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2011 Volume 27 Issue 12
2011, 27(12):
Abstract:
2011, 27(12): 2733-2742
doi: 10.3866/PKU.WHXB20112733
Abstract:
The analysis of experimental configurations is the foundation for quantitative analysis in sum frequency generation vibrational spectroscopy (SFG-VS). The incident angles affect the signal intensity of some modes of vibration and the detection efficiency of the SFG signal. However, the issue of detection efficiency has not been included in previous experimental configuration analysis studies. According to the principle of the conservation of energy and momentum in coherent optics we simulated and analyzed the effect of incident angles, frequency of the incident light, and other factors on the output signal angle of difference frequency generation vibrational spectroscopy (DFG-VS) and SFG-VS. We intended to determine the reasonable and effective experimental configurations with more combinations of incident angles and less dispersion of the signal output angle. We found that SFG-VS with the co-propagation experimental configuration and DFG-VS with the counter-propagation experimental configuration favour the collection of the signal and quantitave analysis of the SFG-VS and DFG-VS.
The analysis of experimental configurations is the foundation for quantitative analysis in sum frequency generation vibrational spectroscopy (SFG-VS). The incident angles affect the signal intensity of some modes of vibration and the detection efficiency of the SFG signal. However, the issue of detection efficiency has not been included in previous experimental configuration analysis studies. According to the principle of the conservation of energy and momentum in coherent optics we simulated and analyzed the effect of incident angles, frequency of the incident light, and other factors on the output signal angle of difference frequency generation vibrational spectroscopy (DFG-VS) and SFG-VS. We intended to determine the reasonable and effective experimental configurations with more combinations of incident angles and less dispersion of the signal output angle. We found that SFG-VS with the co-propagation experimental configuration and DFG-VS with the counter-propagation experimental configuration favour the collection of the signal and quantitave analysis of the SFG-VS and DFG-VS.
2011, 27(12): 2743-2748
doi: 10.3866/PKU.WHXB20112743
Abstract:
The absorption spectra of L- and DL-Fudosteine were measured using terahertz time-domain (THz-TDS) system at room temperature. Experimental results show that L- and DL-Fudosteine both have distinct fingerprint spectra in the THz region and their characteristics are different from each other. The absorption frequencies for the vibration and rotation of Fudosteine in the THz spectral range were simulated and the results are consistent with the experimental results. We also interpret the origin of the absorption peaks using a simulation. Finally, the absorption spectra of the Fudosteine capsule, pure L-Fudosteine and DL- Fudosteine are compared. The results verify that the main component of the capsule is L-Fudosteine. This study provides a reference for the analysis of the main ingredients of compounds.
The absorption spectra of L- and DL-Fudosteine were measured using terahertz time-domain (THz-TDS) system at room temperature. Experimental results show that L- and DL-Fudosteine both have distinct fingerprint spectra in the THz region and their characteristics are different from each other. The absorption frequencies for the vibration and rotation of Fudosteine in the THz spectral range were simulated and the results are consistent with the experimental results. We also interpret the origin of the absorption peaks using a simulation. Finally, the absorption spectra of the Fudosteine capsule, pure L-Fudosteine and DL- Fudosteine are compared. The results verify that the main component of the capsule is L-Fudosteine. This study provides a reference for the analysis of the main ingredients of compounds.
2011, 27(12): 2749-2754
doi: 10.3866/PKU.WHXB20112749
Abstract:
Using threshold photoelectron-photoion coincidence time-of-flight mass spectrometry, the photoionization and photodissociation of methyl chloride in the excitation energy range of 13-17 eV were investigated. CH3Cl+ ions in the A2A1 and B2E excited states were generated, both of which were completely dissociative. CH3+ fragments were mainly produced while CH2Cl+ fragment ions were observed as well. By fitting the time-of-flight profile the kinetic energy released distributions of CH3+ during the dissociation of the energy-selected CH3Cl+ ions were obtained. The dissociation of the CH3Cl+ (A2A1) ion followed rapid direct fragmentation while that of the B2E state showed statistical dissociation. Moreover, with the aid of the calculated potential energy surface the CH2Cl + fragment ions observed in the A2A1 state were generated from the statistical dissociation of the high vibrational excited CH3Cl+ (X2E) ions produced by the autoionization of the CH3Cl molecule.
Using threshold photoelectron-photoion coincidence time-of-flight mass spectrometry, the photoionization and photodissociation of methyl chloride in the excitation energy range of 13-17 eV were investigated. CH3Cl+ ions in the A2A1 and B2E excited states were generated, both of which were completely dissociative. CH3+ fragments were mainly produced while CH2Cl+ fragment ions were observed as well. By fitting the time-of-flight profile the kinetic energy released distributions of CH3+ during the dissociation of the energy-selected CH3Cl+ ions were obtained. The dissociation of the CH3Cl+ (A2A1) ion followed rapid direct fragmentation while that of the B2E state showed statistical dissociation. Moreover, with the aid of the calculated potential energy surface the CH2Cl + fragment ions observed in the A2A1 state were generated from the statistical dissociation of the high vibrational excited CH3Cl+ (X2E) ions produced by the autoionization of the CH3Cl molecule.
2011, 27(12): 2755-2761
doi: 10.3866/PKU.WHXB20112755
Abstract:
Using automatic generation software for hydrocarbon oxidation mechanisms, a detailed mechanism for the high-temperature combustion of n-dodecane was developed. A semi-detailed mechanism consisting of 202 species and 738 reactions was obtained by rate-of-production analysis while a skeletal mechanism including 53 species and 228 reactions was obtained using path flux analysis. Both the semi-detailed mechanism and the skeletal mechanism were validated by comparing simulation results including the ignition delay time, high-temperature pyrolysis, and the laminar flame speed with experiments. The current mechanism generation method and the generated semi-detailed and skeletal mechanisms for n-dodecane should be useful in computational fluid dynamics simulations. Finally, the major reaction pathways of n-dodecane oxidation and the important reactions in the ignition process were investigated by reaction path analysis and sensitivity analysis, respectively.
Using automatic generation software for hydrocarbon oxidation mechanisms, a detailed mechanism for the high-temperature combustion of n-dodecane was developed. A semi-detailed mechanism consisting of 202 species and 738 reactions was obtained by rate-of-production analysis while a skeletal mechanism including 53 species and 228 reactions was obtained using path flux analysis. Both the semi-detailed mechanism and the skeletal mechanism were validated by comparing simulation results including the ignition delay time, high-temperature pyrolysis, and the laminar flame speed with experiments. The current mechanism generation method and the generated semi-detailed and skeletal mechanisms for n-dodecane should be useful in computational fluid dynamics simulations. Finally, the major reaction pathways of n-dodecane oxidation and the important reactions in the ignition process were investigated by reaction path analysis and sensitivity analysis, respectively.
2011, 27(12): 2762-2766
doi: 10.3866/PKU.WHXB20112762
Abstract:
Experimental dynamic viscosity and conductivity data of the air- and water-stable hydrophobic ionic liquids (ILs) N-alkylpyridinium bis(trifluoromethylsulfonyl)imide ([Cnpy][NTf2] n=2, 4, 5) were recorded at temperatures ranging from 298.15 to 338.15 K and from 283.15 to 338.15 K with an interval of 5 K. The dynamic viscosity and conductivity values of the [Cnpy][NTf2] (n=2, 4, 5) ILs were fitted using the Arrhenius equation and the Fulcher equation. The molar conductivity was calculated at temperatures ranging from 283.15 to 338.15 K from the conductivity and density data. The relationship between the dynamic viscosity and the molar conductivity was discussed in terms of Walden's rule.
Experimental dynamic viscosity and conductivity data of the air- and water-stable hydrophobic ionic liquids (ILs) N-alkylpyridinium bis(trifluoromethylsulfonyl)imide ([Cnpy][NTf2] n=2, 4, 5) were recorded at temperatures ranging from 298.15 to 338.15 K and from 283.15 to 338.15 K with an interval of 5 K. The dynamic viscosity and conductivity values of the [Cnpy][NTf2] (n=2, 4, 5) ILs were fitted using the Arrhenius equation and the Fulcher equation. The molar conductivity was calculated at temperatures ranging from 283.15 to 338.15 K from the conductivity and density data. The relationship between the dynamic viscosity and the molar conductivity was discussed in terms of Walden's rule.
2011, 27(12): 2767-2772
doi: 10.3866/PKU.WHXB20112767
Abstract:
Three tetradecyl aryl sulfonates of high purity were synthesized. Their static adsorption performance on oil sand from the Daqing oilfield was studied and the influence of adsorption time, adsorption temperature, concentrations of sulfonate, NaCl, NaOH, and n-butyl alcohol on the efficiency of adsorption were investigated. The experimental results show that with an increase in the concentrations of the sulfonates the adsorption capacity initially increased and then remained constant. The adsorption capacity increased with the addition of NaCl and NaOH while it decreased with the addition of n-butyl alcohol and the increase of temperature. In the structural isomer, upon moving the aryl from the terminal to the center of the long alkyl chain, the adsorption capacity decreased and the impact of the additive was reduced. Thermodynamic results show that the adsorption of tetradecyl aryl sulfonates onto oil sand could be well described by the Langmuir isotherm. The constants of each equation were calculated from the experimental data and indicated the characteristics of oil sand adsorption. The dynamic results showed that the adsorption capacity changing with time as described by the Elovich equation.
Three tetradecyl aryl sulfonates of high purity were synthesized. Their static adsorption performance on oil sand from the Daqing oilfield was studied and the influence of adsorption time, adsorption temperature, concentrations of sulfonate, NaCl, NaOH, and n-butyl alcohol on the efficiency of adsorption were investigated. The experimental results show that with an increase in the concentrations of the sulfonates the adsorption capacity initially increased and then remained constant. The adsorption capacity increased with the addition of NaCl and NaOH while it decreased with the addition of n-butyl alcohol and the increase of temperature. In the structural isomer, upon moving the aryl from the terminal to the center of the long alkyl chain, the adsorption capacity decreased and the impact of the additive was reduced. Thermodynamic results show that the adsorption of tetradecyl aryl sulfonates onto oil sand could be well described by the Langmuir isotherm. The constants of each equation were calculated from the experimental data and indicated the characteristics of oil sand adsorption. The dynamic results showed that the adsorption capacity changing with time as described by the Elovich equation.
2011, 27(12): 2773-2778
doi: 10.3866/PKU.WHXB20112773
Abstract:
A method that can be used for gas hydrate exploitation is the injection of a brine solution into hydrate reservoir, therefore, the hydrate dissociation conditions and the influencing factors in brine solution should be investigated under reservoir pressure. In this paper, methane hydrate dissociation conditions in NaCl, MgCl2, and CaCl2 solutions were investigated. The results show that the dissociation temperature depressions are (4.8, 2.4, 1.0 K (NaCl)), (5.3, 1.5 K (MgCl2)), (4.3, 1.8 K (CaCl2)) in NaCl (2.0, 1.0, 0.5 mol· L-1), MgCl2 (1.0, 0.5 mol·L-1), and CaCl2 (1.0, 0.5 mol·L-1) solutions, respectively, relative to those in pure water. The experimental values were in od agreement with the calculated values based on the van der Waals and Platteeuw thermodynamic model and the Pitzer-Mayorga equation for the water activity of electrolyte solution. In chloride salt solution the water molecule solvent effect and the salting-out effect that is caused by an electrostatic field decreases the water activity resulting in a depression of the hydrate dissociation temperature.
A method that can be used for gas hydrate exploitation is the injection of a brine solution into hydrate reservoir, therefore, the hydrate dissociation conditions and the influencing factors in brine solution should be investigated under reservoir pressure. In this paper, methane hydrate dissociation conditions in NaCl, MgCl2, and CaCl2 solutions were investigated. The results show that the dissociation temperature depressions are (4.8, 2.4, 1.0 K (NaCl)), (5.3, 1.5 K (MgCl2)), (4.3, 1.8 K (CaCl2)) in NaCl (2.0, 1.0, 0.5 mol· L-1), MgCl2 (1.0, 0.5 mol·L-1), and CaCl2 (1.0, 0.5 mol·L-1) solutions, respectively, relative to those in pure water. The experimental values were in od agreement with the calculated values based on the van der Waals and Platteeuw thermodynamic model and the Pitzer-Mayorga equation for the water activity of electrolyte solution. In chloride salt solution the water molecule solvent effect and the salting-out effect that is caused by an electrostatic field decreases the water activity resulting in a depression of the hydrate dissociation temperature.
2011, 27(12): 2779-2785
doi: 10.3866/PKU.WHXB20112779
Abstract:
Car-Parrinello molecular dynamics (CPMD) calculations were performed on the solvent structure properties of water, methanol, and ethanol. The results show that the first O…O peaks of the radial distribution functions (RDFs) in the three systems are 0.278 nm for water, 0.276 nm for methanol, and 0.275 nm for ethanol. The first O…H peaks of the radial distribution functions (RDFs) in the three systems are at 0.178 nm for water, 0.176 nm for methanol, and 0.177 nm for ethanol. This indicates that the hydrophobic groupings (hydrogen, methyl, and ethyl) have little influence on the first peak position. However, the intensity of the RDFs increases from water to methanol and ethanol. The spatial distribution functions show that the oxygen and hydrogen atoms of other solvent molecules have characteristic orientations on the reference molecules in these systems. The results are in agreement with the first sharp peak of the radial distribution functions. We analyzed the hydrogen bonds using a statistical method. The results show that the average hydrogen bond numbers are 3.62 for water, 1.99 for methanol, and 1.87 for ethanol. Therefore, different hydrogen-bonded network structures are formed for liquid water, methanol, and ethanol via hydrogen bonds.
Car-Parrinello molecular dynamics (CPMD) calculations were performed on the solvent structure properties of water, methanol, and ethanol. The results show that the first O…O peaks of the radial distribution functions (RDFs) in the three systems are 0.278 nm for water, 0.276 nm for methanol, and 0.275 nm for ethanol. The first O…H peaks of the radial distribution functions (RDFs) in the three systems are at 0.178 nm for water, 0.176 nm for methanol, and 0.177 nm for ethanol. This indicates that the hydrophobic groupings (hydrogen, methyl, and ethyl) have little influence on the first peak position. However, the intensity of the RDFs increases from water to methanol and ethanol. The spatial distribution functions show that the oxygen and hydrogen atoms of other solvent molecules have characteristic orientations on the reference molecules in these systems. The results are in agreement with the first sharp peak of the radial distribution functions. We analyzed the hydrogen bonds using a statistical method. The results show that the average hydrogen bond numbers are 3.62 for water, 1.99 for methanol, and 1.87 for ethanol. Therefore, different hydrogen-bonded network structures are formed for liquid water, methanol, and ethanol via hydrogen bonds.
2011, 27(12): 2786-2792
doi: 10.3866/PKU.WHXB20112786
Abstract:
The electron localization function (ELF) is an important tool to study electronic structure. In this article, the concept of electron localization is introduced and the overlap between the physical meaning and functional form of the ELF is discussed in detail from two points of view: electron pair density and kinetic energy density. Additionally, we extend the ELF to a generalized spin-polarized form. From case studies we found that the reference term plays an important role in the ELF. A comparison between the two spinpolarized forms of ELF shows that the form used in the CheckDen and TopMoD programs is unreasonable as they obviously underestimate the degree of localization in the single-electron region. Finally, we point out some mistakes in the literature because of a misunderstanding of the ELF.
The electron localization function (ELF) is an important tool to study electronic structure. In this article, the concept of electron localization is introduced and the overlap between the physical meaning and functional form of the ELF is discussed in detail from two points of view: electron pair density and kinetic energy density. Additionally, we extend the ELF to a generalized spin-polarized form. From case studies we found that the reference term plays an important role in the ELF. A comparison between the two spinpolarized forms of ELF shows that the form used in the CheckDen and TopMoD programs is unreasonable as they obviously underestimate the degree of localization in the single-electron region. Finally, we point out some mistakes in the literature because of a misunderstanding of the ELF.
2011, 27(12): 2793-2798
doi: 10.3866/PKU.WHXB20112793
Abstract:
First-principles calculations were performed to determine the equilibrium crystal structures, energetic properties, and stability of MgxTi(1-x)H2 (x=0.25, 0.5, 0.75, 0.875) systems containing different amounts of titanium using the pseudopotential plane-wave method based on density functional theory. The calculation results show that the hydrogen atoms in the MgxTi(1-x)H2 hydrides roughly occupy the tetrahedral interstitial sites. The calculated H―Ti distances are less than the H―Mg distances. This indicates that Ti has a more notable affinity for hydrogen than Mg. The bonding strength of H―Mg is weaker when the Ti atom attracts surrounding hydrogen atoms. The stabilization and dehydrogenation temperatures of the hydrides MgxTi(1-x)H2 are lower than those of MgH2 with an increasing Ti content. This indicates that titanium can reduce the decomposition temperature of the MgxTi(1-x)H2 hydrides and play a significant catalytic role in improving the dehydrogenation dynamic properties of the MgxTi(1-x)H2 hydrides.
First-principles calculations were performed to determine the equilibrium crystal structures, energetic properties, and stability of MgxTi(1-x)H2 (x=0.25, 0.5, 0.75, 0.875) systems containing different amounts of titanium using the pseudopotential plane-wave method based on density functional theory. The calculation results show that the hydrogen atoms in the MgxTi(1-x)H2 hydrides roughly occupy the tetrahedral interstitial sites. The calculated H―Ti distances are less than the H―Mg distances. This indicates that Ti has a more notable affinity for hydrogen than Mg. The bonding strength of H―Mg is weaker when the Ti atom attracts surrounding hydrogen atoms. The stabilization and dehydrogenation temperatures of the hydrides MgxTi(1-x)H2 are lower than those of MgH2 with an increasing Ti content. This indicates that titanium can reduce the decomposition temperature of the MgxTi(1-x)H2 hydrides and play a significant catalytic role in improving the dehydrogenation dynamic properties of the MgxTi(1-x)H2 hydrides.
