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1988 Volume 4 Issue 5
1988, 4(05): 449-450
doi: 10.3866/PKU.WHXB19880501
Abstract:
Halide glasses are a new family of glasses and, at present, are receiving increasing attention because of their technological potentials especially for new waveguide fibers. Using the Fumi-Tosi pair potential, we have performed simulations of the cooling of molten salt, lithium chloride, at the rate about 5×10~(12) K s~(-1) to study the glass transition and the structural and dynamic properties of the simulated supercooled liquid. It can be seen from our calculation that over the range from 498 K to 298 K, the peak of the radia distribution function is split into two subpeaks and the self-diffusion cofficient decrease rapidly. So the simulated glass transition temperature should occur at this rangs. At 298 K the first coordination number of Li~+ or Cl~- calculated from the cumulative coordination number curve N(r) is about 4. The sorting present that the number of the counter ions nearest each Li~+ (or Cl~-) are not the same. All the behavior of our simulated LiCl glass is that of laboratory glass. Also there exists hole which is as large as Cl~- ion in simulated lithium chloride glass. This implies that the holes in molten salt do not vanish when the molten salt is supercooled.
Halide glasses are a new family of glasses and, at present, are receiving increasing attention because of their technological potentials especially for new waveguide fibers. Using the Fumi-Tosi pair potential, we have performed simulations of the cooling of molten salt, lithium chloride, at the rate about 5×10~(12) K s~(-1) to study the glass transition and the structural and dynamic properties of the simulated supercooled liquid. It can be seen from our calculation that over the range from 498 K to 298 K, the peak of the radia distribution function is split into two subpeaks and the self-diffusion cofficient decrease rapidly. So the simulated glass transition temperature should occur at this rangs. At 298 K the first coordination number of Li~+ or Cl~- calculated from the cumulative coordination number curve N(r) is about 4. The sorting present that the number of the counter ions nearest each Li~+ (or Cl~-) are not the same. All the behavior of our simulated LiCl glass is that of laboratory glass. Also there exists hole which is as large as Cl~- ion in simulated lithium chloride glass. This implies that the holes in molten salt do not vanish when the molten salt is supercooled.
1988, 4(05): 451-453
doi: 10.3866/PKU.WHXB19880502
Abstract:
The structure of molten LiF, KCl and LiF-KCl solution have been simulated by molecular dynamics method. The thermodynamic, structural and dynamic properties, such as the internal energy, temperature and pressure, the radial distribution function and structure factor, the mean square displacements, have been calculated.
The structure have been studied with the following main results: 1, the partial radial distribution curve of Li~+-F~- ion pairs in LiF-KCl mixture exhibits a high first peak, whereas the first peak of the partial radial distribution function of L~+-Cl~- pairs in LiF-KCl mixture is lower than that of pure KCl melt. 2, there exists hole in molten salt, the size and the environment of the hole, the disintegration scheme and the mean lifetime of the hole are related to the radii of the ions.
The structure of molten LiF, KCl and LiF-KCl solution have been simulated by molecular dynamics method. The thermodynamic, structural and dynamic properties, such as the internal energy, temperature and pressure, the radial distribution function and structure factor, the mean square displacements, have been calculated.
The structure have been studied with the following main results: 1, the partial radial distribution curve of Li~+-F~- ion pairs in LiF-KCl mixture exhibits a high first peak, whereas the first peak of the partial radial distribution function of L~+-Cl~- pairs in LiF-KCl mixture is lower than that of pure KCl melt. 2, there exists hole in molten salt, the size and the environment of the hole, the disintegration scheme and the mean lifetime of the hole are related to the radii of the ions.
1988, 4(05): 454-457
doi: 10.3866/PKU.WHXB19880503
Abstract:
The in-situ absorbance-time curves at λ=950 nm were measured during triangular potential scan of PPy(Cl) film. A cyclic voltammogram can be obtained from the time derivative of the absorbance. The effects of capacitance current and H~+ discharge in aqueous solution could be elimenated completely in the cyclic voltammogram obtained in this way. Selection of light wavelength and the limitation of the method are discussed.
The in-situ absorbance-time curves at λ=950 nm were measured during triangular potential scan of PPy(Cl) film. A cyclic voltammogram can be obtained from the time derivative of the absorbance. The effects of capacitance current and H~+ discharge in aqueous solution could be elimenated completely in the cyclic voltammogram obtained in this way. Selection of light wavelength and the limitation of the method are discussed.
1988, 4(05): 458-460
doi: 10.3866/PKU.WHXB19880504
Abstract:
Surface enhanced Raman spectroscopy (SERS) provides a powerful means of obtaining information on adsorbate/surface interactions in view of its unique sensitivity~[4]. With SERS, we started a preliminary study of the adsorption and subsequent electropolymerization of aniline on Ag and Au electrodes respectively. A set of potential-dependent SER spectra of aniline adsorbed at Ag electrodes are shown in figure 1. The charateristic adsorbate-surface vibrations around 306 and 226 cm~(-1) indicate that aniline is adsorbed via its N atom and at more positive potentials Cl~- is coadsorbed with aniline on the surface. With increasingly negative potentials, the considerable changes of the SER spectra are mainly due to that adsorbed aniline changes its orientation from perpendicular to parallel to the surface, which is in contrast to the case of Ag/pyridine system~[7]. In another series of SERS experiments aniline was oxidized at Au electrodes as the potential was moved in positive direction (fig.2). The SER spectrum at +0.8 V is very similar to that of polyaniline at the same potential. It follows that the ppolymerization of aniline has taken place on the Au electrode. At less positive potentials (around +0.3 V) the distinct differences of the SER spectra with a high luminesence background are presumably due to the formation of oli mers of aniline at the surface.
