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2016 Volume 32 Issue 5
2016, 32(5): 1043-1044
doi: 10.3866/PKU.WHXB201604221
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2016, 32(5): 1045-1046
doi: 10.3866/PKU.WHXB201604183
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2016, 32(5): 1047-1048
doi: 10.3866/PKU.WHXB201604191
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2016, 32(5): 1049-1050
doi: 10.3866/PKU.WHXB201604181
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2016, 32(5): 1051-1052
doi: 10.3866/PKU.WHXB201603301
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2016, 32(5): 1053-1054
doi: 10.3866/PKU.WHXB201603302
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2016, 32(5): 1055-1055
doi: 10.3866/PKU.WHXB201604211
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2016, 32(5): 1056-1061
doi: 10.3866/PKU.WHXB201603092
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In order to ameliorate the severe capacity fading of LiNi0.5Co0.2Mn0.3O2 cathode materials at elevated temperatures, a Zr-doping strategy was performed via a solid-state method, and the influence of the doping content on the structural and electrochemical properties of LiNi0.5Co0.2Mn0.3O2 was studied. The results indicate that the Li+/Ni2+ cation mixing can be reduced and the electrochemical performance, especially the hightemperature cycling performance, can be improved when the doping content of zirconium is 0.01. After 95 cycles, the capacity retention of Li(Ni0.5Co0.2Mn0.3)0.99Zr0.01O2 is 92.13% at 1C between 3.0 and 4.3 V, which is higher than that of the LiNi0.5Co0.2Mn0.3O2 (87.61%). When cycling at 55 ℃, Li(Ni0.5Co0.2Mn0.3)0.99Zr0.01O2 exhibits a capacity retention of 82.96% after 115 cycles at 1C, while that of the bare sample remains at only 67.63%. Therefore, a small amount of zirconium doping is notably beneficial to the electrochemical performance of LiNi0.5Co0.2Mn0.3O2 at elevated temperatures.
In order to ameliorate the severe capacity fading of LiNi0.5Co0.2Mn0.3O2 cathode materials at elevated temperatures, a Zr-doping strategy was performed via a solid-state method, and the influence of the doping content on the structural and electrochemical properties of LiNi0.5Co0.2Mn0.3O2 was studied. The results indicate that the Li+/Ni2+ cation mixing can be reduced and the electrochemical performance, especially the hightemperature cycling performance, can be improved when the doping content of zirconium is 0.01. After 95 cycles, the capacity retention of Li(Ni0.5Co0.2Mn0.3)0.99Zr0.01O2 is 92.13% at 1C between 3.0 and 4.3 V, which is higher than that of the LiNi0.5Co0.2Mn0.3O2 (87.61%). When cycling at 55 ℃, Li(Ni0.5Co0.2Mn0.3)0.99Zr0.01O2 exhibits a capacity retention of 82.96% after 115 cycles at 1C, while that of the bare sample remains at only 67.63%. Therefore, a small amount of zirconium doping is notably beneficial to the electrochemical performance of LiNi0.5Co0.2Mn0.3O2 at elevated temperatures.
2016, 32(5): 1062-1071
doi: 10.3866/PKU.WHXB201603231
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In response to energy shortages and environmental concerns, global energy consumption is transitioning from a reliance on fossil fuels to multiple, clean and efficient power sources. Energy storage is central to the development of electric vehicles and smart grids, and hence to the emerging nationally strategic industries. Today, lithium-ion batteries (LIBs) are among the most widely used energy storage devices in daily life, but they face a severe challenge to meet the rigorous requirements of energy/power density, cycle life and cost for electric vehicles and smart grids. The search for next-generation energy storage technologies with large energy density, long cycle life, high safety and low cost is vital in the post-LIB era. Consequently, lithium-sulfur and lithium-air batteries with high energy density, and safe, low-cost room-temperature sodium-ion batteries, have attracted increasing interest. In this article, we briefly summarize recent progress in next-generation rechargeable batteries and their key electrode materials, with a particular focus on Li-S, Li-air, and Na-ion batteries. The prospects for the future development of these new energy storage technologies are also discussed.
In response to energy shortages and environmental concerns, global energy consumption is transitioning from a reliance on fossil fuels to multiple, clean and efficient power sources. Energy storage is central to the development of electric vehicles and smart grids, and hence to the emerging nationally strategic industries. Today, lithium-ion batteries (LIBs) are among the most widely used energy storage devices in daily life, but they face a severe challenge to meet the rigorous requirements of energy/power density, cycle life and cost for electric vehicles and smart grids. The search for next-generation energy storage technologies with large energy density, long cycle life, high safety and low cost is vital in the post-LIB era. Consequently, lithium-sulfur and lithium-air batteries with high energy density, and safe, low-cost room-temperature sodium-ion batteries, have attracted increasing interest. In this article, we briefly summarize recent progress in next-generation rechargeable batteries and their key electrode materials, with a particular focus on Li-S, Li-air, and Na-ion batteries. The prospects for the future development of these new energy storage technologies are also discussed.
2016, 32(5): 1072-1086
doi: 10.3866/PKU.WHXB201603071
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Poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) block polyethers are typical nonionic polymeric surfactants, which allow for wide structural design, exhibit temperature-dependent micellization of the copolymers, and function in a variety of solvent systems. It greatly enriched the investigation of their aggregation behaviors in various solutions. In this paper, an overview based on our research work was provided about the basic properties of linear and branched PEO-PPO block polyethers in aqueous solutions. Furthermore, the effects of additives including acid/base, inorganic salts, alcohols, surfactants and polymers on the aggregation behaviors of PEO-PPO polyethers are examined. PEO-PPO block polyethers have good biocompatibility. They can form micelles in aqueous solutions, with a hydrophobic core and a hydrophilic corona around the micelle interior. This micelle structure provides local hydrophobic microenvironments for hydrophobic drugs. Thus, the application of PEO-PPO polyethers in the field of drug delivery is presented; they can be the theoretical dosage support structure in future drug discovery research.
Poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) block polyethers are typical nonionic polymeric surfactants, which allow for wide structural design, exhibit temperature-dependent micellization of the copolymers, and function in a variety of solvent systems. It greatly enriched the investigation of their aggregation behaviors in various solutions. In this paper, an overview based on our research work was provided about the basic properties of linear and branched PEO-PPO block polyethers in aqueous solutions. Furthermore, the effects of additives including acid/base, inorganic salts, alcohols, surfactants and polymers on the aggregation behaviors of PEO-PPO polyethers are examined. PEO-PPO block polyethers have good biocompatibility. They can form micelles in aqueous solutions, with a hydrophobic core and a hydrophilic corona around the micelle interior. This micelle structure provides local hydrophobic microenvironments for hydrophobic drugs. Thus, the application of PEO-PPO polyethers in the field of drug delivery is presented; they can be the theoretical dosage support structure in future drug discovery research.
2016, 32(5): 1087-1104
doi: 10.3866/PKU.WHXB201602224
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The metal oxide heterojunction has often been used to improve the gas sensing properties of resistive metal oxide semiconductor gas sensors. Metal oxide heterojunctions have been demonstrated to have many unique properties such as Fermi-level mediated charge transfer effects as well as synergistic behavior of different components. In this short review, we summarize the fundamental types of metal oxide heterojunction materials reported in domestic and foreign research in recent years. Metal oxide heterojunctions are mainly divided into five categories of mixed composite structures, multi-layer films, structure modified with a second phase, 1D nanostructure and core-shell structure. We review the enhanced gas sensing mechanisms of metal oxide heterojunctions. These mechanisms are discussed in detail, including the role of the heterojunction, synergistic effects, the spill-over effect, response-type inversion, separation of charge carriers, and microstructure manipulation. We also analyze the remaining challenges of metal oxide heterojunction gas sensors. Finally, we provide an outlook for future development of metal oxide heterojunction gas sensors. The future research directions of metal oxide heterojunction gas sensors can be developed from the definition of heterojunction interface mechanisms. It is hoped that determining the heterojunction interface mechanisms will provide some reference for the design of needed gas sensors in a bottom-up route.
The metal oxide heterojunction has often been used to improve the gas sensing properties of resistive metal oxide semiconductor gas sensors. Metal oxide heterojunctions have been demonstrated to have many unique properties such as Fermi-level mediated charge transfer effects as well as synergistic behavior of different components. In this short review, we summarize the fundamental types of metal oxide heterojunction materials reported in domestic and foreign research in recent years. Metal oxide heterojunctions are mainly divided into five categories of mixed composite structures, multi-layer films, structure modified with a second phase, 1D nanostructure and core-shell structure. We review the enhanced gas sensing mechanisms of metal oxide heterojunctions. These mechanisms are discussed in detail, including the role of the heterojunction, synergistic effects, the spill-over effect, response-type inversion, separation of charge carriers, and microstructure manipulation. We also analyze the remaining challenges of metal oxide heterojunction gas sensors. Finally, we provide an outlook for future development of metal oxide heterojunction gas sensors. The future research directions of metal oxide heterojunction gas sensors can be developed from the definition of heterojunction interface mechanisms. It is hoped that determining the heterojunction interface mechanisms will provide some reference for the design of needed gas sensors in a bottom-up route.
2016, 32(5): 1105-1122
doi: 10.3866/PKU.WHXB201603015
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Micro-microporous composite zeolites with binary (or more) structures not only possess the advantages of the two kinds of molecular sieves, but also tailor the pore structure and acid property of the composite samples. These changes induce the formation of special properties of the composites and further present special catalytic performance, which drives many research studies. Based on synthetic methods and micro-structural features, micro-microporous composites can mainly be divided into two types: intergrowth or co-existence composite zeolites. The former has a structural rearrangement that is produced by the stacking of distinct layers and leads to the generation of a new crystal structure. The latter is formed by staggered growth and has a compound interface when two or more zeolites appeared in the same gel system. Compared with the intergrowth zeolites, the co-existence zeolites do not possess the new and perfect crystal structure. This review summarizes the development of micro-microporous composites, focusing on their synthesis and structural characteristics as well as the application of intergrowth and co-existence composite zeolites in the field of catalytic reactions.
Micro-microporous composite zeolites with binary (or more) structures not only possess the advantages of the two kinds of molecular sieves, but also tailor the pore structure and acid property of the composite samples. These changes induce the formation of special properties of the composites and further present special catalytic performance, which drives many research studies. Based on synthetic methods and micro-structural features, micro-microporous composites can mainly be divided into two types: intergrowth or co-existence composite zeolites. The former has a structural rearrangement that is produced by the stacking of distinct layers and leads to the generation of a new crystal structure. The latter is formed by staggered growth and has a compound interface when two or more zeolites appeared in the same gel system. Compared with the intergrowth zeolites, the co-existence zeolites do not possess the new and perfect crystal structure. This review summarizes the development of micro-microporous composites, focusing on their synthesis and structural characteristics as well as the application of intergrowth and co-existence composite zeolites in the field of catalytic reactions.
2016, 32(5): 1123-1128
doi: 10.3866/PKU.WHXB201603234
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The existing form of super-resolution microscopy based on specific fluorescent tagging is unable to obtain super-resolution images of non-fluorescent samples. Hence, we have developed optical subtraction microscopy for obtaining super-resolution imaging in such cases. This method is based on image subtraction between the two optical scattering images from general confocal excitation and doughnut-shaped excitation, respectively. Unlike super-resolution fluorescence microscopy, subtraction microscopy requires no preprocessing of the sample, and the excitation power can be kept low to avoid sample damage. The non-fluorescent imaging of gold nanobeads and polymer nanofibers has been realized to demonstrate the feasibility of super-resolution subtraction microscopy. The lateral resolution decreases to 215 nm (0.33λ, 1λ = 650 nm) in subtraction imaging, and greater imaging detail of the sample is achieved via optical scattering.
The existing form of super-resolution microscopy based on specific fluorescent tagging is unable to obtain super-resolution images of non-fluorescent samples. Hence, we have developed optical subtraction microscopy for obtaining super-resolution imaging in such cases. This method is based on image subtraction between the two optical scattering images from general confocal excitation and doughnut-shaped excitation, respectively. Unlike super-resolution fluorescence microscopy, subtraction microscopy requires no preprocessing of the sample, and the excitation power can be kept low to avoid sample damage. The non-fluorescent imaging of gold nanobeads and polymer nanofibers has been realized to demonstrate the feasibility of super-resolution subtraction microscopy. The lateral resolution decreases to 215 nm (0.33λ, 1λ = 650 nm) in subtraction imaging, and greater imaging detail of the sample is achieved via optical scattering.
2016, 32(5): 1129-1133
doi: 10.3866/PKU.WHXB201602195
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The gas viscosity and thermal conductivity are important fluid transport properties, and are related to thermodynamic states. Currently, the main methods to measure the viscosity and thermal conductivity require the gaseous samples to be exposed to non-stationary processes or non-equilibrium processes with gradients of the physical properties. Therefore, the gaseous samples are not located at a definitive thermodynamic state in time or space for each measurement. In this paper, a method to measure the gas viscosity and thermal conductivity at definitive thermodynamic states was studied by analyzing the dissipation of sound energy, which is controlled by the gas viscosity and thermal conductivity. This was performed using the transport theory for a dilute gas, based on the fixed path interference method with a cylindrical resonator. The results were verified by measuring the argon viscosity and thermal conductivity. The results agreed with data in the literature.
The gas viscosity and thermal conductivity are important fluid transport properties, and are related to thermodynamic states. Currently, the main methods to measure the viscosity and thermal conductivity require the gaseous samples to be exposed to non-stationary processes or non-equilibrium processes with gradients of the physical properties. Therefore, the gaseous samples are not located at a definitive thermodynamic state in time or space for each measurement. In this paper, a method to measure the gas viscosity and thermal conductivity at definitive thermodynamic states was studied by analyzing the dissipation of sound energy, which is controlled by the gas viscosity and thermal conductivity. This was performed using the transport theory for a dilute gas, based on the fixed path interference method with a cylindrical resonator. The results were verified by measuring the argon viscosity and thermal conductivity. The results agreed with data in the literature.
2016, 32(5): 1134-1142
doi: 10.3866/PKU.WHXB201602194
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The solubility of ammonium metavanadate (NH4VO3) in NH4H2PO4-H2O and (NH4)3PO4-H2O systems at T = 298.15-328.15 K was measured using the classic isothermal dissolution method. The densities and pH values of the solutions were also determined. The solubility of NH4VO3 decreased at first and then increased with increasing NH4H2PO4 or (NH4)3PO4 concentrations. This was considered to be caused by the common ionic effect, chemical reaction equilibrium and ionic activity. At T = 298.15 K, the solubility of NH4VO3 in the NH4H2PO4-H2O system was the highest, and was lower in the (NH4)3PO4-H2O system. The solubility in the (NH4)2HPO4-H2O system was the lowest. The mean ionic activity coefficients were calculated for the three phosphate solutions at C = 0.5 mol·kg-1 using the pH values and dissolution reaction constant. The mean ionic activity coefficients were the largest for the (NH4)2HPO4-H2O system, and were smaller for the (NH4)3PO4-H2O system. The mean ionic activity coefficients were the smallest for the NH4H2PO4-H2O system, which agrees with the solubility variations of NH4VO3 in the three phosphate systems.
The solubility of ammonium metavanadate (NH4VO3) in NH4H2PO4-H2O and (NH4)3PO4-H2O systems at T = 298.15-328.15 K was measured using the classic isothermal dissolution method. The densities and pH values of the solutions were also determined. The solubility of NH4VO3 decreased at first and then increased with increasing NH4H2PO4 or (NH4)3PO4 concentrations. This was considered to be caused by the common ionic effect, chemical reaction equilibrium and ionic activity. At T = 298.15 K, the solubility of NH4VO3 in the NH4H2PO4-H2O system was the highest, and was lower in the (NH4)3PO4-H2O system. The solubility in the (NH4)2HPO4-H2O system was the lowest. The mean ionic activity coefficients were calculated for the three phosphate solutions at C = 0.5 mol·kg-1 using the pH values and dissolution reaction constant. The mean ionic activity coefficients were the largest for the (NH4)2HPO4-H2O system, and were smaller for the (NH4)3PO4-H2O system. The mean ionic activity coefficients were the smallest for the NH4H2PO4-H2O system, which agrees with the solubility variations of NH4VO3 in the three phosphate systems.
2016, 32(5): 1143-1150
doi: 10.3866/PKU.WHXB201602184
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Research on the hydrated structure of KCl and NaCl mixed solutions with a concentration range between 0 and 26% was conducted using X-ray diffraction and Raman spectroscopy at 25 ℃. Their reduced structure functions, F(Q), and reduced pair distribution functions, G(r), obtained from X-ray diffraction indicate that compared with Na+, the hydration numbers and shell radii of the hydrated K+ ions are larger. This explains why the solubility of NaCl is higher than that of KCl at 25 ℃. According to the Raman spectroscopy, the tetrahedral hydrogen bonds of water molecules will be destroyed with the increase in KCl concentration and the decrease in NaCl concentration. The extent of the bond destruction has systematic variations; for example, increasing at first and then decreasing. These results show that the destruction of the hydrogen bond structure resulting from Na+ is more serious than from K+. Also, with the appropriate K+ content in the NaCl solution, Na+ will behave as a structure breaker instead of a structure maker, which enhances the destructiveness of the solution structure.
Research on the hydrated structure of KCl and NaCl mixed solutions with a concentration range between 0 and 26% was conducted using X-ray diffraction and Raman spectroscopy at 25 ℃. Their reduced structure functions, F(Q), and reduced pair distribution functions, G(r), obtained from X-ray diffraction indicate that compared with Na+, the hydration numbers and shell radii of the hydrated K+ ions are larger. This explains why the solubility of NaCl is higher than that of KCl at 25 ℃. According to the Raman spectroscopy, the tetrahedral hydrogen bonds of water molecules will be destroyed with the increase in KCl concentration and the decrease in NaCl concentration. The extent of the bond destruction has systematic variations; for example, increasing at first and then decreasing. These results show that the destruction of the hydrogen bond structure resulting from Na+ is more serious than from K+. Also, with the appropriate K+ content in the NaCl solution, Na+ will behave as a structure breaker instead of a structure maker, which enhances the destructiveness of the solution structure.
2016, 32(5): 1151-1160
doi: 10.3866/PKU.WHXB201602174
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A new mechanism for IC8H18 with nitric oxide (IC8H18-NO) in homogeneous charge compression ignition (HCCI) combustion is presented to investigate the effects of NO in exhaust gas recirculation (EGR) on combustion. The IC8H18 sub-mechanism consists of 112 species and 467 reactions. A NO sub-mechanism is developed through reaction path analysis. The reaction paths of NO are summarized on the basis of the detailed NO mechanism reported by Anderlohr to describe the effects of NO on IC8H18. A new IC8H18-NO mechanism with 167 species and 835 reactions is described. The IC8H18 sub-mechanism of IC8H18-NO mechanism was validated by the ignition delay times in a shock tube. Experimental and computational results are in good agreement with those of ignition delay times at 855 to 1269 K and at 2 and 6 MPa with equivalence ratios of 0.5 and 1.0. The new IC8H18-NO mechanism is also validated in an HCCI engine. Computational results are consistent with experimental data of ignition delay times at a NO concentration range of 0 to 500 × 10-6 (volume fraction). The effects of NO on IC8H18 differ as the NO concentration increases. Therefore, the effects of NO on IC8H18 are simulated using a zero-dimensional model using the CHEMKIN PRO software. Key reactions at different NO concentrations are proposed by analyzing the sensitivity and productivity rates. The resource of OH for initial IC8H18 consumption is mainly generated through R476, which occurs as a result of the promoting effect of NO reon IC8H18 consumption. The ability of NO to combine with active radicals, such as those in R476, is enhanced as the NO concentration is increased.
A new mechanism for IC8H18 with nitric oxide (IC8H18-NO) in homogeneous charge compression ignition (HCCI) combustion is presented to investigate the effects of NO in exhaust gas recirculation (EGR) on combustion. The IC8H18 sub-mechanism consists of 112 species and 467 reactions. A NO sub-mechanism is developed through reaction path analysis. The reaction paths of NO are summarized on the basis of the detailed NO mechanism reported by Anderlohr to describe the effects of NO on IC8H18. A new IC8H18-NO mechanism with 167 species and 835 reactions is described. The IC8H18 sub-mechanism of IC8H18-NO mechanism was validated by the ignition delay times in a shock tube. Experimental and computational results are in good agreement with those of ignition delay times at 855 to 1269 K and at 2 and 6 MPa with equivalence ratios of 0.5 and 1.0. The new IC8H18-NO mechanism is also validated in an HCCI engine. Computational results are consistent with experimental data of ignition delay times at a NO concentration range of 0 to 500 × 10-6 (volume fraction). The effects of NO on IC8H18 differ as the NO concentration increases. Therefore, the effects of NO on IC8H18 are simulated using a zero-dimensional model using the CHEMKIN PRO software. Key reactions at different NO concentrations are proposed by analyzing the sensitivity and productivity rates. The resource of OH for initial IC8H18 consumption is mainly generated through R476, which occurs as a result of the promoting effect of NO reon IC8H18 consumption. The ability of NO to combine with active radicals, such as those in R476, is enhanced as the NO concentration is increased.
2016, 32(5): 1161-1167
doi: 10.3866/PKU.WHXB201602232
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The values of the density and surface tension for an aqueous solution of the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate [C2mim][OAc] with various molalities were measured from 288.15 to 318.15 K with intervals of 5 K. Based on the thermodynamic model of the surface tension of a solution proposed by LI Yi-Gui et al., a new concept of the molar surface Gibbs free energy was proposed and a linear empirical equation between the molar surface Gibbs free energy and the concentration of the solution was established. Using this empirical equation, the molar surface Gibbs free energy of aqueous [C2mim][OAc] was estimated. Using the estimated molar surface Gibbs free energy, the surface tension of the solution was predicted. The predicted values and corresponding experimental values are in agreement. Thus, the molar surface Gibbs free energy may become a semi-empirical method to predict the properties of ILs and their solution parachor. From the molar Gibbs free energy, a new Eötvös equation was obtained and each parameter of the new equation has a clear physical meaning.
The values of the density and surface tension for an aqueous solution of the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate [C2mim][OAc] with various molalities were measured from 288.15 to 318.15 K with intervals of 5 K. Based on the thermodynamic model of the surface tension of a solution proposed by LI Yi-Gui et al., a new concept of the molar surface Gibbs free energy was proposed and a linear empirical equation between the molar surface Gibbs free energy and the concentration of the solution was established. Using this empirical equation, the molar surface Gibbs free energy of aqueous [C2mim][OAc] was estimated. Using the estimated molar surface Gibbs free energy, the surface tension of the solution was predicted. The predicted values and corresponding experimental values are in agreement. Thus, the molar surface Gibbs free energy may become a semi-empirical method to predict the properties of ILs and their solution parachor. From the molar Gibbs free energy, a new Eötvös equation was obtained and each parameter of the new equation has a clear physical meaning.
2016, 32(5): 1168-1174
doi: 10.3866/PKU.WHXB201602186
Abstract:
The effect of electrolytes on the interfacial behavior of nonionic-anionic surfactant solutions is studied using molecular dynamics (MD) simulations. The z-dependent surfactant density, radial distribution, coordination number, spatial distribution function, and mean-squared displacement are used to analyze the interaction of electrolytes and surfactants. Based on our simulated results, the three counter ions Na+, Ca2+, and Mg2+ have an effect on the hydration shell structure. On a micro level, the binding strength of the Na2+ counter ion is less than Ca2+, which is less than Mg2+, and this simulated result is consistent with the experimental results. The diffusion results can explain the interfacial tension (IFT) equilibrium time and have a significant effect on the optimal mixture method.
The effect of electrolytes on the interfacial behavior of nonionic-anionic surfactant solutions is studied using molecular dynamics (MD) simulations. The z-dependent surfactant density, radial distribution, coordination number, spatial distribution function, and mean-squared displacement are used to analyze the interaction of electrolytes and surfactants. Based on our simulated results, the three counter ions Na+, Ca2+, and Mg2+ have an effect on the hydration shell structure. On a micro level, the binding strength of the Na2+ counter ion is less than Ca2+, which is less than Mg2+, and this simulated result is consistent with the experimental results. The diffusion results can explain the interfacial tension (IFT) equilibrium time and have a significant effect on the optimal mixture method.
2016, 32(5): 1175-1182
doi: 10.3866/PKU.WHXB201602221
Abstract:
Density functional theory (DFT) calculations were performed to gain mechanistic insight into the methanol C―H and O―H bond activations mediated by ruthenium-doped platinum cationic clusters [PtnRum]+ (m + n = 3, n ≥ 1). The charge effect on the reactivity has been elucidated. Calculations show that positive charge is evenly distributed on the three Pt atoms of the [Pt3]+ cluster, while in the Ru-doped clusters, positive charge is mainly distributed on the Ru atom(s). The reactivity of [PtnRum]+ is significantly greater than neutral [PtnRum] during the initial C―H bond cleavage, while only [Pt3]+ exhibits greater reactivity than [Pt3] in the course of O―H bond cleavage. This study may aid in deeper understanding of C―H/O―H bond activations mediated by metal clusters.
Density functional theory (DFT) calculations were performed to gain mechanistic insight into the methanol C―H and O―H bond activations mediated by ruthenium-doped platinum cationic clusters [PtnRum]+ (m + n = 3, n ≥ 1). The charge effect on the reactivity has been elucidated. Calculations show that positive charge is evenly distributed on the three Pt atoms of the [Pt3]+ cluster, while in the Ru-doped clusters, positive charge is mainly distributed on the Ru atom(s). The reactivity of [PtnRum]+ is significantly greater than neutral [PtnRum] during the initial C―H bond cleavage, while only [Pt3]+ exhibits greater reactivity than [Pt3] in the course of O―H bond cleavage. This study may aid in deeper understanding of C―H/O―H bond activations mediated by metal clusters.
2016, 32(5): 1183-1190
doi: 10.3866/PKU.WHXB201603032
Abstract:
The structural and electronic properties of Pt4 nanoparticles adsorbed on monolayer graphitic carbon nitride (Pt4/g-C3N4), as well as the adsorption behavior of oxygen molecules on the Pt4/g-C3N4 surface have been investigated through first-principles density-functional theory (DFT) calculations with the generalized gradient approximation (GGA). The interaction of the oxygen molecules with the bare g-C3N4 and the Pt4 clusters was also calculated for comparison. Our calculations show that Pt nanoparticles prefer to bond with four edge N atoms on heptazine phase g-C3N4 (HGCN) surfaces, forming two hexagonal rings. For s-triazine phase g-C3N4 (TGCN) surfaces, Pt nanoparticles prefer to sit atop the single vacancy site, forming three bonds with the nearest nitrogen atoms. Stronger hybridization of the Pt nanoparticles with the sp2 dangling bonds of neighboring nitrogen atoms leads to the Pt4 clusters strongly binding on both types of g-C3N4 surface. In addition, the results from Mulliken charge population analyses suggest that there are electrons flowing from the Pt clusters to g-C3N4. According to the comparative analyses of the O2 adsorbed on the Pt4/HGCN, Pt4/TGCN, and pure g-C3N4 systems, the presence of metal clusters promotes greater electron transfer to oxygen molecules and elongates the O―O bond. Meanwhile, its greater adsorbate-substrate distortion and large adsorption energy render the Pt4/HGCN system slightly superior to the Pt4/TGCN system in catalytic performance. The results validate that being supported on g-C3N4 may be a good way to modify the electronic structure of materials and their surface properties improve their catalytic performance.
The structural and electronic properties of Pt4 nanoparticles adsorbed on monolayer graphitic carbon nitride (Pt4/g-C3N4), as well as the adsorption behavior of oxygen molecules on the Pt4/g-C3N4 surface have been investigated through first-principles density-functional theory (DFT) calculations with the generalized gradient approximation (GGA). The interaction of the oxygen molecules with the bare g-C3N4 and the Pt4 clusters was also calculated for comparison. Our calculations show that Pt nanoparticles prefer to bond with four edge N atoms on heptazine phase g-C3N4 (HGCN) surfaces, forming two hexagonal rings. For s-triazine phase g-C3N4 (TGCN) surfaces, Pt nanoparticles prefer to sit atop the single vacancy site, forming three bonds with the nearest nitrogen atoms. Stronger hybridization of the Pt nanoparticles with the sp2 dangling bonds of neighboring nitrogen atoms leads to the Pt4 clusters strongly binding on both types of g-C3N4 surface. In addition, the results from Mulliken charge population analyses suggest that there are electrons flowing from the Pt clusters to g-C3N4. According to the comparative analyses of the O2 adsorbed on the Pt4/HGCN, Pt4/TGCN, and pure g-C3N4 systems, the presence of metal clusters promotes greater electron transfer to oxygen molecules and elongates the O―O bond. Meanwhile, its greater adsorbate-substrate distortion and large adsorption energy render the Pt4/HGCN system slightly superior to the Pt4/TGCN system in catalytic performance. The results validate that being supported on g-C3N4 may be a good way to modify the electronic structure of materials and their surface properties improve their catalytic performance.
2016, 32(5): 1191-1198
doi: 10.3866/PKU.WHXB201603021
Abstract:
In this work, we used density functional theory with the Tkatchenko and Scheffler method to investigate the adsorption of diazinon, hinosan, chlorpyrifos, and parathion organophosphorus pesticides on the surface of B36N36 nanocage and its Fe doped derivatives. The assessments revealed that van der Waals interaction is a key factor in organophosphate adsorption on the surface of these nanocages as well as overlapping. The results of Fukui indices and atomic partial charges calculations indicated that these pesticides and nanocages act as nucleophile and electrophile, respectively, and the adsorption sites of all four organophosphates on these nanocages are thiophosphate groups, as well as the aromatic ring in diazinon, and the nitro group in parathion. In addition, the calculated adsorption energies yielded the best result for diazinon, and the best Fe doped B36N36 derivative for adsorbing organophosphates in aqueous solution is the one in which Fe atom is located in the boron position of the square ring of B36N36.
In this work, we used density functional theory with the Tkatchenko and Scheffler method to investigate the adsorption of diazinon, hinosan, chlorpyrifos, and parathion organophosphorus pesticides on the surface of B36N36 nanocage and its Fe doped derivatives. The assessments revealed that van der Waals interaction is a key factor in organophosphate adsorption on the surface of these nanocages as well as overlapping. The results of Fukui indices and atomic partial charges calculations indicated that these pesticides and nanocages act as nucleophile and electrophile, respectively, and the adsorption sites of all four organophosphates on these nanocages are thiophosphate groups, as well as the aromatic ring in diazinon, and the nitro group in parathion. In addition, the calculated adsorption energies yielded the best result for diazinon, and the best Fe doped B36N36 derivative for adsorbing organophosphates in aqueous solution is the one in which Fe atom is located in the boron position of the square ring of B36N36.
2016, 32(5): 1199-1206
doi: 10.3866/PKU.WHXB201602222
Abstract:
Graphene/cotton composite fabrics for use as flexible electrodes were prepared using a thermal reduction method. The reducing condition significantly influenced the conductivity of the graphene/cotton fabrics. The conductive graphene/cotton fabrics with hierarchical structures used as flexible electrode substrates facilitate the loading of pseudocapacitor materials, enhancing electron transport and electrolyte ion diffusion. The electrode structure was characterized in detail using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and the standard four-point probe method. After further electrochemical deposition of MnO2 sheets on the composite fabrics, the resulting MnO2/graphene/cotton composite fabrics for use as electrode materials had excellent electrochemical performance and great flexibility. The specific capacitance reached 536 F·g-1 at a scan rate of 5 mV·s-1. The electrochemical test results indicate that it can be further used for flexible energy storage materials.
Graphene/cotton composite fabrics for use as flexible electrodes were prepared using a thermal reduction method. The reducing condition significantly influenced the conductivity of the graphene/cotton fabrics. The conductive graphene/cotton fabrics with hierarchical structures used as flexible electrode substrates facilitate the loading of pseudocapacitor materials, enhancing electron transport and electrolyte ion diffusion. The electrode structure was characterized in detail using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and the standard four-point probe method. After further electrochemical deposition of MnO2 sheets on the composite fabrics, the resulting MnO2/graphene/cotton composite fabrics for use as electrode materials had excellent electrochemical performance and great flexibility. The specific capacitance reached 536 F·g-1 at a scan rate of 5 mV·s-1. The electrochemical test results indicate that it can be further used for flexible energy storage materials.
2016, 32(5): 1207-1213
doi: 10.3866/PKU.WHXB201602241
Abstract:
Insulating oxides of SiO2, ZrO2, and Al2O3 were coated using a dipping method on the surface of mesoporous TiO2 nanoparticles for perovskite solar cells. The effects of the insulating oxide coatings on the performance of the perovskite solar cells and the interface charge recombination dynamics were investigated in detail. The efficiency of devices after SiO2 coating improved by 13.7% due to their FF (fill factor) increasing from 67.6% to 72.3%. However, the devices with ZrO2 and Al2O3 coatings exhibited an increase in Voc of up to 50 mV and a decrease in Jsc and FF. Transient absorption spectroscopy on a timescale from nanoseconds to milliseconds was performed to study the interface recombination lifetime between electrons and holes and the changes of the device performances are discussed.
Insulating oxides of SiO2, ZrO2, and Al2O3 were coated using a dipping method on the surface of mesoporous TiO2 nanoparticles for perovskite solar cells. The effects of the insulating oxide coatings on the performance of the perovskite solar cells and the interface charge recombination dynamics were investigated in detail. The efficiency of devices after SiO2 coating improved by 13.7% due to their FF (fill factor) increasing from 67.6% to 72.3%. However, the devices with ZrO2 and Al2O3 coatings exhibited an increase in Voc of up to 50 mV and a decrease in Jsc and FF. Transient absorption spectroscopy on a timescale from nanoseconds to milliseconds was performed to study the interface recombination lifetime between electrons and holes and the changes of the device performances are discussed.
2016, 32(5): 1214-1220
doi: 10.3866/PKU.WHXB201602176
Abstract:
The wetting properties of the poly(methyl methacrylate) (PMMA) surface by aqueous solutions of the branched zwitterionic surfactants, hexadecanol glycidyl ether glycine betaine and hexadecanol polyoxyethylene(3) glycidyl ether glycine betaine, and branched cationic surfactants, hexadecanol glycidyl ether ammonium chloride and hexadecanol polyoxyethylene (3) glycidyl ether ammonium chloride, were investigated using sessile drop analysis. The influence of the surfactant type, structure, and concentration on contact angle was explored. The results indicate that the PMMA surface was slightly hydrophobically modified with the bulk concentration of surfactant before reaching the critical micelle concentration (cmc) because the adsorbed surfactant molecules are parallel to the substrate surface through hydrogen bonding and the hydrophilic groups are close to the surface. At this stage, the contact angle stays almost constant because of the simultaneous decrease in the surface tension and adhesional tension. However, at concentrations higher than the cmc, the surfactant molecules can adsorb on the PMMA surface through the hydrophobic interactions and the hydrophilic groups toward the bulk phase of solution. This leads to the increase in the hydrophilic character of the PMMA surface. The contact angle decreases dramatically with the increase in bulk surfactant concentration. The variation in the surfactant type and the introduction of ethylene oxide units has little effect on the contact angle because the alkyl chain in these four surfactant molecules is branched in the same way.
The wetting properties of the poly(methyl methacrylate) (PMMA) surface by aqueous solutions of the branched zwitterionic surfactants, hexadecanol glycidyl ether glycine betaine and hexadecanol polyoxyethylene(3) glycidyl ether glycine betaine, and branched cationic surfactants, hexadecanol glycidyl ether ammonium chloride and hexadecanol polyoxyethylene (3) glycidyl ether ammonium chloride, were investigated using sessile drop analysis. The influence of the surfactant type, structure, and concentration on contact angle was explored. The results indicate that the PMMA surface was slightly hydrophobically modified with the bulk concentration of surfactant before reaching the critical micelle concentration (cmc) because the adsorbed surfactant molecules are parallel to the substrate surface through hydrogen bonding and the hydrophilic groups are close to the surface. At this stage, the contact angle stays almost constant because of the simultaneous decrease in the surface tension and adhesional tension. However, at concentrations higher than the cmc, the surfactant molecules can adsorb on the PMMA surface through the hydrophobic interactions and the hydrophilic groups toward the bulk phase of solution. This leads to the increase in the hydrophilic character of the PMMA surface. The contact angle decreases dramatically with the increase in bulk surfactant concentration. The variation in the surfactant type and the introduction of ethylene oxide units has little effect on the contact angle because the alkyl chain in these four surfactant molecules is branched in the same way.
2016, 32(5): 1221-1226
doi: 10.3866/PKU.WHXB201602175
Abstract:
In this work, 1H,1H, 2H,2H-perfluorodecyltrichlorosilane (FDTS) self-assembled monolayers (SAMs) were prepared using liquid-phase deposition. To prepare the FDTS SAMs, the FDTS solution was first hydrolyzed for 15 min at room temperature, and then mica was immersed into the FDTS solution for self-assembly for 30 min. It was confirmed that the new method can effectively prevent aggregation of FDTS in the liquid phase deposition using atomic force microscopy (AFM). The FDTS SAMs were successfully prepared with a high surface coverage of (85% ± 2%) and low root mean square surface roughness (0.58 nm). The growth process of the SAMs can be described using the Langmuir first-order adsorption kinetics model. However, if hydrolysis and assembly occur at the same time and these processes last more than 30 min, the FDTS would be aggregated in the liquid-phase deposition process, which would greatly reduce the quality of the SAMs.
In this work, 1H,1H, 2H,2H-perfluorodecyltrichlorosilane (FDTS) self-assembled monolayers (SAMs) were prepared using liquid-phase deposition. To prepare the FDTS SAMs, the FDTS solution was first hydrolyzed for 15 min at room temperature, and then mica was immersed into the FDTS solution for self-assembly for 30 min. It was confirmed that the new method can effectively prevent aggregation of FDTS in the liquid phase deposition using atomic force microscopy (AFM). The FDTS SAMs were successfully prepared with a high surface coverage of (85% ± 2%) and low root mean square surface roughness (0.58 nm). The growth process of the SAMs can be described using the Langmuir first-order adsorption kinetics model. However, if hydrolysis and assembly occur at the same time and these processes last more than 30 min, the FDTS would be aggregated in the liquid-phase deposition process, which would greatly reduce the quality of the SAMs.
2016, 32(5): 1227-1235
doi: 10.3866/PKU.WHXB201602223
Abstract:
Two imidazole-based surface active ionic liquids (CnmimBr) were synthesized, and their aggregation behavior at the air/water interface was studied via an oscillating bubble method. The effects of the CnmimBr concentration, inorganic salts (NaBr and CaBr2), and temperature on the aggregation behavior were investigated. The results of the adsorption dynamics showed that the adsorption-controlled process dominated, but the relaxation process was not purely mono-exponential. The addition of inorganic salt or increase in temperature improved the surface activity of the CnmimBr and lowered the dynamic surface tension. The dilational rheological results revealed that the dilational modulus, elastic modules, and viscous modules increased with increasing oscillating frequencies, and the modulus reached a maximum value with increasing CnmimBr concentration. Increasing the temperature or adding inorganic salts (NaBr or CaBr2) decreased the dilational modulus. The elastic modulus was dominant for the CnmimBr layer, and the elastic modulus of C14mimBr was larger than that of C12mimBr.
Two imidazole-based surface active ionic liquids (CnmimBr) were synthesized, and their aggregation behavior at the air/water interface was studied via an oscillating bubble method. The effects of the CnmimBr concentration, inorganic salts (NaBr and CaBr2), and temperature on the aggregation behavior were investigated. The results of the adsorption dynamics showed that the adsorption-controlled process dominated, but the relaxation process was not purely mono-exponential. The addition of inorganic salt or increase in temperature improved the surface activity of the CnmimBr and lowered the dynamic surface tension. The dilational rheological results revealed that the dilational modulus, elastic modules, and viscous modules increased with increasing oscillating frequencies, and the modulus reached a maximum value with increasing CnmimBr concentration. Increasing the temperature or adding inorganic salts (NaBr or CaBr2) decreased the dilational modulus. The elastic modulus was dominant for the CnmimBr layer, and the elastic modulus of C14mimBr was larger than that of C12mimBr.
2016, 32(5): 1236-1246
doi: 10.3866/PKU.WHXB201602251
Abstract:
MnOx/SAPO-11 catalysts were prepared by impregnation, citric acid, and precipitation methods for low-temperature selective catalytic reduction (SCR) of NO with NH3. The results indicated that the MnOx/SAPO-11 catalyst with 20%(w) Mn loading prepared by the precipitation method showed the best SCR activity and N2 selectivity. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), atomic absorption spectrometry (AAS), N2 adsorption-desorption, X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), NH3 temperature-programmed desorption (NH3-TPD), NO/O2 temperature-programmed desorption, and mass spectrometry (NO/O2-TPD-MS) were used to analyze the structural properties and catalytic performance of the catalysts. The results indicated that different manganese oxides were formed on the surface of SAPO-11 by the three different preparation methods. MnOx loaded via the precipitation method existed as MnO2 phase and amorphous MnOx. The advantages of the catalyst prepared via this method were a large mesoporous and external surface area, the highest content of chemisorbed oxygen and Mn4+ as well as more favorable medium and strong acid sites. Thus, more NO2 was produced on the catalyst during low-temperature SCR, which was a primary goal. MnOx prepared by all three methods could be well-dispersed on the surface of SAPO-11. The dispersive action of SAPO-11 could affect the formation of MnOx, which could affect the acidity of the catalysts. Thus, the temperature window was widened and N2 selectivity was improved compared with pure MnOx, with SAPO-11 acting as an excellent carrier.
MnOx/SAPO-11 catalysts were prepared by impregnation, citric acid, and precipitation methods for low-temperature selective catalytic reduction (SCR) of NO with NH3. The results indicated that the MnOx/SAPO-11 catalyst with 20%(w) Mn loading prepared by the precipitation method showed the best SCR activity and N2 selectivity. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), atomic absorption spectrometry (AAS), N2 adsorption-desorption, X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), NH3 temperature-programmed desorption (NH3-TPD), NO/O2 temperature-programmed desorption, and mass spectrometry (NO/O2-TPD-MS) were used to analyze the structural properties and catalytic performance of the catalysts. The results indicated that different manganese oxides were formed on the surface of SAPO-11 by the three different preparation methods. MnOx loaded via the precipitation method existed as MnO2 phase and amorphous MnOx. The advantages of the catalyst prepared via this method were a large mesoporous and external surface area, the highest content of chemisorbed oxygen and Mn4+ as well as more favorable medium and strong acid sites. Thus, more NO2 was produced on the catalyst during low-temperature SCR, which was a primary goal. MnOx prepared by all three methods could be well-dispersed on the surface of SAPO-11. The dispersive action of SAPO-11 could affect the formation of MnOx, which could affect the acidity of the catalysts. Thus, the temperature window was widened and N2 selectivity was improved compared with pure MnOx, with SAPO-11 acting as an excellent carrier.
2016, 32(5): 1247-1256
doi: 10.3866/PKU.WHXB201602231
Abstract:
A Bi(OH)3 precursor was prepared using a precipitation method using bismuth nitrate as a starting material and ammonia as the precipitation agent. Bi(OH)3 was then calcined at different temperatures and different time. X-ray diffraction (XRD), Raman spectroscopy, thermogravimetry (TG), scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and UV-Vis diffuse reflectance spectroscopy (UVVis DRS) were used to investigate the phase transformation from Bi(OH)3 to Bi2O3 and the particle size, morphology, and optical properties of Bi2O3 during the phase transformation. It was found that Bi(OH)3 after calcination undergoes the following process: Bi(OH)3 → Bi5O7NO3 → β-Bi2O3/Bi5O7NO3 → β-Bi2O3/Bi5O7NO3/α-Bi2O3 → α-Bi2O3. It was observed that the above phase transformation from Bi(OH)3 to Bi2O3 and the growth of the particle size are interrelated. It was also found that the phase transition from β-Bi2O3 to α-Bi2O3 was faster compared with the phase transition from Bi5O7NO3 to β-Bi2O3. Also, the degradation of Rhodamine B (RhB) was studied to investigate and compare the photocatalytic performance of Bi2O3 with different crystalline phases. The result indicates that Bi5O7NO3 and β-Bi2O3 exhibit excellent photocatalytic performance, while α-Bi2O3 has a low photocatalytic activity.
A Bi(OH)3 precursor was prepared using a precipitation method using bismuth nitrate as a starting material and ammonia as the precipitation agent. Bi(OH)3 was then calcined at different temperatures and different time. X-ray diffraction (XRD), Raman spectroscopy, thermogravimetry (TG), scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and UV-Vis diffuse reflectance spectroscopy (UVVis DRS) were used to investigate the phase transformation from Bi(OH)3 to Bi2O3 and the particle size, morphology, and optical properties of Bi2O3 during the phase transformation. It was found that Bi(OH)3 after calcination undergoes the following process: Bi(OH)3 → Bi5O7NO3 → β-Bi2O3/Bi5O7NO3 → β-Bi2O3/Bi5O7NO3/α-Bi2O3 → α-Bi2O3. It was observed that the above phase transformation from Bi(OH)3 to Bi2O3 and the growth of the particle size are interrelated. It was also found that the phase transition from β-Bi2O3 to α-Bi2O3 was faster compared with the phase transition from Bi5O7NO3 to β-Bi2O3. Also, the degradation of Rhodamine B (RhB) was studied to investigate and compare the photocatalytic performance of Bi2O3 with different crystalline phases. The result indicates that Bi5O7NO3 and β-Bi2O3 exhibit excellent photocatalytic performance, while α-Bi2O3 has a low photocatalytic activity.
2016, 32(5): 1257-1266
doi: 10.3866/PKU.WHXB201603072
Abstract:
As a main source of lubricant contamination, water is one of the most important causes of failure and life reduction of lubricants and mechanical systems. To simulate the interfacial behaviors of real heterogeneous systems, a high-precision point contact experiment apparatus was constructed to study the classical immiscible displacement problem. The interfacial behaviors between water and oil, which are always carried out in the static and parallel space, have been extended to the dynamic point contact wedge in a confined space. The interfacial behaviors of water droplets invading the oil pool around the dynamic point contact region were investigated. Emphasis is placed on the influences of the wettability and the relative separation motion of the solid surfaces on the dynamic behaviors of the droplets. The spreading coefficient has been determined to be the key parameter influencing the coalescing and separating behaviors of the two-phase interface. The influence of the wettability of the solid surface and the relative separation between the ball and the disc on the final coalescing form has been determined. Surface tension and adhesion energy are used to interpret these observations.
As a main source of lubricant contamination, water is one of the most important causes of failure and life reduction of lubricants and mechanical systems. To simulate the interfacial behaviors of real heterogeneous systems, a high-precision point contact experiment apparatus was constructed to study the classical immiscible displacement problem. The interfacial behaviors between water and oil, which are always carried out in the static and parallel space, have been extended to the dynamic point contact wedge in a confined space. The interfacial behaviors of water droplets invading the oil pool around the dynamic point contact region were investigated. Emphasis is placed on the influences of the wettability and the relative separation motion of the solid surfaces on the dynamic behaviors of the droplets. The spreading coefficient has been determined to be the key parameter influencing the coalescing and separating behaviors of the two-phase interface. The influence of the wettability of the solid surface and the relative separation between the ball and the disc on the final coalescing form has been determined. Surface tension and adhesion energy are used to interpret these observations.
2016, 32(5): 1267-1272
doi: 10.3866/PKU.WHXB201603014
Abstract:
Because of their low toxicity and excellent water-solubility, graphene quantum dots have been highly anticipated for use in cellular imaging. However, their limited optical properties are hampering this use. To address this issue, graphene quantum dots surface passivated by branched polyethylenimine (GQDs-BPEI) were proposed in this paper. We discussed optical properties when prepared under different conditions including reaction time, temperature, and pH value. The results indicate that GQDs-BPEI prepared at pH 12, at a temperature of 200 ℃, and with a 20 h reaction in an autoclave can achieve a higher UV absorbency and better PL properties with a high quantum yield.
Because of their low toxicity and excellent water-solubility, graphene quantum dots have been highly anticipated for use in cellular imaging. However, their limited optical properties are hampering this use. To address this issue, graphene quantum dots surface passivated by branched polyethylenimine (GQDs-BPEI) were proposed in this paper. We discussed optical properties when prepared under different conditions including reaction time, temperature, and pH value. The results indicate that GQDs-BPEI prepared at pH 12, at a temperature of 200 ℃, and with a 20 h reaction in an autoclave can achieve a higher UV absorbency and better PL properties with a high quantum yield.
2016, 32(5): 1273-1281
doi: 10.3866/PKU.WHXB201602193
Abstract:
Although considerable improvements have been achieved in novel materials and device architectures for organic light-emitting diodes (OLEDs), great challenges remain in efficiency, color purity, and stability for blue emitters because of their intrinsic wide band-gap. In this study, trinaphthylbenzene (TNB), a propeller-shaped conjugated system, is employed as the central moiety for the construction of the organic lightemitting materials. Its nonplanar propeller-shaped structure and easy chemical modification are beneficial for building three-dimensional (3D) π-π conjugated systems to suppress aggregates and excimers. We have demonstrated a facile approach for the synthesis of a set of propeller-shaped blue-emitting oligomers based on the TNB core with peripheral units of naphthalene, anthracene or triphenylamine via the combination of SiCl4-catalyzed cyclotrimerization and Suzuki coupling reactions. The thermal, optical, and electrochemical properties of the materials were investigated. The results indicate that the naphthalene and triphenylamine substituted oligomers, 1,3,5-tris(3-(1-methoxynaphthalen-2-yl)-4-methoxynaphthalen-1-yl)benzene (TNNB) and 1,3,5-tris (3-(4-(N,N-diphenylamino)phenyl)-4-methoxynaphthalen-1-yl) benzene (TPANB), have the best thermal stability. They exhibit deep blue photoluminescence (PL) emission at 382 and 415 nm in solution, respectively. In comparison with the solution spectra, the emission spectra in films show only a very slight red-shift of 1 nm for TNNB and a blue-shift of 6 nm for TPANB. The electroluminescent device fabricated using TNNB as the emitter has a pure blue emission with a brightness of 5273 cd·m-2 and Commission Internationale de L′Eclairage (CIE) coordinates of (0.17, 0.11).
Although considerable improvements have been achieved in novel materials and device architectures for organic light-emitting diodes (OLEDs), great challenges remain in efficiency, color purity, and stability for blue emitters because of their intrinsic wide band-gap. In this study, trinaphthylbenzene (TNB), a propeller-shaped conjugated system, is employed as the central moiety for the construction of the organic lightemitting materials. Its nonplanar propeller-shaped structure and easy chemical modification are beneficial for building three-dimensional (3D) π-π conjugated systems to suppress aggregates and excimers. We have demonstrated a facile approach for the synthesis of a set of propeller-shaped blue-emitting oligomers based on the TNB core with peripheral units of naphthalene, anthracene or triphenylamine via the combination of SiCl4-catalyzed cyclotrimerization and Suzuki coupling reactions. The thermal, optical, and electrochemical properties of the materials were investigated. The results indicate that the naphthalene and triphenylamine substituted oligomers, 1,3,5-tris(3-(1-methoxynaphthalen-2-yl)-4-methoxynaphthalen-1-yl)benzene (TNNB) and 1,3,5-tris (3-(4-(N,N-diphenylamino)phenyl)-4-methoxynaphthalen-1-yl) benzene (TPANB), have the best thermal stability. They exhibit deep blue photoluminescence (PL) emission at 382 and 415 nm in solution, respectively. In comparison with the solution spectra, the emission spectra in films show only a very slight red-shift of 1 nm for TNNB and a blue-shift of 6 nm for TPANB. The electroluminescent device fabricated using TNNB as the emitter has a pure blue emission with a brightness of 5273 cd·m-2 and Commission Internationale de L′Eclairage (CIE) coordinates of (0.17, 0.11).
2016, 32(5): 1282-1288
doi: 10.3866/PKU.WHXB201602185
Abstract:
DNA is the main genetic material for living organisms including many viruses. DNA duplex, coded with A＝T and G≡C base pairs, is well suited for biological information storage. The interactions between two bases in a base pair contribute to the stability of DNA duplex, and are further related to gene replication and transcription. In this study, we use all-atom Molecular dynamics (MD) simulations combined with Umbrella sampling (US) method to determine the free energy profiles and explore the molecular details for base pair dissociations. Four groups of DNA duplexes with different sequences have been constructed and a total of 4.3 μs MD simulations have been carried out. In the potential of mean force (PMF) profile for G≡C base pair dissociation (denoted as PMF-PGC), we observed three peaks, which correspond to the three moments G≡C base pair loses its three hydrogen bonds respectively. Differently, A＝T base pair loses its two hydrogen bonds within a very short time. As a result, only one hydrogen bond rupture peak was observed in its PMF curve (denoted as PMF-PAT). Compared with PMF-PAT, the overall free energy barrier in PMF-PGC is higher, which is due to the better stability of G≡C than A＝T. In the latter sections of both PMFs, free energies are still increasing, which is mainly resulted from the rigidity of DNA duplex backbone. We have also investigated the impact of neighboring base pairs on the stability of middle one. It is found that neighboring G≡C base pairs increase the stability of A＝T base pair while neighboring C≡G base pairs reduce the stability of A＝T base pair. Additionally, neighboring T＝A base pairs have little influence on the stability of A＝T base pair.
DNA is the main genetic material for living organisms including many viruses. DNA duplex, coded with A＝T and G≡C base pairs, is well suited for biological information storage. The interactions between two bases in a base pair contribute to the stability of DNA duplex, and are further related to gene replication and transcription. In this study, we use all-atom Molecular dynamics (MD) simulations combined with Umbrella sampling (US) method to determine the free energy profiles and explore the molecular details for base pair dissociations. Four groups of DNA duplexes with different sequences have been constructed and a total of 4.3 μs MD simulations have been carried out. In the potential of mean force (PMF) profile for G≡C base pair dissociation (denoted as PMF-PGC), we observed three peaks, which correspond to the three moments G≡C base pair loses its three hydrogen bonds respectively. Differently, A＝T base pair loses its two hydrogen bonds within a very short time. As a result, only one hydrogen bond rupture peak was observed in its PMF curve (denoted as PMF-PAT). Compared with PMF-PAT, the overall free energy barrier in PMF-PGC is higher, which is due to the better stability of G≡C than A＝T. In the latter sections of both PMFs, free energies are still increasing, which is mainly resulted from the rigidity of DNA duplex backbone. We have also investigated the impact of neighboring base pairs on the stability of middle one. It is found that neighboring G≡C base pairs increase the stability of A＝T base pair while neighboring C≡G base pairs reduce the stability of A＝T base pair. Additionally, neighboring T＝A base pairs have little influence on the stability of A＝T base pair.
2016, 32(5): 1289-1296
doi: 10.3866/PKU.WHXB201602291
Abstract:
Structural and spectroscopic features of a model dipeptide, glycine dipeptide (GLYD), were systematically investigated in the gas phase and in aqueous solution. Normal mode analysis was performed on the representative GLYD-D2O clusters selected from molecular dynamics (MD) trajectory for the vibrational parameters of amide-I mode, which is known to be sensitive to the secondary structure of proteins. On this basis, the correlation between the vibrational spectrum and the structural features of specific groups in the polypeptide was constructed. The electrostatic potential from the solvent molecules was calculated and projected onto the backbone of GLYD, and related to the amide-I frequency difference for GLYD in gas phase and solution phase. The secondary structure-dependent normal mode amide-I frequency database was also introduced for the consideration of the possible vibrational coupling that is intrinsically included in GLYD conformers. An electrostatic frequency map with secondary structural sensitivity was then built for the fast and accurate vibrational frequency prediction of the amide-I vibrational band for polypeptides in solution.
Structural and spectroscopic features of a model dipeptide, glycine dipeptide (GLYD), were systematically investigated in the gas phase and in aqueous solution. Normal mode analysis was performed on the representative GLYD-D2O clusters selected from molecular dynamics (MD) trajectory for the vibrational parameters of amide-I mode, which is known to be sensitive to the secondary structure of proteins. On this basis, the correlation between the vibrational spectrum and the structural features of specific groups in the polypeptide was constructed. The electrostatic potential from the solvent molecules was calculated and projected onto the backbone of GLYD, and related to the amide-I frequency difference for GLYD in gas phase and solution phase. The secondary structure-dependent normal mode amide-I frequency database was also introduced for the consideration of the possible vibrational coupling that is intrinsically included in GLYD conformers. An electrostatic frequency map with secondary structural sensitivity was then built for the fast and accurate vibrational frequency prediction of the amide-I vibrational band for polypeptides in solution.
