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2016 Volume 32 Issue 1
2016, 32(1): 1-1
doi: 10.3866/PKU.WHXB201601041
Abstract:
2016, 32(1): 2-13
doi: 10.3866/PKU.WHXB201510192
Abstract:
One of the most appealing ways to resolve the worldwide energy crisis and environmental pollution is by converting solar energy into storable chemical energy as hydrogen through solar water splitting. The redox reactions of photogenerated charge carriers occurring on the surface of photocatalysts during the process of solar water splitting are particularly complex. Owing to the high reaction overpotentials and sluggish desorption kinetics of gas products, surface reaction is the rate-determining step in the solar water splitting process. Therefore, a great deal of attention has been focused on this specific research area. The recent advances and prospects for future directions regarding the importance of surface reactions for solar water splitting are presented. The main strategies to enhance the surface water splitting reaction kinetics are summarized. The roles and classifications of surface cocatalysts, as well as the effects of passivating the surface states and coating surface protective layers, are discussed by integrating the principles of photocatalysis. Prospects for the future development of surface reaction research are also proposed.
One of the most appealing ways to resolve the worldwide energy crisis and environmental pollution is by converting solar energy into storable chemical energy as hydrogen through solar water splitting. The redox reactions of photogenerated charge carriers occurring on the surface of photocatalysts during the process of solar water splitting are particularly complex. Owing to the high reaction overpotentials and sluggish desorption kinetics of gas products, surface reaction is the rate-determining step in the solar water splitting process. Therefore, a great deal of attention has been focused on this specific research area. The recent advances and prospects for future directions regarding the importance of surface reactions for solar water splitting are presented. The main strategies to enhance the surface water splitting reaction kinetics are summarized. The roles and classifications of surface cocatalysts, as well as the effects of passivating the surface states and coating surface protective layers, are discussed by integrating the principles of photocatalysis. Prospects for the future development of surface reaction research are also proposed.
2016, 32(1): 14-27
doi: 10.3866/PKU.WHXB201511133
Abstract:
Glass, an amorphous oxide material with a long history, is widely used in our daily life. Graphene is a novel two-dimensional material formed by carbon atoms. The unique properties of graphene, such as excellent mechanical strength, high electrical and thermal conductivity and optical transparency, serve as complementary components to those of glass. Therefore, the combination of graphene and glass would endow noticeable electrical/thermal conductivity and surface hydrophobicity without sacrificing the transparency of conventional glass. Previously reported routes for integrating graphene with glass mainly used solution-casting of liquid-exfoliated graphene nanoplatelets and transfer-coating of graphene films grown on metals. Compared with the existing methods, the direct growth of graphene on glass could avoid contamination and damage during the integration process, thereby resulting in good graphene quality and scalability, high thickness/ coverage uniformity, much reduced breakage density, and a tight and clean interface with the underlying glass. In this article, we review our recent progress on the direct growth of graphene on various glass by chemical vapor deposition (CVD). With the consideration of the thermo-stabilities of glass and application requirements, three different CVD routes are developed, i.e., high-temperature, atmospheric pressure CVD on solid-state thermostable glass and molten-state glass, as well as low-temperature plasma enhanced CVD on solid-state soda-lime floating glass. We also explore the practical applications of the as-grown graphene glass, where electrochromic windows, defoggers, cell proliferation, and photocatalytic plates were fabricated based on our CVD-grown graphene glass. The high performance of these devices promises practical usage of graphene glass in daily-life applications.
Glass, an amorphous oxide material with a long history, is widely used in our daily life. Graphene is a novel two-dimensional material formed by carbon atoms. The unique properties of graphene, such as excellent mechanical strength, high electrical and thermal conductivity and optical transparency, serve as complementary components to those of glass. Therefore, the combination of graphene and glass would endow noticeable electrical/thermal conductivity and surface hydrophobicity without sacrificing the transparency of conventional glass. Previously reported routes for integrating graphene with glass mainly used solution-casting of liquid-exfoliated graphene nanoplatelets and transfer-coating of graphene films grown on metals. Compared with the existing methods, the direct growth of graphene on glass could avoid contamination and damage during the integration process, thereby resulting in good graphene quality and scalability, high thickness/ coverage uniformity, much reduced breakage density, and a tight and clean interface with the underlying glass. In this article, we review our recent progress on the direct growth of graphene on various glass by chemical vapor deposition (CVD). With the consideration of the thermo-stabilities of glass and application requirements, three different CVD routes are developed, i.e., high-temperature, atmospheric pressure CVD on solid-state thermostable glass and molten-state glass, as well as low-temperature plasma enhanced CVD on solid-state soda-lime floating glass. We also explore the practical applications of the as-grown graphene glass, where electrochromic windows, defoggers, cell proliferation, and photocatalytic plates were fabricated based on our CVD-grown graphene glass. The high performance of these devices promises practical usage of graphene glass in daily-life applications.
2016, 32(1): 28-47
doi: 10.3866/PKU.WHXB201512081
Abstract:
Because of the potential applications of TiO2 in photocatalytic hydrogen production and pollutant degradation, over the past few decades we have witnessed increasing interest in and effort toward developing TiO2-based photocatalysts, and improving the efficiency and exploring the reaction mechanisms at the atomic and molecular levels. Because surface science studies on single crystal surfaces under ultrahigh vacuum (UHV) conditions can provide fundamental insights into these important processes, both the thermo- and photo-chemistry on TiO2, especially on rutile TiO2(110) surfaces, have been extensively investigated with a variety of experimental and theoretical approaches. In this review, commencing with the properties of TiO2, we then focus on charge transport and trapping, and electron transfer dynamics. Next, we summarize recent progress made in the study of elementary photocatalytic chemistry of methanol on mainly rutile TiO2(110), as well as in some studies on rutile TiO2(011) and anatase TiO2(101). These studies have provided fundamental insights into surface photocatalysis and stimulated new investigations in this exciting area. The implications of these studies for the development of new photocatalysis models are also discussed.
Because of the potential applications of TiO2 in photocatalytic hydrogen production and pollutant degradation, over the past few decades we have witnessed increasing interest in and effort toward developing TiO2-based photocatalysts, and improving the efficiency and exploring the reaction mechanisms at the atomic and molecular levels. Because surface science studies on single crystal surfaces under ultrahigh vacuum (UHV) conditions can provide fundamental insights into these important processes, both the thermo- and photo-chemistry on TiO2, especially on rutile TiO2(110) surfaces, have been extensively investigated with a variety of experimental and theoretical approaches. In this review, commencing with the properties of TiO2, we then focus on charge transport and trapping, and electron transfer dynamics. Next, we summarize recent progress made in the study of elementary photocatalytic chemistry of methanol on mainly rutile TiO2(110), as well as in some studies on rutile TiO2(011) and anatase TiO2(101). These studies have provided fundamental insights into surface photocatalysis and stimulated new investigations in this exciting area. The implications of these studies for the development of new photocatalysis models are also discussed.
2016, 32(1): 48-60
doi: 10.3866/PKU.WHXB201511092
Abstract:
Au catalysis is representative of nanocatalysis. Au catalysis has been demonstrated to be very complex and structure-sensitive. In this short review we summarize the literature reports on Au catalysis and our recent progress on the fundamental understanding of Au catalysis using model catalysts from single crystals to nanocrystals. We demonstrate the structure-sensitivity of Au catalysis used for NO decomposition, CO oxidation, and propylene epoxidation with H2 and O2 and the corresponding active Au structures. We discuss the effects of the geometric and electronic structures and the Au-oxide support interactions on Au catalysis, and the origin of high catalytic activity of the Au surface at low temperatures. Finally, we provide an outlook for future research directions of structure-sensitive Au catalysis.
Au catalysis is representative of nanocatalysis. Au catalysis has been demonstrated to be very complex and structure-sensitive. In this short review we summarize the literature reports on Au catalysis and our recent progress on the fundamental understanding of Au catalysis using model catalysts from single crystals to nanocrystals. We demonstrate the structure-sensitivity of Au catalysis used for NO decomposition, CO oxidation, and propylene epoxidation with H2 and O2 and the corresponding active Au structures. We discuss the effects of the geometric and electronic structures and the Au-oxide support interactions on Au catalysis, and the origin of high catalytic activity of the Au surface at low temperatures. Finally, we provide an outlook for future research directions of structure-sensitive Au catalysis.
2016, 32(1): 61-74
doi: 10.3866/PKU.WHXB201511101
Abstract:
There has been a surge of interest in using supported gold catalysts in green synthesis and clean reactions. Complementary to their traditional platinum-group metal counterparts, catalysis using nano-gold offers a unique opportunity to obtain target products in high yields, control the chemoselectivity, and access more complex organic molecules in a compact, atom- and step-efficient way. Therefore, it has emerged as a hot topic in the field of green catalysis. This review summarizes our research progress in the area of nano-Aucatalyzed green reactions and their versatility, application in clean chemical synthesis, especially for the construction of N-containing compounds as well as valorization of biomass-derived feedstocks via goldcatalyzed transformations.
There has been a surge of interest in using supported gold catalysts in green synthesis and clean reactions. Complementary to their traditional platinum-group metal counterparts, catalysis using nano-gold offers a unique opportunity to obtain target products in high yields, control the chemoselectivity, and access more complex organic molecules in a compact, atom- and step-efficient way. Therefore, it has emerged as a hot topic in the field of green catalysis. This review summarizes our research progress in the area of nano-Aucatalyzed green reactions and their versatility, application in clean chemical synthesis, especially for the construction of N-containing compounds as well as valorization of biomass-derived feedstocks via goldcatalyzed transformations.
2016, 32(1): 75-84
doi: 10.3866/PKU.WHXB201512153
Abstract:
Metal-free carbon catalysts have been receiving increasing attention in the fields of nanomaterials and catalysis. Compared with conventional metal catalysts, there are many advantages for metal-free carbon catalysts, such as simple synthesis, stable structure, large surface area, and diverse applications. Graphene is one layer of carbon atoms and has a periodic structure of aromatic carbon atoms. Graphene oxide is a highly oxidized form of graphene. As a new carbon material, its application in catalysis has emerged over the past 5 years. Graphene-based materials can efficiently catalyze hydrocarbon conversion, organic synthesis, energy conversion, and other heterogeneous catalytic processes. This review highlights the recent progress in the development of metal-free graphene-based catalysts (graphene oxide and graphene) and associated catalytic reactions.
Metal-free carbon catalysts have been receiving increasing attention in the fields of nanomaterials and catalysis. Compared with conventional metal catalysts, there are many advantages for metal-free carbon catalysts, such as simple synthesis, stable structure, large surface area, and diverse applications. Graphene is one layer of carbon atoms and has a periodic structure of aromatic carbon atoms. Graphene oxide is a highly oxidized form of graphene. As a new carbon material, its application in catalysis has emerged over the past 5 years. Graphene-based materials can efficiently catalyze hydrocarbon conversion, organic synthesis, energy conversion, and other heterogeneous catalytic processes. This review highlights the recent progress in the development of metal-free graphene-based catalysts (graphene oxide and graphene) and associated catalytic reactions.
2016, 32(1): 85-97
doi: 10.3866/PKU.WHXB201511061
Abstract:
With the rapid growth of the biodiesel industry, huge amounts of glycerol have been produced as a byproduct. Thus, it is highly desirable to convert low-cost glycerol into highly valuable chemicals, which can both expedite the development of the biodiesel process and save abundant petroleum resources. In this context, one of the most promising approaches is the catalytic hydrogenolysis of glycerol to synthesize 1,2- propanediol (1,2-PDO), 1,3-propanediol (1,3-PDO), ethylene glycol (EG), and propanols, because these target products have higher selectivity, economic value and potential for industrial application. In this paper, glycerol chemistry will be briefly introduced and then the reaction mechanisms, including dehydration-hydrogenation, dehydrogenation-dehydration-hydrogenation, direct hydrogenolysis, and ionic hydrogenation, will be discussed because of their importance for understanding the catalytic chemistry. Subsequently, the catalytic applications of glycerol hydrogenolysis to obtain 1,2-PDO, 1,3-PDO, EG, and propanols will be reviewed in detail based on various catalysts. In the end, we will provide a short summary and an outlook on the future prospects for glycerol hydrogenolysis.
With the rapid growth of the biodiesel industry, huge amounts of glycerol have been produced as a byproduct. Thus, it is highly desirable to convert low-cost glycerol into highly valuable chemicals, which can both expedite the development of the biodiesel process and save abundant petroleum resources. In this context, one of the most promising approaches is the catalytic hydrogenolysis of glycerol to synthesize 1,2- propanediol (1,2-PDO), 1,3-propanediol (1,3-PDO), ethylene glycol (EG), and propanols, because these target products have higher selectivity, economic value and potential for industrial application. In this paper, glycerol chemistry will be briefly introduced and then the reaction mechanisms, including dehydration-hydrogenation, dehydrogenation-dehydration-hydrogenation, direct hydrogenolysis, and ionic hydrogenation, will be discussed because of their importance for understanding the catalytic chemistry. Subsequently, the catalytic applications of glycerol hydrogenolysis to obtain 1,2-PDO, 1,3-PDO, EG, and propanols will be reviewed in detail based on various catalysts. In the end, we will provide a short summary and an outlook on the future prospects for glycerol hydrogenolysis.
2016, 32(1): 98-118
doi: 10.3866/PKU.WHXB201510302
Abstract:
Density functional reactivity theory (DFRT) is a recent endeavor to appreciate and quantify molecular reactivity with simple density functionals. Examples of such density functionals recently investigated in the literature included Shannon entropy, Fisher information, and other quantities from information theory. This review presents an overview on the principles of the information-theoretic approach in DFRT, including the extreme physical information principle, minimum information gain principle, and information conservation principle. Three representations of this approach with electron density, shape function, and atoms-in-molecules are also summarized. Moreover, their applications in quantifying steric effect, electrophilicity, nucleophilicity, and regioselectivity are highlighted, so are the recent results in a completely new understanding about the nature and origin of ortho/para and meta group directing phenomena in electrophilic aromatic substitution reactions. A brief outlook of a few possible future developments is discussed at the end.
Density functional reactivity theory (DFRT) is a recent endeavor to appreciate and quantify molecular reactivity with simple density functionals. Examples of such density functionals recently investigated in the literature included Shannon entropy, Fisher information, and other quantities from information theory. This review presents an overview on the principles of the information-theoretic approach in DFRT, including the extreme physical information principle, minimum information gain principle, and information conservation principle. Three representations of this approach with electron density, shape function, and atoms-in-molecules are also summarized. Moreover, their applications in quantifying steric effect, electrophilicity, nucleophilicity, and regioselectivity are highlighted, so are the recent results in a completely new understanding about the nature and origin of ortho/para and meta group directing phenomena in electrophilic aromatic substitution reactions. A brief outlook of a few possible future developments is discussed at the end.
2016, 32(1): 119-130
doi: 10.3866/PKU.WHXB201512011
Abstract:
Recent progresses on a new generation density functional XYG3 and the construction of potential energy surfaces using neural networks are reviewed in this article. Using H3 and CH5 systems as illustrative examples, it is concluded that highly reliable dynamics results can be obtained from the combination of electronic structure calculations based on efficient and accurate density functionals and accurate potential energy surfaces using neural networks. It holds promise for future applications in larger and more complicated systems.
Recent progresses on a new generation density functional XYG3 and the construction of potential energy surfaces using neural networks are reviewed in this article. Using H3 and CH5 systems as illustrative examples, it is concluded that highly reliable dynamics results can be obtained from the combination of electronic structure calculations based on efficient and accurate density functionals and accurate potential energy surfaces using neural networks. It holds promise for future applications in larger and more complicated systems.
2016, 32(1): 131-153
doi: 10.3866/PKU.WHXB201512151
Abstract:
Chemical kinetic modeling has become more and more important in the analysis of combustion systems. Considerable progress has been made in the development of combustion models in recent years. This review includes the following contents: electronic structure methods for combustion kinetics, recent developments on the calculation methods of thermodynamic parameters and rate constants in combustion, developments of combustion mechanisms and reduction techniques, molecular simulations with reactive force fields, combustion intermediate measurements, experiments for ignition delay time with shock wave tubes and combustion diagnostics. Due to the extreme complexity of reaction networks, the combustion mechanism is still not clearly understood by researchers. Owing to the strong application background, the combustion kinetics have attracted attention in recent years. The solver for reaction rate of intermediate species during combustion occupies the central point in combustion simulation. The progress in the research on reactionturbulence interactions, and the combination of combustion kinetics with computational fluid dynamics, will facilitate fuel design and combustion simulation. To build a reliable combustion model for achieving a reasonable flow field structure description of engines is another important aspect.
Chemical kinetic modeling has become more and more important in the analysis of combustion systems. Considerable progress has been made in the development of combustion models in recent years. This review includes the following contents: electronic structure methods for combustion kinetics, recent developments on the calculation methods of thermodynamic parameters and rate constants in combustion, developments of combustion mechanisms and reduction techniques, molecular simulations with reactive force fields, combustion intermediate measurements, experiments for ignition delay time with shock wave tubes and combustion diagnostics. Due to the extreme complexity of reaction networks, the combustion mechanism is still not clearly understood by researchers. Owing to the strong application background, the combustion kinetics have attracted attention in recent years. The solver for reaction rate of intermediate species during combustion occupies the central point in combustion simulation. The progress in the research on reactionturbulence interactions, and the combination of combustion kinetics with computational fluid dynamics, will facilitate fuel design and combustion simulation. To build a reliable combustion model for achieving a reasonable flow field structure description of engines is another important aspect.
2016, 32(1): 154-170
doi: 10.3866/PKU.WHXB201512041
Abstract:
The construction of covalently bonded molecular structures on single crystal metal surfaces has attracted increasing attention because of the synthetic strategies used and their potential application to molecular electronics and optoelectronics. Unlike traditional organic synthesis, surface-assisted reactions have advantages for structural control of the produced polymers, providing detailed understanding of reaction processes, and, most importantly, they produce new materials that cannot be synthesized by traditional means. The types of reactant, the choice of metal surface, and the initial conditions are critical controlling parameters in surface-assisted reactions. Covalent bonds formed in the reaction ensure that the produced structures have higher mechanical and thermodynamic stability compared with self-assembled monolayers (SAMs). Meanwhile, some conjugated polymers are ideal candidates for semiconductors in next-generation carbon-based electronics. In this review, we summarize the surface assisted reactions reported in recent years and analyze the mechanisms involved, comparing them with the corresponding reactions that occur in solution. Finally, we discuss the important role of substrate surface played in the reaction process.
The construction of covalently bonded molecular structures on single crystal metal surfaces has attracted increasing attention because of the synthetic strategies used and their potential application to molecular electronics and optoelectronics. Unlike traditional organic synthesis, surface-assisted reactions have advantages for structural control of the produced polymers, providing detailed understanding of reaction processes, and, most importantly, they produce new materials that cannot be synthesized by traditional means. The types of reactant, the choice of metal surface, and the initial conditions are critical controlling parameters in surface-assisted reactions. Covalent bonds formed in the reaction ensure that the produced structures have higher mechanical and thermodynamic stability compared with self-assembled monolayers (SAMs). Meanwhile, some conjugated polymers are ideal candidates for semiconductors in next-generation carbon-based electronics. In this review, we summarize the surface assisted reactions reported in recent years and analyze the mechanisms involved, comparing them with the corresponding reactions that occur in solution. Finally, we discuss the important role of substrate surface played in the reaction process.
2016, 32(1): 171-182
doi: 10.3866/PKU.WHXB201512152
Abstract:
Photoemission electron microscopy (PEEM)/low energy electron microscopy (LEEM) are surface techniques that can be used to image surface structure, electronic states, and surface chemistry. Important applications of the technique in catalysis, energy, nano science, and material sciences have been seen. In this paper, we briefly introduce the principle of PEEM/LEEM and the recent advances of the technique. Then, some applications of PEEM/LEEM in dynamic studies of surface physics and chemistry of two-dimensional (2D) atomic crystals are highlighted, which include the growth of 2D atomic crystals, the formation of 2D heterostructures, the intercalation of the 2D materials, and chemical reactions confined under the 2D materials. Using surface imaging, micro-region low energy electron diffraction (μ-LEED), and the intensity-voltage (I-V) curves, the kinetics of 2D material growth and reactions at the 2D material/solid interfaces can be deeply understood.
Photoemission electron microscopy (PEEM)/low energy electron microscopy (LEEM) are surface techniques that can be used to image surface structure, electronic states, and surface chemistry. Important applications of the technique in catalysis, energy, nano science, and material sciences have been seen. In this paper, we briefly introduce the principle of PEEM/LEEM and the recent advances of the technique. Then, some applications of PEEM/LEEM in dynamic studies of surface physics and chemistry of two-dimensional (2D) atomic crystals are highlighted, which include the growth of 2D atomic crystals, the formation of 2D heterostructures, the intercalation of the 2D materials, and chemical reactions confined under the 2D materials. Using surface imaging, micro-region low energy electron diffraction (μ-LEED), and the intensity-voltage (I-V) curves, the kinetics of 2D material growth and reactions at the 2D material/solid interfaces can be deeply understood.
2016, 32(1): 183-194
doi: 10.3866/PKU.WHXB201512113
Abstract:
Single crystalline oxide thin film has been delegated as an important approach to studying oxide materials. The related researches are at the frontier of model catalysis. In this review, we try to summarize what has been researched so far around the CaO(001) films, which have been recently developed in Prof. Hajo Freund's group at the Fritz-Haber Institute. The revealed properties of CaO films have displayed the common characteristics of supported ultrathin oxide films, which are sensitively dependent on the interface structures and film thicknesses, but they have also shown new aspects such as the novel tuning effects from self-doping by substrate ions. Low-temperature scanning tunneling microscopy (LT-STM) has been applied through all detailed studies, including the characterizations of atomic structure and electronic properties, recognition of various defects and charge analyses of various surface species. The microscopic information received from delicate STM measurements provides atomic views of the effective factors involved in manipulating the oxide surface properties. With the aid of theoretical calculations, deep insights of the doping mechanism and selection principles of the dopants are achieved, which should largely assist the design of new catalysts.
Single crystalline oxide thin film has been delegated as an important approach to studying oxide materials. The related researches are at the frontier of model catalysis. In this review, we try to summarize what has been researched so far around the CaO(001) films, which have been recently developed in Prof. Hajo Freund's group at the Fritz-Haber Institute. The revealed properties of CaO films have displayed the common characteristics of supported ultrathin oxide films, which are sensitively dependent on the interface structures and film thicknesses, but they have also shown new aspects such as the novel tuning effects from self-doping by substrate ions. Low-temperature scanning tunneling microscopy (LT-STM) has been applied through all detailed studies, including the characterizations of atomic structure and electronic properties, recognition of various defects and charge analyses of various surface species. The microscopic information received from delicate STM measurements provides atomic views of the effective factors involved in manipulating the oxide surface properties. With the aid of theoretical calculations, deep insights of the doping mechanism and selection principles of the dopants are achieved, which should largely assist the design of new catalysts.
2016, 32(1): 195-200
doi: 10.3866/PKU.WHXB201511261
Abstract:
Self-similar fractals have been extensively investigated because of their importance in mathematics and aesthetics. Chemists have attempted to synthesize various molecular fractal structures through sophisticated design. But because of poor solubility, synthesis of defect-free fractals with large sizes in solution usually proves difficult. Recently, we reported the formation of extended and defect-free Sierpiński triangle fractals by halogen or coordination bonds on surfaces under ultrahigh vacuum conditions. Their growth mechanism has been systematically studied by scanning tunneling microscopy. Using 4,4"'-dibromo- 1,1':3',1":4",1"'-quaterphenyl molecules, a series of Sierpiński triangles were successfully prepared on Ag(111) through self-assembly. A slow cooling rate is crucial for growing fractals of higher order. These fractals are only observed below liquid-nitrogen temperature because of the weak interactions in halogen bonds. More stable metal-organic Sierpiński triangles were fabricated by depositing 4,4″-dicyano-1,1':3',1″-terphenyl molecules and Fe atoms on Au(111) and annealing at around 100 °C for 10 min. The fractals are stabilized through coordination interaction between Fe atoms and N atoms in molecules. Density functional theory calculations revealed their imaging mechanism. Monte Carlo simulations displayed the formation process of surface-supported fractal structures. Three-fold nodes are believed to dominate the structure formation of Sierpiński triangles.
Self-similar fractals have been extensively investigated because of their importance in mathematics and aesthetics. Chemists have attempted to synthesize various molecular fractal structures through sophisticated design. But because of poor solubility, synthesis of defect-free fractals with large sizes in solution usually proves difficult. Recently, we reported the formation of extended and defect-free Sierpiński triangle fractals by halogen or coordination bonds on surfaces under ultrahigh vacuum conditions. Their growth mechanism has been systematically studied by scanning tunneling microscopy. Using 4,4"'-dibromo- 1,1':3',1":4",1"'-quaterphenyl molecules, a series of Sierpiński triangles were successfully prepared on Ag(111) through self-assembly. A slow cooling rate is crucial for growing fractals of higher order. These fractals are only observed below liquid-nitrogen temperature because of the weak interactions in halogen bonds. More stable metal-organic Sierpiński triangles were fabricated by depositing 4,4″-dicyano-1,1':3',1″-terphenyl molecules and Fe atoms on Au(111) and annealing at around 100 °C for 10 min. The fractals are stabilized through coordination interaction between Fe atoms and N atoms in molecules. Density functional theory calculations revealed their imaging mechanism. Monte Carlo simulations displayed the formation process of surface-supported fractal structures. Three-fold nodes are believed to dominate the structure formation of Sierpiński triangles.
2016, 32(1): 201-213
doi: 10.3866/PKU.WHXB201512031
Abstract:
Quantum dot-sensitized solar cells (QDSCs) have attracted much attention in the past few years because of the advantages of quantum dots (QDs), including low cost, easy fabrication, size-dependence bandgap, and multiple exciton generation (MEG). The properties of QD sensitizers influence the performance of QDSCs, such as their photoelectric characteristics, preparation methods, surface defects, chemical stability, and their sensitization towards TiO2 photoanodes. This review demonstrates the development of QD sensitizers, including narrow bandgap binary QDs, ternary or quaternary alloyed QDs, and Type-II core-shell QDs, especially the preparation methods of colloidal QDs. Furthermore, the deposition and sensitization methods of QDs are introduced in detail, particularly bifunctional-assisted self-assembly deposition. Meanwhile, methods to improve electron injection efficiency and reduce charge recombination are also summarized. Finally, a brief introduction is provided to the development of electrolytes and counter electrodes in QDSCs.
Quantum dot-sensitized solar cells (QDSCs) have attracted much attention in the past few years because of the advantages of quantum dots (QDs), including low cost, easy fabrication, size-dependence bandgap, and multiple exciton generation (MEG). The properties of QD sensitizers influence the performance of QDSCs, such as their photoelectric characteristics, preparation methods, surface defects, chemical stability, and their sensitization towards TiO2 photoanodes. This review demonstrates the development of QD sensitizers, including narrow bandgap binary QDs, ternary or quaternary alloyed QDs, and Type-II core-shell QDs, especially the preparation methods of colloidal QDs. Furthermore, the deposition and sensitization methods of QDs are introduced in detail, particularly bifunctional-assisted self-assembly deposition. Meanwhile, methods to improve electron injection efficiency and reduce charge recombination are also summarized. Finally, a brief introduction is provided to the development of electrolytes and counter electrodes in QDSCs.
2016, 32(1): 214-226
doi: 10.3866/PKU.WHXB201511022
Abstract:
Gemini surfactants consist of two amphiphilic moieties covalently connected by a spacer at the level of the head groups. Compared with the corresponding monomeric surfactants, gemini surfactants exhibit higher surface activity, possess unique structural variations, display special aggregate transitions, and form variable aggregate structures. Their aggregation ability and aggregate structures can be effectively adjusted by varying their molecular structures, which results in different intra- or intermolecular interactions. This short review is focused on the behavior of gemini surfactants in aqueous solutions reported in recent years, and summarizes the effects of different molecular structures, including spacers, hydrophobic chains, hydrophilic headgroups, counterions, and functional groups. The mechanisms and trends of the interactions in gemini surfactants are also presented.
Gemini surfactants consist of two amphiphilic moieties covalently connected by a spacer at the level of the head groups. Compared with the corresponding monomeric surfactants, gemini surfactants exhibit higher surface activity, possess unique structural variations, display special aggregate transitions, and form variable aggregate structures. Their aggregation ability and aggregate structures can be effectively adjusted by varying their molecular structures, which results in different intra- or intermolecular interactions. This short review is focused on the behavior of gemini surfactants in aqueous solutions reported in recent years, and summarizes the effects of different molecular structures, including spacers, hydrophobic chains, hydrophilic headgroups, counterions, and functional groups. The mechanisms and trends of the interactions in gemini surfactants are also presented.
2016, 32(1): 227-238
doi: 10.3866/PKU.WHXB201511181
Abstract:
Supramolecular gels, an important type of soft matter, have showed unique advantages in the construction of functional soft materials, such as multiple stimuli responsive, photoelectrical, and biological compatibility materials. Through supramolecular gelation, diverse, uniform nanostructures can be obtained in a large quantity. On the other hand, most gelators are chiral molecules, so supramolecular gel is a medium to realize the expression of the chirality in supramolecular and nano level, especially to realize effectively chirality transfer, amplification, and asymmetric catalysis, and to fabricate various chiral architectures. In this paper, we describe the structural diversity and chirality in supramolecular gels, and discuss the future prospects for supramolecular gels.
Supramolecular gels, an important type of soft matter, have showed unique advantages in the construction of functional soft materials, such as multiple stimuli responsive, photoelectrical, and biological compatibility materials. Through supramolecular gelation, diverse, uniform nanostructures can be obtained in a large quantity. On the other hand, most gelators are chiral molecules, so supramolecular gel is a medium to realize the expression of the chirality in supramolecular and nano level, especially to realize effectively chirality transfer, amplification, and asymmetric catalysis, and to fabricate various chiral architectures. In this paper, we describe the structural diversity and chirality in supramolecular gels, and discuss the future prospects for supramolecular gels.
2016, 32(1): 239-248
doi: 10.3866/PKU.WHXB201511241
Abstract:
Excess spectroscopy was proposed following the idea of excess thermodynamic functions. It is complementary to classical excess functions because it provides rich information on molecular interactions. In this review, we introduce in detail the concept of excess spectroscopy and the measurement of excess spectra for the case of infrared spectroscopy. We then describe the merits of using excess spectroscopy to enhance apparent spectral resolution, judge the non-ideality of mixtures, determine the selectivity of molecular interactions, identify distinct species or clusters in solutions, and provide information related to charge distributions in molecules. Following this, we review the progress in methodology where excess spectroscopy is extended to partial molar excess spectroscopy and Raman spectroscopy. The extension of binary mixtures to pseudo binary mixtures and/or liquid samples to solid samples is also described. Finally, we discuss several recent applications of excess spectroscopy in the study of hydrogen-bonding interactions in ionic liquidmolecular solvent systems, halogen-bonding interactions in benzene derivative-dimethylsulfoxide (DMSO) mixtures, and interactions between inorganic cations/anions and water molecules. Clearly, excess spectroscopy has opened a new window through which we can view rich information about molecular interactions.
Excess spectroscopy was proposed following the idea of excess thermodynamic functions. It is complementary to classical excess functions because it provides rich information on molecular interactions. In this review, we introduce in detail the concept of excess spectroscopy and the measurement of excess spectra for the case of infrared spectroscopy. We then describe the merits of using excess spectroscopy to enhance apparent spectral resolution, judge the non-ideality of mixtures, determine the selectivity of molecular interactions, identify distinct species or clusters in solutions, and provide information related to charge distributions in molecules. Following this, we review the progress in methodology where excess spectroscopy is extended to partial molar excess spectroscopy and Raman spectroscopy. The extension of binary mixtures to pseudo binary mixtures and/or liquid samples to solid samples is also described. Finally, we discuss several recent applications of excess spectroscopy in the study of hydrogen-bonding interactions in ionic liquidmolecular solvent systems, halogen-bonding interactions in benzene derivative-dimethylsulfoxide (DMSO) mixtures, and interactions between inorganic cations/anions and water molecules. Clearly, excess spectroscopy has opened a new window through which we can view rich information about molecular interactions.
2016, 32(1): 249-260
doi: 10.3866/PKU.WHXB201512042
Abstract:
Application of ionic liquid surfactants in chemical synthesis, materials preparation, and environmental pollution control is closely dependent on their self-assembly behavior and aggregate structure in aqueous solution. Thus, the study of the aggregation behavior of ionic liquid surfactants in water is of significant importance. In this review, we focus our attention on the recent progress made in the regulation and control of the self-assembly behavior of ionic liquid surfactants and related microstructure of their aggregates in aqueous solutions by alkyl chain length, cationic structure, anionic type of the ionic liquid surfactants, addition of inorganic salt and organic solvent, and environmental factors such as temperature, solution pH, and light. Some regularities have been summarized for the regulation and control of the self-assembly behavior of ionic liquid surfactants, and the challenges to future development in this field are explained.
Application of ionic liquid surfactants in chemical synthesis, materials preparation, and environmental pollution control is closely dependent on their self-assembly behavior and aggregate structure in aqueous solution. Thus, the study of the aggregation behavior of ionic liquid surfactants in water is of significant importance. In this review, we focus our attention on the recent progress made in the regulation and control of the self-assembly behavior of ionic liquid surfactants and related microstructure of their aggregates in aqueous solutions by alkyl chain length, cationic structure, anionic type of the ionic liquid surfactants, addition of inorganic salt and organic solvent, and environmental factors such as temperature, solution pH, and light. Some regularities have been summarized for the regulation and control of the self-assembly behavior of ionic liquid surfactants, and the challenges to future development in this field are explained.
2016, 32(1): 261-266
doi: 10.3866/PKU.WHXB201512101
Abstract:
The electrocatalytic reduction of CO2 to HCOOH is an interesting topic and the efficiency usually depends strongly on the materials of the electrodes. Herein, nanostructured Cu2S on Cu-foam was prepared by electro-deposition method and characterized by means of scanning electron microscope (SEM) and X-ray diffraction (XRD). The Cu2S/Cu-foam electrode was used for the first time in the electrocatalytic reduction of CO2 to HCOOH, and acetonitrile (MeCN) with 0.5 mol·L-1 1-butyl-3- methylimidazolium tetrafluoroborate (BmimBF4) was used as the electrolyte. It was demonstrated that the electrolysis system was very efficient for the electrochemical reaction, and faradaic efficiency of HCOOH (FEHCOOH) and reduction current density could reach 85% and 5.3 mA·cm-2, respectively.
The electrocatalytic reduction of CO2 to HCOOH is an interesting topic and the efficiency usually depends strongly on the materials of the electrodes. Herein, nanostructured Cu2S on Cu-foam was prepared by electro-deposition method and characterized by means of scanning electron microscope (SEM) and X-ray diffraction (XRD). The Cu2S/Cu-foam electrode was used for the first time in the electrocatalytic reduction of CO2 to HCOOH, and acetonitrile (MeCN) with 0.5 mol·L-1 1-butyl-3- methylimidazolium tetrafluoroborate (BmimBF4) was used as the electrolyte. It was demonstrated that the electrolysis system was very efficient for the electrochemical reaction, and faradaic efficiency of HCOOH (FEHCOOH) and reduction current density could reach 85% and 5.3 mA·cm-2, respectively.
2016, 32(1): 267-273
doi: 10.3866/PKU.WHXB201510303
Abstract:
The pyridinium-based ionic liquids [C6py][DCA] (N-hexyl-pyridinium dicyanamide) was prepared and characterized using 1H and 13C nuclear magnetic responancec (NMR) spectroscopies, Fourier transform infrared (FT-IR) spectroscopy, and differential scanning calorimetry (DSC). The density (ρ), surface tension (γ), and refractive indices (nD) were measured at the temperature range from 288.15 to 338.15 K. Molecular volume (Vm), energy of surface (Ea), molar polarization (Rm), and polarization coefficient of [C6py][DCA] (αp) were calculated from the experimental data. Ea, Rm, and αp were approximately temperature-independent. The concept of molar surface Gibbs free energy (gs) was conceived, for which a new Eötvös equation was derived. The gs, critical temperature (Tc), and Eötvös empirical parameter related to polarity (kE) were also obtained. The new Eötvös equation was used to predict the surface tension and the predicted values of [C6py][DCA] are in close agreement with the corresponding experimental ones.
The pyridinium-based ionic liquids [C6py][DCA] (N-hexyl-pyridinium dicyanamide) was prepared and characterized using 1H and 13C nuclear magnetic responancec (NMR) spectroscopies, Fourier transform infrared (FT-IR) spectroscopy, and differential scanning calorimetry (DSC). The density (ρ), surface tension (γ), and refractive indices (nD) were measured at the temperature range from 288.15 to 338.15 K. Molecular volume (Vm), energy of surface (Ea), molar polarization (Rm), and polarization coefficient of [C6py][DCA] (αp) were calculated from the experimental data. Ea, Rm, and αp were approximately temperature-independent. The concept of molar surface Gibbs free energy (gs) was conceived, for which a new Eötvös equation was derived. The gs, critical temperature (Tc), and Eötvös empirical parameter related to polarity (kE) were also obtained. The new Eötvös equation was used to predict the surface tension and the predicted values of [C6py][DCA] are in close agreement with the corresponding experimental ones.
2016, 32(1): 274-282
doi: 10.3866/PKU.WHXB201511021
Abstract:
The thermodynamics of the interaction between human serum albumin (HSA) and imidacloprid (IMI) was investigated using fluorescence, UV-Vis absorbance, and circular dichroism spectroscopy, in addition to molecular modeling under physiological conditions. The fluorescence quenching of HSA by IMI was a static process, which was confirmed by the UV-Vis absorption spectra. The calculated enthalpy (ΔH) and entropy (ΔS) changes implied that hydrogen bonds and van der Waals forces played a predominant role in the binding process. Site marker competitive experiments along with molecular docking indicated that the binding of IMI to HSA took place primarily in site Ⅰ. The circular dichroism and synchronous fluorescence spectroscopy demonstrated that the secondary structure of HSA changed after its interaction with IMI, causing the α-helix content to decrease with an increase in anunordered structure. The peptide structure extended after binding with IMI.
The thermodynamics of the interaction between human serum albumin (HSA) and imidacloprid (IMI) was investigated using fluorescence, UV-Vis absorbance, and circular dichroism spectroscopy, in addition to molecular modeling under physiological conditions. The fluorescence quenching of HSA by IMI was a static process, which was confirmed by the UV-Vis absorption spectra. The calculated enthalpy (ΔH) and entropy (ΔS) changes implied that hydrogen bonds and van der Waals forces played a predominant role in the binding process. Site marker competitive experiments along with molecular docking indicated that the binding of IMI to HSA took place primarily in site Ⅰ. The circular dichroism and synchronous fluorescence spectroscopy demonstrated that the secondary structure of HSA changed after its interaction with IMI, causing the α-helix content to decrease with an increase in anunordered structure. The peptide structure extended after binding with IMI.
2016, 32(1): 283-289
doi: 10.3866/PKU.WHXB201511132
Abstract:
The interfacial morphology of a single crystal Si wafer anode during the first discharging-charging cycle was investigated using in situ atomic force microscopy (AFM). The solid-electrolyte interphase (SEI) began to grow from 1.5 V, developing rapidly between 1.25 and 1.0 V, and slowed down after 0.6 V. The morphology suggested that the SEI had a layered structure. The outer layer of SEI was soft and easy to be scraped off during the AFM tip scanning. The underlayer of SEI had granular features. During the lithiation process, the Si surface became grainy because of the insertion of Li ions. After the first cycle, the Si surface was completely covered by inhomogeneous SEI. The thickness of the SEI was approximately 10-40 nm.
The interfacial morphology of a single crystal Si wafer anode during the first discharging-charging cycle was investigated using in situ atomic force microscopy (AFM). The solid-electrolyte interphase (SEI) began to grow from 1.5 V, developing rapidly between 1.25 and 1.0 V, and slowed down after 0.6 V. The morphology suggested that the SEI had a layered structure. The outer layer of SEI was soft and easy to be scraped off during the AFM tip scanning. The underlayer of SEI had granular features. During the lithiation process, the Si surface became grainy because of the insertion of Li ions. After the first cycle, the Si surface was completely covered by inhomogeneous SEI. The thickness of the SEI was approximately 10-40 nm.
2016, 32(1): 290-300
doi: 10.3866/PKU.WHXB201512072
Abstract:
The understanding of factors that affect the optical properties of azo dyes sheds insight to the design of novel optoelectronic devices. The effect of the acidity or alkalinity and the solvent on the absorption spectra of ortho-methyl red (o-MR) aqueous solutions was investigated using UV/Vis experiments and density functional theory (DFT) calculations. The spectra of o-MR aqueous solutions showed a red shift of the maximum absorption peak from 430 nm to 520 nm when the pH of the solution was decreased from 13.1 to 0.5. In various acidity or alkalinity conditions, three main forms of o-MR coexisted in the aqueous solutions, i.e., diprotic o-H2MR+ (strong acid condition), nonionic o-HMR (weak acid condition), and o-MR- (basic condition), whose electronic structures were studied by DFT. The lowest dipole-allowed excitation energies of o-MR in aqueous solutions have been estimated by performing timedependent density functional theory (TD-DFT) calculations. Both polarized continuum model (PCM) and explicit water cluster model were applied to study the solvent effects on the electronic structures and calculated spectra. The intramolecular hydrogen bond increases the planarity of o-H2MR+ and o-HMR, leading to the enhancement of π-conjugation and, hence, a red shift in the spectra. Significant solvent effects on the calculated UV/Vis spectra of o-MR- (under basic condition) were revealed. Strong dipole–dipole interactions between the polar o-MR– and solvent water molecules may contribute to the red shift in the spectra.
The understanding of factors that affect the optical properties of azo dyes sheds insight to the design of novel optoelectronic devices. The effect of the acidity or alkalinity and the solvent on the absorption spectra of ortho-methyl red (o-MR) aqueous solutions was investigated using UV/Vis experiments and density functional theory (DFT) calculations. The spectra of o-MR aqueous solutions showed a red shift of the maximum absorption peak from 430 nm to 520 nm when the pH of the solution was decreased from 13.1 to 0.5. In various acidity or alkalinity conditions, three main forms of o-MR coexisted in the aqueous solutions, i.e., diprotic o-H2MR+ (strong acid condition), nonionic o-HMR (weak acid condition), and o-MR- (basic condition), whose electronic structures were studied by DFT. The lowest dipole-allowed excitation energies of o-MR in aqueous solutions have been estimated by performing timedependent density functional theory (TD-DFT) calculations. Both polarized continuum model (PCM) and explicit water cluster model were applied to study the solvent effects on the electronic structures and calculated spectra. The intramolecular hydrogen bond increases the planarity of o-H2MR+ and o-HMR, leading to the enhancement of π-conjugation and, hence, a red shift in the spectra. Significant solvent effects on the calculated UV/Vis spectra of o-MR- (under basic condition) were revealed. Strong dipole–dipole interactions between the polar o-MR– and solvent water molecules may contribute to the red shift in the spectra.
2016, 32(1): 301-312
doi: 10.3866/PKU.WHXB201512112
Abstract:
The experimentally-measured two-photon absorption (TPA) spectra of fluorescent proteins (FPs) show quite different characteristics with one-photon absorption (OPA) spectra in both the low- and high-frequency regions. To reveal the mechanism that results in the discrepancies between OPA and TPA spectra, and to obtain the fundamental structure-property relationships of FPs, here we conduct a theoretical study of OPA and TPA properties of three FP chromophores, including a neutral chromophore in enhanced cyan fluorescent protein (ECFP) and two anionic FP chromophores in DsRed2 and TagRFP. Both the pure electronic and vibrationally-resolved TPA spectra have been calculated. The calculated spectra were found to be highly dependent on the density functional theory exchange-correlation functional used. The experimental spectral lineshapes of vibronic spectra can be well produced when the Franck- Condon (FC) scattering and Herzberg-Teller (HT) vibronic coupling effects were taken into account and the structure parameters produced by CAM-B3LYP were applied in the theoretical calculations. The HT effects affect the low-frequency absorption bands corresponding to the electronic transition from S0 to S1 for two anionic chromophores, leading to a blue-shift of the TPA maximum relative to OPA maximum, while the HT effect is insignificant in the higher-frequency region of the TPA spectra. The intramolecular charge-transfer character of higher-lying excited states explains why the TPA spectra in the higher-frequency region are much stronger than those in the low-frequency region.
The experimentally-measured two-photon absorption (TPA) spectra of fluorescent proteins (FPs) show quite different characteristics with one-photon absorption (OPA) spectra in both the low- and high-frequency regions. To reveal the mechanism that results in the discrepancies between OPA and TPA spectra, and to obtain the fundamental structure-property relationships of FPs, here we conduct a theoretical study of OPA and TPA properties of three FP chromophores, including a neutral chromophore in enhanced cyan fluorescent protein (ECFP) and two anionic FP chromophores in DsRed2 and TagRFP. Both the pure electronic and vibrationally-resolved TPA spectra have been calculated. The calculated spectra were found to be highly dependent on the density functional theory exchange-correlation functional used. The experimental spectral lineshapes of vibronic spectra can be well produced when the Franck- Condon (FC) scattering and Herzberg-Teller (HT) vibronic coupling effects were taken into account and the structure parameters produced by CAM-B3LYP were applied in the theoretical calculations. The HT effects affect the low-frequency absorption bands corresponding to the electronic transition from S0 to S1 for two anionic chromophores, leading to a blue-shift of the TPA maximum relative to OPA maximum, while the HT effect is insignificant in the higher-frequency region of the TPA spectra. The intramolecular charge-transfer character of higher-lying excited states explains why the TPA spectra in the higher-frequency region are much stronger than those in the low-frequency region.
2016, 32(1): 313-320
doi: 10.3866/PKU.WHXB201512161
Abstract:
Urea is known for protein denaturation. The counteracting effect of trimethylamine-N-oxide (TMAO) against urea-induced protein denaturation is also well established. However, what is largely unknown is the mechanism TMAO counteracts urea. In this article, the hydration of the interior of a simple single-walled carbon nanotube in a urea/TMAO mixture is studied as a model system for hydrophobic hydration using molecular dynamic simulations. The results show that TMAO counteracts the hydration effect of urea to the nanotube interior through strong interactions among TMAO, water, and urea. The strong interactions of TMAO and water stabilize the water structure, which counteracts the effects of urea indirectly.
Urea is known for protein denaturation. The counteracting effect of trimethylamine-N-oxide (TMAO) against urea-induced protein denaturation is also well established. However, what is largely unknown is the mechanism TMAO counteracts urea. In this article, the hydration of the interior of a simple single-walled carbon nanotube in a urea/TMAO mixture is studied as a model system for hydrophobic hydration using molecular dynamic simulations. The results show that TMAO counteracts the hydration effect of urea to the nanotube interior through strong interactions among TMAO, water, and urea. The strong interactions of TMAO and water stabilize the water structure, which counteracts the effects of urea indirectly.
2016, 32(1): 321-328
doi: 10.3866/PKU.WHXB201512091
Abstract:
N-doped graphene has aroused much interest owing to its high activity and stability in oxygen reduction reaction (ORR) catalysis. However, the contribution of different types of N-doped graphene to ORR activity remains in dispute. Based on this issue, this paper conducts a comparative study of the ORR on graphitic N-doped graphene (GNG) and pyridinic N-doped grapheme (PNG). Band structure calculations show that the conductivity of GNG decreases as the nitrogen content increases; while that of PNG first increases to the highest at nitrogen content of 4.2% (atomic fraction), and then decreases. The conductivity of PNG is always higher than GNG when the doped nitrogen content is greater than 1.4%. Additionally, the free energy diagram of ORR shows that protonation of O2 is the potential-determining step among the whole ORR process, and the free energy change of this step on GNG is lower than on PNG, suggesting that GNG has higher ORR activity than PNG if their electron transport ability are the same. When the N content is lower than 2.8%, the conductivity difference between GNG and PNG is almost negligible, thus GNG with a higher capacity of O2 protonation exhibits better ORR activity than PNG. When the N content is greater than 2.8%, in this case, conductivity rather than free energy change will dominate, therefore the ORR on PNG will occur faster than on GNG because of its higher conductivity.
N-doped graphene has aroused much interest owing to its high activity and stability in oxygen reduction reaction (ORR) catalysis. However, the contribution of different types of N-doped graphene to ORR activity remains in dispute. Based on this issue, this paper conducts a comparative study of the ORR on graphitic N-doped graphene (GNG) and pyridinic N-doped grapheme (PNG). Band structure calculations show that the conductivity of GNG decreases as the nitrogen content increases; while that of PNG first increases to the highest at nitrogen content of 4.2% (atomic fraction), and then decreases. The conductivity of PNG is always higher than GNG when the doped nitrogen content is greater than 1.4%. Additionally, the free energy diagram of ORR shows that protonation of O2 is the potential-determining step among the whole ORR process, and the free energy change of this step on GNG is lower than on PNG, suggesting that GNG has higher ORR activity than PNG if their electron transport ability are the same. When the N content is lower than 2.8%, the conductivity difference between GNG and PNG is almost negligible, thus GNG with a higher capacity of O2 protonation exhibits better ORR activity than PNG. When the N content is greater than 2.8%, in this case, conductivity rather than free energy change will dominate, therefore the ORR on PNG will occur faster than on GNG because of its higher conductivity.
2016, 32(1): 329-336
doi: 10.3866/PKU.WHXB201511031
Abstract:
Unlocking the dynamics of the evolution of the excited state at the complicated titania/dye/ electrolyte interface in organic dye-sensitized solar cells is crucial to provide a basis for the rational design of low-energy-gap organic photosensitizers. By constructing two organic donor-acceptor dyes composed of benzothiadiazole-benzoic acid (BTBA) and pyridothiadiazole-benzoic acid (PTBA) as electron acceptors, we have identified the images of multiple-step relaxations of the excited state and multiple-state electron injections at the titania/dye/electrolyte interface using ultrafast transient absorption spectroscopic measurements in conjunction with theoretical simulations. Density functional theory and time-dependent density functional theory calculations indicate that there should be torsion-induced excited state relaxations from an optically generated “hot” excited state to the equilibrium excited state characteristic of a more planar conjugated backbone and a quinonoid structure for dye molecules on the titania surface, suggesting the probable presence of multiple-state electron injections at the titania/dye/electrolyte interface. In virtue of a target analysis of femtosecond transient absorption spectra, we have found that the dye with PTBA features a much lower overall electron injection yield with respect to the dye with BTBA owing to the sluggish electron injection and short lifetime of the excited state, accounting for a lower maximum of external quantum efficiencies of the device made from the dye with PTBA as an acceptor.
Unlocking the dynamics of the evolution of the excited state at the complicated titania/dye/ electrolyte interface in organic dye-sensitized solar cells is crucial to provide a basis for the rational design of low-energy-gap organic photosensitizers. By constructing two organic donor-acceptor dyes composed of benzothiadiazole-benzoic acid (BTBA) and pyridothiadiazole-benzoic acid (PTBA) as electron acceptors, we have identified the images of multiple-step relaxations of the excited state and multiple-state electron injections at the titania/dye/electrolyte interface using ultrafast transient absorption spectroscopic measurements in conjunction with theoretical simulations. Density functional theory and time-dependent density functional theory calculations indicate that there should be torsion-induced excited state relaxations from an optically generated “hot” excited state to the equilibrium excited state characteristic of a more planar conjugated backbone and a quinonoid structure for dye molecules on the titania surface, suggesting the probable presence of multiple-state electron injections at the titania/dye/electrolyte interface. In virtue of a target analysis of femtosecond transient absorption spectra, we have found that the dye with PTBA features a much lower overall electron injection yield with respect to the dye with BTBA owing to the sluggish electron injection and short lifetime of the excited state, accounting for a lower maximum of external quantum efficiencies of the device made from the dye with PTBA as an acceptor.
2016, 32(1): 337-342
doi: 10.3866/PKU.WHXB201509144
Abstract:
We designed and synthesized carbon-supported cubic Pt3Ni nanoparticles (NPs) with Pd monolayer shells (Pt3Ni@Pd/C) by a two-step method: generally, CO-assisted preparation of cubic Pt3Ni NPs, Pd monolayer deposition through underpotential deposition of a Cu monolayer, and displacement of Cu with Pd. The as-synthesized Pt3Ni@Pd/C catalyst was characterized with inductively coupled plasma elemental analysis, X-ray diffraction, and transmission electron microscopy. Most Pt3Ni NPs had a cubic nanostructure enclosed by {100} facets, on which the Pd monolayer shells were deposited epitaxially via electrodeposition, by which the Pd monolayers gained the crystallographic orientation of the {100} facets. We then used Pt3Ni@Pd/C as an electrocatalyst for formic acid oxidation (FAO), comparing it with commercial Pd/C and the pristine Pt3Ni/C catalysts. The Pt3Ni@Pd/C exhibited superior electrocatalytic performance because of its monolayer structure and exposed Pd{100} facets. The noble-metal mass activity of the Pt3Ni/C with the deposited Pd monolayer shell was 7.5 times greater than that of the Pt3Ni/C catalyst alone. Moreover, the area-specific and Pd mass activities of Pt3Ni@Pd/C were 2.5 and 8.3 times greater than those of the commercial Pd/C catalyst, respectively.
We designed and synthesized carbon-supported cubic Pt3Ni nanoparticles (NPs) with Pd monolayer shells (Pt3Ni@Pd/C) by a two-step method: generally, CO-assisted preparation of cubic Pt3Ni NPs, Pd monolayer deposition through underpotential deposition of a Cu monolayer, and displacement of Cu with Pd. The as-synthesized Pt3Ni@Pd/C catalyst was characterized with inductively coupled plasma elemental analysis, X-ray diffraction, and transmission electron microscopy. Most Pt3Ni NPs had a cubic nanostructure enclosed by {100} facets, on which the Pd monolayer shells were deposited epitaxially via electrodeposition, by which the Pd monolayers gained the crystallographic orientation of the {100} facets. We then used Pt3Ni@Pd/C as an electrocatalyst for formic acid oxidation (FAO), comparing it with commercial Pd/C and the pristine Pt3Ni/C catalysts. The Pt3Ni@Pd/C exhibited superior electrocatalytic performance because of its monolayer structure and exposed Pd{100} facets. The noble-metal mass activity of the Pt3Ni/C with the deposited Pd monolayer shell was 7.5 times greater than that of the Pt3Ni/C catalyst alone. Moreover, the area-specific and Pd mass activities of Pt3Ni@Pd/C were 2.5 and 8.3 times greater than those of the commercial Pd/C catalyst, respectively.
2016, 32(1): 343-348
doi: 10.3866/PKU.WHXB201510133
Abstract:
One of the major challenges with Li-O2 batteries is that the discharge product, Li2O2, blocks the gas pathway because of its poor solubility in aprotic solvents. In this work, 12-crown-4 ether was used as an additive to capture Li+, and its influence on the solubility of the discharge products of the oxygen electrode was investigated. Multiple electrochemical methods, including cyclic voltammetry and rotatingring disk electrode, were used. The results show that the addition of only 5% of 12-crown-4 ether significantly improves the stability of the oxygen reduction product O2-, and decreases the formation of solid Li2O2. We used a combination of the hard-soft-acid-base theory and ab initio calculations to explain these observations.
One of the major challenges with Li-O2 batteries is that the discharge product, Li2O2, blocks the gas pathway because of its poor solubility in aprotic solvents. In this work, 12-crown-4 ether was used as an additive to capture Li+, and its influence on the solubility of the discharge products of the oxygen electrode was investigated. Multiple electrochemical methods, including cyclic voltammetry and rotatingring disk electrode, were used. The results show that the addition of only 5% of 12-crown-4 ether significantly improves the stability of the oxygen reduction product O2-, and decreases the formation of solid Li2O2. We used a combination of the hard-soft-acid-base theory and ab initio calculations to explain these observations.
2016, 32(1): 349-355
doi: 10.3866/PKU.WHXB201512073
Abstract:
We report on the in-situ preparation of Na2Ti3O7 nanosheets and their application as highperformance anode material for sodium ion batteries. Nanosheets with interconnected micro-nano architectures are prepared by simply engraving commercial titanium foils. Furthermore, the foils can be used directly as electrodes without redundant conductive additives or binders. The electrode material exhibits excellent electrochemical performance with reversible capacity of 175 mAh·g-1 at 50 mA·g-1 and 120 mAh·g-1 at 2000 mA·g-1 after 3000 cycles (capacity retention of 96.5%). The superior electrochemical performance of Na2Ti3O7 nanosheets results from the short ion/electron diffusion pathway of the twodimensional architecture and the good conductive capability of the binder-free structure. The anode of the binder-free Na2Ti3O7 nanosheets effectively overcomes poor ion/electron conductivity, the main drawback of Na2Ti3O7 electrodes, and is promising for rechargeable sodium ion batteries.
We report on the in-situ preparation of Na2Ti3O7 nanosheets and their application as highperformance anode material for sodium ion batteries. Nanosheets with interconnected micro-nano architectures are prepared by simply engraving commercial titanium foils. Furthermore, the foils can be used directly as electrodes without redundant conductive additives or binders. The electrode material exhibits excellent electrochemical performance with reversible capacity of 175 mAh·g-1 at 50 mA·g-1 and 120 mAh·g-1 at 2000 mA·g-1 after 3000 cycles (capacity retention of 96.5%). The superior electrochemical performance of Na2Ti3O7 nanosheets results from the short ion/electron diffusion pathway of the twodimensional architecture and the good conductive capability of the binder-free structure. The anode of the binder-free Na2Ti3O7 nanosheets effectively overcomes poor ion/electron conductivity, the main drawback of Na2Ti3O7 electrodes, and is promising for rechargeable sodium ion batteries.
2016, 32(1): 356-364
doi: 10.3866/PKU.WHXB201512012
Abstract:
The critical micelle concentrations of binary systems of surface active ionic liquid lauryl isoquinolium bromide ([C12iQuin]Br) with nonionic surfactant Triton X-100 in aqueous solution were investigated by isothermal titration calorimetry. The location of [C12iQuin]Br and Triton X-100 in the mixed micelle was studied using 1H nuclear magnetic resonance (NMR) and two-dimensional nuclear Overhauser enhancement spectroscopy (2D NOESY). It was found that the polyoxyethylene chain of Triton X-100 forms random coils around the isoquinolinium ring. The interaction of molecules in the mixed micelle of [C12iQuin]Br- Triton X-100 was also studied using regular solution theory and the cloud point measurement technique, with comparison to the interaction of doceyl trimethyl ammonium bromide (DTAB)-Triton X-100.
The critical micelle concentrations of binary systems of surface active ionic liquid lauryl isoquinolium bromide ([C12iQuin]Br) with nonionic surfactant Triton X-100 in aqueous solution were investigated by isothermal titration calorimetry. The location of [C12iQuin]Br and Triton X-100 in the mixed micelle was studied using 1H nuclear magnetic resonance (NMR) and two-dimensional nuclear Overhauser enhancement spectroscopy (2D NOESY). It was found that the polyoxyethylene chain of Triton X-100 forms random coils around the isoquinolinium ring. The interaction of molecules in the mixed micelle of [C12iQuin]Br- Triton X-100 was also studied using regular solution theory and the cloud point measurement technique, with comparison to the interaction of doceyl trimethyl ammonium bromide (DTAB)-Triton X-100.
2016, 32(1): 365-372
doi: 10.3866/PKU.WHXB201511102
Abstract:
Hydrolyzed polyacrylamides (HPAMs) are shear-thinning polymers and have wide application in enhanced oil recovery (EOR), whereas worm-like micelles (WLMs) are known as “living polymers”, which can be constructed by the self-assembly of surfactant molecules. Here, a series of experiments were conducted on the fluid behavior of HPAMs and worm-like micelles in microscale capillaries with radii from 1 to 10 μm. The results show that the size of capillary has a decisive effect on the in-situ viscosity of the polymer aqueous phase. It was observed that the shear thinning effect of HPAMs is more pronounced in smaller size of capillaries, where the non-Newtonian polymer flow turns into the Newtonian flow. Evidences from filtration with a microporous filter and transmission electron microscopy (TEM) reveal that the polymer network was broken down when entering into the capillary. Conversely, WLMs can maintain their bulk viscosity to a wide extent. We assume that surfactant molecules may reassemble their aggregates and recover their network in-situ. The results suggest that WLMs have a much lower viscosity, but display similar thickening power compared with large polymers in the low or ultra-low permeability reservoirs.
Hydrolyzed polyacrylamides (HPAMs) are shear-thinning polymers and have wide application in enhanced oil recovery (EOR), whereas worm-like micelles (WLMs) are known as “living polymers”, which can be constructed by the self-assembly of surfactant molecules. Here, a series of experiments were conducted on the fluid behavior of HPAMs and worm-like micelles in microscale capillaries with radii from 1 to 10 μm. The results show that the size of capillary has a decisive effect on the in-situ viscosity of the polymer aqueous phase. It was observed that the shear thinning effect of HPAMs is more pronounced in smaller size of capillaries, where the non-Newtonian polymer flow turns into the Newtonian flow. Evidences from filtration with a microporous filter and transmission electron microscopy (TEM) reveal that the polymer network was broken down when entering into the capillary. Conversely, WLMs can maintain their bulk viscosity to a wide extent. We assume that surfactant molecules may reassemble their aggregates and recover their network in-situ. The results suggest that WLMs have a much lower viscosity, but display similar thickening power compared with large polymers in the low or ultra-low permeability reservoirs.
2016, 32(1): 373-379
doi: 10.3866/PKU.WHXB201511091
Abstract:
A new and optically stable fluorescent derivative (OPBMQ) of 1,4-bis(phenylethynyl)benzene (BPEB) with 8-hydroxyquinoline (8-HQ) as a capturing unit and cholesterol (Chol) as an auxiliary structure was designed and synthesized. Fluorescence studies demonstrated that the fluorescence emission of the compound in the aqueous phase is characterized by two distinct and independent emissions, of which one originates from 8-HQ and the other from BPEB. Importantly, the emission is highly selective and sensitive to the presence of diethyl chlorophosphate (DCP), a simulant of Sarin. The calculated detection limit (DL) is lower than 1 × 10-9 mol·L-1. Moreover, no significant response was observed when the probe was exposed to simulants of other nerve agents, relevant organophosphorus pesticides, or even their mixtures. More importantly, regardless of whether Milli-Q water, tap water or even sea water was employed as solvent, the presence of the mixture of the interferents studied did not show any significant effect on the detection of DCP. In particular, the sensitive and highly selective detection of DCP was also realized by naked-eye observation, providing a simple and low-cost protocol for the on-site and real-time detection of the chemical. Based on this discovery, a DCP monitoring device was successfully developed.
A new and optically stable fluorescent derivative (OPBMQ) of 1,4-bis(phenylethynyl)benzene (BPEB) with 8-hydroxyquinoline (8-HQ) as a capturing unit and cholesterol (Chol) as an auxiliary structure was designed and synthesized. Fluorescence studies demonstrated that the fluorescence emission of the compound in the aqueous phase is characterized by two distinct and independent emissions, of which one originates from 8-HQ and the other from BPEB. Importantly, the emission is highly selective and sensitive to the presence of diethyl chlorophosphate (DCP), a simulant of Sarin. The calculated detection limit (DL) is lower than 1 × 10-9 mol·L-1. Moreover, no significant response was observed when the probe was exposed to simulants of other nerve agents, relevant organophosphorus pesticides, or even their mixtures. More importantly, regardless of whether Milli-Q water, tap water or even sea water was employed as solvent, the presence of the mixture of the interferents studied did not show any significant effect on the detection of DCP. In particular, the sensitive and highly selective detection of DCP was also realized by naked-eye observation, providing a simple and low-cost protocol for the on-site and real-time detection of the chemical. Based on this discovery, a DCP monitoring device was successfully developed.
2016, 32(1): 380-390
doi: 10.3866/PKU.WHXB201511193
Abstract:
Rich phase behavior was observed in salt-free cationic/anionic (catanionic) surfactant mixtures of lauric acid (LA) with a nonionic surfactant, tetradecyldimethylamine oxide (C14DMAO), in water. The phase behavior and microstructures of the LA/C14DMAO/H2O system were investigated by freeze-fracture transmission electron microscope (FF-TEM), polarized optical microscope (POM), differential scanning calorimetry (DSC), rheological measurements, and 2H NMR. A variety of self-assembled microstructures were determined, including micelles (L1 phase), lamellae (Lαl phase), vesicles (Lαv phase) and gels. Using the L1 and Lαl phases as the templates, gold nanoparticles could be produced, as confirmed by transmission electron microscope (TEM) and energy dispersive spectrometer (EDS). Compared with the traditional method of preparing Au nanomaterials in aqueous solutions, this method can avoid the addition of NaBH4 as a reducing agent. The sample solution plays roles as a template and a reductant and the reduction process does not destroy the original self-assembled microstructures in the solution. Hence, by controlling the aggregate structures of the template solution, one can achieve the goal of regulating the morphology of Au nanomaterials, which provides a new path for the preparation of noble metal nanostructured materials with different shapes and structures. The results of the methyl thiazolyl tetrazolium (MTT) assay with HK-2 cells show that, as a gene carrier, spherical Au-nanoparticles prepared in a micellar phase possess the characteristics of higher loading efficiency and lower toxicity than those obtained in traditional surfactant systems, demonstrating potential applications in gene therapy.
Rich phase behavior was observed in salt-free cationic/anionic (catanionic) surfactant mixtures of lauric acid (LA) with a nonionic surfactant, tetradecyldimethylamine oxide (C14DMAO), in water. The phase behavior and microstructures of the LA/C14DMAO/H2O system were investigated by freeze-fracture transmission electron microscope (FF-TEM), polarized optical microscope (POM), differential scanning calorimetry (DSC), rheological measurements, and 2H NMR. A variety of self-assembled microstructures were determined, including micelles (L1 phase), lamellae (Lαl phase), vesicles (Lαv phase) and gels. Using the L1 and Lαl phases as the templates, gold nanoparticles could be produced, as confirmed by transmission electron microscope (TEM) and energy dispersive spectrometer (EDS). Compared with the traditional method of preparing Au nanomaterials in aqueous solutions, this method can avoid the addition of NaBH4 as a reducing agent. The sample solution plays roles as a template and a reductant and the reduction process does not destroy the original self-assembled microstructures in the solution. Hence, by controlling the aggregate structures of the template solution, one can achieve the goal of regulating the morphology of Au nanomaterials, which provides a new path for the preparation of noble metal nanostructured materials with different shapes and structures. The results of the methyl thiazolyl tetrazolium (MTT) assay with HK-2 cells show that, as a gene carrier, spherical Au-nanoparticles prepared in a micellar phase possess the characteristics of higher loading efficiency and lower toxicity than those obtained in traditional surfactant systems, demonstrating potential applications in gene therapy.