Surface enhanced Raman spectroscopy (SERS) provides a powerful means of obtaining information on adsorbate/surface interactions in view of its unique sensitivity~[4]. With SERS, we started a preliminary study of the adsorption and subsequent electropolymerization of aniline on Ag and Au electrodes respectively. A set of potential-dependent SER spectra of aniline adsorbed at Ag electrodes are shown in figure 1. The charateristic adsorbate-surface vibrations around 306 and 226 cm~(-1) indicate that aniline is adsorbed via its N atom and at more positive potentials Cl~- is coadsorbed with aniline on the surface. With increasingly negative potentials, the considerable changes of the SER spectra are mainly due to that adsorbed aniline changes its orientation from perpendicular to parallel to the surface, which is in contrast to the case of Ag/pyridine system~[7]. In another series of SERS experiments aniline was oxidized at Au electrodes as the potential was moved in positive direction (fig.2). The SER spectrum at +0.8 V is very similar to that of polyaniline at the same potential. It follows that the ppolymerization of aniline has taken place on the Au electrode. At less positive potentials (around +0.3 V) the distinct differences of the SER spectra with a high luminesence background are presumably due to the formation of oli mers of aniline at the surface.
1988, 4(05): 461-465
doi: 10.3866/PKU.WHXB19880505
Abstract:
The molecular structures of 4-NH_2-2-OH-isocytosine (for short, iso-lactim) and N_3-H-4-NH_2-2-OXO-cytosine (for short, iso-lactam) have been optimized by MINDO/3. Iso-lactam is more stable than iso-lactim by ΔE=4.9kcal mol~(-1).
The geometric parameters of the transition state have been optimized by Powell's procedure which is contained in MINDO/3 program. The reaction pathway of the iso-lactam<=>iso-lactim has been studied by K. Fukui's IRC theory. The activation energies are 43.4 kcal mol~(-1) and 38.5 kcal mol~(-1) for the forward and backward reaction, respectively. An electron transfer scheme has been suggested to explain the nature of the tautomeric reactions of the tautomers of cytosine.
The molecular structures of 4-NH_2-2-OH-isocytosine (for short, iso-lactim) and N_3-H-4-NH_2-2-OXO-cytosine (for short, iso-lactam) have been optimized by MINDO/3. Iso-lactam is more stable than iso-lactim by ΔE=4.9kcal mol~(-1).
The geometric parameters of the transition state have been optimized by Powell's procedure which is contained in MINDO/3 program. The reaction pathway of the iso-lactam<=>iso-lactim has been studied by K. Fukui's IRC theory. The activation energies are 43.4 kcal mol~(-1) and 38.5 kcal mol~(-1) for the forward and backward reaction, respectively. An electron transfer scheme has been suggested to explain the nature of the tautomeric reactions of the tautomers of cytosine.
1988, 4(05): 466-472
doi: 10.3866/PKU.WHXB19880506
Abstract:
The complexes LnBr_3(18-C-6)·nH_2O (Ln=La, n=1; Ln=Nd, Sm, Gd, Tb, Er, Y, n=3)were prepared and those FT-IR, Raman spectra were measured over the region of 3500—100 cm~(-1).
By means of normal coordinatiou analysis of La(NO_3)_3(18-C-6) and structural determination of some crown ether complexes, the bands charactering Ln—O_6 (crown), Lu—O(H_2) and Ln—Br as well as the coupling mode between vibrations of Ln—O(crown) and Ln—Br can be assigned respectively. The band near 880 cm~(-1) is attribued to the symmetrical vibration of the ring inherent in the fragment LnO_6 (crown) which is important for clarifying whether or not Ln~(3+) in the complex is coordinated to the crown ring. Due to a similar trend existing in the low frequency spectra of Ln=La, Nd, Sm, Gd, Tb, Er complexes except Y, the analo us structures would be expected.
As a consequence, La~(3+) (n=1) is coordinated by six oxygen atoms of crown ether ring, three bromine atoms and one oxgaen atom from the water with CN=10. For complexes of Ln=Nd, Sm, Gd, Tb (n=3), the molecular structures are like La-complex additionally more two lattice water. As the smaller ionic radius of Y~(3+), the Y-complex exists with CN=9. Therefore the structure of YBr_3 (18-C-6)·3H_2O may be similar to [GdCl_2(18-C-6)·EtOH]~+Cl~-, e.g.[YBr_2(18-C-6)·OH_2]~+Br~- with CN=9, that can explain why the low frequency spectrum of Y-complex is different from the others.
The complexes LnBr_3(18-C-6)·nH_2O (Ln=La, n=1; Ln=Nd, Sm, Gd, Tb, Er, Y, n=3)were prepared and those FT-IR, Raman spectra were measured over the region of 3500—100 cm~(-1).
By means of normal coordinatiou analysis of La(NO_3)_3(18-C-6) and structural determination of some crown ether complexes, the bands charactering Ln—O_6 (crown), Lu—O(H_2) and Ln—Br as well as the coupling mode between vibrations of Ln—O(crown) and Ln—Br can be assigned respectively. The band near 880 cm~(-1) is attribued to the symmetrical vibration of the ring inherent in the fragment LnO_6 (crown) which is important for clarifying whether or not Ln~(3+) in the complex is coordinated to the crown ring. Due to a similar trend existing in the low frequency spectra of Ln=La, Nd, Sm, Gd, Tb, Er complexes except Y, the analo us structures would be expected.
As a consequence, La~(3+) (n=1) is coordinated by six oxygen atoms of crown ether ring, three bromine atoms and one oxgaen atom from the water with CN=10. For complexes of Ln=Nd, Sm, Gd, Tb (n=3), the molecular structures are like La-complex additionally more two lattice water. As the smaller ionic radius of Y~(3+), the Y-complex exists with CN=9. Therefore the structure of YBr_3 (18-C-6)·3H_2O may be similar to [GdCl_2(18-C-6)·EtOH]~+Cl~-, e.g.[YBr_2(18-C-6)·OH_2]~+Br~- with CN=9, that can explain why the low frequency spectrum of Y-complex is different from the others.
1988, 4(05): 473-477
doi: 10.3866/PKU.WHXB19880507
Abstract:
In this article, the prominent transient characteristic of photocurrent on thermal-formed iron oxide electrode was discussed. This accounts for the fact that photocurrent values measured with lock-in amplifier greatly exceed their average algebraic values. The photoresponse of anodic-formed iron oxide passive film is similar to that of thermal-formed with some differences. Our present experimental technique is still insufficient for monitoring structural changes of film during the formation of the latter. Nevertheless, our results showed after the film was principally formed, photocurrent is proportional to film thickness. Before this period, there is a positive deviation of photocurrent and the linear relationship does not hold.
In this article, the prominent transient characteristic of photocurrent on thermal-formed iron oxide electrode was discussed. This accounts for the fact that photocurrent values measured with lock-in amplifier greatly exceed their average algebraic values. The photoresponse of anodic-formed iron oxide passive film is similar to that of thermal-formed with some differences. Our present experimental technique is still insufficient for monitoring structural changes of film during the formation of the latter. Nevertheless, our results showed after the film was principally formed, photocurrent is proportional to film thickness. Before this period, there is a positive deviation of photocurrent and the linear relationship does not hold.
1988, 4(05): 478-482
doi: 10.3866/PKU.WHXB19880508
Abstract:
The reduction behavior of CuO supported on SnO_2, ZnO and Al_2O_3 has been examined, the effect of support and Pd investigated as well. The catalyst samples were studied by TPR and electric conductivity measurement simultaneously.
It was observed that CuO supported on n-type semiconductor oxides SnO_2 and ZnO was more easily reduced than bulk CuO and that on Al_2O_3. The TPR peak of CuO was shifted from 285 ℃ to 210 ℃ and 240 ℃ when supported on SnO_2 and ZnO respectively. By introducing a small amount of Pd (0.4-0.5 Wt.%) onto the catalyst, the reduction peak was further shifted to below 100 ℃ in the case of SnO_2 and by 50-60 ℃ in the case of ZnO.
The conductivity-temperature curve of SnO_2 and ZnO in Ar-H_2 (5%) atmosphere revealed that the n-defects were promptly generated around 200-250 ℃, it was the same temperature region at which the reduction of CuO on these supoorts occurred.
In the presence of Pd additve the onset of conductivity increasing would be observed on SnO_2 and ZnO by exposure to reducing atmosphere even at room temperature, while for CuO/SnO_2 and CuO/ZnO the abrupt change of conductivity occurred around 100-150 ℃. Thus it was reasonably explained that Pd, being an activator for H_2 molecules, promoted the defect generation in semicoductor and in turn the reduction of supported CuO was further enhanced. Noticeably in the case of the occurrence of CuO reduction the electric conductivity change of semiconductor was moderated, it seemed that the negative charge was transferred from support to CuO.
As for the catalyst with Al_2O_3 as support, in accordance with that Al_2O_3 was an insulator, no charge transfer property and no promoting effect on CuO reduction was observed at all.
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Project supported by the Science Fund of Chinese Academy of Sciences
The reduction behavior of CuO supported on SnO_2, ZnO and Al_2O_3 has been examined, the effect of support and Pd investigated as well. The catalyst samples were studied by TPR and electric conductivity measurement simultaneously.
It was observed that CuO supported on n-type semiconductor oxides SnO_2 and ZnO was more easily reduced than bulk CuO and that on Al_2O_3. The TPR peak of CuO was shifted from 285 ℃ to 210 ℃ and 240 ℃ when supported on SnO_2 and ZnO respectively. By introducing a small amount of Pd (0.4-0.5 Wt.%) onto the catalyst, the reduction peak was further shifted to below 100 ℃ in the case of SnO_2 and by 50-60 ℃ in the case of ZnO.
The conductivity-temperature curve of SnO_2 and ZnO in Ar-H_2 (5%) atmosphere revealed that the n-defects were promptly generated around 200-250 ℃, it was the same temperature region at which the reduction of CuO on these supoorts occurred.
In the presence of Pd additve the onset of conductivity increasing would be observed on SnO_2 and ZnO by exposure to reducing atmosphere even at room temperature, while for CuO/SnO_2 and CuO/ZnO the abrupt change of conductivity occurred around 100-150 ℃. Thus it was reasonably explained that Pd, being an activator for H_2 molecules, promoted the defect generation in semicoductor and in turn the reduction of supported CuO was further enhanced. Noticeably in the case of the occurrence of CuO reduction the electric conductivity change of semiconductor was moderated, it seemed that the negative charge was transferred from support to CuO.
As for the catalyst with Al_2O_3 as support, in accordance with that Al_2O_3 was an insulator, no charge transfer property and no promoting effect on CuO reduction was observed at all.
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Project supported by the Science Fund of Chinese Academy of Sciences
1988, 4(05): 483-488
doi: 10.3866/PKU.WHXB19880509
Abstract:
Well resolved ESR spectra of CuTAPP [Copper tetra-(p-trimethylammoniumphenyl) porphine iodide] supported on active carbon was obtained by proper dilution of CuTAPP on the substrate. The hyperfine lines of copper, super-hyperfine lines of the four nitrogen atoms and anomalous lines appeared on the spectrum. Computer simulated spectrum of CuTAPP was found to be in od accordance with the experimental one. The ESR spectrum of CuTAPP supported on active carbon was discussed in detail to yield the ESR and derived parameters, which are found to be close to those of non-supported copper porphins and phthalocyanins.
Well resolved ESR spectra of CuTAPP [Copper tetra-(p-trimethylammoniumphenyl) porphine iodide] supported on active carbon was obtained by proper dilution of CuTAPP on the substrate. The hyperfine lines of copper, super-hyperfine lines of the four nitrogen atoms and anomalous lines appeared on the spectrum. Computer simulated spectrum of CuTAPP was found to be in od accordance with the experimental one. The ESR spectrum of CuTAPP supported on active carbon was discussed in detail to yield the ESR and derived parameters, which are found to be close to those of non-supported copper porphins and phthalocyanins.
1988, 4(05): 489-493
doi: 10.3866/PKU.WHXB19880510
Abstract:
By using SETARAM heat-flow calorimeter the differential heats of adsorption for cyclohexene and 2-methyl-pentene-1 on NaY, CaY, R_EY and HY zeolites at ambient temperature have been measured. By means of Benson's method for the estimation of thermochemical data, the heats of adsorption for tertiary and secondary carbonium ions have been obtained. According to the differnce between heats of adsorption for cyclohexene and 2-methyl-pentene-1 at the same adsorption amounts the adsorption mechanism for cyclohexene and 2-methyl-pentene-1 on the zeolites has been discussed.
By using SETARAM heat-flow calorimeter the differential heats of adsorption for cyclohexene and 2-methyl-pentene-1 on NaY, CaY, R_EY and HY zeolites at ambient temperature have been measured. By means of Benson's method for the estimation of thermochemical data, the heats of adsorption for tertiary and secondary carbonium ions have been obtained. According to the differnce between heats of adsorption for cyclohexene and 2-methyl-pentene-1 at the same adsorption amounts the adsorption mechanism for cyclohexene and 2-methyl-pentene-1 on the zeolites has been discussed.
1988, 4(05): 494-498
doi: 10.3866/PKU.WHXB19880511
Abstract:
The fluorescence quenching of nine L_4EuQH type complexes by stable free radical was studied. Results show that the bimolecular quenching constants were much less than the diffusion rate constant and the existence of a sphere of action within which the probability of quenching is not unity as usually reported in current literature.
The fluorescence quenching of nine L_4EuQH type complexes by stable free radical was studied. Results show that the bimolecular quenching constants were much less than the diffusion rate constant and the existence of a sphere of action within which the probability of quenching is not unity as usually reported in current literature.
1988, 4(05): 499-504
doi: 10.3866/PKU.WHXB19880512
Abstract:
Various amounts of a liquid crystal such as 4-methoxybenzylidene-4'-n-butylaniline (MBBA) were added respectively into chlorophyll a (Chla)-isooctane solutions of the same concentration. These solutions were coated respectively on to platinum plates to form liquid crystal-chlorophyll platinum electrodes for determining the different photo-induced potential ΔE. On the other hand, these solutions were coated respectively on to glass plates to form the glass plates with the liquid crystal-chlorophyll layer for determining the different height of 743 nm characteristic peak of derivative spectrum h/h_T. It was found that both of ΔE and h/h_T apear the maximum values with the increase in quantity of MBBA. The same result can be found by substituting iso-octane by the petroleum ether and the isooctane-petroleum ether (1:9V/V). The MBBA molar concentration range in which all of the six maximum values from above three solvent systems occur is 0.001±0.0005. The regularity of the experimental results was theoretically elucidated by the principle of derivative spectrum, the molecular structure and the characteristics of liquid crystal.
Various amounts of a liquid crystal such as 4-methoxybenzylidene-4'-n-butylaniline (MBBA) were added respectively into chlorophyll a (Chla)-isooctane solutions of the same concentration. These solutions were coated respectively on to platinum plates to form liquid crystal-chlorophyll platinum electrodes for determining the different photo-induced potential ΔE. On the other hand, these solutions were coated respectively on to glass plates to form the glass plates with the liquid crystal-chlorophyll layer for determining the different height of 743 nm characteristic peak of derivative spectrum h/h_T. It was found that both of ΔE and h/h_T apear the maximum values with the increase in quantity of MBBA. The same result can be found by substituting iso-octane by the petroleum ether and the isooctane-petroleum ether (1:9V/V). The MBBA molar concentration range in which all of the six maximum values from above three solvent systems occur is 0.001±0.0005. The regularity of the experimental results was theoretically elucidated by the principle of derivative spectrum, the molecular structure and the characteristics of liquid crystal.
1988, 4(05): 505-510
doi: 10.3866/PKU.WHXB19880513
Abstract:
Ortho-diaminobenzene (ODB), Ortho-aminophenol (OAP) can be easily electropolymerized in acid aqueous solution, form continouus and adherent films. The polymer are 1,4-para position coupling. When pH<4, PODB is electroactive, its redox reaction which leads to the electrochromic behavior is concerned with H~+ ions. The electrode potentials of PODB, POAP behave Nernstian response vs. pH values from pH=4—10, electrode coefficience are 59mV/pH and 57mV/pH respectively. The Polymer H~+ ion selective electrode have realtively short respones time (less than 3 min.), od selectivity, reproductivity and stability. PODB, POAP are able to form complexes with transtion-metal ions Ni~(2+) and Co~(2+). The polymercomplex film show very stable cyclic voltametric behavior in alkaline media, the metal ions in film can be exchanced by H+ ion. —NH_2 group in PODB electrode can be remodified o introduce the quinone/hydroquinone functional group.
Ortho-diaminobenzene (ODB), Ortho-aminophenol (OAP) can be easily electropolymerized in acid aqueous solution, form continouus and adherent films. The polymer are 1,4-para position coupling. When pH<4, PODB is electroactive, its redox reaction which leads to the electrochromic behavior is concerned with H~+ ions. The electrode potentials of PODB, POAP behave Nernstian response vs. pH values from pH=4—10, electrode coefficience are 59mV/pH and 57mV/pH respectively. The Polymer H~+ ion selective electrode have realtively short respones time (less than 3 min.), od selectivity, reproductivity and stability. PODB, POAP are able to form complexes with transtion-metal ions Ni~(2+) and Co~(2+). The polymercomplex film show very stable cyclic voltametric behavior in alkaline media, the metal ions in film can be exchanced by H+ ion. —NH_2 group in PODB electrode can be remodified o introduce the quinone/hydroquinone functional group.
1988, 4(05): 511-515
doi: 10.3866/PKU.WHXB19880514
Abstract:
Absorption, Fluorescence and Phosphorescence Spectra of uracil, 1,3-dimethyl uracil, thymine, 1,3-dimethylthymine, 6-aza-uracil, 1,3-dimethyl-6-aza-uracil, 6-aza-thymine, 1,3-dimethy-6-aza-thymine, guanine and 8-aza-guanine were determined. Relationship of molecular structure with photophysics and excited state was discussed.
The conclusion is that the singlet state of these compounds is neither pure ~1(n, π~*) nor pure ~1(π, π~*). It is suitable when the mixing state was used to describe the singlet state of the compounds.
Absorption, Fluorescence and Phosphorescence Spectra of uracil, 1,3-dimethyl uracil, thymine, 1,3-dimethylthymine, 6-aza-uracil, 1,3-dimethyl-6-aza-uracil, 6-aza-thymine, 1,3-dimethy-6-aza-thymine, guanine and 8-aza-guanine were determined. Relationship of molecular structure with photophysics and excited state was discussed.
The conclusion is that the singlet state of these compounds is neither pure ~1(n, π~*) nor pure ~1(π, π~*). It is suitable when the mixing state was used to describe the singlet state of the compounds.
1988, 4(05): 516-522
doi: 10.3866/PKU.WHXB19880515
Abstract:
The non-proportion substitutive SAPO-5 and the selective substitutive SAPO-5 were synthesized by taking triethylamine as the template under certain experimental conditions. They result from substituting Si for P, Al in non-proportion and partly replacing of P with Si in the framework of APO-5 respectively. The compositions are as follows:
H_(y-x) (Al_(12-x)Si_x) (P_(12-y)Si_y) O_(48)·zH_2O y-x=0.5~2.01 y+x=1.3～3.09 H_xAl_(12)(P_(12_x)Si_x) O_(48)·zH_2O x=0.7~2.66
The charge in framework and the acidity enhances considerably with the difference between P and Al in the framework. The area of NH_3-TPD of the sample of the difference 1.86 is 7.4 times as that of APO-5.
The crystal structures of two SAPO-5 containing Na~+ were determineted by powder X-ray diffraction at 400 ℃. Then the structure parameters were refined by Rietveld method. The unit cells of the two SAPO-5 contain Na_(y-x) (Al_(12-x)Si_x) and (P_(12-y)Si_y)O_(48) and Na_xAl_(12) (P_(12-x)Si_y)O_(48), respectively. The constructions of their framework are quite similar to APO-5. The space group is C_(6v)~2-P6cc. The lattice parameters: a=b=1.3761(5) nm, c=0.8402(3) nm; a=b=1.3805(7) nm, c=0.8428(4) nm respectively. The “ odness of fit” is shown in Table 1. The average bod lengths of P(Si)-O, Al(Si)-O are 1.494A, 1.695A respectively and their difference equals 0.196A for the non-proportional substitutive SAPO-5. The average bond lengths of P(Si)-O, Al-O are 1.504A, 1.702A respectively and their difference equals 0.198A for the selective substitutive SAPO-5. Both of the differences are much larger than that of the disordered APO-5 and the proportional substitutiue sAPO-5. It is concluded that the ordered degree of P and Al is fairly hight in the two frameworks of SAPO-5.
There is a 12-ring straight channel ca. 0.8 nm in diameter and Na~+ are located at center of the hexa nal prism in the framework. The Brönsted center or activative center in SAPO-5 and the unique disabsorption peak of NH_3 appears in TPD spectra.
The non-proportion substitutive SAPO-5 and the selective substitutive SAPO-5 were synthesized by taking triethylamine as the template under certain experimental conditions. They result from substituting Si for P, Al in non-proportion and partly replacing of P with Si in the framework of APO-5 respectively. The compositions are as follows:
H_(y-x) (Al_(12-x)Si_x) (P_(12-y)Si_y) O_(48)·zH_2O y-x=0.5~2.01 y+x=1.3～3.09 H_xAl_(12)(P_(12_x)Si_x) O_(48)·zH_2O x=0.7~2.66
The charge in framework and the acidity enhances considerably with the difference between P and Al in the framework. The area of NH_3-TPD of the sample of the difference 1.86 is 7.4 times as that of APO-5.
The crystal structures of two SAPO-5 containing Na~+ were determineted by powder X-ray diffraction at 400 ℃. Then the structure parameters were refined by Rietveld method. The unit cells of the two SAPO-5 contain Na_(y-x) (Al_(12-x)Si_x) and (P_(12-y)Si_y)O_(48) and Na_xAl_(12) (P_(12-x)Si_y)O_(48), respectively. The constructions of their framework are quite similar to APO-5. The space group is C_(6v)~2-P6cc. The lattice parameters: a=b=1.3761(5) nm, c=0.8402(3) nm; a=b=1.3805(7) nm, c=0.8428(4) nm respectively. The “ odness of fit” is shown in Table 1. The average bod lengths of P(Si)-O, Al(Si)-O are 1.494A, 1.695A respectively and their difference equals 0.196A for the non-proportional substitutive SAPO-5. The average bond lengths of P(Si)-O, Al-O are 1.504A, 1.702A respectively and their difference equals 0.198A for the selective substitutive SAPO-5. Both of the differences are much larger than that of the disordered APO-5 and the proportional substitutiue sAPO-5. It is concluded that the ordered degree of P and Al is fairly hight in the two frameworks of SAPO-5.
There is a 12-ring straight channel ca. 0.8 nm in diameter and Na~+ are located at center of the hexa nal prism in the framework. The Brönsted center or activative center in SAPO-5 and the unique disabsorption peak of NH_3 appears in TPD spectra.
1988, 4(05): 523-526
doi: 10.3866/PKU.WHXB19880516
Abstract:
The influences of a variety of external salts on the solution viscosity of sodium-cellulose sulfate half-ester were studied by viscometry method. The dependences of polymer conformation structure on salt concentration and cation as well as anion of salt were discussed seperately. The influences of polyvalent cation was also discussed simply.
The influences of a variety of external salts on the solution viscosity of sodium-cellulose sulfate half-ester were studied by viscometry method. The dependences of polymer conformation structure on salt concentration and cation as well as anion of salt were discussed seperately. The influences of polyvalent cation was also discussed simply.
1988, 4(05): 527-530
doi: 10.3866/PKU.WHXB19880517
Abstract:
Transfer behavior of nickle ion extracted electrochemically by 2,2′-bipyridine at the water/nitrobenzene interface has been investigated by cyclic voitammetry. The preceding or following chemical reaction was coupied to the electrolytic transfer process,respectively. The extracted species are successive complexes between Ni(Ⅱ) and 2,2′-bipyridine An irreversible phenomenon similar to that observed at the metal electrode/electrolyte solution interface was observed directly. Voltam metric behaviors with coupled chemical reactions have been discussed.
Transfer behavior of nickle ion extracted electrochemically by 2,2′-bipyridine at the water/nitrobenzene interface has been investigated by cyclic voitammetry. The preceding or following chemical reaction was coupied to the electrolytic transfer process,respectively. The extracted species are successive complexes between Ni(Ⅱ) and 2,2′-bipyridine An irreversible phenomenon similar to that observed at the metal electrode/electrolyte solution interface was observed directly. Voltam metric behaviors with coupled chemical reactions have been discussed.
1988, 4(05): 531-534
doi: 10.3866/PKU.WHXB19880518
Abstract:
(η~5-C_5H_5)_4Mo_4Fe_2(μ_3-S)_5(CO)_5 have been prepared from (η~5-C_5H_5)_2Mo_2(CO)_6 and Fe_8S_2(CO)_9 under toluene reflux for 14.5 hrs.The crystal and molecular structures of (η~5-C_5H_5)_4Mo_4Fe_2(μ_3-S)_5(CO)_5 were studied by X-ray structure analysis. The Crystallographic data are as follows: monoclinic, space group P2_1/n, unit cell: a=1.0589(4), b=1.7260(4), c=1.8963(4) nm, β=101.44(2)°, V=3.3967 nm, D_c=2.06 gcm~(-3) for Z=4, X-ray data were obtained over the range of 2°<2θ<50° via the ω-2θ scan mode with MoKα radiation on an Enraf-Nonius CAD4 diffractometer. The structure was solved by direct method (MULTAN) and refined by full matrix least-squares techniques for 3993 reflections with I>2σ(I), The final R=0.081. Figure 1 illustrates the configuration of the molecule (η~5-C_5H_5)_4Mo_4Fe_2(μ_3-S)_5(CO)_5, composing of a cubane-like (FeMo_3S_4) core and a tri nal pyramid (MoFe_2S) core, which linked by sharing Fe(1) atom.
(η~5-C_5H_5)_4Mo_4Fe_2(μ_3-S)_5(CO)_5 have been prepared from (η~5-C_5H_5)_2Mo_2(CO)_6 and Fe_8S_2(CO)_9 under toluene reflux for 14.5 hrs.The crystal and molecular structures of (η~5-C_5H_5)_4Mo_4Fe_2(μ_3-S)_5(CO)_5 were studied by X-ray structure analysis. The Crystallographic data are as follows: monoclinic, space group P2_1/n, unit cell: a=1.0589(4), b=1.7260(4), c=1.8963(4) nm, β=101.44(2)°, V=3.3967 nm, D_c=2.06 gcm~(-3) for Z=4, X-ray data were obtained over the range of 2°<2θ<50° via the ω-2θ scan mode with MoKα radiation on an Enraf-Nonius CAD4 diffractometer. The structure was solved by direct method (MULTAN) and refined by full matrix least-squares techniques for 3993 reflections with I>2σ(I), The final R=0.081. Figure 1 illustrates the configuration of the molecule (η~5-C_5H_5)_4Mo_4Fe_2(μ_3-S)_5(CO)_5, composing of a cubane-like (FeMo_3S_4) core and a tri nal pyramid (MoFe_2S) core, which linked by sharing Fe(1) atom.
1988, 4(05): 535-538
doi: 10.3866/PKU.WHXB19880519
Abstract:
The measurement of the kinetic rate constant of the reaction of O(~3P) atoms with n-butanone at 288K is carried out. O(~3P) atoms were generated by a microwave discharge flow system and the residual concentration was detected by NO_2* chemiluminescence. The specific rate constant obtained is
κ=(6.2±1.2)×10~(-15)cm~3 molecule~(-1) s~(-1) (T=288 K).
A correlation diagram of molecular orbitals for the reaction is discussed.
The measurement of the kinetic rate constant of the reaction of O(~3P) atoms with n-butanone at 288K is carried out. O(~3P) atoms were generated by a microwave discharge flow system and the residual concentration was detected by NO_2* chemiluminescence. The specific rate constant obtained is
κ=(6.2±1.2)×10~(-15)cm~3 molecule~(-1) s~(-1) (T=288 K).
A correlation diagram of molecular orbitals for the reaction is discussed.
1988, 4(05): 539-544
doi: 10.3866/PKU.WHXB19880520
Abstract:
A spherical model for solid state reactions controlled by diffusion has been developed in this paper. Two equations between the conversion ratio and reaction time and temperature were derived from the model. The equations were tested by the solid state reaction of Synthesis of Si_3N_4 from silicon and nitrogen. The results show that the model is applicable for solid state reactions controlled by diffusion.
A spherical model for solid state reactions controlled by diffusion has been developed in this paper. Two equations between the conversion ratio and reaction time and temperature were derived from the model. The equations were tested by the solid state reaction of Synthesis of Si_3N_4 from silicon and nitrogen. The results show that the model is applicable for solid state reactions controlled by diffusion.
1988, 4(05): 545-548
doi: 10.3866/PKU.WHXB19880521
Abstract:
The dispersed fluorescence spectra of Pb_2 dimer were recorded from the excitation of Ar~+ laser in HPOR. By the detailed spectroscopic analysis for this well-resolved fluorescence spectra, the ground state of pb_2 molecule and one of its electronically excited state were assigned preliminarily to be X~1∑_g~+ and F′Ⅱ_u state respectively.
The spectral constants of the X and F are ω_e″=108.5 cm~(-1),ω_e″X_e″ = 0.209 cm~(-1), ω_e′=152.4 cm~(-1), ω_e′X_e′=0.636 cm~(-1) and T_e=19818,1 cm~(-1)., respectively
The dispersed fluorescence spectra of Pb_2 dimer were recorded from the excitation of Ar~+ laser in HPOR. By the detailed spectroscopic analysis for this well-resolved fluorescence spectra, the ground state of pb_2 molecule and one of its electronically excited state were assigned preliminarily to be X~1∑_g~+ and F′Ⅱ_u state respectively.
The spectral constants of the X and F are ω_e″=108.5 cm~(-1),ω_e″X_e″ = 0.209 cm~(-1), ω_e′=152.4 cm~(-1), ω_e′X_e′=0.636 cm~(-1) and T_e=19818,1 cm~(-1)., respectively
1988, 4(05): 549-553
doi: 10.3866/PKU.WHXB19880522
Abstract:
The isomerization products of fac- and mer-[Co(β-ala)_3] in neutral and acidic media were separated with Na~+-type SP-Sephaex C-25 column and determined by spectrophotometry. At high temperatures(>90 ℃)the fac-isomer readily isomerizes to mer-[Co(β-ala)_3] and simultaneously hydrolyzes to yield a brown slurry in neutral solution.However, in acidic solution hydrolysis does not occur, the products are mer-isomer and a small amount of red complex cation, which is strongly adsorbed at the top of SP-Scphadex column and would probably be the fac-[Co(β-ala)_2[Co(β-alaH)(H_2O]~+.
At 90 ℃ the mer-[Co(β-ala)_3]is hydrolyzed rapidly to yield a brown precipitate in neutral solution and isomerizes in small amount to fac-isomer. In acidic solution the mer-isomer isomerizes slightly to fac-isomer, and at the top of SP-Sephadex column, a violet complex cation which would probably be mer-[Co(β-ala)_2(β-alaH)(H_2O]~+ is abserved.
The kinetic parameters of isomerization of fac-[Co(β-ala)_3] in neutral, basic and acidic solutions have been determined with spectrophotometric method at 534 nm. The resufts obtained indicate that reaction rates v with respect to fac-[Co(β-ala)_3] in neutral, basic and acidic media are all in first order, and under constant initial concentration of fac-[Co(β-ala)_3] the reaction rates v with respect zation of fac-[Co(β-ala)_3] in neutral, [OH~-]=4.04×10~(-4) molL~(-1), [HCl]=1.56×10~(-2) molL~(-1) and [HClO_4]=1.56×10~(-2) molL~(-1) media at 90 ℃ are 0.0195, 57.3, 3.43 and 0.978 min~(-1) while the activation energies are 194.2, 103.1, 134.1 and 113.8 kJ.mol~(-1) respectively.
The isomerization products of fac- and mer-[Co(β-ala)_3] in neutral and acidic media were separated with Na~+-type SP-Sephaex C-25 column and determined by spectrophotometry. At high temperatures(>90 ℃)the fac-isomer readily isomerizes to mer-[Co(β-ala)_3] and simultaneously hydrolyzes to yield a brown slurry in neutral solution.However, in acidic solution hydrolysis does not occur, the products are mer-isomer and a small amount of red complex cation, which is strongly adsorbed at the top of SP-Scphadex column and would probably be the fac-[Co(β-ala)_2[Co(β-alaH)(H_2O]~+.
At 90 ℃ the mer-[Co(β-ala)_3]is hydrolyzed rapidly to yield a brown precipitate in neutral solution and isomerizes in small amount to fac-isomer. In acidic solution the mer-isomer isomerizes slightly to fac-isomer, and at the top of SP-Sephadex column, a violet complex cation which would probably be mer-[Co(β-ala)_2(β-alaH)(H_2O]~+ is abserved.
The kinetic parameters of isomerization of fac-[Co(β-ala)_3] in neutral, basic and acidic solutions have been determined with spectrophotometric method at 534 nm. The resufts obtained indicate that reaction rates v with respect to fac-[Co(β-ala)_3] in neutral, basic and acidic media are all in first order, and under constant initial concentration of fac-[Co(β-ala)_3] the reaction rates v with respect zation of fac-[Co(β-ala)_3] in neutral, [OH~-]=4.04×10~(-4) molL~(-1), [HCl]=1.56×10~(-2) molL~(-1) and [HClO_4]=1.56×10~(-2) molL~(-1) media at 90 ℃ are 0.0195, 57.3, 3.43 and 0.978 min~(-1) while the activation energies are 194.2, 103.1, 134.1 and 113.8 kJ.mol~(-1) respectively.
1988, 4(05): 554-557
doi: 10.3866/PKU.WHXB19880523
Abstract:
A new chemical oscillating system involving aminoacid——the system of aspartic acid-BrO_3~--Mn~(2+)-Fe(Phen)_3~2-H_2SO_4 has been described and its oscillating feature has been studied. It is shown that chloride ion, bromide ion,acetone, bromine and acrylonitrile inhibit the oscillation. The analysis of reacting products shows that oxalacetie acid and bromooxaiacetie acid are two of the products of this oscillating reaction. According to the experimental facts and the FKN mechanism, the model, called the Br_2-hydrolysis control model, has been proposed. The oscillating figure calculated from this model is in od agreement with the experimental figure. With this model we give the successful explanation of all the experimental observations and the role of the two metal ions in the oscillating reaction is described.
A new chemical oscillating system involving aminoacid——the system of aspartic acid-BrO_3~--Mn~(2+)-Fe(Phen)_3~2-H_2SO_4 has been described and its oscillating feature has been studied. It is shown that chloride ion, bromide ion,acetone, bromine and acrylonitrile inhibit the oscillation. The analysis of reacting products shows that oxalacetie acid and bromooxaiacetie acid are two of the products of this oscillating reaction. According to the experimental facts and the FKN mechanism, the model, called the Br_2-hydrolysis control model, has been proposed. The oscillating figure calculated from this model is in od agreement with the experimental figure. With this model we give the successful explanation of all the experimental observations and the role of the two metal ions in the oscillating reaction is described.
1988, 4(05): 558-560
doi: 10.3866/PKU.WHXB19880524
Abstract:
XPS studies show that the dominant surface oxide is Nb_2O_5 for air exposed Nb metal at both room temperature and 300 ℃. The thickness of the room temperature Nb_2O_5 formed by 18 hours air exposure is less than the photoelectron escape depth. The room temperature Nb_2O_5 can be converted into Nb metal after heating the sample in vacuum at 350 ℃ for 30 minutes. If the surface Nb_2O_5 is formed at above 300 ℃, however, it can not be converted into Nb metal after heating the sample in vacuum at 350 ℃ for as long as 4 hours. It is suggested that the very thin room temperature surface Nb_2O_5 can differ from the bulk Nb_2O_5 on thermodynamical property.
XPS studies show that the dominant surface oxide is Nb_2O_5 for air exposed Nb metal at both room temperature and 300 ℃. The thickness of the room temperature Nb_2O_5 formed by 18 hours air exposure is less than the photoelectron escape depth. The room temperature Nb_2O_5 can be converted into Nb metal after heating the sample in vacuum at 350 ℃ for 30 minutes. If the surface Nb_2O_5 is formed at above 300 ℃, however, it can not be converted into Nb metal after heating the sample in vacuum at 350 ℃ for as long as 4 hours. It is suggested that the very thin room temperature surface Nb_2O_5 can differ from the bulk Nb_2O_5 on thermodynamical property.
