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2008 Volume 24 Issue 11
2008, 24(11):
Abstract:
2008, 24(11): 1941-1944
doi: 10.1016/S1872-1508(08)60075-3
Abstract:
By assembling polystyrene microsphores on a sample surface, the surface Raman signal could be enhanced. The dependence of the enhancement effect on the size of microparticles was systematically investigated and it was found that microparticles with a diameter of 3.00 μm showed the highest enhancement of ca 5 folds. By utilizing the enhancement effect of the microspheres, the surface Raman intensity of malachite green isothiocyanate (MGITC) adsorbed on Au(111) surface could be enhanced by 20 folds, indicating that thismethod could effectively improve the detection sensitivity of surface Raman spectroscopy for the adsorbed species on single crystal surface. The later signal increment corresponds to the Raman enhancement effect of nearly 3 orders of magnitude. The enhancement effect is mainly owing to the formation of nanojets when a laser is focused on the microspheres of appropriate diameter. The formation of nanojets will lead to the highly localized electromagnetic field, which will then significantly enhance the Raman process in the nanojets. The main reason for obtaining different enhancements on two types of samples was analyzed.
2008, 24(11): 1945-1949
doi: 10.1016/S1872-1508(08)60076-5
Abstract:
A new compound dicetyltrimethylammonium hexafluorotitanium dihydrate, [(n-C16H33)N(CH3)3]2[TiF6]·2H2O (compound 1), was hydrothermally synthesized at 150 ℃ and characterized by single crystal X-ray diffraction, Fourier-transform infrared (FTIR) spectroscopy, elemental analysis, and thermogravimetric analysis. Compound 1 crystallizes in the monoclinic system, space group C2/c. It consists of hexafluorotitanium cations [TiF6]2-, water molecular (H2O), and cetyltrimethylammonium ions [(n-C16H33)N(CH3)3]+, which are connected together by extensive hydrogen bonding.
A new compound dicetyltrimethylammonium hexafluorotitanium dihydrate, [(n-C16H33)N(CH3)3]2[TiF6]·2H2O (compound 1), was hydrothermally synthesized at 150 ℃ and characterized by single crystal X-ray diffraction, Fourier-transform infrared (FTIR) spectroscopy, elemental analysis, and thermogravimetric analysis. Compound 1 crystallizes in the monoclinic system, space group C2/c. It consists of hexafluorotitanium cations [TiF6]2-, water molecular (H2O), and cetyltrimethylammonium ions [(n-C16H33)N(CH3)3]+, which are connected together by extensive hydrogen bonding.
2008, 24(11): 1950-1956
doi: 10.1016/S1872-1508(08)60077-7
Abstract:
Two triphenylamine-based dyes (TPAR3 and TPAR6) containing two carboxylic acid groups with different conjugated lengths were synthesized and characterized with regard to their photophysical and photoelectrochemical properties. Experimental results showed that the λmax of TPAR6 either in methanol solution or on TiO2 filmwas red-shifted and broadened by extending the π-conjugated bridge. However, the performance of TPAR3-based dye-sensitized solar cell (DSC) was superior to that of TPAR6. This reason was due to the serious self-quenching of the electronically excited state in TPAR6 molecule, resulting from its cis-trans isomerization. The effects of addition of guanidine thiocyanate (GT) in the electrolyte on the performance of DSCs based on TPAR3 were also investigated, revealing a maximum energy conversion efficiency of 4.02%at 0.100 mol·L-1 GT.
Two triphenylamine-based dyes (TPAR3 and TPAR6) containing two carboxylic acid groups with different conjugated lengths were synthesized and characterized with regard to their photophysical and photoelectrochemical properties. Experimental results showed that the λmax of TPAR6 either in methanol solution or on TiO2 filmwas red-shifted and broadened by extending the π-conjugated bridge. However, the performance of TPAR3-based dye-sensitized solar cell (DSC) was superior to that of TPAR6. This reason was due to the serious self-quenching of the electronically excited state in TPAR6 molecule, resulting from its cis-trans isomerization. The effects of addition of guanidine thiocyanate (GT) in the electrolyte on the performance of DSCs based on TPAR3 were also investigated, revealing a maximum energy conversion efficiency of 4.02%at 0.100 mol·L-1 GT.
2008, 24(11): 1957-1963
doi: 10.1016/S1872-1508(08)60078-9
Abstract:
An intermediate product that was yellow, soluble, and solid was obtained in a high-radiation flash pyrolysis reactor. Under two different radiant heat fluxes, the yields tended to both increase initially until achieving a steady state, and then increase again with the progress of reaction. The compositional analysis of the yellow product was performed on high performance liquid chromatography (HPLC). It was indicated that the product mainly consisted of oli saccharides, glucose, levoglucosan, methylglyoxal and so on. The compounds including oli saccharides such as cellobiose and cellotriose, and monosaccharides such as glucose were regarded as active cellulose. Under the higher heat flux, the relative yield of the active cellulose increased initially, followed by a decreasing trend, and achieved a maximummass fraction of 68% (w) in the soluble yellowproduct. The oli saccharides with higher degree of polymerization (DP) were the primary components. Under the lower heat flux the yield of active cellulose was relatively lower, achieving a maximum of about 57% (w), and more saccharides with lower DP were contained. It was suggested that active cellulose was quite unstable at high temperature, and easily decomposed into saccharides with lower DP, even char, volatiles, and gaseous products. Finally an improved mechanism was proposed to describe the reaction route of formation and consequent evolution of active cellulose during cellulose pyrolysis.
An intermediate product that was yellow, soluble, and solid was obtained in a high-radiation flash pyrolysis reactor. Under two different radiant heat fluxes, the yields tended to both increase initially until achieving a steady state, and then increase again with the progress of reaction. The compositional analysis of the yellow product was performed on high performance liquid chromatography (HPLC). It was indicated that the product mainly consisted of oli saccharides, glucose, levoglucosan, methylglyoxal and so on. The compounds including oli saccharides such as cellobiose and cellotriose, and monosaccharides such as glucose were regarded as active cellulose. Under the higher heat flux, the relative yield of the active cellulose increased initially, followed by a decreasing trend, and achieved a maximummass fraction of 68% (w) in the soluble yellowproduct. The oli saccharides with higher degree of polymerization (DP) were the primary components. Under the lower heat flux the yield of active cellulose was relatively lower, achieving a maximum of about 57% (w), and more saccharides with lower DP were contained. It was suggested that active cellulose was quite unstable at high temperature, and easily decomposed into saccharides with lower DP, even char, volatiles, and gaseous products. Finally an improved mechanism was proposed to describe the reaction route of formation and consequent evolution of active cellulose during cellulose pyrolysis.
2008, 24(11): 1964-1968
doi: 10.3866/PKU.WHXB20081105
Abstract:
The diffusion behavior of hydrogen atomin perfect δ-Pu metal was studied with density functional theory (DFT) and periodical model. The stablest site for hydrogen is the octahedral interstitial site. A single hydrogen atom has the minimum embedding energy about -3.12 and -2.22 eV in the octahedral interstitial site of fcc δ-Pu at non-spin polarization and spin-polarization levels, respectively. The embedding energy in tetrahedral interstitial site is little larger than that in tetrahedral interstitial site. Hydrogen atom in δ-Pu crystal most preferably diffuses along the path linked with different interstitials. The diffusion barrier along the path from octahedral interstitial site to tetrahedral interstitial site is 1.06 eV. The diffusion barrier along the reverse path is 0.38 eV. In addition, the diffusion barrier along the path from tetrahedral interstitial site to tetrahedral interstitial site is 1.83 eV, and the path from octahedral interstitial site to octahedral interstitial site corresponds to the highest diffusion barrier.
The diffusion behavior of hydrogen atomin perfect δ-Pu metal was studied with density functional theory (DFT) and periodical model. The stablest site for hydrogen is the octahedral interstitial site. A single hydrogen atom has the minimum embedding energy about -3.12 and -2.22 eV in the octahedral interstitial site of fcc δ-Pu at non-spin polarization and spin-polarization levels, respectively. The embedding energy in tetrahedral interstitial site is little larger than that in tetrahedral interstitial site. Hydrogen atom in δ-Pu crystal most preferably diffuses along the path linked with different interstitials. The diffusion barrier along the path from octahedral interstitial site to tetrahedral interstitial site is 1.06 eV. The diffusion barrier along the reverse path is 0.38 eV. In addition, the diffusion barrier along the path from tetrahedral interstitial site to tetrahedral interstitial site is 1.83 eV, and the path from octahedral interstitial site to octahedral interstitial site corresponds to the highest diffusion barrier.
