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2017 Volume 33 Issue 4
2017, 33(4):
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2017, 33(4): 645-646
doi: 10.3866/PKU.WHXB201703031
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2017, 33(4): 647-648
doi: 10.3866/PKU.WHXB201703071
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2017, 33(4): 649-650
doi: 10.3866/PKU.WHXB201703072
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2017, 33(4): 651-652
doi: 10.3866/PKU.WHXB201703091
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2017, 33(4): 653-654
doi: 10.3866/PKU.WHXB201703092
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2017, 33(4): 655-655
doi: 10.3866/PKU.WHXB201703093
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2017, 33(4): 656-660
doi: 10.3866/PKU.WHXB201701162
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It is an important challenge to balance the degradability and stability of polymer vesicles. We report a thermo-responsive vesicle based on poly[(N-isopropyl acrylamide-stat-7-(2-methacryloyloxyethoxy)-4-methylcoumarin)-b-(L-glutamic acid)] [P(NIPAM45-stat-CMA5)-b-PGA42] diblock copolymer, which was synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization and ring-opening polymerization (ROP). The membrane of the vesicle consists of thermo-responsive PNIPAM and photo-cross-linkable PCMA. The PGA chains in the vesicle coronas can colloidally stabilize the vesicles in water and can be postfunctionalized for further applications. Transmission electron microscopy and dynamic light scattering studies confirmed the formation of vesicles. Overall, we prepared a new functional thermo-responsive vesicle based on polypeptide copolymers that may be used as nanocarriers for the facile loading of a range of molecules in future.
It is an important challenge to balance the degradability and stability of polymer vesicles. We report a thermo-responsive vesicle based on poly[(N-isopropyl acrylamide-stat-7-(2-methacryloyloxyethoxy)-4-methylcoumarin)-b-(L-glutamic acid)] [P(NIPAM45-stat-CMA5)-b-PGA42] diblock copolymer, which was synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization and ring-opening polymerization (ROP). The membrane of the vesicle consists of thermo-responsive PNIPAM and photo-cross-linkable PCMA. The PGA chains in the vesicle coronas can colloidally stabilize the vesicles in water and can be postfunctionalized for further applications. Transmission electron microscopy and dynamic light scattering studies confirmed the formation of vesicles. Overall, we prepared a new functional thermo-responsive vesicle based on polypeptide copolymers that may be used as nanocarriers for the facile loading of a range of molecules in future.
2017, 33(4): 661-669
doi: 10.3866/PKU.WHXB201701171
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The surface plasmons of metal nanocrystals provide a new opportunity for converting solar energy to chemical energy. In this article, we outline the mechanisms of surface plasmons in catalytic organic hydrogenation based on our recent studies, where efficient conversion of solar to chemical energy was achieved. This paved the way to replacing heat-based catalysis in conventional chemical manufacturing with solar energy, providing guidance for designing plasmonic catalytic materials.
The surface plasmons of metal nanocrystals provide a new opportunity for converting solar energy to chemical energy. In this article, we outline the mechanisms of surface plasmons in catalytic organic hydrogenation based on our recent studies, where efficient conversion of solar to chemical energy was achieved. This paved the way to replacing heat-based catalysis in conventional chemical manufacturing with solar energy, providing guidance for designing plasmonic catalytic materials.
2017, 33(4): 670-690
doi: 10.3866/PKU.WHXB201701101
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The counter electrode (CE) is an important part of a quantum dot-sensitized solar cell (QDSSC). Improving CE performance is an effective approach to enhance the photovoltaic conversion efficiency of QDSSCs. In this paper, the required properties of CEs are briefly introduced. Recent progress in the study and fabrication methods of QDSSC CEs composed of various materials, including metals, conductive polymers, carbon, metal sulfide, other inorganic metallic compounds, and composites, are reviewed. CEs made of inorganic metallic compounds like copper sulfide, cobalt sulfide, and lead sulfide are the most widely studied because of their high catalytic ability and low cost. Meanwhile, research on CEs made of conductive polymers, new carbon materials, and a variety of composite materials is expanding because of their respective advantages.
The counter electrode (CE) is an important part of a quantum dot-sensitized solar cell (QDSSC). Improving CE performance is an effective approach to enhance the photovoltaic conversion efficiency of QDSSCs. In this paper, the required properties of CEs are briefly introduced. Recent progress in the study and fabrication methods of QDSSC CEs composed of various materials, including metals, conductive polymers, carbon, metal sulfide, other inorganic metallic compounds, and composites, are reviewed. CEs made of inorganic metallic compounds like copper sulfide, cobalt sulfide, and lead sulfide are the most widely studied because of their high catalytic ability and low cost. Meanwhile, research on CEs made of conductive polymers, new carbon materials, and a variety of composite materials is expanding because of their respective advantages.
2017, 33(4): 691-708
doi: 10.3866/PKU.WHXB201612191
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Enzymatic catalytic processes generally involve substrate delivery, selective catalytic reaction, and product release. Owing to the complex protein environment effect, any nonchemical or chemical step may determine the enzyme activity. Herein, to comprehensively understand enzymatic activity, extensive combined quantum mechanics/molecular mechanics (QM/MM) and molecular mechanics (MM) molecular dynamics (MD) simulations were carried out on several kinds of enzymes. Possible reaction mechanisms, roles of the conserved residues, and effects of the protein environment on the whole enzymatic process are discussed in detail, which will enrich the knowledge of reactivity in proteins. With the improvement and development of multiscale models and computational methods, it is expected that global simulations of extremely large and complicated enzymes will enable and lend support to enzyme engineering.
Enzymatic catalytic processes generally involve substrate delivery, selective catalytic reaction, and product release. Owing to the complex protein environment effect, any nonchemical or chemical step may determine the enzyme activity. Herein, to comprehensively understand enzymatic activity, extensive combined quantum mechanics/molecular mechanics (QM/MM) and molecular mechanics (MM) molecular dynamics (MD) simulations were carried out on several kinds of enzymes. Possible reaction mechanisms, roles of the conserved residues, and effects of the protein environment on the whole enzymatic process are discussed in detail, which will enrich the knowledge of reactivity in proteins. With the improvement and development of multiscale models and computational methods, it is expected that global simulations of extremely large and complicated enzymes will enable and lend support to enzyme engineering.
