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2005 Volume 21 Issue 4
2005, 21(04): 343-346
doi: 10.3866/PKU.WHXB20050401
Abstract:
The combination of template synthesis method of nanowire/nanotube and conductive atomic force microscopy (C-AFM) is an efficient way that can be used to probe the conductivity of single one-dimension nanomaterial and its array. This communication reports the conductivity of an electrochemically prepared single polyaniline (PANI) nanowire determined using C-AFM and dependences of the conductivity on its diameter and redox state. Our preliminary results of measured current-voltage curves show that the volt-ampere characteristic is similar to that of semiconductor, except that reverse breakdown characteristic has not been observed in the bias range of our test. The possible reason is that the conducting partial oxidized state is reduced into insulating reduced state under the applied reverse bias. The conductivity is lineally increased while the decrease of the diameter of nanowire. Meanwhile, the conductivity of oxidized state and reduced state doped with ClO4－ ion is lower than that of partial oxidized state by two order of magnitude.
The combination of template synthesis method of nanowire/nanotube and conductive atomic force microscopy (C-AFM) is an efficient way that can be used to probe the conductivity of single one-dimension nanomaterial and its array. This communication reports the conductivity of an electrochemically prepared single polyaniline (PANI) nanowire determined using C-AFM and dependences of the conductivity on its diameter and redox state. Our preliminary results of measured current-voltage curves show that the volt-ampere characteristic is similar to that of semiconductor, except that reverse breakdown characteristic has not been observed in the bias range of our test. The possible reason is that the conducting partial oxidized state is reduced into insulating reduced state under the applied reverse bias. The conductivity is lineally increased while the decrease of the diameter of nanowire. Meanwhile, the conductivity of oxidized state and reduced state doped with ClO4－ ion is lower than that of partial oxidized state by two order of magnitude.
2005, 21(04): 347-353
doi: 10.3866/PKU.WHXB20050402
Abstract:
A simulation study has been performed for the evolutions of microstructures in a liquid metal Ni system during solidification process under different cooling rates by means of molecular dynamics method and EAM model potential. It shows that the cooling rate plays a critical role to the evolution of microstructures. As the cooling rate being 1.0×1014 K•s-1 and 4.0×1013 K•s-1, the amorphous structures would be formed in the system with 1551, 1541 and 1431 bond-types as the main body in the system. As the cooling rate being 2.0×1013 K•s-1 and 1.0×1012 K•s-1, both kinds of crystal structures would be formed, respectively；the first one possesses the coexist of the fcc and hcp structures with 1421 and 1422 bond-types as the main body；the second one possesses only the fcc structure with 1421 bond-type as the main body；and their crystallization transition temperatures Tc, would be 1073 and 1173 K, respectively. At the same time, it is found that the mean coordination number of atoms (i.e. the nearest neighbor number) in the system is rather sensitive to the variation of temperature and cooling rate, and their sudden transition points, as shown in Fig. 5, just corresponding to the crystallization transition temperatures Tc, this will give us a new way for researching the crystallization transition processes of liquid metals.
A simulation study has been performed for the evolutions of microstructures in a liquid metal Ni system during solidification process under different cooling rates by means of molecular dynamics method and EAM model potential. It shows that the cooling rate plays a critical role to the evolution of microstructures. As the cooling rate being 1.0×1014 K•s-1 and 4.0×1013 K•s-1, the amorphous structures would be formed in the system with 1551, 1541 and 1431 bond-types as the main body in the system. As the cooling rate being 2.0×1013 K•s-1 and 1.0×1012 K•s-1, both kinds of crystal structures would be formed, respectively；the first one possesses the coexist of the fcc and hcp structures with 1421 and 1422 bond-types as the main body；the second one possesses only the fcc structure with 1421 bond-type as the main body；and their crystallization transition temperatures Tc, would be 1073 and 1173 K, respectively. At the same time, it is found that the mean coordination number of atoms (i.e. the nearest neighbor number) in the system is rather sensitive to the variation of temperature and cooling rate, and their sudden transition points, as shown in Fig. 5, just corresponding to the crystallization transition temperatures Tc, this will give us a new way for researching the crystallization transition processes of liquid metals.
2005, 21(04): 354-359
doi: 10.3866/PKU.WHXB20050403
Abstract:
In order to study the coordination chemistry of calixcrowns in solution, the single crystals of 25,27-bis-octyloxy-calix[4]arene-26,28-crown-6 (BOC6) and 1,3-alternate biscrown-6 (BisC6) are presented in the paper. By using NMR and XAFS, the coordination behaviors of BOC6 and BisC6 in CDCl3 and NPME (o-nitro-phenyl methyl ether) or OA (n-octyl alcohol) with alkali metal ion are studied respectively. The results indicate that the symmetry of the crown ether chain is improved obviously as the cesium ion is imbedded in. The coordination number of cesium is seven and the complex structure with seven-oxygen coordination is stable in solution. One of the nitrate radical oxygen might coordinate with cesium directly.
In order to study the coordination chemistry of calixcrowns in solution, the single crystals of 25,27-bis-octyloxy-calix[4]arene-26,28-crown-6 (BOC6) and 1,3-alternate biscrown-6 (BisC6) are presented in the paper. By using NMR and XAFS, the coordination behaviors of BOC6 and BisC6 in CDCl3 and NPME (o-nitro-phenyl methyl ether) or OA (n-octyl alcohol) with alkali metal ion are studied respectively. The results indicate that the symmetry of the crown ether chain is improved obviously as the cesium ion is imbedded in. The coordination number of cesium is seven and the complex structure with seven-oxygen coordination is stable in solution. One of the nitrate radical oxygen might coordinate with cesium directly.
2005, 21(04): 360-366
doi: 10.3866/PKU.WHXB20050404
Abstract:
The distances among the vertices spaced by the double bond are different in the cis-alkenes from those in its trans-isomers. By the geometric principle, the distances among the vertices adjacent to the double bond were quantified, based on which a modified distance matrix (MD) of the alkene molecular graph was constructed. According to the definition of vertex degree-distance index (VDI) and edge degree-distance index (EDI) in our preceding work, two descriptors, the modified vertex degree-distance index (MVDI) and modified edge degree-distance index (MEDI) were calculated from the modified distance matrix (MD) instead of the distance matrix (D). The MVDI together with MEDI can characterize the molecular structural information well for the cis-and trans-isomers of alkenes. Multiple linear regression analysis was carried out on these descriptors and a series of physico-chemical properties for cis- and trans-isomers of alkenes, such as boiling point (b. p.), refractive index (nD20), density (D20), and molar refractive index (nM). The QSPR (quantitative structure-property relationship) models were obtained with correlation coefficients 0.9981, 0.9570, 0.9884, and 0.9999, respectively. Furthermore, leave-one-out cross validation and random sampling prediction were performed, which confirmed the od stability and powerful prediction of these models.
The distances among the vertices spaced by the double bond are different in the cis-alkenes from those in its trans-isomers. By the geometric principle, the distances among the vertices adjacent to the double bond were quantified, based on which a modified distance matrix (MD) of the alkene molecular graph was constructed. According to the definition of vertex degree-distance index (VDI) and edge degree-distance index (EDI) in our preceding work, two descriptors, the modified vertex degree-distance index (MVDI) and modified edge degree-distance index (MEDI) were calculated from the modified distance matrix (MD) instead of the distance matrix (D). The MVDI together with MEDI can characterize the molecular structural information well for the cis-and trans-isomers of alkenes. Multiple linear regression analysis was carried out on these descriptors and a series of physico-chemical properties for cis- and trans-isomers of alkenes, such as boiling point (b. p.), refractive index (nD20), density (D20), and molar refractive index (nM). The QSPR (quantitative structure-property relationship) models were obtained with correlation coefficients 0.9981, 0.9570, 0.9884, and 0.9999, respectively. Furthermore, leave-one-out cross validation and random sampling prediction were performed, which confirmed the od stability and powerful prediction of these models.
2005, 21(04): 367-371
doi: 10.3866/PKU.WHXB20050405
Abstract:
The reaction microscopic mechanism of aqueous solution of chlorobenzene with nitrous acid in the presence of O2 and absence of O2 was studied by laser flash photolysis. The main characteristic peaks in these transient absorbance spectra were attributed and the build-up/decay trends of several transient species were investigated. •OH radical can be produced in aqueous solution of nitrous acid exposed to 355 nm laser beam. The rate constant of the reaction between •OH radical and chlorobenzene was measured to be （6. 6～7. 0）×109 L•mol-1•s-1. The transient product C6H5Cl-OH reacted with O2 to form C6H5Cl-OHO2 with a rate constant of (1. 6±0. 2) ×109 L•mol-1•s-1. The photolysis products were analyzed by GC/MS method and the possible reaction pathways were discussed.
The reaction microscopic mechanism of aqueous solution of chlorobenzene with nitrous acid in the presence of O2 and absence of O2 was studied by laser flash photolysis. The main characteristic peaks in these transient absorbance spectra were attributed and the build-up/decay trends of several transient species were investigated. •OH radical can be produced in aqueous solution of nitrous acid exposed to 355 nm laser beam. The rate constant of the reaction between •OH radical and chlorobenzene was measured to be （6. 6～7. 0）×109 L•mol-1•s-1. The transient product C6H5Cl-OH reacted with O2 to form C6H5Cl-OHO2 with a rate constant of (1. 6±0. 2) ×109 L•mol-1•s-1. The photolysis products were analyzed by GC/MS method and the possible reaction pathways were discussed.
