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2004 Volume 20 Issue 12
2004, 20(12): 1399-1403
doi: 10.3866/PKU.WHXB20041201
Abstract:
Crack-free homogeneous nanoporous silica films on silicon wafers have been synthesized via supercritical drying of wet gel films that were obtained by spin coating the polymeric silica sol using sol-gel method with tetraethoxysilane(TEOS) as precursor. The silica film was composed of Si－O－Si and Si－OR characterized by FTIR and was hydrophobic. But the silica film became hydrophilic because of Si－OH group after it was heat treated above 250 ℃ in air. So the silica film was modified by trimethylchlorosilane(TMCS) in order to get hydrophobic, thermal stable film with low dielectric constant. The modified silica film was characterized by FTIR, AFM and spectroellipsometer. The modified silica film can keep hydrophobic and its nanoporous structure at temperature lower than 450 ℃ in nitrogen. The sizes of SiO2 primary particles and pores of silica film became larger after modification. The modified silica film had higher porosity and lower dielectric constant. Its dielectric constant could be reduced to below 2.5.
Crack-free homogeneous nanoporous silica films on silicon wafers have been synthesized via supercritical drying of wet gel films that were obtained by spin coating the polymeric silica sol using sol-gel method with tetraethoxysilane(TEOS) as precursor. The silica film was composed of Si－O－Si and Si－OR characterized by FTIR and was hydrophobic. But the silica film became hydrophilic because of Si－OH group after it was heat treated above 250 ℃ in air. So the silica film was modified by trimethylchlorosilane(TMCS) in order to get hydrophobic, thermal stable film with low dielectric constant. The modified silica film was characterized by FTIR, AFM and spectroellipsometer. The modified silica film can keep hydrophobic and its nanoporous structure at temperature lower than 450 ℃ in nitrogen. The sizes of SiO2 primary particles and pores of silica film became larger after modification. The modified silica film had higher porosity and lower dielectric constant. Its dielectric constant could be reduced to below 2.5.
2004, 20(12): 1404-1410
doi: 10.3866/PKU.WHXB20041202
Abstract:
A theoretical investigation of solvent effects on hydroformylation has been carried out at the B3LYP/6-31G (d, p) level (LANL2DZ + Polar for Rh, P) via Onsager model. All stagnation points in the reaction potential profile are optimized completely under condition of cyclohexane (C6H12, ε=2.02), benzene (C6H6, ε=2.25), tetrahydrofuran (THF, ε=7.58), dichloromethane (CH2Cl2, ε=8.93), methanol (CH3OH, ε=32.63) and water (H2O, ε=78.39) as solvent respectively. The free energies and activating free energies are also calculated at the same level and comparison of the data in different solvents are made at all points. These results demonstrate that the activating free energies fall down with increasing of ε value of solvent. Therefore, water with ε=78.39 as solvent for hydroformylation of olefin is considered to be better than the others. The conclusion is consistent with a body of experimental studies.
A theoretical investigation of solvent effects on hydroformylation has been carried out at the B3LYP/6-31G (d, p) level (LANL2DZ + Polar for Rh, P) via Onsager model. All stagnation points in the reaction potential profile are optimized completely under condition of cyclohexane (C6H12, ε=2.02), benzene (C6H6, ε=2.25), tetrahydrofuran (THF, ε=7.58), dichloromethane (CH2Cl2, ε=8.93), methanol (CH3OH, ε=32.63) and water (H2O, ε=78.39) as solvent respectively. The free energies and activating free energies are also calculated at the same level and comparison of the data in different solvents are made at all points. These results demonstrate that the activating free energies fall down with increasing of ε value of solvent. Therefore, water with ε=78.39 as solvent for hydroformylation of olefin is considered to be better than the others. The conclusion is consistent with a body of experimental studies.
