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2002 Volume 18 Issue 10
2002, 18(10): 865-870
doi: 10.3866/PKU.WHXB20021001
Abstract:
A new rare earth complex La(C15H12N5O2)( C15H11N5O2)•2.5H2O has been synthesized. Attempts have been made to ascertain its probable structure on the basis of elemental analyzes, molar conductivities, IR, 1H NMR and TG-DTG. It is suggested that the complex has a eight-coordinated configuration. The enthalpies of solution in DMF for the complex were measured by means of a micro calorimeter. The data of standard molar enthalpy of solution (ΔsolHmΘ=－135.62 kJ•mol－1) and the empirical formulae of enthalpy of solution (ΔsolH=－135.62－11633b＋3761.5b1/2) for the complex at different concentration b (mol•kg－1) were obtained. And relative apparent molar enthalpy (Li),relative partial molar enthalpy (Li)) and enthalpy of dilution (ΔdilH1,2) were drawn up respectively by the data of enthalpies of solution of the complex: Li=－11633b＋2761.5b1/2, Li=－23266b＋5642.2b1/2 and ΔdilH1,2=－11633(b21/2－b11/2)＋3761.5(b2－b1).The second-stage decomposition reaction for the complex was studied and the apparent activation energy was obtained by the Kissinger's formulae.
A new rare earth complex La(C15H12N5O2)( C15H11N5O2)•2.5H2O has been synthesized. Attempts have been made to ascertain its probable structure on the basis of elemental analyzes, molar conductivities, IR, 1H NMR and TG-DTG. It is suggested that the complex has a eight-coordinated configuration. The enthalpies of solution in DMF for the complex were measured by means of a micro calorimeter. The data of standard molar enthalpy of solution (ΔsolHmΘ=－135.62 kJ•mol－1) and the empirical formulae of enthalpy of solution (ΔsolH=－135.62－11633b＋3761.5b1/2) for the complex at different concentration b (mol•kg－1) were obtained. And relative apparent molar enthalpy (Li),relative partial molar enthalpy (Li)) and enthalpy of dilution (ΔdilH1,2) were drawn up respectively by the data of enthalpies of solution of the complex: Li=－11633b＋2761.5b1/2, Li=－23266b＋5642.2b1/2 and ΔdilH1,2=－11633(b21/2－b11/2)＋3761.5(b2－b1).The second-stage decomposition reaction for the complex was studied and the apparent activation energy was obtained by the Kissinger's formulae.
2002, 18(10): 871-877
doi: 10.3866/PKU.WHXB20021002
Abstract:
The chiral purity of biochemical monomers——only L-amino acids are present in proteins and D-sugars in the DNA and RNA of living organisms——is today accepted as an absolute necessity for the existence of life. All previous studies on amino acids reported the naturally occurring L-form to be stabilized by weak neutral currents. Two recent papers dealing with electro weak quantum calculations of the parity-violating energy shifts of alanine in gaseous phase and in solution have defied this long held belief. The parity-violating energy difference (PVED) of D- and L-alanine was undertaken as a function of the dihedral angle θ of the carboxylate plane with respect to the Cα-Hα plane. Dihedral angles was calculated from the atomic coordinates of O(1)O(2)C(1)C(2)H(4) of D- and L-alanine under the temperature dependence of X-ray diffraction data. According to Quack’s theoretical results by means of highest level ab initio studies (MC-LR), the ΔEPV value is 1.2×10－19 Hartree (3.3×10－18 eV/ molecule), namely L-alanine is more stable than D-alanine. The present paper proved definitely that in the single crystal state L-alanine is lower in energy than D-alanine both by X-ray diffraction data and the differential scanning calorimetry.
The chiral purity of biochemical monomers——only L-amino acids are present in proteins and D-sugars in the DNA and RNA of living organisms——is today accepted as an absolute necessity for the existence of life. All previous studies on amino acids reported the naturally occurring L-form to be stabilized by weak neutral currents. Two recent papers dealing with electro weak quantum calculations of the parity-violating energy shifts of alanine in gaseous phase and in solution have defied this long held belief. The parity-violating energy difference (PVED) of D- and L-alanine was undertaken as a function of the dihedral angle θ of the carboxylate plane with respect to the Cα-Hα plane. Dihedral angles was calculated from the atomic coordinates of O(1)O(2)C(1)C(2)H(4) of D- and L-alanine under the temperature dependence of X-ray diffraction data. According to Quack’s theoretical results by means of highest level ab initio studies (MC-LR), the ΔEPV value is 1.2×10－19 Hartree (3.3×10－18 eV/ molecule), namely L-alanine is more stable than D-alanine. The present paper proved definitely that in the single crystal state L-alanine is lower in energy than D-alanine both by X-ray diffraction data and the differential scanning calorimetry.
2002, 18(10): 878-883
doi: 10.3866/PKU.WHXB20021003
Abstract:
A series of AMP catalysts with different composition were prepared. These catalysts have been characterized by XRD, H2-TPR, XPS, EPR, NH3-DRIFT, and decomposition of isopropanol reaction. The catalytic performance of oxidative dehydrogenation of propane on these catalysts was also examined. These results indicate that “coherent interface” exists between MoO3 and AgMoO2PO4 in AMP catalysts, leading to synergetic catalytic effect. The strength of synergetic effect is due to interaction and mutual covering of the two phases. The synergetic effect modified the concentration of Mo5＋, the reducibility and the acidity of AMP catalysts, leading to the influence on catalytic performance of oxidative dehydrogenation of propane to propene. The higher selectivity and yield of propene can be obtained on AMP catalysts with available quantity of MoO3.
A series of AMP catalysts with different composition were prepared. These catalysts have been characterized by XRD, H2-TPR, XPS, EPR, NH3-DRIFT, and decomposition of isopropanol reaction. The catalytic performance of oxidative dehydrogenation of propane on these catalysts was also examined. These results indicate that “coherent interface” exists between MoO3 and AgMoO2PO4 in AMP catalysts, leading to synergetic catalytic effect. The strength of synergetic effect is due to interaction and mutual covering of the two phases. The synergetic effect modified the concentration of Mo5＋, the reducibility and the acidity of AMP catalysts, leading to the influence on catalytic performance of oxidative dehydrogenation of propane to propene. The higher selectivity and yield of propene can be obtained on AMP catalysts with available quantity of MoO3.
2002, 18(10): 884-889
doi: 10.3866/PKU.WHXB20021004
Abstract:
The coating process of nano-scale hydrous silica film on TiO2 pigmentary particles by chemical deposition in aqueous solution has been investigated. Through the analysis of TEM images and dissolving the samples with hot sulfuric acid, it is proved that a uniform dense film of hydrous silica on TiO2 pigmentary particles is produced. Samples were taken in the coating process and analyzed by X-ray photoelectron spectroscopy (XPS),X-ray fluorescence (XRF),zeta-potential analyzer and transmission electron microscope (TEM). The silica composition and structure of the film on the coated particles in the coating process were measured and analyzed. It is inferred that polymeric silicate ions first hydrolyze into Si(OH)4,the later then reacts with OH－ groups on the surface of TiO2 particles. The silica acids subsequently produced condense on the surface of the core particles, forming a nano-scale film of polymerized silica. According to the chemical shift of binding energy of Ti 2p,Si 2p and O 1s on the coated particles, the Ti－O－Si bond formation is inferred at the interface of the film and the surface of TiO2 particles. The thickness of the film increases with coating time and aging time. Zeta potential measurement shows that a very thin film coating of 0.5％ mass fraction can change the electrokinetic’s behavior of the particle surface remarkably.
The coating process of nano-scale hydrous silica film on TiO2 pigmentary particles by chemical deposition in aqueous solution has been investigated. Through the analysis of TEM images and dissolving the samples with hot sulfuric acid, it is proved that a uniform dense film of hydrous silica on TiO2 pigmentary particles is produced. Samples were taken in the coating process and analyzed by X-ray photoelectron spectroscopy (XPS),X-ray fluorescence (XRF),zeta-potential analyzer and transmission electron microscope (TEM). The silica composition and structure of the film on the coated particles in the coating process were measured and analyzed. It is inferred that polymeric silicate ions first hydrolyze into Si(OH)4,the later then reacts with OH－ groups on the surface of TiO2 particles. The silica acids subsequently produced condense on the surface of the core particles, forming a nano-scale film of polymerized silica. According to the chemical shift of binding energy of Ti 2p,Si 2p and O 1s on the coated particles, the Ti－O－Si bond formation is inferred at the interface of the film and the surface of TiO2 particles. The thickness of the film increases with coating time and aging time. Zeta potential measurement shows that a very thin film coating of 0.5％ mass fraction can change the electrokinetic’s behavior of the particle surface remarkably.
2002, 18(10): 890-895
doi: 10.3866/PKU.WHXB20021005
Abstract:
The semi empirical molecular orbital computations of the enontioselective alkynylation of benzaldehyde catalyzed by oxazaborolidine catalysts are performed. As illustrated, this enantioselective alkynylation reduction is exothermic and the controlling step is the transfer of alkynyl from the alkynylborane moiety to the carbonyl carbon of benzaldehyde. The transition state for the alkynyl transfer is a twisted chair structure. The alkynyl reduction leads to R-chiral alcohols.
The semi empirical molecular orbital computations of the enontioselective alkynylation of benzaldehyde catalyzed by oxazaborolidine catalysts are performed. As illustrated, this enantioselective alkynylation reduction is exothermic and the controlling step is the transfer of alkynyl from the alkynylborane moiety to the carbonyl carbon of benzaldehyde. The transition state for the alkynyl transfer is a twisted chair structure. The alkynyl reduction leads to R-chiral alcohols.
2002, 18(10): 896-900
doi: 10.3866/PKU.WHXB20021006
Abstract:
A TiO2 reverse micelle solution was prepared by mixing water-Triton X-100-cyclohexane reverse micelle with a mixture of titanium isobutoxide and isopentanol, and then three TiO2 films supported on glass have been made by dip-coating in the reverse micelle solution under different performance. Film A was dipped once immediately in the as-prepared reverse micelle solution, film B was dipped ten times in the as-prepared reverse solution, film C was dipped in the reverse micelle solution which had been aged six hours. The morphology of the films was studied by XRD, SEM, and AFM. The results showed that on the film A TiO2 nanometer particles distributed homogenously, but on film B and C the nano-particles were aggregated in different fashions, and formed second particles like island, the surface roughness of the film surface increased obviously, especially film C was the most rough one. According to the fractal geometry analysis, all films surface structural morphology has properties of fractal structural morphology with estimated dimension 2.22, 2.20, and 2.34, respectively.
A TiO2 reverse micelle solution was prepared by mixing water-Triton X-100-cyclohexane reverse micelle with a mixture of titanium isobutoxide and isopentanol, and then three TiO2 films supported on glass have been made by dip-coating in the reverse micelle solution under different performance. Film A was dipped once immediately in the as-prepared reverse micelle solution, film B was dipped ten times in the as-prepared reverse solution, film C was dipped in the reverse micelle solution which had been aged six hours. The morphology of the films was studied by XRD, SEM, and AFM. The results showed that on the film A TiO2 nanometer particles distributed homogenously, but on film B and C the nano-particles were aggregated in different fashions, and formed second particles like island, the surface roughness of the film surface increased obviously, especially film C was the most rough one. According to the fractal geometry analysis, all films surface structural morphology has properties of fractal structural morphology with estimated dimension 2.22, 2.20, and 2.34, respectively.
2002, 18(10): 901-906
doi: 10.3866/PKU.WHXB20021007
Abstract:
The catalytic reduction of SO2 by CO has been systematically investigated over the sulfided CoMo catalysts (4.0％CoO, 15.0％MoO3) supported on Al2O3, Al2O3-TiO2 and TiO2.The results show that CO and SO2 could be converted completely to CO2 and elemental sulfur at 350 ℃, 350～400 ℃ and 400 ℃ respectively on those catalysts mentioned above. Interestingly, two kind of mechanism, namely COS as intermediate and modified Redox mechanism, were found to perform simultaneously over the catalysts supported on TiO2 or Al2O3-TiO2 above 200 ℃,which greatly suppressed the COS production and resulted in a higher sulfur selectivity than that on the Al2O3-supported catalyst. The reaction mechanism was also discussed.
The catalytic reduction of SO2 by CO has been systematically investigated over the sulfided CoMo catalysts (4.0％CoO, 15.0％MoO3) supported on Al2O3, Al2O3-TiO2 and TiO2.The results show that CO and SO2 could be converted completely to CO2 and elemental sulfur at 350 ℃, 350～400 ℃ and 400 ℃ respectively on those catalysts mentioned above. Interestingly, two kind of mechanism, namely COS as intermediate and modified Redox mechanism, were found to perform simultaneously over the catalysts supported on TiO2 or Al2O3-TiO2 above 200 ℃,which greatly suppressed the COS production and resulted in a higher sulfur selectivity than that on the Al2O3-supported catalyst. The reaction mechanism was also discussed.
2002, 18(10): 907-910
doi: 10.3866/PKU.WHXB20021008
Abstract:
A 12-residue peptide (R1G2T3F4W5V6d-P7S8V9N10Y11F12, β2) with cross-strand amino acid pairs V6V9, F4Y11 and Y3F12, predicted to form β-hairpin, was designed and synthesized by Fmoc/But strategy. The circular dichroism spectrum ofβ2 in PBS buffer shows a maximum at about 202 nm and a minimum at about 217.5 nm, a typical β-hairpin characteristics that have been postulated as the common contribution from a β-turn mixed with a β-sheet. The FT-IR experiments confirmed the secondary structural contents of β2.
A 12-residue peptide (R1G2T3F4W5V6d-P7S8V9N10Y11F12, β2) with cross-strand amino acid pairs V6V9, F4Y11 and Y3F12, predicted to form β-hairpin, was designed and synthesized by Fmoc/But strategy. The circular dichroism spectrum ofβ2 in PBS buffer shows a maximum at about 202 nm and a minimum at about 217.5 nm, a typical β-hairpin characteristics that have been postulated as the common contribution from a β-turn mixed with a β-sheet. The FT-IR experiments confirmed the secondary structural contents of β2.
2002, 18(10): 911-915
doi: 10.3866/PKU.WHXB20021009
Abstract:
A convenient synthesis of mesoporous molecular sieve MCM-48 by hydrothermal method using nonionic surfactant p-Octyl polyethylene glycol phenyl ether and cationic surfactant cetyltrimethyl-ammoniun bromide as co-template is reported. In this approach, nonionic surfactant p-Octyl polyethylene glycol phenyl ether by strong van der Waals and hydrogen bonding can greatly lower the amount of cationic surfactant necessary to synthesize molecular sieve MCM-48, at the same time, the with introduction of nonionic surfactant to the mixed surfactants micelle more extensively cross-linked framework and therefore higher thermal stability and higher crystallinity MCM-48 mesoporous molecular sieves were obtained. The synthesis was conducted at a very low mass fraction of mixed surfactants (about 4.6％) and a very low molar ratio of total surfactants to silica (about 0.152:1). Several mesoporous molecular sieves could be prepared by simply adjusting the molar ratio of p-Octyl polyethylene glycol phenyl ether to cetyltrimethyl-ammoniun bromide within a certain range.
A convenient synthesis of mesoporous molecular sieve MCM-48 by hydrothermal method using nonionic surfactant p-Octyl polyethylene glycol phenyl ether and cationic surfactant cetyltrimethyl-ammoniun bromide as co-template is reported. In this approach, nonionic surfactant p-Octyl polyethylene glycol phenyl ether by strong van der Waals and hydrogen bonding can greatly lower the amount of cationic surfactant necessary to synthesize molecular sieve MCM-48, at the same time, the with introduction of nonionic surfactant to the mixed surfactants micelle more extensively cross-linked framework and therefore higher thermal stability and higher crystallinity MCM-48 mesoporous molecular sieves were obtained. The synthesis was conducted at a very low mass fraction of mixed surfactants (about 4.6％) and a very low molar ratio of total surfactants to silica (about 0.152:1). Several mesoporous molecular sieves could be prepared by simply adjusting the molar ratio of p-Octyl polyethylene glycol phenyl ether to cetyltrimethyl-ammoniun bromide within a certain range.
2002, 18(10): 916-919
doi: 10.3866/PKU.WHXB20021010
Abstract:
The stability with time-on-stream of NaBr-promoted KY zeolite catalyst for the oxidative methylation of toluene with methane has been investigated. The results showed that during 50 h of reaction, the toluene conversion and the total C8 selectivity decreased fast at the first and then basically remained unchanged, they kept at about 35％ and 65％－70％ respectively. The selectivity of styrene decreased while the selectivity of ethyl benzene increased during the reaction process. This result was ascribed to the estimation that the styrene was formed by the dehydrogenation of ethyl benzene and the dehydrogenation activity decreased in the reaction process. In addition, the structure of the catalyst used was also studied by XRD, IR and XPS. It was found that the zeolite catalyst suffered dealumination, elimination of KBr and partial destruction of structure but the zeolite framework still retained.
The stability with time-on-stream of NaBr-promoted KY zeolite catalyst for the oxidative methylation of toluene with methane has been investigated. The results showed that during 50 h of reaction, the toluene conversion and the total C8 selectivity decreased fast at the first and then basically remained unchanged, they kept at about 35％ and 65％－70％ respectively. The selectivity of styrene decreased while the selectivity of ethyl benzene increased during the reaction process. This result was ascribed to the estimation that the styrene was formed by the dehydrogenation of ethyl benzene and the dehydrogenation activity decreased in the reaction process. In addition, the structure of the catalyst used was also studied by XRD, IR and XPS. It was found that the zeolite catalyst suffered dealumination, elimination of KBr and partial destruction of structure but the zeolite framework still retained.
2002, 18(10): 920-923
doi: 10.3866/PKU.WHXB20021011
Abstract:
The phase behavior of aqueous mixture of octyltrimethylamonium bromide (OTAB) and sodium octyl sulfate (SOS)was studied. In concentrated solution, a liquid crystal phase formed and converted form hexan nal structure to lamellar when the molar ratio of OTAB/SOS approached to 1.The mixed surfactant solution is a homogeneous and transparent liquid in middle concentration range. When the concentration is low, aqueous two-phase system appears in a wide range of OTAB/SOS molar ratio. In the aqueous surfactant two phase system, both vesicles and micelles exist in the surfactant-poor phase, while concentrated vesicle aggregates were contained in the surfactant-rich phase. Solubilization amount of oil-soluble dye in the surfactant-rich phase is much higher than that in the surfactant-poor phase.
The phase behavior of aqueous mixture of octyltrimethylamonium bromide (OTAB) and sodium octyl sulfate (SOS)was studied. In concentrated solution, a liquid crystal phase formed and converted form hexan nal structure to lamellar when the molar ratio of OTAB/SOS approached to 1.The mixed surfactant solution is a homogeneous and transparent liquid in middle concentration range. When the concentration is low, aqueous two-phase system appears in a wide range of OTAB/SOS molar ratio. In the aqueous surfactant two phase system, both vesicles and micelles exist in the surfactant-poor phase, while concentrated vesicle aggregates were contained in the surfactant-rich phase. Solubilization amount of oil-soluble dye in the surfactant-rich phase is much higher than that in the surfactant-poor phase.
2002, 18(10): 924-929
doi: 10.3866/PKU.WHXB20021012
Abstract:
In this paper, it has been elaborately elucidated that many instances of co linearity and the relationship among the rank of data matrix, the number of chemical components and the number of independent reactions. In addition, how to use rank augment technique to estimate the number of component is well discussed. Besides, it is specially explained that materials exchange among reactions has an effect on rank of data matrix. Furthermore, a set of approaches based on rank analysis technique, which can be used to determine the number of chemical components, independent reactions and the possible reaction mechanism in kinetic systems, are well developed. In the end, the rank analysis technique is applied to investigate the reaction mechanism between the polyaniline and the proton acid. The results, to see equation (24),show that there is a two-step Interco version among three absorbing structures under experimental condition of [H＋]=0.01～0.1 mol•L－1.
In this paper, it has been elaborately elucidated that many instances of co linearity and the relationship among the rank of data matrix, the number of chemical components and the number of independent reactions. In addition, how to use rank augment technique to estimate the number of component is well discussed. Besides, it is specially explained that materials exchange among reactions has an effect on rank of data matrix. Furthermore, a set of approaches based on rank analysis technique, which can be used to determine the number of chemical components, independent reactions and the possible reaction mechanism in kinetic systems, are well developed. In the end, the rank analysis technique is applied to investigate the reaction mechanism between the polyaniline and the proton acid. The results, to see equation (24),show that there is a two-step Interco version among three absorbing structures under experimental condition of [H＋]=0.01～0.1 mol•L－1.
2002, 18(10): 930-933
doi: 10.3866/PKU.WHXB20021013
Abstract:
Fe nanowire arrays have been prepared by electrodeposition in porous anodic aluminum oxide template from a composite electrolyte solution. These nanowires have uniform diameter of approximate 25 nm. The micrographs and crystal structures of Fe nanowires are studied by transmission electron microscopy (TEM),selected-area electron diffraction (SAED),and X-ray diffraction(XRD).It is found that each nanowire is essentially a single crystal and has a different orientation in the array.
Fe nanowire arrays have been prepared by electrodeposition in porous anodic aluminum oxide template from a composite electrolyte solution. These nanowires have uniform diameter of approximate 25 nm. The micrographs and crystal structures of Fe nanowires are studied by transmission electron microscopy (TEM),selected-area electron diffraction (SAED),and X-ray diffraction(XRD).It is found that each nanowire is essentially a single crystal and has a different orientation in the array.
2002, 18(10): 934-937
doi: 10.3866/PKU.WHXB20021014
Abstract:
A novel composite scanning micro pH electrode was fabricated. The IrOx-pH electrode produced in a carbonate melts exhibited high stability, a fast potential response and ideal Nernstian response. The slope of the electrode at 15 ℃ was 56.8 mV/pH, which was very close to the theoretical value. The 90％ potential response time for a pH change from 1.75 to 13.90 was less than 0.5 s. The composite scanning micro pH electrode is a promising apparatus for detecting the pH distribution on metal/solution interface. pH image on the surface of Al/Cu galvanic couple showed that both the anodic and cathodic areas could be sensed well. Localized corrosion took place on the interface of Al/Cu couple. The localized corrosion developed with time and pH value around the pitting decreased gradually.
A novel composite scanning micro pH electrode was fabricated. The IrOx-pH electrode produced in a carbonate melts exhibited high stability, a fast potential response and ideal Nernstian response. The slope of the electrode at 15 ℃ was 56.8 mV/pH, which was very close to the theoretical value. The 90％ potential response time for a pH change from 1.75 to 13.90 was less than 0.5 s. The composite scanning micro pH electrode is a promising apparatus for detecting the pH distribution on metal/solution interface. pH image on the surface of Al/Cu galvanic couple showed that both the anodic and cathodic areas could be sensed well. Localized corrosion took place on the interface of Al/Cu couple. The localized corrosion developed with time and pH value around the pitting decreased gradually.
2002, 18(10): 938-942
doi: 10.3866/PKU.WHXB20021015
Abstract:
NiP and NiPB amorphous alloys were prepared by chemical reduction method using nickel hypophosphite as reactant. Their physical properties were characterized by ICP, XRD and TEM. The effect of preparation conditions such as temperature, pH value, concentration of the reactants and additives on the yield and composition of NiP amorphous alloy was studied. The NiP amorphous alloy particle was found to be spherical and its average particle size was about 30 nm at 300 K. The effect of the concentration and mole ratio of the reactants on the composition of NiPB amorphous alloy was also studied. The average particle size of NiPB amorphous alloy (sample 5) was about 15 nm. It was convenient to obtain NiPB amorphous alloy with expected composition by changing the initial concentration and the mole ratio of the reactants.
NiP and NiPB amorphous alloys were prepared by chemical reduction method using nickel hypophosphite as reactant. Their physical properties were characterized by ICP, XRD and TEM. The effect of preparation conditions such as temperature, pH value, concentration of the reactants and additives on the yield and composition of NiP amorphous alloy was studied. The NiP amorphous alloy particle was found to be spherical and its average particle size was about 30 nm at 300 K. The effect of the concentration and mole ratio of the reactants on the composition of NiPB amorphous alloy was also studied. The average particle size of NiPB amorphous alloy (sample 5) was about 15 nm. It was convenient to obtain NiPB amorphous alloy with expected composition by changing the initial concentration and the mole ratio of the reactants.
2002, 18(10): 943-946
doi: 10.3866/PKU.WHXB20021016
Abstract:
CdS nanowire arrays were prepared by a new electrochemical method. XRD and TEM measurements show that CdS nanowires were composed of cubic and hexa nal phases, and the mechanism of deposition was discussed based on ion diffusion. The length of the nanowire can be controlled by electrochemical deposition time and the diameter can be controlled by the aperture of porous alumina template. The method of depositting nanowires on alumina template is a general route for preparing other nanowire arrays. The photoluminescence measurements show that CdS nanowires have three ultraviolet luminescence bands and one yellow-green luminescence band.
CdS nanowire arrays were prepared by a new electrochemical method. XRD and TEM measurements show that CdS nanowires were composed of cubic and hexa nal phases, and the mechanism of deposition was discussed based on ion diffusion. The length of the nanowire can be controlled by electrochemical deposition time and the diameter can be controlled by the aperture of porous alumina template. The method of depositting nanowires on alumina template is a general route for preparing other nanowire arrays. The photoluminescence measurements show that CdS nanowires have three ultraviolet luminescence bands and one yellow-green luminescence band.
2002, 18(10): 947-951
doi: 10.3866/PKU.WHXB20021017
Abstract:
The molar heat capacities (Cp,m) of crystalline potassium dichromate (K2Cr2O7) were measured with a precision automated adiabatic calorimeter over the temperature range from 100 K to 390 K. No phase transition or other thermal anomaly was observed in this temperature region. However, it was found that the relationship of Cp,m with respect to temperature T is different in different temperature regions. The polynomial functions of Cp,m vs. T were established in different temperature regions based on the heat capacity measurements by means of the least-fitting square method. These functions are as following: for 100 K ≤ T ≤ 275 K, Cp,m=0.0050T2－1.0320T＋125.22 (J•K－1•mol－1)；for 275 K ≤ T ≤ 350 K, Cp,m=209.37 J•K－1•mol－1；for 350 K ≤ T ≤390 K, Cp,m=0.0266T2－18.823T＋3542.3 J•K－1•mol－1.According to the relationship of Cp,m vs. T and thermodynamic equations, the values of thermodynamic function of potassium dichromate were calculated in the temperature range of 298.15～400.15 K with 5 K intervals.
The molar heat capacities (Cp,m) of crystalline potassium dichromate (K2Cr2O7) were measured with a precision automated adiabatic calorimeter over the temperature range from 100 K to 390 K. No phase transition or other thermal anomaly was observed in this temperature region. However, it was found that the relationship of Cp,m with respect to temperature T is different in different temperature regions. The polynomial functions of Cp,m vs. T were established in different temperature regions based on the heat capacity measurements by means of the least-fitting square method. These functions are as following: for 100 K ≤ T ≤ 275 K, Cp,m=0.0050T2－1.0320T＋125.22 (J•K－1•mol－1)；for 275 K ≤ T ≤ 350 K, Cp,m=209.37 J•K－1•mol－1；for 350 K ≤ T ≤390 K, Cp,m=0.0266T2－18.823T＋3542.3 J•K－1•mol－1.According to the relationship of Cp,m vs. T and thermodynamic equations, the values of thermodynamic function of potassium dichromate were calculated in the temperature range of 298.15～400.15 K with 5 K intervals.
2002, 18(10): 952-955
doi: 10.3866/PKU.WHXB20021018
Abstract:
Based on the relativistic effective core potential (RECP) for Pu atom and 6-311G* basis sets for H atom, the thermodynamic functions for PuH2(g) have been calculated by ab initio method, and the thermodynamic functions formed for PuH2(g)molecules have been worked out by thermodynamic method. The results of calculation show that PuH2(g) molecules are not thermodynamic stable.
Based on the relativistic effective core potential (RECP) for Pu atom and 6-311G* basis sets for H atom, the thermodynamic functions for PuH2(g) have been calculated by ab initio method, and the thermodynamic functions formed for PuH2(g)molecules have been worked out by thermodynamic method. The results of calculation show that PuH2(g) molecules are not thermodynamic stable.
2002, 18(10): 956-960
doi: 10.3866/PKU.WHXB20021019
Abstract:
It is found by experiment that Na2SeO3 can improve the current efficiency remarkably. The reaction mechanism of the promotion of the current efficiency of electro-deposition of Zn-Mn alloy by the addition of Na2SeO3 to the cathode has been studied by cyclic voltammetry, linear sweep voltammetry, chronopotentiometry and electro-chemical impedance methods. It is found that under the conditions of Zn-Mn alloys electro-deposition, Na2SeO3 is reduced to Se32－, which is adsorbed on the surface of cathode, because of the adsorption of Se32－, the adsorption of H is prevented, the partial potential curve of hydrogen moves to negative region about 0.2 V in the presence of 0.1 g•L－1 Na2SeO3.
It is found by experiment that Na2SeO3 can improve the current efficiency remarkably. The reaction mechanism of the promotion of the current efficiency of electro-deposition of Zn-Mn alloy by the addition of Na2SeO3 to the cathode has been studied by cyclic voltammetry, linear sweep voltammetry, chronopotentiometry and electro-chemical impedance methods. It is found that under the conditions of Zn-Mn alloys electro-deposition, Na2SeO3 is reduced to Se32－, which is adsorbed on the surface of cathode, because of the adsorption of Se32－, the adsorption of H is prevented, the partial potential curve of hydrogen moves to negative region about 0.2 V in the presence of 0.1 g•L－1 Na2SeO3.
