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2016 Volume 32 Issue 10
2016, 32(10):
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2016, 32(10): 2383-2384
doi: 10.3866/PKU.WHXB201609071
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2016, 32(10): 2385-2386
doi: 10.3866/PKU.WHXB201609212
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2016, 32(10): 2387-2387
doi: 10.3866/PKU.WHXB201609211
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2016, 32(10): 2388-2389
doi: 10.3866/PKU.WHXB201609011
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2016, 32(10): 2390-2398
doi: 10.3866/PKU.WHXB201607132
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Graphene and its derivatives have attracted increasing attention during the last decade as efficient materials for the storage and conversion of energy. In most cases, however, these graphene materials possess large numbers of structural defects such as cavities, heteroatoms and functional groups, making them quite different from the precisely-defined "single carbon layer of graphite" observed for graphene. These materials also differ considerably in terms of their electrochemical properties because of their variable structures, which are strongly influenced by the methods used during their preparation. Structural analyses have indicated that these materials consist of graphene subunits, which are interconnected by organic linkers with properties lying between those of graphene and polymers, which we have defined as "graphenal polymers". The thermal crosslinking reactions of porous polymer networks fabricated from small organic molecules using a bottom-up strategy also result in graphene-like subunits, which are covalently interconnected by polymeric fractions. These materials cover a series of transitional intermediates belonging to the "graphenal polymers" family, where polymers and graphene sit at opposite ends of family spectrum. Moreover, the special structures and properties of these materials make them ideal electrode materials for the storage and conversion of energy via electronic and ionic transport pathways, allowing for a deeper evaluation of the structure-property relationships of different electrode materials.
Graphene and its derivatives have attracted increasing attention during the last decade as efficient materials for the storage and conversion of energy. In most cases, however, these graphene materials possess large numbers of structural defects such as cavities, heteroatoms and functional groups, making them quite different from the precisely-defined "single carbon layer of graphite" observed for graphene. These materials also differ considerably in terms of their electrochemical properties because of their variable structures, which are strongly influenced by the methods used during their preparation. Structural analyses have indicated that these materials consist of graphene subunits, which are interconnected by organic linkers with properties lying between those of graphene and polymers, which we have defined as "graphenal polymers". The thermal crosslinking reactions of porous polymer networks fabricated from small organic molecules using a bottom-up strategy also result in graphene-like subunits, which are covalently interconnected by polymeric fractions. These materials cover a series of transitional intermediates belonging to the "graphenal polymers" family, where polymers and graphene sit at opposite ends of family spectrum. Moreover, the special structures and properties of these materials make them ideal electrode materials for the storage and conversion of energy via electronic and ionic transport pathways, allowing for a deeper evaluation of the structure-property relationships of different electrode materials.
2016, 32(10): 2399-2410
doi: 10.3866/PKU.WHXB201606242
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Over the past decade, graphene has been the focus of intensive research because of its remarkable physical and chemical properties. Researchers have made many efforts to synthesize graphene and investigate its potential applications. In this article, we first briefly review the fabrication processes and properties of graphene. Then, we discuss the application of graphene/Ag hybrid films as transparent conductive films (TCFs). Next, we introduce our results on this topic. Graphene and Ag nanowires were synthesized by chemical vapor deposition (CVD) and the polyol process, respectively. We successfully fabricated a graphene/Ag hybrid film with a low sheet resistance (Rs) of 26 Ω·□-1. Finally, we describe the main challenges facing graphene hybrid films and their potential applications in a wide range of optoelectronic devices.
Over the past decade, graphene has been the focus of intensive research because of its remarkable physical and chemical properties. Researchers have made many efforts to synthesize graphene and investigate its potential applications. In this article, we first briefly review the fabrication processes and properties of graphene. Then, we discuss the application of graphene/Ag hybrid films as transparent conductive films (TCFs). Next, we introduce our results on this topic. Graphene and Ag nanowires were synthesized by chemical vapor deposition (CVD) and the polyol process, respectively. We successfully fabricated a graphene/Ag hybrid film with a low sheet resistance (Rs) of 26 Ω·□-1. Finally, we describe the main challenges facing graphene hybrid films and their potential applications in a wide range of optoelectronic devices.
2016, 32(10): 2411-2426
doi: 10.3866/PKU.WHXB201606227
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Microbial fuel cell (MFC) is a novel bioelectrochemical device that uses a biocatalyst to convert chemical energy stored in organic wastewater into electrical energy. However, multiple factors limit the practical applications of MFCs, such as the high cost of electrode production and their low conversion efficiencies of power density and energy. Therefore, improving the catalytic performance of the electrodes and lowering the cost of electrode production have become focuses in MFC research. Because of the excellent electrical conductivity and catalytic properties of graphene-based hybrid materials, the development of these electrode materials for use in MFCs has attracted much attention. This review summarizes recent advances of graphene-based hybrid electrodes in MFCs. The preparation methods and the catalytic performance of graphene-modified electrodes, metal and non-metallic/graphene hybrid electrodes, metal oxide/graphene hybrid electrodes, polymer/graphene hybrid electrodes, and graphene gel electrodes are discussed in detail. The influence of graphene-based hybrid anodes and cathodes on the electricity generation performance of MFCs is analyzed. Finally, the problems facing graphene-based hybrid electrodes for MFCs are summarized, and the application prospects of MFCs are considered.
Microbial fuel cell (MFC) is a novel bioelectrochemical device that uses a biocatalyst to convert chemical energy stored in organic wastewater into electrical energy. However, multiple factors limit the practical applications of MFCs, such as the high cost of electrode production and their low conversion efficiencies of power density and energy. Therefore, improving the catalytic performance of the electrodes and lowering the cost of electrode production have become focuses in MFC research. Because of the excellent electrical conductivity and catalytic properties of graphene-based hybrid materials, the development of these electrode materials for use in MFCs has attracted much attention. This review summarizes recent advances of graphene-based hybrid electrodes in MFCs. The preparation methods and the catalytic performance of graphene-modified electrodes, metal and non-metallic/graphene hybrid electrodes, metal oxide/graphene hybrid electrodes, polymer/graphene hybrid electrodes, and graphene gel electrodes are discussed in detail. The influence of graphene-based hybrid anodes and cathodes on the electricity generation performance of MFCs is analyzed. Finally, the problems facing graphene-based hybrid electrodes for MFCs are summarized, and the application prospects of MFCs are considered.
2016, 32(10): 2427-2446
doi: 10.3866/PKU.WHXB201607261
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With the rapid development of wearable devices, flexible conductive materials, which are one of the most important components of flexible electronics, have continued to attract increasing attention as important materials. Conventional electrodes mainly consist of rigid metallic materials, and consequently lack flexibility. Some of the strategies commonly used to make flexible metal electrodes include reducing the thickness of the electrode and designing electrodes with unique structural features. However, these techniques are generally complicated and expensive. Nanocarbon materials, especially carbon nanotubes and graphene, are highly flexible and exhibit excellent conductivity, superior thermal stability, good chemical stability, and high transmittance, making them good alternative materials for the preparation of flexible conductors. In this review, we have summarized recent advances towards the development of flexible conductors based on different types of nanocarbon materials, including carbon nanotubes arrays, carbon nanotubes films, carbon nanotubes fibers, graphene prepared using exfoliation or chemical vapor deposition techniques and graphene fibers. We have also provided a brief review of flexible conductive materials based on graphene/carbon nanotube composites, as well as a summary of the synthesis, fabrication and performances of these conductors. Finally, we have discussed the future challenges and possible research directions of flexible conductors based on nanocarbon materials.
With the rapid development of wearable devices, flexible conductive materials, which are one of the most important components of flexible electronics, have continued to attract increasing attention as important materials. Conventional electrodes mainly consist of rigid metallic materials, and consequently lack flexibility. Some of the strategies commonly used to make flexible metal electrodes include reducing the thickness of the electrode and designing electrodes with unique structural features. However, these techniques are generally complicated and expensive. Nanocarbon materials, especially carbon nanotubes and graphene, are highly flexible and exhibit excellent conductivity, superior thermal stability, good chemical stability, and high transmittance, making them good alternative materials for the preparation of flexible conductors. In this review, we have summarized recent advances towards the development of flexible conductors based on different types of nanocarbon materials, including carbon nanotubes arrays, carbon nanotubes films, carbon nanotubes fibers, graphene prepared using exfoliation or chemical vapor deposition techniques and graphene fibers. We have also provided a brief review of flexible conductive materials based on graphene/carbon nanotube composites, as well as a summary of the synthesis, fabrication and performances of these conductors. Finally, we have discussed the future challenges and possible research directions of flexible conductors based on nanocarbon materials.
2016, 32(10): 2447-2461
doi: 10.3866/PKU.WHXB201607141
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Metalloporphyrins are a class of metal-organic complexes that exhibit a wide range of interesting properties with prosperous applications in photoelectric conversion devices, catalysis, sensors and medicines. Besides inorganic two-dimensional (2D) materials (e.g., graphene and transitional metal dichalcogenide nanosheets), two-dimensional metal-organic nanosheets have also attracted considerable attention in recent years as interesting materials. Based on the rapid progress of two-dimensional metal-organic and porphyrinoid nanomaterials, this review aims to provide a brief review of the history of two-dimensional metal-organic nanomaterials, followed by a detailed summary of the synthetic methods used to prepare free-standing 2D nanosheets as well as 2D thin film of metalloporphyrins. We have also provided an up-to-date review of the applications of these materials in solar cells, photo- and electric catalysts as well as optical sensors, and a discussion pertaining to the problems associated with the synthesis, properties, and possible applications of metalloporphyrin 2D materials.
