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2007 Volume 23 Issue 1
2007, 23(01): 1-5
doi: 10.1016/S1872-1508(07)60001-1
Abstract:
Poly(4-diazosulfonate styrene-co-4-vinylpyridine) (P(DSS-co-VP)) can self-assemble (SA) with polyaniline via H-bond interaction. The SA film was then photo-crosslinked under UV irradiation to form a covalent crosslinking structure. The photocurrent of the crosslinked SA films was detenmined directly in aqueous salt solution. The results showed that the polyaniline SA films were materials possessing od photoelectron conversion properties.
Poly(4-diazosulfonate styrene-co-4-vinylpyridine) (P(DSS-co-VP)) can self-assemble (SA) with polyaniline via H-bond interaction. The SA film was then photo-crosslinked under UV irradiation to form a covalent crosslinking structure. The photocurrent of the crosslinked SA films was detenmined directly in aqueous salt solution. The results showed that the polyaniline SA films were materials possessing od photoelectron conversion properties.
Direct Electrochemistry and Bioelectrocatalysis of Myoglobin at a Carbon Nanotube-Modified Electrode
2007, 23(01): 5-11
doi: 10.1016/S1872-1508(07)60002-3
Abstract:
Myoglobin (Mb) was immobilized onto the surface of carbon nanotube (CNT) and was characterized by AFM, XPS, UV-Vis, and FTIR spectroscopy. The promotion effect of CNT on direct electron transfer (DET) reaction of Mb was studied. Cyclic voltammetric results showed a pair of well-defined redox peaks, which corresponded to DET of Mb, with the formal potential (E0′) of (−0.343±0.001) V (vs SCE) in the phosphate buffer solution (PBS, pH 7.0). The electrochemical parameters, such as apparent heterogeneous electron transfer rate constant (ks) and E0′, were determined. The dependence of E0′ on solution pH indicated that DET reaction of Mb was coupled with proton transfer. The experimental results also demonstrated that the immobilized Mb retained its bioelectrocatalytic activity toward the reduction of H2O2 and O2.
Myoglobin (Mb) was immobilized onto the surface of carbon nanotube (CNT) and was characterized by AFM, XPS, UV-Vis, and FTIR spectroscopy. The promotion effect of CNT on direct electron transfer (DET) reaction of Mb was studied. Cyclic voltammetric results showed a pair of well-defined redox peaks, which corresponded to DET of Mb, with the formal potential (E0′) of (−0.343±0.001) V (vs SCE) in the phosphate buffer solution (PBS, pH 7.0). The electrochemical parameters, such as apparent heterogeneous electron transfer rate constant (ks) and E0′, were determined. The dependence of E0′ on solution pH indicated that DET reaction of Mb was coupled with proton transfer. The experimental results also demonstrated that the immobilized Mb retained its bioelectrocatalytic activity toward the reduction of H2O2 and O2.
2007, 23(01): 12-15
doi: 10.3866/PKU.WHXB20070103
Abstract:
The dilational properties of sodium 2-hydroxy-3,5-didecyl benzene sulfonate were expounded at both water-air and water-decane interfaces. It showed that the dilational moduli were one order of magnitude higher than ordinary surfactants such as alkyl benzene sulfonates and the dilational phase angles had lower negative values. These results were attributed to the hydrogen bond formed between surfactant molecules at the interface.
The dilational properties of sodium 2-hydroxy-3,5-didecyl benzene sulfonate were expounded at both water-air and water-decane interfaces. It showed that the dilational moduli were one order of magnitude higher than ordinary surfactants such as alkyl benzene sulfonates and the dilational phase angles had lower negative values. These results were attributed to the hydrogen bond formed between surfactant molecules at the interface.
2007, 23(01): 16-20
doi: 10.3866/PKU.WHXB20070104
Abstract:
A series of TiO2/bentonite catalysts (with different loadings and calcined at different temperatures) were prepared by sol-gel method. The prepared catalysts were employed to photocatalytically degrade organic dye Rhodamine B (RhB) under UV irradiation. The capabilities to degrade organic pollutants were studied by detecting the change of their absorbance and chemical oxygen demand (COD) under UV light irradiation. The results showed that they had a better catalytic reactivity when the loading was 50% and calcination temperature was 400 ℃ (Ti400). Their minerialization activity was slightly less than P25, when UV light irradiation time was 4 h, COD changes of P25 and TiO2/bentonite calcinated at 400 ℃ were 99.7% and 97.0%, respectively. But they were easier to be reused. Ti400 catalyst was employed to degrade RhB, and its photocatalytic activity was kept almost the same after recycling 7 times. The catalysts were further characterized by XRD, BET, and UV-Vis DRS. The experimental results showed that they would have a better activity when their BET surface area was larger.
A series of TiO2/bentonite catalysts (with different loadings and calcined at different temperatures) were prepared by sol-gel method. The prepared catalysts were employed to photocatalytically degrade organic dye Rhodamine B (RhB) under UV irradiation. The capabilities to degrade organic pollutants were studied by detecting the change of their absorbance and chemical oxygen demand (COD) under UV light irradiation. The results showed that they had a better catalytic reactivity when the loading was 50% and calcination temperature was 400 ℃ (Ti400). Their minerialization activity was slightly less than P25, when UV light irradiation time was 4 h, COD changes of P25 and TiO2/bentonite calcinated at 400 ℃ were 99.7% and 97.0%, respectively. But they were easier to be reused. Ti400 catalyst was employed to degrade RhB, and its photocatalytic activity was kept almost the same after recycling 7 times. The catalysts were further characterized by XRD, BET, and UV-Vis DRS. The experimental results showed that they would have a better activity when their BET surface area was larger.
2007, 23(01): 21-26
doi: 10.3866/PKU.WHXB20070105
Abstract:
The inhibition action and adsorption behavior of three Schiff base tetrazole compounds of BIT, BIOHT, and BIMMT on copper in aqueous NaHCO3 (mass fraction 5%) solution were investigated by means of weight loss and electrochemical techniques. The results indicated that the three compounds have od corosion inhibition for copper in NaHCO3 solution. The inhibition efficiency of the three compounds was found to decrease as follows: BIMMT>BIOHT>BIT. The adsorption processes were exothermic reaction and belong to physical adsorption, and the adsorption behavior followed Langmuir isotherm.
