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2006 Volume 22 Issue 8
2006, 22(08): 913-916
doi: 10.1016/S1872-1508(06)60039-9
Abstract:
The vesicle aggregation induced by multivalent metal ions in the mixed system of polyelectrolyte(hydrolyzed random copolymer of maleic anhydride-styrene, SMA)-surfactant(dodecyltriethylammonium bromide, DEAB) was investigated through transmission electron microscopy (TEM) observation and turbidity measurement. It was found that a small quantity of Ca2+ (in the magnitude of 10-4 mol·L-1) can induce vesicle aggregation. Adding EDTA can dissociate the vesicle aggregation. Further investigation suggested that the vesicle aggregation followed the salt-linkage mechanism.
2006, 22(08): 917-920
doi: 10.1016/S1872-1508(06)60040-5
Abstract:
The ability of detecting multiple analytes simultaneously is an important advantage of protein sensors. But the denaturation of proteins on surfaces is still a challenge. In this paper, a protein biosensor providing high selectivity is introduced. This approach is based on DNA-Directed Immobilization (DDI) method, in which protein-DNA conjugates are immobilized on surface through DNA hybridization. Nonspecific binding is reduced by applying fluorescence resonance energy transfer (FRET) and scanning potential hairpin denaturation (SPHD) technologies. Excellent discrimination on different recognition patterns is obtained.
2006, 22(08): 921-925
doi: 10.3866/PKU.WHXB20060803
Abstract:
The reaction mechanism of CH3CHF radical reacting with HNCO had been investigated by density functional theory (DFT). The geometries and frequencies of reactants, intermediates, transition states and products had been calculated at the B3LYP/6- 311++G (d, p) level. To obtain more accurate energy result, single point energies were calculated at the QCISD(T)/6- 311++G(d, p) level. The vibration analysis and the IRC analysis approved the authenticity of intermediates and transition states, and the reaction processes were confirmed by the changes of charge density at bond- forming critical points. Seven feasible reaction pathways of this reaction had been found and studied. The results indicated that the pathway which produced the stable molecule fluoroalkyl imide had the lowest activation barrier and it was a competitive pathway that took place easier than the hydrogen transfer process.
The reaction mechanism of CH3CHF radical reacting with HNCO had been investigated by density functional theory (DFT). The geometries and frequencies of reactants, intermediates, transition states and products had been calculated at the B3LYP/6- 311++G (d, p) level. To obtain more accurate energy result, single point energies were calculated at the QCISD(T)/6- 311++G(d, p) level. The vibration analysis and the IRC analysis approved the authenticity of intermediates and transition states, and the reaction processes were confirmed by the changes of charge density at bond- forming critical points. Seven feasible reaction pathways of this reaction had been found and studied. The results indicated that the pathway which produced the stable molecule fluoroalkyl imide had the lowest activation barrier and it was a competitive pathway that took place easier than the hydrogen transfer process.
2006, 22(08): 926-931
doi: 10.3866/PKU.WHXB20060804
Abstract:
Glow discharge plasma was used to modify NiO/SrTiO3 photocatalyst prepared by impregnation method. According to XRD, XPS, and TEM characterizations, the metal dispersion and stability of catalyst were greatly improved. XPS, thermo- gravimetric, and XRD characterizations showed that impregnated Ni(NO3)2 was decomposed into amorphous NiO clusters at room temperature. These clusters may have a strong interaction with the support, contributing to the enhanced metal dispersion and stability. The high metal dispersion can improve the electron transfer from semiconductor to metal and provide more active sites. The photocatalytic activity for water splitting to hydrogen and methanol solution conversion to hydrogen is 1.3 and 1.8 times of that of conventional catalyst.
Glow discharge plasma was used to modify NiO/SrTiO3 photocatalyst prepared by impregnation method. According to XRD, XPS, and TEM characterizations, the metal dispersion and stability of catalyst were greatly improved. XPS, thermo- gravimetric, and XRD characterizations showed that impregnated Ni(NO3)2 was decomposed into amorphous NiO clusters at room temperature. These clusters may have a strong interaction with the support, contributing to the enhanced metal dispersion and stability. The high metal dispersion can improve the electron transfer from semiconductor to metal and provide more active sites. The photocatalytic activity for water splitting to hydrogen and methanol solution conversion to hydrogen is 1.3 and 1.8 times of that of conventional catalyst.
2006, 22(08): 932-936
doi: 10.1016/S1872-1508(06)60041-7
Abstract:
In terms of rigid rotor model, time- dependent Schrodinger equation is solved by using the pseudospectral method, and the alignment behaviors of diatomic molecular N2 and O2 are studied in laser field. The evolution of the field- free rotational wave- packet of the molecules after the laser pulse is over has been discussed. The results show that the alignment parameter of the molecules depends on the temperature. Both N2 and O2 molecules are better aligned at lower temperature, whereas they are poorly aligned at higher temperature. The behavior can be attributed to the population of the angular moment in the rotational wave- packet of molecules at different temperatures.
In terms of rigid rotor model, time- dependent Schrodinger equation is solved by using the pseudospectral method, and the alignment behaviors of diatomic molecular N2 and O2 are studied in laser field. The evolution of the field- free rotational wave- packet of the molecules after the laser pulse is over has been discussed. The results show that the alignment parameter of the molecules depends on the temperature. Both N2 and O2 molecules are better aligned at lower temperature, whereas they are poorly aligned at higher temperature. The behavior can be attributed to the population of the angular moment in the rotational wave- packet of molecules at different temperatures.
2006, 22(08): 937-941
doi: 10.3866/PKU.WHXB20060806
Abstract:
The structures and stabilities of twenty- three B28N28 alternant structures have been investigated at the B3LYP/6- 31G* level of density functional theory. It is found that stability index of all the isomers obey a simple N4x4(x=0, 1, 2) topological rule characterizing the number of bonds between squares. The relative energies show an increasing tendency with the rising of x in N4x4(x=0, 1, 2), in which N404 is dominant. The present study provides a simple topological criterion that can be used to sort an approximate stability order of all the isomers and select the more stable candidate from the ISR(isolated square rule) structures. The simple filtering scheme is ideally suited for prescreening the thermodynamically viable structures of large boron nitride clusters.
The structures and stabilities of twenty- three B28N28 alternant structures have been investigated at the B3LYP/6- 31G* level of density functional theory. It is found that stability index of all the isomers obey a simple N4x4(x=0, 1, 2) topological rule characterizing the number of bonds between squares. The relative energies show an increasing tendency with the rising of x in N4x4(x=0, 1, 2), in which N404 is dominant. The present study provides a simple topological criterion that can be used to sort an approximate stability order of all the isomers and select the more stable candidate from the ISR(isolated square rule) structures. The simple filtering scheme is ideally suited for prescreening the thermodynamically viable structures of large boron nitride clusters.
2006, 22(08): 942-946
doi: 10.3866/PKU.WHXB20060807
Abstract:
Some complexes of rare earth and valine were synthesized: monovalino -hexaquo-neodymium, samarium. Their property was determined by the EDTA titration, element analysis, infrared spectrum, thermogravimetry, differential thermal analysis and melting point measure. The thermal decomposition mechanism had been deduced, and non-isothermal kinetics of the thermal decomposition of the complexes also had been studied with the methods of Achar and Coats-Redfern. These parameters were carried out that the activation energy (E ), the values of logarithm of preexponential factore {ln(A/s-1)} and the kinetics equation of the complexes’ first step reaction which belong to the stagy of water-loss and the framework of amino acid breaking down.
Some complexes of rare earth and valine were synthesized: monovalino -hexaquo-neodymium, samarium. Their property was determined by the EDTA titration, element analysis, infrared spectrum, thermogravimetry, differential thermal analysis and melting point measure. The thermal decomposition mechanism had been deduced, and non-isothermal kinetics of the thermal decomposition of the complexes also had been studied with the methods of Achar and Coats-Redfern. These parameters were carried out that the activation energy (E ), the values of logarithm of preexponential factore {ln(A/s-1)} and the kinetics equation of the complexes’ first step reaction which belong to the stagy of water-loss and the framework of amino acid breaking down.
2006, 22(08): 947-952
doi: 10.3866/PKU.WHXB20060808
Abstract:
Zeolite Y encapsulated symmetrical and unsymmetrical Co(II)Salen- type Schiff base complexes with different substituents were prepared by flexible ligand method and characterized by XRD, FTIR, UV- Vis, and thermal analysis. The effects of substituents on encapsulation and catalytic activity of the encapsulated complexes were also investigated. The results indicated that the complexes could be formed and encapsulated in the supercages without affecting the zeolite framework structure. The prepared castalysts exhibited high activity, selectivity, as well as stability in the epoxidation of styrene with molecular oxygen. The highest conversion and selectivity towards styrene oxide could reach 93.2% and 75.6% respectively at 110 ℃ under 0.1 g catalyst, 5 mmol of styrene and oxygen saturated conditions. The recycled catalyst did not show any decrease in catalytic activity and selectivity. Substitution of the aromatic hydrogen atom of the Salen ligand with electron withdrawing group Br decreased the amount of the complex encapsulated in the zeolite cavities, but could improve the catalytic activity of the encapsulated complex. Density functional theory calculation results indicated that the catalytic activities depended on orbital energy of metal complexes.
Zeolite Y encapsulated symmetrical and unsymmetrical Co(II)Salen- type Schiff base complexes with different substituents were prepared by flexible ligand method and characterized by XRD, FTIR, UV- Vis, and thermal analysis. The effects of substituents on encapsulation and catalytic activity of the encapsulated complexes were also investigated. The results indicated that the complexes could be formed and encapsulated in the supercages without affecting the zeolite framework structure. The prepared castalysts exhibited high activity, selectivity, as well as stability in the epoxidation of styrene with molecular oxygen. The highest conversion and selectivity towards styrene oxide could reach 93.2% and 75.6% respectively at 110 ℃ under 0.1 g catalyst, 5 mmol of styrene and oxygen saturated conditions. The recycled catalyst did not show any decrease in catalytic activity and selectivity. Substitution of the aromatic hydrogen atom of the Salen ligand with electron withdrawing group Br decreased the amount of the complex encapsulated in the zeolite cavities, but could improve the catalytic activity of the encapsulated complex. Density functional theory calculation results indicated that the catalytic activities depended on orbital energy of metal complexes.
