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1993 Volume 9 Issue 6
1993, 9(06): 721-723
doi: 10.3866/PKU.WHXB19930601
Abstract:
In-situ time resolved Raman spectroscopy has been used to study the coadsorption of thiourea (TU) and ClO_4~- at Ag electrodes. The time resolved SERS intensities were monitored following electrode potential steps. As the electrode potential was stepped from -0.3 V to -0.9 V, the SERS intensities of TU were able to follow the potential change immediately. However, pro-longed time was needed for the intensities to follow the step from -0.9 V to -0.3 V. Significant difference of the rate of intensity change for different SERS bands of TU was observed even in such a potential step, which may be related to the changes in orientation of TU or its configuration with the coadsorbed ClO_4~-.
In-situ time resolved Raman spectroscopy has been used to study the coadsorption of thiourea (TU) and ClO_4~- at Ag electrodes. The time resolved SERS intensities were monitored following electrode potential steps. As the electrode potential was stepped from -0.3 V to -0.9 V, the SERS intensities of TU were able to follow the potential change immediately. However, pro-longed time was needed for the intensities to follow the step from -0.9 V to -0.3 V. Significant difference of the rate of intensity change for different SERS bands of TU was observed even in such a potential step, which may be related to the changes in orientation of TU or its configuration with the coadsorbed ClO_4~-.
1993, 9(06): 724-727
doi: 10.3866/PKU.WHXB19930602
Abstract:
Continuous sampling technique—an improvement of the gas stripping method has been proposed for the determination of large value activity coefficients at infinite dilution (γ~∞>10~2). In this technique, the outlet gas flow from the equilibrium cell is introduced directly into a detector of a gas chromatograph. The curve of the concentration of the solute in the flow gas versus the stripping time will be gained continueously, and the variation slope can be obtained more precisely. Experimental activity coefficient results have been compared with the literature values which were obtained by the other methods.
Continuous sampling technique—an improvement of the gas stripping method has been proposed for the determination of large value activity coefficients at infinite dilution (γ~∞>10~2). In this technique, the outlet gas flow from the equilibrium cell is introduced directly into a detector of a gas chromatograph. The curve of the concentration of the solute in the flow gas versus the stripping time will be gained continueously, and the variation slope can be obtained more precisely. Experimental activity coefficient results have been compared with the literature values which were obtained by the other methods.
1993, 9(06): 728-734
doi: 10.3866/PKU.WHXB19930603
Abstract:
The morphology of the precipitates of ferric hydrous oxides formed by forced hydrolysis of acidic ferric salts solutions at elevated temperature is strongly affected by the addition of EDTA to such system before aging. At lower content of EDTA, the sizes of the particles formed increase with EDTA until certain value which corresponds to point B in the typical Langmuir-type adsorption isotherm of EDTA on growing nuclei or tiny particles. The opposite phenomena have been observed at higher EDTA concentrations. These are due to the formation of ferric-DETA complex, which restricts the hydrolysis of free ferric ions and therefore the growth of crystals. In addition, any factor, e.g. anions presented in the aging solution, which will affect the adsorption of EDTA on growing nuclei or the complexing of EDTA with ferric ions might influence the extent of the effect of EDTA.
The morphology of the precipitates of ferric hydrous oxides formed by forced hydrolysis of acidic ferric salts solutions at elevated temperature is strongly affected by the addition of EDTA to such system before aging. At lower content of EDTA, the sizes of the particles formed increase with EDTA until certain value which corresponds to point B in the typical Langmuir-type adsorption isotherm of EDTA on growing nuclei or tiny particles. The opposite phenomena have been observed at higher EDTA concentrations. These are due to the formation of ferric-DETA complex, which restricts the hydrolysis of free ferric ions and therefore the growth of crystals. In addition, any factor, e.g. anions presented in the aging solution, which will affect the adsorption of EDTA on growing nuclei or the complexing of EDTA with ferric ions might influence the extent of the effect of EDTA.
1993, 9(06): 735-739
doi: 10.3866/PKU.WHXB19930604
Abstract:
High-temperature X-ray diffractometer is employed to study the dispersion capacities of KCI and NaCl in zeolite supports. The capacities are strongly affected by temperature. The higher the temperature is, the greater the capacities are. It was also found that the capacity obtained by impregnating and drying at low temperature is much smaller than that obtained by impregnating and heating at high temperature. For example, only a small amount of KCl can disperse into NaA Zeolite pores by impregnating, and this is most likely owing to the competition adsorption of water and the salt in zeolite pores.
