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2016 Volume 32 Issue 12
2016, 32(12):
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2016, 32(12): 2819-2820
doi: 10.3866/PKU.WHXB201611081
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2016, 32(12): 2821-2821
doi: 10.3866/PKU.WHXB201610282
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2016, 32(12): 2822-2823
doi: 10.3866/PKU.WHXB201610281
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2016, 32(12): 2824-2824
doi: 10.3866/PKU.WHXB201611011
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2016, 32(12): 2825-2825
doi: 10.3866/PKU.WHXB201611031
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2016, 32(12): 2826-2840
doi: 10.3866/PKU.WHXB201609141
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Ordered mesoporous carbon materials (OMCs) have potentially broad applications in many fields, such as adsorption, separation, catalysis, and energy storage/conversion. Compared with the elaborate hardtemplate strategy, the soft-template approach, which is based on the self-assembly between amphiphilic block copolymers and polymerizable precursors (e.g., phenolic resins), is a more effective and efficient method for the synthesis of OMCs. In this review, the mechanism and characteristics for three main soft-template methods, i.e., solvent evaporation-induced self-assembly synthesis, aqueous cooperative self-assembly synthesis and solvent-free synthesis, are discussed and compared. In addition, a few highlights of recent progress, including application of novel carbon precursors, structural modification and functionalization of OMCs, are outlined. Finally, we summarize the crucial issues to be addressed in developing the synthesis methodology of OMCs.
Ordered mesoporous carbon materials (OMCs) have potentially broad applications in many fields, such as adsorption, separation, catalysis, and energy storage/conversion. Compared with the elaborate hardtemplate strategy, the soft-template approach, which is based on the self-assembly between amphiphilic block copolymers and polymerizable precursors (e.g., phenolic resins), is a more effective and efficient method for the synthesis of OMCs. In this review, the mechanism and characteristics for three main soft-template methods, i.e., solvent evaporation-induced self-assembly synthesis, aqueous cooperative self-assembly synthesis and solvent-free synthesis, are discussed and compared. In addition, a few highlights of recent progress, including application of novel carbon precursors, structural modification and functionalization of OMCs, are outlined. Finally, we summarize the crucial issues to be addressed in developing the synthesis methodology of OMCs.
2016, 32(12): 2841-2870
doi: 10.3866/PKU.WHXB201611021
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Bi-based semiconductor photocatalysts are important visible-light-driven photocatalysts. However, the photocatalytic performance of bulk bismuth-containing compounds remains unsatisfactory. Many investigations indicate that morphology control and surface modification are effective methods for improving the photocatalytic activity of these compounds. Herein, we review recent advances in this field, including ultrathin nanoplate fabrication, facet ratio control, hierarchical and hollow architecture construction, functional group and quantum-sized nanoparticle modification, surface defect regulation, and in situ formation of metal bismuth and bismuth compounds. The characteristics and advantages of these modification methods are introduced. In addition, mechanisms for improving light absorption, separation, and utilization of excited carriers are discussed. Trends in the development of Bi-based photocatalysts using morphology control and surface modification, as well as the challenges involved, are also analyzed and summarized.
Bi-based semiconductor photocatalysts are important visible-light-driven photocatalysts. However, the photocatalytic performance of bulk bismuth-containing compounds remains unsatisfactory. Many investigations indicate that morphology control and surface modification are effective methods for improving the photocatalytic activity of these compounds. Herein, we review recent advances in this field, including ultrathin nanoplate fabrication, facet ratio control, hierarchical and hollow architecture construction, functional group and quantum-sized nanoparticle modification, surface defect regulation, and in situ formation of metal bismuth and bismuth compounds. The characteristics and advantages of these modification methods are introduced. In addition, mechanisms for improving light absorption, separation, and utilization of excited carriers are discussed. Trends in the development of Bi-based photocatalysts using morphology control and surface modification, as well as the challenges involved, are also analyzed and summarized.
2016, 32(12): 2871-2878
doi: 10.3866/PKU.WHXB201609281
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Current research on the effects of cyclodextrins (CDs) on the sweetness of aspartame (ASP) focuses on the stability of aspartame as protected by CDs. We propose a relationship between the sweetness intensity of aspartame and its thermodynamic binding affinity with CDs. In this paper, we describe the sensory evaluation of aspartame with the five CDs α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), γ-cyclodextrin (γ-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD), and methyl-β-cyclodextrin (Met-β-CD). β-CD was found to significantly enhance the sweetness intensity of aspartame. The binding affinity of CDs with aspartame was then investigated using isothermal titration calorimetry (ITC) and fluorescence spectroscopy. The binding of aspartame with β-CD resulted in a free energy change with the largest binding constant. Differential scanning calorimetry (DSC), nuclear magnetic resonance (1H NMR), and Fourier transform infrared (FT-IR) spectroscopy further revealed the mechanism behind the complexation. This research gives insight to the contribution of the thermodynamic binding affinity to the sweetness intensity of aspartame. It also provides an approach for screening flavorretention agents by measuring binding constants.
