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2001 Volume 17 Issue 12
2001, 17(12): 1057-1061
doi: 10.3866/PKU.WHXB20011201
Abstract:
Silica nanoparticle thin films were built up from SiO2 colloid and poly（diallyldimethylammonium chloride）(PDDA) by using the electrostatic self-assembly technique.The TEM image(to see Fig.3) of a 40-bilayer thin film revealed that SiO2 nanoparticles were closely packed and that the coverage of the SiO2 nanoparticles over the thin film was uniform. The electron diffraction pattern showed that the self-assembled thin film was amorphous. The transmissivity of a glass slide coated with PDDA/SiO2 multilayers exhibited periodical oscillation as the bilayer number of the thin film was increased (to see Fig.4). The composite thin films under some bilayers were antireflection coatings. A net increment of more than 5％ in the transmissivity of a glass slide could be yielded over the same wavelength range after PDDA/SiO2 composite thin films were assembled onto both sides of the slide (to see Fig.5). Within the composite thin films,the average physical thickness of one PDDA/SiO2 bilayer was less than the average diameter of the SiO2 particles, which implied substantial overlap between the adjacent SiO2 nanoparticle layers. Although the PDDA/SiO2 multilayer thin films were prepared in the alternating layer-by-layer assembly fashion, the optical properties of the composite thin films were determined mainly by the SiO2 nanoparticles, and the composite thin films served the function of single-layer coatings.
Silica nanoparticle thin films were built up from SiO2 colloid and poly（diallyldimethylammonium chloride）(PDDA) by using the electrostatic self-assembly technique.The TEM image(to see Fig.3) of a 40-bilayer thin film revealed that SiO2 nanoparticles were closely packed and that the coverage of the SiO2 nanoparticles over the thin film was uniform. The electron diffraction pattern showed that the self-assembled thin film was amorphous. The transmissivity of a glass slide coated with PDDA/SiO2 multilayers exhibited periodical oscillation as the bilayer number of the thin film was increased (to see Fig.4). The composite thin films under some bilayers were antireflection coatings. A net increment of more than 5％ in the transmissivity of a glass slide could be yielded over the same wavelength range after PDDA/SiO2 composite thin films were assembled onto both sides of the slide (to see Fig.5). Within the composite thin films,the average physical thickness of one PDDA/SiO2 bilayer was less than the average diameter of the SiO2 particles, which implied substantial overlap between the adjacent SiO2 nanoparticle layers. Although the PDDA/SiO2 multilayer thin films were prepared in the alternating layer-by-layer assembly fashion, the optical properties of the composite thin films were determined mainly by the SiO2 nanoparticles, and the composite thin films served the function of single-layer coatings.
2001, 17(12): 1062-1066
doi: 10.3866/PKU.WHXB20011202
Abstract:
The interaction between malachite green (MG) and cetyltrimethyl ammonium bromide (CTAB) micelle simulating life system has been studied in the CTAB micelle using UV-Vis and fluorescent spectra.The results show that MG can locate in the palisade of CTAB micelle spontaneously,which leads to the increase of the aggregation number (N) and the decrease of the micro-polarity (I1/I3) of CTAB micelle.Both of the binding constant K of MG with CTAB micelle and the distribution coefficient KD of MG between the CTAB micelles and the aqueous phase decrease with the increase of the concentration of MG.These results indicate that the interaction between MG molecules and CTAB micelles decreases with the increase of MG concentration.
The interaction between malachite green (MG) and cetyltrimethyl ammonium bromide (CTAB) micelle simulating life system has been studied in the CTAB micelle using UV-Vis and fluorescent spectra.The results show that MG can locate in the palisade of CTAB micelle spontaneously,which leads to the increase of the aggregation number (N) and the decrease of the micro-polarity (I1/I3) of CTAB micelle.Both of the binding constant K of MG with CTAB micelle and the distribution coefficient KD of MG between the CTAB micelles and the aqueous phase decrease with the increase of the concentration of MG.These results indicate that the interaction between MG molecules and CTAB micelles decreases with the increase of MG concentration.
2001, 17(12): 1067-1071
doi: 10.3866/PKU.WHXB20011203
Abstract:
The electrochemical behavior of Mn(III)/Mn(II) on platinum electrode in acetic acid-anhydride was investigated. The results show that the conditional electrode potential of Mn(III)/Mn(II) was 0.719 V(vs SCE) in the solution of 1.5 mol•L－1 KOAc＋HOAc-Ac2O(3:1 volume ratio) at 25 ℃. The results of potential sweep and RDE on platinum electrode show that the rate determing step of the electrode processes for Mn(II) anodic oxidation was a charge-transfer step. The anodic charge-transfer kinetic parameters were determined. The results show that the anodic charge-transfer coefficient is 0.347, the exchange current density i0 is 5.84×10－6 A•cm－2, the conditional charge-transfer rate constant ka is 1.35×10－8 m•s－1 at 25 ℃. The rate was found to be first order with respect to the concentration of both Mn(II) and OAc－.
The electrochemical behavior of Mn(III)/Mn(II) on platinum electrode in acetic acid-anhydride was investigated. The results show that the conditional electrode potential of Mn(III)/Mn(II) was 0.719 V(vs SCE) in the solution of 1.5 mol•L－1 KOAc＋HOAc-Ac2O(3:1 volume ratio) at 25 ℃. The results of potential sweep and RDE on platinum electrode show that the rate determing step of the electrode processes for Mn(II) anodic oxidation was a charge-transfer step. The anodic charge-transfer kinetic parameters were determined. The results show that the anodic charge-transfer coefficient is 0.347, the exchange current density i0 is 5.84×10－6 A•cm－2, the conditional charge-transfer rate constant ka is 1.35×10－8 m•s－1 at 25 ℃. The rate was found to be first order with respect to the concentration of both Mn(II) and OAc－.
2001, 17(12): 1072-1076
doi: 10.3866/PKU.WHXB20011204
Abstract:
A series of Pt/BaAl2O4-Al2O3 NOx trap samples were prepared by coprecipitation-impregnation method. The supports BaAl2O4-Al2O3 were calcined at 800 ℃ and 1000 ℃, respectively. X-ray Diffraction(XRD), X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure(EXAFS) were used to characterize the microcosmic structure of barium and platinum species in the samples. It is shown that the barium exists in the forms of BaAl2O4 and BaCO3 crystallites. With the decreasing of calcination temperature and barium content, the dispersion of BaAl2O4 phase becomes higher. Platinum in the samples mainly exists as small atomic clusters, which possess very high dispersion. In comparison with the standard compound of platinum, the magnitude for Pt－Pt coordination shell is significantly decreased, and the coordination distance is also shortened about 0.01 nm. All the results suggest that the BaAl2O4 crystallites should be the centers for NOx storage, while the fine-grained platinum species with high dispersion are deduced as the centers for the capture and oxidation of NOx species.
A series of Pt/BaAl2O4-Al2O3 NOx trap samples were prepared by coprecipitation-impregnation method. The supports BaAl2O4-Al2O3 were calcined at 800 ℃ and 1000 ℃, respectively. X-ray Diffraction(XRD), X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure(EXAFS) were used to characterize the microcosmic structure of barium and platinum species in the samples. It is shown that the barium exists in the forms of BaAl2O4 and BaCO3 crystallites. With the decreasing of calcination temperature and barium content, the dispersion of BaAl2O4 phase becomes higher. Platinum in the samples mainly exists as small atomic clusters, which possess very high dispersion. In comparison with the standard compound of platinum, the magnitude for Pt－Pt coordination shell is significantly decreased, and the coordination distance is also shortened about 0.01 nm. All the results suggest that the BaAl2O4 crystallites should be the centers for NOx storage, while the fine-grained platinum species with high dispersion are deduced as the centers for the capture and oxidation of NOx species.
2001, 17(12): 1077-1085
doi: 10.3866/PKU.WHXB20011205
Abstract:
The first unifying principle in biochemistry is that the key molecules have the same handedness or chirality.The parity violating of electroweak neutral current (mediated by the Z0 boson) is suggested as the main force inducing the observed homochirality.After exposing D-/L-alanine and valine crystals to temperatures ranging from 300 K to 100 K,we observed a second order phase transition by differential scanning calorimetry and DC magnetic susceptibilities measurement.No configuration change was found by chirasil-Val capillary column gas chromatography thus failing to validate Salam′s predicted parity-violating energy difference (PVED) induced DL phase transition.The present studies show the experimental evidence provided by quantitative and apparently reliable estimates of PVED in phase transition of D- / L-alanine and valine crystals.
The first unifying principle in biochemistry is that the key molecules have the same handedness or chirality.The parity violating of electroweak neutral current (mediated by the Z0 boson) is suggested as the main force inducing the observed homochirality.After exposing D-/L-alanine and valine crystals to temperatures ranging from 300 K to 100 K,we observed a second order phase transition by differential scanning calorimetry and DC magnetic susceptibilities measurement.No configuration change was found by chirasil-Val capillary column gas chromatography thus failing to validate Salam′s predicted parity-violating energy difference (PVED) induced DL phase transition.The present studies show the experimental evidence provided by quantitative and apparently reliable estimates of PVED in phase transition of D- / L-alanine and valine crystals.
2001, 17(12): 1086-1091
doi: 10.3866/PKU.WHXB20011206
Abstract:
Electrochemical impedance spectra (EIS) of RE(NiCoMnTi)5 alloys (RE=La,Ce,Pr,Nd) were measured and analyzed under different depths of discharge (DOD).The results reveal that at different phase areas,such as β,α＋β and α,the alloy shows quite different characteristics in their discharge kinetics. At the same DOD of 50％,the surface hydrogen adsorbing resistance Rsf and Faraday resistance RF of the four alloys represent an approximate linear relationship to their the maximum discharge capacity C50,max and the high-rate-dischargeabi-lity κ respectively,indicating the alloy with a higher Rsf and RF will have a larger capacity and better dischargeability.
Electrochemical impedance spectra (EIS) of RE(NiCoMnTi)5 alloys (RE=La,Ce,Pr,Nd) were measured and analyzed under different depths of discharge (DOD).The results reveal that at different phase areas,such as β,α＋β and α,the alloy shows quite different characteristics in their discharge kinetics. At the same DOD of 50％,the surface hydrogen adsorbing resistance Rsf and Faraday resistance RF of the four alloys represent an approximate linear relationship to their the maximum discharge capacity C50,max and the high-rate-dischargeabi-lity κ respectively,indicating the alloy with a higher Rsf and RF will have a larger capacity and better dischargeability.
2001, 17(12): 1092-1096
doi: 10.3866/PKU.WHXB20011207
Abstract:
A podand carrying terminal naphthalene as energy donor and anthracene as energy acceptor groups (DSA) has been synthesized. Absorption spectroscopy showed that there was no intramolecular interaction between the two chromophores in ground state. Selective excitation of the naphthalene moiety a decrease in the naphthalene fluorescence is observed accompanied by an increase in the anthracene emission. The results indicate that singlet-singlet energy transfer from naphthalene to anthracene occurs. It is demonstrated that the efficiency of energy transfer is influenced by the solvent polarity attributed to the differences in the conformation about the central C－C bond of the －OCH2CH2O－ unit which is predominantly trans in low-polarity solvent such as benzene but predominantly gauche in high-polarity solvent such as acetonitrile. This in turn is expected to lead to variations of the naphthalene-anthracene separation that effects energy transfer efficiency. It is concluded that energy transfer can be used as a diagnostic tool to probe solvent-specific conformational properties of a D-A system with a flexible bridging ligand.
A podand carrying terminal naphthalene as energy donor and anthracene as energy acceptor groups (DSA) has been synthesized. Absorption spectroscopy showed that there was no intramolecular interaction between the two chromophores in ground state. Selective excitation of the naphthalene moiety a decrease in the naphthalene fluorescence is observed accompanied by an increase in the anthracene emission. The results indicate that singlet-singlet energy transfer from naphthalene to anthracene occurs. It is demonstrated that the efficiency of energy transfer is influenced by the solvent polarity attributed to the differences in the conformation about the central C－C bond of the －OCH2CH2O－ unit which is predominantly trans in low-polarity solvent such as benzene but predominantly gauche in high-polarity solvent such as acetonitrile. This in turn is expected to lead to variations of the naphthalene-anthracene separation that effects energy transfer efficiency. It is concluded that energy transfer can be used as a diagnostic tool to probe solvent-specific conformational properties of a D-A system with a flexible bridging ligand.
2001, 17(12): 1097-1101
doi: 10.3866/PKU.WHXB20011208
Abstract:
The melting process of Ni atom clusters with different size has been studied by molecular dynamics simulation. The initial configuration of clusters is the structure of FCC. The results indicate that melting first occurs at the edges of the clusters, and after the outer shells started to form the liquid layer, melting of the whole clusters began from the liquid to core region. The change in the melting temperature of the clusters is size dependent. The melting process can be referred as heterogeneous melting since the free surfaces act as the heterogeneous nucleation site for the liquid phase; for comparison, the melting point of the bulk solid of Ni has been simulated. It can be superheated up to 400 K above the experimental melting point. For system without free surface, there is no effective heterogeneous nucleation site for the liquid phase,melting is an intrinsic process initiated by a spontaneous homogeneous nucleation mechanism.
The melting process of Ni atom clusters with different size has been studied by molecular dynamics simulation. The initial configuration of clusters is the structure of FCC. The results indicate that melting first occurs at the edges of the clusters, and after the outer shells started to form the liquid layer, melting of the whole clusters began from the liquid to core region. The change in the melting temperature of the clusters is size dependent. The melting process can be referred as heterogeneous melting since the free surfaces act as the heterogeneous nucleation site for the liquid phase; for comparison, the melting point of the bulk solid of Ni has been simulated. It can be superheated up to 400 K above the experimental melting point. For system without free surface, there is no effective heterogeneous nucleation site for the liquid phase,melting is an intrinsic process initiated by a spontaneous homogeneous nucleation mechanism.
2001, 17(12): 1102-1106
doi: 10.3866/PKU.WHXB20011209
Abstract:
Phosphomolytungstenbdic anions were adsorbed by electrostatic attraction ld electrode on modified L-cysteine self-assembled monolayers.The formation of the film was studied.Experiments showed that acidic medium was benefit to the adsorption of phosphomolytungstenbdic anions.The adsorbing quantity Γ0 is 2.57×10－10 mol•cm－2,which means a single layer on the surface.Cyclic voltammetry,chronocoulmetry,FTIR and SEM were used for the characterization and electrochemical properties of the films.Three stable and reversible redox couples were observed in 1.0 mol•L－1 H2SO4 in the range of 0.8～－0.2 V,which could be attributed to three electrochemical processes of phosphomolytungstenbdic anions.Charge transfer coefficient is 2.64×10－7 cm2•s－1 by chronocoulmetry.Redox properties were also described.
Phosphomolytungstenbdic anions were adsorbed by electrostatic attraction ld electrode on modified L-cysteine self-assembled monolayers.The formation of the film was studied.Experiments showed that acidic medium was benefit to the adsorption of phosphomolytungstenbdic anions.The adsorbing quantity Γ0 is 2.57×10－10 mol•cm－2,which means a single layer on the surface.Cyclic voltammetry,chronocoulmetry,FTIR and SEM were used for the characterization and electrochemical properties of the films.Three stable and reversible redox couples were observed in 1.0 mol•L－1 H2SO4 in the range of 0.8～－0.2 V,which could be attributed to three electrochemical processes of phosphomolytungstenbdic anions.Charge transfer coefficient is 2.64×10－7 cm2•s－1 by chronocoulmetry.Redox properties were also described.
2001, 17(12): 1107-1111
doi: 10.3866/PKU.WHXB20011210
Abstract:
The effect of Cl－ on the corrosion behavior of copper electrode in weak-alkaline medium was studied by cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), in-situ ellipsometry and electrochemical impedance spectroscopy(EIS). The results showed that Cl－ had remarkable influence on the corrosion behavior of copper. The corrosion current of copper electrode in solution with Cl－ was about 10 times larger than that without Cl－. It was due to the decrease of the corrosion resistance of the film because the film was doped by Cl－ ion. The ellipsometry results not only were in od agreement with the electrochemical and XPS measurements qualitatively, but also could be used to distinguish every stage of corrosion, such as the formation of Cu2O film, the Cu2O film doped by Cl－ ion, the formation of CuO, and so on. Moreover, based on reasonable models as well as optical results, the composition, thickness and refractive index of the surface film on the electrode could be calculated quantitatively, which would provide important evidences for the reaction mechanism studies.
The effect of Cl－ on the corrosion behavior of copper electrode in weak-alkaline medium was studied by cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), in-situ ellipsometry and electrochemical impedance spectroscopy(EIS). The results showed that Cl－ had remarkable influence on the corrosion behavior of copper. The corrosion current of copper electrode in solution with Cl－ was about 10 times larger than that without Cl－. It was due to the decrease of the corrosion resistance of the film because the film was doped by Cl－ ion. The ellipsometry results not only were in od agreement with the electrochemical and XPS measurements qualitatively, but also could be used to distinguish every stage of corrosion, such as the formation of Cu2O film, the Cu2O film doped by Cl－ ion, the formation of CuO, and so on. Moreover, based on reasonable models as well as optical results, the composition, thickness and refractive index of the surface film on the electrode could be calculated quantitatively, which would provide important evidences for the reaction mechanism studies.
2001, 17(12): 1112-1116
doi: 10.3866/PKU.WHXB20011211
Abstract:
Preparation of hydrophobic SiO2 thin film is reported.The solution is prepared by a acid/base 2-step method and then modified by TMCS (trimethylchlorosilane).Ellipsometry,FTIR,SEM,and contact angle instrument were used to measure the physical properties of the thin films.The results show that the refractive index of thin film is controlled between 1.33 and 1.18,OH groups on the surface of SiO2 particles have been partly replaced by CH3 groups,the contact angle is increased to 120 degree of modified films from 40 degree of unmodified films.
Preparation of hydrophobic SiO2 thin film is reported.The solution is prepared by a acid/base 2-step method and then modified by TMCS (trimethylchlorosilane).Ellipsometry,FTIR,SEM,and contact angle instrument were used to measure the physical properties of the thin films.The results show that the refractive index of thin film is controlled between 1.33 and 1.18,OH groups on the surface of SiO2 particles have been partly replaced by CH3 groups,the contact angle is increased to 120 degree of modified films from 40 degree of unmodified films.
2001, 17(12): 1117-1121
doi: 10.3866/PKU.WHXB20011212
Abstract:
A rapid synthesis of mesoporous molecular sieve MCM-41 with nanometer size by sol-gel method under microwave radiation heating is reported. The effect of different factors, such as raw materials ratio, acidity, power and duration of microwave radiation employed in crystallization and removal of organic template processes on the morphology of the products was systemically investigated and the optimum reaction conditions were also selected. The resulting samples were characterized with such techniques as XRD, HRTEM, IR, TG, photoluminescence spectroscopy and N2 adsorption isotherm, etc. The results showed that reaction time and energy required in the synthesis of MCM-41 mesophase by microwave radiation method were greatly reduced in contrast with those needed by hydrothermal method. The samples, which displayed a hexa nal mesostructure with short-range order having pore diameter of about 2.5 nm exhibited a photoluminescence effect due to the nanometer-diameter crystallites(about 40 nm, see Fig.2～3). The as-prepared MCM-41 mesoporous molecular sieve was found to possess a huge surface area, pore volume and od thermal stability (see Table 3).
A rapid synthesis of mesoporous molecular sieve MCM-41 with nanometer size by sol-gel method under microwave radiation heating is reported. The effect of different factors, such as raw materials ratio, acidity, power and duration of microwave radiation employed in crystallization and removal of organic template processes on the morphology of the products was systemically investigated and the optimum reaction conditions were also selected. The resulting samples were characterized with such techniques as XRD, HRTEM, IR, TG, photoluminescence spectroscopy and N2 adsorption isotherm, etc. The results showed that reaction time and energy required in the synthesis of MCM-41 mesophase by microwave radiation method were greatly reduced in contrast with those needed by hydrothermal method. The samples, which displayed a hexa nal mesostructure with short-range order having pore diameter of about 2.5 nm exhibited a photoluminescence effect due to the nanometer-diameter crystallites(about 40 nm, see Fig.2～3). The as-prepared MCM-41 mesoporous molecular sieve was found to possess a huge surface area, pore volume and od thermal stability (see Table 3).
2001, 17(12): 1122-1125
doi: 10.3866/PKU.WHXB20011213
Abstract:
The ability of forming micell, the efficiency and the ability of reducing surface tension by the interaction of zwitterionic and anionic surfactants (C12H25N＋(CH3)2 CH2COO－/C12H25SO4Na) has been investi- gated. It is found that when the molar fraction of C12BE is about 0.6, the surface activity shows a maximum. The influence of NaCl and alcohols on surface properties of the mixed system has also been studied. The surface activity is enhanced and the cmc value of C12BE/SDS system is reduced with the increase of NaCl concentration, because sodium ions induce a decrease of electrostatic repulsion between hydrophilic groups in surfactant molecules. The effect is more complex with the addition of alcohols, the surface activity improves with increasing the volume fraction of n-butanol. But no remarkble influence on surface activity has been observed for alcohols of short chain, for example ethanol.
The ability of forming micell, the efficiency and the ability of reducing surface tension by the interaction of zwitterionic and anionic surfactants (C12H25N＋(CH3)2 CH2COO－/C12H25SO4Na) has been investi- gated. It is found that when the molar fraction of C12BE is about 0.6, the surface activity shows a maximum. The influence of NaCl and alcohols on surface properties of the mixed system has also been studied. The surface activity is enhanced and the cmc value of C12BE/SDS system is reduced with the increase of NaCl concentration, because sodium ions induce a decrease of electrostatic repulsion between hydrophilic groups in surfactant molecules. The effect is more complex with the addition of alcohols, the surface activity improves with increasing the volume fraction of n-butanol. But no remarkble influence on surface activity has been observed for alcohols of short chain, for example ethanol.
2001, 17(12): 1126-1128
doi: 10.3866/PKU.WHXB20011214
Abstract:
The direct electrochemistry of cytochrome C551 from pseudomonas aeruginosa has been investigated at indium-doped tin oxide(ITO) optically transparent electrodes without any surface promoters or mediators. The cyclic voltammograms show a quasi-reversible electrode reaction. Plots of peak reduction current against square root of scan rate are linear over the range 5 mV•s－1 to 100 mV•s－1. The diffusion coefficient of C551 is calculated from the slope of the line. The rate constant for heterogeneous electron transfer is determined by measuring cyclic voltammetry peak separation as a function of scan rate.
The direct electrochemistry of cytochrome C551 from pseudomonas aeruginosa has been investigated at indium-doped tin oxide(ITO) optically transparent electrodes without any surface promoters or mediators. The cyclic voltammograms show a quasi-reversible electrode reaction. Plots of peak reduction current against square root of scan rate are linear over the range 5 mV•s－1 to 100 mV•s－1. The diffusion coefficient of C551 is calculated from the slope of the line. The rate constant for heterogeneous electron transfer is determined by measuring cyclic voltammetry peak separation as a function of scan rate.