High-temperature X-ray diffractometer is employed to study the dispersion capacities of KCI and NaCl in zeolite supports. The capacities are strongly affected by temperature. The higher the temperature is, the greater the capacities are. It was also found that the capacity obtained by impregnating and drying at low temperature is much smaller than that obtained by impregnating and heating at high temperature. For example, only a small amount of KCl can disperse into NaA Zeolite pores by impregnating, and this is most likely owing to the competition adsorption of water and the salt in zeolite pores.
1993, 9(06): 740-745
doi: 10.3866/PKU.WHXB19930605
Abstract:
A new approach to the computation of entropy-related properties of fluid in a Monte Carlo molecular simulation is presented. Application of the new technique to hard sphere fluid shows that it is capable of providing reliable estimates of such properties as chemical potential and Helmholtz free energy, even at high density where other existed methods are difficult to apply. Moreover, the chemical potentials of an infinite dilute component in hard sphere systems are estimated and compared with that calculated from the Carnahan-starling equation.
A new approach to the computation of entropy-related properties of fluid in a Monte Carlo molecular simulation is presented. Application of the new technique to hard sphere fluid shows that it is capable of providing reliable estimates of such properties as chemical potential and Helmholtz free energy, even at high density where other existed methods are difficult to apply. Moreover, the chemical potentials of an infinite dilute component in hard sphere systems are estimated and compared with that calculated from the Carnahan-starling equation.
1993, 9(06): 746-751
doi: 10.3866/PKU.WHXB19930606
Abstract:
According to the results of investigation in a series of Na_2SnO_3 catalysts for oxidative coupling of methane, a sample (5 mol%Li_2 SO_4-Na_2SnO_3) with od catalytic properties was selected as the main research object. By using electron paramagentic resonance(EPR) method, the form of surface adsorbed oxygen has been investigated. The EPR results confirm that a signal with g value of 2.013 is from the species of surface adsorbed oxygen, and that it can be assigned to adsorbed superoxide species O_2~-. At 300 ℃ or the above this type of oxygen species can form on that catalyst sample.
The species O_2~- is stable under conditions of room temperature and vacuum of 1.33×10~(-2) Pa. But at 700 ℃ the reaction between O_2~- and CH_4 occured, and at the same time the intensity of O_2~- signal considerably decreased. The resuls show that the surface species O_2~- might play an important role in activating CH_4 molecules in the oxidative coupling reaction of methane.
According to the results of investigation in a series of Na_2SnO_3 catalysts for oxidative coupling of methane, a sample (5 mol%Li_2 SO_4-Na_2SnO_3) with od catalytic properties was selected as the main research object. By using electron paramagentic resonance(EPR) method, the form of surface adsorbed oxygen has been investigated. The EPR results confirm that a signal with g value of 2.013 is from the species of surface adsorbed oxygen, and that it can be assigned to adsorbed superoxide species O_2~-. At 300 ℃ or the above this type of oxygen species can form on that catalyst sample.
The species O_2~- is stable under conditions of room temperature and vacuum of 1.33×10~(-2) Pa. But at 700 ℃ the reaction between O_2~- and CH_4 occured, and at the same time the intensity of O_2~- signal considerably decreased. The resuls show that the surface species O_2~- might play an important role in activating CH_4 molecules in the oxidative coupling reaction of methane.
1993, 9(06): 752-759
doi: 10.3866/PKU.WHXB19930607
Abstract:
Six compounds of M_2F_3·12H_2O (M=Eu, Gd, Tb, Y, Er, Lu; H_2F=Fumaric acid) have been synthesized. The structures of Eu(Ⅲ), Tb(Ⅲ), Y(Ⅲ), Er(Ⅲ) and Lu(Ⅲ) compounds have been determined by single crystal X-ray diffraction method. The complex of Eu(Ⅲ) crystallizes in triclinic space group P(1), and the coordination number of Eu~(3+) is ten. The other four complexes crystallize in monclinic space group P2_(1/c), and the coordination numbers of the metal ions are eight. Each of the complexes shows a three-dimensional net structure.
