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2005 Volume 21 Issue 12
2005, 21(12): 1331-1336
doi: 10.3866/PKU.WHXB20051201
Abstract:
The potential energy surfaces for the abstraction reaction of germylene with thiirane have been char-acterized in detail using density functional theory (DFT). All the stationary points were determined at the B3LYP/6-311++G (d, p) level of the theory. The transition states both to the reactants and the product direction in the reaction paths were examined by using the intrinsic reaction coordinate (IRC). The major conclusion is as follows: the reaction is in two steps, (1) germylenes and thiirane form an intermediate complex through an exothermal reaction without any barrier; (2) the intermediate complexes isomerize to give the products. Furthermore, the stronger the π-donation is or the more electronegative the substituents are the bigger the ΔEST of X2Ge, the higher the activation energy for the abstraction reactions will be. In other words, it is the electronic factors, rather than the steric factors, that play a decisive role in the chemistry of the germylene species. A configuration mixing model based on the work of Pross and Shaik is used to rationalize the computational results.
The potential energy surfaces for the abstraction reaction of germylene with thiirane have been char-acterized in detail using density functional theory (DFT). All the stationary points were determined at the B3LYP/6-311++G (d, p) level of the theory. The transition states both to the reactants and the product direction in the reaction paths were examined by using the intrinsic reaction coordinate (IRC). The major conclusion is as follows: the reaction is in two steps, (1) germylenes and thiirane form an intermediate complex through an exothermal reaction without any barrier; (2) the intermediate complexes isomerize to give the products. Furthermore, the stronger the π-donation is or the more electronegative the substituents are the bigger the ΔEST of X2Ge, the higher the activation energy for the abstraction reactions will be. In other words, it is the electronic factors, rather than the steric factors, that play a decisive role in the chemistry of the germylene species. A configuration mixing model based on the work of Pross and Shaik is used to rationalize the computational results.
2005, 21(12): 1337-1342
doi: 10.3866/PKU.WHXB20051202
Abstract:
A series of Ni-V/γ-Al2O3 catalysts were prepared and used in the one-step synthesis of aniline from benzene, hydrogen peroxide, and aqueous ammonia and/or urea. It was found that both Ni/γ-Al2O3 and V/γ-Al2O3 catalysts were effective for the activation of C—H bond of benzene, and the co-existed Ni and V on γ-Al2O3 exhibited synergetic effects which promoted the formation of aniline. When the molar ratio of Ni to V was 5.5, the Ni-V/γ-Al2O3 catalyst showed the highest activity and selectivity for aniline. The highest selectivity to aniline obtained was 85%, which was far higher than that to the by-product phenol. The optimal conditions obtained in present work were as the following: reaction time, 2 h; reaction temperature, about 333 K. Urea was found to be one possible aminating agent for this one-step process in basic reaction media. The synergic effect between ammonia and urea under the conditions investigated was found favorable for the production of aniline.
A series of Ni-V/γ-Al2O3 catalysts were prepared and used in the one-step synthesis of aniline from benzene, hydrogen peroxide, and aqueous ammonia and/or urea. It was found that both Ni/γ-Al2O3 and V/γ-Al2O3 catalysts were effective for the activation of C—H bond of benzene, and the co-existed Ni and V on γ-Al2O3 exhibited synergetic effects which promoted the formation of aniline. When the molar ratio of Ni to V was 5.5, the Ni-V/γ-Al2O3 catalyst showed the highest activity and selectivity for aniline. The highest selectivity to aniline obtained was 85%, which was far higher than that to the by-product phenol. The optimal conditions obtained in present work were as the following: reaction time, 2 h; reaction temperature, about 333 K. Urea was found to be one possible aminating agent for this one-step process in basic reaction media. The synergic effect between ammonia and urea under the conditions investigated was found favorable for the production of aniline.
2005, 21(12): 1343-1346
doi: 10.3866/PKU.WHXB20051203
Abstract:
Based on the relativistic effective core potential (RECP/SDD) for Pd atom and AUG-cc-pVTZ basis function for N atom, the structure of PdN and PdN2 have been optimized using B3LYP method, and the thermodynamic functions for PdN and PdN2 have been calculated. The vibrational energy, electronic and vibrational entropy of the molecules in their solid states are assumed, ΔHӨ, ΔSӨ and ΔGӨ and nitrogen equilibrium pressures of the nitrogenating reaction have been calculated based on this approximation. It is deduced that at 1.01325×105 Pa and 298.15～998.15 K, adsorption of N2 on Pd surface proceeds as Pd(s) + N2 = PdN2(s). The formation enthalpy for PdN(s) at 298.15 K is 254.37 kJ·mol-1, and the formation enthalpy for PdN2(s) at 298.15 K is －80.59 kJ·mol-1. The nitrogen equilibrium pressure is about 100 times of the hydrogen equilibrium pressure, so it is difficult for Pd to adsorb N2.