2017, 33(4): 709-728
doi: 10.3866/PKU.WHXB201612201
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Two-dimensional (2D) materials possess nanoscale thickness with large aspect ratios on the other two dimensions. The ultrahigh surface-to-volume ratio of 2D materials is the most important property different from their bulk counterparts, and is beneficial for mass and heat transport, and ion diffusion. Among the various 2D materials, carbon-based materials have attracted tremendous attentions since the first explosive research on graphene. Therefore, they provide opportunities for applications in adsorption, catalysis, and electrical energy storage. The porous structure of such carbon materials is a key influence on the properties of these 2D materials. This review focuses on recent developments in synthesis strategies for 2D carbon-based materials, especially the preparation of carbon nanosheets and carbon-inorganic hybrids/composites nanosheets. The main factors influencing the porous structure of the material are discussed for each method. Applications of the materials are introduced, mainly in the fields of adsorption, heterogeneous catalysis, and electrical energy storage. Finally, the leading-edge issues of novel 2D carbon-based materials for the future are discussed.
Two-dimensional (2D) materials possess nanoscale thickness with large aspect ratios on the other two dimensions. The ultrahigh surface-to-volume ratio of 2D materials is the most important property different from their bulk counterparts, and is beneficial for mass and heat transport, and ion diffusion. Among the various 2D materials, carbon-based materials have attracted tremendous attentions since the first explosive research on graphene. Therefore, they provide opportunities for applications in adsorption, catalysis, and electrical energy storage. The porous structure of such carbon materials is a key influence on the properties of these 2D materials. This review focuses on recent developments in synthesis strategies for 2D carbon-based materials, especially the preparation of carbon nanosheets and carbon-inorganic hybrids/composites nanosheets. The main factors influencing the porous structure of the material are discussed for each method. Applications of the materials are introduced, mainly in the fields of adsorption, heterogeneous catalysis, and electrical energy storage. Finally, the leading-edge issues of novel 2D carbon-based materials for the future are discussed.
2017, 33(4): 729-735
doi: 10.3866/PKU.WHXB201611291
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Seven series of 3,4'-disubstituted stilbenes were synthesized, with meta-substituents X (m-XSBYp) including: NO2, I, CHCH2, Ph, Et, NMe2, and CCH (m-XSBY-p). The longest wavelength maximum λmax (nm) in ultraviolet absorption spectra of the compounds were measured. A quantitative correlation analysis was performed in terms of energy, the Vmax (cm-1) for 3,4'-disubstituted stilbenes. The excited-state substituent constants σCC(m)ex of the seven meta-substituents were determined by curve-fitting. The constants σCCex of the metaand para-substituents were compared with their Hammett constants σ. The results indicated that σCCex and σ express the substituent electrostatic effects in the excited-and ground-states, respectively. In addition, 10 samples of aryl Schiff bases and 14 samples of 3,3'-disubstituted stilbenes with meta-substituents X were synthesized, and their λmax,pred. were predicated based on the obtained constants σCC(m)ex. These results showed that the λmax,pred. values agreed well with the experimental values, and confirmed the reliability of the obtained σCC(m)ex values. We also collected Vmax values of 225 samples of disubstituted stilbenes and disubstituted benzenes and established a general quantitative equation to express the change regularity of their Vmax.
Seven series of 3,4'-disubstituted stilbenes were synthesized, with meta-substituents X (m-XSBYp) including: NO2, I, CHCH2, Ph, Et, NMe2, and CCH (m-XSBY-p). The longest wavelength maximum λmax (nm) in ultraviolet absorption spectra of the compounds were measured. A quantitative correlation analysis was performed in terms of energy, the Vmax (cm-1) for 3,4'-disubstituted stilbenes. The excited-state substituent constants σCC(m)ex of the seven meta-substituents were determined by curve-fitting. The constants σCCex of the metaand para-substituents were compared with their Hammett constants σ. The results indicated that σCCex and σ express the substituent electrostatic effects in the excited-and ground-states, respectively. In addition, 10 samples of aryl Schiff bases and 14 samples of 3,3'-disubstituted stilbenes with meta-substituents X were synthesized, and their λmax,pred. were predicated based on the obtained constants σCC(m)ex. These results showed that the λmax,pred. values agreed well with the experimental values, and confirmed the reliability of the obtained σCC(m)ex values. We also collected Vmax values of 225 samples of disubstituted stilbenes and disubstituted benzenes and established a general quantitative equation to express the change regularity of their Vmax.
2017, 33(4): 736-744
doi: 10.3866/PKU.WHXB201612293
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Two air and water stable hydrophobic phosphonium ionic liquids (ILs), tributyl-hexylphosphonium tetrafluoroborate ([P4446][BF4]) and tributyl-hexylphosphonium bis(trifluoromethylsulfonyl)imide ([P4446][NTf2]), were prepared by the traditional method. Their basic physico-chemical properties of density, dynamic viscosity, and electrical conductivity were measured in the temperature range of 283.15-353.15 K. The effect of the temperature and structure of the anion on the thermodynamic properties were discussed. The properties are compared with the cation structures changing of the phosphonium type ILs. The most important thermodynamic properties for their practical application, such as molecular volume, standard molar entropy, and lattice energy, were calculated from their density using empirical equations. The calculated values were compared with those of imdazolium and pyridinium type ILs. Molar electrical conductivity was determined from density and electrical conductivity. The applicability of the Vogel-Fulcher-Tamman (VFT) and Arrhenius equations to the fitting of the dynamic viscosity and electrical conductivity was validated. The activation of the electrical conductivity and dynamic viscosity were obtained from the final VFT equation. According to the Walden rule, the density, dynamic viscosity, and electrical conductivity were described by the Walden equation. The results are very important for academic studies as well as industrial applications of these ILs.