2008, 24(11): 1969-1974
doi: 10.3866/PKU.WHXB20081106
Abstract:
Conductive composites were prepared by filling high density polyethylene (HDPE) with various amounts of multi-walled carbon nanotubes (MWNTs) and were characterized by using a terahertz time-domain spectroscopy (THz-TDS) setup assisted with conductivity measurements. The direct current (dc) conductivity measurement indicated that the percolation threshold was about 5%in volume fraction. The frequence and filler concentration dependences of alternating current (ac) conductivity were investigated and the results could be understood with the polarization effects between clusters, anomalous diffusion within the clusters as well as the percolating structures. With increasing the MWNT particles, the absorption coefficient and refractive index all increased at THz band due to the increase of the charge carrier density. The experimental data were analyzed with Cole-Cole formula of dipole relaxation under the assumption that conductive particles dispersed in the matrix behaved like dipoles and contributed mainly to the dielectric loss in the THz frequency range.
Conductive composites were prepared by filling high density polyethylene (HDPE) with various amounts of multi-walled carbon nanotubes (MWNTs) and were characterized by using a terahertz time-domain spectroscopy (THz-TDS) setup assisted with conductivity measurements. The direct current (dc) conductivity measurement indicated that the percolation threshold was about 5%in volume fraction. The frequence and filler concentration dependences of alternating current (ac) conductivity were investigated and the results could be understood with the polarization effects between clusters, anomalous diffusion within the clusters as well as the percolating structures. With increasing the MWNT particles, the absorption coefficient and refractive index all increased at THz band due to the increase of the charge carrier density. The experimental data were analyzed with Cole-Cole formula of dipole relaxation under the assumption that conductive particles dispersed in the matrix behaved like dipoles and contributed mainly to the dielectric loss in the THz frequency range.
2008, 24(11): 1975-1980
doi: 10.3866/PKU.WHXB20081107
Abstract:
A series of nanocomposite of TiO2 thin films and multi-walled carbon nanotubes (MWCNTs) in different forms were prepared by sol-gel methods. The surface morphologies of the nanocomposite films were characterized via scanning electron microscopy (SEM). The effects of inducing MWCNTs into TiO2 thin film on the structure and absorption properties of TiO2 were characterized by X-ray diffraction (XRD) and UV-Vis spectrophotometer methods. The nanocomposite films were also characterized by photoelectrochemical methods. The results showed that the MWCNTs/TiO2 nanocomposite films were porous and rough and the absorption edge can extend to visible light region. The photoelectrochemical properties of TiO2 could be evidently enhanced by bottom distribution mode, or otherwise, decreased by surface distribution mode and uniform distribution mode. The effects of composite modes on the photoelectrochemical activities were discussed in terms of separation of charge carriers. MWCNTs distributed in bottommode within the nanocomposite filmcould improve electron-collecting efficiency and reduce recombination.
A series of nanocomposite of TiO2 thin films and multi-walled carbon nanotubes (MWCNTs) in different forms were prepared by sol-gel methods. The surface morphologies of the nanocomposite films were characterized via scanning electron microscopy (SEM). The effects of inducing MWCNTs into TiO2 thin film on the structure and absorption properties of TiO2 were characterized by X-ray diffraction (XRD) and UV-Vis spectrophotometer methods. The nanocomposite films were also characterized by photoelectrochemical methods. The results showed that the MWCNTs/TiO2 nanocomposite films were porous and rough and the absorption edge can extend to visible light region. The photoelectrochemical properties of TiO2 could be evidently enhanced by bottom distribution mode, or otherwise, decreased by surface distribution mode and uniform distribution mode. The effects of composite modes on the photoelectrochemical activities were discussed in terms of separation of charge carriers. MWCNTs distributed in bottommode within the nanocomposite filmcould improve electron-collecting efficiency and reduce recombination.
2008, 24(11): 1981-1987
doi: 10.3866/PKU.WHXB20081108
Abstract:
To investigate the non-covalent interaction between glutathione and D-amino acids, stoichiometric reduced glutathione (GSH) and three D-amino acids, including D-phenylalanine (D-Phe), D-histidine (D-His), and D-glutamine (D-Gln), were mixed respectively, and then incubated at room temperature for 1 h to reach equilibrium. The electrospray ionization mass spectrometry (ESI-MS) results indicated that glutathione and three D-amino acids could formnon-covalent complexes in physiological pH conditions, respectively. The binding of glutathione to D-amino acid was further confirmed by collision-induced dissociation (CID) in a tandem mass spectrometer. Additionally, the complexes exhibited different features and properties from the reactants in UV spectroscopy, which also confirmed the results of ESI-MS. To avoid distinct ionization efficiency discrepancy and signal suppression in ESI-MS measurements, the interaction between glutathione (GSH) and D-glutamine (Gln) was quantitatively evaluated. A series of samples with different initial concentrations of glutathione and D-amino acids were mixed, and then series of peak intensities for different species in the mixture were achieved by ESI-MS. The dissociation constants of three complexes formed by glutathione and D-amino acids were calculated. The calculation results revealed that the reduced tripeptide γ-glutathione could interact with D-amino acids to formnon-covalent complexes with different affinities, the stabilities of the three complexes increased gradually according to the order of D-glutamine, D-phenylalanine, and D-histidine.
To investigate the non-covalent interaction between glutathione and D-amino acids, stoichiometric reduced glutathione (GSH) and three D-amino acids, including D-phenylalanine (D-Phe), D-histidine (D-His), and D-glutamine (D-Gln), were mixed respectively, and then incubated at room temperature for 1 h to reach equilibrium. The electrospray ionization mass spectrometry (ESI-MS) results indicated that glutathione and three D-amino acids could formnon-covalent complexes in physiological pH conditions, respectively. The binding of glutathione to D-amino acid was further confirmed by collision-induced dissociation (CID) in a tandem mass spectrometer. Additionally, the complexes exhibited different features and properties from the reactants in UV spectroscopy, which also confirmed the results of ESI-MS. To avoid distinct ionization efficiency discrepancy and signal suppression in ESI-MS measurements, the interaction between glutathione (GSH) and D-glutamine (Gln) was quantitatively evaluated. A series of samples with different initial concentrations of glutathione and D-amino acids were mixed, and then series of peak intensities for different species in the mixture were achieved by ESI-MS. The dissociation constants of three complexes formed by glutathione and D-amino acids were calculated. The calculation results revealed that the reduced tripeptide γ-glutathione could interact with D-amino acids to formnon-covalent complexes with different affinities, the stabilities of the three complexes increased gradually according to the order of D-glutamine, D-phenylalanine, and D-histidine.
2008, 24(11): 1988-1994
doi: 10.3866/PKU.WHXB20081109
Abstract:
The physical and electrochemical behaviors of the tantalum substrate born-doped diamond (Ta/BDD)electrode prepared by hot filament chemical vapor deposition (HFCVD) technique and its application in electrochemical oxidation of wastewater containing nitrophenol were studied. Raman spectroscopy and scanning electron microscopy (SEM) examinations demonstrated that the electrode had well-defined diamond features. It was observed that the Ta/BDD electrode had a much higher overpotential for water electrolysis prohibiting the evolution of oxygen in the cyclic voltammetry test. During the electrochemical oxidation of wastewater containing nitrophenol, the results obtained by high performance liquid chromatography (HPLC) and chemical oxygen demand (COD) tests showed that the electrochemical process was suitable for completely degrading nitrophenol. The influence of current density, temperature, support electrolyte, and electrolyte concentration was investigated in order to find the best conditions for COD removal. od electrochemical stability of Ta/BDD electrode was obtained in the accelerated life test. According to the results, Ta/BDD anode is consitered to be a unique electrode for the degradation of nitrophenol and COD simultaneously.
The physical and electrochemical behaviors of the tantalum substrate born-doped diamond (Ta/BDD)electrode prepared by hot filament chemical vapor deposition (HFCVD) technique and its application in electrochemical oxidation of wastewater containing nitrophenol were studied. Raman spectroscopy and scanning electron microscopy (SEM) examinations demonstrated that the electrode had well-defined diamond features. It was observed that the Ta/BDD electrode had a much higher overpotential for water electrolysis prohibiting the evolution of oxygen in the cyclic voltammetry test. During the electrochemical oxidation of wastewater containing nitrophenol, the results obtained by high performance liquid chromatography (HPLC) and chemical oxygen demand (COD) tests showed that the electrochemical process was suitable for completely degrading nitrophenol. The influence of current density, temperature, support electrolyte, and electrolyte concentration was investigated in order to find the best conditions for COD removal. od electrochemical stability of Ta/BDD electrode was obtained in the accelerated life test. According to the results, Ta/BDD anode is consitered to be a unique electrode for the degradation of nitrophenol and COD simultaneously.
2008, 24(11): 1995-1999
doi: 10.3866/PKU.WHXB20081110
Abstract:
The adsorption of N2 molecule on the UO(100) surface was studied with periodic slab model by VWN-BP approach of GGA within the framework of density functional theory (DFT). The results of geometry optimization indicated that the most stable structure of adsorption was N2 adsorbed parallelly on the hollow site with an adsorption energy of 79.0 kJ·mol -1. The analysis of Mulliken population and density of states indicated that 2π antibonding orbitals of N2 molecules t electrons from d and f orbitals in uranium. The vibration wave number of N—N range from 1770 to 2143 cm-1. Complete linear synchronous transit (LST) and quadratic synchronous transit (QST) were used to search the transition state for dissociation reaction. The predicted lowest energy barrier was 266.9 kJ·mol-1.
The adsorption of N2 molecule on the UO(100) surface was studied with periodic slab model by VWN-BP approach of GGA within the framework of density functional theory (DFT). The results of geometry optimization indicated that the most stable structure of adsorption was N2 adsorbed parallelly on the hollow site with an adsorption energy of 79.0 kJ·mol -1. The analysis of Mulliken population and density of states indicated that 2π antibonding orbitals of N2 molecules t electrons from d and f orbitals in uranium. The vibration wave number of N—N range from 1770 to 2143 cm-1. Complete linear synchronous transit (LST) and quadratic synchronous transit (QST) were used to search the transition state for dissociation reaction. The predicted lowest energy barrier was 266.9 kJ·mol-1.
2008, 24(11): 2000-2006
doi: 10.3866/PKU.WHXB20081111
Abstract:
Quantum chemistry ab initio methods were applied to study the blue-and red-shifted H-bonds between HNO and (HF)1≤n≤shifts were caused by repolarization, rehybridization, and intramolecular hyperconjugation. All of the X…H—F (X=O, N, F) are red-shifted, and intermolecular hyperconjugation led to the red shifts. In these chains of H-bonds, the variations of intermolecular hyperconjugations, electron densities at the bond critical points (BCPs), and strengths and frequency shifts of the H-bonds were correlated with each other by definite rules.
Quantum chemistry ab initio methods were applied to study the blue-and red-shifted H-bonds between HNO and (HF)1≤n≤shifts were caused by repolarization, rehybridization, and intramolecular hyperconjugation. All of the X…H—F (X=O, N, F) are red-shifted, and intermolecular hyperconjugation led to the red shifts. In these chains of H-bonds, the variations of intermolecular hyperconjugations, electron densities at the bond critical points (BCPs), and strengths and frequency shifts of the H-bonds were correlated with each other by definite rules.
2008, 24(11): 2007-2012
doi: 10.3866/PKU.WHXB20081112
Abstract:
Diffused and reactive O atom in process of internal oxidation in Ag-Sn-O system was calculated by density functional perturbation approximation theory (DFPT). The results showed binding energy, enthalpy, heat capacity and Gibbs free energy of the phases in Ag-Sn-O system. O atom was on tetrahedron positions in Ag lattice. The system energy of O atom on the octahedron positions was 288.23 kJ·mol-1 higher than that of O atom on the tetrahedron positions. However, Sn atom was on the replacement positions in Ag lattice. The order of cohesive energies (Ec) in Ag-Sn-O system was Ag6O2>SnO2>Ag2SnO3>SnO>Ag2O. The enthalpy of SnO2 was -591.1 kJ·mol-1, which was in agreement with experiment. SnO, Ag6O2, and Ag2SnO3 were the metastable phases in the normal temperature. Because the bonding ability of Sn—O was higher than that of Ag—O, there was no silver-oxide in Ag-Sn-O system. The heat capacity of Ag2SnO3 was much bigger than those of other compounds, and its Debye temperature was about 500 K. SnO2 was the most stable phase in Ag-Sn-O system, which was showed by population analysis and Gibbs free energy.
Diffused and reactive O atom in process of internal oxidation in Ag-Sn-O system was calculated by density functional perturbation approximation theory (DFPT). The results showed binding energy, enthalpy, heat capacity and Gibbs free energy of the phases in Ag-Sn-O system. O atom was on tetrahedron positions in Ag lattice. The system energy of O atom on the octahedron positions was 288.23 kJ·mol-1 higher than that of O atom on the tetrahedron positions. However, Sn atom was on the replacement positions in Ag lattice. The order of cohesive energies (Ec) in Ag-Sn-O system was Ag6O2>SnO2>Ag2SnO3>SnO>Ag2O. The enthalpy of SnO2 was -591.1 kJ·mol-1, which was in agreement with experiment. SnO, Ag6O2, and Ag2SnO3 were the metastable phases in the normal temperature. Because the bonding ability of Sn—O was higher than that of Ag—O, there was no silver-oxide in Ag-Sn-O system. The heat capacity of Ag2SnO3 was much bigger than those of other compounds, and its Debye temperature was about 500 K. SnO2 was the most stable phase in Ag-Sn-O system, which was showed by population analysis and Gibbs free energy.
2008, 24(11): 2013-2018
doi: 10.3866/PKU.WHXB20081113
Abstract:
The density functional theory (DFT) and self-consistent periodic calculation were used to investigate the methanol adsorption on Pt-Mo(111)/C surface. The adsorption energy, equilibrium geometry and vibrational frequency of CH3OH on four sites (top, fcc, hcp and bridge) and nine types of models on Pt-Mo(111)/C surface were predicted and the favorite adsorption site for methanol is top-Pt site. After Mo is doped, the valence band and the conduction band position are depressed, and the change of the electronic structure enables the doped PtMo(111)/C to have a higher catalytic activity. Compared with the adsorption energy of CH3OHon Pt(111)/C surface, the adsorption energy of CO is higher, and Pt(111)/C is favorable to be oxidized and lose the activity. It indicates that the adsorption of COon Pt(111)/C surface counteracts the adsorption of CH3OH, which is disadvantageous for the process of catalysis. The catalyst Pt-Mo(111)/C which is in favor of decomposing methanol is of better antipoisoning ability than that of Pt(111)/C.
The density functional theory (DFT) and self-consistent periodic calculation were used to investigate the methanol adsorption on Pt-Mo(111)/C surface. The adsorption energy, equilibrium geometry and vibrational frequency of CH3OH on four sites (top, fcc, hcp and bridge) and nine types of models on Pt-Mo(111)/C surface were predicted and the favorite adsorption site for methanol is top-Pt site. After Mo is doped, the valence band and the conduction band position are depressed, and the change of the electronic structure enables the doped PtMo(111)/C to have a higher catalytic activity. Compared with the adsorption energy of CH3OHon Pt(111)/C surface, the adsorption energy of CO is higher, and Pt(111)/C is favorable to be oxidized and lose the activity. It indicates that the adsorption of COon Pt(111)/C surface counteracts the adsorption of CH3OH, which is disadvantageous for the process of catalysis. The catalyst Pt-Mo(111)/C which is in favor of decomposing methanol is of better antipoisoning ability than that of Pt(111)/C.
2008, 24(11): 2019-2024
doi: 10.1016/S1872-1508(08)60079-0
Abstract:
N-FcodopedTiO2 (TONF) photocatalystswere prepared usingacidcatalyzed hydrolysismethod frommixed aqueous solution of TiCl4 and NH4F. The photocatalytic activity of the TONF was evaluated through the degradation of phenol under both visible and UVlight irradiation. X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), scanning electron microscope (SEM), and N2 adsorption isotherm were used to characterize the obtained powders. The results showed that N-F co-doped TiO2 exhibited significant improvement of visible light catalytic activity. N-F co-doping could improve dispersion of TiO2, inhibit particle size agglomeration, and retard phase transformation. Doped N could extend the light response of TiO2 to visible light region. In addition, narrower band gap formed by F-doping was beneficial to the high visible light photocatalytic activity.
N-FcodopedTiO2 (TONF) photocatalystswere prepared usingacidcatalyzed hydrolysismethod frommixed aqueous solution of TiCl4 and NH4F. The photocatalytic activity of the TONF was evaluated through the degradation of phenol under both visible and UVlight irradiation. X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), scanning electron microscope (SEM), and N2 adsorption isotherm were used to characterize the obtained powders. The results showed that N-F co-doped TiO2 exhibited significant improvement of visible light catalytic activity. N-F co-doping could improve dispersion of TiO2, inhibit particle size agglomeration, and retard phase transformation. Doped N could extend the light response of TiO2 to visible light region. In addition, narrower band gap formed by F-doping was beneficial to the high visible light photocatalytic activity.
2008, 24(11): 2025-2031
doi: 10.3866/PKU.WHXB20081115
Abstract:
Formaldehyde adsorption on CeO2(111) surface terminated by bridge O atom was systematically investigated by periodic density functional theory (DFT) with the generalized gradient approximation (GGA) developed by projector augmented wave (PAW). According to the analysis of the optimized structures of adsorbed formaldehyde, adsorption energies at different coverages and different adsorption sites, it is found that there are two types of adsorbed formaldehyde on CeO2(111) surface. For the chemisorbed formaldehyde, the carbon and oxygen atoms of formaldehyde interact with the corresponding oxygen and cerium atoms of CeO2(111) surface, and form chemical bonds. The adsorption energies decrease with the increase of formaldehyde coverage on CeO2(111) surface. However, the optimized structures of the physically adsorbed formaldehyde are almost unchanged compared with the free formaldehyde molecule. The corresponding adsorption energies are generally lower than -27 kJ·mol-1. It is learned from the density of states of the chemically adsorbed formaldehyde that the energy of the highest occupied molecular orbital (HOMO), nO, shifts downward greatly, while the oxygen electrons of CeO2(111) surface transfer to the lowest unoccupied molecular orbital (LUMO) of formaldehyde, π*CO . Therefore, newCe—O2 bonds formand the corresponding C—O1 bonds of formaldehyde are elongated. Based on the investigation above, the potential energy for the first H atom dissociation reaction of formaldehyde was calculated using climbing nudged elastic band (CNEB) to be ca 1.71 eV, which was much higher than that of the barrier for the desorption of formaldehyde, 0.80 eV. It is indicated that the main reaction for the temprature programmed desorption (TPD) of formaldehyde over clean CeO2 (111) surface is the desorption of formaldehyde instead of its dissociation reaction, which is well consistent with experimental data.
Formaldehyde adsorption on CeO2(111) surface terminated by bridge O atom was systematically investigated by periodic density functional theory (DFT) with the generalized gradient approximation (GGA) developed by projector augmented wave (PAW). According to the analysis of the optimized structures of adsorbed formaldehyde, adsorption energies at different coverages and different adsorption sites, it is found that there are two types of adsorbed formaldehyde on CeO2(111) surface. For the chemisorbed formaldehyde, the carbon and oxygen atoms of formaldehyde interact with the corresponding oxygen and cerium atoms of CeO2(111) surface, and form chemical bonds. The adsorption energies decrease with the increase of formaldehyde coverage on CeO2(111) surface. However, the optimized structures of the physically adsorbed formaldehyde are almost unchanged compared with the free formaldehyde molecule. The corresponding adsorption energies are generally lower than -27 kJ·mol-1. It is learned from the density of states of the chemically adsorbed formaldehyde that the energy of the highest occupied molecular orbital (HOMO), nO, shifts downward greatly, while the oxygen electrons of CeO2(111) surface transfer to the lowest unoccupied molecular orbital (LUMO) of formaldehyde, π*CO . Therefore, newCe—O2 bonds formand the corresponding C—O1 bonds of formaldehyde are elongated. Based on the investigation above, the potential energy for the first H atom dissociation reaction of formaldehyde was calculated using climbing nudged elastic band (CNEB) to be ca 1.71 eV, which was much higher than that of the barrier for the desorption of formaldehyde, 0.80 eV. It is indicated that the main reaction for the temprature programmed desorption (TPD) of formaldehyde over clean CeO2 (111) surface is the desorption of formaldehyde instead of its dissociation reaction, which is well consistent with experimental data.
2008, 24(11): 2032-2036
doi: 10.3866/PKU.WHXB20081116
Abstract:
The electrodeposition of metallic Co from a 1-ethyl-3-methylimidazolium chloride (EMIC) ionic liquid containing ethylene glycol (EG) and CoCl2 was investigated on copper substrates. Cyclic voltammogram indicated that the redox waves increased with increasing ethylene glycol content, because ethylene glycol accelerated the ionization of EMIC. The electrodeposition of metallic Co in EMIC-CoCl2-EG electrolyte was controlled by diffusion and irreversible growth process. At Pt electrode the cathodal transfer coefficient (α) and diffusion coefficient (D0) of Co(II) in EMIC-CoCl2-EG electrolyte were determined. Their values were obtained as follows: α=0.30 and D0=4.16×10-6 cm·s-1. Chronoamperometric results indicated that the electrodeposition of metallic Co at Pt electrode belonged to a three-dimensional progressive nucleation mechanism. The micromorphology of electrodeposits was observed by field emission scanning electron microscopy (FE-SEM). SEM images of the electrodeposits showed that the crystallite was small and compact. X-ray diffraction (XRD) approved that the obtained electrodeposits were pure cobalt. The results indicated that metallic Co electrodeposited from the 1-ethyl-3-methylimidazolium chloride ionic liquid containing ethylene glycol and CoCl2 was a mixed phase of crystalline and microcrystalline. The average size of cobalt crystalline grain was several tens nanometers.
The electrodeposition of metallic Co from a 1-ethyl-3-methylimidazolium chloride (EMIC) ionic liquid containing ethylene glycol (EG) and CoCl2 was investigated on copper substrates. Cyclic voltammogram indicated that the redox waves increased with increasing ethylene glycol content, because ethylene glycol accelerated the ionization of EMIC. The electrodeposition of metallic Co in EMIC-CoCl2-EG electrolyte was controlled by diffusion and irreversible growth process. At Pt electrode the cathodal transfer coefficient (α) and diffusion coefficient (D0) of Co(II) in EMIC-CoCl2-EG electrolyte were determined. Their values were obtained as follows: α=0.30 and D0=4.16×10-6 cm·s-1. Chronoamperometric results indicated that the electrodeposition of metallic Co at Pt electrode belonged to a three-dimensional progressive nucleation mechanism. The micromorphology of electrodeposits was observed by field emission scanning electron microscopy (FE-SEM). SEM images of the electrodeposits showed that the crystallite was small and compact. X-ray diffraction (XRD) approved that the obtained electrodeposits were pure cobalt. The results indicated that metallic Co electrodeposited from the 1-ethyl-3-methylimidazolium chloride ionic liquid containing ethylene glycol and CoCl2 was a mixed phase of crystalline and microcrystalline. The average size of cobalt crystalline grain was several tens nanometers.
2008, 24(11): 2037-2041
doi: 10.3866/PKU.WHXB20081117
Abstract:
Surface-modified hollow LaF3 nanoparticles were prepared in an oleate/cetyltrimethylammoniumbromide micellar emulsion. Their morphology and structure were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transforminfrared spectroscopy (FTIR), thermal analysis (TG-DTG), and energy dispersive X-ray spectroscopy (EDS). The results showed that the LaF3 nanoparticles were hollow, with diameters of ca. 17.5 nm, and an oleate layer was present on their surfaces. The effect of additive concentration and load on nanoparticles’ antiwear and friction reduction properties (as additives in lubricating oil) were evaluated with a four-ball tester. The LaF3 nanoparticles exhibited excellent antiwear and friction reduction properties. The mechanism of hollow nanoparticle
formation was also discussed.
Surface-modified hollow LaF3 nanoparticles were prepared in an oleate/cetyltrimethylammoniumbromide micellar emulsion. Their morphology and structure were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transforminfrared spectroscopy (FTIR), thermal analysis (TG-DTG), and energy dispersive X-ray spectroscopy (EDS). The results showed that the LaF3 nanoparticles were hollow, with diameters of ca. 17.5 nm, and an oleate layer was present on their surfaces. The effect of additive concentration and load on nanoparticles’ antiwear and friction reduction properties (as additives in lubricating oil) were evaluated with a four-ball tester. The LaF3 nanoparticles exhibited excellent antiwear and friction reduction properties. The mechanism of hollow nanoparticle
formation was also discussed.
2008, 24(11): 2042-2046
doi: 10.3866/PKU.WHXB20081118
Abstract:
The melting processes of little size metal clusters were simulated by molecular dynamics method. The atomic interaction was described by embedded atommethod (EAM). The root-mean-square (rms) bond length fluctuation and heat capacity versus temperature in heating were calculated. The melting processes of face centered cubic (FCC) Au clusters with 55 and 56 atoms are very similar. But those FCCCu clusters with same size show different trends. Cu55 and Cu56 clusters have structure transitions from FCC structures to icosahedrons during heating processes. Due to one more atom than Cu55 on surface, Cu56 has a pre-melting process. The heat capacity curve of Cu56 has also one more peak than that of Cu55. All the results show that the small cluster’s solid-liquid transition of the small clusters depends on atomtype, structure, and atomnumber of the cluster.
The melting processes of little size metal clusters were simulated by molecular dynamics method. The atomic interaction was described by embedded atommethod (EAM). The root-mean-square (rms) bond length fluctuation and heat capacity versus temperature in heating were calculated. The melting processes of face centered cubic (FCC) Au clusters with 55 and 56 atoms are very similar. But those FCCCu clusters with same size show different trends. Cu55 and Cu56 clusters have structure transitions from FCC structures to icosahedrons during heating processes. Due to one more atom than Cu55 on surface, Cu56 has a pre-melting process. The heat capacity curve of Cu56 has also one more peak than that of Cu55. All the results show that the small cluster’s solid-liquid transition of the small clusters depends on atomtype, structure, and atomnumber of the cluster.
2008, 24(11): 2047-2052
doi: 10.3866/PKU.WHXB20081119
Abstract:
Classical molecular dynamics simulations were employed to investigate the structural and dynamical properties of water near an Au nanoparticle at roomtemperature. The simulation results showed that a well-defined multi-layered structure of water was formed close to the surface of the Au nanoparticle and the orientation of water molecules in the interfacial region changed gradually fromthe random arrangement to the ordered arrangement with the reduction in the radial distance. By analyzing the mean square displacement and occupation time distribution in different water layers, we found that water molecules in the first and second layers display very low diffusivity, whereas water molecules in the third and fourth layers could migrate fromthe interfacial region to the bulk region at short time. Additionally, the average number of hydrogen bonds per water molecule in the interfacial region was higher than that in the bulk phase.
Classical molecular dynamics simulations were employed to investigate the structural and dynamical properties of water near an Au nanoparticle at roomtemperature. The simulation results showed that a well-defined multi-layered structure of water was formed close to the surface of the Au nanoparticle and the orientation of water molecules in the interfacial region changed gradually fromthe random arrangement to the ordered arrangement with the reduction in the radial distance. By analyzing the mean square displacement and occupation time distribution in different water layers, we found that water molecules in the first and second layers display very low diffusivity, whereas water molecules in the third and fourth layers could migrate fromthe interfacial region to the bulk region at short time. Additionally, the average number of hydrogen bonds per water molecule in the interfacial region was higher than that in the bulk phase.
2008, 24(11): 2053-2058
doi: 10.3866/PKU.WHXB20081120
Abstract:
The reactions of HCHO+X (X=F, Cl, Br) were studied at CCSD/6-311++G(d,p)//B3LYP/6-311++G (d,p) level. The computational results show that the reaction channel of halogen atom X (X=F, Cl, Br) which gains H atom of the HCHOto get HCO+HX(X=F, Cl, Br) is the main reaction channel. Except this reaction channel, a stable complex forms firstly, then the complex via two channels to get the products, one is that the halogen atom gains a hydrogen from HCHO to form HCO+HX(X=F, Cl, Br) and the other is that the complex decomposes directly to H and XCHO (X=F, Cl, Br). The first channel is the main channel and the HCO+HX(X=F, Cl, Br) are the main products. Furthermore, because the energy barriers of the three reactions are low, these reactions could occur easily. The topological analysis of electron density shows that there is a T-shape structure transition state (STS) in the channel (b) of HCHO+X reaction, the STS appears later than the energy transition state (ETS). And the STS appears later and later in the sequence of F, Cl, Br.
The reactions of HCHO+X (X=F, Cl, Br) were studied at CCSD/6-311++G(d,p)//B3LYP/6-311++G (d,p) level. The computational results show that the reaction channel of halogen atom X (X=F, Cl, Br) which gains H atom of the HCHOto get HCO+HX(X=F, Cl, Br) is the main reaction channel. Except this reaction channel, a stable complex forms firstly, then the complex via two channels to get the products, one is that the halogen atom gains a hydrogen from HCHO to form HCO+HX(X=F, Cl, Br) and the other is that the complex decomposes directly to H and XCHO (X=F, Cl, Br). The first channel is the main channel and the HCO+HX(X=F, Cl, Br) are the main products. Furthermore, because the energy barriers of the three reactions are low, these reactions could occur easily. The topological analysis of electron density shows that there is a T-shape structure transition state (STS) in the channel (b) of HCHO+X reaction, the STS appears later than the energy transition state (ETS). And the STS appears later and later in the sequence of F, Cl, Br.
2008, 24(11): 2059-2064
doi: 10.3866/PKU.WHXB20081121
Abstract:
A detailed density functional theory (DFT) investigation revealed three possible micro-mechanisms of the water-gas shift reaction catalyzed by copper. Geometries of stationary points (reactants, intermediates, transition states and products) were optimized with the self-consistent Perdew-Wang-91 generalized gradient approximation (GGA-PW91) method. All transition states were verified by the frequency analysis method. Results showed that the formate mechanismhad a lowprobability, while the carboxyl mechanismand the redox mechanismwere more probable. During the carboxyl mechanism, the intermediate COOH(s) was formed followed by its decomposition via disproportionation with OH (s). The calculated activation energy barrier for the carboxyl mechanism was 3.8 kJ·mol-1, which was lower than that for the redox mechanism.
A detailed density functional theory (DFT) investigation revealed three possible micro-mechanisms of the water-gas shift reaction catalyzed by copper. Geometries of stationary points (reactants, intermediates, transition states and products) were optimized with the self-consistent Perdew-Wang-91 generalized gradient approximation (GGA-PW91) method. All transition states were verified by the frequency analysis method. Results showed that the formate mechanismhad a lowprobability, while the carboxyl mechanismand the redox mechanismwere more probable. During the carboxyl mechanism, the intermediate COOH(s) was formed followed by its decomposition via disproportionation with OH (s). The calculated activation energy barrier for the carboxyl mechanism was 3.8 kJ·mol-1, which was lower than that for the redox mechanism.
2008, 24(11): 2065-2070
doi: 10.3866/PKU.WHXB20081122
Abstract:
B3LYP/6-311++G** and MP2/6-311++G** calculations were used to analyze the interaction between thioperoxy radical (HSO) and ozone (O3) in gas-phase, which are of interest in atmospheric chemistry. The results showed that there were three equilibrium geometries (complexes I, II, and III) at the B3LYP/6-311++G** level, but only one stable configuration (complexes II) at MP2/6-311++G** level. And all the equilibrium geometries were confirmed to be stable states by analytical frequency computations. Complexes I and III use the 1H atom of HSO as proton donor and the terminal 4O atom of O3 as acceptor to form red shift hydrogen bond systems. However, complex II uses the same proton donor and acceptor to form a blue shift hydrogen bond system. Interaction energies of the complexes corrected with basis set superposition error (BSSE) and zero point vibrational energy (ZPVE) lie in the range from -3.37 to -4.55 kJ·mol-1 at B3LYP/6-311++G** level. The natural bond orbital (NBO) and atoms in molecules (AIM) theories were also applied to explain the structures and the electron density topology properties of the three hydrogen bond complexes.
B3LYP/6-311++G** and MP2/6-311++G** calculations were used to analyze the interaction between thioperoxy radical (HSO) and ozone (O3) in gas-phase, which are of interest in atmospheric chemistry. The results showed that there were three equilibrium geometries (complexes I, II, and III) at the B3LYP/6-311++G** level, but only one stable configuration (complexes II) at MP2/6-311++G** level. And all the equilibrium geometries were confirmed to be stable states by analytical frequency computations. Complexes I and III use the 1H atom of HSO as proton donor and the terminal 4O atom of O3 as acceptor to form red shift hydrogen bond systems. However, complex II uses the same proton donor and acceptor to form a blue shift hydrogen bond system. Interaction energies of the complexes corrected with basis set superposition error (BSSE) and zero point vibrational energy (ZPVE) lie in the range from -3.37 to -4.55 kJ·mol-1 at B3LYP/6-311++G** level. The natural bond orbital (NBO) and atoms in molecules (AIM) theories were also applied to explain the structures and the electron density topology properties of the three hydrogen bond complexes.
