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2009 Volume 25 Issue 2
2009, 25(02):
Abstract:
2009, 25(02): 201-206
doi: 10.3866/PKU.WHXB20090201
Abstract:
Fluoroethylene carbonate (FEC) with a volume ratio of 2%was added to the electrolyte containing 1 mol·L-1 LiPF6 in ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) (1:1:1 by volume). The effects of FEC on lithiumion battery performance and on the mesocarbon microbead (MCMB) electrode/electrolyte interphase were studied by cyclic voltammetry (CV), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and electrochemical impedance spectroscopy (EIS). The results indicated that the application of a 2% (volume ratio) of FEC suppressed electrolyte decomposition and caused the formation of an excellent solid electrolyte interphase (SEI) film on the MCMB electrode. The battery resistance decreased while the specific capacity and cyclic stability of the battery increased.
Fluoroethylene carbonate (FEC) with a volume ratio of 2%was added to the electrolyte containing 1 mol·L-1 LiPF6 in ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) (1:1:1 by volume). The effects of FEC on lithiumion battery performance and on the mesocarbon microbead (MCMB) electrode/electrolyte interphase were studied by cyclic voltammetry (CV), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and electrochemical impedance spectroscopy (EIS). The results indicated that the application of a 2% (volume ratio) of FEC suppressed electrolyte decomposition and caused the formation of an excellent solid electrolyte interphase (SEI) film on the MCMB electrode. The battery resistance decreased while the specific capacity and cyclic stability of the battery increased.
2009, 25(02): 207-212
doi: 10.3866/PKU.WHXB20090202
Abstract:
The Brownian dynamics method was used to simulate the influence of gravity on the process of particle coagulation in a dilute solution. By including or excluding the gravitational influence in a computer simulation, the relative change in the number of aggregates with time for these two gravitational conditions could be compared. Time-dependent variations of the number and size of all aggregates under the gravitational conditions were obtained. We conclude that the influence of gravity is negligible during the earlier stage of the coagulation process and that the rate of aggregation is accelerated by the gravitational force in the latter stage. The effect of gravitational force on the process of particle aggregation in suspension is discussed by using a dynamic analysis method.
The Brownian dynamics method was used to simulate the influence of gravity on the process of particle coagulation in a dilute solution. By including or excluding the gravitational influence in a computer simulation, the relative change in the number of aggregates with time for these two gravitational conditions could be compared. Time-dependent variations of the number and size of all aggregates under the gravitational conditions were obtained. We conclude that the influence of gravity is negligible during the earlier stage of the coagulation process and that the rate of aggregation is accelerated by the gravitational force in the latter stage. The effect of gravitational force on the process of particle aggregation in suspension is discussed by using a dynamic analysis method.
2009, 25(02): 213-217
doi: 10.3866/PKU.WHXB20090203
Abstract:
The stability of Pd-Fe alloy catalysts for the oxygen reduction reaction (ORR) was characterized in situ by using the rotating disk electrode and electrochemical quartz crystal microbalance (EQCM) techniques, both in acidic and alkaline solutions. The alloy catalyst was found to be unstable in the acidic solution because of the electrochemical and chemical dissolution of the catalyst. This dissolution resulted in a reduction of activity for the oxygen reduction reaction and also a reduction in the mass of the catalyst. In an alkaline solution, the mass of the Pd-Fe alloy catalyst deposited on the electrode surface and its electrochemically active surface area hardly changed. Consequently, the catalyst kept its activity for stable oxygen reduction.
The stability of Pd-Fe alloy catalysts for the oxygen reduction reaction (ORR) was characterized in situ by using the rotating disk electrode and electrochemical quartz crystal microbalance (EQCM) techniques, both in acidic and alkaline solutions. The alloy catalyst was found to be unstable in the acidic solution because of the electrochemical and chemical dissolution of the catalyst. This dissolution resulted in a reduction of activity for the oxygen reduction reaction and also a reduction in the mass of the catalyst. In an alkaline solution, the mass of the Pd-Fe alloy catalyst deposited on the electrode surface and its electrochemically active surface area hardly changed. Consequently, the catalyst kept its activity for stable oxygen reduction.
2009, 25(02): 218-222
doi: 10.3866/PKU.WHXB20090204
Abstract:
A grand canonical ensemble Monte Carlo simulation was performed to investigate the adsorption and distribution of thiophene, as well as the mixture of thiophene and iso-octane on MCM-22 zeolite. The adsorption isotherms and the isosteric heat of thiophene on MCM-22 zeolite were obtained at different temperatures (298, 363 and 393 K). The simulated results showed that the adsorptive capacity of pure thiophene on MCM-22 could be affected by temperature and pressure. The isosteric heats were similar at different temperatures. For the mixture of thiophene and iso-octane, competitive adsorption of thiophene and iso-octane occurred on MCM-22 zeolite at 298 K. Thiophene can distribute throughout two independent channels of MCM-22 but iso-octane mainly adsorbs within the supercage of MCM-22. Thus, thiophene and iso-octane can be separated effectively by MCM-22 zeolite.
A grand canonical ensemble Monte Carlo simulation was performed to investigate the adsorption and distribution of thiophene, as well as the mixture of thiophene and iso-octane on MCM-22 zeolite. The adsorption isotherms and the isosteric heat of thiophene on MCM-22 zeolite were obtained at different temperatures (298, 363 and 393 K). The simulated results showed that the adsorptive capacity of pure thiophene on MCM-22 could be affected by temperature and pressure. The isosteric heats were similar at different temperatures. For the mixture of thiophene and iso-octane, competitive adsorption of thiophene and iso-octane occurred on MCM-22 zeolite at 298 K. Thiophene can distribute throughout two independent channels of MCM-22 but iso-octane mainly adsorbs within the supercage of MCM-22. Thus, thiophene and iso-octane can be separated effectively by MCM-22 zeolite.
2009, 25(02): 223-228
doi: 10.3866/PKU.WHXB20090205
Abstract:
The supramolecular structure of diflunisal intercalated layered double hydroxides (DIF/LDHs) was modeled bymolecular dynamics (MD)methods.Hydrogen bonding, hydration and swelling properties of DIF/LDHs were investigated. The interlayer spacing dc was found to be constant (ca 1.80 nm) when Nw(the ratio of the numbers of water molecule to DIF)≤3. The interlayer spacing dc gradually increases as Nw≥4 and this increase follows the linear equation dc =1.2611Nw+13.63. The hydration energy gradually increases as the water content increases. LDHs/DIF hydrates when Nw≤16 because hydration energy ⊿UH<-41.84 kJ·mol-1. At Nw≥24 the hydration of LDHs/DIF does not occur because ⊿UH>-41.84 kJ·mol -1. Swelling of LDHs/DIF is thus limited in an aqueous environment. The interlayer of DIF/LDHs contains a complex hydrogen bonding network. The hydration of DIF/LDHs occurs as follows: water molecules initially form hydrogen bond with layers and anions. While the anions gradually reach a saturation state and water molecules continue to form hydrogen bonds with the hydroxyls of the layers. The L-Wtype hydrogen bond gradually substitutes the L-A type hydrogen bond and the anions move to the center of an interlayer and then separate with the layers. Last, a well-ordered structural water layer is formed on the surface hydroxyls of DIF/LDHs.
The supramolecular structure of diflunisal intercalated layered double hydroxides (DIF/LDHs) was modeled bymolecular dynamics (MD)methods.Hydrogen bonding, hydration and swelling properties of DIF/LDHs were investigated. The interlayer spacing dc was found to be constant (ca 1.80 nm) when Nw(the ratio of the numbers of water molecule to DIF)≤3. The interlayer spacing dc gradually increases as Nw≥4 and this increase follows the linear equation dc =1.2611Nw+13.63. The hydration energy gradually increases as the water content increases. LDHs/DIF hydrates when Nw≤16 because hydration energy ⊿UH<-41.84 kJ·mol-1. At Nw≥24 the hydration of LDHs/DIF does not occur because ⊿UH>-41.84 kJ·mol -1. Swelling of LDHs/DIF is thus limited in an aqueous environment. The interlayer of DIF/LDHs contains a complex hydrogen bonding network. The hydration of DIF/LDHs occurs as follows: water molecules initially form hydrogen bond with layers and anions. While the anions gradually reach a saturation state and water molecules continue to form hydrogen bonds with the hydroxyls of the layers. The L-Wtype hydrogen bond gradually substitutes the L-A type hydrogen bond and the anions move to the center of an interlayer and then separate with the layers. Last, a well-ordered structural water layer is formed on the surface hydroxyls of DIF/LDHs.
2009, 25(02): 229-236
doi: 10.3866/PKU.WHXB20090206
Abstract:
To improve electrochemical properties of activated carbon (AC), a commercial AC was modified by
means of soaking in manganese nitrate solution and subsequent pyrolysis. Nitrogen adsorption at 77 K, SEM, and XRD were used to study the surface area, porosity, profile of modified AC, and the crystal structure of deposited manganese oxides. The performance of electrochemical capacitors using the modified AC as electrode materials was investigated by cyclic voltammograms, ac (alternating current) impedance, and constant current charge/discharge. Results showed that manganese oxides, especially α-Mn2O3, produced from the Mn(NO3)2 decomposition had an obvious pseudo-capacitance effect. This effect was coupled with the electrical double layer capacitance of AC to form a complex capacitance so that the specific capacitance of modified AC could be as high as 254 F·g-1 which is 54% higher than that of the unmodified AC. In addition, the tested capacitor with modified AC electrodes showed excellent performance during reversible charge-discharge and also displayed high stability. Its equivalent series resistance was small at 0.40 Ω. After a long termtest of 2000-cycles the capacitance retained nearly 100% of its original value.
To improve electrochemical properties of activated carbon (AC), a commercial AC was modified by
means of soaking in manganese nitrate solution and subsequent pyrolysis. Nitrogen adsorption at 77 K, SEM, and XRD were used to study the surface area, porosity, profile of modified AC, and the crystal structure of deposited manganese oxides. The performance of electrochemical capacitors using the modified AC as electrode materials was investigated by cyclic voltammograms, ac (alternating current) impedance, and constant current charge/discharge. Results showed that manganese oxides, especially α-Mn2O3, produced from the Mn(NO3)2 decomposition had an obvious pseudo-capacitance effect. This effect was coupled with the electrical double layer capacitance of AC to form a complex capacitance so that the specific capacitance of modified AC could be as high as 254 F·g-1 which is 54% higher than that of the unmodified AC. In addition, the tested capacitor with modified AC electrodes showed excellent performance during reversible charge-discharge and also displayed high stability. Its equivalent series resistance was small at 0.40 Ω. After a long termtest of 2000-cycles the capacitance retained nearly 100% of its original value.
2009, 25(02): 237-241
doi: 10.3866/PKU.WHXB20090207
Abstract:
The synthesis of AlH3with LiAlH4 and AlCl3was done by ball-milling solid phase chemical reaction under H2 atmosphere. The effects of different milling times (4-20 h) on the solid state chemical reaction and dehydrogenation properties of the milled mixture were investigated comprehensively using X-ray diffraction (XRD), thermal analysis (TG-DSC), mass spectroscopy (MS), scanning electron microscopy (SEM), and dehydrogenation measurements. The milled reaction was found to proceed as follows: 3LiAlH4+AlCl3→4AlH3+3LiCl. The reaction was almost complete after milling for 20 h and amorphous AlH3 was formed. With an increase in milling time dehydrogenation kinetics was improved resulting in hydrogen desorption at a temperature lower than 100 ℃. The maximum desorbed hydrogen capacities reached 2.6%-3.6% (w), which is close to the theoretical capacity of 4.85% (w) for the reaction. A decrease in the maximum desorbed hydrogen capacity can be attributed to the formation of LiCl·H2O and also to the decomposition of AlH3 during the milling process.
The synthesis of AlH3with LiAlH4 and AlCl3was done by ball-milling solid phase chemical reaction under H2 atmosphere. The effects of different milling times (4-20 h) on the solid state chemical reaction and dehydrogenation properties of the milled mixture were investigated comprehensively using X-ray diffraction (XRD), thermal analysis (TG-DSC), mass spectroscopy (MS), scanning electron microscopy (SEM), and dehydrogenation measurements. The milled reaction was found to proceed as follows: 3LiAlH4+AlCl3→4AlH3+3LiCl. The reaction was almost complete after milling for 20 h and amorphous AlH3 was formed. With an increase in milling time dehydrogenation kinetics was improved resulting in hydrogen desorption at a temperature lower than 100 ℃. The maximum desorbed hydrogen capacities reached 2.6%-3.6% (w), which is close to the theoretical capacity of 4.85% (w) for the reaction. A decrease in the maximum desorbed hydrogen capacity can be attributed to the formation of LiCl·H2O and also to the decomposition of AlH3 during the milling process.
2009, 25(02): 242-246
doi: 10.3866/PKU.WHXB20090208
Abstract:
Fe-Zr oxides with different Zr/Fe molar ratios were prepared by a co-precipitation method and used as catalysts for the vapor phase ortho-selective alkylation of phenol with methanol. Results showed that the Fe-Zr oxide catalysts had relatively high activity and ortho-selectivity. Among them, the sample with nZr/nFe=0.5/100 exhibited the highest activity (99.2% phenol conversion) with a selectivity of 22.6% to o-cresol and 77.0% to 2,6-xylenol. An increase in reaction temperature could further improve selectivity for 2,6-xylenol. The presence of relatively strong acid-base sites may be responsible for the high phenol conversion and the high 2,6-xylenol selectivity.
Fe-Zr oxides with different Zr/Fe molar ratios were prepared by a co-precipitation method and used as catalysts for the vapor phase ortho-selective alkylation of phenol with methanol. Results showed that the Fe-Zr oxide catalysts had relatively high activity and ortho-selectivity. Among them, the sample with nZr/nFe=0.5/100 exhibited the highest activity (99.2% phenol conversion) with a selectivity of 22.6% to o-cresol and 77.0% to 2,6-xylenol. An increase in reaction temperature could further improve selectivity for 2,6-xylenol. The presence of relatively strong acid-base sites may be responsible for the high phenol conversion and the high 2,6-xylenol selectivity.
2009, 25(02): 247-252
doi: 10.3866/PKU.WHXB20090209
Abstract:
V2.1TiNi0.4Zr0.06Cu0.03M0.10 (M=Cr, Co, Fe, Nb, Ta) hydrogen storage alloys were prepared by induction melting with magnetic levitation. The effects of an additive elementMon the microstructure and electrochemical properties of these alloys were investigated by means of X-ray diffractiuon (XRD), scanning electron midroscopy( SEM), electron diffraction spectroscopy (EDS) analyses and electrochemical measurements. The results show that all these alloys consist of a V-based solid solution main phase with bcc structure and a C14-type Laves secondary phase in the form of a three-dimensional network. Cr, Nb or Ta predominantly exist in the main phase and Co or Fe is mainly distributed in the secondary phase. Adding Cr, Co, Fe, Nb or Ta into the V2.1TiNi0.4Zr0.06Cu0.03 alloy can effectively restrict the dissolution of vanadium and titanium as well as improve the corrosion resistance and cycling stability of the alloy electrode. The maximum discharge capacity of the alloy, however, decreases to some extent. Doping with Cr, Co, Nb or Ta increases the high-rate dischargeability of the alloy. Among the alloy samples studied, the V2.1TiNi0.4Zr0.06Cu0.03Cr0.10 alloy possessed the best overall electrochemical properties.
V2.1TiNi0.4Zr0.06Cu0.03M0.10 (M=Cr, Co, Fe, Nb, Ta) hydrogen storage alloys were prepared by induction melting with magnetic levitation. The effects of an additive elementMon the microstructure and electrochemical properties of these alloys were investigated by means of X-ray diffractiuon (XRD), scanning electron midroscopy( SEM), electron diffraction spectroscopy (EDS) analyses and electrochemical measurements. The results show that all these alloys consist of a V-based solid solution main phase with bcc structure and a C14-type Laves secondary phase in the form of a three-dimensional network. Cr, Nb or Ta predominantly exist in the main phase and Co or Fe is mainly distributed in the secondary phase. Adding Cr, Co, Fe, Nb or Ta into the V2.1TiNi0.4Zr0.06Cu0.03 alloy can effectively restrict the dissolution of vanadium and titanium as well as improve the corrosion resistance and cycling stability of the alloy electrode. The maximum discharge capacity of the alloy, however, decreases to some extent. Doping with Cr, Co, Nb or Ta increases the high-rate dischargeability of the alloy. Among the alloy samples studied, the V2.1TiNi0.4Zr0.06Cu0.03Cr0.10 alloy possessed the best overall electrochemical properties.
2009, 25(02): 253-260
doi: 10.3866/PKU.WHXB20090210
Abstract:
Ni/Al2O3 catalyst was prepared by evaporation method. Ni/α-Al2O3 and Ni/γ-Al2O3 catalysts were prepared using traditional incipient wetness impregnation. Dry reforming of methane over the prepared catalysts and the commercial catalyst Z118Y for steam reforming of natural gas was investigated. Properties of the carbon species deposited on the surface of the catalysts were characterized by H2-temperature programmed reduction (H2-TPR), Brunauer-Emmett-Teller (BET) specific surface area analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetry-differential scanning calorimetry (TG-DSC), and temperature programmed hydrogenation (TPH). The results showed that there are three main carbon species on the surface of the catalysts, namely amorphous, filamentous, and graphitic carbon. In addition, the content of carbon deposited on these catalysts varied because of different structures and properties of alumina. Filamentous carbon (namely carbon nanotubes) was the main species deposited on catalysts Z118Y, Ni/Al2O3, and Ni/α-Al2O3 while the graphitic carbon species was dominant on the Ni/γ-Al2O3 catalyst. Furthermore, the particle size of nickel on the Ni/γ-Al2O3 catalyst was small (less than 15 nm) and narrowly distributed while it also showed a high dispersion of metallic nickel on the support. It is recognized that the high dispersion of nickel particles would not only decrease the deposition of carbon on the surface of the catalyst but also depress the growth of filamentous carbon effectively.
Ni/Al2O3 catalyst was prepared by evaporation method. Ni/α-Al2O3 and Ni/γ-Al2O3 catalysts were prepared using traditional incipient wetness impregnation. Dry reforming of methane over the prepared catalysts and the commercial catalyst Z118Y for steam reforming of natural gas was investigated. Properties of the carbon species deposited on the surface of the catalysts were characterized by H2-temperature programmed reduction (H2-TPR), Brunauer-Emmett-Teller (BET) specific surface area analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetry-differential scanning calorimetry (TG-DSC), and temperature programmed hydrogenation (TPH). The results showed that there are three main carbon species on the surface of the catalysts, namely amorphous, filamentous, and graphitic carbon. In addition, the content of carbon deposited on these catalysts varied because of different structures and properties of alumina. Filamentous carbon (namely carbon nanotubes) was the main species deposited on catalysts Z118Y, Ni/Al2O3, and Ni/α-Al2O3 while the graphitic carbon species was dominant on the Ni/γ-Al2O3 catalyst. Furthermore, the particle size of nickel on the Ni/γ-Al2O3 catalyst was small (less than 15 nm) and narrowly distributed while it also showed a high dispersion of metallic nickel on the support. It is recognized that the high dispersion of nickel particles would not only decrease the deposition of carbon on the surface of the catalyst but also depress the growth of filamentous carbon effectively.
2009, 25(02): 261-266
doi: 10.3866/PKU.WHXB20090211
Abstract:
Structures and vibrational frequencies of InnNa and InnNa+(n=2-8) clusters were investigated with density functional theory at B3LYP level. The results show that the most stable structures of InnNa (n=2,3,4, 6) have C2v, C3v, C4v and C2v symmetry, respectively. The InnNa (n=5, 7, 8) clusters have a C1 point group symmetry. InnNa (n=4-8) clusters have the same character as Na is located within the plane formed by the four In atoms. The most stable structures for InnNa+(n=2-8) clusters are similar to their neutral structures, except for In2Na+, In4Na+ and In7Na+. The average binding energy, second-order difference of energy and adiabatic ionization potentials of InnNa (n=2-8) clusters were calculated at the same theoretical level. We found an odd-even alternative character between the second-order difference of energy and the cluster size. In4Na and In6Na are more stable than the other studied compounds. The calculated adiabatic ionization potentials are in od agreement with experiment values.
Structures and vibrational frequencies of InnNa and InnNa+(n=2-8) clusters were investigated with density functional theory at B3LYP level. The results show that the most stable structures of InnNa (n=2,3,4, 6) have C2v, C3v, C4v and C2v symmetry, respectively. The InnNa (n=5, 7, 8) clusters have a C1 point group symmetry. InnNa (n=4-8) clusters have the same character as Na is located within the plane formed by the four In atoms. The most stable structures for InnNa+(n=2-8) clusters are similar to their neutral structures, except for In2Na+, In4Na+ and In7Na+. The average binding energy, second-order difference of energy and adiabatic ionization potentials of InnNa (n=2-8) clusters were calculated at the same theoretical level. We found an odd-even alternative character between the second-order difference of energy and the cluster size. In4Na and In6Na are more stable than the other studied compounds. The calculated adiabatic ionization potentials are in od agreement with experiment values.
2009, 25(02): 267-272
doi: 10.3866/PKU.WHXB20090212
Abstract:
Vermicular mesoporous nanostructured WO3 thin films were prepared from a chloro-alkoxide sol-gel method via controlled EISA (evaporate induced self-assembly) process using TMDD (HO(EO)xC14(EO)yOH) surfactant as the structure-directing template. This template was eliminated by calcination of 300 ℃. The as-prepared films could be continuous, uniform, and transparent. SEM, TEM, and Raman spectra were used for the nanostructural examinations. Spectrophotometric, XPS, and ellipsometry methods were also introduced to determine the electrochromic behaviors of the nanostructured films. The results showed that the cyclic reversible transmittance modulation range more than 75% has been realized above wavelength of 633 nm, and the electrochromic mechanism of the nanostructured WO3 films exhibited double-inserted absorbing characteristics.
Vermicular mesoporous nanostructured WO3 thin films were prepared from a chloro-alkoxide sol-gel method via controlled EISA (evaporate induced self-assembly) process using TMDD (HO(EO)xC14(EO)yOH) surfactant as the structure-directing template. This template was eliminated by calcination of 300 ℃. The as-prepared films could be continuous, uniform, and transparent. SEM, TEM, and Raman spectra were used for the nanostructural examinations. Spectrophotometric, XPS, and ellipsometry methods were also introduced to determine the electrochromic behaviors of the nanostructured films. The results showed that the cyclic reversible transmittance modulation range more than 75% has been realized above wavelength of 633 nm, and the electrochromic mechanism of the nanostructured WO3 films exhibited double-inserted absorbing characteristics.
2009, 25(02): 273-277
doi: 10.3866/PKU.WHXB20090213
Abstract:
A new type of hydrogen-bonded layer-by-layer (LBL) photoalignment film was fabricated and studied. The photosensitive hydrogen donor containing cinnamoyl groups (Poly(4-acryloyloxy)-cinnamic acid, PCA) was self-assembled with hydrogen accepter poly (4-vinylpyridine) (PVPy) in an organic solvent. Then a hydrogen-bonding-directed ultrathin film was formed. The uniformity and linear growth of the deposition procedure was proven by UV-Vis spectra and the interaction between PVPy and PCA was identified as hydrogen bonding using FT-IR spectroscopy. When linearly polarized ultraviolet light (LPUVL) irradiated the multilayer film, only the photosensitive double bond parallel to the polarization direction of LPUVL could be polymerized via [2+2] cycloaddition. After the irradiation an anisotropic film was prepared, and we used this anisotropic film as an alignment layer of nematic liquid crystals, and obtained uniformand stable alignment results.
A new type of hydrogen-bonded layer-by-layer (LBL) photoalignment film was fabricated and studied. The photosensitive hydrogen donor containing cinnamoyl groups (Poly(4-acryloyloxy)-cinnamic acid, PCA) was self-assembled with hydrogen accepter poly (4-vinylpyridine) (PVPy) in an organic solvent. Then a hydrogen-bonding-directed ultrathin film was formed. The uniformity and linear growth of the deposition procedure was proven by UV-Vis spectra and the interaction between PVPy and PCA was identified as hydrogen bonding using FT-IR spectroscopy. When linearly polarized ultraviolet light (LPUVL) irradiated the multilayer film, only the photosensitive double bond parallel to the polarization direction of LPUVL could be polymerized via [2+2] cycloaddition. After the irradiation an anisotropic film was prepared, and we used this anisotropic film as an alignment layer of nematic liquid crystals, and obtained uniformand stable alignment results.
2009, 25(02): 278-284
doi: 10.3866/PKU.WHXB20090214
Abstract:
Mechanical and electronic properties of different SnO2 crystal structures were studied by density functional theory. For the exchange-correction energy we employed the generalized gradient approximation (GGA) in the PBE (Perdew, Burke and Ernzerhof) form. The lattice constants, bulk modulus and Young’s modulus of the studied isomers are obtained. By comparing the space groups of Pbca and Pnam in SnO2 the Vickers hardness of the two crystal structures was found to be consistent. There was a difference in the band gap between the SnO2 isomers. Energies of valence bands varied from -10 to 0 eV and -20 to -15 eV for all SnO2 crystals. These valence bands resulted from the O 2p and 2s orbitals. Optical properties of these SnO2 isomers were also calculated. The absorption spectrum of Pnam showed a strong peak in the ultraviolet range. Rules for electron transitions were determined for the different space groups of SnO2.
Mechanical and electronic properties of different SnO2 crystal structures were studied by density functional theory. For the exchange-correction energy we employed the generalized gradient approximation (GGA) in the PBE (Perdew, Burke and Ernzerhof) form. The lattice constants, bulk modulus and Young’s modulus of the studied isomers are obtained. By comparing the space groups of Pbca and Pnam in SnO2 the Vickers hardness of the two crystal structures was found to be consistent. There was a difference in the band gap between the SnO2 isomers. Energies of valence bands varied from -10 to 0 eV and -20 to -15 eV for all SnO2 crystals. These valence bands resulted from the O 2p and 2s orbitals. Optical properties of these SnO2 isomers were also calculated. The absorption spectrum of Pnam showed a strong peak in the ultraviolet range. Rules for electron transitions were determined for the different space groups of SnO2.
2009, 25(02): 285-290
doi: 10.3866/PKU.WHXB20090215
Abstract:
The adsorption of methane in AFS molecular sieves was investigated by a grand canonical Monte Carlo (GCMC) simulation. The results were compared with the methane adsorption in IRMOF-6 materials obtained by Dvren et al. (Langmuir, 2004, 20: 2683). It was indicated that the adsorbed amouts in AFS were very striking. AFS molecular sieve is relative ideal adsorbent in the adsorbs storage natural gas system at the medium and low pressure. The Dubinin-Astakhov (DA) method was employed to analyze the physical factors that affect the storage of methane.
The adsorption of methane in AFS molecular sieves was investigated by a grand canonical Monte Carlo (GCMC) simulation. The results were compared with the methane adsorption in IRMOF-6 materials obtained by Dvren et al. (Langmuir, 2004, 20: 2683). It was indicated that the adsorbed amouts in AFS were very striking. AFS molecular sieve is relative ideal adsorbent in the adsorbs storage natural gas system at the medium and low pressure. The Dubinin-Astakhov (DA) method was employed to analyze the physical factors that affect the storage of methane.
2009, 25(02): 291-298
doi: 10.3866/PKU.WHXB20090216
Abstract:
Molecular geometries and electronic structures of adducts between the hydroxyl radical and the cytosine of 2’-deoxycytidine-5’-monophosphate acid (dCMP) were investigated by density functional theory, B3LYP/DZP++. Computational results reveal that the relative stability sequence of single hydroxyl radical adducts of cytosine of dCMP is C5>C6>>C4≥C2. The C5 atom of dCMP is most reactive for addition of the first hydroxyl radical whereas the C6 atomis not only the next most reactive site for addition of the first hydroxyl radical but also the second reactive site forthe second hydroxyl radical addition when one dCMP molecule is attacked by multiple hydroxyl radicals. This sequence was established by analyses of their stabilities, spin densities, electrostatic potentials of adducts and electron densities, electrostatic potentials, and charge distributions of dCMP. Once the C2-adduct of dCMP is produced either a fatal gene mutation during DNA replication or a DNA-DNA, DNA-protein cross-link leading to more complicated damage of DNA might occur. In contrast, neither the C5- nor C6-adduct of dCMP has a significant effect on the stability of DNA.
Molecular geometries and electronic structures of adducts between the hydroxyl radical and the cytosine of 2’-deoxycytidine-5’-monophosphate acid (dCMP) were investigated by density functional theory, B3LYP/DZP++. Computational results reveal that the relative stability sequence of single hydroxyl radical adducts of cytosine of dCMP is C5>C6>>C4≥C2. The C5 atom of dCMP is most reactive for addition of the first hydroxyl radical whereas the C6 atomis not only the next most reactive site for addition of the first hydroxyl radical but also the second reactive site forthe second hydroxyl radical addition when one dCMP molecule is attacked by multiple hydroxyl radicals. This sequence was established by analyses of their stabilities, spin densities, electrostatic potentials of adducts and electron densities, electrostatic potentials, and charge distributions of dCMP. Once the C2-adduct of dCMP is produced either a fatal gene mutation during DNA replication or a DNA-DNA, DNA-protein cross-link leading to more complicated damage of DNA might occur. In contrast, neither the C5- nor C6-adduct of dCMP has a significant effect on the stability of DNA.
2009, 25(02): 299-303
doi: 10.3866/PKU.WHXB20090217
Abstract:
Froma dynamic ball-grinding solid-state reaction, a series of red-emitting phosphors Ca0.54Sr0.16-δEu0.08Gd0.12 (MoO4)0.2(WO4)0.8 (δ=0-0.16) were synthesized by charge compensation. Three approaches to charge compensation were used and are (a) 3Ca2+/Sr2+→2Eu3+/Gd3++vacancy; (b) 2 Ca2+/Sr2+→2Eu3+/Gd3++M+, where M+ is a monovalent cation like Li+, Na+, or K+ employed as a charge compensator; (c) Ca2+/Sr2+→2Eu3+/Gd3++N-, where N- is a monovalent anion like F-, Cl-, Br- or I- employed as a charge compensator. The results showed that model (b) was better at charge compensation. One red light-emitting diode (LED) was made by combining a phosphor with a 390-405 nm emitting LED chip under a 20 mA forward-bias current. The chromaticity coordinates (CIE), color purity, light intensity, and luminous efficiency were x=0.65, y=0.33, 100%, 6200 cd·m2, and 95 lm·W-1, respectively. Furthermore, the CIE and color purity of the apparatus changed little and the color was stable. This red-emitting phosphor in the field of new generation white-light LEDs has broad application prospects.
