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2005 Volume 21 Issue 3
2005, 21(03): 229-233
doi: 10.3866/PKU.WHXB20050301
Abstract:
Silica-modified titanium dioxides were prepared by co-precipitation method and then characterized by XRD, FT-IR, XPS, TEM, and UV-Vis absorption spectroscopy. The results showed that there was a strong interaction between SiO2 and SiO2, and Ti－O－Si bonds formed on silica-modified titanium dioxide surfaces. The addition of silica in SiO2 particle could effectively suppress the formation of rutile phase, the decrease of surface area and the growth of titanium dioxide crystals. The band-gap transition increased with the increase of silica content. In comparison with pure SiO2 nanoparticles, the silica-modified SiO2 nanoparticles exhibited better photocatalytic activity, and the activity increased with the silica content.
Silica-modified titanium dioxides were prepared by co-precipitation method and then characterized by XRD, FT-IR, XPS, TEM, and UV-Vis absorption spectroscopy. The results showed that there was a strong interaction between SiO2 and SiO2, and Ti－O－Si bonds formed on silica-modified titanium dioxide surfaces. The addition of silica in SiO2 particle could effectively suppress the formation of rutile phase, the decrease of surface area and the growth of titanium dioxide crystals. The band-gap transition increased with the increase of silica content. In comparison with pure SiO2 nanoparticles, the silica-modified SiO2 nanoparticles exhibited better photocatalytic activity, and the activity increased with the silica content.
2005, 21(03): 234-238
doi: 10.3866/PKU.WHXB20050302
Abstract:
The effects of cephanone on the surface activity and aggregation behavior of Triton X-100 molecule were studied by the methods of surface tension and fluorescence, respectively. The binding constant between cephanone and Triton X-100 micelles was determined by the method of steady state fluorescence. The location of cephanone in Triton X-100 micelles was investigated through nuclear magnetic spectroscopy (NMR). The results showed that the surface activity of Triton X-100 decreased with the increase of cephanone concentration. With the increase of Triton X-100 concentration, the binding constant between cephanone and Triton X-100 micelles decreased, but the distribution coefficient of cephanone between Triton X-100 micelles and water continuous phase kept being invariable. The results of 1H-NMR showed that cephanone was located around the polar group of Triton X-100 micelle.
The effects of cephanone on the surface activity and aggregation behavior of Triton X-100 molecule were studied by the methods of surface tension and fluorescence, respectively. The binding constant between cephanone and Triton X-100 micelles was determined by the method of steady state fluorescence. The location of cephanone in Triton X-100 micelles was investigated through nuclear magnetic spectroscopy (NMR). The results showed that the surface activity of Triton X-100 decreased with the increase of cephanone concentration. With the increase of Triton X-100 concentration, the binding constant between cephanone and Triton X-100 micelles decreased, but the distribution coefficient of cephanone between Triton X-100 micelles and water continuous phase kept being invariable. The results of 1H-NMR showed that cephanone was located around the polar group of Triton X-100 micelle.
2005, 21(03): 239-243
doi: 10.3866/PKU.WHXB20050303
Abstract:
Uniform ZnO nanobelts and toothed-nanobelts were synthesized respectively through pure zinc powder evaporation without catalyst at temperature of 600 ℃. In each processing, the total gas flow rate of ar n and oxygen was 200～300 cm3•min－1, and the fraction of oxygen was 1％～5％ according to changes of the conditions. The experiments indicated that the key of the preparation method is to control the flow rates and partial pressures of ar n, oxygen, and zinc vapor. The flow rates and partial pressures influenced the size of nanostructures, and more sensitively determined the belts with or without teeth. Scanning electron microscopy (SEM) observations showed that the fabricated ZnO nanobelts had several types in morphology. The high-resolution transmission electron microscopy (HRTEM) images and selected area electron diffraction (SAED) patterns revealed that the ZnO nanobelts were single crystalline. HRTEM images and SAED patterns also suggested that the teeth of the toothed-nanobelts grew along the [0001] or [2110] direction, i. e., the teeth of such belts may grow in “c” or “a” direction, the backbones of the belts may grow in “a” or “c” direction accordingly. X-ray diffraction (XRD) investigations on the structures showed that all the deposited nanobelts on the silicon substrate were pure ZnO with hexa nal wurtzite structure. Investigations through HRTEM and XRD indicated that the growth of ZnO nanobelts was controlled by vapor-solid (VS) mechanism. Photoluminescence(PL) spectrum of ZnO toothed-nanobelts at room temperature was measured and showed a UV emission at ～390 nm and a broad green emission with 4 subordinate peaks at 455～495 nm.
Uniform ZnO nanobelts and toothed-nanobelts were synthesized respectively through pure zinc powder evaporation without catalyst at temperature of 600 ℃. In each processing, the total gas flow rate of ar n and oxygen was 200～300 cm3•min－1, and the fraction of oxygen was 1％～5％ according to changes of the conditions. The experiments indicated that the key of the preparation method is to control the flow rates and partial pressures of ar n, oxygen, and zinc vapor. The flow rates and partial pressures influenced the size of nanostructures, and more sensitively determined the belts with or without teeth. Scanning electron microscopy (SEM) observations showed that the fabricated ZnO nanobelts had several types in morphology. The high-resolution transmission electron microscopy (HRTEM) images and selected area electron diffraction (SAED) patterns revealed that the ZnO nanobelts were single crystalline. HRTEM images and SAED patterns also suggested that the teeth of the toothed-nanobelts grew along the [0001] or [2110] direction, i. e., the teeth of such belts may grow in “c” or “a” direction, the backbones of the belts may grow in “a” or “c” direction accordingly. X-ray diffraction (XRD) investigations on the structures showed that all the deposited nanobelts on the silicon substrate were pure ZnO with hexa nal wurtzite structure. Investigations through HRTEM and XRD indicated that the growth of ZnO nanobelts was controlled by vapor-solid (VS) mechanism. Photoluminescence(PL) spectrum of ZnO toothed-nanobelts at room temperature was measured and showed a UV emission at ～390 nm and a broad green emission with 4 subordinate peaks at 455～495 nm.
