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2001 Volume 17 Issue 3
2001, 17(03): 193-195
doi: 10.3866/PKU.WHXB20010301
Abstract:
2001, 17(03): 196-200
doi: 10.3866/PKU.WHXB20010302
Abstract:
Based on the calculated band structures of four onedimensional C36 m odel polymers by the semiempirical selfconsistent field crystal orbital method , and provided by a half filled band model with doping of an electron per unit c ell, the intermolecular electronphonon couplings of the polymers a estimated b y means of the meanfield approximation and the deformation potential theory. T he influences of the couplings on the superconductivity and metalinsulator pha se transition temperatures are also investigated. It is found that the intermole cular electronphonon couplings of all the model polymers studied here are very small,having the values of ≈10－5～10－4, being two or three orders of magnitu de less than that of a 1D C60 polymer (=0.054). These very small values of coupl ing constants lead to extremely low superconducting phase transition and metal insulator transition temperatures, which indicate that the intermolecular coupli ngs in 1D C36 polymers have no significant influence on these phase transitions.
Based on the calculated band structures of four onedimensional C36 m odel polymers by the semiempirical selfconsistent field crystal orbital method , and provided by a half filled band model with doping of an electron per unit c ell, the intermolecular electronphonon couplings of the polymers a estimated b y means of the meanfield approximation and the deformation potential theory. T he influences of the couplings on the superconductivity and metalinsulator pha se transition temperatures are also investigated. It is found that the intermole cular electronphonon couplings of all the model polymers studied here are very small,having the values of ≈10－5～10－4, being two or three orders of magnitu de less than that of a 1D C60 polymer (=0.054). These very small values of coupl ing constants lead to extremely low superconducting phase transition and metal insulator transition temperatures, which indicate that the intermolecular coupli ngs in 1D C36 polymers have no significant influence on these phase transitions.
2001, 17(03): 201-205
doi: 10.3866/PKU.WHXB20010303
Abstract:
The ignition processes for the catalytic partial oxidation of methane( POM) to synthesis gas over the oxidized nickel, metallic nickel as well as Pta dded oxidized nickel catalysts (represented as NiO, Ni0 and PtNiO, respectivel y) were studied by temperatureprogrammed surface reaction (TPSR)technique. The results showed that the ignition behavior for POM on NiO was almost similar to that on Ni0 in the reacting atmosphere of CH4 and O2, Ni0 was first oxidized to NiO, then the deep oxidation of methane took place on NiO at T< 760 ℃. POM gr adually initiated at ～ 770 ℃ on Ni0 and NiO catalysts, however, even at ～ 520 ℃ could POM rapidly take place on PtNiO catalyst. the catalytic performance of POM initiated on PtNiO catalyst at about 500 ℃ in a fluidized bed was the same as that on Ni0, which indicated that the addition of Pt was beneficial to t he reduction of NiO to active Ni0, therefore the addition of Pt reduced the init ial temperature for POM.
The ignition processes for the catalytic partial oxidation of methane( POM) to synthesis gas over the oxidized nickel, metallic nickel as well as Pta dded oxidized nickel catalysts (represented as NiO, Ni0 and PtNiO, respectivel y) were studied by temperatureprogrammed surface reaction (TPSR)technique. The results showed that the ignition behavior for POM on NiO was almost similar to that on Ni0 in the reacting atmosphere of CH4 and O2, Ni0 was first oxidized to NiO, then the deep oxidation of methane took place on NiO at T< 760 ℃. POM gr adually initiated at ～ 770 ℃ on Ni0 and NiO catalysts, however, even at ～ 520 ℃ could POM rapidly take place on PtNiO catalyst. the catalytic performance of POM initiated on PtNiO catalyst at about 500 ℃ in a fluidized bed was the same as that on Ni0, which indicated that the addition of Pt was beneficial to t he reduction of NiO to active Ni0, therefore the addition of Pt reduced the init ial temperature for POM.
