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2017 Volume 33 Issue 11
2017, 33(11):
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2017, 33(11): 2113-2114
doi: 10.3866/PKU.WHXB201706095
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2017, 33(11): 2115-2116
doi: 10.3866/PKU.WHXB201706155
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2017, 33(11): 2117-2118
doi: 10.3866/PKU.WHXB201706152
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2017, 33(11): 2119-2120
doi: 10.3866/PKU.WHXB201706141
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The Direct Mechanism for the Formation of the First C-C Bond in the Methanol to Hydrocarbon Reaction
2017, 33(11): 2121-2122
doi: 10.3866/PKU.WHXB201706142
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2017, 33(11): 2123-2124
doi: 10.3866/PKU.WHXB201706143
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2017, 33(11): 2125-2126
doi: 10.3866/PKU.WHXB201706154
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2017, 33(11): 2127-2132
doi: 10.3866/PKU.WHXB201705244
Abstract:
Si-based anode materials in Li-ion batteries (LIBs) suffer from severe volume expansion/contraction during repetitive discharge/charge, which results in the pulverization of active materials, continuous growth of solid electrolyte interface (SEI) layers, loss of electrical conduction, and, eventually, battery failure. Herein, we present unprecedented low-content phosphorene (single-layer black phosphorus) encapsulation of silicon particles as an effective method for improving the electrochemical performance of Si-based LIB anodes. The incorporation of low phosphorene amounts (1%, mass fraction) into Si anodes effectively suppresses the detrimental effects of volume expansion and SEI growth, preserving the structural integrity of the electrode during cycling and achieving enhanced Coulombic efficiency, capacity retention, and cycling stability for Li-ion storage. Thus, the developed method can also be applied to other battery materials with high energy density exhibiting substantial volume changes.
Si-based anode materials in Li-ion batteries (LIBs) suffer from severe volume expansion/contraction during repetitive discharge/charge, which results in the pulverization of active materials, continuous growth of solid electrolyte interface (SEI) layers, loss of electrical conduction, and, eventually, battery failure. Herein, we present unprecedented low-content phosphorene (single-layer black phosphorus) encapsulation of silicon particles as an effective method for improving the electrochemical performance of Si-based LIB anodes. The incorporation of low phosphorene amounts (1%, mass fraction) into Si anodes effectively suppresses the detrimental effects of volume expansion and SEI growth, preserving the structural integrity of the electrode during cycling and achieving enhanced Coulombic efficiency, capacity retention, and cycling stability for Li-ion storage. Thus, the developed method can also be applied to other battery materials with high energy density exhibiting substantial volume changes.
2017, 33(11): 2133-2140
doi: 10.3866/PKU.WHXB201706051
Abstract:
This monograph focuses on recent progress in the research field of metallophilicity, in combination of our latest results on Cu(I)-based cyclic trinuclear complexes, mainly discussing two examples with very different cuprophilicity. One is by constructing triangular coordination prisms bearing cyclic trinuclear units, confirming that strong cuprophilic attraction could exist in the phosphorescent emissive state under frontal packing mode even when the cuprophilicity is extreme weak at ground state, and by coordination with a Cu2I2 cluster with an additional coordinate site in the ligand, so that a self-calibrated wide-range luminescent molecular thermometer was obtained. The other is the realization of the shortest Cu-Cu distance so far in this field by Br-Br halogen bond orthogonal to cuprophilicity, followed by the investigation using several kinds of electronic structure analysis. The result shows that even when the Cu-Cu distance approaches the van der Waals radii sum of Cu, its nature is still closed-shell interaction, which is also the nature of all Br-Br interaction, and the strongest Br-Br interaction in this system displays good matching between the σ-hole of a Br atom and the belt of negative potential of another Br atom.
This monograph focuses on recent progress in the research field of metallophilicity, in combination of our latest results on Cu(I)-based cyclic trinuclear complexes, mainly discussing two examples with very different cuprophilicity. One is by constructing triangular coordination prisms bearing cyclic trinuclear units, confirming that strong cuprophilic attraction could exist in the phosphorescent emissive state under frontal packing mode even when the cuprophilicity is extreme weak at ground state, and by coordination with a Cu2I2 cluster with an additional coordinate site in the ligand, so that a self-calibrated wide-range luminescent molecular thermometer was obtained. The other is the realization of the shortest Cu-Cu distance so far in this field by Br-Br halogen bond orthogonal to cuprophilicity, followed by the investigation using several kinds of electronic structure analysis. The result shows that even when the Cu-Cu distance approaches the van der Waals radii sum of Cu, its nature is still closed-shell interaction, which is also the nature of all Br-Br interaction, and the strongest Br-Br interaction in this system displays good matching between the σ-hole of a Br atom and the belt of negative potential of another Br atom.
2017, 33(11): 2141-2152
doi: 10.3866/PKU.WHXB201705223
Abstract:
Aerogels have been developed rapidly in recent years due to their excellent physicochemical properties and broad range of applications. However, most efforts have been devoted to traditional aerogel 3D monoliths, and particular requirements regarding the shape and size of the aerogels for some special uses have been neglected. Shaping aerogel into microspheres, that is, the fabrication of aerogel microspheres, may facilitate potential applications and extension of the range of applications of porous microspheres. Herein, we will present the fabrication and performance of various aerogel microspheres such as silica aerogel microspheres, cellulose aerogel microspheres, RF/carbon aerogel microspheres, and graphene aerogel microspheres. The current challenges and future developments of the aerogel microspheres are also discussed briefly in this review.
Aerogels have been developed rapidly in recent years due to their excellent physicochemical properties and broad range of applications. However, most efforts have been devoted to traditional aerogel 3D monoliths, and particular requirements regarding the shape and size of the aerogels for some special uses have been neglected. Shaping aerogel into microspheres, that is, the fabrication of aerogel microspheres, may facilitate potential applications and extension of the range of applications of porous microspheres. Herein, we will present the fabrication and performance of various aerogel microspheres such as silica aerogel microspheres, cellulose aerogel microspheres, RF/carbon aerogel microspheres, and graphene aerogel microspheres. The current challenges and future developments of the aerogel microspheres are also discussed briefly in this review.
2017, 33(11): 2153-2172
doi: 10.3866/PKU.WHXB201705313
Abstract:
Phosphorene is a novel two-dimensional material that is more advanced than graphene. This material possesses excellent physical, chemical, and mechanical properties, which are useful for potential applications in a variety of electronic devices. Thus far, a comprehensive review on the latest fabrication methods, property tuning, and applications of phosphorene is lacking. Therefore, a comprehensive review of the synthetic methods, structures, properties, modification methods, and device applications of phosphorene has been presented. The preparation strategies of phosphorene including top-bottom and bottom-up methods have been introduced, followed by a summary of its structure and properties. The modification methods of phosphorene have also been discussed. Finally, the applications of phosphorene in electronic devices have been discussed in detail. Future prospects and potential research areas of phosphorene have also been presented in this review.
Phosphorene is a novel two-dimensional material that is more advanced than graphene. This material possesses excellent physical, chemical, and mechanical properties, which are useful for potential applications in a variety of electronic devices. Thus far, a comprehensive review on the latest fabrication methods, property tuning, and applications of phosphorene is lacking. Therefore, a comprehensive review of the synthetic methods, structures, properties, modification methods, and device applications of phosphorene has been presented. The preparation strategies of phosphorene including top-bottom and bottom-up methods have been introduced, followed by a summary of its structure and properties. The modification methods of phosphorene have also been discussed. Finally, the applications of phosphorene in electronic devices have been discussed in detail. Future prospects and potential research areas of phosphorene have also been presented in this review.
2017, 33(11): 2173-2183
doi: 10.3866/PKU.WHXB201705312
Abstract:
Water is an indispensable resource for all biological life on earth. It is crucial for the existence of human beings and civilizations have historically thrived around water bodies. However, there still remains an enormous cognitive gap about the abnormal properties of water, its influence in the field of physics, chemistry, and biology, and the underlying mechanism of its effect on natural processes. Hydroscience has gradually entered the arena for scientific discussion and transformed into a main research area. While the majority of water on earth exists as bulk water, it typically participates in different physical and chemical processes in the form of interface/confined water under both natural and scientific research conditions. Nanoconfined water generally exists in natural and synthetic nanoscale environments, and its distinction from bulk water is mainly reflected in its dynamic and thermodynamic properties. The existence of confined water also has a profound impact on the development of devices composed of nanomaterials and their applications in the fields of biology, environmental science, geology etc. In this paper, the hydrogen bond structure of nanoconfined water has been analyzed and its dynamic, thermodynamic, and electrical properties have been generalized. A summary of the different research methods and their corresponding developmental history, together with examples of the application potential of nanoconfined water in the fields of environmental and material science have been presented. A summary of the progress made and existing problems in the research area of confined water is given along with the prospects for future developments.
Water is an indispensable resource for all biological life on earth. It is crucial for the existence of human beings and civilizations have historically thrived around water bodies. However, there still remains an enormous cognitive gap about the abnormal properties of water, its influence in the field of physics, chemistry, and biology, and the underlying mechanism of its effect on natural processes. Hydroscience has gradually entered the arena for scientific discussion and transformed into a main research area. While the majority of water on earth exists as bulk water, it typically participates in different physical and chemical processes in the form of interface/confined water under both natural and scientific research conditions. Nanoconfined water generally exists in natural and synthetic nanoscale environments, and its distinction from bulk water is mainly reflected in its dynamic and thermodynamic properties. The existence of confined water also has a profound impact on the development of devices composed of nanomaterials and their applications in the fields of biology, environmental science, geology etc. In this paper, the hydrogen bond structure of nanoconfined water has been analyzed and its dynamic, thermodynamic, and electrical properties have been generalized. A summary of the different research methods and their corresponding developmental history, together with examples of the application potential of nanoconfined water in the fields of environmental and material science have been presented. A summary of the progress made and existing problems in the research area of confined water is given along with the prospects for future developments.
2017, 33(11): 2184-2190
doi: 10.3866/PKU.WHXB201705222
Abstract:
Herein, we prepared four samples, namely gold/poly(sodium-p-styrenesulfonate) (Au/PSS), gold/silicon dioxide (Au/SiO2), gold/titanium dioxide (Au/TiO2), and gold/cuprous oxide (Au/Cu2O) core/shell nanocomposites, to investigate how the surrounding medium affects the ultrafast plasmon dynamics of Au nanoparticles (NPs). We recorded femtosecond transient absorption spectra of Au NPs in Au/PSS, Au/SiO2, Au/TiO2, and Au/Cu2O core/shell nanocomposites at various time delays. We found that the spectral features in the femtosecond transient absorption spectra of Au NPs in Au/TiO2 and Au/Cu2O core/shell nanocomposites were dramatically different from those of Au NPs in Au/PSS and Au/SiO2 core/shell nanocomposites. A comprehensive analysis of the ultrafast plasmon dynamics of Au NPs in the core/shell nanocomposites revealed that following excitation of the resonance plasmon band of Au NPs, the exited electrons could be efficiently transferred into the conduction bands of TiO2 and Cu2O in Au/TiO2 and Au/Cu2O core/shell nanocomposites.
Herein, we prepared four samples, namely gold/poly(sodium-p-styrenesulfonate) (Au/PSS), gold/silicon dioxide (Au/SiO2), gold/titanium dioxide (Au/TiO2), and gold/cuprous oxide (Au/Cu2O) core/shell nanocomposites, to investigate how the surrounding medium affects the ultrafast plasmon dynamics of Au nanoparticles (NPs). We recorded femtosecond transient absorption spectra of Au NPs in Au/PSS, Au/SiO2, Au/TiO2, and Au/Cu2O core/shell nanocomposites at various time delays. We found that the spectral features in the femtosecond transient absorption spectra of Au NPs in Au/TiO2 and Au/Cu2O core/shell nanocomposites were dramatically different from those of Au NPs in Au/PSS and Au/SiO2 core/shell nanocomposites. A comprehensive analysis of the ultrafast plasmon dynamics of Au NPs in the core/shell nanocomposites revealed that following excitation of the resonance plasmon band of Au NPs, the exited electrons could be efficiently transferred into the conduction bands of TiO2 and Cu2O in Au/TiO2 and Au/Cu2O core/shell nanocomposites.
2017, 33(11): 2191-2198
doi: 10.3866/PKU.WHXB201705242
Abstract:
Room temperature ionic liquids (RTILs) have been extensively studied with various applications owing to their non-volatility, excellent stability, good electrochemical properties and they can be easily manipulated by designing an appropriate structure and property. They differ from conventional solvents in that they have structural heterogeneity, which is one of the most essential natures of RTILs. In this work, the triplet excited state dynamics of meso-tetraphenylporphyrin (TPP) in the ionic liquid [Bmim][BF4] were studied, and it was observed that the triplet state lifetime of TPP increases remarkably from 2.95 to 184 μs upon laser irradiation. These results of the dynamics of TPP triplet excited state are probably caused by the laser-induced microstructure changes of the ionic liquid, and the redistribution of oxygen molecules polarized by the external laser field and/or the ions in the heterogeneous microenvironment of the ionic liquid upon laser irradiation.
Room temperature ionic liquids (RTILs) have been extensively studied with various applications owing to their non-volatility, excellent stability, good electrochemical properties and they can be easily manipulated by designing an appropriate structure and property. They differ from conventional solvents in that they have structural heterogeneity, which is one of the most essential natures of RTILs. In this work, the triplet excited state dynamics of meso-tetraphenylporphyrin (TPP) in the ionic liquid [Bmim][BF4] were studied, and it was observed that the triplet state lifetime of TPP increases remarkably from 2.95 to 184 μs upon laser irradiation. These results of the dynamics of TPP triplet excited state are probably caused by the laser-induced microstructure changes of the ionic liquid, and the redistribution of oxygen molecules polarized by the external laser field and/or the ions in the heterogeneous microenvironment of the ionic liquid upon laser irradiation.
2017, 33(11): 2199-2206
doi: 10.3866/PKU.WHXB201705226
Abstract:
In this paper, a real-time time-dependent density functional theory (TDDFT) coupled with the classical electrodynamics finite difference time domain (FDTD) technique is employed to investigate the optical properties of hybrid systems composed of gold nanoparticles (NPs) and the azobenzene adsorbate. The results demonstrate that the molecular absorption spectra over the entire energy range can be enhanced by localized surface plasmon resonance (LSPR) of Au NPs. However, the electronic coupling between the azobenzene and Au nanoparticles influences the energy and intensity of some special absorption peaks, leading to quite different spectral profiles of the hybrid complexes compared to those of isolated molecules or sole NPs. The plasmonic enhancement is also dependent on the NP-molecule separation distance and the geometrical parameters of NPs.
In this paper, a real-time time-dependent density functional theory (TDDFT) coupled with the classical electrodynamics finite difference time domain (FDTD) technique is employed to investigate the optical properties of hybrid systems composed of gold nanoparticles (NPs) and the azobenzene adsorbate. The results demonstrate that the molecular absorption spectra over the entire energy range can be enhanced by localized surface plasmon resonance (LSPR) of Au NPs. However, the electronic coupling between the azobenzene and Au nanoparticles influences the energy and intensity of some special absorption peaks, leading to quite different spectral profiles of the hybrid complexes compared to those of isolated molecules or sole NPs. The plasmonic enhancement is also dependent on the NP-molecule separation distance and the geometrical parameters of NPs.
2017, 33(11): 2207-2218
doi: 10.3866/PKU.WHXB201705227
Abstract:
In this work, the harmonic and anharmonic rate constants of the decomposition reaction of monomethylhydrazine (MMH) radicals have been calculated by using transition state (TS) and Rice-Ramsperger-Kassel-Marcus (RRKM) theories with either MP2 or B3LYP method at 6-311++G(3df,2p) basis set, respectively. The reaction mechanism and anharmonic effect of the MMH radicals are studied in detail and both of the harmonic and anharmonic rate constants increase sharply with increasing temperature in the canonical system. In the microcanonical system, these constants also show sharp increase with the energies. Overall, the anharmonic effect becomes more pronounced with the increasing temperature or energy in the canonical and microcanonical systems, respectively. These results indicate that the anharmonic effect of the decomposition reaction of MMH radicals is quite significant and cannot be ignored.
In this work, the harmonic and anharmonic rate constants of the decomposition reaction of monomethylhydrazine (MMH) radicals have been calculated by using transition state (TS) and Rice-Ramsperger-Kassel-Marcus (RRKM) theories with either MP2 or B3LYP method at 6-311++G(3df,2p) basis set, respectively. The reaction mechanism and anharmonic effect of the MMH radicals are studied in detail and both of the harmonic and anharmonic rate constants increase sharply with increasing temperature in the canonical system. In the microcanonical system, these constants also show sharp increase with the energies. Overall, the anharmonic effect becomes more pronounced with the increasing temperature or energy in the canonical and microcanonical systems, respectively. These results indicate that the anharmonic effect of the decomposition reaction of MMH radicals is quite significant and cannot be ignored.
2017, 33(11): 2219-2226
doi: 10.3866/PKU.WHXB201705192
Abstract:
Helium, which primarily occurs as a component of natural gas, has an irreplaceable role in both scientific and industrial fields. Therefore, it is crucial to separate helium from natural gas efficiently. Using density functional theory (DFT), we systematically investigate the adsorption, selectivity, and permeability characteristics of the rhombic-graphyne (R-GY) monolayer membrane for He and other components of natural gas (Ne, Ar, CO2, N2, and CH4). These results demonstrate that the R-GY monolayer can fulfill the requirements of both high selectivity and high permeance as a membrane for He separation. At 300 K, the He selectivities of the R-GY membrane can be up to 2×107, 3×1020, 9×1026, 7×1037, and 5×1051 over Ne, CO2, N2, Ar, and CH4, respectively. The membrane can maintain high selectivity even at 600 K. In addition, the He permeance of R-GY at room temperature can reach 10-6 mol·m-2·s-1·Pa-1, which is higher than the industrial standard by about three orders of magnitude, because of its low diffusion energy barrier. In contrast, the permeance of the other gas components is only 10-58-10-14 mol·m-2·s-1·Pa-1 at room temperature, indicating the impermeability of the R-GY to these components.