Froma dynamic ball-grinding solid-state reaction, a series of red-emitting phosphors Ca0.54Sr0.16-δEu0.08Gd0.12 (MoO4)0.2(WO4)0.8 (δ=0-0.16) were synthesized by charge compensation. Three approaches to charge compensation were used and are (a) 3Ca2+/Sr2+→2Eu3+/Gd3++vacancy; (b) 2 Ca2+/Sr2+→2Eu3+/Gd3++M+, where M+ is a monovalent cation like Li+, Na+, or K+ employed as a charge compensator; (c) Ca2+/Sr2+→2Eu3+/Gd3++N-, where N- is a monovalent anion like F-, Cl-, Br- or I- employed as a charge compensator. The results showed that model (b) was better at charge compensation. One red light-emitting diode (LED) was made by combining a phosphor with a 390-405 nm emitting LED chip under a 20 mA forward-bias current. The chromaticity coordinates (CIE), color purity, light intensity, and luminous efficiency were x=0.65, y=0.33, 100%, 6200 cd·m2, and 95 lm·W-1, respectively. Furthermore, the CIE and color purity of the apparatus changed little and the color was stable. This red-emitting phosphor in the field of new generation white-light LEDs has broad application prospects.
2009, 25(02): 304-308
doi: 10.3866/PKU.WHXB20090218
Abstract:
Nanosized poly(3,4-ethylenedioxythiophene)/manganese oxide (PEDOT/MnO2) composite was prepared by an interfacial polymerization method. The structure and morphology of the product was characterized by IR, XRD, BET surface area, SEM, and TEMtechniques. The results showed that the as-prepared amorphous nanocomposite had a porous structure. The pore size was about 5-25 nm and the surface area reached 98 m2·g-1. Electrochemical properties of the PEDOT/MnO2 electrode were determined by cyclic voltammetry (CV), galvanostatic charge/discharge, and electrochemical impedance spectrometry (EIS). The results indicated that the specific capacitance of the PEDOT/MnO2 nanocomposite as a single electrode was 196.3 F·g-1 at a current density of 0.5 A·g-1 in 0.5 mol·L-1 Na2SO4 electrolyte within a potential range of -0.2 - 0.8 V(vs SCE). The capacity retention of the PEDOT/MnO2 electrode was about 90% after 500 cycles.
Nanosized poly(3,4-ethylenedioxythiophene)/manganese oxide (PEDOT/MnO2) composite was prepared by an interfacial polymerization method. The structure and morphology of the product was characterized by IR, XRD, BET surface area, SEM, and TEMtechniques. The results showed that the as-prepared amorphous nanocomposite had a porous structure. The pore size was about 5-25 nm and the surface area reached 98 m2·g-1. Electrochemical properties of the PEDOT/MnO2 electrode were determined by cyclic voltammetry (CV), galvanostatic charge/discharge, and electrochemical impedance spectrometry (EIS). The results indicated that the specific capacitance of the PEDOT/MnO2 nanocomposite as a single electrode was 196.3 F·g-1 at a current density of 0.5 A·g-1 in 0.5 mol·L-1 Na2SO4 electrolyte within a potential range of -0.2 - 0.8 V(vs SCE). The capacity retention of the PEDOT/MnO2 electrode was about 90% after 500 cycles.
2009, 25(02): 309-313
doi: 10.3866/PKU.WHXB20090219
Abstract:
Thermal behavior of 3,6-dihydrazino-1,2,4,5-tetrazine (DHT) was studied by differential scanning calorimetry (DSC) and thermogravimetry-derivative thermogravimetry (TG-DTG), and the decomposition process can be divided into two exothermic decomposition stages. Values of the apparent activation energy (E) and pre-exponential constant (A) of the two exothermic decomposition stages are 154.8 and 123.4 kJ·mol-1, 1016.63 and 109.48 s-1, respectively. The critical temperature of thermal explosion is 426.10 K. The specific heat capacity of DHT was determined by the micro-DSC method and theoretical calculation method. The standard molar specific heat capacity was found to be 183.61 J·mol-1·K-1 at 298.15 K. The adiabatic time-to-explosion of DHT was calculated to be a certain value between 263.84 s and 297.58 s.
Thermal behavior of 3,6-dihydrazino-1,2,4,5-tetrazine (DHT) was studied by differential scanning calorimetry (DSC) and thermogravimetry-derivative thermogravimetry (TG-DTG), and the decomposition process can be divided into two exothermic decomposition stages. Values of the apparent activation energy (E) and pre-exponential constant (A) of the two exothermic decomposition stages are 154.8 and 123.4 kJ·mol-1, 1016.63 and 109.48 s-1, respectively. The critical temperature of thermal explosion is 426.10 K. The specific heat capacity of DHT was determined by the micro-DSC method and theoretical calculation method. The standard molar specific heat capacity was found to be 183.61 J·mol-1·K-1 at 298.15 K. The adiabatic time-to-explosion of DHT was calculated to be a certain value between 263.84 s and 297.58 s.
2009, 25(02): 314-318
doi: 10.3866/PKU.WHXB20090220
Abstract:
Electronic spectra and second-order nonlinear optical (NLO) properties of eight thiazole chromophores were calculated by density functional theory (DFT) at B3LYP/6-31+G* level. Results showed that thiazole chromophore molecules with active hydroxy-ethyl, alkoxy-ethyl, fluoro-ethyl, and amino-ethyl groups have high β values of about 1.6×10-28 esu which are in od agreement with the available experimental results. Maximum absorption wavelengths λmax of the compounds in the gas phase ranged from 480 to 488 nm. The λmax was red-shifted as the solvent polarity increased for the thiazole chromophore molecules with an active hydroxy-ethyl group.
Electronic spectra and second-order nonlinear optical (NLO) properties of eight thiazole chromophores were calculated by density functional theory (DFT) at B3LYP/6-31+G* level. Results showed that thiazole chromophore molecules with active hydroxy-ethyl, alkoxy-ethyl, fluoro-ethyl, and amino-ethyl groups have high β values of about 1.6×10-28 esu which are in od agreement with the available experimental results. Maximum absorption wavelengths λmax of the compounds in the gas phase ranged from 480 to 488 nm. The λmax was red-shifted as the solvent polarity increased for the thiazole chromophore molecules with an active hydroxy-ethyl group.
2009, 25(02): 319-326
doi: 10.3866/PKU.WHXB20090221
Abstract:
The kinetics of micellar-catalyzed oxidation of mannose by N-bromophthalimide was studied in the presence of sulfuric acid at 313 K. The orders of reaction with respect to [mannose], [oxidant], and [H+] were found to be fractional, first, and negative fractional order, respectively. Anionic micelles of sodiumdodecyl sulfate showed a partial inhibitory effect, while cationic micelles of cetyltrimethylammonium bromide increased the reaction rate with the same kinetic behavior. The reaction was catalyzed by cationic micelles, because of favorable electrostatic/thermodynamic/hydrophobic/hydrogen bonding between reactants and cationic micelles. Their catalytic roles are best explained by Berezin’s model. A variation of [phthalimide] showed that the rate of reaction decreased with increasing [phthalimide]. It was observed that, an increase of [mercuric acetate] had no effect on reaction velocity. The influence of salts on the reaction rate was also studied. The rate constant (kW ), binding constants (KS+KO), and corresponding activation parameters (Ea, ⊿H#, ⊿S#, and ⊿G#) were determined. A detailed mechanism with associated reaction kinetics is presented and discussed.
The kinetics of micellar-catalyzed oxidation of mannose by N-bromophthalimide was studied in the presence of sulfuric acid at 313 K. The orders of reaction with respect to [mannose], [oxidant], and [H+] were found to be fractional, first, and negative fractional order, respectively. Anionic micelles of sodiumdodecyl sulfate showed a partial inhibitory effect, while cationic micelles of cetyltrimethylammonium bromide increased the reaction rate with the same kinetic behavior. The reaction was catalyzed by cationic micelles, because of favorable electrostatic/thermodynamic/hydrophobic/hydrogen bonding between reactants and cationic micelles. Their catalytic roles are best explained by Berezin’s model. A variation of [phthalimide] showed that the rate of reaction decreased with increasing [phthalimide]. It was observed that, an increase of [mercuric acetate] had no effect on reaction velocity. The influence of salts on the reaction rate was also studied. The rate constant (kW ), binding constants (KS+KO), and corresponding activation parameters (Ea, ⊿H#, ⊿S#, and ⊿G#) were determined. A detailed mechanism with associated reaction kinetics is presented and discussed.
2009, 25(02): 327-330
doi: 10.3866/PKU.WHXB20090222
Abstract:
Polypyrrole was obtained by chemical synthesis. The extension of polymerization time to 96 h produced a polypyrrole that was suitable for absorbing moisture. The structure and morphology of polypyrrole were characterized by infrared (IR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Properties of this humidity sensor were investigated and complex impedance plots were obtained from 20 Hz to 100 kHz. The sensing mechanism was discussed based on test results. Using complex impedance analysis we studied the working principle of the humidity sensor and confirmed the identity of the conductive particles.
Polypyrrole was obtained by chemical synthesis. The extension of polymerization time to 96 h produced a polypyrrole that was suitable for absorbing moisture. The structure and morphology of polypyrrole were characterized by infrared (IR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Properties of this humidity sensor were investigated and complex impedance plots were obtained from 20 Hz to 100 kHz. The sensing mechanism was discussed based on test results. Using complex impedance analysis we studied the working principle of the humidity sensor and confirmed the identity of the conductive particles.
2009, 25(02): 331-335
doi: 10.3866/PKU.WHXB20090223
Abstract:
Phase equilibria of the reciprocal quaternary system Mg2+, K+//Cl-, B4O2-7-H2O at 288 K were studied by the isothermal solution equilibrium method. Solubilities and densities in solution of the system were determined experimentally. The equilibrium phase diagram and the density-composition diagram of the quaternary system were plotted using experimental data. Experimental results also showed that the double salt KCl·MgCl2·6H2O formed in the quaternary system Mg2+, K+//Cl-, B4O2-7-H2O at 288 K. The quaternary system at 288 K had three invariant points (F1, F2, and F3), seven univariant curves, and five fields of crystallization [MgB4O7·9H2O, K2B4O7·4H2O, KCl, MgCl2·6H2O, and KCl·MgCl2·6H2O]. The results are discussed simply.
Phase equilibria of the reciprocal quaternary system Mg2+, K+//Cl-, B4O2-7-H2O at 288 K were studied by the isothermal solution equilibrium method. Solubilities and densities in solution of the system were determined experimentally. The equilibrium phase diagram and the density-composition diagram of the quaternary system were plotted using experimental data. Experimental results also showed that the double salt KCl·MgCl2·6H2O formed in the quaternary system Mg2+, K+//Cl-, B4O2-7-H2O at 288 K. The quaternary system at 288 K had three invariant points (F1, F2, and F3), seven univariant curves, and five fields of crystallization [MgB4O7·9H2O, K2B4O7·4H2O, KCl, MgCl2·6H2O, and KCl·MgCl2·6H2O]. The results are discussed simply.
2009, 25(02): 336-340
doi: 10.3866/PKU.WHXB20090224
Abstract:
The synthesis of 1,1,1,2-tetrafluoroethane from 2-chloro-1,1,1-trifluoroethane was performed over CrOx-Y2O3 catalysts prepared by a co-precipitation method. The effect of yttrium precursor on the CrOx species was investigated. The catalysts were prepared using hydroxide, chloride, and nitrate yttrium precursors and were denoted as CrYO-H, CrYO-Cl, and CrYO-N, respectively. After the pre-fluorination these catalycts were denoted as CrYF-H, CrYF-Cl, and CrYF-N, respectively. Catalytic activity decreased in the following order: CrYF-H>CrYF-Cl>CrYF-N. The highest activity obtained for the CrYF-H catalyst could be attributed to the highest content of Cr(VI) on the catalyst surface. This species then transformed into an active species such as CrOxFy or Cr(OH)xFy during the activation process. The presence of CrF3, which originated fromthe Cr(VI), resulted in decreased activity.
The synthesis of 1,1,1,2-tetrafluoroethane from 2-chloro-1,1,1-trifluoroethane was performed over CrOx-Y2O3 catalysts prepared by a co-precipitation method. The effect of yttrium precursor on the CrOx species was investigated. The catalysts were prepared using hydroxide, chloride, and nitrate yttrium precursors and were denoted as CrYO-H, CrYO-Cl, and CrYO-N, respectively. After the pre-fluorination these catalycts were denoted as CrYF-H, CrYF-Cl, and CrYF-N, respectively. Catalytic activity decreased in the following order: CrYF-H>CrYF-Cl>CrYF-N. The highest activity obtained for the CrYF-H catalyst could be attributed to the highest content of Cr(VI) on the catalyst surface. This species then transformed into an active species such as CrOxFy or Cr(OH)xFy during the activation process. The presence of CrF3, which originated fromthe Cr(VI), resulted in decreased activity.
2009, 25(02): 341-346
doi: 10.3866/PKU.WHXB20090225
Abstract:
The copolymerization of glyceryl methacrylate (GMA) and methyl methacrylate (MMA) was conducted in a solution polymerization systemresulting in the formation of copolymerP (GMA-co-MMA). Parahydroxybenzaldehyde was then bound to the side chains of P(GMA-co-MMA) via ring-opening and ether-forming reactions of the epoxy groups on P(GMA-co-MMA). A benzaldehyde (BA)-bound copolymer BA-P(GMA-co-MMA) was thus prepared. The simultaneous synthesis and linkage of the porphyrin onto the side chains of P(GMA-co-MMA) was realized successfully using the Adler method in a homogeneous system. Benzaldehyde, BA-P(GMA-co-MMA), and pyrrole were used as reactants, resulting in the porphyrin (PP)-functionalized line-type macromolecule PP-P(GMA-co-MMA). The chemical structure of PP-P(GMA-co-MMA) was characterized by Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (1H-NMR) spectroscopy. The spectral properties of PP-P(GMA-co-MMA) were studied and its photophysical behavior was investigated in depth. Experimental results show that PP-P(GMA-co-MMA) has the same electronic absorption spectrum and fluorescence emission spectrum as tetraphenyl porphyrin. In the electronic absorption spectra of PP-P(GMA-co-MMA) both the Soret absorption band and the Q absorption band strengthen as the amount of bound porphyrin increaseds. The Q emission band intensity of PP-P(GMA-co-MMA) also first increases with the increase of the amount of bound porphyrin until to a maximum, and then decreases if more porphyrin units are present. Intramolecular energy transfer of the macromolecule PP-P(GMA-co-MMA) should be responsible for this behavior.