2001, 17(03): 206-209
doi: 10.3866/PKU.WHXB20010304
Abstract:
Cyclic voltammetry was used to study the electroreduction of Ho(III) i n Ho(NO3)3LiClO4DMF. The results showed that traces of water in this system blocked the electroreduct ion of Ho(III) by forming LiOH and Ho(OH)3 films on the electrode surface. Cod eposition of Ho and Ni was studied in dimethylformamide by cyclic voltammetry an d potentiostatic deposition at room temperature. Potentiostatic deposition was u sed to prepare HoNi alloys. EDAX, SEM and XRD were used to analyze the films. The results indicated that black, adhesive and amorphous HoNi alloy films on C u were produced where the content of Ho could be as high as 72.7 ％.
Cyclic voltammetry was used to study the electroreduction of Ho(III) i n Ho(NO3)3LiClO4DMF. The results showed that traces of water in this system blocked the electroreduct ion of Ho(III) by forming LiOH and Ho(OH)3 films on the electrode surface. Cod eposition of Ho and Ni was studied in dimethylformamide by cyclic voltammetry an d potentiostatic deposition at room temperature. Potentiostatic deposition was u sed to prepare HoNi alloys. EDAX, SEM and XRD were used to analyze the films. The results indicated that black, adhesive and amorphous HoNi alloy films on C u were produced where the content of Ho could be as high as 72.7 ％.
2001, 17(03): 210-215
doi: 10.3866/PKU.WHXB20010305
Abstract:
On the basis of the N3 and N－3molecular geometries optimized at the B 3P86/6311＋G level,six different coupling mechanism have been determined for the N3＋N－3electron transfer system in the ground state,the corresponding geom etrical properties,activation energy,stabilization energy,the coupling matrix el ements and the density of the electronic state also have been predicted for the various coupling encounter complexes,the electron transfer rates have been calcu lated by using the ldenrule scheme,the effect of the coupling pathways on th e electron transfer rate has been discussed.
On the basis of the N3 and N－3molecular geometries optimized at the B 3P86/6311＋G level,six different coupling mechanism have been determined for the N3＋N－3electron transfer system in the ground state,the corresponding geom etrical properties,activation energy,stabilization energy,the coupling matrix el ements and the density of the electronic state also have been predicted for the various coupling encounter complexes,the electron transfer rates have been calcu lated by using the ldenrule scheme,the effect of the coupling pathways on th e electron transfer rate has been discussed.
2001, 17(03): 216-221
doi: 10.3866/PKU.WHXB20010306
Abstract:
A new method of liquid impregnation combining air oxidition is employe d to modify the surface and pore structure of PANbased activated carbon (PAN ACF) under moderate condition.By this method,a molecular sieve type PANACF is prepared having high selectivity to separate N2 from O2.TGADGA,electronic bala nce and XPS are used to characterize the performance and surface chemistry of th e samples.The results show that PANACF impregnated with condensed coal tar has a slight weight loss during 100～400 ℃,the benzenoid and heterocyclic compound graft with carbon fiber by the aid of oxygen molecule to tailor the pore and su rface structure of fibers.After oxidizing by air,the selectivity and adsorptive capacity of PANACF are improved significantly,the selectivity reaches 5.6 of N 2/O2.There are many kinds of function group such as hydroxyl group,ether,carbony l and carboxyl after the impregnation of PANACF with condensed coal tar and ox idized by air,during oxidition the content of various function group changes,gra phitelike carbon increases with the increase of impregnated concentration.
A new method of liquid impregnation combining air oxidition is employe d to modify the surface and pore structure of PANbased activated carbon (PAN ACF) under moderate condition.By this method,a molecular sieve type PANACF is prepared having high selectivity to separate N2 from O2.TGADGA,electronic bala nce and XPS are used to characterize the performance and surface chemistry of th e samples.The results show that PANACF impregnated with condensed coal tar has a slight weight loss during 100～400 ℃,the benzenoid and heterocyclic compound graft with carbon fiber by the aid of oxygen molecule to tailor the pore and su rface structure of fibers.After oxidizing by air,the selectivity and adsorptive capacity of PANACF are improved significantly,the selectivity reaches 5.6 of N 2/O2.There are many kinds of function group such as hydroxyl group,ether,carbony l and carboxyl after the impregnation of PANACF with condensed coal tar and ox idized by air,during oxidition the content of various function group changes,gra phitelike carbon increases with the increase of impregnated concentration.
2001, 17(03): 222-228
doi: 10.3866/PKU.WHXB20010307
Abstract:
With the spectral measurements of molecular absorption, fluorescence, and resonance light scattering, the binding mode of neutral red (NR) with double stranded DNA has been characterized in a neutral aqueous medium. Depending on t he molar ratio R of NR: DNA, it was found that the binding involves in two proce sses at pH 7.63 and ionic strength lower than 0.01. The first process occurs in R > 2.22, where enhanced resonance light scattering was found, indicating the ag gregation of NR molecules on the molecular surface of double stranded DNA. Scatc hard plot was used to discuss the aggregation features based on the measurements of RLS data. The second process occurs in R < 2.22, characterized by bathochrom ic and hyperchromic molecular absorption of the interacting system, indicating t he intercalative binding of NR into the base pairs of the double stranded DNA mo lecules. Energy transfer from DNA to NR molecules in the second interacting proc ess occurs, resulting in strong enhancement of fluorescence, which proves NR can be used as a fluorescent probe as DNA structure.
With the spectral measurements of molecular absorption, fluorescence, and resonance light scattering, the binding mode of neutral red (NR) with double stranded DNA has been characterized in a neutral aqueous medium. Depending on t he molar ratio R of NR: DNA, it was found that the binding involves in two proce sses at pH 7.63 and ionic strength lower than 0.01. The first process occurs in R > 2.22, where enhanced resonance light scattering was found, indicating the ag gregation of NR molecules on the molecular surface of double stranded DNA. Scatc hard plot was used to discuss the aggregation features based on the measurements of RLS data. The second process occurs in R < 2.22, characterized by bathochrom ic and hyperchromic molecular absorption of the interacting system, indicating t he intercalative binding of NR into the base pairs of the double stranded DNA mo lecules. Energy transfer from DNA to NR molecules in the second interacting proc ess occurs, resulting in strong enhancement of fluorescence, which proves NR can be used as a fluorescent probe as DNA structure.
2001, 17(03): 261-264
doi: 10.3866/PKU.WHXB20010316
Abstract:
The uniform transparent TiO2/SiO2 composite nanometer thin films were prepared via solgel processing on the soda lime glass substrates.The photocata lytic activity of the asprepared TiO2/SiO2 composite nanometer thin films obvi ously decreases when the amount of SiO2 addition is large.However,the photocatal ytic activity has no obvious change when the amount of SiO2 addition is small (T able 2).The addition of SiO2 can suppress the grain growth of TiO2 crystal,incre ase the hydroxyl content of TiO2 film,decrease the contact angle for water of Ti O2 films and enhance the hydrophilic property of TiO2 films.The superhydrophil ic TiO2/SiO2 composite nanometer films with the contact angle of 0o were obtaine d by the addition of 10％20％ (mole fraction) SiO2.
The uniform transparent TiO2/SiO2 composite nanometer thin films were prepared via solgel processing on the soda lime glass substrates.The photocata lytic activity of the asprepared TiO2/SiO2 composite nanometer thin films obvi ously decreases when the amount of SiO2 addition is large.However,the photocatal ytic activity has no obvious change when the amount of SiO2 addition is small (T able 2).The addition of SiO2 can suppress the grain growth of TiO2 crystal,incre ase the hydroxyl content of TiO2 film,decrease the contact angle for water of Ti O2 films and enhance the hydrophilic property of TiO2 films.The superhydrophil ic TiO2/SiO2 composite nanometer films with the contact angle of 0o were obtaine d by the addition of 10％20％ (mole fraction) SiO2.
2001, 17(03): 265-270
doi: 10.3866/PKU.WHXB20010317
Abstract:
The photocatalyst of TiO2/SnO2 compound semiconductor was prepared by improved solgel method.The coupling mechanism and the factors affecting photoc atalytic efficiency were studied by using XRD,gas chromatography,granularity equ ipment and surface photovoltage spectroscopy.TiO2/SnO2 catalysts were employed f or photocatalytic degradation of formaldehyde.The experimental results showed th at phtocatalytic efficiency of TiO2 catalyst was greatly enhanced by adding SnO2 into TiO2,and the optimum content of SnO2 was about 20 ％(mol).According to the particle close packing rule and experimental result,the strong and weak couplin g effect models for TiO2/SnO2 compound semiconductor were proposed.The coupling effect was derived from the close packing structure of the photocatalyst particl es.The critical bourn between enhanced and weaken effect depends on whether the close packing structure is threedimensional or not.The photocatalyst doped wit h SnO2 less than 20 ％(mol) presented a threedimensional structure,which impro ved the activity of the photocatalyst due to effective separation of the photoge nerated carriers.The opposite situation was occurred when content of SnO2 was mo re than 20 ％(mol).
The photocatalyst of TiO2/SnO2 compound semiconductor was prepared by improved solgel method.The coupling mechanism and the factors affecting photoc atalytic efficiency were studied by using XRD,gas chromatography,granularity equ ipment and surface photovoltage spectroscopy.TiO2/SnO2 catalysts were employed f or photocatalytic degradation of formaldehyde.The experimental results showed th at phtocatalytic efficiency of TiO2 catalyst was greatly enhanced by adding SnO2 into TiO2,and the optimum content of SnO2 was about 20 ％(mol).According to the particle close packing rule and experimental result,the strong and weak couplin g effect models for TiO2/SnO2 compound semiconductor were proposed.The coupling effect was derived from the close packing structure of the photocatalyst particl es.The critical bourn between enhanced and weaken effect depends on whether the close packing structure is threedimensional or not.The photocatalyst doped wit h SnO2 less than 20 ％(mol) presented a threedimensional structure,which impro ved the activity of the photocatalyst due to effective separation of the photoge nerated carriers.The opposite situation was occurred when content of SnO2 was mo re than 20 ％(mol).
2001, 17(03): 270-272
doi: 10.3866/PKU.WHXB20010318
Abstract:
/TiO2 catalysts were prepared by microwave,composite and conventional methods and characterized by Xray diffraction (XRD),N2 sorption analysis apply ing BET method,UVVis diffuse reflection spectroscopy(DRS) and laser Raman spec trum.The effect of different preparation methods on photocatalytic oxidation of C2H4 in air stream was studied.The results showed that the photocatalytic activi ty was obviously increased by the microwave method.The conversion of ethylene wa s 80％ contrast to those of composite and conventional methods being only 58％ a nd 41％,respectively.The catalyst by microwave method exhibited higher content o f anatase,higher specific surface area,larger band gap.The Raman scattering shif ted to low wave number direction helped to increase the transition probability o f photongenerated electrons and improved photoefficiency.
/TiO2 catalysts were prepared by microwave,composite and conventional methods and characterized by Xray diffraction (XRD),N2 sorption analysis apply ing BET method,UVVis diffuse reflection spectroscopy(DRS) and laser Raman spec trum.The effect of different preparation methods on photocatalytic oxidation of C2H4 in air stream was studied.The results showed that the photocatalytic activi ty was obviously increased by the microwave method.The conversion of ethylene wa s 80％ contrast to those of composite and conventional methods being only 58％ a nd 41％,respectively.The catalyst by microwave method exhibited higher content o f anatase,higher specific surface area,larger band gap.The Raman scattering shif ted to low wave number direction helped to increase the transition probability o f photongenerated electrons and improved photoefficiency.
2001, 17(03): 273-277
doi: 10.3866/PKU.WHXB20010319
Abstract:
Titania sols were prepared by acid hydrolysis of a TiCl4 precursor and mixed oxides SiO2TiO2,ZrO2TiO2,WO3TiO3 and MoO3TiO2 as well as Pt/TiO2 catalysts for the photocatalytic oxidation of formaldehyde were obtained by usin g the method of the modification of sol particles.The influence of the additives on the photocatalytic activity was investigated.Comparing with pure TiO2,the ad dition of silica or zirconia increased the photocatalytic activity,while the add ition of Pt and MoO3 decreased the activity,and the addition of WO3 had little e ffect on the activity.Among these catalysts,the activity of the SiO2TiO2 catal yst was the best while that of the MoO3TiO2 catalyst was the worst.It is of gr eat significance that the conversion of formaldehyde was increased up to 94％ ov er the SiO2TiO2 catalyst.The increased activity of the SiO2TiO2 catalyst was due to the higher surface area and porosity,the smaller crystallite size and th e stronger adsorption of UV light.A comparison of our catalyst compositions with those in the literature suggested that the difference in activity due to the ad dition of a second metal oxide maybe caused by the surface chemistry of the cata lysts,particularly the acidity.
Titania sols were prepared by acid hydrolysis of a TiCl4 precursor and mixed oxides SiO2TiO2,ZrO2TiO2,WO3TiO3 and MoO3TiO2 as well as Pt/TiO2 catalysts for the photocatalytic oxidation of formaldehyde were obtained by usin g the method of the modification of sol particles.The influence of the additives on the photocatalytic activity was investigated.Comparing with pure TiO2,the ad dition of silica or zirconia increased the photocatalytic activity,while the add ition of Pt and MoO3 decreased the activity,and the addition of WO3 had little e ffect on the activity.Among these catalysts,the activity of the SiO2TiO2 catal yst was the best while that of the MoO3TiO2 catalyst was the worst.It is of gr eat significance that the conversion of formaldehyde was increased up to 94％ ov er the SiO2TiO2 catalyst.The increased activity of the SiO2TiO2 catalyst was due to the higher surface area and porosity,the smaller crystallite size and th e stronger adsorption of UV light.A comparison of our catalyst compositions with those in the literature suggested that the difference in activity due to the ad dition of a second metal oxide maybe caused by the surface chemistry of the cata lysts,particularly the acidity.
2001, 17(03): 278-281
doi: 10.3866/PKU.WHXB20010320
Abstract:
The adsorption state of reactants,free radical intermediates and the r eaction mechanism have been studied by means of temperature programmed descripti on (TPD),electron spin resonance (ESR) and spin trapingESR in the photocatalyt ic oxidation of formaldehyde.The results showed that O2 adsorbed on the surface of photocatalyst could be reduced to •O－2 by photogenerated electrons and H2O could be oxidized to •OH by holes.Both free radicals are active oxidants in the reaction of photocatalytic oxidation of HCHO.The photocatalytic oxidation of HC HO carried out with two steps.Firstly,HCHO was oxidized into HCOOH,then HCOOH co nverted into final product of CO2 and H2O.
The adsorption state of reactants,free radical intermediates and the r eaction mechanism have been studied by means of temperature programmed descripti on (TPD),electron spin resonance (ESR) and spin trapingESR in the photocatalyt ic oxidation of formaldehyde.The results showed that O2 adsorbed on the surface of photocatalyst could be reduced to •O－2 by photogenerated electrons and H2O could be oxidized to •OH by holes.Both free radicals are active oxidants in the reaction of photocatalytic oxidation of HCHO.The photocatalytic oxidation of HC HO carried out with two steps.Firstly,HCHO was oxidized into HCOOH,then HCOOH co nverted into final product of CO2 and H2O.
2001, 17(03): 282-285
doi: 10.3866/PKU.WHXB20010321
Abstract:
The iron doping titanium dioxide was prepared by solgel,step precipi tation,coprecipitation and immersion methods,respectively.The photocatalytic a ctivities of these prepared samples were evaluated in X3B dispersion irradiate d under UV.The experimental results showed that the immersion method,especially using the nano TiO2 as immersion matrix,greatly enhanced the photocatalytic acti vity.One fold enhancement in photocatalytic activity was observed in the case of the sample prepared by immersion doping method.This may be attributed to the na nosize effect,the irreversible hole trapper in nonsaturated bonding field of Fe3＋ and larger lattice strain.
The iron doping titanium dioxide was prepared by solgel,step precipi tation,coprecipitation and immersion methods,respectively.The photocatalytic a ctivities of these prepared samples were evaluated in X3B dispersion irradiate d under UV.The experimental results showed that the immersion method,especially using the nano TiO2 as immersion matrix,greatly enhanced the photocatalytic acti vity.One fold enhancement in photocatalytic activity was observed in the case of the sample prepared by immersion doping method.This may be attributed to the na nosize effect,the irreversible hole trapper in nonsaturated bonding field of Fe3＋ and larger lattice strain.
2001, 17(03): 286-288
doi: 10.3866/PKU.WHXB20010322
Abstract:
TiO2 treated in hydrogen atmosphere showed enhanced photocatalytic act ivity in degrading the sulfosalicylic acid (SSal).The results of the electrochem ical impedance spectroscopy (EIS) investigation showed that the diameters of the capacitive arcs for the HTiO2 were much smaller than those of bare TiO2 and t hermally treated TiO2 in air,indicating that the charge transfer of the HTiO2 occurs more rapidly,thus inviting a higher photocatalytic activity.When an exter nal bias was applied on the HTiO2,the arc of the EIS Nyquist plot decreased ob viously than without the bias,suggesting more efficient separation of the photo generated carriers.
TiO2 treated in hydrogen atmosphere showed enhanced photocatalytic act ivity in degrading the sulfosalicylic acid (SSal).The results of the electrochem ical impedance spectroscopy (EIS) investigation showed that the diameters of the capacitive arcs for the HTiO2 were much smaller than those of bare TiO2 and t hermally treated TiO2 in air,indicating that the charge transfer of the HTiO2 occurs more rapidly,thus inviting a higher photocatalytic activity.When an exter nal bias was applied on the HTiO2,the arc of the EIS Nyquist plot decreased ob viously than without the bias,suggesting more efficient separation of the photo generated carriers.
2001, 17(03): 229-233
doi: 10.3866/PKU.WHXB20010308
Abstract:
The in situ spectroelectrochemical experiment shows that an absorption peak at 580.5 nm attributable to poly(methylene blue) grows slowly at the begin ning of the electrolysis of methylene blue, and then this peak grows more quickl y. The visible spectra prove that there are two absorption peaks at 580.5 and 6 90.2 nm respectively for the mixture solution after electrolysis. The former on e indicates that poly(methylene blue)polymerized on the ITO electrode is partly soluble; the latter one is attributed to a watersoluble polymer since it compl etely dissolves in the aqueous solution. The result from the rotating ringdisk electrode identifies that an intermediate is produced at the disk electrode, wh ich is collected at the ring electrode. The ring current increases with decreasi ng the ring potential and with increasing the rotation rate. Thus, the intermedi ate is a species carrying a positive charge and not too stable.The result from t he XPS experiment shows that the anions can be doped into poly(methylene blue) f ilm and dedoped from it during oxidation and reduction processes. The results fr om the impedance experiment indicate that the charge transfer impedance of poly( methylene blue) decreases with decreasing potential.
The in situ spectroelectrochemical experiment shows that an absorption peak at 580.5 nm attributable to poly(methylene blue) grows slowly at the begin ning of the electrolysis of methylene blue, and then this peak grows more quickl y. The visible spectra prove that there are two absorption peaks at 580.5 and 6 90.2 nm respectively for the mixture solution after electrolysis. The former on e indicates that poly(methylene blue)polymerized on the ITO electrode is partly soluble; the latter one is attributed to a watersoluble polymer since it compl etely dissolves in the aqueous solution. The result from the rotating ringdisk electrode identifies that an intermediate is produced at the disk electrode, wh ich is collected at the ring electrode. The ring current increases with decreasi ng the ring potential and with increasing the rotation rate. Thus, the intermedi ate is a species carrying a positive charge and not too stable.The result from t he XPS experiment shows that the anions can be doped into poly(methylene blue) f ilm and dedoped from it during oxidation and reduction processes. The results fr om the impedance experiment indicate that the charge transfer impedance of poly( methylene blue) decreases with decreasing potential.
2001, 17(03): 234-237
doi: 10.3866/PKU.WHXB20010309
Abstract:
The synthesized chiral amino acid modified porphyrinatozinc(II) exhibi ted characterized CD spectrum in Soret region. The coupling between the carbonyl group of the amino acid residue and the porphyrin unit is the origin of the CD spectrum. The premise of the above coupling is the intramolecular interaction be tween the amino acid residue and the porphyrin unit.
The synthesized chiral amino acid modified porphyrinatozinc(II) exhibi ted characterized CD spectrum in Soret region. The coupling between the carbonyl group of the amino acid residue and the porphyrin unit is the origin of the CD spectrum. The premise of the above coupling is the intramolecular interaction be tween the amino acid residue and the porphyrin unit.
2001, 17(03): 238-240
doi: 10.3866/PKU.WHXB20010310
Abstract:
A series of oscillators of pH and conductivity in emulsion structure c hange were found from composition change and component substitution of triglycer ide hydrolysis oscillator which had been discovered by the author.The experiment al results show that without any chemical reaction there are still various oscil lations in the inner diffusion of the emulsion. During the oscillatory process, periodic change of interface membrane in the emulsion could be obseved by a 100 × microscope. The oscillation phenomena have been briefly explained by Maran n i effect due to component substitution.
A series of oscillators of pH and conductivity in emulsion structure c hange were found from composition change and component substitution of triglycer ide hydrolysis oscillator which had been discovered by the author.The experiment al results show that without any chemical reaction there are still various oscil lations in the inner diffusion of the emulsion. During the oscillatory process, periodic change of interface membrane in the emulsion could be obseved by a 100 × microscope. The oscillation phenomena have been briefly explained by Maran n i effect due to component substitution.
2001, 17(03): 241-244
doi: 10.3866/PKU.WHXB20010311
Abstract:
The diffusing behavior of water through alkyd coatings with different pigment volume concentration (PVC) has been studied by EIS and SEM techniques. T he corresponding diffusion coefficients were also calculated. The experimental r esults showed that, in 0.5 mol•L－1 NaCl solution, the diffusion process of wat er through alkyd coatings with different PVC followed the idealFick′s law in the initial period.Within the PVC value concerned, the diffusion coefficients in itially decreased with the increase of PVC parameter, reaching a minimum value a t 60 ％, which is the CPVC of micaceous iron oxide, and then increased with the PVC increase. When the PVC was less than CPVC, the barrier property produced by the pigment was the main factor that affected the water diffusion behavior. Howe ver, the microstructure of the alkyd coatings played an important role when the PVC was greater than CPVC.
The diffusing behavior of water through alkyd coatings with different pigment volume concentration (PVC) has been studied by EIS and SEM techniques. T he corresponding diffusion coefficients were also calculated. The experimental r esults showed that, in 0.5 mol•L－1 NaCl solution, the diffusion process of wat er through alkyd coatings with different PVC followed the idealFick′s law in the initial period.Within the PVC value concerned, the diffusion coefficients in itially decreased with the increase of PVC parameter, reaching a minimum value a t 60 ％, which is the CPVC of micaceous iron oxide, and then increased with the PVC increase. When the PVC was less than CPVC, the barrier property produced by the pigment was the main factor that affected the water diffusion behavior. Howe ver, the microstructure of the alkyd coatings played an important role when the PVC was greater than CPVC.
2001, 17(03): 245-247
doi: 10.3866/PKU.WHXB20010312
Abstract:
The standard molar formation enthalpies of (A＋)2Cd2(SO4)3[A＋ is NH＋ 4 or K＋] are determined from the enthalpies of dissolution (ΔsHm) of [(A＋)2SO 4(s)＋2CdSO4(s)] and (A＋)2Cd2(SO4)3(s) in twice distilled water or 3 mol•L－1 HNO3 solvent respectively,at 298.2 K,as: ΔfHm [(NH4)2Cd2(SO4)3,s,298.2K]=－3031.74±0.08 kJ•mol－1 ΔfHm [K2Cd2(SO4)3,s,298.2K]=－3305.52±0.17 kJ•mol－1
The standard molar formation enthalpies of (A＋)2Cd2(SO4)3[A＋ is NH＋ 4 or K＋] are determined from the enthalpies of dissolution (ΔsHm) of [(A＋)2SO 4(s)＋2CdSO4(s)] and (A＋)2Cd2(SO4)3(s) in twice distilled water or 3 mol•L－1 HNO3 solvent respectively,at 298.2 K,as: ΔfHm [(NH4)2Cd2(SO4)3,s,298.2K]=－3031.74±0.08 kJ•mol－1 ΔfHm [K2Cd2(SO4)3,s,298.2K]=－3305.52±0.17 kJ•mol－1
2001, 17(03): 248-251
doi: 10.3866/PKU.WHXB20010313
Abstract:
As catalytic materials, nanometer rare earth perovskites LaMnO3 were p repared by NaOHNa2CO3 coprecipitation, followed by supercritical drying, vacuu m drying and air drying respectively. The effect of drying processes was studied on the catalyst performance through XRD, TEM, SEM and BET analysis. The results demonstrated that about 30 nm LaMnO3 particles could be prepared by three dryin g processes respectively. The catalyst materials LaMnO3 dried in vacuum presente d the largest specific surface area as 28.71 m2•g－1. Compared to the catalyst prepared by dipping cordierite directly in the salt solutions, nanometer LaMnO3 showed better catalytic activity. The lightoff temperatures for CO and HC oxid ation were both lowered by 100 ℃, and its NOx conversion could be up to 100 ％ at 570 ℃.
As catalytic materials, nanometer rare earth perovskites LaMnO3 were p repared by NaOHNa2CO3 coprecipitation, followed by supercritical drying, vacuu m drying and air drying respectively. The effect of drying processes was studied on the catalyst performance through XRD, TEM, SEM and BET analysis. The results demonstrated that about 30 nm LaMnO3 particles could be prepared by three dryin g processes respectively. The catalyst materials LaMnO3 dried in vacuum presente d the largest specific surface area as 28.71 m2•g－1. Compared to the catalyst prepared by dipping cordierite directly in the salt solutions, nanometer LaMnO3 showed better catalytic activity. The lightoff temperatures for CO and HC oxid ation were both lowered by 100 ℃, and its NOx conversion could be up to 100 ％ at 570 ℃.
2001, 17(03): 252-256
doi: 10.3866/PKU.WHXB20010314
Abstract:
Using layerbylayer selfassembly technique,we have successfully c onstructed nanostructured composite films of conjugated polymer (sulfonic acid r ing substituted polyaniline, SPAn)/ semiconductor nanoparticles(QCdS).The proc esses synthesis have been studied by UVVis, contact angle measurement, XPS and AFM techniques.The results indicated that the selfassembly processes were dep endent on the pH of the solution of each component and the doping time.It has be en found that the roughness of the assembled nanocomposite films increases as the layer number increases.The main reason can be attributed to the generation o f adsorption defects from partially adsorbed film surface in film fabrication pr ocesses.
Using layerbylayer selfassembly technique,we have successfully c onstructed nanostructured composite films of conjugated polymer (sulfonic acid r ing substituted polyaniline, SPAn)/ semiconductor nanoparticles(QCdS).The proc esses synthesis have been studied by UVVis, contact angle measurement, XPS and AFM techniques.The results indicated that the selfassembly processes were dep endent on the pH of the solution of each component and the doping time.It has be en found that the roughness of the assembled nanocomposite films increases as the layer number increases.The main reason can be attributed to the generation o f adsorption defects from partially adsorbed film surface in film fabrication pr ocesses.
2001, 17(03): 257-260
doi: 10.3866/PKU.WHXB20010315
Abstract:
The reaction between chlorite and thiourea could display batch oli os cillation and CSTR oscillation of pH.Batch pH peak has the same character with p H oscillation in a CSTR.The oxidation of thiourea produced intermediates such as HOSC(NH)NH2,HO2SC(NH)NH2,HO3S(NH)NH2 and bisulfite.The valence change of sulfur has close relation with pH dynamics.Through the mechanistic analysis,a general model of sulfur(－II) oxidation,which consists of negative hydrogen ion feedback (S(－II) to S(0)),a transition process of S(0) to S(IV) and positive proton feed back from S(IV) to S(VI),could simulate batch oli oscillation and CSTR oscillat ion.This result is setting up a new channel to uncover the reaction mechanism an d simulate the nonlinear phenomena in the reactions between chlorite and Sulfur( －II).
The reaction between chlorite and thiourea could display batch oli os cillation and CSTR oscillation of pH.Batch pH peak has the same character with p H oscillation in a CSTR.The oxidation of thiourea produced intermediates such as HOSC(NH)NH2,HO2SC(NH)NH2,HO3S(NH)NH2 and bisulfite.The valence change of sulfur has close relation with pH dynamics.Through the mechanistic analysis,a general model of sulfur(－II) oxidation,which consists of negative hydrogen ion feedback (S(－II) to S(0)),a transition process of S(0) to S(IV) and positive proton feed back from S(IV) to S(VI),could simulate batch oli oscillation and CSTR oscillat ion.This result is setting up a new channel to uncover the reaction mechanism an d simulate the nonlinear phenomena in the reactions between chlorite and Sulfur( －II).
