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2016 Volume 32 Issue 2
2016, 32(2): 391-398
doi: 10.3866/PKU.WHXB201511023
Abstract:
Thermal analysis calorimeters can be used with different temperature control modes. Dynamic, isothermal, isoperibolic, and adiabatic modes are commonly used. A kinetic compensation effect was discovered when the kinetic parameters were calculated using the Arrhenius equation, based on dynamic and isothermal data. To determine whether the kinetic compensation effect existed in adiabatic mode, accelerating rate calorimetry (ARC) and differential scanning calorimetry (DSC) were used to obtain thermal decomposition curves of dicumyl peroxide (DCP), 40%(w) DCP in ethylbenzene, glucose, and 45% (w) glucose in water. The apparent activation energies (E) and pre-exponential factors (A) were calculated based on the Arrhenius rate constant. An obvious kinetic compensation effect was observed in a plot of lnA vs E for a given sample at different concentrations or for the same set of ARC data analyzed with different reaction orders n. Although the calculated lnA and E values using the dynamic differential scanning calorimetry data were usually lower than those using the adiabatic ARC data, a significant kinetic compensation effect existed between the two sets of results. This result suggested that the kinetic compensation effect existed between the activation energy and pre-exponential factor in reactions with the same or similar reaction mechanisms, regardless of the temperature control mode.
Thermal analysis calorimeters can be used with different temperature control modes. Dynamic, isothermal, isoperibolic, and adiabatic modes are commonly used. A kinetic compensation effect was discovered when the kinetic parameters were calculated using the Arrhenius equation, based on dynamic and isothermal data. To determine whether the kinetic compensation effect existed in adiabatic mode, accelerating rate calorimetry (ARC) and differential scanning calorimetry (DSC) were used to obtain thermal decomposition curves of dicumyl peroxide (DCP), 40%(w) DCP in ethylbenzene, glucose, and 45% (w) glucose in water. The apparent activation energies (E) and pre-exponential factors (A) were calculated based on the Arrhenius rate constant. An obvious kinetic compensation effect was observed in a plot of lnA vs E for a given sample at different concentrations or for the same set of ARC data analyzed with different reaction orders n. Although the calculated lnA and E values using the dynamic differential scanning calorimetry data were usually lower than those using the adiabatic ARC data, a significant kinetic compensation effect existed between the two sets of results. This result suggested that the kinetic compensation effect existed between the activation energy and pre-exponential factor in reactions with the same or similar reaction mechanisms, regardless of the temperature control mode.
2016, 32(2): 399-404
doi: 10.3866/PKU.WHXB201511272
Abstract:
Photochemically induced dynamic nuclear polarization (photo-CIDNP) is an effect that produces non-Boltzmann nuclear spin polarization, which can be observed as a modification of signal intensity in nuclear magnetic resonance (NMR) spectroscopy. The effect is well known in liquid-state NMR, where it is explained most generally by the classical radical pair mechanism (RPM). In the solid-state, additional mechanisms are operative in the spin-dynamics of radical pairs, such as three-spin mixing (TSM), differential decay (DD) and differential relaxation (DR). The observed solid-state photo-CIDNP effect is strongly magnetic field dependent, and this field-dependence is well distinguished for the various nuclei. Here, we provide an account of the phenomenology, theory and properties of the magnetic field dependence of the solid-state photo-CIDNP effect.
Photochemically induced dynamic nuclear polarization (photo-CIDNP) is an effect that produces non-Boltzmann nuclear spin polarization, which can be observed as a modification of signal intensity in nuclear magnetic resonance (NMR) spectroscopy. The effect is well known in liquid-state NMR, where it is explained most generally by the classical radical pair mechanism (RPM). In the solid-state, additional mechanisms are operative in the spin-dynamics of radical pairs, such as three-spin mixing (TSM), differential decay (DD) and differential relaxation (DR). The observed solid-state photo-CIDNP effect is strongly magnetic field dependent, and this field-dependence is well distinguished for the various nuclei. Here, we provide an account of the phenomenology, theory and properties of the magnetic field dependence of the solid-state photo-CIDNP effect.
2016, 32(2): 405-414
doi: 10.3866/PKU.WHXB201511192
Abstract:
Stable and metastable solid-liquid equilibria phenomena and complex salt-forming behaviors exist in complex salt-water systems. To realize the relationship between salt-forming behavior and liquid structure, the characteristics of ion association structures of SO42- in Na+, Mg2+//SO42-, Cl-, H2O system and its binary, ternary subsystems were studied by Raman spectroscopy, combined with a Gauss-Lorentz peak fitting program. The spectrum experimental results show that there were two ion association structures of SO42- as non-associated SO42- and SO42- groups in the Na2SO4-H2O system, while in the MgSO4-H2O, MgSO4-MgCl2-H2O, and Na+, Mg2+//SO42-, Cl-, H2O systems, there were also Mg2+-H2O-SO42- and Mg2+-OSO32- structures. Non-associated SO42- was the main structure in the ν1-SO42- band of binary (MgSO4 Na2SO4) and ternary (MgSO4-MgCl2-H2O) subsystems, and with varying SO42- concentration, these four types of SO42- ion association structure varied regularly. Likewise, the ion association structures of SO42- in the Na+, Mg2+//SO42-, Cl-, H2O system changed regularly during both the processes of NaCl crystallization and isothermal evaporation. This was evident when, during the process of decreasing NaCl concentration and increasing MgSO4, the content of non-associated SO42- decreased, the chance of Mg2+-H2O-SO42- and Mg2+-OSO32- structure formation increased, and the SO42- group structure appeared in the astrachanite region. More importantly, the adaptive changes in solution structure during the progress of evaporation can result in the appearance of metastable phenomena. Further linear analysis showed that the concentration and Jänecke index (J) value of SO42- were positively related to the intensity and peak area of the ν1-SO42- band, and the concentration of Mg2+ affected the contents of four ion association structures in the ν1-SO42- band mainly.
Stable and metastable solid-liquid equilibria phenomena and complex salt-forming behaviors exist in complex salt-water systems. To realize the relationship between salt-forming behavior and liquid structure, the characteristics of ion association structures of SO42- in Na+, Mg2+//SO42-, Cl-, H2O system and its binary, ternary subsystems were studied by Raman spectroscopy, combined with a Gauss-Lorentz peak fitting program. The spectrum experimental results show that there were two ion association structures of SO42- as non-associated SO42- and SO42- groups in the Na2SO4-H2O system, while in the MgSO4-H2O, MgSO4-MgCl2-H2O, and Na+, Mg2+//SO42-, Cl-, H2O systems, there were also Mg2+-H2O-SO42- and Mg2+-OSO32- structures. Non-associated SO42- was the main structure in the ν1-SO42- band of binary (MgSO4 Na2SO4) and ternary (MgSO4-MgCl2-H2O) subsystems, and with varying SO42- concentration, these four types of SO42- ion association structure varied regularly. Likewise, the ion association structures of SO42- in the Na+, Mg2+//SO42-, Cl-, H2O system changed regularly during both the processes of NaCl crystallization and isothermal evaporation. This was evident when, during the process of decreasing NaCl concentration and increasing MgSO4, the content of non-associated SO42- decreased, the chance of Mg2+-H2O-SO42- and Mg2+-OSO32- structure formation increased, and the SO42- group structure appeared in the astrachanite region. More importantly, the adaptive changes in solution structure during the progress of evaporation can result in the appearance of metastable phenomena. Further linear analysis showed that the concentration and Jänecke index (J) value of SO42- were positively related to the intensity and peak area of the ν1-SO42- band, and the concentration of Mg2+ affected the contents of four ion association structures in the ν1-SO42- band mainly.