Two air and water stable hydrophobic phosphonium ionic liquids (ILs), tributyl-hexylphosphonium tetrafluoroborate ([P4446][BF4]) and tributyl-hexylphosphonium bis(trifluoromethylsulfonyl)imide ([P4446][NTf2]), were prepared by the traditional method. Their basic physico-chemical properties of density, dynamic viscosity, and electrical conductivity were measured in the temperature range of 283.15-353.15 K. The effect of the temperature and structure of the anion on the thermodynamic properties were discussed. The properties are compared with the cation structures changing of the phosphonium type ILs. The most important thermodynamic properties for their practical application, such as molecular volume, standard molar entropy, and lattice energy, were calculated from their density using empirical equations. The calculated values were compared with those of imdazolium and pyridinium type ILs. Molar electrical conductivity was determined from density and electrical conductivity. The applicability of the Vogel-Fulcher-Tamman (VFT) and Arrhenius equations to the fitting of the dynamic viscosity and electrical conductivity was validated. The activation of the electrical conductivity and dynamic viscosity were obtained from the final VFT equation. According to the Walden rule, the density, dynamic viscosity, and electrical conductivity were described by the Walden equation. The results are very important for academic studies as well as industrial applications of these ILs.
2017, 33(4): 745-754
doi: 10.3866/PKU.WHXB201701161
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The thermal decomposition mechanisms of cyclotrimethylene trinitramine (RDX) and its derivatives are investigated using ReaxFF reactive molecular dynamics simulation at high temperatures (2000, 2500, and 3000 K). It is shown that the first pyrolysis step of RDX and its derivatives is the N―NO2 homolytic cleavage to produce NO2; however, the subsequent reaction mechanism is completely different due to the different sixmembered rings and side chain groups. In these four model systems, NO2 and NO molecules are common intermediates in the thermal decomposition process, which eventually transform to N2 in the following reactions. The most stable products are N2, H2O, and CO2 in the thermal process, among which N2 has the maximum molecular number (more than 20). The numbers of cracked H2O and CO2 molecules are very different in the four model systems due to the different C/N and H/O ratios. At different temperatures, the maximum numbers of carbon atoms in the carbon clusters are all small in the unit cell simulations of the four systems. In the further super cell simulation for RDX and RDX-D2 the numbers of carbon atoms reach about 30 and 16, respectively, which are higher than those from the unit cell simulation. In both the unit and super cell simulations for RDX-D1 and RDX-D3, the carbon cluster cannot be formed and there exist only small carbon molecular fragments. Therefore, the initial molecular structure and elemental ratio have a large effect on the production of carbon clusters.
The thermal decomposition mechanisms of cyclotrimethylene trinitramine (RDX) and its derivatives are investigated using ReaxFF reactive molecular dynamics simulation at high temperatures (2000, 2500, and 3000 K). It is shown that the first pyrolysis step of RDX and its derivatives is the N―NO2 homolytic cleavage to produce NO2; however, the subsequent reaction mechanism is completely different due to the different sixmembered rings and side chain groups. In these four model systems, NO2 and NO molecules are common intermediates in the thermal decomposition process, which eventually transform to N2 in the following reactions. The most stable products are N2, H2O, and CO2 in the thermal process, among which N2 has the maximum molecular number (more than 20). The numbers of cracked H2O and CO2 molecules are very different in the four model systems due to the different C/N and H/O ratios. At different temperatures, the maximum numbers of carbon atoms in the carbon clusters are all small in the unit cell simulations of the four systems. In the further super cell simulation for RDX and RDX-D2 the numbers of carbon atoms reach about 30 and 16, respectively, which are higher than those from the unit cell simulation. In both the unit and super cell simulations for RDX-D1 and RDX-D3, the carbon cluster cannot be formed and there exist only small carbon molecular fragments. Therefore, the initial molecular structure and elemental ratio have a large effect on the production of carbon clusters.
2017, 33(4): 755-762
doi: 10.3866/PKU.WHXB201612292
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A scheme that explicitly contains electrostatic, polarization, and dispersion interactions to rapidly simulate anion-π interactions is proposed and assessed by structural and energetic comparison with those produced via the complete basis set limit of the coupled-cluster singles and doubles plus perturbative triples [CCSD(T)/CBS] method for a set of X-…C6H6-nRn complexes where X- = F-, Cl-, Br- and R = CN, F. We use the chemical bonds C≡N, C―F, and C―H of the substituted benzenes as bond dipoles. The electrostatic interactions are estimated by calculating the interactions between the charge of the anion and the bond dipole moments of the substituted benzene. The polarization interactions are described according to the variation of the magnitudes of the bond dipole moments with the local environment. The parameters needed are produced by fitting the high-quality CCSD(T)/CBS potential energy curves. Calculation results show that our scheme produces equilibrium intermolecular distances with a root-mean-square deviation of 0.004 nm and interaction energies with a root-mean-square deviation of 2.81 kJ·mol-1 compared with the CCSD(T)/CBS results. The calculation results also show that our scheme reproduces the CCSD(T)/CBS potential energy curves well. These comparisons indicate the scheme proposed here is accurate and efficient, suggesting it may be a helpful tool to design and simulate relevant molecular materials.