2005, 21(04): 372-377
doi: 10.3866/PKU.WHXB20050406
Abstract:
In current work, the correlations between Caco-2 permeability(lgPeff) and molecular structures were investigated using genetic al rithm(GA). A group of multiple regression models with od statistical significance were obtained based on a training set of 51 molecules, from the statistical analyses of the descriptors used in the evolution procedure, four of them, including the distribution coefficient(lgD), radius of gyration(rgyr), shadow-X length（length of molecule in the X dimension）, and NHBD, may have the largest impact on diffusion through Caco-2 cell.
In current work, the correlations between Caco-2 permeability(lgPeff) and molecular structures were investigated using genetic al rithm(GA). A group of multiple regression models with od statistical significance were obtained based on a training set of 51 molecules, from the statistical analyses of the descriptors used in the evolution procedure, four of them, including the distribution coefficient(lgD), radius of gyration(rgyr), shadow-X length（length of molecule in the X dimension）, and NHBD, may have the largest impact on diffusion through Caco-2 cell.
2005, 21(04): 378-382
doi: 10.3866/PKU.WHXB20050407
Abstract:
In this paper, different Sn doped TiO2 nanoparticles were prepared by a sol-gel method, and were mainly characterized by surface photovoltage spectroscopy (SPS) and photoluminescence spectroscopy (PL). The photocatalytic activity of the as-prepared samples was evaluated by degrading the phenol solution. The effects of the calcination temperature and doping Sn content on the separation of surface photoinduced charge carriers and photocatalytic activity of TiO2 nanoparticles were discussed, and the modification mechanisms of Sn were analyzed. The results showed that the appropriate content of Sn dopant could effectively promote the separation of surface photoinduced charge carrier of TiO2 nanoparticles calcined at appropriate temperature, which was responsible for the remarkable increase in photocatalytic activity.
In this paper, different Sn doped TiO2 nanoparticles were prepared by a sol-gel method, and were mainly characterized by surface photovoltage spectroscopy (SPS) and photoluminescence spectroscopy (PL). The photocatalytic activity of the as-prepared samples was evaluated by degrading the phenol solution. The effects of the calcination temperature and doping Sn content on the separation of surface photoinduced charge carriers and photocatalytic activity of TiO2 nanoparticles were discussed, and the modification mechanisms of Sn were analyzed. The results showed that the appropriate content of Sn dopant could effectively promote the separation of surface photoinduced charge carrier of TiO2 nanoparticles calcined at appropriate temperature, which was responsible for the remarkable increase in photocatalytic activity.
2005, 21(04): 383-387
doi: 10.3866/PKU.WHXB20050408
Abstract:
The possible reaction paths of butene isomerization catalyzed by 4-H and 5-H of 1-ethyl-3-methyl-imidazolium (EMIM+) have been studied by using density functional theory (DFT) at B3LYP/6-31G** levels. The geometries of the reactants, transition states and products are fully optimized by energy gradient technology and the equilibrium states and transition states are verified according to the number of imaginary frequency obtained through vibrational analysis. The computed results indicate that the butene molecule approaches to 4-H or 5-H of EMIM+ at the first and then forms a supermolecule due to physical adsorption. Whereafter the isomerization of butene double bond is catalytically performed. The forward energy barriers of the rearrangement reaction catalyzed by 4-H and 5-H atom of EMIM+ are 204.2 and 207.3 kJ•mol-1, and the reverse energy barriers are 220.9 and 223.8 kJ•mol-1, respectively. The isomerization of butene catalyzed by the proton of the imidazolium ring may proceed through multi-channel at one-step process.
The possible reaction paths of butene isomerization catalyzed by 4-H and 5-H of 1-ethyl-3-methyl-imidazolium (EMIM+) have been studied by using density functional theory (DFT) at B3LYP/6-31G** levels. The geometries of the reactants, transition states and products are fully optimized by energy gradient technology and the equilibrium states and transition states are verified according to the number of imaginary frequency obtained through vibrational analysis. The computed results indicate that the butene molecule approaches to 4-H or 5-H of EMIM+ at the first and then forms a supermolecule due to physical adsorption. Whereafter the isomerization of butene double bond is catalytically performed. The forward energy barriers of the rearrangement reaction catalyzed by 4-H and 5-H atom of EMIM+ are 204.2 and 207.3 kJ•mol-1, and the reverse energy barriers are 220.9 and 223.8 kJ•mol-1, respectively. The isomerization of butene catalyzed by the proton of the imidazolium ring may proceed through multi-channel at one-step process.
