Login In
2002 Volume 18 Issue 8
2002, 18(08): 673-675
doi: 10.3866/PKU.WHXB20020801
Abstract:
With confocal microscopy and grating spectrograph, the absorption and fluorescence emission spectra of single Anabaena strain PCC 7120 cells have been studied in intact filaments in situ. The different spectra between vegetative cells and heterocysts are observed. The evident heterogeneities in heterocysts that have not been reported previously are attributed to the different stages of the evolution of phycobilisomes and photosystems in heterocysts.
With confocal microscopy and grating spectrograph, the absorption and fluorescence emission spectra of single Anabaena strain PCC 7120 cells have been studied in intact filaments in situ. The different spectra between vegetative cells and heterocysts are observed. The evident heterogeneities in heterocysts that have not been reported previously are attributed to the different stages of the evolution of phycobilisomes and photosystems in heterocysts.
2002, 18(08): 676-679
doi: 10.3866/PKU.WHXB20020802
Abstract:
Hydrophobicity and hydrogen bonds are main factors verning protein-protein interaction. We have developed a new method, which only uses these two characteristics to figure the properties of protein-protein interface. With this method, we can easily pick out key residues at the interface and display this kind of characteristics using graphic software. This method has been applied to some examples and proved to be an useful tool for in-depth studies on protein-protein recognition.
Hydrophobicity and hydrogen bonds are main factors verning protein-protein interaction. We have developed a new method, which only uses these two characteristics to figure the properties of protein-protein interface. With this method, we can easily pick out key residues at the interface and display this kind of characteristics using graphic software. This method has been applied to some examples and proved to be an useful tool for in-depth studies on protein-protein recognition.
2002, 18(08): 680-685
doi: 10.3866/PKU.WHXB20020803
Abstract:
Using grand canonical ensemble Monte Carlo method, adsorption isotherms, phase transition behaviors and structures of methane adsorbed in two pores of MCM-41, with 3.5 and 5.0 nm diameters, at 74.05 K and 300 K have been simulated. It is found that capillary condensation occurs at a lower chemical potential for the smaller MCM-41 at 74.05 K, compared that with the pore of 5.0 nm. For the two pore sizes in this study, hysteresis loops of capillary condensations are so wide that layering transitions are found within them. In the two MCM-41 pores at 74.05 K, a highly ordered structure for methane molecules in 3.5 nm pores is observed, in contrast to less ordered arrangement of the molecules for the 5.0 nm pore. When the temperature is increased to 300 K, only methane molecules near the walls of MCM-41 are arranged in order, while the molecules near the centers of pores are arranged almost randomly.
Using grand canonical ensemble Monte Carlo method, adsorption isotherms, phase transition behaviors and structures of methane adsorbed in two pores of MCM-41, with 3.5 and 5.0 nm diameters, at 74.05 K and 300 K have been simulated. It is found that capillary condensation occurs at a lower chemical potential for the smaller MCM-41 at 74.05 K, compared that with the pore of 5.0 nm. For the two pore sizes in this study, hysteresis loops of capillary condensations are so wide that layering transitions are found within them. In the two MCM-41 pores at 74.05 K, a highly ordered structure for methane molecules in 3.5 nm pores is observed, in contrast to less ordered arrangement of the molecules for the 5.0 nm pore. When the temperature is increased to 300 K, only methane molecules near the walls of MCM-41 are arranged in order, while the molecules near the centers of pores are arranged almost randomly.
2002, 18(08): 686-691
doi: 10.3866/PKU.WHXB20020804
Abstract:
Three kinds of naphthalene containing poly-amino-compounds with different chain length have been synthesized in this work. Their fluorescence spectra were recorded under different pH conditions and showed that the fluorescence intensity of studied compounds depends on the pH value very strongly. It means that this kind of compounds can be used as a probe for the determination of pH value of solution. In the solution of these compounds, different kinds of nucleoside phosphate (ATP, ADP and AMP) were introduced respectively. It was found that the fluorescence of compounds studied in this work such as C10H7CH2(NHCH2CH2)3NH2 (compound 3) can be quenched by different nucleoside phosphate and their quenching ability which was evaluated by the Stern-Volmer constants or quenching constants were also different. The results obtained showed that the ATP has the strongest ability to the fluorescence quenching of compound 3. It demonstrated that the molecular size matching and the sterically arrangement of groups of studied compounds with nucleoside phosphates are very important for the interaction of them. And the quenching ability depends on the interaction of these species strongly. Evidently, this phenomenon can be used as a method for the molecular recognition of nucleoside phosphate by the changing of fluorescence intensity of these compounds.
Three kinds of naphthalene containing poly-amino-compounds with different chain length have been synthesized in this work. Their fluorescence spectra were recorded under different pH conditions and showed that the fluorescence intensity of studied compounds depends on the pH value very strongly. It means that this kind of compounds can be used as a probe for the determination of pH value of solution. In the solution of these compounds, different kinds of nucleoside phosphate (ATP, ADP and AMP) were introduced respectively. It was found that the fluorescence of compounds studied in this work such as C10H7CH2(NHCH2CH2)3NH2 (compound 3) can be quenched by different nucleoside phosphate and their quenching ability which was evaluated by the Stern-Volmer constants or quenching constants were also different. The results obtained showed that the ATP has the strongest ability to the fluorescence quenching of compound 3. It demonstrated that the molecular size matching and the sterically arrangement of groups of studied compounds with nucleoside phosphates are very important for the interaction of them. And the quenching ability depends on the interaction of these species strongly. Evidently, this phenomenon can be used as a method for the molecular recognition of nucleoside phosphate by the changing of fluorescence intensity of these compounds.
2002, 18(08): 692-698
doi: 10.3866/PKU.WHXB20020805
Abstract:
Storage capacities of H2 in a kind of multi-walled carbon nanotubes (MWCNTs) and its corresponding system modified with K＋ salt were measured using volumetric method, and characteristics of adsorption and desorption of hydrogen on MWCNTs were studied by means of temperature-programmed desorption (TPD) method. The results showed that the storage capacities of H2 in the purified MWCNTs could reach 1.51％ (mass fraction) under condition of room temperature and 9.0 MPa, with adsorption of ～99％ of the H2 being reversible. A comparative study indicated that the modification of the K＋ salt to the MWCNTs did not improve its storage capacity of hydrogen, but led to elevating of desorption temperature of adsorbed hydrogen H2(a) to a certain extent; in addition, the K＋ modification resulted also in changing of surface property of the MWCNTs from original hydrophobicity to hydrophilicity. The products desorbed on H2/MWCNTs involved exclusively H2 at T≤ 723 K, and main part of H2 and small amount of CH4,C2H4,and C2H2 at T ≥ 773 K; whereas on H2/K＋-MWCNTs,H2O was also involved in the desorbed products, in addition to H2 and small amount of C1/C2-hydrocarbons.The adsorption of H2 on the MWCNTs-based materials is in the two models: associative (molecular state) and dissociative (atomic state).
Storage capacities of H2 in a kind of multi-walled carbon nanotubes (MWCNTs) and its corresponding system modified with K＋ salt were measured using volumetric method, and characteristics of adsorption and desorption of hydrogen on MWCNTs were studied by means of temperature-programmed desorption (TPD) method. The results showed that the storage capacities of H2 in the purified MWCNTs could reach 1.51％ (mass fraction) under condition of room temperature and 9.0 MPa, with adsorption of ～99％ of the H2 being reversible. A comparative study indicated that the modification of the K＋ salt to the MWCNTs did not improve its storage capacity of hydrogen, but led to elevating of desorption temperature of adsorbed hydrogen H2(a) to a certain extent; in addition, the K＋ modification resulted also in changing of surface property of the MWCNTs from original hydrophobicity to hydrophilicity. The products desorbed on H2/MWCNTs involved exclusively H2 at T≤ 723 K, and main part of H2 and small amount of CH4,C2H4,and C2H2 at T ≥ 773 K; whereas on H2/K＋-MWCNTs,H2O was also involved in the desorbed products, in addition to H2 and small amount of C1/C2-hydrocarbons.The adsorption of H2 on the MWCNTs-based materials is in the two models: associative (molecular state) and dissociative (atomic state).
2002, 18(08): 699-704
doi: 10.3866/PKU.WHXB20020806
Abstract:
To extend the recently proposed density functional theory(DFT)methodology to non-uniform non-hard sphere fluid, a new bridge functional as a function of indirect correlation function was proposed, which was based on analysis on the asymptotic behavior of the Ornstein-Zernike equation system and the Taylor expansion series whose re-normalization resulted in an adjustable parameter determined by combining the new bridge functional with the DFT methodology to make the contact density from a single hard wall satisfy the sum rule. The combination of the new bridge functional and the DFT methodology predicted well the density distribution profile of hard sphere fluid near a hard wall or confined in a spherical cavity, Lennard-Jones fluid and adhesive hard sphere fluid confined between two hard walls when compared with the available computer simulation data.
To extend the recently proposed density functional theory(DFT)methodology to non-uniform non-hard sphere fluid, a new bridge functional as a function of indirect correlation function was proposed, which was based on analysis on the asymptotic behavior of the Ornstein-Zernike equation system and the Taylor expansion series whose re-normalization resulted in an adjustable parameter determined by combining the new bridge functional with the DFT methodology to make the contact density from a single hard wall satisfy the sum rule. The combination of the new bridge functional and the DFT methodology predicted well the density distribution profile of hard sphere fluid near a hard wall or confined in a spherical cavity, Lennard-Jones fluid and adhesive hard sphere fluid confined between two hard walls when compared with the available computer simulation data.
2002, 18(08): 705-709
doi: 10.3866/PKU.WHXB20020807
Abstract:
A novel electrochemical method (RPG method) has been theoretically and experimentally developed to determine the diffusion coefficient of intercalary species within insertion-host materials on the basis of the spherical diffusion model. Theoretical results show that the diffusion coefficient D is dependent to the ratio (q) of the potentio-charge capacity to the galvano-charge capacity (abridged as RPG), the radius of insertion-host particle R, and the galvano-charge time tG. The RPG equation obtained is as D=R2/(15.36qtG)(q ≤ 0.5).Using this method, the values of the Li＋ diffusion coefficient determined at different galvano-charge currents with 1.5 V cutoff voltage are all around the value of 1.060×10－10 cm2•s－1.This result indicates that the RPG method has a od reliability for determination of the diffusion coefficient. The Li＋ diffusion coefficient in graphite has been reduced from 4.292×10－10 to 1.219×10－11 cm2•s－1 among the voltage range of 1.0～2.5 V (vs Li/Li＋),respectively.
A novel electrochemical method (RPG method) has been theoretically and experimentally developed to determine the diffusion coefficient of intercalary species within insertion-host materials on the basis of the spherical diffusion model. Theoretical results show that the diffusion coefficient D is dependent to the ratio (q) of the potentio-charge capacity to the galvano-charge capacity (abridged as RPG), the radius of insertion-host particle R, and the galvano-charge time tG. The RPG equation obtained is as D=R2/(15.36qtG)(q ≤ 0.5).Using this method, the values of the Li＋ diffusion coefficient determined at different galvano-charge currents with 1.5 V cutoff voltage are all around the value of 1.060×10－10 cm2•s－1.This result indicates that the RPG method has a od reliability for determination of the diffusion coefficient. The Li＋ diffusion coefficient in graphite has been reduced from 4.292×10－10 to 1.219×10－11 cm2•s－1 among the voltage range of 1.0～2.5 V (vs Li/Li＋),respectively.
2002, 18(08): 710-715
doi: 10.3866/PKU.WHXB20020808
Abstract:
The coal-petroleum coke-water slurries(CPCWS) are complex fluids. It has been known that the 1H-NMR can provide the quantitative information on the hydrophobic property of carbonaceous solid and on the microstructure and dynamics behavior about water in the slurry. In this paper, 1H-NMR has been used to study the microstructure of water and their dynamics. Two relationships have been attained, that the chemical shifts of all water and the bound water in slurries, respectively, increase linearly with the increase of the weight percent of coal in the total of coal and petroleum coke (PC). The fraction of bound water can be obtained by a formula drawn from these two relationships. The spin-lattice relaxation time T1 of the PC-water slurry is 42 times longer than that of the coal-water slurry. The tendency of change of T1 with the increase of the coal content has been discussed.
The coal-petroleum coke-water slurries(CPCWS) are complex fluids. It has been known that the 1H-NMR can provide the quantitative information on the hydrophobic property of carbonaceous solid and on the microstructure and dynamics behavior about water in the slurry. In this paper, 1H-NMR has been used to study the microstructure of water and their dynamics. Two relationships have been attained, that the chemical shifts of all water and the bound water in slurries, respectively, increase linearly with the increase of the weight percent of coal in the total of coal and petroleum coke (PC). The fraction of bound water can be obtained by a formula drawn from these two relationships. The spin-lattice relaxation time T1 of the PC-water slurry is 42 times longer than that of the coal-water slurry. The tendency of change of T1 with the increase of the coal content has been discussed.
2002, 18(08): 716-720
doi: 10.3866/PKU.WHXB20020809
Abstract:
The method proposed by us to carry out high accurate density functional calculations in a local region of a large system was applied to the calculation of a series of different type of molecules and the data such as Mulliken charges, bond lengths, bond dissociation energies, the first ionization potentials and electro negativities were obtained. The high accurate calculations for the same set of molecules and the correspondent model molecules with a hydrogen atom replacing the part of a molecule surrounding the local region were also carried out with the conventional method for comparison. It is found that the results obtained by the local high accurate calculation are in od agreement with those obtained by the conventional high accurate calculation while the calculated results for the model molecules show larger deviation. The results presented in this paper show further that the local high accurate calculation method proposed by us is practical and valuable.
The method proposed by us to carry out high accurate density functional calculations in a local region of a large system was applied to the calculation of a series of different type of molecules and the data such as Mulliken charges, bond lengths, bond dissociation energies, the first ionization potentials and electro negativities were obtained. The high accurate calculations for the same set of molecules and the correspondent model molecules with a hydrogen atom replacing the part of a molecule surrounding the local region were also carried out with the conventional method for comparison. It is found that the results obtained by the local high accurate calculation are in od agreement with those obtained by the conventional high accurate calculation while the calculated results for the model molecules show larger deviation. The results presented in this paper show further that the local high accurate calculation method proposed by us is practical and valuable.
2002, 18(08): 721-726
doi: 10.3866/PKU.WHXB20020810
Abstract:
The geometries of the reactants, transition state, and products of hydrogen transfer reaction CH3＋CH3NO2→CH4＋CH2NO2 have been optimized at the UMP2(full)/6-311G(d, p) level. The forward and reverse reaction potential barriers are 58.21 kJ•mol－1 and 67.17 kJ•mol－1 respectively. Along the IRC, the reaction is a coordinative process and there is a reactivity normal-mode, which lead reaction from reactants to product. The variation of forward reaction rate constant versus temperature, obtained by using the variation transition-state theory (CVT) and ICVT, have identical tendency with experimental values.
The geometries of the reactants, transition state, and products of hydrogen transfer reaction CH3＋CH3NO2→CH4＋CH2NO2 have been optimized at the UMP2(full)/6-311G(d, p) level. The forward and reverse reaction potential barriers are 58.21 kJ•mol－1 and 67.17 kJ•mol－1 respectively. Along the IRC, the reaction is a coordinative process and there is a reactivity normal-mode, which lead reaction from reactants to product. The variation of forward reaction rate constant versus temperature, obtained by using the variation transition-state theory (CVT) and ICVT, have identical tendency with experimental values.
2002, 18(08): 727-731
doi: 10.3866/PKU.WHXB20020811
Abstract:
It was reported that after the rapid formation of a gel by mixing of MMA and samarium triisopropoxide, the PMMA materials containing samarium were prepared by the in situ polymerization, the so called the non-water gel in situ polymerization. The effect of samarium triisopropoxide on the structure and properties of PMMA was studied. The results showed that by the increasing of samarium mass fraction the linear structure of PMMA containing samarium changed into crosslink network and resulted in improvement of the properties, such as resistance to heat and solvent, storage modulus. ESEM revealed the crosslink network structure of the PMMA material and no conglomerate; the samarium element was uniformly distributed. Moreover, the PMMA materials exhibited the characteristic fluorescence of samarium ion. In the concentration range studied, the fluorescent strength increased with the increasing of samarium mass fraction.
It was reported that after the rapid formation of a gel by mixing of MMA and samarium triisopropoxide, the PMMA materials containing samarium were prepared by the in situ polymerization, the so called the non-water gel in situ polymerization. The effect of samarium triisopropoxide on the structure and properties of PMMA was studied. The results showed that by the increasing of samarium mass fraction the linear structure of PMMA containing samarium changed into crosslink network and resulted in improvement of the properties, such as resistance to heat and solvent, storage modulus. ESEM revealed the crosslink network structure of the PMMA material and no conglomerate; the samarium element was uniformly distributed. Moreover, the PMMA materials exhibited the characteristic fluorescence of samarium ion. In the concentration range studied, the fluorescent strength increased with the increasing of samarium mass fraction.
2002, 18(08): 732-736
doi: 10.3866/PKU.WHXB20020812
Abstract:
The cyclic voltemmetry method was used to investigate the electrochemical behaviors of Y（Ⅲ）,Mg（Ⅱ）and Co（Ⅱ） in Y(NO3)3-LiClO4-DMF,Mg(ClO4)2-LiClO4-DMF and CoCl2-LiClO4-DMF systems on Pt cathode. Experimental results indicate that the electro-reduction of Y（Ⅲ）,Mg（Ⅱ）and Co（Ⅱ） to Y、Mg and Co is an one-step irreversible in process. The diffusion coefficient and transfer coefficient of Y（Ⅲ）in Y(NO3)3-LiClO4-DMF system at 301 K are 1.68×10－5 cm2•s－1,0.10; Mg(Ⅱ)in Mg(ClO4)2-LiClO4-DMF system at 301 K are 2.95×10－6 cm2•s－1,0.11; Co(Ⅱ) in CoCl2-LiClO4-DMF system at 301 K are 1.34×10－5 cm2•s－1 and 0.24 respectively. Y-Mg-Co alloy films containing Y from 3.88％ to 58.66％ and Mg from 4.51％ to 17.52％ were prepared by potentiostatic electrodeposition on Cu substrate with deposition potential ranging from －1.50 V to －3.00 V(vs SCE).Their surface morphologies were smooth, adhesive, uniform and have metallic luster.
The cyclic voltemmetry method was used to investigate the electrochemical behaviors of Y（Ⅲ）,Mg（Ⅱ）and Co（Ⅱ） in Y(NO3)3-LiClO4-DMF,Mg(ClO4)2-LiClO4-DMF and CoCl2-LiClO4-DMF systems on Pt cathode. Experimental results indicate that the electro-reduction of Y（Ⅲ）,Mg（Ⅱ）and Co（Ⅱ） to Y、Mg and Co is an one-step irreversible in process. The diffusion coefficient and transfer coefficient of Y（Ⅲ）in Y(NO3)3-LiClO4-DMF system at 301 K are 1.68×10－5 cm2•s－1,0.10; Mg(Ⅱ)in Mg(ClO4)2-LiClO4-DMF system at 301 K are 2.95×10－6 cm2•s－1,0.11; Co(Ⅱ) in CoCl2-LiClO4-DMF system at 301 K are 1.34×10－5 cm2•s－1 and 0.24 respectively. Y-Mg-Co alloy films containing Y from 3.88％ to 58.66％ and Mg from 4.51％ to 17.52％ were prepared by potentiostatic electrodeposition on Cu substrate with deposition potential ranging from －1.50 V to －3.00 V(vs SCE).Their surface morphologies were smooth, adhesive, uniform and have metallic luster.
2002, 18(08): 737-740
doi: 10.3866/PKU.WHXB20020813
Abstract:
The equilibrium geometry and potential energy curve for the ground state of molecule LaH have been calculated on several single-reference state methods of HF,B3LYP,MPn,QCISD(T) with energy-consistent relativistic effective core potential approximation. It is found that the potential energy curves of the metal-hydrogen system, which is far from equilibrium, cannot meet the dissociation limit using almost all the above methods. A calculation method to get the global analytical potential energy function is proposed. Murrell-Sorbie analytical potential function has been derived by a nonlinear least square fitting of the data calculated at B3LYP level around the equilibrium position. The calculated spectroscopic constants from the analytical potential energy function are in od agreement with the experimental results of vibrotational spectra.
The equilibrium geometry and potential energy curve for the ground state of molecule LaH have been calculated on several single-reference state methods of HF,B3LYP,MPn,QCISD(T) with energy-consistent relativistic effective core potential approximation. It is found that the potential energy curves of the metal-hydrogen system, which is far from equilibrium, cannot meet the dissociation limit using almost all the above methods. A calculation method to get the global analytical potential energy function is proposed. Murrell-Sorbie analytical potential function has been derived by a nonlinear least square fitting of the data calculated at B3LYP level around the equilibrium position. The calculated spectroscopic constants from the analytical potential energy function are in od agreement with the experimental results of vibrotational spectra.
2002, 18(08): 741-745
doi: 10.3866/PKU.WHXB20020814
Abstract:
Calmodulin(CaM) as a major intracellular Ca2＋ receptor, was self-assembled on Au electrode and investigated by electrochemical impedance spectroscopy(EIS). The results demonstrated that the self-assembly process of CaM could be divided into rapid and slow steps clearly. The influence of pH value on the new modified electrode was found to be regular, and the most packed structure appeared at the calmodulin’s isoelectric-point, the combining process of calmodulin with Ca2＋ was found to be composed of three stages. In conclusion, our AC impedance study of CaM is meaningful to reveal the mechanism of CaM in the real life system.
Calmodulin(CaM) as a major intracellular Ca2＋ receptor, was self-assembled on Au electrode and investigated by electrochemical impedance spectroscopy(EIS). The results demonstrated that the self-assembly process of CaM could be divided into rapid and slow steps clearly. The influence of pH value on the new modified electrode was found to be regular, and the most packed structure appeared at the calmodulin’s isoelectric-point, the combining process of calmodulin with Ca2＋ was found to be composed of three stages. In conclusion, our AC impedance study of CaM is meaningful to reveal the mechanism of CaM in the real life system.
2002, 18(08): 746-749
doi: 10.3866/PKU.WHXB20020815
Abstract:
The new mixed metal cluster (μ3-S)FeCo2(CO)7(dppfe) (2) (dppfe= Ph2PC5H4FeC5H4PPh2) has been synthesized by facile substitution reaction, in which dppfe replaces two equatorial carbonyls from two Co(CO)3 groups, respectively. IR, 1H NMR, MS and X-ray crystallography characterized the new cluster 2. The cluster 2 crystallizes in triclinic space group Pī,with a=1.132 4(15) nm, b=1.367 0(17) nm, c=1.576 9(2) nm,α=114.646(2)°,β=100.340(2)°,γ=100.113(3)°,V=2.095 3(5) nm3.
The new mixed metal cluster (μ3-S)FeCo2(CO)7(dppfe) (2) (dppfe= Ph2PC5H4FeC5H4PPh2) has been synthesized by facile substitution reaction, in which dppfe replaces two equatorial carbonyls from two Co(CO)3 groups, respectively. IR, 1H NMR, MS and X-ray crystallography characterized the new cluster 2. The cluster 2 crystallizes in triclinic space group Pī,with a=1.132 4(15) nm, b=1.367 0(17) nm, c=1.576 9(2) nm,α=114.646(2)°,β=100.340(2)°,γ=100.113(3)°,V=2.095 3(5) nm3.
2002, 18(08): 750-753
doi: 10.3866/PKU.WHXB20020816
Abstract:
Supercapacitors are playing great roles in research-and-development field of power engineering as a new energy store device. The porous carbon material developed in our laboratory exhibits perfect physical structure and properties. Its od electrochemical performances were confirmed by the experiment of CV and alternating current impedance analysis etc. The specific capacitance of active carbon was 172 F•g－1 at the 20 mA•cm－2 current density discharge. The RuO2/active carbon composite electrode was prepared and the specific capacitance amounts to 359 F•g－1,electrochemical performance of supercapacitor composed of RuO2/active carbon composite electrode and the “pseudo-capacitance” characteristic of ruthenium oxide was discussed in detail in this paper
Supercapacitors are playing great roles in research-and-development field of power engineering as a new energy store device. The porous carbon material developed in our laboratory exhibits perfect physical structure and properties. Its od electrochemical performances were confirmed by the experiment of CV and alternating current impedance analysis etc. The specific capacitance of active carbon was 172 F•g－1 at the 20 mA•cm－2 current density discharge. The RuO2/active carbon composite electrode was prepared and the specific capacitance amounts to 359 F•g－1,electrochemical performance of supercapacitor composed of RuO2/active carbon composite electrode and the “pseudo-capacitance” characteristic of ruthenium oxide was discussed in detail in this paper
2002, 18(08): 754-758
doi: 10.3866/PKU.WHXB20020817
Abstract:
ZnO nanoparticles were prepared by calcining the precursor, zinc carbonate hydroxide,and Pd/ZnO and Ag/ZnO composite nanoparticles with the noble metal content of 0.5％(mass fraction) were obtained by photoreduction method. The as-prepared samples were also characterized by the XRD，TEM，XPS and SPS techniques, respectively. The results showed that the deposited noble metal of both Pd and Ag existed as the form of atomic clusters,and the possible reasons of forming the atomic clusters of noble metal on the surface of ZnO nanoparticles were primarily discussed. The intensity of SPS responses of ZnO nanoparticle remarkably decreased by depositing the appropriate noble metal on its surface. Moreover, Pd/ZnO and Ag/ZnO composite nanoparticles exhibited higher photocatalytic activity than ZnO nanoparticles in the experiment of photocatalytic oxidation of gas phase n-heptane. The essential reasons why the photocatalytic activity of ZnO nanoparticles improved by depositing noble metal Pd or Ag on its surface were also further discussed. In addition, the point was put forward that the photocatalytic activity of nanoparticle could be primarily evaluated by its SPS response, i.e., the weaker the SPS responseis, the higher the photoactivity.
ZnO nanoparticles were prepared by calcining the precursor, zinc carbonate hydroxide,and Pd/ZnO and Ag/ZnO composite nanoparticles with the noble metal content of 0.5％(mass fraction) were obtained by photoreduction method. The as-prepared samples were also characterized by the XRD，TEM，XPS and SPS techniques, respectively. The results showed that the deposited noble metal of both Pd and Ag existed as the form of atomic clusters,and the possible reasons of forming the atomic clusters of noble metal on the surface of ZnO nanoparticles were primarily discussed. The intensity of SPS responses of ZnO nanoparticle remarkably decreased by depositing the appropriate noble metal on its surface. Moreover, Pd/ZnO and Ag/ZnO composite nanoparticles exhibited higher photocatalytic activity than ZnO nanoparticles in the experiment of photocatalytic oxidation of gas phase n-heptane. The essential reasons why the photocatalytic activity of ZnO nanoparticles improved by depositing noble metal Pd or Ag on its surface were also further discussed. In addition, the point was put forward that the photocatalytic activity of nanoparticle could be primarily evaluated by its SPS response, i.e., the weaker the SPS responseis, the higher the photoactivity.
Product Distribution of Conversions of Methane and Carbon Dioxide Using Dielectric Barrier Discharge
2002, 18(08): 759-763
doi: 10.3866/PKU.WHXB20020818
Abstract:
Direct conversion of methane to more useful chemicals and fuels remains a challenge for the 21st century because of the high stability of methane molecule. In this work, direct conversion of methane and carbon dioxide using dielectric barrier discharge plasma was investigated. The discharge gaps applied are 1.8 mm and 1.1 mm, respectively. The product includes gaseous hydrocarbons (C2 to C5), syngas, liquid hydrocarbons (C5 to C11) and oxygenates. The liquid hydrocarbons are highly branched which presents a high octane number as liquid fuel; and oxygenates mainly consist of alcohols and acids. With the increasing of carbon atoms in the molecule, selectivity of hydrocarbons and oxygenates decreases accordingly. A detailed analysis of product distribution has been conducted under variable feed conditions with different discharge gaps. Higher CH4 concentration in the feed is more favored for production of hydrocarbons, while the highest selectivity of alcohols and acids is obtained at the methane feed concentration of 75.1％ (volume fraction) and 67.4％ (volume fraction),respectively. To achieve a large conversion of CH4 and CO2 and a high yield of hydrocarbons and acids, the narrower discharge gap (1.1 mm) is preferred, while a wider discharge gap (1.8 mm) induces a more selectivity production of alcohols.
Direct conversion of methane to more useful chemicals and fuels remains a challenge for the 21st century because of the high stability of methane molecule. In this work, direct conversion of methane and carbon dioxide using dielectric barrier discharge plasma was investigated. The discharge gaps applied are 1.8 mm and 1.1 mm, respectively. The product includes gaseous hydrocarbons (C2 to C5), syngas, liquid hydrocarbons (C5 to C11) and oxygenates. The liquid hydrocarbons are highly branched which presents a high octane number as liquid fuel; and oxygenates mainly consist of alcohols and acids. With the increasing of carbon atoms in the molecule, selectivity of hydrocarbons and oxygenates decreases accordingly. A detailed analysis of product distribution has been conducted under variable feed conditions with different discharge gaps. Higher CH4 concentration in the feed is more favored for production of hydrocarbons, while the highest selectivity of alcohols and acids is obtained at the methane feed concentration of 75.1％ (volume fraction) and 67.4％ (volume fraction),respectively. To achieve a large conversion of CH4 and CO2 and a high yield of hydrocarbons and acids, the narrower discharge gap (1.1 mm) is preferred, while a wider discharge gap (1.8 mm) induces a more selectivity production of alcohols.
2002, 18(08): 764-768
doi: 10.3866/PKU.WHXB20020819
Abstract:
The cyclic voltammetry and potentiostatic electrolysis were used to investigate the preparation of Er-Ni-Co alloy films in LiClO4-DMSO system. Experimental results indicate that Er-Ni-Co alloy films containing Er from 9.21％ to 18.90％ were prepared from 0.1 mol•L－1 ErCl3-0.1 mol•L－1 NiCl2- 0.1 mol•L－1 CoCl2-0.1 mol•L－1LiClO4-DMSO system by potentiostatic electrolysis on Cu substrates at deposition potential from －2.20～－2.50 V (vs SCE). Their surfaces are black, uniform, adhesive, and have metallic luster.
The cyclic voltammetry and potentiostatic electrolysis were used to investigate the preparation of Er-Ni-Co alloy films in LiClO4-DMSO system. Experimental results indicate that Er-Ni-Co alloy films containing Er from 9.21％ to 18.90％ were prepared from 0.1 mol•L－1 ErCl3-0.1 mol•L－1 NiCl2- 0.1 mol•L－1 CoCl2-0.1 mol•L－1LiClO4-DMSO system by potentiostatic electrolysis on Cu substrates at deposition potential from －2.20～－2.50 V (vs SCE). Their surfaces are black, uniform, adhesive, and have metallic luster.
