2004 Volume 20 Issue 4
2004, 20(04): 337-343
doi: 10.3866/PKU.WHXB20040401
Abstract:
The phase behaviors of Poly(N-isopropylacrylamide) (PNIPA) and Poly(N,N-diethylacrylamide) (PDEA) were investigated individually in mixed solvent of water-methanol using UV-Vis spectroscopy. The results show that the low critical solution temperature (TLCS) of PNIPA system under es reentrant change, while the TLCS of PDEA system shifts to higher temperature as the volume fraction of methanol (φ) increases. Refractive index measurement shows the formation of water-methanol complexes in PDEA system as well as in PNIPA system. To explain the different phase behavior of PDEA system from PNIPA, the conformational changes of PNIPA and PDEA molecular chains in mixed solvent of water-methanol were studied using the viscometry and Fourier Transform Infrared Spectroscopy. It was found that unlike the PNIPA, which underwent reentrant coil-to-globule-to-coil transition, the PDEA chains experienced homogeneous expansion-to-contraction-to-expansion as φ increased. It is believed that the different phase behavior of PDEA system from PNIPA is due to the more lipophilic property of PDEA structure than that of PNIPA, and consequently, the difference of solvating abilities of water-methanol complexes toward molecules PNIPA and PDEA.
The phase behaviors of Poly(N-isopropylacrylamide) (PNIPA) and Poly(N,N-diethylacrylamide) (PDEA) were investigated individually in mixed solvent of water-methanol using UV-Vis spectroscopy. The results show that the low critical solution temperature (TLCS) of PNIPA system under es reentrant change, while the TLCS of PDEA system shifts to higher temperature as the volume fraction of methanol (φ) increases. Refractive index measurement shows the formation of water-methanol complexes in PDEA system as well as in PNIPA system. To explain the different phase behavior of PDEA system from PNIPA, the conformational changes of PNIPA and PDEA molecular chains in mixed solvent of water-methanol were studied using the viscometry and Fourier Transform Infrared Spectroscopy. It was found that unlike the PNIPA, which underwent reentrant coil-to-globule-to-coil transition, the PDEA chains experienced homogeneous expansion-to-contraction-to-expansion as φ increased. It is believed that the different phase behavior of PDEA system from PNIPA is due to the more lipophilic property of PDEA structure than that of PNIPA, and consequently, the difference of solvating abilities of water-methanol complexes toward molecules PNIPA and PDEA.
2004, 20(04): 344-349
doi: 10.3866/PKU.WHXB20040402
Abstract:
Some alkyl bromides (CHBr3, CH2Br2, C2H5Br, C2H4Br2) have been studied at 234 nm and 267 nm in the time-of-flight mass spectrometer by means of multiphoton dissociation and ionization. Under the radiation of UV laser, alkyl bromides are photolyzed after absorbing one photon, release Br atoms, absorbing photons continuously, and (2+1)resonance-enhanced multiphoton ionization of Br atoms takes place. The Br atoms from the dissociation of the bromides are probably at the ground state Br(2P03/2) or at the excitated state Br*(2P01/2),and the branching ratio of Br atom N(Br*)/N(Br) is obtained. We find that the branching ratio at 267 nm is obviously bigger than the result at 234 nm. After discussing the mechanics of the multiphoton process, we conclude that the change tendency of the branching ratio with the wavelength is due to the different dissociation channels.
Some alkyl bromides (CHBr3, CH2Br2, C2H5Br, C2H4Br2) have been studied at 234 nm and 267 nm in the time-of-flight mass spectrometer by means of multiphoton dissociation and ionization. Under the radiation of UV laser, alkyl bromides are photolyzed after absorbing one photon, release Br atoms, absorbing photons continuously, and (2+1)resonance-enhanced multiphoton ionization of Br atoms takes place. The Br atoms from the dissociation of the bromides are probably at the ground state Br(2P03/2) or at the excitated state Br*(2P01/2),and the branching ratio of Br atom N(Br*)/N(Br) is obtained. We find that the branching ratio at 267 nm is obviously bigger than the result at 234 nm. After discussing the mechanics of the multiphoton process, we conclude that the change tendency of the branching ratio with the wavelength is due to the different dissociation channels.
2004, 20(04): 350-354
doi: 10.3866/PKU.WHXB20040403
Abstract:
The electronic spectra and photo-physical behaviors of oxonol compound which is a cynine-like dye with negative charge in solution have been studied. It was found that evident difference was observed for the absorption spectra of this compound when it was dissolved in protic and in aprotic solvents respectively. It could be considered as the neutralization of this compound in non-polar solvent and the change of the whole molecular conjugation of oxonol. As compared with usual intra-molecular conjugated charge transfer compounds different behaviors were observed either for absorption spectrum or for fluorescence spectrum of this compound. All of these differences for spectra, especially the behavior of negative solvato-chromism in polar solvents, and the effect of pH value on the tautomerization of compound have been discussed in detail.
The electronic spectra and photo-physical behaviors of oxonol compound which is a cynine-like dye with negative charge in solution have been studied. It was found that evident difference was observed for the absorption spectra of this compound when it was dissolved in protic and in aprotic solvents respectively. It could be considered as the neutralization of this compound in non-polar solvent and the change of the whole molecular conjugation of oxonol. As compared with usual intra-molecular conjugated charge transfer compounds different behaviors were observed either for absorption spectrum or for fluorescence spectrum of this compound. All of these differences for spectra, especially the behavior of negative solvato-chromism in polar solvents, and the effect of pH value on the tautomerization of compound have been discussed in detail.