Helium, which primarily occurs as a component of natural gas, has an irreplaceable role in both scientific and industrial fields. Therefore, it is crucial to separate helium from natural gas efficiently. Using density functional theory (DFT), we systematically investigate the adsorption, selectivity, and permeability characteristics of the rhombic-graphyne (R-GY) monolayer membrane for He and other components of natural gas (Ne, Ar, CO2, N2, and CH4). These results demonstrate that the R-GY monolayer can fulfill the requirements of both high selectivity and high permeance as a membrane for He separation. At 300 K, the He selectivities of the R-GY membrane can be up to 2×107, 3×1020, 9×1026, 7×1037, and 5×1051 over Ne, CO2, N2, Ar, and CH4, respectively. The membrane can maintain high selectivity even at 600 K. In addition, the He permeance of R-GY at room temperature can reach 10-6 mol·m-2·s-1·Pa-1, which is higher than the industrial standard by about three orders of magnitude, because of its low diffusion energy barrier. In contrast, the permeance of the other gas components is only 10-58-10-14 mol·m-2·s-1·Pa-1 at room temperature, indicating the impermeability of the R-GY to these components.
2017, 33(11): 2227-2236
doi: 10.3866/PKU.WHXB201705221
Abstract:
In order to clarify the influence of different electron-withdrawing groups on the electronic structures and memory properties of naphthalimides, three 1,8-naphthalimides, namely N-(4-triphenylamino)-1,8-naphthalimide (NA-ATPA), N-(4-triphenylamino)-(4-cyano)-1,8-naphthalimide (NA(CN)-ATPA) and N-(4-triphenylamine)-(4-nitro)-1,8-naphthalimide (NA(NO2)-ATPA), were designed and synthesized using triphenylamine (TPA) as the electron donor and 1,8-naphthalene dianhydride containing different electron-withdrawing moieties (-H,-CN,-NO2) as the electron acceptor. The photophysical properties and electrochemical characteristics of the compounds were investigated by ultraviolet-visible spectroscopy (UV-Vis), fluorescence spectroscopy (FL) and cyclic voltammetry (CyV). The synthesized products were applied as the active layer in sandwich devices, whose memory characteristics were tested. NA-ATPA shows volatile static random access memory (SRAM) behavior, while NACN-ATPA and NANO2-ATPA show nonvolatile flash and write-once read-many times memory (WORM) behavior, respectively. Experimental results indicated that the synthesized compounds possessed small energy gaps and wide absorption ranges. The introduction of electron-withdrawing groups on the 4-position of the 1,8-naphthalimides reduced the LUMO energy level and the energy gap, leading to improved stability of the charge-transfer state and volatile-to-nonvolatile memory transfer. To elucidate the switching mechanism, molecular simulation results, including molecular orbitals, energy levels, optimized geometries, and Mulliken charge populations, were discussed.
In order to clarify the influence of different electron-withdrawing groups on the electronic structures and memory properties of naphthalimides, three 1,8-naphthalimides, namely N-(4-triphenylamino)-1,8-naphthalimide (NA-ATPA), N-(4-triphenylamino)-(4-cyano)-1,8-naphthalimide (NA(CN)-ATPA) and N-(4-triphenylamine)-(4-nitro)-1,8-naphthalimide (NA(NO2)-ATPA), were designed and synthesized using triphenylamine (TPA) as the electron donor and 1,8-naphthalene dianhydride containing different electron-withdrawing moieties (-H,-CN,-NO2) as the electron acceptor. The photophysical properties and electrochemical characteristics of the compounds were investigated by ultraviolet-visible spectroscopy (UV-Vis), fluorescence spectroscopy (FL) and cyclic voltammetry (CyV). The synthesized products were applied as the active layer in sandwich devices, whose memory characteristics were tested. NA-ATPA shows volatile static random access memory (SRAM) behavior, while NACN-ATPA and NANO2-ATPA show nonvolatile flash and write-once read-many times memory (WORM) behavior, respectively. Experimental results indicated that the synthesized compounds possessed small energy gaps and wide absorption ranges. The introduction of electron-withdrawing groups on the 4-position of the 1,8-naphthalimides reduced the LUMO energy level and the energy gap, leading to improved stability of the charge-transfer state and volatile-to-nonvolatile memory transfer. To elucidate the switching mechanism, molecular simulation results, including molecular orbitals, energy levels, optimized geometries, and Mulliken charge populations, were discussed.
2017, 33(11): 2237-2244
doi: 10.3866/PKU.WHXB201705231
Abstract:
Development of electrocatalysts is one of the challenges in the development of the lithium-oxygen battery, especially the synthesis of catalysts with special pore structures and excellent bifunctional catalytic performance for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). In this article, a reduced graphene oxide-LaFeO3 (RGO-LaFeO3) nanocomposite electrocatalyst was synthesized by combining sol-gel and hydrothermal methods and using graphene oxide, lanthanum nitrate, ferric nitrate, and citric acid as raw materials. The prepared samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and scanning electron microscopy. The results confirmed that the RGO-LaFeO3 was composed of pure phase LaFeO3 with a perovskite structure and RGO and that the LaFeO3 nanoparticles were loaded uniformly on the RGO layer surface. In comparison with a LaFeO3 nanoparticle (NP-LaFeO3) catalyst, RGO-LaFeO3 exhibited superior activity for both the ORR and the OER when it served as the cathode of a lithium-oxygen battery. The higher catalytic activity of the RGO-LaFeO3 is attributed to the synergistic effect of the special three-dimensional electronic conductive structure of RGO and the intrinsic catalytic property of LaFeO3. It was shown that the lithium-oxygen battery with the RGO-LaFeO3 cathode can be cycled stably up to 36 reversible cycles under conditions of a limit discharge depth of 1000 mAh·g-1 and a 100 mA·g-1 current density for charge-discharge. The study illustrates that the RGO-LaFeO3 bifunctional electrocatalyst is a promising candidate for the cathode in lithium-oxygen batteries.
Development of electrocatalysts is one of the challenges in the development of the lithium-oxygen battery, especially the synthesis of catalysts with special pore structures and excellent bifunctional catalytic performance for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). In this article, a reduced graphene oxide-LaFeO3 (RGO-LaFeO3) nanocomposite electrocatalyst was synthesized by combining sol-gel and hydrothermal methods and using graphene oxide, lanthanum nitrate, ferric nitrate, and citric acid as raw materials. The prepared samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and scanning electron microscopy. The results confirmed that the RGO-LaFeO3 was composed of pure phase LaFeO3 with a perovskite structure and RGO and that the LaFeO3 nanoparticles were loaded uniformly on the RGO layer surface. In comparison with a LaFeO3 nanoparticle (NP-LaFeO3) catalyst, RGO-LaFeO3 exhibited superior activity for both the ORR and the OER when it served as the cathode of a lithium-oxygen battery. The higher catalytic activity of the RGO-LaFeO3 is attributed to the synergistic effect of the special three-dimensional electronic conductive structure of RGO and the intrinsic catalytic property of LaFeO3. It was shown that the lithium-oxygen battery with the RGO-LaFeO3 cathode can be cycled stably up to 36 reversible cycles under conditions of a limit discharge depth of 1000 mAh·g-1 and a 100 mA·g-1 current density for charge-discharge. The study illustrates that the RGO-LaFeO3 bifunctional electrocatalyst is a promising candidate for the cathode in lithium-oxygen batteries.
2017, 33(11): 2245-2252
doi: 10.3866/PKU.WHXB201705241
Abstract:
Recently, preparation of carbon materials using biomass as precursors has received much attention owning to their merits of low cost, abundance, renewability, and environmental benignity. In this study, honeycomb-like porous gelatin was synthesized and subsequently used as the precursor to prepare activated carbon through carbonization followed by activation. The prepared activated carbon had a higher specific surface area (up to 3692 m2·g-1) and supercapacitor performance than that of activated carbon derived from commercial gelatin. In a 6 mol·L-1 KOH solution, the activated carbon prepared from porous gelatin through 600℃ carbonization and 700℃ activation delivered high specific capacitances of 357 and 227 F·g-1 at current densities of 1 and 100 A·g-1, respectively. In addition, after 7500 charge/discharge cycles at a current density of 10 A·g-1, it showed 93.0% retention of the initial capacitance, demonstrating excellent cycling stability. Moreover, a symmetric supercapacitor was assembled, which delivered an energy density of 10.3, 9.7, and 8.2 Wh·kg-1 at power densities of 250, 2500, and 25000 W·kg-1, respectively. Furthermore, a capacity retention as high as 97.6% was achieved after 10000 cycles at 10 A·g-1 using this symmetric supercapacitor. This work has demonstrated that the activated carbon derived from honeycomb-like porous gelatin has great potential for application in high-performance supercapacitors.
Recently, preparation of carbon materials using biomass as precursors has received much attention owning to their merits of low cost, abundance, renewability, and environmental benignity. In this study, honeycomb-like porous gelatin was synthesized and subsequently used as the precursor to prepare activated carbon through carbonization followed by activation. The prepared activated carbon had a higher specific surface area (up to 3692 m2·g-1) and supercapacitor performance than that of activated carbon derived from commercial gelatin. In a 6 mol·L-1 KOH solution, the activated carbon prepared from porous gelatin through 600℃ carbonization and 700℃ activation delivered high specific capacitances of 357 and 227 F·g-1 at current densities of 1 and 100 A·g-1, respectively. In addition, after 7500 charge/discharge cycles at a current density of 10 A·g-1, it showed 93.0% retention of the initial capacitance, demonstrating excellent cycling stability. Moreover, a symmetric supercapacitor was assembled, which delivered an energy density of 10.3, 9.7, and 8.2 Wh·kg-1 at power densities of 250, 2500, and 25000 W·kg-1, respectively. Furthermore, a capacity retention as high as 97.6% was achieved after 10000 cycles at 10 A·g-1 using this symmetric supercapacitor. This work has demonstrated that the activated carbon derived from honeycomb-like porous gelatin has great potential for application in high-performance supercapacitors.
2017, 33(11): 2253-2260
doi: 10.3866/PKU.WHXB201705292
Abstract:
In this work, the effect of different phenolic substituents on the electrochemical oxidation of phenols on a boron doped diamond (BDD) electrode was investigated. The specific relationship between the position and type of substituent and the electrochemical oxidation activity on the BDD electrode was systematically studied by employing Chemical Oxygen Demand and concentration variation. Electrochemical mineralization of hydroquinone was conducted on electrodes with different oxygen evolution potentials. It was found that there exists an important relationship between the electrochemical activity and the ability to generate hydroxyl radicals. A high activity was achieved on the BDD electrode owing to its higher electro-generation ability for hydroxyl radicals. The mineralization of substituted phenols is indirectly conducted by the hydroxyl radicals and the divorce of the substituent group is the rate determining step for the mineralization process. Meanwhile, the electrochemical mineralization rate towards substituted phenol contaminants is limited by the electronic effects of the substituents. The mineralization rate increases with increasing electron donating ability of the substituent. A linear relationship is found to exist between the reaction rate and the Hammett constant during degradation of substituted phenols.
In this work, the effect of different phenolic substituents on the electrochemical oxidation of phenols on a boron doped diamond (BDD) electrode was investigated. The specific relationship between the position and type of substituent and the electrochemical oxidation activity on the BDD electrode was systematically studied by employing Chemical Oxygen Demand and concentration variation. Electrochemical mineralization of hydroquinone was conducted on electrodes with different oxygen evolution potentials. It was found that there exists an important relationship between the electrochemical activity and the ability to generate hydroxyl radicals. A high activity was achieved on the BDD electrode owing to its higher electro-generation ability for hydroxyl radicals. The mineralization of substituted phenols is indirectly conducted by the hydroxyl radicals and the divorce of the substituent group is the rate determining step for the mineralization process. Meanwhile, the electrochemical mineralization rate towards substituted phenol contaminants is limited by the electronic effects of the substituents. The mineralization rate increases with increasing electron donating ability of the substituent. A linear relationship is found to exist between the reaction rate and the Hammett constant during degradation of substituted phenols.
2017, 33(11): 2261-2267
doi: 10.3866/PKU.WHXB201705293
Abstract:
Li3V2(PO4)3/C (LVP/C) cathode materials were successfully prepared by a rheological phase method using alginic acid as the carbon source. The X-ray diffraction (XRD) patterns demonstrate that all the samples contain pure LVP with the same monoclinic structure. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show that LVP/C materials have a uniform particle size. The LVP/C sample with 10% (w) alginic acid shows the best cycling stability. It delivers a discharge capacity of 117.5 mAh·g-1 (3.0-4.3 V), which can be maintained at 116.5 mAh·g-1 after 50 cycles at a rate of 0.1C. Its capacity retentions of 99.1% (3.0-4.3 V) and 76.8% (3.0-4.8 V) after 50 cycles are prominently higher than those of pristine Li3V2(PO4)3, which are 89.7% (3.0-4.3 V) and 62.39% (3.0-4.8 V). These outstanding electrochemical performances are mainly attributed to the alginic acid-based carbon coating, which can increase the electronic conductivity of materials and buffer the mechanical damage of the active materials during the Li ion insertion/extraction process, thus improving the electrochemical performance of the LVP/C samples.
Li3V2(PO4)3/C (LVP/C) cathode materials were successfully prepared by a rheological phase method using alginic acid as the carbon source. The X-ray diffraction (XRD) patterns demonstrate that all the samples contain pure LVP with the same monoclinic structure. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show that LVP/C materials have a uniform particle size. The LVP/C sample with 10% (w) alginic acid shows the best cycling stability. It delivers a discharge capacity of 117.5 mAh·g-1 (3.0-4.3 V), which can be maintained at 116.5 mAh·g-1 after 50 cycles at a rate of 0.1C. Its capacity retentions of 99.1% (3.0-4.3 V) and 76.8% (3.0-4.8 V) after 50 cycles are prominently higher than those of pristine Li3V2(PO4)3, which are 89.7% (3.0-4.3 V) and 62.39% (3.0-4.8 V). These outstanding electrochemical performances are mainly attributed to the alginic acid-based carbon coating, which can increase the electronic conductivity of materials and buffer the mechanical damage of the active materials during the Li ion insertion/extraction process, thus improving the electrochemical performance of the LVP/C samples.
2017, 33(11): 2268-2276
doi: 10.3866/PKU.WHXB201705252
Abstract:
A series of multi-branched dithienylpyrrole (SNS) monomers with rigid phenyl (PhSNS) and biphenyl rings (BPhSNS) as bridges were designed and synthesized, and were fabricated to form cross-linked polymers (pPhSNS, pBPhSNS) by electrochemical polymerization. Cyclic voltammetry (CV) results showed that PhSNS and BPhSNS exhibited similar oxidative properties except for one new higher-potential oxidative peak appearing in the curves of PhSNS. Theoretical calculations indicated that it should be attributed to the different steric configuration between the two dithienylpyrrole (SNS) units in PhSNS. One SNS unit possessed a larger twist angle (40.2°) between thiophene and pyrrole rings than the other one (21.2°), which indicated that PhSNS possessed a relatively larger energy gap (~0.4 eV) between HOMO-1 and HOMO than BPhSNS, for which HOMO and HOMO-1 levels were of almost the same energy. However, both PhSNS and BPhSNS showed similar onset oxidation potentials. The CV curves of pPhSNS and pBPhSNS showed that they presented similar oxidative properties, which enabled their corresponding electrochemical polymers to exhibit similar electrochromic properties. The UV-vis spectra of the corresponding polymers showed that both pPhSNS and pBPhSNS possessed similar optical absorption and similar multicolor switching between yellow (-0.8 V), greyish-green (0.9 V) and gray (1.1 V) colors. Besides, pPhSNS and pBPhSNS showed fast switching times of 0.57 s and 0.93 s at 1100 nm, respectively and reasonable contrasts of 46% and 31% at 1100 nm, respectively. These investigations may help understand the relationship between structural configuration and the electrochemistry/electrochromic properties for polymer electrochromic (PEC) materials research.
A series of multi-branched dithienylpyrrole (SNS) monomers with rigid phenyl (PhSNS) and biphenyl rings (BPhSNS) as bridges were designed and synthesized, and were fabricated to form cross-linked polymers (pPhSNS, pBPhSNS) by electrochemical polymerization. Cyclic voltammetry (CV) results showed that PhSNS and BPhSNS exhibited similar oxidative properties except for one new higher-potential oxidative peak appearing in the curves of PhSNS. Theoretical calculations indicated that it should be attributed to the different steric configuration between the two dithienylpyrrole (SNS) units in PhSNS. One SNS unit possessed a larger twist angle (40.2°) between thiophene and pyrrole rings than the other one (21.2°), which indicated that PhSNS possessed a relatively larger energy gap (~0.4 eV) between HOMO-1 and HOMO than BPhSNS, for which HOMO and HOMO-1 levels were of almost the same energy. However, both PhSNS and BPhSNS showed similar onset oxidation potentials. The CV curves of pPhSNS and pBPhSNS showed that they presented similar oxidative properties, which enabled their corresponding electrochemical polymers to exhibit similar electrochromic properties. The UV-vis spectra of the corresponding polymers showed that both pPhSNS and pBPhSNS possessed similar optical absorption and similar multicolor switching between yellow (-0.8 V), greyish-green (0.9 V) and gray (1.1 V) colors. Besides, pPhSNS and pBPhSNS showed fast switching times of 0.57 s and 0.93 s at 1100 nm, respectively and reasonable contrasts of 46% and 31% at 1100 nm, respectively. These investigations may help understand the relationship between structural configuration and the electrochemistry/electrochromic properties for polymer electrochromic (PEC) materials research.
2017, 33(11): 2277-2283
doi: 10.3866/PKU.WHXB201705251
Abstract:
Shape-selective catalysts for alkylation of biphenyl with cyclohexanol were prepared by modification of MCM-22 zeolite using chemical liquid deposition (CLD) process with tetraethyl orthosilicate (TEOS). The modified MCM-22 catalysts were characterized by X-ray diffraction (XRD), N2 physical adsorption-desorption, NH3 temperature-programmed desorption (NH3-TPD), and adsorbed pyridine infrared spectroscopy (Py-IR). The results showed that SiO2 was mainly deposited on the external zeolite surfaces, with no significant structural changes observed in the MCM-22 zeolite after modification. The deposited SiO2 could reduce the number of external Brønsted acid sites of the zeolites, without noticeably reducing the total amount of acid sites. Shape-selective alkylation of biphenyl with cyclohexanol was carried out over the synthesized catalysts. The selectivity of 4-cyclohexylbiphenyl (4-CBP) and 4,4'-cyclohexylbiphenyl (4,4'-DCBP) reached a maximum of 80.4% and 63.7%, respectively, when the reaction was carried out for 200 min at 190℃ under atmospheric pressure. The characterization data indicated that the isomerization reactions at the external Brønsted acid sites were diminished effectively. In addition, the catalytic activity of the used zeolites was almost recovered by calcination.
Shape-selective catalysts for alkylation of biphenyl with cyclohexanol were prepared by modification of MCM-22 zeolite using chemical liquid deposition (CLD) process with tetraethyl orthosilicate (TEOS). The modified MCM-22 catalysts were characterized by X-ray diffraction (XRD), N2 physical adsorption-desorption, NH3 temperature-programmed desorption (NH3-TPD), and adsorbed pyridine infrared spectroscopy (Py-IR). The results showed that SiO2 was mainly deposited on the external zeolite surfaces, with no significant structural changes observed in the MCM-22 zeolite after modification. The deposited SiO2 could reduce the number of external Brønsted acid sites of the zeolites, without noticeably reducing the total amount of acid sites. Shape-selective alkylation of biphenyl with cyclohexanol was carried out over the synthesized catalysts. The selectivity of 4-cyclohexylbiphenyl (4-CBP) and 4,4'-cyclohexylbiphenyl (4,4'-DCBP) reached a maximum of 80.4% and 63.7%, respectively, when the reaction was carried out for 200 min at 190℃ under atmospheric pressure. The characterization data indicated that the isomerization reactions at the external Brønsted acid sites were diminished effectively. In addition, the catalytic activity of the used zeolites was almost recovered by calcination.
2017, 33(11): 2284-2292
doi: 10.3866/PKU.WHXB201705184
Abstract:
A special ZnO/graphene composite with an ink slab-like shape was synthesized by a facile one-step solution method. The morphology of the ink slab-like ZnO/graphene composites produced under different reaction conditions was studied by scanning electron microscopy (SEM), field emission SEM (FESEM), and high resolution transmission electron microscopy (HRTEM). The photocatalytic properties of the products obtained under different reaction conditions were evaluated to determine the effect of reaction conditions and morphology. Photoluminescence (PL) and UV-visible spectra were measured to study the recombination of electron-hole pairs and absorption of UV-visible light. The results showed that the growth process of the ink slab-like ZnO involves the ‘corrosion mechanism’. The combination of graphene greatly enhanced the photocatalytic performance by enhancing light absorption, decreasing the band gap, and reducing the recombination probability of electron-hole pairs. Moreover, the bottom of the ink slab-like ZnO with a rough surface can greatly increase the reaction area. The extremely thin bottom of the ink slab offers a considerable build-in internal electric field that accelerates the separation of electron-hole pairs, thus decreasing the recombination probability and enhancing the photocatalytic performance.
A special ZnO/graphene composite with an ink slab-like shape was synthesized by a facile one-step solution method. The morphology of the ink slab-like ZnO/graphene composites produced under different reaction conditions was studied by scanning electron microscopy (SEM), field emission SEM (FESEM), and high resolution transmission electron microscopy (HRTEM). The photocatalytic properties of the products obtained under different reaction conditions were evaluated to determine the effect of reaction conditions and morphology. Photoluminescence (PL) and UV-visible spectra were measured to study the recombination of electron-hole pairs and absorption of UV-visible light. The results showed that the growth process of the ink slab-like ZnO involves the ‘corrosion mechanism’. The combination of graphene greatly enhanced the photocatalytic performance by enhancing light absorption, decreasing the band gap, and reducing the recombination probability of electron-hole pairs. Moreover, the bottom of the ink slab-like ZnO with a rough surface can greatly increase the reaction area. The extremely thin bottom of the ink slab offers a considerable build-in internal electric field that accelerates the separation of electron-hole pairs, thus decreasing the recombination probability and enhancing the photocatalytic performance.
2017, 33(11): 2293-2300
doi: 10.3866/PKU.WHXB201705294
Abstract:
Acquiring the spatial distribution of Li and the valence state of transition metals (TMs) in lithium ion battery (LIB) electrode materials is critical for understanding their electrochemical performances. Electron energy loss spectrum (EELS) is in principle optimum for analyzing light elements; however, quantitative analysis of Li, the lightest solid element in the periodic table, using EELS remains challenging. This is not only because of the overlap of the Li-K edge and the M23 edge of TMs but also due to the normally large particle sizes of LIB electrode materials (hundreds of nm), leading to significant plural scattering effect in the EELS spectra. Using LiNi0.5Mn1.5O4 (LNMO) as the cathode material, we obtained the spatial distribution of Li, Ni, and Mn by dual EELS spectral imaging, which allows us to simultaneously acquire the zero loss and core loss spectra, thus eliminating both the energy drift and plural scattering effects. Our results reveal that the as-prepared LNMO particles have a Mn/Ni-enriched and Li-poor surface layer of thickness 1-2 nm, and the valence of Mn gradually changed from +4 in the bulk to +2 in the surface layer. Given that the low-valent Mn2+ dissolution is a critical reason for structure damage and capacity degradation of LNMO, our results indicate that rational synthesis of LNMO with decreased low-valent Mn2+ content could be a previously neglected approach to enhance their electrochemical performance.
Acquiring the spatial distribution of Li and the valence state of transition metals (TMs) in lithium ion battery (LIB) electrode materials is critical for understanding their electrochemical performances. Electron energy loss spectrum (EELS) is in principle optimum for analyzing light elements; however, quantitative analysis of Li, the lightest solid element in the periodic table, using EELS remains challenging. This is not only because of the overlap of the Li-K edge and the M23 edge of TMs but also due to the normally large particle sizes of LIB electrode materials (hundreds of nm), leading to significant plural scattering effect in the EELS spectra. Using LiNi0.5Mn1.5O4 (LNMO) as the cathode material, we obtained the spatial distribution of Li, Ni, and Mn by dual EELS spectral imaging, which allows us to simultaneously acquire the zero loss and core loss spectra, thus eliminating both the energy drift and plural scattering effects. Our results reveal that the as-prepared LNMO particles have a Mn/Ni-enriched and Li-poor surface layer of thickness 1-2 nm, and the valence of Mn gradually changed from +4 in the bulk to +2 in the surface layer. Given that the low-valent Mn2+ dissolution is a critical reason for structure damage and capacity degradation of LNMO, our results indicate that rational synthesis of LNMO with decreased low-valent Mn2+ content could be a previously neglected approach to enhance their electrochemical performance.
2017, 33(11): 2301-2309
doi: 10.3866/PKU.WHXB201705261
Abstract:
Supported MoFe/X (X=SnO2, ZrO2, CeO2, TiO2, CNTs (Carbon nano-tubes)), MgO and MoFe oxide catalysts were prepared for use in the catalytic conversion of glycerol to allyl alcohol. The prepared catalysts were characterized by XRD, BET, XPS, H2-TPR, and NH3-TPD. The results showed that Fe and Mo oxides with high chemical value (Fe3+ and Mo6+) predominated in MoFe/X MoFe oxide catalysts, which exhibited only weakly acidic properties. The applied supports with different physicochemical characteristics showed distinct interactions with Mo and Fe oxides, modifying the concentration of surface weak acid site, acid strength, and reducibility of MoFe/X oxide catalysts. The catalysts, based on their catalytic performance for glycerol conversion to allyl alcohol, can be ranked in terms of allyl alcohol yield as MoFe/TiO2 > MoFe/CeO2 > MoFe/ZrO2 > MoFe/CNTs >> MoFe/SnO2 > MoFe >> MoFe/MgO. Over the MoFe/TiO2, a maximum allyl alcohol yield of 22.3% was from glycerol conversion of 83.4%, which had a selectivity of 26.7%. The MoFe/TiO2 also showed higher catalytic stability than the MoFe/CeO2, MoFe/ZrO2, and MoFe/CNTs oxide catalysts. The glycerol conversion showed positive relationship with the surface weak acid concentration of MoFe and MoFe/X catalysts, while the allyl alcohol was produced over the redox sites (non-acid sites) of catalysts. With increasing reaction temperature, the glycerol conversion increased, while the allyl alcohol selectivity decreased, over the MoFe/X oxide catalysts.
Supported MoFe/X (X=SnO2, ZrO2, CeO2, TiO2, CNTs (Carbon nano-tubes)), MgO and MoFe oxide catalysts were prepared for use in the catalytic conversion of glycerol to allyl alcohol. The prepared catalysts were characterized by XRD, BET, XPS, H2-TPR, and NH3-TPD. The results showed that Fe and Mo oxides with high chemical value (Fe3+ and Mo6+) predominated in MoFe/X MoFe oxide catalysts, which exhibited only weakly acidic properties. The applied supports with different physicochemical characteristics showed distinct interactions with Mo and Fe oxides, modifying the concentration of surface weak acid site, acid strength, and reducibility of MoFe/X oxide catalysts. The catalysts, based on their catalytic performance for glycerol conversion to allyl alcohol, can be ranked in terms of allyl alcohol yield as MoFe/TiO2 > MoFe/CeO2 > MoFe/ZrO2 > MoFe/CNTs >> MoFe/SnO2 > MoFe >> MoFe/MgO. Over the MoFe/TiO2, a maximum allyl alcohol yield of 22.3% was from glycerol conversion of 83.4%, which had a selectivity of 26.7%. The MoFe/TiO2 also showed higher catalytic stability than the MoFe/CeO2, MoFe/ZrO2, and MoFe/CNTs oxide catalysts. The glycerol conversion showed positive relationship with the surface weak acid concentration of MoFe and MoFe/X catalysts, while the allyl alcohol was produced over the redox sites (non-acid sites) of catalysts. With increasing reaction temperature, the glycerol conversion increased, while the allyl alcohol selectivity decreased, over the MoFe/X oxide catalysts.
2017, 33(11): 2310-2316
doi: 10.3866/PKU.WHXB201706093
Abstract:
Monodisperse Fe3O4 microspheres with tunable diameters and high magnetic saturation were synthesized by a solvothermal reduction method. It was found that the morphology and structure of the Fe3O4 microspheres could be tuned by simply altering the amount of the reactants such as ferric chloride, sodium acetate, water, and the reaction time. The Fe3O4 microspheres obtained via this method possessed high purity, crystallinity, and a nearly spherical shape. Furthermore, they were monodispersed and no aggregation was found. Such monodisperse Fe3O4 microspheres had tunable diameters of 400-700 nm and the fabrication time was only 2-4 h. The products showed high magnetic saturation values, and their yields were typically more than 94%.
Monodisperse Fe3O4 microspheres with tunable diameters and high magnetic saturation were synthesized by a solvothermal reduction method. It was found that the morphology and structure of the Fe3O4 microspheres could be tuned by simply altering the amount of the reactants such as ferric chloride, sodium acetate, water, and the reaction time. The Fe3O4 microspheres obtained via this method possessed high purity, crystallinity, and a nearly spherical shape. Furthermore, they were monodispersed and no aggregation was found. Such monodisperse Fe3O4 microspheres had tunable diameters of 400-700 nm and the fabrication time was only 2-4 h. The products showed high magnetic saturation values, and their yields were typically more than 94%.