2016, 32(2): 415-421
doi: 10.3866/PKU.WHXB201511191
Abstract:
Arylnitrenes and arylnitrenium ions are both short-lived intermediates that are highly reactive. In this work, nanosecond transient absorption and transient resonance Raman spectroscopic measurements were used to detect and identify the intermediates generated from the singlet 4'-nitro-4-biphenylnitrene after photolysis of the corresponding aryl azide in acetonitrile and aqueous solution. Combined with the density functional theory (DFT) simulation results, the structural and electronic characteristics of the above experimental intermediates were specified. The spectral results indicate that in aprotic solvents (such as acetonitrile), the singlet 4'-nitro-4-biphenylnitrene undergoes intersystem crossing (ISC) to the triplet nitrene. In contrast, in a protic solvent (such as the mixed aqueous solution used in this work), the singlet 4'-nitro-4-biphenylnitrene can be protonated to produce the nitrenium ion. Compared with its un-substituted counterpart, the nitro substitution has little influence on the ISC reaction pathway of the singlet 4-biphenylnitrene. With regard to the un-substituted nitrenium ion, the nitro group decreases its reactivity towards water and azide anion, while accelerating its reaction rate towards 2'-deoxyguanosine based on the different quench reaction rates between the nitrenium ion and azide anion/2'-deoxyguanosine. These results provide rich structural and kinetic information about related arylnitrenes and arylnitrenium ions, providing insights into their photolysis mechanism(s) through electronic and vibrational spectroscopic techniques.
Arylnitrenes and arylnitrenium ions are both short-lived intermediates that are highly reactive. In this work, nanosecond transient absorption and transient resonance Raman spectroscopic measurements were used to detect and identify the intermediates generated from the singlet 4'-nitro-4-biphenylnitrene after photolysis of the corresponding aryl azide in acetonitrile and aqueous solution. Combined with the density functional theory (DFT) simulation results, the structural and electronic characteristics of the above experimental intermediates were specified. The spectral results indicate that in aprotic solvents (such as acetonitrile), the singlet 4'-nitro-4-biphenylnitrene undergoes intersystem crossing (ISC) to the triplet nitrene. In contrast, in a protic solvent (such as the mixed aqueous solution used in this work), the singlet 4'-nitro-4-biphenylnitrene can be protonated to produce the nitrenium ion. Compared with its un-substituted counterpart, the nitro substitution has little influence on the ISC reaction pathway of the singlet 4-biphenylnitrene. With regard to the un-substituted nitrenium ion, the nitro group decreases its reactivity towards water and azide anion, while accelerating its reaction rate towards 2'-deoxyguanosine based on the different quench reaction rates between the nitrenium ion and azide anion/2'-deoxyguanosine. These results provide rich structural and kinetic information about related arylnitrenes and arylnitrenium ions, providing insights into their photolysis mechanism(s) through electronic and vibrational spectroscopic techniques.
2016, 32(2): 422-428
doi: 10.3866/PKU.WHXB201512082
Abstract:
The kinetics of the acid-catalyzed Smiles rearrangement reactions of 2,6-dimethoxy-2-pyrimidinyloxy-N-arylbenzylamine derivatives was investigated. The effects of initial concentrations of hydrochloric acid, solvent, temperature, and substituent on reaction rates were examined. The results show that the rates increase with an increase in the initial concentration of hydrochloric acid. The reactivity order is CH3OH > C2H5OH > CH3SOCH3 > CH3CN in a single solvent, but rates markedly increase in mixed CH3OH/H2O (1:1, V/V) and the apparent reaction rate constant (kobs) is 5.27 times that of methanol. The rates for the derivatives are found to increase with an increase in temperature at 25-45 ℃, and no significant differences in activation energy (73.99-76.92 kJ·mol-1), activation enthalpy (71.57-74.38 kJ·mol-1), and Gibbs free energy (81.51-85.77 kJ·mol-1) are observed between them, except that there is difference in activation entropy (-24.38 --47.11 J·K-1·mol-1). There is a good linear relationship between substituents and the apparent reaction rate constants, and it is speculated that electron-withdrawing groups in the benzene ring will increase the reaction rates. A relevant reaction mechanism is suggested.
The kinetics of the acid-catalyzed Smiles rearrangement reactions of 2,6-dimethoxy-2-pyrimidinyloxy-N-arylbenzylamine derivatives was investigated. The effects of initial concentrations of hydrochloric acid, solvent, temperature, and substituent on reaction rates were examined. The results show that the rates increase with an increase in the initial concentration of hydrochloric acid. The reactivity order is CH3OH > C2H5OH > CH3SOCH3 > CH3CN in a single solvent, but rates markedly increase in mixed CH3OH/H2O (1:1, V/V) and the apparent reaction rate constant (kobs) is 5.27 times that of methanol. The rates for the derivatives are found to increase with an increase in temperature at 25-45 ℃, and no significant differences in activation energy (73.99-76.92 kJ·mol-1), activation enthalpy (71.57-74.38 kJ·mol-1), and Gibbs free energy (81.51-85.77 kJ·mol-1) are observed between them, except that there is difference in activation entropy (-24.38 --47.11 J·K-1·mol-1). There is a good linear relationship between substituents and the apparent reaction rate constants, and it is speculated that electron-withdrawing groups in the benzene ring will increase the reaction rates. A relevant reaction mechanism is suggested.
2016, 32(2): 429-435
doi: 10.3866/PKU.WHXB201511201
Abstract:
Adenylate kinase is a kind of important enzymes which can catalyze the reversible reaction Mg2+ + ATP + AMP ⇌ 2ADP + Mg2+where the Mg2+ coordination around the active site plays a crucial role. It was shown experimentally that one Mg2+ ion can coordinate to both ADP molecules right after the chemical step of the catalytic reaction. During the substrate releasing and separation, the Mg2+ may transfer to one of the ADP molecules. However, it is unclear which ADP molecule binds with the Mg2+ during the substrate releasing. In this work, by using metadynamics method, we conducted molecular simulations on the adenylate kinase complexed with two ADP molecules and one Mg2+, which corresponds to the postcatalysis enzyme-substrate complex. We constructed the free energy landscapes characterizing the Mg2+ transfer to the individual ADP molecules. Our results show that the Mg2+ has preference to attach with the ADP molecule of the LID domain. We found that only when the LID domain ADP is protonated, and simultaneously the NMP domain ADP is deprotonated, the Mg2+ tends to attach with the NMP domain ADP. We also characterized the ligand exchange and dehydration processes during the Mg2+ transfer. Our results provide insights into the molecular process during the late state of the adenylate kinase catalytic cycle.
Adenylate kinase is a kind of important enzymes which can catalyze the reversible reaction Mg2+ + ATP + AMP ⇌ 2ADP + Mg2+where the Mg2+ coordination around the active site plays a crucial role. It was shown experimentally that one Mg2+ ion can coordinate to both ADP molecules right after the chemical step of the catalytic reaction. During the substrate releasing and separation, the Mg2+ may transfer to one of the ADP molecules. However, it is unclear which ADP molecule binds with the Mg2+ during the substrate releasing. In this work, by using metadynamics method, we conducted molecular simulations on the adenylate kinase complexed with two ADP molecules and one Mg2+, which corresponds to the postcatalysis enzyme-substrate complex. We constructed the free energy landscapes characterizing the Mg2+ transfer to the individual ADP molecules. Our results show that the Mg2+ has preference to attach with the ADP molecule of the LID domain. We found that only when the LID domain ADP is protonated, and simultaneously the NMP domain ADP is deprotonated, the Mg2+ tends to attach with the NMP domain ADP. We also characterized the ligand exchange and dehydration processes during the Mg2+ transfer. Our results provide insights into the molecular process during the late state of the adenylate kinase catalytic cycle.
