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2016 Volume 32 Issue 3
2016, 32(3): 595-604
doi: 10.3866/PKU.WHXB201512211
Abstract:
Directed relation graph (DRG) based skeletal reduction methods have become the mainstream approach for skeletal mechanism generation because of their simple concept and low computational cost. Within the DRG framework, the definitions of the interaction coefficients and the connection weights in different DRG methods control the resulting skeletal mechanisms. In this work, based on DRG methods, four contemporary definitions of the interaction coefficients in conjunction with both standard DRG and error propagation (EP) graph search methods are used to derive skeletal mechanisms for methyl butanoate (MB) combustion. Detailed comparisons of contemporary DRG based methods are performed by systematic error analysis. To further evaluate the performance of the different DRG-based methods, reaction paths are investigated via element flux analysis to check the chemical kinetics of the resulting skeletal mechanisms. Furthermore, a 96-species skeletal mechanism for MB combustion is proposed. Reaction path analysis highlights the importance of propene chemistry during MB oxidation. This work reveals the applicability of reaction path analysis in skeletal reduction using different DRG-based methods, and also provides critical information for further development of skeletal reduction methods.
Directed relation graph (DRG) based skeletal reduction methods have become the mainstream approach for skeletal mechanism generation because of their simple concept and low computational cost. Within the DRG framework, the definitions of the interaction coefficients and the connection weights in different DRG methods control the resulting skeletal mechanisms. In this work, based on DRG methods, four contemporary definitions of the interaction coefficients in conjunction with both standard DRG and error propagation (EP) graph search methods are used to derive skeletal mechanisms for methyl butanoate (MB) combustion. Detailed comparisons of contemporary DRG based methods are performed by systematic error analysis. To further evaluate the performance of the different DRG-based methods, reaction paths are investigated via element flux analysis to check the chemical kinetics of the resulting skeletal mechanisms. Furthermore, a 96-species skeletal mechanism for MB combustion is proposed. Reaction path analysis highlights the importance of propene chemistry during MB oxidation. This work reveals the applicability of reaction path analysis in skeletal reduction using different DRG-based methods, and also provides critical information for further development of skeletal reduction methods.
2016, 32(3): 605-610
doi: 10.3866/PKU.WHXB201512241
Abstract:
Four tetrabutylphosphonium carboxylate ionic liquids ([P4444][CA]) were prepared, and their densities, viscosities, refractive indices, and conductivities were measured and correlated with thermodynamic and empirical equations in the temperature range of 298.15-348.15 K. The influence of temperature on these four properties of [P4444][CA] was discussed, and their thermal expansion coefficient values were calculated. The CO2 absorption capacity of [P4444][CA] was studied at 313.15 K and 100 kPa. The results indicated that [P4444][Buty] had the highest CO2 capture capacity among these ionic liquids, with an absorption capacity of 0.4 mol·mol-1 and balance time of less than 5 min.
Four tetrabutylphosphonium carboxylate ionic liquids ([P4444][CA]) were prepared, and their densities, viscosities, refractive indices, and conductivities were measured and correlated with thermodynamic and empirical equations in the temperature range of 298.15-348.15 K. The influence of temperature on these four properties of [P4444][CA] was discussed, and their thermal expansion coefficient values were calculated. The CO2 absorption capacity of [P4444][CA] was studied at 313.15 K and 100 kPa. The results indicated that [P4444][Buty] had the highest CO2 capture capacity among these ionic liquids, with an absorption capacity of 0.4 mol·mol-1 and balance time of less than 5 min.
2016, 32(3): 611-616
doi: 10.3866/PKU.WHXB201601044
Abstract:
A ferrocene homodimer was assembled via the ureidopyrimidinone quadruple hydrogen-bonded module in this paper. Remarkable electronic communication was found between the two ferrocene centers across the ureidopyrimidinone bridge in chloroform. The separation between the two redox potentials (ΔE) of the ferrocenyl moieties was 260 mV. Upon protonation of the hydrogen-bonded bridge by successive addition of 0.5, 1, and 2 equivalents of trifluoroacetic acid, the extent of the electronic communication between the subunits gradually lowered, with ΔE decreasing to 150, 100, and 0 mV, respectively, because of the stepwise dissociation of the pyrimidinone hydrogen-bonded bridge. This phenomenon is reversible, and the initial voltammogram can be recovered stepwise by successive addition of triethylamine, demonstrating effective control of the electronic communication between two ferrocene centers.
A ferrocene homodimer was assembled via the ureidopyrimidinone quadruple hydrogen-bonded module in this paper. Remarkable electronic communication was found between the two ferrocene centers across the ureidopyrimidinone bridge in chloroform. The separation between the two redox potentials (ΔE) of the ferrocenyl moieties was 260 mV. Upon protonation of the hydrogen-bonded bridge by successive addition of 0.5, 1, and 2 equivalents of trifluoroacetic acid, the extent of the electronic communication between the subunits gradually lowered, with ΔE decreasing to 150, 100, and 0 mV, respectively, because of the stepwise dissociation of the pyrimidinone hydrogen-bonded bridge. This phenomenon is reversible, and the initial voltammogram can be recovered stepwise by successive addition of triethylamine, demonstrating effective control of the electronic communication between two ferrocene centers.
2016, 32(3): 617-623
doi: 10.3866/PKU.WHXB201512171
Abstract:
The functional ionic liquid (FIL) 1-(cyanopropyl)-3-methylimidazolium bis[(trifluoromethyl)sulfonyl] imide [PCNMIM][NTf2] was synthesized using an ion-exchange method. Density, dynamic viscosity, electrical conductivity, and refractive index were determined in the temperature range 283.15-353.15 K. The effect of methylene group introduction is discussed for the FILs and imidazolium ionic liquids (ILs). The thermal expansion coefficient, molecular volume, standard molar entropy, and lattice energy were determined by the empirical equations from the measurement values. The temperature dependence on electrical conductivity and dynamic viscosity of the FILs were fitted by the Vogel-Fulcher-Tammann (VFT) equation. The adaptability of the Arrhenius equation was also discussed for the electrical conductivity and dynamic viscosity. The study of the thermodynamic properties of the FIL is important for synthesis of new ILs and their application.
The functional ionic liquid (FIL) 1-(cyanopropyl)-3-methylimidazolium bis[(trifluoromethyl)sulfonyl] imide [PCNMIM][NTf2] was synthesized using an ion-exchange method. Density, dynamic viscosity, electrical conductivity, and refractive index were determined in the temperature range 283.15-353.15 K. The effect of methylene group introduction is discussed for the FILs and imidazolium ionic liquids (ILs). The thermal expansion coefficient, molecular volume, standard molar entropy, and lattice energy were determined by the empirical equations from the measurement values. The temperature dependence on electrical conductivity and dynamic viscosity of the FILs were fitted by the Vogel-Fulcher-Tammann (VFT) equation. The adaptability of the Arrhenius equation was also discussed for the electrical conductivity and dynamic viscosity. The study of the thermodynamic properties of the FIL is important for synthesis of new ILs and their application.
2016, 32(3): 624-630
doi: 10.3866/PKU.WHXB201512291
Abstract:
The excited-state intramolecular proton transfer of 2-(2-aminophenyl)benzothiazole (APBT) in different environments was detected by steady-state and transient fluorescence spectral measurements and quantum chemical calculations. The results showed that the polarity and protonation of the solution strongly affect the proton transfer of APBT. When APBT and cucurbit[7]uril (CB[7]) were mixed with each other, we found that the proton transfer process of APBT was restrained by the formation of a complex with a stoichiometric ratio of 1 : 1. The association constant and thermodynamic parameters of this complex were calculated. 1H NMR spectroscopy and quantum chemical calculation data indicated that a 1 : 1 APBT@CB[7] complex of the amine or imine tautomer of APBT formed.
The excited-state intramolecular proton transfer of 2-(2-aminophenyl)benzothiazole (APBT) in different environments was detected by steady-state and transient fluorescence spectral measurements and quantum chemical calculations. The results showed that the polarity and protonation of the solution strongly affect the proton transfer of APBT. When APBT and cucurbit[7]uril (CB[7]) were mixed with each other, we found that the proton transfer process of APBT was restrained by the formation of a complex with a stoichiometric ratio of 1 : 1. The association constant and thermodynamic parameters of this complex were calculated. 1H NMR spectroscopy and quantum chemical calculation data indicated that a 1 : 1 APBT@CB[7] complex of the amine or imine tautomer of APBT formed.
2016, 32(3): 631-637
doi: 10.3866/PKU.WHXB201512281
Abstract:
Based on the cluster model of molten ternary silicates, the thermodynamic properties, including entropy, enthalpy, and heat capacity of Na2O-Al2O3-SiO2 at 1473, 1873, and 2000 K were calculated by the modified neglect of differential overlap (MNDO/d) semi-empirical method based on the primitive assumption of clusters in the melt. The mixing free energies of the Na2O-Al2O3-SiO2 ternary system were derived. The mixing free energy of the Na2O-Al2O3-SiO2 ternary system is the sum of all the cluster units that exist according to the Boltzmann distribution law. The thermodynamic properties of this ternary silicate melt depend on its microstructure.
Based on the cluster model of molten ternary silicates, the thermodynamic properties, including entropy, enthalpy, and heat capacity of Na2O-Al2O3-SiO2 at 1473, 1873, and 2000 K were calculated by the modified neglect of differential overlap (MNDO/d) semi-empirical method based on the primitive assumption of clusters in the melt. The mixing free energies of the Na2O-Al2O3-SiO2 ternary system were derived. The mixing free energy of the Na2O-Al2O3-SiO2 ternary system is the sum of all the cluster units that exist according to the Boltzmann distribution law. The thermodynamic properties of this ternary silicate melt depend on its microstructure.
2016, 32(3): 638-646
doi: 10.3866/PKU.WHXB201512181
Abstract:
Mesoporous TiO2 was prepared by calcinating H2Ti205 at 773.15 K. The sample was characterized by Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), Raman spectroscopy, and X-ray diffraction (XRD) analysis. The adsorption behavior and mechanism of mesoporous TiO2 for lysozyme were investigated by isothermal adsorption experiments. The results show that the equilibrium experimental data were correlated with the Langmuir isotherm equation. The adsorption capacity first increased and then decreased with increasing pH value. The capacity showed a maximum value of 72.5 mg·g-1 when the pH value was 7.2. Lysozyme adsorbed on mesoporous TiO2 was extremely stable, and its amount on mesoporous TiO2 maintained 81.6% of its initial value after five adsorption and regeneration cycles. Furthermore, kinetic analysis was conducted using pseudo-first and pseudo-second order models. The adsorption of lysozyme on mesoporous TiO2 was described well by the pseudo-second order rate equation. The rate-determining step of the adsorption was the combined action of film diffusion and intraparticle diffusion. The adsorption thermodynamic analysis suggested ΔG0 < 0, ΔH0 > 0, and ΔS0 > 0, which indicated that the adsorption was a spontaneous and endothermic process with entropy increased.
Mesoporous TiO2 was prepared by calcinating H2Ti205 at 773.15 K. The sample was characterized by Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), Raman spectroscopy, and X-ray diffraction (XRD) analysis. The adsorption behavior and mechanism of mesoporous TiO2 for lysozyme were investigated by isothermal adsorption experiments. The results show that the equilibrium experimental data were correlated with the Langmuir isotherm equation. The adsorption capacity first increased and then decreased with increasing pH value. The capacity showed a maximum value of 72.5 mg·g-1 when the pH value was 7.2. Lysozyme adsorbed on mesoporous TiO2 was extremely stable, and its amount on mesoporous TiO2 maintained 81.6% of its initial value after five adsorption and regeneration cycles. Furthermore, kinetic analysis was conducted using pseudo-first and pseudo-second order models. The adsorption of lysozyme on mesoporous TiO2 was described well by the pseudo-second order rate equation. The rate-determining step of the adsorption was the combined action of film diffusion and intraparticle diffusion. The adsorption thermodynamic analysis suggested ΔG0 < 0, ΔH0 > 0, and ΔS0 > 0, which indicated that the adsorption was a spontaneous and endothermic process with entropy increased.
2016, 32(3): 647-655
doi: 10.3866/PKU.WHXB201601042
Abstract:
The structure and thermodynamics of CeCl3 in molten LiCl-KCl-CeCl3 mixtures were studied by molecular dynamics simulation. The relationship formulas of temperature and density, and composition and density were obtained. The first peak for the gCe-Cl(r) radial distribution function was located at 0.259 nm and the corresponding first coordination number of Ce3+ was ~6.9. This inconsistency between molecular dynamics and experimental data could be attributed to the fact that our values were obtained for molten LiCl-KCl-CeCl3 mixtures, in which the interaction between Ce3+ and Cl- was more powerful than that in pure molten CeCl3. Regarding self-diffusion coefficients, the activation energy of Ce3+ was 22.5 kJ·mol-1, which is smaller than that of U3+ (25.8 kJ·mol-1). Furthermore, the pre-exponential factors for Ce3+ decreased from 31.9×10-5 to 21.8×10-5 cm2·s-1 as the molar fraction of Ce3+ increased from 0.005 to 0.05. This means that in the unit volume (ignoring the change of total volume), the diffusion resistance of Ce3+ increased, and the self-diffusion ability decreased, which resulted in a decrease of pre-exponential factors.
The structure and thermodynamics of CeCl3 in molten LiCl-KCl-CeCl3 mixtures were studied by molecular dynamics simulation. The relationship formulas of temperature and density, and composition and density were obtained. The first peak for the gCe-Cl(r) radial distribution function was located at 0.259 nm and the corresponding first coordination number of Ce3+ was ~6.9. This inconsistency between molecular dynamics and experimental data could be attributed to the fact that our values were obtained for molten LiCl-KCl-CeCl3 mixtures, in which the interaction between Ce3+ and Cl- was more powerful than that in pure molten CeCl3. Regarding self-diffusion coefficients, the activation energy of Ce3+ was 22.5 kJ·mol-1, which is smaller than that of U3+ (25.8 kJ·mol-1). Furthermore, the pre-exponential factors for Ce3+ decreased from 31.9×10-5 to 21.8×10-5 cm2·s-1 as the molar fraction of Ce3+ increased from 0.005 to 0.05. This means that in the unit volume (ignoring the change of total volume), the diffusion resistance of Ce3+ increased, and the self-diffusion ability decreased, which resulted in a decrease of pre-exponential factors.
2016, 32(3): 656-664
doi: 10.3866/PKU.WHXB201512292
Abstract:
Density functional theory calculations were carried out on oxygen-deficient TiO2-B to evaluate the effect of oxygen vacancies on its electrochemical properties. The computational studies focused on the lithium (Li)-ion transport and electronic conductivity of this defect-containing material. Calculations on TiO2-B with low Li-ion concentration (x(Li/Ti) ⩽ 0.25) suggest that compared with defect-free TiO2-B, oxygen-deficient TiO2-B has a higher intercalation voltage and lower migration activation energy along the b-axis channel. This facilitates Li-ion intercalation, which is beneficial for the charge process of rechargeable batteries. Meanwhile, for TiO2-B with high Li-ion concentration (x(Li/Ti) = 1), saturated oxygen-deficient TiO2-B with lower insertion voltage favors Li-ion deintercalation, which aids the discharge process. Electronic structure calculations suggest that the band gap of this defect-containing material is within 1.0-2.0 eV, which is narrower than that of defect-free TiO2-B (3.0 eV). The main contributor to the band-gap narrowing is the density of the Ti-Ov-3d state, which becomes much higher as the oxygen vacancy content increases, which increases electronic conductivity.
Density functional theory calculations were carried out on oxygen-deficient TiO2-B to evaluate the effect of oxygen vacancies on its electrochemical properties. The computational studies focused on the lithium (Li)-ion transport and electronic conductivity of this defect-containing material. Calculations on TiO2-B with low Li-ion concentration (x(Li/Ti) ⩽ 0.25) suggest that compared with defect-free TiO2-B, oxygen-deficient TiO2-B has a higher intercalation voltage and lower migration activation energy along the b-axis channel. This facilitates Li-ion intercalation, which is beneficial for the charge process of rechargeable batteries. Meanwhile, for TiO2-B with high Li-ion concentration (x(Li/Ti) = 1), saturated oxygen-deficient TiO2-B with lower insertion voltage favors Li-ion deintercalation, which aids the discharge process. Electronic structure calculations suggest that the band gap of this defect-containing material is within 1.0-2.0 eV, which is narrower than that of defect-free TiO2-B (3.0 eV). The main contributor to the band-gap narrowing is the density of the Ti-Ov-3d state, which becomes much higher as the oxygen vacancy content increases, which increases electronic conductivity.
2016, 32(3): 665-670
doi: 10.3866/PKU.WHXB201512252
Abstract:
Supramolecular complex (1) was obtained from a mixture of squaric acid and 2,6-bis(2-benzimidazolyl)pyridine in deuterated dimethylsulfoxide (d-DMSO) and characterized by single-crystal X-ray diffraction. The crystal structure data showed that 1 was a one-dimensional chain polymer assembled through π-π stacking and hydrogen bonding interactions. Infrared vibrational spectra of 1 were measured at different temperatures and sample concentrations in carbon tetrachloride. Moreover, the hydrogen bonding in the crystals was further evaluated by density functional theory (DFT) and atoms in molecules (AIM) theory. The calculated hydrogen bonding energies were about 135.65 and 49.40 J·mol-1, respectively.
Supramolecular complex (1) was obtained from a mixture of squaric acid and 2,6-bis(2-benzimidazolyl)pyridine in deuterated dimethylsulfoxide (d-DMSO) and characterized by single-crystal X-ray diffraction. The crystal structure data showed that 1 was a one-dimensional chain polymer assembled through π-π stacking and hydrogen bonding interactions. Infrared vibrational spectra of 1 were measured at different temperatures and sample concentrations in carbon tetrachloride. Moreover, the hydrogen bonding in the crystals was further evaluated by density functional theory (DFT) and atoms in molecules (AIM) theory. The calculated hydrogen bonding energies were about 135.65 and 49.40 J·mol-1, respectively.
2016, 32(3): 671-682
doi: 10.3866/PKU.WHXB201512293
Abstract:
Acting as a molecular linker, the pnicogen bond plays an important role in crystal engineering and supramolecular synthesis. The structures and properties of π-hole pnicogen-bonded complexes PO2X…PX3 and PO2X…PH2X (X = F, Cl, Br, CH3, NH2) were investigated by ab initio MP2/aug-cc-pVTZ calculations and topological analyses of electron density. Two sets of π-hole pnicogen-bonded complexes were found on the potential surfaces. Type-A complexes have P…P and type-B ones have P…X pnicogen bonds. The atoms-inmolecules (AIM) theory, electron localization function (ELF) theory, noncovalent interaction (NCI) index method as well as the adaptive natural density partitioning (AdNDP) approach were used to expand the nature of the interactions considered. The substituent groups strongly affect the properties of pnicogen bond interactions. Pnicogen bonds were covalent interactions for the electron-donating substituents (CH3, NH2), while they were noncovalent, partly covalent and covalent interactions when the substituents were electron-withdrawing groups. Natural bond orbital (NBO) analyses indicated that the larger the Wiberg bond order of the pnicogen-bonded interaction, the more covalent the bond and the greater its strength will be. In type-B conformations, charge transfer mainly occurs from an X lone pair of the PX3/PH2X molecule to the π*(P＝O) orbital of PO2X.
Acting as a molecular linker, the pnicogen bond plays an important role in crystal engineering and supramolecular synthesis. The structures and properties of π-hole pnicogen-bonded complexes PO2X…PX3 and PO2X…PH2X (X = F, Cl, Br, CH3, NH2) were investigated by ab initio MP2/aug-cc-pVTZ calculations and topological analyses of electron density. Two sets of π-hole pnicogen-bonded complexes were found on the potential surfaces. Type-A complexes have P…P and type-B ones have P…X pnicogen bonds. The atoms-inmolecules (AIM) theory, electron localization function (ELF) theory, noncovalent interaction (NCI) index method as well as the adaptive natural density partitioning (AdNDP) approach were used to expand the nature of the interactions considered. The substituent groups strongly affect the properties of pnicogen bond interactions. Pnicogen bonds were covalent interactions for the electron-donating substituents (CH3, NH2), while they were noncovalent, partly covalent and covalent interactions when the substituents were electron-withdrawing groups. Natural bond orbital (NBO) analyses indicated that the larger the Wiberg bond order of the pnicogen-bonded interaction, the more covalent the bond and the greater its strength will be. In type-B conformations, charge transfer mainly occurs from an X lone pair of the PX3/PH2X molecule to the π*(P＝O) orbital of PO2X.
2016, 32(3): 683-690
doi: 10.3866/PKU.WHXB201512302
Abstract:
Based on density functional theory (DFT) calculations, the molecular recognition of α,β-unsaturated carbonyl compounds and chiral molecules by uranyl-salophen receptors was investigated theoretically. The results showed that the U atom of the receptors was coordinated by the O3 atom of the guests, and the binding energies between receptors and guests increased with the enlargement of the aromatic substituent of the uranylsalophen receptors. In addition, the U―O3 coordination bonds of R2-and R3-series complexes are more stable than those of R1-series complexes, and the conjugation between the C＝C and C＝O bonds of the α,β-unsaturated carbonyl compounds in the coordination complexes was weakened. Moreover, according to circular dichroism (CD) spectra and binding-energy calculations, the molecular-recognition selectivity of an asymmetrical pyrenyl uranyl-salophen (receptor 3) for (R)-1-(2-naphthyl)ethylamine was much higher than that for (S)-1-(2-naphthyl)ethylamine. These results shed new light on the recognition ability of asymmetric uranyl-salophens.
Based on density functional theory (DFT) calculations, the molecular recognition of α,β-unsaturated carbonyl compounds and chiral molecules by uranyl-salophen receptors was investigated theoretically. The results showed that the U atom of the receptors was coordinated by the O3 atom of the guests, and the binding energies between receptors and guests increased with the enlargement of the aromatic substituent of the uranylsalophen receptors. In addition, the U―O3 coordination bonds of R2-and R3-series complexes are more stable than those of R1-series complexes, and the conjugation between the C＝C and C＝O bonds of the α,β-unsaturated carbonyl compounds in the coordination complexes was weakened. Moreover, according to circular dichroism (CD) spectra and binding-energy calculations, the molecular-recognition selectivity of an asymmetrical pyrenyl uranyl-salophen (receptor 3) for (R)-1-(2-naphthyl)ethylamine was much higher than that for (S)-1-(2-naphthyl)ethylamine. These results shed new light on the recognition ability of asymmetric uranyl-salophens.
2016, 32(3): 691-700
doi: 10.3866/PKU.WHXB201512182
Abstract:
Different charged functional groups including ―COO- and ―NH3+ were added to the interior and entrance of (15,15) armchair carbon nanotubes (CNTs) with a diameter larger than 2 nm to construct membranes that imitated the structure of the protein aquaporin-4. The potential of mean force, conductance, and density distributions of ions in the CNTs were calculated. The results showed that under 200 MPa, CNTs modified with oppositely charged groups in their interior and at their entrance could greatly improve salt desalination on the basis of high water flux. When five pairs of ―COO- and ―NH3+ functional groups were added to the interior of a CNT or four pairs of ―COO- and ―NH3+ functional groups were added to the interior of a CNT with another pair at the entrance, 100% Cl- rejection and 88% Na+ rejection were achieved. The lowest water conductivity of the functionalized CNTs was 4.6 times that of (8,8) unfunctionalized CNTs, and even slightly lower than that of unfunctionalized (15,15) CNTs.
Different charged functional groups including ―COO- and ―NH3+ were added to the interior and entrance of (15,15) armchair carbon nanotubes (CNTs) with a diameter larger than 2 nm to construct membranes that imitated the structure of the protein aquaporin-4. The potential of mean force, conductance, and density distributions of ions in the CNTs were calculated. The results showed that under 200 MPa, CNTs modified with oppositely charged groups in their interior and at their entrance could greatly improve salt desalination on the basis of high water flux. When five pairs of ―COO- and ―NH3+ functional groups were added to the interior of a CNT or four pairs of ―COO- and ―NH3+ functional groups were added to the interior of a CNT with another pair at the entrance, 100% Cl- rejection and 88% Na+ rejection were achieved. The lowest water conductivity of the functionalized CNTs was 4.6 times that of (8,8) unfunctionalized CNTs, and even slightly lower than that of unfunctionalized (15,15) CNTs.
2016, 32(3): 701-710
doi: 10.3866/PKU.WHXB201512303
Abstract:
The mechanism for the biradical reaction of HS with HO2 is investigated at the CCSD(T)/6-311++ G(3df,2pd)//B3LYP/6-311+G(2df,2p) level on both the singlet and triplet potential energy surfaces, along with rate constant calculations of the major channel. The results show that there are eight reaction channels involved in the HS + HO2 reaction system. The major channel R1 of the title reaction occurs on the triplet potential energy surfaces, and includes two pathways: Path 1 (R → 3IM1 → 3TS1 → P1(3O2 + H2S)) and Path 1a (R → 3IM1a → 3TS1a → P1(3O2 + H2S)). The rate constants kTST, kCVT, and kCVT/SCT of Paths 1 and 1a for Channel R1 were evaluated using classical transition state theory (TST) and the canonical variational transition state theory (CVT), in which the small-curvature tunneling correction was included. The calculated results show that kTST, kCVT, and kCVT/SCT of these two pathways decrease with rising temperature within the temperature range of 200-800 K. The variational effect was not negligible in the entire process of Path 1 and Path 1a, at the same time, the tunneling effect was considerable at lower temperature. The fitted three-parameter expressions of kCVT/SCT for Paths 1 and 1a are k1CVT/SCT(200-800 K) = 1.54×10-5T-2.70exp(1154/T) cm3·molecule-1·s-1 and k1aCVT/SCT (200-800 K) = 5.82×10-8T-1.84exp(1388/T) cm3·molecule-1·s-1, respectively.
The mechanism for the biradical reaction of HS with HO2 is investigated at the CCSD(T)/6-311++ G(3df,2pd)//B3LYP/6-311+G(2df,2p) level on both the singlet and triplet potential energy surfaces, along with rate constant calculations of the major channel. The results show that there are eight reaction channels involved in the HS + HO2 reaction system. The major channel R1 of the title reaction occurs on the triplet potential energy surfaces, and includes two pathways: Path 1 (R → 3IM1 → 3TS1 → P1(3O2 + H2S)) and Path 1a (R → 3IM1a → 3TS1a → P1(3O2 + H2S)). The rate constants kTST, kCVT, and kCVT/SCT of Paths 1 and 1a for Channel R1 were evaluated using classical transition state theory (TST) and the canonical variational transition state theory (CVT), in which the small-curvature tunneling correction was included. The calculated results show that kTST, kCVT, and kCVT/SCT of these two pathways decrease with rising temperature within the temperature range of 200-800 K. The variational effect was not negligible in the entire process of Path 1 and Path 1a, at the same time, the tunneling effect was considerable at lower temperature. The fitted three-parameter expressions of kCVT/SCT for Paths 1 and 1a are k1CVT/SCT(200-800 K) = 1.54×10-5T-2.70exp(1154/T) cm3·molecule-1·s-1 and k1aCVT/SCT (200-800 K) = 5.82×10-8T-1.84exp(1388/T) cm3·molecule-1·s-1, respectively.
2016, 32(3): 711-716
doi: 10.3866/PKU.WHXB201512242
Abstract:
The electrochemical responses of heavily doped n-type single-crystal silicon (CSi) during the formation of porous silicon (PSi) layers in hydrofluoric acid-based electrolytes were investigated. A series of PSi layers were fabricated by constantly applying different anodic current densities, which were selected according to the linear polarization curve. The surface and cross-sectional morphologies of the PSi layers were studied by scanning electron microscopy. The electrochemical behavior of CSi and PSi electrodes was compared by linear sweep polarization and chronopotentiometry techniques. The important parameters associated with the electrochemical reactions at the electrodes were evaluated by analyzing the Tafel plots and chronopotentiograms obtained before and after the PSi formation. Structural models of the CSi electrode/electrolyte and PSi electrode/ electrolyte interfaces were suggested based on the experimental data. Accordingly, the interfacial characteristics of CSi and PSi electrodes were discussed.
The electrochemical responses of heavily doped n-type single-crystal silicon (CSi) during the formation of porous silicon (PSi) layers in hydrofluoric acid-based electrolytes were investigated. A series of PSi layers were fabricated by constantly applying different anodic current densities, which were selected according to the linear polarization curve. The surface and cross-sectional morphologies of the PSi layers were studied by scanning electron microscopy. The electrochemical behavior of CSi and PSi electrodes was compared by linear sweep polarization and chronopotentiometry techniques. The important parameters associated with the electrochemical reactions at the electrodes were evaluated by analyzing the Tafel plots and chronopotentiograms obtained before and after the PSi formation. Structural models of the CSi electrode/electrolyte and PSi electrode/ electrolyte interfaces were suggested based on the experimental data. Accordingly, the interfacial characteristics of CSi and PSi electrodes were discussed.
2016, 32(3): 717-722
doi: 10.3866/PKU.WHXB201512301
Abstract:
We synthesized layered lithium-rich cathode materials by a novel ethanol-based one-step oxalate coprecipitation method. Using this method, all the elements including lithium could be coprecipitated during the coprecipitation reaction process to realize a homogeneous mixture of lithium and transition metal elements. In addition, compared with the conventional ammonium oxalate coprecipitation method, the precursor preheating process was eliminated, which should decrease reaction time and cost. X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical measurements were used to investigate the differences in the crystal structure, morphology and electrochemical performance of samples synthesized using the above two methods. Compared with the samples synthesized by the conventional ammonium oxalate coprecipitation method, samples prepared by our novel one-step oxalate coprecipitation method exhibit higher crystallinity with larger interlayer spacing, and smaller, more homogeneous particles. Such crystal structure and morphology endow the samples prepared by the oxalate coprecipitation method with better discharge capacity, cycle performance and rate performance than those synthesized by the conventional method. The simple, efficient coprecipitation method developed here may provide a new approach to fabricate layered materials for highperformance lithium-ion batteries.
We synthesized layered lithium-rich cathode materials by a novel ethanol-based one-step oxalate coprecipitation method. Using this method, all the elements including lithium could be coprecipitated during the coprecipitation reaction process to realize a homogeneous mixture of lithium and transition metal elements. In addition, compared with the conventional ammonium oxalate coprecipitation method, the precursor preheating process was eliminated, which should decrease reaction time and cost. X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical measurements were used to investigate the differences in the crystal structure, morphology and electrochemical performance of samples synthesized using the above two methods. Compared with the samples synthesized by the conventional ammonium oxalate coprecipitation method, samples prepared by our novel one-step oxalate coprecipitation method exhibit higher crystallinity with larger interlayer spacing, and smaller, more homogeneous particles. Such crystal structure and morphology endow the samples prepared by the oxalate coprecipitation method with better discharge capacity, cycle performance and rate performance than those synthesized by the conventional method. The simple, efficient coprecipitation method developed here may provide a new approach to fabricate layered materials for highperformance lithium-ion batteries.
2016, 32(3): 723-727
doi: 10.3866/PKU.WHXB201512141
Abstract:
Graphene oxide (GO) composite membranes were fabricated via layer-by-layer (LBL) assembling poly(ethylenimine) (PEI) and a mixture of GO and poly(acrylic acid) (PAA) on a poly(acrylonitrile) (PAN) support membrane. The composite membranes and their application performance were characterized and evaluated. The X-ray powder diffraction (XRD) spectrum shows that GO was successfully synthesized by the modified Hummers method, and it was homogenously dispersed in the composite membranes. Scanning electron microscopy (SEM) shows the successful assembly of multiple polyelectrolyte PEI and a mixture of GO and PAA bilayers on the PAN support membrane. The ultraviolet-visible (UV-Vis) spectrum indicates that the uniformity and continuity of the composite membrane were enhanced with the increasing number of assembled layers. The hydrophilic and selectivity tests reveals that the addition of GO decreased the water contact angle and enhanced the selectivity for monovalent cations of the multilayer polyelectrolyte composite membranes. All these advantages combine to fabricate a high-flux, high selectivity, and anti-fouling composite membrane for separation applications and water softening.
Graphene oxide (GO) composite membranes were fabricated via layer-by-layer (LBL) assembling poly(ethylenimine) (PEI) and a mixture of GO and poly(acrylic acid) (PAA) on a poly(acrylonitrile) (PAN) support membrane. The composite membranes and their application performance were characterized and evaluated. The X-ray powder diffraction (XRD) spectrum shows that GO was successfully synthesized by the modified Hummers method, and it was homogenously dispersed in the composite membranes. Scanning electron microscopy (SEM) shows the successful assembly of multiple polyelectrolyte PEI and a mixture of GO and PAA bilayers on the PAN support membrane. The ultraviolet-visible (UV-Vis) spectrum indicates that the uniformity and continuity of the composite membrane were enhanced with the increasing number of assembled layers. The hydrophilic and selectivity tests reveals that the addition of GO decreased the water contact angle and enhanced the selectivity for monovalent cations of the multilayer polyelectrolyte composite membranes. All these advantages combine to fabricate a high-flux, high selectivity, and anti-fouling composite membrane for separation applications and water softening.
2016, 32(3): 728-736
doi: 10.3866/PKU.WHXB201511303
Abstract:
A novel Zn-Mo-CdS/g-C3N4 heterojunction photocatalyst was prepared by hydrothermal posttreatment using dicyandiamide, zinc acetate, ammonium molybdate, cadmium acetate, and sodium sulfide as raw materials. X-ray diffraction (XRD), ultraviolet-visible (UV-Vis), inductively coupled plasma atomic emission (ICP-AES), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS) were used to characterize the prepared catalysts. The results indicate that heterojunctions are formed across the g-C3N4/Zn-Mo-CdS interface, which promotes interfacial charge transfer and inhibits the recombination of electrons and holes. The activities of as-prepared catalysts were tested through the photocatalytic degradation of Rhodamine B (RhB) under visible light. The results show that the Zn-Mo-CdS/g-C3N4 heterojunction photocatalyst clearly displayed increased activity compared with single g-C3N4 and Zn-Mo-CdS. At an optimal g-C3N4 mass fraction of 20%, the as-prepared heterojunction photocatalyst displayed the highest rate constant under visible light, which was 30 and 10 times of single g-C3N4 and Zn-Mo-CdS, respectively. Not only Zn-Mo-CdS, but also Mo-Ni-CdS and Ni-Sn-CdS can form heterojunctions with g-C3N4 to promote the rate of separation of electrons and holes and improve photocatalytic activity.
A novel Zn-Mo-CdS/g-C3N4 heterojunction photocatalyst was prepared by hydrothermal posttreatment using dicyandiamide, zinc acetate, ammonium molybdate, cadmium acetate, and sodium sulfide as raw materials. X-ray diffraction (XRD), ultraviolet-visible (UV-Vis), inductively coupled plasma atomic emission (ICP-AES), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS) were used to characterize the prepared catalysts. The results indicate that heterojunctions are formed across the g-C3N4/Zn-Mo-CdS interface, which promotes interfacial charge transfer and inhibits the recombination of electrons and holes. The activities of as-prepared catalysts were tested through the photocatalytic degradation of Rhodamine B (RhB) under visible light. The results show that the Zn-Mo-CdS/g-C3N4 heterojunction photocatalyst clearly displayed increased activity compared with single g-C3N4 and Zn-Mo-CdS. At an optimal g-C3N4 mass fraction of 20%, the as-prepared heterojunction photocatalyst displayed the highest rate constant under visible light, which was 30 and 10 times of single g-C3N4 and Zn-Mo-CdS, respectively. Not only Zn-Mo-CdS, but also Mo-Ni-CdS and Ni-Sn-CdS can form heterojunctions with g-C3N4 to promote the rate of separation of electrons and holes and improve photocatalytic activity.
2016, 32(3): 737-744
doi: 10.3866/PKU.WHXB201512184
Abstract:
A novel composite material TiO2-HNbMoO6 was prepared by an intercalation-pillar route. The phase and its microstructure, skeleton feature, spectral-response characteristics, and the interaction between interlayer species and nanosheets were characterized using powder X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), laser Raman spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), and H2 temperature-programmed reduction (H2-TPR). The specific surface areas of the samples were measured by N2 adsorption-desorption isotherms. The synergistic effect between the host and the guest of the composites was evaluated by the degradation of methylene blue (MB) dye under simulated sunlight. The results, such as the increase of the d-spacing, the absence of TiO2 crystalline phase, and the change of the Nb―O bond in the main body and the Ti―O bond in TiO2 before and after composition, demonstrate that TiO2 is uniformly dispersed in the interlayer of HNbMoO6, indicating the interaction between the host laminates and the guest titanium oxide species. The specific surface area of the composite was four times that of its host material, the narrowing band gap, the better adsorption ability, and the superior photocatalytic activity of TiO2-HNbMoO6 were because of the synergistic effect between the host and the guest.
A novel composite material TiO2-HNbMoO6 was prepared by an intercalation-pillar route. The phase and its microstructure, skeleton feature, spectral-response characteristics, and the interaction between interlayer species and nanosheets were characterized using powder X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), laser Raman spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), and H2 temperature-programmed reduction (H2-TPR). The specific surface areas of the samples were measured by N2 adsorption-desorption isotherms. The synergistic effect between the host and the guest of the composites was evaluated by the degradation of methylene blue (MB) dye under simulated sunlight. The results, such as the increase of the d-spacing, the absence of TiO2 crystalline phase, and the change of the Nb―O bond in the main body and the Ti―O bond in TiO2 before and after composition, demonstrate that TiO2 is uniformly dispersed in the interlayer of HNbMoO6, indicating the interaction between the host laminates and the guest titanium oxide species. The specific surface area of the composite was four times that of its host material, the narrowing band gap, the better adsorption ability, and the superior photocatalytic activity of TiO2-HNbMoO6 were because of the synergistic effect between the host and the guest.
2016, 32(3): 745-752
doi: 10.3866/PKU.WHXB201512185
Abstract:
MFI/CHA core-shell zeolites were synthesized by a two-step hydrothermal synthesis strategy (epitaxial growth). The growth of silicoaluminophosphate SAPO-34 fabricates crystalline layers over ZSM-5 nanocrystal crystallites. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), and Fourier transform infrared (FTIR) spectroscopy. The analyses indicate that the pretreatment step of the core phase was an important step during the synthesis. The growth kinetics of the MFI/CHAcore-shell zeolites were investigated by analyzing the products obtained with different secondary crystallization times and temperatures. The core-shell zeolite shows good shape-selective catalytic performance for converting methanol to aromatic compounds.
MFI/CHA core-shell zeolites were synthesized by a two-step hydrothermal synthesis strategy (epitaxial growth). The growth of silicoaluminophosphate SAPO-34 fabricates crystalline layers over ZSM-5 nanocrystal crystallites. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), and Fourier transform infrared (FTIR) spectroscopy. The analyses indicate that the pretreatment step of the core phase was an important step during the synthesis. The growth kinetics of the MFI/CHAcore-shell zeolites were investigated by analyzing the products obtained with different secondary crystallization times and temperatures. The core-shell zeolite shows good shape-selective catalytic performance for converting methanol to aromatic compounds.
2016, 32(3): 753-762
doi: 10.3866/PKU.WHXB201512294
Abstract:
Two modified bacterial celluloses, xanthate-modified bacterial cellulose (XMBC) and sulfate-modified bacterial cellulose (SMBC), were prepared from bacterial cellulose (BC) esterified with xanthate and sulfate, respectively, using microwave irradiation. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS), Fourier transform infrared (FT-IR) spectroscopy, and Brunauer-Emmett-Teller (BET) surface analysis. Batch experiments were carried out to determine the ability of XMBC and SMBC to remove Pb(II) from solution. The effects of pH, contact time, temperature, initial adsorption concentration, and ionic strength on Pb(II) removal were investigated along with regeneration performance. Both the specific surface area and total pore volume of the modified biosorbents were higher than those of unmodified bacterial cellulose. The adsorption of Pb(II) decreased with increasing temperature and ionic strength, and the optimal pH was 5.0. The introduction of thiol groups on bacterial cellulose increased its adsorption capacity for Pb(II); the modified biosorbents exhibited adsorption capacities of 144.93 mg·g-1 for XMBC and 126.58 mg·g-1 for SMBC. The adsorption rate closely followed a pseudo-second order model and the adsorption isotherm data were consistent with the Langmuir model. The adsorption of Pb(II) was exothermic, and the spent adsorbents could be readily regenerated for reuse. As a result, SMBC and XMBC are promising materials for the preconcentration and separation of heavy metals from large volumes of aqueous solutions.
Two modified bacterial celluloses, xanthate-modified bacterial cellulose (XMBC) and sulfate-modified bacterial cellulose (SMBC), were prepared from bacterial cellulose (BC) esterified with xanthate and sulfate, respectively, using microwave irradiation. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS), Fourier transform infrared (FT-IR) spectroscopy, and Brunauer-Emmett-Teller (BET) surface analysis. Batch experiments were carried out to determine the ability of XMBC and SMBC to remove Pb(II) from solution. The effects of pH, contact time, temperature, initial adsorption concentration, and ionic strength on Pb(II) removal were investigated along with regeneration performance. Both the specific surface area and total pore volume of the modified biosorbents were higher than those of unmodified bacterial cellulose. The adsorption of Pb(II) decreased with increasing temperature and ionic strength, and the optimal pH was 5.0. The introduction of thiol groups on bacterial cellulose increased its adsorption capacity for Pb(II); the modified biosorbents exhibited adsorption capacities of 144.93 mg·g-1 for XMBC and 126.58 mg·g-1 for SMBC. The adsorption rate closely followed a pseudo-second order model and the adsorption isotherm data were consistent with the Langmuir model. The adsorption of Pb(II) was exothermic, and the spent adsorbents could be readily regenerated for reuse. As a result, SMBC and XMBC are promising materials for the preconcentration and separation of heavy metals from large volumes of aqueous solutions.
2016, 32(3): 763-770
doi: 10.3866/PKU.WHXB201512111
Abstract:
Thermoresponsive hybrid particles of SiO2-PNIPAM (PNIPAM: poly(N-isopropyl acrylamide) were synthesized by surface initiated atom transfer radical polymerization (SI-ATRP). The structure of hybrid particles was characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The grafting ratio of PNIPAM on the silica surface was about 103.7%as measured by thermogravimetric analysis (TGA). The thermoresponsive behavior of monodisperse hybrid particles was analyzed by dynamic light scattering (DLS), and its lower critical solution temperature (LCST) is 30 ℃. The influence of anions on the wettability of hybrid particles was studied by measuring the surface contact angle. A large stability difference of the emulsion based on SiO2-PNIPAM exists between 40 and 10 ℃. The degree of flocculation of hybrid particles shows a significant influence on the stability of the emulsion. The emulsion stability is dependent on the electrostatic interaction and salting out caused by the solvation effect. This stability is tunable by introducing different anions at different concentrations.
Thermoresponsive hybrid particles of SiO2-PNIPAM (PNIPAM: poly(N-isopropyl acrylamide) were synthesized by surface initiated atom transfer radical polymerization (SI-ATRP). The structure of hybrid particles was characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The grafting ratio of PNIPAM on the silica surface was about 103.7%as measured by thermogravimetric analysis (TGA). The thermoresponsive behavior of monodisperse hybrid particles was analyzed by dynamic light scattering (DLS), and its lower critical solution temperature (LCST) is 30 ℃. The influence of anions on the wettability of hybrid particles was studied by measuring the surface contact angle. A large stability difference of the emulsion based on SiO2-PNIPAM exists between 40 and 10 ℃. The degree of flocculation of hybrid particles shows a significant influence on the stability of the emulsion. The emulsion stability is dependent on the electrostatic interaction and salting out caused by the solvation effect. This stability is tunable by introducing different anions at different concentrations.
2016, 32(3): 771-779
doi: 10.3866/PKU.WHXB201601043
Abstract:
The photophysical properties of pentafluorophenyl-substituted gallium corroles in halogenated benzenes were investigated using ultraviolet-visible (UV-Vis), steady-state, time-resolved fluorescence, and femtosecond transient absorption spectroscopies. The results showed that the absorption maximum wavelength of the gallium corroles was mainly related to the dispersion force of the halogenated benzene solvents. The external heavy atom effect of halogenated benzenes may markedly lower the fluorescence quantum yield of gallium corrole complexes. Photoinduced electron transfer between the gallium corroles and halogenated benzene solvents was detected by femtosecond transient absorption spectroscopy. The experimental evidence showed that the heavy atom effect of the solvent might lower the charge recombination rate of charge-separated gallium corrole-solvent complexes.
The photophysical properties of pentafluorophenyl-substituted gallium corroles in halogenated benzenes were investigated using ultraviolet-visible (UV-Vis), steady-state, time-resolved fluorescence, and femtosecond transient absorption spectroscopies. The results showed that the absorption maximum wavelength of the gallium corroles was mainly related to the dispersion force of the halogenated benzene solvents. The external heavy atom effect of halogenated benzenes may markedly lower the fluorescence quantum yield of gallium corrole complexes. Photoinduced electron transfer between the gallium corroles and halogenated benzene solvents was detected by femtosecond transient absorption spectroscopy. The experimental evidence showed that the heavy atom effect of the solvent might lower the charge recombination rate of charge-separated gallium corrole-solvent complexes.
2016, 32(3): 780-786
doi: 10.3866/PKU.WHXB201512154
Abstract:
The correlation between structural factors and hydrogen storage capacity of nonstoichiometric TiMnx (x = 1.4, 1.5, 1.6, 1.7) alloys was investigated systematically. The capacities of TiMnx alloys were different with changing the x value, although all the alloys show a C14-type Laves phase. The TiMn1.4 alloy shows 0.65% (w, mass fraction) capacity and a sloping plateau with hysteresis, and the TiMn1.5 alloy exhibits the highest capacity of 1.2% (w) and a flat plateau. By further increasing the x value, the hydrogen storage capacity was reduced significantly, such as approximately 0.30% (w) and zero for the alloys with x = 1.6, 1.7, respectively. Structural analysis shows that the Ti atoms partially occupy the Mn(2a) site in the nonstoichiometric TiMnx alloys, and the increasing occupation factor (g) exhibits a negative effect on the volume of tetrahedron interstitials for hydrogen storage. The key factors for changing the volume of tetrahedron interstitials are the bond lengths of Ti―Ti and Mn(2a)―Mn(2a), where Mn(2a)―Mn(2a) bonds play a dominant role in improving the hydrogen storage capacity.
The correlation between structural factors and hydrogen storage capacity of nonstoichiometric TiMnx (x = 1.4, 1.5, 1.6, 1.7) alloys was investigated systematically. The capacities of TiMnx alloys were different with changing the x value, although all the alloys show a C14-type Laves phase. The TiMn1.4 alloy shows 0.65% (w, mass fraction) capacity and a sloping plateau with hysteresis, and the TiMn1.5 alloy exhibits the highest capacity of 1.2% (w) and a flat plateau. By further increasing the x value, the hydrogen storage capacity was reduced significantly, such as approximately 0.30% (w) and zero for the alloys with x = 1.6, 1.7, respectively. Structural analysis shows that the Ti atoms partially occupy the Mn(2a) site in the nonstoichiometric TiMnx alloys, and the increasing occupation factor (g) exhibits a negative effect on the volume of tetrahedron interstitials for hydrogen storage. The key factors for changing the volume of tetrahedron interstitials are the bond lengths of Ti―Ti and Mn(2a)―Mn(2a), where Mn(2a)―Mn(2a) bonds play a dominant role in improving the hydrogen storage capacity.
2016, 32(3): 787-792
doi: 10.3866/PKU.WHXB201512183
Abstract:
Epitaxial graphene by chemical vapor deposition (CVD) is one of the main methods to fabricate high-quality wafer-scale graphene materials. However, CVD-grown graphene on metal substrates has some disadvantages, such as the need for a transfer process and carbon atoms dissolved into the metal substrate. In this work, we evaluate sapphire substrates to overcome those disadvantages. The morphology and crystal quality of the samples grown at different temperatures were characterized by atomic force microscopy (AFM), optical microscopy (OM), Raman spectroscopy, and a Hall measurement system. To ease the etching process of carbon atoms to the substrate, we adopt a very low carbon concentration of 0.01%. AFM and Raman results show that the surface morphologies of samples grown at lower temperatures were smoother, whereas the quality of samples grown at higher temperatures was better. The sapphire substrate was etched in an H2 environment, while it was not etched only by carbon source without H2 environment. Epitaxial graphene with flat surface morphology and good crystal quality was prepared on a c-plane sapphire substrate (diameter: 50 mm) at a growth temperature of 1200 ℃. The carrier mobility is above 1000 cm2·V-1·s-1 at room temperature.
Epitaxial graphene by chemical vapor deposition (CVD) is one of the main methods to fabricate high-quality wafer-scale graphene materials. However, CVD-grown graphene on metal substrates has some disadvantages, such as the need for a transfer process and carbon atoms dissolved into the metal substrate. In this work, we evaluate sapphire substrates to overcome those disadvantages. The morphology and crystal quality of the samples grown at different temperatures were characterized by atomic force microscopy (AFM), optical microscopy (OM), Raman spectroscopy, and a Hall measurement system. To ease the etching process of carbon atoms to the substrate, we adopt a very low carbon concentration of 0.01%. AFM and Raman results show that the surface morphologies of samples grown at lower temperatures were smoother, whereas the quality of samples grown at higher temperatures was better. The sapphire substrate was etched in an H2 environment, while it was not etched only by carbon source without H2 environment. Epitaxial graphene with flat surface morphology and good crystal quality was prepared on a c-plane sapphire substrate (diameter: 50 mm) at a growth temperature of 1200 ℃. The carrier mobility is above 1000 cm2·V-1·s-1 at room temperature.
2016, 32(3): 793-794
doi: 10.3866/PKU.WHXB201602181
Abstract:
2016, 32(3): 795-796
doi: 10.3866/PKU.WHXB201602191
Abstract:
2016, 32(3): 797-799
doi: 10.3866/PKU.WHXB201602192
Abstract:
2016, 32(3): 800-801
doi: 10.3866/PKU.WHXB201602171
Abstract:
2016, 32(3): 802-802
doi: 10.3866/PKU.WHXB201602172
Abstract:
