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2005 Volume 21 Issue 5
2005, 21(05): 463-467
doi: 10.3866/PKU.WHXB20050501
Abstract:
The potential-time curves under constant current and cyclic voltammetry curves were measured, and the potential activation process of copper plating on iron substrate in cyanide electrolyte was shown. The initial process of pyrophosphate copper plating on the iron electrode was studied. The results show that deposition potential of copper is positive and copper deposits on the inactive surface of electrode. The bond intensity of plating layer is very bad. By using Ar ion sputtering and X-ray photoelectron spectroscopy, the oxygen contents between the copper plating layer and iron substrate were examined and the existence of oxygen layer was proved. Through adding assistant complexing agent and controlling initial current density, cathodic polarization was intensified in cyanide-free electrolyte. When the deposition potential of copper is less than activation potential of the iron substrate, the potential activation process was shown. The bond intensity of the plating layer is close to that of cyanide copper plating.
The potential-time curves under constant current and cyclic voltammetry curves were measured, and the potential activation process of copper plating on iron substrate in cyanide electrolyte was shown. The initial process of pyrophosphate copper plating on the iron electrode was studied. The results show that deposition potential of copper is positive and copper deposits on the inactive surface of electrode. The bond intensity of plating layer is very bad. By using Ar ion sputtering and X-ray photoelectron spectroscopy, the oxygen contents between the copper plating layer and iron substrate were examined and the existence of oxygen layer was proved. Through adding assistant complexing agent and controlling initial current density, cathodic polarization was intensified in cyanide-free electrolyte. When the deposition potential of copper is less than activation potential of the iron substrate, the potential activation process was shown. The bond intensity of the plating layer is close to that of cyanide copper plating.
2005, 21(05): 468-473
doi: 10.3866/PKU.WHXB20050502
Abstract:
A sol-gel method was employed to prepare M/(M )y(CeO2)1－y (M=Ni, Co, Cu) catalyst for methane combustion. The relationship between the catalytic activity of Ni/(M )y(CeO2)1－y and the content of Ce was studied. Ni/(M )0.9(CeO2)0.1 was found to have the highest catalytic activity and the best thermal stability. The effect of the activity of M/(M )0.9(CeO2)0.1 (M=Ni, Co, Cu) on combustion of methane was investigated. Cu/(M )0.9(CeO2)0.1 had the highest activity, but was sintered after second evaluation. The catalytic activity of Ni/(M )0.9(CeO2)0.1 catalyst was similar to that of Cu/(M )0.9(CeO2)0.1 catalyst and Ni/(M )0.9(CeO2)0.1 catalyst had the best thermal stability. Co/(M )0.9(CeO2)0.1 catalyst exhibited the lowest activity and a mediate stability, it retained a large specific surface area after second evaluation. Ni/(M )0.9(CeO2)0.1 catalyst calcined at 1000 ℃ still had a specific surface area of 14.32 m2•g－1 and high catalytic activity as well as od thermal stability.
A sol-gel method was employed to prepare M/(M )y(CeO2)1－y (M=Ni, Co, Cu) catalyst for methane combustion. The relationship between the catalytic activity of Ni/(M )y(CeO2)1－y and the content of Ce was studied. Ni/(M )0.9(CeO2)0.1 was found to have the highest catalytic activity and the best thermal stability. The effect of the activity of M/(M )0.9(CeO2)0.1 (M=Ni, Co, Cu) on combustion of methane was investigated. Cu/(M )0.9(CeO2)0.1 had the highest activity, but was sintered after second evaluation. The catalytic activity of Ni/(M )0.9(CeO2)0.1 catalyst was similar to that of Cu/(M )0.9(CeO2)0.1 catalyst and Ni/(M )0.9(CeO2)0.1 catalyst had the best thermal stability. Co/(M )0.9(CeO2)0.1 catalyst exhibited the lowest activity and a mediate stability, it retained a large specific surface area after second evaluation. Ni/(M )0.9(CeO2)0.1 catalyst calcined at 1000 ℃ still had a specific surface area of 14.32 m2•g－1 and high catalytic activity as well as od thermal stability.
2005, 21(05): 474-478
doi: 10.3866/PKU.WHXB20050503
Abstract:
α-conotoxins, extracted from conus venoms, are a family of active peptides. The most characteristic and predominant features of these small peptides are fewer disulfide bonds, simpler structure, and higher toxicity compared with other families of conotoxins that they have anta nists of nicotinic acetylcholine and target to subtypes of nicotinic acetylcholine receptor at neuromuscular junction, α-conotoxins make themselves effective tools for identifying the subtypes of nicotinic acetylcholine receptors and the best lead compounds for reconstructing structures of conotoxins. Electronic structures of eight typicalα-conotoxins were calculated by quantum chemical semi-empirical AM1 method of HyperChem soft package. Results of studies on electronic structures and structure-relationship indicated that resemblance of global structures make them target to the same receptors, and difference of electronic structures led by difference of local structures make them target to differential subtypes of receptors. Based on the results, seven analogs of conotoxin GI were designed and calculated by quantum chemical method. Features of GI and analogs on the aspect of spatial structure and electronic structure were compared.
α-conotoxins, extracted from conus venoms, are a family of active peptides. The most characteristic and predominant features of these small peptides are fewer disulfide bonds, simpler structure, and higher toxicity compared with other families of conotoxins that they have anta nists of nicotinic acetylcholine and target to subtypes of nicotinic acetylcholine receptor at neuromuscular junction, α-conotoxins make themselves effective tools for identifying the subtypes of nicotinic acetylcholine receptors and the best lead compounds for reconstructing structures of conotoxins. Electronic structures of eight typicalα-conotoxins were calculated by quantum chemical semi-empirical AM1 method of HyperChem soft package. Results of studies on electronic structures and structure-relationship indicated that resemblance of global structures make them target to the same receptors, and difference of electronic structures led by difference of local structures make them target to differential subtypes of receptors. Based on the results, seven analogs of conotoxin GI were designed and calculated by quantum chemical method. Features of GI and analogs on the aspect of spatial structure and electronic structure were compared.
2005, 21(05): 479-484
doi: 10.3866/PKU.WHXB20050504
Abstract:
All structures of X@B12P12 (X=Li0/+, Na0/+, K0/+, Be0/2+, Mg0/2+, Ca0/2+, H and He) are optimized at the B3LYP/6-31G-density functional level of theory, and the corresponding frequency calculations at the same level are used to characterize the optimized structures with energy minima without imaginary frequencies. The geometries，natural bond orbitals (NBO). dipole moments, adiabatic ionization potentials, inclusion energies, vibrational frequencies, energy gaps and spin densities are also discussed． The calculations predict that X= Li, Na0/+, K0/+, Mg0/2+, Ca0/2+ and He are in the vicinity of 0.006 nm of the cage center, and Be2+ is displaced by 0.279 nm from the cage center along the threefold axis of B12P12. Be@B12P12 and H@B12P12 have endohedral Be－B and H－B bonds respectively． Except for Li@B12P12, Be2+@B12P12, and He@B12P12, all conformations favor Cs symmetry．
All structures of X@B12P12 (X=Li0/+, Na0/+, K0/+, Be0/2+, Mg0/2+, Ca0/2+, H and He) are optimized at the B3LYP/6-31G-density functional level of theory, and the corresponding frequency calculations at the same level are used to characterize the optimized structures with energy minima without imaginary frequencies. The geometries，natural bond orbitals (NBO). dipole moments, adiabatic ionization potentials, inclusion energies, vibrational frequencies, energy gaps and spin densities are also discussed． The calculations predict that X= Li, Na0/+, K0/+, Mg0/2+, Ca0/2+ and He are in the vicinity of 0.006 nm of the cage center, and Be2+ is displaced by 0.279 nm from the cage center along the threefold axis of B12P12. Be@B12P12 and H@B12P12 have endohedral Be－B and H－B bonds respectively． Except for Li@B12P12, Be2+@B12P12, and He@B12P12, all conformations favor Cs symmetry．
2005, 21(05): 485-489
doi: 10.3866/PKU.WHXB20050505
Abstract:
Using sol-gel method and dip-coating process, TiO2 and sandwiched TiO2-V2O5 composite films (TiO2/TiO2-V2O5/TiO2) have been used to coat the surface of 316L stainless steel. The morphology and structure of the films have been analyzed by AFM and XRD. The anticorrosion properties of the composite films have been studied under dark condition by electrochemical methods. The performance of photogenerated cathodic protection of the composite coatings has been measured in 0.5 mol•L-1 NaCl solution (pH=4.6) by combining photoelectrochemical system with corrosion electrochemical system under UV illumination. The results show a significant dual protective performance for the composite films. Under UV illumination the photo-generated cathodic protection is active, and after the UV light is shut off, it takes about 6 hours for the photogenerated potential to shift from －0.25 V to －0.14 V, which implies a possibility to remain a cathodic protection of metal even in the dark condition. Furthermore, under the dark condition the sandwiched TiO2/TiO2-V2O5/TiO2 composite coatings as excellent barrier layers are able to provide a protection for the 316L in a corrosive environment.
Using sol-gel method and dip-coating process, TiO2 and sandwiched TiO2-V2O5 composite films (TiO2/TiO2-V2O5/TiO2) have been used to coat the surface of 316L stainless steel. The morphology and structure of the films have been analyzed by AFM and XRD. The anticorrosion properties of the composite films have been studied under dark condition by electrochemical methods. The performance of photogenerated cathodic protection of the composite coatings has been measured in 0.5 mol•L-1 NaCl solution (pH=4.6) by combining photoelectrochemical system with corrosion electrochemical system under UV illumination. The results show a significant dual protective performance for the composite films. Under UV illumination the photo-generated cathodic protection is active, and after the UV light is shut off, it takes about 6 hours for the photogenerated potential to shift from －0.25 V to －0.14 V, which implies a possibility to remain a cathodic protection of metal even in the dark condition. Furthermore, under the dark condition the sandwiched TiO2/TiO2-V2O5/TiO2 composite coatings as excellent barrier layers are able to provide a protection for the 316L in a corrosive environment.
2005, 21(05): 490-493
doi: 10.3866/PKU.WHXB20050506
Abstract:
Density functional theory (DFT) B3LYP method was employed to study the mechanism of the reaction of CH3CF2O2 radical and HO2 radical at the 6-311G、6-311+G(d)、6-311++G(d, p) levels. The results indicate that there are two reaction pathways in this reaction. The main reaction pathway is CH3CF2O2 +HO2→IM1→TS1→CH3CF2OOH+O2, the corresponding activation energy is 77.21 kJ•mol－1, and the main products are O2 and CH3CF2OOH. They are in od agreement with the experimental results. The other reaction pathway is CH3CF2O + HO2→IM2→TS2→IM3→TS3→IM4 + IM5→IM4 + TS4→IM4 + OH + O2→TS5 + OH + O2→CH3 + CF2O + OH + O2→CH3OH + CF2O + O2, and the corresponding activation energy is 93.42 kJ•mol－1. The results show that this reaction pathway can also occur, and it is in agreement with the results in literatures.
Density functional theory (DFT) B3LYP method was employed to study the mechanism of the reaction of CH3CF2O2 radical and HO2 radical at the 6-311G、6-311+G(d)、6-311++G(d, p) levels. The results indicate that there are two reaction pathways in this reaction. The main reaction pathway is CH3CF2O2 +HO2→IM1→TS1→CH3CF2OOH+O2, the corresponding activation energy is 77.21 kJ•mol－1, and the main products are O2 and CH3CF2OOH. They are in od agreement with the experimental results. The other reaction pathway is CH3CF2O + HO2→IM2→TS2→IM3→TS3→IM4 + IM5→IM4 + TS4→IM4 + OH + O2→TS5 + OH + O2→CH3 + CF2O + OH + O2→CH3OH + CF2O + O2, and the corresponding activation energy is 93.42 kJ•mol－1. The results show that this reaction pathway can also occur, and it is in agreement with the results in literatures.
2005, 21(05): 494-498
doi: 10.3866/PKU.WHXB20050507
Abstract:
Nanoporous glassy carbons(NPGCs) with different pore structures were prepared from phenolic-resin by carbonization at 600 ℃, followed by CO2-acitvation at 900 ℃ for different times. Specific surface areas and characteristic pore sizes obtained from gas adsorption isotherms were correlated with ion electroadsorption at the electrical double layer obtained from the data of specific capacitance (CV). Results show that in dilute aqueous solution, there is no ion electroadsorption in the minimum region of CV curves of carbon electrode, which should be close to the point of zero charge (PZC), leading to remarkable diffusion of electrical double layer and a decrease in capacitance. Further, the smaller the pore sizes of carbon electrodes, the more diffusible electrical double layer is, resulting in a sharp decrease in capacitance. But, the effect of diffusible double-layer on double layer capacitance is reduced and even eliminated through increasing pore sizes of carbon electrodes or electrolyte concentration. The high specific capacitance of unit surface area of carbon electrodes merely indicates a high utilization ratio of specific surface area. Only with high capacitance of unit area and large specific surface area, can carbon electrode have high double-layer capacity. Hydration of ion has bad influences on double-layer capacitance of carbon electrode, which can be reduced effectively by selecting large ion or increasing pore size of carbon electrode.
Nanoporous glassy carbons(NPGCs) with different pore structures were prepared from phenolic-resin by carbonization at 600 ℃, followed by CO2-acitvation at 900 ℃ for different times. Specific surface areas and characteristic pore sizes obtained from gas adsorption isotherms were correlated with ion electroadsorption at the electrical double layer obtained from the data of specific capacitance (CV). Results show that in dilute aqueous solution, there is no ion electroadsorption in the minimum region of CV curves of carbon electrode, which should be close to the point of zero charge (PZC), leading to remarkable diffusion of electrical double layer and a decrease in capacitance. Further, the smaller the pore sizes of carbon electrodes, the more diffusible electrical double layer is, resulting in a sharp decrease in capacitance. But, the effect of diffusible double-layer on double layer capacitance is reduced and even eliminated through increasing pore sizes of carbon electrodes or electrolyte concentration. The high specific capacitance of unit surface area of carbon electrodes merely indicates a high utilization ratio of specific surface area. Only with high capacitance of unit area and large specific surface area, can carbon electrode have high double-layer capacity. Hydration of ion has bad influences on double-layer capacitance of carbon electrode, which can be reduced effectively by selecting large ion or increasing pore size of carbon electrode.
2005, 21(05): 499-503
doi: 10.3866/PKU.WHXB20050508
Abstract:
20 proteins were selected from Thermoanaerobacter tengcongensis proteome as the pilot group of targets for a structural genomics project which aims to fish for proteins with new folds and important biological functions. BLASTP, PSI-BLAST and TBLASTN searches were performed against pdb, nr and est-human databases, respectively, in order to find proteins that are least homolo us to PDB proteins and most homolo us to human proteins. Transmembrane protein predicting programs were used to classify membrane and soluble proteins. The selection was then made with further considerations on functions and parameters such as molecular weight and cysteine ratio. A validation made by the ProtoNet protein sequence hierarchical classification database showed that 95% of our target proteins locate in clusters that have no structures solved. Secondary structures and shapes of the target proteins predicted by PredictProtein program provided useful information for the experimental efforts. 8 selected proteins were cloned, expressed and purified, of which 2 were crystallized. Our experimental results and some recently published results show that some of our selected proteins bear new fold.
20 proteins were selected from Thermoanaerobacter tengcongensis proteome as the pilot group of targets for a structural genomics project which aims to fish for proteins with new folds and important biological functions. BLASTP, PSI-BLAST and TBLASTN searches were performed against pdb, nr and est-human databases, respectively, in order to find proteins that are least homolo us to PDB proteins and most homolo us to human proteins. Transmembrane protein predicting programs were used to classify membrane and soluble proteins. The selection was then made with further considerations on functions and parameters such as molecular weight and cysteine ratio. A validation made by the ProtoNet protein sequence hierarchical classification database showed that 95% of our target proteins locate in clusters that have no structures solved. Secondary structures and shapes of the target proteins predicted by PredictProtein program provided useful information for the experimental efforts. 8 selected proteins were cloned, expressed and purified, of which 2 were crystallized. Our experimental results and some recently published results show that some of our selected proteins bear new fold.
2005, 21(05): 504-507
doi: 10.3866/PKU.WHXB20050509
Abstract:
Fourteen scoring functions (Ligscore1, Ligscore2, Plp1, Plp2, Jain, Pmf, Ludi1, Ludi2, Ludi3, D-score, Pmf-score, G-score, Chemscore and Xscore) have been compared on a testing set containing 230 protein-ligand complexes to evaluate their abilities to reproduce experimentally determined structures and binding free energies after conformational sampling by the program Ligandfit. When applied to predict the binding free energy of the 230 protein-ligand complexes, Plp1, Plp2, G-score, Pmf and Xscore can give linear correlation coefficients over 0.50 between experimental determined and computed values. When employed to identify the experimentally observed conformation, if using root-mean-square deviation(rmsd)≤0.20 nm as the criterion, Ligscore1, Ligscore2, Plp1, Plp2 and Xscore can gain success rate larger than 70%. Combining any two or three of the 14 scoring functions into a consensus scoring function further improves the success rate to 80%. The results suggest that Xscore, plp1 and plp2 are more practicable than others in docking and scoring.
Fourteen scoring functions (Ligscore1, Ligscore2, Plp1, Plp2, Jain, Pmf, Ludi1, Ludi2, Ludi3, D-score, Pmf-score, G-score, Chemscore and Xscore) have been compared on a testing set containing 230 protein-ligand complexes to evaluate their abilities to reproduce experimentally determined structures and binding free energies after conformational sampling by the program Ligandfit. When applied to predict the binding free energy of the 230 protein-ligand complexes, Plp1, Plp2, G-score, Pmf and Xscore can give linear correlation coefficients over 0.50 between experimental determined and computed values. When employed to identify the experimentally observed conformation, if using root-mean-square deviation(rmsd)≤0.20 nm as the criterion, Ligscore1, Ligscore2, Plp1, Plp2 and Xscore can gain success rate larger than 70%. Combining any two or three of the 14 scoring functions into a consensus scoring function further improves the success rate to 80%. The results suggest that Xscore, plp1 and plp2 are more practicable than others in docking and scoring.
2005, 21(05): 508-511
doi: 10.3866/PKU.WHXB20050510
Abstract:
Phage antibody chips, prepared by coupling the recombinant phage displaying scFv with carboxyl-terminated silicon, can be applied in detecting proteins and proteomes. In previous work, we immobilized phages displaying scFv on the coat protein pⅢ on silicon surface as model chips. To improve the sensitivity and the ratio of signal to noise, in this work, scFv specific binding to thrombin was displayed by pⅧ display system, which is the major coat protein on the phage. As the results of changing from pⅢ to pⅧ display, the sensitivity and the ratio of signal to noise of chips were enhanced prominently, due to the increase of the copy number and the decrease of steric hindrance. It is concluded that scFv fused to the coat protein pⅧ is a promising candidate for the preparation of novel protein chips.
Phage antibody chips, prepared by coupling the recombinant phage displaying scFv with carboxyl-terminated silicon, can be applied in detecting proteins and proteomes. In previous work, we immobilized phages displaying scFv on the coat protein pⅢ on silicon surface as model chips. To improve the sensitivity and the ratio of signal to noise, in this work, scFv specific binding to thrombin was displayed by pⅧ display system, which is the major coat protein on the phage. As the results of changing from pⅢ to pⅧ display, the sensitivity and the ratio of signal to noise of chips were enhanced prominently, due to the increase of the copy number and the decrease of steric hindrance. It is concluded that scFv fused to the coat protein pⅧ is a promising candidate for the preparation of novel protein chips.
2005, 21(05): 512-516
doi: 10.3866/PKU.WHXB20050511
Abstract:
The structural, dielectric, ferroelectric and pyroelectric, properties of Pb(ZrxTi1－x)O3 (PZT) ferroelectric thin films and their compositionally graded thin films on LaNiO3/Si substrates were reported. Firstly, LaNiO3 (LNO) thin films were prepared on Si(100) wafer by metalorganic decomposition (MOD) method. Then, Pb(ZrxTi1－x)O3 ferroelectric thin films and their compositionally graded thin films were prepared on LaNiO3/Si substrates by sol-gel method. The composition depth profile of a typical up-graded film was determined by using a combination of auger electron spectroscopy and Ar ion etching. The results confirm that the processing method produces graded composition change. XRD analysis shows that the graded thin films possess composite structure of tetra nal and rhombohedral. The dielectric constant of the graded thin films is higher than that of single-phase thin film, but dissipation factor is similar with each other at 10 kHz. The dielectric constants and dissipation factor for graded thin film annealed at 600 °C for 0.5 h are found to be 317 and 0.057 at 10 kHz, respectively. The hysteresis loops show that the remanent polarization of graded thin film is higher than that of single-phase thin film, but the coercive field is smaller than them. The remnant polarization (Pr) and coercive field (Ec) of the graded film are estimated to be 29.96 μC•cm－2 and 54.12 kV•cm－1, respectively. The pyroelectric coefficient of the graded thin film, which is 5.54×10-8 C•cm－2•K－1 at room temperature, shows gradual increase with the temperature and is higher than that of single-phase thin film.
The structural, dielectric, ferroelectric and pyroelectric, properties of Pb(ZrxTi1－x)O3 (PZT) ferroelectric thin films and their compositionally graded thin films on LaNiO3/Si substrates were reported. Firstly, LaNiO3 (LNO) thin films were prepared on Si(100) wafer by metalorganic decomposition (MOD) method. Then, Pb(ZrxTi1－x)O3 ferroelectric thin films and their compositionally graded thin films were prepared on LaNiO3/Si substrates by sol-gel method. The composition depth profile of a typical up-graded film was determined by using a combination of auger electron spectroscopy and Ar ion etching. The results confirm that the processing method produces graded composition change. XRD analysis shows that the graded thin films possess composite structure of tetra nal and rhombohedral. The dielectric constant of the graded thin films is higher than that of single-phase thin film, but dissipation factor is similar with each other at 10 kHz. The dielectric constants and dissipation factor for graded thin film annealed at 600 °C for 0.5 h are found to be 317 and 0.057 at 10 kHz, respectively. The hysteresis loops show that the remanent polarization of graded thin film is higher than that of single-phase thin film, but the coercive field is smaller than them. The remnant polarization (Pr) and coercive field (Ec) of the graded film are estimated to be 29.96 μC•cm－2 and 54.12 kV•cm－1, respectively. The pyroelectric coefficient of the graded thin film, which is 5.54×10-8 C•cm－2•K－1 at room temperature, shows gradual increase with the temperature and is higher than that of single-phase thin film.
2005, 21(05): 517-522
doi: 10.3866/PKU.WHXB20050512
Abstract:
The reaction mechanisms of 1-methylimidazole with a number of alkyl halides including ethyl chloride, butyl chloride, ethyl bromide and butyl bromide were determined using density-functional theory (DFT). At the B3LYP/6-31++G**//B3LYP/6-31G* basis sets, two mechanisms were found: path A (reactants→TS1→P1) and path B (reactants→TS2→P2). For path A, the halide ions form hydrogen bonds with the C2-H; for path B, the halide ions form hydrogen bonds with the C5-H. Hydrogen bonds play a fundamental role in the synthesis of the alkylimidazolium-based ionic liquids, especially the hydrogen on the C2 affects the reaction significantly. The activation energies of reactions passing through TS1 are lower than that passing through TS2, which indicate that reactions passing through TS1 are favored by reaction dynamics. In agreement with experimental findings, the calculations showed that the reactions through TS1 are exothermic processes.
The reaction mechanisms of 1-methylimidazole with a number of alkyl halides including ethyl chloride, butyl chloride, ethyl bromide and butyl bromide were determined using density-functional theory (DFT). At the B3LYP/6-31++G**//B3LYP/6-31G* basis sets, two mechanisms were found: path A (reactants→TS1→P1) and path B (reactants→TS2→P2). For path A, the halide ions form hydrogen bonds with the C2-H; for path B, the halide ions form hydrogen bonds with the C5-H. Hydrogen bonds play a fundamental role in the synthesis of the alkylimidazolium-based ionic liquids, especially the hydrogen on the C2 affects the reaction significantly. The activation energies of reactions passing through TS1 are lower than that passing through TS2, which indicate that reactions passing through TS1 are favored by reaction dynamics. In agreement with experimental findings, the calculations showed that the reactions through TS1 are exothermic processes.
2005, 21(05): 523-527
doi: 10.3866/PKU.WHXB20050513
Abstract:
The Mn-substituted Ni(OH)2 samples were prepared by a coprecipitation method, and their structure was characterized by X-ray diffraction(XRD). Their electrochemical performance was also investigated by various electrochemical techniques. The results of XRD indicated that the Ni(OH)2 samples with Mn contents less than 20% mainly consist of β-phase, and the sample with a pure α structure can be obtained when the Mn content reaches 28.3%. The results of the electrochemical experiments showed that the Mn-substituted Ni(OH)2 samples manifest high electrochemical cycling stability, and the samples with lower manganese contents exhibit larger discharge capacity and higher discharge potential. It was also found that the doping of Mn obviously increases the oxygen evolution potential and leads to the formation of proton deficiency.
The Mn-substituted Ni(OH)2 samples were prepared by a coprecipitation method, and their structure was characterized by X-ray diffraction(XRD). Their electrochemical performance was also investigated by various electrochemical techniques. The results of XRD indicated that the Ni(OH)2 samples with Mn contents less than 20% mainly consist of β-phase, and the sample with a pure α structure can be obtained when the Mn content reaches 28.3%. The results of the electrochemical experiments showed that the Mn-substituted Ni(OH)2 samples manifest high electrochemical cycling stability, and the samples with lower manganese contents exhibit larger discharge capacity and higher discharge potential. It was also found that the doping of Mn obviously increases the oxygen evolution potential and leads to the formation of proton deficiency.
2005, 21(05): 528-533
doi: 10.3866/PKU.WHXB20050514
Abstract:
The determination of the acidity of ionic liquids is of crucial significance to the utilization of ionic liquids. By using pyridine and acetonitrile as IR spectroscopic probes, the acidity of common room temperature ionic liquids was determined. For the probe pyridine, the IR band near 1450, 1540 cm－1 of pyridine is indicative the Lewis/Brønsted acidity of ionic liquids respectively. For another probe acetonitrile, the increase of the C≡N stretching wave number near 2253 cm－1 with a new band appear at the higher wave number is indicative of the Lewis acidity. The influence of the structure of ionic liquids on the Lewis/Brønsted acidity by the IR spectroscopy was investigated. The Lewis acid strength of different ionic liquids has been compared through the shift of the 1450 cm－1 of pyridine. A more obvious comparison of the Lewis acid intensity of different ionic liquids has been made by acetonitrile probe.
The determination of the acidity of ionic liquids is of crucial significance to the utilization of ionic liquids. By using pyridine and acetonitrile as IR spectroscopic probes, the acidity of common room temperature ionic liquids was determined. For the probe pyridine, the IR band near 1450, 1540 cm－1 of pyridine is indicative the Lewis/Brønsted acidity of ionic liquids respectively. For another probe acetonitrile, the increase of the C≡N stretching wave number near 2253 cm－1 with a new band appear at the higher wave number is indicative of the Lewis acidity. The influence of the structure of ionic liquids on the Lewis/Brønsted acidity by the IR spectroscopy was investigated. The Lewis acid strength of different ionic liquids has been compared through the shift of the 1450 cm－1 of pyridine. A more obvious comparison of the Lewis acid intensity of different ionic liquids has been made by acetonitrile probe.
2005, 21(05): 534-538
doi: 10.3866/PKU.WHXB20050515
Abstract:
The redox behaviors of I－ and I3－ in 3-methoxypropionitrile (MePN) with different concentrations of 1,2-dimethyl-3-propylimidazolium iodide (DMPII) and iodine were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The photovoltaic performance of dye-sensitized solar cells (DSCs) was compared with electrolytes containing different concentrations of DMPII and iodine. The DSCs with the electrolyte (1.0 mol•dm-3 DMPII, 0.10 mol•dm-3 LiI, 0.12 mol•dm-3 I2, 0.50 mol•dm-3 4-tert-butylpyridine, in MePN) gave short circuit photocurrent density (Jsc) of 16.76 mA•cm-3, open circuit voltage (Voc) of 0.69 V, and fill factor (FF) of 0.70, corresponding to a photoelectric conversion efficiency (η) of 8.08% under one Sun (AM1.5).
The redox behaviors of I－ and I3－ in 3-methoxypropionitrile (MePN) with different concentrations of 1,2-dimethyl-3-propylimidazolium iodide (DMPII) and iodine were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The photovoltaic performance of dye-sensitized solar cells (DSCs) was compared with electrolytes containing different concentrations of DMPII and iodine. The DSCs with the electrolyte (1.0 mol•dm-3 DMPII, 0.10 mol•dm-3 LiI, 0.12 mol•dm-3 I2, 0.50 mol•dm-3 4-tert-butylpyridine, in MePN) gave short circuit photocurrent density (Jsc) of 16.76 mA•cm-3, open circuit voltage (Voc) of 0.69 V, and fill factor (FF) of 0.70, corresponding to a photoelectric conversion efficiency (η) of 8.08% under one Sun (AM1.5).
2005, 21(05): 539-543
doi: 10.3866/PKU.WHXB20050516
Abstract:
The vacuum ultraviolet photoionization and photodissociation of pentafluoroethane have been studied by using synchrotron radiation. The ionization potential of pentafluoroethane is determined to be (12.25±0.10) eV. Photoionization efficiency (PIE) curves for CF2CF3+、CHFCF3+、CF2CF2+、CF3+、CHF2+、CHF+ and CF+ have been measured. The appearance potentials (AP) of these ions are obtained from their PIE curves, and they are (13.93±0.10) eV, (15.25±0.10) eV, (15.12±0.10) eV, (13.30±0.05) eV, (13.05±0.08) eV, (19.17±0.10) eV and (19.56±0.15) eV, respectively. In addition, the energetics of the dissociative photoionizations have been examined by ab initio Gaussian-3 calculations. The computational results are useful in establishing the dissociation channels near the ionization thresholds. According to the experimental results and the energies calculated by Gaussian-3 theory, the main possible pathways of the photodissociation have been analyzed. And the dissociation energies of the molecule and its cation have been derived from experiment and calculation.
The vacuum ultraviolet photoionization and photodissociation of pentafluoroethane have been studied by using synchrotron radiation. The ionization potential of pentafluoroethane is determined to be (12.25±0.10) eV. Photoionization efficiency (PIE) curves for CF2CF3+、CHFCF3+、CF2CF2+、CF3+、CHF2+、CHF+ and CF+ have been measured. The appearance potentials (AP) of these ions are obtained from their PIE curves, and they are (13.93±0.10) eV, (15.25±0.10) eV, (15.12±0.10) eV, (13.30±0.05) eV, (13.05±0.08) eV, (19.17±0.10) eV and (19.56±0.15) eV, respectively. In addition, the energetics of the dissociative photoionizations have been examined by ab initio Gaussian-3 calculations. The computational results are useful in establishing the dissociation channels near the ionization thresholds. According to the experimental results and the energies calculated by Gaussian-3 theory, the main possible pathways of the photodissociation have been analyzed. And the dissociation energies of the molecule and its cation have been derived from experiment and calculation.
2005, 21(05): 544-549
doi: 10.3866/PKU.WHXB20050517
Abstract:
The equation of transient response for the system with Rs(C1(R1(C2(R2(C3R3))))) equivalent circuit was presented, and some other transient response equations to a small amplitude coulostatic perturbation for multi-time constant electrode processes were also deduced. In the present work, impedance spectra were obtained by transforming coulostatic transient data in time domain into the frequency domain. Using this method, the number of time constant can be determined easily, and the kinetic parameters of the studied electrode process can be estimated correctly. The validity of the proposed method is demonstrated by calculation results based on equivalent circuit and one real corrosion system.
The equation of transient response for the system with Rs(C1(R1(C2(R2(C3R3))))) equivalent circuit was presented, and some other transient response equations to a small amplitude coulostatic perturbation for multi-time constant electrode processes were also deduced. In the present work, impedance spectra were obtained by transforming coulostatic transient data in time domain into the frequency domain. Using this method, the number of time constant can be determined easily, and the kinetic parameters of the studied electrode process can be estimated correctly. The validity of the proposed method is demonstrated by calculation results based on equivalent circuit and one real corrosion system.
2005, 21(05): 550-555
doi: 10.3866/PKU.WHXB20050518
Abstract:
A bolaamphiphile containing cinnamic acid moiety, [4-(10-hydroxydecanyloxy)-10-hydroxydecanylcinnamate, abbreviated HDC], was synthesized and the LB films of HDC were studied. It was found from the results of π－A isotherms that multilayers of HDC were formed at the air/water interface. The photoreaction of HDC in LB films induced by UV light was investigated with UV and IR measurements. Photodimerization also took place in the mixed LB films of HDC and 1,16-hexadecanediol. The spectra results showed that the HDC molecules assembled orderly due to the separated recognition of π-π interaction and the zigzag stacking of methylene groups. XRD studies indicated that bilayers formed in the LB films with a tilt angle of 58.8° and 53.2° before and after UV irradiation, respectively. A packing model of HDC was also proposed.
A bolaamphiphile containing cinnamic acid moiety, [4-(10-hydroxydecanyloxy)-10-hydroxydecanylcinnamate, abbreviated HDC], was synthesized and the LB films of HDC were studied. It was found from the results of π－A isotherms that multilayers of HDC were formed at the air/water interface. The photoreaction of HDC in LB films induced by UV light was investigated with UV and IR measurements. Photodimerization also took place in the mixed LB films of HDC and 1,16-hexadecanediol. The spectra results showed that the HDC molecules assembled orderly due to the separated recognition of π-π interaction and the zigzag stacking of methylene groups. XRD studies indicated that bilayers formed in the LB films with a tilt angle of 58.8° and 53.2° before and after UV irradiation, respectively. A packing model of HDC was also proposed.
2005, 21(05): 556-559
doi: 10.3866/PKU.WHXB20050519
Abstract:
TiO2 nanocrystalline material has been synthesized by stearic-acid gel method. The TiO2 crystal species and grains are characterized by XRD. TEM showed that the TiO2 grains are spherical and well dispersed. The results of XPS illustrated that the absorbed oxygen on anatase TiO2 is much more than that on rutile TiO2. The sensitivity of the two species to trimethylamine (TMA) was studied. The results showed that anatase TiO2 has much higher sensitivity to TMA than rutile TiO2. The mechanism of TiO2 sensitivity to TMA was discussed.
TiO2 nanocrystalline material has been synthesized by stearic-acid gel method. The TiO2 crystal species and grains are characterized by XRD. TEM showed that the TiO2 grains are spherical and well dispersed. The results of XPS illustrated that the absorbed oxygen on anatase TiO2 is much more than that on rutile TiO2. The sensitivity of the two species to trimethylamine (TMA) was studied. The results showed that anatase TiO2 has much higher sensitivity to TMA than rutile TiO2. The mechanism of TiO2 sensitivity to TMA was discussed.
2005, 21(05): 560-564
doi: 10.3866/PKU.WHXB20050520
Abstract:
ZnS photonic crystals were prepared by using silica collodial crystals as templates and infiltrating with ZnS semiconductor nanocrystals in opal templates via solvothermal approach. Solvothermal method offers several advantages over previous techniques including homogenous ZnS growth within the opal voids and high quality of the obtained ZnS nanocrystals. XRD patterns and Raman spectroscopy results confirmed the ZnS nanocrystals to be zinc blende, and the mechanism of ZnS crystal growth in opals was discussed. FESEM images and UV-Vis transmission spectra showed that the as-obtained ZnS/opal system and ZnS inverse opal kept the three-dimensional ordered structure of the opals. The appearance of Bragg diffraction peak at Г-L direction (the direction normal to the (111) planes) indicated that the two structures had excellent photonic crystals properties. Furthermore, the optical properties of the infiltrated opals with different ZnS filling ratios are also studied by transmission spectroscopy. It is proposed that the position of the stop band can be easily designed by controlling the infiltration ratio of ZnS. These results demonstrated an easy-to-handle and efficient route to obtain high performance photonic crystal structures. The material system is believed to have potential applications in optoelectronic and photonic devices.
ZnS photonic crystals were prepared by using silica collodial crystals as templates and infiltrating with ZnS semiconductor nanocrystals in opal templates via solvothermal approach. Solvothermal method offers several advantages over previous techniques including homogenous ZnS growth within the opal voids and high quality of the obtained ZnS nanocrystals. XRD patterns and Raman spectroscopy results confirmed the ZnS nanocrystals to be zinc blende, and the mechanism of ZnS crystal growth in opals was discussed. FESEM images and UV-Vis transmission spectra showed that the as-obtained ZnS/opal system and ZnS inverse opal kept the three-dimensional ordered structure of the opals. The appearance of Bragg diffraction peak at Г-L direction (the direction normal to the (111) planes) indicated that the two structures had excellent photonic crystals properties. Furthermore, the optical properties of the infiltrated opals with different ZnS filling ratios are also studied by transmission spectroscopy. It is proposed that the position of the stop band can be easily designed by controlling the infiltration ratio of ZnS. These results demonstrated an easy-to-handle and efficient route to obtain high performance photonic crystal structures. The material system is believed to have potential applications in optoelectronic and photonic devices.
2005, 21(05): 565-568
doi: 10.3866/PKU.WHXB20050521
Abstract:
The amorphous Mg-Fe-Ni composites have been synthesized by mechanical ball-milling. The microstructure and electrochemical properties of the composites were characterized by XRD, SEM and electrochemical testing. The electrochemical properties of the composites vary greatly with the amount of Mg content and Ni introduced. For the (xMg+Fe)+200% (mass fraction) Ni (x=2, 3) composites, it is found that the maximal discharge capacity increases with increasing Mg content in the composites. The maximal discharge capacities of the composites with x=2, 3 were 391.9 mA•h•g-1 and 480.8 mA•h•g-1, respectively. The result also indicates that, for the ball-milled (3Mg+Fe)+y% Ni (y=50, 100, 200) composites, with increasing Ni content in the composites, the discharge capacity increases first and then decreases, and reaches a maximum value of 519.5 mA•h•g-1 as y=100. In contrast, the discharge capacity of nickel-free (3Mg+Fe) composite is just 23.8 mA•h•g-1. The microstructure analysis shows that the composites are mix structure composed two single phases with Mg and Fe for the nickel-free composite even after being milled for 120 h, but no new phase is formed. The composites milled with the addition of nickel powder could easily form Mg-Fe amorphous structure. Besides, the nickel powder in the composites plays a role of electro-catalysis, hereby the electrochemical properties of the Mg-Fe-Ni composites are effectively improved.
The amorphous Mg-Fe-Ni composites have been synthesized by mechanical ball-milling. The microstructure and electrochemical properties of the composites were characterized by XRD, SEM and electrochemical testing. The electrochemical properties of the composites vary greatly with the amount of Mg content and Ni introduced. For the (xMg+Fe)+200% (mass fraction) Ni (x=2, 3) composites, it is found that the maximal discharge capacity increases with increasing Mg content in the composites. The maximal discharge capacities of the composites with x=2, 3 were 391.9 mA•h•g-1 and 480.8 mA•h•g-1, respectively. The result also indicates that, for the ball-milled (3Mg+Fe)+y% Ni (y=50, 100, 200) composites, with increasing Ni content in the composites, the discharge capacity increases first and then decreases, and reaches a maximum value of 519.5 mA•h•g-1 as y=100. In contrast, the discharge capacity of nickel-free (3Mg+Fe) composite is just 23.8 mA•h•g-1. The microstructure analysis shows that the composites are mix structure composed two single phases with Mg and Fe for the nickel-free composite even after being milled for 120 h, but no new phase is formed. The composites milled with the addition of nickel powder could easily form Mg-Fe amorphous structure. Besides, the nickel powder in the composites plays a role of electro-catalysis, hereby the electrochemical properties of the Mg-Fe-Ni composites are effectively improved.
2005, 21(05): 569-572
doi: 10.3866/PKU.WHXB20050522
Abstract:
Nickel nanoparticles were successfully synthesized by a replacement reaction of nickelous 2-ethylhexanoate with metal sodium in liquid paraffin under ultrasonic irradiation. The morphology, structure and thermal stability of the samples obtained were characterized with TEM, ED, XRD, XPS and TG. The TEM and ED results reveal that the produced nickel nanoparticles have single crystal structure and their size distribution is relatively narrow. XRD and XPS analyses display that the produced nickel nanoparticles possess the same hexa nal crystal structure as bulk nickel materials and there is a very small fraction of Ni(Ⅱ) on the surface of the Ni nanoparticles, respectively. In addition, the result of TG indicates that the as-synthesized samples have high thermostability.
Nickel nanoparticles were successfully synthesized by a replacement reaction of nickelous 2-ethylhexanoate with metal sodium in liquid paraffin under ultrasonic irradiation. The morphology, structure and thermal stability of the samples obtained were characterized with TEM, ED, XRD, XPS and TG. The TEM and ED results reveal that the produced nickel nanoparticles have single crystal structure and their size distribution is relatively narrow. XRD and XPS analyses display that the produced nickel nanoparticles possess the same hexa nal crystal structure as bulk nickel materials and there is a very small fraction of Ni(Ⅱ) on the surface of the Ni nanoparticles, respectively. In addition, the result of TG indicates that the as-synthesized samples have high thermostability.
2005, 21(05): 573-576
doi: 10.3866/PKU.WHXB20050523
Abstract:
The molar heat capacities of 4-pyridinemethanol were measured with a precision automated adiabatic calorimeter over the temperature rang from 79 K to 380 K. No phase transition or other thermal anomaly was observed in the range of 79～301 K. The melting point, molar enthalpy, ΔfusHm, and molar entropy, ΔfusSm, of fusion for this compound were determined to be 325.12 K, 11.78 kJ•mol-1 and 36.23 J•K-1•mol-1, respectively. The thermodynamic functions relative to the reference temperature (298.15 K) were calculated based on the heat capacity measurements in the temperature range from 80 K to 380 K. The TG-DTG results demonstrated that the maximum rate of mass loss of the sample took place at about 490 K, which corresponds to the boiling temperature of the compound under the experimental conditions.
The molar heat capacities of 4-pyridinemethanol were measured with a precision automated adiabatic calorimeter over the temperature rang from 79 K to 380 K. No phase transition or other thermal anomaly was observed in the range of 79～301 K. The melting point, molar enthalpy, ΔfusHm, and molar entropy, ΔfusSm, of fusion for this compound were determined to be 325.12 K, 11.78 kJ•mol-1 and 36.23 J•K-1•mol-1, respectively. The thermodynamic functions relative to the reference temperature (298.15 K) were calculated based on the heat capacity measurements in the temperature range from 80 K to 380 K. The TG-DTG results demonstrated that the maximum rate of mass loss of the sample took place at about 490 K, which corresponds to the boiling temperature of the compound under the experimental conditions.
2005, 21(05): 577-582
doi: 10.3866/PKU.WHXB20050524
Abstract:
Static fluorescence technique has been proved to be an important method for studying surfactant systems. It is very sensitive to the phase transition in aqueous solution. The methods and principles of the fluorescence technique in studying the interaction between surfactants and macromolecules are systematically summarized combining with our work.
Static fluorescence technique has been proved to be an important method for studying surfactant systems. It is very sensitive to the phase transition in aqueous solution. The methods and principles of the fluorescence technique in studying the interaction between surfactants and macromolecules are systematically summarized combining with our work.