Six compounds of M_2F_3·12H_2O (M=Eu, Gd, Tb, Y, Er, Lu; H_2F=Fumaric acid) have been synthesized. The structures of Eu(Ⅲ), Tb(Ⅲ), Y(Ⅲ), Er(Ⅲ) and Lu(Ⅲ) compounds have been determined by single crystal X-ray diffraction method. The complex of Eu(Ⅲ) crystallizes in triclinic space group P(1), and the coordination number of Eu~(3+) is ten. The other four complexes crystallize in monclinic space group P2_(1/c), and the coordination numbers of the metal ions are eight. Each of the complexes shows a three-dimensional net structure.
1993, 9(06): 760-764
doi: 10.3866/PKU.WHXB19930608
Abstract:
The metallic surface structure of supported Ru catalysts, activated at different pretreatment conditions, was investigated by following the development of IR bands due to adsorbed CO, as well as by following the methane formation in temperature-programmed surface reaction(TPSR-MS) of adsorbed CO in a H_2 flow. It revealed that there existed three kinds of active sites, designated as S_1, S_2 and S_3 sites, respectively. The S_1 sites, characterized by low frequency(LF) bands of 1980～2060 cm~(-1) for linearly adsorbed CO, were attributed to metallic Ru particles with almost no interaction with the support. The TPSR-MS results showed that, when reaction with H_2, the adsorbed CO on these sites changed into CH_4 at a lower temperature of ca. 450 K, varying with activated conditions. On the other hand, the S_2 sites were visualized to be interfacial Ru particles in direct contact with supporting materials, and exhibited stronger interaction with support. As a result of this MSI effect, the S_2 sites would result in the formation of electron-deficient Ru~(δ+) sites, and maintain high dispersive states of metal catalysts, and also adsorb CO with configuation of Ru~(δ+)-CO at 2075±5 cm~(-1) mediun frequency (MF_2). Upon hydrogenation, the adsorbed CO of formed methane at a much higher temperature of ca. 650 K. Obviously, the S_1 and S_2 sites are static sites of the conventional nature.
The interaction of CO with supported Ru catalysts led to the oxidative disruption of soluble surface Ru atoms or clusters with coordinatively unsaturation on the S_1 sites, as indicated by the slow transformation of the bands at 1980～2060 cm~(-1) due to Ru_x~0-CO to bands at 2135±5 cm (HF) and 2075±(MF_1) cm~(-1) attributed to surface-anchored carbonyl [(support-O)_2Ru(CO)_3]_n (n=1,2…) species, referred to as S_3 sites. The oxidative corrosive carbonylation of Ru is both favored ther-modynamically and feasible kinetically under our experimental conditions. It was demonstrated that at higher temperature, the presence of CO, especially with high partial pressure of hydrogen, such as in the case of TPSR-MS experiments, causes the reductive agglomeration of the S_3 sites, and the soluble Ru particles or clusters on the S_1 sites will be restored. These observation led us to postulate that the S_3 sites were active sites formed dynamically during the course of the Fischer-Tropsch reaction.
The metallic surface structure of supported Ru catalysts, activated at different pretreatment conditions, was investigated by following the development of IR bands due to adsorbed CO, as well as by following the methane formation in temperature-programmed surface reaction(TPSR-MS) of adsorbed CO in a H_2 flow. It revealed that there existed three kinds of active sites, designated as S_1, S_2 and S_3 sites, respectively. The S_1 sites, characterized by low frequency(LF) bands of 1980～2060 cm~(-1) for linearly adsorbed CO, were attributed to metallic Ru particles with almost no interaction with the support. The TPSR-MS results showed that, when reaction with H_2, the adsorbed CO on these sites changed into CH_4 at a lower temperature of ca. 450 K, varying with activated conditions. On the other hand, the S_2 sites were visualized to be interfacial Ru particles in direct contact with supporting materials, and exhibited stronger interaction with support. As a result of this MSI effect, the S_2 sites would result in the formation of electron-deficient Ru~(δ+) sites, and maintain high dispersive states of metal catalysts, and also adsorb CO with configuation of Ru~(δ+)-CO at 2075±5 cm~(-1) mediun frequency (MF_2). Upon hydrogenation, the adsorbed CO of formed methane at a much higher temperature of ca. 650 K. Obviously, the S_1 and S_2 sites are static sites of the conventional nature.
The interaction of CO with supported Ru catalysts led to the oxidative disruption of soluble surface Ru atoms or clusters with coordinatively unsaturation on the S_1 sites, as indicated by the slow transformation of the bands at 1980～2060 cm~(-1) due to Ru_x~0-CO to bands at 2135±5 cm (HF) and 2075±(MF_1) cm~(-1) attributed to surface-anchored carbonyl [(support-O)_2Ru(CO)_3]_n (n=1,2…) species, referred to as S_3 sites. The oxidative corrosive carbonylation of Ru is both favored ther-modynamically and feasible kinetically under our experimental conditions. It was demonstrated that at higher temperature, the presence of CO, especially with high partial pressure of hydrogen, such as in the case of TPSR-MS experiments, causes the reductive agglomeration of the S_3 sites, and the soluble Ru particles or clusters on the S_1 sites will be restored. These observation led us to postulate that the S_3 sites were active sites formed dynamically during the course of the Fischer-Tropsch reaction.
1993, 9(06): 765-769
doi: 10.3866/PKU.WHXB19930609
Abstract:
The photovoltaic characters of the sandwich cell, SnO_2/chla/PVA/SnO_2, were reported. The mechanism of photovoltaic effect of the cell was discussed, so that the dark rectifying effect was explained and the charge seperation under irradiation was occured at the junction of chla/SnO_2. We measured the output parameters of the cell, and improved the cell efficiency by adding hydro-quinone and so on into it. As a result, the short current and power conversion yield were increased over one digital order.
The photovoltaic characters of the sandwich cell, SnO_2/chla/PVA/SnO_2, were reported. The mechanism of photovoltaic effect of the cell was discussed, so that the dark rectifying effect was explained and the charge seperation under irradiation was occured at the junction of chla/SnO_2. We measured the output parameters of the cell, and improved the cell efficiency by adding hydro-quinone and so on into it. As a result, the short current and power conversion yield were increased over one digital order.
1993, 9(06): 770-775
doi: 10.3866/PKU.WHXB19930610
Abstract:
At the level of ab initio 3-21G, the equilibrum geometries of linear carbon clusters C_n~e(n≤8, |e|≤2) have been optimized by using an energy gradient method. Ionization potentials obtained display odd-even alternations with the increase of carbon atoms in clusters. Based on ab initio calculations, occupied canonical molecular orbitals(CMO) are localized with Boys local-ization method. Analysis of the properties of LMOs shows that there are two-centre σ and π bonds, multi-centre σ and π bonds and bending bonds in the linear carbon clusters C_n~e. Such as this variety of bonding types could be considered as the character of bonding behavior for small carbon clusters. Furthermore, the relations between bonding properties and stabilities are discussed. It is shown that the conjugation of chemical bonds plays a significant role for the stabilities of small carbon element clusters.
At the level of ab initio 3-21G, the equilibrum geometries of linear carbon clusters C_n~e(n≤8, |e|≤2) have been optimized by using an energy gradient method. Ionization potentials obtained display odd-even alternations with the increase of carbon atoms in clusters. Based on ab initio calculations, occupied canonical molecular orbitals(CMO) are localized with Boys local-ization method. Analysis of the properties of LMOs shows that there are two-centre σ and π bonds, multi-centre σ and π bonds and bending bonds in the linear carbon clusters C_n~e. Such as this variety of bonding types could be considered as the character of bonding behavior for small carbon clusters. Furthermore, the relations between bonding properties and stabilities are discussed. It is shown that the conjugation of chemical bonds plays a significant role for the stabilities of small carbon element clusters.
1993, 9(06): 776-787
doi: 10.3866/PKU.WHXB19930611
Abstract:
In this paper, the authors modify the technique for determining the activity coefficients by the method of head-space gas chromatography and improve the accuracy of the measurement. The activity coefficients of volatile components and densities of the solutions are measured for diluent-diluent, TBP-diluent and TBP-diluent-diluent systems and those TBP-containing systems with saturated water. The diluents used are n-C_6G_(14), n-C_7H_(16), n-C_8H_(18), C_6H_6, cy-C_6H_(12), CCl_4 and CHCl_3.
A simple activity coefficient model is derived on the basis of Pierott's theory with modified hard-sphere residual chemical potential and radial distribution function. Every kinds of forces between molecules are considered. The model is used to calculate the activity coefficients of TBP and diluents systems, From the molecular parameters regressed from two-component systems, the activity coefficients of three-component systems are calculated.
