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2017 Volume 33 Issue 5
2017, 33(5):
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2017, 33(5): 853-854
doi: 10.3866/PKU.WHXB201703171
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2017, 33(5): 855-856
doi: 10.3866/PKU.WHXB201703203
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2017, 33(5): 857-858
doi: 10.3866/PKU.WHXB201703172
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2017, 33(5): 859-860
doi: 10.3866/PKU.WHXB201703141
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2017, 33(5): 861-862
doi: 10.3866/PKU.WHXB201703201
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2017, 33(5): 863-864
doi: 10.3866/PKU.WHXB201703202
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2017, 33(5): 865-866
doi: 10.3866/PKU.WHXB201703231
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2017, 33(5): 869-885
doi: 10.3866/PKU.WHXB201702088
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Hydrogen produced from electrochemical water-splitting driven by renewable resource-derived electricity is considered a promising candidate for clean energy. However, sustainable hydrogen production from water splitting requires highly active catalysts to make the process efficient. Catalysts based on graphene-like two-dimensional (2D) materials present great potential in the hydrogen evolution reaction (HER) and thus gain attention. In this review, which is a combination of our recent works, we highlight research efforts towards electrocatalysts for the HER based on 2D materials including transition metal disulfides, MXenes, and boron monolayers. Finally, we summarize the challenges and prospects for future development of electrocatalysts for the hydrogen evolution reaction.
Hydrogen produced from electrochemical water-splitting driven by renewable resource-derived electricity is considered a promising candidate for clean energy. However, sustainable hydrogen production from water splitting requires highly active catalysts to make the process efficient. Catalysts based on graphene-like two-dimensional (2D) materials present great potential in the hydrogen evolution reaction (HER) and thus gain attention. In this review, which is a combination of our recent works, we highlight research efforts towards electrocatalysts for the HER based on 2D materials including transition metal disulfides, MXenes, and boron monolayers. Finally, we summarize the challenges and prospects for future development of electrocatalysts for the hydrogen evolution reaction.
2017, 33(5): 886-902
doi: 10.3866/PKU.WHXB201702092
Abstract:
Non-precious metal catalysts should be studied to substitute precious Pt catalysts. Recent developments of non-precious-metal catalysts (combined with the achievements of our group) are summarized in this paper. The main issues that exist in the transition metal oxides, metal-nitrogen-carbon material, and heteroatom-doped carbon material are highlighted from the aspects of the synthetic methods and mechanisms. The research tendency and perspective of these non-precious metal catalysts are provided.
Non-precious metal catalysts should be studied to substitute precious Pt catalysts. Recent developments of non-precious-metal catalysts (combined with the achievements of our group) are summarized in this paper. The main issues that exist in the transition metal oxides, metal-nitrogen-carbon material, and heteroatom-doped carbon material are highlighted from the aspects of the synthetic methods and mechanisms. The research tendency and perspective of these non-precious metal catalysts are provided.
2017, 33(5): 903-917
doi: 10.3866/PKU.WHXB201702091
Abstract:
Nitric oxide (NO)—an endogenous diatomic molecule—plays key roles in various physiological and pathological processes, including smooth muscle relaxation in blood vessels, immune response, neurotransmission, respiration, and cell apoptosis. The biological functions of this molecule greatly depend on the location, timing, and dosage at which it is released. It is important to develop NO-delivery platforms capable of holding NO stably during storage and subsequently release optimal amounts of NO spatiotemporally at the desired location and time. In this review, recent advancements in the preparation of new exogenous NO donors including diazeniumdiolates, S-nitrosothiols, nitrobenzene, and metal-nitrosyl complexes are discussed. The integration of these NO donors with various nanoplatforms for controlled NO delivery and their potential applications in the biomedical field are highlighted.
Nitric oxide (NO)—an endogenous diatomic molecule—plays key roles in various physiological and pathological processes, including smooth muscle relaxation in blood vessels, immune response, neurotransmission, respiration, and cell apoptosis. The biological functions of this molecule greatly depend on the location, timing, and dosage at which it is released. It is important to develop NO-delivery platforms capable of holding NO stably during storage and subsequently release optimal amounts of NO spatiotemporally at the desired location and time. In this review, recent advancements in the preparation of new exogenous NO donors including diazeniumdiolates, S-nitrosothiols, nitrobenzene, and metal-nitrosyl complexes are discussed. The integration of these NO donors with various nanoplatforms for controlled NO delivery and their potential applications in the biomedical field are highlighted.
2017, 33(5): 918-926
doi: 10.3866/PKU.WHXB201701163
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The purpose of this paper is to present a novel way to building quantitative structure-propertyrelationship (QSPR) models for predicting the gas-to-benzene solvation enthalpy (ΔHSolv) of 158 organiccompounds based on molecular descriptors calculated from the structure alone. Different kinds of descriptorswere calculated for each compounds using dragon package. The variable selection technique of enhancedreplacement method (ERM) was employed to select optimal subset of descriptors. Our investigation revealsthat the dependence of physico-chemical properties on solvation enthalpy is a nonlinear observable fact andthat ERM method is unable to model the solvation enthalpy accurately. The standard error value of predictionset for support vector machine (SVM) is 1.681 kJ·mol-1 while it is 4.624 kJ·mol-1 for ERM. The resultsestablished that the calculated ΔHSolv values by SVM were in good agreement with the experimental ones, andthe performances of the SVM models were superior to those obtained by ERM one. This indicates that SVMcan be used as an alternative modeling tool for QSPR studies.
The purpose of this paper is to present a novel way to building quantitative structure-propertyrelationship (QSPR) models for predicting the gas-to-benzene solvation enthalpy (ΔHSolv) of 158 organiccompounds based on molecular descriptors calculated from the structure alone. Different kinds of descriptorswere calculated for each compounds using dragon package. The variable selection technique of enhancedreplacement method (ERM) was employed to select optimal subset of descriptors. Our investigation revealsthat the dependence of physico-chemical properties on solvation enthalpy is a nonlinear observable fact andthat ERM method is unable to model the solvation enthalpy accurately. The standard error value of predictionset for support vector machine (SVM) is 1.681 kJ·mol-1 while it is 4.624 kJ·mol-1 for ERM. The resultsestablished that the calculated ΔHSolv values by SVM were in good agreement with the experimental ones, andthe performances of the SVM models were superior to those obtained by ERM one. This indicates that SVMcan be used as an alternative modeling tool for QSPR studies.