Current research on the effects of cyclodextrins (CDs) on the sweetness of aspartame (ASP) focuses on the stability of aspartame as protected by CDs. We propose a relationship between the sweetness intensity of aspartame and its thermodynamic binding affinity with CDs. In this paper, we describe the sensory evaluation of aspartame with the five CDs α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), γ-cyclodextrin (γ-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD), and methyl-β-cyclodextrin (Met-β-CD). β-CD was found to significantly enhance the sweetness intensity of aspartame. The binding affinity of CDs with aspartame was then investigated using isothermal titration calorimetry (ITC) and fluorescence spectroscopy. The binding of aspartame with β-CD resulted in a free energy change with the largest binding constant. Differential scanning calorimetry (DSC), nuclear magnetic resonance (1H NMR), and Fourier transform infrared (FT-IR) spectroscopy further revealed the mechanism behind the complexation. This research gives insight to the contribution of the thermodynamic binding affinity to the sweetness intensity of aspartame. It also provides an approach for screening flavorretention agents by measuring binding constants.
2016, 32(12): 2879-2890
doi: 10.3866/PKU.WHXB201609303
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Dual-fuel compression ignition, or reactivity controlled compression ignition (RCCI) is a promising strategy for engines to achieve high efficiency and clean combustion from low to mid-high load. To extend the operating range to high engine load, further examination of the in-cylinder fuel stratification and combustion processes is required. In this paper, fuel-tracer planar laser-induced fluorescence (PLIF) was used to quantify the fuel stratification of RCCI in an optical engine. Toluene was chosen as the tracer, which was mixed with isooctane and n-heptane. A laser of 266 nm was used to stimulate the toluene fluorescence. The engine was run at 1200 r·min-1 under a load of 6.9×105 Pa IMEP (indicated mean effective pressure). Iso-octane was delivered via the intake port and n-heptane was injected directly into the cylinder at -10° CA (crank angle) after top dead center (ATDC). A fuel-gas adiabatic mixing assumption was adopted to correct temperature non-uniformity of the PLIF images. As an example, the results obtained at 5° CA ATDC gave an overestimated maximum equivalence ratio in the diagnostic region before any correction of 15%. Based on the measurements, the effects of reactivity, concentration and temperature stratification on ignition delay of RCCI were evaluated using Chemkin software. The results indicated that the reactivity stratification and concentration stratification dominated the ignition delay of RCCI, with the reactivity stratification being more significant than the concentration stratification. The temperature stratification had only minor effects on the ignition delay. The high-speed imaging of the RCCI combustion showed that the initial ignition sites emerged at the edge of the combustion chamber where the local fuel reactivity or fuel concentration was high. The flames then progressed into the center of the combustion chamber where the fuel was leaner and less reactive. The soot emissions shown by the soot radiation images mainly formed in the high reactive region.
Dual-fuel compression ignition, or reactivity controlled compression ignition (RCCI) is a promising strategy for engines to achieve high efficiency and clean combustion from low to mid-high load. To extend the operating range to high engine load, further examination of the in-cylinder fuel stratification and combustion processes is required. In this paper, fuel-tracer planar laser-induced fluorescence (PLIF) was used to quantify the fuel stratification of RCCI in an optical engine. Toluene was chosen as the tracer, which was mixed with isooctane and n-heptane. A laser of 266 nm was used to stimulate the toluene fluorescence. The engine was run at 1200 r·min-1 under a load of 6.9×105 Pa IMEP (indicated mean effective pressure). Iso-octane was delivered via the intake port and n-heptane was injected directly into the cylinder at -10° CA (crank angle) after top dead center (ATDC). A fuel-gas adiabatic mixing assumption was adopted to correct temperature non-uniformity of the PLIF images. As an example, the results obtained at 5° CA ATDC gave an overestimated maximum equivalence ratio in the diagnostic region before any correction of 15%. Based on the measurements, the effects of reactivity, concentration and temperature stratification on ignition delay of RCCI were evaluated using Chemkin software. The results indicated that the reactivity stratification and concentration stratification dominated the ignition delay of RCCI, with the reactivity stratification being more significant than the concentration stratification. The temperature stratification had only minor effects on the ignition delay. The high-speed imaging of the RCCI combustion showed that the initial ignition sites emerged at the edge of the combustion chamber where the local fuel reactivity or fuel concentration was high. The flames then progressed into the center of the combustion chamber where the fuel was leaner and less reactive. The soot emissions shown by the soot radiation images mainly formed in the high reactive region.