In this paper, the authors modify the technique for determining the activity coefficients by the method of head-space gas chromatography and improve the accuracy of the measurement. The activity coefficients of volatile components and densities of the solutions are measured for diluent-diluent, TBP-diluent and TBP-diluent-diluent systems and those TBP-containing systems with saturated water. The diluents used are n-C_6G_(14), n-C_7H_(16), n-C_8H_(18), C_6H_6, cy-C_6H_(12), CCl_4 and CHCl_3.
A simple activity coefficient model is derived on the basis of Pierott's theory with modified hard-sphere residual chemical potential and radial distribution function. Every kinds of forces between molecules are considered. The model is used to calculate the activity coefficients of TBP and diluents systems, From the molecular parameters regressed from two-component systems, the activity coefficients of three-component systems are calculated.
1993, 9(06): 788-790
doi: 10.3866/PKU.WHXB19930612
Abstract:
In this parper, the decarboxylation reaction of acrylic acid in the singlet and triplet excited states were investigated by semi-empirical self-consistent-field molecular orbital method (AM1). Our results support the mechanism of photolysis proposed th Robert. In combintion with experiment, it can be deduced that the first step of photodecarboxylation reaction is in the singlet pathway, the second step in triplet pathway. The reactants, transition states, reaction intermedi-ates and products corresponding to the singlet and triplet pathways were optimized by gradient techniques. All of the transition states and intermediates were confirmed by full vibrational analysis.
In this parper, the decarboxylation reaction of acrylic acid in the singlet and triplet excited states were investigated by semi-empirical self-consistent-field molecular orbital method (AM1). Our results support the mechanism of photolysis proposed th Robert. In combintion with experiment, it can be deduced that the first step of photodecarboxylation reaction is in the singlet pathway, the second step in triplet pathway. The reactants, transition states, reaction intermedi-ates and products corresponding to the singlet and triplet pathways were optimized by gradient techniques. All of the transition states and intermediates were confirmed by full vibrational analysis.
1993, 9(06): 791-794
doi: 10.3866/PKU.WHXB19930613
Abstract:
In this work, the influence of temperature, wavelength and surface treatment on the transient behavior of n-InP in Fe~(3+)/Fe~(2+) solution with pulsed light technique is investigated.
The wavelength does not influence the time constant of the transient curve. The peak pho-tovoltage decreases when the temperature increases, it is similar to the silicon cell. The decay of photovoltage-time curve is rapid with temperature because of increasing of the back diffusion rate. If the electrode is polished by emerg parper, the peak valus drops and the decay of the curve is very rapid, it can be restored by treatment with H_2SO_4+H_2O_2 (1:1) etching solution continuousely, this phenomenon can be explained by surface states.
In this work, the influence of temperature, wavelength and surface treatment on the transient behavior of n-InP in Fe~(3+)/Fe~(2+) solution with pulsed light technique is investigated.
The wavelength does not influence the time constant of the transient curve. The peak pho-tovoltage decreases when the temperature increases, it is similar to the silicon cell. The decay of photovoltage-time curve is rapid with temperature because of increasing of the back diffusion rate. If the electrode is polished by emerg parper, the peak valus drops and the decay of the curve is very rapid, it can be restored by treatment with H_2SO_4+H_2O_2 (1:1) etching solution continuousely, this phenomenon can be explained by surface states.
1993, 9(06): 795-801
doi: 10.3866/PKU.WHXB19930614
Abstract:
The crystal and molecular structures of the mesogenic 2,5-bis-(4-ethylbenzoyl) oxystyrene(Ⅰ) and 2,5-bis(4-methoxybenzoyl) oxybenzaldehyde (Ⅱ) have been determined by single crystal X-ray diffraction methods. Both compound Ⅰ and compound Ⅱ are liquid crystalline.
Crystal data:
Compound Ⅰ, C_2H_5·C_6H_4·COO·C_6H_3(CH:CH_2)·OOC·C_6H_4·C_2H_5, triclinic, space group P(1) (No.2), a=0.9356(6), b=0.9842(6), c=1.3357(8) nm, α=108.68(5)°, β=105.67(5)°, γ=96.36(5)°, Z=2; Compound Ⅱ, H_3CO·C_6H_4·COO·C_6H_3(CHO)·OOC·C_6H_4·OCH_3, monoclinic, space group Pn (No.7), a=0.9109(2), b=0.9187(3), c=2.3166(8) nm, β=93.93(2)°, Z=2.
In both crystals, the molecules take fully extended form with the long molecular axes of 2.27 nm for compound I and of 2.22 nm for compound II. The molecules of these two compounds are not plate-like but rather rod-like. The middle phenyl rings of the molecules rotate from the other two phenyl rings by 86.3° and 135.8 for compound I; and by 84.9° and 84.7° for compound II. All molecules are arranged parallel along their long axes in the crystals.
Compound I is a polymerizalbe monomer, it easily forms high molecular weight polymer upon heating without any initiators at about 140 ℃. Its high polymerizability might be explained by the fact that the molecules are packed such that the lateral vinyl groups of neighbouring molecules are closely correlated with a distance of only 0.47 nm and the energy-favorable parallel molecular arrangement, which is similar to the arrangment of the mesogens in its polymer.
The crystal and molecular structures of the mesogenic 2,5-bis-(4-ethylbenzoyl) oxystyrene(Ⅰ) and 2,5-bis(4-methoxybenzoyl) oxybenzaldehyde (Ⅱ) have been determined by single crystal X-ray diffraction methods. Both compound Ⅰ and compound Ⅱ are liquid crystalline.
Crystal data:
Compound Ⅰ, C_2H_5·C_6H_4·COO·C_6H_3(CH:CH_2)·OOC·C_6H_4·C_2H_5, triclinic, space group P(1) (No.2), a=0.9356(6), b=0.9842(6), c=1.3357(8) nm, α=108.68(5)°, β=105.67(5)°, γ=96.36(5)°, Z=2; Compound Ⅱ, H_3CO·C_6H_4·COO·C_6H_3(CHO)·OOC·C_6H_4·OCH_3, monoclinic, space group Pn (No.7), a=0.9109(2), b=0.9187(3), c=2.3166(8) nm, β=93.93(2)°, Z=2.
In both crystals, the molecules take fully extended form with the long molecular axes of 2.27 nm for compound I and of 2.22 nm for compound II. The molecules of these two compounds are not plate-like but rather rod-like. The middle phenyl rings of the molecules rotate from the other two phenyl rings by 86.3° and 135.8 for compound I; and by 84.9° and 84.7° for compound II. All molecules are arranged parallel along their long axes in the crystals.
Compound I is a polymerizalbe monomer, it easily forms high molecular weight polymer upon heating without any initiators at about 140 ℃. Its high polymerizability might be explained by the fact that the molecules are packed such that the lateral vinyl groups of neighbouring molecules are closely correlated with a distance of only 0.47 nm and the energy-favorable parallel molecular arrangement, which is similar to the arrangment of the mesogens in its polymer.
1993, 9(06): 802-807
doi: 10.3866/PKU.WHXB19930615
Abstract:
The heat capacities of samples were measured by Differential Scanning Calorimetry(DSC), using scanning enthalpy method. The accuracy of the heat capacity measurements was appoximately 1 per cent by the method. The heat capacities of bis(n-octadecylammonium) tetrachlorometal-iates (Ⅱ), (n-C_(18)H_(37)NH_3)_2MCl_4 (M=Mn, Zn; short notation C_(18)M), were measured from 190 to 410 K. The enthalpies and entropies of the solid-solid phase transitions for C_(18)M were calculated. The selected thermodynamic functions were given at intervals of 5 K from 190 to 410 K.
The heat capacities of samples were measured by Differential Scanning Calorimetry(DSC), using scanning enthalpy method. The accuracy of the heat capacity measurements was appoximately 1 per cent by the method. The heat capacities of bis(n-octadecylammonium) tetrachlorometal-iates (Ⅱ), (n-C_(18)H_(37)NH_3)_2MCl_4 (M=Mn, Zn; short notation C_(18)M), were measured from 190 to 410 K. The enthalpies and entropies of the solid-solid phase transitions for C_(18)M were calculated. The selected thermodynamic functions were given at intervals of 5 K from 190 to 410 K.
1993, 9(06): 808-814
doi: 10.3866/PKU.WHXB19930616
Abstract:
The iron-sulfur cluster ions, Fe_nS_m~+(n=1-13, m=1-13), were produced by diredt laser vaporization of a solid sample containing a mixture of iron and sulfur powder. UV photodissociation of the cluster ions was studied with a tandem time-of-flight mass spectrometer. It was found that all the cluster ions with compositions of m=n, m=n-1 or m=n+5 have relatively larger abundaces, indicating that they were more stable. The photodissociation results of Fe_nS_m~+ ions showed that, when n≈m, the main channels were losses of neutral S atoms until n≈m, while for parent ions with n≈m, the main product ions have the m=n or m=n-1 compositions. Form these experimental results, it was proposed that the Fe_nS_n~+ ions might have structures similar to those of the Fe_nS_n cores in iron-sulfur proteins, while the structures of the Fe_nS_m~+ (m>n) cluster ions could be considered to have a pattern of the Fe_nS_n~+ cores with some peripheral S atoms.
The iron-sulfur cluster ions, Fe_nS_m~+(n=1-13, m=1-13), were produced by diredt laser vaporization of a solid sample containing a mixture of iron and sulfur powder. UV photodissociation of the cluster ions was studied with a tandem time-of-flight mass spectrometer. It was found that all the cluster ions with compositions of m=n, m=n-1 or m=n+5 have relatively larger abundaces, indicating that they were more stable. The photodissociation results of Fe_nS_m~+ ions showed that, when n≈m, the main channels were losses of neutral S atoms until n≈m, while for parent ions with n≈m, the main product ions have the m=n or m=n-1 compositions. Form these experimental results, it was proposed that the Fe_nS_n~+ ions might have structures similar to those of the Fe_nS_n cores in iron-sulfur proteins, while the structures of the Fe_nS_m~+ (m>n) cluster ions could be considered to have a pattern of the Fe_nS_n~+ cores with some peripheral S atoms.
1993, 9(06): 815-818
doi: 10.3866/PKU.WHXB19930617
Abstract:
This paper describes the preparation of monodispersed sol of zirconium basic carbonate consisting of particles with diameter less than 0.6 μm by aging Zr(Ⅳ) solution at elevated temperature in the presence of urea and glycerol. The composition of the monodispersed particles has primarily been determined by the IR spectra and the weight-loss of the particles on calcination. The monodispersed particles of ZrO_2 were obtained by calcination of the monodispersed particles separated from the sol at 850 ℃ for 2 h.
This paper describes the preparation of monodispersed sol of zirconium basic carbonate consisting of particles with diameter less than 0.6 μm by aging Zr(Ⅳ) solution at elevated temperature in the presence of urea and glycerol. The composition of the monodispersed particles has primarily been determined by the IR spectra and the weight-loss of the particles on calcination. The monodispersed particles of ZrO_2 were obtained by calcination of the monodispersed particles separated from the sol at 850 ℃ for 2 h.
1993, 9(06): 819-822
doi: 10.3866/PKU.WHXB19930618
Abstract:
(NH_4)_2SO_4-TiO_2 have been treated at different temperatures. The samples obtained have been characteristized by IR and XPS as well as XRD. The results show that below 573 K there exists dispersion of ammonium sulfate on the surface of TiO_2, and there might be a decomposition of sulfate to some extent. The dispersion the sulfate ion may be favorable for the transformation from the isolated ion to the bidentatedly bound state. The latter may interact with Ti on the surface to form the surface S-Ti coordination complex. Above 573 K the S-Ti complex will decompose gradually as the treatment temperature es up further.
(NH_4)_2SO_4-TiO_2 have been treated at different temperatures. The samples obtained have been characteristized by IR and XPS as well as XRD. The results show that below 573 K there exists dispersion of ammonium sulfate on the surface of TiO_2, and there might be a decomposition of sulfate to some extent. The dispersion the sulfate ion may be favorable for the transformation from the isolated ion to the bidentatedly bound state. The latter may interact with Ti on the surface to form the surface S-Ti coordination complex. Above 573 K the S-Ti complex will decompose gradually as the treatment temperature es up further.
1993, 9(06): 823-826
doi: 10.3866/PKU.WHXB19930619
Abstract:
Time-of-flight mass spectra of both positive and negative ions were recorded on a home-made instrument by laser ablation of YBa_2Cu_3O_(7-x) superconducting material. Among the observed cations, Ba~+ has the highest intensity, and Cu~- for anions. In addition, three seires of oxides clusters cations of very broad mass range were observed, with compositions of BaYO_2(Y_2O_3)_n, Ba_2YO_3(Y_2O_3)_n and BaCuYO_3(Y_2O_3)_n. The experimental results were disscused and attributed to the interactions among consisting elements. As comparision, the samples of the CuO, Y_2O_3 and BaO as well as their mixture have also been studied in the same experimental condition.
Time-of-flight mass spectra of both positive and negative ions were recorded on a home-made instrument by laser ablation of YBa_2Cu_3O_(7-x) superconducting material. Among the observed cations, Ba~+ has the highest intensity, and Cu~- for anions. In addition, three seires of oxides clusters cations of very broad mass range were observed, with compositions of BaYO_2(Y_2O_3)_n, Ba_2YO_3(Y_2O_3)_n and BaCuYO_3(Y_2O_3)_n. The experimental results were disscused and attributed to the interactions among consisting elements. As comparision, the samples of the CuO, Y_2O_3 and BaO as well as their mixture have also been studied in the same experimental condition.
1993, 9(06): 827-831
doi: 10.3866/PKU.WHXB19930620
Abstract:
Acidity and coking activity of(NH_4)_2SiF_6 dealuminated faujasites have been investigated by means of infrared spectroscopy. Results show that with the increasing framework Si/Al ratio of (NH_4)_2SiF_6 dealuminated Faujasties, (1) Pyridine can interact gradually with the OH groups in the small cavites, while partial OH groups in supercages can not interact with pyridine, (3) the amount of bronsted acid sites dcreases, while the amount of its strong part increases. There is no Lewis acid essentially, (4) the coking rate and coke quantity both decrease, which is in consistent with the acidity of faujasites determined by pyridine.
Acidity and coking activity of(NH_4)_2SiF_6 dealuminated faujasites have been investigated by means of infrared spectroscopy. Results show that with the increasing framework Si/Al ratio of (NH_4)_2SiF_6 dealuminated Faujasties, (1) Pyridine can interact gradually with the OH groups in the small cavites, while partial OH groups in supercages can not interact with pyridine, (3) the amount of bronsted acid sites dcreases, while the amount of its strong part increases. There is no Lewis acid essentially, (4) the coking rate and coke quantity both decrease, which is in consistent with the acidity of faujasites determined by pyridine.
1993, 9(06): 832-835
doi: 10.3866/PKU.WHXB19930621
Abstract:
On soaking the ultrathin polyamine capsules in bis-(2-ethyl) phosphate (Abbraviated P204), we prepared the functional capsules with P204 in the porous film. P204 in the pores of the capsule wall existed in the form of bilayer structure. It acted as a prohibitor to the permeation of core material KCl and the permeable efficiency was decreased remarkbly. When we added Ca~(2+) to the external water phase, the hydrophilic headgroup of P204 reacted with Ca~(2+), and the multibilayer order was spoiled. The permeable efficiency was increased. On treating with EDTA Ca~(2+) reacted with EDTA, the permeable efficiency recovered its original value. Moreover, if the capsules were put in an electric field, the permeable efficiency was increased because the multibilayer order was spoiled with the orientation of the hydrophilic headgroup. On removing the electric field, the permeable efficiency recovered its original value. Therefore, the capsules with P204 have reversible functional permeation controlled by chemical reaction and electric field.
On soaking the ultrathin polyamine capsules in bis-(2-ethyl) phosphate (Abbraviated P204), we prepared the functional capsules with P204 in the porous film. P204 in the pores of the capsule wall existed in the form of bilayer structure. It acted as a prohibitor to the permeation of core material KCl and the permeable efficiency was decreased remarkbly. When we added Ca~(2+) to the external water phase, the hydrophilic headgroup of P204 reacted with Ca~(2+), and the multibilayer order was spoiled. The permeable efficiency was increased. On treating with EDTA Ca~(2+) reacted with EDTA, the permeable efficiency recovered its original value. Moreover, if the capsules were put in an electric field, the permeable efficiency was increased because the multibilayer order was spoiled with the orientation of the hydrophilic headgroup. On removing the electric field, the permeable efficiency recovered its original value. Therefore, the capsules with P204 have reversible functional permeation controlled by chemical reaction and electric field.
1993, 9(06): 836-839
doi: 10.3866/PKU.WHXB19930622
Abstract:
According to the transition state theory of reaction rates, we have calculated the thermokinetic properties of bacterial growth: Activation entropy (△S~≠), Activation Gibbs free energy (△G~≠) and equilibrium constant (K~≠).
According to the transition state theory of reaction rates, we have calculated the thermokinetic properties of bacterial growth: Activation entropy (△S~≠), Activation Gibbs free energy (△G~≠) and equilibrium constant (K~≠).
