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2016 Volume 32 Issue 6
2016, 32(6):
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2016, 32(6): 1297-1298
doi: 10.3866/PKU.WHXB201605251
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2016, 32(6): 1299-1299
doi: 10.3866/PKU.WHXB201605051
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2016, 32(6): 1300-1300
doi: 10.3866/PKU.WHXB201605253
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2016, 32(6): 1301-1302
doi: 10.3866/PKU.WHXB201605102
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2016, 32(6): 1303-1304
doi: 10.3866/PKU.WHXB201605161
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2016, 32(6): 1305-1305
doi: 10.3866/PKU.WHXB201605254
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2016, 32(6): 1306-1306
doi: 10.3866/PKU.WHXB201605252
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2016, 32(6): 1307-1313
doi: 10.3866/PKU.WHXB201604083
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We develop a novel hole extracting buffer layer material, namely PbI2. The structure of the device we fabricate is ITO/PbI2/P3HT:PC61BM/Al (indium tin oxide/lead iodide/poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester/aluminum cathode). The preparation method involves spin-coating and thermal evaporation. We study the effectiveness of using PbI2 in the prototype ITO/P3HT:PC61BM/Al polymer solar cell devices. The concentration, annealing temperature, and annealing time all have an influence on the quality of the PbI2 films. Obviously, higher-quality PbI2 films will lead to better power conversion efficiency. The transmittance, crystallization, and morphology properties of the PbI2 films can be used to describe the quality of the films. We characterize the PbI2 film affording the best performance by UV-Vis spectrophotometry, X-ray powder diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM). Our results reveal that the performance of the solar cell device is sensitive to the concentration of PbI2, and the best conditions are a concentration of 3 mg·mL-1, annealing temperature of 100 ℃, and annealing time of 30 min. The open circuit voltage (Voc) is 0.45 V, the short circuit current density (Jsc) is 7.9 mA·cm-2, and the fill factor (FF) is 0.46. Compared with the devices without any buffer layer (0.85%), the power conversion efficiency (PCE) using PbI2 as the buffer layer can reach 1.64%.
We develop a novel hole extracting buffer layer material, namely PbI2. The structure of the device we fabricate is ITO/PbI2/P3HT:PC61BM/Al (indium tin oxide/lead iodide/poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester/aluminum cathode). The preparation method involves spin-coating and thermal evaporation. We study the effectiveness of using PbI2 in the prototype ITO/P3HT:PC61BM/Al polymer solar cell devices. The concentration, annealing temperature, and annealing time all have an influence on the quality of the PbI2 films. Obviously, higher-quality PbI2 films will lead to better power conversion efficiency. The transmittance, crystallization, and morphology properties of the PbI2 films can be used to describe the quality of the films. We characterize the PbI2 film affording the best performance by UV-Vis spectrophotometry, X-ray powder diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM). Our results reveal that the performance of the solar cell device is sensitive to the concentration of PbI2, and the best conditions are a concentration of 3 mg·mL-1, annealing temperature of 100 ℃, and annealing time of 30 min. The open circuit voltage (Voc) is 0.45 V, the short circuit current density (Jsc) is 7.9 mA·cm-2, and the fill factor (FF) is 0.46. Compared with the devices without any buffer layer (0.85%), the power conversion efficiency (PCE) using PbI2 as the buffer layer can reach 1.64%.
2016, 32(6): 1314-1329
doi: 10.3866/PKU.WHXB201605035
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This paper focuses on application of graphdiyne (GDY) in both energy storage and conversion fields, including the most recent theoretical and experimental progress. The unique three-dimensional pore structure formed by stacking of the GDY layer, make it possess the natural advantage which can be applied to lithium storage and hydrogen storage. Because of its lithiumstorage ability, GDY can be used in energy storage devices, such as lithium ion batteries and lithium ion capacitors. While with the hydrogen storage property, GDY can be used as a hydrogen storage material in fuel cells. By doping method, the performance of GDY for lithium and hydrogen storage can be further improved. Owing to acetylene units composed of sp hybridized carbon atoms and benzene rings composed of sp2 hybridized carbon atoms, GDY possesses multiple conjugated electronic structures. Thus, its band gap can be regulated through many ways accompanied with existence of Dirac cones. This property means that GDY can not only be used as a high-activity non-metal catalyst in place of noble metal catalysts in photocatalysis, but it also plays a promotional role in the hole transport layer and electron transport layer of solar cells. All of the reported results including theoretical and experimental data reviewed here, show the great potential of GDY in energy field applications.
This paper focuses on application of graphdiyne (GDY) in both energy storage and conversion fields, including the most recent theoretical and experimental progress. The unique three-dimensional pore structure formed by stacking of the GDY layer, make it possess the natural advantage which can be applied to lithium storage and hydrogen storage. Because of its lithiumstorage ability, GDY can be used in energy storage devices, such as lithium ion batteries and lithium ion capacitors. While with the hydrogen storage property, GDY can be used as a hydrogen storage material in fuel cells. By doping method, the performance of GDY for lithium and hydrogen storage can be further improved. Owing to acetylene units composed of sp hybridized carbon atoms and benzene rings composed of sp2 hybridized carbon atoms, GDY possesses multiple conjugated electronic structures. Thus, its band gap can be regulated through many ways accompanied with existence of Dirac cones. This property means that GDY can not only be used as a high-activity non-metal catalyst in place of noble metal catalysts in photocatalysis, but it also plays a promotional role in the hole transport layer and electron transport layer of solar cells. All of the reported results including theoretical and experimental data reviewed here, show the great potential of GDY in energy field applications.
2016, 32(6): 1330-1346
doi: 10.3866/PKU.WHXB201603073
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CdTe and Cu(In,Ga)(S,Se)2 (CIGSSe) light absorber materials have dominated the research field of compound semiconductor solar cells. Despite the high power conversion efficiencies and technological advances of CdTe and CIGS photovoltaic technologies, certain issues, like rare earth constituent elements or toxic elements, limit their future upscaled applications. In recent years, Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cells have become research hotspots, drawing increased interest. With earth-abundant and environmentallybenign constituent elements, CZTSSe light absorber materials are widely regarded as the next-generation photovoltaic technology that can replace CdTe and CIGS as a promising candidate for terawatt-level power output. In this review, the synthesis, structure, and properties of CZTSSe materials will be discussed. This review will primarily demonstrate the developments and recent advances of different fabrication techniques and deposition methods, such as vacuum-based and solution-based deposition methods, covering their advantages and disadvantages. Recent developments in CZTSSe fabrication methods and CZTSSe nanocrystal preparation approaches will also be reviewed. Finally, some limitations on CZTSSe photovoltaic technology will be analyzed, and directions for improvement will be suggested, helping scientists to make future developments in this field.
CdTe and Cu(In,Ga)(S,Se)2 (CIGSSe) light absorber materials have dominated the research field of compound semiconductor solar cells. Despite the high power conversion efficiencies and technological advances of CdTe and CIGS photovoltaic technologies, certain issues, like rare earth constituent elements or toxic elements, limit their future upscaled applications. In recent years, Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cells have become research hotspots, drawing increased interest. With earth-abundant and environmentallybenign constituent elements, CZTSSe light absorber materials are widely regarded as the next-generation photovoltaic technology that can replace CdTe and CIGS as a promising candidate for terawatt-level power output. In this review, the synthesis, structure, and properties of CZTSSe materials will be discussed. This review will primarily demonstrate the developments and recent advances of different fabrication techniques and deposition methods, such as vacuum-based and solution-based deposition methods, covering their advantages and disadvantages. Recent developments in CZTSSe fabrication methods and CZTSSe nanocrystal preparation approaches will also be reviewed. Finally, some limitations on CZTSSe photovoltaic technology will be analyzed, and directions for improvement will be suggested, helping scientists to make future developments in this field.