2005, 21(04): 388-391
doi: 10.3866/PKU.WHXB20050409
Abstract:
Quasiclassical trajectory calculations (QCT) of the energy transfer between highly vibrationally excited pyrazine (C4N2H4) and N2, O2, NH3, and ground state C4N2H4 were performed respectively. The calculations show when colliding with N2 and O2 the vibrational energy of C4N2H4 transferred mainly to the vibrational contributions of N2 and O2, and they are V-V energy transfers. Colliding with NH3, the vibrational energy of C4N2H4 transferred mainly to the rotational contributions of NH3, and it is V-R energy transfer. Colliding with ground state C4N2H4 the energy transferred mainly to the vibrational and rotational contributions, and it is V-V(R) energy transfer. Comparing with the collision energy transfers between highly vibrationally excited C4N2H4, C6F6, C6H6 and their own ground state molecules, we found that V-V energy transfer is easier if the molecule has higher symmetry.
Quasiclassical trajectory calculations (QCT) of the energy transfer between highly vibrationally excited pyrazine (C4N2H4) and N2, O2, NH3, and ground state C4N2H4 were performed respectively. The calculations show when colliding with N2 and O2 the vibrational energy of C4N2H4 transferred mainly to the vibrational contributions of N2 and O2, and they are V-V energy transfers. Colliding with NH3, the vibrational energy of C4N2H4 transferred mainly to the rotational contributions of NH3, and it is V-R energy transfer. Colliding with ground state C4N2H4 the energy transferred mainly to the vibrational and rotational contributions, and it is V-V(R) energy transfer. Comparing with the collision energy transfers between highly vibrationally excited C4N2H4, C6F6, C6H6 and their own ground state molecules, we found that V-V energy transfer is easier if the molecule has higher symmetry.
2005, 21(04): 392-396
doi: 10.3866/PKU.WHXB20050410
Abstract:
Active nitrogen has been prepared by hollow-cathode discharge of N2 in a flowing afterglow system. Strong emission spectra of NBr(b1Σ+→X3Σ-) have been observed when alkyl bromides (CHBr3, CH2Br2, C2H5Br, C4H9Br) are added to a stream of active nitrogen. In addition, weak CN(A2π, B2π→X2Σ+) emission spectra have been detected only in the case of CHBr3 or CH2Br2 as reagents. Some tentative experiments show that the electronically excited NBr(b1Σ+) is formed by mechanism of metastable N2(A3Σu+) electronic-to-electronic energy transfer from ground state NBr(X3Σ-), which is from the reaction of N(4S) with alkyl bromides. The excited CN (A2π, B2π) comes from the reaction of N(4S) with CBr formed due to CHBr3(or CH2Br2) dissociation by N2(A3Σu+).
Active nitrogen has been prepared by hollow-cathode discharge of N2 in a flowing afterglow system. Strong emission spectra of NBr(b1Σ+→X3Σ-) have been observed when alkyl bromides (CHBr3, CH2Br2, C2H5Br, C4H9Br) are added to a stream of active nitrogen. In addition, weak CN(A2π, B2π→X2Σ+) emission spectra have been detected only in the case of CHBr3 or CH2Br2 as reagents. Some tentative experiments show that the electronically excited NBr(b1Σ+) is formed by mechanism of metastable N2(A3Σu+) electronic-to-electronic energy transfer from ground state NBr(X3Σ-), which is from the reaction of N(4S) with alkyl bromides. The excited CN (A2π, B2π) comes from the reaction of N(4S) with CBr formed due to CHBr3(or CH2Br2) dissociation by N2(A3Σu+).
2005, 21(04): 397-401
doi: 10.3866/PKU.WHXB20050411
Abstract:
Li-ferrierite (Li-FER) fine powder was prepared via an ion exchange process using lithium ions to replace the hydrogen atoms in hydroxyl group of FER. Compared with bare LiClO4 /PEO [poly(ethylene oxide)] polymer electrolyte, the ionic conductivity of PEO composite polymer electrolyte was enhanced more than three orders by adding the Li-FER powder in it. The results of electrochemical measurements show that the Li+ transference number increased obviously by adding the Li-FER powder. The crystal properties of the composite polymer electrolytes were investigated by XRD, DSC, and polarized light microscopy (PLM) methods. It was found that the Li-FER fine powder could act as crystal nucleator to make grain refinement and provide more continuous amorphous domain, in which Li+ ions can move more easily. Therefore the conductivity of the PEO composite polymer electrolytes increased greatly.
