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2004 Volume 20 Issue 11
2004, 20(11): 1287-1291
doi: 10.3866/PKU.WHXB20041101
Abstract:
A novel strategy has been developed to fabricate PANI nanowires or nanotubes with smaller diameter in AAO template by chemical modification of selected surfactants. With the assistance of surfactant octadecanoic acid (R18), we t the PANI nanowires which diameter is 7 nm in AAO pores with a diameter of 14 nm. By comparing different surfactants, we concluded that by assembling selected surfactant with different length alky group to AAO templates, the diameters of polymer nanowires or nanotubes could be controlled.
A novel strategy has been developed to fabricate PANI nanowires or nanotubes with smaller diameter in AAO template by chemical modification of selected surfactants. With the assistance of surfactant octadecanoic acid (R18), we t the PANI nanowires which diameter is 7 nm in AAO pores with a diameter of 14 nm. By comparing different surfactants, we concluded that by assembling selected surfactant with different length alky group to AAO templates, the diameters of polymer nanowires or nanotubes could be controlled.
2004, 20(11): 1292-1296
doi: 10.3866/PKU.WHXB20041102
Abstract:
γ-thiopropyl tri-methyl silicane and surface pre-adsorption hydrolysis technique were used to accommodate CdS and TiO2 nanoparticles into the tunnels of MCM-41 meso-porous sieves. UV-Vis spectra showed that MCM-41 extracted CdS nanoparticles effectively from the reverse micelles by the chelation of thiol-groups. The changes of meso-tunnel diameter of MCM-41 were also observed with the introducing of nanoparticles in the low angle XRD patterns.
γ-thiopropyl tri-methyl silicane and surface pre-adsorption hydrolysis technique were used to accommodate CdS and TiO2 nanoparticles into the tunnels of MCM-41 meso-porous sieves. UV-Vis spectra showed that MCM-41 extracted CdS nanoparticles effectively from the reverse micelles by the chelation of thiol-groups. The changes of meso-tunnel diameter of MCM-41 were also observed with the introducing of nanoparticles in the low angle XRD patterns.
2004, 20(11): 1297-1302
doi: 10.3866/PKU.WHXB20041103
Abstract:
According to the experimental results and the basic concept that the capacitive contribution of the coating/metal system to EIS can reflect the change occurring at interface sensitively, the quantitative relationship between the adhesion and the analytical result of EIS is established. The approach is using the transmission line model (CR circuit) to obtain the discrete capacitance values, analyzing the physical meaning of the slope at the region in which the discrete capacitances change linearly with the discrete characteristic frequency. The data handling method is also given in detail. The relationship is validated by experiments. The results show that under certain conditions, the slopes are mainly determined by the speed of instantaneous delamination at organic coating/metal interface and are not influenced by the corrosion product built up at the artificial defect, so they have od reproducibility despite the EIS of duplicate samples showing very different configuration. The analytical results from EIS are often higher than that of mechanical measurements when adhesion is strong. Explanation of the discrepancy shows that the results from EIS are more accurate and reasonable. In regard to epoxy powder paints and A3 steel, the results also indicate that the pretreatment of substrate using silane with and without hot-dip galvanized or phosphate treatment can influence markedly the adhesion between substrate and coating.
According to the experimental results and the basic concept that the capacitive contribution of the coating/metal system to EIS can reflect the change occurring at interface sensitively, the quantitative relationship between the adhesion and the analytical result of EIS is established. The approach is using the transmission line model (CR circuit) to obtain the discrete capacitance values, analyzing the physical meaning of the slope at the region in which the discrete capacitances change linearly with the discrete characteristic frequency. The data handling method is also given in detail. The relationship is validated by experiments. The results show that under certain conditions, the slopes are mainly determined by the speed of instantaneous delamination at organic coating/metal interface and are not influenced by the corrosion product built up at the artificial defect, so they have od reproducibility despite the EIS of duplicate samples showing very different configuration. The analytical results from EIS are often higher than that of mechanical measurements when adhesion is strong. Explanation of the discrepancy shows that the results from EIS are more accurate and reasonable. In regard to epoxy powder paints and A3 steel, the results also indicate that the pretreatment of substrate using silane with and without hot-dip galvanized or phosphate treatment can influence markedly the adhesion between substrate and coating.