2011, 27(12): 2799-2804
doi: 10.3866/PKU.WHXB20112799
Abstract:
The proton-transfer processes of the adenine-thymine (A-T) base pair anion (AT)- and the Cu2+ cationized (A-T) base pair anion were investigated using the B3LYP/DZP ++ method. A single protontransfer process was found for the (A-T) base pair anion in which proton H26 at the N25 site of thymine transferred to the N10 site of adenine. The metal cation Cu2+ can coordinate to the N4 and N13 sites of adenine as well as the O24 and O28 sites of thymine in (AT)- by coordination interactions. For Cu2+ coordinated to the O24 and O28 sites of thymine the single proton transfer from thymine to adenine is possible. However, when Cu2+ interacts with the N4 or N13 of adenine the double proton-transferred product was found to be stable.
The proton-transfer processes of the adenine-thymine (A-T) base pair anion (AT)- and the Cu2+ cationized (A-T) base pair anion were investigated using the B3LYP/DZP ++ method. A single protontransfer process was found for the (A-T) base pair anion in which proton H26 at the N25 site of thymine transferred to the N10 site of adenine. The metal cation Cu2+ can coordinate to the N4 and N13 sites of adenine as well as the O24 and O28 sites of thymine in (AT)- by coordination interactions. For Cu2+ coordinated to the O24 and O28 sites of thymine the single proton transfer from thymine to adenine is possible. However, when Cu2+ interacts with the N4 or N13 of adenine the double proton-transferred product was found to be stable.
2011, 27(12): 2805-2813
doi: 10.3866/PKU.WHXB20112805
Abstract:
Density functional theory (DFT) based on the pseudo-potential plane wave basis set was used to investigate the electronic structures and optical properties of CuAlX2 (X=S, Se, Te) crystals with a chalcopyrite structure. The results indicate that these compounds have a similar band structure and the bandgap decreases from S to Te. Except for the static birefringence, which is just opposite to a change in the bandgap, the static dielectric constant, refractive index and second harmonic generation (SHG) coefficient d36 of this series of compounds increased from S to Te. The SHG response of the three semiconductors can be attributed to transitions from the occupied bands near the top of the valence band to the unoccupied bands that are contributed to by the p states of the Al and X atoms. Among the three crystals, the optical properties of the CuAlTe2 crystal are better than those of CuAlS2 and CuAlSe2 crystals except that the corresponding static birefringence is too small.
Density functional theory (DFT) based on the pseudo-potential plane wave basis set was used to investigate the electronic structures and optical properties of CuAlX2 (X=S, Se, Te) crystals with a chalcopyrite structure. The results indicate that these compounds have a similar band structure and the bandgap decreases from S to Te. Except for the static birefringence, which is just opposite to a change in the bandgap, the static dielectric constant, refractive index and second harmonic generation (SHG) coefficient d36 of this series of compounds increased from S to Te. The SHG response of the three semiconductors can be attributed to transitions from the occupied bands near the top of the valence band to the unoccupied bands that are contributed to by the p states of the Al and X atoms. Among the three crystals, the optical properties of the CuAlTe2 crystal are better than those of CuAlS2 and CuAlSe2 crystals except that the corresponding static birefringence is too small.
2011, 27(12): 2814-2820
doi: 10.3866/PKU.WHXB20112814
Abstract:
For a better design of quantum dots (QDs) based photoelectrochemical sensors, photoinduced electron transfer between CdS QDs and ld electrodes was studied. First, a theoretical study and mathematical model are given wherein several electron tunneling processes compete with each other to give a photocurrent under illumination. Second, simulations with different parameters were carried out. Finally, photocurrents from CdS QDs modified ld electrodes with dithiol groups were measured under different conditions. The results show that the amplitudes and directions of the photocurrents are affected by the applied potential, the light intensity, and the concentrations of oxidants and reducers. The experimental results were then compared with the simulation results and analyzed based on the model given. By comparing the simulation and experimental results the theoretical study and the mathematical model are shown to be accurate.
For a better design of quantum dots (QDs) based photoelectrochemical sensors, photoinduced electron transfer between CdS QDs and ld electrodes was studied. First, a theoretical study and mathematical model are given wherein several electron tunneling processes compete with each other to give a photocurrent under illumination. Second, simulations with different parameters were carried out. Finally, photocurrents from CdS QDs modified ld electrodes with dithiol groups were measured under different conditions. The results show that the amplitudes and directions of the photocurrents are affected by the applied potential, the light intensity, and the concentrations of oxidants and reducers. The experimental results were then compared with the simulation results and analyzed based on the model given. By comparing the simulation and experimental results the theoretical study and the mathematical model are shown to be accurate.
2011, 27(12): 2821-2825
doi: 10.3866/PKU.WHXB20112821
Abstract:
We deposited CdS thin films onto F-doped SnO2 transparent conductive glass by ultrasonic agitation chemical bath deposition (UCBD). The influence of the annealing and CdCl2-treatment on the surface morphology, crystal structure, and direct band gap of the UCBD-CdS thin films was investigated. The effect of deposition time on the grain size of the CdS aggregates and the stack denseness of the UCBD-CdS thin films was compared. The results reveal that the small grains in the CdS aggregates were melted together and the CdS aggregate size did not change in the UCBD-CdS thin films after the CdCl2-treatment procedure. It is interesting that the ratio of the horizontal to vertical deposition rate varied with deposition time over the deposition period of the UCBD-CdS thin films. The deposition time was very important to obtain large CdS aggregate grains and dense UCBD-CdS thin films. Over a deposition time of 40 min the resulting UCBD-CdS thin films were dense and had a 180 nm grain size of CdS aggregates and a 80.8 nm of thin film thickness. The large-grained and dense UCBD-CdS thin films were suitable for thin film solar cells as a window layer.
We deposited CdS thin films onto F-doped SnO2 transparent conductive glass by ultrasonic agitation chemical bath deposition (UCBD). The influence of the annealing and CdCl2-treatment on the surface morphology, crystal structure, and direct band gap of the UCBD-CdS thin films was investigated. The effect of deposition time on the grain size of the CdS aggregates and the stack denseness of the UCBD-CdS thin films was compared. The results reveal that the small grains in the CdS aggregates were melted together and the CdS aggregate size did not change in the UCBD-CdS thin films after the CdCl2-treatment procedure. It is interesting that the ratio of the horizontal to vertical deposition rate varied with deposition time over the deposition period of the UCBD-CdS thin films. The deposition time was very important to obtain large CdS aggregate grains and dense UCBD-CdS thin films. Over a deposition time of 40 min the resulting UCBD-CdS thin films were dense and had a 180 nm grain size of CdS aggregates and a 80.8 nm of thin film thickness. The large-grained and dense UCBD-CdS thin films were suitable for thin film solar cells as a window layer.
2011, 27(12): 2826-2830
doi: 10.3866/PKU.WHXB20112826
Abstract:
We prepared copper indium gallium diselenide (CIGS) thin films by potentiostatic electrodeposition in an ethanol solution. The thin films were characterized by scanning electron microscopy (SEM), X-ray energy dispersive spectrometry (EDS), X-ray diffraction (XRD), and UV-visible-near infrared (UV-VIS-NIR) spectrophotometry to determine their morphology, composition, crystal structure, and absorption properties. The results show that the chalcopyrite structured CuIn0.7Ga0.3Se2 thin films can be obtained by annealing the electrodeposited films at -1.6 V (vs SCE) at 450 °C. The obtained thin film has uniform morphology, od crystallinity, and a bandgap of about 1.17 eV. We found that ethanol as a solvent can effectively avoid the hydrogen evolution phenomenon, which often occurs in aqueous solution and reduces the deposition potential limitation.
We prepared copper indium gallium diselenide (CIGS) thin films by potentiostatic electrodeposition in an ethanol solution. The thin films were characterized by scanning electron microscopy (SEM), X-ray energy dispersive spectrometry (EDS), X-ray diffraction (XRD), and UV-visible-near infrared (UV-VIS-NIR) spectrophotometry to determine their morphology, composition, crystal structure, and absorption properties. The results show that the chalcopyrite structured CuIn0.7Ga0.3Se2 thin films can be obtained by annealing the electrodeposited films at -1.6 V (vs SCE) at 450 °C. The obtained thin film has uniform morphology, od crystallinity, and a bandgap of about 1.17 eV. We found that ethanol as a solvent can effectively avoid the hydrogen evolution phenomenon, which often occurs in aqueous solution and reduces the deposition potential limitation.
2011, 27(12): 2831-2835
doi: 10.3866/PKU.WHXB20112831
Abstract:
A series of graphene oxide ( ) thin films were prepared by a dip-coating method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-Vis) light absorption, and photoelectrochemical measurements. A cathodic photocurrent was observed for the electrodes and the photocurrent density was influenced by the thickness of the films. The film electrode with an average thickness of 27 nm gave a photocurrent density of 0.25 μA·cm-2. The photoresponse of the electrodes was found to be influenced by UV irradiation and the cathodic photocurrent decreased gradually with UV irradiation time. This work provides a simple method to change the photoelectrochemical property of films by controlling the film thickness or UV irradiation time.
A series of graphene oxide ( ) thin films were prepared by a dip-coating method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-Vis) light absorption, and photoelectrochemical measurements. A cathodic photocurrent was observed for the electrodes and the photocurrent density was influenced by the thickness of the films. The film electrode with an average thickness of 27 nm gave a photocurrent density of 0.25 μA·cm-2. The photoresponse of the electrodes was found to be influenced by UV irradiation and the cathodic photocurrent decreased gradually with UV irradiation time. This work provides a simple method to change the photoelectrochemical property of films by controlling the film thickness or UV irradiation time.
2011, 27(12): 2836-2840
doi: 10.3866/PKU.WHXB20112836
Abstract:
Microporous carbons (PSC-1 and PSC-2) were obtained directly by the carbonization of peanut shells without and with NaOH solution pretreatment, respectively. Both samples have a main pore size of ~0.8 nm. The surface area increases from 552 m2·g-1 for PSC-1 to 726 m2·g-1 for PSC-2. Cyclic voltammograms (CVs) of the PSC-1 and PSC-2 electrodes and the symmetrical supercapacitors show almost rectangular shape indicating excellent capacitance features. The specific capacitances of PSC-1 and PSC-2 can reach 233 and 378 F·g-1, respectively, at a current density of 0.1 A·g-1 in a three-electrode system using porous carbon as the working electrode, a platinum electrode as the counter electrode and a Ag/AgCl electrode as the reference electrode. Furthermore, the electrodes in both three-electrode systems and supercapacitors show high stability and capacitance retainability after 1000 cycles. The formation mechanisms for the two microporous carbons and the relationship between the carbon materials and their electrochemical properties are discussed based on the experimental results.
Microporous carbons (PSC-1 and PSC-2) were obtained directly by the carbonization of peanut shells without and with NaOH solution pretreatment, respectively. Both samples have a main pore size of ~0.8 nm. The surface area increases from 552 m2·g-1 for PSC-1 to 726 m2·g-1 for PSC-2. Cyclic voltammograms (CVs) of the PSC-1 and PSC-2 electrodes and the symmetrical supercapacitors show almost rectangular shape indicating excellent capacitance features. The specific capacitances of PSC-1 and PSC-2 can reach 233 and 378 F·g-1, respectively, at a current density of 0.1 A·g-1 in a three-electrode system using porous carbon as the working electrode, a platinum electrode as the counter electrode and a Ag/AgCl electrode as the reference electrode. Furthermore, the electrodes in both three-electrode systems and supercapacitors show high stability and capacitance retainability after 1000 cycles. The formation mechanisms for the two microporous carbons and the relationship between the carbon materials and their electrochemical properties are discussed based on the experimental results.
2011, 27(12): 2841-2848
doi: 10.3866/PKU.WHXB20112841
Abstract:
The inhibition effect of nitrotetrazolium blue chloride (NTBC) on the corrosion of cold rolled steel (CRS) in 1.0-5.0 mol·L-1 HCl solution was investigated by weight loss method, potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The results show that NTBC is a od inhibitor for CRS in 1.0 mol·L-1 HCl solution and the adsorption of NTBC on the CRS surface obeys the Langmuir adsorption isotherm. Inhibition efficiency increases with inhibitor concentration while it decreases with hydrochloric acid concentration and temperature. The adsorption thermodynamic parameters (adsorption free energy ΔG0, adsorption enthalpy ΔH0, adsorption entropy ΔS0) and corrosion kinetic parameters (corrosion rate constant k, kinetic reaction constant B) were also calculated. Based on these parameters the inhibitive mechanism is discussed. Potentiodynamic polarization curves show that NTBC acts a mixed-type inhibitor. EIS spectra exhibit one capacitive loop at high frequency and this is followed by a small inductive loop at low frequency, and the charge transfer resistance increases with inhibitor concentrations. SEM clearly shows that the addition of NTBC can drastically retard the corrosion of steel in hydrochloric acid media.
The inhibition effect of nitrotetrazolium blue chloride (NTBC) on the corrosion of cold rolled steel (CRS) in 1.0-5.0 mol·L-1 HCl solution was investigated by weight loss method, potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The results show that NTBC is a od inhibitor for CRS in 1.0 mol·L-1 HCl solution and the adsorption of NTBC on the CRS surface obeys the Langmuir adsorption isotherm. Inhibition efficiency increases with inhibitor concentration while it decreases with hydrochloric acid concentration and temperature. The adsorption thermodynamic parameters (adsorption free energy ΔG0, adsorption enthalpy ΔH0, adsorption entropy ΔS0) and corrosion kinetic parameters (corrosion rate constant k, kinetic reaction constant B) were also calculated. Based on these parameters the inhibitive mechanism is discussed. Potentiodynamic polarization curves show that NTBC acts a mixed-type inhibitor. EIS spectra exhibit one capacitive loop at high frequency and this is followed by a small inductive loop at low frequency, and the charge transfer resistance increases with inhibitor concentrations. SEM clearly shows that the addition of NTBC can drastically retard the corrosion of steel in hydrochloric acid media.
2011, 27(12): 2849-2856
doi: 10.3866/PKU.WHXB20112849
Abstract:
A NiCo2O4 spinel composite oxide was obtained by co-precipitation. A Ni/NiCo2O4 composite coating was prepared by composite electrodeposition in a Ni plating solution by mixing with NiCo2O4 powder. The best plating conditions for the composite electrodeposition were investigated by changing factors such as the plating bath pH and the cathode current density jk. The surface morphology, the NiCo2O4 content, and the structure of the Ni/NiCo2O4 composite coating were characterized by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray diffraction (XRD). As a result, the NiCo2O4 content in the Ni/NiCo2O4 composite coating was found to be the highest (30.6%, w) for a bath pH of 6.2 and a cathodic current density jk of 100 mA·cm-2. In 5 mol·L-1 KOH solution the electrocatalytic properties toward the oxygen evolution reaction (OER) of the Ni/NiCo2O4 composite electrode was studied using cyclic voltammetry, electrochemical steady-state polarization, and electrochemical impendence spectroscopy (EIS). Compared with the Ni electrode, the electrocatalytic properties for the OER of the Ni/NiCo2O4 composite electrode improved greatly and the apparent activation energy was reduced to 53.2 kJ·mol-1. The apparent exchange current density of the Ni/NiCo2O4 composite electrode toward the OER was 7 times as high as that of a nickel electrode. An electrochemical impendence spectroscopy analysis indicated that the oxygen evolution reaction of the Ni/NiCo2O4 composite electrode was co-controlled by an electrochemical step and a diffusion step. Constant potential electrolysis over extended periods for the OER shows that the stability of the Ni/NiCo2O4 composite electrode is od.
A NiCo2O4 spinel composite oxide was obtained by co-precipitation. A Ni/NiCo2O4 composite coating was prepared by composite electrodeposition in a Ni plating solution by mixing with NiCo2O4 powder. The best plating conditions for the composite electrodeposition were investigated by changing factors such as the plating bath pH and the cathode current density jk. The surface morphology, the NiCo2O4 content, and the structure of the Ni/NiCo2O4 composite coating were characterized by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray diffraction (XRD). As a result, the NiCo2O4 content in the Ni/NiCo2O4 composite coating was found to be the highest (30.6%, w) for a bath pH of 6.2 and a cathodic current density jk of 100 mA·cm-2. In 5 mol·L-1 KOH solution the electrocatalytic properties toward the oxygen evolution reaction (OER) of the Ni/NiCo2O4 composite electrode was studied using cyclic voltammetry, electrochemical steady-state polarization, and electrochemical impendence spectroscopy (EIS). Compared with the Ni electrode, the electrocatalytic properties for the OER of the Ni/NiCo2O4 composite electrode improved greatly and the apparent activation energy was reduced to 53.2 kJ·mol-1. The apparent exchange current density of the Ni/NiCo2O4 composite electrode toward the OER was 7 times as high as that of a nickel electrode. An electrochemical impendence spectroscopy analysis indicated that the oxygen evolution reaction of the Ni/NiCo2O4 composite electrode was co-controlled by an electrochemical step and a diffusion step. Constant potential electrolysis over extended periods for the OER shows that the stability of the Ni/NiCo2O4 composite electrode is od.
2011, 27(12): 2857-2862
doi: 10.3866/PKU.WHXB20112857
Abstract:
A binary metallic catalyst (PtSn/C) and a ternary metallic catalyst (PtSnCo/C) with a metal mass fraction of 20% were prepared by borohydride reduction and subsequent hydrothermal treatment in a glycol liquid phase. The structure and composition of the as-prepared electrocatalysts were characterized by X-ray diffraction (XRD) and energy-dispersive spectrometry (EDS). Their activity and stability for the catalysis of methanol oxidation were evaluated by anodic linear sweep voltammetry (LSV), cyclic voltammetry (CV), and the anodic stripping of a pre-adsorbed CO monolayer. We found that the PtSnCo/C catalyst gave the best catalytic activity for the methanol oxidation of all the catalysts including the commercial JM-PtRu/C catalyst. After 100 cycles, the peak current of methanol oxidation for the PtSn/C catalyst rapidly decreased to 11% of its initial peak current but PtSnCo/C decreased to only 50%. This result suggests that the PtSnCo/C catalyst has better chemical stability for the catalysis of methanol oxidation compared to the PtSn/C catalyst. The more negative onset potential of methanol oxidation for the PtSnCo/C catalyst relative to pre-adsorbed CO oxidation implies that the intermediates of methanol oxidation on the PtSnCo/C catalyst may be ones, which can be more easily oxidized than CO, instead of CO.
A binary metallic catalyst (PtSn/C) and a ternary metallic catalyst (PtSnCo/C) with a metal mass fraction of 20% were prepared by borohydride reduction and subsequent hydrothermal treatment in a glycol liquid phase. The structure and composition of the as-prepared electrocatalysts were characterized by X-ray diffraction (XRD) and energy-dispersive spectrometry (EDS). Their activity and stability for the catalysis of methanol oxidation were evaluated by anodic linear sweep voltammetry (LSV), cyclic voltammetry (CV), and the anodic stripping of a pre-adsorbed CO monolayer. We found that the PtSnCo/C catalyst gave the best catalytic activity for the methanol oxidation of all the catalysts including the commercial JM-PtRu/C catalyst. After 100 cycles, the peak current of methanol oxidation for the PtSn/C catalyst rapidly decreased to 11% of its initial peak current but PtSnCo/C decreased to only 50%. This result suggests that the PtSnCo/C catalyst has better chemical stability for the catalysis of methanol oxidation compared to the PtSn/C catalyst. The more negative onset potential of methanol oxidation for the PtSnCo/C catalyst relative to pre-adsorbed CO oxidation implies that the intermediates of methanol oxidation on the PtSnCo/C catalyst may be ones, which can be more easily oxidized than CO, instead of CO.
2011, 27(12): 2863-2871
doi: 10.3866/PKU.WHXB20112863
Abstract:
Tungsten carbide and titania nanocomposite with a core-shell structure was fabricated by combing chemical immersion with carbonization-reduction, using titania nanopowder as a support and tungsten hexachloride as a tungsten precursor. The crystal phase, morphology, microstructure, and chemical composition of the sample were characterized by X-ray diffraction, transmission electron microscopy, high resolution scanning transmission imaging, and energy dispersive spectroscopy (EDS). The results show that the crystal phase of the sample is composed of rutile, Ti4O7, WC, W2C, and WxC. The tungsten carbide particles coat onto the surface of the rutile support and thus form a core-shell structure. The electrocatalytic activity of the sample for methanol was measured by cyclic voltammetry with a three-electrode system in an alkaline solution. The results indicate that the electrocatalytic activity of the sample is higher than that of a pure titania phase and WC. The improvement in electrocatalytic activity is related to the reduction-carbonization time, the W to Ti molar ratio, the completeness of the shell layer in the core-shell structure, and the crystal phase of the sample. These factors can be correlated to a synergistic effect between titania and tungsten carbide in the nanocomposite. These imply that titania is a suitable support for the enhancement of the electrocatalytic activity of tungsten carbide.
Tungsten carbide and titania nanocomposite with a core-shell structure was fabricated by combing chemical immersion with carbonization-reduction, using titania nanopowder as a support and tungsten hexachloride as a tungsten precursor. The crystal phase, morphology, microstructure, and chemical composition of the sample were characterized by X-ray diffraction, transmission electron microscopy, high resolution scanning transmission imaging, and energy dispersive spectroscopy (EDS). The results show that the crystal phase of the sample is composed of rutile, Ti4O7, WC, W2C, and WxC. The tungsten carbide particles coat onto the surface of the rutile support and thus form a core-shell structure. The electrocatalytic activity of the sample for methanol was measured by cyclic voltammetry with a three-electrode system in an alkaline solution. The results indicate that the electrocatalytic activity of the sample is higher than that of a pure titania phase and WC. The improvement in electrocatalytic activity is related to the reduction-carbonization time, the W to Ti molar ratio, the completeness of the shell layer in the core-shell structure, and the crystal phase of the sample. These factors can be correlated to a synergistic effect between titania and tungsten carbide in the nanocomposite. These imply that titania is a suitable support for the enhancement of the electrocatalytic activity of tungsten carbide.
2011, 27(12): 2872-2880
doi: 10.3866/PKU.WHXB20112872
Abstract:
α-MnO2-supported ld catalysts (xAu/α-MnO2, x=0-7 (corresponding to the Au loading (mass fraction) of 0-7%) were prepared by a deposition- precipitation method using urea as a precipitation agent and characterized by different techniques such as X-ray diffraction (XRD), N2 adsorption-desorption measurements, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and H2 temperature-programmed reduction (TPR). The catalytic activities of the materials were evaluated for the oxidation of CO and benzene. The Au particle size was found to be related to the Au loading of the xAu/ α-MnO2 samples and increased with Au loading. XPS results showed that the mole ratios of O2-/(O22- or O-), Mn4+/Mn3+ and Au3+/Au0 increased upon the addition of Au. The loading of ld over α-MnO2 significantly modified the catalytic activities. The catalytic performance of xAu/α-MnO2 strongly depended on the Au loading, and 3Au/α-MnO2 gained the best activity at T90=80 °C and T90=20 °C for the catalytic oxidation of CO and benzene, respectively. The excellent performance of 3Au/α-MnO2 is associated with highly dispersed Au, od low-temperature reducibility, and a synergism at the interface between theAu and MnO2 nanodomains.
α-MnO2-supported ld catalysts (xAu/α-MnO2, x=0-7 (corresponding to the Au loading (mass fraction) of 0-7%) were prepared by a deposition- precipitation method using urea as a precipitation agent and characterized by different techniques such as X-ray diffraction (XRD), N2 adsorption-desorption measurements, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and H2 temperature-programmed reduction (TPR). The catalytic activities of the materials were evaluated for the oxidation of CO and benzene. The Au particle size was found to be related to the Au loading of the xAu/ α-MnO2 samples and increased with Au loading. XPS results showed that the mole ratios of O2-/(O22- or O-), Mn4+/Mn3+ and Au3+/Au0 increased upon the addition of Au. The loading of ld over α-MnO2 significantly modified the catalytic activities. The catalytic performance of xAu/α-MnO2 strongly depended on the Au loading, and 3Au/α-MnO2 gained the best activity at T90=80 °C and T90=20 °C for the catalytic oxidation of CO and benzene, respectively. The excellent performance of 3Au/α-MnO2 is associated with highly dispersed Au, od low-temperature reducibility, and a synergism at the interface between theAu and MnO2 nanodomains.
2011, 27(12): 2881-2886
doi: 10.3866/PKU.WHXB20112881
Abstract:
Second metals (Fe, Al, Cu, Ni, Co, Mo, Cr) were incorporated into V-HMS catalyst by impregnation to enhance the catalytic activity for the hydroxylation of benzene with hydrogen peroxide as the oxidant. Among the studied second metals, Fe was found to be effective in improving the catalytic performance. Therefore, we synthesized a series of FexVy-HMS catalysts containing different amounts of Fe and V by the co-synthesis method. The catalysts were characterized by powder X-ray diffraction (XRD), N2 physisorption, transmission electron microscopy (TEM), NH3 temperature-programmed desorption (NH3- TPD), and H2 temperature-programmed reduction (H2-TPR). The characterization results show that the mesoporous structure of HMS is maintained and the addition of Fe creates new acid sites and a stronger redox ability. Catalytic tests show that vanadium species are the active species and that the iron species promote the reaction. Under optimal reaction conditions, the Fe0.04V0.06-HMS catalyst gives the best catalytic performance with a highest phenol yield of 18.1% by comparison with 13.1% over the Fe-free catalyst Fe0.00V0.06-HMS. We propose a possible mechanism involving the Fe and V species for the hydroxylation of benzene with H2O2 as the oxidant.
Second metals (Fe, Al, Cu, Ni, Co, Mo, Cr) were incorporated into V-HMS catalyst by impregnation to enhance the catalytic activity for the hydroxylation of benzene with hydrogen peroxide as the oxidant. Among the studied second metals, Fe was found to be effective in improving the catalytic performance. Therefore, we synthesized a series of FexVy-HMS catalysts containing different amounts of Fe and V by the co-synthesis method. The catalysts were characterized by powder X-ray diffraction (XRD), N2 physisorption, transmission electron microscopy (TEM), NH3 temperature-programmed desorption (NH3- TPD), and H2 temperature-programmed reduction (H2-TPR). The characterization results show that the mesoporous structure of HMS is maintained and the addition of Fe creates new acid sites and a stronger redox ability. Catalytic tests show that vanadium species are the active species and that the iron species promote the reaction. Under optimal reaction conditions, the Fe0.04V0.06-HMS catalyst gives the best catalytic performance with a highest phenol yield of 18.1% by comparison with 13.1% over the Fe-free catalyst Fe0.00V0.06-HMS. We propose a possible mechanism involving the Fe and V species for the hydroxylation of benzene with H2O2 as the oxidant.