2005, 21(03): 244-249
doi: 10.3866/PKU.WHXB20050304
Abstract:
Using density functional theory associated with B3LYP method with 6-31G* and 6-311＋G(3df) basis sets, the optimization of the geometries and electronic structures and the calculation of frequencies for CnBδ(δ=0,±1; n=1～6) clusters have been carried out. In addition, the detachment energy ,adiabatic electron affinities of CnB and energy gap of CnBδ(δ=0, ±1) were obtained. The results show that the ground state structures of CnB－(n=1～6) clusters are linear as Cn clusters due to their isoelectrons. For CnB (n=1～6) clusters, the ground state structure of C2B is asymmetric triangle and C6B is C2v symmetry planar monocycle, while the other clusters are linear.C2B＋ ,C3B＋and C6B＋ are C2v symmetry in CnB＋(n=1～6) clusters. From the geometrical parameters and vibrational frequencies of boron-carbon clusters from 6-311＋G(3df) and 6-31G* basis sets, it was found that the B3LYP functional is less sensitive to the selection of the basis set in investigating the boron-carbon clusters. The photoelectron spectrum of CnB(n=1～6) clusters indicates that C4B is easy to accept one electron and difficult to lose one electron, which is in od agreement with the experimental result.
Using density functional theory associated with B3LYP method with 6-31G* and 6-311＋G(3df) basis sets, the optimization of the geometries and electronic structures and the calculation of frequencies for CnBδ(δ=0,±1; n=1～6) clusters have been carried out. In addition, the detachment energy ,adiabatic electron affinities of CnB and energy gap of CnBδ(δ=0, ±1) were obtained. The results show that the ground state structures of CnB－(n=1～6) clusters are linear as Cn clusters due to their isoelectrons. For CnB (n=1～6) clusters, the ground state structure of C2B is asymmetric triangle and C6B is C2v symmetry planar monocycle, while the other clusters are linear.C2B＋ ,C3B＋and C6B＋ are C2v symmetry in CnB＋(n=1～6) clusters. From the geometrical parameters and vibrational frequencies of boron-carbon clusters from 6-311＋G(3df) and 6-31G* basis sets, it was found that the B3LYP functional is less sensitive to the selection of the basis set in investigating the boron-carbon clusters. The photoelectron spectrum of CnB(n=1～6) clusters indicates that C4B is easy to accept one electron and difficult to lose one electron, which is in od agreement with the experimental result.
2005, 21(03): 250-254
doi: 10.3866/PKU.WHXB20050305
Abstract:
The process of rotationally inelastic collision of He-LiH complex has been discussed with close-coupling method based on the CCSD(T) potential energy surface. State-to-state partial and integral cross sections are calculated. The partial cross sections show that the transition cross sections of j=0→j′originate from the contributions of both the anisotropic short-range interaction and the long-range “soft” repulsion, while there is no evident for the long－range attraction. The state-to-state integral cross sections display an oscillatory structure. The long-range “soft” repulsion partial cross sections have only an effect on the integral cross sections for j=0→j′=1,2,3,and the cross sections for j′≥ 4 are almost decided by the anisotropic short-range partial.
The process of rotationally inelastic collision of He-LiH complex has been discussed with close-coupling method based on the CCSD(T) potential energy surface. State-to-state partial and integral cross sections are calculated. The partial cross sections show that the transition cross sections of j=0→j′originate from the contributions of both the anisotropic short-range interaction and the long-range “soft” repulsion, while there is no evident for the long－range attraction. The state-to-state integral cross sections display an oscillatory structure. The long-range “soft” repulsion partial cross sections have only an effect on the integral cross sections for j=0→j′=1,2,3,and the cross sections for j′≥ 4 are almost decided by the anisotropic short-range partial.
2005, 21(03): 255-260
doi: 10.3866/PKU.WHXB20050306
Abstract:
The simultaneous removal of NOx and soot was studied by the temperature program reaction (TPR) technology over La0.8K0.2MnO3 catalyst assisted by plasma. When the experiment was carried out by catalysis process, the results showed that La0.8K0.2MnO3 catalyst had the excellent catalytic performance for the reduction of NOx by soot in the oxygen rich atmosphere. When the experiment was conducted by catalysis with the assistant of plasma in the same gases condition, the results showed that plasma improved the catalytic activity for simultaneous removal of NOx and soot, and reduced the combustion temperature of soot. As a consequence, the ignition temperature of soot was reduced from 300 ℃ to 280 ℃, and the burning out temperature was also decreased from 425 ℃ to 380 ℃. The conversion efficiency of NOx to N2 was improved by plasma, and the selectivity to N2 formation was enhanced from 1.12％ to 1.53％. In addition, the catalytic property for soot removal was studied at various gas compositions with or without plasma. The results also showed that plasma improved the catalytic activity for the combustion of soot and the conversion efficiency of NOx to N2 whether in the NO＋O2 or NO atmosphere. Also, the mechanism of plasma-assisted catalysis for simultaneous removal of NOx and soot was discussed in this paper.