2004, 20(04): 355-359
doi: 10.3866/PKU.WHXB20040404
Abstract:
Under the condition that negative effects of proton starvation and photo-generated electron-hole recombination to the Cr6+ photocatalytic reduction process were minimized for the photocatalytic activities of TiO2 and Ag/TiO2 for Cr6+ reduction were comparatively investigated. Combined with the results of EPR, the mechanism of silver modification for the enhanced photocatalytic reduction of Cr6+ on TiO2 was discussed. The result revealed that Cr6+ reduction by the UV-Ag/TiO2 process was more effective than the UV-TiO2 process under the same conditions. Electron transfer from surface Ti3+ to Cr6+ was the key step for Cr6+ reduction. Cr6+ photocatalytic reduction by directly capturing photo-generated electrons is possible, but it occurs mainly indirectly by getting electrons from surface Ti3+. The higher reduction activity of Ag/TiO2 photocatalyst came mainly from the higher number of surface Ti3+.
Under the condition that negative effects of proton starvation and photo-generated electron-hole recombination to the Cr6+ photocatalytic reduction process were minimized for the photocatalytic activities of TiO2 and Ag/TiO2 for Cr6+ reduction were comparatively investigated. Combined with the results of EPR, the mechanism of silver modification for the enhanced photocatalytic reduction of Cr6+ on TiO2 was discussed. The result revealed that Cr6+ reduction by the UV-Ag/TiO2 process was more effective than the UV-TiO2 process under the same conditions. Electron transfer from surface Ti3+ to Cr6+ was the key step for Cr6+ reduction. Cr6+ photocatalytic reduction by directly capturing photo-generated electrons is possible, but it occurs mainly indirectly by getting electrons from surface Ti3+. The higher reduction activity of Ag/TiO2 photocatalyst came mainly from the higher number of surface Ti3+.
2004, 20(04): 360-363
doi: 10.3866/PKU.WHXB20040405
Abstract:
The effect of free volume and water affinity of coating polymers on the corrosion protection of epoxy resin coatings was evaluated using a series of epoxy resin coatings obtained by curing o-cresol novolac epoxy resin with mixed hardener comprising novolac resin (NOV) and novolac acetate resin (NOVA) in different molar ratios. It was found that, as the molar content of NOVA increased, the room- temperature density of the cured resins decreased with increase in free volume and decrease in water affinity. The results of the water sorption of the resins suggested that water affinity is more important than free volume in determining water sorption of the coatings. While the water sorption of the coating decreased linearly with the decrease of water affinity of the coating, the corrosion protection of the coatings increased much more significantly. The great improvement in corrosion protection of the coating with less water affinity can be mainly attributed to the less amount of water that reaches the coating/metal interface as demonstrated by electrochemical impedance spectroscopic measurement. However, owing to the larger diameter of the water passages in the NOVA cured epoxy resin matrix, diffusion of hydrated ion to the polymer/coating interface is easier which resulted in an increase of the concentration of corrosive ions in the interfacial region, and therefore, the corrosion tendency of the metal substrate at the wetted places under the coating is larger than that of general coating.
The effect of free volume and water affinity of coating polymers on the corrosion protection of epoxy resin coatings was evaluated using a series of epoxy resin coatings obtained by curing o-cresol novolac epoxy resin with mixed hardener comprising novolac resin (NOV) and novolac acetate resin (NOVA) in different molar ratios. It was found that, as the molar content of NOVA increased, the room- temperature density of the cured resins decreased with increase in free volume and decrease in water affinity. The results of the water sorption of the resins suggested that water affinity is more important than free volume in determining water sorption of the coatings. While the water sorption of the coating decreased linearly with the decrease of water affinity of the coating, the corrosion protection of the coatings increased much more significantly. The great improvement in corrosion protection of the coating with less water affinity can be mainly attributed to the less amount of water that reaches the coating/metal interface as demonstrated by electrochemical impedance spectroscopic measurement. However, owing to the larger diameter of the water passages in the NOVA cured epoxy resin matrix, diffusion of hydrated ion to the polymer/coating interface is easier which resulted in an increase of the concentration of corrosive ions in the interfacial region, and therefore, the corrosion tendency of the metal substrate at the wetted places under the coating is larger than that of general coating.
2004, 20(04): 364-367
doi: 10.3866/PKU.WHXB20040406
Abstract:
Li2ZrO3 materials were synthesized under different conditions for CO2 absorption at high temperature. The crystal structure of the Li2ZrO3 material was analyzed using an X-ray powder diffractometer (XRD), the surface morphologies of all the samples were observed by using scanning electron microscopy (SEM) and the CO2-absorption ability of the Li2ZrO3 material was studied using a thermogravimetric (TG) analyzer. The experimental results show that the synthesis temperature affects both the structure (Fig.3) and the morphology (Fig.4) of the material, and hence its CO2 absorption ability. As a result, Li2ZrO3 materials synthesized at 800 ℃ exhibit superior absorption ability; whereas Li2ZrO3 materials derived under either excessively high or low synthesis temperatures show poorer absorption ability (Fig.2). In addition, the CO2 concentration in the atmosphere also has influence on the CO2 absorption rate of the Li2ZrO3 material. Li2ZrO3 materials display better absorption abilities at higher percentage concentrations of CO2 in the atmosphere (Fig.5). Furthermore, the Li2ZrO3 material in this research, which displayed better absorption ability, was synthesized without doping any elements.
