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2018 Volume 34 Issue 5
2018, 34(5): 445-446
doi: 10.3866/PKU.WHXB201709293
Abstract:
2018, 34(5): 447-448
doi: 10.3866/PKU.WHXB201710123
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2018, 34(5): 449-450
doi: 10.3866/PKU.WHXB201710121
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2018, 34(5): 451-452
doi: 10.3866/PKU.WHXB201710122
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2018, 34(5): 453-454
doi: 10.3866/PKU.WHXB201710272
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2018, 34(5): 455-455
doi: 10.3866/PKU.WHXB201711082
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2018, 34(5): 456-475
doi: 10.3866/PKU.WHXB201709211
Abstract:
The frequency of oil-spill accidents and industrial wastewater discharges have caused severe water pollution, not only resulting in huge economic losses but also threatening the ecological system. Recently, researchers have developed different types of materials with special wettability (such as superhydrophobicity or superoleophobicity) and used them successfully for oil-water separation. Superhydrophobic and superoleophobic surfaces can generally be obtained by designing the surface geometric micro-topography and chemical composition of solid materials. Endowing porous materials with reverse super-wettability to water and oil using various microfabrication technologies is the key to separate oil-water mixtures. In this review we initially identify the significance of fabricating oil/water-separating materials and achieving effective separations. Then, the typical theoretical principles underlying surface wettability are briefly introduced. According to the difference in surface wettabilities toward water and oil, we classify the current oil-water separating materials into three categories: (ⅰ) superhydrophobic/superoleophilic materials, (ⅱ) superoleophobic/ superhydrophilic materials, and (ⅲ) smart-response materials with switchable wettability. This review summarizes the representative research work for each of these materials, including their fabrication methods, principle and process of oil-water separation, and main characteristics and applications. Finally, existing problems, challenges, and future prospects of this fast-growing field of special wettability porous materials for the separation of oil-water mixtures are discussed.
The frequency of oil-spill accidents and industrial wastewater discharges have caused severe water pollution, not only resulting in huge economic losses but also threatening the ecological system. Recently, researchers have developed different types of materials with special wettability (such as superhydrophobicity or superoleophobicity) and used them successfully for oil-water separation. Superhydrophobic and superoleophobic surfaces can generally be obtained by designing the surface geometric micro-topography and chemical composition of solid materials. Endowing porous materials with reverse super-wettability to water and oil using various microfabrication technologies is the key to separate oil-water mixtures. In this review we initially identify the significance of fabricating oil/water-separating materials and achieving effective separations. Then, the typical theoretical principles underlying surface wettability are briefly introduced. According to the difference in surface wettabilities toward water and oil, we classify the current oil-water separating materials into three categories: (ⅰ) superhydrophobic/superoleophilic materials, (ⅱ) superoleophobic/ superhydrophilic materials, and (ⅲ) smart-response materials with switchable wettability. This review summarizes the representative research work for each of these materials, including their fabrication methods, principle and process of oil-water separation, and main characteristics and applications. Finally, existing problems, challenges, and future prospects of this fast-growing field of special wettability porous materials for the separation of oil-water mixtures are discussed.
2018, 34(5): 476-482
doi: 10.3866/PKU.WHXB201709151
Abstract:
Two new coordination polymers, namely, [[Zn2(TTR4A)(L)2]·DMF·4H2O]n (compound 1) and [[Co(TTR4A)Cl2]·DMA·H2O]n (compound 2), have been synthesized under solvothermal conditions (TTR4A = tetrakis(1, 2, 4-triazol-ylmethylresorcin[4]arene), L = 4, 4'-biphenyldicarboxylic acid, DMF = N, N-dimethylformamide and DMA = N, N-dimethylacetamide). Crystal structures of the coordination compounds 1 and 2 were determined by single-crystal X-ray diffraction analyses, and further characterized by infrared spectra, elemental analyses, powder X-ray diffraction, and thermogravimetric analyses. In coordination compound 1, four L ligands bridge four adjacent Zn(Ⅱ) atoms to generate macrocyclic Zn4L4 units, which are further linked by the TTR4A ligands into a one-dimensional chain structure. In coordination compound 2, four 1, 2, 4-triazole groups of each TTR4A ligand bridge four Co(Ⅱ) atoms to form a two-dimensional layer structure. Furthermore, studies on the luminescent properties of compound 1 in solid state at room temperature reveal that it exhibits an intense emission peak. Luminescent-sensing detections for Fe3+, Cr2O72−, and nitrobenzene solvents were also investigated by using compound 1 as the potential luminescent sensor.
Two new coordination polymers, namely, [[Zn2(TTR4A)(L)2]·DMF·4H2O]n (compound 1) and [[Co(TTR4A)Cl2]·DMA·H2O]n (compound 2), have been synthesized under solvothermal conditions (TTR4A = tetrakis(1, 2, 4-triazol-ylmethylresorcin[4]arene), L = 4, 4'-biphenyldicarboxylic acid, DMF = N, N-dimethylformamide and DMA = N, N-dimethylacetamide). Crystal structures of the coordination compounds 1 and 2 were determined by single-crystal X-ray diffraction analyses, and further characterized by infrared spectra, elemental analyses, powder X-ray diffraction, and thermogravimetric analyses. In coordination compound 1, four L ligands bridge four adjacent Zn(Ⅱ) atoms to generate macrocyclic Zn4L4 units, which are further linked by the TTR4A ligands into a one-dimensional chain structure. In coordination compound 2, four 1, 2, 4-triazole groups of each TTR4A ligand bridge four Co(Ⅱ) atoms to form a two-dimensional layer structure. Furthermore, studies on the luminescent properties of compound 1 in solid state at room temperature reveal that it exhibits an intense emission peak. Luminescent-sensing detections for Fe3+, Cr2O72−, and nitrobenzene solvents were also investigated by using compound 1 as the potential luminescent sensor.
2018, 34(5): 543-550
doi: 10.3866/PKU.WHXB201709291
Abstract:
Three kinds of novel coordination compounds [Re3+-C] (Re = La, Gd, Er; C = Catechin) were synthesized by the liquid-phase method, and characterized by Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV) spectrophotometry, X-ray photoelectron spectroscopy (XPS), and coordination number determination. The results indicated that the coordination number of the complexes is 8. Moreover, the antibacterial activities of Re3+-C against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Salmonella were evaluated by the Oxford cup, minimum inhibition concentration (MIC), and minimum bactericidal concentration (MBC) approaches. Compared with Re3+ and C, the as-prepared complexes exhibited excellent antimicrobial activity toward the four strains. The MIC of Gd3+-C to these food-borne bacteria was 1.550, 0.0968, 0.775, and 1.550 μmol·mL−1, respectively, while the corresponding MBC values were 3.100, 0.194, 1.550, and 1.550 μmol·mL−1. It is clear that the Gd3+-C complex showed the best antibacterial and germicidal activity against S. aureus.
Three kinds of novel coordination compounds [Re3+-C] (Re = La, Gd, Er; C = Catechin) were synthesized by the liquid-phase method, and characterized by Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV) spectrophotometry, X-ray photoelectron spectroscopy (XPS), and coordination number determination. The results indicated that the coordination number of the complexes is 8. Moreover, the antibacterial activities of Re3+-C against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Salmonella were evaluated by the Oxford cup, minimum inhibition concentration (MIC), and minimum bactericidal concentration (MBC) approaches. Compared with Re3+ and C, the as-prepared complexes exhibited excellent antimicrobial activity toward the four strains. The MIC of Gd3+-C to these food-borne bacteria was 1.550, 0.0968, 0.775, and 1.550 μmol·mL−1, respectively, while the corresponding MBC values were 3.100, 0.194, 1.550, and 1.550 μmol·mL−1. It is clear that the Gd3+-C complex showed the best antibacterial and germicidal activity against S. aureus.
2018, 34(5): 483-491
doi: 10.3866/PKU.WHXB201709111
Abstract:
X-ray scattering measurements were performed on 1.0 mol·dm-3 RbCl and CsCl aqueous solutions. The X-ray structure factors were subjected to empirical potential structure refinement to extract detailed structural information on hydrated Cl-, Rb+, Cs+, and ion association, as well as bulk water, in terms of the individual site-site pair correlation functions, coordination number distributions, and spatial density functions (three-dimensional structure). Cl- is found to have a relatively stable six-fold coordination of water molecules with a Cl--H2O distance of 0.321 nm, and without a significant cation effect on its local structure. Rb+ is surrounded on an average by 7.3 ± 1.4 water molecules with a Rb+-H2O distance of 0.297 nm, whereas 8.4 ± 1.6 water molecules hydrate Cs+ at a Cs+-H2O distance of 0.312 nm. It is likely that Rb+ has a stronger hydration shell than Cs+, as evidenced by the presence of the second hydration shell of the former. Contact ion-pairs are partially formed in both solutions and characterized by the Rb+-Cl- and Cs+-Cl- distances of 0.324 nm and 0.336 nm. The solvent-separated ion pairs for both ions are discernible at around 0.6 nm. Rb+ has a stronger electrostatic interaction and hence a relatively stronger ion association with Cl- than Cs+.
X-ray scattering measurements were performed on 1.0 mol·dm-3 RbCl and CsCl aqueous solutions. The X-ray structure factors were subjected to empirical potential structure refinement to extract detailed structural information on hydrated Cl-, Rb+, Cs+, and ion association, as well as bulk water, in terms of the individual site-site pair correlation functions, coordination number distributions, and spatial density functions (three-dimensional structure). Cl- is found to have a relatively stable six-fold coordination of water molecules with a Cl--H2O distance of 0.321 nm, and without a significant cation effect on its local structure. Rb+ is surrounded on an average by 7.3 ± 1.4 water molecules with a Rb+-H2O distance of 0.297 nm, whereas 8.4 ± 1.6 water molecules hydrate Cs+ at a Cs+-H2O distance of 0.312 nm. It is likely that Rb+ has a stronger hydration shell than Cs+, as evidenced by the presence of the second hydration shell of the former. Contact ion-pairs are partially formed in both solutions and characterized by the Rb+-Cl- and Cs+-Cl- distances of 0.324 nm and 0.336 nm. The solvent-separated ion pairs for both ions are discernible at around 0.6 nm. Rb+ has a stronger electrostatic interaction and hence a relatively stronger ion association with Cl- than Cs+.
2018, 34(5): 492-496
doi: 10.3866/PKU.WHXB201709221
Abstract:
The density functional theory and its extension to ensembles of excited states can be formalized as thermodynamics. However, these theories are not unique because one of their key quantities, the kinetic energy density, can be defined in several ways. Usually, the everywhere positive gradient form is applied; however, other forms are also acceptable, provided they integrate to the true kinetic energy. Recently, a kinetic energy density of the ground-state theory maximizing the information entropy has been proposed. Here, ensemble kinetic energy density, leading to extremum information entropy, is derived via constrained search. The corresponding ensemble temperature is found to be constant.
The density functional theory and its extension to ensembles of excited states can be formalized as thermodynamics. However, these theories are not unique because one of their key quantities, the kinetic energy density, can be defined in several ways. Usually, the everywhere positive gradient form is applied; however, other forms are also acceptable, provided they integrate to the true kinetic energy. Recently, a kinetic energy density of the ground-state theory maximizing the information entropy has been proposed. Here, ensemble kinetic energy density, leading to extremum information entropy, is derived via constrained search. The corresponding ensemble temperature is found to be constant.
2018, 34(5): 497-502
doi: 10.3866/PKU.WHXB201709222
Abstract:
o-Thioquinones can undergo either [2+4] or [4+2] cycloaddition reactions with acyclic dienes. To illustrate the bonding processes in these cycloadditions, the natural orbital Fukui function (NOFF) and bonding reactivity descriptor have been employed. The electrophilicity of a bond or an orbital in the o-thioquinone as well as in the acyclic diene has been found using the NOFF, which suggests that electron transfer takes place from an electron-donating bonding orbital to an electron-accepting antibonding/bonding orbital, leading to the cyclic product via the formation of a circular loop and two covalent bonds. The bonding reactivity descriptor shows that covalent bonds readily form between atom k1 of one molecule with a large fk1+ value and atom k2 of another molecule with a large fk2- value. Both the NOFF and the bonding reactivity descriptor are efficient tools for interpreting the mechanism underlying the [2+4] and [4+2] cycloaddition between o-thioquinones and acyclic dienes.
o-Thioquinones can undergo either [2+4] or [4+2] cycloaddition reactions with acyclic dienes. To illustrate the bonding processes in these cycloadditions, the natural orbital Fukui function (NOFF) and bonding reactivity descriptor have been employed. The electrophilicity of a bond or an orbital in the o-thioquinone as well as in the acyclic diene has been found using the NOFF, which suggests that electron transfer takes place from an electron-donating bonding orbital to an electron-accepting antibonding/bonding orbital, leading to the cyclic product via the formation of a circular loop and two covalent bonds. The bonding reactivity descriptor shows that covalent bonds readily form between atom k1 of one molecule with a large fk1+ value and atom k2 of another molecule with a large fk2- value. Both the NOFF and the bonding reactivity descriptor are efficient tools for interpreting the mechanism underlying the [2+4] and [4+2] cycloaddition between o-thioquinones and acyclic dienes.
2018, 34(5): 503-513
doi: 10.3866/PKU.WHXB201709252
Abstract:
Numerous real space functions have been purposed so far for unveiling chemically interesting molecular electronic structure characteristics, such as chemical bonds, lone pairs, and multicenter electronic conjugations. Among these analysis methods, electron localization function (ELF), Laplacian of electron density (∇2ρ), and deformation density (ρdef) were widely employed in practical research work. It is well known that the analysis of total molecular electron density is not sufficient for revealing much information about the molecular electronic structure like the above-mentioned methods. However, in this work, using several instances and by comparing with the ELF, ∇2ρ, and ρdef values, we show that it is possible to explore molecular electronic structure characteristics if one solely focuses on investigating the valence electron density distribution. It is found that for most cases, analysis of the very simple valence electron density conveys analogous information as ELF, ∇2ρ and ρdef analyses, with additional advantage of reduced computational complexity. We hope that this work will bring chemists' attention to the high importance of valence electron density, which has been largely ignored for a long time. It should also be noticed that the valence electron density analysis is not free from drawbacks, and when this method is unable to provide an informative picture, one has to use other analysis methods.
Numerous real space functions have been purposed so far for unveiling chemically interesting molecular electronic structure characteristics, such as chemical bonds, lone pairs, and multicenter electronic conjugations. Among these analysis methods, electron localization function (ELF), Laplacian of electron density (∇2ρ), and deformation density (ρdef) were widely employed in practical research work. It is well known that the analysis of total molecular electron density is not sufficient for revealing much information about the molecular electronic structure like the above-mentioned methods. However, in this work, using several instances and by comparing with the ELF, ∇2ρ, and ρdef values, we show that it is possible to explore molecular electronic structure characteristics if one solely focuses on investigating the valence electron density distribution. It is found that for most cases, analysis of the very simple valence electron density conveys analogous information as ELF, ∇2ρ and ρdef analyses, with additional advantage of reduced computational complexity. We hope that this work will bring chemists' attention to the high importance of valence electron density, which has been largely ignored for a long time. It should also be noticed that the valence electron density analysis is not free from drawbacks, and when this method is unable to provide an informative picture, one has to use other analysis methods.
2018, 34(5): 514-518
doi: 10.3866/PKU.WHXB201710101
Abstract:
In this study, we show how to generalize Hirshfeld partitioning methods to possibly include non-spherical proatom densities. While this generalization is numerically challenging (requiring global optimization of a large number of parameters), it is conceptually appealing because it allows the proatoms to be pre-polarized, or even promoted, to a state that more closely resembles the atom in a molecule. This method is based on first characterizing the convex set of proatom densities associated with the degenerate ground states of isolated atoms and atomic ions. The preferred orientation of the proatoms' densities are then obtained by minimizing the information–theoretic distance between the promolecular and molecular densities. If contributions from excited states (and not just degenerate ground states) are included in the convex set, this method can describe promoted atoms. While the procedure is intractable in general, if one includes only atomic states that have differing electron-numbers and/or spins, the variational principle becomes a simple convex optimization with a single unique solution.
In this study, we show how to generalize Hirshfeld partitioning methods to possibly include non-spherical proatom densities. While this generalization is numerically challenging (requiring global optimization of a large number of parameters), it is conceptually appealing because it allows the proatoms to be pre-polarized, or even promoted, to a state that more closely resembles the atom in a molecule. This method is based on first characterizing the convex set of proatom densities associated with the degenerate ground states of isolated atoms and atomic ions. The preferred orientation of the proatoms' densities are then obtained by minimizing the information–theoretic distance between the promolecular and molecular densities. If contributions from excited states (and not just degenerate ground states) are included in the convex set, this method can describe promoted atoms. While the procedure is intractable in general, if one includes only atomic states that have differing electron-numbers and/or spins, the variational principle becomes a simple convex optimization with a single unique solution.
2018, 34(5): 519-527
doi: 10.3866/PKU.WHXB201710126
Abstract:
Regioselectivities of electrophilic addition reactions of hydrogen chloride to asymmetric alkenes and benzeneselenenyl bromide to substituted styrenes have been investigated by using reactivity descriptors, including Fukui function f(r), local softness s(r), generalized Fukui function fG(r), and generalized local softness sG(r). All of them are obtained from the finite difference approximation method calculated by ab initio method at MP2/6-311++G(d, p) level of theory and our ABEEMσπ model, respectively. According to the generalized version of the local hard-soft and acid-base (HSAB) principle, the forecasted regioselectivities of our investigated additions using the ABEEMσπ model are in fair agreement with the experimental values. In particular, we can also rationalize their reaction rate constants by the generalized local softness, i.e., the softest the site is, the easiest the reaction is. Hence, the generalized reactivity descriptors work quite well.
Regioselectivities of electrophilic addition reactions of hydrogen chloride to asymmetric alkenes and benzeneselenenyl bromide to substituted styrenes have been investigated by using reactivity descriptors, including Fukui function f(r), local softness s(r), generalized Fukui function fG(r), and generalized local softness sG(r). All of them are obtained from the finite difference approximation method calculated by ab initio method at MP2/6-311++G(d, p) level of theory and our ABEEMσπ model, respectively. According to the generalized version of the local hard-soft and acid-base (HSAB) principle, the forecasted regioselectivities of our investigated additions using the ABEEMσπ model are in fair agreement with the experimental values. In particular, we can also rationalize their reaction rate constants by the generalized local softness, i.e., the softest the site is, the easiest the reaction is. Hence, the generalized reactivity descriptors work quite well.
2018, 34(5): 528-536
doi: 10.3866/PKU.WHXB201710111
Abstract:
Tools have been designed obtain information about chemical bonds from quantum mechanical calculations. They work well for solutions of the stationary Schrödinger equation, but it is not clear whether Lewis electron pairs they aim to reproduce survive in time-dependent processes, in spite of the underlying Pauli principle being obeyed in this regime. A simple model of two same-spin non-interacting fermions in a one-dimensional box with an opaque wall, is used to study this problem, because it allows presenting the detailed structure of the wave function. It is shown that ⅰ) oscillations persisting after the Hamiltonian stopped changing produce for certain time intervals states where Lewis electron pairs are spatially separated, and ⅱ) methods (like density analysis, or the electron localization function) that are widely used for describing bonding in the stationary case, have limitations in such situations. An exception is provided by the maximum probability domain (the spatial domain that maximizes the probability to find a given number of particles in it). It is conceptually simple, and satisfactorily describes the phenomenon.
Tools have been designed obtain information about chemical bonds from quantum mechanical calculations. They work well for solutions of the stationary Schrödinger equation, but it is not clear whether Lewis electron pairs they aim to reproduce survive in time-dependent processes, in spite of the underlying Pauli principle being obeyed in this regime. A simple model of two same-spin non-interacting fermions in a one-dimensional box with an opaque wall, is used to study this problem, because it allows presenting the detailed structure of the wave function. It is shown that ⅰ) oscillations persisting after the Hamiltonian stopped changing produce for certain time intervals states where Lewis electron pairs are spatially separated, and ⅱ) methods (like density analysis, or the electron localization function) that are widely used for describing bonding in the stationary case, have limitations in such situations. An exception is provided by the maximum probability domain (the spatial domain that maximizes the probability to find a given number of particles in it). It is conceptually simple, and satisfactorily describes the phenomenon.
2018, 34(5): 537-542
doi: 10.3866/PKU.WHXB201710161
Abstract:
Herein we have investigated the interaction between hydrazoic acid (HN3) and a pristine graphyne system based on density functional theory (DFT) method using generalized gradient approximation. The van der Waals dispersion correction is also considered for predicting the possibility of using the graphyne system for detection of hydrazoic acid. Pristine graphyne has a band gap of 0.453 eV, which decreases to 0.424 eV when HN3 is adsorbed on graphyne. The electrical conductivity of HN3-adsorbed graphyne is greater than that of its pristine counterpart. Charge transfer analysis reveals that the HN3-adsorbed graphyne system behaves as an n-type semiconductor; however, its pristine analogue acts as an intrinsic semiconductor. Pristine graphyne has zero dipole moment; however, its interaction with HN3 increases its dipole moment. The electronic properties of graphyne is significantly influenced by the presence of HN3, leading to the possibility of designing graphyne-based sensors for HN3 detection.
Herein we have investigated the interaction between hydrazoic acid (HN3) and a pristine graphyne system based on density functional theory (DFT) method using generalized gradient approximation. The van der Waals dispersion correction is also considered for predicting the possibility of using the graphyne system for detection of hydrazoic acid. Pristine graphyne has a band gap of 0.453 eV, which decreases to 0.424 eV when HN3 is adsorbed on graphyne. The electrical conductivity of HN3-adsorbed graphyne is greater than that of its pristine counterpart. Charge transfer analysis reveals that the HN3-adsorbed graphyne system behaves as an n-type semiconductor; however, its pristine analogue acts as an intrinsic semiconductor. Pristine graphyne has zero dipole moment; however, its interaction with HN3 increases its dipole moment. The electronic properties of graphyne is significantly influenced by the presence of HN3, leading to the possibility of designing graphyne-based sensors for HN3 detection.
