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2005 Volume 21 Issue 7
2005, 21(07): 703-706
doi: 10.3866/PKU.WHXB20050701
Abstract:
The surface of ultrafine polytetrafluoroethylene (PTFE) particles has been activated by sodium naphthalide solution. The 11-Aminoundecanoic acid [NH2(CH2)10COOH] molecules have been grafted on the activated PTFE particle surface. The activated and grafted PTFE particles have been characterized by infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS). The results show that the hydroxyl groups, carbonyl groups, and carboxyl groups are formed on the ultrafine PTFE particle surface after activated in sodium naphthalide solution. The hydroxyl groups are turned into carbonyl groups, and then to carboxyl groups with the increase of sodium naphthalide concentration and the activating time. The sodium naphthalide solution is effective in activating the ultrafine PTFE particle surface. The amidogens of 11-Aminoundecanoic acid molecules can react with the surface hydroxyl groups; as a result, the 11-Aminoundecanoic acid molecules can be anchored on the activated PTFE particles surfaces through chemical bonding.
The surface of ultrafine polytetrafluoroethylene (PTFE) particles has been activated by sodium naphthalide solution. The 11-Aminoundecanoic acid [NH2(CH2)10COOH] molecules have been grafted on the activated PTFE particle surface. The activated and grafted PTFE particles have been characterized by infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS). The results show that the hydroxyl groups, carbonyl groups, and carboxyl groups are formed on the ultrafine PTFE particle surface after activated in sodium naphthalide solution. The hydroxyl groups are turned into carbonyl groups, and then to carboxyl groups with the increase of sodium naphthalide concentration and the activating time. The sodium naphthalide solution is effective in activating the ultrafine PTFE particle surface. The amidogens of 11-Aminoundecanoic acid molecules can react with the surface hydroxyl groups; as a result, the 11-Aminoundecanoic acid molecules can be anchored on the activated PTFE particles surfaces through chemical bonding.
2005, 21(07): 707-710
doi: 10.3866/PKU.WHXB20050702
Abstract:
LiFePO4 thin films have been successfully fabricated by using pulsed laser deposition (PLD) coupled with high temperature annealing. The morphology, structure and electrochemical behaviors of the obtained thin films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), the charge/discharge and cyclic voltammetry (CV) measurements. These results indicated that LiFePO4 thin films had a well-crystallized olivinetype structure before and after annealed at 650 ℃. The annealed LiFePO4 thin film exhibited a 3.45/3.40 V plateau vs Li+/Li in the discharge/charge curves. The first discharge capacity was found to be 27 mAh•g－1 and the discharge capacity kept 49% of the first discharge capacity after cycling 100 times. The low reversible capacity and poor cycling performance of LiFePO4 thin films fabricated by pulsed laser deposition may be due to the lower electrochemical activity of the large particle on the surface of thin film electrode, the existence of part of Fe2O3 produced by the high temperature annealing and the poor conductivity of LiFePO4 material.
LiFePO4 thin films have been successfully fabricated by using pulsed laser deposition (PLD) coupled with high temperature annealing. The morphology, structure and electrochemical behaviors of the obtained thin films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), the charge/discharge and cyclic voltammetry (CV) measurements. These results indicated that LiFePO4 thin films had a well-crystallized olivinetype structure before and after annealed at 650 ℃. The annealed LiFePO4 thin film exhibited a 3.45/3.40 V plateau vs Li+/Li in the discharge/charge curves. The first discharge capacity was found to be 27 mAh•g－1 and the discharge capacity kept 49% of the first discharge capacity after cycling 100 times. The low reversible capacity and poor cycling performance of LiFePO4 thin films fabricated by pulsed laser deposition may be due to the lower electrochemical activity of the large particle on the surface of thin film electrode, the existence of part of Fe2O3 produced by the high temperature annealing and the poor conductivity of LiFePO4 material.
2005, 21(07): 711-715
doi: 10.3866/PKU.WHXB20050703
Abstract:
Polycondensate of benzoguanamine(BGA) and pyromellitic dianhydride(PMDA) as well as p-π conjugate polycondensates with differ side chains were designed and synthesized on the basis of quantum chemical PM3/CIS(configuration interaction singles) method, using the sum-over-states(SOS) expression, the geometries of the polyamic acids with different side chains and their monomer are optimized, and their third-order nonlinear optical susceptibilities (γ) have been calculated. The effects of the different side chains on the third-order nonlinear optical property have been studied. These results give inspiration for synthesizing the third-order nonlinear optical material with od machining performance.
Polycondensate of benzoguanamine(BGA) and pyromellitic dianhydride(PMDA) as well as p-π conjugate polycondensates with differ side chains were designed and synthesized on the basis of quantum chemical PM3/CIS(configuration interaction singles) method, using the sum-over-states(SOS) expression, the geometries of the polyamic acids with different side chains and their monomer are optimized, and their third-order nonlinear optical susceptibilities (γ) have been calculated. The effects of the different side chains on the third-order nonlinear optical property have been studied. These results give inspiration for synthesizing the third-order nonlinear optical material with od machining performance.
2005, 21(07): 716-720
doi: 10.3866/PKU.WHXB20050704
Abstract:
The electronic structure of V and VHx (x=0, 1, 2) in vanadium-based solid solution was calculated by using self-consistent-charge discrete variational (SCC-DV-Xα) method of quantum chemistry. The results demonstrated that the interaction between V and H in VH and VH2 was not only ionic but also covalent; the V－H bond between V and H bands in hydride VH2 was weaker than that in VH. The bonds were due to interaction between the V 4s and H 1s in hydride VH, and the interaction between V 4s, V 3d and H 1s in VH2. Fermi energy level in VH was lower than in VH2. The results suggested that VH is more stable.
The electronic structure of V and VHx (x=0, 1, 2) in vanadium-based solid solution was calculated by using self-consistent-charge discrete variational (SCC-DV-Xα) method of quantum chemistry. The results demonstrated that the interaction between V and H in VH and VH2 was not only ionic but also covalent; the V－H bond between V and H bands in hydride VH2 was weaker than that in VH. The bonds were due to interaction between the V 4s and H 1s in hydride VH, and the interaction between V 4s, V 3d and H 1s in VH2. Fermi energy level in VH was lower than in VH2. The results suggested that VH is more stable.
2005, 21(07): 721-724
doi: 10.3866/PKU.WHXB20050705
Abstract:
Tungsten carbide powder microelectrode (WC-PME) was prepared from tungsten carbide (WC) powders to be used as an electrocatalyst. Electrochemical reduction behaviour of p-nitrophenol (PNP) on the WC-PME was investigated using cyclic voltammetry (CV) and linear sweep voltammetry. It was found that reduction potential of PNP on the WC-PME was more positive than that on the Cu-Hg microelectrode and that WC had higher catalytic activity in the electroredution of PNP than Cu-Hg. Although the reduction potentials of PNP on the WC-PME and the Pt microelectrode were close to each other, the reduction current of PNP on the WC-PME was about 5 times as large as that on the Pt microelectrode. This result was mainly attributed to the surface morphological structure of WC.
Tungsten carbide powder microelectrode (WC-PME) was prepared from tungsten carbide (WC) powders to be used as an electrocatalyst. Electrochemical reduction behaviour of p-nitrophenol (PNP) on the WC-PME was investigated using cyclic voltammetry (CV) and linear sweep voltammetry. It was found that reduction potential of PNP on the WC-PME was more positive than that on the Cu-Hg microelectrode and that WC had higher catalytic activity in the electroredution of PNP than Cu-Hg. Although the reduction potentials of PNP on the WC-PME and the Pt microelectrode were close to each other, the reduction current of PNP on the WC-PME was about 5 times as large as that on the Pt microelectrode. This result was mainly attributed to the surface morphological structure of WC.
2005, 21(07): 725-729
doi: 10.3866/PKU.WHXB20050706
Abstract:
The effect of co-doping with Ti and Mg ions in LiNi0.4Co0.2Mn0.4O2 on structure and electrochemical performance was investigated by using SEM, XRD, EIS and galvanostatic charge-discharge experiment. The XRD showed that some characteristic peak intensity ratios have significant change. The rate discharge capability and cycle stability of LiNi0.4Co0.2Mn0.4O2 can be improved significantly by a small amount of Ti, Mg ions co-doping (1% molar ratio). AC impedance was used to study the processes of charge-discharge cycle. The result showed that (Ti4+, Mg2+) multiple-ion dopant can evidently suppress the increasing of the electrochemical reaction resistant Rct at 1C & 2C discharge rates. Co-doping of metal ions with diferent valences is a useful method to improve large current discharge capability of the lithium insertion nickel cobalt manganese oxides.
The effect of co-doping with Ti and Mg ions in LiNi0.4Co0.2Mn0.4O2 on structure and electrochemical performance was investigated by using SEM, XRD, EIS and galvanostatic charge-discharge experiment. The XRD showed that some characteristic peak intensity ratios have significant change. The rate discharge capability and cycle stability of LiNi0.4Co0.2Mn0.4O2 can be improved significantly by a small amount of Ti, Mg ions co-doping (1% molar ratio). AC impedance was used to study the processes of charge-discharge cycle. The result showed that (Ti4+, Mg2+) multiple-ion dopant can evidently suppress the increasing of the electrochemical reaction resistant Rct at 1C & 2C discharge rates. Co-doping of metal ions with diferent valences is a useful method to improve large current discharge capability of the lithium insertion nickel cobalt manganese oxides.
2005, 21(07): 730-734
doi: 10.3866/PKU.WHXB20050707
Abstract:
Catalytically grown carbon nanofibers with different carbon layer arrangements, fishbone-shaped and parallel, were treated in a mixture of concentrated nitric and sulfuric acids (90, 120, 150 ℃) to introduce the oxygen-containing surface functional groups. The surface properties were characterized with high-resolution electron microscope, FT-IR, and ion-exchange method. The results showed that much more oxygen-containing groups were formed on the fishbone surface shaped of carbon nanofibers than those on the parallel type surface in the mixed acids treatment. This tendency became pronounced with the increase of treatment temperatures. When the treated CNFs were used as the carrier of Pd-Pt metal catalysts, it was found that the interaction became stronger between the supported metals and the carbon nanofibers with the increase of the concentration of the surface oxygen-containing groups. The activity of the supported catalyst on the carbon nanofibers of the fishbone type was much higher than that on the parallel type for the hydrogenation of naphthalene to tetralin.