2004, 20(11): 1303-1307
doi: 10.3866/PKU.WHXB20041104
Abstract:
Grand canonical Monte Carlo (GCMC) simulation and statistics integral equation (SIE) have been used to determine the pore size distribution (PSD) of the silica hollow microspheres (SHMS).HRTEM, XRD and nitrogen adsorption results indicate the occurrence of disordered mesopores on the shells of SHMS. In the simulation, the SHMS have been modeled as cylindrical pore with pore size distribution according to the experimental data. The nitrogen is considered as Lennard-Jones (LJ) spherical molecule. The completely analytical potential model proposed by Wang[10] recently is applied to represent the interactions between the atoms inside the wall and the fluid molecules. The calculated results show that the simulated PSD data are in od agreement with the experimental date, which means that the proposed model for the SHMS is reliable and the combined method of GCMC and SIE is powerful for evaluation of the PSD of the silica hollow spheres.
Grand canonical Monte Carlo (GCMC) simulation and statistics integral equation (SIE) have been used to determine the pore size distribution (PSD) of the silica hollow microspheres (SHMS).HRTEM, XRD and nitrogen adsorption results indicate the occurrence of disordered mesopores on the shells of SHMS. In the simulation, the SHMS have been modeled as cylindrical pore with pore size distribution according to the experimental data. The nitrogen is considered as Lennard-Jones (LJ) spherical molecule. The completely analytical potential model proposed by Wang[10] recently is applied to represent the interactions between the atoms inside the wall and the fluid molecules. The calculated results show that the simulated PSD data are in od agreement with the experimental date, which means that the proposed model for the SHMS is reliable and the combined method of GCMC and SIE is powerful for evaluation of the PSD of the silica hollow spheres.
2004, 20(11): 1308-1312
doi: 10.3866/PKU.WHXB20041105
Abstract:
The CdSe-quantum dots were grown in situ on the multiwalled carbon nanotubes (MWCNTs) using thioglycollic acid as the stabilizer in mild reaction conditions (in aqueous solution and at 90 ℃).The as prepared CdSe-MWCNTs quantum dots heterojunctions (CdSe-MWCNTs) were characterized by TEM, HRTEM, EDS, XRD and XPS measurements. The EDS and XPS analysis shows that the quantum dots are mainly composed of Se and Cd elements and their binding energies correspond to that of semiconductor CdSe. The XRD measurement suggests that the CdSe quantum dots have the cubic phase. The HRTEM results reveal that the diameter of CdSe quantum dots is about 4 nm. It is also found that the thioglycollic acid can prohibit the conglomeration of the individual nanocrystals. The distinct optical properties were visualized by the photoluminescent measurements.
The CdSe-quantum dots were grown in situ on the multiwalled carbon nanotubes (MWCNTs) using thioglycollic acid as the stabilizer in mild reaction conditions (in aqueous solution and at 90 ℃).The as prepared CdSe-MWCNTs quantum dots heterojunctions (CdSe-MWCNTs) were characterized by TEM, HRTEM, EDS, XRD and XPS measurements. The EDS and XPS analysis shows that the quantum dots are mainly composed of Se and Cd elements and their binding energies correspond to that of semiconductor CdSe. The XRD measurement suggests that the CdSe quantum dots have the cubic phase. The HRTEM results reveal that the diameter of CdSe quantum dots is about 4 nm. It is also found that the thioglycollic acid can prohibit the conglomeration of the individual nanocrystals. The distinct optical properties were visualized by the photoluminescent measurements.
2004, 20(11): 1313-1319
doi: 10.3866/PKU.WHXB20041106
Abstract:
Series of Ba1－xLaxFeAl11O19－δ hexaaluminate catalysts were prepared by (NH4)2CO3 co-precipitation method and their performance for methane catalytic combustion was studied. The obtained materials were characterized by XRD, Diffuse UV-Vis, FT-IR, TPR, and N2 BET techniques. The results showed that partial substitution of Ba with La in Fe-hexaaluminates could enhance catalytic activity for methane combustion, and the optimal catalyst was Ba0.2La0.8FeAl11O19－δ hexaaluminate, whose light-off temperature was as low as 495 ℃ denoted by 10％ conversion of methane (VCH4/VO2/VN2=1/4/95). XRD and SEM characterization indicated that the samples formed well-defined hexaaluminate phase after calcination at 1 200 ℃ for 5 h, and the dopant of La could promote the formation of hexaaluminate phases. UV-Vis-DR characterization revealed that the oxide state of Fe is ＋3 in Ba1－xLaxFeAl11O19－δcatalysts. The synergism between Ba, La and Fe was observed based on the results of UV-VisDR, FT-IR and TPR.
Series of Ba1－xLaxFeAl11O19－δ hexaaluminate catalysts were prepared by (NH4)2CO3 co-precipitation method and their performance for methane catalytic combustion was studied. The obtained materials were characterized by XRD, Diffuse UV-Vis, FT-IR, TPR, and N2 BET techniques. The results showed that partial substitution of Ba with La in Fe-hexaaluminates could enhance catalytic activity for methane combustion, and the optimal catalyst was Ba0.2La0.8FeAl11O19－δ hexaaluminate, whose light-off temperature was as low as 495 ℃ denoted by 10％ conversion of methane (VCH4/VO2/VN2=1/4/95). XRD and SEM characterization indicated that the samples formed well-defined hexaaluminate phase after calcination at 1 200 ℃ for 5 h, and the dopant of La could promote the formation of hexaaluminate phases. UV-Vis-DR characterization revealed that the oxide state of Fe is ＋3 in Ba1－xLaxFeAl11O19－δcatalysts. The synergism between Ba, La and Fe was observed based on the results of UV-VisDR, FT-IR and TPR.
2004, 20(11): 1320-1323
doi: 10.3866/PKU.WHXB20041107
Abstract:
Bamboo-like nanotubes with a diameter of 20～40 nm were prepared by thermal decomposition of pyridine at 700～800 ℃. EDX and XPS measurements show that they are nitrogen-doped carbon nanotubes. It was found that the intensity of the D band in the Raman spectrum of the N-doped tubes is much higher than that of undoped tubes. It was also found by TGA that the doped tubes were oxidized at much lower temperature. These both indicate that nitrogen-doping introduces defects into the graphite sheets of the tubes. HRTEM result is in od agreement with this.
Bamboo-like nanotubes with a diameter of 20～40 nm were prepared by thermal decomposition of pyridine at 700～800 ℃. EDX and XPS measurements show that they are nitrogen-doped carbon nanotubes. It was found that the intensity of the D band in the Raman spectrum of the N-doped tubes is much higher than that of undoped tubes. It was also found by TGA that the doped tubes were oxidized at much lower temperature. These both indicate that nitrogen-doping introduces defects into the graphite sheets of the tubes. HRTEM result is in od agreement with this.
2004, 20(11): 1324-1328
doi: 10.3866/PKU.WHXB20041108
Abstract:
The hydrogen bonds between the HCN and pyrrole were subjected to density functional theory (DFT) calculations using 6-311G(d, p) basis set. The structures and vibrational frequencies of the hydrogen-bonding complexes were computed at the B3LYP/6-311G(d, p) level. To obtain the accurate binding energies, single-point calculations were performed at the B3LYP/aug-cc-pVDZ and MP2/aug-cc-pVDZ level, respectively. After BSSE (basic set superposition error) correction by the counterpoise method, the interaction energies of the complexes between HCN and pyrrole are －25.10, －19.30 kJ·mol－1 at MP2 level, respectively. The calculations indicate that solvents enhance significantly the strength of hydrogen bond as shown by the decrease of the N…H distance and cause appreciable red shift of the H－N vibration mode. The solvent effect is obvious when dielectric constant ε is within 1.5～30.0 and is weak when ε exceeds 30.0.
The hydrogen bonds between the HCN and pyrrole were subjected to density functional theory (DFT) calculations using 6-311G(d, p) basis set. The structures and vibrational frequencies of the hydrogen-bonding complexes were computed at the B3LYP/6-311G(d, p) level. To obtain the accurate binding energies, single-point calculations were performed at the B3LYP/aug-cc-pVDZ and MP2/aug-cc-pVDZ level, respectively. After BSSE (basic set superposition error) correction by the counterpoise method, the interaction energies of the complexes between HCN and pyrrole are －25.10, －19.30 kJ·mol－1 at MP2 level, respectively. The calculations indicate that solvents enhance significantly the strength of hydrogen bond as shown by the decrease of the N…H distance and cause appreciable red shift of the H－N vibration mode. The solvent effect is obvious when dielectric constant ε is within 1.5～30.0 and is weak when ε exceeds 30.0.
2004, 20(11): 1329-1334
doi: 10.3866/PKU.WHXB20041109
Abstract:
First-principle density functional theory, at DND basis set level, was used to optimize the structure ofα-[XMo12O40]n－(X=P, Si, Ge). The optimized structure parameters coincide with those obtained by X-ray diffraction. Based on the optimized structure, frequency analyses were carried out by non-empirical method for the first time. In general, the agreement between the experimental vibrational spectra and the calculated values, on both the frequencies and intensities, is od. The assignment for all of the 22 infrared (IR) active and 44 Raman active frequencies is carried out and compared with that obtained by empirical methods. At the same time, a number of previously reported assignments have been conformed or clarified. In addition, the characteristic group frequencies of IR spectra forα-[XMo12O40]n－(X=P, Si, Ge) obey the P >Si >Ge rule, whereas those of Raman spectra are not the case. Meanwhile, a rational interpretation is offered.
First-principle density functional theory, at DND basis set level, was used to optimize the structure ofα-[XMo12O40]n－(X=P, Si, Ge). The optimized structure parameters coincide with those obtained by X-ray diffraction. Based on the optimized structure, frequency analyses were carried out by non-empirical method for the first time. In general, the agreement between the experimental vibrational spectra and the calculated values, on both the frequencies and intensities, is od. The assignment for all of the 22 infrared (IR) active and 44 Raman active frequencies is carried out and compared with that obtained by empirical methods. At the same time, a number of previously reported assignments have been conformed or clarified. In addition, the characteristic group frequencies of IR spectra forα-[XMo12O40]n－(X=P, Si, Ge) obey the P >Si >Ge rule, whereas those of Raman spectra are not the case. Meanwhile, a rational interpretation is offered.
2004, 20(11): 1335-1338
doi: 10.3866/PKU.WHXB20041110
Abstract:
The solubility and phase diagram of Na＋, NH4+// CrO42－, HCO3－-H2O system are determined in this paper. According to the solubility and phase diagram, the solid phases in carbonation process of sodium chromate in ammonia solution are discussed. The results show that a crystalline zone of NaNH4CrO4·2H2O exists, NaHCO3, NaNH4CrO4·2H2O and (NH4)2CrO4 crystallize out in turn during carbonation process as the concentration of sodium chromate in ammonia water exceeds the concentration corresponding to P2(P2′) in phase diagram. Proper concentration is 0.8633～1.1377 g/g H2O for sodium chromate, 0.0611～0.0986 g/g H2O for ammonia, lower than the concentration corresponding to P2(P2′) plot. The NaHCO3 and NaNH4CrO4·2H2O crystals can be separated by hydrocyclone.
The solubility and phase diagram of Na＋, NH4+// CrO42－, HCO3－-H2O system are determined in this paper. According to the solubility and phase diagram, the solid phases in carbonation process of sodium chromate in ammonia solution are discussed. The results show that a crystalline zone of NaNH4CrO4·2H2O exists, NaHCO3, NaNH4CrO4·2H2O and (NH4)2CrO4 crystallize out in turn during carbonation process as the concentration of sodium chromate in ammonia water exceeds the concentration corresponding to P2(P2′) in phase diagram. Proper concentration is 0.8633～1.1377 g/g H2O for sodium chromate, 0.0611～0.0986 g/g H2O for ammonia, lower than the concentration corresponding to P2(P2′) plot. The NaHCO3 and NaNH4CrO4·2H2O crystals can be separated by hydrocyclone.
2004, 20(11): 1339-1344
doi: 10.3866/PKU.WHXB20041111
Abstract:
The mechanisms of cycloaddition reactions of singlet dibromocarbene and formaldehyde have been studied using density functional theory of quantum chemistry method at B3LYP/6-31G* level. The geometrical parameters, harmonic vibrational frequencies and energies of stationary points on the potential energy surface are calculated. The structures of the stationary points were optimized, and the intermediates and transition states were detected by the frequency analysis. The calculation results show that the reaction has four possible reaction pathways. According to the data of the activation energy, we predict that path c would be the major reactive channel of the cycloaddition reactions of singlet dibromocarbene with formaldehyde, which proceeds in three steps and the energy barrier for the key step is 13.7 kJ·mol－1.
The mechanisms of cycloaddition reactions of singlet dibromocarbene and formaldehyde have been studied using density functional theory of quantum chemistry method at B3LYP/6-31G* level. The geometrical parameters, harmonic vibrational frequencies and energies of stationary points on the potential energy surface are calculated. The structures of the stationary points were optimized, and the intermediates and transition states were detected by the frequency analysis. The calculation results show that the reaction has four possible reaction pathways. According to the data of the activation energy, we predict that path c would be the major reactive channel of the cycloaddition reactions of singlet dibromocarbene with formaldehyde, which proceeds in three steps and the energy barrier for the key step is 13.7 kJ·mol－1.
2004, 20(11): 1345-1351
doi: 10.3866/PKU.WHXB20041112
Abstract:
The role of chirality determines the origin of life that almost all amino acids utilized in living systems are of the L-type. Starting from Z0 interactions, Salam speculated on an explanation in terms of quantum mechanical cooperative and condensation phenomena where the electron-nucleon system has the same status as Cooper-pairing, which could give rise to second-order phase transitions(including D to L transformations) below a critical temperature Tc(～250 K). Neutron diffraction of single crystal D- and L-alanine was performed to look for the characteristic structural feature above and below the Tc (295 K and 60 K) and the possibility of D- to L-type transformation. Data analysis of the temperature effect on the crystal lattice together with the NH3＋ torsional motion, parity-violating energy difference (ΔEPV) as a function of dihedral angle (ω), the CO2(θ) and NH3(ψ)torsion angles and the contribution of Cα－H…O=C hydrogen bond is discussed. Observation of the behavior of weak hydrogen bonding during the cooling process threw a light on the distinction between D- and L-alanine, which could be attributed to the parity-violating weak interactions. Measurements of the neutron crystal-structure of D-alanine rule out the possibility of configuration transition to L-alanine, which means that Salam phase transition is not a conventional structure transition.
The role of chirality determines the origin of life that almost all amino acids utilized in living systems are of the L-type. Starting from Z0 interactions, Salam speculated on an explanation in terms of quantum mechanical cooperative and condensation phenomena where the electron-nucleon system has the same status as Cooper-pairing, which could give rise to second-order phase transitions(including D to L transformations) below a critical temperature Tc(～250 K). Neutron diffraction of single crystal D- and L-alanine was performed to look for the characteristic structural feature above and below the Tc (295 K and 60 K) and the possibility of D- to L-type transformation. Data analysis of the temperature effect on the crystal lattice together with the NH3＋ torsional motion, parity-violating energy difference (ΔEPV) as a function of dihedral angle (ω), the CO2(θ) and NH3(ψ)torsion angles and the contribution of Cα－H…O=C hydrogen bond is discussed. Observation of the behavior of weak hydrogen bonding during the cooling process threw a light on the distinction between D- and L-alanine, which could be attributed to the parity-violating weak interactions. Measurements of the neutron crystal-structure of D-alanine rule out the possibility of configuration transition to L-alanine, which means that Salam phase transition is not a conventional structure transition.
2004, 20(11): 1352-1356
doi: 10.3866/PKU.WHXB20041113
Abstract:
The nanosize Ni-B and Ni-Mo-B amorphous alloy powders were prepared by chemical reduction with KBH4 in aqueous solution .Their amorphous structures were determined by XRD .The SEM characterization demonstrates that all samples exhibit a spherical or sphere-like morphology with an average size of around 10 nm. The XPS characterization shows that the molybdenum species in the Ni-Mo-B samples are mainly present on the surface of Ni-Mo-B alloy in the oxidized form. Compared with Ni-B alloy, the surface atomic content of alloying boron and alloying nickel of Ni-Mo-B alloy shows a considerable increase, the surface atomic content of oxidized boron, oxidized nickel and oxygen of Ni-Mo-B alloy shows a considerable decrease. Thus, XPS results have proven that the Ni-Mo-B amorphous alloy exhibits stronger antioxidation ability than the amorphous Ni-B alloy. XPS characterization also shows that Ni2B is presented in the Ni-B and Ni-Mo-B samples, and the alloying nickel is electron-enriched while the alloying boron is electron-deficient. Ni2O3 and B2O3 are byproducts of the Ni2B oxidation.
The nanosize Ni-B and Ni-Mo-B amorphous alloy powders were prepared by chemical reduction with KBH4 in aqueous solution .Their amorphous structures were determined by XRD .The SEM characterization demonstrates that all samples exhibit a spherical or sphere-like morphology with an average size of around 10 nm. The XPS characterization shows that the molybdenum species in the Ni-Mo-B samples are mainly present on the surface of Ni-Mo-B alloy in the oxidized form. Compared with Ni-B alloy, the surface atomic content of alloying boron and alloying nickel of Ni-Mo-B alloy shows a considerable increase, the surface atomic content of oxidized boron, oxidized nickel and oxygen of Ni-Mo-B alloy shows a considerable decrease. Thus, XPS results have proven that the Ni-Mo-B amorphous alloy exhibits stronger antioxidation ability than the amorphous Ni-B alloy. XPS characterization also shows that Ni2B is presented in the Ni-B and Ni-Mo-B samples, and the alloying nickel is electron-enriched while the alloying boron is electron-deficient. Ni2O3 and B2O3 are byproducts of the Ni2B oxidation.
2004, 20(11): 1357-1363
doi: 10.3866/PKU.WHXB20041114
Abstract:
The dynamics feature and mechanism of preparation of layered double hydroxides pillared by Cl－ anion(LDH-Cl) with coprecipitation reaction had been investigated, based on the result of monitoring concentrations during reaction course, and on the result of EDS, IR, XRD, TEM and TG-DTA characterization for samples produced from different reaction course. The results testified that the generating of LDH-Cl was controlled by polynuclcar layer surface reaction mechanism. It was also found that the lattice parameter c decreased from 2.421 nm to 2.399 nm, and h from 0.3321 nm to 0.3228 nm, with grain size increasing of Da from 6.40 nm to 15.16 nm, Dc from 7.43 nm to 10.93 nm, and increasing of aspect ratio from 0.86 to 1.39 during the whole reaction course, in addition, the strength of interaction between sheet and anions and the structure stability of sheet enhancing with reaction course as showed by IR and TG-DTA characterization.
The dynamics feature and mechanism of preparation of layered double hydroxides pillared by Cl－ anion(LDH-Cl) with coprecipitation reaction had been investigated, based on the result of monitoring concentrations during reaction course, and on the result of EDS, IR, XRD, TEM and TG-DTA characterization for samples produced from different reaction course. The results testified that the generating of LDH-Cl was controlled by polynuclcar layer surface reaction mechanism. It was also found that the lattice parameter c decreased from 2.421 nm to 2.399 nm, and h from 0.3321 nm to 0.3228 nm, with grain size increasing of Da from 6.40 nm to 15.16 nm, Dc from 7.43 nm to 10.93 nm, and increasing of aspect ratio from 0.86 to 1.39 during the whole reaction course, in addition, the strength of interaction between sheet and anions and the structure stability of sheet enhancing with reaction course as showed by IR and TG-DTA characterization.
2004, 20(11): 1364-1368
doi: 10.3866/PKU.WHXB20041115
Abstract:
The gas phase reaction mechanism of F2＋2HI=2HF＋I2 has been investigated by B3LYP and MP2 all at 3-21G** base, and a series of four-centred and three-centred transition states have been obtained. The following result is achieved by comparing the activation energy of six reaction paths, i.e. the activation energies of the bimolecular elementary reactions F2＋HI→HF＋IF and IF＋HI→I2＋HF are less than the dissociation energy of F2, HI and IF. It is thus theoretically proved that the title reaction occurs more easily in the bimolecular form with two medium steps.
The gas phase reaction mechanism of F2＋2HI=2HF＋I2 has been investigated by B3LYP and MP2 all at 3-21G** base, and a series of four-centred and three-centred transition states have been obtained. The following result is achieved by comparing the activation energy of six reaction paths, i.e. the activation energies of the bimolecular elementary reactions F2＋HI→HF＋IF and IF＋HI→I2＋HF are less than the dissociation energy of F2, HI and IF. It is thus theoretically proved that the title reaction occurs more easily in the bimolecular form with two medium steps.
2004, 20(11): 1369-1371
doi: 10.3866/PKU.WHXB20041116
Abstract:
Based on the characteristics of molecular topological structure of linear alkane substituted derivatives, linear alkane substituted derivatives were divided into linear chain unit and substituted groups. Then according to the characteristics of the topological structure of each part, the formulae for the calculation of Wiener index have been given. So a new and simple al rithm for calculating Wiener index has been proposed, which simplified the calculation of Wiener index. This new al rithm has the advantages of high efficiency, accurate compared with that of the traditional al rithm for Wiener index, and can be easily used in computer program for Wiener index. Thus the practicability of Wiener index has been improved.
Based on the characteristics of molecular topological structure of linear alkane substituted derivatives, linear alkane substituted derivatives were divided into linear chain unit and substituted groups. Then according to the characteristics of the topological structure of each part, the formulae for the calculation of Wiener index have been given. So a new and simple al rithm for calculating Wiener index has been proposed, which simplified the calculation of Wiener index. This new al rithm has the advantages of high efficiency, accurate compared with that of the traditional al rithm for Wiener index, and can be easily used in computer program for Wiener index. Thus the practicability of Wiener index has been improved.
2004, 20(11): 1372-1375
doi: 10.3866/PKU.WHXB20041117
Abstract:
New proton exchange membranes of sulfonated poly(ether ether ketone)(SPEEK) and sulfonated phenolphthalein poly(ether sulfone)(SPES-C) were prepared and their proton conductivity and methanol permeability were investigated. The new membranes show a high proton conductivity, which is close to that of Nafion especially at high temperature. Methanol permeability of the new membranes is 1～2 order lower than that of Nafion and the SPEEK membrane has the lowest methanol permeability. Direct methanol fuel cell (DMFC) performances of the new PEMs were also studied and the result demonstrates that the membranes with low methanol permeability show a high open circuit voltage. However, the performance of the DMFC is mainly controlled by the proton conductivity of the membranes at high current density.
New proton exchange membranes of sulfonated poly(ether ether ketone)(SPEEK) and sulfonated phenolphthalein poly(ether sulfone)(SPES-C) were prepared and their proton conductivity and methanol permeability were investigated. The new membranes show a high proton conductivity, which is close to that of Nafion especially at high temperature. Methanol permeability of the new membranes is 1～2 order lower than that of Nafion and the SPEEK membrane has the lowest methanol permeability. Direct methanol fuel cell (DMFC) performances of the new PEMs were also studied and the result demonstrates that the membranes with low methanol permeability show a high open circuit voltage. However, the performance of the DMFC is mainly controlled by the proton conductivity of the membranes at high current density.
2004, 20(11): 1376-1379
doi: 10.3866/PKU.WHXB20041118
Abstract:
Association of polyoxyethylene n-octylphenol ether(OP) with β-cyclodextrin(β-CD) was investigated using OP as a fluorescent probe. The results show that the n-octyl with phenyl ring was entrapped into the cavity of β-CD. 1-bromo-naphthaline (BN) was further employed as a phosphorescent probe to monitor the binding site of OP and the spatial effect of OP on BN. The n-octyl chain of OP was located in the cavity of β-CD in a compressed manner. As a result, the binding strength of BN to the β-CD cavity occupied by OP decreases due to the geometric considerations.
Association of polyoxyethylene n-octylphenol ether(OP) with β-cyclodextrin(β-CD) was investigated using OP as a fluorescent probe. The results show that the n-octyl with phenyl ring was entrapped into the cavity of β-CD. 1-bromo-naphthaline (BN) was further employed as a phosphorescent probe to monitor the binding site of OP and the spatial effect of OP on BN. The n-octyl chain of OP was located in the cavity of β-CD in a compressed manner. As a result, the binding strength of BN to the β-CD cavity occupied by OP decreases due to the geometric considerations.
2004, 20(11): 1380-1384
doi: 10.3866/PKU.WHXB20041119
Abstract:
Density functional(B3LYP) method has been used to optimize the possible structures of PdH2 and YH2 molecules by contracted valence basis set(SDD) for Pd and Y atoms, the 6-311＋＋G** basis set for H atom. The results show that the ground state of PdH2 molecule is C2v symmetry and X 1A1 state. The parameters of structure and the harmonic frequencies are RPdH=0.1692 nm, ∠HPdH=29.4°, De=5.5212 eV and ν1=1470.1 cm－1,ν2=1007.9 cm－1,ν3=2907.0 cm－1 respectively. The results also show that the ground state of YH2 molecule is C2v symmetry and X 2A1 state. The parameters of structure and the harmonic frequencies are RYH=0.1962 nm,∠HYH=114.3°, De=5.6691 eV and ν1=1457.9 cm－1,ν2=475.9 cm－1,ν3=1506.3 cm－1 respectively. The potential energy functions of PdH2 and YH2 have been derived from the normal equation fitting and the many-body expansion theory which is successfully used for describing the equilibrium geometry of PdH2 and YH2.Molecular reaction kinetics of Pd ＋ H2 and Y ＋ H2 based on this potential energy function is discussed briefly.
Density functional(B3LYP) method has been used to optimize the possible structures of PdH2 and YH2 molecules by contracted valence basis set(SDD) for Pd and Y atoms, the 6-311＋＋G** basis set for H atom. The results show that the ground state of PdH2 molecule is C2v symmetry and X 1A1 state. The parameters of structure and the harmonic frequencies are RPdH=0.1692 nm, ∠HPdH=29.4°, De=5.5212 eV and ν1=1470.1 cm－1,ν2=1007.9 cm－1,ν3=2907.0 cm－1 respectively. The results also show that the ground state of YH2 molecule is C2v symmetry and X 2A1 state. The parameters of structure and the harmonic frequencies are RYH=0.1962 nm,∠HYH=114.3°, De=5.6691 eV and ν1=1457.9 cm－1,ν2=475.9 cm－1,ν3=1506.3 cm－1 respectively. The potential energy functions of PdH2 and YH2 have been derived from the normal equation fitting and the many-body expansion theory which is successfully used for describing the equilibrium geometry of PdH2 and YH2.Molecular reaction kinetics of Pd ＋ H2 and Y ＋ H2 based on this potential energy function is discussed briefly.
2004, 20(11): 1385-1388
doi: 10.3866/PKU.WHXB20041120
Abstract:
In this paper, the viscoelastic properties of partially hydrolyzed polyacrylamide(HPAM) solution were investigated with a cone-and-plate measuring system. Results show that the existence of viscoelastic structure in HPAM solution can be detected quite sensitively by the apparatus. Meanwhile, we also obtained the relationship between the elastic component and the viscous component. It is shown that there exists a maximum value corresponding to the elastic component of solution at the HPAM concentration range of 0.1～0.4 g·L－1. At shear rate ṝ=0.36 s－1, high molecular weight hydrolyzed polyacrylamide solution has apparent viscoelastic properties. With the addition of salts, viscoelastic properties of HPAM solution decrease. Moreover, the network structures in HPAM solution are destroyed at higher salt concentration, and the elastic behaviors vanish. For PAAM(polyacrylamide) solution, viscoelastic properties weren′t observed at the range of 0.36～1.36 s－1. A weak viscoelasticity was observed only when ṝ ≥1.65 s－1.
In this paper, the viscoelastic properties of partially hydrolyzed polyacrylamide(HPAM) solution were investigated with a cone-and-plate measuring system. Results show that the existence of viscoelastic structure in HPAM solution can be detected quite sensitively by the apparatus. Meanwhile, we also obtained the relationship between the elastic component and the viscous component. It is shown that there exists a maximum value corresponding to the elastic component of solution at the HPAM concentration range of 0.1～0.4 g·L－1. At shear rate ṝ=0.36 s－1, high molecular weight hydrolyzed polyacrylamide solution has apparent viscoelastic properties. With the addition of salts, viscoelastic properties of HPAM solution decrease. Moreover, the network structures in HPAM solution are destroyed at higher salt concentration, and the elastic behaviors vanish. For PAAM(polyacrylamide) solution, viscoelastic properties weren′t observed at the range of 0.36～1.36 s－1. A weak viscoelasticity was observed only when ṝ ≥1.65 s－1.
2004, 20(11): 1389-1393
doi: 10.3866/PKU.WHXB20041121
Abstract:
The composite powders of tetrapod-shaped ZnO whiskers (T-ZnO whiskers) coated with Cu shell were prepared by electroless plating technique. The components and morphology of the powders were studied by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) analysis. It was demonstrated that the pure zinc oxide powders had a hexa nal structure and the chemical composition of the coated layer was copper. The whiskers were tetrapod-shaped structure. The electromagnetic parameters of the powders were measured with varying shell thickness. It was shown that the absorption Cu/T-ZnO towards microwaves increased significantly.
The composite powders of tetrapod-shaped ZnO whiskers (T-ZnO whiskers) coated with Cu shell were prepared by electroless plating technique. The components and morphology of the powders were studied by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) analysis. It was demonstrated that the pure zinc oxide powders had a hexa nal structure and the chemical composition of the coated layer was copper. The whiskers were tetrapod-shaped structure. The electromagnetic parameters of the powders were measured with varying shell thickness. It was shown that the absorption Cu/T-ZnO towards microwaves increased significantly.
2004, 20(11): 1394-1398
doi: 10.3866/PKU.WHXB20041122
Abstract:
The multiple-scattering-cluster(MSC) method has been employed to calculate the nitrogen 1s near edge X-ray absorption fine structure(NEXAFS) of the N2O multilayer. The local structure model of the N2O multilayer has been proposed for the first time. The MSC calculation shows that the N2O molecules in the multilayer are arranged as layered dislocation chains, which show a short-range order. The distances between the neighbor molecules and between the neighbor molecular layers are equal to 0.233 nm and 0.240～0.245 nm, respectively. The self-consistent field (SCF) DV-Xα method has been employed to calculate the electronic structure of the N2O multilayer, which confirms the MSC results, and reveals the physical origin of the weak features in the N 1s NEXAFS spectrum. The analysis of the interaction between the N2O molecules has shown that the structure of the N2O multilayer shows a self-assembly characteristic.
The multiple-scattering-cluster(MSC) method has been employed to calculate the nitrogen 1s near edge X-ray absorption fine structure(NEXAFS) of the N2O multilayer. The local structure model of the N2O multilayer has been proposed for the first time. The MSC calculation shows that the N2O molecules in the multilayer are arranged as layered dislocation chains, which show a short-range order. The distances between the neighbor molecules and between the neighbor molecular layers are equal to 0.233 nm and 0.240～0.245 nm, respectively. The self-consistent field (SCF) DV-Xα method has been employed to calculate the electronic structure of the N2O multilayer, which confirms the MSC results, and reveals the physical origin of the weak features in the N 1s NEXAFS spectrum. The analysis of the interaction between the N2O molecules has shown that the structure of the N2O multilayer shows a self-assembly characteristic.