The copolymerization of glyceryl methacrylate (GMA) and methyl methacrylate (MMA) was conducted in a solution polymerization systemresulting in the formation of copolymerP (GMA-co-MMA). Parahydroxybenzaldehyde was then bound to the side chains of P(GMA-co-MMA) via ring-opening and ether-forming reactions of the epoxy groups on P(GMA-co-MMA). A benzaldehyde (BA)-bound copolymer BA-P(GMA-co-MMA) was thus prepared. The simultaneous synthesis and linkage of the porphyrin onto the side chains of P(GMA-co-MMA) was realized successfully using the Adler method in a homogeneous system. Benzaldehyde, BA-P(GMA-co-MMA), and pyrrole were used as reactants, resulting in the porphyrin (PP)-functionalized line-type macromolecule PP-P(GMA-co-MMA). The chemical structure of PP-P(GMA-co-MMA) was characterized by Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (1H-NMR) spectroscopy. The spectral properties of PP-P(GMA-co-MMA) were studied and its photophysical behavior was investigated in depth. Experimental results show that PP-P(GMA-co-MMA) has the same electronic absorption spectrum and fluorescence emission spectrum as tetraphenyl porphyrin. In the electronic absorption spectra of PP-P(GMA-co-MMA) both the Soret absorption band and the Q absorption band strengthen as the amount of bound porphyrin increaseds. The Q emission band intensity of PP-P(GMA-co-MMA) also first increases with the increase of the amount of bound porphyrin until to a maximum, and then decreases if more porphyrin units are present. Intramolecular energy transfer of the macromolecule PP-P(GMA-co-MMA) should be responsible for this behavior.
2009, 25(02): 347-352
doi: 10.3866/PKU.WHXB20090226
Abstract:
Electronic structures and spectroscopic properties of 4-[(1,2-diphenyl)-4’-(N,N-diphenyl-4-vinylbenzenamine)] biphenyl and its difluorinated derivatives were studied. B3LYP/6-31G(d) and CIS/6-31G(d)methods were used to optimize the ground and excited state geometries, respectively, and the data for ionization potentials (IPs) and electron affinities (EAs) were also obtained. Absorption and emission spectra were calculated using time-dependent density functional theory (TD-DFT) based on ground and excited state geometries.We found that the main emission peak intensity at 469-474 nmis far more larger than the second emission peak at 372-387 nm, which indicates that this type of compound has its own highly pure emission wavelength. Difluoro-substituted derivatives on the benzene of the main chain (B, C and D) cause an energy lowering of the lowest unoccupied molecular orbital (LUMO) energy levels obviously, which facilitates the injection of electron carriers from the metal electrode. Difluoro-substituted derivatives on the benzene of benzenamine (D and E) cause an energy lowering of the highest occupied molecular orbitals (HOMO) obviously. The increasing of IP and energy gap, which is proper to hold hole transfer from the emission layer to the electron transport layer, reduces the formation of exciplexes at the interface and causes a blue-shift of spectra. The difluoro-substituted derivative of benzene on both the main chain and benzenamine (D) is better for a balance of electron and hole injection which should result in even better emission properties.
Electronic structures and spectroscopic properties of 4-[(1,2-diphenyl)-4’-(N,N-diphenyl-4-vinylbenzenamine)] biphenyl and its difluorinated derivatives were studied. B3LYP/6-31G(d) and CIS/6-31G(d)methods were used to optimize the ground and excited state geometries, respectively, and the data for ionization potentials (IPs) and electron affinities (EAs) were also obtained. Absorption and emission spectra were calculated using time-dependent density functional theory (TD-DFT) based on ground and excited state geometries.We found that the main emission peak intensity at 469-474 nmis far more larger than the second emission peak at 372-387 nm, which indicates that this type of compound has its own highly pure emission wavelength. Difluoro-substituted derivatives on the benzene of the main chain (B, C and D) cause an energy lowering of the lowest unoccupied molecular orbital (LUMO) energy levels obviously, which facilitates the injection of electron carriers from the metal electrode. Difluoro-substituted derivatives on the benzene of benzenamine (D and E) cause an energy lowering of the highest occupied molecular orbitals (HOMO) obviously. The increasing of IP and energy gap, which is proper to hold hole transfer from the emission layer to the electron transport layer, reduces the formation of exciplexes at the interface and causes a blue-shift of spectra. The difluoro-substituted derivative of benzene on both the main chain and benzenamine (D) is better for a balance of electron and hole injection which should result in even better emission properties.
2009, 25(02): 353-359
doi: 10.3866/PKU.WHXB20090227
Abstract:
A series of hydrotalcite-like precursors with different Zn contents of ZnxMg3-xAl-HT (x=0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0) were synthesized by co-precipitation methods, and by keeping the atomic ratio of M2+/M3+ constant at 3. Mixed oxides derived from these precursors through calcination were applied to N2O catalytic decomposition. X-ray diffraction (XRD), BET surface area, thermal analysis (TG-DSC), and Fourier transform infrared (FT-IR) techniques were used to study the influence of Zn content on the composition and structure of precursors and corresponding mixed oxides. N2O catalytic decomposition behavior over ZnxMg3 -xAlO catalysts was investigated and impacts of reaction conditions, such as N2O concentration, space velocity, O2 and H2O on catalytic activity, were studied in detail. The results showed that the complete hydrotalcite layer structure was formed in all precursors. After calcination the main catalyst phase is Zn-Al spinel. The introduction of Zn promotes the formation of the spinel. Mg can improve the thermal stability of catalysts to some degree. Zn content has an important influence on the thermal stability, surface area and activity of the catalyst. As Zn content increases the surface area of the catalyst decreases. Surface area is, however, not an important factor in N2O catalytic decomposition. Zn2.0Mg1.0AlO catalyst, calcined at 650 ℃, shows relatively od activity for N2O decomposition. The N2O concentration, space velocity, and O2 have little impact on activity, while H2O obviously influences the activity of N2O catalytic decomposition.
A series of hydrotalcite-like precursors with different Zn contents of ZnxMg3-xAl-HT (x=0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0) were synthesized by co-precipitation methods, and by keeping the atomic ratio of M2+/M3+ constant at 3. Mixed oxides derived from these precursors through calcination were applied to N2O catalytic decomposition. X-ray diffraction (XRD), BET surface area, thermal analysis (TG-DSC), and Fourier transform infrared (FT-IR) techniques were used to study the influence of Zn content on the composition and structure of precursors and corresponding mixed oxides. N2O catalytic decomposition behavior over ZnxMg3 -xAlO catalysts was investigated and impacts of reaction conditions, such as N2O concentration, space velocity, O2 and H2O on catalytic activity, were studied in detail. The results showed that the complete hydrotalcite layer structure was formed in all precursors. After calcination the main catalyst phase is Zn-Al spinel. The introduction of Zn promotes the formation of the spinel. Mg can improve the thermal stability of catalysts to some degree. Zn content has an important influence on the thermal stability, surface area and activity of the catalyst. As Zn content increases the surface area of the catalyst decreases. Surface area is, however, not an important factor in N2O catalytic decomposition. Zn2.0Mg1.0AlO catalyst, calcined at 650 ℃, shows relatively od activity for N2O decomposition. The N2O concentration, space velocity, and O2 have little impact on activity, while H2O obviously influences the activity of N2O catalytic decomposition.
2009, 25(02): 360-364
doi: 10.3866/PKU.WHXB20090228
Abstract:
Theoretical calculations on a series of intramolecular α-hydrogen transfer reactions for organometallic tantalum complexes were carried out using the B3LYP method. Optimal structures for reactants, transition states, and products were located. Calculated results indicate that sp2 hybridization is adopted by the central carbon atoms, from which the hydrogen atom shifts, for all 16 transition states. Both electron donating groups and electron withdrawing groups will delocalize the unpaired electron in the pz orbital of the central carbon atomin some way and will thus result in a lower reaction barrier. The reaction barrier of Ta(CH3)4CH(SiMe3)2 had the lowest value.
Theoretical calculations on a series of intramolecular α-hydrogen transfer reactions for organometallic tantalum complexes were carried out using the B3LYP method. Optimal structures for reactants, transition states, and products were located. Calculated results indicate that sp2 hybridization is adopted by the central carbon atoms, from which the hydrogen atom shifts, for all 16 transition states. Both electron donating groups and electron withdrawing groups will delocalize the unpaired electron in the pz orbital of the central carbon atomin some way and will thus result in a lower reaction barrier. The reaction barrier of Ta(CH3)4CH(SiMe3)2 had the lowest value.
2009, 25(02): 365-370
doi: 10.3866/PKU.WHXB20090229
Abstract:
SnS materials with differentmorphologies and sizeswere synthesized by ball milling,microwave-assisted, and chemical methods. Structures and morphologies of the as-prepared SnS were studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The as-prepared SnS had different morphologies including nanoparticles, flakes, and nanorods. All prepared SnS samples were investigated electrochemically as electrodes for lithium ion batteries. SnS nanoparticles prepared by ball milling and chemical method without surfactant had superior electrochemical performance and had remaining capacities of 375 and 414 mAh·g-1 after 40 cycles. Compact nanostructure, morphology, and size were responsible for excellent electrochemical performances of nanoscale SnS. The inactive Li2S phase probably helped to maintain a stable electrode structure during the discharge-charge process, but the morphology and size of SnS were the key factors in obtaining an outstanding SnS anode.
SnS materials with differentmorphologies and sizeswere synthesized by ball milling,microwave-assisted, and chemical methods. Structures and morphologies of the as-prepared SnS were studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The as-prepared SnS had different morphologies including nanoparticles, flakes, and nanorods. All prepared SnS samples were investigated electrochemically as electrodes for lithium ion batteries. SnS nanoparticles prepared by ball milling and chemical method without surfactant had superior electrochemical performance and had remaining capacities of 375 and 414 mAh·g-1 after 40 cycles. Compact nanostructure, morphology, and size were responsible for excellent electrochemical performances of nanoscale SnS. The inactive Li2S phase probably helped to maintain a stable electrode structure during the discharge-charge process, but the morphology and size of SnS were the key factors in obtaining an outstanding SnS anode.
2009, 25(02): 371-376
doi: 10.3866/PKU.WHXB20090230
Abstract:
The mechanism, potential energy surface, substituent effect and salvation effect of two types of Diels-Alder reactions between silabenzenes and some dienophiles were investigated using density functional theory (DFT) at B3LYP/6-311G(d,p) level. All the studied reactions proceeded in a concerted way. The influence of phenyl at the C atom of dienophiles on the asynchronicity in the bond-formation process and the activation barrier of the reaction were determined by the relative position of phenyl in products. The CCl3 group at the Si atom of the silabenzene molecule favors the hetero-Diels-Alder reactions. The hetero-Diels-Alder reactions associated with the C—Si forming bond proceed much more easily than traditional Diels-Alder reactions both thermodynamically and kinetically. The complete regioselectivity observed experimentally in hetero-Diels-Alder reactions were reproduced well by theoretical calculations and are controlled by kinetic factors. Reactions between silabenzene and olefins proceed more easily than those between silabenzene and corresponding alkynes kinetically, but thermodynamically, this is reversed. Benzene as a solvent only has a trivial influence on the potential energy surface of the studied reactions.
The mechanism, potential energy surface, substituent effect and salvation effect of two types of Diels-Alder reactions between silabenzenes and some dienophiles were investigated using density functional theory (DFT) at B3LYP/6-311G(d,p) level. All the studied reactions proceeded in a concerted way. The influence of phenyl at the C atom of dienophiles on the asynchronicity in the bond-formation process and the activation barrier of the reaction were determined by the relative position of phenyl in products. The CCl3 group at the Si atom of the silabenzene molecule favors the hetero-Diels-Alder reactions. The hetero-Diels-Alder reactions associated with the C—Si forming bond proceed much more easily than traditional Diels-Alder reactions both thermodynamically and kinetically. The complete regioselectivity observed experimentally in hetero-Diels-Alder reactions were reproduced well by theoretical calculations and are controlled by kinetic factors. Reactions between silabenzene and olefins proceed more easily than those between silabenzene and corresponding alkynes kinetically, but thermodynamically, this is reversed. Benzene as a solvent only has a trivial influence on the potential energy surface of the studied reactions.
2009, 25(02): 377-381
doi: 10.3866/PKU.WHXB20090231
Abstract:
Interactions between the electron acceptor cyclobis(paraquat-phenylene)tetracationic cyclophane (CPQT) and electron donating phenyl ether derivatives in acetonitrile were simulated by molecular dynamics (MD). The structure of CPQTwas optimized by AM1 and B3LYP/6-31+g. Charges generated by theMaterial Studio software were substituted by calculated charges at B3LYP/6-31+g level. The results show that the order of binding energies for the three phenyl ether derivatives and CPQT are as follows: BHEEB·CPQT>BHEB·CPQT>1/4DMB·CPQT. Stabilities of the pseudorotaxanes are found to decrease as the temperature increases. These simulated results are consistent with reported experimental results.
Interactions between the electron acceptor cyclobis(paraquat-phenylene)tetracationic cyclophane (CPQT) and electron donating phenyl ether derivatives in acetonitrile were simulated by molecular dynamics (MD). The structure of CPQTwas optimized by AM1 and B3LYP/6-31+g. Charges generated by theMaterial Studio software were substituted by calculated charges at B3LYP/6-31+g level. The results show that the order of binding energies for the three phenyl ether derivatives and CPQT are as follows: BHEEB·CPQT>BHEB·CPQT>1/4DMB·CPQT. Stabilities of the pseudorotaxanes are found to decrease as the temperature increases. These simulated results are consistent with reported experimental results.
2009, 25(02): 382-388
doi: 10.3866/PKU.WHXB20090232
Abstract:
Recently, plenty of attention has been paid to the dispersion of carbon nanotubes by amphiphilic molecules. In this paper, different mechanisms for a non-covalent dispersion of carbon nanotubes are summarized from the three fields of surfactants, polymers, and biomacromolecules. Ionic surfactants or polyelectrolytes mainly depend on an electrostatic repulsion between hydrophilic groups to prevent carbon nanotube aggregation while non-ionic surfactants or polymers mainly rely on a steric stabilization of hydrophilic groups to disperse the carbon nanotubes.
Recently, plenty of attention has been paid to the dispersion of carbon nanotubes by amphiphilic molecules. In this paper, different mechanisms for a non-covalent dispersion of carbon nanotubes are summarized from the three fields of surfactants, polymers, and biomacromolecules. Ionic surfactants or polyelectrolytes mainly depend on an electrostatic repulsion between hydrophilic groups to prevent carbon nanotube aggregation while non-ionic surfactants or polymers mainly rely on a steric stabilization of hydrophilic groups to disperse the carbon nanotubes.
2009, 25(02): 389-400
doi: 10.3866/PKU.WHXB20090233
Abstract:
Metal-coordinated compounds with well-defined shapes and abundant functionalities are ideal building blocks for constructing functional nanostructures. These types of compounds have been widely used in various fields such as catalysis as well as sensor and nanodevice fabrication. Recently, our group has systematically investigated the self-assembly of metal-coordinated compounds on solid surfaces by scanning tunneling microscopy (STM). Functional molecular nanostructures were constructed based on direct observations of ligands and complex molecules at sub-molecular or molecular resolutions. This paper summarizes results from the self-assembly of metal-coordinated compounds as reported by our group as well as some recent progress in this field. It is expected that this review paper will be helpful for the exploration of assembly rules of metal-coordinated compounds on solid surfaces.
Metal-coordinated compounds with well-defined shapes and abundant functionalities are ideal building blocks for constructing functional nanostructures. These types of compounds have been widely used in various fields such as catalysis as well as sensor and nanodevice fabrication. Recently, our group has systematically investigated the self-assembly of metal-coordinated compounds on solid surfaces by scanning tunneling microscopy (STM). Functional molecular nanostructures were constructed based on direct observations of ligands and complex molecules at sub-molecular or molecular resolutions. This paper summarizes results from the self-assembly of metal-coordinated compounds as reported by our group as well as some recent progress in this field. It is expected that this review paper will be helpful for the exploration of assembly rules of metal-coordinated compounds on solid surfaces.