Catalytically grown carbon nanofibers with different carbon layer arrangements, fishbone-shaped and parallel, were treated in a mixture of concentrated nitric and sulfuric acids (90, 120, 150 ℃) to introduce the oxygen-containing surface functional groups. The surface properties were characterized with high-resolution electron microscope, FT-IR, and ion-exchange method. The results showed that much more oxygen-containing groups were formed on the fishbone surface shaped of carbon nanofibers than those on the parallel type surface in the mixed acids treatment. This tendency became pronounced with the increase of treatment temperatures. When the treated CNFs were used as the carrier of Pd-Pt metal catalysts, it was found that the interaction became stronger between the supported metals and the carbon nanofibers with the increase of the concentration of the surface oxygen-containing groups. The activity of the supported catalyst on the carbon nanofibers of the fishbone type was much higher than that on the parallel type for the hydrogenation of naphthalene to tetralin.
2005, 21(07): 735-739
doi: 10.3866/PKU.WHXB20050708
Abstract:
The structures of (BN)n(n≤12) clusters were studied by using genetic al rithm combined with empirical two- and three-body potentials. The low-energy structures were further optimized on the HF/6-31G(d) level. New stable isomers with line, fan, ring, double-ring, triple-ring and cage structures were obtained. The bonding properties of BN bonds in the clusters were analyzed. While atom N forms sp2 hybrid orbitals, atom B forms sp hybrid orbitals in the ring structure. Atom B bonds to three neighbor atoms by sp2 orbitals only when it is located at a node. (BN)6 is the only ring structure without tension.
The structures of (BN)n(n≤12) clusters were studied by using genetic al rithm combined with empirical two- and three-body potentials. The low-energy structures were further optimized on the HF/6-31G(d) level. New stable isomers with line, fan, ring, double-ring, triple-ring and cage structures were obtained. The bonding properties of BN bonds in the clusters were analyzed. While atom N forms sp2 hybrid orbitals, atom B forms sp hybrid orbitals in the ring structure. Atom B bonds to three neighbor atoms by sp2 orbitals only when it is located at a node. (BN)6 is the only ring structure without tension.
2005, 21(07): 740-745
doi: 10.3866/PKU.WHXB20050709
Abstract:
Using polarization scan, electrochemical impedance spectroscopy and capacitance measurement, the correlation of corrosion resistance and semiconductor properties for electrochemically modified passive film formed on stainless steel in 0.5 mol•L-1 NaCl solution was investigated, and the mechanism of the corrosion resistance of the electrochemically modified passive film was further studied. The result reveals that the films behave as n-type and p-type semiconductors in the potential range above and below the flat band potential, respectively. This behavior is assumed to be the consequence of the semiconducting properties of the iron oxide and chromium oxide regions which compose the passive film. Compared with natural passive film, electrochemically modified passive film has lower donor and acceptor density. The change of EFB was discussed as a function of anions adsorption on surface of passive film. With low donor and acceptor density and anion adsorption on surface of passive film, effectively preventing the adsorption of Cl－ in passive film, the resistance to localize corrosion of passive film was greatly improved.
Using polarization scan, electrochemical impedance spectroscopy and capacitance measurement, the correlation of corrosion resistance and semiconductor properties for electrochemically modified passive film formed on stainless steel in 0.5 mol•L-1 NaCl solution was investigated, and the mechanism of the corrosion resistance of the electrochemically modified passive film was further studied. The result reveals that the films behave as n-type and p-type semiconductors in the potential range above and below the flat band potential, respectively. This behavior is assumed to be the consequence of the semiconducting properties of the iron oxide and chromium oxide regions which compose the passive film. Compared with natural passive film, electrochemically modified passive film has lower donor and acceptor density. The change of EFB was discussed as a function of anions adsorption on surface of passive film. With low donor and acceptor density and anion adsorption on surface of passive film, effectively preventing the adsorption of Cl－ in passive film, the resistance to localize corrosion of passive film was greatly improved.
2005, 21(07): 746-751
doi: 10.3866/PKU.WHXB20050710
Abstract:
The catalytic oxidative performance of Mg-Al-Ru-CO3 hydrotalcite, Co-Al-Ru-CO3 hydrotalcite, Ru-Co(OH)2-CeO2 was well designed and tuned with substitution method. The XRD characterization presented that both the Mg-Al-Ru-CO3 catalyst and Co-Al-Ru-CO3 catalyst could keep hydrotalcite structure after the partial substitution of Al with Ru. However, after the substitution of Al with Ce, the structure of the obtained Ru-Co(OH)2-CeO2 catalyst was microcrystals of cobalt hydroxide and cerium oxide. The results of XPS and Ru K-edge XAFS suggested that the isolated Ru atom in Mg-Al-Ru-CO3 hydrotalcite was surrounded by 6 oxygen atoms with only one type of Ru-O shells, which catalyzed alcohols oxidation efficiently; the isolated Ru atom in Co-Al-Ru-CO3 hydrotalcite was surrounded by 6 oxygen atoms with two types of Ru-O shells, therein unsaturated Ru═O double bond was responsible for higher catalytic efficient for alcohols oxidation; the isolated Ru atom in Ru-Co(OH)2-CeO2 catalyst surrounded by 5 oxygen atoms with two types of Ru-O shells, therein the unsaturated coordination of Ru was the key to attain higher ability for various kinds of alcohols oxidation.
The catalytic oxidative performance of Mg-Al-Ru-CO3 hydrotalcite, Co-Al-Ru-CO3 hydrotalcite, Ru-Co(OH)2-CeO2 was well designed and tuned with substitution method. The XRD characterization presented that both the Mg-Al-Ru-CO3 catalyst and Co-Al-Ru-CO3 catalyst could keep hydrotalcite structure after the partial substitution of Al with Ru. However, after the substitution of Al with Ce, the structure of the obtained Ru-Co(OH)2-CeO2 catalyst was microcrystals of cobalt hydroxide and cerium oxide. The results of XPS and Ru K-edge XAFS suggested that the isolated Ru atom in Mg-Al-Ru-CO3 hydrotalcite was surrounded by 6 oxygen atoms with only one type of Ru-O shells, which catalyzed alcohols oxidation efficiently; the isolated Ru atom in Co-Al-Ru-CO3 hydrotalcite was surrounded by 6 oxygen atoms with two types of Ru-O shells, therein unsaturated Ru═O double bond was responsible for higher catalytic efficient for alcohols oxidation; the isolated Ru atom in Ru-Co(OH)2-CeO2 catalyst surrounded by 5 oxygen atoms with two types of Ru-O shells, therein the unsaturated coordination of Ru was the key to attain higher ability for various kinds of alcohols oxidation.
2005, 21(07): 752-757
doi: 10.3866/PKU.WHXB20050711
Abstract:
The thermal decomposition kinetics of magnesium hydroxide was investigated using the non-isothermal approach. It was proved that the mechanism of this reaction corresponded to the nucleation and growth mechanism A, but changed from A2 to A1.5 with rising heating rate. The activation energy of decomposition, both estimated by the non-mechanismic Kinssinger equation and calculated by a numerical regression method according to the deduced mechanism, was around 148 kJ•mol-1. Further investigation revealed that water vapor had an extraordinarily significant effect on the thermal decomposition mechanism of magnesium hydroxide.
The thermal decomposition kinetics of magnesium hydroxide was investigated using the non-isothermal approach. It was proved that the mechanism of this reaction corresponded to the nucleation and growth mechanism A, but changed from A2 to A1.5 with rising heating rate. The activation energy of decomposition, both estimated by the non-mechanismic Kinssinger equation and calculated by a numerical regression method according to the deduced mechanism, was around 148 kJ•mol-1. Further investigation revealed that water vapor had an extraordinarily significant effect on the thermal decomposition mechanism of magnesium hydroxide.
2005, 21(07): 758-762
doi: 10.3866/PKU.WHXB20050712
Abstract:
Effects of particle size on kinetic parameters were studied by the reaction of nano-ZnO with solution of sodium bisulfate, and the cause of the apparent activation energy decreasing was discussed. The results show that the reaction rate is only related to the concentration of reactant when the particle size of reactant, the reaction temperature and the stirring rate are constant. The particle size has obvious effects on the reaction order, the rate constant, the activation energy and the pre-exponential factor. With decreasing the particle size, the rate constant and the reaction order increase, while the pre-exponential factor and the apparent activation energy decrease. There is a linear relation between the apparent activation energy and the reciprocal of the size, and the particle size exerts influences on kinetic parameters of a heterogeneous reaction through the mole surface area, the mole surface energy and the mole surface entropy.
Effects of particle size on kinetic parameters were studied by the reaction of nano-ZnO with solution of sodium bisulfate, and the cause of the apparent activation energy decreasing was discussed. The results show that the reaction rate is only related to the concentration of reactant when the particle size of reactant, the reaction temperature and the stirring rate are constant. The particle size has obvious effects on the reaction order, the rate constant, the activation energy and the pre-exponential factor. With decreasing the particle size, the rate constant and the reaction order increase, while the pre-exponential factor and the apparent activation energy decrease. There is a linear relation between the apparent activation energy and the reciprocal of the size, and the particle size exerts influences on kinetic parameters of a heterogeneous reaction through the mole surface area, the mole surface energy and the mole surface entropy.
2005, 21(07): 763-768
doi: 10.3866/PKU.WHXB20050713
Abstract:
The influence of n-hexadecyltrimethylammoniumbromide (CTAB) on the reaction between cobalt tetrasulphonated phthalocyanine (CoTsPc) and sodium sulfide has been investigated. The result shows that in the presence of the micelles, cobalt tetrasulphonated phthalocyanine can be reduced by sodium sulfide at pH 8.5~9.5 to forms the corresponding Co(I) complex. The mechanism of the reaction is also discussed. Using the method of multi-wavelength and double-parameter, UV-Vis spectra of the system are analyzed and the thermodynamics of the reaction is reported. In the CTAB micelle(cCTAB=8.36×10-3 mol•L-1) and 303 K, the changes of standard free energy, enthalpy and entropy of the reaction(ΔGΘ, ΔHΘ and ΔSΘ) are －17.28 kJ•mol-1, 84.1 kJ•mol-1 and 335 J•mol-1•K-1 respectively.
The influence of n-hexadecyltrimethylammoniumbromide (CTAB) on the reaction between cobalt tetrasulphonated phthalocyanine (CoTsPc) and sodium sulfide has been investigated. The result shows that in the presence of the micelles, cobalt tetrasulphonated phthalocyanine can be reduced by sodium sulfide at pH 8.5~9.5 to forms the corresponding Co(I) complex. The mechanism of the reaction is also discussed. Using the method of multi-wavelength and double-parameter, UV-Vis spectra of the system are analyzed and the thermodynamics of the reaction is reported. In the CTAB micelle(cCTAB=8.36×10-3 mol•L-1) and 303 K, the changes of standard free energy, enthalpy and entropy of the reaction(ΔGΘ, ΔHΘ and ΔSΘ) are －17.28 kJ•mol-1, 84.1 kJ•mol-1 and 335 J•mol-1•K-1 respectively.
2005, 21(07): 769-773
doi: 10.3866/PKU.WHXB20050714
Abstract:
Boric acid is used as a flux and reactant to synthesize a novel hydrated rare earth polyborate, La[B5O8(OH)(H2O)]NO3•2H2O. The structure of the title compound is established by single X-ray diffraction data. It crystallizes in monoclinic structures (P21/n) and consists of a double three-membered ring composed of three BO4 and two BO3 groups as the fundamental building block (FBB). The FBB shares four common oxygen atoms with thethe adjacent FBBs producing a borate layer containing nine-membered borate ring window. Lanthanum cations are located around the center of the nine-membered ring. The borate layers are stacked along the b axis and are interlinked by the La－O bond. Nitrate ions and some water molecules are sandwiched between the borate layers. This study further demonstrates that the low temperature synthesis approach by using molten boric acid as a flux is effective for the syntheses of hydrated rare earth polyborates.
Boric acid is used as a flux and reactant to synthesize a novel hydrated rare earth polyborate, La[B5O8(OH)(H2O)]NO3•2H2O. The structure of the title compound is established by single X-ray diffraction data. It crystallizes in monoclinic structures (P21/n) and consists of a double three-membered ring composed of three BO4 and two BO3 groups as the fundamental building block (FBB). The FBB shares four common oxygen atoms with thethe adjacent FBBs producing a borate layer containing nine-membered borate ring window. Lanthanum cations are located around the center of the nine-membered ring. The borate layers are stacked along the b axis and are interlinked by the La－O bond. Nitrate ions and some water molecules are sandwiched between the borate layers. This study further demonstrates that the low temperature synthesis approach by using molten boric acid as a flux is effective for the syntheses of hydrated rare earth polyborates.
2005, 21(07): 774-781
doi: 10.3866/PKU.WHXB20050715
Abstract:
The results of X-ray diffraction of single crystal D- and L-alanine at 300, 270, 250 K and neutron diffraction of D-alanine at 300, 260, 250, 240 K were presented to look for the static and dynamical structure feature of Salam phase transition. No change in the space group P212121 symmetry was observed. The data rule out the hypothesis of a conventional structural phase transition and reveal a subtle and continuous symmetry breaking that occurs below ~250 K. A vibrationally generated electronic ring current model was explained the temperature effect on magnetic susceptibilities and opposite optical rotation phenomena related to the bond lengths of αC－H(2), N(1)－H(1), N(1)－H(4), and N(1)－H(6) lengthening (or contraction). A picture of dynamic disorder due to the protonic motion was presented in the intermolecular hydrogen bonds between the NH3+ group and the CO2－ group. Salam predicted the enhancement of parity-violating energy difference (PVED) due to temperature-induced phase transition. Tunneling dynamics of amino acids with PVED may provide a bifurcation mechanism for much faster development of homochirality.
The results of X-ray diffraction of single crystal D- and L-alanine at 300, 270, 250 K and neutron diffraction of D-alanine at 300, 260, 250, 240 K were presented to look for the static and dynamical structure feature of Salam phase transition. No change in the space group P212121 symmetry was observed. The data rule out the hypothesis of a conventional structural phase transition and reveal a subtle and continuous symmetry breaking that occurs below ~250 K. A vibrationally generated electronic ring current model was explained the temperature effect on magnetic susceptibilities and opposite optical rotation phenomena related to the bond lengths of αC－H(2), N(1)－H(1), N(1)－H(4), and N(1)－H(6) lengthening (or contraction). A picture of dynamic disorder due to the protonic motion was presented in the intermolecular hydrogen bonds between the NH3+ group and the CO2－ group. Salam predicted the enhancement of parity-violating energy difference (PVED) due to temperature-induced phase transition. Tunneling dynamics of amino acids with PVED may provide a bifurcation mechanism for much faster development of homochirality.
2005, 21(07): 782-785
doi: 10.3866/PKU.WHXB20050716
Abstract:
The lithium ion conductor Li1.3Ti1.7Al0.3(PO4)3 is a NASICON structural functional material, which has very high selectivity of ion exchange for Na+. The effects of temperature on Na/Li ion exchange reaction for the Li1.3Ti1.7Al0.3(PO4)3 in sodium chloride and lithium chloride solutions were investigated. The experimental results show that the Na/Li ion exchange reaction rate increases obviously for Li1.3Ti1.7Al0.3(PO4)3 with increasing temperature in the same infiltration time, and the Li1.3Ti1.7Al0.3(PO4)3 is very effective to separate sodium impurity from lithium chloride solution.
The lithium ion conductor Li1.3Ti1.7Al0.3(PO4)3 is a NASICON structural functional material, which has very high selectivity of ion exchange for Na+. The effects of temperature on Na/Li ion exchange reaction for the Li1.3Ti1.7Al0.3(PO4)3 in sodium chloride and lithium chloride solutions were investigated. The experimental results show that the Na/Li ion exchange reaction rate increases obviously for Li1.3Ti1.7Al0.3(PO4)3 with increasing temperature in the same infiltration time, and the Li1.3Ti1.7Al0.3(PO4)3 is very effective to separate sodium impurity from lithium chloride solution.
2005, 21(07): 786-791
doi: 10.3866/PKU.WHXB20050717
Abstract:
Phenolic resin based activated carbon fibers (ACF-H2O) prepared using steam activation at 800 ℃ were investigated by means of N2 adsorption, AC impedance and constant current discharge techniques. The relationship between the specific surface area and pore size distribution of ACF-H2O with their electrochemical performance as electrodes of electric double layer capacitors (EDLC) in 1 mol•L-1 LiClO4/PC was discussed in detail. It is found that the ultramicropores(d ＜ 0.7 nm＝ cannot be accessed by electrolyte solution. With increasing steam activation time, the specific surface area and pore volume increase gradually, whereas the micropore (2.0 nm＞ d ＞ 0.7 nm ) and meso-pore ratios change little due to the deepening and broadening of the micropore formed during carbonization. However, excessive activation destroyed the pore structure, causing a sharp decrease of both specific surface area and pore volume. For those samples with well-developed pore structure, there is a linear relationship between capacitance and specific surface area (C－S), and a maximum specific capacitance of 109.6 F•g-1 was achieved. The double layer capacitance per unit surface area is not the same for all porous surface, and the capacitances of 8.44 μF•cm-2 and 4.29 μF•cm-2 are obtained, for the micropore and mesopore surfaces respectively. The double layer capacitance and AC impedance data strongly depend on the porous structure, the bigger the pore, the easier and faster being accessed electrochemically, the less the time constant and resistance should be, and it can be discharged/charged at higher current density. ACF with larger pore surface and less ultramicropore is desirable for those applications either as energy devices or as power storage devices. Steam activation can only obtain carbon materials with small mesopore, thus the higher electrochemical behavior attainable in EDLC using non-aqueous electrolyte is restricted.
Phenolic resin based activated carbon fibers (ACF-H2O) prepared using steam activation at 800 ℃ were investigated by means of N2 adsorption, AC impedance and constant current discharge techniques. The relationship between the specific surface area and pore size distribution of ACF-H2O with their electrochemical performance as electrodes of electric double layer capacitors (EDLC) in 1 mol•L-1 LiClO4/PC was discussed in detail. It is found that the ultramicropores(d ＜ 0.7 nm＝ cannot be accessed by electrolyte solution. With increasing steam activation time, the specific surface area and pore volume increase gradually, whereas the micropore (2.0 nm＞ d ＞ 0.7 nm ) and meso-pore ratios change little due to the deepening and broadening of the micropore formed during carbonization. However, excessive activation destroyed the pore structure, causing a sharp decrease of both specific surface area and pore volume. For those samples with well-developed pore structure, there is a linear relationship between capacitance and specific surface area (C－S), and a maximum specific capacitance of 109.6 F•g-1 was achieved. The double layer capacitance per unit surface area is not the same for all porous surface, and the capacitances of 8.44 μF•cm-2 and 4.29 μF•cm-2 are obtained, for the micropore and mesopore surfaces respectively. The double layer capacitance and AC impedance data strongly depend on the porous structure, the bigger the pore, the easier and faster being accessed electrochemically, the less the time constant and resistance should be, and it can be discharged/charged at higher current density. ACF with larger pore surface and less ultramicropore is desirable for those applications either as energy devices or as power storage devices. Steam activation can only obtain carbon materials with small mesopore, thus the higher electrochemical behavior attainable in EDLC using non-aqueous electrolyte is restricted.
2005, 21(07): 792-795
doi: 10.3866/PKU.WHXB20050718
Abstract:
The binding reaction between cefodizime sodium (CDZM) and bovine serum albumin (BSA) in aqueous solution was studied by fluorescence spectra. The binding constant KA was found to be 5.31×104 and the binding sits n to be 0.94 at 299 K by fluorescence quenching method. The quenching mechanism of fluorescence of BSA by cefodizime sodium has been discussed. The thermodynamic parameters of binding reaction were determined as follows： the molar change of enthalpy ΔrHm=－15.8 kJ•mol-1, the molar change of Gibbs function ΔrGm=－27.0 kJ•mol-1 and the molar change of entropy ΔrSm=－90.0 J•K-1•mol-1, and the binding power between cefodizime sodium and bovine serum albumin has been considered. Furthermore, the binding distance (r=3.13 nm) between cefodizime sodium and bovine serum albumin was obtained according to the theory of Föster′s dipile-dipile non-radiation energy transfer mechanism, and the effect of cefodizime sodium on the conformation of bovine serum albumin was analyzed using synchronous fluorescence spectrometry.
The binding reaction between cefodizime sodium (CDZM) and bovine serum albumin (BSA) in aqueous solution was studied by fluorescence spectra. The binding constant KA was found to be 5.31×104 and the binding sits n to be 0.94 at 299 K by fluorescence quenching method. The quenching mechanism of fluorescence of BSA by cefodizime sodium has been discussed. The thermodynamic parameters of binding reaction were determined as follows： the molar change of enthalpy ΔrHm=－15.8 kJ•mol-1, the molar change of Gibbs function ΔrGm=－27.0 kJ•mol-1 and the molar change of entropy ΔrSm=－90.0 J•K-1•mol-1, and the binding power between cefodizime sodium and bovine serum albumin has been considered. Furthermore, the binding distance (r=3.13 nm) between cefodizime sodium and bovine serum albumin was obtained according to the theory of Föster′s dipile-dipile non-radiation energy transfer mechanism, and the effect of cefodizime sodium on the conformation of bovine serum albumin was analyzed using synchronous fluorescence spectrometry.
2005, 21(07): 796-799
doi: 10.3866/PKU.WHXB20050719
Abstract:
Ordered hexa nal mesoporous silica (HMS) and Al-containing hexa nal silica (AlSBA) are prepared directly from sepiolite using leaching and sequent template synthesis. The structure, surface acidity, and specific surface area of mesoporous materials are investigated by means of SAXRD, TPD, and BET adsorption methods. Mesoporous materials with features of HMS are prepared after the sepiolite is treated by 5 mol•L-1 HCl acid solution and then kept in NaOH solution at 120 ℃ for 72 h. The ordered organization of materials improves with the formation of the AlSBA framework when modified-sepiolite is treated with NaAlO2 solution. Specific surface areas of HMS and AlSBA are 508 m2•g-1 and 946 m2•g-1, and the pore sizes are 3.4 nm and 3.9 nm, respectively. NH3-TPD results show that two acid centers appear on AlSBA and HMS surfaces, and the acidity and acid strength of acid centers in AlSBA are stronger than that of corresponding acidic centers in the HMS mesoporous materials.
Ordered hexa nal mesoporous silica (HMS) and Al-containing hexa nal silica (AlSBA) are prepared directly from sepiolite using leaching and sequent template synthesis. The structure, surface acidity, and specific surface area of mesoporous materials are investigated by means of SAXRD, TPD, and BET adsorption methods. Mesoporous materials with features of HMS are prepared after the sepiolite is treated by 5 mol•L-1 HCl acid solution and then kept in NaOH solution at 120 ℃ for 72 h. The ordered organization of materials improves with the formation of the AlSBA framework when modified-sepiolite is treated with NaAlO2 solution. Specific surface areas of HMS and AlSBA are 508 m2•g-1 and 946 m2•g-1, and the pore sizes are 3.4 nm and 3.9 nm, respectively. NH3-TPD results show that two acid centers appear on AlSBA and HMS surfaces, and the acidity and acid strength of acid centers in AlSBA are stronger than that of corresponding acidic centers in the HMS mesoporous materials.
2005, 21(07): 800-803
doi: 10.3866/PKU.WHXB20050720
Abstract:
A selective pseudoreceptor models for the inhibitors at GABA receptors of fly and rat were built via Flarm program. The pseudoreceptor models simulated the receptors very well and had od predicting ability. The q2 values of the training sets were 0.874 and 0.897, and the r2 values of the predict sets were 0.962 and 0.733. The Flarm models predicted that there are five binding sites when the compounds bind with GABA receptors, but there might be some different favoritism between the GABA receptors of fly and rat. The results were in accordance with pharmacorphore models built in previous research, and all the results gave insight to find the relations and differences between the inhibitors acting on the GABA receptor of fly and rat.
A selective pseudoreceptor models for the inhibitors at GABA receptors of fly and rat were built via Flarm program. The pseudoreceptor models simulated the receptors very well and had od predicting ability. The q2 values of the training sets were 0.874 and 0.897, and the r2 values of the predict sets were 0.962 and 0.733. The Flarm models predicted that there are five binding sites when the compounds bind with GABA receptors, but there might be some different favoritism between the GABA receptors of fly and rat. The results were in accordance with pharmacorphore models built in previous research, and all the results gave insight to find the relations and differences between the inhibitors acting on the GABA receptor of fly and rat.
2005, 21(07): 804-807
doi: 10.3866/PKU.WHXB20050721
Abstract:
Electrooxidation behavior of ethylene glycol (EG) at the Pt-WO3//C and Pt/C electrodes was investigated using cyclic voltammogram(CV) and linear sweeping voltammogram(LSV) techniques. It was found that the electrocatalytic activity of the Pt-WO3//C electrode for electrooxidation of EG was higher than that of the Pt/C electrode. The higher electrocatalytic activity of the Pt-WO3//C was due to that WO3/ could supply the oxygen-containingspecies necessary for the electrooxidation of EG, and WO3/ could reduce the adsorption intensity of CO at Pt, which was an intermediate of the electrooxidation of EG.
Electrooxidation behavior of ethylene glycol (EG) at the Pt-WO3//C and Pt/C electrodes was investigated using cyclic voltammogram(CV) and linear sweeping voltammogram(LSV) techniques. It was found that the electrocatalytic activity of the Pt-WO3//C electrode for electrooxidation of EG was higher than that of the Pt/C electrode. The higher electrocatalytic activity of the Pt-WO3//C was due to that WO3/ could supply the oxygen-containingspecies necessary for the electrooxidation of EG, and WO3/ could reduce the adsorption intensity of CO at Pt, which was an intermediate of the electrooxidation of EG.
2005, 21(07): 808-812
doi: 10.3866/PKU.WHXB20050722
Abstract:
Adsorption of a divalent quaternary ammonium named molecular deposition film flooding agent (MDFFA) on clay was studied. It is characterized by its surface non-activity. Two source clays were selected： montmorillonite (Su-M) and bentonite (B), and their cation exchange capacities (CEC) are 0.44 and 0.88 mmol•g-1 clay, respectively. At low ionic strength, all cations were completely adsorbed on the clay. Besides, the absorbed amounts of MDFFA on Su-M reach 100% of the CEC, while the absorbed amounts of MDFFA on B only reach 77% of the CEC. From FT-IR spectra, we deduced that the MDFFA only binds to the electronegative adsorption sites and does not bind to the external Si－OH groups which act as neutral adsorption sites. XRD data show that the basal spacings of the two kinds of clay decreased slightly with added amount of MDFFA. Based on the theoretical size of molecules, we think that only horizontal monolayer of MDFFA exists in clay interlayer.
Adsorption of a divalent quaternary ammonium named molecular deposition film flooding agent (MDFFA) on clay was studied. It is characterized by its surface non-activity. Two source clays were selected： montmorillonite (Su-M) and bentonite (B), and their cation exchange capacities (CEC) are 0.44 and 0.88 mmol•g-1 clay, respectively. At low ionic strength, all cations were completely adsorbed on the clay. Besides, the absorbed amounts of MDFFA on Su-M reach 100% of the CEC, while the absorbed amounts of MDFFA on B only reach 77% of the CEC. From FT-IR spectra, we deduced that the MDFFA only binds to the electronegative adsorption sites and does not bind to the external Si－OH groups which act as neutral adsorption sites. XRD data show that the basal spacings of the two kinds of clay decreased slightly with added amount of MDFFA. Based on the theoretical size of molecules, we think that only horizontal monolayer of MDFFA exists in clay interlayer.
2005, 21(07): 813-816
doi: 10.3866/PKU.WHXB20050723
Abstract:
The tricritical phenomena of quasi-ternary solutions of H2O＋formamide(FA)＋cyclohexane＋diethylene glycol monobutyl ether have been studied by measurements of the volume ratios of the coexisting phases for a series of solutions with various overall compositions at various temperatures. Taking (H2O＋FA) as a quasi “pure” component, the mass fraction FA in the quasi “pure” component controlled the approach to the tricritical point. As the mass fraction increased from 0 to 0.206, the ΔT of the three-phase region reduced from 1.500 ℃ to 0.228 ℃. By extrapolation of the experimental data, the tricritical mass fraction of FA in the quasi “pure” component and the tricritical temperature were obtained to be 0.286±0.003 and (54.8±0.69) ℃, respectively. It was found that the water-oil sides of three-phase triangles at the middle temperatures of the three-phase regions were almost parallel to the water-oil sides of the triangle coordinates. The dependences of lengths of the water-oil side of the three-phase triangle and the corresponding altitude to the water-oil side on ΔT were consistent with the classical theory.
The tricritical phenomena of quasi-ternary solutions of H2O＋formamide(FA)＋cyclohexane＋diethylene glycol monobutyl ether have been studied by measurements of the volume ratios of the coexisting phases for a series of solutions with various overall compositions at various temperatures. Taking (H2O＋FA) as a quasi “pure” component, the mass fraction FA in the quasi “pure” component controlled the approach to the tricritical point. As the mass fraction increased from 0 to 0.206, the ΔT of the three-phase region reduced from 1.500 ℃ to 0.228 ℃. By extrapolation of the experimental data, the tricritical mass fraction of FA in the quasi “pure” component and the tricritical temperature were obtained to be 0.286±0.003 and (54.8±0.69) ℃, respectively. It was found that the water-oil sides of three-phase triangles at the middle temperatures of the three-phase regions were almost parallel to the water-oil sides of the triangle coordinates. The dependences of lengths of the water-oil side of the three-phase triangle and the corresponding altitude to the water-oil side on ΔT were consistent with the classical theory.
2005, 21(07): 817-821
doi: 10.3866/PKU.WHXB20050724
Abstract:
A novel magnetorheological (MR) suspension is based on the mixture of poly(ethylene glycol)-coated carbonyl iron particles, prepared by the co-sol-gel reaction using carbonyl iron particles as raw materials, and water without any additive. The microstructure, magnetic and magnetorheological properties of the core-shell particles are characterized by SEM、TEM、FT-IR、VSM. The results show that the particles prepared have core-shell structure with a polymer shell of less than 100 nm; both the core-shell particles and its water based MR suspension exhibit excellent soft magnetic performance; the water based MR suspension shows low zero viscosity and high MR effects, especially greatly improved anti-settlement and redispersibility. The phenomena are attributed to the hydrophilic thin shell of the core-shell particles.
A novel magnetorheological (MR) suspension is based on the mixture of poly(ethylene glycol)-coated carbonyl iron particles, prepared by the co-sol-gel reaction using carbonyl iron particles as raw materials, and water without any additive. The microstructure, magnetic and magnetorheological properties of the core-shell particles are characterized by SEM、TEM、FT-IR、VSM. The results show that the particles prepared have core-shell structure with a polymer shell of less than 100 nm; both the core-shell particles and its water based MR suspension exhibit excellent soft magnetic performance; the water based MR suspension shows low zero viscosity and high MR effects, especially greatly improved anti-settlement and redispersibility. The phenomena are attributed to the hydrophilic thin shell of the core-shell particles.
2005, 21(07): 822-824
doi: 10.3866/PKU.WHXB20050725
Abstract:
Carbon nanotubes can vertically grow in the nanopores of AAO template. However, when out nanopores, carbon nanotubes are no longer aligned and become bended, and their film surface is not even. So, their application is heavily limited. In order to get aligned carbon film with even surface, the carbon nanotube film was switched the bottom and top by transferring them to other substrate. The even surface that can provide working surface in the application of carbon nanotube film was obtained by disposal of aluminum and alumina oxide gradually. The disposal results of alumina by 5% NaOH and 6%H3PO4＋1.8%H2CrO4 were compared
Carbon nanotubes can vertically grow in the nanopores of AAO template. However, when out nanopores, carbon nanotubes are no longer aligned and become bended, and their film surface is not even. So, their application is heavily limited. In order to get aligned carbon film with even surface, the carbon nanotube film was switched the bottom and top by transferring them to other substrate. The even surface that can provide working surface in the application of carbon nanotube film was obtained by disposal of aluminum and alumina oxide gradually. The disposal results of alumina by 5% NaOH and 6%H3PO4＋1.8%H2CrO4 were compared
