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2004 Volume 20 Issue 3
2004, 20(03): 225-227
doi: 10.3866/PKU.WHXB20040301
Abstract:
Multicharged xenon ions with charge upto 11 have been observed in laser ionization of xenon beam by a 25 ns Nd-YAG 532 nm laser at laser intensity about 1011 W•cm－2.Experiment results indicated that the multicharged ions appeared only when the laser interacted with the middle part of the pulsed beam, and its intensities increase with increase the backing pressure of Xe source gas, indicates that the clusters in the beam is essential to the production of multicharged ions. From the experimental results, we think that the cluster is ionized via multiphoton ionization and form a nanoplasma ball, which can absorb the laser resonantly to further ionize the single charge ion to high charge state.
Multicharged xenon ions with charge upto 11 have been observed in laser ionization of xenon beam by a 25 ns Nd-YAG 532 nm laser at laser intensity about 1011 W•cm－2.Experiment results indicated that the multicharged ions appeared only when the laser interacted with the middle part of the pulsed beam, and its intensities increase with increase the backing pressure of Xe source gas, indicates that the clusters in the beam is essential to the production of multicharged ions. From the experimental results, we think that the cluster is ionized via multiphoton ionization and form a nanoplasma ball, which can absorb the laser resonantly to further ionize the single charge ion to high charge state.
2004, 20(03): 228-232
doi: 10.3866/PKU.WHXB20040302
Abstract:
Ab initio UMP2 method was used to study the reaction mechanism of CH3 radical with HNCO. The geometric configurations of reactants, products, intermediates and transition states were optimized at UMP2(full)/6-311＋＋G** level. The results show that the reaction of CH3 radical with HNCO has three pathways: (1) CH3 radical reacts with HNCO to form a hydrogen-bond complex M of which the relative stable energy is 4.56 kJ•mol－1,and then forms another complex M′through a transition state TS, and breaks down into CH4 and NCO radical in the end. (2) CH3 radical reacts with HNCO to form a stable trans- intermediate (trans-int), then through a transition state (trans-ts) breaks down into CH3NH and CO. (3) CH3 radical reacts with HNCO to form a stable cis-intermediate (cis-int), and then through a transition state(cis-ts) breaks down into CH3NH and CO. Comparing the activation energy of the three pathways, we can draw a conclusion that the pathway of forming CH4 and NCO radical is more feasible.
Ab initio UMP2 method was used to study the reaction mechanism of CH3 radical with HNCO. The geometric configurations of reactants, products, intermediates and transition states were optimized at UMP2(full)/6-311＋＋G** level. The results show that the reaction of CH3 radical with HNCO has three pathways: (1) CH3 radical reacts with HNCO to form a hydrogen-bond complex M of which the relative stable energy is 4.56 kJ•mol－1,and then forms another complex M′through a transition state TS, and breaks down into CH4 and NCO radical in the end. (2) CH3 radical reacts with HNCO to form a stable trans- intermediate (trans-int), then through a transition state (trans-ts) breaks down into CH3NH and CO. (3) CH3 radical reacts with HNCO to form a stable cis-intermediate (cis-int), and then through a transition state(cis-ts) breaks down into CH3NH and CO. Comparing the activation energy of the three pathways, we can draw a conclusion that the pathway of forming CH4 and NCO radical is more feasible.
2004, 20(03): 233-236
doi: 10.3866/PKU.WHXB20040303
Abstract:
The structural stability of S-Al, S-Co co-doped spinel structure lithium manganese oxide was investigated with self-consistent-charge discrete variational(SCC-DV-Xα) method of quantum chemistry. The calculated results show that the average covalences of S-Al co-doped spinel [LixMn3Al3O20S6]n－ and S-Co co-doped spinel [LixMn3Co3O20S6]n－ both are stronger than that of undoped spinel [LixMn6O26]n－, and approach to that of MnO2, the charge of Mn in [LixMn3Al3O20S6]n－ also approaches to that in MnO2 model [Mn6O26]28－； the order of the charge density of Mn atom in various model is as fellows: MnO2≈[LixMn3Al3O20S6]n－≈[LixMn3Co3O20S6]n－< [LixMn6O26]n－. It is said that the state of Mn in [LixMn3Co3O20S6]n－ and[LixMn3Al3O20S6]n－ is similar to that in MnO2. These results revealed the reason that structural stability of S-Al, S-Co co-doped spinel structure lithium manganese oxide was enhanced during electrochemical cycle.
The structural stability of S-Al, S-Co co-doped spinel structure lithium manganese oxide was investigated with self-consistent-charge discrete variational(SCC-DV-Xα) method of quantum chemistry. The calculated results show that the average covalences of S-Al co-doped spinel [LixMn3Al3O20S6]n－ and S-Co co-doped spinel [LixMn3Co3O20S6]n－ both are stronger than that of undoped spinel [LixMn6O26]n－, and approach to that of MnO2, the charge of Mn in [LixMn3Al3O20S6]n－ also approaches to that in MnO2 model [Mn6O26]28－； the order of the charge density of Mn atom in various model is as fellows: MnO2≈[LixMn3Al3O20S6]n－≈[LixMn3Co3O20S6]n－< [LixMn6O26]n－. It is said that the state of Mn in [LixMn3Co3O20S6]n－ and[LixMn3Al3O20S6]n－ is similar to that in MnO2. These results revealed the reason that structural stability of S-Al, S-Co co-doped spinel structure lithium manganese oxide was enhanced during electrochemical cycle.