Based on the relativistic effective core potential (RECP/SDD) for Pd atom and AUG-cc-pVTZ basis function for N atom, the structure of PdN and PdN2 have been optimized using B3LYP method, and the thermodynamic functions for PdN and PdN2 have been calculated. The vibrational energy, electronic and vibrational entropy of the molecules in their solid states are assumed, ΔHӨ, ΔSӨ and ΔGӨ and nitrogen equilibrium pressures of the nitrogenating reaction have been calculated based on this approximation. It is deduced that at 1.01325×105 Pa and 298.15～998.15 K, adsorption of N2 on Pd surface proceeds as Pd(s) + N2 = PdN2(s). The formation enthalpy for PdN(s) at 298.15 K is 254.37 kJ·mol-1, and the formation enthalpy for PdN2(s) at 298.15 K is －80.59 kJ·mol-1. The nitrogen equilibrium pressure is about 100 times of the hydrogen equilibrium pressure, so it is difficult for Pd to adsorb N2.
2005, 21(12): 1347-1351
doi: 10.3866/PKU.WHXB20051204
Abstract:
The reaction mechanism of HNCS (isothiocyanic acid) and C2H(X2Π) radical has been investigated by using the density functional theory (DFT) at the B3LYP/6-311+G** level. The single point energies along the minimum energy path have been further refined at the UQCISD (T)/6-311+G** level. The dual-level direct dynamics method was employed to gain the information of potential energy surface for the reaction of HNCS with C2H(X2Π) radical. The rate constants were calculated over the temperature range of 250～2500 K by using variational transition state theory, and the small-curvature tunneling is included. The results show that the reaction mechanism of HNCS and C2H(X2Π) radical involves three path and NCS+C2H2 are main products. It is found that the rate constants of the reaction are positively dependent on temperature. The variational effect for the rate constant calculation is very small in whole temperature range and the small-curvature tunnelling effect is only important in the lower temperature range. The reaction is exothermic.
The reaction mechanism of HNCS (isothiocyanic acid) and C2H(X2Π) radical has been investigated by using the density functional theory (DFT) at the B3LYP/6-311+G** level. The single point energies along the minimum energy path have been further refined at the UQCISD (T)/6-311+G** level. The dual-level direct dynamics method was employed to gain the information of potential energy surface for the reaction of HNCS with C2H(X2Π) radical. The rate constants were calculated over the temperature range of 250～2500 K by using variational transition state theory, and the small-curvature tunneling is included. The results show that the reaction mechanism of HNCS and C2H(X2Π) radical involves three path and NCS+C2H2 are main products. It is found that the rate constants of the reaction are positively dependent on temperature. The variational effect for the rate constant calculation is very small in whole temperature range and the small-curvature tunnelling effect is only important in the lower temperature range. The reaction is exothermic.
2005, 21(12): 1352-1356
doi: 10.3866/PKU.WHXB20051205
Abstract:
The optical emission spectroscopy of NO/N2 in dielectric barrier discharge (DBD) plasmas using a. c. with frequeucies of 50 Hz and 5 kHz has been studied at atmospheric pressure. Excited-state nitrogen atom was detected at 632, 674.5, 715.5 and 742 nm. The concentrations of the mixtures were measured by using chemilluminescence NOx analyzer and N2O infrared gas analyzer; the production of O2 was also monitored by an on-line mass spectrograph after the discharge. The reaction mechanism of the removal of NO in N2 in DBD plasma was discussed.
The optical emission spectroscopy of NO/N2 in dielectric barrier discharge (DBD) plasmas using a. c. with frequeucies of 50 Hz and 5 kHz has been studied at atmospheric pressure. Excited-state nitrogen atom was detected at 632, 674.5, 715.5 and 742 nm. The concentrations of the mixtures were measured by using chemilluminescence NOx analyzer and N2O infrared gas analyzer; the production of O2 was also monitored by an on-line mass spectrograph after the discharge. The reaction mechanism of the removal of NO in N2 in DBD plasma was discussed.
2005, 21(12): 1357-1362
doi: 10.3866/PKU.WHXB20051206
Abstract:
Two rare earths composite oxides of La0.5RE0.3Sr0.2FeO3－δ(RE = Nd, Ce, Sm) with A-site doped Sr2+ samples were synthesized by Glycine-Nitrate processes (GNP). The formation process of the perovskite structure was analyzed by means of X-ray powder diffraction and TG-DSC. The relative density of the ceramics was measured by Archimedes method, and the electrical conductivity of the samples was studied by four-probe technique. The results show that the sample for RE = Nd presents a single perovskite-type phase with a cubic symmetry after sintering at 1200 ℃ for 2 h, while the samples with Ce doped showed a separated cubic phase of CeO2, and the specimen doped with Sm is a cubic perovskite-type phase accompanied by some faint impure peaks. The electrical conductivity of La0.5Nd0.3Sr0.2FeO3－δ (LNSF) sample obtained from being sintered at 1250 ℃ for 2 h was over 100 S•cm-1, significantly higher than that of the La0.5Ce0.3Sr0.2FeO3－δ(LCSF) and La0.5Sm0.3Sr0.2FeO3－δ (LSSF) at the same conditions. The results indicate that La0.5Nd0.3Sr0.2FeO3－δ may be a suitable cathode material for intermediate temperature SOFC.
Two rare earths composite oxides of La0.5RE0.3Sr0.2FeO3－δ(RE = Nd, Ce, Sm) with A-site doped Sr2+ samples were synthesized by Glycine-Nitrate processes (GNP). The formation process of the perovskite structure was analyzed by means of X-ray powder diffraction and TG-DSC. The relative density of the ceramics was measured by Archimedes method, and the electrical conductivity of the samples was studied by four-probe technique. The results show that the sample for RE = Nd presents a single perovskite-type phase with a cubic symmetry after sintering at 1200 ℃ for 2 h, while the samples with Ce doped showed a separated cubic phase of CeO2, and the specimen doped with Sm is a cubic perovskite-type phase accompanied by some faint impure peaks. The electrical conductivity of La0.5Nd0.3Sr0.2FeO3－δ (LNSF) sample obtained from being sintered at 1250 ℃ for 2 h was over 100 S•cm-1, significantly higher than that of the La0.5Ce0.3Sr0.2FeO3－δ(LCSF) and La0.5Sm0.3Sr0.2FeO3－δ (LSSF) at the same conditions. The results indicate that La0.5Nd0.3Sr0.2FeO3－δ may be a suitable cathode material for intermediate temperature SOFC.
2005, 21(12): 1363-1367
doi: 10.3866/PKU.WHXB20051207
Abstract:
TiO2/SiO2 aerogel microspheres were prepared by using TiOSO4 and silica sols as raw materials, and formamide as a drying control chemical additive, which was used to improve the gel texture and the structure evolution. Wet gel microspheres were formed by sol-gel process in W/O emulsion, and then aged by a successively solvent exchanging of alcohol, tetraethylorthosilicate (TEOS)/alcohol and alcohol at a certain temperature. The aged gel microspheres were dried at ambient pressure to obtain TiO2/SiO2 aerogel microspheres. The aerogel microsphere samples were characterized with optical microscope, SEM, TEM and BET techniques. The results show that the aerogel microsphere samples were comprised of dispersed TiO2, and SiO2 nanoparticles with sizes of about 15 nm. The density of the typical sample is 177 kg•m-3, the specific surface area is 372 m2•g-1 and the average pore size is 22.78 nm with porosity of 92.0%. By changing the preparation condition, the diameters of TiO2/SiO2 aerogel microspheres can be varied in the range of 10 m to 200 m, the densities in the range of 150～300 kg•m-3, the specific surface areas in 300～400 m2•g-1, and the average pore sizes in the range of 18.71～22.78 nm.
TiO2/SiO2 aerogel microspheres were prepared by using TiOSO4 and silica sols as raw materials, and formamide as a drying control chemical additive, which was used to improve the gel texture and the structure evolution. Wet gel microspheres were formed by sol-gel process in W/O emulsion, and then aged by a successively solvent exchanging of alcohol, tetraethylorthosilicate (TEOS)/alcohol and alcohol at a certain temperature. The aged gel microspheres were dried at ambient pressure to obtain TiO2/SiO2 aerogel microspheres. The aerogel microsphere samples were characterized with optical microscope, SEM, TEM and BET techniques. The results show that the aerogel microsphere samples were comprised of dispersed TiO2, and SiO2 nanoparticles with sizes of about 15 nm. The density of the typical sample is 177 kg•m-3, the specific surface area is 372 m2•g-1 and the average pore size is 22.78 nm with porosity of 92.0%. By changing the preparation condition, the diameters of TiO2/SiO2 aerogel microspheres can be varied in the range of 10 m to 200 m, the densities in the range of 150～300 kg•m-3, the specific surface areas in 300～400 m2•g-1, and the average pore sizes in the range of 18.71～22.78 nm.
2005, 21(12): 1368-1372
doi: 10.3866/PKU.WHXB20051208
Abstract:
The hybrid density functional B3LYP has been used with basis set 6-31G* to study the equilibrium geometry, electronic structure, vibrational properties, polarizability and hyperpolarizability of ring-like structure of Al8P8 cluster. The bond properties of the cluster were analyzed by using natural bond orbital (NBO) method, covalent bonds coexisted with ionic bonds in the cluster, P and Al atoms have different hybridizations in different orbitals. The optimized structure is two-layer ring-like structure. The density of states for Al8P8 cluster shows a semiconductor-like property. The primary IR and Raman vibration located at 530.65 cm-1 and 366.54 cm-1 respectively.
The hybrid density functional B3LYP has been used with basis set 6-31G* to study the equilibrium geometry, electronic structure, vibrational properties, polarizability and hyperpolarizability of ring-like structure of Al8P8 cluster. The bond properties of the cluster were analyzed by using natural bond orbital (NBO) method, covalent bonds coexisted with ionic bonds in the cluster, P and Al atoms have different hybridizations in different orbitals. The optimized structure is two-layer ring-like structure. The density of states for Al8P8 cluster shows a semiconductor-like property. The primary IR and Raman vibration located at 530.65 cm-1 and 366.54 cm-1 respectively.
2005, 21(12): 1373-1377
doi: 10.3866/PKU.WHXB20051209
Abstract:
A novel precursor for BCN compound, C3H6N6(H3BO3)2, was synthesized with C3H6N6 melamine and H3BO3 as raw materials in aqueous solution. The precursor was characterized by elementary analysis, XRD, FT-IR, electrospray mass spectrometry and single crystal X-ray diffraction. It revealed that the precursor contained the characteristic groups of C3H6N6 and H3BO3 such as triazine ring, NH2, and B—OH. The precursor crystallized in monoclinic space group P2l/c, with the cell parameters a=0.35970(7) nm, b=2.0105(4) nm, c=1.4112(3) nm, β=92.07(3)°, Z=4. One crystallographically distinct C3H6N6 molecule and two H3BO3 molecules constituted the asymmetric unit of the precursor. A 3D supramolecular network was constructed by different hydrogen-bonding interactions between C3H6N6 and H3BO3 molecules. The precursor was further pyrolyzed at 1900 ℃ under flowing N2 atmosphere. XRD and XPS analysis were applied for the characterization of the pyrolysis product. The results indicated that a new BCN ternary compound with turbostratic graphite structure was obtained. B—N, B—C, and C—N chemical bonds were established and there was no phase separation between graphite and h-BN, which suggests an atomic-level hybrid of B, C, and N elements in the compound. The BCN compound has lower carbon content and its empirical formula can be expressed as B3CN3.