The inhibition action and adsorption behavior of three Schiff base tetrazole compounds of BIT, BIOHT, and BIMMT on copper in aqueous NaHCO3 (mass fraction 5%) solution were investigated by means of weight loss and electrochemical techniques. The results indicated that the three compounds have od corosion inhibition for copper in NaHCO3 solution. The inhibition efficiency of the three compounds was found to decrease as follows: BIMMT>BIOHT>BIT. The adsorption processes were exothermic reaction and belong to physical adsorption, and the adsorption behavior followed Langmuir isotherm.
2007, 23(01): 27-31
doi: 10.1016/S1872-1508(07)60003-5
Abstract:
The electronic structures of Ni7O12H122+, Ni6ZnO12H122+, Ni6CuO12H122+, and Ni6CaO12H122+ clusters were calculated using the DV-Xα method of quantum chemistry. By analyzing the density of states, the orbital populations, the net charges, the ionization energies, the transition energies, and the electric charge density differences of the selected clusters, it was indicated that the interaction between Ni and O was enhanced by adding Zn and Cu to nickel hydroxide, and the Ni—O bond was strengthened. As a result, the structural stability of nickel hydroxide was improved and the cycling life of the electrode was extended. However, the addition of Ca weakened the interaction. The ionization energy was dropped and transition energy was elevated by the doping of Zn, Cu, and Ca, and thus the transfer of electrons in electrode materials was accelerated and the electrochemical performance of nickel hydroxide electrode was improved. However, excessive Ca-dopped will change the structure of nickel hydroxide and will deteriorate its electrochemical performance.
The electronic structures of Ni7O12H122+, Ni6ZnO12H122+, Ni6CuO12H122+, and Ni6CaO12H122+ clusters were calculated using the DV-Xα method of quantum chemistry. By analyzing the density of states, the orbital populations, the net charges, the ionization energies, the transition energies, and the electric charge density differences of the selected clusters, it was indicated that the interaction between Ni and O was enhanced by adding Zn and Cu to nickel hydroxide, and the Ni—O bond was strengthened. As a result, the structural stability of nickel hydroxide was improved and the cycling life of the electrode was extended. However, the addition of Ca weakened the interaction. The ionization energy was dropped and transition energy was elevated by the doping of Zn, Cu, and Ca, and thus the transfer of electrons in electrode materials was accelerated and the electrochemical performance of nickel hydroxide electrode was improved. However, excessive Ca-dopped will change the structure of nickel hydroxide and will deteriorate its electrochemical performance.
2007, 23(01): 32-36
doi: 10.3866/PKU.WHXB20070107
Abstract:
Glycine was adsorbed on the surface of kaolinite from aqueous solution with variable concentrations and pH values. The TG/DTA, FT-IR and in situ DRIFT techniques were employed to characterize the adsorption and thermal condensation performances of glycine on kaolinite. The results of the adsorption experiment indicated that the weakly acidic solution favored the adsorption greatly, and gave the largest adsorption amount, however, the adsorption isotherm did not meet the Langmuir model. FT-IR results showed that in the strongly acidic, weakly acidic, and basic solutions, the glycine exists in the form of cation, zwitterion, and anion, respectively. In the weakly acidic solution, the hydrogen bond interaction between —NH3+ and ≡S—O− groups should be the driving force of the adsorption, the hydroxylation of ≡S—O− group in strongly acidic solution and the conversion of —NH3+ to —NH2 in the basic solution were the main reasons for the decrease of adsorption amount. The in situ DRIFT results revealed that linear dimer of glycine was formed during 110−160 ℃ region. Up to 210 ℃, the dimer underwent further intra-molecular condensation to form the cyclodimer diketopiperazine (DKP). During the reaction, no any evidence of the formation of R—CO—O—S(S=Si or Al) intermediates from the esterification reaction was found. The reaction should proceed by the self-condensation mechanism promoted by the hydrogen bond interaction between glycine and kaolinite. The presence of the kaolinite has remarkably decreased the temperature of the condensation reaction.
Glycine was adsorbed on the surface of kaolinite from aqueous solution with variable concentrations and pH values. The TG/DTA, FT-IR and in situ DRIFT techniques were employed to characterize the adsorption and thermal condensation performances of glycine on kaolinite. The results of the adsorption experiment indicated that the weakly acidic solution favored the adsorption greatly, and gave the largest adsorption amount, however, the adsorption isotherm did not meet the Langmuir model. FT-IR results showed that in the strongly acidic, weakly acidic, and basic solutions, the glycine exists in the form of cation, zwitterion, and anion, respectively. In the weakly acidic solution, the hydrogen bond interaction between —NH3+ and ≡S—O− groups should be the driving force of the adsorption, the hydroxylation of ≡S—O− group in strongly acidic solution and the conversion of —NH3+ to —NH2 in the basic solution were the main reasons for the decrease of adsorption amount. The in situ DRIFT results revealed that linear dimer of glycine was formed during 110−160 ℃ region. Up to 210 ℃, the dimer underwent further intra-molecular condensation to form the cyclodimer diketopiperazine (DKP). During the reaction, no any evidence of the formation of R—CO—O—S(S=Si or Al) intermediates from the esterification reaction was found. The reaction should proceed by the self-condensation mechanism promoted by the hydrogen bond interaction between glycine and kaolinite. The presence of the kaolinite has remarkably decreased the temperature of the condensation reaction.
2007, 23(01): 37-43
doi: 10.3866/PKU.WHXB20070108
Abstract:
A new descriptor, vector of principal component scores for GETAWAY index, was derived from a principal components analysis of a matrix of 197 GETAWAY indexes of 20 natural amino acids. The scale was then applied to construct three panels of polypeptide quantitative structure activity relationship (QSAR) based on partial least squares (PLS) regression. The correlation coefficient (Rcum2) and cross-validation correlation coefficient (Qcum2) of the obtained models were 0.887 and 0.753 for 48 bitter tasting dipeptides, 0.995 and 0.708 for 31 bradykinin-potentiating pentapeptides, 0.999 and 0.802 for 20 thromboplastin inhibitors, respectively. The satisfactory results showed that, as new amino acid scales, data of VSGETAWAY may be a useful structural expression methodology for study on peptide QSAR due to its many advantages such as easy manipulation, plentiful structural information and high characterization competence.
A new descriptor, vector of principal component scores for GETAWAY index, was derived from a principal components analysis of a matrix of 197 GETAWAY indexes of 20 natural amino acids. The scale was then applied to construct three panels of polypeptide quantitative structure activity relationship (QSAR) based on partial least squares (PLS) regression. The correlation coefficient (Rcum2) and cross-validation correlation coefficient (Qcum2) of the obtained models were 0.887 and 0.753 for 48 bitter tasting dipeptides, 0.995 and 0.708 for 31 bradykinin-potentiating pentapeptides, 0.999 and 0.802 for 20 thromboplastin inhibitors, respectively. The satisfactory results showed that, as new amino acid scales, data of VSGETAWAY may be a useful structural expression methodology for study on peptide QSAR due to its many advantages such as easy manipulation, plentiful structural information and high characterization competence.
2007, 23(01): 44-49
doi: 10.3866/PKU.WHXB20070109
Abstract:
Sulfonated poly(ether ether ketone) (SPEEK) is a very promising alternative membrane material for direct methanol fuel cells. However, with fairly high degree of sulfonation (DS), which enables high proton conductivity, SPEEK membranes can excessively swell or even dissolve. To deal with this contradictory, poly(ether sulfone) (PES) was blended into SPEEK to prepare PES/SPEEK blend membranes by solvent evaporating. Characteristics of the blend membranes, including thermal property, swelling degree, methanol permeability, proton conductivity and single cell performance, were investigated. DSC results reveal that the two polymers show od miscibility, which results in the homogeneity of the blend membranes. Methanol permeability and swelling degree of the blend membranes are both improved efficiently. The membranes with 20%−30%(w) of PES present the methanol permeability in the order of 1×10−7 cm2•s−1, which is an order of magnitude lower than that of Nafion 115. High proton conductivity of the blend membranes can also be achieved because of increased applicable temperature of membranes. Under 100% relative humidity, the conductivity of blend membrane with 30%(w) PES shows to be 0.078 S•cm−1 at 80 ℃. The single cell performance of blend membrane with 30%(w) PES is better than that of Nafion 115 membrane for its reduced thickness and thereby the resistance.
Sulfonated poly(ether ether ketone) (SPEEK) is a very promising alternative membrane material for direct methanol fuel cells. However, with fairly high degree of sulfonation (DS), which enables high proton conductivity, SPEEK membranes can excessively swell or even dissolve. To deal with this contradictory, poly(ether sulfone) (PES) was blended into SPEEK to prepare PES/SPEEK blend membranes by solvent evaporating. Characteristics of the blend membranes, including thermal property, swelling degree, methanol permeability, proton conductivity and single cell performance, were investigated. DSC results reveal that the two polymers show od miscibility, which results in the homogeneity of the blend membranes. Methanol permeability and swelling degree of the blend membranes are both improved efficiently. The membranes with 20%−30%(w) of PES present the methanol permeability in the order of 1×10−7 cm2•s−1, which is an order of magnitude lower than that of Nafion 115. High proton conductivity of the blend membranes can also be achieved because of increased applicable temperature of membranes. Under 100% relative humidity, the conductivity of blend membrane with 30%(w) PES shows to be 0.078 S•cm−1 at 80 ℃. The single cell performance of blend membrane with 30%(w) PES is better than that of Nafion 115 membrane for its reduced thickness and thereby the resistance.
2007, 23(01): 50-54
doi: 10.1016/S1872-1508(07)60004-7
Abstract:
Dielectric relaxation of alcohols (1-propanol, 1-butanol, sec-butanol, tert-butanol, 1-pentanol, 1-heptanol, 1-octanol, and 1-decanol) with acrylic esters (methyl methacrylate, ethyl methacrylate, and butyl methacrylate) at 9.84 GHz were studied in n-heptane at 298 K. The result showed that 1:1 complex was predominant in these systems. The relaxation time showed a linear dependence with alkyl chain length of both alcohols and acrylic esters, but the dielectric constant showed a reverse trend. A comparative study of the free energy of activation for the dielectric relaxation and viscous flow suggested that a greater interference by neighboring atom was observed in the process of viscous flow than in dielectric relaxation, as the latter involved rotational form of motion, whereas the viscous flow involved both rotational and translational forms of motion.
Dielectric relaxation of alcohols (1-propanol, 1-butanol, sec-butanol, tert-butanol, 1-pentanol, 1-heptanol, 1-octanol, and 1-decanol) with acrylic esters (methyl methacrylate, ethyl methacrylate, and butyl methacrylate) at 9.84 GHz were studied in n-heptane at 298 K. The result showed that 1:1 complex was predominant in these systems. The relaxation time showed a linear dependence with alkyl chain length of both alcohols and acrylic esters, but the dielectric constant showed a reverse trend. A comparative study of the free energy of activation for the dielectric relaxation and viscous flow suggested that a greater interference by neighboring atom was observed in the process of viscous flow than in dielectric relaxation, as the latter involved rotational form of motion, whereas the viscous flow involved both rotational and translational forms of motion.
2007, 23(01): 55-58
doi: 10.1016/S1872-1508(07)60005-9
Abstract:
Single crystalline Sn-doped ZnO nanobelts were successfully synthesized by the carbon thermal reduction deposition process without using any catalyst. XRD investigation confirmed that the products were the wurtzite structure of ZnO. SEM, EDS, and TEM analyses showed that the Sn-doped ZnO nanostructures contained a belt-like morphology with Sn doping content about 1.9%, and the growth direction of nanobelts was along the [0001] direction. A weak UV emission peak at around 398.4 nm and a strong green emission peak at around 494.8 nm were observed at room temperature. The luminescence mechanism of the Sn/ZnO nanobelts was also discussed. These nanobelts were promising building blocks for fabrication of nanoscale optoelectronic devices.
Single crystalline Sn-doped ZnO nanobelts were successfully synthesized by the carbon thermal reduction deposition process without using any catalyst. XRD investigation confirmed that the products were the wurtzite structure of ZnO. SEM, EDS, and TEM analyses showed that the Sn-doped ZnO nanostructures contained a belt-like morphology with Sn doping content about 1.9%, and the growth direction of nanobelts was along the [0001] direction. A weak UV emission peak at around 398.4 nm and a strong green emission peak at around 494.8 nm were observed at room temperature. The luminescence mechanism of the Sn/ZnO nanobelts was also discussed. These nanobelts were promising building blocks for fabrication of nanoscale optoelectronic devices.
2007, 23(01): 59-63
doi: 10.3866/PKU.WHXB20070112
Abstract:
Influence of polydispersity on UV absorption spectra of ZnO nanoparticles, which were prepared from zinc bromide and sodium hydroxide as well as zinc acetate and sodium hydroxide in 2-propanol, had been studied. The particle size was measured with UV absorption spectrometry in-situ and high resolution transmission electron microscope (HRTEM). The growth kinetics of ZnO nanoparticles was in agreement with LSW (Lifshitz-Slyozov-Wagner) model for coarsening where the particle volume was proportional to aging time. However, the particle size distribution was found to be inconsistent with the LSW model, which has been reported previously for other systems. Computer numerical calculation was used to determine the effect of the distribution function on the UV absorption spectra of ZnO suspension. It was found that absorption spectra bent near the UV absorption edge and shifted with the increase of standard deviation (SD) of normal distribution function, which can lead to an over-estimation of the particle size from UV spectra. For monodispersed ZnO suspensions (SD/γ<5%), the over-estimation of particle size is only about 2%. If SD/γ of the particle is 15%, the over-estimation can be as high as 15.1%.
Influence of polydispersity on UV absorption spectra of ZnO nanoparticles, which were prepared from zinc bromide and sodium hydroxide as well as zinc acetate and sodium hydroxide in 2-propanol, had been studied. The particle size was measured with UV absorption spectrometry in-situ and high resolution transmission electron microscope (HRTEM). The growth kinetics of ZnO nanoparticles was in agreement with LSW (Lifshitz-Slyozov-Wagner) model for coarsening where the particle volume was proportional to aging time. However, the particle size distribution was found to be inconsistent with the LSW model, which has been reported previously for other systems. Computer numerical calculation was used to determine the effect of the distribution function on the UV absorption spectra of ZnO suspension. It was found that absorption spectra bent near the UV absorption edge and shifted with the increase of standard deviation (SD) of normal distribution function, which can lead to an over-estimation of the particle size from UV spectra. For monodispersed ZnO suspensions (SD/γ<5%), the over-estimation of particle size is only about 2%. If SD/γ of the particle is 15%, the over-estimation can be as high as 15.1%.
2007, 23(01): 64-67
doi: 10.1016/S1872-1508(07)60006-0
Abstract:
With n-hexanol as cosurfactant, quaternary ammonium Gemini surfactants C12-EOx-C12•2Br (x=1, 2, 3)formed reverse micelles in n-heptane. The critical reverse micelle concentrations (cmch) were determined using the absorption spectrum method with iodine as the probe. All values were less than the corresponding critical micelle concentration (cmcaq) in aqueous solution, where C12-EOx-C12•2Br formed the normal micelles. The cmch increased with increasing x, which was similar to the variation of cmcaq with x. The saturated amount of water solubilizated by the reverse micelles was enhanced by either increasing x or by raising the temperature.
With n-hexanol as cosurfactant, quaternary ammonium Gemini surfactants C12-EOx-C12•2Br (x=1, 2, 3)formed reverse micelles in n-heptane. The critical reverse micelle concentrations (cmch) were determined using the absorption spectrum method with iodine as the probe. All values were less than the corresponding critical micelle concentration (cmcaq) in aqueous solution, where C12-EOx-C12•2Br formed the normal micelles. The cmch increased with increasing x, which was similar to the variation of cmcaq with x. The saturated amount of water solubilizated by the reverse micelles was enhanced by either increasing x or by raising the temperature.
2007, 23(01): 68-72
doi: 10.3866/PKU.WHXB20070114
Abstract:
Porous silicon electrodes with electrodeposited Pt nanoparticles by cyclic voltammetry (Pt/Si) could be used as catalytic electrodes in micro proton exchange membrane fuel cells. As-deposited Pt nanoparticles with a mean diameter of ca 7 nm are highly dispersed on the surface of porous silicon. As compared to the electrode prepared by brushing nanosized Pt/C catalyst on the surface of porous silicon (Pt-C/Si), the Pt/Si modified electrodes exhibited high Pt utilization and enhanced catalytic performances for the hydrogen adsorption/desorption and for methanol oxidation. The maximum electrochemical specific area of ca 148 cm2•mg−1 was obtained with an electrodeposited Pt loading of ca 0.38 mg•cm−2, which is ca 2 times higher than that of the Pt-C/Si electrode with similar Pt loading of ca 0.40 mg•cm−2. Such a Pt/Si electrode showed an enhanced catalytic activity for methanol oxidation. After polarization at 0.5 V(vs SCE) for 1 h in 0.5 mol•L−1 CH3OH+0.5 mol•L−1 H2SO4, the obtained current density on this electrode was ca 4.52 mA•cm−2, which was much higher than the current density of 0.36 mA•cm−2 on Pt-C/Si electrode, again assessing high catalytic activity and od stability of electrodeposited Pt modified electrodes.
Porous silicon electrodes with electrodeposited Pt nanoparticles by cyclic voltammetry (Pt/Si) could be used as catalytic electrodes in micro proton exchange membrane fuel cells. As-deposited Pt nanoparticles with a mean diameter of ca 7 nm are highly dispersed on the surface of porous silicon. As compared to the electrode prepared by brushing nanosized Pt/C catalyst on the surface of porous silicon (Pt-C/Si), the Pt/Si modified electrodes exhibited high Pt utilization and enhanced catalytic performances for the hydrogen adsorption/desorption and for methanol oxidation. The maximum electrochemical specific area of ca 148 cm2•mg−1 was obtained with an electrodeposited Pt loading of ca 0.38 mg•cm−2, which is ca 2 times higher than that of the Pt-C/Si electrode with similar Pt loading of ca 0.40 mg•cm−2. Such a Pt/Si electrode showed an enhanced catalytic activity for methanol oxidation. After polarization at 0.5 V(vs SCE) for 1 h in 0.5 mol•L−1 CH3OH+0.5 mol•L−1 H2SO4, the obtained current density on this electrode was ca 4.52 mA•cm−2, which was much higher than the current density of 0.36 mA•cm−2 on Pt-C/Si electrode, again assessing high catalytic activity and od stability of electrodeposited Pt modified electrodes.
2007, 23(01): 73-78
doi: 10.1016/S1872-1508(07)60007-2
Abstract:
Ce0.35Zr0.55La0.10O1.95 solid solution was prepared by coprecipitation technique and characterized by specific surface area measurements (BET), X-ray diffraction (XRD), and temperature-programmed (TP) technique. Ce0.35Zr0.55La0.10O1.95 was used to prepare low Pt-Rh three-way catalyst (TWC) and its influence on the performance of TWC was investigated. The results showed that Ce0.35Zr0.55La0.10O1.95 had a cubic structure similar to Ce0.50Zr0.50O2 and high specific area after calcined at 600 ℃ for 5 h. Furthermore, after being aged at 1000 ℃ for 5 h, Ce0.35Zr0.55La0.10O1.95 still maintained a stable cubic structure and a specific surface area of 47.25 m2•g−1. The results of H2-TPR and O2-TPO indicated that Ce0.35Zr0.55La0.10O1.95 had od redox properties. The catalyst containing Ce0.35Zr0.55La0.10O1.95 possessed fairly wide range of three-way working-windows, od low temperature light-off properties, and better ability of water-gas shift. Being hydrothermal aged at 1000 ℃, the catalyst containing Ce0.35Zr0.55La0.10O1.95 still showed od catalytic activity in comparison with Ce0.50Zr0.50O2 TWC, which indicated that Ce0.35Zr0.55La0.10O1.95 improved the anti-aging properties of the catalyst.
Ce0.35Zr0.55La0.10O1.95 solid solution was prepared by coprecipitation technique and characterized by specific surface area measurements (BET), X-ray diffraction (XRD), and temperature-programmed (TP) technique. Ce0.35Zr0.55La0.10O1.95 was used to prepare low Pt-Rh three-way catalyst (TWC) and its influence on the performance of TWC was investigated. The results showed that Ce0.35Zr0.55La0.10O1.95 had a cubic structure similar to Ce0.50Zr0.50O2 and high specific area after calcined at 600 ℃ for 5 h. Furthermore, after being aged at 1000 ℃ for 5 h, Ce0.35Zr0.55La0.10O1.95 still maintained a stable cubic structure and a specific surface area of 47.25 m2•g−1. The results of H2-TPR and O2-TPO indicated that Ce0.35Zr0.55La0.10O1.95 had od redox properties. The catalyst containing Ce0.35Zr0.55La0.10O1.95 possessed fairly wide range of three-way working-windows, od low temperature light-off properties, and better ability of water-gas shift. Being hydrothermal aged at 1000 ℃, the catalyst containing Ce0.35Zr0.55La0.10O1.95 still showed od catalytic activity in comparison with Ce0.50Zr0.50O2 TWC, which indicated that Ce0.35Zr0.55La0.10O1.95 improved the anti-aging properties of the catalyst.
2007, 23(01): 79-83
doi: 10.1016/S1872-1508(07)60008-4
Abstract:
Measurements of density (ρ), viscosity (η), and refractive index (n), were carried out on α-amino acids, DL-alanine (Ala), D-phenylalanine (Phe), and DL-threonine (Thr) (0.01−0.05 mol•L−1), in 0.05 mol•L−1 aqueous caffeine solution at 298.15, 303.15, 308.15, and 313.15 K. These measurements have been carried out to evaluate some important parameters, viz., apparent molar volume (øv), partial molar volume (øv0), transfer volume (øv0(tr)), viscosity A and B coefficients of Jones-Dole equation, free energies of activation per mole of solvent (Δμ10#) and solute (Δμ20#), enthalpies (ΔH*) and entropies (ΔS*) of activation of viscous flow, variation of B with temperature (∂B/∂T)P, and molar refractive index (RD). These parameters have been interpreted in terms of solute-solute and solute-solvent interactions and structure making/breaking ability of solutes in the given solution.
Measurements of density (ρ), viscosity (η), and refractive index (n), were carried out on α-amino acids, DL-alanine (Ala), D-phenylalanine (Phe), and DL-threonine (Thr) (0.01−0.05 mol•L−1), in 0.05 mol•L−1 aqueous caffeine solution at 298.15, 303.15, 308.15, and 313.15 K. These measurements have been carried out to evaluate some important parameters, viz., apparent molar volume (øv), partial molar volume (øv0), transfer volume (øv0(tr)), viscosity A and B coefficients of Jones-Dole equation, free energies of activation per mole of solvent (Δμ10#) and solute (Δμ20#), enthalpies (ΔH*) and entropies (ΔS*) of activation of viscous flow, variation of B with temperature (∂B/∂T)P, and molar refractive index (RD). These parameters have been interpreted in terms of solute-solute and solute-solvent interactions and structure making/breaking ability of solutes in the given solution.
2007, 23(01): 84-87
doi: 10.3866/PKU.WHXB20070117
Abstract:
The thermal denaturation of solid lysozyme and the effects of denaturants and their concentrations on denaturation of lysozyme in aqueous solutions were studied by differential scanning calorimetry (DSC). The results showed that both denaturation temperature and denaturation enthalpy of lysozyme decreased as the existence of water and the addition of urea and guanidine hydrochloride (GuHCl). In addition, denaturation temperature and denaturation enthalpy decreased as the concentrations of urea and GuHCl increased. As a denaturant, GuHCl is more effective than urea due to its added ability of electrostatic interaction.
The thermal denaturation of solid lysozyme and the effects of denaturants and their concentrations on denaturation of lysozyme in aqueous solutions were studied by differential scanning calorimetry (DSC). The results showed that both denaturation temperature and denaturation enthalpy of lysozyme decreased as the existence of water and the addition of urea and guanidine hydrochloride (GuHCl). In addition, denaturation temperature and denaturation enthalpy decreased as the concentrations of urea and GuHCl increased. As a denaturant, GuHCl is more effective than urea due to its added ability of electrostatic interaction.
2007, 23(01): 88-91
doi: 10.1016/S1872-1508(07)60009-6
Abstract:
SnO2:Sb xerogel was prepared using the sol-gel technique with SnCl2•2H2O and SbCl3 as the starting materials. Partial sublimation of SnO2:Sb xerogel during oxidation was utilized to treat the as-prepared ZnS:Mn phosphor. The mass ratio of SnO2:Sb xerogel to ZnS:Mn phosphors changed from 0.5 to 4.0 and the range of the oxidation temperature was 300−600 ℃ under the given oxygen flux (0.2 L•min−1) and oxidation duration (30 min). The treated phosphors were characterized by X-ray diffraction (XRD), photoluminescence (PL), transmittance electron microscopy (TEM), and electrical resistance measurements. The results showed that the conductivity of the treated ZnS:Mn phosphors was obviously improved when the mass ratio of SnO2:Sb xerogel to ZnS:Mn phosphors and the oxidation temperature were 3.0 and 500 ℃, respectively. The photoluminescence characteristics and crystal structure of the treated ZnS:Mn phosphors remained the same as the as-prepared phosphors.
SnO2:Sb xerogel was prepared using the sol-gel technique with SnCl2•2H2O and SbCl3 as the starting materials. Partial sublimation of SnO2:Sb xerogel during oxidation was utilized to treat the as-prepared ZnS:Mn phosphor. The mass ratio of SnO2:Sb xerogel to ZnS:Mn phosphors changed from 0.5 to 4.0 and the range of the oxidation temperature was 300−600 ℃ under the given oxygen flux (0.2 L•min−1) and oxidation duration (30 min). The treated phosphors were characterized by X-ray diffraction (XRD), photoluminescence (PL), transmittance electron microscopy (TEM), and electrical resistance measurements. The results showed that the conductivity of the treated ZnS:Mn phosphors was obviously improved when the mass ratio of SnO2:Sb xerogel to ZnS:Mn phosphors and the oxidation temperature were 3.0 and 500 ℃, respectively. The photoluminescence characteristics and crystal structure of the treated ZnS:Mn phosphors remained the same as the as-prepared phosphors.
2007, 23(01): 92-97
doi: 10.1016/S1872-1508(07)60010-2
Abstract:
PtMoSi/C nanocatalysts were prepared by chemical reduction using formaldehyde, H2, and hydrazine as reducing agents, respectively. The nanocompositions were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). XRD patterns showed a face-centered cubic crystal structure, and TEM images indicated that the nanoparticles that were uniformly dispersed on carbon were 3−4 nm in diameter. XPS analysis revealed that the catalysts contained mostly Pt(0), Mo(VI), and Si(IV). The effects of preparation methods and additives on the catalytic activity were then studied by linear sweep voltammetry (LSV) and cyclic voltammetry (CV). It was found that the PtMoSi/C nanocatalysts (nPt:nMo=3:1 was the optimal ratio of Pt to Mo) prepared using formaldehyde as reducing agent showed higher electrocatalytic activity and better tolerance to poisoning species in methanol oxidation compared with the homemade PtRu/C and the commercial E-TEK PtRu/C catalysts, and this could be ascribed to the high dispersion of Pt nanoparticles on the carbon by the addition of silicomolybdic acid.
PtMoSi/C nanocatalysts were prepared by chemical reduction using formaldehyde, H2, and hydrazine as reducing agents, respectively. The nanocompositions were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). XRD patterns showed a face-centered cubic crystal structure, and TEM images indicated that the nanoparticles that were uniformly dispersed on carbon were 3−4 nm in diameter. XPS analysis revealed that the catalysts contained mostly Pt(0), Mo(VI), and Si(IV). The effects of preparation methods and additives on the catalytic activity were then studied by linear sweep voltammetry (LSV) and cyclic voltammetry (CV). It was found that the PtMoSi/C nanocatalysts (nPt:nMo=3:1 was the optimal ratio of Pt to Mo) prepared using formaldehyde as reducing agent showed higher electrocatalytic activity and better tolerance to poisoning species in methanol oxidation compared with the homemade PtRu/C and the commercial E-TEK PtRu/C catalysts, and this could be ascribed to the high dispersion of Pt nanoparticles on the carbon by the addition of silicomolybdic acid.
2007, 23(01): 98-102
doi: 10.3866/PKU.WHXB20070120
Abstract:
The effects of Mo on the catalytic and surface properties of amorphous alloy Ni-B/TiO2-Al2O3(S) had been studied. Liquid-phase furfural hydrogenation to furfural alcohol was selected as probe reaction. The properties of the catalysts were characterized using ICP, DSC, N2 adsorption, TPD, and TPR, respectively. The catalytic activity of Ni-B/TiO2-Al2O3(S) was higher than that of Ni-B/γ-Al2O3, which was due to the more Ni content in the former. Moreover, the decrease of micro-pore number leaded to higher selectivity, since the diffusion of the product in micropore was difficult. The addition of Mo could make Ni be reduced easier, produce new active centers over the surface of the catalyst, weaken the strength of Ni—H bond, and increase the number of adsorption centers, which resulted in the increasing activity of Ni-B/TiO2-Al2O3(S). Mo could enlarge the average pore size and volume, resulting in the easier diffusion of furfural alcohol to the surface of catalyst. At the same time, the results of TPD showed that Mo made furfural alcohol desorb easier from the catalyst surface. Therefore, the selectivity of the catalyst was improved. When Mo Content was 1.25%, both of the activity and selectivity of the catalysts reached to 100%.
The effects of Mo on the catalytic and surface properties of amorphous alloy Ni-B/TiO2-Al2O3(S) had been studied. Liquid-phase furfural hydrogenation to furfural alcohol was selected as probe reaction. The properties of the catalysts were characterized using ICP, DSC, N2 adsorption, TPD, and TPR, respectively. The catalytic activity of Ni-B/TiO2-Al2O3(S) was higher than that of Ni-B/γ-Al2O3, which was due to the more Ni content in the former. Moreover, the decrease of micro-pore number leaded to higher selectivity, since the diffusion of the product in micropore was difficult. The addition of Mo could make Ni be reduced easier, produce new active centers over the surface of the catalyst, weaken the strength of Ni—H bond, and increase the number of adsorption centers, which resulted in the increasing activity of Ni-B/TiO2-Al2O3(S). Mo could enlarge the average pore size and volume, resulting in the easier diffusion of furfural alcohol to the surface of catalyst. At the same time, the results of TPD showed that Mo made furfural alcohol desorb easier from the catalyst surface. Therefore, the selectivity of the catalyst was improved. When Mo Content was 1.25%, both of the activity and selectivity of the catalysts reached to 100%.
2007, 23(01): 103-106
doi: 10.3866/PKU.WHXB20070121
Abstract:
Raman spectra of solutions of NaX (X=F, Cl, Br, I), Na2S, NaOH, NaNO3, Na2CO3, Na2SO4 and water were compared. The results showed that all of the studied anions broke the structure of water. The effects of the studied anions on Raman spectrum of water could be summed up into two kinds. F−, OH−, S2−, CO32− belonged to one kind, and Cl−, Br−, I−, NO3−, and SO42− belonged to the other. The main differences lay on their effects on 3600 cm−1 and 2900−3100 cm−1 of OH stretching Raman spectrum of water. And the reason that conduced to these differences was the intensity of hydrogen bond between anion and water molecule. Parameters of the anion influencing OH stretching Raman spectra of water included ion radius, ion charge and ion structure. The order of their effects on water structure was ion structure>ion charge>ion radius
Raman spectra of solutions of NaX (X=F, Cl, Br, I), Na2S, NaOH, NaNO3, Na2CO3, Na2SO4 and water were compared. The results showed that all of the studied anions broke the structure of water. The effects of the studied anions on Raman spectrum of water could be summed up into two kinds. F−, OH−, S2−, CO32− belonged to one kind, and Cl−, Br−, I−, NO3−, and SO42− belonged to the other. The main differences lay on their effects on 3600 cm−1 and 2900−3100 cm−1 of OH stretching Raman spectrum of water. And the reason that conduced to these differences was the intensity of hydrogen bond between anion and water molecule. Parameters of the anion influencing OH stretching Raman spectra of water included ion radius, ion charge and ion structure. The order of their effects on water structure was ion structure>ion charge>ion radius
2007, 23(01): 107-110
doi: 10.3866/PKU.WHXB20070122
Abstract:
An economical method to produce hydrogen by direct electrolysis of methanol is developed. It is demonstrated that the hydrogen produced by the electrolysis of methanol can considerably reduce the consumption of electricity. The novelty of this technique is the inherent simplicity and the substantially lowered cost. Using these modified proton exchange membrane fuel cell membrane electrode assembly (PEMFC-MEA) as an electrolyzer, any scale requirements can be easily achieved. The combination of this electrolyzer concept with the concept of solar cells would economically produce hydrogen for storage and subsequent use in, or for in situ use in, fuel cells and chemical engineering applications.
An economical method to produce hydrogen by direct electrolysis of methanol is developed. It is demonstrated that the hydrogen produced by the electrolysis of methanol can considerably reduce the consumption of electricity. The novelty of this technique is the inherent simplicity and the substantially lowered cost. Using these modified proton exchange membrane fuel cell membrane electrode assembly (PEMFC-MEA) as an electrolyzer, any scale requirements can be easily achieved. The combination of this electrolyzer concept with the concept of solar cells would economically produce hydrogen for storage and subsequent use in, or for in situ use in, fuel cells and chemical engineering applications.
2007, 23(01): 111-115
doi: 10.3866/PKU.WHXB20070123
Abstract:
The Bi2WO6 films on ITO glass substrates have been prepared from amorphous complex precursor by dip-coating technique. The structure and photoelectrochemical properties of the films were investigated by using FE-SEM, XRD, Raman, DRS, IPCE (incident photon-to-current conversion efficiency) and photocurrent action curves. The crystalline Bi2WO6 film could be obtained above 450 ℃, which was composed of Bi2WO6 nanoparticles growing along (131) face. The size of Bi2WO6 nanoparticles was increased with the calcination temperature, and the space between the nanoparticles also increased. Under the visible light (λ>400 nm) irradiation, the photocurrent was generated from the ITO/Bi2WO6 photo-electrode, with the photocurrent density linear to the light intensity. The photocurrent density and IPCE can be controlled by modifying the surface structure of Bi2WO6 films, which can be achieved by changing the preparation conditions (such as calcination temperature).
The Bi2WO6 films on ITO glass substrates have been prepared from amorphous complex precursor by dip-coating technique. The structure and photoelectrochemical properties of the films were investigated by using FE-SEM, XRD, Raman, DRS, IPCE (incident photon-to-current conversion efficiency) and photocurrent action curves. The crystalline Bi2WO6 film could be obtained above 450 ℃, which was composed of Bi2WO6 nanoparticles growing along (131) face. The size of Bi2WO6 nanoparticles was increased with the calcination temperature, and the space between the nanoparticles also increased. Under the visible light (λ>400 nm) irradiation, the photocurrent was generated from the ITO/Bi2WO6 photo-electrode, with the photocurrent density linear to the light intensity. The photocurrent density and IPCE can be controlled by modifying the surface structure of Bi2WO6 films, which can be achieved by changing the preparation conditions (such as calcination temperature).
2007, 23(01): 116-119
doi: 10.3866/PKU.WHXB20070124
Abstract:
The association of α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD) with sodium polyoxyethylene dodecyl sulfonate (C12EnS, n=1, 3) was studied by means of isothermal titration calorimetry and 1H NMR measurements in aqueous solution at 298.15 K. The results indicated that the binding processes of β-CD with the surfactants were characterized by both enthalpy favorable and entropy favorable, while those of α-CD with the surfactants were mainly entropy driven. The stoichiometry of β-CD binding with the surfactants varied with numbers of oxyethyl groups in surfactant molecules, while that of α-CD binding with the surfactants made no difference. The 1H NMR spectra revealed that chemical shift data of all protons in α-CD and β-CD molecules moved to high field in the presence of C12EnS, which could be regarded as a microscopic evidence of the occurrence of inclusion interaction.
The association of α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD) with sodium polyoxyethylene dodecyl sulfonate (C12EnS, n=1, 3) was studied by means of isothermal titration calorimetry and 1H NMR measurements in aqueous solution at 298.15 K. The results indicated that the binding processes of β-CD with the surfactants were characterized by both enthalpy favorable and entropy favorable, while those of α-CD with the surfactants were mainly entropy driven. The stoichiometry of β-CD binding with the surfactants varied with numbers of oxyethyl groups in surfactant molecules, while that of α-CD binding with the surfactants made no difference. The 1H NMR spectra revealed that chemical shift data of all protons in α-CD and β-CD molecules moved to high field in the presence of C12EnS, which could be regarded as a microscopic evidence of the occurrence of inclusion interaction.
2007, 23(01): 120-123
doi: 10.3866/PKU.WHXB20070125
Abstract:
The structures of BH4+, BH4, and BH4− were optimized at the level of B3LYP/6-311+G(d,p) and CCSD/6-311+G(d,p). The topological analyses of electronic density for chemical bonds of the neutral and charged BH4 were performed. The calculated results show that the symmetries of BH4+, BH4, and BH4− are C2v, C2v, and Td, respectively. There are B—H bond, H—H bond and atom-molecular bond in BH4+ and BH4. There are four equivalent B—H bonds in BH4−. In the case of BH4 there is an unpaired electron that occurs near the boron atom.
The structures of BH4+, BH4, and BH4− were optimized at the level of B3LYP/6-311+G(d,p) and CCSD/6-311+G(d,p). The topological analyses of electronic density for chemical bonds of the neutral and charged BH4 were performed. The calculated results show that the symmetries of BH4+, BH4, and BH4− are C2v, C2v, and Td, respectively. There are B—H bond, H—H bond and atom-molecular bond in BH4+ and BH4. There are four equivalent B—H bonds in BH4−. In the case of BH4 there is an unpaired electron that occurs near the boron atom.
2007, 23(01): 124-128
doi: 10.3866/PKU.WHXB20070126
Abstract:
The excess molar enthalpies for binary systems of tributylphosphate(TBP) +methanol/ethanol/1-propanol/1-butanol were measured by calorimetry at 298.15 K as well as a little mixtures at 293.15 K and 303.15 K. The experimental results were in the range of −0.3 − 0.3 kJ•mol−1 and were invariant with the change of temperature. The excess molar entropies, excess molar Gibbs free energies, and activity coefficients for the binary mixtures had been obtained according to the athermal solution model. The thermodynamic analysis showed that the model provided reliable results for binary mixtures of TBP+methanol/ethanol/propan-1-ol, but did not for TBP+butan-1-ol.
The excess molar enthalpies for binary systems of tributylphosphate(TBP) +methanol/ethanol/1-propanol/1-butanol were measured by calorimetry at 298.15 K as well as a little mixtures at 293.15 K and 303.15 K. The experimental results were in the range of −0.3 − 0.3 kJ•mol−1 and were invariant with the change of temperature. The excess molar entropies, excess molar Gibbs free energies, and activity coefficients for the binary mixtures had been obtained according to the athermal solution model. The thermodynamic analysis showed that the model provided reliable results for binary mixtures of TBP+methanol/ethanol/propan-1-ol, but did not for TBP+butan-1-ol.
2007, 23(01): 129-133
doi: 10.3866/PKU.WHXB20070127
Abstract:
Kinetics of electrode processes of LiFePO4 in saturated LiNO3 solution was investigated by analyses of cyclic voltammetry (CV), charge/discharge test, and potentiostatic intermittent titration (PITT). The results showed that LiFePO4 had od electrochemical reversibility in saturated LiNO3 solution. The first discharge capacity was about 116.2 mAh•g−1, and its charge/discharge efficiency was 92%. The lithium diffusion coefficients, corresponding to anodic peak and cathodic peak in LiFePO4, obtained from CV were 4.3×10−11 cm2•s−1 and 3.8×10−11 cm2•s−1. The lithium diffusion coefficients obtained from PITT varied with potentials, and the lowest value was about 5.5×10−11 cm2•s−1, coinciding with the voltage plateau region in the charge curves.
Kinetics of electrode processes of LiFePO4 in saturated LiNO3 solution was investigated by analyses of cyclic voltammetry (CV), charge/discharge test, and potentiostatic intermittent titration (PITT). The results showed that LiFePO4 had od electrochemical reversibility in saturated LiNO3 solution. The first discharge capacity was about 116.2 mAh•g−1, and its charge/discharge efficiency was 92%. The lithium diffusion coefficients, corresponding to anodic peak and cathodic peak in LiFePO4, obtained from CV were 4.3×10−11 cm2•s−1 and 3.8×10−11 cm2•s−1. The lithium diffusion coefficients obtained from PITT varied with potentials, and the lowest value was about 5.5×10−11 cm2•s−1, coinciding with the voltage plateau region in the charge curves.
2007, 23(01): 134-138
doi: 10.3866/PKU.WHXB20070128
Abstract:
LiNi0.01Co0.01Mn1.98O4 materials were prepared by two different methods: starch-assisted combustion (SAC), and traditional solid-state reaction. The product characteristics such as phase composition, particle morphology, and size of as-prepared materials were examined with powder X-ray diffraction (XRD), the Brunauer-Emmett-Teller (BET) surface area method, particle size analysis, and analytical scanning electron microscope (SEM), respectively. Both materials exhibited pure spinel structure. The SAC method provided better control of the morphology, particle size, and distribution of the active material. The as-prepared powders were used as positive electrode materials for lithium-ion battery, whose discharge capacity and cycle voltammogram properties were examined. The results showed that the material synthesized by SAC method had high initial specific capacity of 121.2 mAh•g−1 and only 3.5% loss of the capacity after 100 cycles at a rate of 0.1C, and the initial specific capacity was 103.5 mAh•g−1 at a discharge rate of 5C. The single-step process of SAC method is time and cost saving, and thus is promising for commercial application.
LiNi0.01Co0.01Mn1.98O4 materials were prepared by two different methods: starch-assisted combustion (SAC), and traditional solid-state reaction. The product characteristics such as phase composition, particle morphology, and size of as-prepared materials were examined with powder X-ray diffraction (XRD), the Brunauer-Emmett-Teller (BET) surface area method, particle size analysis, and analytical scanning electron microscope (SEM), respectively. Both materials exhibited pure spinel structure. The SAC method provided better control of the morphology, particle size, and distribution of the active material. The as-prepared powders were used as positive electrode materials for lithium-ion battery, whose discharge capacity and cycle voltammogram properties were examined. The results showed that the material synthesized by SAC method had high initial specific capacity of 121.2 mAh•g−1 and only 3.5% loss of the capacity after 100 cycles at a rate of 0.1C, and the initial specific capacity was 103.5 mAh•g−1 at a discharge rate of 5C. The single-step process of SAC method is time and cost saving, and thus is promising for commercial application.