A scheme that explicitly contains electrostatic, polarization, and dispersion interactions to rapidly simulate anion-π interactions is proposed and assessed by structural and energetic comparison with those produced via the complete basis set limit of the coupled-cluster singles and doubles plus perturbative triples [CCSD(T)/CBS] method for a set of X-…C6H6-nRn complexes where X- = F-, Cl-, Br- and R = CN, F. We use the chemical bonds C≡N, C―F, and C―H of the substituted benzenes as bond dipoles. The electrostatic interactions are estimated by calculating the interactions between the charge of the anion and the bond dipole moments of the substituted benzene. The polarization interactions are described according to the variation of the magnitudes of the bond dipole moments with the local environment. The parameters needed are produced by fitting the high-quality CCSD(T)/CBS potential energy curves. Calculation results show that our scheme produces equilibrium intermolecular distances with a root-mean-square deviation of 0.004 nm and interaction energies with a root-mean-square deviation of 2.81 kJ·mol-1 compared with the CCSD(T)/CBS results. The calculation results also show that our scheme reproduces the CCSD(T)/CBS potential energy curves well. These comparisons indicate the scheme proposed here is accurate and efficient, suggesting it may be a helpful tool to design and simulate relevant molecular materials.
2017, 33(4): 763-768
doi: 10.3866/PKU.WHXB201701091
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Hydrogen abstraction from alkanes by hydroperoxyl radical is an important reaction class in the combustion of hydrocarbon fuel, particularly at low and intermediate temperature regimes. In this study, kinetic parameters for this reaction class are calculated using the isodesmic reaction method based on conservation of geometric structures for the reaction center of the transition states. The geometries for all the reactants, transition states, and products are optimized at the HF/6-31+G(d) level. Hydrogen abstraction from ethane by hydroperoxyl radical is chosen as the reference reaction; other reactions are target reactions. The isodesmic reaction method is used to correct the approximate energy barriers and rate constants of the target reactions at the HF/6-31+G(d) level. To validate the reliability of the isodesmic reaction method, the energy barriers calculated by the isodesmic reaction method and at a high level of CCSD(T)/CBS for alkanes containing less than five carbon atoms are compared. The maximum absolute difference of energy barriers between the isodesmic reaction method and CCSD(T)/CBS method is 5.58 kJ·mol-1. Therefore, after correction, using the isodesmic reaction method, the low-level HF method can reproduce the high-level CCSD(T)/CBS calculated energy barriers. Thus, we have solved the problem of accurately calculating energy barriers for large molecular systems in this reaction class. The present work provides accurate kinetic parameters for hydrogen abstraction from alkanes by hydroperoxyl radical, which are important for combustion modeling at low and intermediate temperature regimes.
Hydrogen abstraction from alkanes by hydroperoxyl radical is an important reaction class in the combustion of hydrocarbon fuel, particularly at low and intermediate temperature regimes. In this study, kinetic parameters for this reaction class are calculated using the isodesmic reaction method based on conservation of geometric structures for the reaction center of the transition states. The geometries for all the reactants, transition states, and products are optimized at the HF/6-31+G(d) level. Hydrogen abstraction from ethane by hydroperoxyl radical is chosen as the reference reaction; other reactions are target reactions. The isodesmic reaction method is used to correct the approximate energy barriers and rate constants of the target reactions at the HF/6-31+G(d) level. To validate the reliability of the isodesmic reaction method, the energy barriers calculated by the isodesmic reaction method and at a high level of CCSD(T)/CBS for alkanes containing less than five carbon atoms are compared. The maximum absolute difference of energy barriers between the isodesmic reaction method and CCSD(T)/CBS method is 5.58 kJ·mol-1. Therefore, after correction, using the isodesmic reaction method, the low-level HF method can reproduce the high-level CCSD(T)/CBS calculated energy barriers. Thus, we have solved the problem of accurately calculating energy barriers for large molecular systems in this reaction class. The present work provides accurate kinetic parameters for hydrogen abstraction from alkanes by hydroperoxyl radical, which are important for combustion modeling at low and intermediate temperature regimes.
2017, 33(4): 769-779
doi: 10.3866/PKU.WHXB201612162
Abstract:
The stepwise and concerted mechanisms of benzene methylation with methanol were studied with the 5T, 12T, 104T9, and 104T12 H-ZSM-5 models using the“our own-N-layered integrated molecular orbital + molecular mechanics”(ONIOM) in combination with density functional theory (DFT) methods. The structures of intermediate species and transition states were described. The effect of the Brønsted (B) acid strength of HZSM-5 catalyst on the reaction mechanism of benzene methylation with methanol was considered. The reaction activation energy results indicate that benzene methylation with methanol preferentially occurs over H-ZSM-5 catalyst with greater B acid strength, and a lowering of the activation barrier was observed. With increasing B acid strength, the reaction activation energy of the stepwise mechanism decreases more than that of the concerted mechanism. Increasing the B acidic strength is more beneficial to the stepwise mechanism. When the stepwise mechanism becomes the dominant reaction path, the secondary reaction arising from further formation of bulky hydrocarbons through the methoxide intermediate produced in the methanol dehydration step of the stepwise mechanism might lead to the inactivation of the H-ZSM-5 catalyst owing to coke formation. Reasonable modulation the acid strength of the H-ZSM-5 catalyst is important in improving its catalytic activity and stability of the catalyst.
The stepwise and concerted mechanisms of benzene methylation with methanol were studied with the 5T, 12T, 104T9, and 104T12 H-ZSM-5 models using the“our own-N-layered integrated molecular orbital + molecular mechanics”(ONIOM) in combination with density functional theory (DFT) methods. The structures of intermediate species and transition states were described. The effect of the Brønsted (B) acid strength of HZSM-5 catalyst on the reaction mechanism of benzene methylation with methanol was considered. The reaction activation energy results indicate that benzene methylation with methanol preferentially occurs over H-ZSM-5 catalyst with greater B acid strength, and a lowering of the activation barrier was observed. With increasing B acid strength, the reaction activation energy of the stepwise mechanism decreases more than that of the concerted mechanism. Increasing the B acidic strength is more beneficial to the stepwise mechanism. When the stepwise mechanism becomes the dominant reaction path, the secondary reaction arising from further formation of bulky hydrocarbons through the methoxide intermediate produced in the methanol dehydration step of the stepwise mechanism might lead to the inactivation of the H-ZSM-5 catalyst owing to coke formation. Reasonable modulation the acid strength of the H-ZSM-5 catalyst is important in improving its catalytic activity and stability of the catalyst.
2017, 33(4): 780-786
doi: 10.3866/PKU.WHXB201612291
Abstract:
Lithium-ion capacitor (LIC) using commercial activated carbon as the cathode and graphite as the anode was assembled. The graphite anode was pre-lithiated by a fast, efficient internal short approach, which involved placing graphite in direct contact with lithium foil with electrolyte additive. The effect of pre-lithiation on the electrochemical performance of the LIC was investigated using a conventional Cu current collector (CCC) and pre-punched Cu current collector (PCC). The LICs containing a CCC and PCC were named CLIC and PLIC, respectively. Although the CCC had slightly higher pre-lithiation level and higher energy density in the CLIC, it suffered from a considerable decrease in performance at higher charge–discharge rates. Meanwhile, 90.0% of the initial capacity was maintained in the PLIC, whereas that of the CLIC was only 73.2% after 1000 cycles in the voltage range from 2.0 to 3.8 V. The CCC led to solid electrolyte interphase (SEI) film expansion and Li metal plating with direct contact between graphite and lithium metal. The deposited thick SEI layer could weaken the adhesion of active materials and the current collector. Moreover, the expansion of the SEI layer itself produced electrical resistance and electrical contact loss between the active materials and current collector. In contrast, a thin, stable SEI layer formed on the surface of graphite after pre-lithiated using the PCC. Therefore, the PLIC showed better rate and cycle performance with the smaller self-discharge, voltage drop, and resistance than those of the CLIC.
Lithium-ion capacitor (LIC) using commercial activated carbon as the cathode and graphite as the anode was assembled. The graphite anode was pre-lithiated by a fast, efficient internal short approach, which involved placing graphite in direct contact with lithium foil with electrolyte additive. The effect of pre-lithiation on the electrochemical performance of the LIC was investigated using a conventional Cu current collector (CCC) and pre-punched Cu current collector (PCC). The LICs containing a CCC and PCC were named CLIC and PLIC, respectively. Although the CCC had slightly higher pre-lithiation level and higher energy density in the CLIC, it suffered from a considerable decrease in performance at higher charge–discharge rates. Meanwhile, 90.0% of the initial capacity was maintained in the PLIC, whereas that of the CLIC was only 73.2% after 1000 cycles in the voltage range from 2.0 to 3.8 V. The CCC led to solid electrolyte interphase (SEI) film expansion and Li metal plating with direct contact between graphite and lithium metal. The deposited thick SEI layer could weaken the adhesion of active materials and the current collector. Moreover, the expansion of the SEI layer itself produced electrical resistance and electrical contact loss between the active materials and current collector. In contrast, a thin, stable SEI layer formed on the surface of graphite after pre-lithiated using the PCC. Therefore, the PLIC showed better rate and cycle performance with the smaller self-discharge, voltage drop, and resistance than those of the CLIC.
2017, 33(4): 787-794
doi: 10.3866/PKU.WHXB201612152
Abstract:
Amolybdenum disulfide-carbon composite (MoS2-C) was prepared by a hydrothermal method. Xray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and N2 adsorption-desorption tests were employed to characterize the physical properties of the composite. The charge storage mechanism of the MoS2-C was also investigated. The MoS2-C can be used as the negative electrode for supercapatteries using Na+-based organic electrolytes. A supercapattery of MoS2-C/AC (activated carbon) was constructed and its electrochemical performance was studied. The fabricated supercapattery exhibited relatively high energy density and power density. It also showed high cycle stability, displaying a 96% capacity retention after 1000 cycles.
Amolybdenum disulfide-carbon composite (MoS2-C) was prepared by a hydrothermal method. Xray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and N2 adsorption-desorption tests were employed to characterize the physical properties of the composite. The charge storage mechanism of the MoS2-C was also investigated. The MoS2-C can be used as the negative electrode for supercapatteries using Na+-based organic electrolytes. A supercapattery of MoS2-C/AC (activated carbon) was constructed and its electrochemical performance was studied. The fabricated supercapattery exhibited relatively high energy density and power density. It also showed high cycle stability, displaying a 96% capacity retention after 1000 cycles.
2017, 33(4): 795-802
doi: 10.3866/PKU.WHXB201612202
Abstract:
The aggregation behavior and thermodynamics of micellization for three Gemini surfactants with diester and rigid spacers in pure water and 10% (mass fraction) organic alcohol-water co-solvents (MA-WR, EG-WR and GL-WR) across a range of temperatures from 283.15 to 308.15 K were investigated by electrical conductivity measurements. The aggregation behavior parameters, including critical micelle concentration (cmc), degree of counter ion dissociation (α), and the thermodynamic parameters of micellization including standard Gibbs energy (ΔGmo), Gibbs energy of transfer (ΔGtranso), Gibbs energy of micellization per alkyl tail (ΔGtailo), standard enthalpy (ΔHmo), and standard entropy (ΔSmo) were calculated and discussed. Gemini surfactants with longer hydrophobic chain length have a lower cmc value, which was found to increase with the increasing number of hydroxyl groups of the alcohol in the organic mixed solvent. The temperature dependence of the cmc value for the Gemini surfactants was U-shaped in all the investigated systems. The micellization process is spontaneous, is endothermic at temperatures below 293.15 K, and becomes exothermic at temperatures above 293.15 K. The micropolarity of the Gemini surfactants in pure water and organic alcohol-water co-solvents were evaluated by steady-state fluorescence spectroscopy. The results showed that the hydrophobicity of the microenvironment for Gemini surfactant solutions becomes stronger with the increasing chain length of the surfactants and the number of hydroxyl groups of the alcohol in the organic mixed solvents. The compensation between the enthalpy and entropy for micellization of all the three gemini surfactants were observed in all the studied mixed media.
The aggregation behavior and thermodynamics of micellization for three Gemini surfactants with diester and rigid spacers in pure water and 10% (mass fraction) organic alcohol-water co-solvents (MA-WR, EG-WR and GL-WR) across a range of temperatures from 283.15 to 308.15 K were investigated by electrical conductivity measurements. The aggregation behavior parameters, including critical micelle concentration (cmc), degree of counter ion dissociation (α), and the thermodynamic parameters of micellization including standard Gibbs energy (ΔGmo), Gibbs energy of transfer (ΔGtranso), Gibbs energy of micellization per alkyl tail (ΔGtailo), standard enthalpy (ΔHmo), and standard entropy (ΔSmo) were calculated and discussed. Gemini surfactants with longer hydrophobic chain length have a lower cmc value, which was found to increase with the increasing number of hydroxyl groups of the alcohol in the organic mixed solvent. The temperature dependence of the cmc value for the Gemini surfactants was U-shaped in all the investigated systems. The micellization process is spontaneous, is endothermic at temperatures below 293.15 K, and becomes exothermic at temperatures above 293.15 K. The micropolarity of the Gemini surfactants in pure water and organic alcohol-water co-solvents were evaluated by steady-state fluorescence spectroscopy. The results showed that the hydrophobicity of the microenvironment for Gemini surfactant solutions becomes stronger with the increasing chain length of the surfactants and the number of hydroxyl groups of the alcohol in the organic mixed solvents. The compensation between the enthalpy and entropy for micellization of all the three gemini surfactants were observed in all the studied mixed media.
2017, 33(4): 803-809
doi: 10.3866/PKU.WHXB201612232
Abstract:
The interfacial dilational rheological properties of 2,5-diethyl-4-nonyl benzene sulfonate(292), 2,5-dipropyl-4-nonyl benzene sulfonate(393), and 2,5-dibutyl-4-nonyl benzene sulfonate(494) at air-water and decane-water interfaces were investigated by drop shape analysis. The influences of ageing time, interfacial pressure, dilational frequency, and bulk concentration on their dilational elasticity and viscosity were expounded. The surface adsorbed film was found to be elastic in nature at lower bulk concentration, and its strength determined by the interactions between the molecules in the film. In contrast, a diffusion-exchange process between the surface and the bulk controlled the properties of film at higher concentration. The insertion of oil molecules weakened the interactions among the adsorbed molecules, causing the diffusion-exchange process to dominate the nature of the interfacial film. However, this effect of the oil molecules decreased with increasing short alkyl chain length. The strength of the surface film could be determined before the adsorption equilibrium, while the nature of the interfacial film varied after saturated adsorption because of the re-arrangement of the interfacial surfactant molecules.
The interfacial dilational rheological properties of 2,5-diethyl-4-nonyl benzene sulfonate(292), 2,5-dipropyl-4-nonyl benzene sulfonate(393), and 2,5-dibutyl-4-nonyl benzene sulfonate(494) at air-water and decane-water interfaces were investigated by drop shape analysis. The influences of ageing time, interfacial pressure, dilational frequency, and bulk concentration on their dilational elasticity and viscosity were expounded. The surface adsorbed film was found to be elastic in nature at lower bulk concentration, and its strength determined by the interactions between the molecules in the film. In contrast, a diffusion-exchange process between the surface and the bulk controlled the properties of film at higher concentration. The insertion of oil molecules weakened the interactions among the adsorbed molecules, causing the diffusion-exchange process to dominate the nature of the interfacial film. However, this effect of the oil molecules decreased with increasing short alkyl chain length. The strength of the surface film could be determined before the adsorption equilibrium, while the nature of the interfacial film varied after saturated adsorption because of the re-arrangement of the interfacial surfactant molecules.
2017, 33(4): 810-815
doi: 10.3866/PKU.WHXB201701032
Abstract:
The patterning and immobilization of protein molecules onto functionalized silicon substrate through surface silane chemistry is of interest because protein patterning is an important prerequisite for the development of protein-based diagnostics in biological and medicinal fields. As a model system, mesoscale netty lysozyme arrays were assembled on oxidized undecyltrichlorosilane (UTSox) monolayer coated silicon surface through nanosphere lithography. The size of the arrays ranged from nanometer to micrometer can be easily adjusted by changing the size of nanospheres applied on the surface. By using nanosphere lithography, we are capable of fabricating a regular array of protein islands over centimeter sample regions. The created lysozyme protein patterns were characterized by atomic force microscopy (AFM) and fluorescence microscope, respectively. The analysis has demonstrated that this newly established approach offers a faster and more reliable process to fabricate netty protein arrays over large areas compared to conventional scanning-probe based fabrication methods. Furthermore, the carboxylic acid-terminated layer on surfaces is particularly effective for immobilizing protein molecules through either electrostatic interactions or covalent attachment via imine bonds. Therefore, the negative-toned protein structure on the surface with carboxylic acid groups coated on the bare areas makes it possible to fabricate two types of protein molecules on one surface.
The patterning and immobilization of protein molecules onto functionalized silicon substrate through surface silane chemistry is of interest because protein patterning is an important prerequisite for the development of protein-based diagnostics in biological and medicinal fields. As a model system, mesoscale netty lysozyme arrays were assembled on oxidized undecyltrichlorosilane (UTSox) monolayer coated silicon surface through nanosphere lithography. The size of the arrays ranged from nanometer to micrometer can be easily adjusted by changing the size of nanospheres applied on the surface. By using nanosphere lithography, we are capable of fabricating a regular array of protein islands over centimeter sample regions. The created lysozyme protein patterns were characterized by atomic force microscopy (AFM) and fluorescence microscope, respectively. The analysis has demonstrated that this newly established approach offers a faster and more reliable process to fabricate netty protein arrays over large areas compared to conventional scanning-probe based fabrication methods. Furthermore, the carboxylic acid-terminated layer on surfaces is particularly effective for immobilizing protein molecules through either electrostatic interactions or covalent attachment via imine bonds. Therefore, the negative-toned protein structure on the surface with carboxylic acid groups coated on the bare areas makes it possible to fabricate two types of protein molecules on one surface.