A novel precursor for BCN compound, C3H6N6(H3BO3)2, was synthesized with C3H6N6 melamine and H3BO3 as raw materials in aqueous solution. The precursor was characterized by elementary analysis, XRD, FT-IR, electrospray mass spectrometry and single crystal X-ray diffraction. It revealed that the precursor contained the characteristic groups of C3H6N6 and H3BO3 such as triazine ring, NH2, and B—OH. The precursor crystallized in monoclinic space group P2l/c, with the cell parameters a=0.35970(7) nm, b=2.0105(4) nm, c=1.4112(3) nm, β=92.07(3)°, Z=4. One crystallographically distinct C3H6N6 molecule and two H3BO3 molecules constituted the asymmetric unit of the precursor. A 3D supramolecular network was constructed by different hydrogen-bonding interactions between C3H6N6 and H3BO3 molecules. The precursor was further pyrolyzed at 1900 ℃ under flowing N2 atmosphere. XRD and XPS analysis were applied for the characterization of the pyrolysis product. The results indicated that a new BCN ternary compound with turbostratic graphite structure was obtained. B—N, B—C, and C—N chemical bonds were established and there was no phase separation between graphite and h-BN, which suggests an atomic-level hybrid of B, C, and N elements in the compound. The BCN compound has lower carbon content and its empirical formula can be expressed as B3CN3.
2005, 21(12): 1378-1383
doi: 10.3866/PKU.WHXB20051210
Abstract:
Mechanisms of adsorption and precipitation of Zn(II) on γ-MnOOH-water interfaces were studied using DFT (density functional theory) and XANES (X-ray absorption near edge structure) simulation at different pH conditions. Optimal adsorption structures showed that only hydrolyzed clusters of double-edge-link mode could explain the H+ release mechanism and experimental bond-length values. Adsorption energy calculations indicated that the stability sequence of adsorption modes was in the order of double-edge (DE)>double-corner (DC)>single-edge-B (SE-B)> single-edge-A (SE-A). Hydrolysis energy calculations showed that the adsorbed Zn2+ of all the linkage modes hydrolyzed easier than Zn2+ in solution. XANES simulations of optimal adsorption clusters did not accord well with experimental results, indicating that mechanisms other than surface adsorption were involved in the adsorption samples. Surface precipitation species were formed in adsorption samples of pH > 7.5, where mixtures of Zn—O tetrahedron and Zn—O octahedron were arranged in the way similar to that of Zn5(OH)6(CO3)2. Simulated and experimental XANES spectrums of Zn5(OH)6(CO3)2 were very close to that of adsorption samples of pH > 7.5. At pH < 7.0, Zn(II) was mainly adsorbed in edge link mode on the surface of γ-MnOOH.
Mechanisms of adsorption and precipitation of Zn(II) on γ-MnOOH-water interfaces were studied using DFT (density functional theory) and XANES (X-ray absorption near edge structure) simulation at different pH conditions. Optimal adsorption structures showed that only hydrolyzed clusters of double-edge-link mode could explain the H+ release mechanism and experimental bond-length values. Adsorption energy calculations indicated that the stability sequence of adsorption modes was in the order of double-edge (DE)>double-corner (DC)>single-edge-B (SE-B)> single-edge-A (SE-A). Hydrolysis energy calculations showed that the adsorbed Zn2+ of all the linkage modes hydrolyzed easier than Zn2+ in solution. XANES simulations of optimal adsorption clusters did not accord well with experimental results, indicating that mechanisms other than surface adsorption were involved in the adsorption samples. Surface precipitation species were formed in adsorption samples of pH > 7.5, where mixtures of Zn—O tetrahedron and Zn—O octahedron were arranged in the way similar to that of Zn5(OH)6(CO3)2. Simulated and experimental XANES spectrums of Zn5(OH)6(CO3)2 were very close to that of adsorption samples of pH > 7.5. At pH < 7.0, Zn(II) was mainly adsorbed in edge link mode on the surface of γ-MnOOH.
2005, 21(12): 1384-1389
doi: 10.3866/PKU.WHXB20051211
Abstract:
Many chemical and biochemical phenomena take place in solution, making the evaluation of solvent effects a critical element for understanding these phenomena. The effect of the solvent on activity coefficients of electrolytes was of interest to chemists and chemical engineers because it may provide useful information. In this paper the thermodynamic properties of HCl-MgSO4-H2O system have been studied by EMF (electromotive force) measurement in the cells without liquid junction Pt, H2 (101.325 kPa )│HCl (m＝0.01000 mol·kg-1)│AgCl-Ag (A) Pt, H2 (101.325 kPa )│HCl (mA), MgSO4 (mB) , H2O│AgCl-Ag (B) at constant total ionic strength I=0.2, 0.4, 0.6, 0.8, 1.0, 1.5 mol·kg-1 and yB=0, 0.10, 0.20, 0.30, 0.50, 0.70 at different temperatures from 278.15 to 318.15 K. Because of secondary dissociation of sulfuric acid in the system, the concentrations of hydrogen ions in equilibrium system have been determined by mathematic iterative technique. The standard electrode of AgCl-Ag in pure water has been determined according to the method of Bates. The activity coefficients of HCl lgγA in the HCl-MgSO4-H2O system have been determined from cell (B). The results show that the activity coefficients of HCl in the solutions still obey Harned’s rule and lgγA is a linear function of the absolute temperature at constant composition of the mixture.
Many chemical and biochemical phenomena take place in solution, making the evaluation of solvent effects a critical element for understanding these phenomena. The effect of the solvent on activity coefficients of electrolytes was of interest to chemists and chemical engineers because it may provide useful information. In this paper the thermodynamic properties of HCl-MgSO4-H2O system have been studied by EMF (electromotive force) measurement in the cells without liquid junction Pt, H2 (101.325 kPa )│HCl (m＝0.01000 mol·kg-1)│AgCl-Ag (A) Pt, H2 (101.325 kPa )│HCl (mA), MgSO4 (mB) , H2O│AgCl-Ag (B) at constant total ionic strength I=0.2, 0.4, 0.6, 0.8, 1.0, 1.5 mol·kg-1 and yB=0, 0.10, 0.20, 0.30, 0.50, 0.70 at different temperatures from 278.15 to 318.15 K. Because of secondary dissociation of sulfuric acid in the system, the concentrations of hydrogen ions in equilibrium system have been determined by mathematic iterative technique. The standard electrode of AgCl-Ag in pure water has been determined according to the method of Bates. The activity coefficients of HCl lgγA in the HCl-MgSO4-H2O system have been determined from cell (B). The results show that the activity coefficients of HCl in the solutions still obey Harned’s rule and lgγA is a linear function of the absolute temperature at constant composition of the mixture.
2005, 21(12): 1390-1394
doi: 10.3866/PKU.WHXB20051212
Abstract:
The geometric structure and Raman frequencies of meso-monophenylporphyrin (H2MPP) were studied by density-functional-theory (DFT). The calculation indicates that meso-monophenyl substitution induces larger distortion to meso-position than to pyrrole ring. All calculated frequencies were scaled with a single factor of 0.971, which gives acceptable results compared with experimental data (the RMS is 6.7 cm-1). The measured Raman spectra were discussed and the assignment of in-plane vibrational normal mode of porphyrin ring was given on the basis of theoretical calculation. Further analysis indicates the splits of some in-plane vibrational normal modes of porphyrin ring (for instance ν6, ν20, ν24, and ν32 mode), which was attributed to the diversification of the structure around Cm atoms and pyrrole structure induced by meso-monophenyl substitution.
The geometric structure and Raman frequencies of meso-monophenylporphyrin (H2MPP) were studied by density-functional-theory (DFT). The calculation indicates that meso-monophenyl substitution induces larger distortion to meso-position than to pyrrole ring. All calculated frequencies were scaled with a single factor of 0.971, which gives acceptable results compared with experimental data (the RMS is 6.7 cm-1). The measured Raman spectra were discussed and the assignment of in-plane vibrational normal mode of porphyrin ring was given on the basis of theoretical calculation. Further analysis indicates the splits of some in-plane vibrational normal modes of porphyrin ring (for instance ν6, ν20, ν24, and ν32 mode), which was attributed to the diversification of the structure around Cm atoms and pyrrole structure induced by meso-monophenyl substitution.
2005, 21(12): 1395-1398
doi: 10.3866/PKU.WHXB20051213
Abstract:
The photon-current conversion properties of ITO/poly(3-hexylthiophene) (ITO/P3HT) and nanostructured TiO2/P3HT film electrode were studied by using the photocurrent action spectra, the photocurrent dependence of potential and UV-Vis absorption spectra. The bandgap of P3HT film is 1.89 eV. The diagram of energy level of P3HT film was determined with cyclic voltammetry and photoelectrochemical method. The conduction band of P3HT film is －5.4 eV. The nanostructured TiO2/P3HT electrode can enlarge the visible optical absorption region and obviously increase the photocurrent in visible region. The p-n heterojunction exists in the TiO2/P3HT nanostructured electrode which favors the separation of electron/hole pairs. Thus, the photon-electron conversion efficiency could be improved.
The photon-current conversion properties of ITO/poly(3-hexylthiophene) (ITO/P3HT) and nanostructured TiO2/P3HT film electrode were studied by using the photocurrent action spectra, the photocurrent dependence of potential and UV-Vis absorption spectra. The bandgap of P3HT film is 1.89 eV. The diagram of energy level of P3HT film was determined with cyclic voltammetry and photoelectrochemical method. The conduction band of P3HT film is －5.4 eV. The nanostructured TiO2/P3HT electrode can enlarge the visible optical absorption region and obviously increase the photocurrent in visible region. The p-n heterojunction exists in the TiO2/P3HT nanostructured electrode which favors the separation of electron/hole pairs. Thus, the photon-electron conversion efficiency could be improved.
2005, 21(12): 1399-1402
doi: 10.3866/PKU.WHXB20051214
Abstract:
Stable electrode modified by aminylferrocene/L-cysteine(L-Cys) was fabricated successfully by linking aminylferrocene to L-Cys self-assembled monolayer(SAM) with coupling reagent. The modified electrode exhibits a pair of reversible redox peaks in pH 7.0 phosphate buffer solution. The electrochemical behaviors of the modified electrode were explored in detail with cyclic voltammetry and a.c. impedance. The apparent electron transfer coefficient and standard rate constant were calculated to be 0.66 and 6.86 s-1 for the modified electrode respectively. The modified electrode shows electrocatalytic activity for oxidation of epinephrine (EP) in pH 7.0 phosphate buffer solution. The peak current was proportional to the concentration of EP in the range of 2.0×10-7～1.0×10-5 mol·dm-3.
Stable electrode modified by aminylferrocene/L-cysteine(L-Cys) was fabricated successfully by linking aminylferrocene to L-Cys self-assembled monolayer(SAM) with coupling reagent. The modified electrode exhibits a pair of reversible redox peaks in pH 7.0 phosphate buffer solution. The electrochemical behaviors of the modified electrode were explored in detail with cyclic voltammetry and a.c. impedance. The apparent electron transfer coefficient and standard rate constant were calculated to be 0.66 and 6.86 s-1 for the modified electrode respectively. The modified electrode shows electrocatalytic activity for oxidation of epinephrine (EP) in pH 7.0 phosphate buffer solution. The peak current was proportional to the concentration of EP in the range of 2.0×10-7～1.0×10-5 mol·dm-3.
2005, 21(12): 1403-1406
doi: 10.3866/PKU.WHXB20051215
Abstract:
Aggregation numbers of micelle of citric triester of tridodecyl triammonium (CTTTA) were determined by steady-state fluorescence probe method in which pyrene was used as fluorescence probe and cetylpyridinium chloride (CPC) as quencher. Satisfactory results were obtained when the solution of surfactant was prepared with saturated aqueous solution of pyrene and the concentrations of CPC were selected in 0.1~0.3 mmol·L-1. The experimental results show that the aggregation number (N) increases linearly with the increase of CTTTA concentra-tion in the range of 6~10 times of cmc and critical micellar aggregation number Nm can be extrapolated from N－c curve. Critical micelle concentration (cmc) was investigated by steady-state fluorescence probe and compared with surface tentsion method.
Aggregation numbers of micelle of citric triester of tridodecyl triammonium (CTTTA) were determined by steady-state fluorescence probe method in which pyrene was used as fluorescence probe and cetylpyridinium chloride (CPC) as quencher. Satisfactory results were obtained when the solution of surfactant was prepared with saturated aqueous solution of pyrene and the concentrations of CPC were selected in 0.1~0.3 mmol·L-1. The experimental results show that the aggregation number (N) increases linearly with the increase of CTTTA concentra-tion in the range of 6~10 times of cmc and critical micellar aggregation number Nm can be extrapolated from N－c curve. Critical micelle concentration (cmc) was investigated by steady-state fluorescence probe and compared with surface tentsion method.
2005, 21(12): 1407-1410
doi: 10.3866/PKU.WHXB20051216
Abstract:
The synthesis and luminescence study of a new platinum quinoxaline complex are reported. The complex, [(DPQ)Pt(acac)](DPQ=2, 3-diphenylquinoxaline, acac=2, 4-pentanedione) was synthesized by reaction of 2, 3-diphenylquinoxaline with K2PtCl4 and shows strong 1MLCT (singlet metal to ligand charge-transfer) and 3MLCT (triplet metal to ligand charge-transfer) absorption at 442 and 485 nm, respectively. Organic light emitting diode (OLED) with a configuration of [ITO/NPB(21 nm) /NPB∶7% (DPQ)Pt(acac)(17.5 nm) /BCP(7 nm)/ Alq3(21 nm)/ Mg∶Ag(10∶1)(120 nm)/Ag(10 nm)] (ITO: indium tin oxide; NPB: 4,4′-bis[N-(1-naphthyl)-N-phenyl-amino] biphenyl; BCP: 2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline; Alq3: tris(8-hydroxyquinoline) aluminum) shows a red emission at 632 nm with an external quantum efficiency of 0.66% at 7.2 V and brightness of 1516 cd·m-2 at 21 V. The power efficiency of the device was 0. 26 lm·W-1 at 7.2 V.
The synthesis and luminescence study of a new platinum quinoxaline complex are reported. The complex, [(DPQ)Pt(acac)](DPQ=2, 3-diphenylquinoxaline, acac=2, 4-pentanedione) was synthesized by reaction of 2, 3-diphenylquinoxaline with K2PtCl4 and shows strong 1MLCT (singlet metal to ligand charge-transfer) and 3MLCT (triplet metal to ligand charge-transfer) absorption at 442 and 485 nm, respectively. Organic light emitting diode (OLED) with a configuration of [ITO/NPB(21 nm) /NPB∶7% (DPQ)Pt(acac)(17.5 nm) /BCP(7 nm)/ Alq3(21 nm)/ Mg∶Ag(10∶1)(120 nm)/Ag(10 nm)] (ITO: indium tin oxide; NPB: 4,4′-bis[N-(1-naphthyl)-N-phenyl-amino] biphenyl; BCP: 2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline; Alq3: tris(8-hydroxyquinoline) aluminum) shows a red emission at 632 nm with an external quantum efficiency of 0.66% at 7.2 V and brightness of 1516 cd·m-2 at 21 V. The power efficiency of the device was 0. 26 lm·W-1 at 7.2 V.
2005, 21(12): 1411-1414
doi: 10.3866/PKU.WHXB20051217
Abstract:
The viscoelastic properties of lamellar liquid crystal, formed by non-ionic surfactant, were studied with small amplitude oscillation frequency sweep, and the effects of surfactant concentration, temperature , AgNO3 and as-produced Ag on them were investigated. The results show that, storage modulus (G′) and loss modulus(G″)increase with increasing surfactant concentration; three different kinds of frequency sweep curves appear with increasing temperature; AgNO3 and as-produced Ag have no effects on the shape of curves, but their effects on the magnitude of G′and G″are different for transitional and pure lamellar phases.
The viscoelastic properties of lamellar liquid crystal, formed by non-ionic surfactant, were studied with small amplitude oscillation frequency sweep, and the effects of surfactant concentration, temperature , AgNO3 and as-produced Ag on them were investigated. The results show that, storage modulus (G′) and loss modulus(G″)increase with increasing surfactant concentration; three different kinds of frequency sweep curves appear with increasing temperature; AgNO3 and as-produced Ag have no effects on the shape of curves, but their effects on the magnitude of G′and G″are different for transitional and pure lamellar phases.
2005, 21(12): 1415-1418
doi: 10.3866/PKU.WHXB20051218
Abstract:
The inclusion interaction between α-cyclodextrin (α-CD) with three cationic gemini surfactants, (CnN)2Cl2 (n =12, 14, 16), in aqueous solutions has been investigated by isothermal titration calorimetry, combining with 1H NMR at 293.15 K. The results show that these complexes are quite stable. As the number of carbon atoms in each of the hydrophobic tail, CnH2n+1, increases, the stoichiometry of stable complexes changes from 2∶1 to 6∶1. Corresponding to the same change of the hydrophobic chain, both formation enthalpy and formation entropy evidently decrease. The results also indicate that the association processes are enthalpy driven ones. The data of proton NMR spectroscopy indicate that chemical shift data of all protons in the α-CD molecule move to high field in the presence of the (C12H25N)2Cl2, which can be regarded as a microscopic evidence of the occurrence of inclusion interaction.
The inclusion interaction between α-cyclodextrin (α-CD) with three cationic gemini surfactants, (CnN)2Cl2 (n =12, 14, 16), in aqueous solutions has been investigated by isothermal titration calorimetry, combining with 1H NMR at 293.15 K. The results show that these complexes are quite stable. As the number of carbon atoms in each of the hydrophobic tail, CnH2n+1, increases, the stoichiometry of stable complexes changes from 2∶1 to 6∶1. Corresponding to the same change of the hydrophobic chain, both formation enthalpy and formation entropy evidently decrease. The results also indicate that the association processes are enthalpy driven ones. The data of proton NMR spectroscopy indicate that chemical shift data of all protons in the α-CD molecule move to high field in the presence of the (C12H25N)2Cl2, which can be regarded as a microscopic evidence of the occurrence of inclusion interaction.
2005, 21(12): 1419-1421
doi: 10.3866/PKU.WHXB20051219
Abstract:
Rodlike ZnO particles were directly precipitated by using zinc acetate and triethanolamine via a simple solution route at low temperature (90 ℃). The obtained ZnO particles were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), thermogravimetry (TG) and differential scanning calorimetry (DSC). The formation mechanism of the rodlike ZnO particles was explained in terms of the theory of crystal nucleation and growth.
Rodlike ZnO particles were directly precipitated by using zinc acetate and triethanolamine via a simple solution route at low temperature (90 ℃). The obtained ZnO particles were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), thermogravimetry (TG) and differential scanning calorimetry (DSC). The formation mechanism of the rodlike ZnO particles was explained in terms of the theory of crystal nucleation and growth.
2005, 21(12): 1422-1425
doi: 10.3866/PKU.WHXB20051220
Abstract:
The electrochemical oxidation of thiosulfate on platinum electrode was investigated by cyclic voltammetry. The results of experiments indicate that the behavior of electrochemical oxidation of thiosulfate depends on the pH and scan rate. When the pH value is 5 or 6, the cyclic voltammograms show three oxidation peaks at about 0.05 V, 0.58 V, and 1.02 V. With increasing pH value and decreasing the scan rate, the first oxidation peak becomes vary clear at about 0.05 V. Moreover the potential and the current of peaks have linear relationship with the logarithm and the square root of scan rate, respectively. When the pH value is 8~9, there are three obvious oxidation peaks at about 0.05 V, 0.91 V, and 1.22 V. The curves of cyclic voltammogram are crossed when decreasing the scan rate, and the system exhibits obvious electrochemical oscillations. But when the pH is over 10, the third oxidation peak disappears. The behavior of electrochemical oxidation of thiosulfate is very complicated and the mechanism varies along with the pH of the system.
The electrochemical oxidation of thiosulfate on platinum electrode was investigated by cyclic voltammetry. The results of experiments indicate that the behavior of electrochemical oxidation of thiosulfate depends on the pH and scan rate. When the pH value is 5 or 6, the cyclic voltammograms show three oxidation peaks at about 0.05 V, 0.58 V, and 1.02 V. With increasing pH value and decreasing the scan rate, the first oxidation peak becomes vary clear at about 0.05 V. Moreover the potential and the current of peaks have linear relationship with the logarithm and the square root of scan rate, respectively. When the pH value is 8~9, there are three obvious oxidation peaks at about 0.05 V, 0.91 V, and 1.22 V. The curves of cyclic voltammogram are crossed when decreasing the scan rate, and the system exhibits obvious electrochemical oscillations. But when the pH is over 10, the third oxidation peak disappears. The behavior of electrochemical oxidation of thiosulfate is very complicated and the mechanism varies along with the pH of the system.
2005, 21(12): 1426-1430
doi: 10.3866/PKU.WHXB20051221
Abstract:
The relationships between the structures of sodium alkylbenzensulfonates with additional side chains and surface properties, especially the influence of the side chains, were studied. From the surface tension measured in pure water and 0.171 mol·L-1 NaCl solutions, the following parameters were calculated：the critical micelle concentration (cmc), the surface excess concentration at surface saturation (Гmax), the minimum area (Amin), the surface tension at the cmc (γmax), the effectiveness of a surfactant in reducing surface tension (πcmc), the efficiency of a surfactant in reducing surface tension(pC20), the standard free energy change upon adsorption (ΔGad0). The main chain and side chain have different effects on the surface properties. With increasing the number of carbons in the main chain or the side chains, cmc decreases, but the decrease degree of cmc is quite different, the main chain decreases cmc to a greater degree than the side chains do. While the number of carbons increases, the main chain increases Гmax, but the side chain decreases Гmax. These surface properties were explained by the structures of sodium alkylbonzensulfonate with additional side chains.
The relationships between the structures of sodium alkylbenzensulfonates with additional side chains and surface properties, especially the influence of the side chains, were studied. From the surface tension measured in pure water and 0.171 mol·L-1 NaCl solutions, the following parameters were calculated：the critical micelle concentration (cmc), the surface excess concentration at surface saturation (Гmax), the minimum area (Amin), the surface tension at the cmc (γmax), the effectiveness of a surfactant in reducing surface tension (πcmc), the efficiency of a surfactant in reducing surface tension(pC20), the standard free energy change upon adsorption (ΔGad0). The main chain and side chain have different effects on the surface properties. With increasing the number of carbons in the main chain or the side chains, cmc decreases, but the decrease degree of cmc is quite different, the main chain decreases cmc to a greater degree than the side chains do. While the number of carbons increases, the main chain increases Гmax, but the side chain decreases Гmax. These surface properties were explained by the structures of sodium alkylbonzensulfonate with additional side chains.
2005, 21(12): 1431-1435
doi: 10.3866/PKU.WHXB20051222
Abstract:
The influence of a lanthanum complex (LaC) on the crystalline characteristics of isotactic polypropylene (iPP) has been investigated using X-ray diffractometer (XRD) and differential scanning calorimeter (DSC). The results of XRD measurements and the melting behavior examined by DSC show that the additive leads to an increase in crystallinity, whereas no obvious change is observed on the crystal modifications. The kinetics of isothermal crystallization of pure iPP (PP) and iPP containing 0.5% of the additive (PP/LaC) have been studied based on the analysis of the DSC experimental data by Avrami equation and Lauritzen-Hoffman theory. The results of Avrami equation analysis reveal that the additive accelerates nucleation and dramatically increases the overall rate of crystallization. The half crystallization period (t1/2) of isothermal crystallization at 130 ℃ decreases from 12.8 min for PP to 7.9 min for PP/LaC. On the other hand, the analysis of Lauritzen-Hoffman theory reveals that the introduction of LaC not only increases nucleus number and accelerates nucleation, but also accelerates the growth rate of crystallization. The nucleation constant (kg) increases from 3.3×105 for PP to 3.8×105 K2 for PP/LaC, while the surface free energy of the developing crystals(σe) decreases from 0.223 J·m-2 to 0.154 J·m-2. All these results suggest that LaC in this system considerably promote crystallization and act as an effective nucleating agent.
The influence of a lanthanum complex (LaC) on the crystalline characteristics of isotactic polypropylene (iPP) has been investigated using X-ray diffractometer (XRD) and differential scanning calorimeter (DSC). The results of XRD measurements and the melting behavior examined by DSC show that the additive leads to an increase in crystallinity, whereas no obvious change is observed on the crystal modifications. The kinetics of isothermal crystallization of pure iPP (PP) and iPP containing 0.5% of the additive (PP/LaC) have been studied based on the analysis of the DSC experimental data by Avrami equation and Lauritzen-Hoffman theory. The results of Avrami equation analysis reveal that the additive accelerates nucleation and dramatically increases the overall rate of crystallization. The half crystallization period (t1/2) of isothermal crystallization at 130 ℃ decreases from 12.8 min for PP to 7.9 min for PP/LaC. On the other hand, the analysis of Lauritzen-Hoffman theory reveals that the introduction of LaC not only increases nucleus number and accelerates nucleation, but also accelerates the growth rate of crystallization. The nucleation constant (kg) increases from 3.3×105 for PP to 3.8×105 K2 for PP/LaC, while the surface free energy of the developing crystals(σe) decreases from 0.223 J·m-2 to 0.154 J·m-2. All these results suggest that LaC in this system considerably promote crystallization and act as an effective nucleating agent.
2005, 21(12): 1436-1454
Abstract:
2005, 21(12): 1455-1466
Abstract:
