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2011 Volume 27 Issue 11
2011, 27(11):
Abstract:
2011, 27(11): 2499-2504
doi: 10.3866/PKU.WHXB20111102
Abstract:
At a concentration of 0-1.0 mol·L-1 the effect of salts (KCl, MgCl2, and CaCl2) on the structure of water was studied from the viewpoint of energy change using differential scanning calorimetry (DSC) and the results were compared with that obtained by the analysis of the chemical shift obtained by 17O-NMR (δ(17OH2)). A linear increase in the δ(17OH2) of water and a linear decrease in the apparent activation energy (-E'/R) of water with an increase in the concentration of salt was obtained. In addition, the rate of change of δ(17OH2) and -E'/R increased as follows: KCl22. Based on a two-state model, we demonstrate that the change in δ(17OH2) of water (Δδ) is proportional to the change in molar energy of water (ΔE). These results indicate that KCl, MgCl2, and CaCl2 promote the formation of the water cluster structure and the energy change of water is equivalent to the chemical shift obtained by 17ONMR for the characterization of the water cluster structure.
At a concentration of 0-1.0 mol·L-1 the effect of salts (KCl, MgCl2, and CaCl2) on the structure of water was studied from the viewpoint of energy change using differential scanning calorimetry (DSC) and the results were compared with that obtained by the analysis of the chemical shift obtained by 17O-NMR (δ(17OH2)). A linear increase in the δ(17OH2) of water and a linear decrease in the apparent activation energy (-E'/R) of water with an increase in the concentration of salt was obtained. In addition, the rate of change of δ(17OH2) and -E'/R increased as follows: KCl22. Based on a two-state model, we demonstrate that the change in δ(17OH2) of water (Δδ) is proportional to the change in molar energy of water (ΔE). These results indicate that KCl, MgCl2, and CaCl2 promote the formation of the water cluster structure and the energy change of water is equivalent to the chemical shift obtained by 17ONMR for the characterization of the water cluster structure.
2011, 27(11): 2505-2511
doi: 10.3866/PKU.WHXB20111103
Abstract:
We investigated the effects of solute concentration on the hydrogen bonding interactions of three-carbon polyalcohol aqueous solutions. In order to inspect the capacity of the solutions to form glass, proton nuclear magnetic resonance (1H NMR) chemical shifts were determined in binary mixtures of water and 1-propanol (NPA), 2-propanol (IPA), 1,2-propanediol (PG), 1,3-propanediol (PD), and glycerol at room temperature and at atmospheric pressure using the external reference method. We found that the alkyl proton chemical shifts of PG with the CH3CH(OH)― group showed biphasic behavior, which was different from other molecules. Water molecules formed relatively strong O ― H···O hydrogen bonds with the alcohol hydroxyls. The proton chemical shifts of H2O and the hydroxyl protons decrease with an increase in the number of alcohol hydroxyls at the same mole fraction. Moreover, the proton chemical shifts of H2O and hydroxyl protons with the same number of alcohol hydroxyls are different because of their different locations. The order of increased basicity agrees with the order of increased ice homogeneous nucleation suppression, that is, glycerol>PG>PD>IPA>NPA. This explains why glycerol and PG are more suitable as cryoprotective agents (CPAs) among the five polyalcohols.
We investigated the effects of solute concentration on the hydrogen bonding interactions of three-carbon polyalcohol aqueous solutions. In order to inspect the capacity of the solutions to form glass, proton nuclear magnetic resonance (1H NMR) chemical shifts were determined in binary mixtures of water and 1-propanol (NPA), 2-propanol (IPA), 1,2-propanediol (PG), 1,3-propanediol (PD), and glycerol at room temperature and at atmospheric pressure using the external reference method. We found that the alkyl proton chemical shifts of PG with the CH3CH(OH)― group showed biphasic behavior, which was different from other molecules. Water molecules formed relatively strong O ― H···O hydrogen bonds with the alcohol hydroxyls. The proton chemical shifts of H2O and the hydroxyl protons decrease with an increase in the number of alcohol hydroxyls at the same mole fraction. Moreover, the proton chemical shifts of H2O and hydroxyl protons with the same number of alcohol hydroxyls are different because of their different locations. The order of increased basicity agrees with the order of increased ice homogeneous nucleation suppression, that is, glycerol>PG>PD>IPA>NPA. This explains why glycerol and PG are more suitable as cryoprotective agents (CPAs) among the five polyalcohols.
2011, 27(11): 2512-2520
doi: 10.3866/PKU.WHXB20111120
Abstract:
The ionic liquids 1-methylimidazolium acetate ([Mim]Ac), 1,3-dimethylimidazolium acetate ([Mmim]Ac), and 1-ethyl-3-methylimidazolium acetate ([Emim]Ac) were prepared and their densities, conductivities, and absolute viscosities were measured at temperatures ranging from 293.15 to 338.14 K. Their corresponding molar conductivities and kinematic viscosities were also calculated. The dependence of densities, conductivities, molar conductivities, absolute viscosities, and kinematic viscosities on temperature were obtained using the least-squares method. The influence of the alkyl chains at the 3-position N atom of the imidazole ring on the above five physicochemical properties of these imidazolium acetates were discussed. The conductivities of binary solutions of [Mim]Ac {or [Mmim]Ac or [Emim]Ac} (1)- H2O (or EtOH) (2) were measured for a full set of mole fractions and the corresponding molar conductivities of the three imidazolium acetates in the six binary solutions were also calculated. In water and ethanol solutions we found that the conductivities and the molar conductivities increased initially and then decreased with an increase in the mole fraction of the imidazolium acetates. At the same concentration a longer alkyl chain at the 3-position of the imidazole ring resulted in higher conductivity and molar conductivity for the imidazolium acetates. Furthermore, the conductivities and molar conductivities of the aqueous solutions are always far higher than those of ethanol solutions.
The ionic liquids 1-methylimidazolium acetate ([Mim]Ac), 1,3-dimethylimidazolium acetate ([Mmim]Ac), and 1-ethyl-3-methylimidazolium acetate ([Emim]Ac) were prepared and their densities, conductivities, and absolute viscosities were measured at temperatures ranging from 293.15 to 338.14 K. Their corresponding molar conductivities and kinematic viscosities were also calculated. The dependence of densities, conductivities, molar conductivities, absolute viscosities, and kinematic viscosities on temperature were obtained using the least-squares method. The influence of the alkyl chains at the 3-position N atom of the imidazole ring on the above five physicochemical properties of these imidazolium acetates were discussed. The conductivities of binary solutions of [Mim]Ac {or [Mmim]Ac or [Emim]Ac} (1)- H2O (or EtOH) (2) were measured for a full set of mole fractions and the corresponding molar conductivities of the three imidazolium acetates in the six binary solutions were also calculated. In water and ethanol solutions we found that the conductivities and the molar conductivities increased initially and then decreased with an increase in the mole fraction of the imidazolium acetates. At the same concentration a longer alkyl chain at the 3-position of the imidazole ring resulted in higher conductivity and molar conductivity for the imidazolium acetates. Furthermore, the conductivities and molar conductivities of the aqueous solutions are always far higher than those of ethanol solutions.
2011, 27(11): 2521-2527
doi: 10.3866/PKU.WHXB20111121
Abstract:
The rapid efflorescence of individual seawater droplets on polytetrafluoroethylene (PTFE, hydrophobic) and quartz (hydrophilic) substrates was investigated using a high-speed camera for imaging and micro-Raman spectroscopy to spatially resolve the particle composition. The morphology of the evaporating sea salt particles was captured using millisecond time resolution and micrometer spatial resolution. Upon rapid desiccation with dry N2 on a quartz substrate, Na2Ca5(SO4)6·3H2O and Na2xCa6-x(SO4)6· 3H2O (0<x<1) crystallized first followed by NaCl and finally KMgCl3·6H2O. We determined the formation behavior of the mixed sodium-calcium salts as crystallization products during the quick desiccation process and CaSO4·2H2O during the slow desiccation process. In addition, the crystallization location of different crystal products were identified and the growth speed of Na2Ca5(SO4)6·3H2O crystal was compared with that of CaSO4·2H2O crystal. Moreover, sea salt particles with a hollow structure were observed on the PTFE substrate at the end of the quick efflorescence process.
The rapid efflorescence of individual seawater droplets on polytetrafluoroethylene (PTFE, hydrophobic) and quartz (hydrophilic) substrates was investigated using a high-speed camera for imaging and micro-Raman spectroscopy to spatially resolve the particle composition. The morphology of the evaporating sea salt particles was captured using millisecond time resolution and micrometer spatial resolution. Upon rapid desiccation with dry N2 on a quartz substrate, Na2Ca5(SO4)6·3H2O and Na2xCa6-x(SO4)6· 3H2O (0<x<1) crystallized first followed by NaCl and finally KMgCl3·6H2O. We determined the formation behavior of the mixed sodium-calcium salts as crystallization products during the quick desiccation process and CaSO4·2H2O during the slow desiccation process. In addition, the crystallization location of different crystal products were identified and the growth speed of Na2Ca5(SO4)6·3H2O crystal was compared with that of CaSO4·2H2O crystal. Moreover, sea salt particles with a hollow structure were observed on the PTFE substrate at the end of the quick efflorescence process.
2011, 27(11): 2528-2534
doi: 10.3866/PKU.WHXB20111101
Abstract:
The influences of rare earth (RE) cations on the stability and acidity of Y zeolites were studied by X-ray powder diffraction (XRD), solid-state magic-angle spinning nuclear magnetic resonance spectroscopy (MAS NMR), temperature-programmed desorption (TPD) of ammonia, and Fourier transform infrared of pyridine (Py-FTIR). The results showed that the stability of Y zeolites was enhanced markedly and the medium acid amount increased, but the strong acid amount of Y zeolites decreased with the introduction of RE cations. Combined with the density functional theory (DFT) calculations, a comprehensive model was proposed to describe the mechanism of RE cations on the stability and acidity of Y zeolites. RE cations located at the sodalite β cage I' sites of Y zeolites bonded strongly with O atoms, which strengthened the interaction between framework Al and its neighbouring O atoms and then enhanced evidently the stability of Y zeolites. It was the enhanced stability of REHY zeolites that restrained the release of framework Al and the formation of extra-framework Al, hence led to weaker Brönsted acid strength of REHY than that of USY. Meanwhile, RE cations located at the sodalite β cage I' sites of Y zeolites made the negative charge of O1 reduce and the bond length of Al―O1 shorten, which resulted in stronger Brönsted acid strength of REHY than that of HY. Moreover, the Bro? nsted acid amount of REHY was more than that of USY, but less than that of HY.
The influences of rare earth (RE) cations on the stability and acidity of Y zeolites were studied by X-ray powder diffraction (XRD), solid-state magic-angle spinning nuclear magnetic resonance spectroscopy (MAS NMR), temperature-programmed desorption (TPD) of ammonia, and Fourier transform infrared of pyridine (Py-FTIR). The results showed that the stability of Y zeolites was enhanced markedly and the medium acid amount increased, but the strong acid amount of Y zeolites decreased with the introduction of RE cations. Combined with the density functional theory (DFT) calculations, a comprehensive model was proposed to describe the mechanism of RE cations on the stability and acidity of Y zeolites. RE cations located at the sodalite β cage I' sites of Y zeolites bonded strongly with O atoms, which strengthened the interaction between framework Al and its neighbouring O atoms and then enhanced evidently the stability of Y zeolites. It was the enhanced stability of REHY zeolites that restrained the release of framework Al and the formation of extra-framework Al, hence led to weaker Brönsted acid strength of REHY than that of USY. Meanwhile, RE cations located at the sodalite β cage I' sites of Y zeolites made the negative charge of O1 reduce and the bond length of Al―O1 shorten, which resulted in stronger Brönsted acid strength of REHY than that of HY. Moreover, the Bro? nsted acid amount of REHY was more than that of USY, but less than that of HY.
2011, 27(11): 2535-2540
doi: 10.3866/PKU.WHXB20111006
Abstract:
Fluorescence spectra of CaCl2, LiCl, and Ca(NO3)2 in methanol were investigated and the structures and excitation energy of possible clusters were optimized by density functional theory (DFT) and time-dependent (TD) DFT theory with B3LYP method. Experimental results indicate that CaCl2 and LiCl are connected to methanol as clusters with od fluorescence properties. A strong increase in fluorescence intensity of CaCl2 and LiCl solutions was observed upon increasing their concentrations. The interaction between Ca(NO3)2 and methanol causes the fluorescence quenching of methanol. The results of the theoretical calculation show that [CaCl(CH3OH)n]+ and LiCl(CH3OH)n clusters strengthen the fluorescence intensity of the salt methanol solution and the oscillator strength of NO3- and the methanol clusters is almost zero. This illustrates the fluorescence quenching phenomenon of the NO3- anion and methanol.
Fluorescence spectra of CaCl2, LiCl, and Ca(NO3)2 in methanol were investigated and the structures and excitation energy of possible clusters were optimized by density functional theory (DFT) and time-dependent (TD) DFT theory with B3LYP method. Experimental results indicate that CaCl2 and LiCl are connected to methanol as clusters with od fluorescence properties. A strong increase in fluorescence intensity of CaCl2 and LiCl solutions was observed upon increasing their concentrations. The interaction between Ca(NO3)2 and methanol causes the fluorescence quenching of methanol. The results of the theoretical calculation show that [CaCl(CH3OH)n]+ and LiCl(CH3OH)n clusters strengthen the fluorescence intensity of the salt methanol solution and the oscillator strength of NO3- and the methanol clusters is almost zero. This illustrates the fluorescence quenching phenomenon of the NO3- anion and methanol.
2011, 27(11): 2541-2546
doi: 10.3866/PKU.WHXB20111021
Abstract:
A series of covalently linked porphyrin (Por)-anthraquinone (AQ) hybrids Por-Cn-AQ (n=1, 4, 10) with flexible different length carbon chains were synthesized and their intramolecular photoinduced electron transfer (PET) properties were investigated mainly by steady-state fluorescence and decayed luminescence spectra. We studied the PET mechanism using density functional theory (DFT). We found that PET occurs from the porphyrin moiety to the anthraquinone moiety of these dyads and that the PET efficiency is influenced considerably by the length of the linkage between the two moieties in the hybrids. From both the experimental and theoretical results, we can conclude that the PET of these dyads is seemingly most compatible with a“through-bond”(super-exchange) mechanism.
A series of covalently linked porphyrin (Por)-anthraquinone (AQ) hybrids Por-Cn-AQ (n=1, 4, 10) with flexible different length carbon chains were synthesized and their intramolecular photoinduced electron transfer (PET) properties were investigated mainly by steady-state fluorescence and decayed luminescence spectra. We studied the PET mechanism using density functional theory (DFT). We found that PET occurs from the porphyrin moiety to the anthraquinone moiety of these dyads and that the PET efficiency is influenced considerably by the length of the linkage between the two moieties in the hybrids. From both the experimental and theoretical results, we can conclude that the PET of these dyads is seemingly most compatible with a“through-bond”(super-exchange) mechanism.
2011, 27(11): 2547-2552
doi: 10.3866/PKU.WHXB20111107
Abstract:
The molecular dynamics behaviors in water solutions are determined by the hydrogen bond (H-bond) relaxations. The H-bond lifetime, as an important experimental and theoretical parameter, is often used to explore the general kinetics of H-bond dynamics. In this work, four different H-bond lifetimes were defined and calculated in dimethyl sulfoxide (DMSO)-water mixtures with two widely-used combined force fields, SPC/E-P2 and SPC/E-OPLS. The continuous and kinetic based H-bond lifetimes, τC and τR, are always shorter than the τPR of stable states due to neglecting of unsuccessful H-bond exchanges. The intermittent H-bond lifetime τI was found to be the longest because of a recount of the reforming events after the successful switching event. The H-bond lifetimes, τC, τI, τR, and τPR increase with the mole fraction of DMSO (xD). This trend is not consistent with that of the molecular diffuse constants. This shows that the molecular mobility is not a decisive factor to the H-bond lifetime. The environment-dependent H-bond lifetimes suggest that the stronger H-bonds should not always remain longer time. The H-bond coordination numbers of water and DMSO decrease with xD. The distortion and elongation probability of the H-bond that was induced by surrounding molecules decreases and, therefore, so the τC and τR approach each other at the limiting concentrations in this work. The facts above show that the labeled H-bond lifetime is closely related to the H-bond density around it. One H-bond switching event only takes place on one new available acceptor there. The localized character of H-bond relaxation is consistent with the trend of the molecular mobility trend. The H-bond lifetimes also rely on the theoretical model used in the simulations.
The molecular dynamics behaviors in water solutions are determined by the hydrogen bond (H-bond) relaxations. The H-bond lifetime, as an important experimental and theoretical parameter, is often used to explore the general kinetics of H-bond dynamics. In this work, four different H-bond lifetimes were defined and calculated in dimethyl sulfoxide (DMSO)-water mixtures with two widely-used combined force fields, SPC/E-P2 and SPC/E-OPLS. The continuous and kinetic based H-bond lifetimes, τC and τR, are always shorter than the τPR of stable states due to neglecting of unsuccessful H-bond exchanges. The intermittent H-bond lifetime τI was found to be the longest because of a recount of the reforming events after the successful switching event. The H-bond lifetimes, τC, τI, τR, and τPR increase with the mole fraction of DMSO (xD). This trend is not consistent with that of the molecular diffuse constants. This shows that the molecular mobility is not a decisive factor to the H-bond lifetime. The environment-dependent H-bond lifetimes suggest that the stronger H-bonds should not always remain longer time. The H-bond coordination numbers of water and DMSO decrease with xD. The distortion and elongation probability of the H-bond that was induced by surrounding molecules decreases and, therefore, so the τC and τR approach each other at the limiting concentrations in this work. The facts above show that the labeled H-bond lifetime is closely related to the H-bond density around it. One H-bond switching event only takes place on one new available acceptor there. The localized character of H-bond relaxation is consistent with the trend of the molecular mobility trend. The H-bond lifetimes also rely on the theoretical model used in the simulations.
2011, 27(11): 2553-2558
doi: 10.3866/PKU.WHXB20111017
Abstract:
We investigated eleven exchange-correlation energy density functionals including generalized gradient approximation (GGA) (PBE, PW91), meta-GGA (M06-L), hyper-GGA (M06-2X, B3LYP, X3LYP), LC-DFT methods (CAM-B3LYP, LC-ωPBE, ωB97X), and density functional theory with dispersion corrections (DFT-D) methods (ωB97X-D, B97-D) for their performance in describing systems with conventional and non-conventional hydrogen bonds. After comparing the results using the benchmark CCSD(T)/aug-cc-pVQZ approach we found that the M06-2X and ωB97X-D functionals provided the most accurate and reliable results for the fifteen systems studied in this work with strong, moderate, and weak hydrogen bonds. It is important to employ an appropriate basis set to predict the binding energy of hydrogen bonds for all DFT methods and we found that the basis set of 6-311++G(2d, 2p) or aug-cc-pVDZ is adequate. The effect of the basis set superposition error (BSSE) is relatively small for the DFT methods tested. All the methods except for ωB97X and ωB97X-D were found to produce equally accurate or even more accurate results without BSSE correction.
We investigated eleven exchange-correlation energy density functionals including generalized gradient approximation (GGA) (PBE, PW91), meta-GGA (M06-L), hyper-GGA (M06-2X, B3LYP, X3LYP), LC-DFT methods (CAM-B3LYP, LC-ωPBE, ωB97X), and density functional theory with dispersion corrections (DFT-D) methods (ωB97X-D, B97-D) for their performance in describing systems with conventional and non-conventional hydrogen bonds. After comparing the results using the benchmark CCSD(T)/aug-cc-pVQZ approach we found that the M06-2X and ωB97X-D functionals provided the most accurate and reliable results for the fifteen systems studied in this work with strong, moderate, and weak hydrogen bonds. It is important to employ an appropriate basis set to predict the binding energy of hydrogen bonds for all DFT methods and we found that the basis set of 6-311++G(2d, 2p) or aug-cc-pVDZ is adequate. The effect of the basis set superposition error (BSSE) is relatively small for the DFT methods tested. All the methods except for ωB97X and ωB97X-D were found to produce equally accurate or even more accurate results without BSSE correction.
2011, 27(11): 2559-2564
doi: 10.3866/PKU.WHXB20111115
Abstract:
A semiclassical dynamics simulation study was undertaken to determine the photophysical deactivation of the lowest excited state of two stacked thymines. Only one thymine, referred to as T, was excited by a laser pulse and the other molecule, referred to as T′, remained in the ground state. The simulation results show that charge transfer between the two thymines because of a π-stacking interaction leads to the formation of an excimer state, which includes a negative T and a positive T′. Additionally, the simulation study indicates that a steric effect of the neighboring bases inhibits the out-of-plane deformation, which is essential in accessing the conical intersection between the lowest electronic-excited state and the ground state. The steric effect eventually leads to a longer electronic-excited state lifetime for the two stacked thymines. The simulation results reveal that when the interbase distance is less than 0.3 nm the molecule T has a remarkable deformation at its C5 and C6 sites resulting in charge recombination. The charge recombination ultimately makes the system electronically neutral. On the other hand, the molecule T′ has a strong twist about its C5′―C6′ bond in the proximity of the avoided crossing by which the system decays to the ground state. Finally, the two thymine molecules in their ground states recover their planar geometries.
A semiclassical dynamics simulation study was undertaken to determine the photophysical deactivation of the lowest excited state of two stacked thymines. Only one thymine, referred to as T, was excited by a laser pulse and the other molecule, referred to as T′, remained in the ground state. The simulation results show that charge transfer between the two thymines because of a π-stacking interaction leads to the formation of an excimer state, which includes a negative T and a positive T′. Additionally, the simulation study indicates that a steric effect of the neighboring bases inhibits the out-of-plane deformation, which is essential in accessing the conical intersection between the lowest electronic-excited state and the ground state. The steric effect eventually leads to a longer electronic-excited state lifetime for the two stacked thymines. The simulation results reveal that when the interbase distance is less than 0.3 nm the molecule T has a remarkable deformation at its C5 and C6 sites resulting in charge recombination. The charge recombination ultimately makes the system electronically neutral. On the other hand, the molecule T′ has a strong twist about its C5′―C6′ bond in the proximity of the avoided crossing by which the system decays to the ground state. Finally, the two thymine molecules in their ground states recover their planar geometries.
2011, 27(11): 2565-2570
doi: 10.3866/PKU.WHXB20111127
Abstract:
The interaction between nitrogen-oxygen heterocyclic compounds and a host (magnesium porphyrin) was investigated. The results showed that the magnesium atoms in the magnesium porphyrin and porphin ring were not coplanar and at a smaller dihedral angle the extent of its non-coplanar nature increased. Natural bond orbital (NBO) analysis indicated that the interaction between the lone pair of electrons on the nitrogen and oxygen atoms and the unoccupied lone pair orbital of magnesium contributes significantly to the stability of the complexes. The reduced density gradient (RDG) isosurface map and the scatter diagram indicated the location and intensity of the axial coordination interactions and the surrounding hydrogen bonding interactions. The conceptual density functional theory (DFT) parameter indicated that the complex compounds are less thermodynamically stable than magnesium porphyrin, however, they have higher reactivity. Aromatic calculations revealed that the interaction between the oxygen-containing heterocycles and the host compound made the porphin ring in the complexes anti-aromatic while the interaction between the nitrogen-containing heterocyclic and the host made the porphin ring in the complexes regionally aromatic.
The interaction between nitrogen-oxygen heterocyclic compounds and a host (magnesium porphyrin) was investigated. The results showed that the magnesium atoms in the magnesium porphyrin and porphin ring were not coplanar and at a smaller dihedral angle the extent of its non-coplanar nature increased. Natural bond orbital (NBO) analysis indicated that the interaction between the lone pair of electrons on the nitrogen and oxygen atoms and the unoccupied lone pair orbital of magnesium contributes significantly to the stability of the complexes. The reduced density gradient (RDG) isosurface map and the scatter diagram indicated the location and intensity of the axial coordination interactions and the surrounding hydrogen bonding interactions. The conceptual density functional theory (DFT) parameter indicated that the complex compounds are less thermodynamically stable than magnesium porphyrin, however, they have higher reactivity. Aromatic calculations revealed that the interaction between the oxygen-containing heterocycles and the host compound made the porphin ring in the complexes anti-aromatic while the interaction between the nitrogen-containing heterocyclic and the host made the porphin ring in the complexes regionally aromatic.
2011, 27(11): 2571-2576
doi: 10.3866/PKU.WHXB20111105
Abstract:
An all-lead redox flow battery in a fluoroboric acid electrolyte is proposed. The same electrolyte was used as both the negative and positive electrodes, and it consists of a high concentration solution of Pb(BF4)2 in aqueous fluoroboric acid, i.e., 0.1, 0.5, 1.0 and 1.5 mol·L-1 Pb(BF4)2 in 1.0 mol·L-1 HBF4. The properties of the graphite and glassy carbon electrodes for both the positive and negative electrodes as current collectors were compared using cyclic voltammetry. We found that the graphite substrate was better than glassy carbon for both the negative electrode and the positive electrode. The all-lead redox flow battery was constructed using graphite substrates as both the positive and negative electrodes with a single electrolyte flow passing though the two electrodes. The performance of the batteries was evaluated using the constant current charge/discharge technique. Typically, an average coulombic efficiency of above 87% and an average energy efficiency of above 68% were obtained. An average energy efficiency of above 74% was achieved with electrolyte containing 1.0 or 1.5 mol·L-1 Pb(BF4)2 + 1.0 mol·L-1 HBF4 at current densities of 10 and 20 mA×cm-2.
An all-lead redox flow battery in a fluoroboric acid electrolyte is proposed. The same electrolyte was used as both the negative and positive electrodes, and it consists of a high concentration solution of Pb(BF4)2 in aqueous fluoroboric acid, i.e., 0.1, 0.5, 1.0 and 1.5 mol·L-1 Pb(BF4)2 in 1.0 mol·L-1 HBF4. The properties of the graphite and glassy carbon electrodes for both the positive and negative electrodes as current collectors were compared using cyclic voltammetry. We found that the graphite substrate was better than glassy carbon for both the negative electrode and the positive electrode. The all-lead redox flow battery was constructed using graphite substrates as both the positive and negative electrodes with a single electrolyte flow passing though the two electrodes. The performance of the batteries was evaluated using the constant current charge/discharge technique. Typically, an average coulombic efficiency of above 87% and an average energy efficiency of above 68% were obtained. An average energy efficiency of above 74% was achieved with electrolyte containing 1.0 or 1.5 mol·L-1 Pb(BF4)2 + 1.0 mol·L-1 HBF4 at current densities of 10 and 20 mA×cm-2.
Optimization of the Photoelectric Performance of Large-Scale All-Flexible Dye-Sensitized Solar Cells
2011, 27(11): 2577-2582
doi: 10.3866/PKU.WHXB20111112
Abstract:
Highly efficient large scale flexible dye-sensitized solar cells (DSCs) were successfully designed and fabricated. By the introduction of a light scattering layer or pressure, the DSC efficiency was greatly improved. The flexible DSCs with a small surface area (0.4 cm × 0.4 cm) gave a high energy conversion efficiency of 5.50%. The energy conversion efficiencies of large area DSCs (2 cm×3 cm, active area of 2.7 cm2) improved from 1.52% to 1.81% and 2.50%, which is an increase of 20.0% and 66.7% compared with the DSCs prepared without any treatment. The 5 cm×7 cm DSCs (active area of 16.2 cm2) without any optimization showed an energy conversion efficiency of 1.60% under a sunlight intensity of 40 mW·cm-2. The mechanism for the improvement in efficiency was also studied. The results of electrochemical impedance spectroscopy (EIS) demonstrated that the pressure method can significantly reduce the series resistance (Rs) and the charge transfer resistance (Rct) in the TiO2/dye/electrolyte interface. Scanning electron microscopy (SEM) showed that the TiO2 particles were far more closely connected after pressing, which was helpful for electron transport in the TiO2 network as well as for dye adsorption. In addition, the photovoltaic parameters of these flexible DSCs were found to be stable after the 900 h stability tests. The experimental results obtained for these flexible DSCs can be used as a foundation for further basic research and for industrialization technical research.
Highly efficient large scale flexible dye-sensitized solar cells (DSCs) were successfully designed and fabricated. By the introduction of a light scattering layer or pressure, the DSC efficiency was greatly improved. The flexible DSCs with a small surface area (0.4 cm × 0.4 cm) gave a high energy conversion efficiency of 5.50%. The energy conversion efficiencies of large area DSCs (2 cm×3 cm, active area of 2.7 cm2) improved from 1.52% to 1.81% and 2.50%, which is an increase of 20.0% and 66.7% compared with the DSCs prepared without any treatment. The 5 cm×7 cm DSCs (active area of 16.2 cm2) without any optimization showed an energy conversion efficiency of 1.60% under a sunlight intensity of 40 mW·cm-2. The mechanism for the improvement in efficiency was also studied. The results of electrochemical impedance spectroscopy (EIS) demonstrated that the pressure method can significantly reduce the series resistance (Rs) and the charge transfer resistance (Rct) in the TiO2/dye/electrolyte interface. Scanning electron microscopy (SEM) showed that the TiO2 particles were far more closely connected after pressing, which was helpful for electron transport in the TiO2 network as well as for dye adsorption. In addition, the photovoltaic parameters of these flexible DSCs were found to be stable after the 900 h stability tests. The experimental results obtained for these flexible DSCs can be used as a foundation for further basic research and for industrialization technical research.
2011, 27(11): 2583-2586
doi: 10.3866/PKU.WHXB20111123
Abstract:
We prepared improved graphene films by freeze drying solvated graphene films, which greatly reduced the serious restacking of graphene layers when they were face-to-face stacked. The results show that the improved graphene film had more corrugations and a larger interplanar distance than the usual graphene films prepared by vacuum filtration leading to improved electrochemical performance. The discharge and charge capacities of the battery were 1189.3 and 645.2 mAh·g-1, respectively, for the first cycle at 50 mA·g-1 and the charge capacity remained above 305 mAh·g-1 after 400 cycles. These values are higher than those of the graphene film prepared by vacuum filtration. Moreover, the mass and cost of the electrode were reduced significantly compared with the commercial graphite-based anode, which is made by coating a mixture of an active material, a polymeric binder, and an electric current collector.
We prepared improved graphene films by freeze drying solvated graphene films, which greatly reduced the serious restacking of graphene layers when they were face-to-face stacked. The results show that the improved graphene film had more corrugations and a larger interplanar distance than the usual graphene films prepared by vacuum filtration leading to improved electrochemical performance. The discharge and charge capacities of the battery were 1189.3 and 645.2 mAh·g-1, respectively, for the first cycle at 50 mA·g-1 and the charge capacity remained above 305 mAh·g-1 after 400 cycles. These values are higher than those of the graphene film prepared by vacuum filtration. Moreover, the mass and cost of the electrode were reduced significantly compared with the commercial graphite-based anode, which is made by coating a mixture of an active material, a polymeric binder, and an electric current collector.
2011, 27(11): 2587-2592
doi: 10.3866/PKU.WHXB20111124
Abstract:
As a new potential cathode material for lithium ion batteries, Li2MnSiO4/C was synthesized by a solution method. The thermal behavior of the precursor for Li2MnSiO4/C was measured by thermogravimetric (TG) analysis and the range of calcination temperatures from 600 to 800°C was determined. X-ray powder diffraction (XRD) patterns indicated that all the Li2MnSiO4/C samples crystallized in an orthorhombic structure with space group Pmn21. The morphology and particle size of the samples were also characterized by scanning electron microscopy (SEM). The effects of calcination temperature on the electrochemical performance of Li2MnSiO4/C were studied using galvanostatic charge-discharge measurements at various current densities. The results showed that the sample prepared at 700°C exhibited a much higher coulombic efficiency and better cyclic performance than the other samples.
As a new potential cathode material for lithium ion batteries, Li2MnSiO4/C was synthesized by a solution method. The thermal behavior of the precursor for Li2MnSiO4/C was measured by thermogravimetric (TG) analysis and the range of calcination temperatures from 600 to 800°C was determined. X-ray powder diffraction (XRD) patterns indicated that all the Li2MnSiO4/C samples crystallized in an orthorhombic structure with space group Pmn21. The morphology and particle size of the samples were also characterized by scanning electron microscopy (SEM). The effects of calcination temperature on the electrochemical performance of Li2MnSiO4/C were studied using galvanostatic charge-discharge measurements at various current densities. The results showed that the sample prepared at 700°C exhibited a much higher coulombic efficiency and better cyclic performance than the other samples.
2011, 27(11): 2593-2599
doi: 10.3866/PKU.WHXB20111104
Abstract:
Nano-sized M3O4 (M=Ni1/3Co1/3Mn1/3) powder with a spinel structure was prepared by sintering co-precipitated M(OH)2 at 500°C for 5 h. The so-obtained M3O4 was then mixed with LiOH and different amounts of nano-M . The mixture was sintered at 850°C for 24 h to synthesize Li(Ni1/3Co1/3Mn1/3)1-xMgxO2 (x=0, 0.01, 0.02, 0.03, 0.04,0.05) cathode materials. The lattice parameters increased while the diffusion coefficients of Li+ ion showed an increasing and then decreasing trend with an increase in the amount of Mg substitution. Li(Ni1/3Co1/3Mn1/3)0.98Mg0.02O2 had the highest Li+ ion diffusion coefficients, which were 29.20× 10-11 cm2·s-1 for Li+ de-intercalation and 4.760×10-11 cm2·s-1 for Li+ intercalation. Its discharge capacity at 3C rate was 139.3 mAh·g-1, which is 9.5 mAh·g-1 higher than that of the pristine material. Furthermore, its cycle performance was also improved significantly compared with the un-doped counterpart.
Nano-sized M3O4 (M=Ni1/3Co1/3Mn1/3) powder with a spinel structure was prepared by sintering co-precipitated M(OH)2 at 500°C for 5 h. The so-obtained M3O4 was then mixed with LiOH and different amounts of nano-M . The mixture was sintered at 850°C for 24 h to synthesize Li(Ni1/3Co1/3Mn1/3)1-xMgxO2 (x=0, 0.01, 0.02, 0.03, 0.04,0.05) cathode materials. The lattice parameters increased while the diffusion coefficients of Li+ ion showed an increasing and then decreasing trend with an increase in the amount of Mg substitution. Li(Ni1/3Co1/3Mn1/3)0.98Mg0.02O2 had the highest Li+ ion diffusion coefficients, which were 29.20× 10-11 cm2·s-1 for Li+ de-intercalation and 4.760×10-11 cm2·s-1 for Li+ intercalation. Its discharge capacity at 3C rate was 139.3 mAh·g-1, which is 9.5 mAh·g-1 higher than that of the pristine material. Furthermore, its cycle performance was also improved significantly compared with the un-doped counterpart.
2011, 27(11): 2600-2604
doi: 10.3866/PKU.WHXB20111126
Abstract:
Nanostructured LiV3O8 powder was synthesized by a low-temperature solid-state method. Scanning election microscopy (SEM) and transmission electron microscopy (TEM) show that the as-prepared material is composed of nanostructured particles. X-ray diffraction (XRD) measurements indicate that the as-prepared material has a monoclinic structure with a space group of P21/m. The electrochemical properties of the LiV3O8 electrodes in 1 mol·L-1 Li2SO4, 2 mol·L-1 Li2SO4, and saturated Li2SO4 aqueous electrolytes were studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in this work. The results show that the LiV3O8 electrode in the saturated Li2SO4 electrolyte has the best electrochemical properties. An aqueous rechargeable lithium battery (ARLB) containing a LiV3O8 anode, a LiNi1/3Co1/3Mn1/3O2 cathode, and a saturated Li2SO4 electrolyte was fabricated. The battery delivered an initial capacity of 95.2 mAh·g-1 and retained a capacity of 37.0 mAh·g-1 after 100 cycles at a charge-discharge rate of 0.5C (1C=300 mA·g-1).
Nanostructured LiV3O8 powder was synthesized by a low-temperature solid-state method. Scanning election microscopy (SEM) and transmission electron microscopy (TEM) show that the as-prepared material is composed of nanostructured particles. X-ray diffraction (XRD) measurements indicate that the as-prepared material has a monoclinic structure with a space group of P21/m. The electrochemical properties of the LiV3O8 electrodes in 1 mol·L-1 Li2SO4, 2 mol·L-1 Li2SO4, and saturated Li2SO4 aqueous electrolytes were studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in this work. The results show that the LiV3O8 electrode in the saturated Li2SO4 electrolyte has the best electrochemical properties. An aqueous rechargeable lithium battery (ARLB) containing a LiV3O8 anode, a LiNi1/3Co1/3Mn1/3O2 cathode, and a saturated Li2SO4 electrolyte was fabricated. The battery delivered an initial capacity of 95.2 mAh·g-1 and retained a capacity of 37.0 mAh·g-1 after 100 cycles at a charge-discharge rate of 0.5C (1C=300 mA·g-1).
2011, 27(11): 2605-2612
doi: 10.3866/PKU.WHXB20111116
Abstract:
We prepared a series of self-supported macroscopic C/Ni-fiber hybrid electrodes by catalytic chemical vapor deposition (CCVD) using methane, ethylene, ethanol and n-butanol as carbon sources to embed carbon onto a three-dimensional network of sinter-locked conductive 8 μm-nickel fibers. For the as-prepared hybrid electrodes, the Ni-microfibrous network serves as a current collector and the carbons as ion storage media while the macroporous void space serves as an electrolyte reservoir. We characterized the hybrid electrodes using scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), N2 isothermal adsorptiondesorption, cyclic voltammetry and electrochemical impedance spectroscopy. The desalination performance of the C/Ni-fiber hybrids was evaluated as electrodes in a capacitive deionization system. The carbon morphology is dependent on the carbonaceous compounds used in CCVD: carbon nanotubes (CNTs) with fishbone-like structure, CNTs with inclined graphene layers parallel to the tube axis, rod-like carbon nanofibers (CNFs) and worm-like CNFs for ethylene, methane, n-butanol and ethanol. The desalination performance of these hybrid electrodes with respect to the carbonaceous compounds decreases as follows: ethylene>n-butanol>methane>ethanol, which correlates with their electrochemical features, pore structures and their carbon nanostructures. The hybrid electrodes obtained using ethylene as the carbon source gave a maximum electrosorption capacity of 159 μmol·g-1 using a direct current voltage of 1.2 V and a 100 mg·L-1 NaCl aqueous solution as raw water.
We prepared a series of self-supported macroscopic C/Ni-fiber hybrid electrodes by catalytic chemical vapor deposition (CCVD) using methane, ethylene, ethanol and n-butanol as carbon sources to embed carbon onto a three-dimensional network of sinter-locked conductive 8 μm-nickel fibers. For the as-prepared hybrid electrodes, the Ni-microfibrous network serves as a current collector and the carbons as ion storage media while the macroporous void space serves as an electrolyte reservoir. We characterized the hybrid electrodes using scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), N2 isothermal adsorptiondesorption, cyclic voltammetry and electrochemical impedance spectroscopy. The desalination performance of the C/Ni-fiber hybrids was evaluated as electrodes in a capacitive deionization system. The carbon morphology is dependent on the carbonaceous compounds used in CCVD: carbon nanotubes (CNTs) with fishbone-like structure, CNTs with inclined graphene layers parallel to the tube axis, rod-like carbon nanofibers (CNFs) and worm-like CNFs for ethylene, methane, n-butanol and ethanol. The desalination performance of these hybrid electrodes with respect to the carbonaceous compounds decreases as follows: ethylene>n-butanol>methane>ethanol, which correlates with their electrochemical features, pore structures and their carbon nanostructures. The hybrid electrodes obtained using ethylene as the carbon source gave a maximum electrosorption capacity of 159 μmol·g-1 using a direct current voltage of 1.2 V and a 100 mg·L-1 NaCl aqueous solution as raw water.
2011, 27(11): 2613-2617
doi: 10.3866/PKU.WHXB20111117
Abstract:
We report a direct electrochemical deposition process to produce ZnO nanorods or a ZnO thin film on an indium tin oxide (ITO) substrate. The ZnO film was etched by an agarose stamp containing HCl as the etchant to form different patterns. The structure, morphology, and electrochemical properties of the ZnO thin films on the ITO substrate were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and scanning electrochemical microscopy (SECM).
We report a direct electrochemical deposition process to produce ZnO nanorods or a ZnO thin film on an indium tin oxide (ITO) substrate. The ZnO film was etched by an agarose stamp containing HCl as the etchant to form different patterns. The structure, morphology, and electrochemical properties of the ZnO thin films on the ITO substrate were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and scanning electrochemical microscopy (SECM).
2011, 27(11): 2618-2624
doi: 10.3866/PKU.WHXB20111109
Abstract:
The effect of rare earth Ce3+ on the growth of sulfate reducing bacterial (SRB) and the microbial induced corrosion (MIC) of aluminum alloy LY12CZ was studied by ultraviolet spectrophotometry (UVS), maximum probable number (MPN), cyclic anodic polarization, electrochemical impedance spectroscopy (EIS), and epi-fluorescence microscopy (EFM). The results showed that the low concentrations of Ce3+ could promote the growth of SRB while high concentrations had an inhibiting effect. Cyclic anodic polarization curves indicated that the pitting sensitivity of LY12CZ became lower in solutions containing rare earth Ce3+. EIS confirmed that corrosion resistance increased with an increase in the concentration of Ce3+. However, when inoculated with 1% SRB, the corrosion resistance was optimal at a Ce3+ concentration of 0.376 mg·L-1 because of a synergistic effect between the biofilm and the rare earth conversion film. The growth of SRB was inhibited with an increase in the Ce3+ concentration which prevented the biofilm forming completely on the surface of the matrix. At the moment, the effect of MIC was more notable than the protection of rare earth conversion film that formed on the surface of aluminum alloy.
The effect of rare earth Ce3+ on the growth of sulfate reducing bacterial (SRB) and the microbial induced corrosion (MIC) of aluminum alloy LY12CZ was studied by ultraviolet spectrophotometry (UVS), maximum probable number (MPN), cyclic anodic polarization, electrochemical impedance spectroscopy (EIS), and epi-fluorescence microscopy (EFM). The results showed that the low concentrations of Ce3+ could promote the growth of SRB while high concentrations had an inhibiting effect. Cyclic anodic polarization curves indicated that the pitting sensitivity of LY12CZ became lower in solutions containing rare earth Ce3+. EIS confirmed that corrosion resistance increased with an increase in the concentration of Ce3+. However, when inoculated with 1% SRB, the corrosion resistance was optimal at a Ce3+ concentration of 0.376 mg·L-1 because of a synergistic effect between the biofilm and the rare earth conversion film. The growth of SRB was inhibited with an increase in the Ce3+ concentration which prevented the biofilm forming completely on the surface of the matrix. At the moment, the effect of MIC was more notable than the protection of rare earth conversion film that formed on the surface of aluminum alloy.
2011, 27(11): 2625-2631
doi: 10.3866/PKU.WHXB20111133
Abstract:
Nd2Fe14B/PANI magnetic powder was prepared by ball milling and in-situ polymerization. The samples were characterized by X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). The function of Nd2Fe14B/PANI in the oxygen transfer process was determined using an electrochemical three electrode system and a zinc air battery. The results showed that Nd2Fe14B/PANI was a one-dimensional lamellar nanostructured material with an electrical conductivity of 0.54 S·cm-1, an intrinsic coercive force of 149.57 kA·m-1, and a residual magnetization of 20.27 A·m2·kg-1. For a 0.40 mg·cm-2 Nd2Fe14B/PANI load density the magnetic electrode reached a higher double electric layer capacitance, a smaller charge transfer resistance than a nonmagnetic electrode and the polarization current of the magnetic zinc air battery also increased. For a 3.60 mg·cm-2 load density the results were contrary to those of the 0.40 mg· cm-2 load density test. We found that the micro magnetic field promoted the oxygen transfer process and improved the zinc air battery performance when the Nd2Fe14B/PANI load density was less than 0.89 mg· cm-2. At a load density higher than 3.56 mg·cm-2, the micro magnetic field inhibited oxygen transfer and reduced the zinc air battery discharge performance. The PANI in this material also improved the zinc air battery discharge performance.
Nd2Fe14B/PANI magnetic powder was prepared by ball milling and in-situ polymerization. The samples were characterized by X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). The function of Nd2Fe14B/PANI in the oxygen transfer process was determined using an electrochemical three electrode system and a zinc air battery. The results showed that Nd2Fe14B/PANI was a one-dimensional lamellar nanostructured material with an electrical conductivity of 0.54 S·cm-1, an intrinsic coercive force of 149.57 kA·m-1, and a residual magnetization of 20.27 A·m2·kg-1. For a 0.40 mg·cm-2 Nd2Fe14B/PANI load density the magnetic electrode reached a higher double electric layer capacitance, a smaller charge transfer resistance than a nonmagnetic electrode and the polarization current of the magnetic zinc air battery also increased. For a 3.60 mg·cm-2 load density the results were contrary to those of the 0.40 mg· cm-2 load density test. We found that the micro magnetic field promoted the oxygen transfer process and improved the zinc air battery performance when the Nd2Fe14B/PANI load density was less than 0.89 mg· cm-2. At a load density higher than 3.56 mg·cm-2, the micro magnetic field inhibited oxygen transfer and reduced the zinc air battery discharge performance. The PANI in this material also improved the zinc air battery discharge performance.
2011, 27(11): 2632-2638
doi: 10.3866/PKU.WHXB20111114
Abstract:
A series of Cu-Fe-Co based catalysts with different mass fractions of Fe and Co were prepared by co-impregnation method. The catalytic performances of the catalysts for mixed alcohols synthesis from carbon monoxide hydrogenation were investigated in a fixed bed flow reactor. The samples were characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscope (FE-SEM), and H2 temperature-programmed reduction (H2-TPR). The results showed that the addition of a suitable content of Co to the Cu-Fe based catalyst significantly improved the space-time yield (STY) and CO conversion while alcohol selectivity was constant. For the catalyst with a mass fraction of Cu, Fe, and Co of 25%, 22%, and 3%, respectively, a STY of 205.6 g·kg-1·h-1 and CO conversion of 56.6% were obtained. The XRD, XPS, and TPR results showed that when the Cu content was unchanged, the introduction of some Co contributed to the formation of a small quantity of the CuFe2O4 phase on the surface of catalysts, which promoted the interaction between Cu and Fe, improved the dispersion of active components and enhanced the catalytic activity and STY of the mixed alcohols. With an increase of the Co content in the catalyst, the interaction between the metallic components was transformed and the Cu-Co spinel phase was generated, leading to a slight decrease of alcohol selectivity.
A series of Cu-Fe-Co based catalysts with different mass fractions of Fe and Co were prepared by co-impregnation method. The catalytic performances of the catalysts for mixed alcohols synthesis from carbon monoxide hydrogenation were investigated in a fixed bed flow reactor. The samples were characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscope (FE-SEM), and H2 temperature-programmed reduction (H2-TPR). The results showed that the addition of a suitable content of Co to the Cu-Fe based catalyst significantly improved the space-time yield (STY) and CO conversion while alcohol selectivity was constant. For the catalyst with a mass fraction of Cu, Fe, and Co of 25%, 22%, and 3%, respectively, a STY of 205.6 g·kg-1·h-1 and CO conversion of 56.6% were obtained. The XRD, XPS, and TPR results showed that when the Cu content was unchanged, the introduction of some Co contributed to the formation of a small quantity of the CuFe2O4 phase on the surface of catalysts, which promoted the interaction between Cu and Fe, improved the dispersion of active components and enhanced the catalytic activity and STY of the mixed alcohols. With an increase of the Co content in the catalyst, the interaction between the metallic components was transformed and the Cu-Co spinel phase was generated, leading to a slight decrease of alcohol selectivity.
2011, 27(11): 2639-2645
doi: 10.3866/PKU.WHXB20111125
Abstract:
A series of Ce-Cu-Fe/SiO2 catalysts with different Ce contents (mole fraction relative to SiO2, 0-20%) were prepared by co-impregnation and their catalytic performances for CO hydrogenation to lower alcohols were investigated using a continuous flow fixed bed micro-reactor. These catalysts were characterized by X-ray diffraction (XRD), N2-adsorption, temperature-programmed reduction of H2 (H2-TPR), Fourier transform infrared of CO adsorption (CO-FTIR), and temperature-programmed desorption of CO (CO-TPD). The results showed that the addition of an appropriate amount of Ce decreased the Cu crystal size and promoted the dispersion of Cu, which greatly increased the amount of adsorbed CO. Additionally, the interaction of doped Ce with Cu increased the associative and dissociate adsorption capacity of CO, which is favorable for the formation of CHx and the insertion reaction of adsorbed CO to CHx. Both the activity and alcohol selectivity of the Cu-Fe/SiO2 catalyst increased under the combined effect of the above-mentioned two aspects. At a Ce content of 10%, the space time yield of lower alcohols improved from 58.0 g·kg-1·h-1 over the Cu-Fe/SiO2 catalyst to 121.0 g·kg-1·h-1 over the Ce-Cu-Fe/SiO2 catalyst at 250 °C, a pressure of 3.0 MPa, a H2/CO molar ratio of 2, and gas hourly space velocity of 6000 mL·g-1·h-1.
A series of Ce-Cu-Fe/SiO2 catalysts with different Ce contents (mole fraction relative to SiO2, 0-20%) were prepared by co-impregnation and their catalytic performances for CO hydrogenation to lower alcohols were investigated using a continuous flow fixed bed micro-reactor. These catalysts were characterized by X-ray diffraction (XRD), N2-adsorption, temperature-programmed reduction of H2 (H2-TPR), Fourier transform infrared of CO adsorption (CO-FTIR), and temperature-programmed desorption of CO (CO-TPD). The results showed that the addition of an appropriate amount of Ce decreased the Cu crystal size and promoted the dispersion of Cu, which greatly increased the amount of adsorbed CO. Additionally, the interaction of doped Ce with Cu increased the associative and dissociate adsorption capacity of CO, which is favorable for the formation of CHx and the insertion reaction of adsorbed CO to CHx. Both the activity and alcohol selectivity of the Cu-Fe/SiO2 catalyst increased under the combined effect of the above-mentioned two aspects. At a Ce content of 10%, the space time yield of lower alcohols improved from 58.0 g·kg-1·h-1 over the Cu-Fe/SiO2 catalyst to 121.0 g·kg-1·h-1 over the Ce-Cu-Fe/SiO2 catalyst at 250 °C, a pressure of 3.0 MPa, a H2/CO molar ratio of 2, and gas hourly space velocity of 6000 mL·g-1·h-1.
