Login In
2006 Volume 22 Issue 1
2006, 22(01): 1-5
doi: 10.3866/PKU.WHXB20060101
Abstract:
Single chain bolaamphiphile containing cinnamyl moiety [4-(ω-hydroxydecanyloxy) (ω-hydroxydecanyl) cinnamate, abr. HDC] was designed and synthesized. The photodimerization of the HDC molecules induced by UV light was the first time realized in organic solutions. The dimerized HDC was separated and formed spherical vesicles in 20% ethanol/water mixed solvents. The solvents’ dielectric constants were found to play an important role in the photodimerization process. Both the occurrence of the photodimerization reaction and the rate of the reaction were affected by the dielectric constant value of the solvents.
Single chain bolaamphiphile containing cinnamyl moiety [4-(ω-hydroxydecanyloxy) (ω-hydroxydecanyl) cinnamate, abr. HDC] was designed and synthesized. The photodimerization of the HDC molecules induced by UV light was the first time realized in organic solutions. The dimerized HDC was separated and formed spherical vesicles in 20% ethanol/water mixed solvents. The solvents’ dielectric constants were found to play an important role in the photodimerization process. Both the occurrence of the photodimerization reaction and the rate of the reaction were affected by the dielectric constant value of the solvents.
2006, 22(01): 6-10
doi: 10.3866/PKU.WHXB20060102
Abstract:
The vinyl radical was generated by photolysing methyl vinyl ketone with 193 nm laser, then was excited and photodissociated by another laser in the 20020～20070 cm-1 range. The dissociated H atom fragments were ionized and detected by (1+1′) resonance-enhanced multiphoton ionization (REMPI) process. The rotationally resolved action spectra of theA2A''(v'=0)←X2A'(v''=0)band of the vinyl radical were recorded by monitoring the H+ ion intensity with dissociation laser wavelength. The corresponding assignments were obtained with the aid of ab initio calculations and spectroscopic simulations, and 40 rotational lines were definitely assigned. Additionally, the predissociative lifetime of the •C2H3 A2A''(v'= 0 ) state was 3.3 ps and independent of the rotational levels, which was derived from the linewidth.
The vinyl radical was generated by photolysing methyl vinyl ketone with 193 nm laser, then was excited and photodissociated by another laser in the 20020～20070 cm-1 range. The dissociated H atom fragments were ionized and detected by (1+1′) resonance-enhanced multiphoton ionization (REMPI) process. The rotationally resolved action spectra of theA2A''(v'=0)←X2A'(v''=0)band of the vinyl radical were recorded by monitoring the H+ ion intensity with dissociation laser wavelength. The corresponding assignments were obtained with the aid of ab initio calculations and spectroscopic simulations, and 40 rotational lines were definitely assigned. Additionally, the predissociative lifetime of the •C2H3 A2A''(v'= 0 ) state was 3.3 ps and independent of the rotational levels, which was derived from the linewidth.
2006, 22(01): 11-15
doi: 10.3866/PKU.WHXB20060103
Abstract:
Benzene adsorption on Au(100)-3×3 surface has been studied with periodical slab model by Vosko-Wilk-Nusair LDA functional under double numeric basis with polarization functions. The results of geometry optimization indicate that the hollow site in the highest coordination is energetically active for benzene adsorbed on Au(100) surface, and the adsorption energy is －184.8~－184.3 kJ•mol-1. The benzene ring has been distorted, and the C—C bond has a considerable elongation. Two opposite carbon atoms are involved in the adsorption process leading to a rehybridization of the two carbon atoms from sp2 to sp3, which makes the adsorbate state intermediate between benzene and 1,4-cyclohexadiene. The benzene adsorbed in the bridge and top positions is found to be energetically less favorable, and the adsorption energies are respectively －156.7~－145.3 kJ•mol-1 and －116.5~－117.0 kJ•mol-1. The geometry of benzene has a slight elongation. The molecular orbital analysis also indicates that the degenerate frontier molecular orbitals lose their degeneracy with decrease of symmetry. The LUMO of benzene has a od overlap with the dz2 orbital of Au atom. The two carbon atoms in the opposite positions are bonded to the near Au atoms with di-σ bonds.
Benzene adsorption on Au(100)-3×3 surface has been studied with periodical slab model by Vosko-Wilk-Nusair LDA functional under double numeric basis with polarization functions. The results of geometry optimization indicate that the hollow site in the highest coordination is energetically active for benzene adsorbed on Au(100) surface, and the adsorption energy is －184.8~－184.3 kJ•mol-1. The benzene ring has been distorted, and the C—C bond has a considerable elongation. Two opposite carbon atoms are involved in the adsorption process leading to a rehybridization of the two carbon atoms from sp2 to sp3, which makes the adsorbate state intermediate between benzene and 1,4-cyclohexadiene. The benzene adsorbed in the bridge and top positions is found to be energetically less favorable, and the adsorption energies are respectively －156.7~－145.3 kJ•mol-1 and －116.5~－117.0 kJ•mol-1. The geometry of benzene has a slight elongation. The molecular orbital analysis also indicates that the degenerate frontier molecular orbitals lose their degeneracy with decrease of symmetry. The LUMO of benzene has a od overlap with the dz2 orbital of Au atom. The two carbon atoms in the opposite positions are bonded to the near Au atoms with di-σ bonds.
2006, 22(01): 16-21
doi: 10.3866/PKU.WHXB20060104
Abstract:
Simulation of the meso-scale structures of diblock copolymers between two parallel plates is performed using dissipative particle dynamics (DPD). The simulation results show that the discontinuous increase of number of layers appears in meso-scale sandwich structure with an existence of atactic transition, when the plate-to-plate distance increases. An approximately linear relationship exists between the sandwich structure conversion, which is approximately in proportion to the 2/3th power of the chain length of copolymer, and number of layers. The end-to-end distance of copolymer chain presents a periodic oscillation behavior, and the amplitude decreases gradually, when the plate-to-plate distance increases.
Simulation of the meso-scale structures of diblock copolymers between two parallel plates is performed using dissipative particle dynamics (DPD). The simulation results show that the discontinuous increase of number of layers appears in meso-scale sandwich structure with an existence of atactic transition, when the plate-to-plate distance increases. An approximately linear relationship exists between the sandwich structure conversion, which is approximately in proportion to the 2/3th power of the chain length of copolymer, and number of layers. The end-to-end distance of copolymer chain presents a periodic oscillation behavior, and the amplitude decreases gradually, when the plate-to-plate distance increases.
2006, 22(01): 22-27
doi: 10.3866/PKU.WHXB20060105
Abstract:
The conductivity behaviour of water-in-alkanol(hexanol, heptanol, octanol, decanol) microemulsions, in which AOT was employed as surfactant, was investigated. The percolation phenomenon induced by water was found only in the water/AOT/decanol system. The effects of organic salts (sodium cholate and sodium salicylate) and temperatureon conductance were then studied. In heptanol and octanol systems the conductivity was decreased with the increase of sodium cholate concentration, whereas it was increased in the case of sodium salicylate. In decanol system the conductivity was hardly changed in the presence of both organic salts. The values of lnσ had a linear correlation with temperature in the range of 5～40 ℃. No percolation threshold induced by temperature was detected either in the absence or in the presence of organic salts. The activation energy for conductance was estimated according to the Arrhenius-type equation.
The conductivity behaviour of water-in-alkanol(hexanol, heptanol, octanol, decanol) microemulsions, in which AOT was employed as surfactant, was investigated. The percolation phenomenon induced by water was found only in the water/AOT/decanol system. The effects of organic salts (sodium cholate and sodium salicylate) and temperatureon conductance were then studied. In heptanol and octanol systems the conductivity was decreased with the increase of sodium cholate concentration, whereas it was increased in the case of sodium salicylate. In decanol system the conductivity was hardly changed in the presence of both organic salts. The values of lnσ had a linear correlation with temperature in the range of 5～40 ℃. No percolation threshold induced by temperature was detected either in the absence or in the presence of organic salts. The activation energy for conductance was estimated according to the Arrhenius-type equation.
2006, 22(01): 28-32
doi: 10.3866/PKU.WHXB20060106
Abstract:
The structure and properties, such as the unit cell parameters, framework vibration bands, characteristic electronic transition, deductibility of heteroatom-containing Y zeolites, were investigated by XRD, FT-IR, UV-Vis-DRS, TG, and NMR. It showed that suitable hetero-atom incorporation into the zeolite framework does not change the crystallographic form of zeolite Y. The unit cell of zeolite BY is shrinked and the framework vibration bands shift to higher frequency comparing with zeolite Y. The unit cell sizes of zeolite TiY and FeY are increased and framework vibration bands shift to lower frequency. The 11B MAS-NMR shows that atom B is in the tetrahedral position of the framework, which differs from zeolite Y impregnated boron. UV-Vis-DRS spectra suggest that atom Ti in zeolite TiY differs from extra atom Ti evidently and the zeolite FeY reduced by hydrogen at 600 ℃ does not have reduction peaks, but zeolite Y impregnated Fe is reduced completely at the same conditions. The results suggest that the hetero-atoms, B, Ti, and Fe, all enter the framework of zeolite Y.
The structure and properties, such as the unit cell parameters, framework vibration bands, characteristic electronic transition, deductibility of heteroatom-containing Y zeolites, were investigated by XRD, FT-IR, UV-Vis-DRS, TG, and NMR. It showed that suitable hetero-atom incorporation into the zeolite framework does not change the crystallographic form of zeolite Y. The unit cell of zeolite BY is shrinked and the framework vibration bands shift to higher frequency comparing with zeolite Y. The unit cell sizes of zeolite TiY and FeY are increased and framework vibration bands shift to lower frequency. The 11B MAS-NMR shows that atom B is in the tetrahedral position of the framework, which differs from zeolite Y impregnated boron. UV-Vis-DRS spectra suggest that atom Ti in zeolite TiY differs from extra atom Ti evidently and the zeolite FeY reduced by hydrogen at 600 ℃ does not have reduction peaks, but zeolite Y impregnated Fe is reduced completely at the same conditions. The results suggest that the hetero-atoms, B, Ti, and Fe, all enter the framework of zeolite Y.
2006, 22(01): 33-37
doi: 10.3866/PKU.WHXB20060107
Abstract:
The structure and oxygen mobility of Ce1-xZrxO2 (0 ≤x≤ 1) samples prepared by citric acid sol-gel method were characterized by XRF, XRD, Raman, XPS, Ar+ etching-XPS and H2-TPR. The data showed that the crystalline structure of Ce1-xZrxO2 can significantly affect the oxygen mobility. When x≤0.15, the samples were found to exist as cubic Ce-Zr-O solid solutions. An increase in x resulted in a shrinking of the crystal unit volume, an increasing in the number of oxygen vacancies, and an increasing in the oxygen mobility as well. When x＞0.15, Ce1-xZrxO2 existed in a mixed phases of tetra nal and cubic Ce-Zr-O solid solutions; the percentage of tetra nal phase increased, oxygen vacancies decreased and oxygen mobility reduced with increasing x in these samples. Therefore, this present work shows that oxygen mobility in the Ce0.85Zr0.152O2 sample is the highest.
The structure and oxygen mobility of Ce1-xZrxO2 (0 ≤x≤ 1) samples prepared by citric acid sol-gel method were characterized by XRF, XRD, Raman, XPS, Ar+ etching-XPS and H2-TPR. The data showed that the crystalline structure of Ce1-xZrxO2 can significantly affect the oxygen mobility. When x≤0.15, the samples were found to exist as cubic Ce-Zr-O solid solutions. An increase in x resulted in a shrinking of the crystal unit volume, an increasing in the number of oxygen vacancies, and an increasing in the oxygen mobility as well. When x＞0.15, Ce1-xZrxO2 existed in a mixed phases of tetra nal and cubic Ce-Zr-O solid solutions; the percentage of tetra nal phase increased, oxygen vacancies decreased and oxygen mobility reduced with increasing x in these samples. Therefore, this present work shows that oxygen mobility in the Ce0.85Zr0.152O2 sample is the highest.
2006, 22(01): 38-42
doi: 10.3866/PKU.WHXB20060108
Abstract:
In-doped ZnO nanodisks were successfully fabricated by thermal evaporation Zn, In2O3, and graphite powder mixture without catalyst. SEM images show that some ZnO nanodisks have perfect hexa nal shape, and others have dodeca n shape. These nanodisks are about 1~3 μm in size and 40~100 nm in thickness. XRD, TEM, and EDS investigations confirm single-crystalline ZnO with wurtzite structure. The hexa nal nanodisks grow mainly along the six symmetric directions of <10-10>, and the dodeca nal nanodisks grow along <2-1-10> and <10-10>, with both kinds of nanodisks′ growth along [0001] being suppressed. The In content of nanodisks reaches 2.2%. A possible mechanism is also proposed. Room temperature photoluminescence spectra of the nanodisks shows that the UV emission peak blueshifts and becomes broader after doping. These materials as building blocks have potential in applications such as optoelectronics.
In-doped ZnO nanodisks were successfully fabricated by thermal evaporation Zn, In2O3, and graphite powder mixture without catalyst. SEM images show that some ZnO nanodisks have perfect hexa nal shape, and others have dodeca n shape. These nanodisks are about 1~3 μm in size and 40~100 nm in thickness. XRD, TEM, and EDS investigations confirm single-crystalline ZnO with wurtzite structure. The hexa nal nanodisks grow mainly along the six symmetric directions of <10-10>, and the dodeca nal nanodisks grow along <2-1-10> and <10-10>, with both kinds of nanodisks′ growth along [0001] being suppressed. The In content of nanodisks reaches 2.2%. A possible mechanism is also proposed. Room temperature photoluminescence spectra of the nanodisks shows that the UV emission peak blueshifts and becomes broader after doping. These materials as building blocks have potential in applications such as optoelectronics.
2006, 22(01): 43-47
doi: 10.3866/PKU.WHXB20060109
Abstract:
The effects of four important factors, including dosage of activating agent, activation temperature, activation time, and flow rate of protecting gas, on the specific surface area of activated carbon nanotubes (ACNTs) using KOH as the activating agent were discussed and the possible reasons were proposed. The results showed that the specific surface area of ACNTs could be greatly affected by modifying the four factors amongst which the dosage of activating agent was found to be the dominant one which could result about 241 m2•g-1 of change in specific surface area. The specific surface area of ACNTs was only continuously enlarged with increasing the activation temperature, but had respective maximum with modifying the other factors in the experiments. The performance of meso-pores and macro-pores of the ACNTs was preserved in the process of modifying the four factors.
The effects of four important factors, including dosage of activating agent, activation temperature, activation time, and flow rate of protecting gas, on the specific surface area of activated carbon nanotubes (ACNTs) using KOH as the activating agent were discussed and the possible reasons were proposed. The results showed that the specific surface area of ACNTs could be greatly affected by modifying the four factors amongst which the dosage of activating agent was found to be the dominant one which could result about 241 m2•g-1 of change in specific surface area. The specific surface area of ACNTs was only continuously enlarged with increasing the activation temperature, but had respective maximum with modifying the other factors in the experiments. The performance of meso-pores and macro-pores of the ACNTs was preserved in the process of modifying the four factors.
2006, 22(01): 48-52
doi: 10.3866/PKU.WHXB20060110
Abstract:
The rheological properties of dispersions of silica in polyethylene glycol (PEG) have been studied under steady and oscillation stress shear performed on AR2000 stress controlled rheometer. The system shows shear thinning and reversible shear thickening behavior. Under steady stress shear, when the stress is less than the critical stress 9.99 Pa(σ＜σcs), the system shows shear thinning, while, the system shows shear thickening when σ＞σcs. Under oscillatory stress shear, when the shear stress is less than the critical stress 15.85 Pa(σ＜σco)、storage modulus(G′) decreases, loss modulus(G″), and the complex viscosity(η*) almost remain unchanged; but when σ＞σ>co, G′、G″ and η* increase synchronously. The magnitude of G″ is larger than the magnitude of G′ in the range of stress studied. The higher frequency used in the experiment leads to the larger value of the critical stress. The systems almost have the same values of the σ>co as the SiO2 mass fraction increasing, but the shear thickening phenomena are more obvious. Compared with the dispersion in PEG200, the dispersion in PEG400 shows lower complex viscosity before the critical point and a more sharp increase in the viscosity beyond the point, but has the same value of the critical stress (σ>co) and comparative viscosity at high stresses.
The rheological properties of dispersions of silica in polyethylene glycol (PEG) have been studied under steady and oscillation stress shear performed on AR2000 stress controlled rheometer. The system shows shear thinning and reversible shear thickening behavior. Under steady stress shear, when the stress is less than the critical stress 9.99 Pa(σ＜σcs), the system shows shear thinning, while, the system shows shear thickening when σ＞σcs. Under oscillatory stress shear, when the shear stress is less than the critical stress 15.85 Pa(σ＜σco)、storage modulus(G′) decreases, loss modulus(G″), and the complex viscosity(η*) almost remain unchanged; but when σ＞σ>co, G′、G″ and η* increase synchronously. The magnitude of G″ is larger than the magnitude of G′ in the range of stress studied. The higher frequency used in the experiment leads to the larger value of the critical stress. The systems almost have the same values of the σ>co as the SiO2 mass fraction increasing, but the shear thickening phenomena are more obvious. Compared with the dispersion in PEG200, the dispersion in PEG400 shows lower complex viscosity before the critical point and a more sharp increase in the viscosity beyond the point, but has the same value of the critical stress (σ>co) and comparative viscosity at high stresses.
2006, 22(01): 53-58
doi: 10.3866/PKU.WHXB20060111
Abstract:
The rate constants for the thermal decomposition reaction of peroxyacetyl nitrate (PAN), PAN→CH3C(O)OO+NO2(R1) were reestimated by RRKM theory and loosing transition state model based on the optimized structures and energies at the G3MP2B3 level of theory and the results agree with the experiment values. Then using the same models, the rate constants for another thermal decomposition reaction of PAN, PAN→CH3(O)O+NO3(R2) were studied. In Troe′s notation, the RRKM curves are presented by the following expressions for the limiting low- and high-pressure rate constants, k0(1)=8.0×10-3exp[－11912.8/T] cm3•molecule-1•s-1; k<∞(1)=2.8×101616exp[－13531.8/T] s-1; k0(2)=6.1×1016exp[－13011.9/T] cm3•molecule-1•s-1; k∞(2)=4.0×1016exp[－15463.1/T] s-1. The results of calculation suggested that the reaction R1 is the main dissociation channel, while R2 is the minor one and the difference between the rates of the two reactions is about 102 at the same conditions.
The rate constants for the thermal decomposition reaction of peroxyacetyl nitrate (PAN), PAN→CH3C(O)OO+NO2(R1) were reestimated by RRKM theory and loosing transition state model based on the optimized structures and energies at the G3MP2B3 level of theory and the results agree with the experiment values. Then using the same models, the rate constants for another thermal decomposition reaction of PAN, PAN→CH3(O)O+NO3(R2) were studied. In Troe′s notation, the RRKM curves are presented by the following expressions for the limiting low- and high-pressure rate constants, k0(1)=8.0×10-3exp[－11912.8/T] cm3•molecule-1•s-1; k<∞(1)=2.8×101616exp[－13531.8/T] s-1; k0(2)=6.1×1016exp[－13011.9/T] cm3•molecule-1•s-1; k∞(2)=4.0×1016exp[－15463.1/T] s-1. The results of calculation suggested that the reaction R1 is the main dissociation channel, while R2 is the minor one and the difference between the rates of the two reactions is about 102 at the same conditions.
2006, 22(01): 59-64
doi: 10.3866/PKU.WHXB20060112
Abstract:
The gas-phase reaction of CrO2+(2A1/4A″) with H2 to yield CrO+(2Σg/5Σg) and H2O is selected as a representative system of activation of H—H σ bond by MO2+. The reaction mechanism has been investigated with density functional theory (DFT) at the UB3LYP/6-311++G(3df, 3pd)//6-311G(2d, p) level. The geometries for reactants, the transition states, and the products were completely optimized. All the transition states were verified by the vibrational analysis and the intrinsic reaction coordinate calculations. The H—H bond has been activated by CrO2+(2A1) on the doublet PES(potential energy surface) while dihydrogen transfer from Cr to O (in longer Cr—O) on the quartet PES. The involving potential energy curve-crossing, with dramatically affecs reaction mechanism and reaction rate, has been discussed in detail. The crossing points (CPs) are localized by means of the Hammond postulate and the intrinsic reaction coordinate (IRC) approach. The formation of the transition metal dihydrogen complex (H2)CrO2+(2IM1 and 4IM1) involves donation of the H2 σ bonding orbital to the metal and the back-donation by the metal electron to the H2 σ* antibonding orbital, as illustrated by the fragment molecular orbital(FMO). In addition, the orbital analysis on the activation of the H—H bond and dihydrogen transfer has been carried out by FMO.
The gas-phase reaction of CrO2+(2A1/4A″) with H2 to yield CrO+(2Σg/5Σg) and H2O is selected as a representative system of activation of H—H σ bond by MO2+. The reaction mechanism has been investigated with density functional theory (DFT) at the UB3LYP/6-311++G(3df, 3pd)//6-311G(2d, p) level. The geometries for reactants, the transition states, and the products were completely optimized. All the transition states were verified by the vibrational analysis and the intrinsic reaction coordinate calculations. The H—H bond has been activated by CrO2+(2A1) on the doublet PES(potential energy surface) while dihydrogen transfer from Cr to O (in longer Cr—O) on the quartet PES. The involving potential energy curve-crossing, with dramatically affecs reaction mechanism and reaction rate, has been discussed in detail. The crossing points (CPs) are localized by means of the Hammond postulate and the intrinsic reaction coordinate (IRC) approach. The formation of the transition metal dihydrogen complex (H2)CrO2+(2IM1 and 4IM1) involves donation of the H2 σ bonding orbital to the metal and the back-donation by the metal electron to the H2 σ* antibonding orbital, as illustrated by the fragment molecular orbital(FMO). In addition, the orbital analysis on the activation of the H—H bond and dihydrogen transfer has been carried out by FMO.
2006, 22(01): 65-70
doi: 10.3866/PKU.WHXB20060113
Abstract:
A new thin film composed of transition metal nitride of Mn4N has been fabricated successfully by using reactive pulsed laser deposition and DC discharge methods in nitrogen ambient. The electrochemical reaction of the Mn4N thin film electrode with Li was firstly investigated by the discharge/charge, cyclic voltammetry, and AC impedance spectroscopy measurements. Mn4N thin film exhibited 420 mAh•g-1 in the first discharge process, and a nearly 50% irreversible capacity loss occurred in the first cycle. X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) were used to characterize the structure, morphology, and composition of the as-deposited, lithiated, and delithiated Mn4N thin films. The reversible reaction of the Mn4N thin film with lithium may involve partial conversion of metal Mn and Li3N into Mn4N. It should be responsible for the large capacity loss between the first and the second discharges.
A new thin film composed of transition metal nitride of Mn4N has been fabricated successfully by using reactive pulsed laser deposition and DC discharge methods in nitrogen ambient. The electrochemical reaction of the Mn4N thin film electrode with Li was firstly investigated by the discharge/charge, cyclic voltammetry, and AC impedance spectroscopy measurements. Mn4N thin film exhibited 420 mAh•g-1 in the first discharge process, and a nearly 50% irreversible capacity loss occurred in the first cycle. X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) were used to characterize the structure, morphology, and composition of the as-deposited, lithiated, and delithiated Mn4N thin films. The reversible reaction of the Mn4N thin film with lithium may involve partial conversion of metal Mn and Li3N into Mn4N. It should be responsible for the large capacity loss between the first and the second discharges.
2006, 22(01): 71-75
doi: 10.3866/PKU.WHXB20060114
Abstract:
An ionic liquid (IL) has been prepared by directly mixing AlCl3 and 1-methyl-3-butylimidazolium chloride (BMIC) with molar ratio 1/1 under dry ar n atmosphere. The densities and surface tensions of the pure IL were determined in the temperature range of (278.2±0.1) to (343.2±0.1) K. The properties for the ionic liquid were discussed in terms of Glasser′s empirical model. The values of volume of anion AlCl4- were obtained. The mean contribution of per methylene (CH2) group to standard entropy of the IL is 35.2 J•K-1•mol-1 and is in od agreement with contribution of 35.1 J•K-1•mol-1 from [Cn-min][NTf2]. The crystal energy of the IL is much lower than that of ionic solids, which is the main reason for the liquid state of the IL at room temperature. In addition, the interstice model was applied to calculate the thermal expansion coefficient of the IL, and the result agrees reasonably with the experimental value.
An ionic liquid (IL) has been prepared by directly mixing AlCl3 and 1-methyl-3-butylimidazolium chloride (BMIC) with molar ratio 1/1 under dry ar n atmosphere. The densities and surface tensions of the pure IL were determined in the temperature range of (278.2±0.1) to (343.2±0.1) K. The properties for the ionic liquid were discussed in terms of Glasser′s empirical model. The values of volume of anion AlCl4- were obtained. The mean contribution of per methylene (CH2) group to standard entropy of the IL is 35.2 J•K-1•mol-1 and is in od agreement with contribution of 35.1 J•K-1•mol-1 from [Cn-min][NTf2]. The crystal energy of the IL is much lower than that of ionic solids, which is the main reason for the liquid state of the IL at room temperature. In addition, the interstice model was applied to calculate the thermal expansion coefficient of the IL, and the result agrees reasonably with the experimental value.
2006, 22(01): 76-81
doi: 10.3866/PKU.WHXB20060115
Abstract:
The geometry and electronic structures of the SnO2(110) surface have been investigated by using the first-principle method. Compared to an ideal surface, the five-fold and six-fold Sn atoms at the top layer shift inwards and outwards, respectively. For the surface oxygen atoms, the in-plane oxygen atoms move outwards, while the displacement of bridged oxygen can be neglectable. When the thickness of slab is smaller than 3 nm, the oscillations of surface energy and the displacements of surface atoms as a function of the number of layers are observed. The results of band structure calculations show that the energy bands mainly originated from the 2i>py/2i>pz orbitals of the bridged oxygen appear in the bottom of the band gap of bulk. Furthermore, the influences of the surface relaxation on the electronic properties of SnO2(110) surface are also discussed.
The geometry and electronic structures of the SnO2(110) surface have been investigated by using the first-principle method. Compared to an ideal surface, the five-fold and six-fold Sn atoms at the top layer shift inwards and outwards, respectively. For the surface oxygen atoms, the in-plane oxygen atoms move outwards, while the displacement of bridged oxygen can be neglectable. When the thickness of slab is smaller than 3 nm, the oscillations of surface energy and the displacements of surface atoms as a function of the number of layers are observed. The results of band structure calculations show that the energy bands mainly originated from the 2i>py/2i>pz orbitals of the bridged oxygen appear in the bottom of the band gap of bulk. Furthermore, the influences of the surface relaxation on the electronic properties of SnO2(110) surface are also discussed.
2006, 22(01): 82-85
doi: 10.3866/PKU.WHXB20060116
Abstract:
Cheletropic addition of sulfur dioxide to 2,4-hexadiene has been calculated by density functional theory(DFT) at the level of B3LYP/6-311+G**, the result of IRC calculation shows that the cheletropic addition is a concerted reaction. In reaction, each reactant gives its electrons in HOMO to the LUMO of other reactant simultaneously, which is different from the conditional mechanism of 4+2 cycloaddition. Before reaction, the difference of energy level between HOMO of sulfur dioxide and LUMO of 2,4-hexadiene is largish(8.4 eV), but in the course of reaction, the antibonding LUMO of 2,4-hexadiene turns into a bonding orbital and decreases its energy, so the electrons in HOMO of sulfur dioxide can flow into this orbital easily. The net result of the reaction is that sulfur dioxide transfers 0.23e negative charge to 2,4-hexadiene.
Cheletropic addition of sulfur dioxide to 2,4-hexadiene has been calculated by density functional theory(DFT) at the level of B3LYP/6-311+G**, the result of IRC calculation shows that the cheletropic addition is a concerted reaction. In reaction, each reactant gives its electrons in HOMO to the LUMO of other reactant simultaneously, which is different from the conditional mechanism of 4+2 cycloaddition. Before reaction, the difference of energy level between HOMO of sulfur dioxide and LUMO of 2,4-hexadiene is largish(8.4 eV), but in the course of reaction, the antibonding LUMO of 2,4-hexadiene turns into a bonding orbital and decreases its energy, so the electrons in HOMO of sulfur dioxide can flow into this orbital easily. The net result of the reaction is that sulfur dioxide transfers 0.23e negative charge to 2,4-hexadiene.
2006, 22(01): 86-91
doi: 10.3866/PKU.WHXB20060117
Abstract:
Organic electrolyte tetrabutyl ammonium bromide ((Bu)4NBr, TBAB) was added into micellar catalysis system in which chloromethylation reaction of polystyrene was carried out, and the effect of TBAB on the catalytic reaction was investigated. The experiment results show that the adding of TBAB speeds up obviously the chloromethylation reaction of polystyrene in the micellar catalytic systems in which nonionic surfactant NP-10 and anionic surfactant SDS are used, especially in the system in which non-ionic surfactant NP-10 is used the acceleration is more distinct. On the contrary, in the micellar catalytic systems in which cationic surfactant CTAB is used, TBAB hardly influences the reaction rate. On one hand the reason for this may attribute to the decrease of critical micelle concentration of SDS and the increase of solubilization of polystyrene in the micellar solution because of adding electrolyte TBAB, on the other hand, a more primary reason is that organic cation (Bu)4N+ of TBAB may be embedded into micelles due to the synergistic effect of electrostatic attraction and hydrophobic interaction between butyl groups and the hydrocarbon chains of SDS , so that the inhibiting effect of anionic head groups of SDS for the nucleophilic substitution reaction that is a controlling step is weakened. Under hydrophobic interaction, organic cation (Bu)4N+ of TBAB may also be combined on the surface of NP-10 micelles, so that the surface of NP-10 micelles charged positively accelerates distinctly the nucleophilic substitution reaction. For CTAB system, the cation (Bu)4N+ can not be closed to the micelles of CTAB owing to electrostatic repellence, so the adding of TBAB can not speed up the rate of chloromethylation reaction of polystyrene.
Organic electrolyte tetrabutyl ammonium bromide ((Bu)4NBr, TBAB) was added into micellar catalysis system in which chloromethylation reaction of polystyrene was carried out, and the effect of TBAB on the catalytic reaction was investigated. The experiment results show that the adding of TBAB speeds up obviously the chloromethylation reaction of polystyrene in the micellar catalytic systems in which nonionic surfactant NP-10 and anionic surfactant SDS are used, especially in the system in which non-ionic surfactant NP-10 is used the acceleration is more distinct. On the contrary, in the micellar catalytic systems in which cationic surfactant CTAB is used, TBAB hardly influences the reaction rate. On one hand the reason for this may attribute to the decrease of critical micelle concentration of SDS and the increase of solubilization of polystyrene in the micellar solution because of adding electrolyte TBAB, on the other hand, a more primary reason is that organic cation (Bu)4N+ of TBAB may be embedded into micelles due to the synergistic effect of electrostatic attraction and hydrophobic interaction between butyl groups and the hydrocarbon chains of SDS , so that the inhibiting effect of anionic head groups of SDS for the nucleophilic substitution reaction that is a controlling step is weakened. Under hydrophobic interaction, organic cation (Bu)4N+ of TBAB may also be combined on the surface of NP-10 micelles, so that the surface of NP-10 micelles charged positively accelerates distinctly the nucleophilic substitution reaction. For CTAB system, the cation (Bu)4N+ can not be closed to the micelles of CTAB owing to electrostatic repellence, so the adding of TBAB can not speed up the rate of chloromethylation reaction of polystyrene.
2006, 22(01): 92-97
doi: 10.3866/PKU.WHXB20060118
Abstract:
The effect of magnetic field on the photocatalytic oxidation of benzene and ethylene contained in air over Pt/TiO2 was studied under 365 nm irradiation in the range of magnetic field intensity of ≤0.2 T. It was found that when the UV lamp was near to or under a magnetic field, the magnetic field could enhance the photocatalytic conversion and mineralization of benzene and ethylene. However, no effect of magnetic field on the reactions was observed when the UV lamp was far away from the magnetic field and the light was transmitted onto the reactor by a focusing fiber. In the former case, the observed enhance of photocatalytic oxidation of the two reactants was a result of the increase of brightness of the UV lamp under magnetic field. This is because that high photo intensity provided high light energy for the reaction and led to increase of the reaction temperature. In the latter case, intensity of UV light wasn′t disturbed by the magnetic field, applying magnetic field had no effect on the two photocatalytic reactions. The results showed that there was no any inherent effect on the gas-solid phase photocatalytic reaction.
The effect of magnetic field on the photocatalytic oxidation of benzene and ethylene contained in air over Pt/TiO2 was studied under 365 nm irradiation in the range of magnetic field intensity of ≤0.2 T. It was found that when the UV lamp was near to or under a magnetic field, the magnetic field could enhance the photocatalytic conversion and mineralization of benzene and ethylene. However, no effect of magnetic field on the reactions was observed when the UV lamp was far away from the magnetic field and the light was transmitted onto the reactor by a focusing fiber. In the former case, the observed enhance of photocatalytic oxidation of the two reactants was a result of the increase of brightness of the UV lamp under magnetic field. This is because that high photo intensity provided high light energy for the reaction and led to increase of the reaction temperature. In the latter case, intensity of UV light wasn′t disturbed by the magnetic field, applying magnetic field had no effect on the two photocatalytic reactions. The results showed that there was no any inherent effect on the gas-solid phase photocatalytic reaction.
2006, 22(01): 98-101
doi: 10.3866/PKU.WHXB20060119
Abstract:
The number of water molecules necessary to stabilize the glycine zwitterions was studied, then the structures and properties of dihydrated zwitterionic glycine complexes were discussed. At the same time, the transition state of dihydrated neutral glycine (2W-GN) to dihydrated zwitterionic glycine (2W-GZ) was calculated. Three conclusions were drawn as below, (1) Two water molecules are necessary to stabilize the glycine zwitterions; (2) It is hydrogen bond which combines the glycine with two water molecules, the bonding energy is relatively large and the complexes are stable; (3) The activation energy of 2W-GN to 2W-GZ is close to the energy of hydrogen bond. All the tasks were calculated by B3LYP, at the 6-31++G** basis set level with the Gaussian98 program.
The number of water molecules necessary to stabilize the glycine zwitterions was studied, then the structures and properties of dihydrated zwitterionic glycine complexes were discussed. At the same time, the transition state of dihydrated neutral glycine (2W-GN) to dihydrated zwitterionic glycine (2W-GZ) was calculated. Three conclusions were drawn as below, (1) Two water molecules are necessary to stabilize the glycine zwitterions; (2) It is hydrogen bond which combines the glycine with two water molecules, the bonding energy is relatively large and the complexes are stable; (3) The activation energy of 2W-GN to 2W-GZ is close to the energy of hydrogen bond. All the tasks were calculated by B3LYP, at the 6-31++G** basis set level with the Gaussian98 program.
2006, 22(01): 102-105
doi: 10.3866/PKU.WHXB20060120
Abstract:
Ni-P nanowire arrays and nanotube arrays were fabricated by electroless deposition using porous aluminum oxide membrane as templates in acidic coating bath at room temperature. The images of Ni-P nanowires and nanotubes are obtained by transmission electron microscope (TEM), respectively. X-ray diffraction (XRD) and selected area electron diffraction (SAED) are employed to study the morphology and chemical composition of the nanowires and nanotubes. The influence of pretreatment of alumina template on the growth of nano-arrays is studied by comparing the growing ways between nanowires and nanotubes. The results indicate that both Ni-P nanowires and nanotubes are amorphous nickel phosphor alloy. The growth of nanowires and nanotubes mainly depends on sensitization and activation process at room temperature. Using sensitization and activation together as pretreatment will cause the formation of nanowires. Using activation only as pretreatment will cause the formation of nanotubes. The thickness of nanotubes wouldn′t rise with time when it reached a certain degree.
Ni-P nanowire arrays and nanotube arrays were fabricated by electroless deposition using porous aluminum oxide membrane as templates in acidic coating bath at room temperature. The images of Ni-P nanowires and nanotubes are obtained by transmission electron microscope (TEM), respectively. X-ray diffraction (XRD) and selected area electron diffraction (SAED) are employed to study the morphology and chemical composition of the nanowires and nanotubes. The influence of pretreatment of alumina template on the growth of nano-arrays is studied by comparing the growing ways between nanowires and nanotubes. The results indicate that both Ni-P nanowires and nanotubes are amorphous nickel phosphor alloy. The growth of nanowires and nanotubes mainly depends on sensitization and activation process at room temperature. Using sensitization and activation together as pretreatment will cause the formation of nanowires. Using activation only as pretreatment will cause the formation of nanotubes. The thickness of nanotubes wouldn′t rise with time when it reached a certain degree.
2006, 22(01): 106-109
doi: 10.3866/PKU.WHXB20060121
Abstract:
The growth of nano-fibrous polyaniline (PANI) film on stainless steel (SS) by pulse galvanostatic method (PGM) in 0.3 mol•L-1 aniline +1 mol•L-1 HNO3 aqueous solution at 1 mA•cm-2 was studied. The electrochemical behavior during the polymerization and the morphology of the PANI films with various deposition charges were characterized by chronopotentiogram and scanning electron microscope (SEM), respectively. Moreover, the rate of aniline electropolymerization was determined by the cyclic voltammetry (CV) technique. The results showed that the polymerization of aniline on SS involved two separate stages. Firstly, polyaniline grew on bare SS electrode and represented granular structure. In this stage, the potential of aniline polymerization was relatively positive (at ca. 1.10 V). After about 30 s, the surface of the SS electrode was entirely covered by a granular PANI film. Secondly, PANI grew further with nano-fibrous morphology on the surface of the granular PANI film. The polymerization potential maintained ca. 0.75 V when the granular PANI film was entirely covered by the nano-fibrous PANI film.
The growth of nano-fibrous polyaniline (PANI) film on stainless steel (SS) by pulse galvanostatic method (PGM) in 0.3 mol•L-1 aniline +1 mol•L-1 HNO3 aqueous solution at 1 mA•cm-2 was studied. The electrochemical behavior during the polymerization and the morphology of the PANI films with various deposition charges were characterized by chronopotentiogram and scanning electron microscope (SEM), respectively. Moreover, the rate of aniline electropolymerization was determined by the cyclic voltammetry (CV) technique. The results showed that the polymerization of aniline on SS involved two separate stages. Firstly, polyaniline grew on bare SS electrode and represented granular structure. In this stage, the potential of aniline polymerization was relatively positive (at ca. 1.10 V). After about 30 s, the surface of the SS electrode was entirely covered by a granular PANI film. Secondly, PANI grew further with nano-fibrous morphology on the surface of the granular PANI film. The polymerization potential maintained ca. 0.75 V when the granular PANI film was entirely covered by the nano-fibrous PANI film.
2006, 22(01): 110-113
doi: 10.3866/PKU.WHXB20060122
Abstract:
Magnesium borate nanobelts, a new kind of quasi one-dimensional nanomaterials, has been synthesized by heating mixed powders of crystalline boron and M nanoparticles in the presence of H2O at 1100 ℃. The produced white sample was characterized by different techniques, such as the X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR). The results show that the products are single-crystalline Mg3B2O6Mg3B2O6 nanobelts except some attached Mg2B2O5 particles. The widths of the nanobelts are in the range of 100～200 nm and the lengths are up to several ten micrometers. The growth direction of the nanobelts nears to crystalline Mg3B2O6[010] direction. Finally, the growth mechanism for these novel Mg3B2O6 nanobelts and the effect of reactive temperature on the products have been primarily presented.
Magnesium borate nanobelts, a new kind of quasi one-dimensional nanomaterials, has been synthesized by heating mixed powders of crystalline boron and M nanoparticles in the presence of H2O at 1100 ℃. The produced white sample was characterized by different techniques, such as the X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR). The results show that the products are single-crystalline Mg3B2O6Mg3B2O6 nanobelts except some attached Mg2B2O5 particles. The widths of the nanobelts are in the range of 100～200 nm and the lengths are up to several ten micrometers. The growth direction of the nanobelts nears to crystalline Mg3B2O6[010] direction. Finally, the growth mechanism for these novel Mg3B2O6 nanobelts and the effect of reactive temperature on the products have been primarily presented.
2006, 22(01): 114-117
doi: 10.3866/PKU.WHXB20060123
Abstract:
Au-doped α-Fe2O3 nanopowders were prepared by coprecipitation, impregnation, and ultraviolet irradiation methods, respectively. The Au/α-Fe2O3 nanopowders were characterized by TG-DTA, XRD, and TEM. The effects of dopping methods, the Au content, and the calcination temperature on gas-sensing properties of α-Fe2O3 were studied. The results showed that α-Fe2O3 sensors presented much higher sensitivity after doped with Au. Among them, the Au-doped α-Fe2O3 (w(Au)=1.5%, calcinated at 400 ℃) prepared by coprecipitation gave the best sensitivity.
Au-doped α-Fe2O3 nanopowders were prepared by coprecipitation, impregnation, and ultraviolet irradiation methods, respectively. The Au/α-Fe2O3 nanopowders were characterized by TG-DTA, XRD, and TEM. The effects of dopping methods, the Au content, and the calcination temperature on gas-sensing properties of α-Fe2O3 were studied. The results showed that α-Fe2O3 sensors presented much higher sensitivity after doped with Au. Among them, the Au-doped α-Fe2O3 (w(Au)=1.5%, calcinated at 400 ℃) prepared by coprecipitation gave the best sensitivity.
2006, 22(01): 119-123
doi: 10.3866/PKU.WHXB20060124
Abstract:
Based on the synthesis and purification of carbon nanotubes (CNTs), CNTs were treated with concentrated HNO3 solution at 50, 75, and 100 ℃ for 5 h. After CNTs were treated in concentrated HNO3 solution at 75 ℃ for 5 h, suitable amount of hydrophilic O-containing surface groups would be formed so that the average size of the Pt particles deposited on the CNTs surface is small, about 3.7 nm, leading to the od electrocatalytic activity of the Pt/CNTs catalyst for the methanol oxidation. If the treatment temperature is as low as 50 ℃, the amount of the hydrophilic O-containing surface groups formed on CNTs is small so that the Pt particles formed on CNTs would be easy to aggregate. If the treatment temperature is as high as 100 ℃, the amount of the hydrophilic O-containing surface groups formed on CNTs is large and the CNTs would be opened. Then, the Pt particles formed on CNTs would be concentrated near the fractures and form large Pt particles, leading to the low electrocatalytic activity of the Pt/CNTs catalyst for the methanol oxidation.
Based on the synthesis and purification of carbon nanotubes (CNTs), CNTs were treated with concentrated HNO3 solution at 50, 75, and 100 ℃ for 5 h. After CNTs were treated in concentrated HNO3 solution at 75 ℃ for 5 h, suitable amount of hydrophilic O-containing surface groups would be formed so that the average size of the Pt particles deposited on the CNTs surface is small, about 3.7 nm, leading to the od electrocatalytic activity of the Pt/CNTs catalyst for the methanol oxidation. If the treatment temperature is as low as 50 ℃, the amount of the hydrophilic O-containing surface groups formed on CNTs is small so that the Pt particles formed on CNTs would be easy to aggregate. If the treatment temperature is as high as 100 ℃, the amount of the hydrophilic O-containing surface groups formed on CNTs is large and the CNTs would be opened. Then, the Pt particles formed on CNTs would be concentrated near the fractures and form large Pt particles, leading to the low electrocatalytic activity of the Pt/CNTs catalyst for the methanol oxidation.
2006, 22(01): 124-130
doi: 10.3866/PKU.WHXB20060125
Abstract:
Recent progress in the field of nanolithography of self-assembled monolayers by scanning probe microscopy (SPM), which is important in microelectronics and sensor technology, is introduced in the paper. According to the working principle, scanning probe lithography (SPL) can be classified into three cate ries, namely STM-based nanolithography, AFM-based nanolithography, and C-AFM-based nanolithography. SPL is a pivot of the fundamental study in the field of nanolithography for its high spatial resolution, ease in fabrication and od controllability in operation. The possible application in information storage has been discussed as well.
Recent progress in the field of nanolithography of self-assembled monolayers by scanning probe microscopy (SPM), which is important in microelectronics and sensor technology, is introduced in the paper. According to the working principle, scanning probe lithography (SPL) can be classified into three cate ries, namely STM-based nanolithography, AFM-based nanolithography, and C-AFM-based nanolithography. SPL is a pivot of the fundamental study in the field of nanolithography for its high spatial resolution, ease in fabrication and od controllability in operation. The possible application in information storage has been discussed as well.