Metalloporphyrins are a class of metal-organic complexes that exhibit a wide range of interesting properties with prosperous applications in photoelectric conversion devices, catalysis, sensors and medicines. Besides inorganic two-dimensional (2D) materials (e.g., graphene and transitional metal dichalcogenide nanosheets), two-dimensional metal-organic nanosheets have also attracted considerable attention in recent years as interesting materials. Based on the rapid progress of two-dimensional metal-organic and porphyrinoid nanomaterials, this review aims to provide a brief review of the history of two-dimensional metal-organic nanomaterials, followed by a detailed summary of the synthetic methods used to prepare free-standing 2D nanosheets as well as 2D thin film of metalloporphyrins. We have also provided an up-to-date review of the applications of these materials in solar cells, photo- and electric catalysts as well as optical sensors, and a discussion pertaining to the problems associated with the synthesis, properties, and possible applications of metalloporphyrin 2D materials.
2016, 32(10): 2462-2474
doi: 10.3866/PKU.WHXB201606293
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Proton exchange membrane fuel cells (PEMFCs) are considered as ideal alternative power devices to traditional internal combustion engines for automobile applications because of their high electric power density, high energy conversion efficiency, and low environmental impact as well as low temperatures for start-up and operation. However, PEMFCs normally require a high loading of the expensive precious metal platinum (Pt) as the electrocatalytic material to maintain desirable energy output. Thus, the development of novel catalysts with lower Pt loading, enhanced activity, and improved durability is vital for the scalable commercialization of PEMFC technology. In this regard, core-shell structure has been demonstrated as an effective strategy to minimize the amount of Pt in PEMFCs because of the following two factors:(1) a core-shell architecture with a Pt-rich shell and M-rich (M represents an earth-abundant element) core can greatly improve the utilization of Pt; (2) the activity and stability of Pt on the surface can be greatly enhanced by strain (geometry) and electronic (alloying) effects caused by the M in the core. First, we briefly discuss the structure-performance relationship of typical core-shell structured electrocatalysts for the oxygen reduction reaction (ORR). Then, we review the development of Pt-based core-shell structured catalysts for the ORR. Finally, a perspective on this research topic is provided.
Proton exchange membrane fuel cells (PEMFCs) are considered as ideal alternative power devices to traditional internal combustion engines for automobile applications because of their high electric power density, high energy conversion efficiency, and low environmental impact as well as low temperatures for start-up and operation. However, PEMFCs normally require a high loading of the expensive precious metal platinum (Pt) as the electrocatalytic material to maintain desirable energy output. Thus, the development of novel catalysts with lower Pt loading, enhanced activity, and improved durability is vital for the scalable commercialization of PEMFC technology. In this regard, core-shell structure has been demonstrated as an effective strategy to minimize the amount of Pt in PEMFCs because of the following two factors:(1) a core-shell architecture with a Pt-rich shell and M-rich (M represents an earth-abundant element) core can greatly improve the utilization of Pt; (2) the activity and stability of Pt on the surface can be greatly enhanced by strain (geometry) and electronic (alloying) effects caused by the M in the core. First, we briefly discuss the structure-performance relationship of typical core-shell structured electrocatalysts for the oxygen reduction reaction (ORR). Then, we review the development of Pt-based core-shell structured catalysts for the ORR. Finally, a perspective on this research topic is provided.
2016, 32(10): 2475-2487
doi: 10.3866/PKU.WHXB201607121
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Two-dimensional layered zeolite precursors (LZPs) with layered structural units of parent threedimensional zeolites possess the properties of the parent materials but with an open framework structure. The structural properties of these materials therefore provide new opportunities to synthesize new zeolites and fabricate sub-zeolites with distinct structures, making them a hot topic in zeolite research. Enormous LZPs were synthesized by the direct crystallization or post-modification of their three-dimensional parent structures. Several layer manipulation strategies, including swelling, delamination, pillaring and layer reassembly have been developed on two-dimensional LZPs. These strategies have provided access to zeolites with new structures as well as materials even violating the theoretical rules, which have greatly enhanced the field of two-dimensional LZPs, and expanded their applications in catalysis and separation. Herein, we have reviewed the structural characteristics of two-dimensional LZPs, as well as summarizing their syntheses, modifications, and catalytic applications. We have also proposed the future perspectives of two-dimensional LZPs.