The simultaneous removal of NOx and soot was studied by the temperature program reaction (TPR) technology over La0.8K0.2MnO3 catalyst assisted by plasma. When the experiment was carried out by catalysis process, the results showed that La0.8K0.2MnO3 catalyst had the excellent catalytic performance for the reduction of NOx by soot in the oxygen rich atmosphere. When the experiment was conducted by catalysis with the assistant of plasma in the same gases condition, the results showed that plasma improved the catalytic activity for simultaneous removal of NOx and soot, and reduced the combustion temperature of soot. As a consequence, the ignition temperature of soot was reduced from 300 ℃ to 280 ℃, and the burning out temperature was also decreased from 425 ℃ to 380 ℃. The conversion efficiency of NOx to N2 was improved by plasma, and the selectivity to N2 formation was enhanced from 1.12％ to 1.53％. In addition, the catalytic property for soot removal was studied at various gas compositions with or without plasma. The results also showed that plasma improved the catalytic activity for the combustion of soot and the conversion efficiency of NOx to N2 whether in the NO＋O2 or NO atmosphere. Also, the mechanism of plasma-assisted catalysis for simultaneous removal of NOx and soot was discussed in this paper.
2005, 21(03): 261-266
doi: 10.3866/PKU.WHXB20050307
Abstract:
This study reports a hybrid capacitor in H2SO4 aqueous electrolyte, which consists of polyaniline as a cathode and activated carbon as an anode. The electrochemical performance of the hybrid capacitor is characterized by cyclic voltammetry and a constant current charge/discharge test. The hybrid capacitor shows capacitor behavior with an extended operating voltage of 1.4 V. From integrating the cyclic voltammetry curve, specific capacitances of 420 F•g－1 and 160 F•g－1 are obtained for polyaniline and activated carbon, respectively. The cycling behavior of the hybrid electrochemical capacitor is examined in a two-electrode cell by means of cyclic voltammetry. From constant current charging and discharging test, the values for the specific energy and real specific power are 15.5 W•h•kg－1 and 2.4 W•g－1, respectively, in the cell voltage range between 0 and 1.4 V. The maximum specific power reach a value of 20.4 W•g－1. The self-discharge rate of this hybrid supercapacitor is much lower than the double layer capacitor composed of activated carbon electrodes.
This study reports a hybrid capacitor in H2SO4 aqueous electrolyte, which consists of polyaniline as a cathode and activated carbon as an anode. The electrochemical performance of the hybrid capacitor is characterized by cyclic voltammetry and a constant current charge/discharge test. The hybrid capacitor shows capacitor behavior with an extended operating voltage of 1.4 V. From integrating the cyclic voltammetry curve, specific capacitances of 420 F•g－1 and 160 F•g－1 are obtained for polyaniline and activated carbon, respectively. The cycling behavior of the hybrid electrochemical capacitor is examined in a two-electrode cell by means of cyclic voltammetry. From constant current charging and discharging test, the values for the specific energy and real specific power are 15.5 W•h•kg－1 and 2.4 W•g－1, respectively, in the cell voltage range between 0 and 1.4 V. The maximum specific power reach a value of 20.4 W•g－1. The self-discharge rate of this hybrid supercapacitor is much lower than the double layer capacitor composed of activated carbon electrodes.
2005, 21(03): 267-272
doi: 10.3866/PKU.WHXB20050308
Abstract:
Polychlorinated biphenyls(PCBs), an important kind of toxic pollutant, are persistent in the environment and accumulative in many species. Ab initio calculations have been performed for all 209 PCB congeners at the HF/6-31G* level. Electrostatic potentials and subsequently derived statistically based structural descriptors have been obtained. Linear relationships between aqueous solubility(lgSW), n-octanol/water partition coefficient (lgKOW),n-octanol/air partition coefficient (lgKOA), soil sorption (lgKOC), aqueous activity coefficient(lgYW), 298 K supercooled liquid vapour pressures(lgpL), total molecular surface area (TSA), gas-chromatographic relative retention time (RRT), enthalpy of sublimation (ΔHsubl), enthalpy of vaporization (ΔHvap), enthalpy of fusion (ΔHfus), Aryl hydrocarbon receptor biding affinity (pEC50),biodegradability (Biodeg％) and Microbial elimination rate constant(－lgk) of PCBs and theoretical descriptors have been established by multiple regression method. It appears that the quantities derived from electrostatic potentials, Vmin, Vs,min, Vs,max, Vs, Π,σ2tot,ΣVs+,>,ΣVs-, together with the molecular surface area and some popular quantum chemical descriptors (e.g. EHOMO and ELUMO) can be well used to express the quantitative structure-property (activity) relationships of PCBs. Although the correlation equations for some physicochemical properties and biological activities are not superior to those previously established with other types of structural parameters, the parameter set used in the present systematic quantitative structure-property relationship (QSPR)/quantitative structure-activity relationship (QSAR) study was proven to have more general applicability.
2005, 21(03): 273-277
doi: 10.3866/PKU.WHXB20050309
Abstract:
The electromotive force(EMF) values of the cell (－)Pt|Ir|Al0.85Sn0.15, Na3AlF6|CaF2|AlxFe1－x(x=0.23～0.33), Na3AlF6|Ir|Pt (＋) were measured between 720 K and 847 K using solid galvanic cells with a single-crystal CaF2 electrolyte. For attaining quick thermodynamic equilibrium of the cell, Al0.85Sn0.15 alloy was used as the reference electrode and DO3-Fe3Al was powdered. It was confirmed that there was no chemical transformation in the working electrode by X-ray diffraction experiments before and after EMF measurement. The Al activities in Fe3Al with DO3-ordered nonstoichiometric intermetallic compounds were derived. The partial molar thermodynamic functions ΔGAl、ΔHAl、ΔSAl of Al were calculated. The activities and partial molar Gibbs energies of Fe in the Fe-Al alloys were derived by Gibbs-Duhem equation. The thermodynamic factor in diffusion of aluminum in the Fe3Al phase at 750 K was calculated, and showed a maximum at a composition near the stoichiometric proportion (xAl=0.25).
The electromotive force(EMF) values of the cell (－)Pt|Ir|Al0.85Sn0.15, Na3AlF6|CaF2|AlxFe1－x(x=0.23～0.33), Na3AlF6|Ir|Pt (＋) were measured between 720 K and 847 K using solid galvanic cells with a single-crystal CaF2 electrolyte. For attaining quick thermodynamic equilibrium of the cell, Al0.85Sn0.15 alloy was used as the reference electrode and DO3-Fe3Al was powdered. It was confirmed that there was no chemical transformation in the working electrode by X-ray diffraction experiments before and after EMF measurement. The Al activities in Fe3Al with DO3-ordered nonstoichiometric intermetallic compounds were derived. The partial molar thermodynamic functions ΔGAl、ΔHAl、ΔSAl of Al were calculated. The activities and partial molar Gibbs energies of Fe in the Fe-Al alloys were derived by Gibbs-Duhem equation. The thermodynamic factor in diffusion of aluminum in the Fe3Al phase at 750 K was calculated, and showed a maximum at a composition near the stoichiometric proportion (xAl=0.25).
2005, 21(03): 278-282
doi: 10.3866/PKU.WHXB20050310
Abstract:
A series of Cu-Mg-Al hydrotalcite compounds with M (II) :Al (III) molar ratio of 3 : 1 were prepared by co-precipitation method. Corresponding mixed oxides were obtained after calcination 500 ℃（wCuO(％)= 0, 5, 10, 20, denoted as w-CMAO, w=0, 5, 10, 20）. Pt/Cu-Mg-Al-O catalysts were prepared by impregnation with H2PtCl6 solution. XRD results showed that Cu was well dispersed in the catalysts and their precursors. NOx storage performance was investigated using NOx adsorption experiment at constant temperature, and decomposition of stored NOx was also studied by TPD method. It was shown that although M content was decreased due to Cu addition, the activity of NO oxidation was improved, and NOx storage performance was increased effectively. TPD results further showed that the decomposition temperature of nitrate formed on the catalysts can be reduced sharply when w=10％～20％ of CuO was added.
A series of Cu-Mg-Al hydrotalcite compounds with M (II) :Al (III) molar ratio of 3 : 1 were prepared by co-precipitation method. Corresponding mixed oxides were obtained after calcination 500 ℃（wCuO(％)= 0, 5, 10, 20, denoted as w-CMAO, w=0, 5, 10, 20）. Pt/Cu-Mg-Al-O catalysts were prepared by impregnation with H2PtCl6 solution. XRD results showed that Cu was well dispersed in the catalysts and their precursors. NOx storage performance was investigated using NOx adsorption experiment at constant temperature, and decomposition of stored NOx was also studied by TPD method. It was shown that although M content was decreased due to Cu addition, the activity of NO oxidation was improved, and NOx storage performance was increased effectively. TPD results further showed that the decomposition temperature of nitrate formed on the catalysts can be reduced sharply when w=10％～20％ of CuO was added.
2005, 21(03): 283-286
doi: 10.3866/PKU.WHXB20050311
Abstract:
Kinetics of the reversible-consecutive reaction of ascorbic acid H2A with hydrogen peroxide was studied in phosphate buffer(μ=0.1 mol•L－1) at pH 7 and 25 ℃ with conduction calorimeter. The apparent rate constants of this reaction, k1, k-1 and k2, were measured at different concentrations of cetyltrimethylammonium bromide(CTAB). The results indicated that the apparent rate constants of the reaction, k1, k-1 and k2, were remarkably affected by the cationic surfactant CTAB. k1 initially increased, up to a maximum, and then fell off with increasing CTAB micellar concentration, while k-1 was hardly affected by CTAB of low concentrations(< 2 mmol•L－1) and increased when the CTAB concentration was more than 5 mmol•L－1; with the increasing concentration of CTAB, k2 decreased before cmc, then increased up to a maximum, and at last fell off. CTAB micelles of low concentration had almost no influence on the activity of intermediate , but high concentrated micelles could promote the dismutation of and inhibit its oxidation reaction. Electrostatic effect, hydrophobic effect, and local concentration effect of CTAB premicelles and micelles were the main factors influencing this reversible－consecutive reaction.
Kinetics of the reversible-consecutive reaction of ascorbic acid H2A with hydrogen peroxide was studied in phosphate buffer(μ=0.1 mol•L－1) at pH 7 and 25 ℃ with conduction calorimeter. The apparent rate constants of this reaction, k1, k-1 and k2, were measured at different concentrations of cetyltrimethylammonium bromide(CTAB). The results indicated that the apparent rate constants of the reaction, k1, k-1 and k2, were remarkably affected by the cationic surfactant CTAB. k1 initially increased, up to a maximum, and then fell off with increasing CTAB micellar concentration, while k-1 was hardly affected by CTAB of low concentrations(< 2 mmol•L－1) and increased when the CTAB concentration was more than 5 mmol•L－1; with the increasing concentration of CTAB, k2 decreased before cmc, then increased up to a maximum, and at last fell off. CTAB micelles of low concentration had almost no influence on the activity of intermediate , but high concentrated micelles could promote the dismutation of and inhibit its oxidation reaction. Electrostatic effect, hydrophobic effect, and local concentration effect of CTAB premicelles and micelles were the main factors influencing this reversible－consecutive reaction.
2005, 21(03): 287-290
doi: 10.3866/PKU.WHXB20050312
Abstract:
The electrochemical oxygen reduction at PtBi ordered intermetallic electrode surface has been investigated using cyclic voltammetry and rotating disk electrode. The results are compared to those at a polycrystalline platinum electrode surface. It was found that in methanol containing electrolyte solution the onset potential for oxygen reduction at PtBi is shifted to more positive potentials and the PtBi catalyst has about 4 times higher limiting current density for oxygen reduction than Pt. Thus the PtBi electrode exhibits superior properties in 0.5 mol•L－1 H2SO4＋0.25 mol•L－1 CH3OH when compared to polycrystalline platinum in terms of oxygen reduction onset potential and current density. In ordered intermetallic PtBi, the Pt-Pt bond length is increased to 0.432 nm. This expansion makes it very difficult for methanol to adsorb on the PtBi surface, leading the PtBi to have the ability of resisting methanol. X-ray photoelectron spectroscopy analysis indicated an increased d-electron vacancy of the Pt in PtBi. Such an increase of 5d vacancies led to an increased 2π electron donation from O2 to the Pt, resulting in an increased O2 adsorption and a weakened O－O bond.
The electrochemical oxygen reduction at PtBi ordered intermetallic electrode surface has been investigated using cyclic voltammetry and rotating disk electrode. The results are compared to those at a polycrystalline platinum electrode surface. It was found that in methanol containing electrolyte solution the onset potential for oxygen reduction at PtBi is shifted to more positive potentials and the PtBi catalyst has about 4 times higher limiting current density for oxygen reduction than Pt. Thus the PtBi electrode exhibits superior properties in 0.5 mol•L－1 H2SO4＋0.25 mol•L－1 CH3OH when compared to polycrystalline platinum in terms of oxygen reduction onset potential and current density. In ordered intermetallic PtBi, the Pt-Pt bond length is increased to 0.432 nm. This expansion makes it very difficult for methanol to adsorb on the PtBi surface, leading the PtBi to have the ability of resisting methanol. X-ray photoelectron spectroscopy analysis indicated an increased d-electron vacancy of the Pt in PtBi. Such an increase of 5d vacancies led to an increased 2π electron donation from O2 to the Pt, resulting in an increased O2 adsorption and a weakened O－O bond.
2005, 21(03): 291-295
doi: 10.3866/PKU.WHXB20050313
Abstract:
The monolayer of dodecanethiol was prepared on ld surface by constant-potential assembly (CPA). The properties of the monolayers were characterized using reflection absorption FT-IR, cyclic voltammetry, and electrochemistry impedance spectroscopy. Experimental results show that monolayers free from pin-hole defects can be obtained after CPA for 1 min. As the assembling time increases, the number of collapsed-site defects decreases and the packing density of the thiol monolayer increases. Compared to the monolayers prepared by self-assembly for 24 h, those obtained by CPA for 5 min have almost identical packing density and less collapsed-site defects.
The monolayer of dodecanethiol was prepared on ld surface by constant-potential assembly (CPA). The properties of the monolayers were characterized using reflection absorption FT-IR, cyclic voltammetry, and electrochemistry impedance spectroscopy. Experimental results show that monolayers free from pin-hole defects can be obtained after CPA for 1 min. As the assembling time increases, the number of collapsed-site defects decreases and the packing density of the thiol monolayer increases. Compared to the monolayers prepared by self-assembly for 24 h, those obtained by CPA for 5 min have almost identical packing density and less collapsed-site defects.
2005, 21(03): 296-299
doi: 10.3866/PKU.WHXB20050314
Abstract:
Onion-like fullerenes(OLFs) with an external diameter between 15 nm and 35 nm were prepared by vacuum heat-treatment methods of graphite powers using Al as catalyst. Resultant OLFs were purified by removing impurities using CS2 treatment and air oxidation method. HRTEM, XRD and TGA are applied to analysize samples before and after purification. The results indicate that CS2 treatment can effectively remove metal catalyst particles. After the succeeding calcination at 610 ℃ for 200 min in air, most of amorphous carbon and graphite pieces are removed, the purity of the OLFs is above 50％(volume ratio).
Onion-like fullerenes(OLFs) with an external diameter between 15 nm and 35 nm were prepared by vacuum heat-treatment methods of graphite powers using Al as catalyst. Resultant OLFs were purified by removing impurities using CS2 treatment and air oxidation method. HRTEM, XRD and TGA are applied to analysize samples before and after purification. The results indicate that CS2 treatment can effectively remove metal catalyst particles. After the succeeding calcination at 610 ℃ for 200 min in air, most of amorphous carbon and graphite pieces are removed, the purity of the OLFs is above 50％(volume ratio).
2005, 21(03): 300-305
doi: 10.3866/PKU.WHXB20050315
Abstract:
Polymer-modified silica sols were synthesized by the ammonia-catalyzed hydrolysis of tetraethoxysilane with polyvinylpyrrolidone (PVP) as polymer modifier in methyl alcohol. By small angle X-ray scattering (SAXS), the microstructure was studied with the assistance of dynamic light scattering (DLS). The dependence of the particle size distribution, fractal characteristics, and the rheology of PVP-modified silica sols on the PVP content, ammonia content and water content in sols was analyzed. It is easy to form hydrogen bonds between the surface hydroxyls of silica particles and the negatively charged oxygen atoms of inner amide in PVP molecules, and this holds back the further growth of silica particles. Thus the gelation was retarded and the rheology of the sol was largely modified by PVP.
Polymer-modified silica sols were synthesized by the ammonia-catalyzed hydrolysis of tetraethoxysilane with polyvinylpyrrolidone (PVP) as polymer modifier in methyl alcohol. By small angle X-ray scattering (SAXS), the microstructure was studied with the assistance of dynamic light scattering (DLS). The dependence of the particle size distribution, fractal characteristics, and the rheology of PVP-modified silica sols on the PVP content, ammonia content and water content in sols was analyzed. It is easy to form hydrogen bonds between the surface hydroxyls of silica particles and the negatively charged oxygen atoms of inner amide in PVP molecules, and this holds back the further growth of silica particles. Thus the gelation was retarded and the rheology of the sol was largely modified by PVP.
2005, 21(03): 306-309
doi: 10.3866/PKU.WHXB20050316
Abstract:
The Monte Carlo method was employed to investigate the adsorption isotherm of carbon monoxide and hydrogen in n-hexane with different densities. The model took into account the effects of n-hexane density on the adsorption amount and adsorption rate of carbon monoxide and hydrogen on the catalyst surface. From the simulation results, the adsorption amount of the solutes is influenced by several factors, such as the system pressure and the competitive adsorption between the solvent and solutes. When the hexane density is lower than its critical density, the increase of the system pressure can evidently enhance the adsorption of CO and H2.However the increase of the solute adsorption becomes slow due to the competitive adsorption of the solvent when the system is in its supercritical state.
The Monte Carlo method was employed to investigate the adsorption isotherm of carbon monoxide and hydrogen in n-hexane with different densities. The model took into account the effects of n-hexane density on the adsorption amount and adsorption rate of carbon monoxide and hydrogen on the catalyst surface. From the simulation results, the adsorption amount of the solutes is influenced by several factors, such as the system pressure and the competitive adsorption between the solvent and solutes. When the hexane density is lower than its critical density, the increase of the system pressure can evidently enhance the adsorption of CO and H2.However the increase of the solute adsorption becomes slow due to the competitive adsorption of the solvent when the system is in its supercritical state.
2005, 21(03): 310-314
doi: 10.3866/PKU.WHXB20050317
Abstract:
The photo-generated carriers properties of TiO2 nanoparticles annealed at different temperatures have been studied by the field induced surface photovoltage spectroscopy(FISPS) and transient photovoltage (TPV)technique. The transport mechanism of photogenerated electron in bulk phase is different from that in nano-TiO2 and space charge region of interface of junction. Due to sufficient surface states of TiO2 annealed under 400 ℃, photovoltage is controlled by the mechanism that photogenerated charge is captured and decaptured by surface states, which is attributed to slow process. After annealed at 800 ℃, the bigger particle is obtained and the energy band has been formed completely. Consequently, except for band-band transition, a band relates to free exciton transition appeared in the band edge in FISPS. The photovoltage is consistent with the direction of external field. The photovoltage is driven by surface built-in field of particles, which is a quick process. While, the powder annealed at 600 ℃, the surface phtovoltage presents the characteristics of homojunction for different crystalline interface. So the low potential barrier presents at interface of anatase phase and rutile phase. The photovoltage is driven by surface built-in field and space charge region of interface of two phases. The photogenerated electron cannot tunnel the interface when it is illuminated by weak light, unless an external electric field is applied.
The photo-generated carriers properties of TiO2 nanoparticles annealed at different temperatures have been studied by the field induced surface photovoltage spectroscopy(FISPS) and transient photovoltage (TPV)technique. The transport mechanism of photogenerated electron in bulk phase is different from that in nano-TiO2 and space charge region of interface of junction. Due to sufficient surface states of TiO2 annealed under 400 ℃, photovoltage is controlled by the mechanism that photogenerated charge is captured and decaptured by surface states, which is attributed to slow process. After annealed at 800 ℃, the bigger particle is obtained and the energy band has been formed completely. Consequently, except for band-band transition, a band relates to free exciton transition appeared in the band edge in FISPS. The photovoltage is consistent with the direction of external field. The photovoltage is driven by surface built-in field of particles, which is a quick process. While, the powder annealed at 600 ℃, the surface phtovoltage presents the characteristics of homojunction for different crystalline interface. So the low potential barrier presents at interface of anatase phase and rutile phase. The photovoltage is driven by surface built-in field and space charge region of interface of two phases. The photogenerated electron cannot tunnel the interface when it is illuminated by weak light, unless an external electric field is applied.
2005, 21(03): 315-318
doi: 10.3866/PKU.WHXB20050318
Abstract:
Diffusivities of equal proportion liquid mixture is studied by computer simulation confined in silicate pore. The diffusivities of liquid ar n and krypton in the macrovolumen systems have been calculated by equilibrium molecular dynamic (EMD) simulations in order to prove the program’s validity. Additionally, the diffusivities of ar n and krypton binary mixture confined in slit porous silicate have been computed by EMD simulation at different reduced densities and distances between two walls at room temperature (T=298 K). According to the simulation data, five experiential models are presented. The models can predict the diffusivities of ar n and krypton binary mixture and be used in industry.
Diffusivities of equal proportion liquid mixture is studied by computer simulation confined in silicate pore. The diffusivities of liquid ar n and krypton in the macrovolumen systems have been calculated by equilibrium molecular dynamic (EMD) simulations in order to prove the program’s validity. Additionally, the diffusivities of ar n and krypton binary mixture confined in slit porous silicate have been computed by EMD simulation at different reduced densities and distances between two walls at room temperature (T=298 K). According to the simulation data, five experiential models are presented. The models can predict the diffusivities of ar n and krypton binary mixture and be used in industry.
2005, 21(03): 319-323
doi: 10.3866/PKU.WHXB20050319
Abstract:
LiFePO4/C doped by Mg ion was obtained by solid phase reaction synthesis route with PVA (polyvinyl alcohol) coating processing. Conduction properties at different temperatures and resistivity change at different dopant contents indicate that conduction mechanism of LiFePO4 will change from n type to p type along with the increasing of doping content. Crystallization of LiFePO4/C with the dopant content of 0.3％(x) at different synthesis temperatures was characterized. For the sample synthesized at 973 K, the particles with a diameter of several hundred nanometers together with carbon decomposed by PVA formed secondary particles with a diameter of 10 micrometer. Along with curves of cyclic voltammetry, two shoulder-peaks showed that another way for lithium ion extraction/ insertion in cathode existed. When batteries were cycled at a rate of 0.1 C, the charge and discharge curves showed flat work voltages and large capacities. When the charge-discharge rate was increased to 0.5 C, LiFePO4 covered by carbon and doped by Mg ion showed capacity of more than 120 mA•h•g－1. After 100 cycles, the capacity fade was neglectable.
LiFePO4/C doped by Mg ion was obtained by solid phase reaction synthesis route with PVA (polyvinyl alcohol) coating processing. Conduction properties at different temperatures and resistivity change at different dopant contents indicate that conduction mechanism of LiFePO4 will change from n type to p type along with the increasing of doping content. Crystallization of LiFePO4/C with the dopant content of 0.3％(x) at different synthesis temperatures was characterized. For the sample synthesized at 973 K, the particles with a diameter of several hundred nanometers together with carbon decomposed by PVA formed secondary particles with a diameter of 10 micrometer. Along with curves of cyclic voltammetry, two shoulder-peaks showed that another way for lithium ion extraction/ insertion in cathode existed. When batteries were cycled at a rate of 0.1 C, the charge and discharge curves showed flat work voltages and large capacities. When the charge-discharge rate was increased to 0.5 C, LiFePO4 covered by carbon and doped by Mg ion showed capacity of more than 120 mA•h•g－1. After 100 cycles, the capacity fade was neglectable.
2005, 21(03): 324-327
doi: 10.3866/PKU.WHXB20050320
Abstract:
Mesoporous aluminosilicates MSU-SMFI with well-ordered hexa nal symmetry were assembled from MFI zeolitic precursors containing abundant protozeolitic nanoclusters. Normal MCM-41 was synthesized by using tetraethyl orthosilicate (TEOS) and sodium aluminate as silica source and aluminum source,respectively. The pore diameter of MSU-SMFI sample and normal MCM-41 both are 2.70 nm, and their BET specific surface areas and pore volumes are comparable as seen from XRD and N2 sorption results. Although both MSU-SMFI and MCM-41 possess weak acidic sites and medium strong acidic sites in NH3-TPD profiles, the density of weak acidic sites and medium strong acidic sites in MSU-SMFI are much higher than that of MCM-41.The catalytic cracking conversion of cumene on MSU-SMFI is 31％ higher than that on MCM-41 with the same Si/Al ratio, and the butylation conversion of naphthalene over MSU-SMFI is 15％ higher than that on the MCM-41 sample. Incorporation of MFI zeolitic nanoclusters into the mesostructured framework of MSU-SMFI led to enhanced acidity.
Mesoporous aluminosilicates MSU-SMFI with well-ordered hexa nal symmetry were assembled from MFI zeolitic precursors containing abundant protozeolitic nanoclusters. Normal MCM-41 was synthesized by using tetraethyl orthosilicate (TEOS) and sodium aluminate as silica source and aluminum source,respectively. The pore diameter of MSU-SMFI sample and normal MCM-41 both are 2.70 nm, and their BET specific surface areas and pore volumes are comparable as seen from XRD and N2 sorption results. Although both MSU-SMFI and MCM-41 possess weak acidic sites and medium strong acidic sites in NH3-TPD profiles, the density of weak acidic sites and medium strong acidic sites in MSU-SMFI are much higher than that of MCM-41.The catalytic cracking conversion of cumene on MSU-SMFI is 31％ higher than that on MCM-41 with the same Si/Al ratio, and the butylation conversion of naphthalene over MSU-SMFI is 15％ higher than that on the MCM-41 sample. Incorporation of MFI zeolitic nanoclusters into the mesostructured framework of MSU-SMFI led to enhanced acidity.
2005, 21(03): 328-332
doi: 10.3866/PKU.WHXB20050321
Abstract:
A series of perovskite-like LaSrCo0.9B’0.1O4 (B’=Mn、Fe、Ni、Cu) mixed oxides were synthesized by polyacrylamide gel method, and the catalytic activity for CO and C3H8 oxidation over these catalysts was investigated. The results show that the catalytic activity over LaSrCo0.9Ni0.1O4 is the best. The 50％ and 100％ conversion temperatures of CO are 194 ℃ and 220 ℃, which are 14 ℃ and 10 ℃ lower than those over LaSrCoO4 catalyst respectively; the 50％ and 100％ conversion temperatures of C3H8 are respectively 18 ℃ and 25 ℃ lower. The LaSrCo0.9Ni0.1O4 and LaSrCoO4 mixed oxides were investigated by using XRD, BET, TEM and TPD methods. The results of XRD indicate that both of the samples have tetra nal K2NiF4 structure, and the results of TEM suggest that they are nanostructured materials. B-site adulteration with nickel enhances the catalytic activity, the O2-adsorption amount and the lattice distortion of LaSrCoO4, while reduces the average crystal size on the same time.
A series of perovskite-like LaSrCo0.9B’0.1O4 (B’=Mn、Fe、Ni、Cu) mixed oxides were synthesized by polyacrylamide gel method, and the catalytic activity for CO and C3H8 oxidation over these catalysts was investigated. The results show that the catalytic activity over LaSrCo0.9Ni0.1O4 is the best. The 50％ and 100％ conversion temperatures of CO are 194 ℃ and 220 ℃, which are 14 ℃ and 10 ℃ lower than those over LaSrCoO4 catalyst respectively; the 50％ and 100％ conversion temperatures of C3H8 are respectively 18 ℃ and 25 ℃ lower. The LaSrCo0.9Ni0.1O4 and LaSrCoO4 mixed oxides were investigated by using XRD, BET, TEM and TPD methods. The results of XRD indicate that both of the samples have tetra nal K2NiF4 structure, and the results of TEM suggest that they are nanostructured materials. B-site adulteration with nickel enhances the catalytic activity, the O2-adsorption amount and the lattice distortion of LaSrCoO4, while reduces the average crystal size on the same time.
2005, 21(03): 333-337
doi: 10.3866/PKU.WHXB20050322
Abstract:
Histone deacetylase (HDAC) greatly affects the chromatin topology and gene expression, and HDAC can be a new strategy in human cancer or tumour therapy. Hydroxamic acid compounds are component of most of the HDAC inhibitors. Studies on quantitative structure-activity relationship (QSAR) with CoMFA for the bioactivities of a series of sulfonamide hydroxamic acid HDAC inhibitors were carried out successfully, and a od cross-validated correlation (q2=0.704) was obtained .The non-cross-validated partial least squares (PLS) model was also well built and analyzed by the prediction of the active data CoMFA steric, and electrostatic contours. The results show that steric field (0.697) plays a more important role in increasing bioactivity than that of electrostatic field (0.303), and the R5 position prefers a larger group, but the R1 position prefers a smaller group.
Histone deacetylase (HDAC) greatly affects the chromatin topology and gene expression, and HDAC can be a new strategy in human cancer or tumour therapy. Hydroxamic acid compounds are component of most of the HDAC inhibitors. Studies on quantitative structure-activity relationship (QSAR) with CoMFA for the bioactivities of a series of sulfonamide hydroxamic acid HDAC inhibitors were carried out successfully, and a od cross-validated correlation (q2=0.704) was obtained .The non-cross-validated partial least squares (PLS) model was also well built and analyzed by the prediction of the active data CoMFA steric, and electrostatic contours. The results show that steric field (0.697) plays a more important role in increasing bioactivity than that of electrostatic field (0.303), and the R5 position prefers a larger group, but the R1 position prefers a smaller group.
Electrochemical Properties of a V2O5/C Composite in Aqueous Solution Used for Zinc Secondary Battery
2005, 21(03): 338-342
doi: 10.3866/PKU.WHXB20050323
Abstract:
A composite of vanadium pentoxide/carbon was prepared by sol-gel method. By using scanning electronic microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR), it was found that the composite was composed of porous particles. Inner part of the composite was carbon particles, which covered by an outer layer of vanadium pentoxide sol. The electrochemical properties of the composite as cathode material in aqueous solution for zinc secondary battery were studied by using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). When the mass ratio of V2O5/C was 1:1,the composite electrode showed od electrochemical properties: open circuit potential of its battery reached 1.64 V; zinc ions were reversibly intercalated into the composite electrode in site A at 1.26 V and site B at 1.01 V, with a highest intercalation rate 70 mA•g－1; cycling performance of the composite electrode was quite od in a test of 20 charge-discharge cycles. The reaction process of V2O5/C composite electrode was controlled by the diffusion rate of zinc ions in V2O5.
A composite of vanadium pentoxide/carbon was prepared by sol-gel method. By using scanning electronic microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR), it was found that the composite was composed of porous particles. Inner part of the composite was carbon particles, which covered by an outer layer of vanadium pentoxide sol. The electrochemical properties of the composite as cathode material in aqueous solution for zinc secondary battery were studied by using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). When the mass ratio of V2O5/C was 1:1,the composite electrode showed od electrochemical properties: open circuit potential of its battery reached 1.64 V; zinc ions were reversibly intercalated into the composite electrode in site A at 1.26 V and site B at 1.01 V, with a highest intercalation rate 70 mA•g－1; cycling performance of the composite electrode was quite od in a test of 20 charge-discharge cycles. The reaction process of V2O5/C composite electrode was controlled by the diffusion rate of zinc ions in V2O5.
