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2012 Volume 28 Issue 3
2012, 28(03):
Abstract:
2012, 28(03): 499-503
doi: 10.3866/PKU.WHXB201112303
Abstract:
The correlation between the X―H bond-length change and the corresponding X―H stretching frequency shift upon X ―H···Y (Y is an electron donor) hydrogen bond formation is the basis for the spectroscopic detection and investigation of the hydrogen bond. However, this view has been questioned in a recent report, suggesting that the widely accepted correlation between the bond-length change and the frequency shift in hydrogen-bonded complexes is unreliable (McDowell, S. A. C.; Buckingham, A. D. J. Am. Chem. Soc. 2005, 127, 15515.). In this work, several robust computational methods have been used to investigate this issue. The results clearly show that a computational artifact leads to the conclusion incorrectly reported by McDowell and Buckingham and that the correlation between the X―H bond-length change and the corresponding X―H stretching frequency shift is still very od in the hydrogen-bonded complexes studied.
The correlation between the X―H bond-length change and the corresponding X―H stretching frequency shift upon X ―H···Y (Y is an electron donor) hydrogen bond formation is the basis for the spectroscopic detection and investigation of the hydrogen bond. However, this view has been questioned in a recent report, suggesting that the widely accepted correlation between the bond-length change and the frequency shift in hydrogen-bonded complexes is unreliable (McDowell, S. A. C.; Buckingham, A. D. J. Am. Chem. Soc. 2005, 127, 15515.). In this work, several robust computational methods have been used to investigate this issue. The results clearly show that a computational artifact leads to the conclusion incorrectly reported by McDowell and Buckingham and that the correlation between the X―H bond-length change and the corresponding X―H stretching frequency shift is still very od in the hydrogen-bonded complexes studied.
2012, 28(03): 504-521
doi: 10.3866/PKU.WHXB201201091
Abstract:
Molecular structures at interfaces determine interfacial properties. In order to optimize the interfacial structures to achieve improved properties of advanced materials, it is important to characterize molecular structures of interfaces in situ in real time. Recently, a nonlinear optical spectroscopic technique, sum frequency generation (SFG) vibrational spectroscopy, has been developed into a powerful and unique tool to elucidate molecular structures of buried interfaces, including liquid/liquid, solid/liquid, and solid/solid interfaces. In this review, applications of SFG to study molecular structures of complex interfaces such as polymer interfaces and biological interfaces have been discussed. Particularly, molecular surface structural changes of various polymers in water, molecular interactions between polymers and silane model adhesion promoters at interfaces, and structures of buried polymer/polymer as well as polymer/metal interfaces have been presented. In addition, interfacial structures of peptides with varied secondary structures and several representative proteins have been introduced. Interfaces play important roles in many disciplines ranging from chemistry, biology, physics, materials science and engineering, to nanotechnology. The development of a unique technique which can probe molecular structures of complex interfaces in situ greatly impacts the research in these disciplines as well as many interdisciplinary studies.
Molecular structures at interfaces determine interfacial properties. In order to optimize the interfacial structures to achieve improved properties of advanced materials, it is important to characterize molecular structures of interfaces in situ in real time. Recently, a nonlinear optical spectroscopic technique, sum frequency generation (SFG) vibrational spectroscopy, has been developed into a powerful and unique tool to elucidate molecular structures of buried interfaces, including liquid/liquid, solid/liquid, and solid/solid interfaces. In this review, applications of SFG to study molecular structures of complex interfaces such as polymer interfaces and biological interfaces have been discussed. Particularly, molecular surface structural changes of various polymers in water, molecular interactions between polymers and silane model adhesion promoters at interfaces, and structures of buried polymer/polymer as well as polymer/metal interfaces have been presented. In addition, interfacial structures of peptides with varied secondary structures and several representative proteins have been introduced. Interfaces play important roles in many disciplines ranging from chemistry, biology, physics, materials science and engineering, to nanotechnology. The development of a unique technique which can probe molecular structures of complex interfaces in situ greatly impacts the research in these disciplines as well as many interdisciplinary studies.
2012, 28(03): 522-527
doi: 10.3866/PKU.WHXB201201122
Abstract:
The ultrafast predissociation dynamics of acrylic acid after excitation to the second electronically excited state (S2) with a 200 nm pump pulse were studied using a femtosecond pump-probe technique combined with time-of-flight mass spectroscopy (TOF-MS). The time-resolved mass spectra signals of the parent ion and fragment ions were collected. By using the kinetic equations to fit and analyze the time-resolved mass spectra ion signals, the existence of the predissociation channel was revealed. The excited molecule populated in the S2 state decayed to the first electronically excited state (S1) through a fast internal conversion process over a period of 210 fs. The excited molecule populated on the S1 state then decayed to the vibrationally hot ground state (S0) through another internal conversion process over a period of 1.49 ps. Finally, on the vibrationally hot ground state surface, the molecule dissociated to the neutral fragments, H2C＝CH and HOCO, H2C＝CHCO and OH via C－C bond fission and C－O bond fission, respectively. The corresponding predissociation time constants were determined to be approximately 4 and 3 ps, respectively. The generation of fragment ions can occur in two ways, both from the dissociation of the parent ion and the ionization of the neutral fragments on the vibrationally hot ground state surface.
The ultrafast predissociation dynamics of acrylic acid after excitation to the second electronically excited state (S2) with a 200 nm pump pulse were studied using a femtosecond pump-probe technique combined with time-of-flight mass spectroscopy (TOF-MS). The time-resolved mass spectra signals of the parent ion and fragment ions were collected. By using the kinetic equations to fit and analyze the time-resolved mass spectra ion signals, the existence of the predissociation channel was revealed. The excited molecule populated in the S2 state decayed to the first electronically excited state (S1) through a fast internal conversion process over a period of 210 fs. The excited molecule populated on the S1 state then decayed to the vibrationally hot ground state (S0) through another internal conversion process over a period of 1.49 ps. Finally, on the vibrationally hot ground state surface, the molecule dissociated to the neutral fragments, H2C＝CH and HOCO, H2C＝CHCO and OH via C－C bond fission and C－O bond fission, respectively. The corresponding predissociation time constants were determined to be approximately 4 and 3 ps, respectively. The generation of fragment ions can occur in two ways, both from the dissociation of the parent ion and the ionization of the neutral fragments on the vibrationally hot ground state surface.
2012, 28(03): 528-535
doi: 10.3866/PKU.WHXB201112202
Abstract:
The effect of hyperbranched polyester (HBP) on the non-isothermal crystallization behavior of polyethylene glycol (PEG) was studied by differential scanning calorimetry (DSC), polarizing microscopy (POM), and Fourier transform infrared (FTIR) spectroscopy. The non-isothermal crystallization data for PEG and HBP/PEG were analyzed by the Ozawa, Jeziorny, and Mo Zhi-Shen methods. The results indicate that the non-isothermal crystallization processes of PEG and HBP/PEG may be described using the kinetic equations of Ozawa and Mo, but do not agree with the Jeziorny equation. The addition of HBP affected the crystallization process and crystal form of pure PEG, and slowed the rate of crystallization. The hydrogen bond formed between the carbonyl group of HBP and the terminated-hydroxyl group of PEG, and the larger size and highly branched structure of HBP are the main reasons for the slower crystallization.
The effect of hyperbranched polyester (HBP) on the non-isothermal crystallization behavior of polyethylene glycol (PEG) was studied by differential scanning calorimetry (DSC), polarizing microscopy (POM), and Fourier transform infrared (FTIR) spectroscopy. The non-isothermal crystallization data for PEG and HBP/PEG were analyzed by the Ozawa, Jeziorny, and Mo Zhi-Shen methods. The results indicate that the non-isothermal crystallization processes of PEG and HBP/PEG may be described using the kinetic equations of Ozawa and Mo, but do not agree with the Jeziorny equation. The addition of HBP affected the crystallization process and crystal form of pure PEG, and slowed the rate of crystallization. The hydrogen bond formed between the carbonyl group of HBP and the terminated-hydroxyl group of PEG, and the larger size and highly branched structure of HBP are the main reasons for the slower crystallization.
2012, 28(03): 536-540
doi: 10.3866/PKU.WHXB201201041
Abstract:
In this paper, a computational method for the substructure search in inorganic crystal structures is proposed. This method is based on the VF2 subgraph isomorphism al rithm. Furthermore, two additional approaches have been introduced into this method to improve the calculation efficiency of VF2: (1) introduction of crystal symmetry information with a view to avoiding redundant calculations among equivalent nodes (atoms); (2) a prescreening encoding treatment to enhance the calculation efficiency by greatly reducing the number of target structures. We tested the efficiency of this method by searching the zeolite crystal structure database from the International Zeolite Association for entries containing specified building units. The test results showed that this method could quickly and correctly retrieve all the entries containing the queried substructure in the zeolite structure database. The introduction of crystal symmetry information and the prescreening encoding treatment greatly reduce the complexity of substructure search. The search speed was significantly enhanced by at least 3-5 orders of magnitude. This method was developed using Perl programming language, ensuring that this method could be easily applied to various platforms.
In this paper, a computational method for the substructure search in inorganic crystal structures is proposed. This method is based on the VF2 subgraph isomorphism al rithm. Furthermore, two additional approaches have been introduced into this method to improve the calculation efficiency of VF2: (1) introduction of crystal symmetry information with a view to avoiding redundant calculations among equivalent nodes (atoms); (2) a prescreening encoding treatment to enhance the calculation efficiency by greatly reducing the number of target structures. We tested the efficiency of this method by searching the zeolite crystal structure database from the International Zeolite Association for entries containing specified building units. The test results showed that this method could quickly and correctly retrieve all the entries containing the queried substructure in the zeolite structure database. The introduction of crystal symmetry information and the prescreening encoding treatment greatly reduce the complexity of substructure search. The search speed was significantly enhanced by at least 3-5 orders of magnitude. This method was developed using Perl programming language, ensuring that this method could be easily applied to various platforms.
2012, 28(03): 541-546
doi: 10.3866/PKU.WHXB201112281
Abstract:
The molecular mapping of atom-level properties (MOLMAP) descriptor was generated on the basis of chemical bond descriptors of a molecule by Kohonen self-organizing map with a specific al rithm. The bond descriptors were composed of the physiochemical properties of the chemical bond, such as the difference of the charges between the two atoms and topological properties, such as the number of hetero-atoms connected to the two atoms. In this paper, the MOLMAP descriptors were used to predict the mutagenicity of 4075 organic substances (2305 mutagens and 1770 nonmutagens in Ames test). Random forests were used to construct mathematical models with three kinds of descriptors: (1) MOLMAP descriptors of different size; (2) global molecular descriptors; (3) the combination of MOLMAP descriptors and global molecular descriptors. The correct prediction percentage of out of bag (OOB) cross-validation of the whole data set reached 85.4%. To test the stability of the prediction model, it was used to predict the properties of a test set that was composed of 472 compounds collected from another database. The percentage of correct prediction of the test set was 86.7%. The prediction results were improved compared with the results of previous work.
The molecular mapping of atom-level properties (MOLMAP) descriptor was generated on the basis of chemical bond descriptors of a molecule by Kohonen self-organizing map with a specific al rithm. The bond descriptors were composed of the physiochemical properties of the chemical bond, such as the difference of the charges between the two atoms and topological properties, such as the number of hetero-atoms connected to the two atoms. In this paper, the MOLMAP descriptors were used to predict the mutagenicity of 4075 organic substances (2305 mutagens and 1770 nonmutagens in Ames test). Random forests were used to construct mathematical models with three kinds of descriptors: (1) MOLMAP descriptors of different size; (2) global molecular descriptors; (3) the combination of MOLMAP descriptors and global molecular descriptors. The correct prediction percentage of out of bag (OOB) cross-validation of the whole data set reached 85.4%. To test the stability of the prediction model, it was used to predict the properties of a test set that was composed of 472 compounds collected from another database. The percentage of correct prediction of the test set was 86.7%. The prediction results were improved compared with the results of previous work.
2012, 28(03): 547-554
doi: 10.3866/PKU.WHXB201112301
Abstract:
We report force field predictions for the hydrogen uptakes of porous aromatic framework (PAF) materials containing carboxylate functional groups with divalent metallic cations. The ab initio calculations were performed on our proposed functional groups and hydrogen molecules using the MP2 method with the TZVPP basis set and basis set superposition error (BSSE) correction. A force field was developed based on the ab initio energetic data. The resulting force field was applied to predict hydrogen adsorption isotherms at different temperatures and pressures using the grand canonical Monte Carlo (GCMC) method. Each functional group of divalent metallic cations and two carboxylic acid groups provided 13 (Mg) or 14 (Ca) binding sites for hydrogen molecules with an average binding energy of 8 kJ·mol-1 per hydrogen molecule. The predicted hydrogen adsorption results were improved remarkably by the functional groups at normal ambient conditions, exceeding the 2015 target set by the department of energy (DOE) of USA. This work reveals the complex relationship between hydrogen uptake and surface area, and the free volumes and binding energies of different materials.
We report force field predictions for the hydrogen uptakes of porous aromatic framework (PAF) materials containing carboxylate functional groups with divalent metallic cations. The ab initio calculations were performed on our proposed functional groups and hydrogen molecules using the MP2 method with the TZVPP basis set and basis set superposition error (BSSE) correction. A force field was developed based on the ab initio energetic data. The resulting force field was applied to predict hydrogen adsorption isotherms at different temperatures and pressures using the grand canonical Monte Carlo (GCMC) method. Each functional group of divalent metallic cations and two carboxylic acid groups provided 13 (Mg) or 14 (Ca) binding sites for hydrogen molecules with an average binding energy of 8 kJ·mol-1 per hydrogen molecule. The predicted hydrogen adsorption results were improved remarkably by the functional groups at normal ambient conditions, exceeding the 2015 target set by the department of energy (DOE) of USA. This work reveals the complex relationship between hydrogen uptake and surface area, and the free volumes and binding energies of different materials.
2012, 28(03): 555-560
doi: 10.3866/PKU.WHXB201112212
Abstract:
Using density functional theory with the B3LYP functional, the optimized structures of the organic alkalides M+ aza222M′- (M, M′ =Li, Na, K, and aza222=Azacryptand[2.2.2]) were calculated. The nonlinear optical (NLO) properties of these species were calculated by the BHandHLYP method. The results indicate that the M+aza222M′- alkalides exhibit very large first hyperpolarizabilities (β0) up to 1.0×106 a.u. (for M=Li, M′ =K). Both the first hyperpolarizabilities and the M-M′ distances of M+aza222M′- were found to depend on the atomic number of the alkali metal atom M(M′). By comparing the β0 values of various organic alkalides, aza222 was found to be preferable to the previously investigated complexants in enhancing the first hyperpolarizabilities of alkalides.
Using density functional theory with the B3LYP functional, the optimized structures of the organic alkalides M+ aza222M′- (M, M′ =Li, Na, K, and aza222=Azacryptand[2.2.2]) were calculated. The nonlinear optical (NLO) properties of these species were calculated by the BHandHLYP method. The results indicate that the M+aza222M′- alkalides exhibit very large first hyperpolarizabilities (β0) up to 1.0×106 a.u. (for M=Li, M′ =K). Both the first hyperpolarizabilities and the M-M′ distances of M+aza222M′- were found to depend on the atomic number of the alkali metal atom M(M′). By comparing the β0 values of various organic alkalides, aza222 was found to be preferable to the previously investigated complexants in enhancing the first hyperpolarizabilities of alkalides.
2012, 28(03): 561-566
doi: 10.3866/PKU.WHXB201201112
Abstract:
Using density functional theory calculations, we have studied the 1-(2-chlorophenyl)-2-thiourea catalyzed reaction of nitrostyrene with a typical sulfur ylide to understand the Michael addition mechanism. Transition state structures for the C―C bond-forming step controlling the stereoselectivity of the reaction have been identified and their relative stabilities evaluated. The role of the catalyst in the reaction has also been determined. The calculated results show that the formation of the anti-product is energetically more favorable than that of the syn-product. Furthermore, the catalyst (proton donor) promotes the reaction by forming a double hydrogen-bonded complex with nitrostyrene (proton acceptor), where the charge transfer between the donor and acceptor increases the eletrophilicity of β-C atom of the nitrostyrene, favoring the nucleophilic attack of the sulfur ylide.
Using density functional theory calculations, we have studied the 1-(2-chlorophenyl)-2-thiourea catalyzed reaction of nitrostyrene with a typical sulfur ylide to understand the Michael addition mechanism. Transition state structures for the C―C bond-forming step controlling the stereoselectivity of the reaction have been identified and their relative stabilities evaluated. The role of the catalyst in the reaction has also been determined. The calculated results show that the formation of the anti-product is energetically more favorable than that of the syn-product. Furthermore, the catalyst (proton donor) promotes the reaction by forming a double hydrogen-bonded complex with nitrostyrene (proton acceptor), where the charge transfer between the donor and acceptor increases the eletrophilicity of β-C atom of the nitrostyrene, favoring the nucleophilic attack of the sulfur ylide.
2012, 28(03): 567-572
doi: 10.3866/PKU.WHXB201112071
Abstract:
By performing first-principles calculations and non-equilibrium Green's function, the energy band structure, transmission spectrum and current-voltage characteristics of the O-doping zigzag boron nitride narrow-nanoribbons (z-BNNNRs) were investigated. The calculation results show that O-doping remarkably changes the z-BNNNRs energy band structure and transform the material from a semiconductor to a metal. It is also demonstrated that the system exhibits an obvious negative differential resistance (NDR) characteristic. Further investigations revealed that the position and concentration of O-doping also affected the NDR behavior over a certain range of bias. The negative differential conductance (NDC) for edge-doping is greater than that for middle-doping and the maximum of the NDC increases with an increase of the concentration of O-doping. This special electronic transport property of O-doping z-BNNNRs makes it more suitable as a candidate for molecular devices.
By performing first-principles calculations and non-equilibrium Green's function, the energy band structure, transmission spectrum and current-voltage characteristics of the O-doping zigzag boron nitride narrow-nanoribbons (z-BNNNRs) were investigated. The calculation results show that O-doping remarkably changes the z-BNNNRs energy band structure and transform the material from a semiconductor to a metal. It is also demonstrated that the system exhibits an obvious negative differential resistance (NDR) characteristic. Further investigations revealed that the position and concentration of O-doping also affected the NDR behavior over a certain range of bias. The negative differential conductance (NDC) for edge-doping is greater than that for middle-doping and the maximum of the NDC increases with an increase of the concentration of O-doping. This special electronic transport property of O-doping z-BNNNRs makes it more suitable as a candidate for molecular devices.
2012, 28(03): 573-577
doi: 10.3866/PKU.WHXB201112191
Abstract:
Spurred by traditional membrane science in which a charged membrane can improve separation efficiency, a forward osmosis membrane containing charged“armchair-type”(8, 8) carbon nanotubes (CNTs) was developed and the transport phenomena of water molecules in this membrane were investigated. In the simulation, 0.5 mol·L-1 NaCl was chosen to mimic seawater, and 1 mol·L-1 MgCl2 was chosen as the draw solution. The effects of electric charge on the density distribution, diffusion of water molecules, and the water flux of the membrane were investigated in detail. Modifying the CNT membrane by charge significantly changes the density distribution, diffusion, and flux of water molecules. The membrane containing CNTs modified by -0.3e can achieve the highest water flux of those developed.
Spurred by traditional membrane science in which a charged membrane can improve separation efficiency, a forward osmosis membrane containing charged“armchair-type”(8, 8) carbon nanotubes (CNTs) was developed and the transport phenomena of water molecules in this membrane were investigated. In the simulation, 0.5 mol·L-1 NaCl was chosen to mimic seawater, and 1 mol·L-1 MgCl2 was chosen as the draw solution. The effects of electric charge on the density distribution, diffusion of water molecules, and the water flux of the membrane were investigated in detail. Modifying the CNT membrane by charge significantly changes the density distribution, diffusion, and flux of water molecules. The membrane containing CNTs modified by -0.3e can achieve the highest water flux of those developed.
2012, 28(03): 578-584
doi: 10.3866/PKU.WHXB201201032
Abstract:
Single-crystalline TiO2 nanowires (SCTNWs) were prepared using a hydrothermal growth method. The (010) crystal face of the titania particles was eroded by NaOH solution to produce Na2Ti4O9 at high temperature and pressure. H2Ti4O9·H2O was generated after washing with distilled water and HCl, which was then linked to a wire by hydrogen bonding. Finally, sintering gave SCTNWs. The SCTNWs were characterized by transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The influence of hydrothermal growth time was investigated. A flexible photoanode was fabricated on Ti foil using a highly stable and uniform titania colloid including the SCTNWs. The photovoltaic performance of dye-sensitized solar cells (DSSCs) containing different contents of SCTNWs was evaluated using scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), ultraviolet-visible (UV-Vis) spectrophotometry, and photovoltaic tests. Under optimized conditions with 7.5% (w) SCTNW, a flexible DSSC with a lightto- electrical energy conversion efficiency of 6.48% was achieved under irradiation with simulated solar light with an intensity of 100 mW·cm-2.
Single-crystalline TiO2 nanowires (SCTNWs) were prepared using a hydrothermal growth method. The (010) crystal face of the titania particles was eroded by NaOH solution to produce Na2Ti4O9 at high temperature and pressure. H2Ti4O9·H2O was generated after washing with distilled water and HCl, which was then linked to a wire by hydrogen bonding. Finally, sintering gave SCTNWs. The SCTNWs were characterized by transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The influence of hydrothermal growth time was investigated. A flexible photoanode was fabricated on Ti foil using a highly stable and uniform titania colloid including the SCTNWs. The photovoltaic performance of dye-sensitized solar cells (DSSCs) containing different contents of SCTNWs was evaluated using scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), ultraviolet-visible (UV-Vis) spectrophotometry, and photovoltaic tests. Under optimized conditions with 7.5% (w) SCTNW, a flexible DSSC with a lightto- electrical energy conversion efficiency of 6.48% was achieved under irradiation with simulated solar light with an intensity of 100 mW·cm-2.
2012, 28(03): 585-590
doi: 10.3866/PKU.WHXB201112302
Abstract:
In order to enhance the dispersion of Fe3O4 nanoparticles in polymer electrolytes for dyesensitized solar cell (DSSC) applications, the ionic conductivity of the polymer electrolytes with different small molecular surfactants was studied. The surfactants used were polyethylene glycol (PEG200), Triton X-100, acetyl acetone, and mixture of these three active agents at 1%(w) doping concentration of Fe3O4 nanoparticles in electrolyte. Comparison of the electrochemical properties of Fe3O4-doped polymer electrolytes containing different surfactants showed that PEG200 was suitable for modifying Fe3O4 nanoparticles to disperse in agarose-based polymer electrolytes. When the mass fraction of PEG200 was 61.8%(w), the electrolyte had excellent conductivity (2.88×10-3 S·cm-1). Electrochemical impedance spectra (EIS) revealed that when the concentration of PEG200 increased, the electron lifetime and combination resistance of a dye-sensitized solar cell increase initially and then decreasd. The longest electron lifetime and the largest combination resistance were achieved when the concentration of PEG200 was 68.3%(w).
In order to enhance the dispersion of Fe3O4 nanoparticles in polymer electrolytes for dyesensitized solar cell (DSSC) applications, the ionic conductivity of the polymer electrolytes with different small molecular surfactants was studied. The surfactants used were polyethylene glycol (PEG200), Triton X-100, acetyl acetone, and mixture of these three active agents at 1%(w) doping concentration of Fe3O4 nanoparticles in electrolyte. Comparison of the electrochemical properties of Fe3O4-doped polymer electrolytes containing different surfactants showed that PEG200 was suitable for modifying Fe3O4 nanoparticles to disperse in agarose-based polymer electrolytes. When the mass fraction of PEG200 was 61.8%(w), the electrolyte had excellent conductivity (2.88×10-3 S·cm-1). Electrochemical impedance spectra (EIS) revealed that when the concentration of PEG200 increased, the electron lifetime and combination resistance of a dye-sensitized solar cell increase initially and then decreasd. The longest electron lifetime and the largest combination resistance were achieved when the concentration of PEG200 was 68.3%(w).
2012, 28(03): 591-595
doi: 10.3866/PKU.WHXB201112161
Abstract:
Al-doped TiO2 thin films were synthesized by the hydrothermal method. To prepare a working electrode, a TiO2 or AlTiO2 slurry was coated onto a fluorine-doped tin oxide glass substrate by the doctor blade method and the coated substrate was sintered at 450 ° C. TiO2 and Al-doped TiO2 films were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and tested by the dye-sensitized solar cell (DSSCs) system. The influences of Al-doping on TiO2 crystal form and the photovoltaic performance of DSSCs were investigated. X-ray photoelectron spectroscopy (XPS) data indicate that the doped Al ions exist in the form of Al3+ , and these ions play a role as e- or h+ traps and reduce the e-/h+ pair recombination rate. The corresponding Mott- Schottky plot indicates that the Al-doped TiO2 photoanode shifts the flat band potential positively. The positive shift of the flat band potential improves the driving force of injected electrons from the LUMO of the dye to the conduction band of TiO2. The Al-doped TiO2 thin film shows a photovoltaic efficiency of 6.48%, which is higher than that of the undoped TiO2 thin film (5.58%) and the short-circuit photocurrent density increases from 16.5 to 18.2 mA·cm-2.
Al-doped TiO2 thin films were synthesized by the hydrothermal method. To prepare a working electrode, a TiO2 or AlTiO2 slurry was coated onto a fluorine-doped tin oxide glass substrate by the doctor blade method and the coated substrate was sintered at 450 ° C. TiO2 and Al-doped TiO2 films were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and tested by the dye-sensitized solar cell (DSSCs) system. The influences of Al-doping on TiO2 crystal form and the photovoltaic performance of DSSCs were investigated. X-ray photoelectron spectroscopy (XPS) data indicate that the doped Al ions exist in the form of Al3+ , and these ions play a role as e- or h+ traps and reduce the e-/h+ pair recombination rate. The corresponding Mott- Schottky plot indicates that the Al-doped TiO2 photoanode shifts the flat band potential positively. The positive shift of the flat band potential improves the driving force of injected electrons from the LUMO of the dye to the conduction band of TiO2. The Al-doped TiO2 thin film shows a photovoltaic efficiency of 6.48%, which is higher than that of the undoped TiO2 thin film (5.58%) and the short-circuit photocurrent density increases from 16.5 to 18.2 mA·cm-2.
2012, 28(03): 596-602
doi: 10.3866/PKU.WHXB201112261
Abstract:
Two novel organic compounds, 5-amino-2,3-dihydro-1,4-dyhydroxy anthraquinone (ADDAQ) and 5-amino-1,4-dyhydroxy anthraquinone (ADAQ), were synthesized as cathode materials for lithium batteries. The compounds were characterized by 1H nuclear magnetic resonance (1H NMR) spectroscopy, mass spectrometry (MS), elemental analysis (EA), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-Vis) spectroscopy. The electrochemical performance of the compounds was investigated by galvanostatic discharge/charge (GD/C) measurements, cyclic voltammetry (CV), and electrochemical impedance spectrum (EIS). Compared with ADDAQ, the initial discharge specific capacity and cycle performance of ADAQ were effectively improved. The initial discharge specific capacity of ADAQ was 185 mAh·g-1, after 50 cycles, the specific capacity was maintained at 93 mAh·g-1. A reason for this improvement is discussed.
Two novel organic compounds, 5-amino-2,3-dihydro-1,4-dyhydroxy anthraquinone (ADDAQ) and 5-amino-1,4-dyhydroxy anthraquinone (ADAQ), were synthesized as cathode materials for lithium batteries. The compounds were characterized by 1H nuclear magnetic resonance (1H NMR) spectroscopy, mass spectrometry (MS), elemental analysis (EA), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-Vis) spectroscopy. The electrochemical performance of the compounds was investigated by galvanostatic discharge/charge (GD/C) measurements, cyclic voltammetry (CV), and electrochemical impedance spectrum (EIS). Compared with ADDAQ, the initial discharge specific capacity and cycle performance of ADAQ were effectively improved. The initial discharge specific capacity of ADAQ was 185 mAh·g-1, after 50 cycles, the specific capacity was maintained at 93 mAh·g-1. A reason for this improvement is discussed.
2012, 28(03): 603-608
doi: 10.3866/PKU.WHXB201112272
Abstract:
The electrocatalytic performance and pseudocapacitive characteristics of a modified graphite electrode (MGE) with Fe3+/Fe2+ in H2SO4 solution were studied by cyclic voltammetry (CV), constant current charge-discharge measurements, and electrochemical impedance spectroscopy (EIS). The results showed that the MGE had high electrocatalytic activity and od reversible characteristics for the redox reaction of Fe3+/Fe2+ because of a large quantity of oxygen-containing functional groups on the MGE surface. The apparent area-specific capacitance of the MGE in 2.0 mol·L-1 H2SO4 solution containing 0.5 mol·L-1 Fe3+ and 0.5 mol·L-1 Fe2+ reached 2.157 F·cm-2, which was almost double that in 2.0 mol·L-1 H2SO4 without Fe3+/ Fe2+ . Meanwhile, increasing the concentration of iron ions increased the capacitance of the MGE. The addition of Fe3+/Fe2+ made the charge-discharge curves more symmetric and change more slowly, which increases the charge-discharge time, and effectively improves the capacitive energy storage and high power performance for an electrochemical capacitor (EC). The obvious capacitive characteristics were confirmed by EIS, and are attributed to the oxygen-containing functional groups on the MGE and the Faraday redox reaction of Fe3+/Fe2+ in the thin electrolyte layer. Therefore, the oxygen-containing functional groups on the MGE surface and redox reaction of Fe3+/Fe2+ can be used together for energy storage and release.
The electrocatalytic performance and pseudocapacitive characteristics of a modified graphite electrode (MGE) with Fe3+/Fe2+ in H2SO4 solution were studied by cyclic voltammetry (CV), constant current charge-discharge measurements, and electrochemical impedance spectroscopy (EIS). The results showed that the MGE had high electrocatalytic activity and od reversible characteristics for the redox reaction of Fe3+/Fe2+ because of a large quantity of oxygen-containing functional groups on the MGE surface. The apparent area-specific capacitance of the MGE in 2.0 mol·L-1 H2SO4 solution containing 0.5 mol·L-1 Fe3+ and 0.5 mol·L-1 Fe2+ reached 2.157 F·cm-2, which was almost double that in 2.0 mol·L-1 H2SO4 without Fe3+/ Fe2+ . Meanwhile, increasing the concentration of iron ions increased the capacitance of the MGE. The addition of Fe3+/Fe2+ made the charge-discharge curves more symmetric and change more slowly, which increases the charge-discharge time, and effectively improves the capacitive energy storage and high power performance for an electrochemical capacitor (EC). The obvious capacitive characteristics were confirmed by EIS, and are attributed to the oxygen-containing functional groups on the MGE and the Faraday redox reaction of Fe3+/Fe2+ in the thin electrolyte layer. Therefore, the oxygen-containing functional groups on the MGE surface and redox reaction of Fe3+/Fe2+ can be used together for energy storage and release.
2012, 28(03): 609-614
doi: 10.3866/PKU.WHXB201201162
Abstract:
Flexible carbon nanotube/polyaniline/graphene (CNT/PANI/GR) composite papers were prepared by electrochemical polymerization of PANI on cyclic voltammetry electrochemical oxidized CNT (CV-CNT) papers and the successive adsorption of GR. CNT, PANI, and GR provided a flexible conducting network skeleton, faradaic pseudocapacitive material, and surface conductivity modification properties, respectively. The composite papers exhibited a sandwich structure with an outer layer of GR and an inner layer composite network of CV-CNT/PANI, taking full advantage of the superior properties of the three components. The structure and morphology were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and Raman spectroscopy. The chemical capacitance characteristics were studied thoroughly. It was shown that PANI nanowhiskers wrapped around the CV-CNT surface evenly. The composite paper exhibited enhanced capacitance and high current charge/discharge characteristics as a supercapacitor electrode. The specific capacitance level could reach 415 F·g-1 at a current density of 0.5 A·g-1 and maintain a level of 106 F·g-1 at the higher current density of 20 A·g-1. In the protection of GR, the composite maintained a higher capacitance than CV-CNT/PANI after 1000 cycles, suggesting that the CV-CNT/PANI/GR composite would be an ideal flexible electrode material for a supercapacitor.
Flexible carbon nanotube/polyaniline/graphene (CNT/PANI/GR) composite papers were prepared by electrochemical polymerization of PANI on cyclic voltammetry electrochemical oxidized CNT (CV-CNT) papers and the successive adsorption of GR. CNT, PANI, and GR provided a flexible conducting network skeleton, faradaic pseudocapacitive material, and surface conductivity modification properties, respectively. The composite papers exhibited a sandwich structure with an outer layer of GR and an inner layer composite network of CV-CNT/PANI, taking full advantage of the superior properties of the three components. The structure and morphology were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and Raman spectroscopy. The chemical capacitance characteristics were studied thoroughly. It was shown that PANI nanowhiskers wrapped around the CV-CNT surface evenly. The composite paper exhibited enhanced capacitance and high current charge/discharge characteristics as a supercapacitor electrode. The specific capacitance level could reach 415 F·g-1 at a current density of 0.5 A·g-1 and maintain a level of 106 F·g-1 at the higher current density of 20 A·g-1. In the protection of GR, the composite maintained a higher capacitance than CV-CNT/PANI after 1000 cycles, suggesting that the CV-CNT/PANI/GR composite would be an ideal flexible electrode material for a supercapacitor.
2012, 28(03): 615-622
doi: 10.3866/PKU.WHXB201201101
Abstract:
A potentiostat is a fundamental piece of equipment for the study of corrosion electrochemistry and research into the application of virtual technology to potentiostats is becoming increasingly important. The functions of virtual potentiostats can be controlled and implemented using software instead of complex hardware. They would be capable of not only meeting the demands of a variety of electrochemical tests, but would also be more flexible offering a simpler structure and operating parameters. This would represent a significant development in virtual electrochemical corrosion instrumentation. In this paper, a virtual potentiostat measurement system VEC11-A (virtual electrochemical corrosion test system) has been designed based on LabVIEW. The virtual instrument system of the potentiostat, based on the proportionintegration- differentiation (PID) control technology operated under the LabVIEW 2010 programming platform, was used to determine corrosion potential measurement, polarization curves, linear polarization curves, cyclic voltammetry curves, dynamic potential anode passivation curves, and constant potential step curves. In contrast with normal electrochemical instruments, the system worked well for electrolyzers of different impedances.
A potentiostat is a fundamental piece of equipment for the study of corrosion electrochemistry and research into the application of virtual technology to potentiostats is becoming increasingly important. The functions of virtual potentiostats can be controlled and implemented using software instead of complex hardware. They would be capable of not only meeting the demands of a variety of electrochemical tests, but would also be more flexible offering a simpler structure and operating parameters. This would represent a significant development in virtual electrochemical corrosion instrumentation. In this paper, a virtual potentiostat measurement system VEC11-A (virtual electrochemical corrosion test system) has been designed based on LabVIEW. The virtual instrument system of the potentiostat, based on the proportionintegration- differentiation (PID) control technology operated under the LabVIEW 2010 programming platform, was used to determine corrosion potential measurement, polarization curves, linear polarization curves, cyclic voltammetry curves, dynamic potential anode passivation curves, and constant potential step curves. In contrast with normal electrochemical instruments, the system worked well for electrolyzers of different impedances.
2012, 28(03): 623-629
doi: 10.3866/PKU.WHXB201112293
Abstract:
A series of novel gemini surfactants containing hydroxyl group have been synthesized including 1,3-bis(dodecyl dimethyl ammonium chloride)-2-propanol, 1,3-bis(myristyl dimethyl ammonium chloride)-2-propanol, 1,3-bis(hexadecyl dimethyl ammonium chloride)-2-propanol, and 1,3-bis(octadecyl dimethyl ammonium chloride)-2-propanol, designated as n-3OH-n (n=12, 14, 16, 18, respectively). The corrosion inhibition for carbon steel in brine solution containing H2S and CO2 was investigated using weight loss method, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The results showed that the inhibition efficiencies (IEs) obtained from all of the methods employed demonstrated a clear trend, with the IEs of the gemini surfactants ranked as 14-3OH-14>12-3OH-12> 16-3OH-16>18-3OH-18. Among them, 14-3OH-14 and 12-3OH-12 acted as excellent corrosion inhibitors with IE values greater than 95% at an additive concentration of 35 mg·L-1. Potentiodynamic polarization curves clearly revealed that the gemini surfactants are mixed-type inhibitors which preferentially inhibit the anodic corrosion process. Adsorption of the synthesized gemini surfactants n-3OH-n (n=12, 14, 16) onto a carbon steel surface obeys the Langmuir adsorption isotherm and they exhibit a mixed physical and chemical adsorption. An adsorption model was proposed to elucidate the inhibition mechanism of gemini surfactants.
A series of novel gemini surfactants containing hydroxyl group have been synthesized including 1,3-bis(dodecyl dimethyl ammonium chloride)-2-propanol, 1,3-bis(myristyl dimethyl ammonium chloride)-2-propanol, 1,3-bis(hexadecyl dimethyl ammonium chloride)-2-propanol, and 1,3-bis(octadecyl dimethyl ammonium chloride)-2-propanol, designated as n-3OH-n (n=12, 14, 16, 18, respectively). The corrosion inhibition for carbon steel in brine solution containing H2S and CO2 was investigated using weight loss method, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The results showed that the inhibition efficiencies (IEs) obtained from all of the methods employed demonstrated a clear trend, with the IEs of the gemini surfactants ranked as 14-3OH-14>12-3OH-12> 16-3OH-16>18-3OH-18. Among them, 14-3OH-14 and 12-3OH-12 acted as excellent corrosion inhibitors with IE values greater than 95% at an additive concentration of 35 mg·L-1. Potentiodynamic polarization curves clearly revealed that the gemini surfactants are mixed-type inhibitors which preferentially inhibit the anodic corrosion process. Adsorption of the synthesized gemini surfactants n-3OH-n (n=12, 14, 16) onto a carbon steel surface obeys the Langmuir adsorption isotherm and they exhibit a mixed physical and chemical adsorption. An adsorption model was proposed to elucidate the inhibition mechanism of gemini surfactants.
2012, 28(03): 630-634
doi: 10.3866/PKU.WHXB201112214
Abstract:
A high dispersed nanofiber cryptomelane-type manganese dioxide was synthesized by a facile hydrothermal reduction route. The morphological characterization was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The structure and electrochemical properties of the synthesized manganese dioxide were characterized by X-ray diffraction (XRD), Brunauer- Emmett-Teller (BET) surface area analyses, and an electrochemical workstation (EW). A glassy carbon electrode (GCE) modified with the nanostructured cryptomelane-type manganese dioxide was investigated for amperometric detection of hydrogen peroxide (H2O2) in phosphate buffer solution with a pH 7.4 at an open circuit potential of 0.2 V. The oxidation peak current was found to increase by 1.3 μA with the addition of 0.1 mmol·L-1 H2O2 based on a MnO2 nanofiber-gelatin/GCE electrode. The amperometric signals are linearly proportional to the H2O2 concentration in the range 0.1-1.5 mmol·L-1 with a correlation coefficient of 0.996 using the GCE modified with 0.1% (w, mass fraction) cryptomelane-type manganese oxides. The sensor is sensitive and its significant electrocatalytic activity results from the nanostructure of the cryptomelane-type manganese oxides. In addition, the sensor has a od reproducibility, a low detection limit, simplicity, and a low cost of construction. These results demonstrate that this material with high electrocatalytic activity offers great promise as a new class of nanostructured electrodes for biosensors.
A high dispersed nanofiber cryptomelane-type manganese dioxide was synthesized by a facile hydrothermal reduction route. The morphological characterization was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The structure and electrochemical properties of the synthesized manganese dioxide were characterized by X-ray diffraction (XRD), Brunauer- Emmett-Teller (BET) surface area analyses, and an electrochemical workstation (EW). A glassy carbon electrode (GCE) modified with the nanostructured cryptomelane-type manganese dioxide was investigated for amperometric detection of hydrogen peroxide (H2O2) in phosphate buffer solution with a pH 7.4 at an open circuit potential of 0.2 V. The oxidation peak current was found to increase by 1.3 μA with the addition of 0.1 mmol·L-1 H2O2 based on a MnO2 nanofiber-gelatin/GCE electrode. The amperometric signals are linearly proportional to the H2O2 concentration in the range 0.1-1.5 mmol·L-1 with a correlation coefficient of 0.996 using the GCE modified with 0.1% (w, mass fraction) cryptomelane-type manganese oxides. The sensor is sensitive and its significant electrocatalytic activity results from the nanostructure of the cryptomelane-type manganese oxides. In addition, the sensor has a od reproducibility, a low detection limit, simplicity, and a low cost of construction. These results demonstrate that this material with high electrocatalytic activity offers great promise as a new class of nanostructured electrodes for biosensors.
2012, 28(03): 635-640
doi: 10.3866/PKU.WHXB201112231
Abstract:
Fe-N codoped TiO2 nanotube arrays were fabricated by anodization of Ti, followed by wet immersion and annealing post-treatment. The doped TiO2 nanotube array photocatalysts were characterized by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES). The results indicated that Fe and N dopants had almost no effect on the morphology and structure of TiO2 nanotube arrays, and that Fe and N were doped into the TiO2 lattice. UV-Vis diffuse reflectance spectra showed that the absorption band edge of Fe-N codoped TiO2 nanotube arrays exhibited a red shift compared with that of pure TiO2 nanotube arrays and Fe- or N-doped TiO2 nanotube arrays. The photocatalytic activity of Fe-N codoped TiO2 nanotube arrays was evaluated by their ability to degrade rhodamine B under visible light irradiation. The degradation rate of rhodamine B over Fe-N codoped TiO2 nanotube arrays was obviously higher than that over pure TiO2 nanotube arrays and Fe- or N-doped TiO2 nanotube arrays, which is attributed to the synergistic effect of the Fe and N codopants.
Fe-N codoped TiO2 nanotube arrays were fabricated by anodization of Ti, followed by wet immersion and annealing post-treatment. The doped TiO2 nanotube array photocatalysts were characterized by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES). The results indicated that Fe and N dopants had almost no effect on the morphology and structure of TiO2 nanotube arrays, and that Fe and N were doped into the TiO2 lattice. UV-Vis diffuse reflectance spectra showed that the absorption band edge of Fe-N codoped TiO2 nanotube arrays exhibited a red shift compared with that of pure TiO2 nanotube arrays and Fe- or N-doped TiO2 nanotube arrays. The photocatalytic activity of Fe-N codoped TiO2 nanotube arrays was evaluated by their ability to degrade rhodamine B under visible light irradiation. The degradation rate of rhodamine B over Fe-N codoped TiO2 nanotube arrays was obviously higher than that over pure TiO2 nanotube arrays and Fe- or N-doped TiO2 nanotube arrays, which is attributed to the synergistic effect of the Fe and N codopants.
2012, 28(03): 641-646
doi: 10.3866/PKU.WHXB201201161
Abstract:
It has been reported that bulk doping or surface modification of TiO2 with fluoride ions can enhance its photocatalytic activity for degradation of organic compounds in water. The effect of the former is ascribed to enhanced separation of photogenerated charge carriers through the surface-formed Ti3 + species, whereas that of the latter is ascribed to enhanced desorption of hydroxyl radicals through the interfacial fluoride ions. However, the difference in activity between two modified catalysts has not been investigated. In this work, different fluoride-doped samples were hydrothermally prepared from butyl titanate and NH4F. Their photocatalytic activities after addition of NaF or AgNO3 to the aqueous suspension were evaluated using phenol degradation as a model reaction. All the fluoride ions in the oxide lattices and in the outer and inner Helmholtz double layers of TiO2 were positive to phenol degradation, but the magnitude of their influences followed a decreasing order. Moreover, phenol degradation in the presence of both NaF and AgNO3 was much faster than the sum of their individual rates. These results indicate that combination of conduction band electron reduction and valence band hole oxidation is an effective way to improve the quantum yield of TiO2 photocatalysis.
It has been reported that bulk doping or surface modification of TiO2 with fluoride ions can enhance its photocatalytic activity for degradation of organic compounds in water. The effect of the former is ascribed to enhanced separation of photogenerated charge carriers through the surface-formed Ti3 + species, whereas that of the latter is ascribed to enhanced desorption of hydroxyl radicals through the interfacial fluoride ions. However, the difference in activity between two modified catalysts has not been investigated. In this work, different fluoride-doped samples were hydrothermally prepared from butyl titanate and NH4F. Their photocatalytic activities after addition of NaF or AgNO3 to the aqueous suspension were evaluated using phenol degradation as a model reaction. All the fluoride ions in the oxide lattices and in the outer and inner Helmholtz double layers of TiO2 were positive to phenol degradation, but the magnitude of their influences followed a decreasing order. Moreover, phenol degradation in the presence of both NaF and AgNO3 was much faster than the sum of their individual rates. These results indicate that combination of conduction band electron reduction and valence band hole oxidation is an effective way to improve the quantum yield of TiO2 photocatalysis.
2012, 28(03): 647-653
doi: 10.3866/PKU.WHXB201201051
Abstract:
A series of novel bismuth oxyhalide Ag/BiOX (X=Cl, Br, I) composite photocatalysts were synthesized by a solution-based photodeposited method at room temperature. The resulting products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) emission spectroscopy, UV-Vis diffuse reflectance spectroscopy (DRS), and N2 physical adsorption. The photocatalytic activity of the samples was evaluated by photocatalytic degradation of acid orange II under visible light (420 nm< λ <660 nm) irradiation. Analysis by N2 physical adsorption showed that deposition of Ag decreased the specific surface area of the catalyst. UV-Vis DRS analysis indicated that the presence of Ag could result in surface plasmon absorption, effectively increasing the visible light absorption ability of BiOCl and BiOBr. Furthermore, PL analysis indicated that Ag could effectively suppress the recombination of photogenerated electron (e-)-hole (h+) pairs of Ag/BiOX. Activity testing indicated that the deposition of an optimal amount of 1%-2% (w, mass fraction) Ag brought about 10, 13, and 2 fold increases in the photocatalytic activity of BiOCl, BiOBr, and BiOI, respectively. The high photocatalytic performance of the composite photocatalysts could be attributed to the strong visible light absorption, silver plasmon photocatalysis role and the recombination restraint of the e-/h+ pairs resulting from the presence of metal silver particles.
A series of novel bismuth oxyhalide Ag/BiOX (X=Cl, Br, I) composite photocatalysts were synthesized by a solution-based photodeposited method at room temperature. The resulting products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) emission spectroscopy, UV-Vis diffuse reflectance spectroscopy (DRS), and N2 physical adsorption. The photocatalytic activity of the samples was evaluated by photocatalytic degradation of acid orange II under visible light (420 nm< λ <660 nm) irradiation. Analysis by N2 physical adsorption showed that deposition of Ag decreased the specific surface area of the catalyst. UV-Vis DRS analysis indicated that the presence of Ag could result in surface plasmon absorption, effectively increasing the visible light absorption ability of BiOCl and BiOBr. Furthermore, PL analysis indicated that Ag could effectively suppress the recombination of photogenerated electron (e-)-hole (h+) pairs of Ag/BiOX. Activity testing indicated that the deposition of an optimal amount of 1%-2% (w, mass fraction) Ag brought about 10, 13, and 2 fold increases in the photocatalytic activity of BiOCl, BiOBr, and BiOI, respectively. The high photocatalytic performance of the composite photocatalysts could be attributed to the strong visible light absorption, silver plasmon photocatalysis role and the recombination restraint of the e-/h+ pairs resulting from the presence of metal silver particles.
2012, 28(03): 654-660
doi: 10.3866/PKU.WHXB201112232
Abstract:
BiPO4 nanorods with controlled morphologies were fabricated using a hydrothermal method. The photocatalytic activity of the BiPO4 nanorods was investigated by their ability to degrade methylene blue (MB). The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV-Vis diffuse reflectance spectroscopy (DRS). It was found that glycerol content, reaction time and temperature, and concentration of precursor influenced the morphology and structure of the product. The glycerol content and concentration of precursor mainly influence the morphology of the product. As the glycerol content increases, the aspect ratio first increases, and then decreases. The aspect ratio of the product increases and the size decreases as the concentration of precursor is lowered. When the reaction time is short, the crystallinity of the product is poor, and it forms a hexa nal phase. Hexa nal BiPO4 transforms into the monoclinic product when the reaction time is longer. The optimal temperature for crystal formation was found to be 160 °C. The results show that BiPO4 nanorods possess excellent photocatalytic activity under ultraviolet light. The photocatalytic activity of BiPO4 increased with an increase of aspect ratio and decrease of particle size. The crystallinity of the product has a significant influence on its photocatalytic activity. BiPO4 with higher crystallinity has higher photocatalytic activity, and monoclinic BiPO4 has higher photocatalytic activity than hexa nal BiPO4.
BiPO4 nanorods with controlled morphologies were fabricated using a hydrothermal method. The photocatalytic activity of the BiPO4 nanorods was investigated by their ability to degrade methylene blue (MB). The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV-Vis diffuse reflectance spectroscopy (DRS). It was found that glycerol content, reaction time and temperature, and concentration of precursor influenced the morphology and structure of the product. The glycerol content and concentration of precursor mainly influence the morphology of the product. As the glycerol content increases, the aspect ratio first increases, and then decreases. The aspect ratio of the product increases and the size decreases as the concentration of precursor is lowered. When the reaction time is short, the crystallinity of the product is poor, and it forms a hexa nal phase. Hexa nal BiPO4 transforms into the monoclinic product when the reaction time is longer. The optimal temperature for crystal formation was found to be 160 °C. The results show that BiPO4 nanorods possess excellent photocatalytic activity under ultraviolet light. The photocatalytic activity of BiPO4 increased with an increase of aspect ratio and decrease of particle size. The crystallinity of the product has a significant influence on its photocatalytic activity. BiPO4 with higher crystallinity has higher photocatalytic activity, and monoclinic BiPO4 has higher photocatalytic activity than hexa nal BiPO4.
2012, 28(03): 661-666
doi: 10.3866/PKU.WHXB201112291
Abstract:
A TiO2-Al2O3 complex support was prepared by the sol-gel method. Nickel phosphide catalyst, Ni2P/TiO2-Al2O3, with citric acid (CA) as a chelating agent, was prepared by impregnation. The catalyst was characterized by X-ray diffraction (XRD), BET specific surface area measurements, H2-temperature programmed reduction (TPR) and temperature programmed oxidation (TPO), and X-ray photoelectron spectroscopy (XPS). The effects of the molar ratio of CA to Ni on catalyst activity for hydrodesulfurization (HDS) of dibenzothiophene (DBT) were studied. Addition of an appropriate amount of CA into the catalyst can change the pores of the Ni2P/TiO2-Al2O3 catalyst, increasing the surface area. The specific surface area reached 126.75 m2·g-1 for n(CA)/n(Ni) of 2/1, an improvement of 57.05 m2·g-1 compared with the catalyst without CA. Regulating n(CA)/n(Ni) can improve the distribution of the active phase and change the active phase species. Addition of CA decreased the temperature required for reduction of nickel and the phosphorus precursor, as well as promoting the formation of the active phase. CA can limit the deposition of carbon on the catalyst surface to some extent, improving its stability. A molar ratio of n(CA)/n(Ni) of 2/1 was found to be optimal for the catalytic activity of the Ni2P/TiO2-Al2O3 catalyst prepared with CA as a chelating agent. At a reaction temperature of 360 °C, pressure of 3.0 MPa, hydrogen/oil ratio of 500 (V/V), and liquid hourly space velocity of 2.0 h-1, the HDS conversion of DBT was 99.5%, which can reduce the sulfur content of a model oil from 2% (w) to 0.01% (w).
A TiO2-Al2O3 complex support was prepared by the sol-gel method. Nickel phosphide catalyst, Ni2P/TiO2-Al2O3, with citric acid (CA) as a chelating agent, was prepared by impregnation. The catalyst was characterized by X-ray diffraction (XRD), BET specific surface area measurements, H2-temperature programmed reduction (TPR) and temperature programmed oxidation (TPO), and X-ray photoelectron spectroscopy (XPS). The effects of the molar ratio of CA to Ni on catalyst activity for hydrodesulfurization (HDS) of dibenzothiophene (DBT) were studied. Addition of an appropriate amount of CA into the catalyst can change the pores of the Ni2P/TiO2-Al2O3 catalyst, increasing the surface area. The specific surface area reached 126.75 m2·g-1 for n(CA)/n(Ni) of 2/1, an improvement of 57.05 m2·g-1 compared with the catalyst without CA. Regulating n(CA)/n(Ni) can improve the distribution of the active phase and change the active phase species. Addition of CA decreased the temperature required for reduction of nickel and the phosphorus precursor, as well as promoting the formation of the active phase. CA can limit the deposition of carbon on the catalyst surface to some extent, improving its stability. A molar ratio of n(CA)/n(Ni) of 2/1 was found to be optimal for the catalytic activity of the Ni2P/TiO2-Al2O3 catalyst prepared with CA as a chelating agent. At a reaction temperature of 360 °C, pressure of 3.0 MPa, hydrogen/oil ratio of 500 (V/V), and liquid hourly space velocity of 2.0 h-1, the HDS conversion of DBT was 99.5%, which can reduce the sulfur content of a model oil from 2% (w) to 0.01% (w).
2012, 28(03): 667-673
doi: 10.3866/PKU.WHXB201112221
Abstract:
Based on a comparison of catalytic performances of Rh-Mn-Li/SiO2 catalysts, in which commercial SiO2 and monodispersed SiO2 synthesized by the Stöber method were used as the support, respectively, the effect of the calcination temperature of the synthesized SiO2 on the catalytic performance of Rh-Mn-Li/SiO2 for CO hydrogenation to C2 oxygenates was investigated. Fourier transform infrared spectroscopy, N2 adsorption-desorption, temperature-programmed reduction with hydrogen (H2-TPR), and temperature-programmed surface reaction (TPSR) were used to characterize the physico-chemical properties of the SiO2 supports and the corresponding catalysts. The results showed that the number of surface Si―OH groups on the SiO2 supports affected the dispersion of metal and the interaction between Rh and Mn. Large amount of surface Si―OH groups was favorable for the dispersion of Rh particles and CO adsorption, and enhanced the activity of the catalyst. An appropriate amount of Si ―OH groups can gain moderate interaction between the Rh and Mn. This interaction is conducive to achieve the right CO dissociation ability, which is favorable for the insertion of CO to CHx, and ultimately increases the selectivity of C2 oxygenates.
Based on a comparison of catalytic performances of Rh-Mn-Li/SiO2 catalysts, in which commercial SiO2 and monodispersed SiO2 synthesized by the Stöber method were used as the support, respectively, the effect of the calcination temperature of the synthesized SiO2 on the catalytic performance of Rh-Mn-Li/SiO2 for CO hydrogenation to C2 oxygenates was investigated. Fourier transform infrared spectroscopy, N2 adsorption-desorption, temperature-programmed reduction with hydrogen (H2-TPR), and temperature-programmed surface reaction (TPSR) were used to characterize the physico-chemical properties of the SiO2 supports and the corresponding catalysts. The results showed that the number of surface Si―OH groups on the SiO2 supports affected the dispersion of metal and the interaction between Rh and Mn. Large amount of surface Si―OH groups was favorable for the dispersion of Rh particles and CO adsorption, and enhanced the activity of the catalyst. An appropriate amount of Si ―OH groups can gain moderate interaction between the Rh and Mn. This interaction is conducive to achieve the right CO dissociation ability, which is favorable for the insertion of CO to CHx, and ultimately increases the selectivity of C2 oxygenates.
2012, 28(03): 674-680
doi: 10.3866/PKU.WHXB201112271
Abstract:
Hydrothermally treated bauxite with high surface area was used as a ruthenium-based catalyst support. A series of Ru/bauxite and 2.0% (mass fraction) Ru/Al2O3 catalysts were prepared by incipientwetness impregnation. The loading content of ruthenium in the Ru/bauxite catalysts was varied from 1.0% to 4.0%. The catalysts were thoroughly characterized by X-ray fluorescence (XRF), low temperature N2 physical adsorption, X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), and CO temperature-programmed desorption (CO-TPD). The performances of the catalysts for the water-gas shift reaction were also investigated. The results indicated that Ru/bauxite catalysts possess an excellent ability to evolve hydrogen in the water-gas shift reaction. This was attributed to the interaction between Ru and Fe2O3 in the modified bauxite, which could decrease the reduction temperature of Fe2O3, and also improve the adsorption-desorption behavior and decrease the desorption temperature of Ru/bauxite catalysts for CO molecules, resulting in higher activity in the water-gas shift reaction.
Hydrothermally treated bauxite with high surface area was used as a ruthenium-based catalyst support. A series of Ru/bauxite and 2.0% (mass fraction) Ru/Al2O3 catalysts were prepared by incipientwetness impregnation. The loading content of ruthenium in the Ru/bauxite catalysts was varied from 1.0% to 4.0%. The catalysts were thoroughly characterized by X-ray fluorescence (XRF), low temperature N2 physical adsorption, X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), and CO temperature-programmed desorption (CO-TPD). The performances of the catalysts for the water-gas shift reaction were also investigated. The results indicated that Ru/bauxite catalysts possess an excellent ability to evolve hydrogen in the water-gas shift reaction. This was attributed to the interaction between Ru and Fe2O3 in the modified bauxite, which could decrease the reduction temperature of Fe2O3, and also improve the adsorption-desorption behavior and decrease the desorption temperature of Ru/bauxite catalysts for CO molecules, resulting in higher activity in the water-gas shift reaction.
2012, 28(03): 681-685
doi: 10.3866/PKU.WHXB201111141
Abstract:
The promotional effect of cerium oxide on the catalytic properties of Ce-Mn-Ti-O composite oxide catalysts prepared by the sol-gel method was studied using NH3-temperature programmed desorption (NH3-TPD), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H2-temperature programmed reduction (H2-TPR), and BET surface area measurements combined with microreactor tests of NO selective catalytic reduction (SCR). The results showed that the addition of a cerium oxide component remarkably increased the low-temperature SCR activity of Mn-Ti-O composite oxide catalyst. When the cerium content was increased, NO conversion increased significantly and reached a maximum around Ce/Mn molar ratio of 0.08. Further increases in the cerium content resulted in a decrease in NO conversion over the catalyst. The experimental results indicated that the addition of a cerium oxide component does not influence the surface acidity of Mn-Ti-O composite oxide catalyst, but increases the surface concentration of catalytically active Mn species, the relative content of Mn4+, and the reducibility of Mn species, leading to an increase in the SCR activity of Ce-Mn-Ti-O composite oxide catalysts. When the Ce/Mn molar ratio was greater than 0.08, the formation of amorphous multilayer Ce-O-Mn species composed of Ce and Mn species may reduce the Mn/Ti molar ratio and the reducibility of Mn species, leading to a decrease in the SCR activity of Ce-Mn-Ti-O composite oxide catalysts.
The promotional effect of cerium oxide on the catalytic properties of Ce-Mn-Ti-O composite oxide catalysts prepared by the sol-gel method was studied using NH3-temperature programmed desorption (NH3-TPD), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H2-temperature programmed reduction (H2-TPR), and BET surface area measurements combined with microreactor tests of NO selective catalytic reduction (SCR). The results showed that the addition of a cerium oxide component remarkably increased the low-temperature SCR activity of Mn-Ti-O composite oxide catalyst. When the cerium content was increased, NO conversion increased significantly and reached a maximum around Ce/Mn molar ratio of 0.08. Further increases in the cerium content resulted in a decrease in NO conversion over the catalyst. The experimental results indicated that the addition of a cerium oxide component does not influence the surface acidity of Mn-Ti-O composite oxide catalyst, but increases the surface concentration of catalytically active Mn species, the relative content of Mn4+, and the reducibility of Mn species, leading to an increase in the SCR activity of Ce-Mn-Ti-O composite oxide catalysts. When the Ce/Mn molar ratio was greater than 0.08, the formation of amorphous multilayer Ce-O-Mn species composed of Ce and Mn species may reduce the Mn/Ti molar ratio and the reducibility of Mn species, leading to a decrease in the SCR activity of Ce-Mn-Ti-O composite oxide catalysts.
2012, 28(03): 686-692
doi: 10.3866/PKU.WHXB201112292
Abstract:
The production of 5-hydroxylmethylfurfural (HMF) from inulin over sulfonated amorphous carbon was studied in an ionic liquid, 1-butyl-3-methylimidazolium chloride ([Bmim]Cl). The effects of reaction solvent, water content, reaction temperature, reaction time, and catalyst dosage on the yield of HMF were investigated. Experimental results indicated that optimum reaction conditions required a reaction temperature of 100 °C, a reaction time of 60 min, an R value of 5 (R represents the molar ratio of added water to fructose units in inulin), and a mass ratio of catalyst to inulin of 1:3, affording HMF in yields of up to 50%.
The production of 5-hydroxylmethylfurfural (HMF) from inulin over sulfonated amorphous carbon was studied in an ionic liquid, 1-butyl-3-methylimidazolium chloride ([Bmim]Cl). The effects of reaction solvent, water content, reaction temperature, reaction time, and catalyst dosage on the yield of HMF were investigated. Experimental results indicated that optimum reaction conditions required a reaction temperature of 100 °C, a reaction time of 60 min, an R value of 5 (R represents the molar ratio of added water to fructose units in inulin), and a mass ratio of catalyst to inulin of 1:3, affording HMF in yields of up to 50%.
2012, 28(03): 693-698
doi: 10.3866/PKU.WHXB201201111
Abstract:
A copper sulfide film with dual scale micro- and nano-structured roughness was constructed on copper foil via a facile solution-phase method using the sodium thiosulphate and cupric chloride as raw materials. The resulting film was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectrometer, and contact angle measurements. After stearic acid hydrophobization, the film exhibited a water contact angle of 161° and a sliding angle of 2.5° for a 5 μL water droplet. The superhydrophobicity was attributed to a combination of the dual scale roughness at the micro- and nano-meter levels and the low surface energy of the stearic acid coating. This is a simple synthetic methodology requiring no complex or harsh equipment. The copper surface obtained has the excellent non-sticking property, long-term storage stability, and relatively od anti-abrasion property.
A copper sulfide film with dual scale micro- and nano-structured roughness was constructed on copper foil via a facile solution-phase method using the sodium thiosulphate and cupric chloride as raw materials. The resulting film was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectrometer, and contact angle measurements. After stearic acid hydrophobization, the film exhibited a water contact angle of 161° and a sliding angle of 2.5° for a 5 μL water droplet. The superhydrophobicity was attributed to a combination of the dual scale roughness at the micro- and nano-meter levels and the low surface energy of the stearic acid coating. This is a simple synthetic methodology requiring no complex or harsh equipment. The copper surface obtained has the excellent non-sticking property, long-term storage stability, and relatively od anti-abrasion property.
2012, 28(03): 699-705
doi: 10.3866/PKU.WHXB201201121
Abstract:
Sr1-x-yMgP2O7:xCe3+,yTb3+ phosphors were successfully synthesized by a solid-state reaction method. The crystal structure, optical properties, luminescence decay, energy transfer, and thermal stability properties were investigated. The results showed that the emission peaks of the co-doped Ce3+ and Tb3+ ions in the SrMgP2O7 host were located at 398 and 545 nm, respectively. The peaks were attributed to 5d-4f and 5D4→7F5 transitions, respectively. An efficient energy transfer from the Ce3+ to Tb3+ ions by means of dipole-dipole interactions was observed and the critical distance of the energy transfer was 0.614 nm. The thermal activation energies of 0.122 and 0.111 eV for SrMgP2O7:Ce3+ and SrMgP2O7:Tb3+, respectively, were obtained from the temperature dependent (313-453 K) luminescence intensities. The Tb3+ ion was found to be superior to Ce3+ ion in the thermal stability of light-emitting diodes.
Sr1-x-yMgP2O7:xCe3+,yTb3+ phosphors were successfully synthesized by a solid-state reaction method. The crystal structure, optical properties, luminescence decay, energy transfer, and thermal stability properties were investigated. The results showed that the emission peaks of the co-doped Ce3+ and Tb3+ ions in the SrMgP2O7 host were located at 398 and 545 nm, respectively. The peaks were attributed to 5d-4f and 5D4→7F5 transitions, respectively. An efficient energy transfer from the Ce3+ to Tb3+ ions by means of dipole-dipole interactions was observed and the critical distance of the energy transfer was 0.614 nm. The thermal activation energies of 0.122 and 0.111 eV for SrMgP2O7:Ce3+ and SrMgP2O7:Tb3+, respectively, were obtained from the temperature dependent (313-453 K) luminescence intensities. The Tb3+ ion was found to be superior to Ce3+ ion in the thermal stability of light-emitting diodes.
2012, 28(03): 706-710
doi: 10.3866/PKU.WHXB201112162
Abstract:
A series of luminescent glasses composed of CaO-B2O3-SiO2 codoped with samarium oxide (Sm2O3), cerium oxide (CeO2), and terbium oxide (Tb4O7) were prepared by melting at high temperature. The spectroscopic properties of the samples were investigated by photoluminescence (PL) measurements and CIE color coordinate. Blue, green, and reddish orange emission bands were observed in the PL spectra of Ce/Tb/Sm codoped glasses. The combination of these emission bands gave white light when the glasses were excited by near ultraviolet light. As the proportion of Tb4O7 was decreased, a gradual shift from green to white emission was observed in the PL spectra of the glasses. These rare earth ions-doped glasses are potential candidates for white light-emitting diodes.
A series of luminescent glasses composed of CaO-B2O3-SiO2 codoped with samarium oxide (Sm2O3), cerium oxide (CeO2), and terbium oxide (Tb4O7) were prepared by melting at high temperature. The spectroscopic properties of the samples were investigated by photoluminescence (PL) measurements and CIE color coordinate. Blue, green, and reddish orange emission bands were observed in the PL spectra of Ce/Tb/Sm codoped glasses. The combination of these emission bands gave white light when the glasses were excited by near ultraviolet light. As the proportion of Tb4O7 was decreased, a gradual shift from green to white emission was observed in the PL spectra of the glasses. These rare earth ions-doped glasses are potential candidates for white light-emitting diodes.
2012, 28(03): 711-719
doi: 10.3866/PKU.WHXB201112213
Abstract:
Nanosilver-decorated carbon nanotubes (CNTs) were prepared by introducing CNTs and silver acetate into an epoxy-imidazole curing system and simultaneous in situ thermal degradation of an Ag-imidazole complex. Differential scanning calorimetry (DSC) results indicated that modified CNTs played a certain role in promoting the curing of the epoxy. The structure of the silver acetate-imidazole complex was characterized by X-ray diffraction (XRD). The size of the nano-silver particles resulting from degradation of the Ag-imidzole complex was between 21 and 24 nm, and between 11 and 13 nm when the Ag-imidzole complex was added to the epoxy matrix. When silver flakes with a mass fraction of 80% was added to the composites, the volume resistivity of the nanosilver-decorated CNTs/epoxy conductive composite was as low as 9×10-5 Ω·cm. The optimum conductivity and shear strength were achieved when the ratio of nanosilver and CNTs was 80:20 (mass ratio). Scanning electron microscopy (SEM) revealed the structural morphology of the composite.
Nanosilver-decorated carbon nanotubes (CNTs) were prepared by introducing CNTs and silver acetate into an epoxy-imidazole curing system and simultaneous in situ thermal degradation of an Ag-imidazole complex. Differential scanning calorimetry (DSC) results indicated that modified CNTs played a certain role in promoting the curing of the epoxy. The structure of the silver acetate-imidazole complex was characterized by X-ray diffraction (XRD). The size of the nano-silver particles resulting from degradation of the Ag-imidzole complex was between 21 and 24 nm, and between 11 and 13 nm when the Ag-imidzole complex was added to the epoxy matrix. When silver flakes with a mass fraction of 80% was added to the composites, the volume resistivity of the nanosilver-decorated CNTs/epoxy conductive composite was as low as 9×10-5 Ω·cm. The optimum conductivity and shear strength were achieved when the ratio of nanosilver and CNTs was 80:20 (mass ratio). Scanning electron microscopy (SEM) revealed the structural morphology of the composite.
2012, 28(03): 720-728
doi: 10.3866/PKU.WHXB201201031
Abstract:
Highly crystalline Fe-Al-EU-1 zeolites were hydrothermally synthesized in a HMBr2-Na2OAl2O3- SiO2-Fe2O3-H2O system by using hexamethonium bromide (HMBr2) as a template. The physical and chemical properties, and the bonding state of Fe in the zeolite framework for the prepared Fe-Al-EU-1 samples were characterized by a series of techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric-derivative thermogravimetric (TG-DTG) analysis, N2 adsorption-desorption, solid-state nuclear magnetic resonance (NMR), UV-visible diffuse reflectance spectroscopy (UV-Vis DRS), and X-ray absorption fine structure (XAFS). The results show that with increasing the mass fraction of Fe in the original sol-gel, the unit cell volume of Fe-Al-EU-1 zeolite inflates; the zeolite doped with Fe causes an increase in its surface area (BET) from 272 to 365 m2·g-1 and a reduced amount of template removal, as well as a decrease in decomposition temperature. Adding Fe ions into sol-gel also leads to lowered zeta potential, easily gathered colloidal particles, and increased shape of zeolite. The UV-Vis spectrum shows that there is a characteristic peak at about 220-250 nm with a sharply increased intensity due to the p-d transition of the bonding electrons from the 2p-orbital of O atom to the d-orbital of the four-coordinated Fe atom in the framework. Also at around 373 nm, the coordination bonding of fourcoordinated Fe atoms and adjacent Si－O groups leads to a d-d charge transition peak with an energy level splitting and increased peak intensity. The XAFS results show that with the crystallization process ing on, the pre-edge absorption peak for 1s→3d and main absorption peak for 1s→4p change significantly. Four-coordinated structural units of iron species formed from the original sol-gel samples are gradually transformed into a tetrahedral coordinated iron-silicon-oxygen skeleton, in which iron-siliconoxygen ionic structural unit is also transformed into skeleton iron species with a tetrahedral covalent bonding structure.
Highly crystalline Fe-Al-EU-1 zeolites were hydrothermally synthesized in a HMBr2-Na2OAl2O3- SiO2-Fe2O3-H2O system by using hexamethonium bromide (HMBr2) as a template. The physical and chemical properties, and the bonding state of Fe in the zeolite framework for the prepared Fe-Al-EU-1 samples were characterized by a series of techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric-derivative thermogravimetric (TG-DTG) analysis, N2 adsorption-desorption, solid-state nuclear magnetic resonance (NMR), UV-visible diffuse reflectance spectroscopy (UV-Vis DRS), and X-ray absorption fine structure (XAFS). The results show that with increasing the mass fraction of Fe in the original sol-gel, the unit cell volume of Fe-Al-EU-1 zeolite inflates; the zeolite doped with Fe causes an increase in its surface area (BET) from 272 to 365 m2·g-1 and a reduced amount of template removal, as well as a decrease in decomposition temperature. Adding Fe ions into sol-gel also leads to lowered zeta potential, easily gathered colloidal particles, and increased shape of zeolite. The UV-Vis spectrum shows that there is a characteristic peak at about 220-250 nm with a sharply increased intensity due to the p-d transition of the bonding electrons from the 2p-orbital of O atom to the d-orbital of the four-coordinated Fe atom in the framework. Also at around 373 nm, the coordination bonding of fourcoordinated Fe atoms and adjacent Si－O groups leads to a d-d charge transition peak with an energy level splitting and increased peak intensity. The XAFS results show that with the crystallization process ing on, the pre-edge absorption peak for 1s→3d and main absorption peak for 1s→4p change significantly. Four-coordinated structural units of iron species formed from the original sol-gel samples are gradually transformed into a tetrahedral coordinated iron-silicon-oxygen skeleton, in which iron-siliconoxygen ionic structural unit is also transformed into skeleton iron species with a tetrahedral covalent bonding structure.
2012, 28(03): 729-732
doi: 10.3866/PKU.WHXB201112211
Abstract:
Polyethylene pyrrole (PVP) and metal nitrate were used as precursors, La and Co co-doped M-type strontium ferrites Sr1-xLaxFe12-xCoxO19 (x=0.12) (SLFC) were prepared by electrospinning, sol-gel, and subsequent heat treatment processing. The crystal structure, morphology, and magnetic properties of the samples were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and superconducting quantum interference device (SQUID). The influences of the variation of sintering temperature on the magnetic properties of SLFC were systematically investigated. The experimental results show that the optimum values of the magnetic properties were obtained at 950 °C for 2 h, and the coercivity (Hc), saturation magnetization (Ms), and remanence (Mr) values of the samples were 498.53 kA·m-1, 70.76 A·m2·kg-1, and 36.35 A·m2·kg-1, respectively. Pure-phase bamboo-like SLFC nanofibres with diameter of about 55 nm were fabricated. The magnetic properties of undoped SrFe12O19 (SF) were improved obviously, and the SF nanofibres exhibited better magnetic properties than the corresponding nanoparticles obtained by the sol-gel processing.
Polyethylene pyrrole (PVP) and metal nitrate were used as precursors, La and Co co-doped M-type strontium ferrites Sr1-xLaxFe12-xCoxO19 (x=0.12) (SLFC) were prepared by electrospinning, sol-gel, and subsequent heat treatment processing. The crystal structure, morphology, and magnetic properties of the samples were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and superconducting quantum interference device (SQUID). The influences of the variation of sintering temperature on the magnetic properties of SLFC were systematically investigated. The experimental results show that the optimum values of the magnetic properties were obtained at 950 °C for 2 h, and the coercivity (Hc), saturation magnetization (Ms), and remanence (Mr) values of the samples were 498.53 kA·m-1, 70.76 A·m2·kg-1, and 36.35 A·m2·kg-1, respectively. Pure-phase bamboo-like SLFC nanofibres with diameter of about 55 nm were fabricated. The magnetic properties of undoped SrFe12O19 (SF) were improved obviously, and the SF nanofibres exhibited better magnetic properties than the corresponding nanoparticles obtained by the sol-gel processing.
2012, 28(03): 733-738
doi: 10.3866/PKU.WHXB201201131
Abstract:
We investigated the electronic structure, photophysical properties, and thermal stability of N- (3-trimethoxysilylethyl)ethylenediamine (TMSEEDA). The optimized structural parameters in the ground state and first excited state were obtained from density functional theory calculations. The results showed that there was probably π electron delocalization within the Si－O skeleton, which induced the long wavelength absorption. A broad and intense blue emission with a maximum at 430 nm was observed for both the solution and the solid state with 270 nm excitation at room temperature. The absorption intensity for the solid state was five-times that of the pure TMSEEDA. For the ethanol solution, the photoluminescence intensity increased with increasing concentration of TMSEEDA and reached a maximum at a concentration of 100%. These results suggest there is no concentration quenching for TMSEEDA. An accepted model of electron delocalization and d-p π-bonding within the Si－O skeleton was applied to explain the long wavelength absorption and blue emission.
We investigated the electronic structure, photophysical properties, and thermal stability of N- (3-trimethoxysilylethyl)ethylenediamine (TMSEEDA). The optimized structural parameters in the ground state and first excited state were obtained from density functional theory calculations. The results showed that there was probably π electron delocalization within the Si－O skeleton, which induced the long wavelength absorption. A broad and intense blue emission with a maximum at 430 nm was observed for both the solution and the solid state with 270 nm excitation at room temperature. The absorption intensity for the solid state was five-times that of the pure TMSEEDA. For the ethanol solution, the photoluminescence intensity increased with increasing concentration of TMSEEDA and reached a maximum at a concentration of 100%. These results suggest there is no concentration quenching for TMSEEDA. An accepted model of electron delocalization and d-p π-bonding within the Si－O skeleton was applied to explain the long wavelength absorption and blue emission.