2017, 33(4): 816-822
doi: 10.3866/PKU.WHXB201612223
Abstract:
We synthesized a series of novel spiro[fluorene-9,9'-xanthene] (SFX)-based host materials via a one-step palladium-catalyzed cross-coupling reaction. These materials have high triple energy levels and high yield, and thus can be used as hosts for blue phosphors. Blue phosphorescent organic light-emitting devices (PHOLEDs) with a bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyri-dyl)iridium(III) (FIrpic) emission were fabricated. Furthermore, we applied cohosts composed of one of the new synthesized materials and the hole transport material di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane (TAPC) to the blue PHOLEDs to successfully acquire efficient blue emissions. The SFX-based material provided efficient energy transfer while TAPC improved the mobility of the cohost as well as reduced the working voltage. Maximum current efficiencies of 22.56 and 25.93 cd·A-1 and the maximum brightnesses of 6421 and 6196 cd·m-2 were obtained for the PHOLEDs with TAPC: 2-(9-phenyl-fluoren-9-yl)spiro[fluorene-9,9'-xanthene] (PF-SFX) and TAPC: 2-(9-(4-(octyloxy)-phenyl)-9H-fluoren-9-yl)spiro[fluorene-9,9'-xanthene] (C8OPF-SFX) cohosts, respectively. The experimental results obtained for the four SFX-based host materials were enough to declare that SFX is an effective main unit that can be used to build efficient host materials for blue phosphors containing only C, H, and O basic elements.
We synthesized a series of novel spiro[fluorene-9,9'-xanthene] (SFX)-based host materials via a one-step palladium-catalyzed cross-coupling reaction. These materials have high triple energy levels and high yield, and thus can be used as hosts for blue phosphors. Blue phosphorescent organic light-emitting devices (PHOLEDs) with a bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyri-dyl)iridium(III) (FIrpic) emission were fabricated. Furthermore, we applied cohosts composed of one of the new synthesized materials and the hole transport material di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane (TAPC) to the blue PHOLEDs to successfully acquire efficient blue emissions. The SFX-based material provided efficient energy transfer while TAPC improved the mobility of the cohost as well as reduced the working voltage. Maximum current efficiencies of 22.56 and 25.93 cd·A-1 and the maximum brightnesses of 6421 and 6196 cd·m-2 were obtained for the PHOLEDs with TAPC: 2-(9-phenyl-fluoren-9-yl)spiro[fluorene-9,9'-xanthene] (PF-SFX) and TAPC: 2-(9-(4-(octyloxy)-phenyl)-9H-fluoren-9-yl)spiro[fluorene-9,9'-xanthene] (C8OPF-SFX) cohosts, respectively. The experimental results obtained for the four SFX-based host materials were enough to declare that SFX is an effective main unit that can be used to build efficient host materials for blue phosphors containing only C, H, and O basic elements.
2017, 33(4): 823-828
doi: 10.3866/PKU.WHXB201701092
Abstract:
The reactions of the pharmaceutical fluoxetine (FLX) with different radicals were investigated by pulse radiolysis. The reaction of hydroxyl radical (·OH) with FLX formed hydroxylated adduct of the aromatic ring, while oxidation of FLX by sulfate radical anion (SO4·-) formed benzene radical cation that further reacted with H2O to yield the ·OH adduct. The determined rate constants of ·OH, hydrated electrons (eaq-), and SO4·- with FLX were 7.8×109, 2.3×109, and 1.1×109 mol·L-1·s-1, respectively. In the steady-state radiolysis study, the degradation of FLX in different radiolytic conditions by electron beam irradiation was detected by HPLC and UV-Vis spectra techniques. It was found that FLX concentration decreased by more than 90% in both N2O and air-saturated solutions after 1.5 kGy irradiation. In contrast, only 43% of FLX was decomposed in N2-saturated solution containing 0.1 mol·L-1 tert-butanol. The degradation rates of FLX in acidic and neutral solutions were higher than those in alkaline solutions. Our results showed that the degradation of FLX is optimal in air-saturated neutral solution, and ·OH-induced degradation is more efficient than SO4·- oxidation of FLX. The obtained kinetic data and optimal conditions give some hints to understand the degradation of FLX.
The reactions of the pharmaceutical fluoxetine (FLX) with different radicals were investigated by pulse radiolysis. The reaction of hydroxyl radical (·OH) with FLX formed hydroxylated adduct of the aromatic ring, while oxidation of FLX by sulfate radical anion (SO4·-) formed benzene radical cation that further reacted with H2O to yield the ·OH adduct. The determined rate constants of ·OH, hydrated electrons (eaq-), and SO4·- with FLX were 7.8×109, 2.3×109, and 1.1×109 mol·L-1·s-1, respectively. In the steady-state radiolysis study, the degradation of FLX in different radiolytic conditions by electron beam irradiation was detected by HPLC and UV-Vis spectra techniques. It was found that FLX concentration decreased by more than 90% in both N2O and air-saturated solutions after 1.5 kGy irradiation. In contrast, only 43% of FLX was decomposed in N2-saturated solution containing 0.1 mol·L-1 tert-butanol. The degradation rates of FLX in acidic and neutral solutions were higher than those in alkaline solutions. Our results showed that the degradation of FLX is optimal in air-saturated neutral solution, and ·OH-induced degradation is more efficient than SO4·- oxidation of FLX. The obtained kinetic data and optimal conditions give some hints to understand the degradation of FLX.
2017, 33(4): 829-835
doi: 10.3866/PKU.WHXB201701062
Abstract:
The leucine zipper lipopeptide is a dimer composed of two lipopeptides with α-helical structures that interact through hydrophobic forces. When heated to its phase transition temperature, the helixes unwind and form a disordered conformation. Based on the thermo-sensitivity of these leucine zipper lipopeptides, we designed and synthesized a series of zipper-structured lipopeptides and then mixed them with lipids to form thermo-sensitive hybrid liposomes. Circular dichroism was used to investigate the secondary structure of the lipopeptides anchored in the liposomal bilayer. Dynamic light scattering measurements were used to assess the diameters and zeta potentials of the liposomes. Fluorescence polarization was measured to study the fluidity of the liposomal bilayer. An ultraviolet spectrophotometer was used to stimulate Doxorubicin (DOX) release in vitro at 37.0 and 45.0℃. We found that Lp-Lipo (hybrid of lipopeptide and liposome) displayed higher thermosensitivity than pure liposome. The cholesterol content and fluidity of the liposomal bilayer affected the thermocontrolled on-off switch of the lipopeptides. Lp-Lipo shows great potential as a novel thermo-sensitive drug carrier.
The leucine zipper lipopeptide is a dimer composed of two lipopeptides with α-helical structures that interact through hydrophobic forces. When heated to its phase transition temperature, the helixes unwind and form a disordered conformation. Based on the thermo-sensitivity of these leucine zipper lipopeptides, we designed and synthesized a series of zipper-structured lipopeptides and then mixed them with lipids to form thermo-sensitive hybrid liposomes. Circular dichroism was used to investigate the secondary structure of the lipopeptides anchored in the liposomal bilayer. Dynamic light scattering measurements were used to assess the diameters and zeta potentials of the liposomes. Fluorescence polarization was measured to study the fluidity of the liposomal bilayer. An ultraviolet spectrophotometer was used to stimulate Doxorubicin (DOX) release in vitro at 37.0 and 45.0℃. We found that Lp-Lipo (hybrid of lipopeptide and liposome) displayed higher thermosensitivity than pure liposome. The cholesterol content and fluidity of the liposomal bilayer affected the thermocontrolled on-off switch of the lipopeptides. Lp-Lipo shows great potential as a novel thermo-sensitive drug carrier.
2017, 33(4): 836-844
doi: 10.3866/PKU.WHXB201612153
Abstract:
Azobenzene-containing glycolipid, Gal-azo-Cn, was synthesized and its photoisomerization behavior within the liquid-gas interfaces was investigated by Langmuir Blodgett (LB) filmmeasurements and atomic force microscopy. The results showed that Gal-azo-Cn could undergo trans-cis and cis-trans isomerization in both pure glycolipid and phospholipid-mixed films. UV-light induced isomerization increased the surface pressure. However, the membrane pressure within the liquid-gas interface could hinder the trans-cis isomerization. The high membrane pressure prevented the increase of surface pressure, weakening the trans-cis isomerization. In contrast, the cis-trans isomerization sped up in the dark. Compared with the isomerization behavior of pure glycolipid, the interaction between phospholipid and glycolipid could promote the trans-cis isomerization within the liquid-gas interface. In themixed system, the increase in phospholipid containing unsaturated carbon chains increased the fluidity of the membrane but decreased its stability, which weaken the promotion effect of isomerization.
Azobenzene-containing glycolipid, Gal-azo-Cn, was synthesized and its photoisomerization behavior within the liquid-gas interfaces was investigated by Langmuir Blodgett (LB) filmmeasurements and atomic force microscopy. The results showed that Gal-azo-Cn could undergo trans-cis and cis-trans isomerization in both pure glycolipid and phospholipid-mixed films. UV-light induced isomerization increased the surface pressure. However, the membrane pressure within the liquid-gas interface could hinder the trans-cis isomerization. The high membrane pressure prevented the increase of surface pressure, weakening the trans-cis isomerization. In contrast, the cis-trans isomerization sped up in the dark. Compared with the isomerization behavior of pure glycolipid, the interaction between phospholipid and glycolipid could promote the trans-cis isomerization within the liquid-gas interface. In themixed system, the increase in phospholipid containing unsaturated carbon chains increased the fluidity of the membrane but decreased its stability, which weaken the promotion effect of isomerization.
2017, 33(4): 845-852
doi: 10.3866/PKU.WHXB201612222
Abstract:
Novel three-dimensional (3D) mesostructured ZnCo2O4 cubes are prepared through a convenient and practical hydrothermal route combined with an annealing treatment. The as-prepared ZnCo2O4 cubes range from 3-4 μm in size, and are composed of a large number of nanoparticles and pores. According to N2 adsorption-desorption measurements, the as-synthesized ZnCo2O4 cubes have a high BET surface area (41.4 m2·g-1) and mesoporous (6.32 nm) nature. Lithium ion batteries (LIBs) are assembled using the as-prepared ZnCo2O4 nanomaterial and metallic lithium as the anode and the cathode, respectively, and their lithium storage performance is investigated. The electrode material exhibits highly reversible lithium storage capacity and strong cycling stability at high current density for 100 cycles. More importantly, the ZnCo2O4 cube electrode still presents a relatively high specific capacity at high rate. The excellent lithium storage performance is attributed to the novel structure of the 3D mesostructured cubes, which can facilitate Li+ diffusion, increase electrode/electrolyte contact area, and endure volume changes the during Li+ insertion/extraction process.
Novel three-dimensional (3D) mesostructured ZnCo2O4 cubes are prepared through a convenient and practical hydrothermal route combined with an annealing treatment. The as-prepared ZnCo2O4 cubes range from 3-4 μm in size, and are composed of a large number of nanoparticles and pores. According to N2 adsorption-desorption measurements, the as-synthesized ZnCo2O4 cubes have a high BET surface area (41.4 m2·g-1) and mesoporous (6.32 nm) nature. Lithium ion batteries (LIBs) are assembled using the as-prepared ZnCo2O4 nanomaterial and metallic lithium as the anode and the cathode, respectively, and their lithium storage performance is investigated. The electrode material exhibits highly reversible lithium storage capacity and strong cycling stability at high current density for 100 cycles. More importantly, the ZnCo2O4 cube electrode still presents a relatively high specific capacity at high rate. The excellent lithium storage performance is attributed to the novel structure of the 3D mesostructured cubes, which can facilitate Li+ diffusion, increase electrode/electrolyte contact area, and endure volume changes the during Li+ insertion/extraction process.