2017, 33(5): 927-940
doi: 10.3866/PKU.WHXB201702211
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In this paper, based on the complex protein structure of third dopamine receptor (D3R) with dopamine (DOP), we have studied the trajectories with the free energy changes of D3R for DOP to move along its molecular channels and then probed the molecular dynamics mechanism of DOP transmitting along molecular channels, using molecular dynamics techniques including the potential mean force (PMF) of umbrella samplings from the GROMACS program (version 4.5). Simulation results show that for DOP located in the space region of D3R to act as a neurotransmitter transmitting toward the outside of cell, the free energy change is 134.6 kJ·mol-1 along the functional molecular channel of y+ axis within D3R, and 211.5 kJ·mol-1 along the y-axis towards the intracellular part. Within the structure of D3R, the free energy changes are 65.8, 245.0, 551.4, 172.8 kJ·mol-1 for DOP to transmit along the x+, x-, z+, z-axes, respectively, towards cell bilayer membrane, indicating that DOP leaves more easily along the x+ axis through the gap between TM5 (the fifth transmembrane helix) and TM6 (the sixth transmembrane helix) from the internal structure of D3R. When free DOP molecules are located in the intercellular spaces, once they start moving along the inverse y+ axis direction under constant pressure and temperature, they spontaneously pass through the functional molecular channel to reach the space region of D3R to act as a neurotransmitter, because the free energy change between DOP and D3R along the inverse y+ axis direction is negative (－134.6 kJ·mol-1). Therefore, DOP interacting with D3R can easily play the role of a neurotransmitter. After DOP molecules have performed the actions of a neurotransmitter, they leave the internal structure of D3R along the x+ axis of a protective molecular channel through the gap between TM5 and TM6 to avoid excessive function as transmitter. According to dopamine functional and protective molecular channels, we suggest new pathologies and the finding and development of new drugs for Parkinson's disease and schizophrenia.
In this paper, based on the complex protein structure of third dopamine receptor (D3R) with dopamine (DOP), we have studied the trajectories with the free energy changes of D3R for DOP to move along its molecular channels and then probed the molecular dynamics mechanism of DOP transmitting along molecular channels, using molecular dynamics techniques including the potential mean force (PMF) of umbrella samplings from the GROMACS program (version 4.5). Simulation results show that for DOP located in the space region of D3R to act as a neurotransmitter transmitting toward the outside of cell, the free energy change is 134.6 kJ·mol-1 along the functional molecular channel of y+ axis within D3R, and 211.5 kJ·mol-1 along the y-axis towards the intracellular part. Within the structure of D3R, the free energy changes are 65.8, 245.0, 551.4, 172.8 kJ·mol-1 for DOP to transmit along the x+, x-, z+, z-axes, respectively, towards cell bilayer membrane, indicating that DOP leaves more easily along the x+ axis through the gap between TM5 (the fifth transmembrane helix) and TM6 (the sixth transmembrane helix) from the internal structure of D3R. When free DOP molecules are located in the intercellular spaces, once they start moving along the inverse y+ axis direction under constant pressure and temperature, they spontaneously pass through the functional molecular channel to reach the space region of D3R to act as a neurotransmitter, because the free energy change between DOP and D3R along the inverse y+ axis direction is negative (－134.6 kJ·mol-1). Therefore, DOP interacting with D3R can easily play the role of a neurotransmitter. After DOP molecules have performed the actions of a neurotransmitter, they leave the internal structure of D3R along the x+ axis of a protective molecular channel through the gap between TM5 and TM6 to avoid excessive function as transmitter. According to dopamine functional and protective molecular channels, we suggest new pathologies and the finding and development of new drugs for Parkinson's disease and schizophrenia.
2017, 33(5): 941-948
doi: 10.3866/PKU.WHXB201702085
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In this study, the electronic structures and photocatalytic properties of Ag3XO4 (X = P, As, V) were investigated using the first principles based on the density functional theory. In comparison to Ag3PO4, Ag3VO4 shows better photocatalytic stability, mainly due to the enhanced Ag―O bonds and improved Ag ion stability, but poorer photocatalytic activity in the visible light region mainly due to the presence of d orbital character at the conduction band minimum (CBM) and lower valence band maximum (VBM) potentials (2.335 V, vs NHE). Ag3AsO4 shows photocatalytic activity superior to Ag3PO4, which may be attributed to the following reasons: (1) the highly dispersive band structure of the CBM resulting fromAg s-Ag s hybridization, (2) a smaller band gap of 1.91 eV, (3) the broader absorption range and higher absorption capacity of visible light. Moreover, our theoretical results demonstrate that though Ag3XO4 (X = P, As, V) species act as indirect band gap photocatalytic semiconductors, only Ag3VO4 is a potential candidate for the photocatalytic hydrogen generation from water. The calculated results mentioned above are in good agreement with experimental results.
In this study, the electronic structures and photocatalytic properties of Ag3XO4 (X = P, As, V) were investigated using the first principles based on the density functional theory. In comparison to Ag3PO4, Ag3VO4 shows better photocatalytic stability, mainly due to the enhanced Ag―O bonds and improved Ag ion stability, but poorer photocatalytic activity in the visible light region mainly due to the presence of d orbital character at the conduction band minimum (CBM) and lower valence band maximum (VBM) potentials (2.335 V, vs NHE). Ag3AsO4 shows photocatalytic activity superior to Ag3PO4, which may be attributed to the following reasons: (1) the highly dispersive band structure of the CBM resulting fromAg s-Ag s hybridization, (2) a smaller band gap of 1.91 eV, (3) the broader absorption range and higher absorption capacity of visible light. Moreover, our theoretical results demonstrate that though Ag3XO4 (X = P, As, V) species act as indirect band gap photocatalytic semiconductors, only Ag3VO4 is a potential candidate for the photocatalytic hydrogen generation from water. The calculated results mentioned above are in good agreement with experimental results.
2017, 33(5): 949-959
doi: 10.3866/PKU.WHXB201702152
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The slip and anisotropy of 2,4,6-triamino-1,3,5-trinitrobenzene (TATB) crystal under shock loading along various directions were investigated using molecular dynamics simulation combined with reactive force field (ReaxFF). The shock strength was approximately 10 GPa, and seven shock orientations normal to the (101), (111), (011), (110), (010), (100), and (001) crystal planes were considered. For these shock directions, the slip systems that are likely to be activated are predicted to be on the {001} plane, whereas others that could not be activated exhibit large shear stress barriers. These slip characteristics are consistent with the layered structure of TATB crystal along the c axis and the planar structure of TATB molecule. The most favorable slip systems are suggested to be (101)/{001}<100>, (111)/{001}<010>, (011)/{001}<010>, (110)/{001}<010>, (010)/{001} <110>, (100)/{001}<120>, and (001)/{001}<010>. TATB crystal exhibits anisotropic response to shock loading, that is, the shear stress, energy, temperature, and chemical reactivity during shear deformation depend on shock direction. For the (100) and (001) shock planes, the shear stress barrier is relatively high and lasts for a long time, leading to fast energy accumulation and temperature increment, which, in turn, increase the chemical reactivity. In contrast, for the (101) and (111) shock planes, the small shear stress barrier results in slow energy accumulation and temperature rise and, thus, low chemical reactivity. The (011), (110), and (010) shock planes exhibit intermediate responses. The sensitivity of the seven shock planes can be ranked as follows: (101), (111) < (011), (110), (010) < (100), (001). This study provides microscale insight into the response mechanisms and structure-property relationship of TATB crystal under dynamic loading and may facilitate designing explosives with high energy but low sensitivity.
The slip and anisotropy of 2,4,6-triamino-1,3,5-trinitrobenzene (TATB) crystal under shock loading along various directions were investigated using molecular dynamics simulation combined with reactive force field (ReaxFF). The shock strength was approximately 10 GPa, and seven shock orientations normal to the (101), (111), (011), (110), (010), (100), and (001) crystal planes were considered. For these shock directions, the slip systems that are likely to be activated are predicted to be on the {001} plane, whereas others that could not be activated exhibit large shear stress barriers. These slip characteristics are consistent with the layered structure of TATB crystal along the c axis and the planar structure of TATB molecule. The most favorable slip systems are suggested to be (101)/{001}<100>, (111)/{001}<010>, (011)/{001}<010>, (110)/{001}<010>, (010)/{001} <110>, (100)/{001}<120>, and (001)/{001}<010>. TATB crystal exhibits anisotropic response to shock loading, that is, the shear stress, energy, temperature, and chemical reactivity during shear deformation depend on shock direction. For the (100) and (001) shock planes, the shear stress barrier is relatively high and lasts for a long time, leading to fast energy accumulation and temperature increment, which, in turn, increase the chemical reactivity. In contrast, for the (101) and (111) shock planes, the small shear stress barrier results in slow energy accumulation and temperature rise and, thus, low chemical reactivity. The (011), (110), and (010) shock planes exhibit intermediate responses. The sensitivity of the seven shock planes can be ranked as follows: (101), (111) < (011), (110), (010) < (100), (001). This study provides microscale insight into the response mechanisms and structure-property relationship of TATB crystal under dynamic loading and may facilitate designing explosives with high energy but low sensitivity.
2017, 33(5): 960-967
doi: 10.3866/PKU.WHXB201702086
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The photoelectrochemical method was combined with the in-situ molecular imprinting technique. Using the chiral ibuprofen enantiomers (S-ibuprofen and R-ibuprofen) as template molecules, S-ibuprofen and R-ibuprofen molecular imprinting sites were constructed on the surface of monocrystalline TiO2 nanorods. The imprinted electrodes were capable of selective recognition and catalytic oxidation of S-ibuprofen and Ribuprofen. The morphology, structure, and composition of the electrode were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy. The electron transfer resistance of the electrode surface was studied with electrochemical impedance spectroscopy. The photoelectrochemical recognition and degradation were measured photoelectrochemically using the prepared imprinted electrodes as the working electrode. The TiO2 prepared was a single crystal nanorod array. The imprinted sites were successfully constructed on the surface of TiO2 nanorods and had shape selective adsorption capacities. The selective recognition and selective oxidative degradation of chiral ibuprofen enantiomers on the surface of artificial photoelectrocatalysts were realized for the first time.
The photoelectrochemical method was combined with the in-situ molecular imprinting technique. Using the chiral ibuprofen enantiomers (S-ibuprofen and R-ibuprofen) as template molecules, S-ibuprofen and R-ibuprofen molecular imprinting sites were constructed on the surface of monocrystalline TiO2 nanorods. The imprinted electrodes were capable of selective recognition and catalytic oxidation of S-ibuprofen and Ribuprofen. The morphology, structure, and composition of the electrode were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy. The electron transfer resistance of the electrode surface was studied with electrochemical impedance spectroscopy. The photoelectrochemical recognition and degradation were measured photoelectrochemically using the prepared imprinted electrodes as the working electrode. The TiO2 prepared was a single crystal nanorod array. The imprinted sites were successfully constructed on the surface of TiO2 nanorods and had shape selective adsorption capacities. The selective recognition and selective oxidative degradation of chiral ibuprofen enantiomers on the surface of artificial photoelectrocatalysts were realized for the first time.
2017, 33(5): 968-975
doi: 10.3866/PKU.WHXB201702093
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Biochar derived from reproducible massive biomasses presents the advantages of low cost and renewable resources. In this work aiming to solve the existing problems of the lithium-sulfur battery, sulfur@biochar (S@biochar) composite cathode materials with high capacity and good cycle performance were developed. Specifically, four kinds of biochar prepared from rice husk, miscanthus, fir, and pomelo peel were used as host matrices for the Li-S battery. Among them, the S@biochar derived from rice husk delivered the highest specific capacity and the best cycle stability according to electrochemical tests. To further optimize its performance, we prepared a highly porous rice husk derived biochar (HPRH-biochar) using silica gel as the template. The S@HPRH-biochar composite (60% (w, mass fraction) S) enables the homogeneous dispersion of amorphous sulfur in the carbon matrix and its porous structure could effectively suppress the dissolution of the polysulfide. As a result, its electrochemical performance improved, achieving a high initial charge capacity of 1534.1 mAh·g-1 and maintaining a high capacity of 738.7 mAh·g-1 after 100 cycles at 0.2C (1C corresponds to a current density of 1675 mA·g-1). It also gives a capacity of 485.3 mAh·g-1 at 2.0C in the rate capacity test.
Biochar derived from reproducible massive biomasses presents the advantages of low cost and renewable resources. In this work aiming to solve the existing problems of the lithium-sulfur battery, sulfur@biochar (S@biochar) composite cathode materials with high capacity and good cycle performance were developed. Specifically, four kinds of biochar prepared from rice husk, miscanthus, fir, and pomelo peel were used as host matrices for the Li-S battery. Among them, the S@biochar derived from rice husk delivered the highest specific capacity and the best cycle stability according to electrochemical tests. To further optimize its performance, we prepared a highly porous rice husk derived biochar (HPRH-biochar) using silica gel as the template. The S@HPRH-biochar composite (60% (w, mass fraction) S) enables the homogeneous dispersion of amorphous sulfur in the carbon matrix and its porous structure could effectively suppress the dissolution of the polysulfide. As a result, its electrochemical performance improved, achieving a high initial charge capacity of 1534.1 mAh·g-1 and maintaining a high capacity of 738.7 mAh·g-1 after 100 cycles at 0.2C (1C corresponds to a current density of 1675 mA·g-1). It also gives a capacity of 485.3 mAh·g-1 at 2.0C in the rate capacity test.
2017, 33(5): 976-983
doi: 10.3866/PKU.WHXB201702089
Abstract:
This work presents the correlation of the enzymatic activity of α-chymotrypsin (α-CT) with the thermodynamics of interaction between α-CT and the cationic gemini surfactant decanediyl-α,ω-bis (dodecyldimethylammonium bromide) (12-10-12). The enzymatic activity was assessed by the rate of 2-naphthyl acetate (2-NA) hydrolysis obtained from UV-Vis absorption spectra. The superactivity of α-CT in the catalytic hydrolysis of 2-NA was obtained by activation with 12-10-12 in a short incubation time; the activated α-CT showed faster denaturation kinetics. The larger superactivities appeared in a bell shape below the critical aggregation concentration (cac12-10-12,CT) of the mixed gemini/α-CT systems in buffered aqueous solution. The results obtained from the variation of the activity with the incubation time highlight that the protein incubated in 12-10-12 has a high catalysis activity and a weakened conformational stability. The mechanism of the superactivity of α-CT in the presence of 12-10-12 has been proposed by combining the results from isothermaltitration calorimetry (ITC), steady state fluorescence, and differential scanning calorimetry (DSC). The superactivity arises from perturbation of the internal structure of α-CT by an interaction between the positively charged 12-10-12 and α-CT, which makes the conformation of α-CT looser than the native one, in the balance of a weak interaction. Such a conformation is favorable for release of the acidic product of 2-NA hydrolysis, whereas it simultaneously leads to instability of the α-CT structure.
This work presents the correlation of the enzymatic activity of α-chymotrypsin (α-CT) with the thermodynamics of interaction between α-CT and the cationic gemini surfactant decanediyl-α,ω-bis (dodecyldimethylammonium bromide) (12-10-12). The enzymatic activity was assessed by the rate of 2-naphthyl acetate (2-NA) hydrolysis obtained from UV-Vis absorption spectra. The superactivity of α-CT in the catalytic hydrolysis of 2-NA was obtained by activation with 12-10-12 in a short incubation time; the activated α-CT showed faster denaturation kinetics. The larger superactivities appeared in a bell shape below the critical aggregation concentration (cac12-10-12,CT) of the mixed gemini/α-CT systems in buffered aqueous solution. The results obtained from the variation of the activity with the incubation time highlight that the protein incubated in 12-10-12 has a high catalysis activity and a weakened conformational stability. The mechanism of the superactivity of α-CT in the presence of 12-10-12 has been proposed by combining the results from isothermaltitration calorimetry (ITC), steady state fluorescence, and differential scanning calorimetry (DSC). The superactivity arises from perturbation of the internal structure of α-CT by an interaction between the positively charged 12-10-12 and α-CT, which makes the conformation of α-CT looser than the native one, in the balance of a weak interaction. Such a conformation is favorable for release of the acidic product of 2-NA hydrolysis, whereas it simultaneously leads to instability of the α-CT structure.
2017, 33(5): 984-992
doi: 10.3866/PKU.WHXB201702084
Abstract:
It is of significance to investigate the support effect in heterogeneous metal catalysts. Pt/Fe3O4, Pt/ γ-Fe2O3, and Pt/α-Fe2O3 nanocomposites with the same Pt nanoclusters were prepared by adsorbing Pt colloidal particles stabilized with simple ions and solvent molecules on different iron oxide supports. The catalytic performances over the as-prepared catalysts for the selective hydrogenation of o-chloronitrobenzene (o-CNB) in the absence of solvent were evaluated. It was found that the catalytic activity and selectivity over the prepared iron oxide-supported Pt nanocluster catalysts were higher than those of a commercial Pt/C catalyst. The selectivity towards o-chloroaniline over Pt/γ-Fe2O3 or Pt/α-Fe2O3 was higher than that over Pt/Fe3O4, while the catalytic activity over Pt/Fe3O4 was 50% higher than that over Pt/α-Fe2O3. The Pt/iron oxide catalysts also exhibited excellent catalytic properties for the solvent-free selective hydrogenation of other tested halonitrobenzenes, with the selectivity to corresponding haloanilines being > 99%. In addition, the influences of temperature and hydrogen pressure on the solvent-free selective hydrogenation of o-CNB over Pt/Fe3O4 were studied. This work is helpful in understanding the superior properties of iron oxide-supported metal nanocluster catalysts and provides a foundation for further developing highly efficient catalytic systems based on metal nanoclusters.
It is of significance to investigate the support effect in heterogeneous metal catalysts. Pt/Fe3O4, Pt/ γ-Fe2O3, and Pt/α-Fe2O3 nanocomposites with the same Pt nanoclusters were prepared by adsorbing Pt colloidal particles stabilized with simple ions and solvent molecules on different iron oxide supports. The catalytic performances over the as-prepared catalysts for the selective hydrogenation of o-chloronitrobenzene (o-CNB) in the absence of solvent were evaluated. It was found that the catalytic activity and selectivity over the prepared iron oxide-supported Pt nanocluster catalysts were higher than those of a commercial Pt/C catalyst. The selectivity towards o-chloroaniline over Pt/γ-Fe2O3 or Pt/α-Fe2O3 was higher than that over Pt/Fe3O4, while the catalytic activity over Pt/Fe3O4 was 50% higher than that over Pt/α-Fe2O3. The Pt/iron oxide catalysts also exhibited excellent catalytic properties for the solvent-free selective hydrogenation of other tested halonitrobenzenes, with the selectivity to corresponding haloanilines being > 99%. In addition, the influences of temperature and hydrogen pressure on the solvent-free selective hydrogenation of o-CNB over Pt/Fe3O4 were studied. This work is helpful in understanding the superior properties of iron oxide-supported metal nanocluster catalysts and provides a foundation for further developing highly efficient catalytic systems based on metal nanoclusters.
2017, 33(5): 993-1000
doi: 10.3866/PKU.WHXB201702087
Abstract:
Noble-metal-free CuMo nanoparticles (NPs) without surfactant or support have been facilely prepared using NaBH4 as a reducing agent. The as-prepared CuMo nanocatalysts were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) surface area measurements, and used as catalysts for the hydrolysis of ammonia borane (AB, NH3BH3) at room temperature. The as-synthesized Cu0.9Mo0.1 NPs exhibited a high activity towards the hydrolysis of AB with a turnover frequency (TOF) of 14.9 min-1, a higher value than that reported for Cu catalysts. Our synthesis is not limited to CuMo NPs alone, but can easily be extended to CuW (3.6 min-1), CuCr (2 min-1), NiMo (55.6 min-1), and CoMo (21.7 min-1) NPs, providing a general approach to Cu-M (M = Mo, W, Cr) and TM-Mo (TM = Cu, Ni, Co) NPs as a series of novel catalysts for the hydrolysis of AB. The enhanced activity of bimetallic NPs may be attributed to the synergistic effects of the Cu-M NPs induced by the strain and ligand effects.
Noble-metal-free CuMo nanoparticles (NPs) without surfactant or support have been facilely prepared using NaBH4 as a reducing agent. The as-prepared CuMo nanocatalysts were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) surface area measurements, and used as catalysts for the hydrolysis of ammonia borane (AB, NH3BH3) at room temperature. The as-synthesized Cu0.9Mo0.1 NPs exhibited a high activity towards the hydrolysis of AB with a turnover frequency (TOF) of 14.9 min-1, a higher value than that reported for Cu catalysts. Our synthesis is not limited to CuMo NPs alone, but can easily be extended to CuW (3.6 min-1), CuCr (2 min-1), NiMo (55.6 min-1), and CoMo (21.7 min-1) NPs, providing a general approach to Cu-M (M = Mo, W, Cr) and TM-Mo (TM = Cu, Ni, Co) NPs as a series of novel catalysts for the hydrolysis of AB. The enhanced activity of bimetallic NPs may be attributed to the synergistic effects of the Cu-M NPs induced by the strain and ligand effects.
2017, 33(5): 1001-1009
doi: 10.3866/PKU.WHXB201701131
Abstract:
A colorful surface plasmon resonance imaging sensor for the in-situ detection of benzopyrene (BaP) in water is presented in this paper. The sensor can provide intuitive image information and can also quantitatively analyze the concentration and adsorption/desorption processes of the analyte by combining the hue algorithm. Both the resonance wavelengths and resonance images for a bare gold film chip were obtained at different incident angles using a home-made surface plasmon resonance (SPR) sensor that possesses wavelengthinterrogating and imaging capabilities. The relationship between the resonance wavelength and the average hue of the color image was established based on the hue algorithm. From this relationship, the initial resonance wavelength at which the SPR sensor can provide optimal hue sensitivity was derived, which was ~650 nm. Polytetrafluoroethylene (PTFE)-coated SPR sensor chips were prepared for the in-situ rapid detection of BaP in water based on the reversible enrichment of BaP molecules in the PTFE film. The results showed that: (1) the average hue of the SPR color image decreases linearly as BaP concentration increases from 20 to 100 nmol·L-1; (2) both the response time and recovery times of the SPR sensor for 100 nmol·L-1 BaP are 7 and 5 s, respectively; (3) since the thickness of the PTFE filmis greater than the penetration depth of the surface plasmon field, the BaP detection is not affected by the refractive index of the solution sample; and (4) in the case of a non-uniform PTFE film, the sensor allows to determine the hue sensitivities for equal-thickness microscale areas of the sensing film. The experimental results show that this type of colorful SPR imaging sensor has widespread applicability for chemical and biological detection.
A colorful surface plasmon resonance imaging sensor for the in-situ detection of benzopyrene (BaP) in water is presented in this paper. The sensor can provide intuitive image information and can also quantitatively analyze the concentration and adsorption/desorption processes of the analyte by combining the hue algorithm. Both the resonance wavelengths and resonance images for a bare gold film chip were obtained at different incident angles using a home-made surface plasmon resonance (SPR) sensor that possesses wavelengthinterrogating and imaging capabilities. The relationship between the resonance wavelength and the average hue of the color image was established based on the hue algorithm. From this relationship, the initial resonance wavelength at which the SPR sensor can provide optimal hue sensitivity was derived, which was ~650 nm. Polytetrafluoroethylene (PTFE)-coated SPR sensor chips were prepared for the in-situ rapid detection of BaP in water based on the reversible enrichment of BaP molecules in the PTFE film. The results showed that: (1) the average hue of the SPR color image decreases linearly as BaP concentration increases from 20 to 100 nmol·L-1; (2) both the response time and recovery times of the SPR sensor for 100 nmol·L-1 BaP are 7 and 5 s, respectively; (3) since the thickness of the PTFE filmis greater than the penetration depth of the surface plasmon field, the BaP detection is not affected by the refractive index of the solution sample; and (4) in the case of a non-uniform PTFE film, the sensor allows to determine the hue sensitivities for equal-thickness microscale areas of the sensing film. The experimental results show that this type of colorful SPR imaging sensor has widespread applicability for chemical and biological detection.
2017, 33(5): 1010-1016
doi: 10.3866/PKU.WHXB201702102
Abstract:
Functional solid substrates modified by self-assembled monolayers (SAMs) have potential applications in biosensors, chromatography, and biocompatible materials. The potential-induced phase transition of N-isobutyryl-L-cysteine (L-NIBC) SAMs on Au(111) surfaces was investigated by in-situ electrochemical scanning tunneling microscopy (EC-STM) in 0.1 mol·L－1 H2SO4 solution. The NIBC SAMs with two distinct structures (α phase and β phase) can be prepared by immersing the Au(111) substrate in pure NIBC aqueous solution and NIBC solution controlled by phosphate buffer at pH 7, respectively. The as-prepared α phase and β phase of NIBC SAMs show various structural changes under the control of electrochemical potentials of the Au(111) in H2SO4 solution. The α phase NIBC SAMs exhibit structural changes from ordered to disordered structures with potential changes from 0.7 V (vs saturated calomel electrode, SCE) to 0.2 V. However, the β phase NIBC SAMs undergo structural changes from disordered structures (E < 0.3 V) to γ phase (0.4 V < E < 0.5 V) and finally to the β phase (0.5 V < E < 0.7 V). EC-STM images also indicate that the phase transition from the β phase NIBC SAMs to the α phase occurs at positive potential. Combined with density functional theory (DFT) calculations, the phase transition from the β phase to the α phase is explained by the potential-induced break of bonding interactions between ―COO－ and the negatively charged gold surfaces.
Functional solid substrates modified by self-assembled monolayers (SAMs) have potential applications in biosensors, chromatography, and biocompatible materials. The potential-induced phase transition of N-isobutyryl-L-cysteine (L-NIBC) SAMs on Au(111) surfaces was investigated by in-situ electrochemical scanning tunneling microscopy (EC-STM) in 0.1 mol·L－1 H2SO4 solution. The NIBC SAMs with two distinct structures (α phase and β phase) can be prepared by immersing the Au(111) substrate in pure NIBC aqueous solution and NIBC solution controlled by phosphate buffer at pH 7, respectively. The as-prepared α phase and β phase of NIBC SAMs show various structural changes under the control of electrochemical potentials of the Au(111) in H2SO4 solution. The α phase NIBC SAMs exhibit structural changes from ordered to disordered structures with potential changes from 0.7 V (vs saturated calomel electrode, SCE) to 0.2 V. However, the β phase NIBC SAMs undergo structural changes from disordered structures (E < 0.3 V) to γ phase (0.4 V < E < 0.5 V) and finally to the β phase (0.5 V < E < 0.7 V). EC-STM images also indicate that the phase transition from the β phase NIBC SAMs to the α phase occurs at positive potential. Combined with density functional theory (DFT) calculations, the phase transition from the β phase to the α phase is explained by the potential-induced break of bonding interactions between ―COO－ and the negatively charged gold surfaces.
2017, 33(5): 1017-1026
doi: 10.3866/PKU.WHXB201702082
Abstract:
A series of SiO2-supported fourth period transition metal catalysts (M/SiO2) was prepared by a wetness impregnation method for the dehydrochlorination of 1,1,2-trichloroethane (TCE) in the gas phase. Among these M/SiO2 catalysts, Zn/SiO2 had the best catalytic activity with the highest TCE conversion (~98%) and excellent selectivity for cis-1,2-dichloroethylene (82%). By increasing the zinc loading, the conversion of TCE using the Zn/SiO2 catalyst was gradually improved, in agreement with the total acidity in the Zn/SiO2 catalyst. Associating the specific activity and specific acidity of the Zn/SiO2 catalyst with different Zn loadings, it was found that higher specific acidity contributed to higher specific activity, indicating that the acid center of Zn/SiO2 was the catalytic active site for the dehydrochlorination of TCE. In the process of dehydrochlorination, the Zn/SiO2 catalyst could be deactivated, mainly due to coke deposition on the catalyst surface. Catalysts with low Zn loading had stronger acid sites, which resulted in more coke formation on the catalyst. The results showed that strong acid sites on the catalyst surface were responsible for the deposition of coke and deactivation of the catalyst.
A series of SiO2-supported fourth period transition metal catalysts (M/SiO2) was prepared by a wetness impregnation method for the dehydrochlorination of 1,1,2-trichloroethane (TCE) in the gas phase. Among these M/SiO2 catalysts, Zn/SiO2 had the best catalytic activity with the highest TCE conversion (~98%) and excellent selectivity for cis-1,2-dichloroethylene (82%). By increasing the zinc loading, the conversion of TCE using the Zn/SiO2 catalyst was gradually improved, in agreement with the total acidity in the Zn/SiO2 catalyst. Associating the specific activity and specific acidity of the Zn/SiO2 catalyst with different Zn loadings, it was found that higher specific acidity contributed to higher specific activity, indicating that the acid center of Zn/SiO2 was the catalytic active site for the dehydrochlorination of TCE. In the process of dehydrochlorination, the Zn/SiO2 catalyst could be deactivated, mainly due to coke deposition on the catalyst surface. Catalysts with low Zn loading had stronger acid sites, which resulted in more coke formation on the catalyst. The results showed that strong acid sites on the catalyst surface were responsible for the deposition of coke and deactivation of the catalyst.
2017, 33(5): 1027-1032
doi: 10.3866/PKU.WHXB201702081
Abstract:
MoS2 nanosheets are prepared with sulfur powder and Na2MoO4 by a one-pot two-phase method at 170－200 ℃ for 8 h. In addition, a three-step growth mechanism based on the aggregation and coalescence model is proposed. The reassembly of sulfur powder ensures the transformation from sulfur powder to H2S to reduce Na2MoO4 and plays a key role in the successful preparation of MoS2 nanosheets. The as-prepared MoS2 nanosheets are rich in unsaturated sulfur atoms, probably resulting from the dislocation cores of the MoS2 nanosheets, which have been found to be beneficial for hydrogen evolution reaction catalysis. The method and growth mechanism adopted in this study may be applied to other transition metal dichalogenides for similar structures. The facile and green method provides an alternative for the preparation of MoS2 nanosheets.
MoS2 nanosheets are prepared with sulfur powder and Na2MoO4 by a one-pot two-phase method at 170－200 ℃ for 8 h. In addition, a three-step growth mechanism based on the aggregation and coalescence model is proposed. The reassembly of sulfur powder ensures the transformation from sulfur powder to H2S to reduce Na2MoO4 and plays a key role in the successful preparation of MoS2 nanosheets. The as-prepared MoS2 nanosheets are rich in unsaturated sulfur atoms, probably resulting from the dislocation cores of the MoS2 nanosheets, which have been found to be beneficial for hydrogen evolution reaction catalysis. The method and growth mechanism adopted in this study may be applied to other transition metal dichalogenides for similar structures. The facile and green method provides an alternative for the preparation of MoS2 nanosheets.
2017, 33(5): 1033-1042
doi: 10.3866/PKU.WHXB201702101
Abstract:
This work reports a controlled green synthesis of highly monodisperse bismuth subcarbonate (BS) micropompons self-assembled by nanosheets using a simple and facile hydrothermal route in which deionized water, bismuth nitrate pentahydrate (BNP), and urea were used as the solvent, bismuth source, and carbon source respectively. Trisodium citrate dihydrate (TCD) was used as a coordination agent to fabricate a complex precursor. The structure and morphology of the BS materials can be finely modulated by adjusting the initial concentration ratios of the reactants or the reaction time. The presence of TCD decreased the formation rate of BS due to a direct competitive interaction for the BiO+ ions between a coordination equilibrium and a precipitation equilibrium. Urea played a crucial role (e.g., carbon source, alkaline source, morphology control agent, and crystal growth control agent) in the formation of the BS microstructures. We obtained three kinds of BS crystals with preferred orientations along [001], [110], and [013] by adjusting the concentration of urea. Our synthesis approach has the advantages of low cost, high reaction yields, monodisperse particles, controlled morphologies and orientations, and not requiring the use of organic solvents, templates, surfactants, high phototemperatures, and long reaction times. Particularly, when compared with those reported by other investigators, the micropompon material exhibited improved photocatalytic performance for Rhodamine B due to a unique microstructure (large specific surface area, high efficiency of photoelectric conversion, small interfacial chargetransfer resistance, and active {001} exposed facets). These results indicate a major advance in the controlled green synthesis and the application of inorganic micro-and nano-materials.
This work reports a controlled green synthesis of highly monodisperse bismuth subcarbonate (BS) micropompons self-assembled by nanosheets using a simple and facile hydrothermal route in which deionized water, bismuth nitrate pentahydrate (BNP), and urea were used as the solvent, bismuth source, and carbon source respectively. Trisodium citrate dihydrate (TCD) was used as a coordination agent to fabricate a complex precursor. The structure and morphology of the BS materials can be finely modulated by adjusting the initial concentration ratios of the reactants or the reaction time. The presence of TCD decreased the formation rate of BS due to a direct competitive interaction for the BiO+ ions between a coordination equilibrium and a precipitation equilibrium. Urea played a crucial role (e.g., carbon source, alkaline source, morphology control agent, and crystal growth control agent) in the formation of the BS microstructures. We obtained three kinds of BS crystals with preferred orientations along [001], [110], and [013] by adjusting the concentration of urea. Our synthesis approach has the advantages of low cost, high reaction yields, monodisperse particles, controlled morphologies and orientations, and not requiring the use of organic solvents, templates, surfactants, high phototemperatures, and long reaction times. Particularly, when compared with those reported by other investigators, the micropompon material exhibited improved photocatalytic performance for Rhodamine B due to a unique microstructure (large specific surface area, high efficiency of photoelectric conversion, small interfacial chargetransfer resistance, and active {001} exposed facets). These results indicate a major advance in the controlled green synthesis and the application of inorganic micro-and nano-materials.
2017, 33(5): 1043-1050
doi: 10.3866/PKU.WHXB201702083
Abstract:
A new method is developed to effectively study the contributions of various coexisting conformations to the actual vibrational spectrum of liquid polyethylene oxide (PEO). By defining six conformations for the －(CH2CH2O)－ unit, four isomers from the combinations of all the same EO conformations [(TGT)10, (TTT)10, (TTG)10, and (GTG)10] and three isomers from the combinations of other EO conformations were constructed. Their optimized geometric structures and the corresponding vibrational frequencies were then computed. The unified standards that describe the different types of the CH2 scissor and CH2 twist vibrational modes for PEO400 are proposed through the analysis of the normal modes. The relationships between the four CH2CH2－OCH2CH2 conformations and the various CH2 scissor and CH2 twist vibrational modes and frequencies are determined, and the results are used to assign the practical vibrational spectra.
A new method is developed to effectively study the contributions of various coexisting conformations to the actual vibrational spectrum of liquid polyethylene oxide (PEO). By defining six conformations for the －(CH2CH2O)－ unit, four isomers from the combinations of all the same EO conformations [(TGT)10, (TTT)10, (TTG)10, and (GTG)10] and three isomers from the combinations of other EO conformations were constructed. Their optimized geometric structures and the corresponding vibrational frequencies were then computed. The unified standards that describe the different types of the CH2 scissor and CH2 twist vibrational modes for PEO400 are proposed through the analysis of the normal modes. The relationships between the four CH2CH2－OCH2CH2 conformations and the various CH2 scissor and CH2 twist vibrational modes and frequencies are determined, and the results are used to assign the practical vibrational spectra.
2017, 33(5): 1051-1056
doi: 10.3866/PKU.WHXB201702201
Abstract:
The reactions of triplet-state difloxacin (DFX) with various amino acids and deoxyguanylic acid in aqueous media were studied using laser flash photolysis. Tryptophan, tyrosine, cysteine, and 2'-deoxyguanosine-5'-monophosphate (dGMP) were found to completely quench the triplet state of DFX in aqueous solution, the corresponding second-order rate constants being 1.97×108, 1.48×108, 1.72×108, and 6.92×107 dm3·mol－1·s－1. The quenching mechanism involves electron transfer to the photoexcited triplet state of DFX from the tryptophan, tyrosine, cysteine, and dGMP moieties, followed by fast protonation of the resulting DFX anion radical.
The reactions of triplet-state difloxacin (DFX) with various amino acids and deoxyguanylic acid in aqueous media were studied using laser flash photolysis. Tryptophan, tyrosine, cysteine, and 2'-deoxyguanosine-5'-monophosphate (dGMP) were found to completely quench the triplet state of DFX in aqueous solution, the corresponding second-order rate constants being 1.97×108, 1.48×108, 1.72×108, and 6.92×107 dm3·mol－1·s－1. The quenching mechanism involves electron transfer to the photoexcited triplet state of DFX from the tryptophan, tyrosine, cysteine, and dGMP moieties, followed by fast protonation of the resulting DFX anion radical.
2017, 33(5): 1057-1064
doi: 10.3866/PKU.WHXB201702161
Abstract:
Two new blue-light-emitting materials based on tetraphenylethylene (TPE), TPE-4Br, and TPE-3Br have been designed and synthesized. They have been used as emitting materials in organic light-emitting diodes (OLEDs) and have been found to form electroplex with an appropriate neighboring hole or electron transporting layer. Using the intrinsic local exciton emission and electroplex emission, desirable white electroluminescence has been obtained. Using TPE-4Br and TPE-3Br in 1,3-di(9H-carbazol-9-yl)benzene (mCP) matrix as the emitting layer, 4,4'-(cyclohexane-1,1-diyl)bis(N,N-di-p-tolylaniline) (TAPC) and 3,3'-(5'-(3-(pyridin-3-yl)phenyl)-[1,1':3',1"-terphenyl]-3,3"-diyl) dipyridine (TmPyPB) as the hole and electron transporting layers, respectively, Device A and Device B have been fabricated with the corresponding CIE coordinates of (0.32, 0.33) and (0.31, 0.34) at 9 V. Device B showed the maximum luminance of 364.66 cd·m－2 and the maximum current efficiency of 0.79 cd·A－1.
Two new blue-light-emitting materials based on tetraphenylethylene (TPE), TPE-4Br, and TPE-3Br have been designed and synthesized. They have been used as emitting materials in organic light-emitting diodes (OLEDs) and have been found to form electroplex with an appropriate neighboring hole or electron transporting layer. Using the intrinsic local exciton emission and electroplex emission, desirable white electroluminescence has been obtained. Using TPE-4Br and TPE-3Br in 1,3-di(9H-carbazol-9-yl)benzene (mCP) matrix as the emitting layer, 4,4'-(cyclohexane-1,1-diyl)bis(N,N-di-p-tolylaniline) (TAPC) and 3,3'-(5'-(3-(pyridin-3-yl)phenyl)-[1,1':3',1"-terphenyl]-3,3"-diyl) dipyridine (TmPyPB) as the hole and electron transporting layers, respectively, Device A and Device B have been fabricated with the corresponding CIE coordinates of (0.32, 0.33) and (0.31, 0.34) at 9 V. Device B showed the maximum luminance of 364.66 cd·m－2 and the maximum current efficiency of 0.79 cd·A－1.
2017, 33(5): 1065-1070
doi: 10.3866/PKU.WHXB201703061
Abstract:
In this paper, the fluorescence dynamics of tryptophan residues in LicT protein is investigated by time-resolved fluorescence method combined with UV absorption and steady-state fluorescence spectroscopy. The local microenvironment and structural changes of LicT protein before and after activation are studied. The activated LicT protein AC 141 prevents the antitermination of gene transcription involved in carbohydrate utilization to accelerate the body's metabolism. The structural properties and microenvironment of activated protein AC 141 and wild-type protein Q 22 were determined by different fluorescence emissions and lifetimes of tryptophan residues. The interaction between tryptophan residues and solvent is elucidated by decay associated spectroscopy (DAS) and time-resolved emission spectra (TRES), indicating that upon activation, the structure of AC 141 is more compact than that of wild-type Q 22. In addition, TRES also showed that tryptophan residues in the protein had a continuous spectral relaxation process. Anisotropy results illustrated the conformational motions of residues and whole proteins, suggesting that tryptophan residues had independent local motions in the protein system, and that the motions were more intense in the activated protein.
In this paper, the fluorescence dynamics of tryptophan residues in LicT protein is investigated by time-resolved fluorescence method combined with UV absorption and steady-state fluorescence spectroscopy. The local microenvironment and structural changes of LicT protein before and after activation are studied. The activated LicT protein AC 141 prevents the antitermination of gene transcription involved in carbohydrate utilization to accelerate the body's metabolism. The structural properties and microenvironment of activated protein AC 141 and wild-type protein Q 22 were determined by different fluorescence emissions and lifetimes of tryptophan residues. The interaction between tryptophan residues and solvent is elucidated by decay associated spectroscopy (DAS) and time-resolved emission spectra (TRES), indicating that upon activation, the structure of AC 141 is more compact than that of wild-type Q 22. In addition, TRES also showed that tryptophan residues in the protein had a continuous spectral relaxation process. Anisotropy results illustrated the conformational motions of residues and whole proteins, suggesting that tryptophan residues had independent local motions in the protein system, and that the motions were more intense in the activated protein.