Effect of Preparation Methods on the Catalytic Activity of Ag-Ru/CeO2 Catalyst for Ammonia Synthesis
2011, 27(11): 2646-2650
doi: 10.3866/PKU.WHXB20111129
Abstract:
Ag-Ru/CeO2 catalysts were prepared by co-precipitation (CP), modified deposition precipitation (MDP), and incipient-wetness impregnation (IP). The obtained catalysts were characterized by N2 physisorption, X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), and temperatureprogrammed desorption of nitrogen (N2-TPD). The results showed that the ammonia synthesis activity of the Ag-Ru/CeO2 catalyst prepared by incipient-wetness impregnation was 9.4% at 10 MPa, 10000 h-1 and 400°C, which was higher than that obtained by other methods. There were obvious differences in the reduction property of Ru/CeO2 and in the nitrogen dissociation behavior among the catalysts prepared by different methods. Catalyst activity for the catalyst prepared by incipient-wetness impregnation improved greatly at a low reaction temperature. The high catalytic activity was due to the easier reduction of Ag-Ru/ CeO2 and the higher amount of dissociation of chemisorbed nitrogen.
Ag-Ru/CeO2 catalysts were prepared by co-precipitation (CP), modified deposition precipitation (MDP), and incipient-wetness impregnation (IP). The obtained catalysts were characterized by N2 physisorption, X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), and temperatureprogrammed desorption of nitrogen (N2-TPD). The results showed that the ammonia synthesis activity of the Ag-Ru/CeO2 catalyst prepared by incipient-wetness impregnation was 9.4% at 10 MPa, 10000 h-1 and 400°C, which was higher than that obtained by other methods. There were obvious differences in the reduction property of Ru/CeO2 and in the nitrogen dissociation behavior among the catalysts prepared by different methods. Catalyst activity for the catalyst prepared by incipient-wetness impregnation improved greatly at a low reaction temperature. The high catalytic activity was due to the easier reduction of Ag-Ru/ CeO2 and the higher amount of dissociation of chemisorbed nitrogen.
2011, 27(11): 2651-2658
doi: 10.3866/PKU.WHXB20111018
Abstract:
A series of CuO-TiO2-ZrO2 mixed oxides with different CuO mass fractions (50%-80%) were prepared by co-precipitation and characterized by X-ray diffraction (XRD), N2 physisorption, temperatureprogrammed reduction of hydrogen (H2-TPR), temperature-programmed desorption of carbon dioxide (CO2-TPD) and hydrogen (H2-TPD), and reactive N2O adsorption techniques. The prepared CuO-TiO2-ZrO2 samples were mixed physically with HZSM-5 zeolite to synthesize dimethyl ether (DME) from CO2 hydrogenation in a fixed bed reactor at 250°C, 3.0 MPa, gas hourly space velocity (GHSV) of 1500 mL·g-1· h-1, and volume ratio of 2.8 for H2 to CO2. We found that the conversion of CO2 increased with an increase in CuO content, reached a maximum at a CuO content of 70% and then decreased. The selectivity of DME increased with an increase in CuO content initially and remained essentially constant when the CuO content was ≥70%. Thus, the yield of DME reached a maximum of 13.2% at 70% CuO content. The productivity of the oxygenated compounds (including methanol and DME) on the CuO-TiO2-ZrO2/HZSM-5 catalysts is closely related to the metallic copper surface area.
A series of CuO-TiO2-ZrO2 mixed oxides with different CuO mass fractions (50%-80%) were prepared by co-precipitation and characterized by X-ray diffraction (XRD), N2 physisorption, temperatureprogrammed reduction of hydrogen (H2-TPR), temperature-programmed desorption of carbon dioxide (CO2-TPD) and hydrogen (H2-TPD), and reactive N2O adsorption techniques. The prepared CuO-TiO2-ZrO2 samples were mixed physically with HZSM-5 zeolite to synthesize dimethyl ether (DME) from CO2 hydrogenation in a fixed bed reactor at 250°C, 3.0 MPa, gas hourly space velocity (GHSV) of 1500 mL·g-1· h-1, and volume ratio of 2.8 for H2 to CO2. We found that the conversion of CO2 increased with an increase in CuO content, reached a maximum at a CuO content of 70% and then decreased. The selectivity of DME increased with an increase in CuO content initially and remained essentially constant when the CuO content was ≥70%. Thus, the yield of DME reached a maximum of 13.2% at 70% CuO content. The productivity of the oxygenated compounds (including methanol and DME) on the CuO-TiO2-ZrO2/HZSM-5 catalysts is closely related to the metallic copper surface area.
2011, 27(11): 2659-2664
doi: 10.3866/PKU.WHXB20111108
Abstract:
A series of SBA-15 supported vanadium oxide catalysts with different active components were prepared by the method of incipient-wet impregnation. The structures of the catalysts were characterized by N2 adsorption, X-ray diffraction (XRD), ultraviolet (UV)-Raman, Fourier transform infrared (FTIR), and ultraviolet-visble diffuse reflectance spectroscopy (UV-Vis DRS) techniques, and their catalytic performances for the selective oxidation of propane were investigated. The results showed that SBA-15 was a better support in the catalyst system than SiO2 for the selective oxidation of propane to aldehydes. The SBA-15 supported low loading catalyst is a highly dispersed catalyst system and the SBA-15 supported vanadium oxide samples with low loading (n(V)/n(Si)<2.5%) have ordered hexa nal mesostructures. For the VOx/SBA-15 catalysts, isolated vanadyl species with tetrahedral coordination are the active sites for aldehyde formation at very low loadings of vanadium (n(V)/n(Si)<0.1%). The polymeric vanadyl species with octahedral coordination and microcrystalline vanadium oxide are active sites for the oxidative dehydrogenation or deep oxidation of propane when the loading of vanadium (n(V)/n(Si)) is higher than 2.5%.
A series of SBA-15 supported vanadium oxide catalysts with different active components were prepared by the method of incipient-wet impregnation. The structures of the catalysts were characterized by N2 adsorption, X-ray diffraction (XRD), ultraviolet (UV)-Raman, Fourier transform infrared (FTIR), and ultraviolet-visble diffuse reflectance spectroscopy (UV-Vis DRS) techniques, and their catalytic performances for the selective oxidation of propane were investigated. The results showed that SBA-15 was a better support in the catalyst system than SiO2 for the selective oxidation of propane to aldehydes. The SBA-15 supported low loading catalyst is a highly dispersed catalyst system and the SBA-15 supported vanadium oxide samples with low loading (n(V)/n(Si)<2.5%) have ordered hexa nal mesostructures. For the VOx/SBA-15 catalysts, isolated vanadyl species with tetrahedral coordination are the active sites for aldehyde formation at very low loadings of vanadium (n(V)/n(Si)<0.1%). The polymeric vanadyl species with octahedral coordination and microcrystalline vanadium oxide are active sites for the oxidative dehydrogenation or deep oxidation of propane when the loading of vanadium (n(V)/n(Si)) is higher than 2.5%.
2011, 27(11): 2665-2670
doi: 10.3866/PKU.WHXB20111106
Abstract:
Much attention has been paid to alkaline ion-exchange membranes with high alkaline stability. In this work, chemically cross-linked poly(vinyl alcohol) modified quaterized hydroxyethylcellulose ethoxylate (PVA/QHECE) membranes were prepared and evaluated as OH--conducting polymer electrolytes. The membranes were characterized using Fourier transform infrared (FTIR) spectra, thermogravimetric (TG) analysis, and the alternating current (AC) impedance technique as for their inner structure, thermal stability, alkaline resistance stability, and OH- conductivity (σ). The OH- conductivity of the membranes was investigated as a function of cross-linking time, the content of cross-linking agent, polymer composition, and water uptake. It was found that membrane swelling decreased with cross-linking time accompanied by an improvement in mechanical properties but no obvious decrease in OH- conductivity resulted from the reduced water uptake. The OH- conductivities in the range of 3.26×10-4-4.44×10-4 S·cm-1 were obtained at room temperature ((19 ± 2)°C), depending on the different PVA/QHECE compositions. TG analysis showed that the PVA/QHECE membrane exhibited high thermal stability at up to 260°C when the QHECE content was 42.9%. In addition, the membranes had a high alkaline stability without a loss of integrity and OH- conductivity after immersion in 6 mol·L-1 KOH at 80°C for 168 h.
Much attention has been paid to alkaline ion-exchange membranes with high alkaline stability. In this work, chemically cross-linked poly(vinyl alcohol) modified quaterized hydroxyethylcellulose ethoxylate (PVA/QHECE) membranes were prepared and evaluated as OH--conducting polymer electrolytes. The membranes were characterized using Fourier transform infrared (FTIR) spectra, thermogravimetric (TG) analysis, and the alternating current (AC) impedance technique as for their inner structure, thermal stability, alkaline resistance stability, and OH- conductivity (σ). The OH- conductivity of the membranes was investigated as a function of cross-linking time, the content of cross-linking agent, polymer composition, and water uptake. It was found that membrane swelling decreased with cross-linking time accompanied by an improvement in mechanical properties but no obvious decrease in OH- conductivity resulted from the reduced water uptake. The OH- conductivities in the range of 3.26×10-4-4.44×10-4 S·cm-1 were obtained at room temperature ((19 ± 2)°C), depending on the different PVA/QHECE compositions. TG analysis showed that the PVA/QHECE membrane exhibited high thermal stability at up to 260°C when the QHECE content was 42.9%. In addition, the membranes had a high alkaline stability without a loss of integrity and OH- conductivity after immersion in 6 mol·L-1 KOH at 80°C for 168 h.
2011, 27(11): 2671-2676
doi: 10.3866/PKU.WHXB20111135
Abstract:
An effective approach to attach silver nanoparticles (AgNPs) directly onto an indium tin oxide (ITO) surface with high density was reported. An NH2+ ion implanted ITO (NH2/ITO) film was prepared and the AgNPs were adsorbed onto the surface of the obtained NH2/ITO film resulting in an AgNPs-attached NH2/ITO (AgNPs/NH2/ITO) substrate. Characterization of stepwise changes in the ITO, NH2/ITO, and AgNPs/NH2/ITO surfaces were carried out using Fourier transform infrared (FT-IR) spectrometry, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM), ultravioletvisible (UV-Vis) spectroscopy, and electrochemical methods. Cyclic voltammtric voltammetry results indicate that the immobilized AgNPs on the NH2/ITO electrode gave excellent electrochemical properties, implying facile electrochemical communication between the AgNPs and the ITO substrate through theby implanted amino groups. Thus, the AgNPs/NH2/ITO surfaces are promising as new functional interfaces because AgNPs can be attached to surfaces without the use of organic binding molecules.
An effective approach to attach silver nanoparticles (AgNPs) directly onto an indium tin oxide (ITO) surface with high density was reported. An NH2+ ion implanted ITO (NH2/ITO) film was prepared and the AgNPs were adsorbed onto the surface of the obtained NH2/ITO film resulting in an AgNPs-attached NH2/ITO (AgNPs/NH2/ITO) substrate. Characterization of stepwise changes in the ITO, NH2/ITO, and AgNPs/NH2/ITO surfaces were carried out using Fourier transform infrared (FT-IR) spectrometry, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM), ultravioletvisible (UV-Vis) spectroscopy, and electrochemical methods. Cyclic voltammtric voltammetry results indicate that the immobilized AgNPs on the NH2/ITO electrode gave excellent electrochemical properties, implying facile electrochemical communication between the AgNPs and the ITO substrate through theby implanted amino groups. Thus, the AgNPs/NH2/ITO surfaces are promising as new functional interfaces because AgNPs can be attached to surfaces without the use of organic binding molecules.
2011, 27(11): 2677-2681
doi: 10.3866/PKU.WHXB20111014
Abstract:
A high specific surface area Cr2O3-α-AlF3 catalyst was prepared using a carbon hard template method. The synthesis procedure consisted of three consecutive steps: (1) the impregnation of a sucrose (C12H22O11) aqueous solution with Cr2O3-γ-Al2O3 and subsequent thermal treatment; (2) the thermal treatment of the obtained solid with HF, C@Cr2O3-γ-Al2O3 can be completely transformed into C@Cr2O3-γ-AlF3 at 400°C with hydrogen fluoride; (3) the removal of the carbon template in C@Cr2O3-γ- AlF3 upon high temperature combustion giving the high surface area Cr2O3-γ-AlF3 (115 m2·g-1). The catalysts were characterized by X-ray diffraction (XRD), N2 physisorption, ammonia temperatureprogrammed desorption (NH3-TPD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersion X-ray (EDX) techniques. We found that the fluorination process was crucial for the resulting Cr2O3-α-AlF3 with a high specific surface area of 115 m2·g-1 under optimal conditions. The Cr2O3-α-AlF3 catalyst with a high specific surface area was more active for the decomposition of 1,1-difluoroethane than the catalyst prepared by the direct fluorination of Cr2O3-γ-Al2O3, because it contained a higher amount of acid sites.
A high specific surface area Cr2O3-α-AlF3 catalyst was prepared using a carbon hard template method. The synthesis procedure consisted of three consecutive steps: (1) the impregnation of a sucrose (C12H22O11) aqueous solution with Cr2O3-γ-Al2O3 and subsequent thermal treatment; (2) the thermal treatment of the obtained solid with HF, C@Cr2O3-γ-Al2O3 can be completely transformed into C@Cr2O3-γ-AlF3 at 400°C with hydrogen fluoride; (3) the removal of the carbon template in C@Cr2O3-γ- AlF3 upon high temperature combustion giving the high surface area Cr2O3-γ-AlF3 (115 m2·g-1). The catalysts were characterized by X-ray diffraction (XRD), N2 physisorption, ammonia temperatureprogrammed desorption (NH3-TPD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersion X-ray (EDX) techniques. We found that the fluorination process was crucial for the resulting Cr2O3-α-AlF3 with a high specific surface area of 115 m2·g-1 under optimal conditions. The Cr2O3-α-AlF3 catalyst with a high specific surface area was more active for the decomposition of 1,1-difluoroethane than the catalyst prepared by the direct fluorination of Cr2O3-γ-Al2O3, because it contained a higher amount of acid sites.
2011, 27(11): 2682-2690
doi: 10.3866/PKU.WHXB20111132
Abstract:
Hypocrellin B (HB) can chelate with Mg2+ and Zn2+ ions to form the coordination complexes Mg2+-HB and Zn2+-HB, which consist of 5-22 repeat units. The structures of these two complexes are characterized by ultraviolet-visible (UV-Vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and 1H nuclear magnetic resonance (1H NMR). The relative quantum yields of singlet oxygen (1O2) for Mg2+-HB and Zn2+-HB are 1.2 and 0.42 times as high as that of HB, respectively. Transient absorption spectra results indicate that O2 is able to quench the triplet excited state of Mg2+-HB and Zn2+-HB with an efficiency higher than 96% . The intersystem crossing efficiency (ΦT) and the fraction of triplet states quenched by O2 that yield 1O2 (fΔT) are considered to be essential for the singlet oxygen quantum yields of HB and its complexes. Electron paramagnetic resonance (EPR) results suggest that Mg2+-HB and Zn2+-HB have a weak ability to generate a semiquinone anion radical, which reduces the generation of the superoxide anion radical (O2·-) by Mg2+-HB and Zn2+-HB. The results of the UV-Vis spectra and the deoxyribonucleic acid (DNA) melting temperature experiments indicate that Mg2+-HB and Zn2+-HB bind with calf thymus (CT) DNA in an electrostatic interaction mode. Under aerobic conditions, the efficiencies of photoinduced damage to CT DNA by Mg2+-HB, HB, and Zn2+-HB are found to be 32%, 25%, and 22%, respectively. The reactive oxygen quencher experiments indicate that singlet oxygen is the main component generated by Mg2+-HB that damages CT DNA.
Hypocrellin B (HB) can chelate with Mg2+ and Zn2+ ions to form the coordination complexes Mg2+-HB and Zn2+-HB, which consist of 5-22 repeat units. The structures of these two complexes are characterized by ultraviolet-visible (UV-Vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and 1H nuclear magnetic resonance (1H NMR). The relative quantum yields of singlet oxygen (1O2) for Mg2+-HB and Zn2+-HB are 1.2 and 0.42 times as high as that of HB, respectively. Transient absorption spectra results indicate that O2 is able to quench the triplet excited state of Mg2+-HB and Zn2+-HB with an efficiency higher than 96% . The intersystem crossing efficiency (ΦT) and the fraction of triplet states quenched by O2 that yield 1O2 (fΔT) are considered to be essential for the singlet oxygen quantum yields of HB and its complexes. Electron paramagnetic resonance (EPR) results suggest that Mg2+-HB and Zn2+-HB have a weak ability to generate a semiquinone anion radical, which reduces the generation of the superoxide anion radical (O2·-) by Mg2+-HB and Zn2+-HB. The results of the UV-Vis spectra and the deoxyribonucleic acid (DNA) melting temperature experiments indicate that Mg2+-HB and Zn2+-HB bind with calf thymus (CT) DNA in an electrostatic interaction mode. Under aerobic conditions, the efficiencies of photoinduced damage to CT DNA by Mg2+-HB, HB, and Zn2+-HB are found to be 32%, 25%, and 22%, respectively. The reactive oxygen quencher experiments indicate that singlet oxygen is the main component generated by Mg2+-HB that damages CT DNA.
2011, 27(11): 2691-2696
doi: 10.3866/PKU.WHXB20111019
Abstract:
A novel photosensitive telechelic polymer C-PDMAEMA was prepared using 2-(dimethylamino) ethyl methacrylate (DAMEMA) as a monomer, azobisisobutyronitrile (AIBN) as inititon, coumarincontaining disulfides (C-S-S-C) as a chain transfer agent in the presence of tributyl phosphine (Bu3P) and water. Characterization was carried out using 1H-nuclear magnetic responance (1H-NMR), gel permeation chromatography (GPC) and Fourier transform infrared (FTIR) spectroscopy. It was found that the coumarin can form a host-guest inclusion complex with β-CD in aqueous solution. The UV-Vis and fluorescence spectra showed that only a 1:1 complex was formed with an inclusion complex K=(1.270±0.062)×104 L· mol-1. The irradiation experiment showed that this host-guest inclusion might have a very small effect on the photodimerization of coumarin end groups.
A novel photosensitive telechelic polymer C-PDMAEMA was prepared using 2-(dimethylamino) ethyl methacrylate (DAMEMA) as a monomer, azobisisobutyronitrile (AIBN) as inititon, coumarincontaining disulfides (C-S-S-C) as a chain transfer agent in the presence of tributyl phosphine (Bu3P) and water. Characterization was carried out using 1H-nuclear magnetic responance (1H-NMR), gel permeation chromatography (GPC) and Fourier transform infrared (FTIR) spectroscopy. It was found that the coumarin can form a host-guest inclusion complex with β-CD in aqueous solution. The UV-Vis and fluorescence spectra showed that only a 1:1 complex was formed with an inclusion complex K=(1.270±0.062)×104 L· mol-1. The irradiation experiment showed that this host-guest inclusion might have a very small effect on the photodimerization of coumarin end groups.
2011, 27(11): 2697-2704
doi: 10.3866/PKU.WHXB20111122
Abstract:
Glycidyl methacrylate (GMA) was graft-polymerized onto micron-sized silica gel particles. Ethylenediamine (EDA) was bonded to the surfaces of PGMA/SiO2 particles by the ring-opening reaction of epoxy groups resulting in the difunctional composite carrier, EDA-PGMA/SiO2, which was used for enzyme immobilization. We immobilized horseradish peroxidase (HRP) using the chemical bonding method. In this work, the effects and action mechanisms of two secondary bond forces, electrostatic interaction and hydrophobic interaction, on the enzyme immobilization were investigated. The experimental results show that the protonated amino groups on the EDA-PGMA/SiO2 particles enable the carrier particles to be positively charged and the zeta potential of the carrier particles are positive over a wider range of pH values. At a pH value of 8.5 for the medium, which is higher than the isoelectric point of HRP, the strong electrostatic interaction between the enzyme protein and the carrier significantly promotes the immobilization of HRP. For the carrier with an EDA bonding rate of about 30%, the strongest electrostatic interaction was observed between the enzyme protein and the carrier while the immobilized enzyme has the highest coupling rate and specific activity. Hydrophobic interaction between the enzyme protein and the carrier also affects HRP immobilization greatly. As the grafted particles PGMA/SiO2 are used as the carrier, the addition of NaCl electrolyte will facilitate the hydrophobic interaction between the enzyme protein and the carrier and it will result in an increase in the coupling rate and specific activity of the immobilized enzyme.