2006, 22(08): 953-957
doi: 10.3866/PKU.WHXB20060809
Abstract:
The Au modified nanosized titanium oxide (TiO2) powders were prepared by sol-gel route at ambient temperature using Ti(OC4H9)4 and HAuCl4 as raw materials. The as-prepared samples were analyzed by XRD, BET, XPS and UV-visible absorption spectra technique. Photodegration for non-ionic surfactant Nonylphenyl poly(oxyethylene)ethers (NPE-10) has been carried out in air-equilibrated Au/TiO2 suspensions. The results suggest that the conformation of Au in the TiO2 composite was largely dependent on concentration of HAuCl4 during the preparation and the Au/TiO2 heat-treated temperature. The doped Au may take place Ti4+ in the lattices of TiO2 as Au3+ or exist at surface of TiO2 particles as atoms. The former may contribute to light adsorption range from.480 to 650 nm and may produce more O vacancies; the later may become the acceptor of photoinduced e- leading to a decrease of e-/h+ recombination. The preparation parameters were optimized by means of NPE-10 degradation. The optimized catalyst was obtained at Au/Ti molar ratio of 0.005 and calcined at 500℃. The degradation rate of NPE-10 could be up to 91.8% after irradiated 4 h in sunlight compared to 66% for the rate of TiO2-P-25 and 50.2% for the rate of no-doping TiO2 .
The Au modified nanosized titanium oxide (TiO2) powders were prepared by sol-gel route at ambient temperature using Ti(OC4H9)4 and HAuCl4 as raw materials. The as-prepared samples were analyzed by XRD, BET, XPS and UV-visible absorption spectra technique. Photodegration for non-ionic surfactant Nonylphenyl poly(oxyethylene)ethers (NPE-10) has been carried out in air-equilibrated Au/TiO2 suspensions. The results suggest that the conformation of Au in the TiO2 composite was largely dependent on concentration of HAuCl4 during the preparation and the Au/TiO2 heat-treated temperature. The doped Au may take place Ti4+ in the lattices of TiO2 as Au3+ or exist at surface of TiO2 particles as atoms. The former may contribute to light adsorption range from.480 to 650 nm and may produce more O vacancies; the later may become the acceptor of photoinduced e- leading to a decrease of e-/h+ recombination. The preparation parameters were optimized by means of NPE-10 degradation. The optimized catalyst was obtained at Au/Ti molar ratio of 0.005 and calcined at 500℃. The degradation rate of NPE-10 could be up to 91.8% after irradiated 4 h in sunlight compared to 66% for the rate of TiO2-P-25 and 50.2% for the rate of no-doping TiO2 .
2006, 22(08): 958-961
doi: 10.3866/PKU.WHXB20060810
Abstract:
Sm0.5Sr0.5CoO3(SSC)－La0.8Sr0.2Ga0.8Mg0.15Co0.05O3(LSGMC5) composite cathodes for intermediate temperature solid oxide fuel cells were prepared using wet-chemistry method. The Sm0.5Sr0.5CoO3(SSC) powders were prepared by the glycine-nitrate method and the La0.8Sr0.2Ga0.8Mg0.15Co0.05O3(LSGMC5) powders were synthesized by the citrate method. XRD pattern of SSC powders calcined at a temperature over 950℃ corresponded to a desired perovskite structure. With the increase in sintering temperature, the size of SSC particles increased, which leaded to a weak adhesion on electrolyte for electrodes based on SSC sintered at high temperatures. Multiple techniques were applied to characterize the oxygen reduction reaction over SSC-LSGMC5 cathodes based on SSC sintered at various temperatures（1173－1373K）. The results demonstrated that the performance of SSC-LSGMC5 composite electrodes depended strongly on the sintering temperature of SSC. Electrodes based on SSC sintered at1223K exhibited the lowest ohmic resistance and polarization resistance among the electrodes studied , and the overpotential at 973 K under 1A· cm-2 current density was as low as 0.077 V.
Sm0.5Sr0.5CoO3(SSC)－La0.8Sr0.2Ga0.8Mg0.15Co0.05O3(LSGMC5) composite cathodes for intermediate temperature solid oxide fuel cells were prepared using wet-chemistry method. The Sm0.5Sr0.5CoO3(SSC) powders were prepared by the glycine-nitrate method and the La0.8Sr0.2Ga0.8Mg0.15Co0.05O3(LSGMC5) powders were synthesized by the citrate method. XRD pattern of SSC powders calcined at a temperature over 950℃ corresponded to a desired perovskite structure. With the increase in sintering temperature, the size of SSC particles increased, which leaded to a weak adhesion on electrolyte for electrodes based on SSC sintered at high temperatures. Multiple techniques were applied to characterize the oxygen reduction reaction over SSC-LSGMC5 cathodes based on SSC sintered at various temperatures（1173－1373K）. The results demonstrated that the performance of SSC-LSGMC5 composite electrodes depended strongly on the sintering temperature of SSC. Electrodes based on SSC sintered at1223K exhibited the lowest ohmic resistance and polarization resistance among the electrodes studied , and the overpotential at 973 K under 1A· cm-2 current density was as low as 0.077 V.
Effect of Connecting Formof Repeat Unit in Polyphenylene Derivatives Conjugated Polymers on Band Gap
2006, 22(08): 962-966
doi: 10.3866/PKU.WHXB20060811
Abstract:
Geometrical optimization was performed on the oli mers of (p- P)2n, (m- P)2n, (m- P1)n, and (m- P2)n(n=1~4) using DFT/B3LYP method. The absorption spectra were calculated by ZINDO and TD- DFT. The rules for the variation of the HOMO- LUMO energy gap and the increasing of maximal absorption wavelength with “n” were analyzed. Based on these results, the corresponding properties of the polymers were obtained by extrapolation. ECL (effective conjugated length) of the polymers was calculated by the regressive expression. ECL was shortened greatly due to the meta- linked fashion of poly(m- phenylene). Compared with poly(p- phenylene), poly(m- phenylene) and derivatives hold wider band gap, and its maximal absorption wavelength blue shifted about 130 nm.
Geometrical optimization was performed on the oli mers of (p- P)2n, (m- P)2n, (m- P1)n, and (m- P2)n(n=1~4) using DFT/B3LYP method. The absorption spectra were calculated by ZINDO and TD- DFT. The rules for the variation of the HOMO- LUMO energy gap and the increasing of maximal absorption wavelength with “n” were analyzed. Based on these results, the corresponding properties of the polymers were obtained by extrapolation. ECL (effective conjugated length) of the polymers was calculated by the regressive expression. ECL was shortened greatly due to the meta- linked fashion of poly(m- phenylene). Compared with poly(p- phenylene), poly(m- phenylene) and derivatives hold wider band gap, and its maximal absorption wavelength blue shifted about 130 nm.
2006, 22(08): 967-971
doi: 10.1016/S1872-1508(06)60042-9
Abstract:
Onion-like Fullerenes (OLFs) were prepared by CVD method, and purified by nitric acid treatment. 10wt. %Pt/OLFs catalyst was prepared by impregnation-reduction method with three different loadings of formaldehyde as the reducing agent and the morphology and structure were characterized. XRD patterns showed the excessive reducer benefits the growth of Pt crystals. HRTEM images showed that Pt particles with the diameter of 2.5nm~3.5nm had well distribution in the Pt/OLFs composite. FTIR spectrum also indicated lots of functional groups existed on the surface of OLFs purified. The reducing action of formaldehyde in the process of supporting was discussed.
Onion-like Fullerenes (OLFs) were prepared by CVD method, and purified by nitric acid treatment. 10wt. %Pt/OLFs catalyst was prepared by impregnation-reduction method with three different loadings of formaldehyde as the reducing agent and the morphology and structure were characterized. XRD patterns showed the excessive reducer benefits the growth of Pt crystals. HRTEM images showed that Pt particles with the diameter of 2.5nm~3.5nm had well distribution in the Pt/OLFs composite. FTIR spectrum also indicated lots of functional groups existed on the surface of OLFs purified. The reducing action of formaldehyde in the process of supporting was discussed.
2006, 22(08): 972-976
doi: 10.3866/PKU.WHXB20060813
Abstract:
The vector correlations between products and reagents for the reaction N(4S)+ NO(X2Π)→N2(X3Σg-)+O(3P) are studied by using quasiclassical trajectory (QCT) method at different collision energies on two lowest 3A and 3A' potential energy surfaces (PESs). The results indicate that the rotational polarizations of product N2 on the two PESs exhibit different characters and trends at different collision energies. As the collision energy increases the reaction occurred on the 3A PES is mainly dominated by out-of-plane mechanism, and that occurred on the 3A' PES tends to be dominated by in-plane mechanism. All these differences arise from the different constructions of the two PESs.
The vector correlations between products and reagents for the reaction N(4S)+ NO(X2Π)→N2(X3Σg-)+O(3P) are studied by using quasiclassical trajectory (QCT) method at different collision energies on two lowest 3A and 3A' potential energy surfaces (PESs). The results indicate that the rotational polarizations of product N2 on the two PESs exhibit different characters and trends at different collision energies. As the collision energy increases the reaction occurred on the 3A PES is mainly dominated by out-of-plane mechanism, and that occurred on the 3A' PES tends to be dominated by in-plane mechanism. All these differences arise from the different constructions of the two PESs.
2006, 22(08): 977-980
doi: 10.1016/S1872-1508(06)60043-0
Abstract:
An ordered Cu/Ni multilayered nanowires array was electrodeposited into the pores of an anodic aluminum oxide ( AAO ) template, with layer thickness in the range of 3 to 100 nm. In order to avoid codeposition of Cu in the Ni layers, two separate Ni and Cu baths have been used. Scanning electronic microscopy ( SEM ), transmission electron microscopy ( TEM ) were used to characterize the morphology of Cu/Ni multilayered nanowires array. The results show that the layer thicknesses are very uniform and the multilayered structure is clear and regular. The diameter of nanowire is about 100nm, which corresponds to the pore size of the AAO template used. Selected-area electron diffraction ( SAED ) result demonstrates that those multiplayer wires exhibit single crystal structures. Hysteresis curves for multilayered Cu/Ni nanowires array with the AAO membrane support were tested by using vibrating sample magnetometer ( VSM ) at room temperature ( 293 K ). It is found that Cu/Ni nanowires alloys have a strong perpendicular magnetic field anisotropy. When the magnetic field is perpendicular or parallel to the AAO template used, the squareness are 0.701 or 0.101 and the coercivity is 589 Oe or 202 Oe respectively. The diameter and the layer thickness of Cu/Ni multilayered wires could be changed according to demands by adjusting the technologic parameters of anodization and electrodeposition.
An ordered Cu/Ni multilayered nanowires array was electrodeposited into the pores of an anodic aluminum oxide ( AAO ) template, with layer thickness in the range of 3 to 100 nm. In order to avoid codeposition of Cu in the Ni layers, two separate Ni and Cu baths have been used. Scanning electronic microscopy ( SEM ), transmission electron microscopy ( TEM ) were used to characterize the morphology of Cu/Ni multilayered nanowires array. The results show that the layer thicknesses are very uniform and the multilayered structure is clear and regular. The diameter of nanowire is about 100nm, which corresponds to the pore size of the AAO template used. Selected-area electron diffraction ( SAED ) result demonstrates that those multiplayer wires exhibit single crystal structures. Hysteresis curves for multilayered Cu/Ni nanowires array with the AAO membrane support were tested by using vibrating sample magnetometer ( VSM ) at room temperature ( 293 K ). It is found that Cu/Ni nanowires alloys have a strong perpendicular magnetic field anisotropy. When the magnetic field is perpendicular or parallel to the AAO template used, the squareness are 0.701 or 0.101 and the coercivity is 589 Oe or 202 Oe respectively. The diameter and the layer thickness of Cu/Ni multilayered wires could be changed according to demands by adjusting the technologic parameters of anodization and electrodeposition.
2006, 22(08): 981-986
doi: 10.3866/PKU.WHXB20060815
Abstract:
One kind of novel chiral Zn porphyrin was synthesized. By means of elementary analysis, UV-Vis, IR, CD spectrum, and 1H-NMR, the chiral Zn porphyrin was charactered. The lowest energy conformation of the chiral zinc porphyrin was obtained by system search on the basis of Tripos force field. Nonlinear optical properties of the chiral porphyrin complexes were studied and refractive indexes were measured by Z-scan techniques. The result indicates that chiral zinc porphyrin has biggish nonlinear refractive index. This is an effective method by modifying chiral structure of porphyrin complexes to increase nonlinear refractive index.
One kind of novel chiral Zn porphyrin was synthesized. By means of elementary analysis, UV-Vis, IR, CD spectrum, and 1H-NMR, the chiral Zn porphyrin was charactered. The lowest energy conformation of the chiral zinc porphyrin was obtained by system search on the basis of Tripos force field. Nonlinear optical properties of the chiral porphyrin complexes were studied and refractive indexes were measured by Z-scan techniques. The result indicates that chiral zinc porphyrin has biggish nonlinear refractive index. This is an effective method by modifying chiral structure of porphyrin complexes to increase nonlinear refractive index.
2006, 22(08): 987-992
doi: 10.3866/PKU.WHXB20060816
Abstract:
The photoionization and dissociative photoionization of 1- and 2-propanol have been studied at the photon energy range of 9.84 - 11.80 eV. Photoionization efficiency spectra for ions CH3CH2CH2OH+, CH3CH2CHOH+, CH2CH2OH+, CH3CH2CH2+, CH3CH=CH2+, CH2OH+ from 1-propanol and CH3CH(OH)CH3+, CH3C(OH)CH3+, CH3CHOH+, CH2=CHOH+, CH3CHCH3+, CH3CH=CH2+ from 2-propanol have been measured. In addition, the energetics of the dissociative photoionization has been examined by ab initio Gaussian-3 (G3) calculations. The computational results are useful in establishing the dissociation channels near the ionization thresholds. With the help of G3 results, the dissociation channels for the formation of the fragment ions CH3CH2CHOH+, CH2CH2OH+, CH3CH2CH2+, CH3CH=CH2+, CH2OH+ from 1-propanol and CH3C(OH)CH3+, CH3CHOH+, CH2=CHOH+, CH3CHCH3+, CH3CH=CH2+ from 2-propanol have been established. The G3 results are in fair to excellent agreement with the experimental data.
The photoionization and dissociative photoionization of 1- and 2-propanol have been studied at the photon energy range of 9.84 - 11.80 eV. Photoionization efficiency spectra for ions CH3CH2CH2OH+, CH3CH2CHOH+, CH2CH2OH+, CH3CH2CH2+, CH3CH=CH2+, CH2OH+ from 1-propanol and CH3CH(OH)CH3+, CH3C(OH)CH3+, CH3CHOH+, CH2=CHOH+, CH3CHCH3+, CH3CH=CH2+ from 2-propanol have been measured. In addition, the energetics of the dissociative photoionization has been examined by ab initio Gaussian-3 (G3) calculations. The computational results are useful in establishing the dissociation channels near the ionization thresholds. With the help of G3 results, the dissociation channels for the formation of the fragment ions CH3CH2CHOH+, CH2CH2OH+, CH3CH2CH2+, CH3CH=CH2+, CH2OH+ from 1-propanol and CH3C(OH)CH3+, CH3CHOH+, CH2=CHOH+, CH3CHCH3+, CH3CH=CH2+ from 2-propanol have been established. The G3 results are in fair to excellent agreement with the experimental data.
2006, 22(08): 993-998
doi: 10.1016/S1872-1508(06)60044-2
Abstract:
A series of TiO2-ZrO2 composite oxides were prepared by a coprecipitation method. They were characterized by N2 adsorption, XRD, TEM, microcalorimetric adsorption of NH3 and CO2, infrared spectra of ammonia adsorption. In comparison with single metal oxide, amorphous composite oxides could be observed with mesoporous structure and higher BET surface area(SBET=218 m2·g-1). Although the initial adsorption heat for all these samples did not vary significantly, composite oxides possessed more Bronsted acid sites than single oxide. With an increase in the incorporated amount of titania, the number of basic sites on the surface of composite oxides was decreased. In the absence of O2, the values of selectivity for propene exceeded 90% for all these catalysts via isopropanol catalytic conversion, revealing that each of the samples had a strong surface acidity. However, in the presence of O2, 70%～85% selectivity for acetone was obtained for TiO2 and ZrO2, suggesting that redox properties were predominant over acidity. Due to the formation of composite oxide, selectivity for propene increased to about 70%, whereas selectivity for acetone decreased to about 30%, indicating that the acidity was enhanced and the redox property was weakened.
A series of TiO2-ZrO2 composite oxides were prepared by a coprecipitation method. They were characterized by N2 adsorption, XRD, TEM, microcalorimetric adsorption of NH3 and CO2, infrared spectra of ammonia adsorption. In comparison with single metal oxide, amorphous composite oxides could be observed with mesoporous structure and higher BET surface area(SBET=218 m2·g-1). Although the initial adsorption heat for all these samples did not vary significantly, composite oxides possessed more Bronsted acid sites than single oxide. With an increase in the incorporated amount of titania, the number of basic sites on the surface of composite oxides was decreased. In the absence of O2, the values of selectivity for propene exceeded 90% for all these catalysts via isopropanol catalytic conversion, revealing that each of the samples had a strong surface acidity. However, in the presence of O2, 70%～85% selectivity for acetone was obtained for TiO2 and ZrO2, suggesting that redox properties were predominant over acidity. Due to the formation of composite oxide, selectivity for propene increased to about 70%, whereas selectivity for acetone decreased to about 30%, indicating that the acidity was enhanced and the redox property was weakened.
2006, 22(08): 999-1003
doi: 10.3866/PKU.WHXB20060818
Abstract:
The changes of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer induced by irradiation and recrystallization have been studied using FT-IR spectrometry, which help to make clear the irradiation modification mechanism. It is found that the fraction of TTTT conformation drops rapidly with absorbed doses, while both TG and T3G conformations increase. The content of every conformation is a fixed value above a proper absorbed dose implying that the reincrease of polarity in copolymer at high dose is independent of the content increase of all trans TTTT conformation. It might be related to boundary effect of highly cross-linking. On the other hand, the conformational changes in recrystallization treatment are just contrary to those in irradiation effect, and the copolymers are in a more stable state due to the conjugate C=C bonds.
The changes of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer induced by irradiation and recrystallization have been studied using FT-IR spectrometry, which help to make clear the irradiation modification mechanism. It is found that the fraction of TTTT conformation drops rapidly with absorbed doses, while both TG and T3G conformations increase. The content of every conformation is a fixed value above a proper absorbed dose implying that the reincrease of polarity in copolymer at high dose is independent of the content increase of all trans TTTT conformation. It might be related to boundary effect of highly cross-linking. On the other hand, the conformational changes in recrystallization treatment are just contrary to those in irradiation effect, and the copolymers are in a more stable state due to the conjugate C=C bonds.
2006, 22(08): 1004-1009
doi: 10.3866/PKU.WHXB20060819
Abstract:
La-Al2O3, Ce0.63Zr0.37O2 (OSM1) and Ce0.5Zr0.3Mn0.2O2(OSM2) were prepared by co-precipitation method. The catalysts of Pt/La-Al2O3 and Pt/OSM were prepared by impregnation with platinum loading of 1%(w). The monolithic catalysts were investigated for the selective catalytic reduction of NO by methane and were characterized by XRD, H2-TPR and XPS. The results reveal that Pt/OSM1 and Pt/OSM2 have excellent purification properties for the catalytic reduction of NO by methane in the condition of 0.8% O2. Both CH4 and NO reach 100% conversion at 500 ℃ over Pt/OSM1, while over Pt/OSM2 the conversions of CH4 and NO are 73% and 100%, respectively. Over Pt/La-Al2O3, CH4 and NO reach almost 100% conversions only when O2 content is below 0.4% at 500 ℃. As O2 is excessive, the activity of Pt/La-Al2O3 decreases sharply. The results of H2-TPR reveal that the interaction of Pt and OSM leads to the formation of reduction phase at low temperature. The high activity of NO reduction by methane in the excessive presence of O2 is due to the interaction of Pt and OSM and the oxygen storage capacity of OSM.
La-Al2O3, Ce0.63Zr0.37O2 (OSM1) and Ce0.5Zr0.3Mn0.2O2(OSM2) were prepared by co-precipitation method. The catalysts of Pt/La-Al2O3 and Pt/OSM were prepared by impregnation with platinum loading of 1%(w). The monolithic catalysts were investigated for the selective catalytic reduction of NO by methane and were characterized by XRD, H2-TPR and XPS. The results reveal that Pt/OSM1 and Pt/OSM2 have excellent purification properties for the catalytic reduction of NO by methane in the condition of 0.8% O2. Both CH4 and NO reach 100% conversion at 500 ℃ over Pt/OSM1, while over Pt/OSM2 the conversions of CH4 and NO are 73% and 100%, respectively. Over Pt/La-Al2O3, CH4 and NO reach almost 100% conversions only when O2 content is below 0.4% at 500 ℃. As O2 is excessive, the activity of Pt/La-Al2O3 decreases sharply. The results of H2-TPR reveal that the interaction of Pt and OSM leads to the formation of reduction phase at low temperature. The high activity of NO reduction by methane in the excessive presence of O2 is due to the interaction of Pt and OSM and the oxygen storage capacity of OSM.
2006, 22(08): 1010-1014
doi: 10.3866/PKU.WHXB20060820
Abstract:
The influence of the calcination procedure on electrocatalytic properties for oxygen evolution at Ti/IrO2 electrodes was investigated by using cyclic voltammetry (CV) and anodic polarization tests. Thermal decomposition at single temperature of 500 ℃ for each layer (conventional method) was adopted as the standard procedure. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and electrochemical impedance spectroscopy (EIS) show the standard procedure leads to compact oxide coatings, with large grain distributing on coatings and high resistance of obtained electrodes. Both applying the lower temperatures in first three under-layers (step-method) and the programming heating in each layer can, to some extent, overcome the disadvantages of the conventional procedure, and thereby improve the electrochemical activities of electrodes. By using the modified procedures, the electrode resistance is found to decrease due to the inhibition of substrate oxidation. When using the controlled programming calcination (heating rate), the coating becomes more porous and rugged.
The influence of the calcination procedure on electrocatalytic properties for oxygen evolution at Ti/IrO2 electrodes was investigated by using cyclic voltammetry (CV) and anodic polarization tests. Thermal decomposition at single temperature of 500 ℃ for each layer (conventional method) was adopted as the standard procedure. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and electrochemical impedance spectroscopy (EIS) show the standard procedure leads to compact oxide coatings, with large grain distributing on coatings and high resistance of obtained electrodes. Both applying the lower temperatures in first three under-layers (step-method) and the programming heating in each layer can, to some extent, overcome the disadvantages of the conventional procedure, and thereby improve the electrochemical activities of electrodes. By using the modified procedures, the electrode resistance is found to decrease due to the inhibition of substrate oxidation. When using the controlled programming calcination (heating rate), the coating becomes more porous and rugged.
2006, 22(08): 1015-1020
doi: 10.3866/PKU.WHXB20060821
Abstract:
Nanobimetallic particles of Au-Pt alloy were synthesized by reducing HAuCl4 and H2PtCl4 mixture solution with NaBH4. UV-Vis spectra, transmission electron microscopy (TEM), and X- ray diffraction (XRD) results revealed that the alloy was single phase with face- centered cube structure. The Au- Pt/Cysteine/glassy carbon electrode was prepared by self- assembling nanobimetallic particles on glassy carbon substrate modified with cysteine and was characterized with scanning electron microscopy (SEM). The average diameter of the particles was 12.6 nm. The electrochemical performance of Au- Pt/ Cysteine/glassy carbon electrode was studied by cyclic voltammetry method. The result showed that the electrode of Au- Pt/ Cysteine /glassy- carbon had od electrocatalytic activity for methanol oxidation.
Nanobimetallic particles of Au-Pt alloy were synthesized by reducing HAuCl4 and H2PtCl4 mixture solution with NaBH4. UV-Vis spectra, transmission electron microscopy (TEM), and X- ray diffraction (XRD) results revealed that the alloy was single phase with face- centered cube structure. The Au- Pt/Cysteine/glassy carbon electrode was prepared by self- assembling nanobimetallic particles on glassy carbon substrate modified with cysteine and was characterized with scanning electron microscopy (SEM). The average diameter of the particles was 12.6 nm. The electrochemical performance of Au- Pt/ Cysteine/glassy carbon electrode was studied by cyclic voltammetry method. The result showed that the electrode of Au- Pt/ Cysteine /glassy- carbon had od electrocatalytic activity for methanol oxidation.
2006, 22(08): 1021-1024
doi: 10.3866/PKU.WHXB20060822
Abstract:
Well-defined silver nanocomposites were prepared by using copolymer polyacrylonitrile-block-poly(ethylene glycol)-block-polyacrylonitrile (PAN-b-PEG-b-PAN) as stabilizer under ultrasonic irradiation. The product was characterized by X-ray diffraction (XRD), Fourier transfer infrared spectrometer (FTIR), transmission electron microscope(TEM), UV-Vis spectrum, and thermal gravity analysis (TGA). FTIR results revealed that the PEG backbone had not been destroyed after ultrasonic irradiation. Low initial silver ion concentration allowed for yielding silver nanoparticles with a small size and the size of the silver nanoparticles increased with the increasing of silver ion concentration. The size of the silver nanoparticles decreased with the increasing of the copolymers concentration. The mechanism of forming silver nanoparticles was discussed.
Well-defined silver nanocomposites were prepared by using copolymer polyacrylonitrile-block-poly(ethylene glycol)-block-polyacrylonitrile (PAN-b-PEG-b-PAN) as stabilizer under ultrasonic irradiation. The product was characterized by X-ray diffraction (XRD), Fourier transfer infrared spectrometer (FTIR), transmission electron microscope(TEM), UV-Vis spectrum, and thermal gravity analysis (TGA). FTIR results revealed that the PEG backbone had not been destroyed after ultrasonic irradiation. Low initial silver ion concentration allowed for yielding silver nanoparticles with a small size and the size of the silver nanoparticles increased with the increasing of silver ion concentration. The size of the silver nanoparticles decreased with the increasing of the copolymers concentration. The mechanism of forming silver nanoparticles was discussed.
2006, 22(08): 1025-1029
doi: 10.3866/PKU.WHXB20060823
Abstract:
Bis-[triethoxysilylpropyl] tetrasulfide silane films were self-assembled on surface of 2A12-T6 aluminum alloy for corrosion protection. The structure of the formed silane films was investigated by using Fourier transform infra-red (FTIR) spectroscopy, and the corrosion performance of the film was evaluated by electrochemical potentiodynamic polarization tests in 3.5% NaCl solution. Compared to the untreated case, both the cathodic and anodic reactions of Al 2A12-T6 treated with the silane films are inhibited obviously. For the film on the surface of Al 2A12-T6 aged at room temperature the corrosion current density is reduced by more than 1 order of magnitude, which is due to the hydrogen bonding between silane molecules and surface of 2A12-T6. For the film on the surface of Al 2A12-T6 cured at temperature of 120 ℃ for 40 min the silane molecules are cross linked through SiOSi, which is closely linked to Al 2A12-T6 surface through formation of SiOAl. The corrosion current density is reduced by more than 2 orders of magnitude. There exist more hydrogen bonded hydroxy groups in the cured film dipped for 10 min in the prepared silane solution than that dipped for 2 s to 1 min.
Bis-[triethoxysilylpropyl] tetrasulfide silane films were self-assembled on surface of 2A12-T6 aluminum alloy for corrosion protection. The structure of the formed silane films was investigated by using Fourier transform infra-red (FTIR) spectroscopy, and the corrosion performance of the film was evaluated by electrochemical potentiodynamic polarization tests in 3.5% NaCl solution. Compared to the untreated case, both the cathodic and anodic reactions of Al 2A12-T6 treated with the silane films are inhibited obviously. For the film on the surface of Al 2A12-T6 aged at room temperature the corrosion current density is reduced by more than 1 order of magnitude, which is due to the hydrogen bonding between silane molecules and surface of 2A12-T6. For the film on the surface of Al 2A12-T6 cured at temperature of 120 ℃ for 40 min the silane molecules are cross linked through SiOSi, which is closely linked to Al 2A12-T6 surface through formation of SiOAl. The corrosion current density is reduced by more than 2 orders of magnitude. There exist more hydrogen bonded hydroxy groups in the cured film dipped for 10 min in the prepared silane solution than that dipped for 2 s to 1 min.
2006, 22(08): 1030-1033
doi: 10.3866/PKU.WHXB20060824
Abstract:
Nanocrytalline BaMgAl10O17∶Eu (BAM) blue- emitting phosphor for plasma display panel(PDP) application was rapidly prepared by low- temperature combustion synthesis. The results of XRD and TEM analysis show that the sample is monophasic and well- crystallized, in which displace as well as twin crystal do not exist. Moreover, BAM nanocrystals exhibit an ideal spherical morphology with a grain size of about 20 nm. The luminescent property of the BAM phosphor is also measured and analyzed. The emission spectrum of the BAM consists of a wide band with the peak at 450 nm, which corresponds to the transition from the 4f 65d excited state to the 4f 7 ground state of Eu2+ ion. The blue emission is excellently consistent with commission international del′eclairage(CIE) chromaticity and quite suitable for plasma display panels. The phosphors synthesized via combustion method exhibit higher emission intensity than those prepared by solid- state method because high purity and od crystallinity of the phosphors synthesized via a combustion process cause an increase in luminescence efficiency.
Nanocrytalline BaMgAl10O17∶Eu (BAM) blue- emitting phosphor for plasma display panel(PDP) application was rapidly prepared by low- temperature combustion synthesis. The results of XRD and TEM analysis show that the sample is monophasic and well- crystallized, in which displace as well as twin crystal do not exist. Moreover, BAM nanocrystals exhibit an ideal spherical morphology with a grain size of about 20 nm. The luminescent property of the BAM phosphor is also measured and analyzed. The emission spectrum of the BAM consists of a wide band with the peak at 450 nm, which corresponds to the transition from the 4f 65d excited state to the 4f 7 ground state of Eu2+ ion. The blue emission is excellently consistent with commission international del′eclairage(CIE) chromaticity and quite suitable for plasma display panels. The phosphors synthesized via combustion method exhibit higher emission intensity than those prepared by solid- state method because high purity and od crystallinity of the phosphors synthesized via a combustion process cause an increase in luminescence efficiency.
2006, 22(08): 1034-1039
doi: 10.3866/PKU.WHXB20060825
Abstract:
A chemical interaction model has been established for the hydrophobic self- association of aliphatic α- amino acids in aqueous solutions. In order to obtain the parameters of the model equation, dilution enthalpies of 5 aliphatic α- amino acids aqueous solutions have been measured at 298.15 K by flow microcalorimetry. The equilibrium constants (K), enthalpy change (ΔHm) and entropy change (ΔSm) have been determined for the equal- step association. It was found that between enthalpy and entropy exists a od compensation relationship. In addition, partial molar excess entropies of water in solutions (SE1) were calculated, and were discussed according to the hydration model for aliphatic α- amino acids. Noteworthily, the parameters in the model equation can be used to explain the homogeneous enthalpic interaction coefficients in McMillan- Mayer model to some extent.
A chemical interaction model has been established for the hydrophobic self- association of aliphatic α- amino acids in aqueous solutions. In order to obtain the parameters of the model equation, dilution enthalpies of 5 aliphatic α- amino acids aqueous solutions have been measured at 298.15 K by flow microcalorimetry. The equilibrium constants (K), enthalpy change (ΔHm) and entropy change (ΔSm) have been determined for the equal- step association. It was found that between enthalpy and entropy exists a od compensation relationship. In addition, partial molar excess entropies of water in solutions (SE1) were calculated, and were discussed according to the hydration model for aliphatic α- amino acids. Noteworthily, the parameters in the model equation can be used to explain the homogeneous enthalpic interaction coefficients in McMillan- Mayer model to some extent.
2006, 22(08): 1040-1042
doi: 10.3866/PKU.WHXB20060826
Abstract:
The oxidative coupling of methane (OCM) at low temperature was examined on Li- ZnO/La2O3 catalyst with w(Li)=2% and w(ZnO)=20%. CH4 conversion of 27.3% with C2 selectivity of 65.2% was obtained at 680 ℃ and the C2 yield reached 21.8% at 700 ℃ under reaction conditions. Raman and XPS results suggested that the low- temperature activity was related to the concentration of adsorbed oxygen species on the catalyst surface and La2O2CO3 was supposed to be responsible for the enhancement of C2 selectivity in OCM.
The oxidative coupling of methane (OCM) at low temperature was examined on Li- ZnO/La2O3 catalyst with w(Li)=2% and w(ZnO)=20%. CH4 conversion of 27.3% with C2 selectivity of 65.2% was obtained at 680 ℃ and the C2 yield reached 21.8% at 700 ℃ under reaction conditions. Raman and XPS results suggested that the low- temperature activity was related to the concentration of adsorbed oxygen species on the catalyst surface and La2O2CO3 was supposed to be responsible for the enhancement of C2 selectivity in OCM.