2008, 24(11): 2071-2076
doi: 10.3866/PKU.WHXB20081123
Abstract:
Cd0.53Zn0.47S was prepared by a coprecipitation method. Pt was loaded onto Cd0.53Zn0.47S by photodeposition method. SiO2 was deposited onto Cd0.53Zn0.47S by hydrolysis of the tetraethylorthosilicate (TEOS), and the effect of the hydrolysis pH on the activity of the catalysts was studied. The samples were characterized by X-ray diffraction (XRD), BET surface area, photoluminescence (PL), UV-Vis diffusive reflectance spectroscopy (UV-Vis DRS), and scanning electron microscope (SEM) techniques. The composite SiO2 prevented effectively photocorrosion and coalescence of Pt-Cd0.53Zn0.47S nanoparticles during the photocatalytic reaction, and improved the charge separation of photogenerated electrons and holes. Therefore, the stability and the activity of Pt-Cd0.53Zn0.47S for photocatalytic hydrogen generation
under visible light irradiation were improved greatly.
Cd0.53Zn0.47S was prepared by a coprecipitation method. Pt was loaded onto Cd0.53Zn0.47S by photodeposition method. SiO2 was deposited onto Cd0.53Zn0.47S by hydrolysis of the tetraethylorthosilicate (TEOS), and the effect of the hydrolysis pH on the activity of the catalysts was studied. The samples were characterized by X-ray diffraction (XRD), BET surface area, photoluminescence (PL), UV-Vis diffusive reflectance spectroscopy (UV-Vis DRS), and scanning electron microscope (SEM) techniques. The composite SiO2 prevented effectively photocorrosion and coalescence of Pt-Cd0.53Zn0.47S nanoparticles during the photocatalytic reaction, and improved the charge separation of photogenerated electrons and holes. Therefore, the stability and the activity of Pt-Cd0.53Zn0.47S for photocatalytic hydrogen generation
under visible light irradiation were improved greatly.
2008, 24(11): 2077-2082
doi: 10.3866/PKU.WHXB20081124
Abstract:
The structures of ionic liquids N-ethyl-pyridinium chloride ([EPy]Cl) and N-ethyl-pyridinium bromide ([EPy]Br) were studied by density functional theory (DFT) and B3LYP/6-31+G(d,p) calculations. Structures and interactions in liquid phase were investigated by conductor-like polarizable continuum model (CPCM). The geometries of ionic liquids in gas phase were fully optimized by energy gradient technology and the number of imaginary frequency was obtained through vibrational analysis. The simulated infrared spectra agreed well with the experimental infrared spectra. Natural bond orbital (NBO) analysis was performed to analyze the atomic charges and charge transfers in the monomers and complexes in gas and liquid phases. The interaction between the anion and the cation was mainly electrostatic. There were also some hydrogen bonds between cations and anions in ionic liquids. According to the geometry structures, the magnitude of the interaction energies of [EPy]Cl and [EPy]Br and the NBO analysis results, the interaction between the anion and the cation became more weak in liquid phase because the liquid environment counteracted part of the electrostatic interaction between the anion and the cation.
The structures of ionic liquids N-ethyl-pyridinium chloride ([EPy]Cl) and N-ethyl-pyridinium bromide ([EPy]Br) were studied by density functional theory (DFT) and B3LYP/6-31+G(d,p) calculations. Structures and interactions in liquid phase were investigated by conductor-like polarizable continuum model (CPCM). The geometries of ionic liquids in gas phase were fully optimized by energy gradient technology and the number of imaginary frequency was obtained through vibrational analysis. The simulated infrared spectra agreed well with the experimental infrared spectra. Natural bond orbital (NBO) analysis was performed to analyze the atomic charges and charge transfers in the monomers and complexes in gas and liquid phases. The interaction between the anion and the cation was mainly electrostatic. There were also some hydrogen bonds between cations and anions in ionic liquids. According to the geometry structures, the magnitude of the interaction energies of [EPy]Cl and [EPy]Br and the NBO analysis results, the interaction between the anion and the cation became more weak in liquid phase because the liquid environment counteracted part of the electrostatic interaction between the anion and the cation.
2008, 24(11): 2083-2088
doi: 10.3866/PKU.WHXB20081125
Abstract:
The reaction of Y+ with CS2, which was selected as the representative system of the reactions of second-row transition metal ions with CS2, was investigated using density functional theory (DFT) with the Stuttgart pseudo potentials and corresponding basis sets for Y+ and the standard 6-311+G(2d) basis sets for C and S atoms. Single-point UCCSD(T) energy calculations were carried out for each stationary point. The object of this investigation was the elucidation of the reaction mechanism. The result shows that the reaction mechanismbetween yttriumion and CS2 is an insertion-elimination mechanism. Intersystemcrossing may occur in the reaction of Y+ with CS2 and a minimumenergy crossing point has been found. All theoretical results are in line with early experiments.
The reaction of Y+ with CS2, which was selected as the representative system of the reactions of second-row transition metal ions with CS2, was investigated using density functional theory (DFT) with the Stuttgart pseudo potentials and corresponding basis sets for Y+ and the standard 6-311+G(2d) basis sets for C and S atoms. Single-point UCCSD(T) energy calculations were carried out for each stationary point. The object of this investigation was the elucidation of the reaction mechanism. The result shows that the reaction mechanismbetween yttriumion and CS2 is an insertion-elimination mechanism. Intersystemcrossing may occur in the reaction of Y+ with CS2 and a minimumenergy crossing point has been found. All theoretical results are in line with early experiments.
2008, 24(11): 2089-2095
doi: 10.3866/PKU.WHXB20081126
Abstract:
Coumarin-containing styrene monomer (CS) was designed and synthesized, which could be used together with styrene (St) and maleic anhydride (MA) to synthesize the photosensitive amphiphilic alternating SMA terpolymer poly(styrene/coumarin-containing styrene-alt-maleic anhydride) (P(St/CS-alt-MA)) via free radical copolymerization. Then a new photosensitive amphiphilic comblike terpolymer (P(St/CS-alt-MAA8)) with long alkyl side chains was obtained by the functional amidolysis reaction between succinic anhydride unit and octylamine, and its structure was characterized by gel permeation in chromatography (GPC), Fourier transforminfrared spectroscopy (FTIR), and 1Hnuclear magnetic resonance (1HNMR). It was found that the comblike polymer could aggregate by the photo-dimerization of the coumarin pendants under UV irradiation (>300 nm), and formnanoscale micelles by self-assembly in selective solvent. The micelles could be modified by the ionization of carboxylic acid groups with NaOH. Pyrene loading experiment and dynamic laser scattering (DLS) showed that the micelle diameter and the loading capacity of precrosslinked polymer were bigger than those of non-crosslinked polymer. Micelles reformed after ionization, which made the hydrophobic area denser and the micelle diameter smaller, while the loading capacity also increased.
Coumarin-containing styrene monomer (CS) was designed and synthesized, which could be used together with styrene (St) and maleic anhydride (MA) to synthesize the photosensitive amphiphilic alternating SMA terpolymer poly(styrene/coumarin-containing styrene-alt-maleic anhydride) (P(St/CS-alt-MA)) via free radical copolymerization. Then a new photosensitive amphiphilic comblike terpolymer (P(St/CS-alt-MAA8)) with long alkyl side chains was obtained by the functional amidolysis reaction between succinic anhydride unit and octylamine, and its structure was characterized by gel permeation in chromatography (GPC), Fourier transforminfrared spectroscopy (FTIR), and 1Hnuclear magnetic resonance (1HNMR). It was found that the comblike polymer could aggregate by the photo-dimerization of the coumarin pendants under UV irradiation (>300 nm), and formnanoscale micelles by self-assembly in selective solvent. The micelles could be modified by the ionization of carboxylic acid groups with NaOH. Pyrene loading experiment and dynamic laser scattering (DLS) showed that the micelle diameter and the loading capacity of precrosslinked polymer were bigger than those of non-crosslinked polymer. Micelles reformed after ionization, which made the hydrophobic area denser and the micelle diameter smaller, while the loading capacity also increased.
2008, 24(11): 2096-2101
doi: 10.3866/PKU.WHXB20081127
Abstract:
The porous nanocrystalline TiO2 doped with La was synthesized by sol-gel method. The combination of the photoacoustic (PA) and the surface photovoltage (SPV) techniques was proved to be a promising experimental method to probe the photogenic electron behaviors and electron structure on the surface. Results showed that active oxygen and hydroxy were formed on the donor-type active centers produced by the La-O-Ti compounds enriched on the surfaces, which resulted in the sensitized photoreaction of charge transfer transitions on the surface after adsorbing oxygen and H2O. It was experimentally confirmed that doping an appropriate amount of La not only enhanced the surface photovoltage characters of the sample, but also suppressed effectivly the nonradiative transitions, leading to the increased photon efficiency. The charge transfer transitions were dependent closely on the nonradiative transitions, while the formation of active oxygen and hydroxy on the adsorptive surface was independent of the nonradiative transitions.
The porous nanocrystalline TiO2 doped with La was synthesized by sol-gel method. The combination of the photoacoustic (PA) and the surface photovoltage (SPV) techniques was proved to be a promising experimental method to probe the photogenic electron behaviors and electron structure on the surface. Results showed that active oxygen and hydroxy were formed on the donor-type active centers produced by the La-O-Ti compounds enriched on the surfaces, which resulted in the sensitized photoreaction of charge transfer transitions on the surface after adsorbing oxygen and H2O. It was experimentally confirmed that doping an appropriate amount of La not only enhanced the surface photovoltage characters of the sample, but also suppressed effectivly the nonradiative transitions, leading to the increased photon efficiency. The charge transfer transitions were dependent closely on the nonradiative transitions, while the formation of active oxygen and hydroxy on the adsorptive surface was independent of the nonradiative transitions.
2008, 24(11): 2102-2107
doi: 10.3866/PKU.WHXB20081128
Abstract:
The catalytic cracking of C4 hydrocarbons was investigated using ZSM-5 with low SiO2/Al2O3 molar ratio (n(SiO2)/n(Al2O3)=20-45) as a catalyst. The reaction results indicated that the catalyst with lower SiO2/Al2O3 molar ratio exhibited higher catalytic activity at low temperatures. The yield of propylene and ethylene over ZSM-5 with low SiO2/Al2O3 molar ratio was lower than that over the catalyst with high SiO2/Al2O3 molar ratio. However the yield of benzene and toluene was reversed. At 625 ℃, the total yield of ethylene, propene, benzene, and toluene was as high as 79.42%over the catalyst with n(SiO2)/n(Al2O3)=20. The acidity characterization by temperature-programmed desorption of ammonia and pyridine adsorption FT-IR showed that ZSM-5 with lower SiO2/Al2O3 molar ratio had more Bronsted (B) and Lewis (L) acid sites. This accounted for the higher activity at low temperature and higher yield of benzene and toluene in the cracking of C4 hydrocarbons.
The catalytic cracking of C4 hydrocarbons was investigated using ZSM-5 with low SiO2/Al2O3 molar ratio (n(SiO2)/n(Al2O3)=20-45) as a catalyst. The reaction results indicated that the catalyst with lower SiO2/Al2O3 molar ratio exhibited higher catalytic activity at low temperatures. The yield of propylene and ethylene over ZSM-5 with low SiO2/Al2O3 molar ratio was lower than that over the catalyst with high SiO2/Al2O3 molar ratio. However the yield of benzene and toluene was reversed. At 625 ℃, the total yield of ethylene, propene, benzene, and toluene was as high as 79.42%over the catalyst with n(SiO2)/n(Al2O3)=20. The acidity characterization by temperature-programmed desorption of ammonia and pyridine adsorption FT-IR showed that ZSM-5 with lower SiO2/Al2O3 molar ratio had more Bronsted (B) and Lewis (L) acid sites. This accounted for the higher activity at low temperature and higher yield of benzene and toluene in the cracking of C4 hydrocarbons.
2008, 24(11): 2108-2113
doi: 10.1016/S1872-1508(08)60080-7
Abstract:
Solid solution CeO2-MOx (M=La3+, Ca2+) promoted Pd/γ-Al2O3 catalysts were prepared by a deposition-precipitation method. The structural properties were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy. The results showed that Mn+ ions incorporated into CeO2 lattice and solid solutions formed in Pd/γ-Al2O3-CeO2-MOx catalysts. The formation of solid solution was confirmed by the change in lattice parameters of CeO2 and the shift of 2θ angles as compared with pure CeO2. A strain formed in the O2- sub-lattice of CeO2 was revealed by Raman analyses, which decreased the intensity of the Raman-active band at around 463 cm-1 owing to the F2g symmetric stretching of Ce—O bond. The appearance of a new band at 615 cm-1 (in the case of Pd/γ-Al2O3-CeO2-CaO) and a shoulder at 320 cm-1 (in the case of Pd/γ-Al2O3-CeO2-La2O3) was also confirmed. Ionic Pdδ+ species were formed in the catalysts, which exhibited higher binding energies (0.5-0.6 eV higher for Pd 3d5/2) than that of normal PdO. The catalysts showed high activity and stability for low temperature methane combustion. 10% and 100% conversions of methane could be obtained at temperatures of 254 and 340 ℃, respectively, over Pd/γ-Al2O3-CeO2-La2O3 catalyst under an hourly space velocity of 50000 h-1.
Solid solution CeO2-MOx (M=La3+, Ca2+) promoted Pd/γ-Al2O3 catalysts were prepared by a deposition-precipitation method. The structural properties were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy. The results showed that Mn+ ions incorporated into CeO2 lattice and solid solutions formed in Pd/γ-Al2O3-CeO2-MOx catalysts. The formation of solid solution was confirmed by the change in lattice parameters of CeO2 and the shift of 2θ angles as compared with pure CeO2. A strain formed in the O2- sub-lattice of CeO2 was revealed by Raman analyses, which decreased the intensity of the Raman-active band at around 463 cm-1 owing to the F2g symmetric stretching of Ce—O bond. The appearance of a new band at 615 cm-1 (in the case of Pd/γ-Al2O3-CeO2-CaO) and a shoulder at 320 cm-1 (in the case of Pd/γ-Al2O3-CeO2-La2O3) was also confirmed. Ionic Pdδ+ species were formed in the catalysts, which exhibited higher binding energies (0.5-0.6 eV higher for Pd 3d5/2) than that of normal PdO. The catalysts showed high activity and stability for low temperature methane combustion. 10% and 100% conversions of methane could be obtained at temperatures of 254 and 340 ℃, respectively, over Pd/γ-Al2O3-CeO2-La2O3 catalyst under an hourly space velocity of 50000 h-1.
2008, 24(11): 2114-2121
doi: 10.3866/PKU.WHXB20081130
Abstract:
The coordination process and structure between amidoxime modified polyacrylonitrile (AO-PAN) fiber and FeCl3 in aqueous solution were studied by using X-ray photoelectron spectroscopy (XPS), Fourier transforminfrared spectrometer (FTIR), dynamic thermal mechanical analyzer (DTMA), and electrical conductivity method, respectively. The coordination Fe-AO-PAN fiber was obtained, and then used as a heterogeneous Fenton catalyst for the oxidative degradation of two azo dyes including C.I. Reactive Red 195(RR 195) and C.I. Acid Black 234(AB 234) in the presence of H2O2. The catalytic function of Fe-AO-PAN on dye degradation was investigated with respect to decoloration percentage in this work. The results indicated that the Fe3+ ion of Fe-AO-PAN was coordinated with three amino nitrogen atoms and three hydroxyl oxygen atoms of three amidoxime units on the surface of AO-PAN by covalent bond, and the coordination number was six. Moreover, the oxidative degradation of two azo dyes in water was significantly accelerated in the presence of Fe-AO-PAN under light irradiation, and the azo linkages and aromatic ring of azo dye molecules were decomposed. Increasing the degree of conversion from nitrile group to amidoxime group on the surface of PAN fiber caused not only higher Fe3+ content of Fe-AO-PAN, but also its stronger catalytic performance
on dye degradation in aqueous solution.
The coordination process and structure between amidoxime modified polyacrylonitrile (AO-PAN) fiber and FeCl3 in aqueous solution were studied by using X-ray photoelectron spectroscopy (XPS), Fourier transforminfrared spectrometer (FTIR), dynamic thermal mechanical analyzer (DTMA), and electrical conductivity method, respectively. The coordination Fe-AO-PAN fiber was obtained, and then used as a heterogeneous Fenton catalyst for the oxidative degradation of two azo dyes including C.I. Reactive Red 195(RR 195) and C.I. Acid Black 234(AB 234) in the presence of H2O2. The catalytic function of Fe-AO-PAN on dye degradation was investigated with respect to decoloration percentage in this work. The results indicated that the Fe3+ ion of Fe-AO-PAN was coordinated with three amino nitrogen atoms and three hydroxyl oxygen atoms of three amidoxime units on the surface of AO-PAN by covalent bond, and the coordination number was six. Moreover, the oxidative degradation of two azo dyes in water was significantly accelerated in the presence of Fe-AO-PAN under light irradiation, and the azo linkages and aromatic ring of azo dye molecules were decomposed. Increasing the degree of conversion from nitrile group to amidoxime group on the surface of PAN fiber caused not only higher Fe3+ content of Fe-AO-PAN, but also its stronger catalytic performance
on dye degradation in aqueous solution.
2008, 24(11): 2122-2127
doi: 10.3866/PKU.WHXB20081131
Abstract:
Single-walled carbon nanotube field-effect transistors (SWCNT FETs) with multi-walled carbon nanotubes (MWCNTs) as interconnects were fabricated, and their field effect properties were measured and compared with those of the case with metal leads as interconnects. Both cases showed almost the same direct current (DC) response, while the MWCNTs interconnected case showed a little better alternating current (AC) properties. AC measurement showed that the MWCNTs interconnected SWCNT FETs worked well at frequency up to 20 MHz.
Single-walled carbon nanotube field-effect transistors (SWCNT FETs) with multi-walled carbon nanotubes (MWCNTs) as interconnects were fabricated, and their field effect properties were measured and compared with those of the case with metal leads as interconnects. Both cases showed almost the same direct current (DC) response, while the MWCNTs interconnected case showed a little better alternating current (AC) properties. AC measurement showed that the MWCNTs interconnected SWCNT FETs worked well at frequency up to 20 MHz.
2008, 24(11): 2128-2132
doi: 10.3866/PKU.WHXB20081132
Abstract:
A model of molecules diffusion in β-zeolite was proposed by assuming that the movement of molecules was a random walk on different adsorption sites. Owing to the topological structures and differences of transition probabilities between adsorption sites through two type of pores, there existed a correlation between diffusion coefficients along two principal axes, which was proved by molecular dynamics simulation of benzene diffusion in β zeolite at different temperatures. The diffusions of ar n with different interaction radii showed that the interaction radius was crucial to the fitness of the randomwalk model; the interaction radius must be large enough (near the size of zeolite pores).
A model of molecules diffusion in β-zeolite was proposed by assuming that the movement of molecules was a random walk on different adsorption sites. Owing to the topological structures and differences of transition probabilities between adsorption sites through two type of pores, there existed a correlation between diffusion coefficients along two principal axes, which was proved by molecular dynamics simulation of benzene diffusion in β zeolite at different temperatures. The diffusions of ar n with different interaction radii showed that the interaction radius was crucial to the fitness of the randomwalk model; the interaction radius must be large enough (near the size of zeolite pores).
2008, 24(11): 2133-2138
doi: 10.3866/PKU.WHXB20081133
Abstract:
The formation of titania nanotubes was achieved by electrochemical anodization in glycerol based
electrolytes. We investigated the effect of three anionic species, anodic time and NaAc concentration on the formation of TiO2 nanotubes. The choice of anion was found to be a key parameter influencing both the nanotube growth rate and the resultant nanotube length. Longer tube lengths were obtained by adding NaNO3 and NaCl, by increasing the current density and by increasing the electrochemical etching rate at tube’s bottom. The current density and the electrochemical etching rate at the tube’s bottom decreased with added NaAc. Electrolytes with added NaAc were much more efficient at producing longer nanotubes, by effectively slowing the chemical dissolution rate at the top of the tube.
The formation of titania nanotubes was achieved by electrochemical anodization in glycerol based
electrolytes. We investigated the effect of three anionic species, anodic time and NaAc concentration on the formation of TiO2 nanotubes. The choice of anion was found to be a key parameter influencing both the nanotube growth rate and the resultant nanotube length. Longer tube lengths were obtained by adding NaNO3 and NaCl, by increasing the current density and by increasing the electrochemical etching rate at tube’s bottom. The current density and the electrochemical etching rate at the tube’s bottom decreased with added NaAc. Electrolytes with added NaAc were much more efficient at producing longer nanotubes, by effectively slowing the chemical dissolution rate at the top of the tube.
2008, 24(11): 2139-2142
doi: 10.3866/PKU.WHXB20081134
Abstract:
Anodic oxidation is a novel and simple method to fabricate TiO2 film with particular morphologies in a mixture of 0.5 mol·L-1 H2SO4+1 mol·L-1 maleic acid solution. The formation of a mixture containing low crystal rutile phase and amorphous structure of TiO2 was confirmed by X-ray diffraction (XRD). Bundle structures of TiO2 film with the breadth of 2-5 μm and the length over 20 μm were observed by atomic force microscope (AFM). Simultaneously, we found that the average diameter of the fine stick within the bundle structures of TiO2 was 80-150 nm. Electrocatalytic reduction of maleic acid to succinic acid was investigated by cyclic voltammetry and galvanostatic electrolysis experiments. The heterogeneous catalytic reduction of maleic acid could be confirmed with a comparison of the cyclic voltammetry recorded in the absence and the presence of maleic acid on the bunchy TiO2 film surface. In-situ activation of the as-anodized TiO2 electrode by galvanic cycle for galvanostatic electrolysis experiments brought the maximum yield of succinic acid and current efficiency.
Anodic oxidation is a novel and simple method to fabricate TiO2 film with particular morphologies in a mixture of 0.5 mol·L-1 H2SO4+1 mol·L-1 maleic acid solution. The formation of a mixture containing low crystal rutile phase and amorphous structure of TiO2 was confirmed by X-ray diffraction (XRD). Bundle structures of TiO2 film with the breadth of 2-5 μm and the length over 20 μm were observed by atomic force microscope (AFM). Simultaneously, we found that the average diameter of the fine stick within the bundle structures of TiO2 was 80-150 nm. Electrocatalytic reduction of maleic acid to succinic acid was investigated by cyclic voltammetry and galvanostatic electrolysis experiments. The heterogeneous catalytic reduction of maleic acid could be confirmed with a comparison of the cyclic voltammetry recorded in the absence and the presence of maleic acid on the bunchy TiO2 film surface. In-situ activation of the as-anodized TiO2 electrode by galvanic cycle for galvanostatic electrolysis experiments brought the maximum yield of succinic acid and current efficiency.
2008, 24(11): 2143-2148
doi: 10.3866/PKU.WHXB20081135
Abstract:
To investigate the influence of different alcohols on the isotropic microemulsion zone of a 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6)/Tween80/toluene system, pseudo ternary phase diagrams of bmimPF6/Tween80/alcohol/toluene systems under different conditions were constructed. Alcohols used were C2H5OH, n-C4H9OH, n-C6H13OH, n-C8H17OH, n-C10H21OH, and i-C5H11OH. Effects of alcohol type and content on the formation of the microemulsion region were investigated. Phase diagrams showed that the microemulsion domain became larger as the Tween80/alcohol weight ratio increased for i-C5H11OH. Different chain lengths of alcohols affected the magnitude of microemulsion regions and this was also dependent on the alcohol solubility in bmimPF6. The single-phase microemulsion area decreased as the alcohol chain length increased. The single-phase region of the ethanol-containing system was the largest among the systems studied. Oil-in-ionic liquid (O/IL) microemulsions, bicontinuous microemulsions, and ionic liquid-in-oil (IL/O) microemulsions in isotropic regions were identified by conductivity measurements. Initial increases of conductivity in ionic liquid microemulsions with increased oil content was due to the oil decreasing ion pairs or ions accumulating in the ionic liquid microemulsion thus increasing the number of charge carriers and improving ionic mobility.
To investigate the influence of different alcohols on the isotropic microemulsion zone of a 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6)/Tween80/toluene system, pseudo ternary phase diagrams of bmimPF6/Tween80/alcohol/toluene systems under different conditions were constructed. Alcohols used were C2H5OH, n-C4H9OH, n-C6H13OH, n-C8H17OH, n-C10H21OH, and i-C5H11OH. Effects of alcohol type and content on the formation of the microemulsion region were investigated. Phase diagrams showed that the microemulsion domain became larger as the Tween80/alcohol weight ratio increased for i-C5H11OH. Different chain lengths of alcohols affected the magnitude of microemulsion regions and this was also dependent on the alcohol solubility in bmimPF6. The single-phase microemulsion area decreased as the alcohol chain length increased. The single-phase region of the ethanol-containing system was the largest among the systems studied. Oil-in-ionic liquid (O/IL) microemulsions, bicontinuous microemulsions, and ionic liquid-in-oil (IL/O) microemulsions in isotropic regions were identified by conductivity measurements. Initial increases of conductivity in ionic liquid microemulsions with increased oil content was due to the oil decreasing ion pairs or ions accumulating in the ionic liquid microemulsion thus increasing the number of charge carriers and improving ionic mobility.
