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2004 Volume 20 Issue 9
2004, 20(09): 1063-1066
doi: 10.3866/PKU.WHXB20040901
Abstract:
High density, well ordered and uniform titanium oxide nanotube arrays were fabricated by electrochemical anodic oxidation on a pure titanium sheet. A number of synthesis parameters for the preparation of titanium oxide nanotube arrays in hydrofluoric-acid have been investigated. The results show that voltage is the most important factor to control the appearance and sizes of TiO2 nanotube arrays. The average tubes diameter increases with increasing anodizing voltage. XRD and SEM techniques have been used to characterize the TiO2 nanotubes. It is showed that the TiO2 structure depends on the heating condition, amorphous phase is found at room temperature, the anatase phase is the predominant phase at 450 ℃,and further heating to 600 ℃ the rutile phase of TiO2 appears in the XRD pattern. The SEM shows that average diameter of the TiO2 nanotubes is about 80～90 nm at 20 V anodizing voltage. A possible growth mechanism for the nanotubes formation has been proposed. Moreover, the I－V of TiO2/Ti interface has been characterized. It is demonstrated that the intense rectifying characterization of TiO2/Ti interface is attributed to the presence of a thick barrier layer between TiO2 nanotubes and the Ti substrate.
High density, well ordered and uniform titanium oxide nanotube arrays were fabricated by electrochemical anodic oxidation on a pure titanium sheet. A number of synthesis parameters for the preparation of titanium oxide nanotube arrays in hydrofluoric-acid have been investigated. The results show that voltage is the most important factor to control the appearance and sizes of TiO2 nanotube arrays. The average tubes diameter increases with increasing anodizing voltage. XRD and SEM techniques have been used to characterize the TiO2 nanotubes. It is showed that the TiO2 structure depends on the heating condition, amorphous phase is found at room temperature, the anatase phase is the predominant phase at 450 ℃,and further heating to 600 ℃ the rutile phase of TiO2 appears in the XRD pattern. The SEM shows that average diameter of the TiO2 nanotubes is about 80～90 nm at 20 V anodizing voltage. A possible growth mechanism for the nanotubes formation has been proposed. Moreover, the I－V of TiO2/Ti interface has been characterized. It is demonstrated that the intense rectifying characterization of TiO2/Ti interface is attributed to the presence of a thick barrier layer between TiO2 nanotubes and the Ti substrate.
2004, 20(09): 1067-1070
doi: 10.3866/PKU.WHXB20040902
Abstract:
A kind of supramolecular assembly with high fluorescence was prepared by reaction of mixed organic ammoniums with mercaptocarboxylic acid stabilized CdSe nanoparticles. The assembly contains double bonds and can polymerize to high polymers with unique structure and properties. Hexadecyltrimethylammonium bromide (HTAB), 4-methoxyl-stilbenyl- dimethylethylammonium bromide (MODAB) and 4-methacryloyloxy trans-stilbenyl- dimethylethylammonium bromide (MSDAB) provide the assembly with oil solubility, fluorescence and polymerizability, respectively. The assembly shows a od balance of these properties when the molar ratio of HTAB:MODAB:MSDAB is 1 : 5.98～5.90 : 0.02～0.10. There was an extraordinary enhancement of the photoluminescent intensity at 495 nm of the assembly and its polymer for the energy transfer from MODAB and MSDAB to CdSe. The solubility of the assembly and its polymer in organic solvent was improved significantly by using mixed organic ammoniums compared with the one using MODAB alone.
A kind of supramolecular assembly with high fluorescence was prepared by reaction of mixed organic ammoniums with mercaptocarboxylic acid stabilized CdSe nanoparticles. The assembly contains double bonds and can polymerize to high polymers with unique structure and properties. Hexadecyltrimethylammonium bromide (HTAB), 4-methoxyl-stilbenyl- dimethylethylammonium bromide (MODAB) and 4-methacryloyloxy trans-stilbenyl- dimethylethylammonium bromide (MSDAB) provide the assembly with oil solubility, fluorescence and polymerizability, respectively. The assembly shows a od balance of these properties when the molar ratio of HTAB:MODAB:MSDAB is 1 : 5.98～5.90 : 0.02～0.10. There was an extraordinary enhancement of the photoluminescent intensity at 495 nm of the assembly and its polymer for the energy transfer from MODAB and MSDAB to CdSe. The solubility of the assembly and its polymer in organic solvent was improved significantly by using mixed organic ammoniums compared with the one using MODAB alone.
2004, 20(09): 1071-1077
doi: 10.3866/PKU.WHXB20040903
Abstract:
The reaction mechanism between ozone and ethylene radical (C2H3) has been studied using the density functional theory (DFT) at B3LYP/6-311G** level. The geometries for reactants, the transition states and the products were completely optimized. All the transition states are verified by the vibrational analysis and the intrisic reaction coordinate (IRC) calculations. The results show that the ethylene radical (C2H3) trends intensively to react with the ozone.
The reaction mechanism between ozone and ethylene radical (C2H3) has been studied using the density functional theory (DFT) at B3LYP/6-311G** level. The geometries for reactants, the transition states and the products were completely optimized. All the transition states are verified by the vibrational analysis and the intrisic reaction coordinate (IRC) calculations. The results show that the ethylene radical (C2H3) trends intensively to react with the ozone.
2004, 20(09): 1078-1082
doi: 10.3866/PKU.WHXB20040904
Abstract:
Oxidation effects of SO2 and SO32－ by gas discharge were studied. Powers of both DC and DC superimposed AC were used to generate gas discharge. The results show that the gas discharge had no effect on SO2 oxidation in gas phase and enhanced oxidation of SO32－ in solution evidently. The enhancement of SO32－ in solution is attributed to that gas discharge can generate free radical OH. The free radical can react with SO32－ in solution to induce a chain reaction, in which SO32－ is oxidized by O2 in air. But the free radical cannot induce a chain reaction in gas phase, which contains SO2. In the meanwhile, gas discharge by power of DC superimposed AC can have a better effect than by power of DC.
Oxidation effects of SO2 and SO32－ by gas discharge were studied. Powers of both DC and DC superimposed AC were used to generate gas discharge. The results show that the gas discharge had no effect on SO2 oxidation in gas phase and enhanced oxidation of SO32－ in solution evidently. The enhancement of SO32－ in solution is attributed to that gas discharge can generate free radical OH. The free radical can react with SO32－ in solution to induce a chain reaction, in which SO32－ is oxidized by O2 in air. But the free radical cannot induce a chain reaction in gas phase, which contains SO2. In the meanwhile, gas discharge by power of DC superimposed AC can have a better effect than by power of DC.
2004, 20(09): 1083-1088
doi: 10.3866/PKU.WHXB20040905
Abstract:
The diphenyl oxide alkylation with dodecene catalyzed by acidic ionic liquids has been studied. The reuse potential of acidic ionic liquids has been investigated. The reasons for the deactivation of the acidic ionic liquids are the decomposition and leaching of the actual catalytic species Al2Cl72－ from the interaction between acidic ionic liquids and diphenyl oxide. The interaction between acidic ionic liquids and diphenyl oxide couldn’t be avoided by changing the cations of ionic liquids. The reuse problem of acidic ionic liquids can be solved when certain amount of AlCl3 is added into the used ionic liquids. The yield of target product is still around 90％ after 8 cycles of the ionic liquids.
The diphenyl oxide alkylation with dodecene catalyzed by acidic ionic liquids has been studied. The reuse potential of acidic ionic liquids has been investigated. The reasons for the deactivation of the acidic ionic liquids are the decomposition and leaching of the actual catalytic species Al2Cl72－ from the interaction between acidic ionic liquids and diphenyl oxide. The interaction between acidic ionic liquids and diphenyl oxide couldn’t be avoided by changing the cations of ionic liquids. The reuse problem of acidic ionic liquids can be solved when certain amount of AlCl3 is added into the used ionic liquids. The yield of target product is still around 90％ after 8 cycles of the ionic liquids.
2004, 20(09): 1089-1092
doi: 10.3866/PKU.WHXB20040906
Abstract:
The singlet vertical excited states of free-base porphin (FBP) have been investigated by TDDFT, ZINDO and INDO/S. The results show that both ZINDO and INDO/S could be effectively applied to the calculation of the low-lying excited states of large biological chromophores.
The singlet vertical excited states of free-base porphin (FBP) have been investigated by TDDFT, ZINDO and INDO/S. The results show that both ZINDO and INDO/S could be effectively applied to the calculation of the low-lying excited states of large biological chromophores.
Cluster Structions and Magic Number Characteristics during Solidification Process of Liquid Metal Al
2004, 20(09): 1093-1098
doi: 10.3866/PKU.WHXB20040907
Abstract:
A simulation study on the formation characteristics of cluster structures during rapid cooling process in a liquid metal system consisting of 100 000 Al atoms has been performed by molecular dynamics method. A cluster-type index method (CTIM) has been used to describe the structural configurations of various clusters. The results demonstrate that, during the solidification process of liquid metal Al, only the icosahedral clusters (12 0 12 0) related to the 1551 bond-types and various cluster structures formed by their combination play the key and critical role for the microstructure evolution; the cluster structures of various levels formed by different numbers and different types of basic clusters would present the peak values in a certain section of atomic number, namely the magic numbers; the magic number order in the system is 13(13); 19(21); 25～28(27); 31～33(29～30); 37,39;…(the numbers in the brackets are the corresponding values in liquid state) as shown in detail in Table 1 and Fig.4, this is quite in agreement with the experimental results obtained by Harris et al. The method used here to research the magic numbers from the cluster structures according to the level order and sections will give these experimental results a rather scientific and reasonable model explanation.
A simulation study on the formation characteristics of cluster structures during rapid cooling process in a liquid metal system consisting of 100 000 Al atoms has been performed by molecular dynamics method. A cluster-type index method (CTIM) has been used to describe the structural configurations of various clusters. The results demonstrate that, during the solidification process of liquid metal Al, only the icosahedral clusters (12 0 12 0) related to the 1551 bond-types and various cluster structures formed by their combination play the key and critical role for the microstructure evolution; the cluster structures of various levels formed by different numbers and different types of basic clusters would present the peak values in a certain section of atomic number, namely the magic numbers; the magic number order in the system is 13(13); 19(21); 25～28(27); 31～33(29～30); 37,39;…(the numbers in the brackets are the corresponding values in liquid state) as shown in detail in Table 1 and Fig.4, this is quite in agreement with the experimental results obtained by Harris et al. The method used here to research the magic numbers from the cluster structures according to the level order and sections will give these experimental results a rather scientific and reasonable model explanation.
2004, 20(09): 1099-1103
doi: 10.3866/PKU.WHXB20040908
Abstract:
Carbon tetrachloride was subjected to transient laser flash photolysis in the presence or absence of oxygen, transient absorption spectra were observed and analyzed. The experiment indicates that a series of micro-reactions occurred under 248 nm laser by a single photon absorption of CCl4, including the dissociation of the solvent and the formation of sophisticated substances－{CCl4－Cl}σ charge transfer complex,( CCl3＋…Cl－) ion pair and CCl3O2. These absorptions decay according to the first order kinetics, and the decay rate constants of {CCl4－Cl}σ charge transfer complex were obtained to be 3.38×106 s－1 and 3.65×106 s－1 in the presence and absence of oxygen, respectively, and its production has nothing to do with the oxygen. The decay rate constants of (CCl3＋…Cl－) were also gained to be 3.73×107 s－1 and 3.02×107 s－1 in the presence and absent of oxygen, respectively. However, CCl3O2 exists only in the presence of oxygen with a decay rate constant of 2.32×104 s－1.
Carbon tetrachloride was subjected to transient laser flash photolysis in the presence or absence of oxygen, transient absorption spectra were observed and analyzed. The experiment indicates that a series of micro-reactions occurred under 248 nm laser by a single photon absorption of CCl4, including the dissociation of the solvent and the formation of sophisticated substances－{CCl4－Cl}σ charge transfer complex,( CCl3＋…Cl－) ion pair and CCl3O2. These absorptions decay according to the first order kinetics, and the decay rate constants of {CCl4－Cl}σ charge transfer complex were obtained to be 3.38×106 s－1 and 3.65×106 s－1 in the presence and absence of oxygen, respectively, and its production has nothing to do with the oxygen. The decay rate constants of (CCl3＋…Cl－) were also gained to be 3.73×107 s－1 and 3.02×107 s－1 in the presence and absent of oxygen, respectively. However, CCl3O2 exists only in the presence of oxygen with a decay rate constant of 2.32×104 s－1.
2004, 20(09): 1104-1107
doi: 10.3866/PKU.WHXB20040909
Abstract:
Density, viscosity and ultrasonic velocity of solutions of four Schiff bases in 1,4-dioxane and dimethylformamide (DMF) were measured at 308.15 K. Various acoustical properties such as specific impedance (Z),adiabatic compressibility (κs), Rao′s molar sound function (Rm), the van der Waals constant (b),molar compressibility (W),intermolecular free length (Lf),relaxation strength(r), solvation number(Sn),were calculated. The results are interpreted in terms of molecular interactions occurring in the solutions.
Density, viscosity and ultrasonic velocity of solutions of four Schiff bases in 1,4-dioxane and dimethylformamide (DMF) were measured at 308.15 K. Various acoustical properties such as specific impedance (Z),adiabatic compressibility (κs), Rao′s molar sound function (Rm), the van der Waals constant (b),molar compressibility (W),intermolecular free length (Lf),relaxation strength(r), solvation number(Sn),were calculated. The results are interpreted in terms of molecular interactions occurring in the solutions.
2004, 20(09): 1108-1111
doi: 10.3866/PKU.WHXB20040910
Abstract:
The effect of Ho3＋ adsorbed on the Pt/C catalyst on the electrooxidation of the adsorbed CO was studied. It was found that Ho3＋ adsorbed on the Pt/C catalyst could promote the electrooxidation of the adsorbed CO in both neutral and acidic solutions in a large temperature range. Firstly, it is due to that Ho3＋ could reduce the adsorption intensity of CO. Secondly, Eox and Ep of CO adsorbed on the Pt-Ho3＋/C catalyst in the neutral solution are more negative than that in the acidic solution, indicating that the promoting effect of Ho3＋ in the neutral solution is larger than that in the acidic solution. Thirdly, in both neutral and acidic solutions, the negative shift of Eox and Ep of CO adsorbed on the Pt-Ho3＋/C catalyst increases with increase of the temperature. Thus, the increase in the temperature promotes the action of Ho3＋. When the temperature is at 60 ℃,the negative shift of Eox and Ep of CO adsorbed on the Pt-Ho3＋/C catalyst is sufficient to avoid poisoning of Pt catalyst by CO. In addition, Pt-Ho3＋/C catalyst is easy to be prepared. Thus, it is possible to apply the Pt-Ho3＋/C catalyst in PEMFC (proton exchange membrane fuel cell) and DMFC(direct methanol fuel cell).