2016, 32(2): 436-444
doi: 10.3866/PKU.WHXB201511302
Abstract:
To understand the allosteric modulation dynamics of non-nucleoside reverse transcriptase inhibitors (NNRTIs), various models and suggestions have been derived from crystallography and simulation. Here, using a new force field, ff12SB, and GPU parallel computing technology, we performed 100-ns-long molecular dynamics simulations on three reverse transcriptase (RT) systems, one bound to inhibitor Efavirenz (EFV) and the others free. Analyses of the influence of the EFV on the conformation of the RT, flexibility of residues and dynamic behaviors of the systems were conducted. The simulations indicate that EFV binding induces structural distortion of the RT, whereas the configuration of the RT is more stable during dynamics, along with a decreasing extent of motion of the residues. EFV suppresses the flexibility of the thumb subunit and reduces that of most residues in the fingers subdomain as well, suggesting that EFV causes not only the so-called“thumb arthritis” but also a slight“fingers arthritis”. No conformational transition occurred throughout the entire simulations and the samples maintained their starting conformations, i.e., free RT with a closed conformation stayed in the functional state and EFV-bound RT remained in open conformation. However, EFV-free RT with an initially open conformation exhibited an evident trend toward the closed state. These results agree with the models from experiments, and present a useful insight into the allosteric inhibition mechanism of NNRTIs. In addition, the simulation methodology has been discussed in detail and will be of significance to the computational simulation of large biological molecules.
To understand the allosteric modulation dynamics of non-nucleoside reverse transcriptase inhibitors (NNRTIs), various models and suggestions have been derived from crystallography and simulation. Here, using a new force field, ff12SB, and GPU parallel computing technology, we performed 100-ns-long molecular dynamics simulations on three reverse transcriptase (RT) systems, one bound to inhibitor Efavirenz (EFV) and the others free. Analyses of the influence of the EFV on the conformation of the RT, flexibility of residues and dynamic behaviors of the systems were conducted. The simulations indicate that EFV binding induces structural distortion of the RT, whereas the configuration of the RT is more stable during dynamics, along with a decreasing extent of motion of the residues. EFV suppresses the flexibility of the thumb subunit and reduces that of most residues in the fingers subdomain as well, suggesting that EFV causes not only the so-called“thumb arthritis” but also a slight“fingers arthritis”. No conformational transition occurred throughout the entire simulations and the samples maintained their starting conformations, i.e., free RT with a closed conformation stayed in the functional state and EFV-bound RT remained in open conformation. However, EFV-free RT with an initially open conformation exhibited an evident trend toward the closed state. These results agree with the models from experiments, and present a useful insight into the allosteric inhibition mechanism of NNRTIs. In addition, the simulation methodology has been discussed in detail and will be of significance to the computational simulation of large biological molecules.
2016, 32(2): 445-452
doi: 10.3866/PKU.WHXB201512013
Abstract:
Investigating the interactions between anionic surfactants and cations is of great theoretical and practical significance to understanding the precipitation and solubility of anionic surfactant products but relevant theoretical interaction models are seldom reported. In this paper, the density functional theory (DFT) method was used to investigate the interactions of the dodecylbenzenesulfonate anion (DBS-) with Na+, Mg2+, and Ca2+ both in the solution and at the air/water interface. In the solution, DBS-/cation interaction models were built and optimized with consideration of two different solutions (i.e. water and n-dodecane). The results indicate that DBScan bind stably with the cations in a bidentate form. The binding energy of the DBS-/cation depends on the properties of both the participating cation and the solvent. At the air/water interface, DBS- formed a stable hydrated complex with six water molecules (i.e. DBS-·6H2O). However, the structure of DBS-·6H2O was greatly disturbed by the introduction of the cation. A dimensionless parameter, def, was proposed to evaluate the deformation extent of the hydration shell. The degree of disturbance by the cations follows the order: Ca2+ >Mg2+ > Na+. A charge analysis reveals that the hydration shell plays an important role in the interactions between the sodium dodecyl benzene sulfonate (SDBS) headgroup and the cation.
Investigating the interactions between anionic surfactants and cations is of great theoretical and practical significance to understanding the precipitation and solubility of anionic surfactant products but relevant theoretical interaction models are seldom reported. In this paper, the density functional theory (DFT) method was used to investigate the interactions of the dodecylbenzenesulfonate anion (DBS-) with Na+, Mg2+, and Ca2+ both in the solution and at the air/water interface. In the solution, DBS-/cation interaction models were built and optimized with consideration of two different solutions (i.e. water and n-dodecane). The results indicate that DBScan bind stably with the cations in a bidentate form. The binding energy of the DBS-/cation depends on the properties of both the participating cation and the solvent. At the air/water interface, DBS- formed a stable hydrated complex with six water molecules (i.e. DBS-·6H2O). However, the structure of DBS-·6H2O was greatly disturbed by the introduction of the cation. A dimensionless parameter, def, was proposed to evaluate the deformation extent of the hydration shell. The degree of disturbance by the cations follows the order: Ca2+ >Mg2+ > Na+. A charge analysis reveals that the hydration shell plays an important role in the interactions between the sodium dodecyl benzene sulfonate (SDBS) headgroup and the cation.
2016, 32(2): 453-464
doi: 10.3866/PKU.WHXB201512071
Abstract:
1,3-Butadiene is an important product in combustion and pyrolysis of hydrocarbon fuels and it is also an important precursor to formpolycyclic aromatic hydrocarbons (PAHs). Currently, a variety of experimental and mechanism studies have been performed on 1,3-butadiene oxidation. However, few studies about pyrolysis mechanism of 1,3-butadiene have been done. In this work, the optimization of the geometries and the vibrational frequencies for the reactants, products, and transition states of the relevant reactions in 1,3-butadiene pyrolysis have been performed at the B3LYP/CBSB7 level. Their single point energies and the thermodynamic parameters are also calculated by using the composite CBS-QB3 method. The high-pressure limit rate constants for tight transition state reactions and barrierless reactions are obtained by transition state theory and variable reaction coordinate transition state theory, respectively. The calculated rate constants in this work are in good agreement with those available from literature. Furthermore, the mechanism of Hidaka et al. is updated with replacing the calculated rate constants of reactions in this work to simulate the shock tube experiment results of 1,3-butadiene pyrolysisand the updated mechanism consists of 45 species and 224 reactions. It can be seen that the updated mechanism can improve the concentration profiles of the main products, ethylene, 1-butylene-3-acetylene, and benzene in 1,3-butadiene pyrolysis. It can also provide reliable kinetic and thermodynamic parameters to further improve the core mechanism of C0-C4 species.
1,3-Butadiene is an important product in combustion and pyrolysis of hydrocarbon fuels and it is also an important precursor to formpolycyclic aromatic hydrocarbons (PAHs). Currently, a variety of experimental and mechanism studies have been performed on 1,3-butadiene oxidation. However, few studies about pyrolysis mechanism of 1,3-butadiene have been done. In this work, the optimization of the geometries and the vibrational frequencies for the reactants, products, and transition states of the relevant reactions in 1,3-butadiene pyrolysis have been performed at the B3LYP/CBSB7 level. Their single point energies and the thermodynamic parameters are also calculated by using the composite CBS-QB3 method. The high-pressure limit rate constants for tight transition state reactions and barrierless reactions are obtained by transition state theory and variable reaction coordinate transition state theory, respectively. The calculated rate constants in this work are in good agreement with those available from literature. Furthermore, the mechanism of Hidaka et al. is updated with replacing the calculated rate constants of reactions in this work to simulate the shock tube experiment results of 1,3-butadiene pyrolysisand the updated mechanism consists of 45 species and 224 reactions. It can be seen that the updated mechanism can improve the concentration profiles of the main products, ethylene, 1-butylene-3-acetylene, and benzene in 1,3-butadiene pyrolysis. It can also provide reliable kinetic and thermodynamic parameters to further improve the core mechanism of C0-C4 species.
2016, 32(2): 465-473
doi: 10.3866/PKU.WHXB201511242
Abstract:
Denitrogeneration of petroleum products can reduce NOx emission during combustion, and relieve the poisoning of catalysts. Because of their high catalytic activities and excellent stabilities, transition metal phosphides exhibit great potential as novel, promising hydrodenitrogeneration (HDN) catalysts. Based on a periodic slab model, we investigated the adsorption and C―N bond cleavage mechanism of aniline on MoP(001) surface by density functional theory (DFT) calculations. The results show that aniline adsorption prefers a flat configuration, with larger adsorption energies, in which the C―C and C―N bonds are activated. The direct C―N bond cleavage mechanism of aniline proceeds mainly via deamination with co-adsorbed H2, producing benzene and ammonia. The C―N bond cleavage mechanism for adsorbed cyclohexylamine proceeds via deamination, with co-adsorbed H, and the main products are cyclohexene and ammonia.
Denitrogeneration of petroleum products can reduce NOx emission during combustion, and relieve the poisoning of catalysts. Because of their high catalytic activities and excellent stabilities, transition metal phosphides exhibit great potential as novel, promising hydrodenitrogeneration (HDN) catalysts. Based on a periodic slab model, we investigated the adsorption and C―N bond cleavage mechanism of aniline on MoP(001) surface by density functional theory (DFT) calculations. The results show that aniline adsorption prefers a flat configuration, with larger adsorption energies, in which the C―C and C―N bonds are activated. The direct C―N bond cleavage mechanism of aniline proceeds mainly via deamination with co-adsorbed H2, producing benzene and ammonia. The C―N bond cleavage mechanism for adsorbed cyclohexylamine proceeds via deamination, with co-adsorbed H, and the main products are cyclohexene and ammonia.
2016, 32(2): 474-480
doi: 10.3866/PKU.WHXB201511104
Abstract:
Polyaniline (PANI) nanomaterials doped with three different sulfonic acid surfactants (perfluorinated sulfonic acid ion exchange resin (Nafion), sodium dodecyl sulfate (SDS), and sodium dodecyl benzene sulfonate (SDBS)) were prepared using an emulsion polymerization method with manganese dioxide (MnO2) as the oxidant. The structure and morphology of the products were studied by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD). Symmetric redox supercapacitor was assembled with doped PANI as the active electrode material. The electrochemical performances of the materials were evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge tests. These results suggest that the introduction of surfactant is beneficial for the formation of a fiber structure and increases the dispersion of PANI. A PANI-Nafion network with distributed porosity and average diameters of 30-40 nm is obtained. The specific capacitances of PANI-Nafion, PANI-SDS, and PANI-SDBS electrodes at 0.1 A·g-1 are 385.3, 359.7, and 401.6 F·g-1, respectively. Among these electrodes PANI-Nafion delivers the best cycle performance, maintaining 70.7% of its initial capacitance after 1000 cycles.
Polyaniline (PANI) nanomaterials doped with three different sulfonic acid surfactants (perfluorinated sulfonic acid ion exchange resin (Nafion), sodium dodecyl sulfate (SDS), and sodium dodecyl benzene sulfonate (SDBS)) were prepared using an emulsion polymerization method with manganese dioxide (MnO2) as the oxidant. The structure and morphology of the products were studied by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD). Symmetric redox supercapacitor was assembled with doped PANI as the active electrode material. The electrochemical performances of the materials were evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge tests. These results suggest that the introduction of surfactant is beneficial for the formation of a fiber structure and increases the dispersion of PANI. A PANI-Nafion network with distributed porosity and average diameters of 30-40 nm is obtained. The specific capacitances of PANI-Nafion, PANI-SDS, and PANI-SDBS electrodes at 0.1 A·g-1 are 385.3, 359.7, and 401.6 F·g-1, respectively. Among these electrodes PANI-Nafion delivers the best cycle performance, maintaining 70.7% of its initial capacitance after 1000 cycles.
2016, 32(2): 481-492
doi: 10.3866/PKU.WHXB201511041
Abstract:
Different kinds of phosphorus-containing activated carbons were prepared by phosphoric acid activation of lignocellulosic precursor and modification with H3PO4. Elemental analysis, X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption were employed to analyze the elemental content, surface chemistry, and pore structures of the activated carbons. The electrochemical properties of the carbon materials were characterized for their application as supercapacitors in KOH and H2SO4 electrolytes using galvanostatic charge/discharge, cyclic voltammetry, and electrochemical impedance spectroscopic analyses. A statistical analysis by an intercept-free multiple linear regression method was employed to investigate the factors that influence the specific capacitance of activated carbon electrodes. In addition, a three-electrode cell setup was used to analyze the cause of the phosphorus contribution on capacitance. The results show that phosphorus increases the specific capacitance of activated carbons by the introduction of pseudo-capacitance; the activated carbon with phosphorus content of 5.88% (w) exhibits a specific capacitance of 185 F·g-1 at 0.1 A·g-1. The statistical analysis showed that mesopores facilitate an access of electrolyte ions to the surface of micropores. The pores in the width ranges of 1.10-1.61 nm, 2.12-2.43 nm and 3.94 -4.37 nm benefit the formation of the electric double layer in 6 mol·L-1 KOH electrolyte; the pores with sizes of 0.67-0.72 nm have a positive effect in 1 mol·L-1 H2SO4 electrolyte.
Different kinds of phosphorus-containing activated carbons were prepared by phosphoric acid activation of lignocellulosic precursor and modification with H3PO4. Elemental analysis, X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption were employed to analyze the elemental content, surface chemistry, and pore structures of the activated carbons. The electrochemical properties of the carbon materials were characterized for their application as supercapacitors in KOH and H2SO4 electrolytes using galvanostatic charge/discharge, cyclic voltammetry, and electrochemical impedance spectroscopic analyses. A statistical analysis by an intercept-free multiple linear regression method was employed to investigate the factors that influence the specific capacitance of activated carbon electrodes. In addition, a three-electrode cell setup was used to analyze the cause of the phosphorus contribution on capacitance. The results show that phosphorus increases the specific capacitance of activated carbons by the introduction of pseudo-capacitance; the activated carbon with phosphorus content of 5.88% (w) exhibits a specific capacitance of 185 F·g-1 at 0.1 A·g-1. The statistical analysis showed that mesopores facilitate an access of electrolyte ions to the surface of micropores. The pores in the width ranges of 1.10-1.61 nm, 2.12-2.43 nm and 3.94 -4.37 nm benefit the formation of the electric double layer in 6 mol·L-1 KOH electrolyte; the pores with sizes of 0.67-0.72 nm have a positive effect in 1 mol·L-1 H2SO4 electrolyte.
2016, 32(2): 493-502
doi: 10.3866/PKU.WHXB201511131
Abstract:
Polypyrrole (PPY)/nitric acid (HNO3) activated carbon aerogel (HCA) composites are prepared through chemical oxidative polymerization with different PPY/HCAmass ratios. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM) were employed to investigate the components and morphology of the samples. The results demonstrate that the synthesized materials maintain the threedimensional nanoporous structure of the carbon aerogel (CA); the activation by nitric acid and composition with PPY do not destroy the porous structure of the carbon aerogel and the complex still has the original threedimensional nanoporous structure. Composites with different mass ratios (3:1, 2:1, 1:1, 1:2, 1:3) of PPY/HCA were prepared and the electrochemical properties were measured by cyclic voltammetry, galvanostatic charge-discharge test, and electrochemical impedance spectroscopy. The results confirm that the PPY/HCA composite with a ratio of 1:1 exhibits the best electrochemical performances; it has a high specific capacitance of 336 F·g-1, which is more than two times higher than that of CA (103 F·g-1); it also exhibits outstanding conductivity and cycling stability, retaining 91% of its initial capacitance after 2000 cycles. Therefore, this composite is quite a promising electrode material for supercapacitors.
Polypyrrole (PPY)/nitric acid (HNO3) activated carbon aerogel (HCA) composites are prepared through chemical oxidative polymerization with different PPY/HCAmass ratios. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM) were employed to investigate the components and morphology of the samples. The results demonstrate that the synthesized materials maintain the threedimensional nanoporous structure of the carbon aerogel (CA); the activation by nitric acid and composition with PPY do not destroy the porous structure of the carbon aerogel and the complex still has the original threedimensional nanoporous structure. Composites with different mass ratios (3:1, 2:1, 1:1, 1:2, 1:3) of PPY/HCA were prepared and the electrochemical properties were measured by cyclic voltammetry, galvanostatic charge-discharge test, and electrochemical impedance spectroscopy. The results confirm that the PPY/HCA composite with a ratio of 1:1 exhibits the best electrochemical performances; it has a high specific capacitance of 336 F·g-1, which is more than two times higher than that of CA (103 F·g-1); it also exhibits outstanding conductivity and cycling stability, retaining 91% of its initial capacitance after 2000 cycles. Therefore, this composite is quite a promising electrode material for supercapacitors.
2016, 32(2): 503-509
doi: 10.3866/PKU.WHXB201512032
Abstract:
Silver-based ceramic composite electrodes are expected to be widely applied in medium-or lowtemperature solid oxide fuel cells (SOFCs), SOFCs operated on carbon-containing fuels, and solid oxide electrolysis cells (SOECs). To optimize the composition of a silver-based ceramic composite electrode, the performances of Ag-YSZ (yttrium-stabilized zirconia) and Ag-GDC (gadolinium doped ceria) are investigated. First, they are used as electrode materials to make symmetric electrodes on a YSZ electrolyte, to which impedance spectra are measured in an ambient atmosphere to evaluate their feasibility as cathode materials. It was found that that Ag-YSZ reaches the lowest polarization resistance when the content of Ag is 65%(w, mass fraction), while for Ag-GDC, the value is 70% (w). The Ag-YSZ and Ag-GDC with the lowest polarization resistance are used as electrode materials to make SOFC single cells whose electrochemical performances are tested. The polarization resistance of an anode of the SOFCs can be obtained by subtracting the cathode polarization resistance from the overall SOFC polarization resistance. Both the polarization resistance result and the output performance show that the performance of Ag-GDC is superior to Ag-YSZ as an anode. In the present work, Ag-YSZ is more suitable as the cathode and the Ag-GDC as the anode. The present work provides not only useful data for Ag-based composite electrodes but also a method for measuring the polarization resistance of SOFC anodes.
Silver-based ceramic composite electrodes are expected to be widely applied in medium-or lowtemperature solid oxide fuel cells (SOFCs), SOFCs operated on carbon-containing fuels, and solid oxide electrolysis cells (SOECs). To optimize the composition of a silver-based ceramic composite electrode, the performances of Ag-YSZ (yttrium-stabilized zirconia) and Ag-GDC (gadolinium doped ceria) are investigated. First, they are used as electrode materials to make symmetric electrodes on a YSZ electrolyte, to which impedance spectra are measured in an ambient atmosphere to evaluate their feasibility as cathode materials. It was found that that Ag-YSZ reaches the lowest polarization resistance when the content of Ag is 65%(w, mass fraction), while for Ag-GDC, the value is 70% (w). The Ag-YSZ and Ag-GDC with the lowest polarization resistance are used as electrode materials to make SOFC single cells whose electrochemical performances are tested. The polarization resistance of an anode of the SOFCs can be obtained by subtracting the cathode polarization resistance from the overall SOFC polarization resistance. Both the polarization resistance result and the output performance show that the performance of Ag-GDC is superior to Ag-YSZ as an anode. In the present work, Ag-YSZ is more suitable as the cathode and the Ag-GDC as the anode. The present work provides not only useful data for Ag-based composite electrodes but also a method for measuring the polarization resistance of SOFC anodes.
2016, 32(2): 510-518
doi: 10.3866/PKU.WHXB201511134
Abstract:
CsNO3/SiO2 catalysts were prepared using an impregnation method, and were applied in the vapor phase catalytic synthesis of vinylidene chloride (VDC) from 1,1,2-trichloroethane (TCE). The influence of reaction temperature on the deactivation of CsNO3/SiO2 catalysts was investigated in detail. It was found that low reaction temperatures (< 350 ℃) lead to a rapid deactivation, while high reaction temperatures (> 400 ℃) result in a high and stable catalytic activity. During the dehydrochlorination process, CsNO3 species were transformed into CsCl, and coke was formed and deposited on the catalyst surface. However, the chemical change of the Cs species and deposited coke were not the main reason for the deactivation of CsNO3/SiO2 catalyst. Some chlorine-containing species (organic products or HCl) were formed during the reaction and were difficult to desorb from the catalyst surface, which accounts for the deactivation of CsNO3/SiO2 catalysts at low reaction temperatures. High temperature treatment (550 ℃) in a non-oxidizing atmosphere could remove the contaminants and regenerate the catalysts completely. The life test of CsNO3/SiO2 catalyst was carried out at 400 ℃ for 100 h. The TCE conversion and the selectivity to VDC remained stable at 98% and 78%, respectively, showing good prospect for industrial applications.
CsNO3/SiO2 catalysts were prepared using an impregnation method, and were applied in the vapor phase catalytic synthesis of vinylidene chloride (VDC) from 1,1,2-trichloroethane (TCE). The influence of reaction temperature on the deactivation of CsNO3/SiO2 catalysts was investigated in detail. It was found that low reaction temperatures (< 350 ℃) lead to a rapid deactivation, while high reaction temperatures (> 400 ℃) result in a high and stable catalytic activity. During the dehydrochlorination process, CsNO3 species were transformed into CsCl, and coke was formed and deposited on the catalyst surface. However, the chemical change of the Cs species and deposited coke were not the main reason for the deactivation of CsNO3/SiO2 catalyst. Some chlorine-containing species (organic products or HCl) were formed during the reaction and were difficult to desorb from the catalyst surface, which accounts for the deactivation of CsNO3/SiO2 catalysts at low reaction temperatures. High temperature treatment (550 ℃) in a non-oxidizing atmosphere could remove the contaminants and regenerate the catalysts completely. The life test of CsNO3/SiO2 catalyst was carried out at 400 ℃ for 100 h. The TCE conversion and the selectivity to VDC remained stable at 98% and 78%, respectively, showing good prospect for industrial applications.
2016, 32(2): 519-526
doi: 10.3866/PKU.WHXB201511243
Abstract:
High-silica MFI zeolite membranes supported on porous α-alumina discs were prepared by a seeded secondary growth method, using tetrapropylammonium hydroxide (TPAOH) as organic template. First, nanocrystals were deposited on rough α-Al2O3 discs by a spin-on process. Then, based on controlling the H2O/Si molar ratio of the synthetic solution, a restricting in-plane h0h-oriented growth method with an ultra-dilute precursor was designed to prepare non-defective zeolite membranes that were as thin as possible. Finally, crosslinked and dense MFI zeolite membranes were prepared after the third synthesis step, giving a membrane layer thickness of about 8 μm, including ~5 μm dense layers and ~3 μm intermediate layers. Anovel, two-step method, coupling by low-temperature hydrocracking and oxidation, is proposed for efficient removal of the template from zeolite membranes. Compared with traditional high-temperature calcination, template removal by the two-step method could eliminate the grain boundary defects formed in response to stresses induced by heat treatment. As a result, the membranes treated by the two-step detemplation method displayed a preferable CO2/N2 separation factor (about 5.2) and high CO2 permeance (5.8 × 10-7 mol·m-2·s-11·Pa-1) at 30 ℃.
High-silica MFI zeolite membranes supported on porous α-alumina discs were prepared by a seeded secondary growth method, using tetrapropylammonium hydroxide (TPAOH) as organic template. First, nanocrystals were deposited on rough α-Al2O3 discs by a spin-on process. Then, based on controlling the H2O/Si molar ratio of the synthetic solution, a restricting in-plane h0h-oriented growth method with an ultra-dilute precursor was designed to prepare non-defective zeolite membranes that were as thin as possible. Finally, crosslinked and dense MFI zeolite membranes were prepared after the third synthesis step, giving a membrane layer thickness of about 8 μm, including ~5 μm dense layers and ~3 μm intermediate layers. Anovel, two-step method, coupling by low-temperature hydrocracking and oxidation, is proposed for efficient removal of the template from zeolite membranes. Compared with traditional high-temperature calcination, template removal by the two-step method could eliminate the grain boundary defects formed in response to stresses induced by heat treatment. As a result, the membranes treated by the two-step detemplation method displayed a preferable CO2/N2 separation factor (about 5.2) and high CO2 permeance (5.8 × 10-7 mol·m-2·s-11·Pa-1) at 30 ℃.
2016, 32(2): 527-535
doi: 10.3866/PKU.WHXB201512033
Abstract:
Mass transfer behaviors of benzene in an in situ crystallization fluid catalytic cracking (FCC) catalyst were measured and discriminated by the frequency response (FR) method and an intelligent gravimetric analyzer (IGA). The texture properties of the FCC catalysts were analyzed by N2 adsorption and scanning electron microscope (SEM). By comparison with the mass transfer performance of a semi-synthetic FCC catalyst, as well as a zeolite Y, the results show that the in situ crystallization FCC catalyst has excellent and improved mass transfer behavior over the semi-synthetic FCC catalyst and that it reduces the mass transfer resistance between the interface of zeolite crystal and substrate, which can be attributed to the excellent porous connectivity of the former with the unique accumulation state of the highly dispersed nanosized Y zeolite crystals. It has been demonstrated that the FR technique can be used to measure and distinguish the complex mass transport processes in hierarchical porous catalytic materials.
Mass transfer behaviors of benzene in an in situ crystallization fluid catalytic cracking (FCC) catalyst were measured and discriminated by the frequency response (FR) method and an intelligent gravimetric analyzer (IGA). The texture properties of the FCC catalysts were analyzed by N2 adsorption and scanning electron microscope (SEM). By comparison with the mass transfer performance of a semi-synthetic FCC catalyst, as well as a zeolite Y, the results show that the in situ crystallization FCC catalyst has excellent and improved mass transfer behavior over the semi-synthetic FCC catalyst and that it reduces the mass transfer resistance between the interface of zeolite crystal and substrate, which can be attributed to the excellent porous connectivity of the former with the unique accumulation state of the highly dispersed nanosized Y zeolite crystals. It has been demonstrated that the FR technique can be used to measure and distinguish the complex mass transport processes in hierarchical porous catalytic materials.
2016, 32(2): 536-542
doi: 10.3866/PKU.WHXB201511103
Abstract:
Rare earth (RE) and B co-doped (RE-B) nano-TiO2 photocatalysts were prepared through a sol-gel method using tetrabutyl titanate, lanthanum nitrate, cerous nitrate, and boric acid. The phase constitution, surface morphology, surface elemental compositions, light responsivity, the band gap and the composite of the electronic hole of catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and ultraviolet-visible spectroscopy (UV-Vis). The results show that all the doped products were anatase TiO2, and RE-B doping generates large lattice distortion and had the function of refining the grain, with the grain size decreasing from 27 nm (TiO2) to 10 nm (La-B-TiO2). The doped TiO2 was flake structure and piled up irregularly. Co-doping enhanced the absorption in the visible region and narrowed the band gap simultaneously. The absorption edge of La-B-TiO2 moved from 405 nm to 466 nm, and the band gap decreased 0.4 eV correspondingly. XPS results show that the doping elements have effectively doped into the titanium dioxide, and PL spectra show that the co-doping can effectively extend the life of the carrier. The photocatalytic activities of the samples were estimated by degrading methylene blue (MB) under visible and ultraviolet light irradiation for 2 h, and show much improved catalytic activity compared to un-doped TiO2. The degradation rate of MB using La/B-TiO2 was 80.67% under ultraviolet light, which is about 2.7 times that of un-doped TiO2, and 74.78 % under visible light.
Rare earth (RE) and B co-doped (RE-B) nano-TiO2 photocatalysts were prepared through a sol-gel method using tetrabutyl titanate, lanthanum nitrate, cerous nitrate, and boric acid. The phase constitution, surface morphology, surface elemental compositions, light responsivity, the band gap and the composite of the electronic hole of catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and ultraviolet-visible spectroscopy (UV-Vis). The results show that all the doped products were anatase TiO2, and RE-B doping generates large lattice distortion and had the function of refining the grain, with the grain size decreasing from 27 nm (TiO2) to 10 nm (La-B-TiO2). The doped TiO2 was flake structure and piled up irregularly. Co-doping enhanced the absorption in the visible region and narrowed the band gap simultaneously. The absorption edge of La-B-TiO2 moved from 405 nm to 466 nm, and the band gap decreased 0.4 eV correspondingly. XPS results show that the doping elements have effectively doped into the titanium dioxide, and PL spectra show that the co-doping can effectively extend the life of the carrier. The photocatalytic activities of the samples were estimated by degrading methylene blue (MB) under visible and ultraviolet light irradiation for 2 h, and show much improved catalytic activity compared to un-doped TiO2. The degradation rate of MB using La/B-TiO2 was 80.67% under ultraviolet light, which is about 2.7 times that of un-doped TiO2, and 74.78 % under visible light.
2016, 32(2): 543-550
doi: 10.3866/PKU.WHXB201511194
Abstract:
ZnO microstructures and nanostructures with controlled-morphology were synthesized by the hydrothermal method. All samples were prepared using precursors at different pH values and then annealed at 500 ℃ for 2 h. The samples were characterized by X-ray diffraction (XRD) patterns, scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-Vis), and BET specific surface area measurement. All samples were confirmed by XRD to be wurtzite ZnO. As the pH value of the precursor increased, sheet-like ZnO disappeared and rod-like ZnO was produced. The major surfaces of sheet-like and rod-like ZnO were polar and nonpolar crystal faces, respectively. At pH 6.5, Cl- was adsorbed onto the (002) polar face and inhibited the growth along the polar crystal face ({Zn2+}crystal surface). A microporous sheet ZnO was formed by annealing the obtained sheet-like Zn5(OH)8Cl2·H2O. When OH- was added into the precursor, Zn(OH)42- was generated via coordination with Zn2+, which was adsorbed onto the (002) polar face and promoted growth along the polar crystal face. Rod-like ZnO was thus produced. The obtained ZnO could photocatalytically reduce CO2 under illumination. Sheet-like ZnO exhibited better photocatalytic performance than rod-like ZnO. This may be because the polar crystal face shows better photocatalytic activity than the unpolar crystal face.
ZnO microstructures and nanostructures with controlled-morphology were synthesized by the hydrothermal method. All samples were prepared using precursors at different pH values and then annealed at 500 ℃ for 2 h. The samples were characterized by X-ray diffraction (XRD) patterns, scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-Vis), and BET specific surface area measurement. All samples were confirmed by XRD to be wurtzite ZnO. As the pH value of the precursor increased, sheet-like ZnO disappeared and rod-like ZnO was produced. The major surfaces of sheet-like and rod-like ZnO were polar and nonpolar crystal faces, respectively. At pH 6.5, Cl- was adsorbed onto the (002) polar face and inhibited the growth along the polar crystal face ({Zn2+}crystal surface). A microporous sheet ZnO was formed by annealing the obtained sheet-like Zn5(OH)8Cl2·H2O. When OH- was added into the precursor, Zn(OH)42- was generated via coordination with Zn2+, which was adsorbed onto the (002) polar face and promoted growth along the polar crystal face. Rod-like ZnO was thus produced. The obtained ZnO could photocatalytically reduce CO2 under illumination. Sheet-like ZnO exhibited better photocatalytic performance than rod-like ZnO. This may be because the polar crystal face shows better photocatalytic activity than the unpolar crystal face.
2016, 32(2): 551-557
doi: 10.3866/PKU.WHXB201511304
Abstract:
Bi2Sn2O7, synthesized through different hydrothermal routes (the microwave hydrothermal method (MH-BSO) and the traditional hydrothermal method (TH-BSO)), was used for photocatalytic removal of arsenic from aqueous solution. The as-synthesized Bi2Sn2O7 products were characterized by X-ray diffraction (XRD), N2 sorption-desorption, UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), transmission electron microscopy (TEM), electron spin resonance (ESR), X-ray photoelectron spectra (XPS), and electrochemistry technology. Under visible light irradiation, the MH-BSO sample exhibited a higher photocatalytic activity (up to 98.7%) than that of the TH-BSO sample during the oxidization of arsenite (AsO3)3-. The active species, O2-· and hVB+, were identified as the primary active species responsible for As(Ⅲ) oxidation. In addition, a possible mechanism for the photo-oxidation of As(Ⅲ) over Bi2Sn2O7 is proposed.
Bi2Sn2O7, synthesized through different hydrothermal routes (the microwave hydrothermal method (MH-BSO) and the traditional hydrothermal method (TH-BSO)), was used for photocatalytic removal of arsenic from aqueous solution. The as-synthesized Bi2Sn2O7 products were characterized by X-ray diffraction (XRD), N2 sorption-desorption, UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), transmission electron microscopy (TEM), electron spin resonance (ESR), X-ray photoelectron spectra (XPS), and electrochemistry technology. Under visible light irradiation, the MH-BSO sample exhibited a higher photocatalytic activity (up to 98.7%) than that of the TH-BSO sample during the oxidization of arsenite (AsO3)3-. The active species, O2-· and hVB+, were identified as the primary active species responsible for As(Ⅲ) oxidation. In addition, a possible mechanism for the photo-oxidation of As(Ⅲ) over Bi2Sn2O7 is proposed.
2016, 32(2): 558-564
doi: 10.3866/PKU.WHXB201511271
Abstract:
Chlorpyrifos (CPF) was firstly included in sulfonated hydroxyethyl-β-cyclodextrin (SBECD) and carboxymethyl-β-cyclodextrin (CMCD) in an ethanol or 1-methyl-2-pyrrolidinone (NMP) solvent. Inclusion complexes (CPF/SBECD and CPF/CMCD) were then intercalated into the galleries of ZnAl-layered double hydroxides (ZAL) to synthesize ZAL-SBECD-CPF and ZAL-CMCD-CPF intercalated materials. The structure and thermal stability of nanohybrids were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and thermal gravimetric and differential thermal analysis (TG-DTA). The results showed that both CPF/SBECD and CPF/SBECD were successfully intercalated in the interlayer. The samples prepared in the NMP solvent had a stronger diffraction peak intensity than those prepared with ethanol. The intercalated CPF molecules had a high thermal stability. Furthermore, the release behaviors of CPF from ZALSBECD-CPF and ZAL-CMCD-CPF nanohybrids were investigated and analyzed at pH 5.0 and 6.8. ZAL-SBECD-CPF had almost no slow-release behavior, while ZAL-CMCD-CPF showed distinct slow-release, which was caused by the different arrangements of cyclodextrin (CD) in the interlayer. BC release from nanohybrids was faster and the amount released higher at pH 6.8 than at pH 5.0. This was closely correlated with the structural type of CD and the release media. The CPF release kinetic process can be fitted well by pseudo-second-order and parabolic diffusion models. ZAL-CMCD-CPF remarkably exhibited controlled release behavior, suggesting that it can be potentially applied as a controlled release pesticide formulation.
Chlorpyrifos (CPF) was firstly included in sulfonated hydroxyethyl-β-cyclodextrin (SBECD) and carboxymethyl-β-cyclodextrin (CMCD) in an ethanol or 1-methyl-2-pyrrolidinone (NMP) solvent. Inclusion complexes (CPF/SBECD and CPF/CMCD) were then intercalated into the galleries of ZnAl-layered double hydroxides (ZAL) to synthesize ZAL-SBECD-CPF and ZAL-CMCD-CPF intercalated materials. The structure and thermal stability of nanohybrids were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and thermal gravimetric and differential thermal analysis (TG-DTA). The results showed that both CPF/SBECD and CPF/SBECD were successfully intercalated in the interlayer. The samples prepared in the NMP solvent had a stronger diffraction peak intensity than those prepared with ethanol. The intercalated CPF molecules had a high thermal stability. Furthermore, the release behaviors of CPF from ZALSBECD-CPF and ZAL-CMCD-CPF nanohybrids were investigated and analyzed at pH 5.0 and 6.8. ZAL-SBECD-CPF had almost no slow-release behavior, while ZAL-CMCD-CPF showed distinct slow-release, which was caused by the different arrangements of cyclodextrin (CD) in the interlayer. BC release from nanohybrids was faster and the amount released higher at pH 6.8 than at pH 5.0. This was closely correlated with the structural type of CD and the release media. The CPF release kinetic process can be fitted well by pseudo-second-order and parabolic diffusion models. ZAL-CMCD-CPF remarkably exhibited controlled release behavior, suggesting that it can be potentially applied as a controlled release pesticide formulation.
2016, 32(2): 565-572
doi: 10.3866/PKU.WHXB201511301
Abstract:
The microcosmic process of bovine serum albumin (BSA) adsorbing onto hydroxyapatite (HA) for different time intervals was investigated by Fourier transform infrared attenuated total internal reflectance (FTIRATR) spectrometry. The initial dissolution and re-precipitation of PO43-, Ca2+, and OH- ions from the HA coating led to the occurrence of the coating including adsorbed BSA on the HA from surface-to subsurface-molecular layers and to in-depth interaction between BSA and HA. The subtraction results gained in the adsorption regions of HA and BSA reveal that the binding of P=O, from the phosphate (PO43-), to the hydrogen of amide II, methyl and methene of the BSA appears to be considerably more rapid and stronger than that of the P―O group. In addition, it is very likely that Ca2+ plays an important role in the interaction of BSA with HA. It appears that the binding of Ca2+ to the carbonyl-oxygen of the peptide bond in BSAcaused a significant, molecular, conformational rearrangement of polypeptide backbones from β-pleated sheet to helical circles of α-helix and β-turn. This change appears to have been followed by much hydrogen of polypeptides being driven to bind PO43- and OHeffectively and much ―C=O and H―N―groups of the peptide bond being freed from inter-chain hydrogenbonding to act on Ca2+ and combine strongly with the HA surface. This might reasonably be expected to promote hard tissue regeneration. BSA seems to be activated by the inductive effect of Ca2+ via the molecular rearrangement of polypeptide backbones from pleated sheet to helical circles and in turn reacts strongly on the HA, resulting in profound effects on the course of biomineralization.
The microcosmic process of bovine serum albumin (BSA) adsorbing onto hydroxyapatite (HA) for different time intervals was investigated by Fourier transform infrared attenuated total internal reflectance (FTIRATR) spectrometry. The initial dissolution and re-precipitation of PO43-, Ca2+, and OH- ions from the HA coating led to the occurrence of the coating including adsorbed BSA on the HA from surface-to subsurface-molecular layers and to in-depth interaction between BSA and HA. The subtraction results gained in the adsorption regions of HA and BSA reveal that the binding of P=O, from the phosphate (PO43-), to the hydrogen of amide II, methyl and methene of the BSA appears to be considerably more rapid and stronger than that of the P―O group. In addition, it is very likely that Ca2+ plays an important role in the interaction of BSA with HA. It appears that the binding of Ca2+ to the carbonyl-oxygen of the peptide bond in BSAcaused a significant, molecular, conformational rearrangement of polypeptide backbones from β-pleated sheet to helical circles of α-helix and β-turn. This change appears to have been followed by much hydrogen of polypeptides being driven to bind PO43- and OHeffectively and much ―C=O and H―N―groups of the peptide bond being freed from inter-chain hydrogenbonding to act on Ca2+ and combine strongly with the HA surface. This might reasonably be expected to promote hard tissue regeneration. BSA seems to be activated by the inductive effect of Ca2+ via the molecular rearrangement of polypeptide backbones from pleated sheet to helical circles and in turn reacts strongly on the HA, resulting in profound effects on the course of biomineralization.
2016, 32(2): 573-580
doi: 10.3866/PKU.WHXB201511105
Abstract:
Metal oxides are promising high-capacity anode materials for lithium and sodium-ion batteries because of the reversible multi-electron structural conversion reactions with lithium and sodium ions. In this study, Fe2O3/rGO (reduced graphene oxide) nanocomposites were prepared using graphene oxide sheets and ferric salt as precursors through a one-step solvothermal method. The experimental results demonstrated that the Fe2O3 nanocrystals were uniformly dispersed on the surface of reduced graphene oxide sheets. The nanocomposite anodes show superior charge-discharge performances and cyclability in lithium and sodium ion batteries,indicating that reduced graphene oxide sheets can reduce the charge-transfer resistance and stabilize the structure change during cycling. It suggests a potential feasibility to use these metal oxide nanocomposites as high capacity anode materials for lithium and sodium ion batteries.
Metal oxides are promising high-capacity anode materials for lithium and sodium-ion batteries because of the reversible multi-electron structural conversion reactions with lithium and sodium ions. In this study, Fe2O3/rGO (reduced graphene oxide) nanocomposites were prepared using graphene oxide sheets and ferric salt as precursors through a one-step solvothermal method. The experimental results demonstrated that the Fe2O3 nanocrystals were uniformly dispersed on the surface of reduced graphene oxide sheets. The nanocomposite anodes show superior charge-discharge performances and cyclability in lithium and sodium ion batteries,indicating that reduced graphene oxide sheets can reduce the charge-transfer resistance and stabilize the structure change during cycling. It suggests a potential feasibility to use these metal oxide nanocomposites as high capacity anode materials for lithium and sodium ion batteries.
2016, 32(2): 581-588
doi: 10.3866/PKU.WHXB201512014
Abstract:
Anatase titania nanocrystals with different shapes were successfully prepared by a solvothermal method, using titanium butoxide as a precursor, ethanol as a solvent, and lauric acid and dodecyl amine as stabilizing agents. The structure, size, morphology, and shape of the nanocrystals were characterized by transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), Fourier transmission infrared (FTIR) spectroscopy, and thermogravimetric-differential thermal analysis (TG-DTA). We discuss how the ratio of lauric acid to dodecyl amine can influence the shape of nanocrystals. XRD results indicate that the phase of titania nanocrystals synthesized under different conditions is pure anatase. The shapes of titania nanocrystals gradually evolve from spheres to rods with increasing dodecyl amine content (at constant total molar content of lauric acid and dodecyl amine). The crystallinity of anatase titania nanocrystals prepared at a molar ratio of 1:1 (lauric acid to dodecyl amine) was better than that of nanocrystals prepared at other molar ratios. The stabilizing agents and nanocrystal core were combined by a bridging coordination ligand, and the content of stabilizing agents in samples was about 5%.
Anatase titania nanocrystals with different shapes were successfully prepared by a solvothermal method, using titanium butoxide as a precursor, ethanol as a solvent, and lauric acid and dodecyl amine as stabilizing agents. The structure, size, morphology, and shape of the nanocrystals were characterized by transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), Fourier transmission infrared (FTIR) spectroscopy, and thermogravimetric-differential thermal analysis (TG-DTA). We discuss how the ratio of lauric acid to dodecyl amine can influence the shape of nanocrystals. XRD results indicate that the phase of titania nanocrystals synthesized under different conditions is pure anatase. The shapes of titania nanocrystals gradually evolve from spheres to rods with increasing dodecyl amine content (at constant total molar content of lauric acid and dodecyl amine). The crystallinity of anatase titania nanocrystals prepared at a molar ratio of 1:1 (lauric acid to dodecyl amine) was better than that of nanocrystals prepared at other molar ratios. The stabilizing agents and nanocrystal core were combined by a bridging coordination ligand, and the content of stabilizing agents in samples was about 5%.
2016, 32(2): 589-594
doi: 10.3866/PKU.WHXB201512083
Abstract:
A 3-aryl-2-cyano acrylamide derivative (Z)-2-cyano-3-(3,4-dimethoxy-phenyl)acrylamide (CDMPA) was designed and synthesized, which exhibited piezochromism and acidchromism properties. Under external mechanical force stimuli, CDMPA showed a red-shift of 20 nm in its fluorescence emission and the mechanically induced luminescence color could return to the original state via heating or solvent vapor treatment. Powder X-ray diffraction (XRD) and fluorescence lifetime experiments indicated that the piezochromic luminescence could be attributed to the transformation from the crystalline to the amorphous phase. Additionally, the fluorescence color changed from blue to yellow with a red-shift of 33 nm using the stimulus of protonation. The emission color was recovered upon fuming with dimethyl formamide (DMF) vapor. Infrared (IR) spectra of CDMPA powder and theoretical calculation of the frontier molecular orbitals showed that protonation of the amino moieties in CDMPA had a significant effect on the frontier molecular orbitals and, thus, caused the acidchromism phenomenon. This study provides comprehensive insight into the stimuli-responsive luminescent mechanisms within this type of compound and the reversible switching of emission color may enable discovery of novel applications of CDMPA for detection and sensing devices.
A 3-aryl-2-cyano acrylamide derivative (Z)-2-cyano-3-(3,4-dimethoxy-phenyl)acrylamide (CDMPA) was designed and synthesized, which exhibited piezochromism and acidchromism properties. Under external mechanical force stimuli, CDMPA showed a red-shift of 20 nm in its fluorescence emission and the mechanically induced luminescence color could return to the original state via heating or solvent vapor treatment. Powder X-ray diffraction (XRD) and fluorescence lifetime experiments indicated that the piezochromic luminescence could be attributed to the transformation from the crystalline to the amorphous phase. Additionally, the fluorescence color changed from blue to yellow with a red-shift of 33 nm using the stimulus of protonation. The emission color was recovered upon fuming with dimethyl formamide (DMF) vapor. Infrared (IR) spectra of CDMPA powder and theoretical calculation of the frontier molecular orbitals showed that protonation of the amino moieties in CDMPA had a significant effect on the frontier molecular orbitals and, thus, caused the acidchromism phenomenon. This study provides comprehensive insight into the stimuli-responsive luminescent mechanisms within this type of compound and the reversible switching of emission color may enable discovery of novel applications of CDMPA for detection and sensing devices.