2011, 27(12): 2887-2892
doi: 10.3866/PKU.WHXB20112887
Abstract:
A supported iridium catalyst stabilized by L-proline was prepared under mild conditions and was applied to the heterogeneous asymmetric hydrogenation of acetophenone and its derivatives. The effect of the support and L-proline on the supported iridium catalyst was studied. The catalyst was characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results showed that L-proline had a marked ability to stabilize and disperse the iridium particles. Reaction conditions for the asymmetric hydrogenation of acetophenone were examined in detail. LiOH enhanced the activity and enantioselectivity of the reaction. The alkali metal cation plays an important role in influencing the enantioselectivity. In addition, a synergistic effect between (1S,2S)-1,2-diphenyl-1,2- ethylenediamine ((1S,2S)-DPEN) and L-proline was observed, which significantly accelerated the reaction rate and enhanced the enantioselectivity. In the presence of (1S,2S)-DPEN as chiral modifier the catalyst 5% (w, mass fraction)Ir/15(the molar ratio of L-proline to Ir) (L-Proline)-γ-Al2O3 exhibited od catalytic performance in the asymmetric hydrogenation of acetophenone and its derivatives. Under optimum conditions the enantiomeric excess (ee) values of (R)-phenylethanol and (R)-2'-(trifluoromethyl) phenylethanol were 71.3% and 79.8%, respectively. Without using phosphine as a stabilizer the preparation of the catalyst was simple and the catalyst was reused several times without a significant loss in activity and enantioselectivity.
A supported iridium catalyst stabilized by L-proline was prepared under mild conditions and was applied to the heterogeneous asymmetric hydrogenation of acetophenone and its derivatives. The effect of the support and L-proline on the supported iridium catalyst was studied. The catalyst was characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results showed that L-proline had a marked ability to stabilize and disperse the iridium particles. Reaction conditions for the asymmetric hydrogenation of acetophenone were examined in detail. LiOH enhanced the activity and enantioselectivity of the reaction. The alkali metal cation plays an important role in influencing the enantioselectivity. In addition, a synergistic effect between (1S,2S)-1,2-diphenyl-1,2- ethylenediamine ((1S,2S)-DPEN) and L-proline was observed, which significantly accelerated the reaction rate and enhanced the enantioselectivity. In the presence of (1S,2S)-DPEN as chiral modifier the catalyst 5% (w, mass fraction)Ir/15(the molar ratio of L-proline to Ir) (L-Proline)-γ-Al2O3 exhibited od catalytic performance in the asymmetric hydrogenation of acetophenone and its derivatives. Under optimum conditions the enantiomeric excess (ee) values of (R)-phenylethanol and (R)-2'-(trifluoromethyl) phenylethanol were 71.3% and 79.8%, respectively. Without using phosphine as a stabilizer the preparation of the catalyst was simple and the catalyst was reused several times without a significant loss in activity and enantioselectivity.
2011, 27(12): 2893-2899
doi: 10.3866/PKU.WHXB20112893
Abstract:
Using N,N,N-trimethyl-8-ammonium tricyclo [5.2.1.02,6] decane iodide as a structure directing agent, B-SSZ-33 molecular sieves with an excellent price-performance ratio was successfully synthesized by process control over 3-4 days. The synthesis of Al-SSZ-33 was achieved by a post-modification procedure of B-SSZ-33 molecular sieves in an Al(NO3)3 solution. These materials were characterized in detail by various techniques such as X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), thermogravimetric (TG) analysis, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), N2 adsorption/desorption, temperature programmed desorption of NH3 (NH3-TPD), and solid state 27Al nuclear magnetic resonance (27Al NMR). The temperature programmed desorption characteristics of toluene for the B-SSZ-33 and Al-SSZ-33 samples were obtained to understand the efficacy of these materials as hydrocarbon traps. The results show that Al-SSZ-33 with framework Al was obtained after the post-modification procedures. Compared with B-SSZ-33, Al-SSZ-33 has a higher acid strength and shows a comparatively higher toluene desorption temperature (Tmax). The presence of extra framework Al and Si species in Al-SSZ-33 modifies its pores and results in a higher desorption end temperature (Tend). Therefore, the synthesized Al-SSZ-33 is a novel catalyst for use as a hydrocarbon trap in automobile tailpipes.
Using N,N,N-trimethyl-8-ammonium tricyclo [5.2.1.02,6] decane iodide as a structure directing agent, B-SSZ-33 molecular sieves with an excellent price-performance ratio was successfully synthesized by process control over 3-4 days. The synthesis of Al-SSZ-33 was achieved by a post-modification procedure of B-SSZ-33 molecular sieves in an Al(NO3)3 solution. These materials were characterized in detail by various techniques such as X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), thermogravimetric (TG) analysis, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), N2 adsorption/desorption, temperature programmed desorption of NH3 (NH3-TPD), and solid state 27Al nuclear magnetic resonance (27Al NMR). The temperature programmed desorption characteristics of toluene for the B-SSZ-33 and Al-SSZ-33 samples were obtained to understand the efficacy of these materials as hydrocarbon traps. The results show that Al-SSZ-33 with framework Al was obtained after the post-modification procedures. Compared with B-SSZ-33, Al-SSZ-33 has a higher acid strength and shows a comparatively higher toluene desorption temperature (Tmax). The presence of extra framework Al and Si species in Al-SSZ-33 modifies its pores and results in a higher desorption end temperature (Tend). Therefore, the synthesized Al-SSZ-33 is a novel catalyst for use as a hydrocarbon trap in automobile tailpipes.
2011, 27(12): 2900-2906
doi: 10.3866/PKU.WHXB20112900
Abstract:
The effect of oxygen vacancy on the optical properties of porous zirconia (ZrO2) was discussed based on the preparation and optical characterization of this material. The configuration coordinate diagram for a discussion of the optical performances of the ZrO2 system was carefully amended. The samples used in the experiments were prepared by the hydrothermal method. The product possesses a porous structure constructed by amorphous zirconia particles and the specific surface area of the product was 151.9 m2·g-1. Deconvolution was used to analyze the photoluminescence (PL) spectra and the results are different in some aspects compared with previous reports. The main PL bands of the as-prepared product were located in the violet to blue region while those of the samples after treatment by H3PO4 red-shifted to the blue-green region. Neither the porous structure nor the existence of phosphor reagents in ZrO2 induced any new PL peaks. The oxygen vacancies in the samples formed a new energy level that trapped electrons to form a color center and then luminescent emissions were induced.
The effect of oxygen vacancy on the optical properties of porous zirconia (ZrO2) was discussed based on the preparation and optical characterization of this material. The configuration coordinate diagram for a discussion of the optical performances of the ZrO2 system was carefully amended. The samples used in the experiments were prepared by the hydrothermal method. The product possesses a porous structure constructed by amorphous zirconia particles and the specific surface area of the product was 151.9 m2·g-1. Deconvolution was used to analyze the photoluminescence (PL) spectra and the results are different in some aspects compared with previous reports. The main PL bands of the as-prepared product were located in the violet to blue region while those of the samples after treatment by H3PO4 red-shifted to the blue-green region. Neither the porous structure nor the existence of phosphor reagents in ZrO2 induced any new PL peaks. The oxygen vacancies in the samples formed a new energy level that trapped electrons to form a color center and then luminescent emissions were induced.
2011, 27(12): 2907-2914
doi: 10.3866/PKU.WHXB20112907
Abstract:
Complexes of horse metmyoglobin (metMb) with the anionic surfactants sodium bis(2- ethylhexyl) sulfosuccinate (AOT) and sodium dodecyl benzene sulfonate (SDBS), the cationic surfactants dodecyl trimethylammonium bromide (CTAB) and dodecyltrimethyl ammonium bromide (DTAB), and the zwitterionic surfactant 3-[(3-cholamidopropyl) dimethylammonio] propanesulfonate (CHAPS) were investigated by UV-Vis absorption, synchronous fluorescence emission, and circular dichroism (CD) spectroscopy. Experimental results show that the anionic and cationic surfactants can interact with metMb intensively depending on the surfactant concentration. The UV-Vis spectra indicate that AOT and SDBS interact with metMb at low concentrations. The addition of AOT (or SDBS) causes the formation of a six-coordinated low-spin heme (6-cLs) hemichrome as is evident from the red shift of the Soret band, the intensity decrease, concomitant appearance of two new Q bands, and the disappearance of ligandto- metal charge transfer (LMCT). The surfactants disturb the Tyr and Trp microenvironment and change the second structure parameter of metMb while the α-helix content decreases. However, the interaction between metMb and CTAB (or DTAB) is different. They cannot disturb heme at very low concentrations but can disturb the Tyr and Trp microenvironment. CTAB and DTAB aggregates can convert metMb to a five-coordinated low-spin heme as shown by the blue shift of the Soret band and cause the heme monomer to leave the hydrophobic cavity of metMb through electrostatic attraction mainly. DTAB/metMb complexes behave in a slightly different way to CTAB/metMb because of their special structure. In contrast, no interaction is evident between the zwitterionic surfactant over a large range of concentrations because of the neutral charge of CHAPS, which precludes an effective electrostatic attraction between the ionic sites of CHAPS and a protein. The significant distance between the ionic sites with opposite charges in metMb precludes a double ionic interaction for each CHAPS surfactant molecule despite the presence of two oppositely charged ionic sites in the CHAPS molecule. Therefore, proteins interact with surfactants in multifarious ways and this depends on the surfactant species, concentration, and structure.
Complexes of horse metmyoglobin (metMb) with the anionic surfactants sodium bis(2- ethylhexyl) sulfosuccinate (AOT) and sodium dodecyl benzene sulfonate (SDBS), the cationic surfactants dodecyl trimethylammonium bromide (CTAB) and dodecyltrimethyl ammonium bromide (DTAB), and the zwitterionic surfactant 3-[(3-cholamidopropyl) dimethylammonio] propanesulfonate (CHAPS) were investigated by UV-Vis absorption, synchronous fluorescence emission, and circular dichroism (CD) spectroscopy. Experimental results show that the anionic and cationic surfactants can interact with metMb intensively depending on the surfactant concentration. The UV-Vis spectra indicate that AOT and SDBS interact with metMb at low concentrations. The addition of AOT (or SDBS) causes the formation of a six-coordinated low-spin heme (6-cLs) hemichrome as is evident from the red shift of the Soret band, the intensity decrease, concomitant appearance of two new Q bands, and the disappearance of ligandto- metal charge transfer (LMCT). The surfactants disturb the Tyr and Trp microenvironment and change the second structure parameter of metMb while the α-helix content decreases. However, the interaction between metMb and CTAB (or DTAB) is different. They cannot disturb heme at very low concentrations but can disturb the Tyr and Trp microenvironment. CTAB and DTAB aggregates can convert metMb to a five-coordinated low-spin heme as shown by the blue shift of the Soret band and cause the heme monomer to leave the hydrophobic cavity of metMb through electrostatic attraction mainly. DTAB/metMb complexes behave in a slightly different way to CTAB/metMb because of their special structure. In contrast, no interaction is evident between the zwitterionic surfactant over a large range of concentrations because of the neutral charge of CHAPS, which precludes an effective electrostatic attraction between the ionic sites of CHAPS and a protein. The significant distance between the ionic sites with opposite charges in metMb precludes a double ionic interaction for each CHAPS surfactant molecule despite the presence of two oppositely charged ionic sites in the CHAPS molecule. Therefore, proteins interact with surfactants in multifarious ways and this depends on the surfactant species, concentration, and structure.
2011, 27(12): 2915-2919
doi: 10.3866/PKU.WHXB20112915
Abstract:
Field emission scanning microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDXS) were used to study the morphology and composition of secondary phase precipitations in induction-melted higher manganese silicide (HMS). Striations of the secondary phase were observed in individual HMS crystals with an average interval of 5-30 μm and a thickness of ~30 nm. The chemical composition of the striations was examined and found to be MnSi, which was observed as an amorphous phase by high resolution transmission electron microscopy (HRTEM). The crystal structure of HMS was determined by selective area electron diffraction (SAED) and the results indicated a single Mn4Si7 phase in the as-prepared material and no other incommensurate HMS phases were found. After ball milling and hot pressing many defects and stress fields were observed in the HMS by transmission electron microscope (TEM), which differentiated substantially from the morphology of the as-melted HMS.
Field emission scanning microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDXS) were used to study the morphology and composition of secondary phase precipitations in induction-melted higher manganese silicide (HMS). Striations of the secondary phase were observed in individual HMS crystals with an average interval of 5-30 μm and a thickness of ~30 nm. The chemical composition of the striations was examined and found to be MnSi, which was observed as an amorphous phase by high resolution transmission electron microscopy (HRTEM). The crystal structure of HMS was determined by selective area electron diffraction (SAED) and the results indicated a single Mn4Si7 phase in the as-prepared material and no other incommensurate HMS phases were found. After ball milling and hot pressing many defects and stress fields were observed in the HMS by transmission electron microscope (TEM), which differentiated substantially from the morphology of the as-melted HMS.
2011, 27(12): 2920-2926
doi: 10.3866/PKU.WHXB20112920
Abstract:
A simple solvothermal route has been successfully used to prepare Cu2ZnSnS4 nanocrystals using metal chloride and L-cysteine as precursors at 180 °C for 16 h. L-cysteine was used as the sulfide source and complexing agent. The phase, structure, morphology, and optical properties of the assynthesized products were characterized by powder X-ray diffraction (XRD), field-emission scan electron microscopy (FESEM), energy dispersive spectrometry (EDS), high-resolution electron transmission microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible (UV-Vis) spectrophotometer. The results showed that pure kesterite-type Cu2ZnSnS4 nanocrystals were prepared under this condition and the diameters of the microspheres were about 400-800 nm while the microspheres consisted of nanoflakes with thickness of 20 nm. The band gap of CZTS nanoparticles was about 1.58 eV，which was close to the optimum band gap of thin film solar cells. A possible formation mechanism was also discussed.
A simple solvothermal route has been successfully used to prepare Cu2ZnSnS4 nanocrystals using metal chloride and L-cysteine as precursors at 180 °C for 16 h. L-cysteine was used as the sulfide source and complexing agent. The phase, structure, morphology, and optical properties of the assynthesized products were characterized by powder X-ray diffraction (XRD), field-emission scan electron microscopy (FESEM), energy dispersive spectrometry (EDS), high-resolution electron transmission microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible (UV-Vis) spectrophotometer. The results showed that pure kesterite-type Cu2ZnSnS4 nanocrystals were prepared under this condition and the diameters of the microspheres were about 400-800 nm while the microspheres consisted of nanoflakes with thickness of 20 nm. The band gap of CZTS nanoparticles was about 1.58 eV，which was close to the optimum band gap of thin film solar cells. A possible formation mechanism was also discussed.
2011, 27(12): 2927-2932
doi: 10.3866/PKU.WHXB20112927
Abstract:
A novel nanoparticle aggregation structure of barium titanate was obtained by the hydrothermal method. Powder X-ray diffraction (XRD) revealed that the aggregates crystallized in the cubic phase. The crystallization of the products became more significant with reaction progress. The growth characteristics of the aggregates was further confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), and electron diffraction (ED) spectroscopy. The aggregation was composed of many 5-8 nm nanoparticles by orientation attachment and we found that the ED patterns indicated a single-crystal property for the aggregates. The size of the aggregates was about 60 nm and they grew as the reaction continued. From the results of energy dispersive X-ray (EDX) spectroscopy analysis and kinetics modeling using the Johnson-Mehl-Avrami (JMA) equation, the diffusion nucleation of Ba2+ ion was found to be dominant during the early stages of aggregation formation. The growth process of “diffusion nucleation-orientation attachment”revealed the formation mechanism of barium titanate nanoparticle aggregations.
A novel nanoparticle aggregation structure of barium titanate was obtained by the hydrothermal method. Powder X-ray diffraction (XRD) revealed that the aggregates crystallized in the cubic phase. The crystallization of the products became more significant with reaction progress. The growth characteristics of the aggregates was further confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), and electron diffraction (ED) spectroscopy. The aggregation was composed of many 5-8 nm nanoparticles by orientation attachment and we found that the ED patterns indicated a single-crystal property for the aggregates. The size of the aggregates was about 60 nm and they grew as the reaction continued. From the results of energy dispersive X-ray (EDX) spectroscopy analysis and kinetics modeling using the Johnson-Mehl-Avrami (JMA) equation, the diffusion nucleation of Ba2+ ion was found to be dominant during the early stages of aggregation formation. The growth process of “diffusion nucleation-orientation attachment”revealed the formation mechanism of barium titanate nanoparticle aggregations.
2011, 27(12): 2933-2938
doi: 10.3866/PKU.WHXB20112933
Abstract:
Ag-loaded titania nanotubes were synthesized by a microwave-assisted hydrothermal method and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption, X-ray photoelectron spectroscopy (XPS), and UV-visible (UV-Vis) diffuse reflectance spectroscopy. The titania nanotubes were found to be in the anatase phase after calcination. The length of the synthesized titania nanotubes was about 200 nm, the average outer diameter was 7-8 nm, the inner diameter was 5-6 nm and the specific surface area was found to be 371 m2·g-1. With Ag loading the silver atoms did not enter the lattices of the nanotubes but dispersed over the nanotube surface. Ag-loading had no effect on the nanostructure and the crystal phase of the TiO2 nanotubes. The Ag-loaded titania nanotubes showed obvious visible light absorption and enhanced visible photocatalytic performance. The photocatalytic activity was evaluated by the photodegradation of a Rhodamine B aqueous solution under visible light. Compared with Ag-loaded P25 and pure titania nanotubes the Ag-loaded titania nanotubes enhanced the photoactivity and reached the maximum activity at a Ag/Ti molar ratio of 0.5%.
Ag-loaded titania nanotubes were synthesized by a microwave-assisted hydrothermal method and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption, X-ray photoelectron spectroscopy (XPS), and UV-visible (UV-Vis) diffuse reflectance spectroscopy. The titania nanotubes were found to be in the anatase phase after calcination. The length of the synthesized titania nanotubes was about 200 nm, the average outer diameter was 7-8 nm, the inner diameter was 5-6 nm and the specific surface area was found to be 371 m2·g-1. With Ag loading the silver atoms did not enter the lattices of the nanotubes but dispersed over the nanotube surface. Ag-loading had no effect on the nanostructure and the crystal phase of the TiO2 nanotubes. The Ag-loaded titania nanotubes showed obvious visible light absorption and enhanced visible photocatalytic performance. The photocatalytic activity was evaluated by the photodegradation of a Rhodamine B aqueous solution under visible light. Compared with Ag-loaded P25 and pure titania nanotubes the Ag-loaded titania nanotubes enhanced the photoactivity and reached the maximum activity at a Ag/Ti molar ratio of 0.5%.
2011, 27(12): 2939-2945
doi: 10.3866/PKU.WHXB20112939
Abstract:
Hydroxyapatite (HAP) nanoribbon spheres with well-defined nanoscale structures and regular morphology were successfully synthesized using a bioactive cooperate template. The spheres are about 5-6 μm in diameter and they form from nanoribbons of 2.5 to 3 μm in length. The morphologies, structures, and surface areas of the products were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and Brunauer-Emmett-Teller (BET) analysis. In addition, the products were used as carried materials for the synthesis of the HAP/ZnO composite catalyst. The degradation rate of rhodamine B (RhB) increased by 125% and the recovery increased by 23.1% when using the composite as a catalyst compared with the ZnO nanoparticles. Possible mechanisms for the formation of the HAP assembly microspheres and their synergistic action are also discussed.
Hydroxyapatite (HAP) nanoribbon spheres with well-defined nanoscale structures and regular morphology were successfully synthesized using a bioactive cooperate template. The spheres are about 5-6 μm in diameter and they form from nanoribbons of 2.5 to 3 μm in length. The morphologies, structures, and surface areas of the products were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and Brunauer-Emmett-Teller (BET) analysis. In addition, the products were used as carried materials for the synthesis of the HAP/ZnO composite catalyst. The degradation rate of rhodamine B (RhB) increased by 125% and the recovery increased by 23.1% when using the composite as a catalyst compared with the ZnO nanoparticles. Possible mechanisms for the formation of the HAP assembly microspheres and their synergistic action are also discussed.
2011, 27(12): 2946-2952
doi: 10.3866/PKU.WHXB20112946
Abstract:
V2O5·xH2O-BiVO4 composite photocatalysts were synthesized using monoclinic V2O5·xH2O nanowires as a precursor under mild conditions. To determine the synthesis-time-dependent phase content, morphology, and photocatalytic performance of the products, three typical V2O5·xH2O-BiVO4 samples were obtained at 6, 12, and 24 h. These samples were investigated using X-ray diffraction, fieldemission scanning electron microscopy, UV-visible diffusion reflectance spectroscopy, and a photocatalytic property test. The results indicate that the V2O5·xH2O-BiVO4 nanocomposites are composed of V2O5·xH2O nanowires and BiVO4 nanocrystals. As the reaction time was extended, the amount of V2O5·xH2O nanowires decreased gradually and that of the BiVO4 nanocrystals increased in the composite. The results of photocatalytic performance indicated that the V2O5·xH2O-BiVO4 composite photocatalysts exhibited enhanced photocatalytic efficiency for the degradation of methylene blue (MB) under visible-light irradiation (λ>400 nm). The V2O5·xH2O-BiVO4 sample obtained at 12 h exhibited the best photocatalytic activity, which is probably because of the appropriate proportion of components and the special microstructures of the sample that were favorable for a synergistic effect between the two photocatalysis mechanisms involving the excitation of the semiconductor and the excitation of the dye, respectively.
V2O5·xH2O-BiVO4 composite photocatalysts were synthesized using monoclinic V2O5·xH2O nanowires as a precursor under mild conditions. To determine the synthesis-time-dependent phase content, morphology, and photocatalytic performance of the products, three typical V2O5·xH2O-BiVO4 samples were obtained at 6, 12, and 24 h. These samples were investigated using X-ray diffraction, fieldemission scanning electron microscopy, UV-visible diffusion reflectance spectroscopy, and a photocatalytic property test. The results indicate that the V2O5·xH2O-BiVO4 nanocomposites are composed of V2O5·xH2O nanowires and BiVO4 nanocrystals. As the reaction time was extended, the amount of V2O5·xH2O nanowires decreased gradually and that of the BiVO4 nanocrystals increased in the composite. The results of photocatalytic performance indicated that the V2O5·xH2O-BiVO4 composite photocatalysts exhibited enhanced photocatalytic efficiency for the degradation of methylene blue (MB) under visible-light irradiation (λ>400 nm). The V2O5·xH2O-BiVO4 sample obtained at 12 h exhibited the best photocatalytic activity, which is probably because of the appropriate proportion of components and the special microstructures of the sample that were favorable for a synergistic effect between the two photocatalysis mechanisms involving the excitation of the semiconductor and the excitation of the dye, respectively.
2011, 27(12): 2953-2959
doi: 10.3866/PKU.WHXB20112953
Abstract:
Graphene is a newly discovered material with many functions. The preparation of graphene on suitable substrates is a challenge in the material preparation field. In this paper, graphene thin films were grown on Si substrates covered with SiC buffer layers (SiC/Si) by the direct deposition of carbon atoms using molecular beam epitaxy (MBE) equipment. The structural properties of the samples produced at different substrate temperatures (800, 900, 1000, 1100 ° C) were investigated by reflection high energy electron diffraction (RHEED), Raman spectroscopy and near-edge X-ray absorption fine structure (NEXAFS). The results indicate that the thin films grown at all temperatures exhibit the characteristics of graphene with a turbostratic stacking structure. As the substrate temperature increases the crystalline quality of the graphene improves. However, a very high temperature decreases the quality of graphene. The best graphene films were obtained at a substrate temperature of 1000 ° C. This is due to the low substrate temperature resulting in a too low carbon atom activity for the formation of an ordered six-member ring of C-sp2. When the substrate temperature was too high the silicon atoms in the substrate became so active that silicon atoms diffused to the surface of the sample through SiC buffer defects and they bonded to the depositing carbon atoms, which resulted in a lower crystallization quality of the carbon layers.
Graphene is a newly discovered material with many functions. The preparation of graphene on suitable substrates is a challenge in the material preparation field. In this paper, graphene thin films were grown on Si substrates covered with SiC buffer layers (SiC/Si) by the direct deposition of carbon atoms using molecular beam epitaxy (MBE) equipment. The structural properties of the samples produced at different substrate temperatures (800, 900, 1000, 1100 ° C) were investigated by reflection high energy electron diffraction (RHEED), Raman spectroscopy and near-edge X-ray absorption fine structure (NEXAFS). The results indicate that the thin films grown at all temperatures exhibit the characteristics of graphene with a turbostratic stacking structure. As the substrate temperature increases the crystalline quality of the graphene improves. However, a very high temperature decreases the quality of graphene. The best graphene films were obtained at a substrate temperature of 1000 ° C. This is due to the low substrate temperature resulting in a too low carbon atom activity for the formation of an ordered six-member ring of C-sp2. When the substrate temperature was too high the silicon atoms in the substrate became so active that silicon atoms diffused to the surface of the sample through SiC buffer defects and they bonded to the depositing carbon atoms, which resulted in a lower crystallization quality of the carbon layers.
2011, 27(12): 2960-2962
doi: 10.3866/PKU.WHXB20112960
Abstract:
The size-dependent nanocatalysis has been well studied in the past three decades, while little concern is paid to the shape of the nanoparticles, which can greatly modify the reaction performance by selectively exposing specific crystal facets. This article highlights the recent progress on the morphology-dependent nanocatalysis published in Chinese Journal of Catalysis of the year 2010. This strategy should be workable in designing and preparing efficient nanocatalysts with tunable size and shape.
The size-dependent nanocatalysis has been well studied in the past three decades, while little concern is paid to the shape of the nanoparticles, which can greatly modify the reaction performance by selectively exposing specific crystal facets. This article highlights the recent progress on the morphology-dependent nanocatalysis published in Chinese Journal of Catalysis of the year 2010. This strategy should be workable in designing and preparing efficient nanocatalysts with tunable size and shape.
2011, 27(12): 2963-2972
Abstract:
一年来(2010 年11 月-2011 年10 月), 有925 位老师(名单按姓名拼音字母排序)非常认真细致、无偿而且及时(初审平均20 天、复审平均10 天)地完成了审稿, 提出了很多客观、中肯的意见和建议. 他们的辛勤劳动和无私奉献使得《物理化学学报》能够高质量、快速(网络版平均出版周期为97 天, 印刷版为154 天)地发表作者的优秀研究成果, 促进了学术交流. 谨向他们致以衷心的谢忱和崇高的敬意!
一年来(2010 年11 月-2011 年10 月), 有925 位老师(名单按姓名拼音字母排序)非常认真细致、无偿而且及时(初审平均20 天、复审平均10 天)地完成了审稿, 提出了很多客观、中肯的意见和建议. 他们的辛勤劳动和无私奉献使得《物理化学学报》能够高质量、快速(网络版平均出版周期为97 天, 印刷版为154 天)地发表作者的优秀研究成果, 促进了学术交流. 谨向他们致以衷心的谢忱和崇高的敬意!
2011, 27(12): 2973-2997
Abstract:
