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2007 Volume 23 Issue 4
2007, 23(04):
Abstract:
2007, 23(04): 455-458
doi: 10.1016/S1872-1508(07)60029-1
Abstract:
High performance organic light-emitting diodes (OLEDs) with lithium tetra-(8-hydroxy-quinolinato) boron (LiBq4), instead of LiF, as the electron injection layer, and aluminum as the cathode were fabricated. In the fabrication of the devices, N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB) was used as the hole transport layer, and tri-(8-quinolinolato) aluminum (Alq3) as the emitting and electron transport layer. By using LiBq4 as the electron injection layer, the device's performance with regard to luminance, current efficiency, and turn-on voltage was superior to that of the device using LiF as the electron injection layer. The experimental results could be explained by the improved electron injection and charge balance.
2007, 23(04): 459-465
doi: 10.1016/S1872-1508(07)60030-8
Abstract:
The photophysical properties of oli thiophenes-functionalized 9,9'-spirobifluorene derivatives in solution and in solid state were investigated in detail. The enhanced red-shift was observed from the absorption and the photoluminescence (PL) spectra of these derivatives in dilute THF solution with the increase of thiophene unit at one branch of 9,9'-spirobifluorene identical with the increased π-electron delocalization and the more effective conjugation length of the whole molecular system. The investigation of the photophysical properties of these compounds further demonstrated that the sp3-hybrid carbon at the spiro-center completely obstructed the correlation between two branches of the 9,9'-spirobifluorene system and made every branch become an independent chromophore. The electrochemical polymerization of 6b as a representative was also investigated.
The photophysical properties of oli thiophenes-functionalized 9,9'-spirobifluorene derivatives in solution and in solid state were investigated in detail. The enhanced red-shift was observed from the absorption and the photoluminescence (PL) spectra of these derivatives in dilute THF solution with the increase of thiophene unit at one branch of 9,9'-spirobifluorene identical with the increased π-electron delocalization and the more effective conjugation length of the whole molecular system. The investigation of the photophysical properties of these compounds further demonstrated that the sp3-hybrid carbon at the spiro-center completely obstructed the correlation between two branches of the 9,9'-spirobifluorene system and made every branch become an independent chromophore. The electrochemical polymerization of 6b as a representative was also investigated.
2007, 23(04): 466-472
doi: 10.3866/PKU.WHXB20070403
Abstract:
First principle calculation was carried out to study the electronic structures of photocatalysts K4Ce2Ta10O30, K4Ce2Nb10O30, and their solid solution compounds, which were all capable of responding to visible light, based on density functional theory (DFT) within plane-wave pesudopotential (PWP) and generalized gradient approximation (GGA) method. The calculation results indicated that conduction bands of K4Ce2Ta10O30 and K4Ce2Nb10O30 were mainly attributable to the Ta 5d and Nb 4d orbitals, respectively. Although the unoccupied Ce 4f orbitals had overlapped at the bottom of the conduction band, they were less effective in transferring electrons and photocatalytic activities for their high localized nature, while their valence bands were composed of hybridization with the bonding of O 2p+Ta 5d (or Nb 4d) and occupied Ce 4f orbitals. The contribution of these orbitals to the energy bands affected the electronic structure of photocatalysts and gave rise to their differences in light absorption and photocatalytic activities. As for the solid solutions compounds of K4Ce2Ta10-xNbxO30 (x=2, 5, 8), their band gaps decreased with an increase of the x value resulting in a corresponding lower reducing ability to evolve H2. The valence band edges in solid solution compounds were lower than that of K4Ce2Ta10O30 and K4Ce2Nb10O30 for the little contribution from occupied Ce 4f. This consequently led to the higher oxidize ability. The results of the analysis of electronic structures were in od accordance with their experimental photocatalytic activities for water decomposition.
First principle calculation was carried out to study the electronic structures of photocatalysts K4Ce2Ta10O30, K4Ce2Nb10O30, and their solid solution compounds, which were all capable of responding to visible light, based on density functional theory (DFT) within plane-wave pesudopotential (PWP) and generalized gradient approximation (GGA) method. The calculation results indicated that conduction bands of K4Ce2Ta10O30 and K4Ce2Nb10O30 were mainly attributable to the Ta 5d and Nb 4d orbitals, respectively. Although the unoccupied Ce 4f orbitals had overlapped at the bottom of the conduction band, they were less effective in transferring electrons and photocatalytic activities for their high localized nature, while their valence bands were composed of hybridization with the bonding of O 2p+Ta 5d (or Nb 4d) and occupied Ce 4f orbitals. The contribution of these orbitals to the energy bands affected the electronic structure of photocatalysts and gave rise to their differences in light absorption and photocatalytic activities. As for the solid solutions compounds of K4Ce2Ta10-xNbxO30 (x=2, 5, 8), their band gaps decreased with an increase of the x value resulting in a corresponding lower reducing ability to evolve H2. The valence band edges in solid solution compounds were lower than that of K4Ce2Ta10O30 and K4Ce2Nb10O30 for the little contribution from occupied Ce 4f. This consequently led to the higher oxidize ability. The results of the analysis of electronic structures were in od accordance with their experimental photocatalytic activities for water decomposition.
2007, 23(04): 473-478
doi: 10.3866/PKU.WHXB20070404
Abstract:
Ni8-Fe2-LSGMC5 composite anodes doped with various amounts of La0.8Sr0.2Ga0.8Mg0.15Co0.05O3 -δ (LSGMC5) were prepared by using the impregnation method. The electrochemical properties of the anodes and the power generation characteristics of corresponding cells were studied by alternating current (AC) impedance spectrometry and direct current (DC) polarization using hydrogen and dimethyl ether as fuels, respectively. The results showed that the introduction of LSGMC5 powders into the Ni-Fe anodes improved the structure of the anodes and the anode/electrolyte interfaces significantly, which decreased the Ohmic resistance of the cell and the polarization resistance of the anodes. The LSGMC5 powders in the composite anodes showed different effects on the electro-catalytic oxidation of hydrogen and dimethyl ether (DME). The polarization resistance of the anode decreased with increasing concentration of LSGMC5, and the anode containing 30% LSGMC5 powder showed the best electrochemical properties when using DME as a fuel. The maximum power densities of the cell in DME based on the anode containing 30% LSGMC5 powder reached 1.00, 0.61, and 0.40W·cm-2 at 1073, 1023, and 973 K, respectively. The anode doped with 20% LSGMC5 powder had the best electrochemical properties when using H2 as a fuel, with the further increase in the amount of LSGMC5 powder the polarization resistance increased quickly.
Ni8-Fe2-LSGMC5 composite anodes doped with various amounts of La0.8Sr0.2Ga0.8Mg0.15Co0.05O3 -δ (LSGMC5) were prepared by using the impregnation method. The electrochemical properties of the anodes and the power generation characteristics of corresponding cells were studied by alternating current (AC) impedance spectrometry and direct current (DC) polarization using hydrogen and dimethyl ether as fuels, respectively. The results showed that the introduction of LSGMC5 powders into the Ni-Fe anodes improved the structure of the anodes and the anode/electrolyte interfaces significantly, which decreased the Ohmic resistance of the cell and the polarization resistance of the anodes. The LSGMC5 powders in the composite anodes showed different effects on the electro-catalytic oxidation of hydrogen and dimethyl ether (DME). The polarization resistance of the anode decreased with increasing concentration of LSGMC5, and the anode containing 30% LSGMC5 powder showed the best electrochemical properties when using DME as a fuel. The maximum power densities of the cell in DME based on the anode containing 30% LSGMC5 powder reached 1.00, 0.61, and 0.40W·cm-2 at 1073, 1023, and 973 K, respectively. The anode doped with 20% LSGMC5 powder had the best electrochemical properties when using H2 as a fuel, with the further increase in the amount of LSGMC5 powder the polarization resistance increased quickly.
2007, 23(04): 479-483
doi: 10.1016/S1872-1508(07)60031-X
Abstract:
The asymmetric hydrogenations of acetophenone and its derivatives over the bimetallic catalyst RuRh/γ-Al2O3 modified by PPh3 and(1S, 2S)-DPEN [(1S, 2S)-1,2-diphenylethane-1,2-diamine]were studied. The effects of the concentration of KOH, temperature, ratio of ruthenium to rhodium, and the concentration of diamine on the asymmetric hydrogenation of acetophenone were investigated in detail. The results showed that this catalyst system had high activity and moderate enantioselectivity for the asymmetric hydrogenation of acetophenone and its derivatives. Under the optimum conditions, the conversions of acetophenone, ethylphenylketone, and isopropylphenylketone were up to 92.5%, 95.9%, and 100%, and the enantioselectivities for the formation of (R)-aromatic alcohols were 79.6%, 81.2%, and 81.4%, respectively.
The asymmetric hydrogenations of acetophenone and its derivatives over the bimetallic catalyst RuRh/γ-Al2O3 modified by PPh3 and(1S, 2S)-DPEN [(1S, 2S)-1,2-diphenylethane-1,2-diamine]were studied. The effects of the concentration of KOH, temperature, ratio of ruthenium to rhodium, and the concentration of diamine on the asymmetric hydrogenation of acetophenone were investigated in detail. The results showed that this catalyst system had high activity and moderate enantioselectivity for the asymmetric hydrogenation of acetophenone and its derivatives. Under the optimum conditions, the conversions of acetophenone, ethylphenylketone, and isopropylphenylketone were up to 92.5%, 95.9%, and 100%, and the enantioselectivities for the formation of (R)-aromatic alcohols were 79.6%, 81.2%, and 81.4%, respectively.
2007, 23(04): 484-488
doi: 10.1016/S1872-1508(07)60032-1
Abstract:
A multilayer ultrathin filmof poly(3,4-ethylene dioxythiophene) (PEDOT) was first prepared by a modified Langmuir-Blodgett (LB) technique. The polymerization of EDOT monomer occured in a multilayer as-prepared LB film by exposing the filmto EDOTvapor. The formation of PEDOTparticles in the LBfilmwas confirmed by UV-Vis-near IR (UV-Vis-NIR) absorption spectrumand X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) investigation of the filmsurface exhibited small PEDOTparticles distributed in stearic acid (SA) LBfilms. Secondary ion mass spectrometry (SIMS) was employed to analyze the location of PEDOT formed and the results showed that PEDOT was well confined in the multilayer structure. A 60-layer PEDOT LB film had higher conductivity (2.6 S·cm-1) than a conventional PEDOT film, and exhibited excellent doping/dedoping characteristics. An investigation of the relationship between film conductivity and exposure time on EDOT ambience revealed that the film obtained steady conductivity after 120 min and it was concluded that the lower oxidizer density in LB film might slow the polymerization speed of EDOT. In a study of sensitive characteristics, the PEDOT film showed faster and nonlinear responses to analyte gas in a lower concentration (φ<30×10^-6), and exhibited a linear response to analyte in a higher concentration (φ=(30-120)^10-6). The result of gas sensitivity also showed that the film had excellent reversible and reproducible response to HCl vapor. The mechanismof conductivity and gas sensitivity of composite LB films were also included.
A multilayer ultrathin filmof poly(3,4-ethylene dioxythiophene) (PEDOT) was first prepared by a modified Langmuir-Blodgett (LB) technique. The polymerization of EDOT monomer occured in a multilayer as-prepared LB film by exposing the filmto EDOTvapor. The formation of PEDOTparticles in the LBfilmwas confirmed by UV-Vis-near IR (UV-Vis-NIR) absorption spectrumand X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) investigation of the filmsurface exhibited small PEDOTparticles distributed in stearic acid (SA) LBfilms. Secondary ion mass spectrometry (SIMS) was employed to analyze the location of PEDOT formed and the results showed that PEDOT was well confined in the multilayer structure. A 60-layer PEDOT LB film had higher conductivity (2.6 S·cm-1) than a conventional PEDOT film, and exhibited excellent doping/dedoping characteristics. An investigation of the relationship between film conductivity and exposure time on EDOT ambience revealed that the film obtained steady conductivity after 120 min and it was concluded that the lower oxidizer density in LB film might slow the polymerization speed of EDOT. In a study of sensitive characteristics, the PEDOT film showed faster and nonlinear responses to analyte gas in a lower concentration (φ<30×10^-6), and exhibited a linear response to analyte in a higher concentration (φ=(30-120)^10-6). The result of gas sensitivity also showed that the film had excellent reversible and reproducible response to HCl vapor. The mechanismof conductivity and gas sensitivity of composite LB films were also included.
2007, 23(04): 489-492
doi: 10.3866/PKU.WHXB20070407
Abstract:
Polycarbonate (PC) membranes were irradiated with swift heavy ions and latent tracks were created along the ions' trajectories. Nanopores, diameters between 100 and 500 nm, were obtained after illuminating the membranes with UV light and etching in NaOH solution. Silver nanowires were produced in the etched ion-track membranes by electrochemical deposition. The morphology and crystallinity of the silver nanowires were studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). Under certain conditions (deposition voltage 25 mV, current density 1-2 mA·cm-2, temperature 50 ℃, electrolyte 0.1 mol·L-1 AgNO3), single-crystalline silver nanowires with preferred orientation along the [111] direction can be synthesized.
Polycarbonate (PC) membranes were irradiated with swift heavy ions and latent tracks were created along the ions' trajectories. Nanopores, diameters between 100 and 500 nm, were obtained after illuminating the membranes with UV light and etching in NaOH solution. Silver nanowires were produced in the etched ion-track membranes by electrochemical deposition. The morphology and crystallinity of the silver nanowires were studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). Under certain conditions (deposition voltage 25 mV, current density 1-2 mA·cm-2, temperature 50 ℃, electrolyte 0.1 mol·L-1 AgNO3), single-crystalline silver nanowires with preferred orientation along the [111] direction can be synthesized.
2007, 23(04): 493-498
doi: 10.3866/PKU.WHXB20070408
Abstract:
[Ni80Fe20 /Cu/Co/Cu]n spin-valve multilayers were fabricated onto n-Si(111) substrates covered with NiFe buffer layers by means of double bath potentiostatic electrodeposition. The electrochemical conditions were determined. A well-defined superlattice structure was characterized by high-angle X-ray diffraction, and the influence of NiFe buffer layer upon the orientation of crystalline growth was studied. Magneto-transport properties of the spin valves were investigated by four-probe technique. Hysteresis loops were tested by vibrating sample magnetometer (VSM) at room temperature. With the increase of the Cu layer thickness (tCu), giant magnetoresistance(GMR) ratio showed a periodical oscillation at first and achieved the maximum at tCu=3.6 nm, then declined gradually. With the increase of the Co and NiFe layer thickness, GMR ratio rose at first, and dropped after the peak point. The maximum room temperature GMR ratio of 5.4%was obtained with a sensitivity up to 0.2%·Oe-1 and a saturation field of 350 Oe for NiFe(25 nm)/[Cu(3.6 nm)/Co(1.2 nm)/Cu(3.6 nm)/NiFe(2.8 nm)]30 structures.
[Ni80Fe20 /Cu/Co/Cu]n spin-valve multilayers were fabricated onto n-Si(111) substrates covered with NiFe buffer layers by means of double bath potentiostatic electrodeposition. The electrochemical conditions were determined. A well-defined superlattice structure was characterized by high-angle X-ray diffraction, and the influence of NiFe buffer layer upon the orientation of crystalline growth was studied. Magneto-transport properties of the spin valves were investigated by four-probe technique. Hysteresis loops were tested by vibrating sample magnetometer (VSM) at room temperature. With the increase of the Cu layer thickness (tCu), giant magnetoresistance(GMR) ratio showed a periodical oscillation at first and achieved the maximum at tCu=3.6 nm, then declined gradually. With the increase of the Co and NiFe layer thickness, GMR ratio rose at first, and dropped after the peak point. The maximum room temperature GMR ratio of 5.4%was obtained with a sensitivity up to 0.2%·Oe-1 and a saturation field of 350 Oe for NiFe(25 nm)/[Cu(3.6 nm)/Co(1.2 nm)/Cu(3.6 nm)/NiFe(2.8 nm)]30 structures.
2007, 23(04): 499-502
doi: 10.3866/PKU.WHXB20070409
Abstract:
DNA modified electrode was prepared by covalent immobilization of ssDNA or dsDNA on a mercaptoethanol monolayer self-assembled ld electrode with the help of N-(3-dimethylaminopropyl)-N'-ethylcarbodiimidehydrochloride (EDC) and N-hydroxysuccinimide (NHS). The electrochemical behaviors of brilliant cresyl blue (BCB) on ssDNA or dsDNA electrodes were studied. BCB had different binding models with ssDNA or dsDNA and the adsorptive constants were 1.67×10^4 L·mol-1 for ssDNA/Au electrode and 3.22×10^4 L·mol-1 for dsDNA/Au electrode. BCB bound to ssDNA via electrostatic interaction while bound to dsDNA through both the electrostatic and intercalative models. The results showed that dsDNA had a stronger appetency for BCB, which indicated that BCB was a suitable electroactive indicator.
DNA modified electrode was prepared by covalent immobilization of ssDNA or dsDNA on a mercaptoethanol monolayer self-assembled ld electrode with the help of N-(3-dimethylaminopropyl)-N'-ethylcarbodiimidehydrochloride (EDC) and N-hydroxysuccinimide (NHS). The electrochemical behaviors of brilliant cresyl blue (BCB) on ssDNA or dsDNA electrodes were studied. BCB had different binding models with ssDNA or dsDNA and the adsorptive constants were 1.67×10^4 L·mol-1 for ssDNA/Au electrode and 3.22×10^4 L·mol-1 for dsDNA/Au electrode. BCB bound to ssDNA via electrostatic interaction while bound to dsDNA through both the electrostatic and intercalative models. The results showed that dsDNA had a stronger appetency for BCB, which indicated that BCB was a suitable electroactive indicator.
2007, 23(04): 503-507
doi: 10.3866/PKU.WHXB20070410
Abstract:
The crystal transformation among ZSM-5, ZSM-57, and mordenite was studied under different conditions, such as SiO2/Al2O3 molar ratio, alkalinity, n-butylamine template, crystallization time, and temperature. The results showed that higher alkalinity and longer crystallization time were of benefit to mordenite; lower alkalinity and higher induction temperature of crystallization were in favor of ZSM-57 with low n(SiO2)/n(Al2O3) ratio; alkalinity was required to be adjusted accurately to synthesize ZSM-5 with low n(SiO2)/n(Al2O3) ratio, shortening of crystallization time, decrease in induction temperature of crystallization, and the addition of seed crystal were all in favor of ZSM-5 with low n(SiO2)/n(Al2O3) ratio. A slight change in the above conditions would result in the transformation among the three crystals, and two or more crystal phases could be observed in the products.
The crystal transformation among ZSM-5, ZSM-57, and mordenite was studied under different conditions, such as SiO2/Al2O3 molar ratio, alkalinity, n-butylamine template, crystallization time, and temperature. The results showed that higher alkalinity and longer crystallization time were of benefit to mordenite; lower alkalinity and higher induction temperature of crystallization were in favor of ZSM-57 with low n(SiO2)/n(Al2O3) ratio; alkalinity was required to be adjusted accurately to synthesize ZSM-5 with low n(SiO2)/n(Al2O3) ratio, shortening of crystallization time, decrease in induction temperature of crystallization, and the addition of seed crystal were all in favor of ZSM-5 with low n(SiO2)/n(Al2O3) ratio. A slight change in the above conditions would result in the transformation among the three crystals, and two or more crystal phases could be observed in the products.
2007, 23(04): 508-512
doi: 10.3866/PKU.WHXB20070411
Abstract:
In order to study size dependence of the thermodynamic properties of chemical reaction, nanoparticles of diamond were simulated by use of spherical C clusters, the properties of chemical reaction of diamond nanoparticles with different sizes and O2 were calculated by quantum chemistry method. The results showed that the particle size had obvious effects on the molar standard entropy of reaction, the molar standard enthalpy of reaction, the molar standard Gibbs free energy, and the standard equilibrium constant in heterogeneous reactions; the molar standard entropy of reaction, the molar standard enthalpy of reaction, and the molar standard Gibbs free energy decreased and the standard equilibrium constant increased with the particle diameters of reactants decreasing. These regularities were consistent with experimental results.
In order to study size dependence of the thermodynamic properties of chemical reaction, nanoparticles of diamond were simulated by use of spherical C clusters, the properties of chemical reaction of diamond nanoparticles with different sizes and O2 were calculated by quantum chemistry method. The results showed that the particle size had obvious effects on the molar standard entropy of reaction, the molar standard enthalpy of reaction, the molar standard Gibbs free energy, and the standard equilibrium constant in heterogeneous reactions; the molar standard entropy of reaction, the molar standard enthalpy of reaction, and the molar standard Gibbs free energy decreased and the standard equilibrium constant increased with the particle diameters of reactants decreasing. These regularities were consistent with experimental results.
2007, 23(04): 513-516
doi: 10.1016/S1872-1508(07)60033-3
Abstract:
Dielectric absorption studies of H-bonded complexes of methyl methacrylate (MMA) and ethyl methacrylate (EMA) with p-cresol, p-chlorophenol, 2,4-dichlorophenol, and p-bromophenol were studied at microwave frequency 9.37 GHz in dilute solution of carbon tetrachloride at 308 K. Different dielectric parameters like dielectric constant ε' and dielectric loss ε'' at microwave frequency, static dielectric constant ε0 and dielectric constant ε∞ at optical frequency were determined. The validity of the single frequency equation of Higasi et al. for multiple relaxation time τ(1) was found to be a function of the hydrogen bonding strength of phenolic hydrogen, whereas the group rotation relaxation time τ(2) was a function of the steric interaction of proton donor. The relaxation time was the maximumat 50:50 (molar ratio) of methacrylates with phenols.
Dielectric absorption studies of H-bonded complexes of methyl methacrylate (MMA) and ethyl methacrylate (EMA) with p-cresol, p-chlorophenol, 2,4-dichlorophenol, and p-bromophenol were studied at microwave frequency 9.37 GHz in dilute solution of carbon tetrachloride at 308 K. Different dielectric parameters like dielectric constant ε' and dielectric loss ε'' at microwave frequency, static dielectric constant ε0 and dielectric constant ε∞ at optical frequency were determined. The validity of the single frequency equation of Higasi et al. for multiple relaxation time τ(1) was found to be a function of the hydrogen bonding strength of phenolic hydrogen, whereas the group rotation relaxation time τ(2) was a function of the steric interaction of proton donor. The relaxation time was the maximumat 50:50 (molar ratio) of methacrylates with phenols.
2007, 23(04): 517-520
doi: 10.3866/PKU.WHXB20070413
Abstract:
Molecular dynamics simulations were performed for studying mechanical properties of nickel nanowires subjected to uniaxial strain using embedded atommethod (EAM) potential. Strain rates applied in the simulations ranged from 5×10^7 s^-1 to 1×10^10 s^-1. The stress, the average atomic energy, the pair correlation function, as well as the transient atomic images of the systems were presented to explore the strain rate dependence of structure of nanowires. It was found that as the strain rates applied to the system were lower than 1×10^8 s^-1, the nanowires underwent plastic deformation and kept crystal structure before fracture during the process of tensioning state, which was testified clearly by the pair correlation function. While as strain rates were higher than 1×10^9 s^-1, the nanowires changed continuously from crystalline structure to amorphous phase and the pair correlation function also exhibited the characteristics of typical amorphous peaks. Amorphization of Ni nanowires was induced under high strain rates.
Molecular dynamics simulations were performed for studying mechanical properties of nickel nanowires subjected to uniaxial strain using embedded atommethod (EAM) potential. Strain rates applied in the simulations ranged from 5×10^7 s^-1 to 1×10^10 s^-1. The stress, the average atomic energy, the pair correlation function, as well as the transient atomic images of the systems were presented to explore the strain rate dependence of structure of nanowires. It was found that as the strain rates applied to the system were lower than 1×10^8 s^-1, the nanowires underwent plastic deformation and kept crystal structure before fracture during the process of tensioning state, which was testified clearly by the pair correlation function. While as strain rates were higher than 1×10^9 s^-1, the nanowires changed continuously from crystalline structure to amorphous phase and the pair correlation function also exhibited the characteristics of typical amorphous peaks. Amorphization of Ni nanowires was induced under high strain rates.
2007, 23(04): 521-525
doi: 10.3866/PKU.WHXB20070414
Abstract:
Proton exchange membrane fuel cells (PEMFC) electrodes were platinized by a modulated pulse current electrodeposition. An uncatalyzed carbon electrode (UCE), on which a layer of Nafion-bonded carbon was dispersed in advance, was served as a substrate for electrodeposition. The platinized electrode by electrodeposition was assessed by cyclic voltammetry, X-ray diffraction, transmission electron microscopy. The preliminary results showed that the height and width of deposition pulse current were critical for the properties of Pt deposit. For instance, as the on-time and off-time were fixed at 300 μs and 1200 μs, respectively, and deposition time fixed at 120 s, the electrode prepared at a peak current density of 100 mA·cm-2 exhibited the best performance, and meanwhile the particle size of the Pt deposits was as small as 5-8 nm. The Pt utilization efficiency of such an electrode was as high as 43.14%. The current efficiency for Pt deposition, in this case, was about 45%.
Proton exchange membrane fuel cells (PEMFC) electrodes were platinized by a modulated pulse current electrodeposition. An uncatalyzed carbon electrode (UCE), on which a layer of Nafion-bonded carbon was dispersed in advance, was served as a substrate for electrodeposition. The platinized electrode by electrodeposition was assessed by cyclic voltammetry, X-ray diffraction, transmission electron microscopy. The preliminary results showed that the height and width of deposition pulse current were critical for the properties of Pt deposit. For instance, as the on-time and off-time were fixed at 300 μs and 1200 μs, respectively, and deposition time fixed at 120 s, the electrode prepared at a peak current density of 100 mA·cm-2 exhibited the best performance, and meanwhile the particle size of the Pt deposits was as small as 5-8 nm. The Pt utilization efficiency of such an electrode was as high as 43.14%. The current efficiency for Pt deposition, in this case, was about 45%.
2007, 23(04): 526-530
doi: 10.3866/PKU.WHXB20070415
Abstract:
Intermolecular interactions between ethylamine or ethylenediamine and H2O or HF were studied theoretically using density functional theory (DFT) at the PBE0/6-31+G(d, p) level. Natural bond orbital (NBO) analyses were employed to elucidate the hydrogen bond characteristics in these complexes. Energy decomposition analysis (EDA) method was applied to complexes of II-1, II-2, III-1, and III-2 at the PBE/TZP level. From this study, four important conclusions were drawn as follows: (1) Both HF and H2O can be stabilized by amines through N…H—F(O), F(O)…H—N or F(O)…H—C hydrogen bonds; (2) Amines have the priority to stabilize HF, because the high electronegativies of florine atom results in the intense N—H…F hydrogen bonds; (3) Stability of the ethylenediamine-associated complexes is higher than that of ethylamine-associated complexes; (4) The most stable complexes, formed by amines with HF or H2O, include F(O)—H…N and F(O)…H—C hydrogen bonds.
Intermolecular interactions between ethylamine or ethylenediamine and H2O or HF were studied theoretically using density functional theory (DFT) at the PBE0/6-31+G(d, p) level. Natural bond orbital (NBO) analyses were employed to elucidate the hydrogen bond characteristics in these complexes. Energy decomposition analysis (EDA) method was applied to complexes of II-1, II-2, III-1, and III-2 at the PBE/TZP level. From this study, four important conclusions were drawn as follows: (1) Both HF and H2O can be stabilized by amines through N…H—F(O), F(O)…H—N or F(O)…H—C hydrogen bonds; (2) Amines have the priority to stabilize HF, because the high electronegativies of florine atom results in the intense N—H…F hydrogen bonds; (3) Stability of the ethylenediamine-associated complexes is higher than that of ethylamine-associated complexes; (4) The most stable complexes, formed by amines with HF or H2O, include F(O)—H…N and F(O)…H—C hydrogen bonds.
2007, 23(04): 531-536
doi: 10.1016/S1872-1508(07)60034-5
Abstract:
The surface chemical compositions of fluorinated latex films and the dynamic contact angle of water were determined using X-ray photoelectron spectroscopy (XPS) and a Krüss interface tension measurement, respectively. The surface tensions of the films were calculated by the equation of state approach using the dynamic contact angles, and the effect of temperature on the wetting behavior of these films was investigated. It was shown that the F 1s signal intensity from the outermost surface of these fluorinated latex films was stronger than that from the interior surface of the film and that the surface tension showed a linear decrease with the increase of density of fluorine atom on the latex film surface to a certain extent. The surface tensions rapidly decreased with the increase of fluorinated lateral chains (Rf) content in the copolymer with longer Rf (carbon atomnumber n＞6). The water receding contact angles (θr) on the latex films sharply decreased with the increase of n value, leveled off nearly at n=10, and almost remained unchanged when n＞10. In addition, θr increased more remarkably with the increase of F content in the poly (protonated acrylate-co-fluorinated acrylate) with shorter hydrocarbon side chains. The water wetting ability of the fluorinate latex films became slightly better only when temperature was more than 40 ℃.
The surface chemical compositions of fluorinated latex films and the dynamic contact angle of water were determined using X-ray photoelectron spectroscopy (XPS) and a Krüss interface tension measurement, respectively. The surface tensions of the films were calculated by the equation of state approach using the dynamic contact angles, and the effect of temperature on the wetting behavior of these films was investigated. It was shown that the F 1s signal intensity from the outermost surface of these fluorinated latex films was stronger than that from the interior surface of the film and that the surface tension showed a linear decrease with the increase of density of fluorine atom on the latex film surface to a certain extent. The surface tensions rapidly decreased with the increase of fluorinated lateral chains (Rf) content in the copolymer with longer Rf (carbon atomnumber n＞6). The water receding contact angles (θr) on the latex films sharply decreased with the increase of n value, leveled off nearly at n=10, and almost remained unchanged when n＞10. In addition, θr increased more remarkably with the increase of F content in the poly (protonated acrylate-co-fluorinated acrylate) with shorter hydrocarbon side chains. The water wetting ability of the fluorinate latex films became slightly better only when temperature was more than 40 ℃.
2007, 23(04): 537-542
doi: 10.1016/S1872-1508(07)60035-7
Abstract:
Lithium-ion battery cathode material Li3-2x(V1-xTix)2(PO4)3 was synthesized using sol-gel/carbothermal reduction method. Electrochemical properties of substituted samples were investigated, which showed the enhancement of discharge capacity and the cycle performance by the substitution of Ti4+. The pure material of Li3V2 (PO4)3 presented three plateaus around 3.58, 3.67, and 4.08 V, but the first two plateaus slightly sloping in the substituted samples and the boundary gradually became ambiguous with the increase in the substitution ratio. The differential thermal analysis (DTA) indicated that a stabilized γ -phase product was obtained. The crystal structure was characterized by the X-ray diffraction and the Rietveld method. The results showed that all the lithium sites were partially occupied, which introduced additional vacancies into the lithium sites. The ionic conductivity of doped material was increased to three orders of magnitudes. The disorder of lithium ion would correspond to the enhancement of the conductivity and specific capacity.
Lithium-ion battery cathode material Li3-2x(V1-xTix)2(PO4)3 was synthesized using sol-gel/carbothermal reduction method. Electrochemical properties of substituted samples were investigated, which showed the enhancement of discharge capacity and the cycle performance by the substitution of Ti4+. The pure material of Li3V2 (PO4)3 presented three plateaus around 3.58, 3.67, and 4.08 V, but the first two plateaus slightly sloping in the substituted samples and the boundary gradually became ambiguous with the increase in the substitution ratio. The differential thermal analysis (DTA) indicated that a stabilized γ -phase product was obtained. The crystal structure was characterized by the X-ray diffraction and the Rietveld method. The results showed that all the lithium sites were partially occupied, which introduced additional vacancies into the lithium sites. The ionic conductivity of doped material was increased to three orders of magnitudes. The disorder of lithium ion would correspond to the enhancement of the conductivity and specific capacity.
2007, 23(04): 543-548
doi: 10.1016/S1872-1508(07)60036-9
Abstract:
The effectiveness of the approach for systematical reconstruction of higher order reduced density matrices with lower order ones, which was developed by Chen (Science in China B, 2006, 49: 402), was compared theoretically with that of Mazziotti's method through Harris model. In the case of omitting the cumulant terms 3△M, 4△M in the latter and the normal product terms 3△, 4△in the former, it was found that the errors from both approaches were comparable. As a better approximation, if only fourth-order terms 4△M and 4△ in both methods are neglected whereas the third-order terms 3△M and 3△are computed from their corresponding fourth-order terms 4△M and 4△ respectively through contractions, the results calculated with Chen's approach not only have the correct signs but also are very close to the exact normal products 3△ whereas some of the results calculated with Mazziotti's method do not even have the correct signs with respect to the exact cumulants 3△M.
The effectiveness of the approach for systematical reconstruction of higher order reduced density matrices with lower order ones, which was developed by Chen (Science in China B, 2006, 49: 402), was compared theoretically with that of Mazziotti's method through Harris model. In the case of omitting the cumulant terms 3△M, 4△M in the latter and the normal product terms 3△, 4△in the former, it was found that the errors from both approaches were comparable. As a better approximation, if only fourth-order terms 4△M and 4△ in both methods are neglected whereas the third-order terms 3△M and 3△are computed from their corresponding fourth-order terms 4△M and 4△ respectively through contractions, the results calculated with Chen's approach not only have the correct signs but also are very close to the exact normal products 3△ whereas some of the results calculated with Mazziotti's method do not even have the correct signs with respect to the exact cumulants 3△M.
2007, 23(04): 549-553
doi: 10.3866/PKU.WHXB20070419
Abstract:
Acidic silicon sol was prepared by ion exchange using Na2SiO3·9H2O as raw material. Spherical SiO2-Al2O3 composites were prepared by oil-drop method after mixing of silicon sol, hexamethylenetetramine, and aluminium sol. The samples were characterized and analysized by XRD, BET, and TPD. The results showed that SiO2 existed in SiO2-Al2O3 composites in amorphous phase and that specific surface area, pore volume, and surface acidity increase with the increase of SiO2 content, accompanied with the decrease of average pore diameter and bulk density. The crash strength kept approximate constant.
Acidic silicon sol was prepared by ion exchange using Na2SiO3·9H2O as raw material. Spherical SiO2-Al2O3 composites were prepared by oil-drop method after mixing of silicon sol, hexamethylenetetramine, and aluminium sol. The samples were characterized and analysized by XRD, BET, and TPD. The results showed that SiO2 existed in SiO2-Al2O3 composites in amorphous phase and that specific surface area, pore volume, and surface acidity increase with the increase of SiO2 content, accompanied with the decrease of average pore diameter and bulk density. The crash strength kept approximate constant.
2007, 23(04): 554-558
doi: 10.3866/PKU.WHXB20070420
Abstract:
Novel binary molten salt electrolytes based on LiClO4 and 2-oxazolidinone (OZO) were prepared. The electrolytes appeared as liquid at room temperature though they were composed of two solids. DSC analysis showed that the LiClO4-OZO electrolyte was liquid with a eutectic temperature about -50 ℃. FTIR spectroscopy indicated that OZO could coordinate with Li+ cation in the LiClO4-OZO system through Li—O bonding. A big coordinate cation was formed and the coulombic force was weakened. Meanwhile, Li—O coordination could also lead to the breakage of hydrogen bonding between OZO molecules, resulting in the decrease of the eutectic temperature of the system compared with pure salt. Some the molten salt samples existed as liquid state at roomtemperature. The electrochemical properties were evaluated by ac impedance spectroscopy and cyclic voltammertry, respectively. The conductivity of LiClO4-OZO electrolyte at molar ratio of 1:4.5 was 0.66×10^-3 S·cm-1 at 25 ℃and 7.33×10^-3 S·cm-1 at 80 ℃, and the electrochemical windowwas about 3.5 V.
Novel binary molten salt electrolytes based on LiClO4 and 2-oxazolidinone (OZO) were prepared. The electrolytes appeared as liquid at room temperature though they were composed of two solids. DSC analysis showed that the LiClO4-OZO electrolyte was liquid with a eutectic temperature about -50 ℃. FTIR spectroscopy indicated that OZO could coordinate with Li+ cation in the LiClO4-OZO system through Li—O bonding. A big coordinate cation was formed and the coulombic force was weakened. Meanwhile, Li—O coordination could also lead to the breakage of hydrogen bonding between OZO molecules, resulting in the decrease of the eutectic temperature of the system compared with pure salt. Some the molten salt samples existed as liquid state at roomtemperature. The electrochemical properties were evaluated by ac impedance spectroscopy and cyclic voltammertry, respectively. The conductivity of LiClO4-OZO electrolyte at molar ratio of 1:4.5 was 0.66×10^-3 S·cm-1 at 25 ℃and 7.33×10^-3 S·cm-1 at 80 ℃, and the electrochemical windowwas about 3.5 V.
2007, 23(04): 559-564
doi: 10.1016/S1872-1508(07)60037-0
Abstract:
The Pt-Ru particles of Pt-Ru/CMK-3 catalyst were found to possess high degree of alloying, small average size, and low relative crystallinity when the Pt-Ru/CMK-3 catalyst was prepared using the general chemical reduction method in the ternary solution system containing tetrahydrofuran (THF), H2O, and ethanol. The Pt-Ru/CMK-3 catalyst showed high electrocatalytic activity for methanol oxidation. It indicated that the alloying degree of Pt-Ru could significantly affect the electrocatalytic activity for methanol oxidation. The Pt-Ru/CMK-3 catalyst with high alloying degree can be obtained because THF and H2PtCl6 can forma complex leading to the reduction potentials of H2PtCl6 and RuCl3, which are close to each other in the aqueous solution with THF.
The Pt-Ru particles of Pt-Ru/CMK-3 catalyst were found to possess high degree of alloying, small average size, and low relative crystallinity when the Pt-Ru/CMK-3 catalyst was prepared using the general chemical reduction method in the ternary solution system containing tetrahydrofuran (THF), H2O, and ethanol. The Pt-Ru/CMK-3 catalyst showed high electrocatalytic activity for methanol oxidation. It indicated that the alloying degree of Pt-Ru could significantly affect the electrocatalytic activity for methanol oxidation. The Pt-Ru/CMK-3 catalyst with high alloying degree can be obtained because THF and H2PtCl6 can forma complex leading to the reduction potentials of H2PtCl6 and RuCl3, which are close to each other in the aqueous solution with THF.
2007, 23(04): 565-568
doi: 10.3866/PKU.WHXB20070422
Abstract:
An adhesive semisolid mixture was used as catalyst precursors for the synthesis of single-walled carbon nanotubes (SWNTs). With atomic forcemicroscopy (AFM),worn-out silicon probeswere driven to approach the glue-like catalyst precursors, followed by chemical vapor deposition (CVD). Thus SWNTs were successfully located on the end of silicon probes as AFM tips. The as-prepared SWNTs and tips were characterized, and the effect of SWNT morphology on imaging stabilization was discussed. The results showed that most of tips were SWNT bundles, which were 5-10 nm in diameter, several hundred nanometers in length and independent of severe thermal vibration. When SWNTs were parallel to the axis of silicon pyramids, the tips could obtain high-resolution images without additional treatments.
An adhesive semisolid mixture was used as catalyst precursors for the synthesis of single-walled carbon nanotubes (SWNTs). With atomic forcemicroscopy (AFM),worn-out silicon probeswere driven to approach the glue-like catalyst precursors, followed by chemical vapor deposition (CVD). Thus SWNTs were successfully located on the end of silicon probes as AFM tips. The as-prepared SWNTs and tips were characterized, and the effect of SWNT morphology on imaging stabilization was discussed. The results showed that most of tips were SWNT bundles, which were 5-10 nm in diameter, several hundred nanometers in length and independent of severe thermal vibration. When SWNTs were parallel to the axis of silicon pyramids, the tips could obtain high-resolution images without additional treatments.
2007, 23(04): 569-574
doi: 10.3866/PKU.WHXB20070423
Abstract:
Nanocrystalline TiO2 was synthesized by sol-gel method. The surface state properties and transport characters of photogenic free charge carriers were probed by the combination of photoacoustic and surface photovoltaic techniques. The results showed that the surface photovoltage (SPV) response appearing at 380 nm of the samples was closely related to the surface electron structure of anatase-type TiO2 nanoparticles, which belonged to a band-band transition; and that the shoulder peak appearing at 470 nm was related to the surface states of TiO2 nanoparticles, which was a sub-band-gap charge transfer (CT) transition, and had an obvious donor character. By the energy complementarity between photoacoustic and surface photovoltaic effects of the samples, it was experimentally proved that the nonradiative transitions were responsible for the increasing intensity of photoacoustic signals with decreasing average particle size of the sample; but the number of the nonradiative transitions could be dramatically decreased by a little increase of anatase content in the sample, resulting in increasing quantum-optical efficiency.
Nanocrystalline TiO2 was synthesized by sol-gel method. The surface state properties and transport characters of photogenic free charge carriers were probed by the combination of photoacoustic and surface photovoltaic techniques. The results showed that the surface photovoltage (SPV) response appearing at 380 nm of the samples was closely related to the surface electron structure of anatase-type TiO2 nanoparticles, which belonged to a band-band transition; and that the shoulder peak appearing at 470 nm was related to the surface states of TiO2 nanoparticles, which was a sub-band-gap charge transfer (CT) transition, and had an obvious donor character. By the energy complementarity between photoacoustic and surface photovoltaic effects of the samples, it was experimentally proved that the nonradiative transitions were responsible for the increasing intensity of photoacoustic signals with decreasing average particle size of the sample; but the number of the nonradiative transitions could be dramatically decreased by a little increase of anatase content in the sample, resulting in increasing quantum-optical efficiency.
2007, 23(04): 575-580
doi: 10.3866/PKU.WHXB20070424
Abstract:
Nitrobenzene was electroreduced to azobenzene in ionic liquid BMimBF4-H2O on Pt electrode at room temperature. The concentrations of nitrobenzene and water in BMimBF4 had complicated influence on the peak potential and peak current of cyclic voltammogram. The results from cyclic voltammetry and constant-potential electrolysis experiments showed that the reaction was a two-molecule and three-step electrochemical process with 8 electrons transferred. In the reaction, anion radical arose in first step, 2 electrons were transferred in second step and accompanied with coupling reaction of radicals, 2 electrons were transferred in third step, and azobenzene was produced.
Nitrobenzene was electroreduced to azobenzene in ionic liquid BMimBF4-H2O on Pt electrode at room temperature. The concentrations of nitrobenzene and water in BMimBF4 had complicated influence on the peak potential and peak current of cyclic voltammogram. The results from cyclic voltammetry and constant-potential electrolysis experiments showed that the reaction was a two-molecule and three-step electrochemical process with 8 electrons transferred. In the reaction, anion radical arose in first step, 2 electrons were transferred in second step and accompanied with coupling reaction of radicals, 2 electrons were transferred in third step, and azobenzene was produced.
Microencapsulation of n-eicosane as Energy StorageMaterial Synthesized by Interfacial Polymerization
2007, 23(04): 581-584
doi: 10.3866/PKU.WHXB20070425
Abstract:
For heat energy storage application, polyurea microcapsules containing phase change material, n-eicosane, were synthesized by interfacial polymerization method with toluene-2,4-diisocyanate (TDI) and ethylene diamine (EDA) asmonomers in an emulsion system. Poly (ethylene glycol) octyl-phenyl ether (OP), a nonionic surfactant, was the emulsifier for the system. The experiments indicated that TDI was reacted with EDA in a mass ratio of 1.9 to 1. The sizes of microcapsules were analyzed with TEM and laser particle analyzer, which showed the empty microcapsules were about 0.2 μm and those containing n-eicosane were 2-6 μm. FTIR spectra proved the formation of wall material, polyurea, from the two monomers, TDI and EDA. Encapsulation efficiency of n-eicosane was about 75%. Microcapsules of n-eicosane melted at a temperature close to that of n-eicosane, while its stored heat energy varied with the amount of core material n-eicosane. Thermogravimetric analysis revealed that the core material n-eicosane, micro-n-eicosane, and wall material polyurea could withstand temperatures up to 130 ℃, 170 ℃, and 270 ℃, respectively.
For heat energy storage application, polyurea microcapsules containing phase change material, n-eicosane, were synthesized by interfacial polymerization method with toluene-2,4-diisocyanate (TDI) and ethylene diamine (EDA) asmonomers in an emulsion system. Poly (ethylene glycol) octyl-phenyl ether (OP), a nonionic surfactant, was the emulsifier for the system. The experiments indicated that TDI was reacted with EDA in a mass ratio of 1.9 to 1. The sizes of microcapsules were analyzed with TEM and laser particle analyzer, which showed the empty microcapsules were about 0.2 μm and those containing n-eicosane were 2-6 μm. FTIR spectra proved the formation of wall material, polyurea, from the two monomers, TDI and EDA. Encapsulation efficiency of n-eicosane was about 75%. Microcapsules of n-eicosane melted at a temperature close to that of n-eicosane, while its stored heat energy varied with the amount of core material n-eicosane. Thermogravimetric analysis revealed that the core material n-eicosane, micro-n-eicosane, and wall material polyurea could withstand temperatures up to 130 ℃, 170 ℃, and 270 ℃, respectively.
2007, 23(04): 585-589
doi: 10.3866/PKU.WHXB20070426
Abstract:
Nanofibrous polyaniline (PANI) was electropolymeried on graphite electrode by cyclic voltammetry (CV), and a glucose bienzyme sensor based on glucose oxidase ( D) and horseradish peroxidase (HRP) immobilized on the modified electrode was fabricated. The bienzymatic sensor was charaterized by ac impedance spectrometry and SEM. The stability and the factors affected the response of the bienzymetic sensor to glucose were studied. The detection of glucose was carried out at 0.05 V (vs SCE) to minimize the electroactive interferences. The linear response range of the as-prepared bienzyme sensor for glucose was between 0.05 mmol·L-1 and 2.0 mmol·L-1.
Nanofibrous polyaniline (PANI) was electropolymeried on graphite electrode by cyclic voltammetry (CV), and a glucose bienzyme sensor based on glucose oxidase ( D) and horseradish peroxidase (HRP) immobilized on the modified electrode was fabricated. The bienzymatic sensor was charaterized by ac impedance spectrometry and SEM. The stability and the factors affected the response of the bienzymetic sensor to glucose were studied. The detection of glucose was carried out at 0.05 V (vs SCE) to minimize the electroactive interferences. The linear response range of the as-prepared bienzyme sensor for glucose was between 0.05 mmol·L-1 and 2.0 mmol·L-1.
2007, 23(04): 590-594
doi: 10.3866/PKU.WHXB20070427
Abstract:
CoNiP-BaFe12O19 magnetic composite thin film was prepared by composite electrodeposition and characterized by SEM, EDS, XRD, and VSM. The results indicated that BaFe12O19 particles were successfully embedded into the CoNiP hard magnetic thin film. The electrochemical behavior of the electrolyte was studied. The effect of incorporating of BaFe12O19 particles and surfactant CTAB on the mass fraction of the composition in composite thin film was investigated. A maximum mass fraction of 20%of BaFe12O19 was obtained when the concentration of the surfactant CTAB was 0.6 g·L-1. A clear enlargement of coercivity and the squareness ratio resulted from the BaFe12O19 particles being embedded in the thin film.
CoNiP-BaFe12O19 magnetic composite thin film was prepared by composite electrodeposition and characterized by SEM, EDS, XRD, and VSM. The results indicated that BaFe12O19 particles were successfully embedded into the CoNiP hard magnetic thin film. The electrochemical behavior of the electrolyte was studied. The effect of incorporating of BaFe12O19 particles and surfactant CTAB on the mass fraction of the composition in composite thin film was investigated. A maximum mass fraction of 20%of BaFe12O19 was obtained when the concentration of the surfactant CTAB was 0.6 g·L-1. A clear enlargement of coercivity and the squareness ratio resulted from the BaFe12O19 particles being embedded in the thin film.
2007, 23(04): 595-600
doi: 10.3866/PKU.WHXB20070428
Abstract:
A novel magnetic solid superacid SO2-4/ZrO2/Fe3O4/Al2O3 was prepared by a co-precipitation method. The physiochemical properties of the materials were characterized by XRD, IR, TG-DSC, TEM, and HRTEM techniques. The results indicated that the crystallization temperature of the materials shifted to higher temperature with the increase of Al2O3 and Fe3O4 content. The introduction of Al2O3 and Fe3O4 increased the temperature corresponding to the phase transformation, Fe3O4 also endowed this solid superacid a super-paramagnetic feature. TEM results indicated that the crystal grew along [101] direction of ZrO2(t). The superacid SZA-20-200-800 has a maximum acid strength (H0<-13.8) measured by Hammett indicator method, indicating that it is a stronger acid than concentrated H2SO4 (H0=-11.9).
A novel magnetic solid superacid SO2-4/ZrO2/Fe3O4/Al2O3 was prepared by a co-precipitation method. The physiochemical properties of the materials were characterized by XRD, IR, TG-DSC, TEM, and HRTEM techniques. The results indicated that the crystallization temperature of the materials shifted to higher temperature with the increase of Al2O3 and Fe3O4 content. The introduction of Al2O3 and Fe3O4 increased the temperature corresponding to the phase transformation, Fe3O4 also endowed this solid superacid a super-paramagnetic feature. TEM results indicated that the crystal grew along [101] direction of ZrO2(t). The superacid SZA-20-200-800 has a maximum acid strength (H0<-13.8) measured by Hammett indicator method, indicating that it is a stronger acid than concentrated H2SO4 (H0=-11.9).
2007, 23(04): 601-604
doi: 10.3866/PKU.WHXB20070429
Abstract:
Sr3Ti2O7 photocatalyst with perovskite-layered structure was synthesized by polymerized complex method (PCM). Cu ion as an effective dopant was loaded onto Sr3Ti2O7 catalyst. Cu/Sr3Ti2O7 catalyst was applied in the mixture of water and methanol, methanol was used as a sacrificial agent under ultra-violet irradiation, and the catalyst was characterized by XPS, XRD, and UV-Vis DRS. The results showed that Cu existed in several kinds of valence and the photocatalytic activity of Cu/Sr3Ti2O7 was superior to that of pure Sr3Ti2O7. Cu+ and adsorbed oxygen can accelerate the interfacial electron transfer. When the amount of Cu was 1.5%(w), the best catalytic effect was obtained and the stable average hydrogen evolution rate was about 550-600 μmol·h-1. The Cu/Sr3Ti2O7 after reduction attained the highest hydrogen evolution rate that was close to 1140.8 μmol·h-1.
Sr3Ti2O7 photocatalyst with perovskite-layered structure was synthesized by polymerized complex method (PCM). Cu ion as an effective dopant was loaded onto Sr3Ti2O7 catalyst. Cu/Sr3Ti2O7 catalyst was applied in the mixture of water and methanol, methanol was used as a sacrificial agent under ultra-violet irradiation, and the catalyst was characterized by XPS, XRD, and UV-Vis DRS. The results showed that Cu existed in several kinds of valence and the photocatalytic activity of Cu/Sr3Ti2O7 was superior to that of pure Sr3Ti2O7. Cu+ and adsorbed oxygen can accelerate the interfacial electron transfer. When the amount of Cu was 1.5%(w), the best catalytic effect was obtained and the stable average hydrogen evolution rate was about 550-600 μmol·h-1. The Cu/Sr3Ti2O7 after reduction attained the highest hydrogen evolution rate that was close to 1140.8 μmol·h-1.
2007, 23(04): 605-608
doi: 10.3866/PKU.WHXB20070430
Abstract:
Thermal decomposition of ferrous oxalate dihydrate was investigated using in situ X-ray diffraction (XRD) analysis and thermogravimetry in static self-generated air. The master plots method along with a statistical procedure was employed to determine the kinetic model and kinetic parameters of the decomposition processes. The dehydration of ferrous oxalate dihydrate conformed to nuclei production and nuclei growth model, and the decomposition of ferrous oxalate conformed to phase boundary reaction. The results showed that the method could estimate the kinetic parameters for nonisothermal decomposition reactions accurately and reliably.
Thermal decomposition of ferrous oxalate dihydrate was investigated using in situ X-ray diffraction (XRD) analysis and thermogravimetry in static self-generated air. The master plots method along with a statistical procedure was employed to determine the kinetic model and kinetic parameters of the decomposition processes. The dehydration of ferrous oxalate dihydrate conformed to nuclei production and nuclei growth model, and the decomposition of ferrous oxalate conformed to phase boundary reaction. The results showed that the method could estimate the kinetic parameters for nonisothermal decomposition reactions accurately and reliably.
2007, 23(04): 609-613
doi: 10.3866/PKU.WHXB20070431
Abstract:
Using Ca(NO3)2·4H2O, Mg(NO3)2·6H2O and Si (OC2H5)4 as precursors, (Ca1-xMgx)SiO3 powders were prepared by sol-gel method with varying x (0.1, 0.2, 0.3, 0.4, 0.5). The phase constitution, sintering characteristic and dielectric properties of (Ca1-xMgx)SiO3 ceramics were studied. The results showed that the solubility limitation of Mg2+ in CaSiO3 was below 0.2 and CaSiO3 phase was transformed into CaMgSi2O6 phase with substituting Ca2+ by Mg2+. When x was 0.3, the growth of grains was restrained and pores were decreased due to the coexistence of CaSiO3 and CaMgSi2O6, and then the ceramic density was enhanced. The dielectric constant and quality factor of (Ca0.7Mg0.3)SiO3 ceramic sintered at 1320 ℃ were 6.62 and 36962 GHz, respectively.
Using Ca(NO3)2·4H2O, Mg(NO3)2·6H2O and Si (OC2H5)4 as precursors, (Ca1-xMgx)SiO3 powders were prepared by sol-gel method with varying x (0.1, 0.2, 0.3, 0.4, 0.5). The phase constitution, sintering characteristic and dielectric properties of (Ca1-xMgx)SiO3 ceramics were studied. The results showed that the solubility limitation of Mg2+ in CaSiO3 was below 0.2 and CaSiO3 phase was transformed into CaMgSi2O6 phase with substituting Ca2+ by Mg2+. When x was 0.3, the growth of grains was restrained and pores were decreased due to the coexistence of CaSiO3 and CaMgSi2O6, and then the ceramic density was enhanced. The dielectric constant and quality factor of (Ca0.7Mg0.3)SiO3 ceramic sintered at 1320 ℃ were 6.62 and 36962 GHz, respectively.
2007, 23(04): 614-616
doi: 10.3866/PKU.WHXB20070432
Abstract:
The data from 75 known phase diagrams of MX-M'X (X=F, Cl, Br, I; M and M' are monovalent metals) systems were processed by using the support vector machine-atomic parameter pattern recognition method. The regularity of the formation of solid solution in these systems was found. The mathematical model obtained predicted that the CsF-RbF system should form solid solution. The phase diagram of the CsF-RbF system was determined using differential thermal analysis. The results indicated that there was no temperature minimumeither in the solidus or in the liquidus and confirmed that the phase diagram was belonged to the continuous solid solubility system, which was in agreement with the computerized results of thermodynamics in the reference.
The data from 75 known phase diagrams of MX-M'X (X=F, Cl, Br, I; M and M' are monovalent metals) systems were processed by using the support vector machine-atomic parameter pattern recognition method. The regularity of the formation of solid solution in these systems was found. The mathematical model obtained predicted that the CsF-RbF system should form solid solution. The phase diagram of the CsF-RbF system was determined using differential thermal analysis. The results indicated that there was no temperature minimumeither in the solidus or in the liquidus and confirmed that the phase diagram was belonged to the continuous solid solubility system, which was in agreement with the computerized results of thermodynamics in the reference.
2007, 23(04): 617-619
doi: 10.3866/PKU.WHXB20070433
Abstract:
The non-equilibrium phase transition, Ising-like phase transition of two-dimensional fully-frustrated Josephson junction arrays driven by external current was studied in the framework of the short-time dynamic scaling method. Within the resistively shunted junction (RSJ) dynamics, besides the critical temperature TC, the static critical exponents 2β/υ and υ, and dynamic critical exponent z were obtained.
The non-equilibrium phase transition, Ising-like phase transition of two-dimensional fully-frustrated Josephson junction arrays driven by external current was studied in the framework of the short-time dynamic scaling method. Within the resistively shunted junction (RSJ) dynamics, besides the critical temperature TC, the static critical exponents 2β/υ and υ, and dynamic critical exponent z were obtained.
2007, 23(04): 620-624
doi: 10.3866/PKU.WHXB20070434
Abstract:
The functionalized SBA-15 with quaternary ammonium organic group was directly synthesized in acid conditions by using nonionic triblock P123 as template, N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride (TMAPS) as modifying agent. By means of XRD, TEM, N2 adsorption-desorption and Raman spectroscopy, the structure and properties of the functionalized SBA-15 were characterized. The results indicated that the regular hexa nal structural character was retained after the functionalization. With increasing of amounts of TMAPS, the BET surface area, pore size, and pore volume of functionalized SBA-15 were decreased.Moreover, Au-SBA-15 had been successfully prepared by ion exchage of TMAPS groups uniformly distributed in the channel of functionalized SBA-15 with HAuCl4.
The functionalized SBA-15 with quaternary ammonium organic group was directly synthesized in acid conditions by using nonionic triblock P123 as template, N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride (TMAPS) as modifying agent. By means of XRD, TEM, N2 adsorption-desorption and Raman spectroscopy, the structure and properties of the functionalized SBA-15 were characterized. The results indicated that the regular hexa nal structural character was retained after the functionalization. With increasing of amounts of TMAPS, the BET surface area, pore size, and pore volume of functionalized SBA-15 were decreased.Moreover, Au-SBA-15 had been successfully prepared by ion exchage of TMAPS groups uniformly distributed in the channel of functionalized SBA-15 with HAuCl4.
