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2005 Volume 21 Issue 10
2005, 21(10): 1067-1072
doi: 10.3866/PKU.WHXB20051001
Abstract:
The electrochemical behavior of ferrocene (Fc) and its interaction with calf thymus DNA at a rotating disk electrode modified with carbon nanotube (CNT) in Tris-NaCl buffer solution (pH=7.2) have been investigated by using cyclic voltammetry, differential pulse voltammetry, rotating disk electrode measurement, and electrochemical impedance spectrum. It is found that a pair of reversible redox waves for Fc are exhibited in the absence and presence of DNA on the immovable CNT-modified electrode. When the modified electrode is rotating, a distinct limiting diffusion current appears. Nyquist plot of Fc shows a suppressed half-circle in the absence and presence of DNA on the rotating CNT-modified electrode. Moreover, there exists an interaction of Fc with DNA under diffusion control based on the decrease of the peak current and limiting diffusion current with the increase of DNA concentration. On the other hand, the interaction between Fc and DNA under electrochemical control is also studied, the results show that the electrochemical reaction resistance of Fc exhibiting on the rotating disk electrode increases with the addition of DNA, and the rate constant at the formal potential decreases in the presence of DNA compared with that in the absence of DNA.
The electrochemical behavior of ferrocene (Fc) and its interaction with calf thymus DNA at a rotating disk electrode modified with carbon nanotube (CNT) in Tris-NaCl buffer solution (pH=7.2) have been investigated by using cyclic voltammetry, differential pulse voltammetry, rotating disk electrode measurement, and electrochemical impedance spectrum. It is found that a pair of reversible redox waves for Fc are exhibited in the absence and presence of DNA on the immovable CNT-modified electrode. When the modified electrode is rotating, a distinct limiting diffusion current appears. Nyquist plot of Fc shows a suppressed half-circle in the absence and presence of DNA on the rotating CNT-modified electrode. Moreover, there exists an interaction of Fc with DNA under diffusion control based on the decrease of the peak current and limiting diffusion current with the increase of DNA concentration. On the other hand, the interaction between Fc and DNA under electrochemical control is also studied, the results show that the electrochemical reaction resistance of Fc exhibiting on the rotating disk electrode increases with the addition of DNA, and the rate constant at the formal potential decreases in the presence of DNA compared with that in the absence of DNA.
2005, 21(10): 1073-1075
doi: 10.3866/PKU.WHXB20051002
Abstract:
Ag/TCNQ bi-layer films with different thicknesses were prepared on glass substrate by successive vacuum deposition of Ag and TCNQ. Ag-TCNQ complex was formed by the solid transport of Ag in the films. The transport behavior of Ag in the thin films was studied using optical transmittance spectra. The transport coefficients(k) were obtained and the activation energy was calculated between 60 and 110 ℃. The results show that the transport distance (x) and transport time (t) accord with parabola law (x2=2kt). The transport coefficient k and the activation energy Q could be expressed by k=k0exp(－Q/RT)=5.62×10－6 exp(－0.53/RT). And the diffusion mechanism was discussed, which was believed to be interstitialcy mechanism.
Ag/TCNQ bi-layer films with different thicknesses were prepared on glass substrate by successive vacuum deposition of Ag and TCNQ. Ag-TCNQ complex was formed by the solid transport of Ag in the films. The transport behavior of Ag in the thin films was studied using optical transmittance spectra. The transport coefficients(k) were obtained and the activation energy was calculated between 60 and 110 ℃. The results show that the transport distance (x) and transport time (t) accord with parabola law (x2=2kt). The transport coefficient k and the activation energy Q could be expressed by k=k0exp(－Q/RT)=5.62×10－6 exp(－0.53/RT). And the diffusion mechanism was discussed, which was believed to be interstitialcy mechanism.
2005, 21(10): 1076-1080
doi: 10.3866/PKU.WHXB20051003
Abstract:
Transition element (Mn, Cr, Cu) substituted titanate nanotubes were fabricated by a simple method, i.e., hydrothermal method. The precursors used were Mn, Cr and Cu doped anatase TiO2 nanopowders, which were 20～30 nm in diameter. The obtained samples were characterized by SEM, TEM, XRD, EDX, PL and Raman spectra. The results show that the fluorescence-emission intensity of the substituted titanate nanotubes decreases to some extent with the substitution of metal ions. It is generally considered that the low recombination efficiency of the electron-holes means the high quantum efficiency of the photons. So the results show that the transition element substituted titanate nanotubes might be applied in the photocatalysis.
Transition element (Mn, Cr, Cu) substituted titanate nanotubes were fabricated by a simple method, i.e., hydrothermal method. The precursors used were Mn, Cr and Cu doped anatase TiO2 nanopowders, which were 20～30 nm in diameter. The obtained samples were characterized by SEM, TEM, XRD, EDX, PL and Raman spectra. The results show that the fluorescence-emission intensity of the substituted titanate nanotubes decreases to some extent with the substitution of metal ions. It is generally considered that the low recombination efficiency of the electron-holes means the high quantum efficiency of the photons. So the results show that the transition element substituted titanate nanotubes might be applied in the photocatalysis.
2005, 21(10): 1081-1085
doi: 10.3866/PKU.WHXB20051004
Abstract:
Nanoparticles of titanium dioxide doped with nitrogen (N-TiO2) were synthesized using sol-gel method. Nano-TiO2 codoped with platinum and nitrogen (Pt/N-TiO2) was prepared by photolysis-deposition of H2PtCl6 on N-TiO2 (0.5% (w) Pt). The onset of the absorption spectrum of Pt/N-TiO2 has a 20 nm red-shift and a weak absorption in the wavelength region from 400 to 500 nm compared with the spectrum of the non- doped catalyst. The photocurrent of Pt/N-TiO2 electrode is five times higher than that of TiO2 electrode. The photodegradation yield of trichloroacetic acid over Pt/N-TiO2 catalyst is 8% under visible light irradiation for 2 ｈ. Doping nitrogen in TiO2 reduces the band gap of anatase, which makes N-TiO2 possess catalytic activity in visible light region. Pt clusters precipitated on nano-TiO2 may retard the recombination of the photo-exited charge carriers and improve interfacial charge transfer. Pt/N-TiO2 catalyst benefited from both of the effects.
Nanoparticles of titanium dioxide doped with nitrogen (N-TiO2) were synthesized using sol-gel method. Nano-TiO2 codoped with platinum and nitrogen (Pt/N-TiO2) was prepared by photolysis-deposition of H2PtCl6 on N-TiO2 (0.5% (w) Pt). The onset of the absorption spectrum of Pt/N-TiO2 has a 20 nm red-shift and a weak absorption in the wavelength region from 400 to 500 nm compared with the spectrum of the non- doped catalyst. The photocurrent of Pt/N-TiO2 electrode is five times higher than that of TiO2 electrode. The photodegradation yield of trichloroacetic acid over Pt/N-TiO2 catalyst is 8% under visible light irradiation for 2 ｈ. Doping nitrogen in TiO2 reduces the band gap of anatase, which makes N-TiO2 possess catalytic activity in visible light region. Pt clusters precipitated on nano-TiO2 may retard the recombination of the photo-exited charge carriers and improve interfacial charge transfer. Pt/N-TiO2 catalyst benefited from both of the effects.
2005, 21(10): 1086-1090
doi: 10.3866/PKU.WHXB20051005
Abstract:
The surface atomic geometry, structural relaxations, and electronic states of clean Cu(110) surface and oxygen-adsorbed Cu(110) c(2×1) surface have been studied by using ab initio total energy calculations. The density functional calculations have been carried out for three possible adsorbed positions of oxygen and the most favorable one has been determined by total energy comparison. It reveals that the added-row reconstruction is the most stable one with maximum adsorption energy in Cu(110) c(2×1) surface and the adsorbed oxygen atom is beyond the outmost surface Cu layer slightly. The adsorbates lie approximately 0.016 nm above the outermost Cu layer and the hybridized band derived from Cu 3d-O 2p hybridization locates in the range of －5.5～－6.0 eV below Fermi energy. The adsorption energy of oxygen in this configuration is determined to be －1.94 eV with respect to oxygen molecule. The work functions of clean Cu(110) and oxygen-adsorbed Cu(110) c(2×1) surface are calculated to be 4.51 eV and 4.68 eV, respectively. The surface electronic structures show that the cohesive effect between adsorbates and the substrate Cu atoms is essentially due to the Cu 3d- O 2p interaction.
The surface atomic geometry, structural relaxations, and electronic states of clean Cu(110) surface and oxygen-adsorbed Cu(110) c(2×1) surface have been studied by using ab initio total energy calculations. The density functional calculations have been carried out for three possible adsorbed positions of oxygen and the most favorable one has been determined by total energy comparison. It reveals that the added-row reconstruction is the most stable one with maximum adsorption energy in Cu(110) c(2×1) surface and the adsorbed oxygen atom is beyond the outmost surface Cu layer slightly. The adsorbates lie approximately 0.016 nm above the outermost Cu layer and the hybridized band derived from Cu 3d-O 2p hybridization locates in the range of －5.5～－6.0 eV below Fermi energy. The adsorption energy of oxygen in this configuration is determined to be －1.94 eV with respect to oxygen molecule. The work functions of clean Cu(110) and oxygen-adsorbed Cu(110) c(2×1) surface are calculated to be 4.51 eV and 4.68 eV, respectively. The surface electronic structures show that the cohesive effect between adsorbates and the substrate Cu atoms is essentially due to the Cu 3d- O 2p interaction.
2005, 21(10): 1091-1095
doi: 10.3866/PKU.WHXB20051006
Abstract:
Two ternary complexes [Pd(bipy)(DL-gly)]Cl•2H2O(1) and [Pd(bipy)(L-lys)]Cl•H2O(2) were synthesized. The stability constants lgβ of two complexes are 13.81(1) and 13.71(2), respectively, and relative stability ΔlgK、lgX are higher than statistical value. The results show that there exists d-p π electronic effect in complexes．Intercalation of the complexes with DNA can be demonstrated by UV-Vis spectra and fluorescence spectra．The binding constsns of the two complexes with sperm DNA are 2.37×106(1) and 4.57×106(2), respectively. It shows that the interaction intensity is 1＜2. The CD spectra also show that the tow complexes were reacted with DNA．The results of gel electrophoresis experiments reveal that plasmid pBR322 DNA was cleaved by the two complexes when complex concentration ranges from 3.00×10-3 to 7.50×10-4 mol •L-1, whereas insertion is main binding model when complex concentration is lower than 3.75×10-4 mol •L-1.
Two ternary complexes [Pd(bipy)(DL-gly)]Cl•2H2O(1) and [Pd(bipy)(L-lys)]Cl•H2O(2) were synthesized. The stability constants lgβ of two complexes are 13.81(1) and 13.71(2), respectively, and relative stability ΔlgK、lgX are higher than statistical value. The results show that there exists d-p π electronic effect in complexes．Intercalation of the complexes with DNA can be demonstrated by UV-Vis spectra and fluorescence spectra．The binding constsns of the two complexes with sperm DNA are 2.37×106(1) and 4.57×106(2), respectively. It shows that the interaction intensity is 1＜2. The CD spectra also show that the tow complexes were reacted with DNA．The results of gel electrophoresis experiments reveal that plasmid pBR322 DNA was cleaved by the two complexes when complex concentration ranges from 3.00×10-3 to 7.50×10-4 mol •L-1, whereas insertion is main binding model when complex concentration is lower than 3.75×10-4 mol •L-1.
2005, 21(10): 1096-1101
doi: 10.3866/PKU.WHXB20051007
Abstract:
The adsorption behavior of imidazoline amide as a cationic inhibitor for inhibiting galvanic corrosion has been investigated by using electrochemical methods and atomic force microscopy (AFM) technology. The results show that the adsorption behavior of the inhibitor is significantly affected by the excess charge on the metal surface. Carbon steel and stainless steel carry negative and positive excess charges when they are immersed in 1% NaCl solution, respectively. The inhibitor adsorbs on the surface of carbon steel, while it does not adsorb on the surface of stainless steel in aqueous NaCl solution. When the two metals are electrically coupled in NaCl solution, positive and negative excess charges are carried on the carbon steel and the stainless steel, respectively. The inhibitor can adsorb on the surfaces of both carbon steel and stainless steel. However, in this case, the surface coverage of the inhibitor film formed on the carbon steel decreases compared with that on the surface of single carbon steel, and the adsorbability of the inhibitor on the surface of carbon steel is weakened.
The adsorption behavior of imidazoline amide as a cationic inhibitor for inhibiting galvanic corrosion has been investigated by using electrochemical methods and atomic force microscopy (AFM) technology. The results show that the adsorption behavior of the inhibitor is significantly affected by the excess charge on the metal surface. Carbon steel and stainless steel carry negative and positive excess charges when they are immersed in 1% NaCl solution, respectively. The inhibitor adsorbs on the surface of carbon steel, while it does not adsorb on the surface of stainless steel in aqueous NaCl solution. When the two metals are electrically coupled in NaCl solution, positive and negative excess charges are carried on the carbon steel and the stainless steel, respectively. The inhibitor can adsorb on the surfaces of both carbon steel and stainless steel. However, in this case, the surface coverage of the inhibitor film formed on the carbon steel decreases compared with that on the surface of single carbon steel, and the adsorbability of the inhibitor on the surface of carbon steel is weakened.
2005, 21(10): 1102-1107
doi: 10.3866/PKU.WHXB20051008
Abstract:
The reaction of Sc+ or Ti+ with CS2, which was selected as a representative system of reactions of first early transition-metal ions with CS2. The reaction mechanism of Sc+ or Ti+ in ground state and excitated state with CS2 has been studied using the density functional theory (DFT) at B3LYP/6-311+G* level. The geometries for reactants, the transition states and the products were completely optimized. All the transition states were verified by the vibrational analysis and the intrinsic reaction coordinate (IRC) calculations. A potential energies curve-crossing diagram was investigated for state correlation between early intermediate IM1 and reactants in the reaction of Sc+，Ti+ with CS2. The result showed that the reaction mechanism between first early transition-metal ions and CS2 was an insertion-elimination mechanism. The main reaction path channel was detected in the reaction of Sc+ or Ti+ ground state and excitated state with CS2.
The reaction of Sc+ or Ti+ with CS2, which was selected as a representative system of reactions of first early transition-metal ions with CS2. The reaction mechanism of Sc+ or Ti+ in ground state and excitated state with CS2 has been studied using the density functional theory (DFT) at B3LYP/6-311+G* level. The geometries for reactants, the transition states and the products were completely optimized. All the transition states were verified by the vibrational analysis and the intrinsic reaction coordinate (IRC) calculations. A potential energies curve-crossing diagram was investigated for state correlation between early intermediate IM1 and reactants in the reaction of Sc+，Ti+ with CS2. The result showed that the reaction mechanism between first early transition-metal ions and CS2 was an insertion-elimination mechanism. The main reaction path channel was detected in the reaction of Sc+ or Ti+ ground state and excitated state with CS2.
2005, 21(10): 1108-1112
doi: 10.3866/PKU.WHXB20051009
Abstract:
The noner dic behavior of κ-carrageenan(KC) thermoreversible gel was studied by static/dynamic light scattering (SLS/DLS). The speckle patterns, measured by SLS, appear in gel state of KC, which proves the noner dic behavior of KC gel. Then the influences of temperature and concentration of KC solution on the noner dic behavior were investigated. The results reveal that the noner dic behavior of KC solution enhances with increasing of concentration, and weakens with increasing of temperature. Moreover, noner dic behavior disappears when the temperature is higher than the one at which the transition from helix to coil conformation can be performed. The electrical field correlation function obtained by DLS shows that the gel state of KC possesses a power law behavior but the solution state of KC bears a stretched exponential behavior.
The noner dic behavior of κ-carrageenan(KC) thermoreversible gel was studied by static/dynamic light scattering (SLS/DLS). The speckle patterns, measured by SLS, appear in gel state of KC, which proves the noner dic behavior of KC gel. Then the influences of temperature and concentration of KC solution on the noner dic behavior were investigated. The results reveal that the noner dic behavior of KC solution enhances with increasing of concentration, and weakens with increasing of temperature. Moreover, noner dic behavior disappears when the temperature is higher than the one at which the transition from helix to coil conformation can be performed. The electrical field correlation function obtained by DLS shows that the gel state of KC possesses a power law behavior but the solution state of KC bears a stretched exponential behavior.
2005, 21(10): 1113-1116
doi: 10.3866/PKU.WHXB20051010
Abstract:
The photoionization of acetonitrile seeded in helium is studied by time- of- flight mass spectrometry using a 25 ns, 1064 nm Nd：YAG laser with intensity near 1011 W•cm－２. Multiply charged ions of Nq+(q=1～5) and Cq+(q=1～4) with hundreds of eV have been observed under laser beam irradiation with the densest portion of the pulsed molecular beam. An electron re-scattering and re-colliding ionization model is proposed to explain the generation of those multiply charged clusters under such low laser intensity.
The photoionization of acetonitrile seeded in helium is studied by time- of- flight mass spectrometry using a 25 ns, 1064 nm Nd：YAG laser with intensity near 1011 W•cm－２. Multiply charged ions of Nq+(q=1～5) and Cq+(q=1～4) with hundreds of eV have been observed under laser beam irradiation with the densest portion of the pulsed molecular beam. An electron re-scattering and re-colliding ionization model is proposed to explain the generation of those multiply charged clusters under such low laser intensity.
2005, 21(10): 1117-1121
doi: 10.3866/PKU.WHXB20051011
Abstract:
Surface enhanced Raman spectroscopy (SERS) was employed to study the adsorption of 2,2′-bipyridine(2,2′-biPy) on an electrochemical roughened Zn electrode. The results suggested that 2,2′-biPy adsorbed on Zn electrode with relatively strong interaction. For a relative positive initial potential, the potential of the 2,2′-biPy adsorption was negatively moved because of the adsorption of Zinc oxide species, while at a relative negative potential, the adsorption of 2,2′-biPy blocked the adsorption of oxygen species, and thus the 2,2′-biPy and oxygen species exhibited a competitive adsorption on Zn electrode. Moreover, the adsorption configuration of 2,2′-biPy was dependent on the applied potential. It was adsorbed through cis conformation to the surface at －1.3 V, while through trans conformation at －1.4 V.
Surface enhanced Raman spectroscopy (SERS) was employed to study the adsorption of 2,2′-bipyridine(2,2′-biPy) on an electrochemical roughened Zn electrode. The results suggested that 2,2′-biPy adsorbed on Zn electrode with relatively strong interaction. For a relative positive initial potential, the potential of the 2,2′-biPy adsorption was negatively moved because of the adsorption of Zinc oxide species, while at a relative negative potential, the adsorption of 2,2′-biPy blocked the adsorption of oxygen species, and thus the 2,2′-biPy and oxygen species exhibited a competitive adsorption on Zn electrode. Moreover, the adsorption configuration of 2,2′-biPy was dependent on the applied potential. It was adsorbed through cis conformation to the surface at －1.3 V, while through trans conformation at －1.4 V.
2005, 21(10): 1122-1126
doi: 10.3866/PKU.WHXB20051012
Abstract:
The effect of Sm, Eu and Gd on electrical properties of a new class of polystalline ceramics based on TiO2 was investigated. The content of added Sm, Eu and Gd is 2% (atomic ratio), while that of the other addition is always maintained at a constant value. The disks were sintered at 1380 ℃ for 4 h. It was found that Sm, Eu and Gd can reduce the voltage values (corresponding to 1 mA current) of TiO2-based varistors effectively, but do not strongly influence the nonlinear values. The voltage values of the doped TiO2-based varistors were 12.7 V (Sm doped), 14.7 V (Eu doped) and 16.1 V (Gd doped). Through impedance analysis, it can be found that those rare-earth ions have great influence on the dielectric properties; the single addition of Sm or Gd could attain very low dielectric constant, low dissipation factor and very high resistivity. Sm, Eu and Gd distribute surrounding the TiO2 grains, but discontinuously.
The effect of Sm, Eu and Gd on electrical properties of a new class of polystalline ceramics based on TiO2 was investigated. The content of added Sm, Eu and Gd is 2% (atomic ratio), while that of the other addition is always maintained at a constant value. The disks were sintered at 1380 ℃ for 4 h. It was found that Sm, Eu and Gd can reduce the voltage values (corresponding to 1 mA current) of TiO2-based varistors effectively, but do not strongly influence the nonlinear values. The voltage values of the doped TiO2-based varistors were 12.7 V (Sm doped), 14.7 V (Eu doped) and 16.1 V (Gd doped). Through impedance analysis, it can be found that those rare-earth ions have great influence on the dielectric properties; the single addition of Sm or Gd could attain very low dielectric constant, low dissipation factor and very high resistivity. Sm, Eu and Gd distribute surrounding the TiO2 grains, but discontinuously.
2005, 21(10): 1127-1131
doi: 10.3866/PKU.WHXB20051013
Abstract:
Multi- walled carbon nanotube (CNT) arrays have been produced on silicon substrate by a one-step route based on the pyrolysis of mixture of ferrocene and melamine under well-chosen synthesis condition. Transmission electron microscope (TEM) and scanning electron microscope (SEM) studies showed the products were all multi-walled CNTs that are about 50 nm in diameter. X-ray photoelectron spectroscopy study revealed that the CNTs were nitrogen-doped. Field effect transistors (FETs) base on the nitrogen-doped MWCNT in an asymmetry- source/drain-electrodes configuration were further fabricated. And electrical transport measurements exhibited typical n-type behavior. The off-state current through the FETs is extremely low, about 100 pA in order. The asymmetry isolation layer between the source/drain electrodes and the gate used in the experiment results in asymmetric modulation of gate electrostatic field to source electrode and drain electrode. Therefore solo gate electrostatic field modulation to the drain electrode is realized.
Multi- walled carbon nanotube (CNT) arrays have been produced on silicon substrate by a one-step route based on the pyrolysis of mixture of ferrocene and melamine under well-chosen synthesis condition. Transmission electron microscope (TEM) and scanning electron microscope (SEM) studies showed the products were all multi-walled CNTs that are about 50 nm in diameter. X-ray photoelectron spectroscopy study revealed that the CNTs were nitrogen-doped. Field effect transistors (FETs) base on the nitrogen-doped MWCNT in an asymmetry- source/drain-electrodes configuration were further fabricated. And electrical transport measurements exhibited typical n-type behavior. The off-state current through the FETs is extremely low, about 100 pA in order. The asymmetry isolation layer between the source/drain electrodes and the gate used in the experiment results in asymmetric modulation of gate electrostatic field to source electrode and drain electrode. Therefore solo gate electrostatic field modulation to the drain electrode is realized.
2005, 21(10): 1132-1137
doi: 10.3866/PKU.WHXB20051014
Abstract:
PtMo/C electrocatalysts were prepared by three different preparation methods, namely 1) chemical reduction with oxalic acid, 2) colloidal precursor, and 3) Adams method respectively. TEM, XRD and CO-stripping in 0.5 mol•L-1 H2SO4 solution were performed to characterize the particle size distribution and electrocatalytic property of the prepared samples. PtMo particles from the colloidal preparation were ca. 5 nm in sizes and were well dispersed on the carbon support. The preparation by Adams method produced aggregated larger PtMo particles with sizes up to tens of nanometers. The sizes and morphology of PtMo particles from the chemical reduction method were found in between those from the colloidal preparation and the Adams method. The electro- oxidation of CO adsorbed on all of the three PtMo/C catalysts showed two distinct peaks, one at very low potential (ca. 0.15 V) and the other at a potential (ca. 0.77 V) very close to that over the conventional Pt/C catalyst. Moreover, the PtMo/C catalyst obtained from the colloidal preparation exhibited, among the three catalysts of this study, the highest electrocatalytic activity for the oxidation of CO. Although the electrochemical surface area of this PtMo/C catalyst was lower in comparison with the conventional PtRu/C catalyst, the removal percentage of CO at low oxidation potentials(0.15～0.50 V) was found to be much higher. Therefore, the presence of Mo component in the catalysts promoted the electro-oxidation of weakly adsorbed CO, whereas it showed little effect on the oxidation of strongly adsorbed CO.
PtMo/C electrocatalysts were prepared by three different preparation methods, namely 1) chemical reduction with oxalic acid, 2) colloidal precursor, and 3) Adams method respectively. TEM, XRD and CO-stripping in 0.5 mol•L-1 H2SO4 solution were performed to characterize the particle size distribution and electrocatalytic property of the prepared samples. PtMo particles from the colloidal preparation were ca. 5 nm in sizes and were well dispersed on the carbon support. The preparation by Adams method produced aggregated larger PtMo particles with sizes up to tens of nanometers. The sizes and morphology of PtMo particles from the chemical reduction method were found in between those from the colloidal preparation and the Adams method. The electro- oxidation of CO adsorbed on all of the three PtMo/C catalysts showed two distinct peaks, one at very low potential (ca. 0.15 V) and the other at a potential (ca. 0.77 V) very close to that over the conventional Pt/C catalyst. Moreover, the PtMo/C catalyst obtained from the colloidal preparation exhibited, among the three catalysts of this study, the highest electrocatalytic activity for the oxidation of CO. Although the electrochemical surface area of this PtMo/C catalyst was lower in comparison with the conventional PtRu/C catalyst, the removal percentage of CO at low oxidation potentials(0.15～0.50 V) was found to be much higher. Therefore, the presence of Mo component in the catalysts promoted the electro-oxidation of weakly adsorbed CO, whereas it showed little effect on the oxidation of strongly adsorbed CO.
2005, 21(10): 1138-1142
doi: 10.3866/PKU.WHXB20051015
Abstract:
The solubilities of five gases, CO2, N2, O2, Ar and CH4, in room temperature ionic liquids were studied by Widom test-particle insertion method. A number of 200000 insertions of the solute was decided. The solubility of CO2 in 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) obtained in this work is superior to that of Pádua et al. As for CO2 in 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), the result in this work is similar to previous studies. Furthermore, the solubilities of CO2 in [bmim][BF4] and [bmim][PF6] at high temperatures were predicted. The experimental relative solubility order for the 5 gases in [bmim][PF6] is reproduced by simulation. In addition, the solubility of 5 gases in different ionic liquids shows that it is bigger in ionic liquids with long alkyl chain or with bis((trifluoromethyl)sulfonyl) amide anion than in [bmim][BF4].
The solubilities of five gases, CO2, N2, O2, Ar and CH4, in room temperature ionic liquids were studied by Widom test-particle insertion method. A number of 200000 insertions of the solute was decided. The solubility of CO2 in 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) obtained in this work is superior to that of Pádua et al. As for CO2 in 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), the result in this work is similar to previous studies. Furthermore, the solubilities of CO2 in [bmim][BF4] and [bmim][PF6] at high temperatures were predicted. The experimental relative solubility order for the 5 gases in [bmim][PF6] is reproduced by simulation. In addition, the solubility of 5 gases in different ionic liquids shows that it is bigger in ionic liquids with long alkyl chain or with bis((trifluoromethyl)sulfonyl) amide anion than in [bmim][BF4].
2005, 21(10): 1143-1145
doi: 10.3866/PKU.WHXB20051016
Abstract:
The affinity fingerprint method was used to functionally classify proteins based on the binding data matrix produced by multiple-docking. The method has been applied to the classification of phospholipase A2 enzymes. Though many of the classifications are similar to those from sequence alignment, the human cPLA2 was successfully grouped with bee PLA2 based on the binding site similarity, which can not be handled by sequence alignment due to cPLA2′s low homology with other PLA2s.
The affinity fingerprint method was used to functionally classify proteins based on the binding data matrix produced by multiple-docking. The method has been applied to the classification of phospholipase A2 enzymes. Though many of the classifications are similar to those from sequence alignment, the human cPLA2 was successfully grouped with bee PLA2 based on the binding site similarity, which can not be handled by sequence alignment due to cPLA2′s low homology with other PLA2s.
2005, 21(10): 1146-1150
doi: 10.3866/PKU.WHXB20051017
Abstract:
A new method of surface modification on hydrogen storage alloy is investigated. The AB5 alloy of metal hydride electrode in MH/Ni battery is treated in the mixed solution of HF and CuSO4. The effects of HF content and copper particle deposition amount on surface modification reaction are studied. The performances of modified alloy are tested and electrochemical impedance spectroscopy (EIS) is applied to analyze the mechanism of treatment. The electrochemical testing results indicate that modified alloy has better rate capability and cycle stability. And the EIS analysis shows that surface modification increases the activity and electrical conductivity of the alloy, and greatly decreases its ohmic and electrochemical impedance, which helps to improve electrochemical properties of the battery. Therefore the modified alloy would well meet the requirement of power sources on electric vehicles.
A new method of surface modification on hydrogen storage alloy is investigated. The AB5 alloy of metal hydride electrode in MH/Ni battery is treated in the mixed solution of HF and CuSO4. The effects of HF content and copper particle deposition amount on surface modification reaction are studied. The performances of modified alloy are tested and electrochemical impedance spectroscopy (EIS) is applied to analyze the mechanism of treatment. The electrochemical testing results indicate that modified alloy has better rate capability and cycle stability. And the EIS analysis shows that surface modification increases the activity and electrical conductivity of the alloy, and greatly decreases its ohmic and electrochemical impedance, which helps to improve electrochemical properties of the battery. Therefore the modified alloy would well meet the requirement of power sources on electric vehicles.
2005, 21(10): 1151-1155
doi: 10.3866/PKU.WHXB20051018
Abstract:
Using thioacetamide (TAA) as precursor, homogeneous and steady monodispersed CdS nanocrystals were synthesized in Perfluorinated Ionomer Membranes (Nafion) by self-assembly. Unlike the ionic precursors such as Na2S and H2S, TAA could diffuse into the cationic- exchangeable ionomer membranes much more uniformly, which led to the homogeneous distribution of CdS nanoparticles in the Nafion membranes. High resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDXA) were used to investigate the synthesis mechanism, the size distribution and the microstructure of these CdS nanoparticles embedded in Nafion membranes. Optical properties of CdS nanoparticles in Nafion were also characterized by UV-Vis absorption and luminescence spectra. The results show that the quantum size effect becomes strong with the decrease of the size of CdS nanocrystals. Blue shift appears both on the absorb edges in the absorption spectra and on the band- edge emission in the luminescence spectrum.
Using thioacetamide (TAA) as precursor, homogeneous and steady monodispersed CdS nanocrystals were synthesized in Perfluorinated Ionomer Membranes (Nafion) by self-assembly. Unlike the ionic precursors such as Na2S and H2S, TAA could diffuse into the cationic- exchangeable ionomer membranes much more uniformly, which led to the homogeneous distribution of CdS nanoparticles in the Nafion membranes. High resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDXA) were used to investigate the synthesis mechanism, the size distribution and the microstructure of these CdS nanoparticles embedded in Nafion membranes. Optical properties of CdS nanoparticles in Nafion were also characterized by UV-Vis absorption and luminescence spectra. The results show that the quantum size effect becomes strong with the decrease of the size of CdS nanocrystals. Blue shift appears both on the absorb edges in the absorption spectra and on the band- edge emission in the luminescence spectrum.
2005, 21(10): 1156-1160
doi: 10.3866/PKU.WHXB20051019
Abstract:
This research is aimed to increase the activity of platinum-ruthenium alloy (Pt-Ru/C) catalysts and thus to lower the catalyst loading in anodes for methanol electrooxidation. The direct methanol fuel cell (DMFC) anode catalysts, Pt-Ru/C, were prepared from three groups of precursors by thermal reduction. The phase structure, particle size, size distribution and the morphology of reduced catalysts were determined by means of high-resolution transmission electron microscopy (TEM) and X-ray diffraction (XRD). It is found that XRD patterns of all the catalysts show Pt reflexion of a face centered cubic (fcc) crystal structure. But there are diffraction peaks indicating the presence of either pure Ru or Ru-rich hexa nal close packed (hcp) phase, which is not alloyed with Pt in Pt-Ru/C catalysts prepared from (NH4)2PtCl6+Ru(OH)3, or H2PtCl6+RuCl3 as precursors. The catalyst prepared from Pt(NH3)2(NO2)2 and Ru compound of self- prepared as precursors had a more homogeneous distribution of Pt- Ru alloy in carbon and a small particle size of about 3.7 nm. Their performance was tested using a glassy carbon working electrode by cyclic voltammetry(CV), chronoamperometric and amperometric i－t curves in a solution of 0.5 mol•L-1 CH3OH and 0.5 mol•L-1 H2SO4 at 25 ℃. The electrocatalytic activity of Pt-Ru/C catalysts prepared from Pt(NH3)2(NO2)2 and Ru compound of self-prepared as precursors has the highest catalyticactivity for methanol electrooxidation. The peak current density in CV is 11.5 mA•cm-2.
This research is aimed to increase the activity of platinum-ruthenium alloy (Pt-Ru/C) catalysts and thus to lower the catalyst loading in anodes for methanol electrooxidation. The direct methanol fuel cell (DMFC) anode catalysts, Pt-Ru/C, were prepared from three groups of precursors by thermal reduction. The phase structure, particle size, size distribution and the morphology of reduced catalysts were determined by means of high-resolution transmission electron microscopy (TEM) and X-ray diffraction (XRD). It is found that XRD patterns of all the catalysts show Pt reflexion of a face centered cubic (fcc) crystal structure. But there are diffraction peaks indicating the presence of either pure Ru or Ru-rich hexa nal close packed (hcp) phase, which is not alloyed with Pt in Pt-Ru/C catalysts prepared from (NH4)2PtCl6+Ru(OH)3, or H2PtCl6+RuCl3 as precursors. The catalyst prepared from Pt(NH3)2(NO2)2 and Ru compound of self- prepared as precursors had a more homogeneous distribution of Pt- Ru alloy in carbon and a small particle size of about 3.7 nm. Their performance was tested using a glassy carbon working electrode by cyclic voltammetry(CV), chronoamperometric and amperometric i－t curves in a solution of 0.5 mol•L-1 CH3OH and 0.5 mol•L-1 H2SO4 at 25 ℃. The electrocatalytic activity of Pt-Ru/C catalysts prepared from Pt(NH3)2(NO2)2 and Ru compound of self-prepared as precursors has the highest catalyticactivity for methanol electrooxidation. The peak current density in CV is 11.5 mA•cm-2.
2005, 21(10): 1161-1163
doi: 10.3866/PKU.WHXB20051020
Abstract:
The supersaturated solution of M •3B2O3-18%MgSO4-H2O was prepared and reacted under hydrothermal conditions at 150 ℃. The solid phases precipitated from the supersaturated solution at different times were identified by chemical analysis, XRD, FT-IR. The results show that the reaction process is unique. The precipitated solid phases of 1 to 5 days were mainly szaibelyite and they gradually dissolved with reaction proceeded. At the same time new solid phases also appeared which composed of MgSO4•H2O and MgSO4•1.25H2O. The latter was an intermediate with less amount. The former was final product. Based on these results the crystallization mechanism of szaibelyite under the hydrothermal conditions and discussed the effects of hydrothermal temperature on the composition of precipitated solid phases was proposed.
The supersaturated solution of M •3B2O3-18%MgSO4-H2O was prepared and reacted under hydrothermal conditions at 150 ℃. The solid phases precipitated from the supersaturated solution at different times were identified by chemical analysis, XRD, FT-IR. The results show that the reaction process is unique. The precipitated solid phases of 1 to 5 days were mainly szaibelyite and they gradually dissolved with reaction proceeded. At the same time new solid phases also appeared which composed of MgSO4•H2O and MgSO4•1.25H2O. The latter was an intermediate with less amount. The former was final product. Based on these results the crystallization mechanism of szaibelyite under the hydrothermal conditions and discussed the effects of hydrothermal temperature on the composition of precipitated solid phases was proposed.
2005, 21(10): 1164-1168
doi: 10.3866/PKU.WHXB20051021
Abstract:
Capacitance characteristics of carbon nanotubes (CNTs) in room temperature molten salt (RTMS) electrolyte of LiTFSI-acetamide were investigated. Cyclic voltammetry (CV) and galvanostatic charge/discharge measurements were employed to investigate the electrochemical performance of the test cells composed of a pair of carbon nanotubes electrodes and RTMS as electrolyte. The CNTs exhibited typical capacitance behavior in LiTFSI-acetamide, and a high specific capacitance of 22 F•g-1 estimated from galvanostatic discharge was obtained. The working voltage of the test cells could reach at 2.0 V, and they also showed a practical od level of durability over cycles of charge and discharge. After 1000 charge and discharge cycles, the capacity loss was just 10% of the initial discharge capacity. The preliminary results suggest that RTMS is a kind of promising electrolyte for supercapacitors.
Capacitance characteristics of carbon nanotubes (CNTs) in room temperature molten salt (RTMS) electrolyte of LiTFSI-acetamide were investigated. Cyclic voltammetry (CV) and galvanostatic charge/discharge measurements were employed to investigate the electrochemical performance of the test cells composed of a pair of carbon nanotubes electrodes and RTMS as electrolyte. The CNTs exhibited typical capacitance behavior in LiTFSI-acetamide, and a high specific capacitance of 22 F•g-1 estimated from galvanostatic discharge was obtained. The working voltage of the test cells could reach at 2.0 V, and they also showed a practical od level of durability over cycles of charge and discharge. After 1000 charge and discharge cycles, the capacity loss was just 10% of the initial discharge capacity. The preliminary results suggest that RTMS is a kind of promising electrolyte for supercapacitors.
EXAFS Study of Zn (II) Adsorption and Precipitation on γ-MnOOH Surface under Different pH Conditions
2005, 21(10): 1169-1173
doi: 10.3866/PKU.WHXB20051022
Abstract:
Mechanisms of adsorption and precipitation of Zn(II) onγ-MnOOH-water interfaces at pH 7.00, 7.50 and 8.00 were studied using EXAFS (extended X-ray absorption fine structure). The Zn—O distance for adsorbed Zn(II) was 0.202 nm, which did not change when pH increased from 7.00 to 8.00. This result implied that Zn2+ was adsorbed as a mixture of tetrahedron and octahedron. At pH 7.00, Zn2+ was adsorbed on (110) or (001) plane of γ-MnOOH by edge linkage mode, which corresponded a Zn—Mn distance of ~0.300 nm. At pH 7.50 and 8.00, most Zn(II) was precipitated as multinuclear hydroxo-complexes with similar structures where the Zn—Zn distances were 0.353 nm (tetrahedron-octahedron linkage) and 0.311 nm (octahedron-octahedron linkage), respectively.
Mechanisms of adsorption and precipitation of Zn(II) onγ-MnOOH-water interfaces at pH 7.00, 7.50 and 8.00 were studied using EXAFS (extended X-ray absorption fine structure). The Zn—O distance for adsorbed Zn(II) was 0.202 nm, which did not change when pH increased from 7.00 to 8.00. This result implied that Zn2+ was adsorbed as a mixture of tetrahedron and octahedron. At pH 7.00, Zn2+ was adsorbed on (110) or (001) plane of γ-MnOOH by edge linkage mode, which corresponded a Zn—Mn distance of ~0.300 nm. At pH 7.50 and 8.00, most Zn(II) was precipitated as multinuclear hydroxo-complexes with similar structures where the Zn—Zn distances were 0.353 nm (tetrahedron-octahedron linkage) and 0.311 nm (octahedron-octahedron linkage), respectively.
2005, 21(10): 1174-1177
doi: 10.3866/PKU.WHXB20051023
Abstract:
Inclusion of β-cyclodextrin (β-CD) with polyoxyethylene lauryl ether (PL) was studied by surface tension, cloud point, color reaction and 1H NMR measurements. It was established that the inclusion of β-CD with PL affords supramolecular complexes with stoichiometric ratios of 2∶1 and 3∶1 in aqueous solution. Inclusion complex with the stoichiometry of 2∶1 arises from the incorporation of lauryl group of PL into the cavity of β-CD, whereas inclusion complex with the stoichiometry of 3∶1 arises from the incorporation of polyoxyethylene group of PL into the cavity of β-CD. A special configuration of the complex has been proposed based on experimental results and molecular sizes.
Inclusion of β-cyclodextrin (β-CD) with polyoxyethylene lauryl ether (PL) was studied by surface tension, cloud point, color reaction and 1H NMR measurements. It was established that the inclusion of β-CD with PL affords supramolecular complexes with stoichiometric ratios of 2∶1 and 3∶1 in aqueous solution. Inclusion complex with the stoichiometry of 2∶1 arises from the incorporation of lauryl group of PL into the cavity of β-CD, whereas inclusion complex with the stoichiometry of 3∶1 arises from the incorporation of polyoxyethylene group of PL into the cavity of β-CD. A special configuration of the complex has been proposed based on experimental results and molecular sizes.
2005, 21(10): 1178-1181
doi: 10.3866/PKU.WHXB20051024
Abstract:
In order to examine the annealing behaviors of aqueous solutions of 10% tertiary butyl alcohol (TBA) and 10% sucrose in freeze- drying, a differential scanning calorimeter (DSC) has been employed to study freezing properties, annealing temperature, and annealing time. The experimental results show that when the solution is cooled, the existence of sucrose hinders the crystallization of TBA and the value of Tg′ decreases from －32.5 ℃ to －42.0 ℃, and TBA devitrifies at －30 ℃ when the solution is heated. When annealed at different temperatures around the devitrification peak, TBA all can crystallize completely and the value of Tg′ increases from －42.0 ℃ to －34.9 ℃. Annealing time depends on annealing temperature. The closer the annealing temperature is to Tg′, the longer the annealing time is. The devitrification will disappear after annealing at －37 ℃ for 20 min.
In order to examine the annealing behaviors of aqueous solutions of 10% tertiary butyl alcohol (TBA) and 10% sucrose in freeze- drying, a differential scanning calorimeter (DSC) has been employed to study freezing properties, annealing temperature, and annealing time. The experimental results show that when the solution is cooled, the existence of sucrose hinders the crystallization of TBA and the value of Tg′ decreases from －32.5 ℃ to －42.0 ℃, and TBA devitrifies at －30 ℃ when the solution is heated. When annealed at different temperatures around the devitrification peak, TBA all can crystallize completely and the value of Tg′ increases from －42.0 ℃ to －34.9 ℃. Annealing time depends on annealing temperature. The closer the annealing temperature is to Tg′, the longer the annealing time is. The devitrification will disappear after annealing at －37 ℃ for 20 min.
2005, 21(10): 1182-1185
doi: 10.3866/PKU.WHXB20051025
Abstract:
The electrooxidation behavior of piperonal (PI) and isosafrole (ISF) on roughened platinum in non-aqueous system was investigated by cyclic voltammogram (CV) and in-situ surface enhanced raman scattering (SERS) spectroscopy. On the one hand, PI would be oxidated to piperic acid if the potential was equal to 1.50 V or higher than 1.50 V. On the other hand, the in- situ SERS results demonatrated that the exciting laser of 632.8 nm promoted the electrooxidation of PI at the oxidation potential (≥1.50 V). As a result, the potential, which was used to directly oxidate ISF to PI should be controlled between 1.20 V and 1.50 V.
The electrooxidation behavior of piperonal (PI) and isosafrole (ISF) on roughened platinum in non-aqueous system was investigated by cyclic voltammogram (CV) and in-situ surface enhanced raman scattering (SERS) spectroscopy. On the one hand, PI would be oxidated to piperic acid if the potential was equal to 1.50 V or higher than 1.50 V. On the other hand, the in- situ SERS results demonatrated that the exciting laser of 632.8 nm promoted the electrooxidation of PI at the oxidation potential (≥1.50 V). As a result, the potential, which was used to directly oxidate ISF to PI should be controlled between 1.20 V and 1.50 V.
2005, 21(10): 1186-1194
doi: 10.3866/PKU.WHXB20051026
Abstract:
The effects of temperature on the parity-violating entropy and energy differences of chiral molecules are investigated both theoretically and experimentally. Statistical thermodynamics calculations indicate the possible occur-rence of sign reversal of parity-violating entropy difference at different temperatures, which is supported by temperature-dependent polarized Raman spectra of D-alanine and L-alanine. An incoherent spontaneous symmetry breaking is proposed to describe the bifurcation mechanism between mirror-image systems at the critical temperature, in which usually violated parity symmetry will be dynamically restored again. An asymmetric double-well potential with a tiny parity-violating energy difference (PVED) in the depths of the two potential wells showed that the presence of PVED can lead to the enrichment of L-form amino acid. Tunneling dynamics of amino acids with PVED provides a plausible mechanism for much faster development of homochirality.
The effects of temperature on the parity-violating entropy and energy differences of chiral molecules are investigated both theoretically and experimentally. Statistical thermodynamics calculations indicate the possible occur-rence of sign reversal of parity-violating entropy difference at different temperatures, which is supported by temperature-dependent polarized Raman spectra of D-alanine and L-alanine. An incoherent spontaneous symmetry breaking is proposed to describe the bifurcation mechanism between mirror-image systems at the critical temperature, in which usually violated parity symmetry will be dynamically restored again. An asymmetric double-well potential with a tiny parity-violating energy difference (PVED) in the depths of the two potential wells showed that the presence of PVED can lead to the enrichment of L-form amino acid. Tunneling dynamics of amino acids with PVED provides a plausible mechanism for much faster development of homochirality.