2016, 32(12): 2891-2897
doi: 10.3866/PKU.WHXB201609133
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To investigate the kinetic behaviors of nanoparticle heterogeneous reactions, we introduced a liquidphase reduction method to control the synthesis of cubic cuprous oxide with a particle size of 55 nm. Based on the differences between nano-Cu2O and bulk Cu2O, in-situ microcalorimetry was used to acquire fine thermodynamic information of Cu2O systems in HNO3. The reaction kinetic parameters of Cu2O were calculated by a combination of thermodynamic principles and kinetic transition state theory, whose results are discussed and verified with the kinetic models of a cube that has been built. The results demonstrate that unlike the higher reaction rate constant than bulk Cu2O, nano-Cu2O shows lower kinetic parameters, including apparent activation energy, pre-exponential factor, activation enthalpy, activation entropy and activation Gibbs free energy. Both the reaction rate constant and activation Gibbs free energy increase with increasing temperature. The kinetic models show that the main factors affecting the reaction kinetic parameters are as follows:(i) the partial molar surface enthalpy affects the apparent activation energy; (ii) the partial molar surface entropy affects the preexponential factor; and (iii) the partial molar surface Gibbs free energy affects the reaction rate constant. We also provide a universal theoretical model and experimental method for gaining and analyzing kinetic parameters of nanomaterial heterogeneous reactions.
To investigate the kinetic behaviors of nanoparticle heterogeneous reactions, we introduced a liquidphase reduction method to control the synthesis of cubic cuprous oxide with a particle size of 55 nm. Based on the differences between nano-Cu2O and bulk Cu2O, in-situ microcalorimetry was used to acquire fine thermodynamic information of Cu2O systems in HNO3. The reaction kinetic parameters of Cu2O were calculated by a combination of thermodynamic principles and kinetic transition state theory, whose results are discussed and verified with the kinetic models of a cube that has been built. The results demonstrate that unlike the higher reaction rate constant than bulk Cu2O, nano-Cu2O shows lower kinetic parameters, including apparent activation energy, pre-exponential factor, activation enthalpy, activation entropy and activation Gibbs free energy. Both the reaction rate constant and activation Gibbs free energy increase with increasing temperature. The kinetic models show that the main factors affecting the reaction kinetic parameters are as follows:(i) the partial molar surface enthalpy affects the apparent activation energy; (ii) the partial molar surface entropy affects the preexponential factor; and (iii) the partial molar surface Gibbs free energy affects the reaction rate constant. We also provide a universal theoretical model and experimental method for gaining and analyzing kinetic parameters of nanomaterial heterogeneous reactions.
2016, 32(12): 2898-2904
doi: 10.3866/PKU.WHXB201609142
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The catalytic effect of H2O and six kinds of organic acids (e.g., formic acid) on the reaction of CH3CHOO with H2O is studied at the CCSD(T)//B3LYP/6-311+G(d,p) level. The results reveal that two possible channels exist as the double proton transfer and addition, of which the latter dominates for the non-catalytic reactions. For the additions, the OH of water is added to the α-C of CH3CHOO, and the H atoms migrate to the end oxygen atoms. Catalysts such as H2O and organic acid can form a hydrogen-bonded complex with CH3CHOO, which promotes the H transfer and thus significantly reduces the elementary reaction energy barrier and apparent activation energy when compared with that of the non-catalytic reaction. The catalytic effect is proportional to the strength of the organic acids. For example, for the formation of syn-HAHP catalyzed by H2O (pKa=15.7), formic acid (pKa=3.75) and oxalic acid (pKa=1.23), the energy barrier is reduced from 69.12 to 40.78, 18.88 and 10.61 kJ·mol-1, respectively. In addition, the non-catalytic reaction has a positive activation energy, whereas the catalytic reactions have an negative apparent activation energy.
The catalytic effect of H2O and six kinds of organic acids (e.g., formic acid) on the reaction of CH3CHOO with H2O is studied at the CCSD(T)//B3LYP/6-311+G(d,p) level. The results reveal that two possible channels exist as the double proton transfer and addition, of which the latter dominates for the non-catalytic reactions. For the additions, the OH of water is added to the α-C of CH3CHOO, and the H atoms migrate to the end oxygen atoms. Catalysts such as H2O and organic acid can form a hydrogen-bonded complex with CH3CHOO, which promotes the H transfer and thus significantly reduces the elementary reaction energy barrier and apparent activation energy when compared with that of the non-catalytic reaction. The catalytic effect is proportional to the strength of the organic acids. For example, for the formation of syn-HAHP catalyzed by H2O (pKa=15.7), formic acid (pKa=3.75) and oxalic acid (pKa=1.23), the energy barrier is reduced from 69.12 to 40.78, 18.88 and 10.61 kJ·mol-1, respectively. In addition, the non-catalytic reaction has a positive activation energy, whereas the catalytic reactions have an negative apparent activation energy.
2016, 32(12): 2905-2912
doi: 10.3866/PKU.WHXB201609201
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Based on the first principles method of density functional theory, the band structure and optical absorption properties of single-layered MoS2 doped with Se were calculated. Additionally, its effect on the properties of water splitting was analyzed. The calculations showed that the intrinsic MoS2 monolayer has a direct band gap structure with a value of 1.740 eV. The bottom edge of the conduction band was 0.43 eV above the reduction potential of H+/H2, while the top edge of the valence band was only 0.08 eV below the oxidation potential of O2/H2O. The results indicated that the intrinsic MoS2 monolayer has the potential for the photocatalytic decomposition of water when exposed to visible light. However, as the values of the oxidation and reduction processes were not balanced, the water splitting efficiency of a single-layer MoS2 photocatalyst would be low. When the MoS2 layer was doped with Se the band gap decreased to 1.727 eV, while the corresponding optical absorption spectrum was almost unchanged, and the formation energy of the system was relatively low. These results indicated that single-layered MoS2 should be thermally stabile following doping with Se. Significantly, the bottom edge of the conduction band decreased to 0.253 eV above reduction potential of H+/H2, while the top edge of the valence band increased to 0.244 eV below the oxidation potential of O2/H2O. Thus, the oxidation and reduction processes were balanced, and the water splitting efficiency of single-layered MoS2 should be greatly improved when exposed to visible light.
Based on the first principles method of density functional theory, the band structure and optical absorption properties of single-layered MoS2 doped with Se were calculated. Additionally, its effect on the properties of water splitting was analyzed. The calculations showed that the intrinsic MoS2 monolayer has a direct band gap structure with a value of 1.740 eV. The bottom edge of the conduction band was 0.43 eV above the reduction potential of H+/H2, while the top edge of the valence band was only 0.08 eV below the oxidation potential of O2/H2O. The results indicated that the intrinsic MoS2 monolayer has the potential for the photocatalytic decomposition of water when exposed to visible light. However, as the values of the oxidation and reduction processes were not balanced, the water splitting efficiency of a single-layer MoS2 photocatalyst would be low. When the MoS2 layer was doped with Se the band gap decreased to 1.727 eV, while the corresponding optical absorption spectrum was almost unchanged, and the formation energy of the system was relatively low. These results indicated that single-layered MoS2 should be thermally stabile following doping with Se. Significantly, the bottom edge of the conduction band decreased to 0.253 eV above reduction potential of H+/H2, while the top edge of the valence band increased to 0.244 eV below the oxidation potential of O2/H2O. Thus, the oxidation and reduction processes were balanced, and the water splitting efficiency of single-layered MoS2 should be greatly improved when exposed to visible light.
2016, 32(12): 2913-2920
doi: 10.3866/PKU.WHXB201609301
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The one- and two-photon absorption and emission properties of the two newly synthesized watersoluble two-photon fluorescent probes (HCH and HCM) for the detection of ClO- were investigated using timedependent density functional theory in combination with response theory. Dramatic changes in the photophysical properties of the molecules following reaction with ClO- were predicted. The photoabsorption and photoemission peaks for both compounds were clearly blue shifted, while the emission intensities were enhanced. Both probes were also found to have large two-photon cross sections. Importantly, in the presence of ClO- the two-photon cross section of the molecules increased significantly, which indicated that both HCH and HCM should be good two-photon fluorescent probes for sensing ClO-. The responsive mechanism of the probes was explored by analyzing the molecular Mulliken charge population, which was attributed to C=N isomerization.
The one- and two-photon absorption and emission properties of the two newly synthesized watersoluble two-photon fluorescent probes (HCH and HCM) for the detection of ClO- were investigated using timedependent density functional theory in combination with response theory. Dramatic changes in the photophysical properties of the molecules following reaction with ClO- were predicted. The photoabsorption and photoemission peaks for both compounds were clearly blue shifted, while the emission intensities were enhanced. Both probes were also found to have large two-photon cross sections. Importantly, in the presence of ClO- the two-photon cross section of the molecules increased significantly, which indicated that both HCH and HCM should be good two-photon fluorescent probes for sensing ClO-. The responsive mechanism of the probes was explored by analyzing the molecular Mulliken charge population, which was attributed to C=N isomerization.
2016, 32(12): 2921-2931
doi: 10.3866/PKU.WHXB201609193
Abstract:
Coordination microstructure and water exchange of Zn2+ aqueous solution were studied through molecular dynamics simulations based on the ABEEMσπ polarizable force field with the precise ABEEM-7P model. Structural and dynamical properties were investigated in detail. We show that the first-shell water coordination number is six, which is in agreement with the experimental value. During the water exchange process, H2O, which attacks or leaves the first solvation shell of Zn2+, is orientated on the upper or lower inclined side of the ∠O-Zn-O bisector. The distance change between Zn2+ and the oxygen atom of the exchange water for the polarizable force field fluctuates more than that observed for the fixed charge force field. The radial distribution function (RDF) of the polarizable force field showed clearly the microstructure of the second and third solvation shells. The subshell of the second solvation shell was found to exchange with the first solvation shell. The polarizable effect of Zn2+ has been fully expressed. The charges of the Zn2+ site and the lone-pair sites in exchange water regularly change, demonstrating the rationality of water exchange. The mean ligand residence time (2.0×10-9 s) of the first-shell water produced by the ABEEMσπ polarizable force field is within the range of the experimental value. Zn2+ aqueous solution can be reasonably simulated through the ABEEMσπ polarizable force field.
Coordination microstructure and water exchange of Zn2+ aqueous solution were studied through molecular dynamics simulations based on the ABEEMσπ polarizable force field with the precise ABEEM-7P model. Structural and dynamical properties were investigated in detail. We show that the first-shell water coordination number is six, which is in agreement with the experimental value. During the water exchange process, H2O, which attacks or leaves the first solvation shell of Zn2+, is orientated on the upper or lower inclined side of the ∠O-Zn-O bisector. The distance change between Zn2+ and the oxygen atom of the exchange water for the polarizable force field fluctuates more than that observed for the fixed charge force field. The radial distribution function (RDF) of the polarizable force field showed clearly the microstructure of the second and third solvation shells. The subshell of the second solvation shell was found to exchange with the first solvation shell. The polarizable effect of Zn2+ has been fully expressed. The charges of the Zn2+ site and the lone-pair sites in exchange water regularly change, demonstrating the rationality of water exchange. The mean ligand residence time (2.0×10-9 s) of the first-shell water produced by the ABEEMσπ polarizable force field is within the range of the experimental value. Zn2+ aqueous solution can be reasonably simulated through the ABEEMσπ polarizable force field.
2016, 32(12): 2932-2940
doi: 10.3866/PKU.WHXB201609302
Abstract:
The stability of M-Au(111) surfaces modified by M (M=In, Ir) was investigated using density functional theory. The most favorable model was selected to explore the chemical reactivity and adsorption of crotonaldehyde. The stability of the M-Au(111) surfaces was calculated using geometric configuration, and formation and cohesive energies. The calculations showed that the stability of the In-Au(111) surface increased as the atomic spacing of In was increased. Conversely, the Ir-Au(111) showed the opposite trend. The adsorption at the TopM site was most stable when the crotonaldehyde on the M-Au(111) surfaces interacting via the C=O. Additionally, the adsorption energies were at their maximum. A combination of structural changes, density of state, deformation density and Mulliken charge analysis showed that the deformation of crotonaldehyde was larger than other adsorption modes, with an obvious charge transfer. Additionally, p and d orbital hybridization between -7.04 eV to Fermi level was found to have an important contribution to the adsorption process. Compared with the Au(111) surface, the stability and adsorption capacity of the M-Au(111) surfaces were significantly improved following modification by M atoms. Importantly, the Ir-Au(111) surface was found to have higher stability and activity, and stronger adsorption of crotonaldehyde than the In-Au(111) surface.
The stability of M-Au(111) surfaces modified by M (M=In, Ir) was investigated using density functional theory. The most favorable model was selected to explore the chemical reactivity and adsorption of crotonaldehyde. The stability of the M-Au(111) surfaces was calculated using geometric configuration, and formation and cohesive energies. The calculations showed that the stability of the In-Au(111) surface increased as the atomic spacing of In was increased. Conversely, the Ir-Au(111) showed the opposite trend. The adsorption at the TopM site was most stable when the crotonaldehyde on the M-Au(111) surfaces interacting via the C=O. Additionally, the adsorption energies were at their maximum. A combination of structural changes, density of state, deformation density and Mulliken charge analysis showed that the deformation of crotonaldehyde was larger than other adsorption modes, with an obvious charge transfer. Additionally, p and d orbital hybridization between -7.04 eV to Fermi level was found to have an important contribution to the adsorption process. Compared with the Au(111) surface, the stability and adsorption capacity of the M-Au(111) surfaces were significantly improved following modification by M atoms. Importantly, the Ir-Au(111) surface was found to have higher stability and activity, and stronger adsorption of crotonaldehyde than the In-Au(111) surface.
2016, 32(12): 2941-2950
doi: 10.3866/PKU.WHXB201609195
Abstract:
This paper studies how particular factors affect hydrogen bromine batteries, including the cell structure, the hydrobromic acid and bromine concentrations, the hydrogen pressure and the proton exchange membrane thickness. After the Pt/C hydrophobic catalyst layer was loaded onto the carbon paper, the hydrogen bromine battery worked at 200 mA·cm-2 current density and the battery Coulombic efficiency was 100%. The bromine electrode electrochemical reaction was controlled by the concentration polarization. The battery performance improved when the hydrobromic acid concentration increased. The bromine solubility also increased at the higher hydrobromic acid concentration and the battery discharge performance improved. When the hydrobromic acid concentration was increased from 0.5 mol·L-1 to 1 mol·L-1, the energy efficiency and the voltage efficiency increased by 27.9% at the current density of 200 mA·cm-2. In the charge process, as the hydrogen pressure was reduced, the battery charging performance improved, but severe membrane acid permeability was observed. In the discharge process, the optimal hydrogen pressure was able to maintain the monolayer hydrogen adsorption on the hydrophobic catalyst layer on the carbon paper. The energy efficiency was 80.2% at 40.0 kPa hydrogen pressure in the charge and discharge processes. In the charge process, the membrane thickness was closely related to the membrane resistance polarization and the membrane acid permeability. After the membrane thickness was reduced from 50.0 to 15.0 μm, acid permeability through the membrane was more severe. This reduced the electrochemical active surface area and a reduction in the battery performance was observed. In the discharge process, the membrane acid permeability was the leading factor at the lower current density; the battery with the 50.0 μm Nafion membrane had a higher discharge performance. As the current density was >200 mA·cm-2, the membrane polarization resistance was the dominated factor; the battery with the 15.0 μm Nafion membrane had a higher discharge performance. With the 20.0 μm proton exchange membrane, the energy efficiency and voltage efficiency of the hydrogen bromine battery were 85.3% and the Coulombic efficiency was 100% at the current density of 200 mA·cm-2 with five cycles.
This paper studies how particular factors affect hydrogen bromine batteries, including the cell structure, the hydrobromic acid and bromine concentrations, the hydrogen pressure and the proton exchange membrane thickness. After the Pt/C hydrophobic catalyst layer was loaded onto the carbon paper, the hydrogen bromine battery worked at 200 mA·cm-2 current density and the battery Coulombic efficiency was 100%. The bromine electrode electrochemical reaction was controlled by the concentration polarization. The battery performance improved when the hydrobromic acid concentration increased. The bromine solubility also increased at the higher hydrobromic acid concentration and the battery discharge performance improved. When the hydrobromic acid concentration was increased from 0.5 mol·L-1 to 1 mol·L-1, the energy efficiency and the voltage efficiency increased by 27.9% at the current density of 200 mA·cm-2. In the charge process, as the hydrogen pressure was reduced, the battery charging performance improved, but severe membrane acid permeability was observed. In the discharge process, the optimal hydrogen pressure was able to maintain the monolayer hydrogen adsorption on the hydrophobic catalyst layer on the carbon paper. The energy efficiency was 80.2% at 40.0 kPa hydrogen pressure in the charge and discharge processes. In the charge process, the membrane thickness was closely related to the membrane resistance polarization and the membrane acid permeability. After the membrane thickness was reduced from 50.0 to 15.0 μm, acid permeability through the membrane was more severe. This reduced the electrochemical active surface area and a reduction in the battery performance was observed. In the discharge process, the membrane acid permeability was the leading factor at the lower current density; the battery with the 50.0 μm Nafion membrane had a higher discharge performance. As the current density was >200 mA·cm-2, the membrane polarization resistance was the dominated factor; the battery with the 15.0 μm Nafion membrane had a higher discharge performance. With the 20.0 μm proton exchange membrane, the energy efficiency and voltage efficiency of the hydrogen bromine battery were 85.3% and the Coulombic efficiency was 100% at the current density of 200 mA·cm-2 with five cycles.
2016, 32(12): 2951-2960
doi: 10.3866/PKU.WHXB201609231
Abstract:
UV-visible (UV-Vis) absorption spectroscopy, fluorescence spectroscopy (FL), dynamic light scattering (DLS) and isothermal titration calorimetry (ITC) were used to study the interactions between bovine serum albumin (BSA) and the three quaternary ammonium surfactants N-dodecyl-N-(2-hydroxyethyl)-N,Ndimethyl ammonium bromide (DHDAB), N-tetradecyl-N-(2-hydroxyethyl)-N,N-dimethyl ammonium bromide (THDAB) and N-cetyl-N-(2-hydroxyethyl)-N,N-dimethyl ammonium bromide (CHDAB). These surfactants quenched the intrinsic fluorescence of BSA, with longer alkyl chains resulting in more significant quenching. This was attributed to static quenching. Further evidence of static quenching was provided by UV-Vis absorption spectroscopy. The particle size of BSA was found to initially increase and then decrease with increasing surfactant concentration. The concentration of surfactant changed the type of interaction mode. This work revealed the mechanism and binding characteristics between surfactants and protein, and provides the basis for further applications of surfactants.
UV-visible (UV-Vis) absorption spectroscopy, fluorescence spectroscopy (FL), dynamic light scattering (DLS) and isothermal titration calorimetry (ITC) were used to study the interactions between bovine serum albumin (BSA) and the three quaternary ammonium surfactants N-dodecyl-N-(2-hydroxyethyl)-N,Ndimethyl ammonium bromide (DHDAB), N-tetradecyl-N-(2-hydroxyethyl)-N,N-dimethyl ammonium bromide (THDAB) and N-cetyl-N-(2-hydroxyethyl)-N,N-dimethyl ammonium bromide (CHDAB). These surfactants quenched the intrinsic fluorescence of BSA, with longer alkyl chains resulting in more significant quenching. This was attributed to static quenching. Further evidence of static quenching was provided by UV-Vis absorption spectroscopy. The particle size of BSA was found to initially increase and then decrease with increasing surfactant concentration. The concentration of surfactant changed the type of interaction mode. This work revealed the mechanism and binding characteristics between surfactants and protein, and provides the basis for further applications of surfactants.
2016, 32(12): 2961-2967
doi: 10.3866/PKU.WHXB201609181
Abstract:
Aseriesof hybridmaterials ([C4mim]3+xPMo12-xVxO40, x=0, 1, 2)basedonV-substitutedphosphomolybdic acidH3+xPMo12-xVxO40 (x=0, 1, 2) and ionic liquid 1-butyl-3-methyl imidazolium bromide ([C4mim]Br) have been prepared by an anion-exchange method. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectrophotometry (FT-IR) and UV-Vis diffuse reflectance spectra (UV-Vis DRS) analysis. The catalytic performances of the samples were tested in oxidation of benzene to produce phenol using H2O2 as the oxidant. The results showed that the hybrids[C4mim]3+xPMo12-xVxO40 exhibit much higher catalytic properties than both the corresponding moieties. In particular, under the optimized conditions, 21% of benzene conversion and 99%selectivity for phenol have been obtained with[C4mim]5PMo10V2O40. The sample also exhibits good reusability and was reused five times without a significant decrease in conversion and selectivity.
Aseriesof hybridmaterials ([C4mim]3+xPMo12-xVxO40, x=0, 1, 2)basedonV-substitutedphosphomolybdic acidH3+xPMo12-xVxO40 (x=0, 1, 2) and ionic liquid 1-butyl-3-methyl imidazolium bromide ([C4mim]Br) have been prepared by an anion-exchange method. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectrophotometry (FT-IR) and UV-Vis diffuse reflectance spectra (UV-Vis DRS) analysis. The catalytic performances of the samples were tested in oxidation of benzene to produce phenol using H2O2 as the oxidant. The results showed that the hybrids[C4mim]3+xPMo12-xVxO40 exhibit much higher catalytic properties than both the corresponding moieties. In particular, under the optimized conditions, 21% of benzene conversion and 99%selectivity for phenol have been obtained with[C4mim]5PMo10V2O40. The sample also exhibits good reusability and was reused five times without a significant decrease in conversion and selectivity.
2016, 32(12): 2968-2975
doi: 10.3866/PKU.WHXB201609194
Abstract:
A novel metal-free D-π-A-π-A-based organic sensitizer OD2 featuring a N,N'-dimethylaniline unit as the donor residue, acetylene and benzene groups as π-spacer units, and benzothiadiazole and cyanoacrylic acid residues as acceptor units, was designed and synthesized. After the spectra and electrochemistry of the organic dye were investigated, it was applied in the development of solar energy conversion, including dyesensitized solar cell (DSSC) and dye-sensitized photocatalytic H2 production. For a typical device based on OD2, a maximum power conversion efficiency (η) of 4.40% was obtained under simulated AM 1.5 irradiation (100 mW·cm-2) with Jsc=10.58 mA·cm-2, Voc=630 mV and FF=0.65. In comparison, the efficiency of photocatalytic H2 production by OD2 sensitized Pt/TiO2 is low with a TON (turnover number)=140 and quantum efficiency for H2 conversion of water (ΦH2)=0.42% under visible light irradiation for 10 h with a 300 W Xe-lamp light source and 10% (volume fraction) aqueous triethanolamine (TEOA) at pH 7.0. The above results showed that OD2 has greater potential in the light-to-electricity conversion than light-to-fuel conversion.
A novel metal-free D-π-A-π-A-based organic sensitizer OD2 featuring a N,N'-dimethylaniline unit as the donor residue, acetylene and benzene groups as π-spacer units, and benzothiadiazole and cyanoacrylic acid residues as acceptor units, was designed and synthesized. After the spectra and electrochemistry of the organic dye were investigated, it was applied in the development of solar energy conversion, including dyesensitized solar cell (DSSC) and dye-sensitized photocatalytic H2 production. For a typical device based on OD2, a maximum power conversion efficiency (η) of 4.40% was obtained under simulated AM 1.5 irradiation (100 mW·cm-2) with Jsc=10.58 mA·cm-2, Voc=630 mV and FF=0.65. In comparison, the efficiency of photocatalytic H2 production by OD2 sensitized Pt/TiO2 is low with a TON (turnover number)=140 and quantum efficiency for H2 conversion of water (ΦH2)=0.42% under visible light irradiation for 10 h with a 300 W Xe-lamp light source and 10% (volume fraction) aqueous triethanolamine (TEOA) at pH 7.0. The above results showed that OD2 has greater potential in the light-to-electricity conversion than light-to-fuel conversion.
2016, 32(12): 2976-2982
doi: 10.3866/PKU.WHXB201610171
Abstract:
A hydrogel photonic crystal (HPC) film was fabricated for the specific detection of cadmium ions. This sensing film was based on a combination of a photonic crystal and a responsive hydrogel. It was fabricated using a "sandwich" filling method with a polystyrene (PS) colloidal crystal template, acrylamide (AM) and 1-allyl-2-thiourea (ATU) monomers. The morphology and responsivity were investigated in detail. The sensing film had an ordered, inverse opal structure and produced an optical signal in response to changes in the concentration of Cd2+. The Bragg diffraction peaks from the sensing film were blue shifted with increasing concentrations of Cd2+, and the color changes were visible to the naked eye. When the optimum ratio of monomers, suitable pH and ionic strength were used, the maximum displacement of the diffraction peak reached 51.1 nm. The presence of other interfering metal ions did not affect the specific response to Cd2+, and the sensing film exhibited a fast response rate. The cyclic tests showed that the sensing films had suitable mechanical and chemical stability because of their highly cross-linked structure. Importantly, these sensing films were allowed for high efficiency and rapid detection of Cd2+ by a color change that was visible to the naked eye.
A hydrogel photonic crystal (HPC) film was fabricated for the specific detection of cadmium ions. This sensing film was based on a combination of a photonic crystal and a responsive hydrogel. It was fabricated using a "sandwich" filling method with a polystyrene (PS) colloidal crystal template, acrylamide (AM) and 1-allyl-2-thiourea (ATU) monomers. The morphology and responsivity were investigated in detail. The sensing film had an ordered, inverse opal structure and produced an optical signal in response to changes in the concentration of Cd2+. The Bragg diffraction peaks from the sensing film were blue shifted with increasing concentrations of Cd2+, and the color changes were visible to the naked eye. When the optimum ratio of monomers, suitable pH and ionic strength were used, the maximum displacement of the diffraction peak reached 51.1 nm. The presence of other interfering metal ions did not affect the specific response to Cd2+, and the sensing film exhibited a fast response rate. The cyclic tests showed that the sensing films had suitable mechanical and chemical stability because of their highly cross-linked structure. Importantly, these sensing films were allowed for high efficiency and rapid detection of Cd2+ by a color change that was visible to the naked eye.