2004, 20(12): 1411-1416
doi: 10.3866/PKU.WHXB20041203
Abstract:
Ni-W-B/ZrO2 composite coating was electrodeposited from the Ni-W-B electrolyte solution containing zirconia particles. The electrodeposition, heat treatment, structure, surface morphology, microhardness, and corrosion resistance of the composite coating were studied by means of differential scanning calorimeter (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical techniques. The results showed that the mass composition of the obtained Ni-W-B/ZrO2 composite coating was Ni 47.5％,W 40.9％, B 0.9％ and ZrO2 10.7％. DSC combined with XRD results illustrated that zirconia took a remarkable influence on the structure of Ni-W-B matrix, leading the composite coating to a more obvious amorphous characteristics. The composite coating presented in higher microhardness compared to Ni-W-B alloy, granular structure with grain boundaries and crack-free. Zirconia particles were dispersed in the Ni-W-B matrix. After heat treatment at 400 ℃ for 1 h, surface morphology of the coating was kept almost no changes. The structure of the matrix was transferred to a crystal of Ni-W solid solution, and W was segregated to the surface of the deposit. The microhardness and corrosion resistance were enhanced, whereas most of zirconia particles were tten rid of from the surface layer.
Ni-W-B/ZrO2 composite coating was electrodeposited from the Ni-W-B electrolyte solution containing zirconia particles. The electrodeposition, heat treatment, structure, surface morphology, microhardness, and corrosion resistance of the composite coating were studied by means of differential scanning calorimeter (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical techniques. The results showed that the mass composition of the obtained Ni-W-B/ZrO2 composite coating was Ni 47.5％,W 40.9％, B 0.9％ and ZrO2 10.7％. DSC combined with XRD results illustrated that zirconia took a remarkable influence on the structure of Ni-W-B matrix, leading the composite coating to a more obvious amorphous characteristics. The composite coating presented in higher microhardness compared to Ni-W-B alloy, granular structure with grain boundaries and crack-free. Zirconia particles were dispersed in the Ni-W-B matrix. After heat treatment at 400 ℃ for 1 h, surface morphology of the coating was kept almost no changes. The structure of the matrix was transferred to a crystal of Ni-W solid solution, and W was segregated to the surface of the deposit. The microhardness and corrosion resistance were enhanced, whereas most of zirconia particles were tten rid of from the surface layer.
2004, 20(12): 1417-1422
doi: 10.3866/PKU.WHXB20041204
Abstract:
The potential energy surfaces for the cycloaddition reactions of singlet germylene X2Ge(X=H, CH3, F, Cl, Br) and ethylene were studied using density functional theory (DFT). All the stationary points were determined at the B3LYP/6-311G** theory level .The reaction paths from the transition states to both the reactants and products direction were examined by using the intrinsic reaction coordinate (IRC) .A configuration mixing model (CMM) was used to explain the barrier height and the reaction enthalpy .The results showed that the ground state of germylene X2Ge is singlet .The more electronegative the substitutes X in X2Ge are, the larger ΔES-T of X2Ge will be. It is the electronic factors, rather than the steric factors, that play a decisive role in determining the chemical reactivity of germylene .The reactions are in two steps: (1) germylenes and ethylene form an intermediate complex through an exothermal reaction without any barrier; (2) the intermediate complexes isomerize to give the products.
The potential energy surfaces for the cycloaddition reactions of singlet germylene X2Ge(X=H, CH3, F, Cl, Br) and ethylene were studied using density functional theory (DFT). All the stationary points were determined at the B3LYP/6-311G** theory level .The reaction paths from the transition states to both the reactants and products direction were examined by using the intrinsic reaction coordinate (IRC) .A configuration mixing model (CMM) was used to explain the barrier height and the reaction enthalpy .The results showed that the ground state of germylene X2Ge is singlet .The more electronegative the substitutes X in X2Ge are, the larger ΔES-T of X2Ge will be. It is the electronic factors, rather than the steric factors, that play a decisive role in determining the chemical reactivity of germylene .The reactions are in two steps: (1) germylenes and ethylene form an intermediate complex through an exothermal reaction without any barrier; (2) the intermediate complexes isomerize to give the products.
2004, 20(12): 1423-1427
doi: 10.3866/PKU.WHXB20041205
Abstract:
The ab initio plane-wave ultrasoft pseudopotential method based on generalized gradient approximation (GGA) has been utilized to compare C49 and C54 TiSi2 in terms of the structural, elastic and electronic properties. It has been and found out that C49 TiSi2 has less symmetry and smaller bulk modulus, lower melting point, stronger antibonding states above Femi level, weaker ionicity than C54 TiSi2, even though their formation energies are almost equal to each other.
The ab initio plane-wave ultrasoft pseudopotential method based on generalized gradient approximation (GGA) has been utilized to compare C49 and C54 TiSi2 in terms of the structural, elastic and electronic properties. It has been and found out that C49 TiSi2 has less symmetry and smaller bulk modulus, lower melting point, stronger antibonding states above Femi level, weaker ionicity than C54 TiSi2, even though their formation energies are almost equal to each other.
2004, 20(12): 1428-1433
doi: 10.3866/PKU.WHXB20041206
Abstract:
Using density functional theory(DFT),the geometries and the vibrational frequencies of linear cluster SC2nS2－(n=1～12) have been investigated at the B3LYP/6-31G* level. Time-dependent density functional theory(TD-DFT) has been used to calculate the vertical transition energies and oscillator strengths for transitions of SC2nS2－ at the B3LYP/cc-pvTZ and B3LYP/cc-pvDZ levels. On the basis of theoretical results, an explicit expression for the size dependence of the excitation energy in linear carbon chains is obtained. Present calculations show that the terminal sulfur atom may significantly affect the excited-state properties of the conjugated carbon chains. At the B3LYP/ 6-311＋G*level, the single-point energies of the ionic clusters have been calculated in order to determine the first ionization energies. The relationship between the cluster size and the first ionization energies of the linear carbon chains is proposed.
Using density functional theory(DFT),the geometries and the vibrational frequencies of linear cluster SC2nS2－(n=1～12) have been investigated at the B3LYP/6-31G* level. Time-dependent density functional theory(TD-DFT) has been used to calculate the vertical transition energies and oscillator strengths for transitions of SC2nS2－ at the B3LYP/cc-pvTZ and B3LYP/cc-pvDZ levels. On the basis of theoretical results, an explicit expression for the size dependence of the excitation energy in linear carbon chains is obtained. Present calculations show that the terminal sulfur atom may significantly affect the excited-state properties of the conjugated carbon chains. At the B3LYP/ 6-311＋G*level, the single-point energies of the ionic clusters have been calculated in order to determine the first ionization energies. The relationship between the cluster size and the first ionization energies of the linear carbon chains is proposed.
2004, 20(12): 1434-1439
doi: 10.3866/PKU.WHXB20041207
Abstract:
Eu/Ti/Si composite photocatalysts were prepared by sol-gel-soaking process and characterized by XRD, FT-IR and EPR. It has been shown that the particle diameter of Eu/Ti/Si photocatalysts decreased, the crystal transformation of titania from anatase to rutile was prevented, and the incorporation of Si4＋ into the matrix of the TiO2 was promoted owing to the co-doping of Si4＋ and Eu3＋. As a model reaction, the photocatalytic degradation of methyl orange was investigated. The adsorption constants of methyl orange over catalysts were evaluated and the adsorption mechanism was also discussed. Optimal doping amounts for Si4＋ and Eu3＋ are wSiO2=39.06％ and wEu=0.03％ respectively, and the co-doping of them shows a synergistic effect for photocatalytic activity of titanium dioxide. Relation between photocatalytic activity and property of the photocatalyst was discussed.
Eu/Ti/Si composite photocatalysts were prepared by sol-gel-soaking process and characterized by XRD, FT-IR and EPR. It has been shown that the particle diameter of Eu/Ti/Si photocatalysts decreased, the crystal transformation of titania from anatase to rutile was prevented, and the incorporation of Si4＋ into the matrix of the TiO2 was promoted owing to the co-doping of Si4＋ and Eu3＋. As a model reaction, the photocatalytic degradation of methyl orange was investigated. The adsorption constants of methyl orange over catalysts were evaluated and the adsorption mechanism was also discussed. Optimal doping amounts for Si4＋ and Eu3＋ are wSiO2=39.06％ and wEu=0.03％ respectively, and the co-doping of them shows a synergistic effect for photocatalytic activity of titanium dioxide. Relation between photocatalytic activity and property of the photocatalyst was discussed.
2004, 20(12): 1440-1444
doi: 10.3866/PKU.WHXB20041208
Abstract:
A novel orgnaosulfur cathode material named phenyl polysulfide(PPS) for lithium batteries was studied. The highly crosslinked stucture of this material with phenyl repeat units covalently linked by －Sx－moieties(x≥ 2) was designed to reduce the generation of small molecule during discharging which was one of the main reasons for its cycling capacity fade. A series of PPS with different sulfur contents were prepared through the reaction between hexachlorobenzene and Na2Sx(x ≥ 2). Galvanostatic cycling and cyclic voltammetry were used to investigate the electrochemical characteristics of this material. The results demonstrated that higher sulfur content of the material led to higher discharge capacity but more serious capacity fade during cycling. The sample PPS-10 containing 91.99％ sulfur exhibited high capacity up to 756 mAh·g－1 in the initial cycle and a stable reversible capacity 367 mAh·g－1 after 20 cycles. The discharge mechanism, the reason for capacity fade during cycling and poor coulomb efficiency of the materials were also discussed.
A novel orgnaosulfur cathode material named phenyl polysulfide(PPS) for lithium batteries was studied. The highly crosslinked stucture of this material with phenyl repeat units covalently linked by －Sx－moieties(x≥ 2) was designed to reduce the generation of small molecule during discharging which was one of the main reasons for its cycling capacity fade. A series of PPS with different sulfur contents were prepared through the reaction between hexachlorobenzene and Na2Sx(x ≥ 2). Galvanostatic cycling and cyclic voltammetry were used to investigate the electrochemical characteristics of this material. The results demonstrated that higher sulfur content of the material led to higher discharge capacity but more serious capacity fade during cycling. The sample PPS-10 containing 91.99％ sulfur exhibited high capacity up to 756 mAh·g－1 in the initial cycle and a stable reversible capacity 367 mAh·g－1 after 20 cycles. The discharge mechanism, the reason for capacity fade during cycling and poor coulomb efficiency of the materials were also discussed.
2004, 20(12): 1445-1450
doi: 10.3866/PKU.WHXB20041209
Abstract:
Oxygen adsorbed on Pt stepped surfaces has been studied by means of the 5-parameter morse potential(5-MP) of interaction between an adatom and metal surface cluster .The theoretical calculated results about O/Pt(s)-[n(111)×(100)] systems draw some conclusions. The four-fold site behind a step that an oxygen atom binds in corresponds to the most stable state named β2-state. And the three-fold site near the four-fold site at a (111) terrace is annihilated, then the other three-fold sites correspond to adsorption states named β1-state. In addition the length of the (111) terrace has effect on the four-fold state.
Oxygen adsorbed on Pt stepped surfaces has been studied by means of the 5-parameter morse potential(5-MP) of interaction between an adatom and metal surface cluster .The theoretical calculated results about O/Pt(s)-[n(111)×(100)] systems draw some conclusions. The four-fold site behind a step that an oxygen atom binds in corresponds to the most stable state named β2-state. And the three-fold site near the four-fold site at a (111) terrace is annihilated, then the other three-fold sites correspond to adsorption states named β1-state. In addition the length of the (111) terrace has effect on the four-fold state.
2004, 20(12): 1451-1454
doi: 10.3866/PKU.WHXB20041210
Abstract:
The relationship of surface property and hydrophobic branched-chain structure was studied using four branched-alkylbenzenesulfonates with additional alkyl substituents synthesized by our laboratory. From the surface tension measurements in pure water and 0.171 mol·L－1 NaCl solutions, the following parameters were calculated: critical micelle concentration (cmc), the surface tension at the cmc (γcmc),surface excess at the cmc (Γmax),area per molecule at the cmc (Amin), pc20, and standard free energy of adsorption (DGadӨ).Lengthening the branched alkyl chain at the meta-position of sulfonic group,Γmax decreased while γcmc decreased; At the same time, cmc decreased, pc20 increased, and DGadӨ became more negative. These results indicated that the hard-disk areas of sodium branched-alkylbenzenesulfonate molecules (as) affected adsorption and surface tension.
The relationship of surface property and hydrophobic branched-chain structure was studied using four branched-alkylbenzenesulfonates with additional alkyl substituents synthesized by our laboratory. From the surface tension measurements in pure water and 0.171 mol·L－1 NaCl solutions, the following parameters were calculated: critical micelle concentration (cmc), the surface tension at the cmc (γcmc),surface excess at the cmc (Γmax),area per molecule at the cmc (Amin), pc20, and standard free energy of adsorption (DGadӨ).Lengthening the branched alkyl chain at the meta-position of sulfonic group,Γmax decreased while γcmc decreased; At the same time, cmc decreased, pc20 increased, and DGadӨ became more negative. These results indicated that the hard-disk areas of sodium branched-alkylbenzenesulfonate molecules (as) affected adsorption and surface tension.
2004, 20(12): 1455-1458
doi: 10.3866/PKU.WHXB20041211
Abstract:
Molecular structures of fourteen 2-thioxanthine tautomers were calculated by the B3LYP /6-311G** method, both in the gas and aqueous phases, with full geometry optimization. The Onsager solvate theory model was employed for aqueous solution calculations. The structures, total energy, standard enthalpy, standard entropy and standard Gibbs free energy were obtained. The calculations show that 2-thioxanthine existing as the thione(keto) forms is the predominant tautomer in the gas and aqueous phases. The thione(keto)-N(7)(H) tautomer is more stable than the thione(keto)-N(9)(H) tautomer in the gas and aqueous phases. The results are in od agreement with available experimental results. The entropy effect on the Gibbs free energy of 2-thioxanthine base is very small and there is little significance for the tautomeric equilibria of the base.The enthalpic term is dominant in the determination of tautomeric equilibria. The free energy of solvation is well correlated with the dipole moments of 2-thioxanthine tautomer. Additionally, the relative stabilities of 2-thioxanthine tautomers and 6-thioxan thine ones were examined.
Molecular structures of fourteen 2-thioxanthine tautomers were calculated by the B3LYP /6-311G** method, both in the gas and aqueous phases, with full geometry optimization. The Onsager solvate theory model was employed for aqueous solution calculations. The structures, total energy, standard enthalpy, standard entropy and standard Gibbs free energy were obtained. The calculations show that 2-thioxanthine existing as the thione(keto) forms is the predominant tautomer in the gas and aqueous phases. The thione(keto)-N(7)(H) tautomer is more stable than the thione(keto)-N(9)(H) tautomer in the gas and aqueous phases. The results are in od agreement with available experimental results. The entropy effect on the Gibbs free energy of 2-thioxanthine base is very small and there is little significance for the tautomeric equilibria of the base.The enthalpic term is dominant in the determination of tautomeric equilibria. The free energy of solvation is well correlated with the dipole moments of 2-thioxanthine tautomer. Additionally, the relative stabilities of 2-thioxanthine tautomers and 6-thioxan thine ones were examined.
2004, 20(12): 1459-1464
doi: 10.3866/PKU.WHXB20041212
Abstract:
Keeping the atomic ratio of nM2+/nM3+ at 3, series of CuMgAl-O oxides (wCuO=0％, 5％, 10％, 15％, 20％, 30％, 40％,denoted as (0, 5, 10, 15, 20, 30, 40)CMAO respectively) were derived from calcination of Cu substituted Mg/Al-mixed anionic clay precursors(CuMgAl-hydrotalites, CMA-HTs), which were synthesized by co-precipitation methods. XRD, TG-DSC, TPR and FT-IR were used to study the influences of the Cu, Mg content upon the properties of precursors and prepared catalysts. Mg could improve thermal stability of catalysts in some degree. With the increase of Cu content, the surface area of catalysts decreased. However, the surface area was not an important factor in soot catalytic combustion. Activity tests showed the calcination affected the activity of CMAO catalysts significantly, and that 15CMAO-800 was the optimal catalyst for soot catalytic combustion and the T10 and T50 were 336 ℃ and 409 ℃ respectively. Moreover, complete structures of hydrotalcite precursors could be formed when wCuO≤30％. However, Cu(OH)2 phase appeared when wCuO =40％. When wCuO < 20％, homogeneous composite oxides could be obtained by calcination at 800 ℃, but CuO phase was isolated when wCuO≥20％. TG-DTA and FT-IR showed that the content of Cu, Mg had significant influences on the thermal decomposition characteristics of CuMgAl-hydrotalcites. TPR results showed that the reduction ability of catalysts was determined by the calcination and composition.
Keeping the atomic ratio of nM2+/nM3+ at 3, series of CuMgAl-O oxides (wCuO=0％, 5％, 10％, 15％, 20％, 30％, 40％,denoted as (0, 5, 10, 15, 20, 30, 40)CMAO respectively) were derived from calcination of Cu substituted Mg/Al-mixed anionic clay precursors(CuMgAl-hydrotalites, CMA-HTs), which were synthesized by co-precipitation methods. XRD, TG-DSC, TPR and FT-IR were used to study the influences of the Cu, Mg content upon the properties of precursors and prepared catalysts. Mg could improve thermal stability of catalysts in some degree. With the increase of Cu content, the surface area of catalysts decreased. However, the surface area was not an important factor in soot catalytic combustion. Activity tests showed the calcination affected the activity of CMAO catalysts significantly, and that 15CMAO-800 was the optimal catalyst for soot catalytic combustion and the T10 and T50 were 336 ℃ and 409 ℃ respectively. Moreover, complete structures of hydrotalcite precursors could be formed when wCuO≤30％. However, Cu(OH)2 phase appeared when wCuO =40％. When wCuO < 20％, homogeneous composite oxides could be obtained by calcination at 800 ℃, but CuO phase was isolated when wCuO≥20％. TG-DTA and FT-IR showed that the content of Cu, Mg had significant influences on the thermal decomposition characteristics of CuMgAl-hydrotalcites. TPR results showed that the reduction ability of catalysts was determined by the calcination and composition.
2004, 20(12): 1465-1468
doi: 10.3866/PKU.WHXB20041213
Abstract:
Under the atmosphere of air and nitrogen, the thermal properties of 1-n-butyl-3-methylimidazolium bromide ionic liquid were studied with TGA-FTIR technique. Experimental results showed that the ionic liquid had certain vaporization pressure around its boiling point. This ionic liquid was mainly evaporated with increasing scanning temperature and no obvious decomposition was observed during the vaporization process. In the process of TGA, carbonization may occur. At the same time, oxidation may occur under the air atmosphere and the rates of carbonization and oxidation were nearly the same. In higher temperature, the carbonization and oxidation products were oxidized thoroughly.
Under the atmosphere of air and nitrogen, the thermal properties of 1-n-butyl-3-methylimidazolium bromide ionic liquid were studied with TGA-FTIR technique. Experimental results showed that the ionic liquid had certain vaporization pressure around its boiling point. This ionic liquid was mainly evaporated with increasing scanning temperature and no obvious decomposition was observed during the vaporization process. In the process of TGA, carbonization may occur. At the same time, oxidation may occur under the air atmosphere and the rates of carbonization and oxidation were nearly the same. In higher temperature, the carbonization and oxidation products were oxidized thoroughly.
2004, 20(12): 1469-1471
doi: 10.3866/PKU.WHXB20041214
Abstract:
Using RBC-Ⅱ type oxygen-bomb combustion calorimeter, the molar combustion enthalpies of room temperature ionic liquid, 1-ethyl-3-methylimidazolium ethyl sulfate (EMIES), and 1-methylimidazole were determined at T=(298.15±0.01) K. For EMIES =(－2671±2) kJ·mol－1 and for 1-methylimidazole (－286.3±0.5) kJ·mol－1, respectively. The standard formation enthalpies were calculated to be (－3060±3) kJ·mol－1 for EMIES and (－2145±4) kJ·mol－1 for 1-methylimidazole. The reaction: ＋ (C2H5)2SO4 → [ ＋ C2H5OSO3－ ](l) is strong exothermic and its reaction heat, , was determined to be (－102.3±1.0) kJ·mol－1. The standard formation enthalpy of EMIES, ΔfHT, at different temperatures was calculated on the basis of the heat capacity data of EMIES.
Using RBC-Ⅱ type oxygen-bomb combustion calorimeter, the molar combustion enthalpies of room temperature ionic liquid, 1-ethyl-3-methylimidazolium ethyl sulfate (EMIES), and 1-methylimidazole were determined at T=(298.15±0.01) K. For EMIES =(－2671±2) kJ·mol－1 and for 1-methylimidazole (－286.3±0.5) kJ·mol－1, respectively. The standard formation enthalpies were calculated to be (－3060±3) kJ·mol－1 for EMIES and (－2145±4) kJ·mol－1 for 1-methylimidazole. The reaction: ＋ (C2H5)2SO4 → [ ＋ C2H5OSO3－ ](l) is strong exothermic and its reaction heat, , was determined to be (－102.3±1.0) kJ·mol－1. The standard formation enthalpy of EMIES, ΔfHT, at different temperatures was calculated on the basis of the heat capacity data of EMIES.
2004, 20(12): 1472-1475
doi: 10.3866/PKU.WHXB20041215
Abstract:
Metallic tin was directly dissolved in ethylene glycol monomethyl ether and Sn(OCH2CH2OCH3)4 was obtained. The products were characterized by using FT-IR and Raman spectrum. The results show that direct electrochemical preparation of tin complexes has high current efficiency and electrolysis yield, and Sn(OCH2CH2OCH3)4 can be dissolved in ethanol solution and directly used as sol-gel precursor for preparation of nanometer SnO2. The results also show that nano-sized SnO2 prepared by this method has tetra nal cassiterite structure with a narrow size distribution of (10.0±0.4) nm.
Metallic tin was directly dissolved in ethylene glycol monomethyl ether and Sn(OCH2CH2OCH3)4 was obtained. The products were characterized by using FT-IR and Raman spectrum. The results show that direct electrochemical preparation of tin complexes has high current efficiency and electrolysis yield, and Sn(OCH2CH2OCH3)4 can be dissolved in ethanol solution and directly used as sol-gel precursor for preparation of nanometer SnO2. The results also show that nano-sized SnO2 prepared by this method has tetra nal cassiterite structure with a narrow size distribution of (10.0±0.4) nm.
2004, 20(12): 1476-1480
doi: 10.3866/PKU.WHXB20041216
Abstract:
Potential energy of poly(m-phenylene)(PMP, P1) and the related derivatives (P2,P3) as a function of torsion angles(f) were constructed by using molecular mechanics method based on force field(Drieding 2.11). It is found that there are four minima in potential energy curve, which correspond to four torsion angles (f ≈－135°, －45°, 135°, 45°) respectively. Furthermore, all constructed PMP and derivatives are minimized by molecular force field, and four main conformations are found. For PMP, two helical conformations have minimal energy, and they have preponderant population. Under the real conditions, PMP and derivatives polymer chain may consist of above stable conformation segments with an equilibrium ratio, which depends on polymer surroundings. The electronic structure (HOMO-LUMO gap) prediction depending on torsion angles was calculated by GGA-DFT method using Dmol3 program. The AM1 method was used to investigate geometry optimization, and the optimized conformations are basically consistent with that simulated by molecular mechanics. In order to get more accurate HOMO-LUMO gap of above optimized geometries, the hybrid functional B3LYP was adopted at the level of 6-31G basis set using Gaussian98 software. At last, it is found that the twist extent of torsion angle between phenyl rings is the main factor that affects HOMO-LUMO gap of PMP and its derivatives.
Potential energy of poly(m-phenylene)(PMP, P1) and the related derivatives (P2,P3) as a function of torsion angles(f) were constructed by using molecular mechanics method based on force field(Drieding 2.11). It is found that there are four minima in potential energy curve, which correspond to four torsion angles (f ≈－135°, －45°, 135°, 45°) respectively. Furthermore, all constructed PMP and derivatives are minimized by molecular force field, and four main conformations are found. For PMP, two helical conformations have minimal energy, and they have preponderant population. Under the real conditions, PMP and derivatives polymer chain may consist of above stable conformation segments with an equilibrium ratio, which depends on polymer surroundings. The electronic structure (HOMO-LUMO gap) prediction depending on torsion angles was calculated by GGA-DFT method using Dmol3 program. The AM1 method was used to investigate geometry optimization, and the optimized conformations are basically consistent with that simulated by molecular mechanics. In order to get more accurate HOMO-LUMO gap of above optimized geometries, the hybrid functional B3LYP was adopted at the level of 6-31G basis set using Gaussian98 software. At last, it is found that the twist extent of torsion angle between phenyl rings is the main factor that affects HOMO-LUMO gap of PMP and its derivatives.
2004, 20(12): 1481-1501
Abstract:
2004, 20(12): 1502-1510
Abstract:
