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2016 Volume 32 Issue 8
2016, 32(8):
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2016, 32(8): 1851-1852
doi: 10.3866/PKU.WHXB201606291
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2016, 32(8): 1853-1853
doi: 10.3866/PKU.WHXB201607061
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2016, 32(8): 1854-1855
doi: 10.3866/PKU.WHXB201607151
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2016, 32(8): 1856-1857
doi: 10.3866/PKU.WHXB201607201
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2016, 32(8): 1858-1858
doi: 10.3866/PKU.WHXB201607211
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2016, 32(8): 1859-1865
doi: 10.3866/PKU.WHXB201606022
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Bipolar interfacial polyelectrolyte membrane fuel cells (BPFCs) are novel devices based on an acidicalkaline bipolar reaction interface. As a result of this innovative bipolar membrane electrode assembly (MEA), BPFCs exhibit outstanding advantages but also present new challenges with regard to the interface. Significant progress has been achieved in BPFCs research in recent years, with the development of key materials and interface technologies. This monograph summarizes the recent advances in MEA technology, including structures, rate-limiting reaction interfaces, water transport mechanisms, and the application of metals other than platinum. These developments in both fundamental theory and primary technologies have established a good foundation for the future research and development of such devices.
Bipolar interfacial polyelectrolyte membrane fuel cells (BPFCs) are novel devices based on an acidicalkaline bipolar reaction interface. As a result of this innovative bipolar membrane electrode assembly (MEA), BPFCs exhibit outstanding advantages but also present new challenges with regard to the interface. Significant progress has been achieved in BPFCs research in recent years, with the development of key materials and interface technologies. This monograph summarizes the recent advances in MEA technology, including structures, rate-limiting reaction interfaces, water transport mechanisms, and the application of metals other than platinum. These developments in both fundamental theory and primary technologies have established a good foundation for the future research and development of such devices.
2016, 32(8): 1866-1879
doi: 10.3866/PKU.WHXB201605261
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As a secondary battery, the Li-air battery has the highest theoretical specific energy and has been considered as one of the most promising power sources for electric vehicles. The Li-air battery based on organic electrolyte has become a topic of interest owing to its excellent theoretical energy density, environmental friendliness and low cost. During the past 20 years, much progress has been made in the development of the reaction mechanism, cathode structure, catalyst and electrolyte materials. But there are still many obstacles to overcome before its practical applications. In this paper, we review some of the latest progress in the research on the reaction mechanism, cathode materials, catalysts, electrolytes, as well as the lithium anode. Future research and development prospects are also discussed.
As a secondary battery, the Li-air battery has the highest theoretical specific energy and has been considered as one of the most promising power sources for electric vehicles. The Li-air battery based on organic electrolyte has become a topic of interest owing to its excellent theoretical energy density, environmental friendliness and low cost. During the past 20 years, much progress has been made in the development of the reaction mechanism, cathode structure, catalyst and electrolyte materials. But there are still many obstacles to overcome before its practical applications. In this paper, we review some of the latest progress in the research on the reaction mechanism, cathode materials, catalysts, electrolytes, as well as the lithium anode. Future research and development prospects are also discussed.
2016, 32(8): 1880-1893
doi: 10.3866/PKU.WHXB201606061
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Singlet exciton fission is the process by which a high-energy singlet exciton splits into two low-energy triplet excitons. Organic solar cells based on singlet fission have the potential to exceed the Shockley-Queisser limit and, in doing so, may improve their efficiency from 30% to 44.4%. Although progress in singlet fission materials and photovoltaic devices has accelerated with recent research, many challenges and debates remain with regard to clarifying the relationship between molecule structures and the rate and efficiency of singlet fission. This review addresses recent advances in singlet fission materials and summarizes the work of our own research group. We begin by introducing the background of singlet fission, following with the general concept, the requirements for singlet fission to proceed, and the applications of transient absorption spectroscopy. Two mechanisms have been proposed to explain singlet fission molecules, intermolecular and intramolecular singlet fission, and these two types of materials are summarized, focusing on dimers, which are novel structures that undergo efficient intramolecular singlet fission. Based on the latest developments in singlet fission, we discuss the possible future advances in, and prospects for the application of, singlet fission materials.
Singlet exciton fission is the process by which a high-energy singlet exciton splits into two low-energy triplet excitons. Organic solar cells based on singlet fission have the potential to exceed the Shockley-Queisser limit and, in doing so, may improve their efficiency from 30% to 44.4%. Although progress in singlet fission materials and photovoltaic devices has accelerated with recent research, many challenges and debates remain with regard to clarifying the relationship between molecule structures and the rate and efficiency of singlet fission. This review addresses recent advances in singlet fission materials and summarizes the work of our own research group. We begin by introducing the background of singlet fission, following with the general concept, the requirements for singlet fission to proceed, and the applications of transient absorption spectroscopy. Two mechanisms have been proposed to explain singlet fission molecules, intermolecular and intramolecular singlet fission, and these two types of materials are summarized, focusing on dimers, which are novel structures that undergo efficient intramolecular singlet fission. Based on the latest developments in singlet fission, we discuss the possible future advances in, and prospects for the application of, singlet fission materials.
2016, 32(8): 1894-1912
doi: 10.3866/PKU.WHXB201605034
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As one of the most promising materials in the field of photovoltaics, organic- inorganic hybrid perovskites have attracted widespread attention in recent years. In addition to their promising applications in the field of photovoltaics, perovskite materials also exhibit outstanding photoluminescence and electroluminescence properties. This paper reviews the latest developments in organic- inorganic hybrid perovskite materials, with particular attention paid to the luminescence. Firstly, a summary of the fundamental issues related to the unique light emitting characteristics and influencing factors of perovskite materials is provided, including the light-emitting mechanism and principles related to spectrum adjustability. The influence of the morphology of perovskite on the photoluminescence properties is discussed. The latest developments and applications of perovskite materials in various devices, including light-emitting diodes, lasers, and lightemitting field effect transistors, are then discussed. Finally, the key issues and challenges of perovskite light emitting materials are addressed and prospects for future perovskite-based applications are discussed.
As one of the most promising materials in the field of photovoltaics, organic- inorganic hybrid perovskites have attracted widespread attention in recent years. In addition to their promising applications in the field of photovoltaics, perovskite materials also exhibit outstanding photoluminescence and electroluminescence properties. This paper reviews the latest developments in organic- inorganic hybrid perovskite materials, with particular attention paid to the luminescence. Firstly, a summary of the fundamental issues related to the unique light emitting characteristics and influencing factors of perovskite materials is provided, including the light-emitting mechanism and principles related to spectrum adjustability. The influence of the morphology of perovskite on the photoluminescence properties is discussed. The latest developments and applications of perovskite materials in various devices, including light-emitting diodes, lasers, and lightemitting field effect transistors, are then discussed. Finally, the key issues and challenges of perovskite light emitting materials are addressed and prospects for future perovskite-based applications are discussed.
2016, 32(8): 1913-1928
doi: 10.3866/PKU.WHXB201605052
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Graphitic carbon nitride (g-C3N4) is a new metal-free material. Owing to its multiple unique physicochemical properties, g-C3N4 has promising applications in various research fields, including heterogeneous catalysis, photocatalysis, fuel cells, and gas storage. Compared with bulk g-C3N4 prepared via direct thermal condensation, mesoporous g-C3N4 possesses a higher surface area and abundant accessible mesoporous pores. These features expose many more surface active sites, thereby improving the performance of this material in catalysis as well as in other applications. Thermal condensation is the most convenient strategy to prepare g-C3N4 and, when fabricating mesoporous g-C3N4, one may employ hard-, soft-, or non-templating method. This paper reviews recent advances in the synthesis of mesoporous g-C3N4 using all three routes. Specifically, several crucial issues regarding the hard-templating method are discussed with regard to the synthetic mechanism associated with various precursors and the physicochemical properties of the g-C3N4 products. Novel soft- and non-templating approaches for the preparation of mesoporous g-C3N4 are also addressed and a detailed comparison to the hard-templating method is provided. Finally, future prospects for the development of mesoporous g-C3N4 materials are also assessed.
Graphitic carbon nitride (g-C3N4) is a new metal-free material. Owing to its multiple unique physicochemical properties, g-C3N4 has promising applications in various research fields, including heterogeneous catalysis, photocatalysis, fuel cells, and gas storage. Compared with bulk g-C3N4 prepared via direct thermal condensation, mesoporous g-C3N4 possesses a higher surface area and abundant accessible mesoporous pores. These features expose many more surface active sites, thereby improving the performance of this material in catalysis as well as in other applications. Thermal condensation is the most convenient strategy to prepare g-C3N4 and, when fabricating mesoporous g-C3N4, one may employ hard-, soft-, or non-templating method. This paper reviews recent advances in the synthesis of mesoporous g-C3N4 using all three routes. Specifically, several crucial issues regarding the hard-templating method are discussed with regard to the synthetic mechanism associated with various precursors and the physicochemical properties of the g-C3N4 products. Novel soft- and non-templating approaches for the preparation of mesoporous g-C3N4 are also addressed and a detailed comparison to the hard-templating method is provided. Finally, future prospects for the development of mesoporous g-C3N4 materials are also assessed.
2016, 32(8): 1929-1932
doi: 10.3866/PKU.WHXB201605092
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This work studied the thermodynamic properties of a single intercage C―C bond in a [C60]fullerene dimer, (C60)2-[P(O)(OCH3)]2, previously synthesized by Wang et al. (Chem. Commun. 2011, 47, 6111). Data obtained from in situ variable temperature electron paramagnetic resonance (EPR) indicated a relatively low bond dissociation enthalpy (BDE) for this bond of 72.4 kJ ·mol-1 (17.3 kcal ·mol-1). This value is only approximately twice that of a typical hydrogen bond, or one fifth of the values determined for bonds in diamond or saturated hydrocarbons. The application of this pre-synthesized dimer to the formation of aligned fullerenes is discussed.
This work studied the thermodynamic properties of a single intercage C―C bond in a [C60]fullerene dimer, (C60)2-[P(O)(OCH3)]2, previously synthesized by Wang et al. (Chem. Commun. 2011, 47, 6111). Data obtained from in situ variable temperature electron paramagnetic resonance (EPR) indicated a relatively low bond dissociation enthalpy (BDE) for this bond of 72.4 kJ ·mol-1 (17.3 kcal ·mol-1). This value is only approximately twice that of a typical hydrogen bond, or one fifth of the values determined for bonds in diamond or saturated hydrocarbons. The application of this pre-synthesized dimer to the formation of aligned fullerenes is discussed.
2016, 32(8): 1933-1940
doi: 10.3866/PKU.WHXB201604212
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Sulfated β-cyclodextrin (β-CD) was prepared by the reaction of β-CD with p-toluenesulfonyl chloride at low temperature in aqueous sodium hydroxide. The product was analyzed by Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H NMR). The novel benzil-bridged β-CD (BB β-CD) was acquired by the reaction of benzil with sulfated β-CD at a molar ratio of 1 : 2. UV spectrophotometry was used to study the synthetic mechanism of BB β-CD and benzil and their adsorption onto U(VI). Scanning electron microscopy (SEM) was used to analyze the surface properties of the materials. The adsorption of BB β-CD onto U(VI) was investigated as a function of pH, contact time, temperature, and interfering ions using the batch adsorption technique. It was found that the adsorption equilibrium of BB β-CD was reached faster than that of benzil. The optimum experimental conditions were pH = 4.5 and shaking for 60 min, achieving the maximum adsorption capacity of 12.16 mg·g-1 and a U(VI) removal ratio of 91.2%. Kinetic studies revealed that the adsorption reached equilibrium within 60 min for U(VI) and followed a pseudo-second-order rate equation. The isothermal data correlated with the Langmuir model better than with the Freundlich model. The thermodynamic data indicated the spontaneous and endothermic nature of the process.
Sulfated β-cyclodextrin (β-CD) was prepared by the reaction of β-CD with p-toluenesulfonyl chloride at low temperature in aqueous sodium hydroxide. The product was analyzed by Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H NMR). The novel benzil-bridged β-CD (BB β-CD) was acquired by the reaction of benzil with sulfated β-CD at a molar ratio of 1 : 2. UV spectrophotometry was used to study the synthetic mechanism of BB β-CD and benzil and their adsorption onto U(VI). Scanning electron microscopy (SEM) was used to analyze the surface properties of the materials. The adsorption of BB β-CD onto U(VI) was investigated as a function of pH, contact time, temperature, and interfering ions using the batch adsorption technique. It was found that the adsorption equilibrium of BB β-CD was reached faster than that of benzil. The optimum experimental conditions were pH = 4.5 and shaking for 60 min, achieving the maximum adsorption capacity of 12.16 mg·g-1 and a U(VI) removal ratio of 91.2%. Kinetic studies revealed that the adsorption reached equilibrium within 60 min for U(VI) and followed a pseudo-second-order rate equation. The isothermal data correlated with the Langmuir model better than with the Freundlich model. The thermodynamic data indicated the spontaneous and endothermic nature of the process.
2016, 32(8): 1941-1949
doi: 10.3866/PKU.WHXB201604223
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Three-dimensional direct numerical simulation is conducted to simulate the auto-ignition of the highoctane fuel PRF70 under partially premixed combustion (PPC) engine conditions. A skeletal primary reference fuel (PRF) chemical kinetic mechanism is adopted, including 33 species and 38 elementary reactions. Compression/expansion effects caused by piston motion, the real engine geometry, and the working conditions are considered. The simulation includes two injections, the first being used to form a relatively uniform base mixture and the second to forma stratified mixture and trigger the ignition. It is found that the combustion process in PPC engines is a rather complex combination of homogeneous combustion, rich premixed and diffusioncontrolled combustion. The region between the two injections is near stoichiometry, resulting in the formation of NOx, while abundant CO is retained in the region with equivalence ratio (φ) > 2, which needs to diffuse to meet the oxidizer and burn in a diffusion flame. The marching cube method is used to extract the 3D flame surface and show the temporal evolution of the reaction front. Finally, the joint PDF of the Gaussian curvature (kg) and principle mean curvature (km) and temporal evolution of the probability density function (PDF) in terms of km show that km plays a more important role and becomes negative as time evolves because of the consumption of rich premixed flame in the center.
Three-dimensional direct numerical simulation is conducted to simulate the auto-ignition of the highoctane fuel PRF70 under partially premixed combustion (PPC) engine conditions. A skeletal primary reference fuel (PRF) chemical kinetic mechanism is adopted, including 33 species and 38 elementary reactions. Compression/expansion effects caused by piston motion, the real engine geometry, and the working conditions are considered. The simulation includes two injections, the first being used to form a relatively uniform base mixture and the second to forma stratified mixture and trigger the ignition. It is found that the combustion process in PPC engines is a rather complex combination of homogeneous combustion, rich premixed and diffusioncontrolled combustion. The region between the two injections is near stoichiometry, resulting in the formation of NOx, while abundant CO is retained in the region with equivalence ratio (φ) > 2, which needs to diffuse to meet the oxidizer and burn in a diffusion flame. The marching cube method is used to extract the 3D flame surface and show the temporal evolution of the reaction front. Finally, the joint PDF of the Gaussian curvature (kg) and principle mean curvature (km) and temporal evolution of the probability density function (PDF) in terms of km show that km plays a more important role and becomes negative as time evolves because of the consumption of rich premixed flame in the center.
2016, 32(8): 1950-1959
doi: 10.3866/PKU.WHXB201605071
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Hexanitrohexaazaisowurtzitane (CL-20) is considered to be a representative high energy density material. It is important to control the microstructure of the crystal during recrystallization to ensure the quality of CL-20. In this study, the effects of different types and concentrations of ionic liquids on CL-20 were investigated by adding them to the solvent or anti-solvent during recrystallization. Three types of ionic liquids acting as a morphology control additive can reduce the crystal size of recrystallized CL-20. Thermal analysis shows that most ionic liquids added to solvents or anti-solvents can increase the transition temperature from the ε crystal to the γ crystal by up to 12.6 ℃, and the decomposition peak temperature increases so the thermal stability of CL-20 improves. The heat output increases to 1344 J·g-1. When DmimCl is added into the solvent, recrystallized CL-20 has smaller particle size and an octahedral shape without sharp edges or agglomeration. With different concentrations of DmimCl in the solvent, the decomposition peak temperature of recrystallized CL-20 increases more than 6 ℃ and the heat output is more than 1100 J·g-1. Therefore, DmimCl is an ideal morphology control additive.
Hexanitrohexaazaisowurtzitane (CL-20) is considered to be a representative high energy density material. It is important to control the microstructure of the crystal during recrystallization to ensure the quality of CL-20. In this study, the effects of different types and concentrations of ionic liquids on CL-20 were investigated by adding them to the solvent or anti-solvent during recrystallization. Three types of ionic liquids acting as a morphology control additive can reduce the crystal size of recrystallized CL-20. Thermal analysis shows that most ionic liquids added to solvents or anti-solvents can increase the transition temperature from the ε crystal to the γ crystal by up to 12.6 ℃, and the decomposition peak temperature increases so the thermal stability of CL-20 improves. The heat output increases to 1344 J·g-1. When DmimCl is added into the solvent, recrystallized CL-20 has smaller particle size and an octahedral shape without sharp edges or agglomeration. With different concentrations of DmimCl in the solvent, the decomposition peak temperature of recrystallized CL-20 increases more than 6 ℃ and the heat output is more than 1100 J·g-1. Therefore, DmimCl is an ideal morphology control additive.
2016, 32(8): 1960-1966
doi: 10.3866/PKU.WHXB201605123
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Imidazolium acetate ionic liquids have a wide range of applications in catalysis, electrochemistry and extraction, and an improved understanding of their thermodynamic properties will provide a theoretical basis for future usages in related fields. In this work, density functional theory (DFT) and the Born-Fajans-Haber (BFH) cycle were used to study the thermodynamic properties of imidazolium acetate ionic liquids [Cnmim][OAc] (n= 1－6). The dissociation, vaporization, latticeand solvation phase transition enthalpies of these liquids were calculated and compared with the corresponding experimental values. The dissociation enthalpies were determined using DFT at the B3LYP/6-311+G(d, p) and M062X/TZVP levels, and the results were compared with literature values. In addition, enthalpy of vaporization values were obtained from molecular volumesin conjunction with enthalpic corrections to the total gas-phase energy and Matlab fitting parameters, and the results were in good agreement with experimental data. Lastly, using the Jenkins formula, the lattice energies and the corresponding lattice enthalpies were determined, while the solvation enthalpies were calculated by employing the BFH cycle.
Imidazolium acetate ionic liquids have a wide range of applications in catalysis, electrochemistry and extraction, and an improved understanding of their thermodynamic properties will provide a theoretical basis for future usages in related fields. In this work, density functional theory (DFT) and the Born-Fajans-Haber (BFH) cycle were used to study the thermodynamic properties of imidazolium acetate ionic liquids [Cnmim][OAc] (n= 1－6). The dissociation, vaporization, latticeand solvation phase transition enthalpies of these liquids were calculated and compared with the corresponding experimental values. The dissociation enthalpies were determined using DFT at the B3LYP/6-311+G(d, p) and M062X/TZVP levels, and the results were compared with literature values. In addition, enthalpy of vaporization values were obtained from molecular volumesin conjunction with enthalpic corrections to the total gas-phase energy and Matlab fitting parameters, and the results were in good agreement with experimental data. Lastly, using the Jenkins formula, the lattice energies and the corresponding lattice enthalpies were determined, while the solvation enthalpies were calculated by employing the BFH cycle.
2016, 32(8): 1967-1976
doi: 10.3866/PKU.WHXB201604292
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The excited-state properties of two-dimensional carbon nitrides, including triazine and tri-s-triazine, were investigated using many-body Green's function theory. Their quasiparticle energies were calculated with the GW method. By solving the Bethe-Salpeter equation (BSE), which takes into account electron － hole interactions, excitation energies and optical spectra were obtained. Strong interactions, mainly originating from exchange interactions, were found between σ and π orbitals in the valence bands of the two carbon nitrides. The quasiparticle corrections for occupied σ and π orbitals are quite different, so both of them need to be calculated at the level of the GWmethod to obtain accurate results for both band gaps and optical spectra from the BSE. Compared with monolayer carbon nitrides, interlayer van der Waals interactions in bilayer systems lower the band gap by 0.6 eV, while the optical absorption spectrum red shifts by 0.2 eV. This is because of the smaller exciton binding energy in bilayer systems. Our calculated positions of the absorption peaks are in good agreement with experiments. The absorption peaks in experiments are dominated by transitions from deep π orbitals to π* orbitals. Coupling between π → π* and σ → π* transitions can lead to a weak absorption tail in the long wavelength region. If we tune the polarization direction of the incident light, new strong absorption peaks originating from σ → π* transitions emerge at lower energies.
The excited-state properties of two-dimensional carbon nitrides, including triazine and tri-s-triazine, were investigated using many-body Green's function theory. Their quasiparticle energies were calculated with the GW method. By solving the Bethe-Salpeter equation (BSE), which takes into account electron － hole interactions, excitation energies and optical spectra were obtained. Strong interactions, mainly originating from exchange interactions, were found between σ and π orbitals in the valence bands of the two carbon nitrides. The quasiparticle corrections for occupied σ and π orbitals are quite different, so both of them need to be calculated at the level of the GWmethod to obtain accurate results for both band gaps and optical spectra from the BSE. Compared with monolayer carbon nitrides, interlayer van der Waals interactions in bilayer systems lower the band gap by 0.6 eV, while the optical absorption spectrum red shifts by 0.2 eV. This is because of the smaller exciton binding energy in bilayer systems. Our calculated positions of the absorption peaks are in good agreement with experiments. The absorption peaks in experiments are dominated by transitions from deep π orbitals to π* orbitals. Coupling between π → π* and σ → π* transitions can lead to a weak absorption tail in the long wavelength region. If we tune the polarization direction of the incident light, new strong absorption peaks originating from σ → π* transitions emerge at lower energies.
2016, 32(8): 1977-1982
doi: 10.3866/PKU.WHXB201604293
Abstract:
To understand the physical and chemical responses of energetic materials, such as 1,3- dinitrobenzene (DNB, C6H4N2O4), hexanitrohexaazaisowurtzitane (CL20, C6H6N12O12), and CL20/DNB co-crystal, to femtosecond laser ablation (FLA), their molecular reaction dynamics have been investigated using the ReaxFF/ lg force field. The computational results indicate that the temperature and pressure of the CL20/DNB system jump during FLA. In particular, the temperature and pressure gradually reach their maxima following an initial cooling process. N―NO2 bond breaking of the CL20 molecule triggers the reactions for both the CL20 and CL20/ DNB systems. However, the CL20 system prevails the CL20/DNB co-crystal in the decomposition rate simply because coexistence of DNB molecules in the mixture and generated decomposition products containing benzene rings greatly reduce the effective collision probability between CL20 and the products.
To understand the physical and chemical responses of energetic materials, such as 1,3- dinitrobenzene (DNB, C6H4N2O4), hexanitrohexaazaisowurtzitane (CL20, C6H6N12O12), and CL20/DNB co-crystal, to femtosecond laser ablation (FLA), their molecular reaction dynamics have been investigated using the ReaxFF/ lg force field. The computational results indicate that the temperature and pressure of the CL20/DNB system jump during FLA. In particular, the temperature and pressure gradually reach their maxima following an initial cooling process. N―NO2 bond breaking of the CL20 molecule triggers the reactions for both the CL20 and CL20/ DNB systems. However, the CL20 system prevails the CL20/DNB co-crystal in the decomposition rate simply because coexistence of DNB molecules in the mixture and generated decomposition products containing benzene rings greatly reduce the effective collision probability between CL20 and the products.
2016, 32(8): 1983-1989
doi: 10.3866/PKU.WHXB201604222
Abstract:
Time-dependent density functional theory (TDDFT) calculations using the B3LYP method were used to investigate the effect of β-substituents on the electronic absorption spectra of a series of manganese(V)-oxo corrole complexes. The geometries, frontier molecular orbitals, and energies of the complexes were analyzed. The calculated results indicate that the steric effect of the β-substituents is the factor controlling the red-shift of the Soret bands and Q bands in these complexes. The sterically hindered β-substituents cause twisting of the corrole ring structure, which leads to reduced orbital energy gaps and a red-shift of the Soret bands and Q bands.
Time-dependent density functional theory (TDDFT) calculations using the B3LYP method were used to investigate the effect of β-substituents on the electronic absorption spectra of a series of manganese(V)-oxo corrole complexes. The geometries, frontier molecular orbitals, and energies of the complexes were analyzed. The calculated results indicate that the steric effect of the β-substituents is the factor controlling the red-shift of the Soret bands and Q bands in these complexes. The sterically hindered β-substituents cause twisting of the corrole ring structure, which leads to reduced orbital energy gaps and a red-shift of the Soret bands and Q bands.
2016, 32(8): 1990-1998
doi: 10.3866/PKU.WHXB201605031
Abstract:
Two novel sensitizers with D-D-π-A (YD2) and 2D-D-π-A (YD3) structures were designed by introducing different numbers of tetrathiafulvalene (TTF) unit as the auxiliary electron donor based on the simple D-π-A triphenylamine sensitizer (YD1) to enhance the electron donating ability. The geometries, electronic structures, and optical properties of YD1－3 before and after binding to TiO2 clusters were investigated. Owing to introduction of TTF unit, YD2 and YD3 show larger steric hindrance and a narrower band gap than YD1. Moreover, the estimated light-harvesting efficiency (LHE), injection driving force (ΔGinject) values, and density of states (DOS) calculations indicate that YD2 and YD3 should show higher short-circuit photocurrent density (Jsc) and open-circuit photovoltage (Voc) than YD1 with the presence of TTF unit. All of the results indicate that TTF unit can be used as an auxiliary electron donor in organic sensitizers to improve their photovoltaic properties.
Two novel sensitizers with D-D-π-A (YD2) and 2D-D-π-A (YD3) structures were designed by introducing different numbers of tetrathiafulvalene (TTF) unit as the auxiliary electron donor based on the simple D-π-A triphenylamine sensitizer (YD1) to enhance the electron donating ability. The geometries, electronic structures, and optical properties of YD1－3 before and after binding to TiO2 clusters were investigated. Owing to introduction of TTF unit, YD2 and YD3 show larger steric hindrance and a narrower band gap than YD1. Moreover, the estimated light-harvesting efficiency (LHE), injection driving force (ΔGinject) values, and density of states (DOS) calculations indicate that YD2 and YD3 should show higher short-circuit photocurrent density (Jsc) and open-circuit photovoltage (Voc) than YD1 with the presence of TTF unit. All of the results indicate that TTF unit can be used as an auxiliary electron donor in organic sensitizers to improve their photovoltaic properties.
2016, 32(8): 1999-2006
doi: 10.3866/PKU.WHXB201605032
Abstract:
A selenium disulfide-impregnated hollow carbon sphere composite was prepared as the cathode material for lithium-ion batteries. The morphology, composition, and structure of the as-synthesized composite were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and the Brunauer-Emmett- Teller (BET) technique. It was found that uniform monodispersive hollow carbon spheres can be synthesized by the template method combined with chemical polymerization. The diameter of the spheres is about 500 nm and the thickness of their wall is about 30 nm. Furthermore, a selenium disulfide-impregnated hollow carbon sphere composite can be achieved by the melting-diffusion method. The electrochemical performance of the as-synthesized composite as a cathode material for lithium-ion batteries was also investigated. Compared with the pristine bulk SeS2 material, the SeS2@HCS composite exhibits higher initial discharge capacity (956 mAh· g-1 at a current density of 100 mA·g-1), longer cycle life (200 cycles at a current density of 100 mA·g-1), and better rate performance. The results indicate that this composite can be considered as a promising candidate for the cathode material of lithium-ion batteries.
A selenium disulfide-impregnated hollow carbon sphere composite was prepared as the cathode material for lithium-ion batteries. The morphology, composition, and structure of the as-synthesized composite were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and the Brunauer-Emmett- Teller (BET) technique. It was found that uniform monodispersive hollow carbon spheres can be synthesized by the template method combined with chemical polymerization. The diameter of the spheres is about 500 nm and the thickness of their wall is about 30 nm. Furthermore, a selenium disulfide-impregnated hollow carbon sphere composite can be achieved by the melting-diffusion method. The electrochemical performance of the as-synthesized composite as a cathode material for lithium-ion batteries was also investigated. Compared with the pristine bulk SeS2 material, the SeS2@HCS composite exhibits higher initial discharge capacity (956 mAh· g-1 at a current density of 100 mA·g-1), longer cycle life (200 cycles at a current density of 100 mA·g-1), and better rate performance. The results indicate that this composite can be considered as a promising candidate for the cathode material of lithium-ion batteries.
2016, 32(8): 2007-2017
doi: 10.3866/PKU.WHXB201604261
Abstract:
The effect of Li+, Zn2+, and Mn2+ ions in aqueous solution on the electrochemical performance of the MnO2 cathode characterized by different crystal structures and morphologies was investigated. The energy storage mechanism of MnO2 in the mixed solution was probed. The results show that in aqueous solution without Mn2+ ions, various MnO2 electrodes exhibit similar electrochemical performance with low capacity and severe attenuation. In an aqueous solution with Zn2+ ions, the capacity of MnO2 electrodes is enhanced, which can be attributed to insertion/extraction of zinc ions. However, the decay of the capacity is drastic. When aqueous solutions containing Mn2+ and Zn2+ ions are used, particle aggregation and crystal structure collapse of MnO2 are effectively prevented owing to the synergistic effect of zinc and manganese ions and the redox reaction process of Mn2+ ions. The negative influence of the ZnSO4·3Zn(OH)2 impurity is also weakened. As a result, the high capacity of MnO2 electrodes resulting from insertion/extraction of zinc ions is maintained (~200 mAh·g-1 at 100 mA·g-1) with excellent cycling stability.
The effect of Li+, Zn2+, and Mn2+ ions in aqueous solution on the electrochemical performance of the MnO2 cathode characterized by different crystal structures and morphologies was investigated. The energy storage mechanism of MnO2 in the mixed solution was probed. The results show that in aqueous solution without Mn2+ ions, various MnO2 electrodes exhibit similar electrochemical performance with low capacity and severe attenuation. In an aqueous solution with Zn2+ ions, the capacity of MnO2 electrodes is enhanced, which can be attributed to insertion/extraction of zinc ions. However, the decay of the capacity is drastic. When aqueous solutions containing Mn2+ and Zn2+ ions are used, particle aggregation and crystal structure collapse of MnO2 are effectively prevented owing to the synergistic effect of zinc and manganese ions and the redox reaction process of Mn2+ ions. The negative influence of the ZnSO4·3Zn(OH)2 impurity is also weakened. As a result, the high capacity of MnO2 electrodes resulting from insertion/extraction of zinc ions is maintained (~200 mAh·g-1 at 100 mA·g-1) with excellent cycling stability.
2016, 32(8): 2018-2026
doi: 10.3866/PKU.WHXB201605271
Abstract:
Anew series of structurally controllable dual hydrophilic diblock copolymers poly(methacrylate acid)-b- poly(N-(2- methacryloylxyethyl) pyrrolidone), PMAA-b-PNMP including PMAA101-b-PNMP153, PMAA101-b- PNMP240, PMAA101-b-PNMP420, and PMAA101-b-PNMP539, were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization and characterized by gel permeation chromatography (GPC) and 1H nuclear magnetic resonance (NMR). The pH- and temperature-induced micellization behavior of PMAA-b-PNMP in aqueous solution was confirmed by static light scattering (SLS) and dynamic light scattering (DLS) and cryogen transmission electron microscopy (cryo-TEM) techniques. The polymerization degree of PNMP strongly affects the micellization behavior. Generally, with higher polymerization degree, the micellization pH was lower and the micellization temperature was higher. During the micellization processes, the weakness of the hydrogen bond interactions between water and PNMP or PMAA and the strength in the inter- and intra-chain interactions between PNMP and PMAA segments are dominant during the pH-induced micellization, as revealed by the pDdependent 1H NMR spectra. However, the weakness in the hydrogen bond interactions between water and PNMP is the major cause of the temperature-induced micellization process. We also provide solid evidence for the ability to control the size of Au NPs by adjusting the pH in the presence of PMAA-b-PNMP. Specifically, with higher pH, the size of the Au NPs was smaller.
Anew series of structurally controllable dual hydrophilic diblock copolymers poly(methacrylate acid)-b- poly(N-(2- methacryloylxyethyl) pyrrolidone), PMAA-b-PNMP including PMAA101-b-PNMP153, PMAA101-b- PNMP240, PMAA101-b-PNMP420, and PMAA101-b-PNMP539, were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization and characterized by gel permeation chromatography (GPC) and 1H nuclear magnetic resonance (NMR). The pH- and temperature-induced micellization behavior of PMAA-b-PNMP in aqueous solution was confirmed by static light scattering (SLS) and dynamic light scattering (DLS) and cryogen transmission electron microscopy (cryo-TEM) techniques. The polymerization degree of PNMP strongly affects the micellization behavior. Generally, with higher polymerization degree, the micellization pH was lower and the micellization temperature was higher. During the micellization processes, the weakness of the hydrogen bond interactions between water and PNMP or PMAA and the strength in the inter- and intra-chain interactions between PNMP and PMAA segments are dominant during the pH-induced micellization, as revealed by the pDdependent 1H NMR spectra. However, the weakness in the hydrogen bond interactions between water and PNMP is the major cause of the temperature-induced micellization process. We also provide solid evidence for the ability to control the size of Au NPs by adjusting the pH in the presence of PMAA-b-PNMP. Specifically, with higher pH, the size of the Au NPs was smaller.
2016, 32(8): 2027-2038
doi: 10.3866/PKU.WHXB201605033
Abstract:
Investigation of the thermodynamics of fatty acid (FA) modulation of lipid membrane behavior is important to understand the mechanisms that occur in cells. Previous research of the interaction between FAs and lipid membranes has been performed in dilute solution, and no study has focused on the effect of an external crowding medium on the phase transition of the lipid membrane induced by FAs. In this paper, the effect of various molecular weights and concentrations of polyethylene glycol (PEG) on the phase transition of 1,2- dimyristoyl-sn-glycero-3-phosphocholine (DMPC) vesicles mixed with FA was systematically investigated by differential scanning calorimetry (DSC). The results show that the effect of PEG on the phase transition of pure DMPC vesicles is both molecular weight and concentration dependent. The presence of PEG significantly changes the phase transition of FA/DMPC vesicles. Phase transition temperature (Tm) of FA/DMPC vesicles increased in PEG for most of the considered concentrations and molecular weights. The original Tm of DMPC induced by short-chain saturated FA or unsaturated FA increased in the presence of PEG. Further investigation revealed that in most cases a collaborative effect of molecular crowding existed and the effect of PEG on Tm was both molecular weight and concentration dependent. Moreover, the cooperative unit (CU) of pure DMPC vesicles and most FA/DMPC systems decreased with increasing PEG concentration, indicating that the crowded medium contributes to the heterogeneity of the bilayers and that fewer molecules cooperatively participate in the phase transition. The results suggest that crowded media might repair disturbed membranes, which should not be ignored in the FA-modulating membrane related area.
Investigation of the thermodynamics of fatty acid (FA) modulation of lipid membrane behavior is important to understand the mechanisms that occur in cells. Previous research of the interaction between FAs and lipid membranes has been performed in dilute solution, and no study has focused on the effect of an external crowding medium on the phase transition of the lipid membrane induced by FAs. In this paper, the effect of various molecular weights and concentrations of polyethylene glycol (PEG) on the phase transition of 1,2- dimyristoyl-sn-glycero-3-phosphocholine (DMPC) vesicles mixed with FA was systematically investigated by differential scanning calorimetry (DSC). The results show that the effect of PEG on the phase transition of pure DMPC vesicles is both molecular weight and concentration dependent. The presence of PEG significantly changes the phase transition of FA/DMPC vesicles. Phase transition temperature (Tm) of FA/DMPC vesicles increased in PEG for most of the considered concentrations and molecular weights. The original Tm of DMPC induced by short-chain saturated FA or unsaturated FA increased in the presence of PEG. Further investigation revealed that in most cases a collaborative effect of molecular crowding existed and the effect of PEG on Tm was both molecular weight and concentration dependent. Moreover, the cooperative unit (CU) of pure DMPC vesicles and most FA/DMPC systems decreased with increasing PEG concentration, indicating that the crowded medium contributes to the heterogeneity of the bilayers and that fewer molecules cooperatively participate in the phase transition. The results suggest that crowded media might repair disturbed membranes, which should not be ignored in the FA-modulating membrane related area.
2016, 32(8): 2039-2044
doi: 10.3866/PKU.WHXB201605122
Abstract:
The multi-network material PDGI/PAAm-PAMPS-PAAm (PDGI/TN) was synthesized, starting from PDGI/PAAm (PDGI/SN). The PDGI/TN was subsequently deswelled to an equilibrium state in an ethanol/water mixture (6 : 4)(V/V) to generate a material termed PDGI/TN-0.6. The results indicate that the swelling radio of the PDGI/TN was increased to 1070% ± 50%, compared with a value of 850% ± 45% for the original PDGI/SN. In addition, the color of the gel changed from blue (λmax = 450 nm) to transparent and the Bragg diffraction peak transitioned to 670 nm. The Bragg diffraction peak could also be tuned over the range from 450 to 670 nm by adjusting triple network and the ethanol/water solution. Loading-unloading cycling in conjunction with tensile and compressive testing demonstrated that the PDGI/TN-0.6 possessed outstanding mechanical properties. The tensile and compressive stresses of PDGI/TN-0.6 were significantly improved from those of the initial PDGI/ SN, to 0.99 and 37.0 MPa, respectively. Loading-unloading cycling data showed that the PDGI/TN-0.6 exhibited excellent responsiveness even after repeated trials. As compressive strain (εc) was increased from 0 to 0.5, the Bragg diffraction peak underwent a blue shift under compression and eventually spanned the entire visible spectrum wavelength range at the same rate that compressive deformation was applied and released. The effect of the triple network on the inner layer distance in this material was also investigated using scanning electron microscopy (SEM).
The multi-network material PDGI/PAAm-PAMPS-PAAm (PDGI/TN) was synthesized, starting from PDGI/PAAm (PDGI/SN). The PDGI/TN was subsequently deswelled to an equilibrium state in an ethanol/water mixture (6 : 4)(V/V) to generate a material termed PDGI/TN-0.6. The results indicate that the swelling radio of the PDGI/TN was increased to 1070% ± 50%, compared with a value of 850% ± 45% for the original PDGI/SN. In addition, the color of the gel changed from blue (λmax = 450 nm) to transparent and the Bragg diffraction peak transitioned to 670 nm. The Bragg diffraction peak could also be tuned over the range from 450 to 670 nm by adjusting triple network and the ethanol/water solution. Loading-unloading cycling in conjunction with tensile and compressive testing demonstrated that the PDGI/TN-0.6 possessed outstanding mechanical properties. The tensile and compressive stresses of PDGI/TN-0.6 were significantly improved from those of the initial PDGI/ SN, to 0.99 and 37.0 MPa, respectively. Loading-unloading cycling data showed that the PDGI/TN-0.6 exhibited excellent responsiveness even after repeated trials. As compressive strain (εc) was increased from 0 to 0.5, the Bragg diffraction peak underwent a blue shift under compression and eventually spanned the entire visible spectrum wavelength range at the same rate that compressive deformation was applied and released. The effect of the triple network on the inner layer distance in this material was also investigated using scanning electron microscopy (SEM).
2016, 32(8): 2045-2051
doi: 10.3866/PKU.WHXB201605042
Abstract:
Fumed silica (F-SiO2) particles were hydrophobized in situ in aqueous solutions of alkanediyl-α,ω- bis(dodecyldimethylammoniumbromide) (12-s-12, s= 2, 6) gemini surfactants. This process was assessed using zeta potential measurements. The particles were found to transit from their original hydrophilic nature to hydrophobic and then back to hydrophilic with increases in the surfactant concentration (C). The hydrophobic particles could spontaneously adsorb at the air/water interface, resulting in significant stabilization of aqueous foams. The re-hydrophilic particles desorbed from the interface, leaving only surfactant molecules to stabilize the foam. The strong interfacial elasticity of the surface films was reflected in the highly stable foams. The length of the surfactant spacer also affected the adsorption of the gemini surfactant on the F-SiO2 particles, and therefore had an effect on the elasticity of the adsorbed film and the stability of the foam. The 12-2-12 surfactant, having a relatively short spacer, carried less positive charges because of the incomplete dissociation of its counter ions, resulting in less initial adsorption on the F-SiO2 particles compared with the 12-6-12, but eventually formed a denser monomeric layer because of decreased repulsion between the adsorbed molecules. The 12-2-12 exhibited stronger adsorption at the air/water interface; therefore, the synergistic action of the F-SiO2 particles together with the 12-2-12 produced better foam stabilization compared with the 12-6-12.
Fumed silica (F-SiO2) particles were hydrophobized in situ in aqueous solutions of alkanediyl-α,ω- bis(dodecyldimethylammoniumbromide) (12-s-12, s= 2, 6) gemini surfactants. This process was assessed using zeta potential measurements. The particles were found to transit from their original hydrophilic nature to hydrophobic and then back to hydrophilic with increases in the surfactant concentration (C). The hydrophobic particles could spontaneously adsorb at the air/water interface, resulting in significant stabilization of aqueous foams. The re-hydrophilic particles desorbed from the interface, leaving only surfactant molecules to stabilize the foam. The strong interfacial elasticity of the surface films was reflected in the highly stable foams. The length of the surfactant spacer also affected the adsorption of the gemini surfactant on the F-SiO2 particles, and therefore had an effect on the elasticity of the adsorbed film and the stability of the foam. The 12-2-12 surfactant, having a relatively short spacer, carried less positive charges because of the incomplete dissociation of its counter ions, resulting in less initial adsorption on the F-SiO2 particles compared with the 12-6-12, but eventually formed a denser monomeric layer because of decreased repulsion between the adsorbed molecules. The 12-2-12 exhibited stronger adsorption at the air/water interface; therefore, the synergistic action of the F-SiO2 particles together with the 12-2-12 produced better foam stabilization compared with the 12-6-12.
2016, 32(8): 2052-2058
doi: 10.3866/PKU.WHXB201604213
Abstract:
The adsorption of Sr2+ ions onto Ta-doped hex-WO3 nanomaterials was studied by measuring the zeta potentials of the powder nanoparticles and by determining the adsorption isotherm and adsorption mechanism. Five important results were obtained: (1) the zeta potential values of the Ta-doped hex-WO3 suspensions in different electrolyte solutions, within the studied pH ranges, increased with an increase in electrolyte valence; and (2) the zeta potential of the Ta-doped hex-WO3 suspensions increased with an increase in ionic strength. (3) Sr2+ ion adsorption increased with a decrease in temperature and ionic strength. (4) The adsorption enthalpy was calculated as －47 kJ·mol-1, and the interaction between the Ta-doped hex-WO3 surface and Sr2+ ions was concluded to be chemical in nature. (5) The adsorption of Sr2+ ions onto the Ta-doped hex-WO3 was attributed to surface chemical adsorption and ion exchange (in tunnels).
The adsorption of Sr2+ ions onto Ta-doped hex-WO3 nanomaterials was studied by measuring the zeta potentials of the powder nanoparticles and by determining the adsorption isotherm and adsorption mechanism. Five important results were obtained: (1) the zeta potential values of the Ta-doped hex-WO3 suspensions in different electrolyte solutions, within the studied pH ranges, increased with an increase in electrolyte valence; and (2) the zeta potential of the Ta-doped hex-WO3 suspensions increased with an increase in ionic strength. (3) Sr2+ ion adsorption increased with a decrease in temperature and ionic strength. (4) The adsorption enthalpy was calculated as －47 kJ·mol-1, and the interaction between the Ta-doped hex-WO3 surface and Sr2+ ions was concluded to be chemical in nature. (5) The adsorption of Sr2+ ions onto the Ta-doped hex-WO3 was attributed to surface chemical adsorption and ion exchange (in tunnels).
2016, 32(8): 2059-2068
doi: 10.3866/PKU.WHXB201604225
Abstract:
The adsorption of sodium salicylate on goethite or hematite surfaces was investigated by Fourier transform infrared (FT-IR) spectroscopy, X-ray photoemission spectroscopy (XPS), and periodic plane-wave density functional theory (DFT) calculations. The core level shift (CLS) and charge transfer of the adsorbed surface iron sites calculated by DFT with periodic interfacial structures were compared with the X-ray photoemission experiments. The FT-IR results reveal that the interfacial structure of sodium salicylate adsorbed on goethite or hematite surfaces can be classified as bidentate binuclear (V) or bidentate mononuclear (IV), respectively. The DFT calculated results indicate that the bidentate binuclear (V) structure of sodium salicylate is favorable on the goethite (101) surface, with an adsorption energy of －5.46 eV, while the adsorption of sodium salicylate on the goethite (101) surface as a bidentate mononuclear (IV) structure is not predicted, as it has a positive adsorption energy of 3.80 eV. Conversely, on the hematite (001) surface, the bidentate mononuclear (IV) structure of the adsorbed sodium salicylate has anadsorption energy of －4.07 eV, confirming its favorability. Moreover, the calculated CLS of Fe 2p (－0.68 eV) for the adsorbed iron site on the goethite (101) surface is consistent with the experimentally observed CLS of Fe 2p (－0.5 eV) for SSa-treated goethite (goethite after the treatment of sodium salicylate). Our calculated CLS of Fe 2p (－0.80 eV) for the adsorbed iron site on the hematite (001) surface is likewise in good agreement with the experimentally observed CLS of Fe 2p (－0.8 eV) for SSa-treated hematite (hematite after the treatment of sodium salicylate). Thus, goethite is predicted to adsorb sodium salicylate as a bidentate binuclear (V) structure via the bonding of one carboxylate oxygen atom and the phenolic oxygen atom of sodium salicylate to two surface iron atoms of goethite (101). Meanwhile, on the hematite surface, the bidentate mononuclear (IV) complex formed via the bonding of one carboxylate oxygen atom and the phenolic oxygen atom of sodium salicylate to one surface iron atom of hematite (001) can be regarded as plausible.
The adsorption of sodium salicylate on goethite or hematite surfaces was investigated by Fourier transform infrared (FT-IR) spectroscopy, X-ray photoemission spectroscopy (XPS), and periodic plane-wave density functional theory (DFT) calculations. The core level shift (CLS) and charge transfer of the adsorbed surface iron sites calculated by DFT with periodic interfacial structures were compared with the X-ray photoemission experiments. The FT-IR results reveal that the interfacial structure of sodium salicylate adsorbed on goethite or hematite surfaces can be classified as bidentate binuclear (V) or bidentate mononuclear (IV), respectively. The DFT calculated results indicate that the bidentate binuclear (V) structure of sodium salicylate is favorable on the goethite (101) surface, with an adsorption energy of －5.46 eV, while the adsorption of sodium salicylate on the goethite (101) surface as a bidentate mononuclear (IV) structure is not predicted, as it has a positive adsorption energy of 3.80 eV. Conversely, on the hematite (001) surface, the bidentate mononuclear (IV) structure of the adsorbed sodium salicylate has anadsorption energy of －4.07 eV, confirming its favorability. Moreover, the calculated CLS of Fe 2p (－0.68 eV) for the adsorbed iron site on the goethite (101) surface is consistent with the experimentally observed CLS of Fe 2p (－0.5 eV) for SSa-treated goethite (goethite after the treatment of sodium salicylate). Our calculated CLS of Fe 2p (－0.80 eV) for the adsorbed iron site on the hematite (001) surface is likewise in good agreement with the experimentally observed CLS of Fe 2p (－0.8 eV) for SSa-treated hematite (hematite after the treatment of sodium salicylate). Thus, goethite is predicted to adsorb sodium salicylate as a bidentate binuclear (V) structure via the bonding of one carboxylate oxygen atom and the phenolic oxygen atom of sodium salicylate to two surface iron atoms of goethite (101). Meanwhile, on the hematite surface, the bidentate mononuclear (IV) complex formed via the bonding of one carboxylate oxygen atom and the phenolic oxygen atom of sodium salicylate to one surface iron atom of hematite (001) can be regarded as plausible.
2016, 32(8): 2069-2076
doi: 10.3866/PKU.WHXB201604224
Abstract:
Au/ZnO hollow spheres with different mass ratios were synthesized by a simple two-step method. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) were used to characterize the as-prepared Au/ZnO hollow spheres. The photocatalytic activity of the Au/ZnO composites was evaluated by the degradation of rhodamine B (RhB) dye under white light. Compared with pure ZnO hollow spheres, the degradation rate of RhB was enhanced by 73%with the appropriate amount of Au in the modified ZnO photocatalysts. The influence of Au decoration on the surface photo-induced charge-transfer behaviour of ZnO was investigated by surface photovoltage spectroscopy (SPS) and transient photovoltage (TPV). The results showed that the improved photodegradation by Au/ZnO hollow spheres was mostly caused by the strong electronic interactions between ZnO and the Au nanoparticles. The appropriate load of Au nanoparticles in ZnO promoted the separation of photogenerated charges, thus extending the transmission time of the charge carrier and increasing the lifetime of the photogenerated charges, resulting in highly efficient photocatalysis.
Au/ZnO hollow spheres with different mass ratios were synthesized by a simple two-step method. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) were used to characterize the as-prepared Au/ZnO hollow spheres. The photocatalytic activity of the Au/ZnO composites was evaluated by the degradation of rhodamine B (RhB) dye under white light. Compared with pure ZnO hollow spheres, the degradation rate of RhB was enhanced by 73%with the appropriate amount of Au in the modified ZnO photocatalysts. The influence of Au decoration on the surface photo-induced charge-transfer behaviour of ZnO was investigated by surface photovoltage spectroscopy (SPS) and transient photovoltage (TPV). The results showed that the improved photodegradation by Au/ZnO hollow spheres was mostly caused by the strong electronic interactions between ZnO and the Au nanoparticles. The appropriate load of Au nanoparticles in ZnO promoted the separation of photogenerated charges, thus extending the transmission time of the charge carrier and increasing the lifetime of the photogenerated charges, resulting in highly efficient photocatalysis.
2016, 32(8): 2077-2083
doi: 10.3866/PKU.WHXB201605081
Abstract:
Hydrothermal processing in conjunction with in situ precipitation were successfully applied to synthesize the magnetic composite catalyst silver bromide/silver phosphate/zinc ferrite (AgBr/Ag3PO4/ZnFe2O4). The phase structure, composition, morphology, and optical property of this material were subsequently assessed by X- ray diffraction, energy dispersive X- ray spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, and UV-Vis diffuse reflectance spectroscopy. Under visible light illumination, the as-prepared AgBr/Ag3PO4/ZnFe2O4 photocatalyst exhibited superior photocatalytic performance during rhodamine B (RhB) degradation compared with Ag3PO4/ZnFe2O4, AgBr/ZnFe2O4, and P25 TiO2. This new catalyst also showed excellent photocatalytic activity in both acidic and basic solutions. The RhB photodegradation rate was slightly increased at higher temperatures, and the activation energy for this reaction was determined to be 31.9 kJ·mol-1 according to the Arrhenius equation. The high performance of the AgBr/Ag3PO4/ZnFe2O4 catalyst can be attributed to efficient photo-induced charge separation, and the generation of superoxide radicals and holes that are responsible for RhB degradation.
Hydrothermal processing in conjunction with in situ precipitation were successfully applied to synthesize the magnetic composite catalyst silver bromide/silver phosphate/zinc ferrite (AgBr/Ag3PO4/ZnFe2O4). The phase structure, composition, morphology, and optical property of this material were subsequently assessed by X- ray diffraction, energy dispersive X- ray spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, and UV-Vis diffuse reflectance spectroscopy. Under visible light illumination, the as-prepared AgBr/Ag3PO4/ZnFe2O4 photocatalyst exhibited superior photocatalytic performance during rhodamine B (RhB) degradation compared with Ag3PO4/ZnFe2O4, AgBr/ZnFe2O4, and P25 TiO2. This new catalyst also showed excellent photocatalytic activity in both acidic and basic solutions. The RhB photodegradation rate was slightly increased at higher temperatures, and the activation energy for this reaction was determined to be 31.9 kJ·mol-1 according to the Arrhenius equation. The high performance of the AgBr/Ag3PO4/ZnFe2O4 catalyst can be attributed to efficient photo-induced charge separation, and the generation of superoxide radicals and holes that are responsible for RhB degradation.
2016, 32(8): 2084-2092
doi: 10.3866/PKU.WHXB201605041
Abstract:
In this study, we regulated copper loading and the atomic ratio of Cu/Mn and investigated the influence on interaction of the active species of Cu-Mn composite oxide catalyst supported on TiO2 (CuxMny/ TiO2). The results indicate that 15% (w, mass fraction) copper loading and a 1 : 1 atomic ratio of Cu/Mn favors formation of analogous Cu-Mn spinel (Cu1.5Mn1.5O4). With increasing loading of copper, oxygen transfers from the lattice oxygen species to defect oxygen. The changes in copper loading and the Cu/Mn atomic ratio have a large influence on the interaction between the active components and the catalytic activity. We found that 90% n-hexanal can be degraded by Cu15Mn15/TiO2 at 225 ℃ (T90). The excellent performance of Cu15Mn15/TiO2 is attributed to the higher contents of Cu2+ and Oads, which can achieve a dual redox process with Mn2+ in Cu15Mn15/TiO2. The analogous Cu-Mn spinel active ingredient can maintain high catalytic stability by redox cycles.
In this study, we regulated copper loading and the atomic ratio of Cu/Mn and investigated the influence on interaction of the active species of Cu-Mn composite oxide catalyst supported on TiO2 (CuxMny/ TiO2). The results indicate that 15% (w, mass fraction) copper loading and a 1 : 1 atomic ratio of Cu/Mn favors formation of analogous Cu-Mn spinel (Cu1.5Mn1.5O4). With increasing loading of copper, oxygen transfers from the lattice oxygen species to defect oxygen. The changes in copper loading and the Cu/Mn atomic ratio have a large influence on the interaction between the active components and the catalytic activity. We found that 90% n-hexanal can be degraded by Cu15Mn15/TiO2 at 225 ℃ (T90). The excellent performance of Cu15Mn15/TiO2 is attributed to the higher contents of Cu2+ and Oads, which can achieve a dual redox process with Mn2+ in Cu15Mn15/TiO2. The analogous Cu-Mn spinel active ingredient can maintain high catalytic stability by redox cycles.
2016, 32(8): 2093-2100
doi: 10.3866/PKU.WHXB201605121
Abstract:
Three-dimensional, nanoporous CoFe2O4 catalysts were synthesized, employing a colloidal crystal template method. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption-desorption were subsequently used to characterize the crystal structures and morphologies of the samples. The catalytic activities of nanoporous CoFe2O4 and CoFe2O4 nanospheres during the thermal decomposition of ammonium perchlorate (AP) were also investigated by differential scanning calorimetry (DSC). The results show that the spinel framework of these materials has an ordered open network of pores averaging 200 nm in diameter. The specific surface area of the nanoporous CoFe2O4 was 55.646 m2·g-1, a value that was higher than that of the nanosphere material. DSC analysis indicates that the catalytic activity of the nanoporous CoFe2O4 is superior to that of the spherical material during the thermal decomposition of AP, and that the nanoporous catalyst makes the peak temperature of high temperature decomposition decrease by 91.46 ℃. The heat release from the AP in the presence of nanoporous CoFe2O4 (1120.88 J·g-1) is 2.3 times that obtained frompureAP. Both the higher specific surface area and greater quantity of active reduction sites on the nanoporous CoFe2O4 relative to the nanosphere material act to reduce the activation energy during the AP decomposition process. Based on the results of this work, a possible catalytic mechanismfor the thermal decomposition of AP over nanoporous CoFe2O4 is proposed, in which gaseous intermediates play an important role.
Three-dimensional, nanoporous CoFe2O4 catalysts were synthesized, employing a colloidal crystal template method. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption-desorption were subsequently used to characterize the crystal structures and morphologies of the samples. The catalytic activities of nanoporous CoFe2O4 and CoFe2O4 nanospheres during the thermal decomposition of ammonium perchlorate (AP) were also investigated by differential scanning calorimetry (DSC). The results show that the spinel framework of these materials has an ordered open network of pores averaging 200 nm in diameter. The specific surface area of the nanoporous CoFe2O4 was 55.646 m2·g-1, a value that was higher than that of the nanosphere material. DSC analysis indicates that the catalytic activity of the nanoporous CoFe2O4 is superior to that of the spherical material during the thermal decomposition of AP, and that the nanoporous catalyst makes the peak temperature of high temperature decomposition decrease by 91.46 ℃. The heat release from the AP in the presence of nanoporous CoFe2O4 (1120.88 J·g-1) is 2.3 times that obtained frompureAP. Both the higher specific surface area and greater quantity of active reduction sites on the nanoporous CoFe2O4 relative to the nanosphere material act to reduce the activation energy during the AP decomposition process. Based on the results of this work, a possible catalytic mechanismfor the thermal decomposition of AP over nanoporous CoFe2O4 is proposed, in which gaseous intermediates play an important role.
2016, 32(8): 2101-2107
doi: 10.3866/PKU.WHXB201604146
Abstract:
The γ-radiolysis of octylphenyl-(N,N-(diisobutyl)carbamoyl-methyl) phosphine oxide (CMPO) in 1- ethyl-3-methylimidazoliumbis (trifluoromethylsulfonyl) imide ([C2mim][NTf2]) was studied. The effect of radiation on CMPO/[C2mim][NTf2] extractability was also investigated. Quantitative analysis of CMPO in irradiated CMPO/ [C2mim][NTf2] systems, identification and semi-quantitative analysis of the radiolytic products were performed using ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF-MS). For comparison, CMPO/dodecane was also studied under the same conditions. The radiolysis ratio of CMPO in [C2mim][NTf2] was found to be lower than in dodecane, because of the different radiolysis pathways. The radiolysis pathway of CMPO in molecular solvent was mainly chain scission of C―P and C―N, while that in [C2mim][NTf2] was the elimination of isobutyl, as well as substitution reactions with [C2mim]+· and ·CF3 generated from solvent [C2mim][NTf2]. Based on the radiolysis study, we propose a radiolysis pathway for CMPO/[C2mim] [NTf2], providing a deeper understanding of the radiolytic mechanism of CMPO in ionic liquids. Finally, the Eu3+ partitioning of CMPO/[C2mim][NTf2] from 0.01 mol·L-1 HNO3 was higher than 99% at 800 kGy.
The γ-radiolysis of octylphenyl-(N,N-(diisobutyl)carbamoyl-methyl) phosphine oxide (CMPO) in 1- ethyl-3-methylimidazoliumbis (trifluoromethylsulfonyl) imide ([C2mim][NTf2]) was studied. The effect of radiation on CMPO/[C2mim][NTf2] extractability was also investigated. Quantitative analysis of CMPO in irradiated CMPO/ [C2mim][NTf2] systems, identification and semi-quantitative analysis of the radiolytic products were performed using ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF-MS). For comparison, CMPO/dodecane was also studied under the same conditions. The radiolysis ratio of CMPO in [C2mim][NTf2] was found to be lower than in dodecane, because of the different radiolysis pathways. The radiolysis pathway of CMPO in molecular solvent was mainly chain scission of C―P and C―N, while that in [C2mim][NTf2] was the elimination of isobutyl, as well as substitution reactions with [C2mim]+· and ·CF3 generated from solvent [C2mim][NTf2]. Based on the radiolysis study, we propose a radiolysis pathway for CMPO/[C2mim] [NTf2], providing a deeper understanding of the radiolytic mechanism of CMPO in ionic liquids. Finally, the Eu3+ partitioning of CMPO/[C2mim][NTf2] from 0.01 mol·L-1 HNO3 was higher than 99% at 800 kGy.
2016, 32(8): 2108-2112
doi: 10.3866/PKU.WHXB201605091
Abstract:
Up-conversion luminescent NaYF4:Yb3+/Er3+ nanomaterials were synthesized using a solvo-thermal method. It was determined that the size, morphology, and luminescence intensity of these nanoparticles can be controlled by varying the concentration of fluoride ions. Low reactant concentrations were found to always result in monodisperse, hexagonal nanocrystals, and to gradually and uniformly decrease the size of the NaYF4 nanocrystals. In contrast, at higher concentrations, the nanocrystals grow to form a mixed phase. Fluoride ion concentrations over a specific range tend to promote the fluorescence emission of the material and may also significantly affect the fluorescent lifetime.
Up-conversion luminescent NaYF4:Yb3+/Er3+ nanomaterials were synthesized using a solvo-thermal method. It was determined that the size, morphology, and luminescence intensity of these nanoparticles can be controlled by varying the concentration of fluoride ions. Low reactant concentrations were found to always result in monodisperse, hexagonal nanocrystals, and to gradually and uniformly decrease the size of the NaYF4 nanocrystals. In contrast, at higher concentrations, the nanocrystals grow to form a mixed phase. Fluoride ion concentrations over a specific range tend to promote the fluorescence emission of the material and may also significantly affect the fluorescent lifetime.
2016, 32(8): 2113-2118
doi: 10.3866/PKU.WHXB201604262
Abstract:
In this paper, we develop a surface atom identification model to perform atom identification and analysis of the surface atoms of a single TiO2 nanoparticle during the heating and sintering process. Cubic mesh was used to obtain the particle structure mesh, and the optimal mesh size of 0.3 nm was determined by volumetric integration of a spherical particle. Surface atoms were classified according to identification of surface meshes, and the number of external meshes in all of the neighbor meshes (Next) was set as a criterion to determine whether the target mesh was a surface mesh. The optimal value was Next = 9. LAMMPS was used to simulate the heating process of a particle with a radius of 0.75 nm. The results show that energy relaxation is significantly faster than structure relaxation. The atom classification analysis with the developed surface atom identification model shows that displacement of the surface atoms is larger than the interior atoms, and surface O atoms are more active in migration than surface Ti atoms. The coordination number of surface atoms is lower than that of interior atoms. The present study provides fundamental information for analyzing the active structure distribution of nanoparticles.
In this paper, we develop a surface atom identification model to perform atom identification and analysis of the surface atoms of a single TiO2 nanoparticle during the heating and sintering process. Cubic mesh was used to obtain the particle structure mesh, and the optimal mesh size of 0.3 nm was determined by volumetric integration of a spherical particle. Surface atoms were classified according to identification of surface meshes, and the number of external meshes in all of the neighbor meshes (Next) was set as a criterion to determine whether the target mesh was a surface mesh. The optimal value was Next = 9. LAMMPS was used to simulate the heating process of a particle with a radius of 0.75 nm. The results show that energy relaxation is significantly faster than structure relaxation. The atom classification analysis with the developed surface atom identification model shows that displacement of the surface atoms is larger than the interior atoms, and surface O atoms are more active in migration than surface Ti atoms. The coordination number of surface atoms is lower than that of interior atoms. The present study provides fundamental information for analyzing the active structure distribution of nanoparticles.
2016, 32(8): 2119-2124
doi: 10.3866/PKU.WHXB201604263
Abstract:
Structure transformation and neck growth during the heat and sintering process of two TiO2 nanoparticles were investigated using molecular dynamics (MD) simulations. Based on the space meshing of the system and analysis of neighboring meshes, a neck atom identification model was developed. The model was successfully applied to identify neck atoms. Combined with the surface atom identification model previously developed by the authors, atoms in the system were further classified and the characteristics of the classified atoms were simulated and analyzed. The results show that sintering occurs when the temperature is above 573 K, the neck area increases with increasing sintering temperature, and it is mostly occupied by interior atoms. Surface atoms occupy less neck area and they are less sensitive to sintering temperature variation. The average displacement of neck atoms is larger than that of surface and interior atoms of the mother particles and O atoms are more active in migration than Ti atoms in the neck. Meanwhile, displacement of outside neck atoms is larger than that of inside neck atoms, meaning that neck growth mainly depends on the motion of outside neck atoms. The proposed model is stable and effective, and it provides fundamental information to analyze nanostructures in different zones.
Structure transformation and neck growth during the heat and sintering process of two TiO2 nanoparticles were investigated using molecular dynamics (MD) simulations. Based on the space meshing of the system and analysis of neighboring meshes, a neck atom identification model was developed. The model was successfully applied to identify neck atoms. Combined with the surface atom identification model previously developed by the authors, atoms in the system were further classified and the characteristics of the classified atoms were simulated and analyzed. The results show that sintering occurs when the temperature is above 573 K, the neck area increases with increasing sintering temperature, and it is mostly occupied by interior atoms. Surface atoms occupy less neck area and they are less sensitive to sintering temperature variation. The average displacement of neck atoms is larger than that of surface and interior atoms of the mother particles and O atoms are more active in migration than Ti atoms in the neck. Meanwhile, displacement of outside neck atoms is larger than that of inside neck atoms, meaning that neck growth mainly depends on the motion of outside neck atoms. The proposed model is stable and effective, and it provides fundamental information to analyze nanostructures in different zones.