Li-ferrierite (Li-FER) fine powder was prepared via an ion exchange process using lithium ions to replace the hydrogen atoms in hydroxyl group of FER. Compared with bare LiClO4 /PEO [poly(ethylene oxide)] polymer electrolyte, the ionic conductivity of PEO composite polymer electrolyte was enhanced more than three orders by adding the Li-FER powder in it. The results of electrochemical measurements show that the Li+ transference number increased obviously by adding the Li-FER powder. The crystal properties of the composite polymer electrolytes were investigated by XRD, DSC, and polarized light microscopy (PLM) methods. It was found that the Li-FER fine powder could act as crystal nucleator to make grain refinement and provide more continuous amorphous domain, in which Li+ ions can move more easily. Therefore the conductivity of the PEO composite polymer electrolytes increased greatly.
2005, 21(04): 402-407
doi: 10.3866/PKU.WHXB20050412
Abstract:
Based on B3LYP method of DFT, the geometry of pyridone azo compounds was optimized at the level of 6-311G* basis, and analyzed by NBO (nature bond orbital) method. Their visible absorption maxima were calculated with TDDFT method and ZINDO/S method, the results agreed with the observed values excellently. It was shown that the visible absorption maxima can be calculated more precisely in much shorter time with ZINDO/S method by adjusting that the value of π-π overlap weighting factor (OWFπ-π) than TDDFT method. In the process of calculation with ZINDO/S, in virtue of the method of regression it was found that the linear relationship between OWFπ-π and ZO(the average net charge on oxygen of the two carbonyl-groups in pyridone) was excellent, OWFπ-π＝0.11425－1.04718ZO, that is, with the drop of ZO, OWFπ-π increased. The relationship not only could be explained in terms of quantum theory, but also could be used to predict the visible absorption maxima of other pyridone azo compounds in the same series. What′s more, the study on molecular orbital implied that the electron transition from the electron donators to electron acceptors of conjugate system resulted in their visible absorption maxima.
Based on B3LYP method of DFT, the geometry of pyridone azo compounds was optimized at the level of 6-311G* basis, and analyzed by NBO (nature bond orbital) method. Their visible absorption maxima were calculated with TDDFT method and ZINDO/S method, the results agreed with the observed values excellently. It was shown that the visible absorption maxima can be calculated more precisely in much shorter time with ZINDO/S method by adjusting that the value of π-π overlap weighting factor (OWFπ-π) than TDDFT method. In the process of calculation with ZINDO/S, in virtue of the method of regression it was found that the linear relationship between OWFπ-π and ZO(the average net charge on oxygen of the two carbonyl-groups in pyridone) was excellent, OWFπ-π＝0.11425－1.04718ZO, that is, with the drop of ZO, OWFπ-π increased. The relationship not only could be explained in terms of quantum theory, but also could be used to predict the visible absorption maxima of other pyridone azo compounds in the same series. What′s more, the study on molecular orbital implied that the electron transition from the electron donators to electron acceptors of conjugate system resulted in their visible absorption maxima.
2005, 21(04): 408-413
doi: 10.3866/PKU.WHXB20050413
Abstract:
The metallomicelle made from surfactant micelle and new crown Schiff base magnesium(Ⅲ) and cobalt(II) complexes were used for bis(4-nitrophenyl) phosphate(BNPP) catalytic hydrolysis. Kinetic studies were carried out by UV-Vis methods with a GBC 916 UV-Vis spectrophotometer equipped with a thermostatic cell holder. The pseudo first order rate constants (kobs) of BNPP hydrolysis were obtained based on the initial rate method by monitoring the release of p-nitrophenol at 400 nm, and the substrate to catalyst concentration ratio was in more than 10-fold excess. The change of ultraviolet characteristic spectra of the reactive systems was analyzed. According to the results of the characteristic spectra analysis in the reaction system, a comparison of the hydrolytic rate of NPP with that of BNPP under same reaction condition, and the pH-dependence of BNPP hydrolysis rate, a mechanism involving transition metal-hydroxide species of the catalytic hydrolysis was proposed. A kinetic mathematical model of BNPP cleavage catalyzed by the metallomicelle was found. The results indicate that the metallomicelle used as mimetic hydrolase in BNPP hydrolysis exhibits efficient catalytic performance. The pseudo-first-order rate constants of BNPP hydrolysis catalyzed by the metallomicelle is 3.05×106 times more than that of spontaneous hydrolysis of BNPP. The catalytic activity of metallomicelle is the highest under pH 8.5 and at 318 K in the solution. The apparent active energy and the preexponential factor for the catalytic reaction were calculated to be 17.5 kJ•mol-1 and 6.02×10-2 s-1 for MnL2Cl, and 17.6 kJ•mol-1 and 5.39×10-2 s-1 for CoL2, respectively. The final products of the titled reaction are found to be p-nitrophenol and H3PO4.
The metallomicelle made from surfactant micelle and new crown Schiff base magnesium(Ⅲ) and cobalt(II) complexes were used for bis(4-nitrophenyl) phosphate(BNPP) catalytic hydrolysis. Kinetic studies were carried out by UV-Vis methods with a GBC 916 UV-Vis spectrophotometer equipped with a thermostatic cell holder. The pseudo first order rate constants (kobs) of BNPP hydrolysis were obtained based on the initial rate method by monitoring the release of p-nitrophenol at 400 nm, and the substrate to catalyst concentration ratio was in more than 10-fold excess. The change of ultraviolet characteristic spectra of the reactive systems was analyzed. According to the results of the characteristic spectra analysis in the reaction system, a comparison of the hydrolytic rate of NPP with that of BNPP under same reaction condition, and the pH-dependence of BNPP hydrolysis rate, a mechanism involving transition metal-hydroxide species of the catalytic hydrolysis was proposed. A kinetic mathematical model of BNPP cleavage catalyzed by the metallomicelle was found. The results indicate that the metallomicelle used as mimetic hydrolase in BNPP hydrolysis exhibits efficient catalytic performance. The pseudo-first-order rate constants of BNPP hydrolysis catalyzed by the metallomicelle is 3.05×106 times more than that of spontaneous hydrolysis of BNPP. The catalytic activity of metallomicelle is the highest under pH 8.5 and at 318 K in the solution. The apparent active energy and the preexponential factor for the catalytic reaction were calculated to be 17.5 kJ•mol-1 and 6.02×10-2 s-1 for MnL2Cl, and 17.6 kJ•mol-1 and 5.39×10-2 s-1 for CoL2, respectively. The final products of the titled reaction are found to be p-nitrophenol and H3PO4.
2005, 21(04): 414-418
doi: 10.3866/PKU.WHXB20050414
Abstract:
Polyaniline (PANi) particles with hierarchy are prepared by adding (NH4)2S2O8 dropwise into aqueous solution containing aniline monomer and HCl acid at 0 ℃ under nitrogen atmosphere with stirring. SEM images show that the resulted PANi particles are composed of their primary particles, which are composed of multi-layer flakes. Symmetric redox supercapacitor (prototype) is assembled with the PANi particles as active electrode materials and 2 mol•L-1 H2SO4 aqueous solution as electrolyte. The electrochemical performances of the supercapacitor are tested with cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. When the charge-discharge current is 7 mA, the specific energy and specific power of the supercapacitor can reach 6.35 Wh•kg-1 and 132 W•kg-1 (based on the mass of PANi), respectively；the capacitance of PANi electrode is about 408 F•g-1 . When the charge-discharge current is 20 mA, the specific energy and specific power of the super-capacitor can reach 4.39 Wh•kg-1 and 328 W•kg-1 (based on the weight of PANi), respectively; the capacitance of PANi electrode is about 324 F•g-1 . During 100 charge-discharge cycles, the discharge capacity of the supercapacitor is constant, and the charge-discharge efficiency is 95%. The results show that the PANi supercapacitor with hierarchial particles as active electrode material can store a great deal of charge and energy in H2SO4 solution.
Polyaniline (PANi) particles with hierarchy are prepared by adding (NH4)2S2O8 dropwise into aqueous solution containing aniline monomer and HCl acid at 0 ℃ under nitrogen atmosphere with stirring. SEM images show that the resulted PANi particles are composed of their primary particles, which are composed of multi-layer flakes. Symmetric redox supercapacitor (prototype) is assembled with the PANi particles as active electrode materials and 2 mol•L-1 H2SO4 aqueous solution as electrolyte. The electrochemical performances of the supercapacitor are tested with cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. When the charge-discharge current is 7 mA, the specific energy and specific power of the supercapacitor can reach 6.35 Wh•kg-1 and 132 W•kg-1 (based on the mass of PANi), respectively；the capacitance of PANi electrode is about 408 F•g-1 . When the charge-discharge current is 20 mA, the specific energy and specific power of the super-capacitor can reach 4.39 Wh•kg-1 and 328 W•kg-1 (based on the weight of PANi), respectively; the capacitance of PANi electrode is about 324 F•g-1 . During 100 charge-discharge cycles, the discharge capacity of the supercapacitor is constant, and the charge-discharge efficiency is 95%. The results show that the PANi supercapacitor with hierarchial particles as active electrode material can store a great deal of charge and energy in H2SO4 solution.
2005, 21(04): 419-424
doi: 10.3866/PKU.WHXB20050415
Abstract:
Synthesis of the FeS2 (pyrite) powders via a solvent-thermal process is reported. Using FeSO4 and NH2CSNH2 as precursors and polyvinylpyrrolidone (PVP) as a protective agent (dispersant), high purity FeS2 powders have been synthesized by reaction in alcohol-water solution at 200 ℃ for 36 h. The experiment result shows that, single-phase pyrite powders can be obtained both in acid environment (pH=5) and in alkali environment (pH=10). Effects of pH value on pyrite powder structure, crystallite size and optical characterization are discussed.
Synthesis of the FeS2 (pyrite) powders via a solvent-thermal process is reported. Using FeSO4 and NH2CSNH2 as precursors and polyvinylpyrrolidone (PVP) as a protective agent (dispersant), high purity FeS2 powders have been synthesized by reaction in alcohol-water solution at 200 ℃ for 36 h. The experiment result shows that, single-phase pyrite powders can be obtained both in acid environment (pH=5) and in alkali environment (pH=10). Effects of pH value on pyrite powder structure, crystallite size and optical characterization are discussed.
2005, 21(04): 425-429
doi: 10.3866/PKU.WHXB20050416
Abstract:
The interactions between four fluorine- polymers, i.e. polyvinylidene fluorine (PVDF), polychlorotrifluoroethylene(PCTFE), fluorine rubber（F2311）, fluorine resin（F2314） and TATB(1,3,5-triamino-2,4,6-trinitrobenzene) crystal have been simulated by molecular dynamics (MD). The results show that the order of binding energies for four fluorine- polymers with TATB are as following: PVDF>F2311>F2314>PCTFE. The abilities of different TATB crystal surfaces to combine fluorine- polymers decrease as following:(001)>(010)>(100). Binding energy is mainly determined by intermolecular hydrogen bond.
The interactions between four fluorine- polymers, i.e. polyvinylidene fluorine (PVDF), polychlorotrifluoroethylene(PCTFE), fluorine rubber（F2311）, fluorine resin（F2314） and TATB(1,3,5-triamino-2,4,6-trinitrobenzene) crystal have been simulated by molecular dynamics (MD). The results show that the order of binding energies for four fluorine- polymers with TATB are as following: PVDF>F2311>F2314>PCTFE. The abilities of different TATB crystal surfaces to combine fluorine- polymers decrease as following:(001)>(010)>(100). Binding energy is mainly determined by intermolecular hydrogen bond.
2005, 21(04): 430-434
doi: 10.3866/PKU.WHXB20050417
Abstract:
Microcapsules for electrophoretic display were prepared by in situ polymerization of urea-formaldehyde, in which organic pigment of benzidine yellow (PY-12) was used as displaying particles, tetrachloroethylene and toluene as dispersion media, oil soluble blue N dye as light absorber and super dispersant CH-2C as stabilizing agent. The morphology and size of microcapsules were checked through optical transmission microscope. The response to the change of electric field and display performance of the microcapsules were investigated. It was shown that the microcapsules without pigment particles made by this method were of od smoothness and transparence. Fast and reversible display of the microcapsules with pigment particles was achieved in an electric field.
Microcapsules for electrophoretic display were prepared by in situ polymerization of urea-formaldehyde, in which organic pigment of benzidine yellow (PY-12) was used as displaying particles, tetrachloroethylene and toluene as dispersion media, oil soluble blue N dye as light absorber and super dispersant CH-2C as stabilizing agent. The morphology and size of microcapsules were checked through optical transmission microscope. The response to the change of electric field and display performance of the microcapsules were investigated. It was shown that the microcapsules without pigment particles made by this method were of od smoothness and transparence. Fast and reversible display of the microcapsules with pigment particles was achieved in an electric field.
2005, 21(04): 435-438
doi: 10.3866/PKU.WHXB20050418
Abstract:
Photodissociation spectroscopy of the complex Mg+-NCSCH3 in the spectral region of 230~440 nm was observed. Mass spectrometry of the products for photo-induced reaction in the complex Mg+-NCSCH3 exhibits the product Mg+ from nonreaction quenching and reactive products Mg+NC, Mg+NCS throughout the whole wavelength range. The reactive products originate from the breaking of S－C chemical bonds. The Photodissociation spectrum consists of two broad peaks corresponding to the atomic transition of Mg+(32P←32S). The absorption spectrum by using CIS method of quantum chemical calculation agrees with the experimental spectrum.
Photodissociation spectroscopy of the complex Mg+-NCSCH3 in the spectral region of 230~440 nm was observed. Mass spectrometry of the products for photo-induced reaction in the complex Mg+-NCSCH3 exhibits the product Mg+ from nonreaction quenching and reactive products Mg+NC, Mg+NCS throughout the whole wavelength range. The reactive products originate from the breaking of S－C chemical bonds. The Photodissociation spectrum consists of two broad peaks corresponding to the atomic transition of Mg+(32P←32S). The absorption spectrum by using CIS method of quantum chemical calculation agrees with the experimental spectrum.
2005, 21(04): 439-442
doi: 10.3866/PKU.WHXB20050419
Abstract:
The consolute curve of benzene-water-ethanol ternary solutions has been measured by using equal-volume titration, and the coexistence curve near isothermal consolute point at 29.00±0.05 ℃ has also been measured. The obtained order-parameter critical index β = 0.38±0.04, and the order-parameter amplitude K =1.3±0.2. It indicates that near the isothermal consolute point, the critical index of the partly soluble ternary solutions fits Fisher renormalization model well, and it has the character of non-classical critical solution theory.
The consolute curve of benzene-water-ethanol ternary solutions has been measured by using equal-volume titration, and the coexistence curve near isothermal consolute point at 29.00±0.05 ℃ has also been measured. The obtained order-parameter critical index β = 0.38±0.04, and the order-parameter amplitude K =1.3±0.2. It indicates that near the isothermal consolute point, the critical index of the partly soluble ternary solutions fits Fisher renormalization model well, and it has the character of non-classical critical solution theory.
2005, 21(04): 443-445
doi: 10.3866/PKU.WHXB20050420
Abstract:
Alumina templates with large-size pores ( > 200 nm) were fabricated by adding organic solvent to electrolyte at 15 ℃. This effective method can shorten electrolysis time and quicken the process of the template preparation. A series of templates with different diameters (20～250 nm) were obtained by the combination of this method and traditional one. Experiment results show that the addition of organic solvent can efficiently avoid the heat produced quickly in the process of electrolysis. Pore diameter of alumina templates relys on controlled the experiment condition.
Alumina templates with large-size pores ( > 200 nm) were fabricated by adding organic solvent to electrolyte at 15 ℃. This effective method can shorten electrolysis time and quicken the process of the template preparation. A series of templates with different diameters (20～250 nm) were obtained by the combination of this method and traditional one. Experiment results show that the addition of organic solvent can efficiently avoid the heat produced quickly in the process of electrolysis. Pore diameter of alumina templates relys on controlled the experiment condition.
2005, 21(04): 446-449
doi: 10.3866/PKU.WHXB20050421
Abstract:
The size of nano ZnO powders was determined to be 30 nm in diameter by SEM. The isobaric molar heat capacity Cp of the nano ZnO was measured with high precision adiabatic low-temperature calorimeter in temperature range from 83 K to 350 K. The relationship of Cp with temperature T was established as: Cp＝－3.249＋0.2400T－3.413×10－4T 2＋4.485×10－7T 3. The thermodynamic functions of the nano ZnO, relative to the standard temperature of 298.15 K, were derived based on the heat capacity data through thermodynamic relationship. The measured Cp values were compared with those of coarse crystal and 18 nm ZnO powders cited from literature and the difference between the Cp curves was analyzed.
The size of nano ZnO powders was determined to be 30 nm in diameter by SEM. The isobaric molar heat capacity Cp of the nano ZnO was measured with high precision adiabatic low-temperature calorimeter in temperature range from 83 K to 350 K. The relationship of Cp with temperature T was established as: Cp＝－3.249＋0.2400T－3.413×10－4T 2＋4.485×10－7T 3. The thermodynamic functions of the nano ZnO, relative to the standard temperature of 298.15 K, were derived based on the heat capacity data through thermodynamic relationship. The measured Cp values were compared with those of coarse crystal and 18 nm ZnO powders cited from literature and the difference between the Cp curves was analyzed.
2005, 21(04): 450-457
doi: 10.3866/PKU.WHXB20050422
Abstract:
This paper mainly introduces the basic properties, the types and some applications of double-chained surfactants in nanomaterials and life science. The differences in the phase behaviours, the formation of the reversed micelle and the properties of the double-chained surfactant sodium bis(2-ethylhexyl) sulfosuccinate(AOT) and sodium bis(2-ethylhexyl)phosphate (NaDEHP) are presented. In addition, the interaction of both AOT and NaDEHP with macromolecules is discussed based on our work.
This paper mainly introduces the basic properties, the types and some applications of double-chained surfactants in nanomaterials and life science. The differences in the phase behaviours, the formation of the reversed micelle and the properties of the double-chained surfactant sodium bis(2-ethylhexyl) sulfosuccinate(AOT) and sodium bis(2-ethylhexyl)phosphate (NaDEHP) are presented. In addition, the interaction of both AOT and NaDEHP with macromolecules is discussed based on our work.
2005, 21(04): 458-462
doi: 10.3866/PKU.WHXB20050423
Abstract:
The proton exchange membrane is one of the key parts in direct methanol fuel cell (DMFC). In this pa-per, the recent progress in the investigation of the new polymer electrolyte membranes used for DMFC was presented.
The proton exchange membrane is one of the key parts in direct methanol fuel cell (DMFC). In this pa-per, the recent progress in the investigation of the new polymer electrolyte membranes used for DMFC was presented.
