2PP, NO2ZnPP, and NH2ZnPP are 1.426, 1.469, 1.608, and 1.581 eV, respectively.
Meso-substituted porphyrin derivatives have demonstrated great potential as sensing materials for toxic gas detection. In this paper, density functional theory (DFT) and its time-dependent DFT approach (TD-DFT) were employed to investigate the ultraviolet-visible (UV-Vis) or the near-ultravioletvisible (near-UV-Vis) absorption spectra of Meso-tetra (o-nitrophenyl/o-aminophenyl) porphyrins (NO2PP, NH2PP) and their corresponding zinc derivatives, NO2ZnPP and NH2ZnPP. The geometry optimizations for these four molecules were obtained from two different exchange-correlation functionals, the generalizedgradient approximation functional PBE (Perdew-Burke-Ernzerhof) and the hybrid functional B3LYP (Becke, three-parameter, Lee-Yang-Parr). The excitation energies and oscillation strengths were obtained from TD-DFT calculations. Calculations show that the optical absorptions are associated with numerous electronic transitions. In addition, the PBE-predicted wavelengths of the B and Q bands are more consistent with experiment than those predicted by B3LYP. The B band of NO2-substituted derivative exhibits a bathochromic shift different from that of NH2-containing material, also consistent with experimental results. In addition, at the PBE/6-31G(d) level of theory, the calculated energies of the lowest triplet excited states of NO2PP, NH2PP, NO2ZnPP, and NH2ZnPP are 1.426, 1.469, 1.608, and 1.581 eV, respectively.
2012, 28(05): 1094-1100
doi: 10.3866/PKU.WHXB201203062
Abstract:
The temperature-resilient, high tensile-strength fiber poly[p-phenylene benzobisoxazole] (PBO) is light-unstable and it degrades under ultraviolet radiation. In this paper we study the photolytic mechanism of the PBO monomer, 2-phenylbenzo[d]oxazole (PO). Following absorption of a photon and excitation into the first excited state (S1), the molecule overcomes an energy barrier of 25.59 kJ·mol-1 to enter the transition state; the oxazole ring is then opened and both benzene rings form a dihedral angle of about 90° to obtain the product, which under es further addition reaction with water. Calculations reveal that ring-opening is easily achieved in the potential surface of S1. However, the pathway through which the oxazole ring opens in the ground state remains obscure. The topological properties of these compounds are in od agreement with the expected bond orders and the photolytic mechanism.
The temperature-resilient, high tensile-strength fiber poly[p-phenylene benzobisoxazole] (PBO) is light-unstable and it degrades under ultraviolet radiation. In this paper we study the photolytic mechanism of the PBO monomer, 2-phenylbenzo[d]oxazole (PO). Following absorption of a photon and excitation into the first excited state (S1), the molecule overcomes an energy barrier of 25.59 kJ·mol-1 to enter the transition state; the oxazole ring is then opened and both benzene rings form a dihedral angle of about 90° to obtain the product, which under es further addition reaction with water. Calculations reveal that ring-opening is easily achieved in the potential surface of S1. However, the pathway through which the oxazole ring opens in the ground state remains obscure. The topological properties of these compounds are in od agreement with the expected bond orders and the photolytic mechanism.
2012, 28(05): 1101-1106
doi: 10.3866/PKU.WHXB201203054
Abstract:
In coal, nitrogen exists in a variety of forms. We presented 11 compounds of different hybridization forms and nitrogen contents. Density functional theory (DFT) simulation method was employed to study the adsorption behaviors of methane on these nitrogen-containing organic compounds. The interactions were studied and characterized by their adsorption energies, Mulliken charges and electrostatic potential surfaces. The adsorption energies varied from 3.81 to 6.82 kJ·mol-1, attributable to the weak hydrogen-bonding and electrostatic interactions. The results revealed that the adsorption energy of sp2-N with methane was higher than that of sp3-N and that higher nitrogen contents provided more positive sites for methane adsorption.
In coal, nitrogen exists in a variety of forms. We presented 11 compounds of different hybridization forms and nitrogen contents. Density functional theory (DFT) simulation method was employed to study the adsorption behaviors of methane on these nitrogen-containing organic compounds. The interactions were studied and characterized by their adsorption energies, Mulliken charges and electrostatic potential surfaces. The adsorption energies varied from 3.81 to 6.82 kJ·mol-1, attributable to the weak hydrogen-bonding and electrostatic interactions. The results revealed that the adsorption energy of sp2-N with methane was higher than that of sp3-N and that higher nitrogen contents provided more positive sites for methane adsorption.
2012, 28(05): 1107-1112
doi: 10.3866/PKU.WHXB201203011
Abstract:
The adsorption reaction of acetylene on the Ge(001) surface is investigated by first-principles calculations. In order to understand the relative populations of the di-σ and paired-end-bridge structures, we calculated the adsorption reaction paths leading to their formation at 0.5 and 1.0 ML coverage. More importantly, we studied the adsorption channel involving sublayer Ge atoms by forming a metastable subdi- σ structure. This sub-di-σ structure represents second reaction pathway that results in the end-bridge structure, which plays an important role in the formation of the adsorption configurations. In contrast to C2H2, the adsorption of C2H4 on the Ge(001) surface involving subsurface Ge atoms, is endothermic. Our calculations show from both kinetic and thermodynamic standpoints that the paired-end-bridge structure is the primary adsorption configuration that explains the experimental observations. Our work also helps to understand the fundamental differences between the adsorption of C2H2 and C2H4 on the Ge(001) surface.
The adsorption reaction of acetylene on the Ge(001) surface is investigated by first-principles calculations. In order to understand the relative populations of the di-σ and paired-end-bridge structures, we calculated the adsorption reaction paths leading to their formation at 0.5 and 1.0 ML coverage. More importantly, we studied the adsorption channel involving sublayer Ge atoms by forming a metastable subdi- σ structure. This sub-di-σ structure represents second reaction pathway that results in the end-bridge structure, which plays an important role in the formation of the adsorption configurations. In contrast to C2H2, the adsorption of C2H4 on the Ge(001) surface involving subsurface Ge atoms, is endothermic. Our calculations show from both kinetic and thermodynamic standpoints that the paired-end-bridge structure is the primary adsorption configuration that explains the experimental observations. Our work also helps to understand the fundamental differences between the adsorption of C2H2 and C2H4 on the Ge(001) surface.
2012, 28(05): 1113-1119
doi: 10.3866/PKU.WHXB201203071
Abstract:
We have investigated the structures, gaps, IR spectra, electronic spectra, Wiberg bond indices (WBIs), and aromaticity of CB5C2H2(C3B2)nC2H2CB5 (n=1-5) with planar pentacoordinate carbons (ppC) and planar tetracoordinate carbons (ptC) at the B3LYP/6-311 + G** level. Calculations indicate that the five compounds with the lowest energies are located at the minima of the potential energy surfaces. The energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) vary between 0.5 and 1.2 eV; the first electronic transition wavelengths are between 1780 and 2910 nm and depend non-monotonically on the size of the compounds. WBIs of the five compounds show that they contain both ppC and ptC. The nucleus-independent chemical shift (NICS(0)) values of the centers of the three-membered rings of the CB5 sections on the right side of these compounds, as well as the C3B2 sections, are negative, while the NICS(0) values of only two centers of the three-membered rings of the CB5 sections on the left side are negative. In addition, since the NICS(0) of the centers of the three-membered rings are consistent with those of NICS(1), then local delocalization of the π electrons must play an important role in stabilizing these compounds.
We have investigated the structures, gaps, IR spectra, electronic spectra, Wiberg bond indices (WBIs), and aromaticity of CB5C2H2(C3B2)nC2H2CB5 (n=1-5) with planar pentacoordinate carbons (ppC) and planar tetracoordinate carbons (ptC) at the B3LYP/6-311 + G** level. Calculations indicate that the five compounds with the lowest energies are located at the minima of the potential energy surfaces. The energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) vary between 0.5 and 1.2 eV; the first electronic transition wavelengths are between 1780 and 2910 nm and depend non-monotonically on the size of the compounds. WBIs of the five compounds show that they contain both ppC and ptC. The nucleus-independent chemical shift (NICS(0)) values of the centers of the three-membered rings of the CB5 sections on the right side of these compounds, as well as the C3B2 sections, are negative, while the NICS(0) values of only two centers of the three-membered rings of the CB5 sections on the left side are negative. In addition, since the NICS(0) of the centers of the three-membered rings are consistent with those of NICS(1), then local delocalization of the π electrons must play an important role in stabilizing these compounds.
2012, 28(05): 1120-1126
doi: 10.3866/PKU.WHXB201203082
Abstract:
Bimolecular nucleophilic substitution (SN2) reactions are among the fundamental organic reactions, in which electron transfer from the nucleophilic group to the leaving group plays an essential role. We use a high-level ab initio CCSD(T)/aug-cc-pVDZ method in conjunction with our previouslydeveloped molecular face (MF) theory, to investigate the SN2 reaction F-+CH3Cl→CH3F+Cl-. Dynamic representations of molecular shape evolution and electron transfer features throughout the reaction are vividly presented. It is found that along the intrinsic reaction coordinate (IRC), from the beginning of the reaction to the prereaction complex, the molecular intrinsic characteristic contour (MICC) of the nucleophile (F-) contracts slowly, while the electron density on the MICC increases slowly. The MICC of F then expands quickly, and the electron density decreases sharply, especially from the transition state to the product complex. However, for the leaving group (Cl), the MICC contracts, and the electron density increases all along the reaction. Investigations of the potential acting on an electron in a molecule (PAEM) show that, as the reaction progresses, the PAEM gradually decreases between fluorine and carbon, while it gradually increases between carbon and chlorine. This study enhances our understanding of the dynamic processes of bond-forming between F and C atoms and bond-breaking between C and Cl atoms.
Bimolecular nucleophilic substitution (SN2) reactions are among the fundamental organic reactions, in which electron transfer from the nucleophilic group to the leaving group plays an essential role. We use a high-level ab initio CCSD(T)/aug-cc-pVDZ method in conjunction with our previouslydeveloped molecular face (MF) theory, to investigate the SN2 reaction F-+CH3Cl→CH3F+Cl-. Dynamic representations of molecular shape evolution and electron transfer features throughout the reaction are vividly presented. It is found that along the intrinsic reaction coordinate (IRC), from the beginning of the reaction to the prereaction complex, the molecular intrinsic characteristic contour (MICC) of the nucleophile (F-) contracts slowly, while the electron density on the MICC increases slowly. The MICC of F then expands quickly, and the electron density decreases sharply, especially from the transition state to the product complex. However, for the leaving group (Cl), the MICC contracts, and the electron density increases all along the reaction. Investigations of the potential acting on an electron in a molecule (PAEM) show that, as the reaction progresses, the PAEM gradually decreases between fluorine and carbon, while it gradually increases between carbon and chlorine. This study enhances our understanding of the dynamic processes of bond-forming between F and C atoms and bond-breaking between C and Cl atoms.
2012, 28(05): 1127-1133
doi: 10.3866/PKU.WHXB201203073
Abstract:
In this paper, ld nanoparticles (NPs) with an average size of (4.7 ± 0.6) nm, capped with mercaptopropionic acid (MPA) ligand, are prepared. The effect of pH and Au NPs on cytochrome c (Cyt c) is investigated by electrochemistry and UV-Vis absorption spectroscopy. UV-Vis absorption spectra indicate that the structures of Cyt c and Cyt c-Au NPs complex do not change appreciably between pH=7.5 and pH=3.0, but their Soret band positions change markedly at pH=2.0, indicating that low pH value induces a conformational change in Cyt c. Cyclic voltammetry (CV) result shows that Au NPs capped with MPA enhance electron transfer between Cyt c and the electrode. The data also reveals that the biocompatibility of Au NPs is improved when citric acid ligand is replaced with MPA. The change in pH value causes a change of peak currents in CV and a shift of peak potential. When pH value deviates from 7.0, levels of electroactive Cyt c decrease. Significant pH change induces irreversible denaturing of Cyt c. The pH at which Cyt c-Au NPs complex denatures completely is one unit higher than that of Cyt c. Combining the results from UV-Vis spectroscopy and CV, we find that addition of Au NPs makes adsorbing state Cyt c more vulnerable to pH.
In this paper, ld nanoparticles (NPs) with an average size of (4.7 ± 0.6) nm, capped with mercaptopropionic acid (MPA) ligand, are prepared. The effect of pH and Au NPs on cytochrome c (Cyt c) is investigated by electrochemistry and UV-Vis absorption spectroscopy. UV-Vis absorption spectra indicate that the structures of Cyt c and Cyt c-Au NPs complex do not change appreciably between pH=7.5 and pH=3.0, but their Soret band positions change markedly at pH=2.0, indicating that low pH value induces a conformational change in Cyt c. Cyclic voltammetry (CV) result shows that Au NPs capped with MPA enhance electron transfer between Cyt c and the electrode. The data also reveals that the biocompatibility of Au NPs is improved when citric acid ligand is replaced with MPA. The change in pH value causes a change of peak currents in CV and a shift of peak potential. When pH value deviates from 7.0, levels of electroactive Cyt c decrease. Significant pH change induces irreversible denaturing of Cyt c. The pH at which Cyt c-Au NPs complex denatures completely is one unit higher than that of Cyt c. Combining the results from UV-Vis spectroscopy and CV, we find that addition of Au NPs makes adsorbing state Cyt c more vulnerable to pH.
2012, 28(05): 1134-1138
doi: 10.3866/PKU.WHXB201203051
Abstract:
The preparation and properties of quasi-solid-state electrolyte films based on polyvinyl butyral were studied. The films were prepared by adding a pore forming agent and auxiliary agents to polyvinyl butyral. Factors affecting the preparation of the films were investigated. The results showed that the films prepared by adding 6.000 g calcium carbonate, 0.310 g calcium chloride, and 0.150 g glucose to 0.200 g polyvinyl butyral performed best. The impact of different pore ratios on device efficiency was investigated as well. The efficiency of dye-sensitized solar cells (DSSCs) using the quasi-solid-state electrolyte film reached 4.720% (open-circuit voltage Voc=0.7194 V, short-circuit current density Jsc=10.014 mA·cm-2, fill factor FF=0.6559), which was 88% of that for the corresponding liquid electrolyte solar cells. The film is easy to use for packaging and its preparation method is simple and non-toxic.
The preparation and properties of quasi-solid-state electrolyte films based on polyvinyl butyral were studied. The films were prepared by adding a pore forming agent and auxiliary agents to polyvinyl butyral. Factors affecting the preparation of the films were investigated. The results showed that the films prepared by adding 6.000 g calcium carbonate, 0.310 g calcium chloride, and 0.150 g glucose to 0.200 g polyvinyl butyral performed best. The impact of different pore ratios on device efficiency was investigated as well. The efficiency of dye-sensitized solar cells (DSSCs) using the quasi-solid-state electrolyte film reached 4.720% (open-circuit voltage Voc=0.7194 V, short-circuit current density Jsc=10.014 mA·cm-2, fill factor FF=0.6559), which was 88% of that for the corresponding liquid electrolyte solar cells. The film is easy to use for packaging and its preparation method is simple and non-toxic.
2012, 28(05): 1139-1145
doi: 10.3866/PKU.WHXB201202233
Abstract:
A comb-like copolymer based on N-propylvinylimidazolium iodide (VImI) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) was synthesized. The VImI/PEGMA copolymer was used to prepare quasi-solid electrolytes. The charge transport and interfacial charge transfer of the dye-sensitized solar cells (DSSCs) based on the quasi-solid electrolytes were investigated using photocurrent density-voltage (J-V) curves, ionic conductivities, and impedance spectra. It was found that the copolymer plays an active role in decreasing the electron recombination at TiO2/electrolyte interface and increases the conduction band edge of TiO2. The photovoltaic characteristics of the DSSCs are therefore not determined entirely by the conductivity of the quasi-solid electrolyte. Based on the dependence of the open-circuit voltage on the VImI/PEGMA molar ratio, the decrease of recombination is primarily ascribed to the contribution of VImI segments. In addition, open-circuit voltage decay (OCVD) and photocurrent transient results indicate that the introduction of the copolymer not only extends the electron lifetime but also tunes the energy distribution of the localized electrons. When the VImI/PEGMA molar ratio reaches 5.0 and the mass fraction of copolymer in the quasi-solid electrolyte is 50%, the DSSC yields an energy conversion efficiency of 4.10% under an illumination intensity of 100 mW·cm-2.
A comb-like copolymer based on N-propylvinylimidazolium iodide (VImI) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) was synthesized. The VImI/PEGMA copolymer was used to prepare quasi-solid electrolytes. The charge transport and interfacial charge transfer of the dye-sensitized solar cells (DSSCs) based on the quasi-solid electrolytes were investigated using photocurrent density-voltage (J-V) curves, ionic conductivities, and impedance spectra. It was found that the copolymer plays an active role in decreasing the electron recombination at TiO2/electrolyte interface and increases the conduction band edge of TiO2. The photovoltaic characteristics of the DSSCs are therefore not determined entirely by the conductivity of the quasi-solid electrolyte. Based on the dependence of the open-circuit voltage on the VImI/PEGMA molar ratio, the decrease of recombination is primarily ascribed to the contribution of VImI segments. In addition, open-circuit voltage decay (OCVD) and photocurrent transient results indicate that the introduction of the copolymer not only extends the electron lifetime but also tunes the energy distribution of the localized electrons. When the VImI/PEGMA molar ratio reaches 5.0 and the mass fraction of copolymer in the quasi-solid electrolyte is 50%, the DSSC yields an energy conversion efficiency of 4.10% under an illumination intensity of 100 mW·cm-2.
2012, 28(05): 1146-1152
doi: 10.3866/PKU.WHXB201202272
Abstract:
The failure processes of a multi-layer coating system (zinc-rich epoxy primer, epoxy middle layer, and fluorocarbon topcoat) in four corrosion environments were studied with electrochemical impedance spectroscopy (EIS). The failure rate of the coating system in the four environments decreases in following order: immersion in a 3.5% NaCl solution under UV light, steam above a water surface at 45 ℃, salt spray at 35 ℃, and immersion in a 3.5% NaCl solution at room temperature. Although the failure rates of the coating system in the four environments are different, the variations of the phase angles at the middle frequency range, particularly 10 Hz, are very close to that of the coating impedance; hence they may be used as a qualitative evaluation parameter for coating inspection.
The failure processes of a multi-layer coating system (zinc-rich epoxy primer, epoxy middle layer, and fluorocarbon topcoat) in four corrosion environments were studied with electrochemical impedance spectroscopy (EIS). The failure rate of the coating system in the four environments decreases in following order: immersion in a 3.5% NaCl solution under UV light, steam above a water surface at 45 ℃, salt spray at 35 ℃, and immersion in a 3.5% NaCl solution at room temperature. Although the failure rates of the coating system in the four environments are different, the variations of the phase angles at the middle frequency range, particularly 10 Hz, are very close to that of the coating impedance; hence they may be used as a qualitative evaluation parameter for coating inspection.
2012, 28(05): 1153-1162
doi: 10.3866/PKU.WHXB201203022
Abstract:
The morphologies and electrochemical characteristics of rust layers generated in seawater and reverse osmosis (RO) product water were investigated by scanning electron microscopy (SEM), infrared spectroscopy (IR), X-ray diffraction (XRD) and electrochemical tests. Experimental results revealed obvious differences in the components, structures and functions of rust layers in two types of solutions, so that the corrosion rates of carbon steel were markedly different. The reduction potential of γ-FeOOH is higher than the corrosion potential of carbon steel in RO product water, such that γ-FeOOH is easily reduced to Fe3O4 and two layers emerge in the rust structures. The outer layer (γ-FeOOH layer) is too thin to inhibit oxygen diffusion, and tends to accelerate the cathodic process via reduction of γ-FeOOH. Because Fe2 + and electrons can pass through the Fe3O4 layer, oxygen can be directly reduced on the surface of the inner layer (Fe3O4 layer). Therefore, the inner rust layer (Fe3O4 layer) can provide a large cathode area on which to promote oxygen reduction. As a result, the corrosion process of carbon steel in RO product water can be accelerated greatly. The corrosion rate of carbon steel is determined by the limiting diffusion rate of oxygen from solution to the inner rust layer. Anti-corrosion measures should inhibit the reduction reaction of γ-FeOOH.
The morphologies and electrochemical characteristics of rust layers generated in seawater and reverse osmosis (RO) product water were investigated by scanning electron microscopy (SEM), infrared spectroscopy (IR), X-ray diffraction (XRD) and electrochemical tests. Experimental results revealed obvious differences in the components, structures and functions of rust layers in two types of solutions, so that the corrosion rates of carbon steel were markedly different. The reduction potential of γ-FeOOH is higher than the corrosion potential of carbon steel in RO product water, such that γ-FeOOH is easily reduced to Fe3O4 and two layers emerge in the rust structures. The outer layer (γ-FeOOH layer) is too thin to inhibit oxygen diffusion, and tends to accelerate the cathodic process via reduction of γ-FeOOH. Because Fe2 + and electrons can pass through the Fe3O4 layer, oxygen can be directly reduced on the surface of the inner layer (Fe3O4 layer). Therefore, the inner rust layer (Fe3O4 layer) can provide a large cathode area on which to promote oxygen reduction. As a result, the corrosion process of carbon steel in RO product water can be accelerated greatly. The corrosion rate of carbon steel is determined by the limiting diffusion rate of oxygen from solution to the inner rust layer. Anti-corrosion measures should inhibit the reduction reaction of γ-FeOOH.
2012, 28(05): 1163-1168
doi: 10.3866/PKU.WHXB201202241
Abstract:
The electrochemical redox reaction of a cytochrome c (Cyt c) adlayer on an indium tin oxide (ITO) electrode was directly monitored and the surface concentrations of Cyt c versus solution concentrations were obtained from cyclic voltammograms. The results indicate that the surface concentration increases from 0.35 × 10-12 to 1.53 × 10-12 mol·cm-2 when the solution concentration is increased from 2 to 10 μmol ·L-1. A quasi-linear relationship between the reciprocals of surface concentration and solution concentration was observed, indicating that Cyt c adsorption on the ITO electrode closely obeys the Langmuir isothermal adsorption model. The cyclic voltammograms of the Cyt c solutions with the ITO electrode reveal that both adsorbed and dissociated Cyt c molecules are involved in the electrode reaction and that the contribution of dissociated molecules is much larger than that of adsorbed ones. The electrode reaction is basically diffusion controlled and quasi-reversible. Based on the Nicholson method, the average standard heterogeneous rate constant was determined to be 1.65×10-3 cm· s-1. The electrochemical activity of the Cyt c adlayer was partially lost when it was kept at 25 °C for 1 h, and was completely lost at 80 °C. The denatured Cyt c adlayer on a ld electrode can effectively inhibit the electrode reaction of K3Fe(CN)6 solution.
The electrochemical redox reaction of a cytochrome c (Cyt c) adlayer on an indium tin oxide (ITO) electrode was directly monitored and the surface concentrations of Cyt c versus solution concentrations were obtained from cyclic voltammograms. The results indicate that the surface concentration increases from 0.35 × 10-12 to 1.53 × 10-12 mol·cm-2 when the solution concentration is increased from 2 to 10 μmol ·L-1. A quasi-linear relationship between the reciprocals of surface concentration and solution concentration was observed, indicating that Cyt c adsorption on the ITO electrode closely obeys the Langmuir isothermal adsorption model. The cyclic voltammograms of the Cyt c solutions with the ITO electrode reveal that both adsorbed and dissociated Cyt c molecules are involved in the electrode reaction and that the contribution of dissociated molecules is much larger than that of adsorbed ones. The electrode reaction is basically diffusion controlled and quasi-reversible. Based on the Nicholson method, the average standard heterogeneous rate constant was determined to be 1.65×10-3 cm· s-1. The electrochemical activity of the Cyt c adlayer was partially lost when it was kept at 25 °C for 1 h, and was completely lost at 80 °C. The denatured Cyt c adlayer on a ld electrode can effectively inhibit the electrode reaction of K3Fe(CN)6 solution.
2012, 28(05): 1169-1176
doi: 10.3866/PKU.WHXB201203012
Abstract:
LiTi2(PO4)3/C composite with a Na+ superionic conductor (NASICON)-type structure was prepared by a sol-gel method. The LiTi2(PO4)3/C composite had a od NASICON structure and od electrochemical properties as revealed by X-ray diffraction (XRD), scanning electron microscopy (SEM), charging/discharging tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The first discharge capacity was 144 mAh·g-1. The EIS results indicated that there appeared semicircles respectively representing the solid electrolyte interface (SEI) film as well as the contact resistance, charge transfer resistance, and phase transformation resistance in the initial lithiation process of LiTi2(PO4)3/C composite electrode. The chemical diffusion coefficients of intercalation and de-intercalation of Li+ in the LiTi2(PO4)3 cathode material were calculated to be 2.40×10-5 and 1.07×10-5 cm2·s-1, respectively.
LiTi2(PO4)3/C composite with a Na+ superionic conductor (NASICON)-type structure was prepared by a sol-gel method. The LiTi2(PO4)3/C composite had a od NASICON structure and od electrochemical properties as revealed by X-ray diffraction (XRD), scanning electron microscopy (SEM), charging/discharging tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The first discharge capacity was 144 mAh·g-1. The EIS results indicated that there appeared semicircles respectively representing the solid electrolyte interface (SEI) film as well as the contact resistance, charge transfer resistance, and phase transformation resistance in the initial lithiation process of LiTi2(PO4)3/C composite electrode. The chemical diffusion coefficients of intercalation and de-intercalation of Li+ in the LiTi2(PO4)3 cathode material were calculated to be 2.40×10-5 and 1.07×10-5 cm2·s-1, respectively.
2012, 28(05): 1177-1182
doi: 10.3866/PKU.WHXB201203092
Abstract:
A doping-coating surface modification method was used to improve the cycle performance of the lithium-ion battery cathode material spinel LiMn2O4. Al was chosen as the doping element and Al(NO3)3 as the raw material. We investigated Al3+ doping of 7.1%(atomic fraction) at the temperatures of 300, 400, 500, 600, 700, 750, and 800 °C. It was found that at increasing temperatures, the maximum specific capacity of the modified samples first increased and then decreased, with a maximum at 700 °C. The fading rate increased initially with temperature as well, and then decreased, followed by a small rise with temperature. This is because the coated layer gradually reacted with the LiMn2O4 granule at elevated temperatures and became a completely solid solution layer by 750 °C. The fading rate reached the minimum at the same time. Subsequently, the solid solution layer diffused into the LiMn2O4 granule, weakening the granule protection so that the fading rate slightly increased. Among these samples, the maximum specific capacity (133.6 mAh·g-1) was for the sample treated at 700 °C for 5 h, and the fading rate was 3.4% after 50 cycles. It is shown that doping-coating surface modification with Al3+ may enable the commercial application of spinel LiMn2O4 cathode material for lithium-ion batteries.
A doping-coating surface modification method was used to improve the cycle performance of the lithium-ion battery cathode material spinel LiMn2O4. Al was chosen as the doping element and Al(NO3)3 as the raw material. We investigated Al3+ doping of 7.1%(atomic fraction) at the temperatures of 300, 400, 500, 600, 700, 750, and 800 °C. It was found that at increasing temperatures, the maximum specific capacity of the modified samples first increased and then decreased, with a maximum at 700 °C. The fading rate increased initially with temperature as well, and then decreased, followed by a small rise with temperature. This is because the coated layer gradually reacted with the LiMn2O4 granule at elevated temperatures and became a completely solid solution layer by 750 °C. The fading rate reached the minimum at the same time. Subsequently, the solid solution layer diffused into the LiMn2O4 granule, weakening the granule protection so that the fading rate slightly increased. Among these samples, the maximum specific capacity (133.6 mAh·g-1) was for the sample treated at 700 °C for 5 h, and the fading rate was 3.4% after 50 cycles. It is shown that doping-coating surface modification with Al3+ may enable the commercial application of spinel LiMn2O4 cathode material for lithium-ion batteries.
2012, 28(05): 1183-1188
doi: 10.3866/PKU.WHXB201202221
Abstract:
A low-temperature approach for efficient preparation of LiFePO4 was developed. The rod-shaped [Fe3(PO4)2·8H2O + Li3PO4] precursor was prepared, using a mechanochemical liquid-phase activation technique, from LiH2PO4 and reduction iron powder. Pure LiFePO4 was then synthesized in boiling tetra(ethylene glycol) (TEG) by polyol processing with the as-prepared precursor. In order to improve the electrical conductivity, carbon coating of the pure LiFePO4 was carried out, using poly(vinyl alcohol) (PVA) as the carbon source. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic charge-discharge test and electrochemical impedance spectroscopy (EIS). The results show that well-crystallized LiFePO4 was successfully synthesized by polyol processing at low temperature. Carbon coating significantly improves the conductive properties of LiFePO4 and reduces charge-transfer impedance. The obtained LiFePO4/C composite delivers specific discharge capacities of 139.8 and 129.5 mAh·g-1 at 1C and 2C rates, respectively, displaying od cycling performance and rate capability.
A low-temperature approach for efficient preparation of LiFePO4 was developed. The rod-shaped [Fe3(PO4)2·8H2O + Li3PO4] precursor was prepared, using a mechanochemical liquid-phase activation technique, from LiH2PO4 and reduction iron powder. Pure LiFePO4 was then synthesized in boiling tetra(ethylene glycol) (TEG) by polyol processing with the as-prepared precursor. In order to improve the electrical conductivity, carbon coating of the pure LiFePO4 was carried out, using poly(vinyl alcohol) (PVA) as the carbon source. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic charge-discharge test and electrochemical impedance spectroscopy (EIS). The results show that well-crystallized LiFePO4 was successfully synthesized by polyol processing at low temperature. Carbon coating significantly improves the conductive properties of LiFePO4 and reduces charge-transfer impedance. The obtained LiFePO4/C composite delivers specific discharge capacities of 139.8 and 129.5 mAh·g-1 at 1C and 2C rates, respectively, displaying od cycling performance and rate capability.
2012, 28(05): 1189-1196
doi: 10.3866/PKU.WHXB201202292
Abstract:
Aerogels with densities in the range 40-175 mg·cm-3 were prepared using a tetraethyl orthosilicate (TEOS) ethanol-water solution as the precursor and hydrofluoric acid as the catalyst via a sol-gel process and CO2 supercritical-fluid drying. The density-gradient aerogels were prepared using layer-by-layer gelation, sol co-gelation, and gradient-sol co-gelation methods and their gradient properties were studied systematically. The results show that aerogels with different densities all have a threedimensional skeleton consisting of spherical particles of diameter about 40-90 nm. The lower the density is, the looser the skeleton and pore-size distributions are, and the larger the peak value of the pore size is. Gradient aerogels prepared via different methods exhibited graded, approximately gradient, or gradient distributions. Dynamic mechanical analysis indicates that the Young's moduli of the aerogels at -100 and 25 °C (changed from 4.6×105 to 1.9×105 Pa and from 5.0×105 to 2.1×105 Pa, respectively) tend to decrease with decreasing density. Thermal constants analysis shows that as the densities of the aerogels decrease, the thermal diffusion coefficients increase and the specific heat capacities decrease, but the thermal conductivities do not change monotonically.
Aerogels with densities in the range 40-175 mg·cm-3 were prepared using a tetraethyl orthosilicate (TEOS) ethanol-water solution as the precursor and hydrofluoric acid as the catalyst via a sol-gel process and CO2 supercritical-fluid drying. The density-gradient aerogels were prepared using layer-by-layer gelation, sol co-gelation, and gradient-sol co-gelation methods and their gradient properties were studied systematically. The results show that aerogels with different densities all have a threedimensional skeleton consisting of spherical particles of diameter about 40-90 nm. The lower the density is, the looser the skeleton and pore-size distributions are, and the larger the peak value of the pore size is. Gradient aerogels prepared via different methods exhibited graded, approximately gradient, or gradient distributions. Dynamic mechanical analysis indicates that the Young's moduli of the aerogels at -100 and 25 °C (changed from 4.6×105 to 1.9×105 Pa and from 5.0×105 to 2.1×105 Pa, respectively) tend to decrease with decreasing density. Thermal constants analysis shows that as the densities of the aerogels decrease, the thermal diffusion coefficients increase and the specific heat capacities decrease, but the thermal conductivities do not change monotonically.
2012, 28(05): 1197-1205
doi: 10.3866/PKU.WHXB201202231
Abstract:
The different effects of poly(ethylene glycol) (PEG) and poly(vinylpyrrolidone) (PVP) on the structure and laser-induced damage threshold of sol-gel silica anti-reflective films were investigated. The results of dynamic light-scattering, transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS) showed that PEG could prompt silica particles to form uniform clusters, whereas in the PVP-modified sol, the growth of silica particles was restricted. This was a result of the strong hydrogen bonds between Si―OH groups and PVP molecules Multi-fractal spectrum (MFS) analysis suggested that PEG improved the uniformity of the silica film but PVP reduced it, therefore the laser-damage resistance of the PEG-modified silica film was enhanced, but that of the PVP-modified silica film was weakened. 29Si magic-angle spinning nuclear magnetic responance (MAS NMR) showed that PEG improved the condensation of Si ―O tetrahedron, but PVP did not. This led to differences between the laser-damage resistances of PEG-modified silica films and PVP-modified silica films.
The different effects of poly(ethylene glycol) (PEG) and poly(vinylpyrrolidone) (PVP) on the structure and laser-induced damage threshold of sol-gel silica anti-reflective films were investigated. The results of dynamic light-scattering, transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS) showed that PEG could prompt silica particles to form uniform clusters, whereas in the PVP-modified sol, the growth of silica particles was restricted. This was a result of the strong hydrogen bonds between Si―OH groups and PVP molecules Multi-fractal spectrum (MFS) analysis suggested that PEG improved the uniformity of the silica film but PVP reduced it, therefore the laser-damage resistance of the PEG-modified silica film was enhanced, but that of the PVP-modified silica film was weakened. 29Si magic-angle spinning nuclear magnetic responance (MAS NMR) showed that PEG improved the condensation of Si ―O tetrahedron, but PVP did not. This led to differences between the laser-damage resistances of PEG-modified silica films and PVP-modified silica films.
2012, 28(05): 1206-1212
doi: 10.3866/PKU.WHXB201202293
Abstract:
The initial shape of a coalesced drop is determined by the conservation of drop volume and the surface free energy before and after two or more condensed drops merge. The coalesced drop is in a metastable state with a driving force to reduce its base radius toward equilibrium state. This driving force and resistance on the three-phase contact line (TPCL) are analyzed during drop transformation. A dynamic equation describing the shape conversion of the drop is proposed and solved. The jumping height of a merged drop is determined by the speed at which the center of gravity moves up when the base radius of the drop reduces to 0 mm on a super-hydrophobic surface. Calculations show that a coalesced drop on a flat surface can transform its shape only in a limited fashion. It will not jump since its transformation stops before it reaches equilibrium. A wetted drop on a rough surface is even more difficult to transform and jump because of the greater TPCL resistance. However, on a two-tier surface, a partially wetted drop impaling only the micro-scale roughness exhibits a shape transition to a Cassie state upon coalescence, but without obvious jumping. Only after the coalescence of two or more small Cassie-state drops on a textured surface, can the merged composite drop easily transform to a 0 mm base radius and jump. It can be concluded that key factors verning condensed-drop jumping are the merged composite drop in a metastable state and a small TPCL resistance on nano or micro-nano two-tier surfaces.
The initial shape of a coalesced drop is determined by the conservation of drop volume and the surface free energy before and after two or more condensed drops merge. The coalesced drop is in a metastable state with a driving force to reduce its base radius toward equilibrium state. This driving force and resistance on the three-phase contact line (TPCL) are analyzed during drop transformation. A dynamic equation describing the shape conversion of the drop is proposed and solved. The jumping height of a merged drop is determined by the speed at which the center of gravity moves up when the base radius of the drop reduces to 0 mm on a super-hydrophobic surface. Calculations show that a coalesced drop on a flat surface can transform its shape only in a limited fashion. It will not jump since its transformation stops before it reaches equilibrium. A wetted drop on a rough surface is even more difficult to transform and jump because of the greater TPCL resistance. However, on a two-tier surface, a partially wetted drop impaling only the micro-scale roughness exhibits a shape transition to a Cassie state upon coalescence, but without obvious jumping. Only after the coalescence of two or more small Cassie-state drops on a textured surface, can the merged composite drop easily transform to a 0 mm base radius and jump. It can be concluded that key factors verning condensed-drop jumping are the merged composite drop in a metastable state and a small TPCL resistance on nano or micro-nano two-tier surfaces.
2012, 28(05): 1213-1217
doi: 10.3866/PKU.WHXB201203053
Abstract:
This paper reports a highly stable foam system generated by the gemini surfactant ethanediyl- α,ω-bis(tetradecyldimethylammonium bromide) (referred to as 14-2-14). The time measured for the collapse of the foam to half its initial height was used to characterize the foam stability; it was as high as 961 min for this system and significantly longer than that (754 min) for ethanediyl-α,ω-bis(dodecyldimethylammonium bromide) (12-2-12) foams. Thus the gemini surfactant structure of a short spacer together with two long tails enabled it to be a highly efficient foam stabilizer. The dilational rheology of the adsorbed films revealed the relationship between the interfacial elasticity and the foam stability. The high-frequency limit of elasticity of the adsorbed film at a specific surface coverage was again found to indicate foam stability. A larger limit of elasticity indicated a more stable foam.
This paper reports a highly stable foam system generated by the gemini surfactant ethanediyl- α,ω-bis(tetradecyldimethylammonium bromide) (referred to as 14-2-14). The time measured for the collapse of the foam to half its initial height was used to characterize the foam stability; it was as high as 961 min for this system and significantly longer than that (754 min) for ethanediyl-α,ω-bis(dodecyldimethylammonium bromide) (12-2-12) foams. Thus the gemini surfactant structure of a short spacer together with two long tails enabled it to be a highly efficient foam stabilizer. The dilational rheology of the adsorbed films revealed the relationship between the interfacial elasticity and the foam stability. The high-frequency limit of elasticity of the adsorbed film at a specific surface coverage was again found to indicate foam stability. A larger limit of elasticity indicated a more stable foam.
2012, 28(05): 1218-1222
doi: 10.3866/PKU.WHXB201202211
Abstract:
The rheological behaviors of mixed aqueous solutions of sodium hexadecyl sulfate (SHS) and a bolaform salt, either N,N'-ethanediyl-α,ω-bis(ethyldimethylammonium bromide) (Bola2Et) or N,N'- propanediyl-α,ω-bis(trimethylammonium bromide) (Bola4), were investigated by steady-state and frequency-sweep measurements. The results showed that long worm-like micelles were formed in both systems at 45 °C, and the solutions exhibited high viscoelasticities, especially the SHS/Bola2Et system in which the solution had very high elasticity. The zero-shear viscosity of SHS/Bola2Et was as high as 2520 Pa·s, and the system was gel-like. These results were attributed to the formation of 2:1 complexes by electrostatic attraction. Since the spacers of both Bola counterions were shorter than the distance between quaternary ammonium ions under electrostatic equilibrium, the generated complex in shape favored formation of worm-like micelles. In comparison, it was difficult to induce SHS to form worm-like micelles by the addition of tetramethylammonium counterions, and the solution exhibited low viscosity.
The rheological behaviors of mixed aqueous solutions of sodium hexadecyl sulfate (SHS) and a bolaform salt, either N,N'-ethanediyl-α,ω-bis(ethyldimethylammonium bromide) (Bola2Et) or N,N'- propanediyl-α,ω-bis(trimethylammonium bromide) (Bola4), were investigated by steady-state and frequency-sweep measurements. The results showed that long worm-like micelles were formed in both systems at 45 °C, and the solutions exhibited high viscoelasticities, especially the SHS/Bola2Et system in which the solution had very high elasticity. The zero-shear viscosity of SHS/Bola2Et was as high as 2520 Pa·s, and the system was gel-like. These results were attributed to the formation of 2:1 complexes by electrostatic attraction. Since the spacers of both Bola counterions were shorter than the distance between quaternary ammonium ions under electrostatic equilibrium, the generated complex in shape favored formation of worm-like micelles. In comparison, it was difficult to induce SHS to form worm-like micelles by the addition of tetramethylammonium counterions, and the solution exhibited low viscosity.
2012, 28(05): 1223-1229
doi: 10.3866/PKU.WHXB201202234
Abstract:
Solid amine adsorbents for low concentration CO2 removal were developed using carbon nanotubes (CNTs) impregnated with tetraethylenepentamine (TEPA) and triethylenetetramine (TETA). The adsorbents were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FITR), N2 adsorption/desorption, elemental analysis and thermogravimetric analysis (TGA). After impregnation, the shapes, fundamental channels and pore structures of the adsorbents were unchanged. However, the surface area and pore volume decreased. The adsorption behavior toward low concentration CO2 was investigated in a fixed-bed column. The results indicated that the adsorption capacity was enhanced substantially by modification. The CO2 adsorption capacity of CNTs-TEPA was higher than that of CNTs-TETA with the same amount of amine loading. The adsorption capacity increased steadily from 126.7 to 139.3 mg·g-1 for CNTs-TEPA and from 101.2 to 110.4 mg·g-1 for CNTs-TETA as the temperature increased from 20 to 30 ℃. The adsorption capacity of the raw CNTs experienced a modest increase, but began to decrease gradually with further temperature increases. Suyadal and Yasyerli deactivation models were applied to investigate the experimental breakthrough curves of raw and modified CNTs. It was concluded that the Yasyerli deactivation model is more appropriate to analyze the breakthrough curves of CO2 adsorption on solid amine adsorbents.
Solid amine adsorbents for low concentration CO2 removal were developed using carbon nanotubes (CNTs) impregnated with tetraethylenepentamine (TEPA) and triethylenetetramine (TETA). The adsorbents were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FITR), N2 adsorption/desorption, elemental analysis and thermogravimetric analysis (TGA). After impregnation, the shapes, fundamental channels and pore structures of the adsorbents were unchanged. However, the surface area and pore volume decreased. The adsorption behavior toward low concentration CO2 was investigated in a fixed-bed column. The results indicated that the adsorption capacity was enhanced substantially by modification. The CO2 adsorption capacity of CNTs-TEPA was higher than that of CNTs-TETA with the same amount of amine loading. The adsorption capacity increased steadily from 126.7 to 139.3 mg·g-1 for CNTs-TEPA and from 101.2 to 110.4 mg·g-1 for CNTs-TETA as the temperature increased from 20 to 30 ℃. The adsorption capacity of the raw CNTs experienced a modest increase, but began to decrease gradually with further temperature increases. Suyadal and Yasyerli deactivation models were applied to investigate the experimental breakthrough curves of raw and modified CNTs. It was concluded that the Yasyerli deactivation model is more appropriate to analyze the breakthrough curves of CO2 adsorption on solid amine adsorbents.
2012, 28(05): 1230-1236
doi: 10.3866/PKU.WHXB201202232
Abstract:
A series of Cu-ZSM-5 catalysts with different Cu loadings were prepared by an incipient wetness impregnation method. These catalysts were used for studies of selective catalytic reduction (SCR) of NO by NH3. The results showed that Cu-ZSM-5 with 5% Cu loading showed the best catalytic activity, the conversion of NO was more than 80% over the temperature range 198-470 ℃, and the highest NO conversion was 96.5%. The SCR activity was only influenced slightly by the addition of H2O or SO2. Visible diffraction of the CuO phase was observed when the Cu content was above 5%. The results of steady-state kinetics studies indicated that the SCR reaction over Cu-ZSM-5 with 5% Cu loading was zero-order with respect to NH3, first-order with respect to NO, and nearly half-order with respect to O2. The apparent activation energy for the reaction was found to be 47.7 kJ·mol-1.
A series of Cu-ZSM-5 catalysts with different Cu loadings were prepared by an incipient wetness impregnation method. These catalysts were used for studies of selective catalytic reduction (SCR) of NO by NH3. The results showed that Cu-ZSM-5 with 5% Cu loading showed the best catalytic activity, the conversion of NO was more than 80% over the temperature range 198-470 ℃, and the highest NO conversion was 96.5%. The SCR activity was only influenced slightly by the addition of H2O or SO2. Visible diffraction of the CuO phase was observed when the Cu content was above 5%. The results of steady-state kinetics studies indicated that the SCR reaction over Cu-ZSM-5 with 5% Cu loading was zero-order with respect to NH3, first-order with respect to NO, and nearly half-order with respect to O2. The apparent activation energy for the reaction was found to be 47.7 kJ·mol-1.
2012, 28(05): 1237-1242
doi: 10.3866/PKU.WHXB201203141
Abstract:
Ce0.45Zr0.45Y0.07La0.03O1.95, an oxygen storage material (OSM), and La-Ba-Al2O3 have been prepared by co-precipitation and peptization, respectively, to be used as supports for Fe2O3 catalysts. The Fe2O3 catalysts were obtained by impregnation methods and then coated on the monolith. The catalytic combustion of low concentration (thin) methane was investigated over the prepared catalysts. The effect of the OSM/La-Ba-Al2O3 mass ratio on the physicochemical properties of the catalysts was investigated using nitrogen adsorption-desorption, oxygen storage capacity (OSC) measurements, X-ray diffraction (XRD), and H2-temperature-programmed reduction (H2-TPR). The highest catalytic activity of both fresh and aged Fe2O3 catalysts for thin methane combustion was observed when the mass ratio of OSM/La-Ba-Al2O3 was 1:1. At this OSM/La-Ba-Al2O3 mass ratio, methane started to convert at 446 °C and completely converted at 553 ° C, with 1% (volume fraction) CH4 and a gas hourly space velocity (GHSV) of 50000 h-1. The Fe-based monolithic catalysts with different mass ratios of OSM to La-Ba-Al2O3 had different specific surface areas and reducibilities. XRD results showed that OSM existed in uniform solid solution and Fe2O3 was well dispersed on the binary supports. Based on the characterizations, the high catalytic activity and thermal stability of the catalysts can be attributed to the proper coordination of OSM and La-Ba-Al2O3 for thin methane combustion.
Ce0.45Zr0.45Y0.07La0.03O1.95, an oxygen storage material (OSM), and La-Ba-Al2O3 have been prepared by co-precipitation and peptization, respectively, to be used as supports for Fe2O3 catalysts. The Fe2O3 catalysts were obtained by impregnation methods and then coated on the monolith. The catalytic combustion of low concentration (thin) methane was investigated over the prepared catalysts. The effect of the OSM/La-Ba-Al2O3 mass ratio on the physicochemical properties of the catalysts was investigated using nitrogen adsorption-desorption, oxygen storage capacity (OSC) measurements, X-ray diffraction (XRD), and H2-temperature-programmed reduction (H2-TPR). The highest catalytic activity of both fresh and aged Fe2O3 catalysts for thin methane combustion was observed when the mass ratio of OSM/La-Ba-Al2O3 was 1:1. At this OSM/La-Ba-Al2O3 mass ratio, methane started to convert at 446 °C and completely converted at 553 ° C, with 1% (volume fraction) CH4 and a gas hourly space velocity (GHSV) of 50000 h-1. The Fe-based monolithic catalysts with different mass ratios of OSM to La-Ba-Al2O3 had different specific surface areas and reducibilities. XRD results showed that OSM existed in uniform solid solution and Fe2O3 was well dispersed on the binary supports. Based on the characterizations, the high catalytic activity and thermal stability of the catalysts can be attributed to the proper coordination of OSM and La-Ba-Al2O3 for thin methane combustion.
2012, 28(05): 1243-1251
doi: 10.3866/PKU.WHXB201203081
Abstract:
Lanthanum-promoted Ni-Mo-B amorphous catalysts were prepared by chemical reduction of the corresponding metal salts with sodium borohydride aqueous solution. Scanning electron microscopy (SEM), X-ray diffraction (XRD), inductively coupled plasma atomic emission spectrometry (ICP-AES), and X-ray photoelectron spectroscopy (XPS) were used to characterize the resulting materials. Phenol was used as model compound to test the hydrodeoxygenation (HDO) activity of the La-Ni-Mo-B amorphous catalysts. Adding lanthanum could decrease the particle size, increase the content of Ni0 and promote the reduction of Mo6+ to Mo4+ . But excess lanthanum would cover some of the Ni0, and Mo4+ active sites. The high hydrogenation activity was attributed to the amorphous structure of the catalyst and the high content of Ni0 and the high degree of deoxygenation was attributed to the high content of MoO2. The HDO reation of phenol on the La-Ni-Mo-B amorphous catalyst proceeded with a hydrogenation-dehydration route, thus decreasing the aromatic content of the HDO products. Both the conversion and the total deoxygenation degree were up to 99.0%. The deactivation of the La-Ni-Mo-B amorphous catalysts during the HDO reation of phenol at high temperature was mainly caused by the crystallization of the amorphous structure.
Lanthanum-promoted Ni-Mo-B amorphous catalysts were prepared by chemical reduction of the corresponding metal salts with sodium borohydride aqueous solution. Scanning electron microscopy (SEM), X-ray diffraction (XRD), inductively coupled plasma atomic emission spectrometry (ICP-AES), and X-ray photoelectron spectroscopy (XPS) were used to characterize the resulting materials. Phenol was used as model compound to test the hydrodeoxygenation (HDO) activity of the La-Ni-Mo-B amorphous catalysts. Adding lanthanum could decrease the particle size, increase the content of Ni0 and promote the reduction of Mo6+ to Mo4+ . But excess lanthanum would cover some of the Ni0, and Mo4+ active sites. The high hydrogenation activity was attributed to the amorphous structure of the catalyst and the high content of Ni0 and the high degree of deoxygenation was attributed to the high content of MoO2. The HDO reation of phenol on the La-Ni-Mo-B amorphous catalyst proceeded with a hydrogenation-dehydration route, thus decreasing the aromatic content of the HDO products. Both the conversion and the total deoxygenation degree were up to 99.0%. The deactivation of the La-Ni-Mo-B amorphous catalysts during the HDO reation of phenol at high temperature was mainly caused by the crystallization of the amorphous structure.
2012, 28(05): 1252-1256
doi: 10.3866/PKU.WHXB201202131
Abstract:
Oxidation and thermal desorption mechanism on the PbTe(111) surface were investigated using X-ray photoemission spectroscopy (XPS), scanning tunneling microscopy (STM), and low-energyelectron diffraction (LEED). The initial cleaning of the surface by 500 VAr+ sputtering followed by annealing at 250 °C yielded a perfect (1×1) PbTe(111) surface. XPS measurements showed that PbO2, PbO, and TeO2 were present at the PbTe(111) surface after air exposure for 2 days, and the intensity ratio of Te 3d5/2 and Pb 4f7/2 increased rapidly compared to that of the clean PbTe(111) surface, indicating Te depletion and Pb enrichment of the surface. XPS and STM measurements showed that the thickness of the oxide layer was more than 2 monolayers (MLs). During thermal treatment, the core levels of PbO2 and TeO2 disappeared and the intensity of the O 1s core level decreased, indicating surface decomposition of PbO2 and TeO2, and desorption of oxygen, whereas PbO was still present on the surface after annealing at up to 350 °C.
Oxidation and thermal desorption mechanism on the PbTe(111) surface were investigated using X-ray photoemission spectroscopy (XPS), scanning tunneling microscopy (STM), and low-energyelectron diffraction (LEED). The initial cleaning of the surface by 500 VAr+ sputtering followed by annealing at 250 °C yielded a perfect (1×1) PbTe(111) surface. XPS measurements showed that PbO2, PbO, and TeO2 were present at the PbTe(111) surface after air exposure for 2 days, and the intensity ratio of Te 3d5/2 and Pb 4f7/2 increased rapidly compared to that of the clean PbTe(111) surface, indicating Te depletion and Pb enrichment of the surface. XPS and STM measurements showed that the thickness of the oxide layer was more than 2 monolayers (MLs). During thermal treatment, the core levels of PbO2 and TeO2 disappeared and the intensity of the O 1s core level decreased, indicating surface decomposition of PbO2 and TeO2, and desorption of oxygen, whereas PbO was still present on the surface after annealing at up to 350 °C.
2012, 28(05): 1257-1264
doi: 10.3866/PKU.WHXB201202212
Abstract:
Xin-Ke-Shu (XKS), a traditional Chinese medicine (TCM) preparation, has been widely used for treatment of coronary heart disease (CHD) in China. However, the active constituents of XKS and their interactions with targets remain unclear. In this study, we assessed two docking programs, LibDock and AutoDock, by calculating the root-mean-square deviation (RMSD) of X-ray structure reproduction and the enrichment factor (EF) in virtual screening; both proved to be practical in our protein-ligand complex systems. Moreover, the combined use of the two programs yielded better EFs for each target. We therefore used a combination of the two programs to investigate the interactions of the 51 chemical constituents identified from XKS with five CHD targets, namely peroxisome proliferator activated receptor γ (PPAR-γ), angiotensin-converting enzyme (ACE), hydroxymethylglutaryl coenzyme A receptor (HMGR), cyclooxygenase-2 (COX2), and thrombin. The docking results suggest that pueroside A, pueroside B, salvianolic acid A, and salvianolic acid C can interact with two or more targets, and the other eight compounds may be potent for at least one of the five targets. In this research, we propose a strategy for studying TCM preparations, and suggest that XKS has a multi-target effect on CHD.
Xin-Ke-Shu (XKS), a traditional Chinese medicine (TCM) preparation, has been widely used for treatment of coronary heart disease (CHD) in China. However, the active constituents of XKS and their interactions with targets remain unclear. In this study, we assessed two docking programs, LibDock and AutoDock, by calculating the root-mean-square deviation (RMSD) of X-ray structure reproduction and the enrichment factor (EF) in virtual screening; both proved to be practical in our protein-ligand complex systems. Moreover, the combined use of the two programs yielded better EFs for each target. We therefore used a combination of the two programs to investigate the interactions of the 51 chemical constituents identified from XKS with five CHD targets, namely peroxisome proliferator activated receptor γ (PPAR-γ), angiotensin-converting enzyme (ACE), hydroxymethylglutaryl coenzyme A receptor (HMGR), cyclooxygenase-2 (COX2), and thrombin. The docking results suggest that pueroside A, pueroside B, salvianolic acid A, and salvianolic acid C can interact with two or more targets, and the other eight compounds may be potent for at least one of the five targets. In this research, we propose a strategy for studying TCM preparations, and suggest that XKS has a multi-target effect on CHD.
2012, 28(05): 1265-1268
doi: 10.3866/PKU.WHXB201202291
Abstract:
Zinc ferrite (ZnFe2O4) hollow fibers have been fabricated by annealing electrospun polyvinylpyrrolidone (PVP)/nitrate salt composite nanofibers at 500 °C for 3 h with a heating rate of 5 °C· min-1. The composite fibers were initially prepared by electrospinning Zn, Fe salts, and PVP from solution. The structure, morphology, and magnetic properties were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). The XRD results indicate a spinel phase structure, while SEM and TEM reveal hollow fibers (200-400 nm in diameter) with walls consisting of packed 25 nm nanoparticles. Room temperature VSM of the ZnFe2O4 hollow fibers reveal a superparamagnetic behavior and a magnetization value of 2.03 emu·g-1 at 10 kOe.
Zinc ferrite (ZnFe2O4) hollow fibers have been fabricated by annealing electrospun polyvinylpyrrolidone (PVP)/nitrate salt composite nanofibers at 500 °C for 3 h with a heating rate of 5 °C· min-1. The composite fibers were initially prepared by electrospinning Zn, Fe salts, and PVP from solution. The structure, morphology, and magnetic properties were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). The XRD results indicate a spinel phase structure, while SEM and TEM reveal hollow fibers (200-400 nm in diameter) with walls consisting of packed 25 nm nanoparticles. Room temperature VSM of the ZnFe2O4 hollow fibers reveal a superparamagnetic behavior and a magnetization value of 2.03 emu·g-1 at 10 kOe.
2012, 28(05): 1269-1274
doi: 10.3866/PKU.WHXB201202242
Abstract:
Because of the chemical reaction between Cr(VI) ions and glutathione, the peak reduction current of Cr(VI) ions decreases while adding glutathione (GSH) into a K2Cr2O7/H2SO4 solution. Thus the concentration of GSH can be detected indirectly by differential pulse voltammetry (DPV) analysis. This electrochemical indirect method was used to study the adsorption of GSH on multi-walled carbon nanotubes (MWCNTs) and activated carbon (AC), and can be used to determine the equilibrium relationship between GSH adsorption and its concentration. Unlike the result obtained from the active carbon, GSH adsorption on MWCNTs agrees better with that predicted by the Freundlich equation compared to that predicted by the Langmuir equation. The morphologies of MWCNTs and activated carbon were observed with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The abundance of aggregated pores in MWCNTs is beneficial for the diffusion and adsorption of small GSH molecules, suggesting that MWCNTs could be developed as an adsorbent for small molecular substances.
Because of the chemical reaction between Cr(VI) ions and glutathione, the peak reduction current of Cr(VI) ions decreases while adding glutathione (GSH) into a K2Cr2O7/H2SO4 solution. Thus the concentration of GSH can be detected indirectly by differential pulse voltammetry (DPV) analysis. This electrochemical indirect method was used to study the adsorption of GSH on multi-walled carbon nanotubes (MWCNTs) and activated carbon (AC), and can be used to determine the equilibrium relationship between GSH adsorption and its concentration. Unlike the result obtained from the active carbon, GSH adsorption on MWCNTs agrees better with that predicted by the Freundlich equation compared to that predicted by the Langmuir equation. The morphologies of MWCNTs and activated carbon were observed with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The abundance of aggregated pores in MWCNTs is beneficial for the diffusion and adsorption of small GSH molecules, suggesting that MWCNTs could be developed as an adsorbent for small molecular substances.