2004, 20(03): 237-239
doi: 10.3866/PKU.WHXB20040304
Abstract:
A series of ion dynamics simulations on Na2O-SiO2 binary system at 6000 K ranging from 0 to 100 GPa pressure have been carried out. These systems include SiO2, Na2O•10SiO2,Na2O•5SiO2, Na2O•2SiO2, Na2O•SiO2, 2Na2O•SiO2. The simulated results show that there exists anomalous pressure dependence for oxygen component diffusion coefficient in SiO2, Na2O•10SiO2, Na2O•5SiO2, Na2O•2SiO2 systems. Besides SiO2 system, others have not been reported earlier. In Na2O•10SiO2, Na2O•5SiO2, Na2O•2SiO2 systems, the silicon component diffusion coefficient also shows anomalous pressure dependence, this result has not been reported earlier. In these systems at about 20 GPa the diffusion coefficient of oxygen component is larger than that at ambient pressure by more than an order of magnitude. That the pressure-induced peak position of oxygen diffusion coefficient is at about 20 GPa is different from the results reported earlier, which is at about 30 GPa. It is observed that the diffusivity maximum in SiO2 system corresponds approximately to a prevalence of five-coordination of silicon by oxygen, but the diffusivity maximum in Na2O•10SiO2 system corresponds approximately to a prevalence of six-coordination of silicon by oxygen. The latter has not been reported earlier.
A series of ion dynamics simulations on Na2O-SiO2 binary system at 6000 K ranging from 0 to 100 GPa pressure have been carried out. These systems include SiO2, Na2O•10SiO2,Na2O•5SiO2, Na2O•2SiO2, Na2O•SiO2, 2Na2O•SiO2. The simulated results show that there exists anomalous pressure dependence for oxygen component diffusion coefficient in SiO2, Na2O•10SiO2, Na2O•5SiO2, Na2O•2SiO2 systems. Besides SiO2 system, others have not been reported earlier. In Na2O•10SiO2, Na2O•5SiO2, Na2O•2SiO2 systems, the silicon component diffusion coefficient also shows anomalous pressure dependence, this result has not been reported earlier. In these systems at about 20 GPa the diffusion coefficient of oxygen component is larger than that at ambient pressure by more than an order of magnitude. That the pressure-induced peak position of oxygen diffusion coefficient is at about 20 GPa is different from the results reported earlier, which is at about 30 GPa. It is observed that the diffusivity maximum in SiO2 system corresponds approximately to a prevalence of five-coordination of silicon by oxygen, but the diffusivity maximum in Na2O•10SiO2 system corresponds approximately to a prevalence of six-coordination of silicon by oxygen. The latter has not been reported earlier.
2004, 20(03): 240-243
doi: 10.3866/PKU.WHXB20040305
Abstract:
Highly uniform Sb nanowire arrays have been fabricated using electrochemical deposition into nanochannels of porous anodic alumina membrane (AAM). X-ray diffraction (XRD) patterns show that the deposited material is hexa nal Sb orientating along the (110) direction. The transmission electron microscope (TEM) observations demonstrate that the diameter of the nanowires is about 40～50 nm, which is the same as that of the AAM used, and the aspect ratio of the nanowires is over 1000.The selected area electron diffraction (SAED) patterns show that the Sb nanowires are single crystals. The field emission scanning electron microscope (FE-SEM) results indicate that the Sb nanowire arrays are highly uniform, and the filling-rate is almost 100％. Finally, several aspects about how to prepare high-quality metal nanowire arrays are also discussed.
Highly uniform Sb nanowire arrays have been fabricated using electrochemical deposition into nanochannels of porous anodic alumina membrane (AAM). X-ray diffraction (XRD) patterns show that the deposited material is hexa nal Sb orientating along the (110) direction. The transmission electron microscope (TEM) observations demonstrate that the diameter of the nanowires is about 40～50 nm, which is the same as that of the AAM used, and the aspect ratio of the nanowires is over 1000.The selected area electron diffraction (SAED) patterns show that the Sb nanowires are single crystals. The field emission scanning electron microscope (FE-SEM) results indicate that the Sb nanowire arrays are highly uniform, and the filling-rate is almost 100％. Finally, several aspects about how to prepare high-quality metal nanowire arrays are also discussed.
2004, 20(03): 244-250
doi: 10.3866/PKU.WHXB20040306
Abstract:
Based on the phase equilibrium conditions for systems containing gels given by Maurer and Prausnitz, a model to correlate and predict the swelling behaviors of hydrogels in aqueous organic solutions is proposed. In the model, gel is considered as a combination of a shell of an elastic semipermeable membrane and a core of a fluid phase. The fluid core consists of only the network building materials and other components that are able to partition in gel phase and surrounding coexisting liquid phase, and is enveloped by the membrane shell. The excess Gibbs energies of the gel phase and the surrounding coexisting fluid phase are calculated using UNIQUAC equation, the elastic properties of polymer network are described by the “phantom network” theory, and the additional differences in the size of the species are taken into account by “free-volume” contribution. To test the model, a series of N-isopropylacrylamide gels, using N,N’-methylene diacrylamide as the crosslinker, are synthesized by free radical polymerization under nitrogen atmosphere. The swelling experiments are conducted in aqueous solution of acetone at 25 ℃. The results show that the increases of swelling capacity of the gels with decreasing amount of crosslinker and total mass fraction of polymerizable materials predicted by the model are in od agreement with the experimental data. Moreover, the model also predicts no difference of acetone concentration in the gel phase and the coexisting liquid phase, as long as the gel is in a swollen state. However, in the region where the swelling degree of the gel is rather small there is a small enrichment of acetone in the gel phase. All these show the potential of the model to correlate and predict the swelling behaviors of hydrogels in aqueous organic solutions.
Based on the phase equilibrium conditions for systems containing gels given by Maurer and Prausnitz, a model to correlate and predict the swelling behaviors of hydrogels in aqueous organic solutions is proposed. In the model, gel is considered as a combination of a shell of an elastic semipermeable membrane and a core of a fluid phase. The fluid core consists of only the network building materials and other components that are able to partition in gel phase and surrounding coexisting liquid phase, and is enveloped by the membrane shell. The excess Gibbs energies of the gel phase and the surrounding coexisting fluid phase are calculated using UNIQUAC equation, the elastic properties of polymer network are described by the “phantom network” theory, and the additional differences in the size of the species are taken into account by “free-volume” contribution. To test the model, a series of N-isopropylacrylamide gels, using N,N’-methylene diacrylamide as the crosslinker, are synthesized by free radical polymerization under nitrogen atmosphere. The swelling experiments are conducted in aqueous solution of acetone at 25 ℃. The results show that the increases of swelling capacity of the gels with decreasing amount of crosslinker and total mass fraction of polymerizable materials predicted by the model are in od agreement with the experimental data. Moreover, the model also predicts no difference of acetone concentration in the gel phase and the coexisting liquid phase, as long as the gel is in a swollen state. However, in the region where the swelling degree of the gel is rather small there is a small enrichment of acetone in the gel phase. All these show the potential of the model to correlate and predict the swelling behaviors of hydrogels in aqueous organic solutions.
2004, 20(03): 251-255
doi: 10.3866/PKU.WHXB20040307
Abstract:
CrOx/ZrO2 samples were prepared by impregnation method and co-precipitation method. During the preparation all the precipitates were digested at 100 ℃ in their mother liquid for 24 h. The prepared samples were characterized by XRD、XPS、BET and TGA-DTA. It was proved that some silica dissolved from the glass vessels was deposited on the precipitates during the digestion and the presence of silica increased the crystallization temperature as well as the thermal stability of zirconia. Introducing CrOx into the system resulted in a further increase in the crystallization temperature of zirconia. In addition, the specific surface area and the thermal stability of the obtained samples were also significantly improved. Compared with impregnation method, co-precipitation method gave better results and a sample with a specific surface area of 121 m2•g－1 after calcination at 1000 ℃ was obtained.
CrOx/ZrO2 samples were prepared by impregnation method and co-precipitation method. During the preparation all the precipitates were digested at 100 ℃ in their mother liquid for 24 h. The prepared samples were characterized by XRD、XPS、BET and TGA-DTA. It was proved that some silica dissolved from the glass vessels was deposited on the precipitates during the digestion and the presence of silica increased the crystallization temperature as well as the thermal stability of zirconia. Introducing CrOx into the system resulted in a further increase in the crystallization temperature of zirconia. In addition, the specific surface area and the thermal stability of the obtained samples were also significantly improved. Compared with impregnation method, co-precipitation method gave better results and a sample with a specific surface area of 121 m2•g－1 after calcination at 1000 ℃ was obtained.
2004, 20(03): 256-259
doi: 10.3866/PKU.WHXB20040308
Abstract:
To obtain boron carbide nanowire, the mixture of carbon nanotubes and boron powder is heated to 1000～1100 ℃ for 30～60 min. The results of transmission electronic microscopy examination show that most of the carbon nanotube in our sample transfer into straight boron carbide nanowire. The structure of the nanowire is studied by the selected area electronic diffraction (SAED) and HRTEM, which shows that most of the nanowire is B4C nanowire. There is a nickel particle at the end of some boron carbide nanowires. The nickel particles come from the catalyst encapsulated in the hollow of the carbon nanotube. The growing mechanism of the boron carbide nanowire is discussed. Carbon nanotube acts as template for the growth of boron carbide nanowire. During the reaction, boron atoms replace some sites of the carbon in the nanotube, resulting in reconstructing the crystal of the nanotube and mending the defects in the carbon nanotube.
To obtain boron carbide nanowire, the mixture of carbon nanotubes and boron powder is heated to 1000～1100 ℃ for 30～60 min. The results of transmission electronic microscopy examination show that most of the carbon nanotube in our sample transfer into straight boron carbide nanowire. The structure of the nanowire is studied by the selected area electronic diffraction (SAED) and HRTEM, which shows that most of the nanowire is B4C nanowire. There is a nickel particle at the end of some boron carbide nanowires. The nickel particles come from the catalyst encapsulated in the hollow of the carbon nanotube. The growing mechanism of the boron carbide nanowire is discussed. Carbon nanotube acts as template for the growth of boron carbide nanowire. During the reaction, boron atoms replace some sites of the carbon in the nanotube, resulting in reconstructing the crystal of the nanotube and mending the defects in the carbon nanotube.
2004, 20(03): 260-264
doi: 10.3866/PKU.WHXB20040309
Abstract:
A novel approach for preparing carbon-encapsulated nanomaterials is reported, in which apoferritin molecules, a kind of biomaterial with hollow cages, were used as the starting nano-sized reactors to trap the precursors of magnetic metals(Mn, Co). It has shown that the nano-sized metal particles can be effectively encapsulated inside the carbon shells that are formed by carbonizing protein molecules below 800 ℃ in a controllable way. The transmission electron microscopy images show that the as-prepared nanoparticles consist of a metal core and a carbon shell with narrow size distribution. The mechanisms of mineralization of apoferritin and carbonization of the mineralized protein are discussed in terms of the structure and properties of the protein precursor. It is believed that this novel approach may provide a new option for preparation of carbon-encapsulated nanomaterials based on other biomaterials such as fungi and actinomycete.
A novel approach for preparing carbon-encapsulated nanomaterials is reported, in which apoferritin molecules, a kind of biomaterial with hollow cages, were used as the starting nano-sized reactors to trap the precursors of magnetic metals(Mn, Co). It has shown that the nano-sized metal particles can be effectively encapsulated inside the carbon shells that are formed by carbonizing protein molecules below 800 ℃ in a controllable way. The transmission electron microscopy images show that the as-prepared nanoparticles consist of a metal core and a carbon shell with narrow size distribution. The mechanisms of mineralization of apoferritin and carbonization of the mineralized protein are discussed in terms of the structure and properties of the protein precursor. It is believed that this novel approach may provide a new option for preparation of carbon-encapsulated nanomaterials based on other biomaterials such as fungi and actinomycete.
2004, 20(03): 265-270
doi: 10.3866/PKU.WHXB20040310
Abstract:
Mesoporous aluminosilicate (denoted as Z-1) nanoparticles were synthesized from assembly of mixture of tetraethylorthosilicate (TEOS) and aluminum nitrate nonahydrate (ANN) with cetyltrimethylammonium bromide (CTAB) as template at low temperture. Important information about textural properties of the material were obtained by powder X-ray diffraction (XRD), N2 adsorption-desorption isotherms at 77 K and transmission electron microscopy (TEM),and the acid properties were determined by temperature-programmed desorption of ammonia (NH3-TPD).The results obtained by these methods indicated that the material possessed hexa nal mesostructure, narrow pore-size distribution and nanoparticles. The NH3-TPD showed that the acdity strength of Z-1 was similar to AlMCM-41, but the amount of medium-acid of Z-1 was more than that of AlMCM-41 prepared by post-synthesis method. In catalytic cracking of cumene and 1,3,5-triisopropylbenzene,Z-1 exhibited higher cataclytic acitivity, selectivity and steam stability (100％ water vapor,800 ℃,2 h) compared with AlMCM-41.
Mesoporous aluminosilicate (denoted as Z-1) nanoparticles were synthesized from assembly of mixture of tetraethylorthosilicate (TEOS) and aluminum nitrate nonahydrate (ANN) with cetyltrimethylammonium bromide (CTAB) as template at low temperture. Important information about textural properties of the material were obtained by powder X-ray diffraction (XRD), N2 adsorption-desorption isotherms at 77 K and transmission electron microscopy (TEM),and the acid properties were determined by temperature-programmed desorption of ammonia (NH3-TPD).The results obtained by these methods indicated that the material possessed hexa nal mesostructure, narrow pore-size distribution and nanoparticles. The NH3-TPD showed that the acdity strength of Z-1 was similar to AlMCM-41, but the amount of medium-acid of Z-1 was more than that of AlMCM-41 prepared by post-synthesis method. In catalytic cracking of cumene and 1,3,5-triisopropylbenzene,Z-1 exhibited higher cataclytic acitivity, selectivity and steam stability (100％ water vapor,800 ℃,2 h) compared with AlMCM-41.
2004, 20(03): 271-274
doi: 10.3866/PKU.WHXB20040311
Abstract:
Carbon nanotubes were synthesized on anodic aluminum oxide (AAO) template by chemical vapor deposition catalyzed by electrodeposited cobalt particles in its pores. The growth of the carbon nanotubes on the basis of top-growth model is fast. Sonication cutting process was applied to shorten the outgrown carbon nanotubes to get aligned carbon nanotube film. With the increase of sonicating time, the ordered orientation of carbon nanotubes on the AAO template is improved. Meanwhile, cobalt catalyst on the top of the carbon nanotube is cut off during the sonication. So the end-opened aligned carbon nanotube film is obtained at last. The mechanism of this treatment is also discussed.
Carbon nanotubes were synthesized on anodic aluminum oxide (AAO) template by chemical vapor deposition catalyzed by electrodeposited cobalt particles in its pores. The growth of the carbon nanotubes on the basis of top-growth model is fast. Sonication cutting process was applied to shorten the outgrown carbon nanotubes to get aligned carbon nanotube film. With the increase of sonicating time, the ordered orientation of carbon nanotubes on the AAO template is improved. Meanwhile, cobalt catalyst on the top of the carbon nanotube is cut off during the sonication. So the end-opened aligned carbon nanotube film is obtained at last. The mechanism of this treatment is also discussed.
2004, 20(03): 275-279
doi: 10.3866/PKU.WHXB20040312
Abstract:
The kinetics of antisynergic extraction of cadmium with D2EHDTPA（di-(2-ethylhexyl)-dithiophosp-horic acid） -TOA（trioctylamine） under the condition of interfacial reaction controlling model was investigated by using an improved constant interfacial area stirred cell. The extraction course was composed of several interphase transfer processes (transfer between bulk phase and interfacial phase (or boundary phase)) and several chemical reactions. The extraction rate equation was : r=1.42*10-7[Cd2+]0.42[BHA]0.47/[B]0.85[H+]0.21 （mol•m-2•s-1） The interfacial concentration was associated with the bulk concentration by using Freundlich adsorption equation. The concentration exponents in the extraction rate equation were decided by the two factors of the interfacial chemical reactions and the interphase transfer processes.The physical meaning of the fractional reaction order in the rate equation was analyzed. The bigger the Freundlich power n of a reactant, the more the repulsion exerted by the interfacial layer. The apparent extraction activation energy E=44.2 kJ•mol－1,the extraction enthalpy ΔH=72.9 kJ•mol－1. The inconsistency in extraction mechanism due to different interface models was also discussed.
The kinetics of antisynergic extraction of cadmium with D2EHDTPA（di-(2-ethylhexyl)-dithiophosp-horic acid） -TOA（trioctylamine） under the condition of interfacial reaction controlling model was investigated by using an improved constant interfacial area stirred cell. The extraction course was composed of several interphase transfer processes (transfer between bulk phase and interfacial phase (or boundary phase)) and several chemical reactions. The extraction rate equation was : r=1.42*10-7[Cd2+]0.42[BHA]0.47/[B]0.85[H+]0.21 （mol•m-2•s-1） The interfacial concentration was associated with the bulk concentration by using Freundlich adsorption equation. The concentration exponents in the extraction rate equation were decided by the two factors of the interfacial chemical reactions and the interphase transfer processes.The physical meaning of the fractional reaction order in the rate equation was analyzed. The bigger the Freundlich power n of a reactant, the more the repulsion exerted by the interfacial layer. The apparent extraction activation energy E=44.2 kJ•mol－1,the extraction enthalpy ΔH=72.9 kJ•mol－1. The inconsistency in extraction mechanism due to different interface models was also discussed.
2004, 20(03): 280-284
doi: 10.3866/PKU.WHXB20040313
Abstract:
Molecular dynamics simulations are employed here to study the behaviors of bulk Ag superheating and melting at high heating rate. The superheating and melting behaviors are found to be strongly affected by the heating rate. The larger the heating rate, the higher the melting temperature, and there is an upper limit for the heating rate induced superheating. Stability study shows that the radomization induced by high heating rate is the main reason for the reduction of the energy barrier on phase transformation and for the existence of dynamic limit of superheating. Both Ag crystals and Ag crystals with defects are studied. The upper limit of heating rate induced superheating of perfect Ag crystal is determined to be around 1 450 K.
Molecular dynamics simulations are employed here to study the behaviors of bulk Ag superheating and melting at high heating rate. The superheating and melting behaviors are found to be strongly affected by the heating rate. The larger the heating rate, the higher the melting temperature, and there is an upper limit for the heating rate induced superheating. Stability study shows that the radomization induced by high heating rate is the main reason for the reduction of the energy barrier on phase transformation and for the existence of dynamic limit of superheating. Both Ag crystals and Ag crystals with defects are studied. The upper limit of heating rate induced superheating of perfect Ag crystal is determined to be around 1 450 K.
2004, 20(03): 285-289
doi: 10.3866/PKU.WHXB20040314
Abstract:
The properties of solution in the reaction process of low concentration and high molecular weight partially hydrolyzed polyacrylamide（HPAM） and aluminum citrate（AlCit） system are investigated by using viscometer, SEM, nuclear pore membrane, dynamic light scattering and 27Al NMR. The experimental results show that the viscosity of HPAM/AlCit crosslinking system is decreased with reaction time in lower shear rate and the system is shear thickening in higher shear rate. After crosslinking the spin-lattice relaxation time（T1）of Al decreases with the reaction time. The linked polymer solution is formed by intra-molecular crosslink of HPAM and AlCit forming linked polymer coil（LPC） in lower concentration of the system. The LPC is a spherical coil with a mean hydrodynamic radius of 238 nm. The ability of the LPS to block the neclear pore film is related to the reaction time of HPAM/AlCit system.
The properties of solution in the reaction process of low concentration and high molecular weight partially hydrolyzed polyacrylamide（HPAM） and aluminum citrate（AlCit） system are investigated by using viscometer, SEM, nuclear pore membrane, dynamic light scattering and 27Al NMR. The experimental results show that the viscosity of HPAM/AlCit crosslinking system is decreased with reaction time in lower shear rate and the system is shear thickening in higher shear rate. After crosslinking the spin-lattice relaxation time（T1）of Al decreases with the reaction time. The linked polymer solution is formed by intra-molecular crosslink of HPAM and AlCit forming linked polymer coil（LPC） in lower concentration of the system. The LPC is a spherical coil with a mean hydrodynamic radius of 238 nm. The ability of the LPS to block the neclear pore film is related to the reaction time of HPAM/AlCit system.
2004, 20(03): 290-295
doi: 10.3866/PKU.WHXB20040315
Abstract:
The geometric configurations, electronic structures and vibrational frequency of the AlmN2 (m=1～8) clusters were studied using the B3LYP(DFT) method at 6-31G* level. The results show that there exist two types of bonding character in the ground state of AlmN2 clusters. One is formed through N－N bonds coordinated with aluminum atom as m≤2, and another is combination of AlnN(n< m) fragments shared with Al or Al－Al bond. It is effective for searching the ground structure of the larger AlmN2 cluster. Furthermore, from the analysis of the second difference of the energy, the AlmN2 with even m is more stable than that of with odd m.
The geometric configurations, electronic structures and vibrational frequency of the AlmN2 (m=1～8) clusters were studied using the B3LYP(DFT) method at 6-31G* level. The results show that there exist two types of bonding character in the ground state of AlmN2 clusters. One is formed through N－N bonds coordinated with aluminum atom as m≤2, and another is combination of AlnN(n< m) fragments shared with Al or Al－Al bond. It is effective for searching the ground structure of the larger AlmN2 cluster. Furthermore, from the analysis of the second difference of the energy, the AlmN2 with even m is more stable than that of with odd m.
2004, 20(03): 296-301
doi: 10.3866/PKU.WHXB20040316
Abstract:
The Photocatalytic degradation reaction of 2-chloroethyl ethyl sulfide (2-CEES) on P25 TiO2 was studied by using flow micro-reaction technique, GC-MS, and in situ FTIR. It was showed that 2-CEES could be oxidized finally into CO2 and H2O at room temperature during the process. Detailed analysis found that C2H4, CH3CHO, CH4, CO, HCl and H2S; a small quantity of low molecular weight carboxylic acids, ethers and sulphones; a trace amount of C2H5SC2H5, C2H5S2C2H5, C2H5SC2H4Cl and CH2ClCH2Cl exist in the gaseous product of reaction besides CO2 and H2O, and some species such as C2H5S2C2H5, C2H5SC2H4OH, C4H9S2C2H5, C2H5S2C2H4OH and SO42- remain on the surface of the catalyst after reaction. According to the above results, a photocatalytic degradation mechanism of 2-CEES was suggested, deducing that 2-CEES was photocatalytically degraded into CO2 and H2O via a complicated process including dechlorination, C－S bond splitting, photo-polymerization and decompose of organo-sulfur intermediates. The accumulation of sulfur-contained species on the surface was thought to result in deactivation of the catalyst.
The Photocatalytic degradation reaction of 2-chloroethyl ethyl sulfide (2-CEES) on P25 TiO2 was studied by using flow micro-reaction technique, GC-MS, and in situ FTIR. It was showed that 2-CEES could be oxidized finally into CO2 and H2O at room temperature during the process. Detailed analysis found that C2H4, CH3CHO, CH4, CO, HCl and H2S; a small quantity of low molecular weight carboxylic acids, ethers and sulphones; a trace amount of C2H5SC2H5, C2H5S2C2H5, C2H5SC2H4Cl and CH2ClCH2Cl exist in the gaseous product of reaction besides CO2 and H2O, and some species such as C2H5S2C2H5, C2H5SC2H4OH, C4H9S2C2H5, C2H5S2C2H4OH and SO42- remain on the surface of the catalyst after reaction. According to the above results, a photocatalytic degradation mechanism of 2-CEES was suggested, deducing that 2-CEES was photocatalytically degraded into CO2 and H2O via a complicated process including dechlorination, C－S bond splitting, photo-polymerization and decompose of organo-sulfur intermediates. The accumulation of sulfur-contained species on the surface was thought to result in deactivation of the catalyst.
2004, 20(03): 302-305
doi: 10.3866/PKU.WHXB20040317
Abstract:
Molecular dynamics(MD) simulation was carried out to investigate the solidification processes of n-hexadecane system and the mixture of n-hexadecane with α-alkyl naphthalene such as octyl, dodecyl and hexadecyl naphthalene. The simulation box contained 10 n-hexadecane molecules and/or one α-alkyl naphthalene. Total 200 ps trajectory for each system was collected to execute the structural, fluctuation and dynamic analysis. The calculated heat capacities of pure n-hexadecane system at 313 and 303 K were consistent with the experimental ones. According to the sharp changes of heat capacities and self-diffusion constants with the simulation temperatures, the solidification point was identified for each system. It was found that the solidification point of n-hexadecane is obviously lowered by mixing with α-alkyl naphthalene, and the calculated solidification points of four systems agreed with the experimental ones. The investigation on the microstructures at temperatures before and after solidification revealed that n-hexadecanes tends to arrange orderly during the solidifying process, which is consistent with the fundamental of entropy-decrease. The reason why α-alkyl naphthalene can lower the solidification point of n-hexadecane was explained as due to the fact that the ring of α-alkyl naphthalene was packed by several n-hexadecane molecules which made the order arrangement of n-hexadecane molecules more difficult.
Molecular dynamics(MD) simulation was carried out to investigate the solidification processes of n-hexadecane system and the mixture of n-hexadecane with α-alkyl naphthalene such as octyl, dodecyl and hexadecyl naphthalene. The simulation box contained 10 n-hexadecane molecules and/or one α-alkyl naphthalene. Total 200 ps trajectory for each system was collected to execute the structural, fluctuation and dynamic analysis. The calculated heat capacities of pure n-hexadecane system at 313 and 303 K were consistent with the experimental ones. According to the sharp changes of heat capacities and self-diffusion constants with the simulation temperatures, the solidification point was identified for each system. It was found that the solidification point of n-hexadecane is obviously lowered by mixing with α-alkyl naphthalene, and the calculated solidification points of four systems agreed with the experimental ones. The investigation on the microstructures at temperatures before and after solidification revealed that n-hexadecanes tends to arrange orderly during the solidifying process, which is consistent with the fundamental of entropy-decrease. The reason why α-alkyl naphthalene can lower the solidification point of n-hexadecane was explained as due to the fact that the ring of α-alkyl naphthalene was packed by several n-hexadecane molecules which made the order arrangement of n-hexadecane molecules more difficult.
2004, 20(03): 306-308
doi: 10.3866/PKU.WHXB20040318
Abstract:
Supersaturated solution of M •3B2O3-H2O was prepared and kept under hydrothermal condition at 120 ℃.The solid phases separated from M •3B2O3-H2O supersaturated solution were identified by means of chemical analysis, XRD and IR. The process was a phase transformation of Mg-borates. Two amorphous intermediate-products are 2M •3B2O3•5H2O and M •B2O3•3H2O and the final product is the crystalling 2M •B2O3•H2O.The mechanism of phase transformation was proposed and the function of MgSO4 in the supersaturated solution of M •3B2O3-18％MgSO4-H2O was discussed.
Supersaturated solution of M •3B2O3-H2O was prepared and kept under hydrothermal condition at 120 ℃.The solid phases separated from M •3B2O3-H2O supersaturated solution were identified by means of chemical analysis, XRD and IR. The process was a phase transformation of Mg-borates. Two amorphous intermediate-products are 2M •3B2O3•5H2O and M •B2O3•3H2O and the final product is the crystalling 2M •B2O3•H2O.The mechanism of phase transformation was proposed and the function of MgSO4 in the supersaturated solution of M •3B2O3-18％MgSO4-H2O was discussed.
2004, 20(03): 309-312
doi: 10.3866/PKU.WHXB20040319
Abstract:
A detailed study on the promotion effect of Zr on Mo-V mixed oxide catalysts in the selective oxidation of propane to acrolein was performed. The catalysts were characterized by BET, XRD, H2-TPR, NH3-TPD and isopropanol decomposition reaction. The addition of Zr modifies the catalysts phase composition and improves their redox and acid-base properties. As a result, the higher catalytic activity and selectivity were obtained over Mo2VZr0.5Ox catalyst.
A detailed study on the promotion effect of Zr on Mo-V mixed oxide catalysts in the selective oxidation of propane to acrolein was performed. The catalysts were characterized by BET, XRD, H2-TPR, NH3-TPD and isopropanol decomposition reaction. The addition of Zr modifies the catalysts phase composition and improves their redox and acid-base properties. As a result, the higher catalytic activity and selectivity were obtained over Mo2VZr0.5Ox catalyst.
2004, 20(03): 313-317
doi: 10.3866/PKU.WHXB20040320
Abstract:
The sol-gel method was used successfully for the preparation of nano-sized silica gel suspension. A fluorophore -naphthyl group was introduced on the surface of silica gel particles by using surface chemical modification. In the study of steady state fluorescence spectrum, it was seen clearly that the naphthyl groups on the particle surface were able to reorganize in different solvents. And in a certain condition the excimer fluorescence of naphthyl group may be observed evidently. The surface fluorescence quenching of particles by different transition cations was studied. It was found that only Cu2＋ cation showed itself very strong ability of quenching the surface fluorescence of studied particles. But for other metal cations almost no any quenching effect was observed. The excellent recognition of Cu2＋ cation of this system provides a possibility to develop a new fluorescence sensor for Cu2＋ cation detection.
The sol-gel method was used successfully for the preparation of nano-sized silica gel suspension. A fluorophore -naphthyl group was introduced on the surface of silica gel particles by using surface chemical modification. In the study of steady state fluorescence spectrum, it was seen clearly that the naphthyl groups on the particle surface were able to reorganize in different solvents. And in a certain condition the excimer fluorescence of naphthyl group may be observed evidently. The surface fluorescence quenching of particles by different transition cations was studied. It was found that only Cu2＋ cation showed itself very strong ability of quenching the surface fluorescence of studied particles. But for other metal cations almost no any quenching effect was observed. The excellent recognition of Cu2＋ cation of this system provides a possibility to develop a new fluorescence sensor for Cu2＋ cation detection.
2004, 20(03): 318-322
doi: 10.3866/PKU.WHXB20040321
Abstract:
The preparation and the thermal decomposition mechanism of nanocrystalline Mg, Al-hydrotalcite were studied. The phase composition and the microstructures of the samples were tested by XRD and TEM. The highly pure acicular nanocrystalline Mg, Al-hydrotalcite was synthesized by the one-step liquid reaction method at atmospheric pressure. Based on the DSC, DTA and TG test results, the thermal properties of the nanocrystalline Mg, Al-hydrotalcite were investigated, and two thermal decomposition process stages were recognized. In its first decomposition stage, the crystal water is released. In its second decomposition stage, the hydroxyl(OH－) octahedral structure is destroyed, with the hydroxyl(OH－) released as the gas of H2O and CO32- anion released as the gas of CO2, and M and Al2O3 are formed. Moreover, it is also found that the longer the reaction time, the higher the beginning decomposition temperature and the more the amount of the residual oxides (M and Al2O3). Besides, the non-isothermal chemical reaction kinetic theory was employed here, and the Šatava-Šesták integral method, Achar differential method and Ozawa integral method were used. After the calculation and comparison, the thermal decomposition mechanical function of the acicular nanocrystalline Mg, Al-hydrotalcite in its second thermal decomposition is confirmed as the functional form of (1－α)－1－1.
The preparation and the thermal decomposition mechanism of nanocrystalline Mg, Al-hydrotalcite were studied. The phase composition and the microstructures of the samples were tested by XRD and TEM. The highly pure acicular nanocrystalline Mg, Al-hydrotalcite was synthesized by the one-step liquid reaction method at atmospheric pressure. Based on the DSC, DTA and TG test results, the thermal properties of the nanocrystalline Mg, Al-hydrotalcite were investigated, and two thermal decomposition process stages were recognized. In its first decomposition stage, the crystal water is released. In its second decomposition stage, the hydroxyl(OH－) octahedral structure is destroyed, with the hydroxyl(OH－) released as the gas of H2O and CO32- anion released as the gas of CO2, and M and Al2O3 are formed. Moreover, it is also found that the longer the reaction time, the higher the beginning decomposition temperature and the more the amount of the residual oxides (M and Al2O3). Besides, the non-isothermal chemical reaction kinetic theory was employed here, and the Šatava-Šesták integral method, Achar differential method and Ozawa integral method were used. After the calculation and comparison, the thermal decomposition mechanical function of the acicular nanocrystalline Mg, Al-hydrotalcite in its second thermal decomposition is confirmed as the functional form of (1－α)－1－1.
2004, 20(03): 323-326
doi: 10.3866/PKU.WHXB20040322
Abstract:
Thermal and electrochemical properties of new low-temperature molten salt electrolytes based on LiClO4 with acetamide or ethyleneurea have been studied by differential scanning calorimetry, ac impedance spectroscopy and cyclic voltammertry, respectively. These electrolytes appear as liquid at room temperature through they are composed of two solids. DSC analysis shows that the LiClO4-acetamide electrolyte has the preferable thermal stability. The conductivity of LiClO4-acetamide electrolyte with a molar ratio of 1.0:5.5 is 1.25×10－3 S•cm－1 at 25 ℃ and 1.15×10－2 S•cm－1 at 80 ℃,and the electrochemical window of it is about 3 V.
Thermal and electrochemical properties of new low-temperature molten salt electrolytes based on LiClO4 with acetamide or ethyleneurea have been studied by differential scanning calorimetry, ac impedance spectroscopy and cyclic voltammertry, respectively. These electrolytes appear as liquid at room temperature through they are composed of two solids. DSC analysis shows that the LiClO4-acetamide electrolyte has the preferable thermal stability. The conductivity of LiClO4-acetamide electrolyte with a molar ratio of 1.0:5.5 is 1.25×10－3 S•cm－1 at 25 ℃ and 1.15×10－2 S•cm－1 at 80 ℃,and the electrochemical window of it is about 3 V.
2004, 20(03): 327-330
doi: 10.3866/PKU.WHXB20040323
Abstract:
It has been known experimentally that, additives, such as LaCl3, lactic acid, Fe2(SO4)3, thiourea and 2,2’-bipyridine, regularly influence the electroless deposition rate, that is, there is a maximum deposition rate with increasing additives concentration. In order to explore this regularity, an adsorption model is proposed and a deposition rate formula is deduced. The deposition rate formula is used to operate nonlinear curve fitting. The fitting curves obtained, correspond with the experimental results. Some parameters can be obtained from the fitting results, such as adsorption equilibrium constants of additives. It is found that the adsorption equilibrium constant on the naked surface (K1) is larger than that on the adsorbed reductant (K2). The larger K1 means that additives adsorb on the naked surface more easily than on the adsorbed reductant. The adsorption ability of different additives also can be illustrated through K1 and K2. For example, the K1, K2 of LaCl3, thiourea and 2,2’-bipyridine are greater than that of lactic acid and Fe2(SO4)3. The comparison indicates that the adsorption ability of LaCl3, thiourea and 2,2’-bipyridine is stronger than that of lactic acid and Fe2(SO4)3. Thus the concentration of LaCl3, thiourea and 2,2’-bipyridine, which corresponds to maximum deposition rate, is smaller than that of lactic acid and Fe2(SO4)3.
It has been known experimentally that, additives, such as LaCl3, lactic acid, Fe2(SO4)3, thiourea and 2,2’-bipyridine, regularly influence the electroless deposition rate, that is, there is a maximum deposition rate with increasing additives concentration. In order to explore this regularity, an adsorption model is proposed and a deposition rate formula is deduced. The deposition rate formula is used to operate nonlinear curve fitting. The fitting curves obtained, correspond with the experimental results. Some parameters can be obtained from the fitting results, such as adsorption equilibrium constants of additives. It is found that the adsorption equilibrium constant on the naked surface (K1) is larger than that on the adsorbed reductant (K2). The larger K1 means that additives adsorb on the naked surface more easily than on the adsorbed reductant. The adsorption ability of different additives also can be illustrated through K1 and K2. For example, the K1, K2 of LaCl3, thiourea and 2,2’-bipyridine are greater than that of lactic acid and Fe2(SO4)3. The comparison indicates that the adsorption ability of LaCl3, thiourea and 2,2’-bipyridine is stronger than that of lactic acid and Fe2(SO4)3. Thus the concentration of LaCl3, thiourea and 2,2’-bipyridine, which corresponds to maximum deposition rate, is smaller than that of lactic acid and Fe2(SO4)3.
2004, 20(03): 331-335
doi: 10.3866/PKU.WHXB20040324
Abstract:
The multi-walled carbon nanotube(MWNT) electrode was constructed using poly-tertrafluoroethylene as binder. The electrochemical behavior of the MWNT electrode in alkaline solution was investigated by chronoamperometry and cyclic voltammetric method, and the electrochemical reduction of dissolved oxygen in alkaline solution was examined on this electrode. Experimental results showed that MWNT electrode had higher porosity and electrochemical surface area than graphite electrode. The reduction of O2 to HO2- on MWNT electrode was a quasi-reversible process, and cathodic peak currents depended linearly on the scan rate over the range of 5～100 mV•s－1, which suggested that the process of the electrode reaction was controlled by the adsorption. The significant differences in voltammetry between the MWNT electrode and the graphite electrode for dissolved oxygen in alkaline solution indicated that MWNT had higher electrocatalytic activity than graphite powders.
The multi-walled carbon nanotube(MWNT) electrode was constructed using poly-tertrafluoroethylene as binder. The electrochemical behavior of the MWNT electrode in alkaline solution was investigated by chronoamperometry and cyclic voltammetric method, and the electrochemical reduction of dissolved oxygen in alkaline solution was examined on this electrode. Experimental results showed that MWNT electrode had higher porosity and electrochemical surface area than graphite electrode. The reduction of O2 to HO2- on MWNT electrode was a quasi-reversible process, and cathodic peak currents depended linearly on the scan rate over the range of 5～100 mV•s－1, which suggested that the process of the electrode reaction was controlled by the adsorption. The significant differences in voltammetry between the MWNT electrode and the graphite electrode for dissolved oxygen in alkaline solution indicated that MWNT had higher electrocatalytic activity than graphite powders.