The effect of Ho3＋ adsorbed on the Pt/C catalyst on the electrooxidation of the adsorbed CO was studied. It was found that Ho3＋ adsorbed on the Pt/C catalyst could promote the electrooxidation of the adsorbed CO in both neutral and acidic solutions in a large temperature range. Firstly, it is due to that Ho3＋ could reduce the adsorption intensity of CO. Secondly, Eox and Ep of CO adsorbed on the Pt-Ho3＋/C catalyst in the neutral solution are more negative than that in the acidic solution, indicating that the promoting effect of Ho3＋ in the neutral solution is larger than that in the acidic solution. Thirdly, in both neutral and acidic solutions, the negative shift of Eox and Ep of CO adsorbed on the Pt-Ho3＋/C catalyst increases with increase of the temperature. Thus, the increase in the temperature promotes the action of Ho3＋. When the temperature is at 60 ℃,the negative shift of Eox and Ep of CO adsorbed on the Pt-Ho3＋/C catalyst is sufficient to avoid poisoning of Pt catalyst by CO. In addition, Pt-Ho3＋/C catalyst is easy to be prepared. Thus, it is possible to apply the Pt-Ho3＋/C catalyst in PEMFC (proton exchange membrane fuel cell) and DMFC(direct methanol fuel cell).
2004, 20(09): 1112-1117
doi: 10.3866/PKU.WHXB20040911
Abstract:
The cross-reaction microscopic mechanism of aqueous benzene with hydrogen peroxide under different conditions was studied by laser flash photolysis. The main characteristic peaks in these transient absorbance spectra were assigned and the build-up/decay trends of several transient species were investigated. •OH radical can be produced in aqueous solution of hydrogen peroxide exposed to 266 nm laser beam. The reaction of •OH radical and benzene produces C6H6-OH adduct with a rate constant of (8.0～8.1)×109 L•mol－1•s－1 in the approximately neutral(pH≈6) and 7.7×109 L•mol－1•s－1 in acid (pH=1.5)solution, while the rate constant is about (6.7～6.9)×109 L•mol－1•s－1 in the basic (pH=9)solution. The C6H6-OH adduct will be able to react with O2 to form C6H6-OHO2, and then decompose into p-benzoquinone. In the meantime, C6H6-OH adducts and excited state of benzene may also react with H2O2 to form p-benzoquinone. The three reaction pathways were concurrently happened.
The cross-reaction microscopic mechanism of aqueous benzene with hydrogen peroxide under different conditions was studied by laser flash photolysis. The main characteristic peaks in these transient absorbance spectra were assigned and the build-up/decay trends of several transient species were investigated. •OH radical can be produced in aqueous solution of hydrogen peroxide exposed to 266 nm laser beam. The reaction of •OH radical and benzene produces C6H6-OH adduct with a rate constant of (8.0～8.1)×109 L•mol－1•s－1 in the approximately neutral(pH≈6) and 7.7×109 L•mol－1•s－1 in acid (pH=1.5)solution, while the rate constant is about (6.7～6.9)×109 L•mol－1•s－1 in the basic (pH=9)solution. The C6H6-OH adduct will be able to react with O2 to form C6H6-OHO2, and then decompose into p-benzoquinone. In the meantime, C6H6-OH adducts and excited state of benzene may also react with H2O2 to form p-benzoquinone. The three reaction pathways were concurrently happened.
2004, 20(09): 1118-1122
doi: 10.3866/PKU.WHXB20040912
Abstract:
All geometry structures of Con(n=2～10) clusters have been optimized, and the energy, frequency and magnetism of Con(n=2～10) clusters were calculated using the local spin density approximation and generalized gradient approximation of density functional theory. We found the same ground state structures in the two methods, and discussed theoretically the influence of the average coordination number, average bond length and symmetry on clusters magnetism. For Con(n=2～4) clusters, the magnetism of ground states strongly depends on average bond length, for Con(n=5～9),it strongly depend on average coordination number, for Co10,the factors of interatomic distance and average coordination number together lead to the same magnetism as Co8 cluster. Average moments of Co5 and Co9 present magnetic magic number.
All geometry structures of Con(n=2～10) clusters have been optimized, and the energy, frequency and magnetism of Con(n=2～10) clusters were calculated using the local spin density approximation and generalized gradient approximation of density functional theory. We found the same ground state structures in the two methods, and discussed theoretically the influence of the average coordination number, average bond length and symmetry on clusters magnetism. For Con(n=2～4) clusters, the magnetism of ground states strongly depends on average bond length, for Con(n=5～9),it strongly depend on average coordination number, for Co10,the factors of interatomic distance and average coordination number together lead to the same magnetism as Co8 cluster. Average moments of Co5 and Co9 present magnetic magic number.
2004, 20(09): 1123-1128
doi: 10.3866/PKU.WHXB20040913
Abstract:
The 5-parameter morse potential (5-MP) of interaction between an adatom and metal surface cluster is put forward and performed on O-Pt low index surface systems. The characteristics of critical points are obtained. The theoretical results show that oxygen atom can only adsorb at the four-fold hollow site on Pt (100) ;O adsorbs at the three-fold hollow site and the long-bridge site on the (110) missing-row reconstruction surface. We ulteriorly analyze heredity and variation of vibrational fingerprint properties of three-fold state on Pt(111). We confirm that the experimental data of 59.49 meV and 40.90 meV in the electron energy loss spectrum on the (110) missing-row reconstruction surface belong to vertical vibrations of adsorption states, which are produced by oxygen atom on the three-fold hollow site and long-bridge site, respectively.
The 5-parameter morse potential (5-MP) of interaction between an adatom and metal surface cluster is put forward and performed on O-Pt low index surface systems. The characteristics of critical points are obtained. The theoretical results show that oxygen atom can only adsorb at the four-fold hollow site on Pt (100) ;O adsorbs at the three-fold hollow site and the long-bridge site on the (110) missing-row reconstruction surface. We ulteriorly analyze heredity and variation of vibrational fingerprint properties of three-fold state on Pt(111). We confirm that the experimental data of 59.49 meV and 40.90 meV in the electron energy loss spectrum on the (110) missing-row reconstruction surface belong to vertical vibrations of adsorption states, which are produced by oxygen atom on the three-fold hollow site and long-bridge site, respectively.
2004, 20(09): 1129-1133
doi: 10.3866/PKU.WHXB20040914
Abstract:
Nucleophilic additions of a series of mimic compounds of pyrroloquinoline quinone(PQQ) and their analogues with ammonia were investigated at the B3LYP/D95(d, p) level of theory in order to study the relationship between structure and reactivity. It is demonstrated that: (1) for the monocarbonyl system, the electrophilicity of the carbonyl carbon affects significantly the reactive energy barrier; (2) for the biscarbonyl system, the hydrogen bond, formed at the transition state between the hydrogen of the nuclephilic reagent ammonia and the ortho-carbonyl oxygen is crucial for reaction activation energy; (3) while the fused ring has little effect on the reactive barrier, the reaction activation energy can be significantly reduced by the hydrogen bond between H of ammonia and N1 atom in the fused hetercycle. Quantitatively, a od linear correlation has been found between the reaction activation energy and the angle (φ(OCN) ) between the attacked carbonyly and the N atom of the nucleophilic NH3 at the transition state.
Nucleophilic additions of a series of mimic compounds of pyrroloquinoline quinone(PQQ) and their analogues with ammonia were investigated at the B3LYP/D95(d, p) level of theory in order to study the relationship between structure and reactivity. It is demonstrated that: (1) for the monocarbonyl system, the electrophilicity of the carbonyl carbon affects significantly the reactive energy barrier; (2) for the biscarbonyl system, the hydrogen bond, formed at the transition state between the hydrogen of the nuclephilic reagent ammonia and the ortho-carbonyl oxygen is crucial for reaction activation energy; (3) while the fused ring has little effect on the reactive barrier, the reaction activation energy can be significantly reduced by the hydrogen bond between H of ammonia and N1 atom in the fused hetercycle. Quantitatively, a od linear correlation has been found between the reaction activation energy and the angle (φ(OCN) ) between the attacked carbonyly and the N atom of the nucleophilic NH3 at the transition state.
2004, 20(09): 1134-1137
doi: 10.3866/PKU.WHXB20040915
Abstract:
Well-ordered large-pore anodic aluminum oxide membranes were one-step prepared in water-deficient electrolytes using ethanol as main solvent. The effects of water content, electrolyte concentration and solvent types were studied with the help of SEM. The results showed that the involved electrochemical anodization and corrosion could be controlled by changing the amount of water added in the electrolyte, and the pores of the AAO membranes could be made in a controlled manner within a long reaction time. The pores were hexa nally ordered and narrowly diameter-distributed ((95±13) nm) in comparison with those produced with normal electrolytes using water as the sole solvent ((95±30) nm). With this method, the applied anodizing voltage spans a wider range, and so does the tuning of the pore diameters. This approach can broaden the application of the AAO templates in the fabrication and processing of nanoarrays and porous materials.
Well-ordered large-pore anodic aluminum oxide membranes were one-step prepared in water-deficient electrolytes using ethanol as main solvent. The effects of water content, electrolyte concentration and solvent types were studied with the help of SEM. The results showed that the involved electrochemical anodization and corrosion could be controlled by changing the amount of water added in the electrolyte, and the pores of the AAO membranes could be made in a controlled manner within a long reaction time. The pores were hexa nally ordered and narrowly diameter-distributed ((95±13) nm) in comparison with those produced with normal electrolytes using water as the sole solvent ((95±30) nm). With this method, the applied anodizing voltage spans a wider range, and so does the tuning of the pore diameters. This approach can broaden the application of the AAO templates in the fabrication and processing of nanoarrays and porous materials.
2004, 20(09): 1138-1143
doi: 10.3866/PKU.WHXB20040916
Abstract:
The grafting of tetraneopentyl-titanium onto the surface of MCM-41 mesoporous molecular sieves prior to pretreatment at 500 ℃ under 10－2 Pa vacuum generated a well-defined bigrafted surface complex (≡Si－O)2Ti(CH2CMe3)2.The (≡Si－O)2Ti(CH2CMe3)2 readily reacts with CH3OH,H2O and O2 to produce (≡Si－O)2Ti(OCH3)2,(≡Si－O)2Ti(OH)2 and (≡Si－O)2Ti(OCH2CMe3)2 at room temperature, respectively. Further calcination in oxygen at 500 ℃ of the hydrolyzed products,(≡Si－O)2Ti(OH)2,resulted in surface titanium oxides. All the above reactions were followed by in situ FTIR and the resulted products were characterized by elemental analysis, XRD, nitrogen adsorption, FTIR and DRS. It is showed that the grafting reaction and post-treatments did not affect the characteristic structure of MCM-41.The surface area and pore diameter of the Ti-MCM-41 are slightly less than that of MCM-41.The Ti atoms are tetrahedrally coordinated on the surface of MCM-41.Catalytic test revealed that the Ti-MCM-41 has evident photocatalytic activity toward ethylene. The reason for photocatalytic activity of the molecular sieve was discussed by comparing for the structure and properties of Ti-MCM-41 with that of [Ti]-MCM-41.
The grafting of tetraneopentyl-titanium onto the surface of MCM-41 mesoporous molecular sieves prior to pretreatment at 500 ℃ under 10－2 Pa vacuum generated a well-defined bigrafted surface complex (≡Si－O)2Ti(CH2CMe3)2.The (≡Si－O)2Ti(CH2CMe3)2 readily reacts with CH3OH,H2O and O2 to produce (≡Si－O)2Ti(OCH3)2,(≡Si－O)2Ti(OH)2 and (≡Si－O)2Ti(OCH2CMe3)2 at room temperature, respectively. Further calcination in oxygen at 500 ℃ of the hydrolyzed products,(≡Si－O)2Ti(OH)2,resulted in surface titanium oxides. All the above reactions were followed by in situ FTIR and the resulted products were characterized by elemental analysis, XRD, nitrogen adsorption, FTIR and DRS. It is showed that the grafting reaction and post-treatments did not affect the characteristic structure of MCM-41.The surface area and pore diameter of the Ti-MCM-41 are slightly less than that of MCM-41.The Ti atoms are tetrahedrally coordinated on the surface of MCM-41.Catalytic test revealed that the Ti-MCM-41 has evident photocatalytic activity toward ethylene. The reason for photocatalytic activity of the molecular sieve was discussed by comparing for the structure and properties of Ti-MCM-41 with that of [Ti]-MCM-41.
2004, 20(09): 1144-1149
doi: 10.3866/PKU.WHXB20040917
Abstract:
Six new rare earth complexes of salicylaldehyde-1H-benzotriazol acetyl hydrazone(C15H13N5O2, SBTH)have been synthesized in methanol. The formulae RE(HL)2ClO4 (RE=Pr, Nd, Sm, Eu, Gd, Tb; HL=C15H12N5O2)were determined by elemental analysis and EDTA volumetric analysis, molar conductivity, IR and 1H NMR. The TG-DTG, DSC were carried out to study the thermodecomposition process and the decomposition enthalpies of the main steps of the complexes were obtained. The apparent activation energies of the main steps were calculated by the Kissinger′s method and Ozawa′s method. The dissolution enthalpies of the complexes were measured in DMF.
Six new rare earth complexes of salicylaldehyde-1H-benzotriazol acetyl hydrazone(C15H13N5O2, SBTH)have been synthesized in methanol. The formulae RE(HL)2ClO4 (RE=Pr, Nd, Sm, Eu, Gd, Tb; HL=C15H12N5O2)were determined by elemental analysis and EDTA volumetric analysis, molar conductivity, IR and 1H NMR. The TG-DTG, DSC were carried out to study the thermodecomposition process and the decomposition enthalpies of the main steps of the complexes were obtained. The apparent activation energies of the main steps were calculated by the Kissinger′s method and Ozawa′s method. The dissolution enthalpies of the complexes were measured in DMF.
2004, 20(09): 1150-1154
doi: 10.3866/PKU.WHXB20040918
Abstract:
ZnCl2/MCM-41 catalysts are prepared by solid-state interaction of ZnCl2 and mesoporous MCM-41 material using different method of microwave heating and conventional heating, as well as the method of solvent dispersion in toluene. The status of ZnCl2 onto the surface of MCM-41 in the samples of ZnCl2/MCM-41 is characterized by XRD, FT-IR, TG-DSC and atomic absorption spectroscopy (AAS).XRD patterns indicate that ZnCl2 can be dispersed completely on the surface of MCM-41 at ZnCl2 loading less than 4 mmol•g－1 if the samples prepared by the method of microwave heating and solvent dispersion. FT-IR spectra, DSC curves and AAS measurement results indicate that the new Lewis acid sites of O－Zn－Cl are formed by the solid-state interaction between ZnCl2 and the surface hydroxyl (Si－OH) under microwave heating. The catalytic performances of ZnCl2/MCM-41 samples prepared by the different methods are also investigated in the Diels-Alder reaction of myrcene and acrolein for high regioselective synthesis of para-myrac aldehyde. It was found that the activity, selectivity for cycloadducts and regiooselectivity of para-myrac aldehyde are higher over the catalysts of ZnCl2/MCM-41 prepared by the methods of microwave heating and solvent dispersion than that over ZnCl2/MCM-41 prepared by conventional heating. Apparently, the catalyst preparation method of microwave heating is simpler than the method of solvent dispersion in toluene. With an increase of ZnCl2 loading, the catalytic activity increases but the selectivity of cycloadducts decrease. The activity and regioselectivity of para/meta increase slightly with the selectivity for cycloadducts decrease markedly when ZnCl2 loading over 4 mmol•g－1,which suggested that new active sites of O－Zn－Cl formed on the surface of MCM-41 plays very important role for high regioselective synthesis of para-myrac aldehyde.
ZnCl2/MCM-41 catalysts are prepared by solid-state interaction of ZnCl2 and mesoporous MCM-41 material using different method of microwave heating and conventional heating, as well as the method of solvent dispersion in toluene. The status of ZnCl2 onto the surface of MCM-41 in the samples of ZnCl2/MCM-41 is characterized by XRD, FT-IR, TG-DSC and atomic absorption spectroscopy (AAS).XRD patterns indicate that ZnCl2 can be dispersed completely on the surface of MCM-41 at ZnCl2 loading less than 4 mmol•g－1 if the samples prepared by the method of microwave heating and solvent dispersion. FT-IR spectra, DSC curves and AAS measurement results indicate that the new Lewis acid sites of O－Zn－Cl are formed by the solid-state interaction between ZnCl2 and the surface hydroxyl (Si－OH) under microwave heating. The catalytic performances of ZnCl2/MCM-41 samples prepared by the different methods are also investigated in the Diels-Alder reaction of myrcene and acrolein for high regioselective synthesis of para-myrac aldehyde. It was found that the activity, selectivity for cycloadducts and regiooselectivity of para-myrac aldehyde are higher over the catalysts of ZnCl2/MCM-41 prepared by the methods of microwave heating and solvent dispersion than that over ZnCl2/MCM-41 prepared by conventional heating. Apparently, the catalyst preparation method of microwave heating is simpler than the method of solvent dispersion in toluene. With an increase of ZnCl2 loading, the catalytic activity increases but the selectivity of cycloadducts decrease. The activity and regioselectivity of para/meta increase slightly with the selectivity for cycloadducts decrease markedly when ZnCl2 loading over 4 mmol•g－1,which suggested that new active sites of O－Zn－Cl formed on the surface of MCM-41 plays very important role for high regioselective synthesis of para-myrac aldehyde.
2004, 20(09): 1155-1158
doi: 10.3866/PKU.WHXB20040919
Abstract:
In order to study the influence of oxygen storage materials′ preparation methods on their properties of oxygen storage capacity (OSC), surface area and reductive property, rare earth oxygen storage materials were prepared by different precipitation methods. Physical-chemical methods such as BET, XRD, H2-TPR and so on were used to study properties of these oxygen storage materials. Results indicated that solid solution could be t whichever method was used. But the properties of samples are sensitive to the preparation methods. When CeO2-ZrO2 was prepared by adding cerium and zirconium nitrate solution and ammonia solution simultaneously, the sample obtained had od OSC and high surface area. When CeO2-ZrO2 was prepared by adding the ammonia solution into the above nitrate solution, the sample obtained had poor but stable OSC and low surface area. When CeO2-ZrO2 was prepared by adding the above nitrate solution into the ammonia solution, the sample obtained had od OSC and low surface area. We also find that the OSC of materials prepared has no dependence on surface area but the reductivity of the materials depends on the surface area.
In order to study the influence of oxygen storage materials′ preparation methods on their properties of oxygen storage capacity (OSC), surface area and reductive property, rare earth oxygen storage materials were prepared by different precipitation methods. Physical-chemical methods such as BET, XRD, H2-TPR and so on were used to study properties of these oxygen storage materials. Results indicated that solid solution could be t whichever method was used. But the properties of samples are sensitive to the preparation methods. When CeO2-ZrO2 was prepared by adding cerium and zirconium nitrate solution and ammonia solution simultaneously, the sample obtained had od OSC and high surface area. When CeO2-ZrO2 was prepared by adding the ammonia solution into the above nitrate solution, the sample obtained had poor but stable OSC and low surface area. When CeO2-ZrO2 was prepared by adding the above nitrate solution into the ammonia solution, the sample obtained had od OSC and low surface area. We also find that the OSC of materials prepared has no dependence on surface area but the reductivity of the materials depends on the surface area.
2004, 20(09): 1159-1162
doi: 10.3866/PKU.WHXB20040920
Abstract:
The crystallization behavior and the structure of the electroless Ni68.6-Fe9.6-P21.8 deposit were studied by DSC and XRD. The results show that the as-plated deposit consists of amorphous phase, crystallizes into metastable Ni5P2(P3) and Fe-Ni(Im3m) at 367.6 ℃, and transforms into Ni3P(I-4) and FeNi3(Pm3m) at 499.2 ℃. Scanning electron microscopy was performed to observe the surface micromorphology of the as-plated deposit and the deposit heat-treated at 500 ℃. The heat-treated consists of many grains with diameters of 10～30 nm. The microhardness of the deposit increases with the increase of the annealing temperature up to 500 ℃, after which it decreases. The as-plated deposit almost has no magnetism, and its magnetic properties increase with the increase of annealing temperature, showing a rapid increase at above 600 ℃. The saturation magnetization and the coercive force increase greatly with the annealing temperature at above 400 ℃. The corrosion resistances of the as-plated deposit and the deposit heat-treated at 600 ℃ in w=3.5％ NaCl solution (pH 7.0) were investigated by mass loss tests and anodic polarization experiments. The results indicate that the as-plated deposit has a better corrosion resistance than that of the heat-treated deposit in this environment, and their anodic polarization behaviors are different. The above properties of the deposits were discussed from the structure and micromorphology of the deposits.
The crystallization behavior and the structure of the electroless Ni68.6-Fe9.6-P21.8 deposit were studied by DSC and XRD. The results show that the as-plated deposit consists of amorphous phase, crystallizes into metastable Ni5P2(P3) and Fe-Ni(Im3m) at 367.6 ℃, and transforms into Ni3P(I-4) and FeNi3(Pm3m) at 499.2 ℃. Scanning electron microscopy was performed to observe the surface micromorphology of the as-plated deposit and the deposit heat-treated at 500 ℃. The heat-treated consists of many grains with diameters of 10～30 nm. The microhardness of the deposit increases with the increase of the annealing temperature up to 500 ℃, after which it decreases. The as-plated deposit almost has no magnetism, and its magnetic properties increase with the increase of annealing temperature, showing a rapid increase at above 600 ℃. The saturation magnetization and the coercive force increase greatly with the annealing temperature at above 400 ℃. The corrosion resistances of the as-plated deposit and the deposit heat-treated at 600 ℃ in w=3.5％ NaCl solution (pH 7.0) were investigated by mass loss tests and anodic polarization experiments. The results indicate that the as-plated deposit has a better corrosion resistance than that of the heat-treated deposit in this environment, and their anodic polarization behaviors are different. The above properties of the deposits were discussed from the structure and micromorphology of the deposits.
2004, 20(09): 1163-1166
doi: 10.3866/PKU.WHXB20040921
Abstract:
The behaviors of adsorption and oxidation of ethanol on a roughened platinum electrode with high SERS activity were studied by using cyclic voltammetry and in-situ surface enhanced Raman spectroscopy, surface Raman spectra of dissociative adsorption of ethanol on Pt electrode in acid medium have been obtained. The results show that ethanol can be dissociated on the Pt surface in acid medium to produce poisoning intermediate CO, which suppresses the further oxidation of ethanol, and some informations of Pt－C and Pt－C－Pt stretching vibration from linearly-adsorbed and bridged-adsorbed CO located in low frequency were obtained, respectively. The investigation also shows that the electro-oxidtion of ethanol on the roughened platinum was a diffuse-controlled reaction in sulfuric acid. By correlating the in-situ SERS data with the electrochemical data,it was found that the oxidation of ethanol proceeded via the parallel mechanism.
The behaviors of adsorption and oxidation of ethanol on a roughened platinum electrode with high SERS activity were studied by using cyclic voltammetry and in-situ surface enhanced Raman spectroscopy, surface Raman spectra of dissociative adsorption of ethanol on Pt electrode in acid medium have been obtained. The results show that ethanol can be dissociated on the Pt surface in acid medium to produce poisoning intermediate CO, which suppresses the further oxidation of ethanol, and some informations of Pt－C and Pt－C－Pt stretching vibration from linearly-adsorbed and bridged-adsorbed CO located in low frequency were obtained, respectively. The investigation also shows that the electro-oxidtion of ethanol on the roughened platinum was a diffuse-controlled reaction in sulfuric acid. By correlating the in-situ SERS data with the electrochemical data,it was found that the oxidation of ethanol proceeded via the parallel mechanism.
2004, 20(09): 1167-1171
doi: 10.3866/PKU.WHXB20040922
Abstract:
In this paper, we successfully fabricated a novel heterojunction composite film composed of 1,4-bis(ferrocene)thiophene and SnO2 nanoparticles. The morphology and microstructure have been investigated by AFM and XRD. Their Optical and photovoltage properties were also studied using UV-Vis spectra and surface photovoltage spectra (SPS). The results indicate that the novel heterojunction composite film has a higher photovoltage response in a wider region of 300～550 nm than the single film.
In this paper, we successfully fabricated a novel heterojunction composite film composed of 1,4-bis(ferrocene)thiophene and SnO2 nanoparticles. The morphology and microstructure have been investigated by AFM and XRD. Their Optical and photovoltage properties were also studied using UV-Vis spectra and surface photovoltage spectra (SPS). The results indicate that the novel heterojunction composite film has a higher photovoltage response in a wider region of 300～550 nm than the single film.
2004, 20(09): 1172-1174
doi: 10.3866/PKU.WHXB20040923
Abstract:
The optimized geometries, electron affinities, and vibrational frequencies of perfluoroadamantine (C10F16) and its radicals(C10F15) have been studied using four density functional theory(DFT) methods in conjunction with DZP＋ basis sets. Three measures of neutral/anion energy differences reported in this work are the adiabatic electron affinity (EAad), the vertical electron affinity (EAvert), and the vertical detachment energy (VDE). The reliable predicted adiabatic electron affinities(DZP＋ B3LYP) are: 1.06 eV (for C10F16), 4.11 and 3.03 eV for the two C10F15 radicals. It is clear that the perfluorination of hydrocarbons dramatically improve the ability to bind an electron and perfluoroadamantane is an effective electron acceptor and may thus be useful in the study of new materials and new reactions.
The optimized geometries, electron affinities, and vibrational frequencies of perfluoroadamantine (C10F16) and its radicals(C10F15) have been studied using four density functional theory(DFT) methods in conjunction with DZP＋ basis sets. Three measures of neutral/anion energy differences reported in this work are the adiabatic electron affinity (EAad), the vertical electron affinity (EAvert), and the vertical detachment energy (VDE). The reliable predicted adiabatic electron affinities(DZP＋ B3LYP) are: 1.06 eV (for C10F16), 4.11 and 3.03 eV for the two C10F15 radicals. It is clear that the perfluorination of hydrocarbons dramatically improve the ability to bind an electron and perfluoroadamantane is an effective electron acceptor and may thus be useful in the study of new materials and new reactions.
