Login In
2004 Volume 20 Issue 1
2004, 20(01): 1-4
doi: 10.3866/PKU.WHXB20040101
Abstract:
We proposed here a simple technique for tracing the chemical oxidation process of single-walled carbon nanotubes (SWNTs) by using silver nanoparticles. SWNTs were prepared by chemical vapor deposition (CVD) and dilute nitricacid (2.6 mol•L－1) was used as oxidant for introducing carboxylic acid groups at the end or surface of the tubes. Based on the interaction between －COOH groups and silver nanoparticles, the oxidation procedure can be traced successfully. The results suggest that refluxing of SWNTs in HNO3 may introduce carboxylic acid groups mostly at the original defect sites and few defects is newly created along the SWNTs walls.
We proposed here a simple technique for tracing the chemical oxidation process of single-walled carbon nanotubes (SWNTs) by using silver nanoparticles. SWNTs were prepared by chemical vapor deposition (CVD) and dilute nitricacid (2.6 mol•L－1) was used as oxidant for introducing carboxylic acid groups at the end or surface of the tubes. Based on the interaction between －COOH groups and silver nanoparticles, the oxidation procedure can be traced successfully. The results suggest that refluxing of SWNTs in HNO3 may introduce carboxylic acid groups mostly at the original defect sites and few defects is newly created along the SWNTs walls.
2004, 20(01): 5-8
doi: 10.3866/PKU.WHXB20040102
Abstract:
By supramolecular self-assembling, 1,6-diphenyl-1,3,5-hexatriene（DPH） can form nanotubes with β-,γ-cyclodextrins, respectively, but not with α-cyclodextrin. Molecular mechanic (MM) calculations and molecular dynamic (MD) simulations were performed to predict the theoretical models of these nanotubes both under neutral and alkaline conditions. The analyses of host-guest interactions and hydrogen bonding indicate that the absence of intermolecular hydrogen bond is the main factor which leads to the nanotube’s breaking down under alkaline condition. Moreover, the calculated results show that the cavity ofα-cyclodextrin is too narrow to form nanotubes with DPH.
By supramolecular self-assembling, 1,6-diphenyl-1,3,5-hexatriene（DPH） can form nanotubes with β-,γ-cyclodextrins, respectively, but not with α-cyclodextrin. Molecular mechanic (MM) calculations and molecular dynamic (MD) simulations were performed to predict the theoretical models of these nanotubes both under neutral and alkaline conditions. The analyses of host-guest interactions and hydrogen bonding indicate that the absence of intermolecular hydrogen bond is the main factor which leads to the nanotube’s breaking down under alkaline condition. Moreover, the calculated results show that the cavity ofα-cyclodextrin is too narrow to form nanotubes with DPH.
2004, 20(01): 9-14
doi: 10.3866/PKU.WHXB20040103
Abstract:
Nano-fibular polyaniline(PANI) film with large specific surface area was prepared by pulse galvanostatic method(PGM) and the electrode of nano-fibular PANI modified by Pt microparticles[Pt/(nano-fibular PANI)] was used as the catalyzed electrode for methanol oxidation in this paper. The research results show that there is a synergism for methanol oxidation on Pt/(nano-fibular PANI) electrode. The Pt/(nano-fibular PANI) electrode exhibits a considerably higher electrocatalytic activity on methanol oxidation than that of the Pt/(granular PANI) electrode when Pt is deposited by cyclic voltammetry method (CVM). The catalytic activity of Pt/(nano-fibular PANI) electrode is 8 times higher than that of Pt/(granular PANI) electrode under the condition of Pt loading of 800 μg•cm－2. Moreover, the research results show that the catalytic activity of Pt/PANI electrode can be further improved when Pt is deposited by PGM. The results of scanning electron microscopy (SEM) show that a large number of Pt microparticles with diameter of about 30 nm are dispersed homogeneously on nano-fibular PANI with diameter about 100 nm. This leads to an increase in specific surface area and dispersion of Pt and hence results in a high catalytic activity of the Pt/PANI composite electrode. The results of electrochemical impedance spectroscopy (EIS) show that the Pt/(nano-fibular PANI) electrode has relatively lower electrochemical impedance for methanol oxidation than that of the Pt/(granular PANI) electrode.
Nano-fibular polyaniline(PANI) film with large specific surface area was prepared by pulse galvanostatic method(PGM) and the electrode of nano-fibular PANI modified by Pt microparticles[Pt/(nano-fibular PANI)] was used as the catalyzed electrode for methanol oxidation in this paper. The research results show that there is a synergism for methanol oxidation on Pt/(nano-fibular PANI) electrode. The Pt/(nano-fibular PANI) electrode exhibits a considerably higher electrocatalytic activity on methanol oxidation than that of the Pt/(granular PANI) electrode when Pt is deposited by cyclic voltammetry method (CVM). The catalytic activity of Pt/(nano-fibular PANI) electrode is 8 times higher than that of Pt/(granular PANI) electrode under the condition of Pt loading of 800 μg•cm－2. Moreover, the research results show that the catalytic activity of Pt/PANI electrode can be further improved when Pt is deposited by PGM. The results of scanning electron microscopy (SEM) show that a large number of Pt microparticles with diameter of about 30 nm are dispersed homogeneously on nano-fibular PANI with diameter about 100 nm. This leads to an increase in specific surface area and dispersion of Pt and hence results in a high catalytic activity of the Pt/PANI composite electrode. The results of electrochemical impedance spectroscopy (EIS) show that the Pt/(nano-fibular PANI) electrode has relatively lower electrochemical impedance for methanol oxidation than that of the Pt/(granular PANI) electrode.
2004, 20(01): 15-20
doi: 10.3866/PKU.WHXB20040104
Abstract:
Amino acids and their derivatives are useful as models of specific aspects of more complex proteins in aqueous solution. In this paper, densities and viscosities of L-threonine in glucose-water, sucrose-water and L-ascorbic acid-water mixed solvents have been measured at 298.15 K by an oscillating-tube densimeter and a viscositymeter . Limiting partial molar volume, transfer partial molar volume, number of hydration and viscosity B-coefficients of L-threonine have been calculated. The viscosity B-coefficients and the numbers of hydration of L-threonine mixed solvent vary with mass concentration of sugar or L-ascorbic acid. The transfer partial molar volumes from water to sugar-water or L-ascorbic acid-water mixtures have been obtained and discussed in terms of the structural hydration interaction model. The results indicate that the transfer partial molar volumes and viscosity B-coefficients of L-threonine increase with increasing of the mass concentration of sugar or L-ascorbic acid, and the hydration numbers of L-threonine decrease owing to the interaction of sugar or L-ascorbic acid with the zwitterionic groups. It is concluded that the degrees of the effect on volume and hydration number are related to the number of OH groups and the structure of mixture solvent.
Amino acids and their derivatives are useful as models of specific aspects of more complex proteins in aqueous solution. In this paper, densities and viscosities of L-threonine in glucose-water, sucrose-water and L-ascorbic acid-water mixed solvents have been measured at 298.15 K by an oscillating-tube densimeter and a viscositymeter . Limiting partial molar volume, transfer partial molar volume, number of hydration and viscosity B-coefficients of L-threonine have been calculated. The viscosity B-coefficients and the numbers of hydration of L-threonine mixed solvent vary with mass concentration of sugar or L-ascorbic acid. The transfer partial molar volumes from water to sugar-water or L-ascorbic acid-water mixtures have been obtained and discussed in terms of the structural hydration interaction model. The results indicate that the transfer partial molar volumes and viscosity B-coefficients of L-threonine increase with increasing of the mass concentration of sugar or L-ascorbic acid, and the hydration numbers of L-threonine decrease owing to the interaction of sugar or L-ascorbic acid with the zwitterionic groups. It is concluded that the degrees of the effect on volume and hydration number are related to the number of OH groups and the structure of mixture solvent.
2004, 20(01): 21-26
doi: 10.3866/PKU.WHXB20040105
Abstract:
Cations of C2H3F＋, CF2CH2＋, cis-CHF=CHF＋, trans-CHF=CHF＋, C2HF3＋, and C2H4＋were studied by using the DFT B3LYP and ab into MP2 methods in conjunction with the 6-31G(d, p), 6-31＋G(d, p), 6-311G(d, p), and 6-311＋G(d, p) basis sets. Geometry optimization calculations indicate that all the six-fluorinated ethylene cations have planar structures, in contrast with the non-planar D2 structure of the ethylene cation. Differences in geometry between the cations and their parent molecules were examined. Natural population analysis calculations indicate that the positive charge resides mainly at the C atom connecting with the F atom and at the H atoms in these cations. The B3LYP calculations with the 6-311＋G(d, p) basis predict vertical and adiabatic ionization potential(VIP and AIP) values of the fluorinated ethylene molecules in od agreement with the experimental values. Diffuse basis functions in the basis sets are important for accurate prediction of the VIPs and AIPs for the fluorinated ethylene molecules.
Cations of C2H3F＋, CF2CH2＋, cis-CHF=CHF＋, trans-CHF=CHF＋, C2HF3＋, and C2H4＋were studied by using the DFT B3LYP and ab into MP2 methods in conjunction with the 6-31G(d, p), 6-31＋G(d, p), 6-311G(d, p), and 6-311＋G(d, p) basis sets. Geometry optimization calculations indicate that all the six-fluorinated ethylene cations have planar structures, in contrast with the non-planar D2 structure of the ethylene cation. Differences in geometry between the cations and their parent molecules were examined. Natural population analysis calculations indicate that the positive charge resides mainly at the C atom connecting with the F atom and at the H atoms in these cations. The B3LYP calculations with the 6-311＋G(d, p) basis predict vertical and adiabatic ionization potential(VIP and AIP) values of the fluorinated ethylene molecules in od agreement with the experimental values. Diffuse basis functions in the basis sets are important for accurate prediction of the VIPs and AIPs for the fluorinated ethylene molecules.
2004, 20(01): 27-32
doi: 10.3866/PKU.WHXB20040106
Abstract:
The interaction of cyanide (CN) with different sites of Pt(100) surface is studied by using density functional theory (DFT). Pt14 cluster is used to simulate the surface. The present calculations show that the top site is more favorable than other adsorption sites when CN is bonded to the surface via the carbon, and the calculated C－N stretching frequency is blue shift in agreement with the experimental results. For other adsorption sites on the Pt(100) surface, the calculated C－N stretching frequencies are red shift. When CN molecule adsorbed on Pt(100),the charge transfer between the σ and π electron of CN molecule and the substrate led to the variation of CN vibrational frequency.
The interaction of cyanide (CN) with different sites of Pt(100) surface is studied by using density functional theory (DFT). Pt14 cluster is used to simulate the surface. The present calculations show that the top site is more favorable than other adsorption sites when CN is bonded to the surface via the carbon, and the calculated C－N stretching frequency is blue shift in agreement with the experimental results. For other adsorption sites on the Pt(100) surface, the calculated C－N stretching frequencies are red shift. When CN molecule adsorbed on Pt(100),the charge transfer between the σ and π electron of CN molecule and the substrate led to the variation of CN vibrational frequency.
2004, 20(01): 33-37
doi: 10.3866/PKU.WHXB20040107
Abstract:
A new method of the multiple rates-isotemperature is proposed to define the most possible mechanism g(α) of thermal decomposition; the iterative isoconversional procedure has been employed to estimate apparent activation energy Ea; the pre-exponential factor A is obtained on the basis of Ea and g(α).By this new method, the thermal analysis kinetic triplet of dehydration of zinc oxalate dihydrate is determined, where apparent activation energy Ea is 87.22 kJ•mol－1; pre-exponential factor A is 4.2120×108～7.2328×108 s－1 and the most probable mechanism belongs to random nucleation and growth Am (Avrami-Erofeer equation) ,with integral form g(α)=[－ln(1－α)] 1/m, and differential form f(α)=m(1－α)•[－ln(1－α)](1－1/m) , accommodation factor m=1.85～2.00.
A new method of the multiple rates-isotemperature is proposed to define the most possible mechanism g(α) of thermal decomposition; the iterative isoconversional procedure has been employed to estimate apparent activation energy Ea; the pre-exponential factor A is obtained on the basis of Ea and g(α).By this new method, the thermal analysis kinetic triplet of dehydration of zinc oxalate dihydrate is determined, where apparent activation energy Ea is 87.22 kJ•mol－1; pre-exponential factor A is 4.2120×108～7.2328×108 s－1 and the most probable mechanism belongs to random nucleation and growth Am (Avrami-Erofeer equation) ,with integral form g(α)=[－ln(1－α)] 1/m, and differential form f(α)=m(1－α)•[－ln(1－α)](1－1/m) , accommodation factor m=1.85～2.00.
2004, 20(01): 38-42
doi: 10.3866/PKU.WHXB20040108
Abstract:
A model based on scaling theory was developed for the description of the diblock copolymer micelle system. The temperature effects on micelle equilibrium properties were investigated by the Flory-Huggins interaction parameter of polymer segment and solvent. By analysis of the chain-state in micelle corona, a multi-section density distribution function was proposed and the temperature effects on aggregation number, corona density distribution, micelle inner and outer radius were observed. The calculation results show that with increasing temperature, the change of chain-state in corona has little effect on the corona density, and the micelle aggregation number will rapidly increase with the slightly growing of the micelle radius, which implies the solvent squeezing from corona and the result is consistent with experiments.
A model based on scaling theory was developed for the description of the diblock copolymer micelle system. The temperature effects on micelle equilibrium properties were investigated by the Flory-Huggins interaction parameter of polymer segment and solvent. By analysis of the chain-state in micelle corona, a multi-section density distribution function was proposed and the temperature effects on aggregation number, corona density distribution, micelle inner and outer radius were observed. The calculation results show that with increasing temperature, the change of chain-state in corona has little effect on the corona density, and the micelle aggregation number will rapidly increase with the slightly growing of the micelle radius, which implies the solvent squeezing from corona and the result is consistent with experiments.
2004, 20(01): 43-46
doi: 10.3866/PKU.WHXB20040109
Abstract:
High performance intermediate temperature solid oxide fuel cells(ITSOFC) based on LaGaO3 electrolytes were constructed, and the electrochemical properties of the cells were studied in detail. Ni-15％ (mole fraction x) Sm3＋ doped CeO2 (Ni-SDC) anode and Sm0.5Sr0.5CoO3 (SSC) cathode were prepared with the impregnation method, and La0.8Sr0.2Ga0.8Mg0.2－xCoxO3 (LSGMC, x=0, 0.01, 0.05, 0.07, 0.09)electrolytes were prepared with solid state reaction. The performance of the cell was improved significantly using LSGMC due to the decrease of ohmic resistance of the cell and the electrode over-potential. The maximum power densities of Ni-SDC/ La0.8Sr0.2Ga0.8Mg0.11Co0.09O3/SSC at 1073, 973, 873 K reached 1.77, 0.92, and 0.41 W•cm-2, respectively. The addition of cobalt into La0.8Sr0.2Ga0.8Mg0.2O3 improved its ionic conductivity significantly while the oxygen transfer number decreased slightly. For an example, the electrical conductivity of La0.8Sr0.2Ga0.8Mg0.11Co0.09O3 was about 0.21 S•cm-1, and the oxygen transfer number was about 0.87 at 1073 K, while the electrical conductivity of La0.8Sr0.2Ga0.8Mg0.2O3 was about 0.12 S•cm-1, and the oxygen transfer number was close to 1.
High performance intermediate temperature solid oxide fuel cells(ITSOFC) based on LaGaO3 electrolytes were constructed, and the electrochemical properties of the cells were studied in detail. Ni-15％ (mole fraction x) Sm3＋ doped CeO2 (Ni-SDC) anode and Sm0.5Sr0.5CoO3 (SSC) cathode were prepared with the impregnation method, and La0.8Sr0.2Ga0.8Mg0.2－xCoxO3 (LSGMC, x=0, 0.01, 0.05, 0.07, 0.09)electrolytes were prepared with solid state reaction. The performance of the cell was improved significantly using LSGMC due to the decrease of ohmic resistance of the cell and the electrode over-potential. The maximum power densities of Ni-SDC/ La0.8Sr0.2Ga0.8Mg0.11Co0.09O3/SSC at 1073, 973, 873 K reached 1.77, 0.92, and 0.41 W•cm-2, respectively. The addition of cobalt into La0.8Sr0.2Ga0.8Mg0.2O3 improved its ionic conductivity significantly while the oxygen transfer number decreased slightly. For an example, the electrical conductivity of La0.8Sr0.2Ga0.8Mg0.11Co0.09O3 was about 0.21 S•cm-1, and the oxygen transfer number was about 0.87 at 1073 K, while the electrical conductivity of La0.8Sr0.2Ga0.8Mg0.2O3 was about 0.12 S•cm-1, and the oxygen transfer number was close to 1.
2004, 20(01): 47-49
doi: 10.3866/PKU.WHXB20040110
Abstract:
Recently, polymer thin films have been increasingly used in microelectronic applications. Poly(ε-caprolactone)/poly(vinyl chloride) (PCL/PVC) blends are widely studied polymers. When PCL and PVC are blended in certain ratio, ring-banded spherulites are formed and the blends are often composed of a PCL crystal phase and a PCL/PVC amorphous phase. Optical microscopy, atomic force microscopy and angle-dependent XPS analyses were used by many scientists to investigate the morphology and composition of the PCL/PVC films. Using XPS and imaging XPS analyses, we have investigated the surface chemical composition and elemental distribution of PCL/PVC films. The results show that PCL enriches to the PCL/PVC polymer-air interface. Besides, the imaging XPS analysis indicates that PVC is concentrated at the spherulite boundaries and the width of the boundaries is about 15 μm. These observations may be valuable for the explanation of the crystallization and morphological behaviors of polymer blends.
Recently, polymer thin films have been increasingly used in microelectronic applications. Poly(ε-caprolactone)/poly(vinyl chloride) (PCL/PVC) blends are widely studied polymers. When PCL and PVC are blended in certain ratio, ring-banded spherulites are formed and the blends are often composed of a PCL crystal phase and a PCL/PVC amorphous phase. Optical microscopy, atomic force microscopy and angle-dependent XPS analyses were used by many scientists to investigate the morphology and composition of the PCL/PVC films. Using XPS and imaging XPS analyses, we have investigated the surface chemical composition and elemental distribution of PCL/PVC films. The results show that PCL enriches to the PCL/PVC polymer-air interface. Besides, the imaging XPS analysis indicates that PVC is concentrated at the spherulite boundaries and the width of the boundaries is about 15 μm. These observations may be valuable for the explanation of the crystallization and morphological behaviors of polymer blends.
2004, 20(01): 50-54
doi: 10.3866/PKU.WHXB20040111
Abstract:
The mechanism of thermal decomposition of aspirin was studied by both thermogravimetry and Mayer bond orders calculated by Cerius2 software. The parameters of thermal decomposition kinetics for aspirin, such as activation energy (E), reaction order (n) and frequency factor (A) were obtained by thermogravimetry. The kinetic equation of thermal decomposition of aspirin is expressed as: dα/dt=4.74×1011[exp－(100.34±5.18)×103/RT]](1－α)2.8±0.3 Melting point, molar enthalpy and entropy of fusion of aspirin were examined to be (409.19±0.22) K, (29.17±0.41) kJ•mol-1 and (71.09±1.06) J•mol-1•K-1, respectively, by means of DSC with a rising temperature program. The results obtained show that theoretical mass-loss derived from Mayer bond orders of aspirin is in very od agreement with that obtained from thermogravimetry experiment.
The mechanism of thermal decomposition of aspirin was studied by both thermogravimetry and Mayer bond orders calculated by Cerius2 software. The parameters of thermal decomposition kinetics for aspirin, such as activation energy (E), reaction order (n) and frequency factor (A) were obtained by thermogravimetry. The kinetic equation of thermal decomposition of aspirin is expressed as: dα/dt=4.74×1011[exp－(100.34±5.18)×103/RT]](1－α)2.8±0.3 Melting point, molar enthalpy and entropy of fusion of aspirin were examined to be (409.19±0.22) K, (29.17±0.41) kJ•mol-1 and (71.09±1.06) J•mol-1•K-1, respectively, by means of DSC with a rising temperature program. The results obtained show that theoretical mass-loss derived from Mayer bond orders of aspirin is in very od agreement with that obtained from thermogravimetry experiment.
2004, 20(01): 55-59
doi: 10.3866/PKU.WHXB20040112
Abstract:
Densities of glycine, L-alanine and L-serine in 2-chloroethanol-water mixed solvents have been measured at 298.15 K by an oscillating-tube densimeter. Apparent molar volumes, limiting partial molar volumes, transfer partial volumes, hydration numbers and volumetric interaction coefficients for these amino acids have been calculated. The results show that all of the transfer partial volumes from water to 2-chloroethanol-water mixed solvents are positive, and increase with increasing 2-chloroethanol concentration; all the hydration numbers decrease with increasing 2-chloroethanol concentration. From the results of the volumetric interaction coefficients, it is concluded that interaction between glycine and 2-chloroethanol is dominated by 1 : 1 and 1 : 2 forms, and interactions between alanine, serine and 2-chloroethanol molecule are dominated by 1 : 1 form.
Densities of glycine, L-alanine and L-serine in 2-chloroethanol-water mixed solvents have been measured at 298.15 K by an oscillating-tube densimeter. Apparent molar volumes, limiting partial molar volumes, transfer partial volumes, hydration numbers and volumetric interaction coefficients for these amino acids have been calculated. The results show that all of the transfer partial volumes from water to 2-chloroethanol-water mixed solvents are positive, and increase with increasing 2-chloroethanol concentration; all the hydration numbers decrease with increasing 2-chloroethanol concentration. From the results of the volumetric interaction coefficients, it is concluded that interaction between glycine and 2-chloroethanol is dominated by 1 : 1 and 1 : 2 forms, and interactions between alanine, serine and 2-chloroethanol molecule are dominated by 1 : 1 form.
2004, 20(01): 60-64
doi: 10.3866/PKU.WHXB20040113
Abstract:
By density functional calculations, it was confirmed that for the reaction of RSCC (residual oil selective catalytic cracking),the catalysts such as zeolite ZSM-5 will endure an enhanced thermal stability when some La3＋ ions are introduced. Due to the strong interaction between La3＋ and the zeolite, the Al－O bond, which would have been easily broken, gets stronger and the process of dealumination is thus effectively retarded. Through the reduction of La(OH)2＋ when heated, LaO(OH) is most likely formed, which can interact with zeolite ZSM-5 and turns out to the structure of Z－La(OH)2＋ or Z-LaO(OH) after geometrical optimization. Z－La(OH)2＋ remains stable under normal conditions; however, as the temperature is raised, it will change slowly into Z-LaO(OH),which stays stable at high temperature. The La3＋ ion in Z-LaO(OH) can offer Lewis acid as the active site for reactions, we believe that this result can provide valuable insight into the elucidation of catalytic mechanism.
By density functional calculations, it was confirmed that for the reaction of RSCC (residual oil selective catalytic cracking),the catalysts such as zeolite ZSM-5 will endure an enhanced thermal stability when some La3＋ ions are introduced. Due to the strong interaction between La3＋ and the zeolite, the Al－O bond, which would have been easily broken, gets stronger and the process of dealumination is thus effectively retarded. Through the reduction of La(OH)2＋ when heated, LaO(OH) is most likely formed, which can interact with zeolite ZSM-5 and turns out to the structure of Z－La(OH)2＋ or Z-LaO(OH) after geometrical optimization. Z－La(OH)2＋ remains stable under normal conditions; however, as the temperature is raised, it will change slowly into Z-LaO(OH),which stays stable at high temperature. The La3＋ ion in Z-LaO(OH) can offer Lewis acid as the active site for reactions, we believe that this result can provide valuable insight into the elucidation of catalytic mechanism.
2004, 20(01): 65-69
doi: 10.3866/PKU.WHXB20040114
Abstract:
Using cetyltriethylammonium bromide and cetyltrimethylammonium bromide as templating agent respectively, and silicasol as silica source,the mesoporous molecular sieves MCM-41 were synthesized by hydrothermal method in basic media. The synthesized samples were characterized by XRD、N2 adsorption-desorption、TG-DTA and IR. The effects of different templating agent on the crystalline structure 、pore diameter and pore size distribution of synthesized silica MCM-41 were investigated. The experimental results show that the templated by cetyltriethylammonium bromide, compared with those templated by cetyltrimethylammonium bromide, have larger pore diameter and pore volume with 4.72 nm and 1.14 cm3•g-1 respectively and narrower pore size distribution. For the preparation of large pore mesoporous MCM-41, cetyltriethylammonium bromide is a more effective templating agent than cetyltrimethylammonium bromide.
Using cetyltriethylammonium bromide and cetyltrimethylammonium bromide as templating agent respectively, and silicasol as silica source,the mesoporous molecular sieves MCM-41 were synthesized by hydrothermal method in basic media. The synthesized samples were characterized by XRD、N2 adsorption-desorption、TG-DTA and IR. The effects of different templating agent on the crystalline structure 、pore diameter and pore size distribution of synthesized silica MCM-41 were investigated. The experimental results show that the templated by cetyltriethylammonium bromide, compared with those templated by cetyltrimethylammonium bromide, have larger pore diameter and pore volume with 4.72 nm and 1.14 cm3•g-1 respectively and narrower pore size distribution. For the preparation of large pore mesoporous MCM-41, cetyltriethylammonium bromide is a more effective templating agent than cetyltrimethylammonium bromide.
2004, 20(01): 70-75
doi: 10.3866/PKU.WHXB20040115
Abstract:
According to the relationship between CR transmission line model (CR circuit) and QR circuit,an approach to calculate the initial value for fitting the former was found. Then,accurate values of its all elements could be obtained by using Z-View software. Based on the distribution of capacitance (Ci) and resistance（Ri）vs characteristic frequency (f*),the function of the relative increment of its elements vs the CPE(constant phase element)－power n could be drawn out. It showed that Ci value increased more quickly than that of Ri when n < 0.5, so the physical meaning of n and its connection with the delamination at the coating/metal interface were interpreted from a new standpoint. As examples of application, the fit of several different types of electrochemical impedance spectroscopy, the inspection of the evolution of impedances in organic coating/metal system with time, discrimination of the effects of corrosion and delamination on the impedance,as well as the samultaneous estimation of capacitance and resistance of coating with various interspace from high impedance system were performed. Finally, the physical meaning of the CR circuit in organic coatings system was discussed for the heterogeneous characteristics of organic coating.
According to the relationship between CR transmission line model (CR circuit) and QR circuit,an approach to calculate the initial value for fitting the former was found. Then,accurate values of its all elements could be obtained by using Z-View software. Based on the distribution of capacitance (Ci) and resistance（Ri）vs characteristic frequency (f*),the function of the relative increment of its elements vs the CPE(constant phase element)－power n could be drawn out. It showed that Ci value increased more quickly than that of Ri when n < 0.5, so the physical meaning of n and its connection with the delamination at the coating/metal interface were interpreted from a new standpoint. As examples of application, the fit of several different types of electrochemical impedance spectroscopy, the inspection of the evolution of impedances in organic coating/metal system with time, discrimination of the effects of corrosion and delamination on the impedance,as well as the samultaneous estimation of capacitance and resistance of coating with various interspace from high impedance system were performed. Finally, the physical meaning of the CR circuit in organic coatings system was discussed for the heterogeneous characteristics of organic coating.
2004, 20(01): 76-80
doi: 10.3866/PKU.WHXB20040116
Abstract:
Three catalysts, NiO-M , NiO-La2O3-M and NiO-CeO2-M containing 10％(w) Ni were prepared by the co-precipitation method. The effects of La2O3 and CeO2 on physico-chemical properties and catalytic performance of NiO-M catalysts were studied by means of BET, XRD, TPR, XPS, TG and reaction activity evaluation. It was found that NiO formed a nickel-magnesia solid solution with M , and La2O3 and CeO2 promoters improved the resistance to sintering of the nickel-magnesia solid solution, which was attributed to the higher specific surface area and smaller size of crystallites of the Nickel-magnesia solid solution. Besides, La2O3 and CeO2 could promote reduction of nickel species in nickel-magnesia solid solution, especially CeO2. Under reaction conditions of CH4/CO2=1(molar ratio), 0.1 MPa, 1023 K and 1073 K, 18 L•g-1•h-1, NiO-La2O3-M and NiO-CeO2-M showed higher activity than NiO-M . However, the three catalysts had similar activity at 1123 K because the reaction was close to the thermodynamic equilibrium under these reaction conditions. La2O3 and CeO2 act as a structural promoter and an electronic promoter respectively to improve the properties of NiO-M .
Three catalysts, NiO-M , NiO-La2O3-M and NiO-CeO2-M containing 10％(w) Ni were prepared by the co-precipitation method. The effects of La2O3 and CeO2 on physico-chemical properties and catalytic performance of NiO-M catalysts were studied by means of BET, XRD, TPR, XPS, TG and reaction activity evaluation. It was found that NiO formed a nickel-magnesia solid solution with M , and La2O3 and CeO2 promoters improved the resistance to sintering of the nickel-magnesia solid solution, which was attributed to the higher specific surface area and smaller size of crystallites of the Nickel-magnesia solid solution. Besides, La2O3 and CeO2 could promote reduction of nickel species in nickel-magnesia solid solution, especially CeO2. Under reaction conditions of CH4/CO2=1(molar ratio), 0.1 MPa, 1023 K and 1073 K, 18 L•g-1•h-1, NiO-La2O3-M and NiO-CeO2-M showed higher activity than NiO-M . However, the three catalysts had similar activity at 1123 K because the reaction was close to the thermodynamic equilibrium under these reaction conditions. La2O3 and CeO2 act as a structural promoter and an electronic promoter respectively to improve the properties of NiO-M .
2004, 20(01): 81-84
doi: 10.3866/PKU.WHXB20040117
Abstract:
The MSU-typed mesoporous organosilica with organic methyl, vinyl, and phenyl functionals were prepared by using inexpensive sodium silicate and organotrialkoxysilane as the silica precursor and nonionic polyethyleneoxide AEO9[C11-15H23-31(CH2CH2O)9H] as the structure-directing agent. The resultant materials were characterized by powder X-ray diffraction (XRD), N2 sorptometry, high resolution transmission electron microscopy (HRTEM) and 29Si CP MAS-NMR. The results indicated that addition of sodium fluorite reduced the possibility of organotrialkoxysilane with small organic group entering the framework walls of the mesostructures at neutral condition. Moreover, pore diameter of material increased upon the increase of pH value.
The MSU-typed mesoporous organosilica with organic methyl, vinyl, and phenyl functionals were prepared by using inexpensive sodium silicate and organotrialkoxysilane as the silica precursor and nonionic polyethyleneoxide AEO9[C11-15H23-31(CH2CH2O)9H] as the structure-directing agent. The resultant materials were characterized by powder X-ray diffraction (XRD), N2 sorptometry, high resolution transmission electron microscopy (HRTEM) and 29Si CP MAS-NMR. The results indicated that addition of sodium fluorite reduced the possibility of organotrialkoxysilane with small organic group entering the framework walls of the mesostructures at neutral condition. Moreover, pore diameter of material increased upon the increase of pH value.
Isobaric Vapor-Liquid Equilibria of Maleic Anhydride-DIBE System Using a Small Modified Ebulliometer
2004, 20(01): 85-89
doi: 10.3866/PKU.WHXB20040118
Abstract:
T, p data for Maleic anhydride and DIBE (di-isobutylhexahydrophthalate) at different feed compositions(q) have been measured with a small modified ebulliometer and T, q data under different pressures have been obtained through interpolation. The vapor-liquid equilibrium data have been calculated by means of the parameters of NRTL equation optimized by the simplex method. The azeotropes are found to change obviously with the pressures. The azeotropes tend to disappear when the pressure is lowered to 20 kPa.
T, p data for Maleic anhydride and DIBE (di-isobutylhexahydrophthalate) at different feed compositions(q) have been measured with a small modified ebulliometer and T, q data under different pressures have been obtained through interpolation. The vapor-liquid equilibrium data have been calculated by means of the parameters of NRTL equation optimized by the simplex method. The azeotropes are found to change obviously with the pressures. The azeotropes tend to disappear when the pressure is lowered to 20 kPa.
2004, 20(01): 90-93
doi: 10.3866/PKU.WHXB20040119
Abstract:
For thermal energy storage application, polyurea microcapsules about 2.5 μm in diameter containing phase change material were prepared using interfacial polycondensation method. In the system droplets in microns are first formed by emulsifying an organic phase consisting of a core material (n-hexadecane) and an oil-soluble reactive monomer, toluene-2,4-diisocyanate (TDI),in an aqueous phase. By adding water-soluble reactive monomer, diamine, monomers TDI and diamine react with each other at the interface of micelles to become a shell. Ethylenediamine (EDA), 1,6-hexane diamine (HDA) and their mixture were employed as water-soluble reactive monomers. The effects of diamine type on chemical structure and thermal properties of the microcapsules were investigated by FT-IR and thermal analysis respectively. The infrared spectra indicate that polyurea microcapsules have been successfully synthesized; all the TG thermographs show microcapsules containing n-hexadecane can sustain high temperature about 300 ℃ without broken and the DSC measurements display that all samples possess a moderate heat of phase transition； thermal cyclic tests show that the encapsulated paraffin kept its energy storage capacity even after 50 cycles of operation. The results obtained from experiments show that the encapsulated n-hexadecane possesses a od potential as a thermal energy storage material.
For thermal energy storage application, polyurea microcapsules about 2.5 μm in diameter containing phase change material were prepared using interfacial polycondensation method. In the system droplets in microns are first formed by emulsifying an organic phase consisting of a core material (n-hexadecane) and an oil-soluble reactive monomer, toluene-2,4-diisocyanate (TDI),in an aqueous phase. By adding water-soluble reactive monomer, diamine, monomers TDI and diamine react with each other at the interface of micelles to become a shell. Ethylenediamine (EDA), 1,6-hexane diamine (HDA) and their mixture were employed as water-soluble reactive monomers. The effects of diamine type on chemical structure and thermal properties of the microcapsules were investigated by FT-IR and thermal analysis respectively. The infrared spectra indicate that polyurea microcapsules have been successfully synthesized; all the TG thermographs show microcapsules containing n-hexadecane can sustain high temperature about 300 ℃ without broken and the DSC measurements display that all samples possess a moderate heat of phase transition； thermal cyclic tests show that the encapsulated paraffin kept its energy storage capacity even after 50 cycles of operation. The results obtained from experiments show that the encapsulated n-hexadecane possesses a od potential as a thermal energy storage material.
2004, 20(01): 94-97
doi: 10.3866/PKU.WHXB20040120
Abstract:
The oxidative behavior of isosafrole (ISF) in non-aqueous system on Pt was investigated by cyclic voltammery. When scanning from -0.55 to 1.95 V (vs Ag/AgCl electrode) at a certain scan rate, two oxidation peaks and one reduction peak appeared. By scanning at different scan rate, the electro-oxidative behavior of isosafrole on Pt was confirmed to be controlled by concentration diffusion, as well as chemical reaction rate. By comparing the two isomers, ISF and SF safrole, the reactive mechanism was dcecussed. Moreover, the active oxidation group of ISF was identified to be the C=C from allyl by developing the in-situ surface enhanced Raman specrum.
The oxidative behavior of isosafrole (ISF) in non-aqueous system on Pt was investigated by cyclic voltammery. When scanning from -0.55 to 1.95 V (vs Ag/AgCl electrode) at a certain scan rate, two oxidation peaks and one reduction peak appeared. By scanning at different scan rate, the electro-oxidative behavior of isosafrole on Pt was confirmed to be controlled by concentration diffusion, as well as chemical reaction rate. By comparing the two isomers, ISF and SF safrole, the reactive mechanism was dcecussed. Moreover, the active oxidation group of ISF was identified to be the C=C from allyl by developing the in-situ surface enhanced Raman specrum.
2004, 20(01): 98-102
doi: 10.3866/PKU.WHXB20040121
Abstract:
In the concentration of 0~1 mol•L-1 ,the chemical shift of 17O-NMR （δ(H217O)）in aqueous solutions of alkali chloride, alkaline earth chloride, sodium halide or some common oxysalt were measured. It is found thatδ(H217O) depends on ion radius, ion charge, outside electron structure of ion and structure of ion. As the other parameters of ions keep unchanged, the larger the ion radius, the more the molarδ(H217O) of the ion is. With the same outer electron structure of ion, the more the ion charge, the more the molarδ(H217O) of the ion is. The molarδ(H217O) of multiple atom ion correlate with the structure of ion much more. It is deduced that the molar δ(H217O) of ion correlate with the effect of ion on water structure. The more the molarδ(H217O) of the ion, the intenser the effect of the ion on promoting water structure.
In the concentration of 0~1 mol•L-1 ,the chemical shift of 17O-NMR （δ(H217O)）in aqueous solutions of alkali chloride, alkaline earth chloride, sodium halide or some common oxysalt were measured. It is found thatδ(H217O) depends on ion radius, ion charge, outside electron structure of ion and structure of ion. As the other parameters of ions keep unchanged, the larger the ion radius, the more the molarδ(H217O) of the ion is. With the same outer electron structure of ion, the more the ion charge, the more the molarδ(H217O) of the ion is. The molarδ(H217O) of multiple atom ion correlate with the structure of ion much more. It is deduced that the molar δ(H217O) of ion correlate with the effect of ion on water structure. The more the molarδ(H217O) of the ion, the intenser the effect of the ion on promoting water structure.
2004, 20(01): 103-106
doi: 10.3866/PKU.WHXB20040122
Abstract:
Water soluble and stable colloidal polyaniline (PAn) aqueous dispersions were obtained using poly(vinyl pyrrolidone) (PVP) as steric stabilizer via dispersion polymerization. The morphology and size of PAn were characerized by transmission electron microscopy (TEM). Doped and dedoped PAn-PVP in the aqueous dipersions were investigated via the UV-Vis spectra. The results showed that when the content of PAn was low（wPAn< 16.78％）, the morphology of PAn-PVP was rice-grain particles. And when the content of PAn was high （wPAn >23.22％）, the morphology of PAn-PVP was spherical particles .The PAn-PVP particles were composites.
Water soluble and stable colloidal polyaniline (PAn) aqueous dispersions were obtained using poly(vinyl pyrrolidone) (PVP) as steric stabilizer via dispersion polymerization. The morphology and size of PAn were characerized by transmission electron microscopy (TEM). Doped and dedoped PAn-PVP in the aqueous dipersions were investigated via the UV-Vis spectra. The results showed that when the content of PAn was low（wPAn< 16.78％）, the morphology of PAn-PVP was rice-grain particles. And when the content of PAn was high （wPAn >23.22％）, the morphology of PAn-PVP was spherical particles .The PAn-PVP particles were composites.
2004, 20(01): 107-111
doi: 10.3866/PKU.WHXB20040123
Abstract:
The microstructures and the evolution mechanism of the self-assemblies of C60-amphiphiles in aqueous solutions are reviewed in the present paper. The results by using the freeze-fracture transmission electron microscopy (FF-TEM) and TEM, small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), and laser light scattering (LLS) are introduced. Some models of the self-assemblies are presented.
The microstructures and the evolution mechanism of the self-assemblies of C60-amphiphiles in aqueous solutions are reviewed in the present paper. The results by using the freeze-fracture transmission electron microscopy (FF-TEM) and TEM, small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), and laser light scattering (LLS) are introduced. Some models of the self-assemblies are presented.
