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2011 Volume 27 Issue 9
2011, 27(09):
Abstract:
2011, 27(09): 2015-2018
doi: 10.3866/PKU.WHXB20110940
Abstract:
2011, 27(09): 2019-2026
doi: 10.3866/PKU.WHXB20110830
Abstract:
Over the last 3 years, the use of graphics processing units (GPU) in general purpose computing has been increasing because of the development of GPU hardware and programming tools such as CUDA (compute unified device architecture). Here, we summarize the progress in al rithms and the corresponding software with regard to computational chemistry using GPU including quantum chemistry and molecular dynamics simulations in detail. We introduce and explore the newly developed TeraChem program, which is unique quantum chemical software and we discuss the al rithms, implementations, and functionality of the program. Finally, we give an optimistic outlook for the use of GPU in computational chemistry.
Over the last 3 years, the use of graphics processing units (GPU) in general purpose computing has been increasing because of the development of GPU hardware and programming tools such as CUDA (compute unified device architecture). Here, we summarize the progress in al rithms and the corresponding software with regard to computational chemistry using GPU including quantum chemistry and molecular dynamics simulations in detail. We introduce and explore the newly developed TeraChem program, which is unique quantum chemical software and we discuss the al rithms, implementations, and functionality of the program. Finally, we give an optimistic outlook for the use of GPU in computational chemistry.
2011, 27(09): 2027-2034
doi: 10.3866/PKU.WHXB20110835
Abstract:
To realize the stable combustion of methane in a micro-combustor it is necessary to investigate the influence of the humidity ratio on the reforming system for methane-wet air reforming. Thus, we studied the effects of the humidity ratio on carbon deposition, methane conversion, H2 production, and the reaction process under lean oxygen below 973 K and at 0.1 MPa theoretically with a constant air-methane ratio or feed gas flux using thermodynamic analysis. Results show that carbon deposition always decreases with a humidity ratio increase at a certain methane mass flow in the micro-combustor. In contrast, the methane conversion ratio decreased initially and then increased while the H2 yield always increased. The main product of methane conversion is CO2. The CO selectivity increases initially and then decreases while the CO2 selectivity always increases with an increase in the humidity ratio. Furthermore, the amount of consumed steam will finally increase to more than the amount of generated steam during the reaction process with an increase in the humidity ratio, which also leads to an increase for steam after the reaction. When the amount of steam is less than the air in the feed gas, a steam consumption-dominant system is always obtained upon varying the steam mass fraction before and after the reaction when the humidity ratio reaches 280 g·kg-1. Additionally, it is beneficial to reduce the carbon deposition and to promote reforming during the reaction process when the humidity ratio is higher than 350 g·kg-1. By meeting the humidity ratio conditions mentioned above a higher methane conversion ratio and H2 yield can be obtained under a constant air-methane ratio condition.
To realize the stable combustion of methane in a micro-combustor it is necessary to investigate the influence of the humidity ratio on the reforming system for methane-wet air reforming. Thus, we studied the effects of the humidity ratio on carbon deposition, methane conversion, H2 production, and the reaction process under lean oxygen below 973 K and at 0.1 MPa theoretically with a constant air-methane ratio or feed gas flux using thermodynamic analysis. Results show that carbon deposition always decreases with a humidity ratio increase at a certain methane mass flow in the micro-combustor. In contrast, the methane conversion ratio decreased initially and then increased while the H2 yield always increased. The main product of methane conversion is CO2. The CO selectivity increases initially and then decreases while the CO2 selectivity always increases with an increase in the humidity ratio. Furthermore, the amount of consumed steam will finally increase to more than the amount of generated steam during the reaction process with an increase in the humidity ratio, which also leads to an increase for steam after the reaction. When the amount of steam is less than the air in the feed gas, a steam consumption-dominant system is always obtained upon varying the steam mass fraction before and after the reaction when the humidity ratio reaches 280 g·kg-1. Additionally, it is beneficial to reduce the carbon deposition and to promote reforming during the reaction process when the humidity ratio is higher than 350 g·kg-1. By meeting the humidity ratio conditions mentioned above a higher methane conversion ratio and H2 yield can be obtained under a constant air-methane ratio condition.
2011, 27(09): 2035-2042
doi: 10.3866/PKU.WHXB20110903
Abstract:
To determine the tautomerism mechanism between the enol form and the keto form of 2- (2-hydroxybenzylidenamino)pyrimidine-4,6-diol (M1) the potential energy surface of the isomerization was studied using density functional theory (DFT) calculations at the B3LYP/6-311+G(d, p) level. We found that there were at least 8 isomers and 10 transition states in the possible reaction pathways. All the possible processes of the reaction were studied. The results showed that the energy of 6-hydroxy-2-(2- hydroxybenzylideneamino) pyrimidine-4(3H)-one (M6) was lower than those of the other isomers in the form of a monomer, a hydrate, and a dimer. Therefore, it was the most stable isomer. In these possible reaction pathways the activation free energy required for intramolecular prototropy was 143.8 kJ·mol-1 and for the proton transfer process that was catalyzed by water was 38.9 kJ·mol-1. The activation free energy in the double-proton transfer of the dimer was 0.6 kJ·mol-1, which was the lowest value. The latter pathway was feasible at room temperature. This implies that hydrogen bonding plays an important role in depressing the activation energy of the reaction.
To determine the tautomerism mechanism between the enol form and the keto form of 2- (2-hydroxybenzylidenamino)pyrimidine-4,6-diol (M1) the potential energy surface of the isomerization was studied using density functional theory (DFT) calculations at the B3LYP/6-311+G(d, p) level. We found that there were at least 8 isomers and 10 transition states in the possible reaction pathways. All the possible processes of the reaction were studied. The results showed that the energy of 6-hydroxy-2-(2- hydroxybenzylideneamino) pyrimidine-4(3H)-one (M6) was lower than those of the other isomers in the form of a monomer, a hydrate, and a dimer. Therefore, it was the most stable isomer. In these possible reaction pathways the activation free energy required for intramolecular prototropy was 143.8 kJ·mol-1 and for the proton transfer process that was catalyzed by water was 38.9 kJ·mol-1. The activation free energy in the double-proton transfer of the dimer was 0.6 kJ·mol-1, which was the lowest value. The latter pathway was feasible at room temperature. This implies that hydrogen bonding plays an important role in depressing the activation energy of the reaction.
2011, 27(09): 2043-2050
doi: 10.3866/PKU.WHXB20110921
Abstract:
The AuClx (x=1, 3)-catalyzed benzannulation mechanisms between benzyne and 2-propynylhypnone were investigated using B3LYP, B3PW91, UB3LYP, and the second-order Møller-Plesset perturbation (MP2) methods with the LanL2DZ basis set for Au and the 6-31G*, 6-311++G** basis sets for C, H, O, Cl. For the AuCl or AuCl3 catalysts the reaction occurs through both the [4 + 2] and the [3 + 2] benzannulation pathways to yield the product. With AuCl, the reaction occurs mainly through the [4 + 2] reaction pathway because of this pathway's low activation free energy. With AuCl3, the reaction occurs by the [4+2] and the [3+2] reaction pathways. These two pathways are competitive because of their close activation free energies. An analysis of these results indicates that the ld oxidation states change the reaction mechanisms and greatly influence the reaction barriers. The calculated results indicate that the AuCl catalyst is more effective than AuCl3 because in the reaction catalyzed by AuCl the activation free energy of the rate determining step is 11.18 kJ·mol-1 lower than that of the reaction catalyzed by AuCl3. These results are in od agreement with the experimental observations.
The AuClx (x=1, 3)-catalyzed benzannulation mechanisms between benzyne and 2-propynylhypnone were investigated using B3LYP, B3PW91, UB3LYP, and the second-order Møller-Plesset perturbation (MP2) methods with the LanL2DZ basis set for Au and the 6-31G*, 6-311++G** basis sets for C, H, O, Cl. For the AuCl or AuCl3 catalysts the reaction occurs through both the [4 + 2] and the [3 + 2] benzannulation pathways to yield the product. With AuCl, the reaction occurs mainly through the [4 + 2] reaction pathway because of this pathway's low activation free energy. With AuCl3, the reaction occurs by the [4+2] and the [3+2] reaction pathways. These two pathways are competitive because of their close activation free energies. An analysis of these results indicates that the ld oxidation states change the reaction mechanisms and greatly influence the reaction barriers. The calculated results indicate that the AuCl catalyst is more effective than AuCl3 because in the reaction catalyzed by AuCl the activation free energy of the rate determining step is 11.18 kJ·mol-1 lower than that of the reaction catalyzed by AuCl3. These results are in od agreement with the experimental observations.
2011, 27(09): 2051-2058
doi: 10.3866/PKU.WHXB20110930
Abstract:
Theoretical predictions are helpful for the spectroscopic identification of complicated organic and biological systems. For nuclear magnetic resonance (NMR) parameters, however, the chemical shift and quadrupole coupling constant (QCC) of the solid crystals are considerably affected by hydrogen bonding and van der Waals interactions from neighboring molecules and the crystal lattice leading to significant spectroscopic differences compared to isolated monomer molecules. Therefore, it is necessary to take these two factors into account for the precise predictions of chemical shifts and QCCs of solid crystals. L-alanylglycine dipeptide and nitrobenzene were selected as model crystals to demonstrate these effects. Here, the chemical shielding (CS) and QCC data were calculated based on the periodic structure model. The incorporation of intermolecular hydrogen bonding and crystal lattice effects by periodic models was found to be crucial in obtaining reliable predictions of CS and QCC values and rendering more explicit spectroscopic assignments for solid organic and biological systems.
Theoretical predictions are helpful for the spectroscopic identification of complicated organic and biological systems. For nuclear magnetic resonance (NMR) parameters, however, the chemical shift and quadrupole coupling constant (QCC) of the solid crystals are considerably affected by hydrogen bonding and van der Waals interactions from neighboring molecules and the crystal lattice leading to significant spectroscopic differences compared to isolated monomer molecules. Therefore, it is necessary to take these two factors into account for the precise predictions of chemical shifts and QCCs of solid crystals. L-alanylglycine dipeptide and nitrobenzene were selected as model crystals to demonstrate these effects. Here, the chemical shielding (CS) and QCC data were calculated based on the periodic structure model. The incorporation of intermolecular hydrogen bonding and crystal lattice effects by periodic models was found to be crucial in obtaining reliable predictions of CS and QCC values and rendering more explicit spectroscopic assignments for solid organic and biological systems.
2011, 27(09): 2059-2064
doi: 10.3866/PKU.WHXB20110914
Abstract:
Eleven types of alkyl imidazolium tetrafluoroborate ionic liquids (ILs) have been investigated using the density functional theory (DFT) B3LYP method together with basis set 6-311++G(d,p). First, we performed geometry optimization of the ion system {[XIM] [BF4]n}(n-1)- (n=2, 3), which is composed of one alkyl imidazolium cation XIM+ and two or three BF4- anions. Then the intramolecular interaction energies were calculated for those structures with the lowest energies, and the basis set superposition error was corrected by the counterpoise method. The relationship between the experimental melting points and the interaction energies was also investigated. A linear correlation was found for the alkyl imidazolium tetrafluoroborate compounds studied, which was also consistent with the linear correlation previously found for amino acid cation based ILs. Our work shows the possibility of designing ILs with the help of quantum chemistry in the future.
Eleven types of alkyl imidazolium tetrafluoroborate ionic liquids (ILs) have been investigated using the density functional theory (DFT) B3LYP method together with basis set 6-311++G(d,p). First, we performed geometry optimization of the ion system {[XIM] [BF4]n}(n-1)- (n=2, 3), which is composed of one alkyl imidazolium cation XIM+ and two or three BF4- anions. Then the intramolecular interaction energies were calculated for those structures with the lowest energies, and the basis set superposition error was corrected by the counterpoise method. The relationship between the experimental melting points and the interaction energies was also investigated. A linear correlation was found for the alkyl imidazolium tetrafluoroborate compounds studied, which was also consistent with the linear correlation previously found for amino acid cation based ILs. Our work shows the possibility of designing ILs with the help of quantum chemistry in the future.
2011, 27(09): 2065-2071
doi: 10.3866/PKU.WHXB20110919
Abstract:
The adsorption and separation of natural gas in the ordered mesoporous carbon material CMK-3 was investigated by molecular simulation and adsorption theory. Grand canonical ensemble Monte Carlo (GCMC) simulations show that a maximum excess uptake of 10.07 and 14.85 mmol·g-1 is obtained at the optimum temperature and pressure of 208 K, 4 MPa for CH4 and 298 K, 6 MPa for CO2 adsorption, respectively. Based on the dual-site Langmuir-Freundlich (DSLF) model, ideal adsorption solution theory (IAST) was used to predict the adsorption and separation of binary mixtures. The adsorption selectivity of SCO2/CH4 is approximately the same as that of SCH4/N2, with a value of about 3 at 298 K and 4 MPa while the highest CO2 selectivity of 7.5 was found in the N2-CO2 system under the same conditions. This indicates that the CMK-3 material is a promising candidate for natural gas separation.
The adsorption and separation of natural gas in the ordered mesoporous carbon material CMK-3 was investigated by molecular simulation and adsorption theory. Grand canonical ensemble Monte Carlo (GCMC) simulations show that a maximum excess uptake of 10.07 and 14.85 mmol·g-1 is obtained at the optimum temperature and pressure of 208 K, 4 MPa for CH4 and 298 K, 6 MPa for CO2 adsorption, respectively. Based on the dual-site Langmuir-Freundlich (DSLF) model, ideal adsorption solution theory (IAST) was used to predict the adsorption and separation of binary mixtures. The adsorption selectivity of SCO2/CH4 is approximately the same as that of SCH4/N2, with a value of about 3 at 298 K and 4 MPa while the highest CO2 selectivity of 7.5 was found in the N2-CO2 system under the same conditions. This indicates that the CMK-3 material is a promising candidate for natural gas separation.
2011, 27(09): 2072-2078
doi: 10.3866/PKU.WHXB20110816
Abstract:
The photofragmentation of C60 fullerene by an ultrafast laser pulse was studied by semiclassical molecular dynamics simulation. Two different laser pulses were used for this study: one with a duration of 40 fs FWHM (full width at half maximum) and the other with a duration of 500 fs FWHM. Both laser pulses had an energy of 2.0 eV. The simulation was run at different laser intensities for each laser pulse. The simulation results showed that a dominant amount of laser energy deposited to C60 fullerene was distributed into electronic energy. From the simulation we find that the electronic excitation from the occupied molecular orbitals to the unoccupied orbitals is closely related to the photofragmentation of C60 fullerene. By analyzing the fragmentation size distribution, the atomic equivalence index, the temperature, and the absorbed energy (including the electronic energy, the potential energy, and the kinetic energy), we found that non-thermal effects play a significant role in the laser fragmentation of C60 fullerene. By examining the fragmentation features of C60 fullerene with two different laser pulses we found that the laser pulse duration affects the fragmentation process significantly and that laser intensity has little effect on the fragmentation after the absorbed electronic energy becomes saturated.
The photofragmentation of C60 fullerene by an ultrafast laser pulse was studied by semiclassical molecular dynamics simulation. Two different laser pulses were used for this study: one with a duration of 40 fs FWHM (full width at half maximum) and the other with a duration of 500 fs FWHM. Both laser pulses had an energy of 2.0 eV. The simulation was run at different laser intensities for each laser pulse. The simulation results showed that a dominant amount of laser energy deposited to C60 fullerene was distributed into electronic energy. From the simulation we find that the electronic excitation from the occupied molecular orbitals to the unoccupied orbitals is closely related to the photofragmentation of C60 fullerene. By analyzing the fragmentation size distribution, the atomic equivalence index, the temperature, and the absorbed energy (including the electronic energy, the potential energy, and the kinetic energy), we found that non-thermal effects play a significant role in the laser fragmentation of C60 fullerene. By examining the fragmentation features of C60 fullerene with two different laser pulses we found that the laser pulse duration affects the fragmentation process significantly and that laser intensity has little effect on the fragmentation after the absorbed electronic energy becomes saturated.
2011, 27(09): 2079-2087
doi: 10.3866/PKU.WHXB20110911
Abstract:
The geometric structures, stabilities, and electronic properties of InnAsn tubelike clusters at up to n=90 and single-walled InAs nanotubes (InAsNTs) were studied by density functional theory (DFT) calculations. The lowest-energy structures and electronic properties of the small InnAsn (n=1-3) clusters are consistent with those found in earlier studies. A family of stable tubelike structures with In-As alternating arrangement was observed when n≥4 and their structural units (four-membered rings and sixmembered rings) obey the general developing formula. The average binding energies of the clusters show that the tubelike cluster with eight atoms in the cross section is the most stable cluster. The sizedependent properties of the frontier molecular orbital surfaces explain why we can successfully obtain long and stable tubelike clusters. They also illustrate the reason why InAsNTs can be synthesized experimentally. We also found that the single-walled InAsNTs can be prepared by the proper assembly of tubelike clusters to form semiconductors with large bandgap.
The geometric structures, stabilities, and electronic properties of InnAsn tubelike clusters at up to n=90 and single-walled InAs nanotubes (InAsNTs) were studied by density functional theory (DFT) calculations. The lowest-energy structures and electronic properties of the small InnAsn (n=1-3) clusters are consistent with those found in earlier studies. A family of stable tubelike structures with In-As alternating arrangement was observed when n≥4 and their structural units (four-membered rings and sixmembered rings) obey the general developing formula. The average binding energies of the clusters show that the tubelike cluster with eight atoms in the cross section is the most stable cluster. The sizedependent properties of the frontier molecular orbital surfaces explain why we can successfully obtain long and stable tubelike clusters. They also illustrate the reason why InAsNTs can be synthesized experimentally. We also found that the single-walled InAsNTs can be prepared by the proper assembly of tubelike clusters to form semiconductors with large bandgap.
2011, 27(09): 2088-2094
doi: 10.3866/PKU.WHXB20110923
Abstract:
We propose a periodic interaction model for the layered double hydroxides, CuxMg3-xAl-LDHs (x=0-3). Based on density functional theory, the geometries of CuxMg3-xAl-LDHs(x=0-3) were optimized using the CASTEP program. The Jahn-Teller effect and the stability were investigated by analyzing the geometric parameters, electronic arrangement, hydrogen-bonding, charge populations, and binding energies. The results show that the Jahn-Teller effect exists in the unfilled Cu2+ d orbital and also exists in the unfilled Mg2+ p orbital. The two orbitals affect the Jahn-Teller distortion of the metal ions. In CuxMg3-xAl-LDHs(x=0-3), both aluminum and magnesium exist in stabilized octahedral forms. With an increase of Cu2+ in the layer the octahedral of copper changes from a flat configuration to a stable elongated configuration and the Jahn-Teller stabilization energy of the system gradually increases. In general, with an increase of Cu2+ in the layer the distortion caused by the Jahn-Teller effect weakens hydrogen-bonding and the electrostatic interactions between the host layer and the guest. The absolute value of the binding energy decreases and the chemical stability of the system decreases as well. This allows us to theoretically understand the Jahn-Teller effect better for the synthesis of copper-containing LDHs.
We propose a periodic interaction model for the layered double hydroxides, CuxMg3-xAl-LDHs (x=0-3). Based on density functional theory, the geometries of CuxMg3-xAl-LDHs(x=0-3) were optimized using the CASTEP program. The Jahn-Teller effect and the stability were investigated by analyzing the geometric parameters, electronic arrangement, hydrogen-bonding, charge populations, and binding energies. The results show that the Jahn-Teller effect exists in the unfilled Cu2+ d orbital and also exists in the unfilled Mg2+ p orbital. The two orbitals affect the Jahn-Teller distortion of the metal ions. In CuxMg3-xAl-LDHs(x=0-3), both aluminum and magnesium exist in stabilized octahedral forms. With an increase of Cu2+ in the layer the octahedral of copper changes from a flat configuration to a stable elongated configuration and the Jahn-Teller stabilization energy of the system gradually increases. In general, with an increase of Cu2+ in the layer the distortion caused by the Jahn-Teller effect weakens hydrogen-bonding and the electrostatic interactions between the host layer and the guest. The absolute value of the binding energy decreases and the chemical stability of the system decreases as well. This allows us to theoretically understand the Jahn-Teller effect better for the synthesis of copper-containing LDHs.
2011, 27(09): 2095-2100
doi: 10.3866/PKU.WHXB20110906
Abstract:
A new Er3+/Yb3+-codoped fluorphosphate glass was prepared by high temperature melting. Its density, absorption spectra, and fluorescence spectra were measured and investigated. The effect of Er3+ and Yb3+ concentrations on the spectroscopic properties of the glass sample are discussed. A Judd-Ofelt theory analysis on the absorption spectra was performed. The oscillator strengths were Ωt (t=2, 4, 6 ), Ω2= 4.36×10-20 cm2, Ω4=1.35×10-20 cm2, and Ω6=0.79×10-20 cm2. The lifetime (τm) of the 4I13/2 level for the Er3+ ions was 8.26 ms and the full width at half maximum (FWHM) of the main emission peak was 68 nm at 1.53 μm. The large stimulated emission cross-section (σe=8.5×10-21 cm2) of the Er3+ was calculated using McCumber theory. The spectroscopic properties of the Er3+ ion were compared among different glasses. The FWHM and σe of Er3+/Yb3+-codoped fluorphosphate glass were found to be larger than those of other glass hosts, which indicates that this glass may be a potentially useful candidate material host for a high-gain erbium-doped fiber amplifier.
A new Er3+/Yb3+-codoped fluorphosphate glass was prepared by high temperature melting. Its density, absorption spectra, and fluorescence spectra were measured and investigated. The effect of Er3+ and Yb3+ concentrations on the spectroscopic properties of the glass sample are discussed. A Judd-Ofelt theory analysis on the absorption spectra was performed. The oscillator strengths were Ωt (t=2, 4, 6 ), Ω2= 4.36×10-20 cm2, Ω4=1.35×10-20 cm2, and Ω6=0.79×10-20 cm2. The lifetime (τm) of the 4I13/2 level for the Er3+ ions was 8.26 ms and the full width at half maximum (FWHM) of the main emission peak was 68 nm at 1.53 μm. The large stimulated emission cross-section (σe=8.5×10-21 cm2) of the Er3+ was calculated using McCumber theory. The spectroscopic properties of the Er3+ ion were compared among different glasses. The FWHM and σe of Er3+/Yb3+-codoped fluorphosphate glass were found to be larger than those of other glass hosts, which indicates that this glass may be a potentially useful candidate material host for a high-gain erbium-doped fiber amplifier.
First-Principles Investigation of Magnetic Properties of Several Wurtzite Half-Metallic Ferromagnets
2011, 27(09): 2101-2106
doi: 10.3866/PKU.WHXB20110724
Abstract:
By performing first-principles calculations based on the density functional theory we optimized the geometric structures of TmZn15S16 (Tm=V, Cr, Mn) and determined their magnetic properties. TmZn15S16 are typical half-metallic ferromagnets. The supercell magnetic moments of VZn15S16, CrZn15S16, and MnZn15S16 are 3.0099μB, 3.9977μB, and 5.0092μB, respectively, and these arise mainly from the Tm ions. The half-metallicity of CrZn15S16 is more stable than that of VZn15S16 and MnZn15S16. These half-metallic ferromagnets have wide spin gaps. Therefore, high Curie temperatures are possible. The electronic structures of the V, Cr, and Mn ions are eg2↑t2g1↑, eg2↑t2g2↑, and eg2↑t2g3↑, respectively.
By performing first-principles calculations based on the density functional theory we optimized the geometric structures of TmZn15S16 (Tm=V, Cr, Mn) and determined their magnetic properties. TmZn15S16 are typical half-metallic ferromagnets. The supercell magnetic moments of VZn15S16, CrZn15S16, and MnZn15S16 are 3.0099μB, 3.9977μB, and 5.0092μB, respectively, and these arise mainly from the Tm ions. The half-metallicity of CrZn15S16 is more stable than that of VZn15S16 and MnZn15S16. These half-metallic ferromagnets have wide spin gaps. Therefore, high Curie temperatures are possible. The electronic structures of the V, Cr, and Mn ions are eg2↑t2g1↑, eg2↑t2g2↑, and eg2↑t2g3↑, respectively.
2011, 27(09): 2107-2110
doi: 10.3866/PKU.WHXB20110819
Abstract:
We studied the transport properties of corrugated graphene nanoribbons by the recursive Green function method. We show that in the presence of ripples the minigaps with zero conductance and minibands with conductance fluctuations form in the zigzag ribbons among the first Van Hove singularity. For the metal armchair ribbons a conductance gap is present in the vicinity of the Fermi energy, which corresponds to a metal-semiconductor transition. With the fluctuation of ripples intensifying the overall averaged conductance decreases for both the zigzag and armchair ribbons and it tends to be zero. These results are useful for a better understanding of the electronic transport properties of realistic graphene nanoribbons and will be helpful for the design of nanodevices based on graphene.
We studied the transport properties of corrugated graphene nanoribbons by the recursive Green function method. We show that in the presence of ripples the minigaps with zero conductance and minibands with conductance fluctuations form in the zigzag ribbons among the first Van Hove singularity. For the metal armchair ribbons a conductance gap is present in the vicinity of the Fermi energy, which corresponds to a metal-semiconductor transition. With the fluctuation of ripples intensifying the overall averaged conductance decreases for both the zigzag and armchair ribbons and it tends to be zero. These results are useful for a better understanding of the electronic transport properties of realistic graphene nanoribbons and will be helpful for the design of nanodevices based on graphene.
2011, 27(09): 2111-2117
doi: 10.3866/PKU.WHXB20110831
Abstract:
The relationship between the synthetic features and the types of final product is critical for the rational synthesis of zeolite-type open-framework materials. In this paper, an AlPO4-5 prediction system based on C5.0 combined with a feature selection is proposed on the basis of the establishment of a database of AlPO syntheses. 26 synthetic parameters associated with gel composition, an organic amine template and a solvent were used as input to predict the formation of AlPO4-5. The effects of different synthetic parameters on the formation of AlPO4-5 were also studied. The performance of the method was evaluated using classification accuracy and a receiver operating characteristic (ROC) curve. The results show that the highest area under the ROC curve (90%) and the classification accuracy (88.18%) was obtained for the decision tree model that contains eight input features and some useful rules with high confidence degrees were extracted from the model. Among the various synthetic parameters the geometric size of the organic template, particularly the second longest distance of the template plays an important role in the formation of AlPO4-5.
The relationship between the synthetic features and the types of final product is critical for the rational synthesis of zeolite-type open-framework materials. In this paper, an AlPO4-5 prediction system based on C5.0 combined with a feature selection is proposed on the basis of the establishment of a database of AlPO syntheses. 26 synthetic parameters associated with gel composition, an organic amine template and a solvent were used as input to predict the formation of AlPO4-5. The effects of different synthetic parameters on the formation of AlPO4-5 were also studied. The performance of the method was evaluated using classification accuracy and a receiver operating characteristic (ROC) curve. The results show that the highest area under the ROC curve (90%) and the classification accuracy (88.18%) was obtained for the decision tree model that contains eight input features and some useful rules with high confidence degrees were extracted from the model. Among the various synthetic parameters the geometric size of the organic template, particularly the second longest distance of the template plays an important role in the formation of AlPO4-5.
2011, 27(09): 2118-2122
doi: 10.3866/PKU.WHXB20110841
Abstract:
Pure spinel-type lithium titanate, Li4Ti5O12, was successfully fabricated by a facile hydrothermal route using anatase TiO2 and LiOH solution as raw materials. The obtained samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and laser particle size distribution (PSD) analysis. The results showed that a spherical well-crystallized Li4Ti5O12 oxide was obtained at a calcination temperature of 800 °C. The optimal Li4Ti5O12 also has excellent electrochemical performance, which reached 162 mAh·g-1 at a current density of 35 mA· g-1 and a od rate capability with a capacity reached 124 mAh·g-1 even at a current density of 720 mA·g-1.
Pure spinel-type lithium titanate, Li4Ti5O12, was successfully fabricated by a facile hydrothermal route using anatase TiO2 and LiOH solution as raw materials. The obtained samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and laser particle size distribution (PSD) analysis. The results showed that a spherical well-crystallized Li4Ti5O12 oxide was obtained at a calcination temperature of 800 °C. The optimal Li4Ti5O12 also has excellent electrochemical performance, which reached 162 mAh·g-1 at a current density of 35 mA· g-1 and a od rate capability with a capacity reached 124 mAh·g-1 even at a current density of 720 mA·g-1.
2011, 27(09): 2123-2128
doi: 10.3866/PKU.WHXB20110902
Abstract:
Porous LiMnPO4 and LiMnPO4/MWCNT (multi-walled carbon nanotube) composites were prepared using a citric acid assisted sol-gel method. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), nitrogen adsorption-desorption isotherms (BET), and transmission electron microscopy (TEM) were performed to characterize their morphologies and structures. The results indicated that fine-sized, well-crystallized olivine LiMnPO4 was synthesized. The interlaced carbon nanotube networks were intimately embedded and incorporated into the porous LiMnPO4 particle to form highlyconductive three-dimensional (3D) networks. The LiMnPO4 particle and LiMnPO4/MWCNT composite had rich hierarchical pores. A detailed analysis showed that the average pore size was in the mesoporous range and specific surface areas of 73.7 and 69.9 m2·g-1 were obtained, respectively. Compared with the LiMnPO4 particle the LiMnPO4/MWCNT composite exhibited much higher specific capacity. When discharged at a rate of 0.05C and 2C the capacities were 108.8 and 33.2 mAh·g-1, respectively. The MWCNT effectively improved the electronic conductivity of the hybrid materials as shown by electrochemical impedance spectroscopy (EIS). The improved electrochemical performance of the LiMnPO4/MWCNT electrode is attributed to the enhanced electrical conductivity caused by the tighter binding of the carbon nanotubes with the LiMnPO4 primary particles as well as by the interconnected open pores with a high surface area.
Porous LiMnPO4 and LiMnPO4/MWCNT (multi-walled carbon nanotube) composites were prepared using a citric acid assisted sol-gel method. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), nitrogen adsorption-desorption isotherms (BET), and transmission electron microscopy (TEM) were performed to characterize their morphologies and structures. The results indicated that fine-sized, well-crystallized olivine LiMnPO4 was synthesized. The interlaced carbon nanotube networks were intimately embedded and incorporated into the porous LiMnPO4 particle to form highlyconductive three-dimensional (3D) networks. The LiMnPO4 particle and LiMnPO4/MWCNT composite had rich hierarchical pores. A detailed analysis showed that the average pore size was in the mesoporous range and specific surface areas of 73.7 and 69.9 m2·g-1 were obtained, respectively. Compared with the LiMnPO4 particle the LiMnPO4/MWCNT composite exhibited much higher specific capacity. When discharged at a rate of 0.05C and 2C the capacities were 108.8 and 33.2 mAh·g-1, respectively. The MWCNT effectively improved the electronic conductivity of the hybrid materials as shown by electrochemical impedance spectroscopy (EIS). The improved electrochemical performance of the LiMnPO4/MWCNT electrode is attributed to the enhanced electrical conductivity caused by the tighter binding of the carbon nanotubes with the LiMnPO4 primary particles as well as by the interconnected open pores with a high surface area.
2011, 27(09): 2129-2134
doi: 10.3866/PKU.WHXB20110933
Abstract:
A core-shell structure of the carbon-coated natural graphite oxide composite was successfully prepared. Natural graphite was initially oxidized using concentrated sulfuric acid and then carbon coated by the carbonization of phenolic resin at high temperature. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman techniques were used to characterize the morphology and structure of the natural graphite materials before and after oxidation and carbon coating by the pyrolysis of the phenolic resin. The results showed that the surface of the natural graphite particles became smoother and the surface defects were effectively modified after oxidation and carbon coating. The electrochemical test results showed that the electrochemical performance of the natural graphite improved significantly by oxidation with sulfuric acid and by carbon coating. When the covering amount of phenolic resin was 9% the modified natural graphite material gave the best electrochemical performance. Its initial discharge capacity was 434.0 mAh·g-1 and it remained 361.6 mAh· g-1 after 40 charge-discharge cycles. The discharge capacity of the untreated natural graphite was only 332.3 mAh·g-1. The modification approach that improved the capacity of the natural graphite effectively is of great significance for the application of natural graphite in lithium ion batteries.
A core-shell structure of the carbon-coated natural graphite oxide composite was successfully prepared. Natural graphite was initially oxidized using concentrated sulfuric acid and then carbon coated by the carbonization of phenolic resin at high temperature. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman techniques were used to characterize the morphology and structure of the natural graphite materials before and after oxidation and carbon coating by the pyrolysis of the phenolic resin. The results showed that the surface of the natural graphite particles became smoother and the surface defects were effectively modified after oxidation and carbon coating. The electrochemical test results showed that the electrochemical performance of the natural graphite improved significantly by oxidation with sulfuric acid and by carbon coating. When the covering amount of phenolic resin was 9% the modified natural graphite material gave the best electrochemical performance. Its initial discharge capacity was 434.0 mAh·g-1 and it remained 361.6 mAh· g-1 after 40 charge-discharge cycles. The discharge capacity of the untreated natural graphite was only 332.3 mAh·g-1. The modification approach that improved the capacity of the natural graphite effectively is of great significance for the application of natural graphite in lithium ion batteries.
2011, 27(09): 2135-2140
doi: 10.3866/PKU.WHXB20110935
Abstract:
According to established routes for the microporous metallization of printed circuit boards (PCB), electroless copper plating using glyoxylic acid as a reducing agent and copper electroplating in a citrate bath were used for microporous metallization with PCB distributing micropores as a template. The results show that electroless copper plating using glyoxylic acid as a reducing agent and copper electroplating in a citrate bath can be successfully applied to the microporous metallization of PCB. After an electric conducting treatment of the micropores by electroless copper plating the copper deposited as fine grains and attached to the inner walls of the micropores. The copper deposit was also found in the loose grain arrangement and the leak plating area. Immediately after thickening treatment by copper electroplating, the resistance toward the copper coating of the inner wall decreased notably. The ratio of the copper electroplating rates at the inner and outer micropores was found to be 0.8:1.0. The copper electrodeposit fully covered the surface of the inner wall including the leak plating area, which means that the electroplated copper grains have a certain sideway growing ability. The copper coating on the inner wall was continuous, compact, and adhesive. This coating highly enhanced the conductivity of the interconnected PCB.
According to established routes for the microporous metallization of printed circuit boards (PCB), electroless copper plating using glyoxylic acid as a reducing agent and copper electroplating in a citrate bath were used for microporous metallization with PCB distributing micropores as a template. The results show that electroless copper plating using glyoxylic acid as a reducing agent and copper electroplating in a citrate bath can be successfully applied to the microporous metallization of PCB. After an electric conducting treatment of the micropores by electroless copper plating the copper deposited as fine grains and attached to the inner walls of the micropores. The copper deposit was also found in the loose grain arrangement and the leak plating area. Immediately after thickening treatment by copper electroplating, the resistance toward the copper coating of the inner wall decreased notably. The ratio of the copper electroplating rates at the inner and outer micropores was found to be 0.8:1.0. The copper electrodeposit fully covered the surface of the inner wall including the leak plating area, which means that the electroplated copper grains have a certain sideway growing ability. The copper coating on the inner wall was continuous, compact, and adhesive. This coating highly enhanced the conductivity of the interconnected PCB.
2011, 27(09): 2141-2147
doi: 10.3866/PKU.WHXB20110809
Abstract:
Pt-Fe/C catalyst for proton exchange membrane fuel cell (PEMFC) was prepared by a pulse-microwave assisted chemical reduction heat-treatment synthesis method. The elemental content was tested by inductively coupled plasma (ICP). The microstructure and morphology of the as-prepared catalyst were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The electrocatalytic performance was measured by cyclic voltammetry (CV). The results indicate that pulse-microwave assisted chemical reduction heat-treatment synthesis is an efficient method for preparing PEMFC catalysts while the temperature and time of heat treatment greatly affect the size and activity of the Pt-Fe nanoparticles. For a heating temperature of 500 °C and a time of 3 h the Pt-Fe nanoparticles were uniform in size. Moreover, the Pt-Fe/C-500-3h alloy catalyst was highly dispersed on the surface of the carbon support and the TEM and XRD showed that the average Pt-Fe nanoparticle size was 1.8 nm. The electrochemical measurements show that the electrochemical surface area (ESA) of the catalyst was 55.14 m2·g-1.
Pt-Fe/C catalyst for proton exchange membrane fuel cell (PEMFC) was prepared by a pulse-microwave assisted chemical reduction heat-treatment synthesis method. The elemental content was tested by inductively coupled plasma (ICP). The microstructure and morphology of the as-prepared catalyst were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The electrocatalytic performance was measured by cyclic voltammetry (CV). The results indicate that pulse-microwave assisted chemical reduction heat-treatment synthesis is an efficient method for preparing PEMFC catalysts while the temperature and time of heat treatment greatly affect the size and activity of the Pt-Fe nanoparticles. For a heating temperature of 500 °C and a time of 3 h the Pt-Fe nanoparticles were uniform in size. Moreover, the Pt-Fe/C-500-3h alloy catalyst was highly dispersed on the surface of the carbon support and the TEM and XRD showed that the average Pt-Fe nanoparticle size was 1.8 nm. The electrochemical measurements show that the electrochemical surface area (ESA) of the catalyst was 55.14 m2·g-1.
2011, 27(09): 2148-2152
doi: 10.3866/PKU.WHXB20110909
Abstract:
N,N-dimethylformamide (DMF) and tetrabutyl ammonium perchlorate (TBAP) were used as a solvent and a supporting electrolyte, respectively. The working electrode was a platinum microelectrode, the auxiliary electrode was a large area platinum wire and the reference electrode was a saturated calomel electrode. The electrochemical behavior of nitroaromatics (NA) was studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The effects of scan rate, numbers of benzene rings and nitro groups on the electrochemical reduction of NA were investigated systematically. The results showed that the reaction of NA on the Pt microelectrode was a quasi-reversible process controlled by the diffusion of NA. We found that NA was more electrochemically reducible when it contained more nitro groups and the reduction peak current of the nitro group decreased in the presence of more benzene rings.
N,N-dimethylformamide (DMF) and tetrabutyl ammonium perchlorate (TBAP) were used as a solvent and a supporting electrolyte, respectively. The working electrode was a platinum microelectrode, the auxiliary electrode was a large area platinum wire and the reference electrode was a saturated calomel electrode. The electrochemical behavior of nitroaromatics (NA) was studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The effects of scan rate, numbers of benzene rings and nitro groups on the electrochemical reduction of NA were investigated systematically. The results showed that the reaction of NA on the Pt microelectrode was a quasi-reversible process controlled by the diffusion of NA. We found that NA was more electrochemically reducible when it contained more nitro groups and the reduction peak current of the nitro group decreased in the presence of more benzene rings.
2011, 27(09): 2153-2159
doi: 10.3866/PKU.WHXB20110910
Abstract:
The kinetics and mechanism of the photoelectrocatalytic degradation of glucose with weak adsorption and potassium hydrogen phthalate with strong adsorption on a self-organized and highly ordered TiO2 nanotube array (TNA) were investigated using a thin layer reactor in which the organic compounds were completely and quickly oxidized. The photogenerated current-time (I-t) profiles were used to analyze the microprocesses of the photoelectrochemical catalytic degradation on the TNA electrode. For glucose the I-t curve increased sharply initially and then decreased rapidly followed by a slow decrease. This is due to the weak adsorbability of glucose and it adsorbed slowly onto the surface of the TNA electrode from the bulk solution. However, the I-t curve for potassium hydrogen phthalate had quite a different trend as it increased sharply initially and then continued to increase and then decreased slowly and this was due to the strong adsorbability and mass existence of potassium hydrogen phthalate on the electrode and, in addition, the low degradability of phthalic acid. The adsorption properties and adsorption coefficient of the organic compounds and the reaction mechanism were also analyzed. We conclude that the obtained photoelectrocatalytic oxidation rate of the organic compounds in the thin-layer cell assisted in determining the surface reaction process and the micro-mechanism of organic compound degradation on the TNA electrode.
The kinetics and mechanism of the photoelectrocatalytic degradation of glucose with weak adsorption and potassium hydrogen phthalate with strong adsorption on a self-organized and highly ordered TiO2 nanotube array (TNA) were investigated using a thin layer reactor in which the organic compounds were completely and quickly oxidized. The photogenerated current-time (I-t) profiles were used to analyze the microprocesses of the photoelectrochemical catalytic degradation on the TNA electrode. For glucose the I-t curve increased sharply initially and then decreased rapidly followed by a slow decrease. This is due to the weak adsorbability of glucose and it adsorbed slowly onto the surface of the TNA electrode from the bulk solution. However, the I-t curve for potassium hydrogen phthalate had quite a different trend as it increased sharply initially and then continued to increase and then decreased slowly and this was due to the strong adsorbability and mass existence of potassium hydrogen phthalate on the electrode and, in addition, the low degradability of phthalic acid. The adsorption properties and adsorption coefficient of the organic compounds and the reaction mechanism were also analyzed. We conclude that the obtained photoelectrocatalytic oxidation rate of the organic compounds in the thin-layer cell assisted in determining the surface reaction process and the micro-mechanism of organic compound degradation on the TNA electrode.
2011, 27(09): 2160-2166
doi: 10.3866/PKU.WHXB20110913
Abstract:
A BiVO4 film electrode was prepared using a home-made BiVO4 nanopowder and the effects of annealing temperature and film thickness on its photoelectrochemical behavior, electron transport and recombination in the BiVO4 electrode were systematically studied by electrochemical techniques. Experimental results indicate that the annealing temperature and film thickness can significantly influence the photoelectrochemical characteristics of the BiVO4 electrode. At low annealing temperature (≤500 °C) the photoelectrochemical activity improved upon increasing the temperature and the optimal activity was obtained for the electrode annealed at 500 ° C. At high temperature (>500 ° C) the photoelectrochemical activity decreased because of a marked increase of bulk traps in the electrode. The BiVO4 electrode showed od photon-to-electron conversion efficiency under visible light and its bandgap was found to be 2.36 eV based on an incident monochromatic photon-to-electric conversion efficiency curve. The flat-band potential (Efb) of BiVO4 was determined to be -0.7 V (vs Ag/AgCl) by the Mött Schottky method. These results give an important reference for the optimization of the BiVO4 photocatalytic system.
A BiVO4 film electrode was prepared using a home-made BiVO4 nanopowder and the effects of annealing temperature and film thickness on its photoelectrochemical behavior, electron transport and recombination in the BiVO4 electrode were systematically studied by electrochemical techniques. Experimental results indicate that the annealing temperature and film thickness can significantly influence the photoelectrochemical characteristics of the BiVO4 electrode. At low annealing temperature (≤500 °C) the photoelectrochemical activity improved upon increasing the temperature and the optimal activity was obtained for the electrode annealed at 500 ° C. At high temperature (>500 ° C) the photoelectrochemical activity decreased because of a marked increase of bulk traps in the electrode. The BiVO4 electrode showed od photon-to-electron conversion efficiency under visible light and its bandgap was found to be 2.36 eV based on an incident monochromatic photon-to-electric conversion efficiency curve. The flat-band potential (Efb) of BiVO4 was determined to be -0.7 V (vs Ag/AgCl) by the Mött Schottky method. These results give an important reference for the optimization of the BiVO4 photocatalytic system.
2011, 27(09): 2167-2172
doi: 10.3866/PKU.WHXB20110833
Abstract:
Elastic vesicles of glycyrrhetic acid (GA) with lysine in the aqueous phase were prepared by the film-high pressure homogenization method. The influence of lysine on the formation of GA elastic vesicles was evaluated in this work. The lysine salt of GA was synthesized and entrapped in elastic vesicles as a control formulation. The particle size, zeta-potential, entrapment efficiency, phase transformation temperature, deformability of the elastic vesicles, and the permeation of GA through rat skin were investigated. By the incorporation of lysine into elastic vesicles the particle size decreased slightly and the phase transformation temperature decreased while the entrapment efficiency and deformability of the elastic vesicles increased obviously. The drug loading reached 1.5 mg·mL-1, which was 30 times higher than that of GA elastic vesicles without lysine. The drug loading and deformability of the elastic vesicles was remarkably higher than that obtained using the lysine salt. In addition, the cumulative amount of GA permeation through rat skin within 8 h and the residual amount in the skin were found to be 4.3 times and 9.2 times higher than that of the vesicles without lysine, which was higher than that of the elastic vesicles with the lysine salt of GA. These results indicate that lysine forms an ion associate with GA, which takes part in the formation of vesicle membranes and subsequently increases the membrane's fluidity. Such a high drug loading capability is a result of the synergistic effect between lysine and the elastic vesicles.
Elastic vesicles of glycyrrhetic acid (GA) with lysine in the aqueous phase were prepared by the film-high pressure homogenization method. The influence of lysine on the formation of GA elastic vesicles was evaluated in this work. The lysine salt of GA was synthesized and entrapped in elastic vesicles as a control formulation. The particle size, zeta-potential, entrapment efficiency, phase transformation temperature, deformability of the elastic vesicles, and the permeation of GA through rat skin were investigated. By the incorporation of lysine into elastic vesicles the particle size decreased slightly and the phase transformation temperature decreased while the entrapment efficiency and deformability of the elastic vesicles increased obviously. The drug loading reached 1.5 mg·mL-1, which was 30 times higher than that of GA elastic vesicles without lysine. The drug loading and deformability of the elastic vesicles was remarkably higher than that obtained using the lysine salt. In addition, the cumulative amount of GA permeation through rat skin within 8 h and the residual amount in the skin were found to be 4.3 times and 9.2 times higher than that of the vesicles without lysine, which was higher than that of the elastic vesicles with the lysine salt of GA. These results indicate that lysine forms an ion associate with GA, which takes part in the formation of vesicle membranes and subsequently increases the membrane's fluidity. Such a high drug loading capability is a result of the synergistic effect between lysine and the elastic vesicles.
2011, 27(09): 2173-2177
doi: 10.3866/PKU.WHXB20110907
Abstract:
Using a nonionic surfactant detergent polyoxyethylene 20 cetyl ether (Brij58) as a template, poly(N-isopropylacrylamide)/Brij58/clay nanocomposite hydrogels (PLH) with a template structure were prepared by free radical polymerization. By comparison with traditional nanocomposite hydrogels the mechanical properties and the hydrophilicity of the PLH hydrogels improved significantly. The result of field-emission scanning electron microscopy (FESEM) showed that the introduction of Brij58 increased the number of pore structures and the interpenetration of the pores. Furthermore, the pore structure was well-defined and connected through many smaller pores. The results of tensile stress-strain, storage modulus，and swelling kinetics showed that the strength, the load，and the elongation at the break increased initially and then decreased with an increase in the Brij58 content, while the storage modulus and the maximum degree of swelling increased with an increase in the Brij58 content. In addition, the obtained surface contact angle showed that because of the effect of the Brij58 template and the adsorption between Brij58 and the clay the surface contact angles of the PLH hydrogels increased initially and then decreased.
Using a nonionic surfactant detergent polyoxyethylene 20 cetyl ether (Brij58) as a template, poly(N-isopropylacrylamide)/Brij58/clay nanocomposite hydrogels (PLH) with a template structure were prepared by free radical polymerization. By comparison with traditional nanocomposite hydrogels the mechanical properties and the hydrophilicity of the PLH hydrogels improved significantly. The result of field-emission scanning electron microscopy (FESEM) showed that the introduction of Brij58 increased the number of pore structures and the interpenetration of the pores. Furthermore, the pore structure was well-defined and connected through many smaller pores. The results of tensile stress-strain, storage modulus，and swelling kinetics showed that the strength, the load，and the elongation at the break increased initially and then decreased with an increase in the Brij58 content, while the storage modulus and the maximum degree of swelling increased with an increase in the Brij58 content. In addition, the obtained surface contact angle showed that because of the effect of the Brij58 template and the adsorption between Brij58 and the clay the surface contact angles of the PLH hydrogels increased initially and then decreased.
2011, 27(09): 2178-2184
doi: 10.3866/PKU.WHXB20110904
Abstract:
CdS/graphene composite photocatalysts were prepared by photocatalytically reducing graphene oxide with CdS nanoparticles in an aqueous ethanol solution. The structure and photoelectrical properties of the resulted materials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and transient photocurrent measurements. The photocatalytic activities of the CdS/graphene composites for hydrogen evolution were evaluated under visible light irradiation (λ≥420 nm). The results show that the graphene oxide can be efficiently reduced by the photogenerated electrons of CdS and thus CdS/graphene composite is formed and it shows strong interactions between CdS and graphene. Compared with CdS, the enhanced photocurrent generation and photocatalytic activity toward hydrogen evolution for the CdS/ graphene composite photocatalysts could be attributed to the ability of graphene to capture and transport electrons, and to promote charge separation.
CdS/graphene composite photocatalysts were prepared by photocatalytically reducing graphene oxide with CdS nanoparticles in an aqueous ethanol solution. The structure and photoelectrical properties of the resulted materials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and transient photocurrent measurements. The photocatalytic activities of the CdS/graphene composites for hydrogen evolution were evaluated under visible light irradiation (λ≥420 nm). The results show that the graphene oxide can be efficiently reduced by the photogenerated electrons of CdS and thus CdS/graphene composite is formed and it shows strong interactions between CdS and graphene. Compared with CdS, the enhanced photocurrent generation and photocatalytic activity toward hydrogen evolution for the CdS/ graphene composite photocatalysts could be attributed to the ability of graphene to capture and transport electrons, and to promote charge separation.
2011, 27(09): 2185-2190
doi: 10.3866/PKU.WHXB20110824
Abstract:
Pd promoted ZnO/Al2O3 catalysts were prepared by impregnation method. The hydrogen production performance upon the steam reforming of ethanol (SRE) over the prepared catalysts was evaluated with n(H2O):n(C2H5OH) of 3:1 at 450 °C and atmospheric pressure. The results show that H2 and CH3CHO were the main products during the SRE reaction over the prepared catalysts. Different from the ZnO/Al2O3 catalysts, the Pd promoted ZnO/Al2O3 catalysts favored C－C scission during the SRE and thus a higher C2H5OH conversion of 65% and a H2 selectivity of 55% were obtained over the prepared Pd promoted catalysts. BET, transmission electron microscopy (TEM), and thermogravimetry-differential scanning calorimetry-mass spectrometry (TG-DSC-MS) coupling techniques were used to analyze the coking behavior on the catalyst surface. We found that Pd promotion does not prevent the formation of coke on the ZnO/Al2O3 catalysts.
Pd promoted ZnO/Al2O3 catalysts were prepared by impregnation method. The hydrogen production performance upon the steam reforming of ethanol (SRE) over the prepared catalysts was evaluated with n(H2O):n(C2H5OH) of 3:1 at 450 °C and atmospheric pressure. The results show that H2 and CH3CHO were the main products during the SRE reaction over the prepared catalysts. Different from the ZnO/Al2O3 catalysts, the Pd promoted ZnO/Al2O3 catalysts favored C－C scission during the SRE and thus a higher C2H5OH conversion of 65% and a H2 selectivity of 55% were obtained over the prepared Pd promoted catalysts. BET, transmission electron microscopy (TEM), and thermogravimetry-differential scanning calorimetry-mass spectrometry (TG-DSC-MS) coupling techniques were used to analyze the coking behavior on the catalyst surface. We found that Pd promotion does not prevent the formation of coke on the ZnO/Al2O3 catalysts.
2011, 27(09): 2191-2199
doi: 10.3866/PKU.WHXB20110924
Abstract:
Using commercially available activated carbon (AC) as a carrier, photocatalysts of activated carbon-supported TiO2 (TiO2/AC) with different specific surface areas and TiO2 loading contents were prepared by the sol-gel method. Nitrogen adsorption, X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to obtain the performance parameters of the TiO2/AC catalysts. The photocatalytic performance of the TiO2/AC catalysts was studied by using gaseous 1,2-dichlorobenzene. The influence of catalyst dose, specific surface area, and gaseous 1,2-dichlorobenzene concentration on this photodegradation was investigated. The results show that a nano-TiO2 deposit was formed with a particle size of approximately 10 nm. The loading of TiO2 onto the AC with a large specific surface area enhanced the photocatalytic activity of TiO2 photocatalysis with regard to the degradation of gaseous 1,2- dichlorobenzene. We show that TiO2/AC catalysts have a synergetic effect on AC adsorption and TiO2 photocatalysis during the degradation of gaseous 1,2-dichlorobenzene by comparing the photocatalytic performance of a commercial P25 catalyst and TiO2/AC catalysts.
Using commercially available activated carbon (AC) as a carrier, photocatalysts of activated carbon-supported TiO2 (TiO2/AC) with different specific surface areas and TiO2 loading contents were prepared by the sol-gel method. Nitrogen adsorption, X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to obtain the performance parameters of the TiO2/AC catalysts. The photocatalytic performance of the TiO2/AC catalysts was studied by using gaseous 1,2-dichlorobenzene. The influence of catalyst dose, specific surface area, and gaseous 1,2-dichlorobenzene concentration on this photodegradation was investigated. The results show that a nano-TiO2 deposit was formed with a particle size of approximately 10 nm. The loading of TiO2 onto the AC with a large specific surface area enhanced the photocatalytic activity of TiO2 photocatalysis with regard to the degradation of gaseous 1,2- dichlorobenzene. We show that TiO2/AC catalysts have a synergetic effect on AC adsorption and TiO2 photocatalysis during the degradation of gaseous 1,2-dichlorobenzene by comparing the photocatalytic performance of a commercial P25 catalyst and TiO2/AC catalysts.
2011, 27(09): 2200-2208
doi: 10.3866/PKU.WHXB20110927
Abstract:
We developed a H2 and C1-C4 heterogeneous mechanism to describe their catalytic reaction on a platinum catalyst. To verify the mechanism we carried out simulations with methane, ethane, propane, and n-butane and compared the results to the reported experimental data. The ignition and combustion (ignition or combustion of CH4, C2H6 with or without adding H2, C3H8 with or without adding H2, C4H10 with adding H2) was of interest. od agreement was obtained and we found that H2 improved the ignition of propane and n-butane, and the combustion of ethane. However, their kinetic processes are different. Therefore, the H2 and C1-C4 heterogeneous mechanism determined in this work is reasonable with some certainty and could be used to describe the characteristics of ignition and combustion, which can be used to analyze the kinetic process.
We developed a H2 and C1-C4 heterogeneous mechanism to describe their catalytic reaction on a platinum catalyst. To verify the mechanism we carried out simulations with methane, ethane, propane, and n-butane and compared the results to the reported experimental data. The ignition and combustion (ignition or combustion of CH4, C2H6 with or without adding H2, C3H8 with or without adding H2, C4H10 with adding H2) was of interest. od agreement was obtained and we found that H2 improved the ignition of propane and n-butane, and the combustion of ethane. However, their kinetic processes are different. Therefore, the H2 and C1-C4 heterogeneous mechanism determined in this work is reasonable with some certainty and could be used to describe the characteristics of ignition and combustion, which can be used to analyze the kinetic process.
2011, 27(09): 2209-2216
doi: 10.3866/PKU.WHXB20110806
Abstract:
X-ray diffraction (XRD), nitrogen adsorption-desorption, ammonia-temperature programmed desorption (NH3-TPD), and pyridine-Fourier transform infrared (pyridine-FT-IR) spectroscopy analyses were performed to characterize V2O5/Al2Ox with different V2O5 loadings. We conclude that a 20%-25% (w) V2O5 loading corresponds to the monolayer coverage of VOx units over the surface of V2O5/Al2O3 according to the VOx unit surface density values. The impregnation of V2O5 led to a decrease in the Lewis acidity of the alumina and the formation of Brønsted acid sites, which resulted from the V―OH groups of the oxidized VOx units. With an increase in V2O5 loading the amount of Brønsted acid sites increased and reached a maximum at a V2O5 loading of about 20%. The influence of V2O5 loading in V2O5/Al2O3 on the oxidative activation performance during n-heptane catalytic cracking was studied. The results show that the highest promotion was obtained upon introducing V2O5/Al2O3 with a 20%-25% V2O5 loading into the HZSM-5 equilibrium catalyst. V2O5/Al2O3 (20%-25% V2O5) had a monolayer coverage of VOx units over its surface and it provided the largest amount of surface lattice oxygen and thus the strongest oxidative activation toward n-heptane was achieved. The performance decreased when the V2O5 loading increased further because of the inhibited participation of surface lattice oxygen in the reaction, which was caused by the formation of bulk V2O5 and AlVO4.
X-ray diffraction (XRD), nitrogen adsorption-desorption, ammonia-temperature programmed desorption (NH3-TPD), and pyridine-Fourier transform infrared (pyridine-FT-IR) spectroscopy analyses were performed to characterize V2O5/Al2Ox with different V2O5 loadings. We conclude that a 20%-25% (w) V2O5 loading corresponds to the monolayer coverage of VOx units over the surface of V2O5/Al2O3 according to the VOx unit surface density values. The impregnation of V2O5 led to a decrease in the Lewis acidity of the alumina and the formation of Brønsted acid sites, which resulted from the V―OH groups of the oxidized VOx units. With an increase in V2O5 loading the amount of Brønsted acid sites increased and reached a maximum at a V2O5 loading of about 20%. The influence of V2O5 loading in V2O5/Al2O3 on the oxidative activation performance during n-heptane catalytic cracking was studied. The results show that the highest promotion was obtained upon introducing V2O5/Al2O3 with a 20%-25% V2O5 loading into the HZSM-5 equilibrium catalyst. V2O5/Al2O3 (20%-25% V2O5) had a monolayer coverage of VOx units over its surface and it provided the largest amount of surface lattice oxygen and thus the strongest oxidative activation toward n-heptane was achieved. The performance decreased when the V2O5 loading increased further because of the inhibited participation of surface lattice oxygen in the reaction, which was caused by the formation of bulk V2O5 and AlVO4.
2011, 27(09): 2217-2221
doi: 10.3866/PKU.WHXB20110915
Abstract:
Surfactin, one of the most surface-active microbial lipopeptides, can readily form an insoluble monolayer at the air/water interface. Consecutive compression-expansion cycles of surfactin with a β-hydroxyl fatty acid chain consisting of 14 carbon atoms were studied by a Langmuir film balance. A larger hysteresis loop was observed when the compression isotherm reached a plateau compared with that expanded at a lower surface pressure (20 mN·m-1). The 2nd cycle was shifted towards smaller molecular areas compared with the 1st cycle. We also studied the hysteresis cycles of the surfactin monolayer on subphase of different pH values. With a decrease in the subphase pH the hysteresis loop became smaller and the expansion isotherm curve underwent a longer pseudo plateau. Furthermore, the morphologies of the surfactin monolayers in the plateau region, which were transferred onto a mica surface, were characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Both AFM and SEM images gave three-dimensional surface aggregates with heights ranging from tens to hundreds of nanometers. The above results suggest that the formation of three-dimensional surface aggregates at the plateau region induces a large hysteresis loop in the surfactin monolayer, which can also be attributed to the submergence of molecules into the subphase when the peptide loop in the surfactin molecule is ionized.
Surfactin, one of the most surface-active microbial lipopeptides, can readily form an insoluble monolayer at the air/water interface. Consecutive compression-expansion cycles of surfactin with a β-hydroxyl fatty acid chain consisting of 14 carbon atoms were studied by a Langmuir film balance. A larger hysteresis loop was observed when the compression isotherm reached a plateau compared with that expanded at a lower surface pressure (20 mN·m-1). The 2nd cycle was shifted towards smaller molecular areas compared with the 1st cycle. We also studied the hysteresis cycles of the surfactin monolayer on subphase of different pH values. With a decrease in the subphase pH the hysteresis loop became smaller and the expansion isotherm curve underwent a longer pseudo plateau. Furthermore, the morphologies of the surfactin monolayers in the plateau region, which were transferred onto a mica surface, were characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Both AFM and SEM images gave three-dimensional surface aggregates with heights ranging from tens to hundreds of nanometers. The above results suggest that the formation of three-dimensional surface aggregates at the plateau region induces a large hysteresis loop in the surfactin monolayer, which can also be attributed to the submergence of molecules into the subphase when the peptide loop in the surfactin molecule is ionized.
2011, 27(09): 2222-2226
doi: 10.3866/PKU.WHXB20110918
Abstract:
The adsorption of Se(IV) onto crushed Beishan granite (BS03, 600 m) was studied by a batch experimental method. The results showed that the distribution coefficient (Kd) remained almost constant in the pH range of 3-7 and decreased at pH>7. The adsorption of Se(IV) did not vary with ionic strength. The presence of Ca2+ (4.10×10-3 mol·L-1) and SO42- (3.17×10-3 mol·L-1) had no effect on Se(IV) adsorption. Moreover, we found that the adsorption of Se(IV) (1.46×10-5 mol·L-1) and Eu(III) (3.33×10-6 mol·L-1) on Beishan granite had no effect on each other in the ternary adsorption system consisting of Se(IV)/Eu(III)/ granite. The adsorption of Se(IV) onto Beishan granite was quantitatively interpreted by considering the two surface complexation reactions of HseO3- to form ≡SHSeO3 and ≡SSeO3- on the ≡SOH general adsorption sites.
The adsorption of Se(IV) onto crushed Beishan granite (BS03, 600 m) was studied by a batch experimental method. The results showed that the distribution coefficient (Kd) remained almost constant in the pH range of 3-7 and decreased at pH>7. The adsorption of Se(IV) did not vary with ionic strength. The presence of Ca2+ (4.10×10-3 mol·L-1) and SO42- (3.17×10-3 mol·L-1) had no effect on Se(IV) adsorption. Moreover, we found that the adsorption of Se(IV) (1.46×10-5 mol·L-1) and Eu(III) (3.33×10-6 mol·L-1) on Beishan granite had no effect on each other in the ternary adsorption system consisting of Se(IV)/Eu(III)/ granite. The adsorption of Se(IV) onto Beishan granite was quantitatively interpreted by considering the two surface complexation reactions of HseO3- to form ≡SHSeO3 and ≡SSeO3- on the ≡SOH general adsorption sites.
2011, 27(09): 2227-2232
doi: 10.3866/PKU.WHXB20110916
Abstract:
Finite length SiO2 nanotubes composed of a three-membered ring (3MR) cross section were investigated by density functional theory. Nuclear magnetic resonance (NMR) results reveal that the isotropic chemical shielding tensor (σiso) and anisotropic chemical shielding tensor (Δσ) of the SiO2 nanotubes oscillate from the terminal end to the intermediate part of the structures with an increase in nanotube lengths, and they tend to reach different stable values. When the length is greater than certain value the σiso and Δσ values obtained from the intermediate part of the finite length nanotube can be used for theoretical predictions of long or infinite length nanotubes. Hence, this investigation is a guide for the selection of reasonable finite length nanotubes to model infinite length nanotubes.
Finite length SiO2 nanotubes composed of a three-membered ring (3MR) cross section were investigated by density functional theory. Nuclear magnetic resonance (NMR) results reveal that the isotropic chemical shielding tensor (σiso) and anisotropic chemical shielding tensor (Δσ) of the SiO2 nanotubes oscillate from the terminal end to the intermediate part of the structures with an increase in nanotube lengths, and they tend to reach different stable values. When the length is greater than certain value the σiso and Δσ values obtained from the intermediate part of the finite length nanotube can be used for theoretical predictions of long or infinite length nanotubes. Hence, this investigation is a guide for the selection of reasonable finite length nanotubes to model infinite length nanotubes.
2011, 27(09): 2233-2238
doi: 10.3866/PKU.WHXB20110820
Abstract:
Silicon (Si)-based materials with a super-hydrophobic surface were prepared using microscale rough surfaces, which were subsequently modified by organic compounds with low surface energies. However, the super-hydrophobicity was gradually lost because of the degradation of the organic compounds when applied to an outer environment. Herein, a Si-based film with a super-hydrophobic surface fabricated by chemical vapor deposition (CVD) using a liquid metal (tin) as the growth substrate is reported. We found that the film was composed of vertical Si/SiO2 hierarchical wires upon characterization by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Reasons for the generation of this super-hydrophobicity are given using the Cassie model. We conclude that the special Si/SiO2 hierarchical structure plays an important role in the super-hydrophobic performance of the film. Compared with the previous Si-based material with a super-hydrophobic surface, this novel structure promises to widen its area of application since its super-hydrophobicity is independent of chemical modification.
Silicon (Si)-based materials with a super-hydrophobic surface were prepared using microscale rough surfaces, which were subsequently modified by organic compounds with low surface energies. However, the super-hydrophobicity was gradually lost because of the degradation of the organic compounds when applied to an outer environment. Herein, a Si-based film with a super-hydrophobic surface fabricated by chemical vapor deposition (CVD) using a liquid metal (tin) as the growth substrate is reported. We found that the film was composed of vertical Si/SiO2 hierarchical wires upon characterization by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Reasons for the generation of this super-hydrophobicity are given using the Cassie model. We conclude that the special Si/SiO2 hierarchical structure plays an important role in the super-hydrophobic performance of the film. Compared with the previous Si-based material with a super-hydrophobic surface, this novel structure promises to widen its area of application since its super-hydrophobicity is independent of chemical modification.
2011, 27(09): 2239-2243
doi: 10.3866/PKU.WHXB20110834
Abstract:
Ordered mesoporous carbon with hexa nal arrays consisting of tubular-type pores (CMK-5) was synthesized via a nanocasting process by the direct use of SBA-15 as a template, furfuryl alcohol as a carbon source and oxalic acid as the catalyst. The structure of CMK-5 was analyzed by different techniques including scanning electron microscopy, powder X-ray diffraction and N2 adsorption analysis. The specific surface area and pore volume were found to be 1856 m2·g-1 and 2.10 cm3·g-1, respectively, with mesopore sizes concentrated at 3.1 and 5.5 nm. Because of the unique structure the adsorption capacities of CMK-5 towards vitamin B12 was found to be as high as 943 mg·g-1 in a short period of 120 min, which is significantly higher than that of commercial activated carbon. The composites of CMK-5 and vitamin B12 without any treatment gave slow-release performance in a simulated body fluid. The concentration of the release solutions remained 9 mg·L-1 under dynamic conditions. A high loading capacity and slow release rate of vitamin B12 on the CMK-5 support suggested that CMK-5 might have a potential application in drug delivery.
Ordered mesoporous carbon with hexa nal arrays consisting of tubular-type pores (CMK-5) was synthesized via a nanocasting process by the direct use of SBA-15 as a template, furfuryl alcohol as a carbon source and oxalic acid as the catalyst. The structure of CMK-5 was analyzed by different techniques including scanning electron microscopy, powder X-ray diffraction and N2 adsorption analysis. The specific surface area and pore volume were found to be 1856 m2·g-1 and 2.10 cm3·g-1, respectively, with mesopore sizes concentrated at 3.1 and 5.5 nm. Because of the unique structure the adsorption capacities of CMK-5 towards vitamin B12 was found to be as high as 943 mg·g-1 in a short period of 120 min, which is significantly higher than that of commercial activated carbon. The composites of CMK-5 and vitamin B12 without any treatment gave slow-release performance in a simulated body fluid. The concentration of the release solutions remained 9 mg·L-1 under dynamic conditions. A high loading capacity and slow release rate of vitamin B12 on the CMK-5 support suggested that CMK-5 might have a potential application in drug delivery.
Superior Graphene for Hydrogen Adsorption Prepared by the Improved Liquid Oxidation-Reduction Method
2011, 27(09): 2244-2250
doi: 10.3866/PKU.WHXB20110838
Abstract:
Graphite oxide ( ) was prepared from liquid oxidation based on Hummers method and the graphene was then prepared using sodium borohydride to reduce the exfoliated graphite oxide by ultrasonication during which moderate sodium dodecyl benzene sulfonate (SDBS) was added into the suspension to reduce the agglomeration among the graphene layers and to obtain a stable graphene suspension. The as-prepared graphene was characterized by X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). XRD results show that the crystal structures are different among graphite, graphite oxide, and graphene. SEM and TEM images show that graphene possesses a gridding structure, a smooth surface, and few defects. AFM analysis indicates that the thickness of the single layer graphene is about 1.3 nm while there are still a few double layers in the sample. The BET specific surface area of the graphene was about 1206 m2·g-1 and its H2 adsorption properties were investigated under high pressure. The samples prepared by liquid oxidation-reduction were compared with that prepared by the improved liquid oxidation-reduction method, which indicates that the addition of SDBS effectively reduces agglomeration among the graphene layers and this generates high quality graphene. The adsorption capacities of H2 on graphene at 25 and 55 °C reached 1.7%(w) and 1.1%(w), respectively, which are much higher than that reported previously.
Graphite oxide ( ) was prepared from liquid oxidation based on Hummers method and the graphene was then prepared using sodium borohydride to reduce the exfoliated graphite oxide by ultrasonication during which moderate sodium dodecyl benzene sulfonate (SDBS) was added into the suspension to reduce the agglomeration among the graphene layers and to obtain a stable graphene suspension. The as-prepared graphene was characterized by X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). XRD results show that the crystal structures are different among graphite, graphite oxide, and graphene. SEM and TEM images show that graphene possesses a gridding structure, a smooth surface, and few defects. AFM analysis indicates that the thickness of the single layer graphene is about 1.3 nm while there are still a few double layers in the sample. The BET specific surface area of the graphene was about 1206 m2·g-1 and its H2 adsorption properties were investigated under high pressure. The samples prepared by liquid oxidation-reduction were compared with that prepared by the improved liquid oxidation-reduction method, which indicates that the addition of SDBS effectively reduces agglomeration among the graphene layers and this generates high quality graphene. The adsorption capacities of H2 on graphene at 25 and 55 °C reached 1.7%(w) and 1.1%(w), respectively, which are much higher than that reported previously.