2016, 32(6): 1347-1370
doi: 10.3866/PKU.WHXB201603143
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Organic-inorganic halide perovskite solar cells (PSCs) have attracted increasing attention because of their desirable properties. A key advance has been the replacement of the liquid electrolytes by solid-state hole-transporting materials (HTMs), which not only improves the power conversion efficiency (PCE) but also enhances the cell stability. HTMs are now an integral part of PSCs. Both organic and inorganic HTMs have found application in PSCs. However, inorganic HTMs are hampered by the limited choice of materials and the relatively low PCE of the solar cells based on them. The development of new organic HTMs is therefore necessary to improve the PCE and stability of PSCs. This has become a focus of various research fields, and new HTMs continue to emerge in large numbers. In this paper, we give an overview of the use of organic HTMs in PSCs. According to their molecular weight, organic HTMs are classified as either molecular or polymeric. We discuss in detail the effects of the functional groups and structures of organic HTMs on the PCE, fill factor, open circuit voltage, and stability of the resulting PSCs, as developed in recent years. The paper also covers the highest occupied molecular orbitals, the hole mobility, and the use of additives in HTMs. Finally, forecasts of the future development of organic HTMs are reviewed.
Organic-inorganic halide perovskite solar cells (PSCs) have attracted increasing attention because of their desirable properties. A key advance has been the replacement of the liquid electrolytes by solid-state hole-transporting materials (HTMs), which not only improves the power conversion efficiency (PCE) but also enhances the cell stability. HTMs are now an integral part of PSCs. Both organic and inorganic HTMs have found application in PSCs. However, inorganic HTMs are hampered by the limited choice of materials and the relatively low PCE of the solar cells based on them. The development of new organic HTMs is therefore necessary to improve the PCE and stability of PSCs. This has become a focus of various research fields, and new HTMs continue to emerge in large numbers. In this paper, we give an overview of the use of organic HTMs in PSCs. According to their molecular weight, organic HTMs are classified as either molecular or polymeric. We discuss in detail the effects of the functional groups and structures of organic HTMs on the PCE, fill factor, open circuit voltage, and stability of the resulting PSCs, as developed in recent years. The paper also covers the highest occupied molecular orbitals, the hole mobility, and the use of additives in HTMs. Finally, forecasts of the future development of organic HTMs are reviewed.
2016, 32(6): 1371-1382
doi: 10.3866/PKU.WHXB201603155
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Graphitic carbon nitride (g-C3N4) is a promising photocatalyst because of its low cost, high stability, and visible-light-induced photocatalytic activity. Z-scheme photocatalysts based on g-C3N4 (Z-g-C3N4) have attracted considerable attention because of their lower recombination rate of electron-holes and higher catalytic efficiency. In this review, the reaction mechanism of Z-scheme photocatalysis and the recent progress in Z-g-C3N4 are introduced and reviewed. The applications of Z-g-C3N4, such as water splitting and CO2 reduction, are presented. The key factors that affect the photocatalytic performance, such as pH and the presence of electron mediators, are discussed. Moreover, the current challenges are described and the future development of Z-g-C3N4 is forecast.
Graphitic carbon nitride (g-C3N4) is a promising photocatalyst because of its low cost, high stability, and visible-light-induced photocatalytic activity. Z-scheme photocatalysts based on g-C3N4 (Z-g-C3N4) have attracted considerable attention because of their lower recombination rate of electron-holes and higher catalytic efficiency. In this review, the reaction mechanism of Z-scheme photocatalysis and the recent progress in Z-g-C3N4 are introduced and reviewed. The applications of Z-g-C3N4, such as water splitting and CO2 reduction, are presented. The key factors that affect the photocatalytic performance, such as pH and the presence of electron mediators, are discussed. Moreover, the current challenges are described and the future development of Z-g-C3N4 is forecast.
2016, 32(6): 1383-1390
doi: 10.3866/PKU.WHXB201603093
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Celecoxib derivatives are widely used, non-steroidal, anti-inflammatory drugs for the treatment of acute or chronic inflammation. Under simulated physiological conditions, we used fluorescence and ultraviolet absorption spectroscopy, circular dichroism, and methods of molecular simulation to study the thermodynamics of the interaction between the celecoxib derivative 1-benzenesulfonamides-3-carboxyl-5-phenyl pyrazole (BCBP) and bovine serum albumin (BSA). The fluorescence quenching of BSA by BCBP was a static process, which was confirmed by the UV-Vis absorption spectra. The calculated enthalpy (ΔH) and entropy (ΔS) changes implied that hydrogen bonds and van der Waals forces played a predominant role in the binding process. The circular dichroism demonstrated that the secondary structure of BSA changed after its interaction with BCBP, causing the α-helix content to decrease, accompanied by an increase in an unordered structure. Molecular docking results confirmed the experimental results.
Celecoxib derivatives are widely used, non-steroidal, anti-inflammatory drugs for the treatment of acute or chronic inflammation. Under simulated physiological conditions, we used fluorescence and ultraviolet absorption spectroscopy, circular dichroism, and methods of molecular simulation to study the thermodynamics of the interaction between the celecoxib derivative 1-benzenesulfonamides-3-carboxyl-5-phenyl pyrazole (BCBP) and bovine serum albumin (BSA). The fluorescence quenching of BSA by BCBP was a static process, which was confirmed by the UV-Vis absorption spectra. The calculated enthalpy (ΔH) and entropy (ΔS) changes implied that hydrogen bonds and van der Waals forces played a predominant role in the binding process. The circular dichroism demonstrated that the secondary structure of BSA changed after its interaction with BCBP, causing the α-helix content to decrease, accompanied by an increase in an unordered structure. Molecular docking results confirmed the experimental results.
2016, 32(6): 1391-1396
doi: 10.3866/PKU.WHXB201603221
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The fluorescent dye thioflavin T (ThT) is widely used for the qualitative and quantitative detection of amyloid fibrils. However, many small-molecular inhibitors have been shown to compete with ThT in binding the fibrils and therefore greatly affect the ThT fluorescence. The effect of ThT on the aggregation kinetics of amyloid proteins is not yet fully understood. Here, using amyloid β-protein 40 (Aβ40) as a model system, we show that ThT significantly alters the aggregation kinetics of Aβ40 in a dose-dependent manner, leading to a decrease-increase trend in the lag time that represents the nucleation rate. Specifically, the lag time decreases as a function of ThT concentration at low ranges, but then begins to increase beyond a specific ThT concentration, which itself increases with Aβ40 concentration. By contrast, the elongation rate slowly increases with ThT concentration. As for the secondary structure and morphology of the fibrils, no significant effects of ThT are observed. Isothermal titration calorimetry suggests that the hydrophobic interaction dominates the binding of ThT to Aβ40. Based on these findings, a working mechanism of the dual effects of ThT on Aβ fibrillization is proposed. These results should aid our understanding of the molecular mechanism of ThT binding with Aβ and allow practical improvements in the measurement of the nucleation kinetics of Aβ fibrillization.
The fluorescent dye thioflavin T (ThT) is widely used for the qualitative and quantitative detection of amyloid fibrils. However, many small-molecular inhibitors have been shown to compete with ThT in binding the fibrils and therefore greatly affect the ThT fluorescence. The effect of ThT on the aggregation kinetics of amyloid proteins is not yet fully understood. Here, using amyloid β-protein 40 (Aβ40) as a model system, we show that ThT significantly alters the aggregation kinetics of Aβ40 in a dose-dependent manner, leading to a decrease-increase trend in the lag time that represents the nucleation rate. Specifically, the lag time decreases as a function of ThT concentration at low ranges, but then begins to increase beyond a specific ThT concentration, which itself increases with Aβ40 concentration. By contrast, the elongation rate slowly increases with ThT concentration. As for the secondary structure and morphology of the fibrils, no significant effects of ThT are observed. Isothermal titration calorimetry suggests that the hydrophobic interaction dominates the binding of ThT to Aβ40. Based on these findings, a working mechanism of the dual effects of ThT on Aβ fibrillization is proposed. These results should aid our understanding of the molecular mechanism of ThT binding with Aβ and allow practical improvements in the measurement of the nucleation kinetics of Aβ fibrillization.
2016, 32(6): 1397-1403
doi: 10.3866/PKU.WHXB201603102
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Based on flexible 1,4-bis(2-methyl-imidazol-1-yl)butane (bib) and three rigid line-shaped carboxylate mix-ligands, three Zn(II) coordination polymers, {[Zn2(bib)2(1,4-ndc)2]·H2O}n (1), {[Zn0.5(bib)0.5(bdc-Br2)0.5]·0.5H2O}n (2), {[Zn2(bib)(4,4'-bpdc)2] · H2O}n (3)(1,4-H2ndc = 1,4-naphthalenedicarboxylic acid, H2bdc-Br2 = 2,5-dibromoterephthalic acid, 4,4'-H2bpdc = 4,4'-biphenyldicarboxylic acid) have been synthesized under solvothermal conditions and characterized by elemental analysis, infrared (IR) spectrometry, and single crystal X-ray diffraction. 1 presents a 4-fold interpenetrating framework including three kinds of zigzag chains. 2 exhibits an unusual [2 + 2] interpenetrating framework. 3 features a 3-fold interpenetrating network. Their thermal decomposition behaviors were investigated by simultaneous thermogravimetry/differential thermal gravity and differential scanning calorimetry (TG/DTG-DSC) techniques. The TG curves indicate that the unusual [2 + 2] interpenetrating framework exhibits the highest thermal stability of the three frameworks, and the 4-fold interpenetrating framework exhibits higher thermal stability than the 3-fold interpenetrating framework. The thermodynamics and kinetics of skeleton collapse for the complexes were calculated by the integral Kissinger's method and Ozawa-Doyle's method. The activation energies (E) of 276.887, 318.515, and 149.310 kJ·mol-1 illustrate the relationship of the reaction rates of complexes 1-3: 3 > 1 > 2. The structural characteristics could be elucidated from the thermodynamics and kinetics. Moreover, the fluorescent properties of complexes 1-3 were also studied.
Based on flexible 1,4-bis(2-methyl-imidazol-1-yl)butane (bib) and three rigid line-shaped carboxylate mix-ligands, three Zn(II) coordination polymers, {[Zn2(bib)2(1,4-ndc)2]·H2O}n (1), {[Zn0.5(bib)0.5(bdc-Br2)0.5]·0.5H2O}n (2), {[Zn2(bib)(4,4'-bpdc)2] · H2O}n (3)(1,4-H2ndc = 1,4-naphthalenedicarboxylic acid, H2bdc-Br2 = 2,5-dibromoterephthalic acid, 4,4'-H2bpdc = 4,4'-biphenyldicarboxylic acid) have been synthesized under solvothermal conditions and characterized by elemental analysis, infrared (IR) spectrometry, and single crystal X-ray diffraction. 1 presents a 4-fold interpenetrating framework including three kinds of zigzag chains. 2 exhibits an unusual [2 + 2] interpenetrating framework. 3 features a 3-fold interpenetrating network. Their thermal decomposition behaviors were investigated by simultaneous thermogravimetry/differential thermal gravity and differential scanning calorimetry (TG/DTG-DSC) techniques. The TG curves indicate that the unusual [2 + 2] interpenetrating framework exhibits the highest thermal stability of the three frameworks, and the 4-fold interpenetrating framework exhibits higher thermal stability than the 3-fold interpenetrating framework. The thermodynamics and kinetics of skeleton collapse for the complexes were calculated by the integral Kissinger's method and Ozawa-Doyle's method. The activation energies (E) of 276.887, 318.515, and 149.310 kJ·mol-1 illustrate the relationship of the reaction rates of complexes 1-3: 3 > 1 > 2. The structural characteristics could be elucidated from the thermodynamics and kinetics. Moreover, the fluorescent properties of complexes 1-3 were also studied.
2016, 32(6): 1404-1415
doi: 10.3866/PKU.WHXB201603162
Abstract:
Reaction heat (Q) is an important parameter in chemical thermodynamics that is widely used in the hazard evaluation and safety design of chemical processes. Reaction heats can be obtained by either calorimetry or estimation. Calorimetry is generally more accurate, but is time-consuming, and sometimes precluded by the experimental conditions. By comparison, estimation techniques are quick and convenient, but are necessarily less accurate. The group contribution method (GCM) is one of the most commonly used estimation techniques. To investigate the accuracy of the estimations and make a primary screening of reaction heats for the industrial application of the GCM, calorimetric measurements of 33 reactions of 11 reaction types, including hydrogenation, reduction, nitration, oxidation, amidation, amination, ester hydrolysis, nitrogen substitution, ring-opening, and esterification, were conducted. The 33 reaction heats were also estimated by the GCM, and were compared with the calorimetric results. The relative errors between calorimetry (Qcalorimetry) and the GCM (QGCM) were also summarized for the different types of reactions. According to the range of relative errors, the reaction types were divided into different groups for calibrating QGCM to Qcalorimetry. Some recommended correction coefficients were proposed to correct QGCM to Qrecommended (Qr) for the different types of reactions, which could be employed in industrial settings where experimental results are difficult to acquire. Finally, the sources of error between Qcalorimetry and QGCM were analyzed, and advice for making accurate estimations was proposed for future work.
Reaction heat (Q) is an important parameter in chemical thermodynamics that is widely used in the hazard evaluation and safety design of chemical processes. Reaction heats can be obtained by either calorimetry or estimation. Calorimetry is generally more accurate, but is time-consuming, and sometimes precluded by the experimental conditions. By comparison, estimation techniques are quick and convenient, but are necessarily less accurate. The group contribution method (GCM) is one of the most commonly used estimation techniques. To investigate the accuracy of the estimations and make a primary screening of reaction heats for the industrial application of the GCM, calorimetric measurements of 33 reactions of 11 reaction types, including hydrogenation, reduction, nitration, oxidation, amidation, amination, ester hydrolysis, nitrogen substitution, ring-opening, and esterification, were conducted. The 33 reaction heats were also estimated by the GCM, and were compared with the calorimetric results. The relative errors between calorimetry (Qcalorimetry) and the GCM (QGCM) were also summarized for the different types of reactions. According to the range of relative errors, the reaction types were divided into different groups for calibrating QGCM to Qcalorimetry. Some recommended correction coefficients were proposed to correct QGCM to Qrecommended (Qr) for the different types of reactions, which could be employed in industrial settings where experimental results are difficult to acquire. Finally, the sources of error between Qcalorimetry and QGCM were analyzed, and advice for making accurate estimations was proposed for future work.
2016, 32(6): 1416-1423
doi: 10.3866/PKU.WHXB2016032501
Abstract:
This study measures the ignition delay times of C2H4/O2/Ar stoichiometric mixtures under Ar diluent mole fractions of 75% and 96% using the shock tube. The experimental temperatures range from 1092 to 1743 K and the pressures range from 1.3 to 3.0 atm (1 atm = 101325 Pa). The logarithm of the ignition delay time is found to be a linear function of the reciprocal temperature. The ignition delay time is shorter in the lower diluent concentrations, as well as decreasing with increasing temperature. Moreover, detonation (or deflagration to detonation) is observed in the lower but not the higher diluent concentrations. In comparative simulations of four different mechanisms, the LLNL mechanism best fits the experimental results. Reaction path analysis shows that the ethylene oxidation paths are affected by temperature rather than diluent rate. With increasing temperature, the number of ethylene oxidation paths decrease from four to three because of the predominance of the reverse reaction C2H4 + H (+ M) → C2H5 (+ M).
This study measures the ignition delay times of C2H4/O2/Ar stoichiometric mixtures under Ar diluent mole fractions of 75% and 96% using the shock tube. The experimental temperatures range from 1092 to 1743 K and the pressures range from 1.3 to 3.0 atm (1 atm = 101325 Pa). The logarithm of the ignition delay time is found to be a linear function of the reciprocal temperature. The ignition delay time is shorter in the lower diluent concentrations, as well as decreasing with increasing temperature. Moreover, detonation (or deflagration to detonation) is observed in the lower but not the higher diluent concentrations. In comparative simulations of four different mechanisms, the LLNL mechanism best fits the experimental results. Reaction path analysis shows that the ethylene oxidation paths are affected by temperature rather than diluent rate. With increasing temperature, the number of ethylene oxidation paths decrease from four to three because of the predominance of the reverse reaction C2H4 + H (+ M) → C2H5 (+ M).
2016, 32(6): 1424-1433
doi: 10.3866/PKU.WHXB201603233
Abstract:
The high temperature oxidative mechanism of a new four-component RP-3 surrogate fuel model was investigated using the ReaxFF MD method. The evolution of the fuel molecules, oxygen, C2H4, and ·CH3, and the underlying reactions, were obtained by systematic analysis of the simulation trajectories with the aid of VARxMD, a unique tool for ReaxFF MD reaction analysis developed by the authors' group. The simulated consumption of fuel and oxygen, as well as the amount of ethylene and methyl radicals, in RP-3 oxidation are of the same magnitude in the ReaxFF MD simulations as that predicted by CHEMKIN under the same temperature and initial pressure conditions. Based on the chemical structures of all the species and the full set of reactions obtained, the detailed mechanisms observed in the simulations broadly agree with the previous literature. The first reactions of the fuel molecules can be categorized into H-abstraction and internal scission, with the latter dominating under various temperature conditions. Observation and statistical analysis of the oxygen reactions reveal that small species of C1-C3 are involved in a relatively large proportion, which may allow the simplification of the reaction mechanism. A reaction network for RP-3 oxidation at high temperature is obtained through the analysis of the reaction mechanisms. This work demonstrates that the ReaxFF MD method, combined with the unique reaction analysis capability of VARxMD, provides useful insights into the mechanism of fuel combustion and should aid the construction of combustion mechanism libraries.
The high temperature oxidative mechanism of a new four-component RP-3 surrogate fuel model was investigated using the ReaxFF MD method. The evolution of the fuel molecules, oxygen, C2H4, and ·CH3, and the underlying reactions, were obtained by systematic analysis of the simulation trajectories with the aid of VARxMD, a unique tool for ReaxFF MD reaction analysis developed by the authors' group. The simulated consumption of fuel and oxygen, as well as the amount of ethylene and methyl radicals, in RP-3 oxidation are of the same magnitude in the ReaxFF MD simulations as that predicted by CHEMKIN under the same temperature and initial pressure conditions. Based on the chemical structures of all the species and the full set of reactions obtained, the detailed mechanisms observed in the simulations broadly agree with the previous literature. The first reactions of the fuel molecules can be categorized into H-abstraction and internal scission, with the latter dominating under various temperature conditions. Observation and statistical analysis of the oxygen reactions reveal that small species of C1-C3 are involved in a relatively large proportion, which may allow the simplification of the reaction mechanism. A reaction network for RP-3 oxidation at high temperature is obtained through the analysis of the reaction mechanisms. This work demonstrates that the ReaxFF MD method, combined with the unique reaction analysis capability of VARxMD, provides useful insights into the mechanism of fuel combustion and should aid the construction of combustion mechanism libraries.
2016, 32(6): 1434-1438
doi: 10.3866/PKU.WHXB201603101
Abstract:
The rearrangements of allylic acetates catalyzed by [Au(C3H2BR)]+ (R = Me, t-Bu) with planar tetracoordinate carbon (ptC) have been theoretically investigated. Calculated results show that the free energy barriers and the reaction free energies of the [Au(C3H2BR)]+-catalyzed rearrangement of allylic acetates are lower than those using [Au(NHC)]+ by 9.2-11.7 kJ·mol-1, indicating that a third type of containing C-terminal ligand besides CO and NHC might have potential applications in coordination and organic chemistry as well.
The rearrangements of allylic acetates catalyzed by [Au(C3H2BR)]+ (R = Me, t-Bu) with planar tetracoordinate carbon (ptC) have been theoretically investigated. Calculated results show that the free energy barriers and the reaction free energies of the [Au(C3H2BR)]+-catalyzed rearrangement of allylic acetates are lower than those using [Au(NHC)]+ by 9.2-11.7 kJ·mol-1, indicating that a third type of containing C-terminal ligand besides CO and NHC might have potential applications in coordination and organic chemistry as well.
2016, 32(6): 1439-1445
doi: 10.3866/PKU.WHXB201603154
Abstract:
Organic/inorganic perovskites have exhibited great potential as photoelectronic materials, achieving remarkable photoelectric conversion efficiency, currently over 20%. The structural, electronic, and optical properties of organic/inorganic hybrid CH3NH3PbxSn1-xI3 perovskites (x = 0-1) have been investigated by the first-principles theory. Our results indicate that the van der Waals (VDW) interaction plays a crucial role in the structure optimization. Accounting for VDW force correction, both the Pb/Sn―I bond lengths and volumes are decreased. By analyzing the density of states and the Bader charge of CH3NH3+ cations, we find that cations contribute only slightly to the band edge, but play the role of charge donors. There exists a combined covalent and ionic interaction between Pb/Sn and I ions. The valence band maximum (VBM) is mainly contributed by the I 5p orbitals with the overlapping of Pb 6s (Sn 5s) orbitals, while the conduction band minimum (CBM) is dominated by Pb 6p (Sn 5p) orbitals. In the visible light region, with increasing wavelength, the absorption intensity demonstrates a decreasing trend; as the Sn/Pb ratio increases, the absorption intensity shows an increasing trend. CH3NH3SnI3 perovskites demonstrate great potential to absorb light in the visible region.
Organic/inorganic perovskites have exhibited great potential as photoelectronic materials, achieving remarkable photoelectric conversion efficiency, currently over 20%. The structural, electronic, and optical properties of organic/inorganic hybrid CH3NH3PbxSn1-xI3 perovskites (x = 0-1) have been investigated by the first-principles theory. Our results indicate that the van der Waals (VDW) interaction plays a crucial role in the structure optimization. Accounting for VDW force correction, both the Pb/Sn―I bond lengths and volumes are decreased. By analyzing the density of states and the Bader charge of CH3NH3+ cations, we find that cations contribute only slightly to the band edge, but play the role of charge donors. There exists a combined covalent and ionic interaction between Pb/Sn and I ions. The valence band maximum (VBM) is mainly contributed by the I 5p orbitals with the overlapping of Pb 6s (Sn 5s) orbitals, while the conduction band minimum (CBM) is dominated by Pb 6p (Sn 5p) orbitals. In the visible light region, with increasing wavelength, the absorption intensity demonstrates a decreasing trend; as the Sn/Pb ratio increases, the absorption intensity shows an increasing trend. CH3NH3SnI3 perovskites demonstrate great potential to absorb light in the visible region.
2016, 32(6): 1446-1452
doi: 10.3866/PKU.WHXB201603241
Abstract:
The properties of plasmon excitations in silicene quantum dot dimers are investigated using timedependent density functional theory. Within a certain gap distance, a long-range charge transfer plasmon mode appears in silicene quantum dot dimers due to an impulse excitation polarized in the direction perpendicular to the quantum dot plane. The π electrons that participate in this plasmon excitation mostly move between the two quantum dots. This plasmon mode is blue-shifted as the gap distance decreases. Moreover, for different gap distances, two main plasmon bands appear, one around 7 eV and the other around 15 eV. In the low-energy region of the spectrum, for an impulse excitation polarized in the direction parallel to the silicene quantum dot plane, the shape of the absorption spectrum and the corresponding peak intensity of the silicene quantum dot dimers are both equivalent to those of a single silicene quantum dot, due to coupling between the two dots.
The properties of plasmon excitations in silicene quantum dot dimers are investigated using timedependent density functional theory. Within a certain gap distance, a long-range charge transfer plasmon mode appears in silicene quantum dot dimers due to an impulse excitation polarized in the direction perpendicular to the quantum dot plane. The π electrons that participate in this plasmon excitation mostly move between the two quantum dots. This plasmon mode is blue-shifted as the gap distance decreases. Moreover, for different gap distances, two main plasmon bands appear, one around 7 eV and the other around 15 eV. In the low-energy region of the spectrum, for an impulse excitation polarized in the direction parallel to the silicene quantum dot plane, the shape of the absorption spectrum and the corresponding peak intensity of the silicene quantum dot dimers are both equivalent to those of a single silicene quantum dot, due to coupling between the two dots.
2016, 32(6): 1453-1459
doi: 10.3866/PKU.WHXB201603172
Abstract:
Using nonequilibrium Green's functions in combination with density-functional theory, we investigate the electronic transport properties of a molecular motor device. The calculations show that the transport behavior of the device is sensitive to the rotational orientation of the rotor component. As the angle between the rotor and the stator is varied between 30° and 150°, the conductance of the molecular device oscillates between high and low. Moreover, when the rotor revolves to become vertically aligned with the stator, the current -voltage characteristics of the device display nonlinear behavior. The current decreases when the bias voltage is increased beyond 2.4 V and displays negative differential resistance behavior.
Using nonequilibrium Green's functions in combination with density-functional theory, we investigate the electronic transport properties of a molecular motor device. The calculations show that the transport behavior of the device is sensitive to the rotational orientation of the rotor component. As the angle between the rotor and the stator is varied between 30° and 150°, the conductance of the molecular device oscillates between high and low. Moreover, when the rotor revolves to become vertically aligned with the stator, the current -voltage characteristics of the device display nonlinear behavior. The current decreases when the bias voltage is increased beyond 2.4 V and displays negative differential resistance behavior.
2016, 32(6): 1460-1466
doi: 10.3866/PKU.WHXB201605101
Abstract:
By combining theoretical calculations with experimental data, this study quantified the effects of both cathode Pt loading and operating backpressure on polymer electrolyte membrane fuel cell (PEMFC) performance, in terms of the kinetic, ohmic and transport losses. Pt loadings of 0.1, 0.2 and 0.4 mg·cm-2 were investigated at backpressure values of 100, 150 and 200 kPa, respectively. The results indicate that, under all conditions, the kinetic, ohmic and transport losses all increased with the increase in current density. However, under the equivalent backpressure the transport loss of a PEMFC decreased with the increase of Pt loading. It was also found that increasing the operating backpressure improved the cell performance, and this enhancement in performance was more pronounced at a lower Pt loading. This result indicates an appropriate increase in operating backpressure should benefit the performance of a low-Pt loading PEMFC. Finally, the mechanism responsible for the observed phenomena was discussed. This study is expected to be helpful in the design and performance optimization of PEMFCs with low or ultra-low Pt loadings.
By combining theoretical calculations with experimental data, this study quantified the effects of both cathode Pt loading and operating backpressure on polymer electrolyte membrane fuel cell (PEMFC) performance, in terms of the kinetic, ohmic and transport losses. Pt loadings of 0.1, 0.2 and 0.4 mg·cm-2 were investigated at backpressure values of 100, 150 and 200 kPa, respectively. The results indicate that, under all conditions, the kinetic, ohmic and transport losses all increased with the increase in current density. However, under the equivalent backpressure the transport loss of a PEMFC decreased with the increase of Pt loading. It was also found that increasing the operating backpressure improved the cell performance, and this enhancement in performance was more pronounced at a lower Pt loading. This result indicates an appropriate increase in operating backpressure should benefit the performance of a low-Pt loading PEMFC. Finally, the mechanism responsible for the observed phenomena was discussed. This study is expected to be helpful in the design and performance optimization of PEMFCs with low or ultra-low Pt loadings.
2016, 32(6): 1467-1472
doi: 10.3866/PKU.WHXB201604144
Abstract:
Direct ethanol fuel cell (DEFC) has received much attention because of its high energy density, environmental friendliness, and low toxicity. Mechanism studies have focused on improving the breaking ratio of the C―C bond during the ethanol oxidation reaction (EOR). We establish an on-line electrochemical transmission infrared spectroscopic (ETIRS) method for electrochemical reactions. The new method is applied to study the effect of the addition of Pb2+ on the EOR catalyzed by Pt in an alkaline solution. We perform a series of electrochemical experiments at different temperatures, different catalyst loadings, and different potentials. The addition of Pb2+ is shown to improve the reaction rate of EOR in each experiment. Additionally, the anodic current becomes more stable with Pb2+ addition in the solutions. By using ETIRS, the products of the EOR are detected. The results show that the current efficiency of the carbonate is obviously higher in the presence of Pb2+ than that without Pb2+. This indicates that Pb2+ may improve the breaking ratio of the C―C bond during the EOR, which results in an increase of the EOR current.
Direct ethanol fuel cell (DEFC) has received much attention because of its high energy density, environmental friendliness, and low toxicity. Mechanism studies have focused on improving the breaking ratio of the C―C bond during the ethanol oxidation reaction (EOR). We establish an on-line electrochemical transmission infrared spectroscopic (ETIRS) method for electrochemical reactions. The new method is applied to study the effect of the addition of Pb2+ on the EOR catalyzed by Pt in an alkaline solution. We perform a series of electrochemical experiments at different temperatures, different catalyst loadings, and different potentials. The addition of Pb2+ is shown to improve the reaction rate of EOR in each experiment. Additionally, the anodic current becomes more stable with Pb2+ addition in the solutions. By using ETIRS, the products of the EOR are detected. The results show that the current efficiency of the carbonate is obviously higher in the presence of Pb2+ than that without Pb2+. This indicates that Pb2+ may improve the breaking ratio of the C―C bond during the EOR, which results in an increase of the EOR current.
2016, 32(6): 1473-1481
doi: 10.3866/PKU.WHXB201603112
Abstract:
A new methanol-tolerant oxygen reduction electrocatalyst, nitrogen-doped hollow carbon microspheres@platinum nanoparticles hybrids (HNCMS@Pt NPs), has been synthesized by a facile template route. In brief, Pt NPs were loaded on the surface of NH2-functionalized SiO2 microspheres (Pt NPs/SiO2). Then, the Pt NPs/SiO2 hybrids were wrapped by polydopamine (PDA) film. After direct carbonization of PDA-wrapped Pt NPs/SiO2 hybrids under a nitrogen atmosphere and further treatment in a hydrofluoric acid solution, Pt NPs embedded within nitrogen-doped hollow carbon microsphere (HNCMS) were obtained and labeled as HNCMS@Pt NPs. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, specific surface area analysis, and X-ray photoelectron spectroscopy were used to characterize the HNCMS@Pt NPs hybrids. The electrochemical properties of the HNCMS@Pt NPs hybrids for oxygen reduction reaction have also been investigated by cyclic voltammetry and linear sweep voltammetry. The results show that the Pt loading mass in the HNCMS@Pt NPs hybrids is up to 11.9% (w, mass fraction). Furthermore, the as-prepared HNCMS@Pt NPs catalyst exhibits good electrocatalytic activity, high stability, and excellent methanol-tolerance toward oxygen reduction reactions, implying potential applications in practical direct methanol fuel cells (DMFCs) as methanol-tolerant cathodic catalysts.
A new methanol-tolerant oxygen reduction electrocatalyst, nitrogen-doped hollow carbon microspheres@platinum nanoparticles hybrids (HNCMS@Pt NPs), has been synthesized by a facile template route. In brief, Pt NPs were loaded on the surface of NH2-functionalized SiO2 microspheres (Pt NPs/SiO2). Then, the Pt NPs/SiO2 hybrids were wrapped by polydopamine (PDA) film. After direct carbonization of PDA-wrapped Pt NPs/SiO2 hybrids under a nitrogen atmosphere and further treatment in a hydrofluoric acid solution, Pt NPs embedded within nitrogen-doped hollow carbon microsphere (HNCMS) were obtained and labeled as HNCMS@Pt NPs. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, specific surface area analysis, and X-ray photoelectron spectroscopy were used to characterize the HNCMS@Pt NPs hybrids. The electrochemical properties of the HNCMS@Pt NPs hybrids for oxygen reduction reaction have also been investigated by cyclic voltammetry and linear sweep voltammetry. The results show that the Pt loading mass in the HNCMS@Pt NPs hybrids is up to 11.9% (w, mass fraction). Furthermore, the as-prepared HNCMS@Pt NPs catalyst exhibits good electrocatalytic activity, high stability, and excellent methanol-tolerance toward oxygen reduction reactions, implying potential applications in practical direct methanol fuel cells (DMFCs) as methanol-tolerant cathodic catalysts.
2016, 32(6): 1482-1488
doi: 10.3866/PKU.WHXB201603153
Abstract:
The critical micelle concentrations (CMCs) of the reversed demulsifiers poly(propylene oxide)-blockpoly( ethylene oxide)-block-poly(propylene oxide)(PPO-PEO-PPO), SP169, and DMEA169 were measured by steady-state fluorescence spectroscopy, with cetylpyridinium chloride (CPC) as the quencher and pyrene as the fluorescent probe. The micellar aggregation numbers (Nagg) and the polarity of the micro-environments inside the micelles were obtained for the first time. The hydrodynamic diameters of the micelles at different demulsifier concentrations were determined by dynamic light scattering (DLS) and the corresponding micelle shapes were simulated by dissipative particle dynamics (DPD). The results indicate that the critical micellar aggregation numbers (Nm) can be extrapolated from the Nagg-cs curves, with Nm(SP169) = 28 and Nm(DMEA169) = 18. The hydrodynamic diameter of SP169 is smaller than that of DMEA169, while the acceleration of the former is faster than that of the latter. The simulations show that the micelle of SP169 is spherical while that of DMEA169 has aclavate shape, because of the different interactions resulting from the initiators among the beads. Moreover, the simulations are in good agreement with the experiments in that they find a smaller hydrodynamic diameter and a less polar micro-environment inside the micelle of SP169 compared with that of DMEA169, while the aggregation number of the former is larger than that of the latter.
The critical micelle concentrations (CMCs) of the reversed demulsifiers poly(propylene oxide)-blockpoly( ethylene oxide)-block-poly(propylene oxide)(PPO-PEO-PPO), SP169, and DMEA169 were measured by steady-state fluorescence spectroscopy, with cetylpyridinium chloride (CPC) as the quencher and pyrene as the fluorescent probe. The micellar aggregation numbers (Nagg) and the polarity of the micro-environments inside the micelles were obtained for the first time. The hydrodynamic diameters of the micelles at different demulsifier concentrations were determined by dynamic light scattering (DLS) and the corresponding micelle shapes were simulated by dissipative particle dynamics (DPD). The results indicate that the critical micellar aggregation numbers (Nm) can be extrapolated from the Nagg-cs curves, with Nm(SP169) = 28 and Nm(DMEA169) = 18. The hydrodynamic diameter of SP169 is smaller than that of DMEA169, while the acceleration of the former is faster than that of the latter. The simulations show that the micelle of SP169 is spherical while that of DMEA169 has aclavate shape, because of the different interactions resulting from the initiators among the beads. Moreover, the simulations are in good agreement with the experiments in that they find a smaller hydrodynamic diameter and a less polar micro-environment inside the micelle of SP169 compared with that of DMEA169, while the aggregation number of the former is larger than that of the latter.
2016, 32(6): 1489-1494
doi: 10.3866/PKU.WHXB2016032802
Abstract:
We performed an aberration-corrected scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS) study of Na0.66Mn0.675Ni0.1625Co0.1625O2, which was prepared via a solidstate reaction for sodium-ion battery applications. Powder X-ray diffraction (XRD) showed that the material had a well-crystallized P2-type layered structure (P63/mmc). Results from further STEM and EDS analyses showed the presence of reconstructed surface layers of thickness about 1-2 nm, which contained a large amount of antisite defects and obvious lattice distortions. Detailed chemical analysis showed an inhomogeneous elemental distribution inside these reconstructed surface layers; they were cobalt rich and nickel deficient. These surface layers further evolved into thicker regions of width 5-10 nm, accompanied by a spinel (Fd3m) phase to rocksalt phase (Fm3m) transition.
We performed an aberration-corrected scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS) study of Na0.66Mn0.675Ni0.1625Co0.1625O2, which was prepared via a solidstate reaction for sodium-ion battery applications. Powder X-ray diffraction (XRD) showed that the material had a well-crystallized P2-type layered structure (P63/mmc). Results from further STEM and EDS analyses showed the presence of reconstructed surface layers of thickness about 1-2 nm, which contained a large amount of antisite defects and obvious lattice distortions. Detailed chemical analysis showed an inhomogeneous elemental distribution inside these reconstructed surface layers; they were cobalt rich and nickel deficient. These surface layers further evolved into thicker regions of width 5-10 nm, accompanied by a spinel (Fd3m) phase to rocksalt phase (Fm3m) transition.
2016, 32(6): 1495-1500
doi: 10.3866/PKU.WHXB2016032803
Abstract:
ZIF-8 membranes were prepared on α-alumina substrates in a urea/choline chloride (ChCl) based deep eutectic solvent using an in situ method. The synthesized ZIF-8 membranes were characterized using Xray diffraction (XRD) and scanning electron microscopy (SEM). The effects of the concentration of the reaction solution and the cooling rate on ZIF-8 membrane synthesis were investigated. The results indicate that increasing the concentration of the reaction solution and reducing the cooling rate are beneficial for synthesizing continuous ZIF-8 membranes. A continuous and compact ZIF-8 membrane with a thickness of about 8 μm was obtained on the substrate by optimizing the synthetic conditions. The single gas permeation and binary mixture gas separation performances of the ZIF-8 membrane prepared under the optimized synthetic conditions were determined using the Wicke-Kallenbach technique. For equimolar gas mixtures at room temperature (293 K), the separation factors for H2/CO2, H2/O2, H2/N2, and H2/CH4 were 7.4, 5.2, 9.1, and 13.8, respectively. All the separation factors exceed the corresponding Knudsen diffusion coefficients, indicating that the ZIF-8 membrane displays molecular sieving performance.
ZIF-8 membranes were prepared on α-alumina substrates in a urea/choline chloride (ChCl) based deep eutectic solvent using an in situ method. The synthesized ZIF-8 membranes were characterized using Xray diffraction (XRD) and scanning electron microscopy (SEM). The effects of the concentration of the reaction solution and the cooling rate on ZIF-8 membrane synthesis were investigated. The results indicate that increasing the concentration of the reaction solution and reducing the cooling rate are beneficial for synthesizing continuous ZIF-8 membranes. A continuous and compact ZIF-8 membrane with a thickness of about 8 μm was obtained on the substrate by optimizing the synthetic conditions. The single gas permeation and binary mixture gas separation performances of the ZIF-8 membrane prepared under the optimized synthetic conditions were determined using the Wicke-Kallenbach technique. For equimolar gas mixtures at room temperature (293 K), the separation factors for H2/CO2, H2/O2, H2/N2, and H2/CH4 were 7.4, 5.2, 9.1, and 13.8, respectively. All the separation factors exceed the corresponding Knudsen diffusion coefficients, indicating that the ZIF-8 membrane displays molecular sieving performance.
2016, 32(6): 1501-1510
doi: 10.3866/PKU.WHXB201603171
Abstract:
α-MnO2 nanorods, γ-MnO2 nanosheets, and δ-MnO2 nanofilm-assembled microspheres were prepared using a hydrothermal method and evaluated as catalysts for the selective catalytic reduction (SCR) of nitrogen oxides (NOx). They were also structurally characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), N2 adsorption-desorption, temperatureprogrammed reduction with hydrogen (H2-TPR), temperature-programmed desorption of ammonia (NH3-TPD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The γ-MnO2 nanosheets performed the best for the reduction of NOx and selectivity of N2, while the α-MnO2 nanorods performed the worst. Structural analysis indicated that the main factor determining the catalytic activities of the nanomaterials was not the specific surface area but the crystal structure and the exposed active crystals. The γ-MnO2 nanosheets performed best because their exposed (131) planes contained multiple Mn cations in coordinatively unsaturated environments, which formed numerous strongly acidic sites. They also benefited from active oxygen species. The active sites allowed the activation of NH3 and NOx at lower temperatures. Moreover, high concentrations of liquid oxygen and Mn cations at high oxidation states facilitated the redox reactions.
α-MnO2 nanorods, γ-MnO2 nanosheets, and δ-MnO2 nanofilm-assembled microspheres were prepared using a hydrothermal method and evaluated as catalysts for the selective catalytic reduction (SCR) of nitrogen oxides (NOx). They were also structurally characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), N2 adsorption-desorption, temperatureprogrammed reduction with hydrogen (H2-TPR), temperature-programmed desorption of ammonia (NH3-TPD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The γ-MnO2 nanosheets performed the best for the reduction of NOx and selectivity of N2, while the α-MnO2 nanorods performed the worst. Structural analysis indicated that the main factor determining the catalytic activities of the nanomaterials was not the specific surface area but the crystal structure and the exposed active crystals. The γ-MnO2 nanosheets performed best because their exposed (131) planes contained multiple Mn cations in coordinatively unsaturated environments, which formed numerous strongly acidic sites. They also benefited from active oxygen species. The active sites allowed the activation of NH3 and NOx at lower temperatures. Moreover, high concentrations of liquid oxygen and Mn cations at high oxidation states facilitated the redox reactions.
2016, 32(6): 1511-1518
doi: 10.3866/PKU.WHXB201603094
Abstract:
Highly dispersed Co catalysts supported on SiO2 were prepared in the presence of ethylene glycol (EG) by co-impregnation and tested in the vapor-phase hydrogenolysis of ethyl lactate to 1,2-propanediol. The synthesis parameters of Co metal loading, ratio of EG to cobalt nitrate, type of alcohol and calcination temperature, which influenced the physical properties of the Co3O4 nanoparticles, were investigated through the use of X-ray diffraction (XRD). It revealed that the ratio of EG to cobalt nitrate and the type of alcohol significantly affected the particle size of Co3O4 supported on SiO2. During co-impregnation with EG, the interaction between Co2+ and the SiO2 support was strongly enhanced, resulting in the high dispersion of cobalt species and the decrease of Co3O4 particle size from 16 nm to below 5 nm; the significantly enhanced cobalt dispersion was associated with the formation of amorphous cobalt silicate. Meanwhile the conversion of ethyl lactate was greatly improved to 98.6% from 69.5%, with 98.0% selectivity of 1,2-propanediol over 10% (w, mass fraction) Co/SiO2 catalysts under the given reaction conditions (2.5 MPa and 160 ℃). The obtained catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), N2 adsorption-desorption measurements, and H2 temperature-programmed reduction (H2-TPR) methods.
Highly dispersed Co catalysts supported on SiO2 were prepared in the presence of ethylene glycol (EG) by co-impregnation and tested in the vapor-phase hydrogenolysis of ethyl lactate to 1,2-propanediol. The synthesis parameters of Co metal loading, ratio of EG to cobalt nitrate, type of alcohol and calcination temperature, which influenced the physical properties of the Co3O4 nanoparticles, were investigated through the use of X-ray diffraction (XRD). It revealed that the ratio of EG to cobalt nitrate and the type of alcohol significantly affected the particle size of Co3O4 supported on SiO2. During co-impregnation with EG, the interaction between Co2+ and the SiO2 support was strongly enhanced, resulting in the high dispersion of cobalt species and the decrease of Co3O4 particle size from 16 nm to below 5 nm; the significantly enhanced cobalt dispersion was associated with the formation of amorphous cobalt silicate. Meanwhile the conversion of ethyl lactate was greatly improved to 98.6% from 69.5%, with 98.0% selectivity of 1,2-propanediol over 10% (w, mass fraction) Co/SiO2 catalysts under the given reaction conditions (2.5 MPa and 160 ℃). The obtained catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), N2 adsorption-desorption measurements, and H2 temperature-programmed reduction (H2-TPR) methods.
2016, 32(6): 1519-1526
doi: 10.3866/PKU.WHXB201603242
Abstract:
BiPO4 photocatalysts were synthesized by refluxing in ethylene glycol, and the effects of reaction temperature and reaction time on the BiPO4 crystal structure, morphology, and properties were investigated. The crystal form of BiPO4 changed from hexagonal to monoclinic on refluxing in the solvent. The produced BiPO4 photocatalysts showed good activities in photodegradation of methylene blue, and the activity could be adjusted by changing the refluxing temperature and time. BiPO4 showed the best catalytic properties when the refluxing time was 2 h at 130 ℃; the kinetic constant was 0.161 min-1. The BiPO4 dispersibility was still high after standing for 2 d, because of the introduction of surface hydroxy groups by refluxing in ethylene glycol.
BiPO4 photocatalysts were synthesized by refluxing in ethylene glycol, and the effects of reaction temperature and reaction time on the BiPO4 crystal structure, morphology, and properties were investigated. The crystal form of BiPO4 changed from hexagonal to monoclinic on refluxing in the solvent. The produced BiPO4 photocatalysts showed good activities in photodegradation of methylene blue, and the activity could be adjusted by changing the refluxing temperature and time. BiPO4 showed the best catalytic properties when the refluxing time was 2 h at 130 ℃; the kinetic constant was 0.161 min-1. The BiPO4 dispersibility was still high after standing for 2 d, because of the introduction of surface hydroxy groups by refluxing in ethylene glycol.
2016, 32(6): 1527-1533
doi: 10.3866/PKU.WHXB201603161
Abstract:
CexNi0.5La0.5-xO (CeNiLaO) catalysts were synthesized using a Ce-La composite oxide as the carrier via co-precipitation. They were applied in the oxidative steamreforming of glycerol (OSRG) in a fixed-bed reactor. The catalysts were characterized by X-ray diffraction (XRD), H2-temperature-programmed reduction (H2-TPR), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Xray photoelectron spectroscopy (XPS). The results showed that La2O3 improved the dispersion of metallic Ni and suppressed the sintering of metallic Ni particles; the lattice oxygen of CeO2 inhibited and eliminated carbon deposition on the surface of the catalysts; and the substitution of some La3+ for Ce4+ ions induced a distortion of the lattice. The synergy of La2O3 and CeO2 lessened the deactivation caused by the sintering and coke deposition and improved the catalytic performance. Among the catalysts with different molar ratios of Ce to La, Ce0.4Ni0.5La0.1O had the best catalytic activity. The conversion of glycerol remained above 95% after a 210 h stability test, while a gaseous reformate of about 50% hydrogen could be steadily produced.
CexNi0.5La0.5-xO (CeNiLaO) catalysts were synthesized using a Ce-La composite oxide as the carrier via co-precipitation. They were applied in the oxidative steamreforming of glycerol (OSRG) in a fixed-bed reactor. The catalysts were characterized by X-ray diffraction (XRD), H2-temperature-programmed reduction (H2-TPR), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Xray photoelectron spectroscopy (XPS). The results showed that La2O3 improved the dispersion of metallic Ni and suppressed the sintering of metallic Ni particles; the lattice oxygen of CeO2 inhibited and eliminated carbon deposition on the surface of the catalysts; and the substitution of some La3+ for Ce4+ ions induced a distortion of the lattice. The synergy of La2O3 and CeO2 lessened the deactivation caused by the sintering and coke deposition and improved the catalytic performance. Among the catalysts with different molar ratios of Ce to La, Ce0.4Ni0.5La0.1O had the best catalytic activity. The conversion of glycerol remained above 95% after a 210 h stability test, while a gaseous reformate of about 50% hydrogen could be steadily produced.
2016, 32(6): 1534-1542
doi: 10.3866/PKU.WHXB201603232
Abstract:
Employing fluorene as substrate, we synthesized a new spirobifluorene derivative, 2'-(9-phenylfluoren-9-yl)-9,9'-spirobi[fluorene] (PF-SBF), through a one-step palladium-catalyzed cross-coupling reaction. Utilizing PF-SBF as an emitter and as a host of the blue phosphor bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyri-dyl))iridium(III)(FIrpic) in organic light-emitting devices (OLEDs), we observed a red light band different from the intrinsic blue emission of PF-SBF and FIrpic. This was attributed to the intermolecular aggregation of PF-SBF and to exciplexes generated at the interfaces of the emitting layer and the electron transport layer. The exciplex emission was then restrained through a suitable selection of hole and electron transport layer. Employing PF-SBF with di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane (TAPC) as a cohost, we obtained high-performance blue and green emissions from FIrpic and tris(2-phenylpyridine)iridium(III)(Ir(ppy)3). The maximum current efficiencies and luminances of the blue and green OLEDs were as high as 16.7 and 50.5 cd·A-1 and 7857 (at 11 V) and 23390 cd·m-2 (at 8 V), respectively. As an alternative to PF-SBF, we also synthesized a new xanthene derivative, 2-(9-phenyl-fluoren-9-yl)spiro[fluorene-9,9'-xanthene] (PF-SFX), with a large triplet energy level of 2.8 eV. Using PF-SFX similarly as a host of FIrpic, the current efficiency and luminance were significantly improved to 22.6 cd·A-1 and 6421 cd·m-2 (at 10 V). These results demonstrate the potential of PF-SBF and PF-SFX as new building blocks for high-efficiency green/blue phosphorescent host materials.
Employing fluorene as substrate, we synthesized a new spirobifluorene derivative, 2'-(9-phenylfluoren-9-yl)-9,9'-spirobi[fluorene] (PF-SBF), through a one-step palladium-catalyzed cross-coupling reaction. Utilizing PF-SBF as an emitter and as a host of the blue phosphor bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyri-dyl))iridium(III)(FIrpic) in organic light-emitting devices (OLEDs), we observed a red light band different from the intrinsic blue emission of PF-SBF and FIrpic. This was attributed to the intermolecular aggregation of PF-SBF and to exciplexes generated at the interfaces of the emitting layer and the electron transport layer. The exciplex emission was then restrained through a suitable selection of hole and electron transport layer. Employing PF-SBF with di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane (TAPC) as a cohost, we obtained high-performance blue and green emissions from FIrpic and tris(2-phenylpyridine)iridium(III)(Ir(ppy)3). The maximum current efficiencies and luminances of the blue and green OLEDs were as high as 16.7 and 50.5 cd·A-1 and 7857 (at 11 V) and 23390 cd·m-2 (at 8 V), respectively. As an alternative to PF-SBF, we also synthesized a new xanthene derivative, 2-(9-phenyl-fluoren-9-yl)spiro[fluorene-9,9'-xanthene] (PF-SFX), with a large triplet energy level of 2.8 eV. Using PF-SFX similarly as a host of FIrpic, the current efficiency and luminance were significantly improved to 22.6 cd·A-1 and 6421 cd·m-2 (at 10 V). These results demonstrate the potential of PF-SBF and PF-SFX as new building blocks for high-efficiency green/blue phosphorescent host materials.
2016, 32(6): 1543-1548
doi: 10.3866/PKU.WHXB201603142
Abstract:
The nanosecond-scale propagations and optical-limiting properties of two fluorene derivatives-2, 7-bis(4'-(dimethylamino)-distyryl)-9H-fluorene (F1) and 2,7-bis(4'-(nitro)-distyryl)-9H-fluorene (F2) with different terminal groups are investigated by solving the coupled rate equations and field intensity equation using an iterative predictor-corrector finite-difference time-domain technique. The influence of the propagation distance (z), particle number density (N), and pulse width (τ) on the optical-limiting properties and two-photon absorption (TPA) of these molecules is analyzed. The calculations show that both F1 and F2 possess large two-photon absorption cross sections and pronounced optical-limiting properties. In addition, the nonlinear optical properties depend crucially on the terminal groups. F2, with terminal groups of ―NO2, has much larger dipole moments, an enhanced two-photon absorption cross section, and superior optical-limiting ability compared with F1, which have terminal groups of ―N(CH3)2.
The nanosecond-scale propagations and optical-limiting properties of two fluorene derivatives-2, 7-bis(4'-(dimethylamino)-distyryl)-9H-fluorene (F1) and 2,7-bis(4'-(nitro)-distyryl)-9H-fluorene (F2) with different terminal groups are investigated by solving the coupled rate equations and field intensity equation using an iterative predictor-corrector finite-difference time-domain technique. The influence of the propagation distance (z), particle number density (N), and pulse width (τ) on the optical-limiting properties and two-photon absorption (TPA) of these molecules is analyzed. The calculations show that both F1 and F2 possess large two-photon absorption cross sections and pronounced optical-limiting properties. In addition, the nonlinear optical properties depend crucially on the terminal groups. F2, with terminal groups of ―NO2, has much larger dipole moments, an enhanced two-photon absorption cross section, and superior optical-limiting ability compared with F1, which have terminal groups of ―N(CH3)2.