Glycidyl methacrylate (GMA) was graft-polymerized onto micron-sized silica gel particles. Ethylenediamine (EDA) was bonded to the surfaces of PGMA/SiO2 particles by the ring-opening reaction of epoxy groups resulting in the difunctional composite carrier, EDA-PGMA/SiO2, which was used for enzyme immobilization. We immobilized horseradish peroxidase (HRP) using the chemical bonding method. In this work, the effects and action mechanisms of two secondary bond forces, electrostatic interaction and hydrophobic interaction, on the enzyme immobilization were investigated. The experimental results show that the protonated amino groups on the EDA-PGMA/SiO2 particles enable the carrier particles to be positively charged and the zeta potential of the carrier particles are positive over a wider range of pH values. At a pH value of 8.5 for the medium, which is higher than the isoelectric point of HRP, the strong electrostatic interaction between the enzyme protein and the carrier significantly promotes the immobilization of HRP. For the carrier with an EDA bonding rate of about 30%, the strongest electrostatic interaction was observed between the enzyme protein and the carrier while the immobilized enzyme has the highest coupling rate and specific activity. Hydrophobic interaction between the enzyme protein and the carrier also affects HRP immobilization greatly. As the grafted particles PGMA/SiO2 are used as the carrier, the addition of NaCl electrolyte will facilitate the hydrophobic interaction between the enzyme protein and the carrier and it will result in an increase in the coupling rate and specific activity of the immobilized enzyme.
2011, 27(11): 2705-2710
doi: 10.3866/PKU.WHXB20111111
Abstract:
The folding dynamics of a completely stretched dexoxyribonucleic acid (DNA) molecule chain is an important feature of single DNA mechanics. By constructing a fully parameterized bead-spring chain model and applying a highly efficient second order semi-implicit predictor-corrector al rithm, we studied the influence of three nonlinear interactions including the excluded volume interaction, the finite extensible nonlinear elastic interaction, and the fluctuating hydrodynamic interaction on the folding process. Simulation results show that the excluded volume interaction decreases the relative radius of gyration of the DNA chain obviously but has no influence on the relaxation time. Instead, the hydrodynamic interaction clearly decreases the relaxation time but it does not change the relative radius of gyration. In addition, the finite extensible elastic interaction was found to decrease the relative radius of gyration of the short chain clearly and increase the relaxation time of the long chain obviously. Furthermore, we obtained a smooth change for the relative radius of gyration with time. The scaling exponent of the relaxation time with the length of chain has two different values under all three nonlinear interactions. These results complete our understanding about single DNA molecule chain mechanics in solution.
The folding dynamics of a completely stretched dexoxyribonucleic acid (DNA) molecule chain is an important feature of single DNA mechanics. By constructing a fully parameterized bead-spring chain model and applying a highly efficient second order semi-implicit predictor-corrector al rithm, we studied the influence of three nonlinear interactions including the excluded volume interaction, the finite extensible nonlinear elastic interaction, and the fluctuating hydrodynamic interaction on the folding process. Simulation results show that the excluded volume interaction decreases the relative radius of gyration of the DNA chain obviously but has no influence on the relaxation time. Instead, the hydrodynamic interaction clearly decreases the relaxation time but it does not change the relative radius of gyration. In addition, the finite extensible elastic interaction was found to decrease the relative radius of gyration of the short chain clearly and increase the relaxation time of the long chain obviously. Furthermore, we obtained a smooth change for the relative radius of gyration with time. The scaling exponent of the relaxation time with the length of chain has two different values under all three nonlinear interactions. These results complete our understanding about single DNA molecule chain mechanics in solution.
2011, 27(11): 2711-2718
doi: 10.3866/PKU.WHXB20111134
Abstract:
Without using aqueous ammonia and a surface modifier, a facile one-step method was developed to fabricate Fe nanoparticles coated with a SiO2 shell (Fe@SiO2) by a modified Stöber method combined with an aqueous reduction method. The Fe@SiO2 was prepared by directly adding potassium borohydride to a mixed solution of tetraethylorthosilicate (TEOS) and anhydrous ferric chloride. The structure and morphology of the as-synthesized powders were investigated by X-ray powder diffraction (XRD), energy dispersion analysis of X-ray (EDAX), transmission electron microscopy (TEM), ultraviolet-visible (UV-Vis) absorption spectroscopy, Fourier-transform infrared (FTIR) spectrometry and X-ray photoelectron spectroscopy (XPS). The feasibility of using the prepared Fe@SiO2 for the reductive immobilization of Cr(VI) in water was studied. The influence of TEOS addition on Cr(VI) removal by Fe@SiO2 was investigated. The results showed that the prepared Fe@SiO2 had a distinct core-shell structure. One or two Fe nanoparticles (20-30 nm in diameter) were homogeneously coated by a porous SiO2 shell. With an increase in the amount of added TEOS the Fe nanoparticles had better dispersion and the thickness of the SiO2 coating increased gradually. Compared with uncoated Fe nanoparticles, Cr(VI) removal by Fe@SiO2 increased greatly. At a TEOS dosage of 0.1 mL the removal ability of the prepared Fe@SiO2 was the highest. The highest removal ability of Fe@SiO2 was 466.67 mg·g-1 and it was only 76.35 mg·g-1 for uncoated Fe nanoparticles.
Without using aqueous ammonia and a surface modifier, a facile one-step method was developed to fabricate Fe nanoparticles coated with a SiO2 shell (Fe@SiO2) by a modified Stöber method combined with an aqueous reduction method. The Fe@SiO2 was prepared by directly adding potassium borohydride to a mixed solution of tetraethylorthosilicate (TEOS) and anhydrous ferric chloride. The structure and morphology of the as-synthesized powders were investigated by X-ray powder diffraction (XRD), energy dispersion analysis of X-ray (EDAX), transmission electron microscopy (TEM), ultraviolet-visible (UV-Vis) absorption spectroscopy, Fourier-transform infrared (FTIR) spectrometry and X-ray photoelectron spectroscopy (XPS). The feasibility of using the prepared Fe@SiO2 for the reductive immobilization of Cr(VI) in water was studied. The influence of TEOS addition on Cr(VI) removal by Fe@SiO2 was investigated. The results showed that the prepared Fe@SiO2 had a distinct core-shell structure. One or two Fe nanoparticles (20-30 nm in diameter) were homogeneously coated by a porous SiO2 shell. With an increase in the amount of added TEOS the Fe nanoparticles had better dispersion and the thickness of the SiO2 coating increased gradually. Compared with uncoated Fe nanoparticles, Cr(VI) removal by Fe@SiO2 increased greatly. At a TEOS dosage of 0.1 mL the removal ability of the prepared Fe@SiO2 was the highest. The highest removal ability of Fe@SiO2 was 466.67 mg·g-1 and it was only 76.35 mg·g-1 for uncoated Fe nanoparticles.
2011, 27(11): 2719-2725
doi: 10.3866/PKU.WHXB20111110
Abstract:
Novel nanoporous silicon was successfully converted from SiO2 aerogels by a template-confined magnesiothermic reduction at low temperature (650°C) based on a gas-solid reaction. The composition, crystal structure, morphology, and pore structure of the samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett- Teller (BET) surface area analysis. Their optical and electrochemical properties were also investigated. The results indicated that the products consisted of nanocrystalline silicon, retained a morphology similar to that of the original templates, and possessed a specific surface area as high as 602 m2·g-1. They also showed red photoluminescence at room temperature and had a high capacity and od Li-ion insertion/extraction properties for use in lithium ion batteries.
Novel nanoporous silicon was successfully converted from SiO2 aerogels by a template-confined magnesiothermic reduction at low temperature (650°C) based on a gas-solid reaction. The composition, crystal structure, morphology, and pore structure of the samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett- Teller (BET) surface area analysis. Their optical and electrochemical properties were also investigated. The results indicated that the products consisted of nanocrystalline silicon, retained a morphology similar to that of the original templates, and possessed a specific surface area as high as 602 m2·g-1. They also showed red photoluminescence at room temperature and had a high capacity and od Li-ion insertion/extraction properties for use in lithium ion batteries.
2011, 27(11): 2726-2732
doi: 10.3866/PKU.WHXB20111131
Abstract:
Well-ordered TiO2 nanotube arrays were prepared by electrochemical anodization onto a pure Ti sheet in an organic solution. Reduced cerium and oxidized cerium were deposited onto the TiO2 nanotube arrays by electrochemical cathodic reduction and then anodic oxidation. The morphology and crystalline phase were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), which indicated that the reduced cerium was in the form of elemental cerium nanofibers and they were dispersed over the surface of the TiO2 nanotube. The oxidized cerium was present as elemental cerium and cerium dioxide after oxidation. The photocurrent was measured and the bandgap energies were calculated. The results showed that the photocurrent response of the TiO2 nanotube arrays modified by the reduced cerium was enhanced in the visible spectra rather than in the UV spectra. The optimum amount of deposition was found for the sample prepared using the 10 mmol·L-1 cerium nitrate solution and with a bandgap energy of 2.88 eV. Also, the carrier density increased and the flat band potentials moved to the negative direction as the cerium content increased. After anodic oxidation, the photocurrent response of the samples increased in the visible spectra and in the UV spectra. However, the photocurrent response modified by oxidized cerium in visible spectra is weaker than that of the TiO2 nanotube arrays modified by reduced cerium.
Well-ordered TiO2 nanotube arrays were prepared by electrochemical anodization onto a pure Ti sheet in an organic solution. Reduced cerium and oxidized cerium were deposited onto the TiO2 nanotube arrays by electrochemical cathodic reduction and then anodic oxidation. The morphology and crystalline phase were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), which indicated that the reduced cerium was in the form of elemental cerium nanofibers and they were dispersed over the surface of the TiO2 nanotube. The oxidized cerium was present as elemental cerium and cerium dioxide after oxidation. The photocurrent was measured and the bandgap energies were calculated. The results showed that the photocurrent response of the TiO2 nanotube arrays modified by the reduced cerium was enhanced in the visible spectra rather than in the UV spectra. The optimum amount of deposition was found for the sample prepared using the 10 mmol·L-1 cerium nitrate solution and with a bandgap energy of 2.88 eV. Also, the carrier density increased and the flat band potentials moved to the negative direction as the cerium content increased. After anodic oxidation, the photocurrent response of the samples increased in the visible spectra and in the UV spectra. However, the photocurrent response modified by oxidized cerium in visible spectra is weaker than that of the TiO2 nanotube arrays modified by reduced cerium.
