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2001 Volume 17 Issue 9
2001, 17(09): 769-772
doi: 10.3866/PKU.WHXB20010901
Abstract:
The thermochemical hole burning properties of two different charge transfer complexes,DEA(TCNQ)2 and TEA(TCNQ)2,were studied in this work.It shows that the data writing on DEA(TCNQ)2 needs a larger threshold voltage compared with TEA(TCNQ)2,and that the DEA(TCNQ)2 gives a smaller hole size and a higher depth/diameter ratio,demonstrating the possibility of optimizing the storage performance with a suitable molecular design.
The thermochemical hole burning properties of two different charge transfer complexes,DEA(TCNQ)2 and TEA(TCNQ)2,were studied in this work.It shows that the data writing on DEA(TCNQ)2 needs a larger threshold voltage compared with TEA(TCNQ)2,and that the DEA(TCNQ)2 gives a smaller hole size and a higher depth/diameter ratio,demonstrating the possibility of optimizing the storage performance with a suitable molecular design.
2001, 17(09): 773-775
doi: 10.3866/PKU.WHXB20010902
Abstract:
Influence of the additions of different type semiconductor oxides to Nibased catalyst on the characteristics of carbon deposition of CH4,C2H6 and C2H4 cracking was studied by using pulse microreaction technique.It was discovered that,the addition of ntype semiconductor CeO2 to Ni catalyst would decrease carbon deposition activity of CH4 and C2H6 cracking,whereas the addition of ptype semiconductor Co3O4 would increase carbon deposition activity of CH4 and C2H6 cracking.On the other hand,the effect of semiconductor oxide additives on the characteristics of carbon deposition of C2H4 cracking is opposite to that of CH4 and C2H6 due to the different activated mechanism.XPS results reveal that there is a metalsemiconductor interaction (MScI) between active metal Ni and semiconductor oxide,which is the most important factor leads to the above phenomenon.
Influence of the additions of different type semiconductor oxides to Nibased catalyst on the characteristics of carbon deposition of CH4,C2H6 and C2H4 cracking was studied by using pulse microreaction technique.It was discovered that,the addition of ntype semiconductor CeO2 to Ni catalyst would decrease carbon deposition activity of CH4 and C2H6 cracking,whereas the addition of ptype semiconductor Co3O4 would increase carbon deposition activity of CH4 and C2H6 cracking.On the other hand,the effect of semiconductor oxide additives on the characteristics of carbon deposition of C2H4 cracking is opposite to that of CH4 and C2H6 due to the different activated mechanism.XPS results reveal that there is a metalsemiconductor interaction (MScI) between active metal Ni and semiconductor oxide,which is the most important factor leads to the above phenomenon.
2001, 17(09): 776-780
doi: 10.3866/PKU.WHXB20010903
Abstract:
A series of Nvinylcarbazole(NVCz) labeled methacrylic acid(MAA)acenaphthylene(ACE) copo-lymers(PMAAACE/NVCz),with ACE content of 4.3,7.5,15.1 and 20.8 mol％,respectively,and a ACEMAA copolymer(PMAAACE) with ACE content of 0.5 mol％ have been synthesized. The fluorescence properties of the dilute aqueous solutions of the copolymers and the effect of pH,surfactants upon the properties have been studied in some detail. It was demonstrated that the hypercoiled conformation of the copolymers at low pH made their fluorescence emission to be dominated by ACE excimer and/or NVCz emission. At higher pH,however,the copolymers adopted an extended coil conformation that decreases significantly the efficiency of nonradiative energy transfer from ACE to NVCz. And therefore,the fluorescence emission of the copolymers at higher pH lacked the characteristics of NVCz. Introduction of surfactants had a significant effect upon the fluorescence properties of the copolymers. At low pH,adding any of sodium dodecyl sulfate(SDS),ammonium hexadecyl trimethyl bromide(AHTB) and Tween 80 decreased the efficiency of nonradiative energy transfer from ACE to NVCz due to partially extension of the copolymer coil,and thereby reduced NVCz characteristics in the fluorescence spectra of the copolymers. At higher pH,AHTB,a cationic surfactant,increased the efficiency of nonradiative energy transfer from ACE to NVCz due to partial neutralization of the negative charges along the copolymer chains,and thereby NVCz emission appeared in the fluorescence spectrum of the copolymer. The introduction of SDS or Tween 80 had little effect upon the fluorescence emission of the copolymers at higher pH.
A series of Nvinylcarbazole(NVCz) labeled methacrylic acid(MAA)acenaphthylene(ACE) copo-lymers(PMAAACE/NVCz),with ACE content of 4.3,7.5,15.1 and 20.8 mol％,respectively,and a ACEMAA copolymer(PMAAACE) with ACE content of 0.5 mol％ have been synthesized. The fluorescence properties of the dilute aqueous solutions of the copolymers and the effect of pH,surfactants upon the properties have been studied in some detail. It was demonstrated that the hypercoiled conformation of the copolymers at low pH made their fluorescence emission to be dominated by ACE excimer and/or NVCz emission. At higher pH,however,the copolymers adopted an extended coil conformation that decreases significantly the efficiency of nonradiative energy transfer from ACE to NVCz. And therefore,the fluorescence emission of the copolymers at higher pH lacked the characteristics of NVCz. Introduction of surfactants had a significant effect upon the fluorescence properties of the copolymers. At low pH,adding any of sodium dodecyl sulfate(SDS),ammonium hexadecyl trimethyl bromide(AHTB) and Tween 80 decreased the efficiency of nonradiative energy transfer from ACE to NVCz due to partially extension of the copolymer coil,and thereby reduced NVCz characteristics in the fluorescence spectra of the copolymers. At higher pH,AHTB,a cationic surfactant,increased the efficiency of nonradiative energy transfer from ACE to NVCz due to partial neutralization of the negative charges along the copolymer chains,and thereby NVCz emission appeared in the fluorescence spectrum of the copolymer. The introduction of SDS or Tween 80 had little effect upon the fluorescence emission of the copolymers at higher pH.
2001, 17(09): 781-787
doi: 10.3866/PKU.WHXB20010904
Abstract:
The influence of S2－ ion and its concentration upon the photoinduced electron transfer and redox reaction of substrates on the surface of modified CdS colloid have been studied by means of ESR technique.The experimental results show that the existence of S2－ ion with high concentration is advantageous to the interfacial photoreduction reaction and may restrain the photooxidation reaction.If the redox potential E0 of the substrate is negative,photoreduction reaction is impossible to occur in the system with low concentration of S2－ ion,but it can take place as the concentration of S2－ ion is sufficient high; when E0 of the substrate is positive,photooxidation reaction can be prohibited entirely under condition of high S2－ ion concentration,even though it is able to occur while the concentration of S2－ ion is low.Due to the strong interaction of S2－ ion with the surface of CdS superfine particles,negative shift in flat potential Efb of CdS leads to a change of gap position,and then to a variation in match relation between the redox potential E0 of the substrate and the position of conducton band to valence band in semiconductor particles.According to Langmuir's adsorption isotherm model,a formula expressing the relation between the concentration c of modification compound and the negative shift ΔEfb in flat potential was derived:ΔEfb=Δ Kc/(1＋Kc).By using this formula,experiment facts may be explained rationally,the higher the concentration,the greater the amount of negative shift ΔEfb,and thus the more favourable to photoreduction reaction.Therefore,by choosing suitable modification substance and adjusting its concentration,the selection,direction as well as the mechanism of interfacial photoreaction can be controlled effectively.
The influence of S2－ ion and its concentration upon the photoinduced electron transfer and redox reaction of substrates on the surface of modified CdS colloid have been studied by means of ESR technique.The experimental results show that the existence of S2－ ion with high concentration is advantageous to the interfacial photoreduction reaction and may restrain the photooxidation reaction.If the redox potential E0 of the substrate is negative,photoreduction reaction is impossible to occur in the system with low concentration of S2－ ion,but it can take place as the concentration of S2－ ion is sufficient high; when E0 of the substrate is positive,photooxidation reaction can be prohibited entirely under condition of high S2－ ion concentration,even though it is able to occur while the concentration of S2－ ion is low.Due to the strong interaction of S2－ ion with the surface of CdS superfine particles,negative shift in flat potential Efb of CdS leads to a change of gap position,and then to a variation in match relation between the redox potential E0 of the substrate and the position of conducton band to valence band in semiconductor particles.According to Langmuir's adsorption isotherm model,a formula expressing the relation between the concentration c of modification compound and the negative shift ΔEfb in flat potential was derived:ΔEfb=Δ Kc/(1＋Kc).By using this formula,experiment facts may be explained rationally,the higher the concentration,the greater the amount of negative shift ΔEfb,and thus the more favourable to photoreduction reaction.Therefore,by choosing suitable modification substance and adjusting its concentration,the selection,direction as well as the mechanism of interfacial photoreaction can be controlled effectively.
2001, 17(09): 788-791
doi: 10.3866/PKU.WHXB20010905
Abstract:
Electrochemically fabricated prussian blue (PB) film modified platinum electrode was studied by cyclic voltammetric and electrochemical impedance techniques. The redox process of the modified layer was discussed with the observed CV plot. The measured impedance spectrum was analyzed and the corresponding equivalent circuit was proposed. The apparent chargetransfer rate constant and the apparent diffusion coefficient of PB redox couple within the modified layer were obtained. The dependence of impedance behaviors of the PB films on varied film thickness was systematically studied. When the modified layer was relatively thin, the apparent chargetransfer rate constant and apparent diffusion coefficient increased with the increasing thickness of PB film and the charge transfer process was enhanced obviously. The charge transfer process was predicted to be controlled by the kinetic factors. On the other hand, if the modified PB layer was comparatively thicker, the charge diffused with restricted rate, and would only reach to a certain distance inside the modified film. The results were well satisfied with the multilayer model of spaced distributed redox modified electrode found in literature.
Electrochemically fabricated prussian blue (PB) film modified platinum electrode was studied by cyclic voltammetric and electrochemical impedance techniques. The redox process of the modified layer was discussed with the observed CV plot. The measured impedance spectrum was analyzed and the corresponding equivalent circuit was proposed. The apparent chargetransfer rate constant and the apparent diffusion coefficient of PB redox couple within the modified layer were obtained. The dependence of impedance behaviors of the PB films on varied film thickness was systematically studied. When the modified layer was relatively thin, the apparent chargetransfer rate constant and apparent diffusion coefficient increased with the increasing thickness of PB film and the charge transfer process was enhanced obviously. The charge transfer process was predicted to be controlled by the kinetic factors. On the other hand, if the modified PB layer was comparatively thicker, the charge diffused with restricted rate, and would only reach to a certain distance inside the modified film. The results were well satisfied with the multilayer model of spaced distributed redox modified electrode found in literature.
Temperature-Independent Activation Energy for Ionic Conduction of Zirconia Based Solid Electrolytes
2001, 17(09): 792-796
doi: 10.3866/PKU.WHXB20010906
Abstract:
Previous studies have shown that the temperature dependence of the ionic conductivity of zirconia based solid electrolytes exhibit an unusual nonlinear Arrhenius behavior and,as a result, the activation energy for ionic conductivity resulting from the analysis according to the classical Arrhenius equation is temperaturedependent.In this paper,a modified Arrhenius equation was proposed,based on the measurement and analysis of the conductivity for three kinds of Y2O3stablized ZrO2,to describe the temperature dependence of the ionic conductivity.It was found that the activation energy deduced from the modified Arrhenius equation is a constant independent of temperature.The validity of such a temperatureindependent activation energy was further discussed based on the transitionstate theory in physical chemistry.
Previous studies have shown that the temperature dependence of the ionic conductivity of zirconia based solid electrolytes exhibit an unusual nonlinear Arrhenius behavior and,as a result, the activation energy for ionic conductivity resulting from the analysis according to the classical Arrhenius equation is temperaturedependent.In this paper,a modified Arrhenius equation was proposed,based on the measurement and analysis of the conductivity for three kinds of Y2O3stablized ZrO2,to describe the temperature dependence of the ionic conductivity.It was found that the activation energy deduced from the modified Arrhenius equation is a constant independent of temperature.The validity of such a temperatureindependent activation energy was further discussed based on the transitionstate theory in physical chemistry.
2001, 17(09): 797-801
doi: 10.3866/PKU.WHXB20010907
Abstract:
A series of solid complexes EuxM1－x(TTA)3(H2O)2 (M=La,Gd) were synthesized.Their compositions were ensured by the ICP analysis.The FTIR spectroscopy showed that no new compound formed besides Eu (TTA)3(H2O)2 and M(TTA)3(H2O)2(M=La,Gd)(to see Table 3).The luminescence property of them was investigated by using luminescence spectroscopy.The results indicated that the luminescence intensity of the complexes did not have a linear relation with the concentration of Eu3＋.Addition of M3＋ (La3＋ or Gd3＋) enhanced the luminescence of Eu3＋.Furthermore,the enhancement by Gd3＋ is more remarkable than by La3＋.The possible intermolecular energy transfer mechanism was discussed,which explained the phenomena very well.
A series of solid complexes EuxM1－x(TTA)3(H2O)2 (M=La,Gd) were synthesized.Their compositions were ensured by the ICP analysis.The FTIR spectroscopy showed that no new compound formed besides Eu (TTA)3(H2O)2 and M(TTA)3(H2O)2(M=La,Gd)(to see Table 3).The luminescence property of them was investigated by using luminescence spectroscopy.The results indicated that the luminescence intensity of the complexes did not have a linear relation with the concentration of Eu3＋.Addition of M3＋ (La3＋ or Gd3＋) enhanced the luminescence of Eu3＋.Furthermore,the enhancement by Gd3＋ is more remarkable than by La3＋.The possible intermolecular energy transfer mechanism was discussed,which explained the phenomena very well.
2001, 17(09): 802-805
doi: 10.3866/PKU.WHXB20010908
Abstract:
The three dimensional carbon fiber reinforced SiC composites (C/SiC) were studied by using XPS,small area XPS and imaging XPS.The results show that Si in surface layer of the composites is oxidized to silicon oxides.The impurities of Fe,Na,Ca and Al are present after heating the composites in combustion gas at 1300 ℃. Beneath the surface layer,silicon is present in the forms of elemental Si,SiC and Si oxides in which elemental Si is produced by infiltration of molten silicon.The results of small area XPS multipoint analyses for the cross section of composite show that the relative content of elemental Si decreases with increasing distance from the cross section edge while the relative content of SiC increases with increasing the distance.The Si 2p XPS images show clearly that SiC is deposited in the boundary region between carbon fiber bundles.However,the content of elemental Si is higher in the margin area than in the center area of the cross section.The thickness of SiC between carbon fiber bundles in the center area and the thickness of elemental Si rich layer in the margin area of the cross section have been estimated by using the line scans of the XPS images.
The three dimensional carbon fiber reinforced SiC composites (C/SiC) were studied by using XPS,small area XPS and imaging XPS.The results show that Si in surface layer of the composites is oxidized to silicon oxides.The impurities of Fe,Na,Ca and Al are present after heating the composites in combustion gas at 1300 ℃. Beneath the surface layer,silicon is present in the forms of elemental Si,SiC and Si oxides in which elemental Si is produced by infiltration of molten silicon.The results of small area XPS multipoint analyses for the cross section of composite show that the relative content of elemental Si decreases with increasing distance from the cross section edge while the relative content of SiC increases with increasing the distance.The Si 2p XPS images show clearly that SiC is deposited in the boundary region between carbon fiber bundles.However,the content of elemental Si is higher in the margin area than in the center area of the cross section.The thickness of SiC between carbon fiber bundles in the center area and the thickness of elemental Si rich layer in the margin area of the cross section have been estimated by using the line scans of the XPS images.
2001, 17(09): 806-810
doi: 10.3866/PKU.WHXB20010909
Abstract:
The conductivity of polythionine is 9.6×10－6 S•cm－1,which is an organic semiconductor.The cyclic voltammograms,discharging curves at a constant potential,ac impedance plots of polythionine and the conductivity of the electrolyte solution were investigated.There are an anodic peak and a cathodic peak in the cyclic voltammogram of polythionine.Their peak currents increase with increasing temperature.The discharging current at constant potential also increases with increasing temperature.The result from ac impedance plots shows that the charge transfer resistance Rct decreases with increasing temperature,i.e.,its exchange current i0 increases with increasing temperature.The resistances of the solution and the film decrease with increasing temperature.These also cause the increase in the current with increasing temperature.Thus,the effect of temperature on the reaction rate of polythionine semiconductor contains several factors of the electrode reaction itself and the conductivity of polythionine etc..The scanning electronic micrograph shows that the surface of polythionine is a fibrillarlike morphology.
The conductivity of polythionine is 9.6×10－6 S•cm－1,which is an organic semiconductor.The cyclic voltammograms,discharging curves at a constant potential,ac impedance plots of polythionine and the conductivity of the electrolyte solution were investigated.There are an anodic peak and a cathodic peak in the cyclic voltammogram of polythionine.Their peak currents increase with increasing temperature.The discharging current at constant potential also increases with increasing temperature.The result from ac impedance plots shows that the charge transfer resistance Rct decreases with increasing temperature,i.e.,its exchange current i0 increases with increasing temperature.The resistances of the solution and the film decrease with increasing temperature.These also cause the increase in the current with increasing temperature.Thus,the effect of temperature on the reaction rate of polythionine semiconductor contains several factors of the electrode reaction itself and the conductivity of polythionine etc..The scanning electronic micrograph shows that the surface of polythionine is a fibrillarlike morphology.
2001, 17(09): 811-816
doi: 10.3866/PKU.WHXB20010910
Abstract:
The siting of B, Al or Ga and the bridging hydroxyl group in mordenite framework were studied by using ab initio HartreeFock methods. The influence of the presence of B or Ga in the framework on the Bronsted acidity of mordenite was investigated. It was shown that energetically, heteroatoms including B,Al or Ga prefer the same Tsites, T3 and T4, when replacing Si in mordenite framework. For the preferred substitution site T4, the chargecompensating proton prefers to attach to O10 in case of Al and Ga substitution while the proton prefers to bond with O2 or O10 in case of B substitution. The proton affinity calculations showed that the acidity of isomorphously substituted mordenite increases in the order:BMORGaMOR< AlMOR.
The siting of B, Al or Ga and the bridging hydroxyl group in mordenite framework were studied by using ab initio HartreeFock methods. The influence of the presence of B or Ga in the framework on the Bronsted acidity of mordenite was investigated. It was shown that energetically, heteroatoms including B,Al or Ga prefer the same Tsites, T3 and T4, when replacing Si in mordenite framework. For the preferred substitution site T4, the chargecompensating proton prefers to attach to O10 in case of Al and Ga substitution while the proton prefers to bond with O2 or O10 in case of B substitution. The proton affinity calculations showed that the acidity of isomorphously substituted mordenite increases in the order:BMORGaMOR< AlMOR.
Photoelectrochromism of Dyesensitized Nanoporous TiO2 Film Combined with Electrodeposited MoO3 Film
2001, 17(09): 817-819
doi: 10.3866/PKU.WHXB20010911
Abstract:
A selfpowered smart window was achieved by combining a dyesensitized nanoporous TiO2 film as photovoltaic layer with an electrodeposited MoO3 film as electrochromic layer. This window changed from almost transparent to blue spontaneously under illumination, and thus could modulate light transmittance.
A selfpowered smart window was achieved by combining a dyesensitized nanoporous TiO2 film as photovoltaic layer with an electrodeposited MoO3 film as electrochromic layer. This window changed from almost transparent to blue spontaneously under illumination, and thus could modulate light transmittance.
2001, 17(09): 820-823
doi: 10.3866/PKU.WHXB20010912
Abstract:
Using a hightemperature Xray diffractometer on liquid metals, the structure factors (SF), pair distribution functions (PDF), the nearest neighbor distances (NND) as well as the coordination number of pure iron melt at different temperatures were obtained. The experimental results show that with the increase of temperature the height of the first peak of SF and PDF of liquid pure iron becomes smaller gradually, but the NND becomes smaller first and then keeps constant basically. Both the coordination number and the correlation radius of atomic cluster of pure iron melt have a sudden change at the temperature range of 1600～1650 ℃, indicating a structural transformation. The physical meaning of the correlation radius rc was also discussed.
Using a hightemperature Xray diffractometer on liquid metals, the structure factors (SF), pair distribution functions (PDF), the nearest neighbor distances (NND) as well as the coordination number of pure iron melt at different temperatures were obtained. The experimental results show that with the increase of temperature the height of the first peak of SF and PDF of liquid pure iron becomes smaller gradually, but the NND becomes smaller first and then keeps constant basically. Both the coordination number and the correlation radius of atomic cluster of pure iron melt have a sudden change at the temperature range of 1600～1650 ℃, indicating a structural transformation. The physical meaning of the correlation radius rc was also discussed.
2001, 17(09): 824-827
doi: 10.3866/PKU.WHXB20010913
Abstract:
A micronanotube of new inorganic compound with external shape of tetra nal prism has been synthesized. It is made of transitional metal oxychloride. From SEM detection, the micronanotube has an external diameter of 100－500 nm and an internal diameter of 60－300 nm. Its wall is very thin, 20－70 nm, and its length is from a dozen micro to dozens of microns(to see Fig.1(ad)). It has been prepared by solid state reaction in a direct growth way. From XRD, TEM and SEM determination, the micronanotube crystal belongs to orthorhombic system and its lattice constants are a=0.5864(2)nm, b=0.6032(2)nm andc=2.972(2)nm(to see Fig.1～2 and Table 1). It possesses semiconducting properties. From curve log(1/ρ)～1/T, its energy gap isEg≈1.2 eV(to see Fig.3). The micronanotube material will be a prospect material used as catalysts, material to store gases or energy, and material used as electrode in photoelectric cell and photoelectrolytic cell. Additionally, the preparation of the micronanotube material by solid state reaction is simple in operation and cheap in cost.
A micronanotube of new inorganic compound with external shape of tetra nal prism has been synthesized. It is made of transitional metal oxychloride. From SEM detection, the micronanotube has an external diameter of 100－500 nm and an internal diameter of 60－300 nm. Its wall is very thin, 20－70 nm, and its length is from a dozen micro to dozens of microns(to see Fig.1(ad)). It has been prepared by solid state reaction in a direct growth way. From XRD, TEM and SEM determination, the micronanotube crystal belongs to orthorhombic system and its lattice constants are a=0.5864(2)nm, b=0.6032(2)nm andc=2.972(2)nm(to see Fig.1～2 and Table 1). It possesses semiconducting properties. From curve log(1/ρ)～1/T, its energy gap isEg≈1.2 eV(to see Fig.3). The micronanotube material will be a prospect material used as catalysts, material to store gases or energy, and material used as electrode in photoelectric cell and photoelectrolytic cell. Additionally, the preparation of the micronanotube material by solid state reaction is simple in operation and cheap in cost.
2001, 17(09): 828-831
doi: 10.3866/PKU.WHXB20010914
Abstract:
Aggregation numbers of micelle (Nm) of SDS and AS were determined by steadystate fluorescence probe method in which pyrene was used as fluorescence probe and benzophenone as quencher.Satisfactory results were obtained as shown in Fig.1～2 when the solution of surfactant was prepared with a saturated aqueous solution of pyrene and the optimum concentration of benzophenone was selected in 0～1.00 mmol L－1.The experimental results in Fig.3～5 and Table 4 show that when concentration of surfactant is in 5～9 times of cmc,Nm increases linearly with the increase of concentration and fluctuats slightly with the increment of temperature.It is indicated that Nm is an eigenvalue at c=cmc,which has been defined herefrom as the critical micellar aggregation number [Nm].[Nm] can be extrapolated from Nm～cSAA experimental curves,as shown in Table 3 for SDS 57 (25℃) and 49 (40℃) and for AS 55 (40℃) ,respectively.
Aggregation numbers of micelle (Nm) of SDS and AS were determined by steadystate fluorescence probe method in which pyrene was used as fluorescence probe and benzophenone as quencher.Satisfactory results were obtained as shown in Fig.1～2 when the solution of surfactant was prepared with a saturated aqueous solution of pyrene and the optimum concentration of benzophenone was selected in 0～1.00 mmol L－1.The experimental results in Fig.3～5 and Table 4 show that when concentration of surfactant is in 5～9 times of cmc,Nm increases linearly with the increase of concentration and fluctuats slightly with the increment of temperature.It is indicated that Nm is an eigenvalue at c=cmc,which has been defined herefrom as the critical micellar aggregation number [Nm].[Nm] can be extrapolated from Nm～cSAA experimental curves,as shown in Table 3 for SDS 57 (25℃) and 49 (40℃) and for AS 55 (40℃) ,respectively.
2001, 17(09): 832-835
doi: 10.3866/PKU.WHXB20010915
Abstract:
The influence of Sb5＋ ions on SnO2x crystallinity and gassensing properties of the sensors based on the SnO2x powders prepared by hydrothemal synthesis technique was investigated by XRD and TEM.The results show that the doping of Sb5＋ ions in the ranges of (2.9～5.8×10－6) makes the grains of the SnO2x a short column in shape and plays an important role in decreasing the resistance values in air (Ra) for the sensor and controlling the sensitivity to CH4,CO,C2H5OH and H2.Finally,the surface electronic defect effect and the size effect of SnO2x crystallite in nanometer level were discussed to understand the gas sensing mechanism of sensors based on the(Sn,Sb)O2x nanostructure thick film materials.
The influence of Sb5＋ ions on SnO2x crystallinity and gassensing properties of the sensors based on the SnO2x powders prepared by hydrothemal synthesis technique was investigated by XRD and TEM.The results show that the doping of Sb5＋ ions in the ranges of (2.9～5.8×10－6) makes the grains of the SnO2x a short column in shape and plays an important role in decreasing the resistance values in air (Ra) for the sensor and controlling the sensitivity to CH4,CO,C2H5OH and H2.Finally,the surface electronic defect effect and the size effect of SnO2x crystallite in nanometer level were discussed to understand the gas sensing mechanism of sensors based on the(Sn,Sb)O2x nanostructure thick film materials.
2001, 17(09): 836-839
doi: 10.3866/PKU.WHXB20010916
Abstract:
The novel complex {[FcCH=CHCO2Sn(nBu)2]2O}2(A) has been synthesized by the reaction of (nBu)2SnO with βFcCH=CHCO2H (Fc=ferrocenyl). This molecule has a center of the structure SnO(Sn2)OSn by elemental analysis, IR and NMR (1H, 13C and 119Sn) spectra. A principle is put firstly forward to assign each carbon peak of the alkyl groups in the type of complex[(RCOOSnR′2)2O]2:(1) to distinguish the endo and exocyclic tin using 119Sn NMR spectrum. The 119Sn signal with larger linewidth should be assigned as an endocyclic tin; (2) to find out which proton of the alkyl chain bonded with endo(or exo)cyclic tin using 1H119Sn HMQC spectrum. The proton of cross peaks through 4J(1H119Sn) coupling which occurs simultaneously to both endo and exocyclic tin should belong to one of the alkyl chain binding directly to endocyclic tin. The proton of cross peak through 4J(1H－119Sn) coupling which occurs only to endo cyclic tin should belong to one of the alkyl chain binding directly to exocyclic tin; (3)to assign each 13C peak of the CH2 groups on alkyl chains through 2D 13C－1H COSY spectrum; (4)to find out which 13C peak of alkyl chains is bonded with endo or exocyclic tin, according to general principle that the 13C peak with higher field should correspond to the proton peak with higher field, that is, if the chemical shift of proton on the alkyl chain bonding directly to endocyclic tin locates at higher field, its related 13C peak located at higher field should belong to endocyclic tin.
The novel complex {[FcCH=CHCO2Sn(nBu)2]2O}2(A) has been synthesized by the reaction of (nBu)2SnO with βFcCH=CHCO2H (Fc=ferrocenyl). This molecule has a center of the structure SnO(Sn2)OSn by elemental analysis, IR and NMR (1H, 13C and 119Sn) spectra. A principle is put firstly forward to assign each carbon peak of the alkyl groups in the type of complex[(RCOOSnR′2)2O]2:(1) to distinguish the endo and exocyclic tin using 119Sn NMR spectrum. The 119Sn signal with larger linewidth should be assigned as an endocyclic tin; (2) to find out which proton of the alkyl chain bonded with endo(or exo)cyclic tin using 1H119Sn HMQC spectrum. The proton of cross peaks through 4J(1H119Sn) coupling which occurs simultaneously to both endo and exocyclic tin should belong to one of the alkyl chain binding directly to endocyclic tin. The proton of cross peak through 4J(1H－119Sn) coupling which occurs only to endo cyclic tin should belong to one of the alkyl chain binding directly to exocyclic tin; (3)to assign each 13C peak of the CH2 groups on alkyl chains through 2D 13C－1H COSY spectrum; (4)to find out which 13C peak of alkyl chains is bonded with endo or exocyclic tin, according to general principle that the 13C peak with higher field should correspond to the proton peak with higher field, that is, if the chemical shift of proton on the alkyl chain bonding directly to endocyclic tin locates at higher field, its related 13C peak located at higher field should belong to endocyclic tin.
2001, 17(09): 840-844
doi: 10.3866/PKU.WHXB20010917
Abstract:
The study of quenching and rotational statetostate energy transfer of NH2(A1,090,423) with Ar,N2,O2, and NH3 was performed at single collisional conditions. The total quenching cross sections σQ for the four partners have been measured to be ≤0.17 nm2， 0.26 nm2，0.30 nm2 and 0.48 nm2, respectively. The relative cross sections of rotational statetostate energy transfer were obtained by measuring the dispersed fluorescent spectra. A collisioncomplex model was used to calculate the quenching cross sections and the theoretical and experimental values show the same trend. This indicates that long range attractive interactions play an important role in the quenching process. It was also found that the relative cross sections of rotational energy transfer decrease approximately with decreasing the reduced mass of the collisionpair. NH3 and O2 present the larger quenching cross sections and smaller cross sections of rotational energy transfer due to the larger dipole momentum and the electronic structure of openshell, respectively.
The study of quenching and rotational statetostate energy transfer of NH2(A1,090,423) with Ar,N2,O2, and NH3 was performed at single collisional conditions. The total quenching cross sections σQ for the four partners have been measured to be ≤0.17 nm2， 0.26 nm2，0.30 nm2 and 0.48 nm2, respectively. The relative cross sections of rotational statetostate energy transfer were obtained by measuring the dispersed fluorescent spectra. A collisioncomplex model was used to calculate the quenching cross sections and the theoretical and experimental values show the same trend. This indicates that long range attractive interactions play an important role in the quenching process. It was also found that the relative cross sections of rotational energy transfer decrease approximately with decreasing the reduced mass of the collisionpair. NH3 and O2 present the larger quenching cross sections and smaller cross sections of rotational energy transfer due to the larger dipole momentum and the electronic structure of openshell, respectively.
2001, 17(09): 845-849
doi: 10.3866/PKU.WHXB20010918
Abstract:
For a Tienriched reductive slag system of CaOSiO2TiOxM Al2O3,creating an optimum physical chemistry condition will selectively enrich TiO2 in perovskite at the drive of its chemical potential during slag's cooling.To investigate this physical chemistry behavior,two approaches were carried out.One was by oxidizing the slag at high temperatures and another was by adjusting the slag basicity.The physical chemical mechanism of selective enrichment was as following: Oxidization of molten slag could change multivalent Ti compounds into TiO2 and increase the activity of TiO2 within the slag.TiO2 combined with CaO in the slag forming perovskite.The oxidation not only changed the compositions and structures of the slag phases but also caused majority of TiO2 migrating into perovskite.The increment of perovskite precipitated by oxidization could up to 30％ to 40％ of the precipitation in its original slag.It was found that raising the slag basicity could increase the activity of CaO in the slag that facilitated the selective precipitation of perovskite as well.Both approaches could promote the forward reaction of perovskite precipitation,TiO2＋CaO = CaTiO3(s),if slag basicity was adjusted up to 1.3 and this slag was oxidized sufficiently,about 80％ amount of TiO2 in slag could be collected in the form of perovskite.
For a Tienriched reductive slag system of CaOSiO2TiOxM Al2O3,creating an optimum physical chemistry condition will selectively enrich TiO2 in perovskite at the drive of its chemical potential during slag's cooling.To investigate this physical chemistry behavior,two approaches were carried out.One was by oxidizing the slag at high temperatures and another was by adjusting the slag basicity.The physical chemical mechanism of selective enrichment was as following: Oxidization of molten slag could change multivalent Ti compounds into TiO2 and increase the activity of TiO2 within the slag.TiO2 combined with CaO in the slag forming perovskite.The oxidation not only changed the compositions and structures of the slag phases but also caused majority of TiO2 migrating into perovskite.The increment of perovskite precipitated by oxidization could up to 30％ to 40％ of the precipitation in its original slag.It was found that raising the slag basicity could increase the activity of CaO in the slag that facilitated the selective precipitation of perovskite as well.Both approaches could promote the forward reaction of perovskite precipitation,TiO2＋CaO = CaTiO3(s),if slag basicity was adjusted up to 1.3 and this slag was oxidized sufficiently,about 80％ amount of TiO2 in slag could be collected in the form of perovskite.
2001, 17(09): 850-854
doi: 10.3866/PKU.WHXB20010919
Abstract:
Catalytic property of Ag/SnO2 catalysts for the combustion of methane was investigated and the state of silver was characterized by using XRD,BET, XPS, TEM and TPR. The results show that Ag/SnO2 system is quite active for the catalytic combustion of methane. When Ag/Sn atomic ratio is lower than 0.20, the main silver species is silver oxide existing in both dispersed state and crystal phase, and all the corresponding catalysts show relatively large surface areas and high catalytic activities. If silver content further increases, metallic silver shows up and becomes the main silver species, and the surface areas as well as the catalytic activities of the samples decrease dramatically. The sample with a Ag/Sn atomic ratio of 0.20 has the highest activity.
Catalytic property of Ag/SnO2 catalysts for the combustion of methane was investigated and the state of silver was characterized by using XRD,BET, XPS, TEM and TPR. The results show that Ag/SnO2 system is quite active for the catalytic combustion of methane. When Ag/Sn atomic ratio is lower than 0.20, the main silver species is silver oxide existing in both dispersed state and crystal phase, and all the corresponding catalysts show relatively large surface areas and high catalytic activities. If silver content further increases, metallic silver shows up and becomes the main silver species, and the surface areas as well as the catalytic activities of the samples decrease dramatically. The sample with a Ag/Sn atomic ratio of 0.20 has the highest activity.
2001, 17(09): 855-858
doi: 10.3866/PKU.WHXB20010920
Abstract:
The power－time curves of the extraction oscillation system were determined at different temperatures and acidities,for the extraction of acetic acid with primary amine N1923 in chloroform,using the perfusion/titration microcalorimetric method.The apparent activation energy were calculated from the induction period (tin),the first oscillation period (tp.1)and the second oscillation period (tp.2).The regularity of the oscillation system was discussed. The following equations were obtained tin=30.857＋1 001.43 cHAc, tp.1=101.714＋252.86 cHAc, tp.2=75.429＋175.71 cHAc .
The power－time curves of the extraction oscillation system were determined at different temperatures and acidities,for the extraction of acetic acid with primary amine N1923 in chloroform,using the perfusion/titration microcalorimetric method.The apparent activation energy were calculated from the induction period (tin),the first oscillation period (tp.1)and the second oscillation period (tp.2).The regularity of the oscillation system was discussed. The following equations were obtained tin=30.857＋1 001.43 cHAc, tp.1=101.714＋252.86 cHAc, tp.2=75.429＋175.71 cHAc .
2001, 17(09): 859-864
doi: 10.3866/PKU.WHXB20010921
Abstract:
An observation is demonstrated that Au/S target,triggered by gallium ion beam (69Ga＋) under experiment of high performance secondary ion mass spectrometry (TOF SIMS),does emit a considerable species of cluster negative ions with general formula of Au1－15S0－5(see Fig.1 and Table 1).Among them,a series of cluster ions with compositions of Au1－15S1－5 is recognized as AuS binary cluster ions,while other series with Au1－15 belongs to monocluster ions of pure ld,appearing in strong oddpredominance of their intensities with number of ld atom (see Fig.2).The AuS cluster ions can be characterized,in some aspects,by existence of the oddpredominance with magnitudes of ld atom (see Fig.3),inherited from the Au monoclusters; by lack of stoichiometric feature,showing that ld atoms range from 1 to 15 but sulfur atoms are always limited to 5 (see Table 1); by void of predominance as compositions as MenSn (for example,CunSn,see Table 2) or MenNn whose priority has been proved as an important feature prevailing in other binary cluster ions of metals (Me) plus sulfur (S) or other nonmetals (N); and by presence of special profiles as similar as those of CP binary cluster ions,a series of typical nonmetalbinary ones (see,Ref.23).These facts suggest that the speciation of AuS cluster ions probably comes from a constitution of relatively intact Au monoclusters,and thus imply in gaseousphase mechanism that a binary aggregation between Au monoclusters and S monoclusters or the confined polysulfur units might contribute to the formation of the AuS binary cluster ions.The aggregation may be based on covalent bindings between the end groups of the two clusters,or on a noncovalent interaction between the clusters,such as electrostatic gravitation between heteroatoms or heteromolecules,but its true mechanism remains to be resolved in future work.
An observation is demonstrated that Au/S target,triggered by gallium ion beam (69Ga＋) under experiment of high performance secondary ion mass spectrometry (TOF SIMS),does emit a considerable species of cluster negative ions with general formula of Au1－15S0－5(see Fig.1 and Table 1).Among them,a series of cluster ions with compositions of Au1－15S1－5 is recognized as AuS binary cluster ions,while other series with Au1－15 belongs to monocluster ions of pure ld,appearing in strong oddpredominance of their intensities with number of ld atom (see Fig.2).The AuS cluster ions can be characterized,in some aspects,by existence of the oddpredominance with magnitudes of ld atom (see Fig.3),inherited from the Au monoclusters; by lack of stoichiometric feature,showing that ld atoms range from 1 to 15 but sulfur atoms are always limited to 5 (see Table 1); by void of predominance as compositions as MenSn (for example,CunSn,see Table 2) or MenNn whose priority has been proved as an important feature prevailing in other binary cluster ions of metals (Me) plus sulfur (S) or other nonmetals (N); and by presence of special profiles as similar as those of CP binary cluster ions,a series of typical nonmetalbinary ones (see,Ref.23).These facts suggest that the speciation of AuS cluster ions probably comes from a constitution of relatively intact Au monoclusters,and thus imply in gaseousphase mechanism that a binary aggregation between Au monoclusters and S monoclusters or the confined polysulfur units might contribute to the formation of the AuS binary cluster ions.The aggregation may be based on covalent bindings between the end groups of the two clusters,or on a noncovalent interaction between the clusters,such as electrostatic gravitation between heteroatoms or heteromolecules,but its true mechanism remains to be resolved in future work.