Li2ZrO3 materials were synthesized under different conditions for CO2 absorption at high temperature. The crystal structure of the Li2ZrO3 material was analyzed using an X-ray powder diffractometer (XRD), the surface morphologies of all the samples were observed by using scanning electron microscopy (SEM) and the CO2-absorption ability of the Li2ZrO3 material was studied using a thermogravimetric (TG) analyzer. The experimental results show that the synthesis temperature affects both the structure (Fig.3) and the morphology (Fig.4) of the material, and hence its CO2 absorption ability. As a result, Li2ZrO3 materials synthesized at 800 ℃ exhibit superior absorption ability; whereas Li2ZrO3 materials derived under either excessively high or low synthesis temperatures show poorer absorption ability (Fig.2). In addition, the CO2 concentration in the atmosphere also has influence on the CO2 absorption rate of the Li2ZrO3 material. Li2ZrO3 materials display better absorption abilities at higher percentage concentrations of CO2 in the atmosphere (Fig.5). Furthermore, the Li2ZrO3 material in this research, which displayed better absorption ability, was synthesized without doping any elements.
2004, 20(04): 368-372
doi: 10.3866/PKU.WHXB20040407
Abstract:
Supramolecular assembly and chirality between a novel gemini surfactant (C12H24-α,ω-(C12H25N+(CH3)2Br-)2), (abbreviated as C12-C12-C12) and TPPS (tetrakis(4-sulfonatophenyl) porphine) at the air/water interface were investigated. It was found that although the gemini surfactant itself could not form a stable monolayer at the air/water interface, when there existed TPPS in the subphase, a stable complex monolayer could be formed. The complex monolayer could be transferred onto solid substrate by a horizontal lifting method. At a certain pH value of the subphase, TPPS could form a J-aggregate. It was further found that the J-aggregate of TPPS showed a strong split Cotton effect in the transferred film although both the gemini surfactant and TPPS are achiral. Further investigation through AFM measurements revealed that the nanothread formed in the transferred film was responsible for the chirality of the multilayer film. In addition, the two positive charge center of the gemini surfactant did not necessarily play the cooperative role in inducing the chirality of TPPS J-aggregate.
Supramolecular assembly and chirality between a novel gemini surfactant (C12H24-α,ω-(C12H25N+(CH3)2Br-)2), (abbreviated as C12-C12-C12) and TPPS (tetrakis(4-sulfonatophenyl) porphine) at the air/water interface were investigated. It was found that although the gemini surfactant itself could not form a stable monolayer at the air/water interface, when there existed TPPS in the subphase, a stable complex monolayer could be formed. The complex monolayer could be transferred onto solid substrate by a horizontal lifting method. At a certain pH value of the subphase, TPPS could form a J-aggregate. It was further found that the J-aggregate of TPPS showed a strong split Cotton effect in the transferred film although both the gemini surfactant and TPPS are achiral. Further investigation through AFM measurements revealed that the nanothread formed in the transferred film was responsible for the chirality of the multilayer film. In addition, the two positive charge center of the gemini surfactant did not necessarily play the cooperative role in inducing the chirality of TPPS J-aggregate.
2004, 20(04): 373-376
doi: 10.3866/PKU.WHXB20040408
Abstract:
Single-walled carbon nanotubes encapsulating C60 (peapods) C60@SWNTs have been successfully synthesized by a vapor diffusion method. High-resolution transmission electron microscopy (HRTEM) and Raman spectrum indicate high-density C60 chains inside the nanotubes. The distance between two adjacent C60 molecules in SWNTs is a little different from that in face centered cubic (fcc) C60 crystal,which reveals that there is a weak van der Waals interaction between the nanotubes and the encapsulated fullerenes. Moreover, in situ e-beam irradiation in the electron microscope caused coalescence of the neighboring C60 molecules inside the SWNTs.
Single-walled carbon nanotubes encapsulating C60 (peapods) C60@SWNTs have been successfully synthesized by a vapor diffusion method. High-resolution transmission electron microscopy (HRTEM) and Raman spectrum indicate high-density C60 chains inside the nanotubes. The distance between two adjacent C60 molecules in SWNTs is a little different from that in face centered cubic (fcc) C60 crystal,which reveals that there is a weak van der Waals interaction between the nanotubes and the encapsulated fullerenes. Moreover, in situ e-beam irradiation in the electron microscope caused coalescence of the neighboring C60 molecules inside the SWNTs.
2004, 20(04): 377-381
doi: 10.3866/PKU.WHXB20040409
Abstract:
LiV3O8 as a cathode material for lithium ion batteries was synthesized by solution reaction and low temperature calcinations technique with V2O5•nH2O hydro-gels and Li2CO3 as raw materials. The precursor and product were characterized by DTA-TG, XRD measurements. Electrochemical behavior of the LiV3O8 as a cathode material for rechargeable lithium-ion batteries was studied by galvanostatic charge-discharge measurement. The experiment showed that the active material LiV3O8 was of higher charge-discharge capacity and excellent cycling behavior. Lithium-ion chemical diffusion coefficient (DLi+) of the LiV3O8 electrode was determined by the potentiostatic intermittent titration technique (PITT).DLi+ values obtained were in the range of 10-8~10-10 cm2•s-1,depending on x-values in Li1+xV3O8.The activation energy of lithium-ion diffusion (Ea) obtained was in the range of 25~42 kJ•mol-1(x=0.18~2.5).
LiV3O8 as a cathode material for lithium ion batteries was synthesized by solution reaction and low temperature calcinations technique with V2O5•nH2O hydro-gels and Li2CO3 as raw materials. The precursor and product were characterized by DTA-TG, XRD measurements. Electrochemical behavior of the LiV3O8 as a cathode material for rechargeable lithium-ion batteries was studied by galvanostatic charge-discharge measurement. The experiment showed that the active material LiV3O8 was of higher charge-discharge capacity and excellent cycling behavior. Lithium-ion chemical diffusion coefficient (DLi+) of the LiV3O8 electrode was determined by the potentiostatic intermittent titration technique (PITT).DLi+ values obtained were in the range of 10-8~10-10 cm2•s-1,depending on x-values in Li1+xV3O8.The activation energy of lithium-ion diffusion (Ea) obtained was in the range of 25~42 kJ•mol-1(x=0.18~2.5).
2004, 20(04): 382-385
doi: 10.3866/PKU.WHXB20040410
Abstract:
The dissociative adsorption of ethylene glycol (EG) on Pt(111) electrode has been investigated with electrochemical cyclic voltammetry and programmed potential step technique. The quantitative results demonstrated that the average rate of dissociative adsorption of ethylene glycol on Pt(111) electrode depends on electrode potentials, yielding a distribution of volcanic shape on adsorption potentials between -0.20 and 0.35 V with the maximum value of 3.90×10-12 mol•cm-2•s-1 located near 0.10 V(vs SCE).From the variation of the quantity of dissociative adsorbates determined through the oxidation charge with adsorption time (tad), the initial rate (vi) of this surface reaction has been evaluated quantitatively. The maximum of vi was ascertained to be 4.35×10-12 mol•cm-2•s-1 at 0.10 V for a solution containing 2×10-3 mol•L-1 EG.
The dissociative adsorption of ethylene glycol (EG) on Pt(111) electrode has been investigated with electrochemical cyclic voltammetry and programmed potential step technique. The quantitative results demonstrated that the average rate of dissociative adsorption of ethylene glycol on Pt(111) electrode depends on electrode potentials, yielding a distribution of volcanic shape on adsorption potentials between -0.20 and 0.35 V with the maximum value of 3.90×10-12 mol•cm-2•s-1 located near 0.10 V(vs SCE).From the variation of the quantity of dissociative adsorbates determined through the oxidation charge with adsorption time (tad), the initial rate (vi) of this surface reaction has been evaluated quantitatively. The maximum of vi was ascertained to be 4.35×10-12 mol•cm-2•s-1 at 0.10 V for a solution containing 2×10-3 mol•L-1 EG.
2004, 20(04): 386-390
doi: 10.3866/PKU.WHXB20040411
Abstract:
Carboxymethylcellulose(CMC) hydrogels have attracted attention as biodegradation absorbent materials in agriculture and forestry. It is important to investigate the biodegradation behavior and kinetics of the bio-degradable reaction. In this paper, CMC hydrogel was prepared by crosslinking with aluminum chloride. The effects of the substrate concentration, enzyme concentration and reaction temperature on the degradation rates were investigated. At the same time, the kinetics of the enzymatic degradation and the relationship between the apparent-activation energy and enzyme concentration were also discussed in detail. The results showed that the optimal temperature for the enzymatic reaction was 37 ℃.The reaction orders for the substrate and enzyme were 1 and 1.2, respectively. A new kinetic model for CMC hydrogel heterogeneous degradation was proposed which was different from the traditional Michaelis-Menten kinetics. The relationship between the apparent-activation energy and the enzyme concentration was also established.
Carboxymethylcellulose(CMC) hydrogels have attracted attention as biodegradation absorbent materials in agriculture and forestry. It is important to investigate the biodegradation behavior and kinetics of the bio-degradable reaction. In this paper, CMC hydrogel was prepared by crosslinking with aluminum chloride. The effects of the substrate concentration, enzyme concentration and reaction temperature on the degradation rates were investigated. At the same time, the kinetics of the enzymatic degradation and the relationship between the apparent-activation energy and enzyme concentration were also discussed in detail. The results showed that the optimal temperature for the enzymatic reaction was 37 ℃.The reaction orders for the substrate and enzyme were 1 and 1.2, respectively. A new kinetic model for CMC hydrogel heterogeneous degradation was proposed which was different from the traditional Michaelis-Menten kinetics. The relationship between the apparent-activation energy and the enzyme concentration was also established.
2004, 20(04): 391-395
doi: 10.3866/PKU.WHXB20040412
Abstract:
Sm0.5Sr0.5CoO3 (SSC) powders were prepared using solid-state reaction. The XRD pattern of SSC corresponded to a desired perovskite structure. SSC electrodes sintered at various temperatures (1173~1373 K) and SSC-La0.8Sr0.2Ga0.8Mg0.15Co0.05O3 (SSC-LSGMC5), SSC- La0.8Sr0.2Ga0.8Mg0.09Co0.11O3 (SSC-LSGMC11) composite cathodes sintered at 1173 K were studied using SEM ,impedance spectroscopy, and DC(direct current) polarization. The electrodes studied were prepared on La0.9Sr0.1Ga0.8Mg0.2O3 electrolytes using screen-printing. The particle size of SSC electrodes increased with sintering temperatures, and the porosity decreased accordingly. The addition of LSGMC5 and LSGMC11 into SSC had no obvious effect on the microstructure of SSC electrodes. The results of AC (alternative current) impedance spectroscopy and DC polarization showed that the activity of SSC electrodes increased with decreasing sintering temperature, and the optimum sintering temperature for SSC electrodes was about 1173 K. The addition of LSGMC5 or LSGMC11 into SSC improved both the activity and stability of SSC electrodes significantly.
Sm0.5Sr0.5CoO3 (SSC) powders were prepared using solid-state reaction. The XRD pattern of SSC corresponded to a desired perovskite structure. SSC electrodes sintered at various temperatures (1173~1373 K) and SSC-La0.8Sr0.2Ga0.8Mg0.15Co0.05O3 (SSC-LSGMC5), SSC- La0.8Sr0.2Ga0.8Mg0.09Co0.11O3 (SSC-LSGMC11) composite cathodes sintered at 1173 K were studied using SEM ,impedance spectroscopy, and DC(direct current) polarization. The electrodes studied were prepared on La0.9Sr0.1Ga0.8Mg0.2O3 electrolytes using screen-printing. The particle size of SSC electrodes increased with sintering temperatures, and the porosity decreased accordingly. The addition of LSGMC5 and LSGMC11 into SSC had no obvious effect on the microstructure of SSC electrodes. The results of AC (alternative current) impedance spectroscopy and DC polarization showed that the activity of SSC electrodes increased with decreasing sintering temperature, and the optimum sintering temperature for SSC electrodes was about 1173 K. The addition of LSGMC5 or LSGMC11 into SSC improved both the activity and stability of SSC electrodes significantly.
2004, 20(04): 396-399
doi: 10.3866/PKU.WHXB20040413
Abstract:
Two high frequency dielectric systems of ZnO-B2O3-SiO2 and BaO-PbO-Nd2O3- Bi2O3-TiO2 were prepared by conventional ceramics technology. Through XRD analysis, the main crystal phases were determined. The volume percentage contents of each phase were calculated according to the X-ray diffraction peak intensity. Then, these data were introduced into Lichnetecker Law, from which the dielectric properties of the systems were obtained. This is a new way to analyze quantitative relationship between the dielectric properties and phase contents of dielectric materials.
Two high frequency dielectric systems of ZnO-B2O3-SiO2 and BaO-PbO-Nd2O3- Bi2O3-TiO2 were prepared by conventional ceramics technology. Through XRD analysis, the main crystal phases were determined. The volume percentage contents of each phase were calculated according to the X-ray diffraction peak intensity. Then, these data were introduced into Lichnetecker Law, from which the dielectric properties of the systems were obtained. This is a new way to analyze quantitative relationship between the dielectric properties and phase contents of dielectric materials.
2004, 20(04): 400-404
doi: 10.3866/PKU.WHXB20040414
Abstract:
The mechanism of reaction Br2+2HI=2HBr+I2 has been carefully investigated with density functional theory(DFT) at B3LYP/3-21G** level, and a series of four-centred and three-centred transition states have been obtained. The activation energies of the bimolecular elementary reactions Br2+HI→HBr+IBr and IBr+HI→I2+HBr(81.02 and 121.08 kJ•mol-1, respectively) are less than the dissociation energy of Br2, HI and IBr(249.21, 320.16, and 232.42 kJ•mol-1). It is thus theoretically proved that the title reaction occurs more easily in the bimolecular form with two medium steps. And it was also found that the reaction of I atom and Br2 to form stable IBr2 molecule is a process without energy barrier, and the energy barrier for decomposition of IBr2 into IBr and Br atom is 70.88 kJ•mol-1.
The mechanism of reaction Br2+2HI=2HBr+I2 has been carefully investigated with density functional theory(DFT) at B3LYP/3-21G** level, and a series of four-centred and three-centred transition states have been obtained. The activation energies of the bimolecular elementary reactions Br2+HI→HBr+IBr and IBr+HI→I2+HBr(81.02 and 121.08 kJ•mol-1, respectively) are less than the dissociation energy of Br2, HI and IBr(249.21, 320.16, and 232.42 kJ•mol-1). It is thus theoretically proved that the title reaction occurs more easily in the bimolecular form with two medium steps. And it was also found that the reaction of I atom and Br2 to form stable IBr2 molecule is a process without energy barrier, and the energy barrier for decomposition of IBr2 into IBr and Br atom is 70.88 kJ•mol-1.
2004, 20(04): 405-408
doi: 10.3866/PKU.WHXB20040415
Abstract:
Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) has been successfully applied to quantifying analysis on layer-by-layer assembled macromolecular films containing diazo-resins. From the changes of -CH2-peaks,uniform adsorption of each single layer of macromolecules has been identified. We calculated the ratio of the decomposited -N≡N+ groups which form covalent bond to all -N≡N+ groups from the characteristic -N≡N+ absorption peaks. The results have provided direct and detailed information on the assembling process.
Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) has been successfully applied to quantifying analysis on layer-by-layer assembled macromolecular films containing diazo-resins. From the changes of -CH2-peaks,uniform adsorption of each single layer of macromolecules has been identified. We calculated the ratio of the decomposited -N≡N+ groups which form covalent bond to all -N≡N+ groups from the characteristic -N≡N+ absorption peaks. The results have provided direct and detailed information on the assembling process.
2004, 20(04): 409-413
doi: 10.3866/PKU.WHXB20040416
Abstract:
Well-aligned carbon nanotubes with multiwall structure were fabricated by using a vapor-phase deposition technique based on the pyrolysis of iron phthalocyanine. The average diameter of single nanotube is about 25 nm, and the length of each is from 4 to 5 μm. The result of measure on the planar field emission of the aligned carbon nanotubes shows a very powerful ability of as-synthesized carbon nanotubes in the field emission with a turn-on voltage of 1.28 V•μm-1 and a threshold voltage of 2.3 V•μm-1. The field emission image of the aligned carbon nanotubes was also observed through using a field emission microscope, and it was found that the field emission of the carbon nanotubes was mainly centered on the edge of the thin film sample, which was attributed to the screening effect caused by the overlarge density of the carbon nanotubes.
Well-aligned carbon nanotubes with multiwall structure were fabricated by using a vapor-phase deposition technique based on the pyrolysis of iron phthalocyanine. The average diameter of single nanotube is about 25 nm, and the length of each is from 4 to 5 μm. The result of measure on the planar field emission of the aligned carbon nanotubes shows a very powerful ability of as-synthesized carbon nanotubes in the field emission with a turn-on voltage of 1.28 V•μm-1 and a threshold voltage of 2.3 V•μm-1. The field emission image of the aligned carbon nanotubes was also observed through using a field emission microscope, and it was found that the field emission of the carbon nanotubes was mainly centered on the edge of the thin film sample, which was attributed to the screening effect caused by the overlarge density of the carbon nanotubes.
2004, 20(04): 414-416
doi: 10.3866/PKU.WHXB20040417
Abstract:
TiO2:Sb nanoscale thin films were deposited on glass substrates by the sol-gel method. The influence of the dopant density on the photo-induced superhydrophilicity of the thin films was investigated and the influences on the structure and the phase transformation of the thin films were studied by X-ray diffraction (XRD) and Raman spectra. The results show that the pure TiO2 thin film composed of not only amorphous but also brookite and anatase. Dopant Sb enhances the crystallization rate of the TiO2 from amorphous to brookite and anatase phase. After doping proper amount of Sb, the thin films show more photo-induced superhydrophilicity than the pure TiO2 thin film as well. The crystalline size of the TiO2:Sb thin films is about 13.3~20.0 nm calculated from the XRD patterns.
TiO2:Sb nanoscale thin films were deposited on glass substrates by the sol-gel method. The influence of the dopant density on the photo-induced superhydrophilicity of the thin films was investigated and the influences on the structure and the phase transformation of the thin films were studied by X-ray diffraction (XRD) and Raman spectra. The results show that the pure TiO2 thin film composed of not only amorphous but also brookite and anatase. Dopant Sb enhances the crystallization rate of the TiO2 from amorphous to brookite and anatase phase. After doping proper amount of Sb, the thin films show more photo-induced superhydrophilicity than the pure TiO2 thin film as well. The crystalline size of the TiO2:Sb thin films is about 13.3~20.0 nm calculated from the XRD patterns.
2004, 20(04): 417-420
doi: 10.3866/PKU.WHXB20040418
Abstract:
NiO/RuO2 composite materials were prepared by chemical co-precipitation method, physical method and then heat-treatment. XRD spectra indicated that RuO2 particles were coated by NiO particles. Introduction of RuO2 into NiO electrodes improved the capacitive properties of electrodes and widened the range of work potential more than onefold. A maximum specific capacitance of 210 F•g-1 and specific energy of 14.2 W•h•kg-1 were obtained for NiO-based composite electrodes with 10% RuO2 in 1 mol•L-1 KOH solution. By comparison of the chemical and physical introduction on the specific capacitance, the chemically modified composite electrodes had more stable properties. After 200 cycles, the specific capacitance of the chemical composite electrodes with 5% RuO2 kept 95% over the initial specific capacitance, but the physical composite electrodes were only 79%.
NiO/RuO2 composite materials were prepared by chemical co-precipitation method, physical method and then heat-treatment. XRD spectra indicated that RuO2 particles were coated by NiO particles. Introduction of RuO2 into NiO electrodes improved the capacitive properties of electrodes and widened the range of work potential more than onefold. A maximum specific capacitance of 210 F•g-1 and specific energy of 14.2 W•h•kg-1 were obtained for NiO-based composite electrodes with 10% RuO2 in 1 mol•L-1 KOH solution. By comparison of the chemical and physical introduction on the specific capacitance, the chemically modified composite electrodes had more stable properties. After 200 cycles, the specific capacitance of the chemical composite electrodes with 5% RuO2 kept 95% over the initial specific capacitance, but the physical composite electrodes were only 79%.
2004, 20(04): 421-423
doi: 10.3866/PKU.WHXB20040419
Abstract:
An O/W type emulsion was made from mixing of oleic acid kerosene solution, NaOH aqueous and CTAB aqueous. It was found that addition of the emulsion could make some Daniell cells, including Cu-Mg, Cu-Al, Cu-Zn, Cu-Fe cell; produce evident electrochemical oscillations which could last more than 4 h in both cell and electrode reactions. Reversible oscillations in the cell were also found after electrified with 2 V, 50 Hz or 100 Hz alternating current for 4 h. The oscillatory mechanism was explained by the adsorption of surfactant on the surface of electrode and emulsion structure changes according to observe under a microscope. The mixing energy of emulsion takes part in the electrochemical reaction.
An O/W type emulsion was made from mixing of oleic acid kerosene solution, NaOH aqueous and CTAB aqueous. It was found that addition of the emulsion could make some Daniell cells, including Cu-Mg, Cu-Al, Cu-Zn, Cu-Fe cell; produce evident electrochemical oscillations which could last more than 4 h in both cell and electrode reactions. Reversible oscillations in the cell were also found after electrified with 2 V, 50 Hz or 100 Hz alternating current for 4 h. The oscillatory mechanism was explained by the adsorption of surfactant on the surface of electrode and emulsion structure changes according to observe under a microscope. The mixing energy of emulsion takes part in the electrochemical reaction.
2004, 20(04): 424-427
doi: 10.3866/PKU.WHXB20040420
Abstract:
The functional photocatalysts of high photocatalytic reactivity under visible light irradiation were prepared by loading precious metals on the vanadium ion implanted titanium oxide. The photocatalytic hydrolysis reaction of methylacetylene was studied under the visible light and solar beam. Those modified titanium oxides were used to construct conversion system of solar to chemical energy. It was found from experimental results that existence of precious metals on the V/TiO2 photocatalysts has the advantage of promotion of hydrogenation reaction in photocatalytic hydrolysis reaction of methylacetylene, and increase of propene product. The photocatalytic reactivities under visible light irradiation have a close relationship with oxidation states of the precious metals on titanium oxide and it is necessary for increasing photcatalytic reactivities that precious metals be reduced to 0 valence.
The functional photocatalysts of high photocatalytic reactivity under visible light irradiation were prepared by loading precious metals on the vanadium ion implanted titanium oxide. The photocatalytic hydrolysis reaction of methylacetylene was studied under the visible light and solar beam. Those modified titanium oxides were used to construct conversion system of solar to chemical energy. It was found from experimental results that existence of precious metals on the V/TiO2 photocatalysts has the advantage of promotion of hydrogenation reaction in photocatalytic hydrolysis reaction of methylacetylene, and increase of propene product. The photocatalytic reactivities under visible light irradiation have a close relationship with oxidation states of the precious metals on titanium oxide and it is necessary for increasing photcatalytic reactivities that precious metals be reduced to 0 valence.
2004, 20(04): 428-431
doi: 10.3866/PKU.WHXB20040421
Abstract:
Three Au/SnO2 catalysts with different ld loading were prepared via deposition-precipitation method, and characterized by XRD and UV-Vis. The effects of pH of deposition solution, Au loading and pretreatment condition on the catalytic activity of Au/SnO2 catalysts for low-temperature CO oxidation were investigated. The results showed that (1) the mean Au particle size of Au/SnO2 catalyst prepared at pH=9~10 deposition condition was the smallest among the samples obtained at different deposition pH; (2) the catalytic activity decreased with the increase of Au loading; (3) among the 2%Au/SnO2 catalyst samples calcined at different temperatures in air for 4 h, the catalytic activity of the sample calcined at 473 K was the highest; (4) the catalyst samples pretreated at low temperature in H2 exhibited higher activity, and the activity of the sample obtained at 373 K for 2 h was the highest among all Au/SnO2 samples in this work.
Three Au/SnO2 catalysts with different ld loading were prepared via deposition-precipitation method, and characterized by XRD and UV-Vis. The effects of pH of deposition solution, Au loading and pretreatment condition on the catalytic activity of Au/SnO2 catalysts for low-temperature CO oxidation were investigated. The results showed that (1) the mean Au particle size of Au/SnO2 catalyst prepared at pH=9~10 deposition condition was the smallest among the samples obtained at different deposition pH; (2) the catalytic activity decreased with the increase of Au loading; (3) among the 2%Au/SnO2 catalyst samples calcined at different temperatures in air for 4 h, the catalytic activity of the sample calcined at 473 K was the highest; (4) the catalyst samples pretreated at low temperature in H2 exhibited higher activity, and the activity of the sample obtained at 373 K for 2 h was the highest among all Au/SnO2 samples in this work.
2004, 20(04): 432-435
doi: 10.3866/PKU.WHXB20040422
Abstract:
To increase the specific capacitance of supercapacitors based on carbon nanotubes (CNTs),activation and surface modification were carried out by using KOH and concentrated nitric acid respectively. The materials were analyzed by transmission electron microscopy (TEM), N2 adsorption and infrared spectra (IR). The effect of activation and surface modification on the performance of the CNTs supercapacitors was also studied by cyclic voltammetry and galvanostatic charge/discharge. The results showed that activation enlarged the BET specific surface area of the CNTs and hence increased the specific capacitance of the supercapacitors from 43 F•g-1 to 73 F•g-1.By surface modification, large quantities of electroactive functional groups were adsorbed on the surface of the CNTs, thus pseudocapacitance was induced and the specific capacitance was further increased to 94 F•g-1.
To increase the specific capacitance of supercapacitors based on carbon nanotubes (CNTs),activation and surface modification were carried out by using KOH and concentrated nitric acid respectively. The materials were analyzed by transmission electron microscopy (TEM), N2 adsorption and infrared spectra (IR). The effect of activation and surface modification on the performance of the CNTs supercapacitors was also studied by cyclic voltammetry and galvanostatic charge/discharge. The results showed that activation enlarged the BET specific surface area of the CNTs and hence increased the specific capacitance of the supercapacitors from 43 F•g-1 to 73 F•g-1.By surface modification, large quantities of electroactive functional groups were adsorbed on the surface of the CNTs, thus pseudocapacitance was induced and the specific capacitance was further increased to 94 F•g-1.
2004, 20(04): 436-439
doi: 10.3866/PKU.WHXB20040423
Abstract:
The methanol electrooxidation behaviors on commercial carbon supported Pt and PtRu catalysts in acid solution were compared by carrying out electrochemical studies. The potentiodynamic and potentiostatic experimental results showed that the PtRu/C has a higher electrocatalytic activity for the electrocatalytic oxidation of methanol than the Pt/C.Alloy formation of Ru with Pt not only modified the characteristics of H2 adsorption on the surface of catalyst but also shifted cathodically the reduction peaks of metal oxide on the cathodic sweep with respect to Pt/C. The interaction of CH3OH with Ru is a temperatureactivated process requiring elevated temperature.
The methanol electrooxidation behaviors on commercial carbon supported Pt and PtRu catalysts in acid solution were compared by carrying out electrochemical studies. The potentiodynamic and potentiostatic experimental results showed that the PtRu/C has a higher electrocatalytic activity for the electrocatalytic oxidation of methanol than the Pt/C.Alloy formation of Ru with Pt not only modified the characteristics of H2 adsorption on the surface of catalyst but also shifted cathodically the reduction peaks of metal oxide on the cathodic sweep with respect to Pt/C. The interaction of CH3OH with Ru is a temperatureactivated process requiring elevated temperature.
2004, 20(04): 440-444
doi: 10.3866/PKU.WHXB20040424
Abstract:
In this paper, the interaction of Cu(phen)22+ (phen=1,10-phenanthroline) with 6-mercaptopurine(6-MP) in Tris-NaCl buffer solution(pH=7.2) has been investigated by electrochemical techniques including cyclic voltammetry, differential pulse voltammetry, rotating disk electrode measurements, AC(alternative current) impedance and its data fitting. The results show that the interaction of Cu(phen)22+ with 6-MP is proved to exist under diffusion control or electrochemistry control. The cyclic voltammograms assume a couple of redox peaks and the electrochemical impedance spectra for Cu(phen)22+ on the platinum disk electrode show two obvious capacitance arches in the absence or presence of 6-MP.However,peak potentials shifted negatively, peak currents decreased significantly, and both the charge transfer resistance and the electrochemical absorption-desorption resistance increased in the presence of 6-MP compared with those in the absence of 6-MP. On the other hand, with the increase of the rotating rate, the values of the charge transfer resistance and the electrochemical absorption-desorption resistance decreased, while the double-layer capacitance and the absorption-desorption capacitance showed an enhanced and a reduced tendences in the absence or presence of 6-MP, respectively.
In this paper, the interaction of Cu(phen)22+ (phen=1,10-phenanthroline) with 6-mercaptopurine(6-MP) in Tris-NaCl buffer solution(pH=7.2) has been investigated by electrochemical techniques including cyclic voltammetry, differential pulse voltammetry, rotating disk electrode measurements, AC(alternative current) impedance and its data fitting. The results show that the interaction of Cu(phen)22+ with 6-MP is proved to exist under diffusion control or electrochemistry control. The cyclic voltammograms assume a couple of redox peaks and the electrochemical impedance spectra for Cu(phen)22+ on the platinum disk electrode show two obvious capacitance arches in the absence or presence of 6-MP.However,peak potentials shifted negatively, peak currents decreased significantly, and both the charge transfer resistance and the electrochemical absorption-desorption resistance increased in the presence of 6-MP compared with those in the absence of 6-MP. On the other hand, with the increase of the rotating rate, the values of the charge transfer resistance and the electrochemical absorption-desorption resistance decreased, while the double-layer capacitance and the absorption-desorption capacitance showed an enhanced and a reduced tendences in the absence or presence of 6-MP, respectively.
2004, 20(04): 445-448
doi: 10.3866/PKU.WHXB20040425
Abstract:
A new experimental method for solubility determination was developed based upon optical and chemical principles. It makes the determination of solubility data more objective and accurate. With the aid of laser, the novel method will be much helpful in getting solid-liquid equilibrium data especially for slight solubility, which is always appearing, in environment issue. It can be widely used not only for traditional chemical engineering research but also for the field of environment-chemical engineering research, which is a boom cross-discipline, especially applicable for water solubility determination. Using this method, solubility data for the binary systems of terephthalic acid+water and terephthalic acid+acetic acid have been measured in a temperature range of 300 to 445 K and all the experimental data have been correlated by Wilson equation and Wilson-T equation. It indicats that Wilson-T model will be better than Wilson model.
A new experimental method for solubility determination was developed based upon optical and chemical principles. It makes the determination of solubility data more objective and accurate. With the aid of laser, the novel method will be much helpful in getting solid-liquid equilibrium data especially for slight solubility, which is always appearing, in environment issue. It can be widely used not only for traditional chemical engineering research but also for the field of environment-chemical engineering research, which is a boom cross-discipline, especially applicable for water solubility determination. Using this method, solubility data for the binary systems of terephthalic acid+water and terephthalic acid+acetic acid have been measured in a temperature range of 300 to 445 K and all the experimental data have been correlated by Wilson equation and Wilson-T equation. It indicats that Wilson-T model will be better than Wilson model.