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2008 Volume 24 Issue 12
2008, 24(12):
Abstract:
2008, 24(12): 2149-2152
doi: 10.3866/PKU.WHXB20081201
Abstract:
Structure-property relationships of four divinyl-biphenyl derivatives and two heterocyclic molecules (A: 4,4’-bis(2-(pyridin-4-yl)vinyl)biphenyl, B: 4,4’-bis(2-(pyridin-2-yl)vinyl)biphenyl, C: 1-methyl-4-(2-(4’-(2-(pyridin-4-yl)vinyl) biphenyl-4-yl)vinyl)pyridinium iodide, D: 1-methyl-2-(2-(4’-2-(pyridin-2-yl)vinyl) biphenyl-4-yl)vinyl) pyridinium iodide, E: 4-(2-(9-Butyl-9H-carbazol-3-yl)vinyl)-1-methyl-pyridinium iodide, and F: 4-(2-(9-butyl-9H-carbazol-3-yl)vinyl)-1-methyl-quinolinium iodide) that contain pyridinium groups were studied by laser spectroscopy. The largest two-photon absorption cross-section is 617.3 GMfor molecule E, and the smallest is 19.3 GM(1 GM=10-50 cm4·s·photon-1) for molecule B. Our research demonstrates that two-photon absorption cross-sections of compounds A-F are evidently dependent on both the pyridiniumgroup symmetry and the cationic structure.
Structure-property relationships of four divinyl-biphenyl derivatives and two heterocyclic molecules (A: 4,4’-bis(2-(pyridin-4-yl)vinyl)biphenyl, B: 4,4’-bis(2-(pyridin-2-yl)vinyl)biphenyl, C: 1-methyl-4-(2-(4’-(2-(pyridin-4-yl)vinyl) biphenyl-4-yl)vinyl)pyridinium iodide, D: 1-methyl-2-(2-(4’-2-(pyridin-2-yl)vinyl) biphenyl-4-yl)vinyl) pyridinium iodide, E: 4-(2-(9-Butyl-9H-carbazol-3-yl)vinyl)-1-methyl-pyridinium iodide, and F: 4-(2-(9-butyl-9H-carbazol-3-yl)vinyl)-1-methyl-quinolinium iodide) that contain pyridinium groups were studied by laser spectroscopy. The largest two-photon absorption cross-section is 617.3 GMfor molecule E, and the smallest is 19.3 GM(1 GM=10-50 cm4·s·photon-1) for molecule B. Our research demonstrates that two-photon absorption cross-sections of compounds A-F are evidently dependent on both the pyridiniumgroup symmetry and the cationic structure.
2008, 24(12): 2153-2158
doi: 10.1016/S1872-1508(08)60081-9
Abstract:
Dynamical spin chirality of α-glycine crystal at 301-302 K was investigated by DC (direct current)-magnetic susceptibility measurement at temperatures ranging from2 to 315 Kunder the external magnetic fields (H=±1 T) parallel to the b axis. The α-glycine crystallizes in space group P21/n with four molecules in a cell, which has centrosymmetric charge distribution. The bifurcated hydrogen bonds N+(3)—H(8)…O(1) and N+(3)—H(8)…O(2) are stacked along the b axis with different bond intensities and angles, which formanti-parallel double layers. Atomic force spectroscopy result at 303 K indicated that the surface molecular structures of α-glycine formed a regular flexuous framework in the b axis direction. The strong temperature dependence is related to the reorientation of NH+3 group and the electron spin flip-flop of (N+H) mode. Under the opposite external magnetic field of 1 T and -1 T, the electron spins of N+(3)—H(8)…O(1) and N+(3)—H(8)…O(2) flip-flop at 301-302 K. These results suggested a mechanism of the magnetoelectric effect based on the dynamical spin chirality of (N +H), which induced the electric polarization to produce the onset of pyroelectricity of α-glycine around 304 K.
Dynamical spin chirality of α-glycine crystal at 301-302 K was investigated by DC (direct current)-magnetic susceptibility measurement at temperatures ranging from2 to 315 Kunder the external magnetic fields (H=±1 T) parallel to the b axis. The α-glycine crystallizes in space group P21/n with four molecules in a cell, which has centrosymmetric charge distribution. The bifurcated hydrogen bonds N+(3)—H(8)…O(1) and N+(3)—H(8)…O(2) are stacked along the b axis with different bond intensities and angles, which formanti-parallel double layers. Atomic force spectroscopy result at 303 K indicated that the surface molecular structures of α-glycine formed a regular flexuous framework in the b axis direction. The strong temperature dependence is related to the reorientation of NH+3 group and the electron spin flip-flop of (N+H) mode. Under the opposite external magnetic field of 1 T and -1 T, the electron spins of N+(3)—H(8)…O(1) and N+(3)—H(8)…O(2) flip-flop at 301-302 K. These results suggested a mechanism of the magnetoelectric effect based on the dynamical spin chirality of (N +H), which induced the electric polarization to produce the onset of pyroelectricity of α-glycine around 304 K.
2008, 24(12): 2159-2164
doi: 10.3866/PKU.WHXB20081203
Abstract:
A new composite of Au nanoparticles (AuNPs) adsorbed on thermoresponsive poly(N-isopropyl acrylamide) (PNIPAM) microgels that combines the thermoresponsive behavior of PNIPAM microgels with the optical properties of Au nanoparticles is reported. The LSPR (localized surface plasmon resonance) of the AuNPs could be changed by adjusting the temperature of the thermoresponsive PNIPAMmicrogels. An increase in temperature led to a red shift of the LSPR of the AuNPs and this change was found to be fully reversible. Optical properties of AuNPs were used to monitor the thermoresponsive behavior of PNIPAM microgels. The morphology, optical properties, and average particle size of AuNPs/PNIPAM particles were characterized by transmission electron microscopy (TEM), UV-Vis spectroscopy and dynamic light scattering.
A new composite of Au nanoparticles (AuNPs) adsorbed on thermoresponsive poly(N-isopropyl acrylamide) (PNIPAM) microgels that combines the thermoresponsive behavior of PNIPAM microgels with the optical properties of Au nanoparticles is reported. The LSPR (localized surface plasmon resonance) of the AuNPs could be changed by adjusting the temperature of the thermoresponsive PNIPAMmicrogels. An increase in temperature led to a red shift of the LSPR of the AuNPs and this change was found to be fully reversible. Optical properties of AuNPs were used to monitor the thermoresponsive behavior of PNIPAM microgels. The morphology, optical properties, and average particle size of AuNPs/PNIPAM particles were characterized by transmission electron microscopy (TEM), UV-Vis spectroscopy and dynamic light scattering.
2008, 24(12): 2165-2171
doi: 10.3866/PKU.WHXB20081204
Abstract:
The effect of a Mg promoter on the physical and chemical properties, as well as catalytic performance of the Co/Mg/HZSM-5 catalyst for the partial oxidation of methane(POM) to syngas was studied by XRD, H2-TPR, TEM, Raman, XPS and activity measurements. The activity and stability of the Co/HZSM-5 catalyst was effectively improved by Mg modification. At T=750 ℃ and SV (space velocity)=1.0×105 mL·h-1·g-1 the Mg-modified catalyst exhibited high activity and od stability during a long run. The unmodified catalyst rapidly deactivated after 10 h on stream. Catalyst deactivation was mainly due to the transformation of Co0 into CoAl2O4 as indicated by TPR and XPS. For the Co/Mg/HZSM-5 catalyst the Co species, in addition to ones existing as Co3O4, reacted with the Mg promoter to produce MgCo2O4. This structure, after reduction, led to a higher dispersion of Co metal, compared with the Mg-free catalyst. From the results of the characterization and activity measurements, the relationship between catalyst structure and performance was discussed.
The effect of a Mg promoter on the physical and chemical properties, as well as catalytic performance of the Co/Mg/HZSM-5 catalyst for the partial oxidation of methane(POM) to syngas was studied by XRD, H2-TPR, TEM, Raman, XPS and activity measurements. The activity and stability of the Co/HZSM-5 catalyst was effectively improved by Mg modification. At T=750 ℃ and SV (space velocity)=1.0×105 mL·h-1·g-1 the Mg-modified catalyst exhibited high activity and od stability during a long run. The unmodified catalyst rapidly deactivated after 10 h on stream. Catalyst deactivation was mainly due to the transformation of Co0 into CoAl2O4 as indicated by TPR and XPS. For the Co/Mg/HZSM-5 catalyst the Co species, in addition to ones existing as Co3O4, reacted with the Mg promoter to produce MgCo2O4. This structure, after reduction, led to a higher dispersion of Co metal, compared with the Mg-free catalyst. From the results of the characterization and activity measurements, the relationship between catalyst structure and performance was discussed.
Solvent Effects on the Solvothermal Synthesis of PureMonoclinic and Tetra nal Zirconia Nanoparticles
2008, 24(12): 2172-2178
doi: 10.3866/PKU.WHXB20081205
Abstract:
We have previously reported the solvothermal synthesis of pure monoclinic and tetra nal zirconia nanoparticles in water and methanol. The solvent effect on this synthesis was studied further for this work. The effects of reaction temperature, reaction time and thermal treatment temperature on the crystal phases of the as-prepared hydrous ZrO2 precipitates formed from the solvothermal reaction of hydrated zirconyl nitrate (ZrO(NO3)2·2H2O) and urea were characterized by X-ray diffraction. Plausible mechanisms for the formation of hydrous precipitates, their transformation and their stabilization were examined. Precipitates formed initially with a tetra nal structure irrespective of the solvent used. These tetra nal precipitates, in water, transform into thermodynamically stable monoclinic structures as a result of higher precipitate solubility under hydrothermal conditions. Dissolution and precipitation processes are thus favored. The tetra nal structure was, however, maintained under methanothermal conditions probably due to poor precipitate solubility in methanol. The removal of water from precipitates by reaction with urea in methanol may make the tetra nal structure more rigid. This contributes to the maintenance of the tetra nal structure after precipitate thermal treatment (at 400 ℃). Differences in precipitate solubility and their reaction with urea in water and methanol may dictate the synthetic pathway for pure monoclinic and tetra nal ZrO2 via the solvothermal method.
We have previously reported the solvothermal synthesis of pure monoclinic and tetra nal zirconia nanoparticles in water and methanol. The solvent effect on this synthesis was studied further for this work. The effects of reaction temperature, reaction time and thermal treatment temperature on the crystal phases of the as-prepared hydrous ZrO2 precipitates formed from the solvothermal reaction of hydrated zirconyl nitrate (ZrO(NO3)2·2H2O) and urea were characterized by X-ray diffraction. Plausible mechanisms for the formation of hydrous precipitates, their transformation and their stabilization were examined. Precipitates formed initially with a tetra nal structure irrespective of the solvent used. These tetra nal precipitates, in water, transform into thermodynamically stable monoclinic structures as a result of higher precipitate solubility under hydrothermal conditions. Dissolution and precipitation processes are thus favored. The tetra nal structure was, however, maintained under methanothermal conditions probably due to poor precipitate solubility in methanol. The removal of water from precipitates by reaction with urea in methanol may make the tetra nal structure more rigid. This contributes to the maintenance of the tetra nal structure after precipitate thermal treatment (at 400 ℃). Differences in precipitate solubility and their reaction with urea in water and methanol may dictate the synthetic pathway for pure monoclinic and tetra nal ZrO2 via the solvothermal method.
2008, 24(12): 2179-2184
doi: 10.3866/PKU.WHXB20081206
Abstract:
Zinc alginate (Alg-Zn) fibers were obtained by wet spinning of sodiumalginate (Alg-Na) into a coagulating bath containing an aqueous zinc chloride solution. ZnO nanostructures were prepared by thermal degradation of the as-obtained zinc alginate fibers at different temperatures in air. The compositions, morphologies, and microstructures of products were investigated by thermal gravimetry (TG), X-ray diffraction (XRD), electron energy-loss spectroscopy (EELS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). Annealing time and temperature influenced final structures and shapes of ZnO nanostructures. ZnO nanorods with diameters of about 120 nm were obtained at 800 ℃ and with a reaction time of more than 24 h in air. A ZnO growth mechanism was proposed by a careful investigation of ZnO nanostructures after different thermal treatment times.
Zinc alginate (Alg-Zn) fibers were obtained by wet spinning of sodiumalginate (Alg-Na) into a coagulating bath containing an aqueous zinc chloride solution. ZnO nanostructures were prepared by thermal degradation of the as-obtained zinc alginate fibers at different temperatures in air. The compositions, morphologies, and microstructures of products were investigated by thermal gravimetry (TG), X-ray diffraction (XRD), electron energy-loss spectroscopy (EELS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). Annealing time and temperature influenced final structures and shapes of ZnO nanostructures. ZnO nanorods with diameters of about 120 nm were obtained at 800 ℃ and with a reaction time of more than 24 h in air. A ZnO growth mechanism was proposed by a careful investigation of ZnO nanostructures after different thermal treatment times.
2008, 24(12): 2185-2190
doi: 10.3866/PKU.WHXB20081207
Abstract:
Scanning tunneling microscope (STM) images and surface relaxations of a reconstructed W(100) c(2×2) surface have been investigated by density functional theory calculations. The distorted displacement (δ) of a tungsten atom along [110] was 0.027 nm. The distortion energy was 80.6 meV·atom-1 and the relaxations of the W(100) c(2×2) surface was calculated to be -7.6% for ⊿d12/d0 and +0.8% for ⊿d23/d0. The surface work function (Φ) was 4.55 eV. Calculated STMimages of the W(100) c(2×2) surface displayed the following unusual features: protrusions in the STM image along the [110] axis are in the middle of a zig-zag chain of tungsten atoms while the dark regions in STM images correspond to valleys between neighboring zig-zag chains. These are due to surface reconstruction. Typical corrugations of a STMscan have been calculated to be between 0.008-0.013 nm for negative bias voltages while the corrugation varies from0.019-0.024 nmfor positive bias voltages.
Scanning tunneling microscope (STM) images and surface relaxations of a reconstructed W(100) c(2×2) surface have been investigated by density functional theory calculations. The distorted displacement (δ) of a tungsten atom along [110] was 0.027 nm. The distortion energy was 80.6 meV·atom-1 and the relaxations of the W(100) c(2×2) surface was calculated to be -7.6% for ⊿d12/d0 and +0.8% for ⊿d23/d0. The surface work function (Φ) was 4.55 eV. Calculated STMimages of the W(100) c(2×2) surface displayed the following unusual features: protrusions in the STM image along the [110] axis are in the middle of a zig-zag chain of tungsten atoms while the dark regions in STM images correspond to valleys between neighboring zig-zag chains. These are due to surface reconstruction. Typical corrugations of a STMscan have been calculated to be between 0.008-0.013 nm for negative bias voltages while the corrugation varies from0.019-0.024 nmfor positive bias voltages.
2008, 24(12): 2191-2197
doi: 10.1016/S1872-1508(08)60082-0
Abstract:
Self-organized TiO2 nanotube arrays with micro-scale length were prepared on fluorine-doped tin oxide (FTO) conducting glass in NH4F/glycerol electrolyte by electrochemical anodization of pure titanium films deposited by radio frequency magnetron sputtering (RFMS) at roomtemperature. The samples were characterized by means of field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and photoelectrochemistry methods. The results showed that Ti films prepared at the condition of Ar pressure 0.5 Pa, power 150 W, and 0.5 h at room temperature possessed the zone T model structure with od homogeneity and high denseness. When the anodization time was prolonged from 1 to 3 h at the voltage of 30 V, the pore diameter of TiO2 nanotubes increased from 50 to 75 nm, and the length increased from750 to 1100 nmand then gradually decreased to 800 nm, while their wall morphology changed from smooth to rough. Also with increasing the anodization voltage, the pore diameter became larger, and the remaining oxide layer reduced, which could be easily removed by ultrasonic-chemical cleaning in 0.05% (w, mass fraction) diluted HF solution. Moreover, the photocurrent response curves and electrochemical impedance spectroscopy (EIS) results indicated that UV-illumination clearly enhanced the effective separation of the electron-hole pairs and the crystallized electrodes from the annealing treatment of as-anodized electrodes at 450 ℃ exhibited a better photoelectrochemical performance.
Self-organized TiO2 nanotube arrays with micro-scale length were prepared on fluorine-doped tin oxide (FTO) conducting glass in NH4F/glycerol electrolyte by electrochemical anodization of pure titanium films deposited by radio frequency magnetron sputtering (RFMS) at roomtemperature. The samples were characterized by means of field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and photoelectrochemistry methods. The results showed that Ti films prepared at the condition of Ar pressure 0.5 Pa, power 150 W, and 0.5 h at room temperature possessed the zone T model structure with od homogeneity and high denseness. When the anodization time was prolonged from 1 to 3 h at the voltage of 30 V, the pore diameter of TiO2 nanotubes increased from 50 to 75 nm, and the length increased from750 to 1100 nmand then gradually decreased to 800 nm, while their wall morphology changed from smooth to rough. Also with increasing the anodization voltage, the pore diameter became larger, and the remaining oxide layer reduced, which could be easily removed by ultrasonic-chemical cleaning in 0.05% (w, mass fraction) diluted HF solution. Moreover, the photocurrent response curves and electrochemical impedance spectroscopy (EIS) results indicated that UV-illumination clearly enhanced the effective separation of the electron-hole pairs and the crystallized electrodes from the annealing treatment of as-anodized electrodes at 450 ℃ exhibited a better photoelectrochemical performance.
2008, 24(12): 2198-2202
doi: 10.3866/PKU.WHXB20081209
Abstract:
Quantitative structure-activity relationship (QSAR) was used to predict the melting points of two kinds of imidazolium ionic liquids. Using a genetic al rithm a three-parameter model with R2 =0.89 was set up for 16 imidazolium tetrafluoroborates and a four-parameter model with R2 =0.85 was developed for 22 imidazolium hexafluorophosphates. Internal reliability validation was performed using a leave-one-out approach with R2=0.82 for the model of imidazolium tetrafluoroborates and R2 =0.77 for the model of imidazolium hexafluorophosphates. To validate predictive abilities of models an external validation was performed for test sets where the mean absolute deviation were 11.43 and 7.78 K, respectively. These values are better than the values found in the literature. The proposed models can be used to predict melting points of imidazoliumionic liquids.
Quantitative structure-activity relationship (QSAR) was used to predict the melting points of two kinds of imidazolium ionic liquids. Using a genetic al rithm a three-parameter model with R2 =0.89 was set up for 16 imidazolium tetrafluoroborates and a four-parameter model with R2 =0.85 was developed for 22 imidazolium hexafluorophosphates. Internal reliability validation was performed using a leave-one-out approach with R2=0.82 for the model of imidazolium tetrafluoroborates and R2 =0.77 for the model of imidazolium hexafluorophosphates. To validate predictive abilities of models an external validation was performed for test sets where the mean absolute deviation were 11.43 and 7.78 K, respectively. These values are better than the values found in the literature. The proposed models can be used to predict melting points of imidazoliumionic liquids.
2008, 24(12): 2203-2206
doi: 10.1016/S1872-1508(08)60083-2
Abstract:
Taking into account the existence of internal noise in small scale biochemical reaction systems, we studied how the internal noise would influence the detection of weak external signal in the cell system using chemical Langevin equation. The weak signal was too small to, separately, fire calcium spikes for the cell. We found that, near the Hopf bifurcation point, the internal noise could help the calcium oscillation signal cross a threshold value, and at an optimal internal noise level, a resonance occurred among the internal noise, the internal noise-induced calcium oscillations, and the weak signal, so as to enhance intensively the ability of the cell system to detect the weak signal. Since the internal noise was changed via the cell size, this phenomenon demonstrated the existence of an optimal cell size for the signal detection. Interestingly, it was found that the optimal size matched well with the real cell size, which was robust to external stimulus, this was of significant biological meaning.
Taking into account the existence of internal noise in small scale biochemical reaction systems, we studied how the internal noise would influence the detection of weak external signal in the cell system using chemical Langevin equation. The weak signal was too small to, separately, fire calcium spikes for the cell. We found that, near the Hopf bifurcation point, the internal noise could help the calcium oscillation signal cross a threshold value, and at an optimal internal noise level, a resonance occurred among the internal noise, the internal noise-induced calcium oscillations, and the weak signal, so as to enhance intensively the ability of the cell system to detect the weak signal. Since the internal noise was changed via the cell size, this phenomenon demonstrated the existence of an optimal cell size for the signal detection. Interestingly, it was found that the optimal size matched well with the real cell size, which was robust to external stimulus, this was of significant biological meaning.
2008, 24(12): 2207-2213
doi: 10.1016/S1872-1508(08)60084-4
Abstract:
The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) on the interaction of chromium dipeptide complex ([Cr(III)-Gly-Gly]2+) with ninhydrin under varying conditions has been investigated. The rates of the reaction were determined in both water and surfactant micelles in the absence and presence of various organic and inorganic salts at 70 ℃ and pH 5.0. The reaction followed first-and fractional-order kinetics with respect to [Cr(III)-Gly-Gly2+] and [ninhydrin]. Increase in the total concentration of CTAB from0 to 40×10-3mol·dm-3 resulted in an increase in the pseudo-first-order rate constant (kψ) by a factor of ca 3. Quantitative kinetic analysis of kψ-[CTAB] data was performed on the basis of the pseudo-phase model of the micelles. As added salts induce structural changes in micellar systems that may modify the substrate-surfactant interactions, the effect of some inorganic (NaBr, NaCl, Na2SO4) and organic (NaBenz, NaSal, NaTos) salts on the rate was also explored. It was found that the tightly bound counterions (derived fromorganic salts) were the most effective.
The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) on the interaction of chromium dipeptide complex ([Cr(III)-Gly-Gly]2+) with ninhydrin under varying conditions has been investigated. The rates of the reaction were determined in both water and surfactant micelles in the absence and presence of various organic and inorganic salts at 70 ℃ and pH 5.0. The reaction followed first-and fractional-order kinetics with respect to [Cr(III)-Gly-Gly2+] and [ninhydrin]. Increase in the total concentration of CTAB from0 to 40×10-3mol·dm-3 resulted in an increase in the pseudo-first-order rate constant (kψ) by a factor of ca 3. Quantitative kinetic analysis of kψ-[CTAB] data was performed on the basis of the pseudo-phase model of the micelles. As added salts induce structural changes in micellar systems that may modify the substrate-surfactant interactions, the effect of some inorganic (NaBr, NaCl, Na2SO4) and organic (NaBenz, NaSal, NaTos) salts on the rate was also explored. It was found that the tightly bound counterions (derived fromorganic salts) were the most effective.
2008, 24(12): 2214-2220
doi: 10.3866/PKU.WHXB20081212
Abstract:
A double extrapolation method was employed to determine the most probable mechanism for the thermal decomposition reaction of the survived β-cyclodextrin (β-CD) from the inclusion complex of β-CD with clove oil. The activation energy (Ea) curve calculated by Flynn-Wall-Ozawa method was clearly divided into three stages for the thermal decomposition process of the survived β-CD. The nearly parallel linear relationship between first and last stages was assessed as an Avrami-Erofe’ev A1.5 model. Furthermore, the platform in the second stage of the decomposition of the survived β-CD in which each point has approximately equivalent Ea was carefully investigated using the reaction order (n) method. A regular decline in n as the temperature increased implied a complicated decomposition reaction mechanism for the survived β-CD in this stage. Infrared spectroscopic profiles from the thermal decomposition of free β-CD and survived β-CD were also compared. The changes in IR spectra below 1000 cm-1 between free β-CD and survived β-CD in the decomposition process were quite different which agreed with the calculated Ea values.
A double extrapolation method was employed to determine the most probable mechanism for the thermal decomposition reaction of the survived β-cyclodextrin (β-CD) from the inclusion complex of β-CD with clove oil. The activation energy (Ea) curve calculated by Flynn-Wall-Ozawa method was clearly divided into three stages for the thermal decomposition process of the survived β-CD. The nearly parallel linear relationship between first and last stages was assessed as an Avrami-Erofe’ev A1.5 model. Furthermore, the platform in the second stage of the decomposition of the survived β-CD in which each point has approximately equivalent Ea was carefully investigated using the reaction order (n) method. A regular decline in n as the temperature increased implied a complicated decomposition reaction mechanism for the survived β-CD in this stage. Infrared spectroscopic profiles from the thermal decomposition of free β-CD and survived β-CD were also compared. The changes in IR spectra below 1000 cm-1 between free β-CD and survived β-CD in the decomposition process were quite different which agreed with the calculated Ea values.
2008, 24(12): 2221-2228
doi: 10.3866/PKU.WHXB20081213
Abstract:
A numerical study based on computational singular perturbation (CSP) in a methane/air premixed combustion system was undertaken. This method splits reaction spaces to eliminate stiffness, identifies quasi-steady-state (QSS) species by analyzing CSP pointer locally and integrally as well as simplifying algebraic relations and differential equations by using two CSP indexes. Finally, a 15-step globally reduced mechanism was constructed based on CSP analyses in a premixed methane/air combustion system. The 15-step reduced mechanism was tested and verified using Sandia’s PREMIX. Advantages of the CSP method are discussed. A new method for analyzing the reduced mechanismmay be used for more complex combustion systems.
A numerical study based on computational singular perturbation (CSP) in a methane/air premixed combustion system was undertaken. This method splits reaction spaces to eliminate stiffness, identifies quasi-steady-state (QSS) species by analyzing CSP pointer locally and integrally as well as simplifying algebraic relations and differential equations by using two CSP indexes. Finally, a 15-step globally reduced mechanism was constructed based on CSP analyses in a premixed methane/air combustion system. The 15-step reduced mechanism was tested and verified using Sandia’s PREMIX. Advantages of the CSP method are discussed. A new method for analyzing the reduced mechanismmay be used for more complex combustion systems.
2008, 24(12): 2229-2235
doi: 10.3866/PKU.WHXB20081214
Abstract:
Theoretical calculations at MP2/6-311+G* level were employed to investigate various reaction mechanisms between singlet dichloromethylene germylene and methanethial. Calculation results indicate that the dominant reaction pathway for this reaction consists of three steps. The two reactants initially forman intermediate INT through a barrier-free exothermic reaction of 103.4 kJ·mol-1. This intermediate then isomerizes to P31 via a transition state TS3 with an energy barrier of 0.7 kJ·mol-1. P31 finally reacts with methanethial to form the germanic heteropolycyclic product P33 with an energy barrier of 32.3 kJ·mol-1. This cycloaddition reaction thus has excellent selectivity.
Theoretical calculations at MP2/6-311+G* level were employed to investigate various reaction mechanisms between singlet dichloromethylene germylene and methanethial. Calculation results indicate that the dominant reaction pathway for this reaction consists of three steps. The two reactants initially forman intermediate INT through a barrier-free exothermic reaction of 103.4 kJ·mol-1. This intermediate then isomerizes to P31 via a transition state TS3 with an energy barrier of 0.7 kJ·mol-1. P31 finally reacts with methanethial to form the germanic heteropolycyclic product P33 with an energy barrier of 32.3 kJ·mol-1. This cycloaddition reaction thus has excellent selectivity.
2008, 24(12): 2236-2242
doi: 10.1016/S1872-1508(08)60085-6
Abstract:
The effect of sodiumcarboxymethyl cellulose (Na-CMC) on the corrosion behavior of mild steel in 1.0 mol·L-1 HCl solution has been investigated by using weight loss (WL) measurement, potentiodynamic polarization, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) methods. These results showed that the inhibition efficiency of Na-CMC increased with increasing the inhibitor concentration. Potentiodynamic polarization studies revealed that the Na-CMC was a mixed type inhibitor in 1.0 mol·L-1 HCl. The adsorption of the inhibitor on mild steel surface has been found to obey the Langmuir isotherm. The effect of temperature on the corrosion behavior of mild steel in 1.0 mol·L -1 HCl with addition of 0.04% of Na-CMC has been studied in the temperature range of 298-328 K. The associated apparent activation energy (E*a) of corrosion reaction has been determined. Scanning electron microscopy (SEM) has been applied to investigate the surface morphology of mild steel in the absence and presence of the inhibitor molecules.
The effect of sodiumcarboxymethyl cellulose (Na-CMC) on the corrosion behavior of mild steel in 1.0 mol·L-1 HCl solution has been investigated by using weight loss (WL) measurement, potentiodynamic polarization, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) methods. These results showed that the inhibition efficiency of Na-CMC increased with increasing the inhibitor concentration. Potentiodynamic polarization studies revealed that the Na-CMC was a mixed type inhibitor in 1.0 mol·L-1 HCl. The adsorption of the inhibitor on mild steel surface has been found to obey the Langmuir isotherm. The effect of temperature on the corrosion behavior of mild steel in 1.0 mol·L -1 HCl with addition of 0.04% of Na-CMC has been studied in the temperature range of 298-328 K. The associated apparent activation energy (E*a) of corrosion reaction has been determined. Scanning electron microscopy (SEM) has been applied to investigate the surface morphology of mild steel in the absence and presence of the inhibitor molecules.
2008, 24(12): 2243-2248
doi: 10.3866/PKU.WHXB20081216
Abstract:
The geometries, electronic structures and spectroscopic properties for a series of osmium(II) complexes [Os(II)(CO)3(tfa)(L)](tfa=trifluoroacetate; L=O^O (1), O^N (2),N^N (3), O^O=hexafluoroacetylacetonate, O^N=quinolinolate, N^N=3-(trifluoromethyl)-5-(2-pyridyl) pyrazole) were investigated theoretically. The Becke’s three parameter functional, the Lee-Yang-Parr (B3LYP) functional and single-excitation configuration interaction (CIS) methods were used to optimize the ground and excited states for complexes 1-3. The time-dependent density functional theory (TD-DFT) at B3LYP level with the polarized continuum model (PCM) was employed to obtain their absorption and phosphorescent emission spectra in CH2Cl2 based on their optimized ground and excited states geometries. The results revealed that the optimized structural parameters agreed well with the corresponding experimental results. There were slight structural differences between ground and excited states, and this was in agreement with the small Stokes-shift observed in the experiments. The lowest-lying absorptions were at 342, 431and 329 nm, and phosphorescent emissions were at 521, 638 and 488 nm for complexes 1-3, respectively. The highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO) of 1-3 mainly manifest as characteristic π and π* orbitals of the L ligands. The lowest-lying absorptions were thus assigned to π-π* transitions with some metal to ligand charge transfer (MLCT) and ligand to ligand charge transfer (LLCT) contributions. High energy absorptions also had intraligand charge transfer (ILCT) and LLCT characteristics. The phosphorescence emissions of these complexes have similar transition properties to their absorptions.
The geometries, electronic structures and spectroscopic properties for a series of osmium(II) complexes [Os(II)(CO)3(tfa)(L)](tfa=trifluoroacetate; L=O^O (1), O^N (2),N^N (3), O^O=hexafluoroacetylacetonate, O^N=quinolinolate, N^N=3-(trifluoromethyl)-5-(2-pyridyl) pyrazole) were investigated theoretically. The Becke’s three parameter functional, the Lee-Yang-Parr (B3LYP) functional and single-excitation configuration interaction (CIS) methods were used to optimize the ground and excited states for complexes 1-3. The time-dependent density functional theory (TD-DFT) at B3LYP level with the polarized continuum model (PCM) was employed to obtain their absorption and phosphorescent emission spectra in CH2Cl2 based on their optimized ground and excited states geometries. The results revealed that the optimized structural parameters agreed well with the corresponding experimental results. There were slight structural differences between ground and excited states, and this was in agreement with the small Stokes-shift observed in the experiments. The lowest-lying absorptions were at 342, 431and 329 nm, and phosphorescent emissions were at 521, 638 and 488 nm for complexes 1-3, respectively. The highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO) of 1-3 mainly manifest as characteristic π and π* orbitals of the L ligands. The lowest-lying absorptions were thus assigned to π-π* transitions with some metal to ligand charge transfer (MLCT) and ligand to ligand charge transfer (LLCT) contributions. High energy absorptions also had intraligand charge transfer (ILCT) and LLCT characteristics. The phosphorescence emissions of these complexes have similar transition properties to their absorptions.
2008, 24(12): 2249-2256
doi: 10.3866/PKU.WHXB20081217
Abstract:
A three dimensional-quantitative structure activity relationship (3D-QSAR) study was performed on a series of CETP inhibitors N,N-disubstituted trifluoro-3-amino-2-propanol derivatives using VolSurf descriptors and the comparative molecular field analysis (CoMFA) method. od results were obtained and the training set was predictable for the test set. VolSurf descriptor analysis showed that suitable hydrophilicity, more hydrogen bond donors and less acceptor were favorable to activity. To some extent, high molecular weight, a smooth surface and high non-globularity were also beneficial to activity. High hydrophobicity and an imbalance between the center of mass and the barycentre of its hydrophobic regions decreased the activity. The result of CoMFA demonstrated that the activity was influenced more by steric effect than electrostatic effect. At the phenoxy meta position in the N-phenyl substituent, groups that have a large volume and strong positive electricity increase the activity. At the meta position of the N-benzyl substituent, groups that have a large volume and suitable electronegativity were beneficial to activity. At the para position of the benzyl group, a large steric effect was detrimental to activity. VolSurf descriptors provided the integral property information of the molecules and CoMFA gave information on substituents. Both methods complemented each other, which can provide assistance to the design of new compounds belonging to this class of inhibitors.
A three dimensional-quantitative structure activity relationship (3D-QSAR) study was performed on a series of CETP inhibitors N,N-disubstituted trifluoro-3-amino-2-propanol derivatives using VolSurf descriptors and the comparative molecular field analysis (CoMFA) method. od results were obtained and the training set was predictable for the test set. VolSurf descriptor analysis showed that suitable hydrophilicity, more hydrogen bond donors and less acceptor were favorable to activity. To some extent, high molecular weight, a smooth surface and high non-globularity were also beneficial to activity. High hydrophobicity and an imbalance between the center of mass and the barycentre of its hydrophobic regions decreased the activity. The result of CoMFA demonstrated that the activity was influenced more by steric effect than electrostatic effect. At the phenoxy meta position in the N-phenyl substituent, groups that have a large volume and strong positive electricity increase the activity. At the meta position of the N-benzyl substituent, groups that have a large volume and suitable electronegativity were beneficial to activity. At the para position of the benzyl group, a large steric effect was detrimental to activity. VolSurf descriptors provided the integral property information of the molecules and CoMFA gave information on substituents. Both methods complemented each other, which can provide assistance to the design of new compounds belonging to this class of inhibitors.
2008, 24(12): 2257-2262
doi: 10.1016/S1872-1508(08)60086-8
Abstract:
Leaf-like Cu(OH)2 single crystals were synthesized via the controlled emulsion interface method using Span80 (sorbitan monooleate) as the stabilizer of the emulsion system. CuO products with nanopores could be simply obtained by the dehydration of Cu(OH)2, while maintaining the strip-shaped architecture. The phase structures and morphologies were measured by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectra, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Experimental results showed that Cu(OH)2 microleaves were single crystals and the growth direction seemed to be in [111] crystal plane of the orthorhombic Cu(OH)2. The formation of the nanopores should be attributed to the water loss of the transformation fromCu(OH)2 to CuO. The formation process of Cu(OH)2was investigated by taking TEMimages at different stages of the reaction. The formed nanoparticles began to rearrange to form nanorods and microleaves possibly via edge-by-edge and side-by-side oriented-attachments because of the formation of larger crystals greatly reducing the interfacial energy. Besides, CuO microarchitectures exhibit blue shifts in UV-Vis spectra and possess larger band gaps compared with those of bulk crystals.
Leaf-like Cu(OH)2 single crystals were synthesized via the controlled emulsion interface method using Span80 (sorbitan monooleate) as the stabilizer of the emulsion system. CuO products with nanopores could be simply obtained by the dehydration of Cu(OH)2, while maintaining the strip-shaped architecture. The phase structures and morphologies were measured by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectra, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Experimental results showed that Cu(OH)2 microleaves were single crystals and the growth direction seemed to be in [111] crystal plane of the orthorhombic Cu(OH)2. The formation of the nanopores should be attributed to the water loss of the transformation fromCu(OH)2 to CuO. The formation process of Cu(OH)2was investigated by taking TEMimages at different stages of the reaction. The formed nanoparticles began to rearrange to form nanorods and microleaves possibly via edge-by-edge and side-by-side oriented-attachments because of the formation of larger crystals greatly reducing the interfacial energy. Besides, CuO microarchitectures exhibit blue shifts in UV-Vis spectra and possess larger band gaps compared with those of bulk crystals.
2008, 24(12): 2263-2267
doi: 10.3866/PKU.WHXB20081219
Abstract:
Zirconium 3-nitrophthalate (Zr(3-NO2-PHT)2·2H2O) was synthesized using 3-nitrophthalic acid, sodium hydroxide, and zirconyl nitrate as raw materials. Its structure was determined by elemental analysis, X-ray fluorescence and FT-IR spectra. The thermal decomposition mechanism and kinetic parameters of the decomposition reaction for Zr(3-NO2-PHT)2·2H2O were investigated by temperature-programmed TG-DTG and condensed-phase thermolysis/FT-IR techniques. A kinetic equation for the decomposition reaction was obtained. The results showed that Zr(3-NO2-PHT)2·2H2O underwent a four-stage decomposition process and that the main decomposition reaction occurred during the second process. The apparent activation energy (Ea) and pre-exponential factor (A) of the main decomposition reaction are 158.84 kJ·mol-1 and 109.85 s-1, respectively. The kinetic equation can thus be expressed as: dα/dt=109.85(1-α)e-1.91×104/T.
Zirconium 3-nitrophthalate (Zr(3-NO2-PHT)2·2H2O) was synthesized using 3-nitrophthalic acid, sodium hydroxide, and zirconyl nitrate as raw materials. Its structure was determined by elemental analysis, X-ray fluorescence and FT-IR spectra. The thermal decomposition mechanism and kinetic parameters of the decomposition reaction for Zr(3-NO2-PHT)2·2H2O were investigated by temperature-programmed TG-DTG and condensed-phase thermolysis/FT-IR techniques. A kinetic equation for the decomposition reaction was obtained. The results showed that Zr(3-NO2-PHT)2·2H2O underwent a four-stage decomposition process and that the main decomposition reaction occurred during the second process. The apparent activation energy (Ea) and pre-exponential factor (A) of the main decomposition reaction are 158.84 kJ·mol-1 and 109.85 s-1, respectively. The kinetic equation can thus be expressed as: dα/dt=109.85(1-α)e-1.91×104/T.
2008, 24(12): 2268-2274
doi: 10.3866/PKU.WHXB20081220
Abstract:
The two-dimensional multilayer PtRu/PtNd alloy nanostructure thin film used for anode electrodes of micro-directmethanol fuel cells (DMFCs) was fabricated by multi-target ion beamsputtering (IBS). The surface chemical state, structure, surface layer structure, and morphology of the PtRu/PtNd thin-film were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXD), and atomic force microscope (AFM). Electrochemical properties were examined by CO-stripping voltammetry, cyclic voltammetry (CV), linear sweep voltammetry (LSV), and chronoamperometry (CA). The structure and surface chemical state of the PtRu/PtNd thin film were found to have changed due to a strong interaction between Pt+, Ru+ and Pt+, Nd+ during the ion beamalternate sputtering deposition process. Abnormal peak widths in the XRD spectra as well as electron transfer between Pt and Nd have also been observed. The PtRu/PtNd thin-film is shown to have a special multiphase structure and electronic structure. The electrochemical activity-specific surface area of PtRu/PtNd thin-film was 115.00 m2·g-1, and therefor PtRu/PtNd thin-film catalysts exhibited higher catalytic activity for methanol electrooxidation in an acidic environment.
The two-dimensional multilayer PtRu/PtNd alloy nanostructure thin film used for anode electrodes of micro-directmethanol fuel cells (DMFCs) was fabricated by multi-target ion beamsputtering (IBS). The surface chemical state, structure, surface layer structure, and morphology of the PtRu/PtNd thin-film were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXD), and atomic force microscope (AFM). Electrochemical properties were examined by CO-stripping voltammetry, cyclic voltammetry (CV), linear sweep voltammetry (LSV), and chronoamperometry (CA). The structure and surface chemical state of the PtRu/PtNd thin film were found to have changed due to a strong interaction between Pt+, Ru+ and Pt+, Nd+ during the ion beamalternate sputtering deposition process. Abnormal peak widths in the XRD spectra as well as electron transfer between Pt and Nd have also been observed. The PtRu/PtNd thin-film is shown to have a special multiphase structure and electronic structure. The electrochemical activity-specific surface area of PtRu/PtNd thin-film was 115.00 m2·g-1, and therefor PtRu/PtNd thin-film catalysts exhibited higher catalytic activity for methanol electrooxidation in an acidic environment.
2008, 24(12): 2275-2281
doi: 10.3866/PKU.WHXB20081221
Abstract:
A scanning microelectrode was used to measure the potential and current distributions on the metal surface of a brass-16Mn steel galvanic couple that was corroded in aqueous NaCl solutions with various concentrations. The potential and current distributions varied with the solution concentration and were also dependent on the distance from the brass-16Mn steel couple joint. These distributions were more symmetrical when the concentration of the solution was higher. The potential polarized greatly and the current density was larger near the couple joint. The potential and current distribution results were confirmed by surface observations of the corroded sample after the immersion test. Experimental results showed that corrosion was concentrated around the joint when solution concentration was low and was distributed more symmetrically as the solution concentration increased.
A scanning microelectrode was used to measure the potential and current distributions on the metal surface of a brass-16Mn steel galvanic couple that was corroded in aqueous NaCl solutions with various concentrations. The potential and current distributions varied with the solution concentration and were also dependent on the distance from the brass-16Mn steel couple joint. These distributions were more symmetrical when the concentration of the solution was higher. The potential polarized greatly and the current density was larger near the couple joint. The potential and current distribution results were confirmed by surface observations of the corroded sample after the immersion test. Experimental results showed that corrosion was concentrated around the joint when solution concentration was low and was distributed more symmetrically as the solution concentration increased.
2008, 24(12): 2282-2286
doi: 10.3866/PKU.WHXB20081222
Abstract:
Ferrihydrite was prepared by three procedures using Fe(III) as a raw material and NaOH as a precipitant. X-ray diffraction (XRD), infrared (IR) spectroscopy, differential thermal analysis (DTA), and kinetic dissolution in an acidic medium were employed to characterize the ferrihydrite synthesized by different methods. The effect of ferrihydrite sub-microstructure on its reactivity was investigated. The results showed that the sub-microstructure and the reactivity of ferrihydrite were related to the different preparation procedures. The structure of ferrihydrite prepared by adding Fe(III) and NaOH solutions to water simultaneously and at a constant pH is so similar to the structure of hematite that it easily transforms into hematite particles.
Ferrihydrite was prepared by three procedures using Fe(III) as a raw material and NaOH as a precipitant. X-ray diffraction (XRD), infrared (IR) spectroscopy, differential thermal analysis (DTA), and kinetic dissolution in an acidic medium were employed to characterize the ferrihydrite synthesized by different methods. The effect of ferrihydrite sub-microstructure on its reactivity was investigated. The results showed that the sub-microstructure and the reactivity of ferrihydrite were related to the different preparation procedures. The structure of ferrihydrite prepared by adding Fe(III) and NaOH solutions to water simultaneously and at a constant pH is so similar to the structure of hematite that it easily transforms into hematite particles.
2008, 24(12): 2287-2292
doi: 10.3866/PKU.WHXB20081223
Abstract:
Spherical Titania (TiO2) with narrow size distribution and nice dispersibility was obtained by hydrolysis in the mixed solvent of 1-propanol and de-ionized water from titanium sulfate (Ti(SO4)2). Parameters like surfactant, precursor concentration, calcination temperature, and calcination time were investigated. The results showed that high quality TiO2 could be synthesized using polyvinylpyrrolidone (PVP) as surfactant when the volume ratio of 1-propanol to de-ionized water was 1:1 at 70-90 ℃. And the optimal surfactant concentration had an important impact on the size distribution and dispersibility. The products were characterized by TG-DSC, SEM, and XRD. The results displayed that the size and size distribution of the particles were affected by the surfactant concentration and the precursor concentration. However, phase transformation of TiO2 was mainly determined by calcination temperature and time. And a LaMer model was introduced to explain the nucleation and growth of the TiO2 particles.
Spherical Titania (TiO2) with narrow size distribution and nice dispersibility was obtained by hydrolysis in the mixed solvent of 1-propanol and de-ionized water from titanium sulfate (Ti(SO4)2). Parameters like surfactant, precursor concentration, calcination temperature, and calcination time were investigated. The results showed that high quality TiO2 could be synthesized using polyvinylpyrrolidone (PVP) as surfactant when the volume ratio of 1-propanol to de-ionized water was 1:1 at 70-90 ℃. And the optimal surfactant concentration had an important impact on the size distribution and dispersibility. The products were characterized by TG-DSC, SEM, and XRD. The results displayed that the size and size distribution of the particles were affected by the surfactant concentration and the precursor concentration. However, phase transformation of TiO2 was mainly determined by calcination temperature and time. And a LaMer model was introduced to explain the nucleation and growth of the TiO2 particles.
2008, 24(12): 2293-2296
doi: 10.3866/PKU.WHXB20081224
Abstract:
The adsorption energy, density of states (DOS) and band structure ofHon a ZnO(10-10) surface were studied using the first-principles projector-augmented-wave (PAW) method based on density functional theory (DFT) within the generalized gradient approximation (GGA) and the supercell model. It was found that: 1) ForHadsorbed on ZnO(101-0) (denoted ZnO(10-10)-H) only the OH group was formed and the ZnH species was not detected. The unoccupied Zn 4s electronic state receives an electron and renders the surface metallic. DOS and the band structure show that the Zn 4s electronic state in the conduction band (CB) receives electrons and migrates toward the forbidden band so that overlapping of the CB and valence band (VB) below the Fermi level is observed. 2) When 2H are adsorbed, the ZnO (10-10) is denoteds ZnO(10-10)-2H. On the surface of ZnO(10-10)-2H two Hs are adsorbed separately on Zn and O and the two dangling bonds on the surface are saturated. The analysis of DOS and band structure of the ZnO(10-10)-2H surface shows that it is the same as a clean ZnO(10-10) surface and that both are insulating surfaces.
The adsorption energy, density of states (DOS) and band structure ofHon a ZnO(10-10) surface were studied using the first-principles projector-augmented-wave (PAW) method based on density functional theory (DFT) within the generalized gradient approximation (GGA) and the supercell model. It was found that: 1) ForHadsorbed on ZnO(101-0) (denoted ZnO(10-10)-H) only the OH group was formed and the ZnH species was not detected. The unoccupied Zn 4s electronic state receives an electron and renders the surface metallic. DOS and the band structure show that the Zn 4s electronic state in the conduction band (CB) receives electrons and migrates toward the forbidden band so that overlapping of the CB and valence band (VB) below the Fermi level is observed. 2) When 2H are adsorbed, the ZnO (10-10) is denoteds ZnO(10-10)-2H. On the surface of ZnO(10-10)-2H two Hs are adsorbed separately on Zn and O and the two dangling bonds on the surface are saturated. The analysis of DOS and band structure of the ZnO(10-10)-2H surface shows that it is the same as a clean ZnO(10-10) surface and that both are insulating surfaces.
2008, 24(12): 2297-2303
doi: 10.3866/PKU.WHXB20081225
Abstract:
The density gradient centrifugation method (DGC) was used to purify three parent coals with obvious deoxidation degrees into two main organic macerals, inertinite and vitrinite accordingly. These coal macerals were studied by molecular mechanics and molecular dynamics. The structure of weakly deoxidized coal was found to be in the structure of sheet layers with many open holes while the strongly deoxidized coal has a stacked structure with many closed holes. The physical aromatic sheet structure of macerals has a strong influence on coal extract yields. The combination of modeling, 13C-NMR and XRD analyses reveals that to obtain higher extraction yields of coal the non-bond chemical force energy should be low. Fewer aromatic sheet layers and lower non-bond chemical force energy within structures would result in higher extraction yields of coal macerals.
The density gradient centrifugation method (DGC) was used to purify three parent coals with obvious deoxidation degrees into two main organic macerals, inertinite and vitrinite accordingly. These coal macerals were studied by molecular mechanics and molecular dynamics. The structure of weakly deoxidized coal was found to be in the structure of sheet layers with many open holes while the strongly deoxidized coal has a stacked structure with many closed holes. The physical aromatic sheet structure of macerals has a strong influence on coal extract yields. The combination of modeling, 13C-NMR and XRD analyses reveals that to obtain higher extraction yields of coal the non-bond chemical force energy should be low. Fewer aromatic sheet layers and lower non-bond chemical force energy within structures would result in higher extraction yields of coal macerals.
2008, 24(12): 2237-2367
Abstract:
2008, 24(12): 2368-2382
Abstract:
2008, 24(12): 2304-2308
doi: 10.3866/PKU.WHXB20081226
Abstract:
Cobalt substituted molecular sieves (CoAPO-5) with different cobalt content were synthesized hydrothermally. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), thermogravimetric(TG) analysis, and inductively coupled plasma-atomic emission spectrometry (ICP-AES). The results indicated that cobalt was incorporated into the framework of AlPO4-5 molecular sieves and the as-synthesized CoAPO-5 was highly crystalline and pure. There is a od linear relationship between the crystal cell parameters and the cobalt content in CoAPO-5. The UV-Vis intensity of Co(II) is significantly reduced through calcinations as Co(II) is oxidized to Co(III) during calcinations. The as-synthesized CoAPO-5 exhibited excellent performance for the oxidation of cyclohexane using molecular oxygen as oxidant. The conversion of cyclohexane and the ratio of cyclohexanol to cyclohexanone in the product increased as the cobalt content increased in CoAPO-5. At nCo/nP=0.04 the conversion of cyclohexane was 23.3%.
Cobalt substituted molecular sieves (CoAPO-5) with different cobalt content were synthesized hydrothermally. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), thermogravimetric(TG) analysis, and inductively coupled plasma-atomic emission spectrometry (ICP-AES). The results indicated that cobalt was incorporated into the framework of AlPO4-5 molecular sieves and the as-synthesized CoAPO-5 was highly crystalline and pure. There is a od linear relationship between the crystal cell parameters and the cobalt content in CoAPO-5. The UV-Vis intensity of Co(II) is significantly reduced through calcinations as Co(II) is oxidized to Co(III) during calcinations. The as-synthesized CoAPO-5 exhibited excellent performance for the oxidation of cyclohexane using molecular oxygen as oxidant. The conversion of cyclohexane and the ratio of cyclohexanol to cyclohexanone in the product increased as the cobalt content increased in CoAPO-5. At nCo/nP=0.04 the conversion of cyclohexane was 23.3%.
2008, 24(12): 2309-2313
doi: 10.3866/PKU.WHXB20081227
Abstract:
Surface properties of Gemini surfactants 12-s-12 (Et)(s=4, 6, 8, 10, 12) in ethanol/water solvents were studied by measurement of surface tension curves. Values of the critical micelle concentration (cmc), surface tension at the cmc (γcmc), saturation adsorption (Γmax) and minimumarea per surfactant molecule (Amin) for Gemini surfactants in various ethanol/water mixture ratios were determined. The effect of ethanol addition on the cmc and γcmc for this series of surfactant systems is discussed.
Surface properties of Gemini surfactants 12-s-12 (Et)(s=4, 6, 8, 10, 12) in ethanol/water solvents were studied by measurement of surface tension curves. Values of the critical micelle concentration (cmc), surface tension at the cmc (γcmc), saturation adsorption (Γmax) and minimumarea per surfactant molecule (Amin) for Gemini surfactants in various ethanol/water mixture ratios were determined. The effect of ethanol addition on the cmc and γcmc for this series of surfactant systems is discussed.
2008, 24(12): 2314-2320
doi: 10.3866/PKU.WHXB20081228
Abstract:
Highly ordered mesoporous C/NiO composites were synthesized via the sol-gel process using an amphi-philic triblock copolymer F127 (Mw=12600, PEO106PPO70PEO106) as a template, Ni(OAc)2 as nickel source and resols as an organic precursor. X-ray diffraction (XRD), transmission electron microscopy (TEM), and nitrogen adsorption were used to characterize the structure. Cyclic voltammetry (CV)was used to test the electrochemical properties of the samples. The results showed that the backbone of the mesoporous structures consisted of NiO nanocrystallites and carbon. The C/NiO composites have a highly ordered mesostructure. The presence of NiO nanocrystallites was expected to improve the capacitance properties of the composite. At a C/NiOratio of 4:1 (molar ratio of phenol to nickel acetate) the composite had a large specific capacitance of 444.1 F·g-1 and the ordered mesostructure remained intact. Ordered mesoporous C/NiO composites thus are promising for applications.
Highly ordered mesoporous C/NiO composites were synthesized via the sol-gel process using an amphi-philic triblock copolymer F127 (Mw=12600, PEO106PPO70PEO106) as a template, Ni(OAc)2 as nickel source and resols as an organic precursor. X-ray diffraction (XRD), transmission electron microscopy (TEM), and nitrogen adsorption were used to characterize the structure. Cyclic voltammetry (CV)was used to test the electrochemical properties of the samples. The results showed that the backbone of the mesoporous structures consisted of NiO nanocrystallites and carbon. The C/NiO composites have a highly ordered mesostructure. The presence of NiO nanocrystallites was expected to improve the capacitance properties of the composite. At a C/NiOratio of 4:1 (molar ratio of phenol to nickel acetate) the composite had a large specific capacitance of 444.1 F·g-1 and the ordered mesostructure remained intact. Ordered mesoporous C/NiO composites thus are promising for applications.
2008, 24(12): 2321-2326
doi: 10.3866/PKU.WHXB20081229
Abstract:
Respective reactions of quinoline and isoquinoline with typical oxidative/reductive transient species, i.e., hydrated electrons, hydroxyl radicals, and hydrogen atoms (obtained after the reaction of an electron beam by proper condition-controlling) were investigated by pulse radiolysis. Absorption spectra of the transient products and their change trends were investigated. Reaction rate constants of hydrated electrons with quinoline and isoquinoline were 7.1×109 and 3.4×109 mol-1·L·s-1, respectively. The hydroxyl radical had rate constants of 7.2×109 and 3.4×109 mol-1·L·s-1, respectively. The rate constants of hydrogen atoms were 5.7×109 and 3.6×109 mol-1·L·s-1, respectively. Results showed that both quinoline and isoquinoline reacted with hydrated electrons, hydroxyl radicals, and hydrogen atoms very quickly. However, reaction rates of quinoline with these transient reductive/oxidative species were faster than that of isoquinoline. Stabilities of the transient products from these reactions were analyzed by electron theory. Reaction products from quinoline’s reaction with transient species were found to be more stable than reaction products from the isoquinoline reaction and this difference was the reason for the difference in rate constants.
Respective reactions of quinoline and isoquinoline with typical oxidative/reductive transient species, i.e., hydrated electrons, hydroxyl radicals, and hydrogen atoms (obtained after the reaction of an electron beam by proper condition-controlling) were investigated by pulse radiolysis. Absorption spectra of the transient products and their change trends were investigated. Reaction rate constants of hydrated electrons with quinoline and isoquinoline were 7.1×109 and 3.4×109 mol-1·L·s-1, respectively. The hydroxyl radical had rate constants of 7.2×109 and 3.4×109 mol-1·L·s-1, respectively. The rate constants of hydrogen atoms were 5.7×109 and 3.6×109 mol-1·L·s-1, respectively. Results showed that both quinoline and isoquinoline reacted with hydrated electrons, hydroxyl radicals, and hydrogen atoms very quickly. However, reaction rates of quinoline with these transient reductive/oxidative species were faster than that of isoquinoline. Stabilities of the transient products from these reactions were analyzed by electron theory. Reaction products from quinoline’s reaction with transient species were found to be more stable than reaction products from the isoquinoline reaction and this difference was the reason for the difference in rate constants.
2008, 24(12): 2327-2330
doi: 10.3866/PKU.WHXB20081230
Abstract:
The influence of N-methylimidazole, benzimidazole, 4-tert-butylpyrdine and 3-ethyl-1-methyl-limidazoliumtrifluoroacetate (EMITA) on apparent diffusion coefficients of I-3 and I- in the electrolyte and the Pt counter electrode electrolyte interface was investigated by ultramicroelectrode and electrochemical impedance spectroscopy. The apparent diffusion coefficient of I-3 in the electrolyte decreased and charge transfer resistance at the Pt counter electrode electrolyte interface increased after the additives were added. The resistance of electrolytes decreased after addition of EMITA. A comparison of the photovoltaic performance of dye-sensitized solar cells (DSCs) containing the additives was undertaken. The additive EMITA increased the open voltage and the fill factor, and the efficiency of dye-sensitized solar cells was up to 5.72%.
The influence of N-methylimidazole, benzimidazole, 4-tert-butylpyrdine and 3-ethyl-1-methyl-limidazoliumtrifluoroacetate (EMITA) on apparent diffusion coefficients of I-3 and I- in the electrolyte and the Pt counter electrode electrolyte interface was investigated by ultramicroelectrode and electrochemical impedance spectroscopy. The apparent diffusion coefficient of I-3 in the electrolyte decreased and charge transfer resistance at the Pt counter electrode electrolyte interface increased after the additives were added. The resistance of electrolytes decreased after addition of EMITA. A comparison of the photovoltaic performance of dye-sensitized solar cells (DSCs) containing the additives was undertaken. The additive EMITA increased the open voltage and the fill factor, and the efficiency of dye-sensitized solar cells was up to 5.72%.
2008, 24(12): 2331-2336
doi: 10.3866/PKU.WHXB20081231
Abstract:
Changes of the sulfate product and optical coefficients during the heterogeneous reaction of SO2 on the surface of hematite at different temperatures were investigated using in situ diffuse reflectance Fourier transform infrared spectroscopy (DFTIRS), ion chromatogram (IC), and transmission electron microscopy (TEM). Simulations revealed that within the ambient temperature of 15-45 ℃, the yield and velocity of sulfate product, absorption coefficient, and backward scattering coefficient firstly increased at 15-35 ℃ and then decreased at 35-45 ℃. At persistent temperature, the velocity of sulfate production showed an initial increase followed by a decrease and finally stabilized. There was a high exponential correlation between the optical coefficients and the amount of sulfate product generated. This result is important in understanding the heterogeneous reaction of SO2 on the surface of hematite in the environment and the assessment of this reaction’s impact on sulfate production and radiative forcing, considering the phenomenon of global warming.
Changes of the sulfate product and optical coefficients during the heterogeneous reaction of SO2 on the surface of hematite at different temperatures were investigated using in situ diffuse reflectance Fourier transform infrared spectroscopy (DFTIRS), ion chromatogram (IC), and transmission electron microscopy (TEM). Simulations revealed that within the ambient temperature of 15-45 ℃, the yield and velocity of sulfate product, absorption coefficient, and backward scattering coefficient firstly increased at 15-35 ℃ and then decreased at 35-45 ℃. At persistent temperature, the velocity of sulfate production showed an initial increase followed by a decrease and finally stabilized. There was a high exponential correlation between the optical coefficients and the amount of sulfate product generated. This result is important in understanding the heterogeneous reaction of SO2 on the surface of hematite in the environment and the assessment of this reaction’s impact on sulfate production and radiative forcing, considering the phenomenon of global warming.