Two-dimensional layered zeolite precursors (LZPs) with layered structural units of parent threedimensional zeolites possess the properties of the parent materials but with an open framework structure. The structural properties of these materials therefore provide new opportunities to synthesize new zeolites and fabricate sub-zeolites with distinct structures, making them a hot topic in zeolite research. Enormous LZPs were synthesized by the direct crystallization or post-modification of their three-dimensional parent structures. Several layer manipulation strategies, including swelling, delamination, pillaring and layer reassembly have been developed on two-dimensional LZPs. These strategies have provided access to zeolites with new structures as well as materials even violating the theoretical rules, which have greatly enhanced the field of two-dimensional LZPs, and expanded their applications in catalysis and separation. Herein, we have reviewed the structural characteristics of two-dimensional LZPs, as well as summarizing their syntheses, modifications, and catalytic applications. We have also proposed the future perspectives of two-dimensional LZPs.
2016, 32(10): 2488-2494
doi: 10.3866/PKU.WHXB201606222
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The effects of Li, Na, and K alkali metal ions on the band structures and carrier transfer of graphitic carbon nitride (g-C3N4) are investigated using the plane-wave ultrasoft pseudopotential method. The generalized gradient approximation and local density approximation are used to calculate total energies of six adsorption configurations. The three alkali ions all tend to adsorb on the large central cavity (F position) in g-C3N4 layers. The calculated band structures and work function values indicate that the interface charge balance of the n-type Schottky junctions formed between the alkali metal ions and g-C3N4 induces the total band edge potential of g-C3N4 to shift down by 1.52 V (Li), 1.07 V (Na), and 0.86 V (K). The incorporation of K ion adjusts the valence and conduction bands to more appropriate redox potentials than those of pure g-C3N4, and increases the distribution of the HOMO and LOMO of g-C3N4, which helps to improve the mobility of carriers. Meanwhile, the non-coplanar HOMO and LOMO favor the separation of electrons and holes.
The effects of Li, Na, and K alkali metal ions on the band structures and carrier transfer of graphitic carbon nitride (g-C3N4) are investigated using the plane-wave ultrasoft pseudopotential method. The generalized gradient approximation and local density approximation are used to calculate total energies of six adsorption configurations. The three alkali ions all tend to adsorb on the large central cavity (F position) in g-C3N4 layers. The calculated band structures and work function values indicate that the interface charge balance of the n-type Schottky junctions formed between the alkali metal ions and g-C3N4 induces the total band edge potential of g-C3N4 to shift down by 1.52 V (Li), 1.07 V (Na), and 0.86 V (K). The incorporation of K ion adjusts the valence and conduction bands to more appropriate redox potentials than those of pure g-C3N4, and increases the distribution of the HOMO and LOMO of g-C3N4, which helps to improve the mobility of carriers. Meanwhile, the non-coplanar HOMO and LOMO favor the separation of electrons and holes.
2016, 32(10): 2495-2502
doi: 10.3866/PKU.WHXB201606295
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Silicon bridge-tuned electronic structures and transport properties of polymetallocenes,[V(Cp)2(SiH2)n]m (n=1 (a), n=2 (b), n=3 (c); m=∞; Cp=cyclopentadienyl), are studied using the densityfunctional theory (DFT) and non-equilibrium Green's function (NEGF) methods. As the silicon bridge islengthened, the V-V ferromagnetic (FM) coupling is weakened, while the antiferromagnetic (AFM) coupling isstrengthened. Polymetallocenes a and b favor the FM ground state, while c prefers the AFM ground state. EachV atom in the FM state of a and b has a magnetic moment of ~3.0μB, three times larger than that in the Vbenzeneor V-cyclopentadiene multidecker complex. The transport properties of a-c are in good agreementwith their electronic structures. Their conductivities follow the sequence c > b > a. For a and b, the spin-downstate has slightly higher conductivity than the spin-up state. Polymetallocenes a and c can both display evidentnegative differential resistance (NDR) behavior, while b cannot. This difference may originate from theorientation of the two V(Cp)2 units, which is V-shaped for a and c (odd number of SiH2 units), leading to ioniclikeinter-quantum dot coupling, and parallel for b (even number of SiH2 units), leading to covalent-like interquantumdot coupling. In addition, the conductivity of a-c is sensitive to the current direction because of theasymmetric coupling between the scattering region and two electrodes.
Silicon bridge-tuned electronic structures and transport properties of polymetallocenes,[V(Cp)2(SiH2)n]m (n=1 (a), n=2 (b), n=3 (c); m=∞; Cp=cyclopentadienyl), are studied using the densityfunctional theory (DFT) and non-equilibrium Green's function (NEGF) methods. As the silicon bridge islengthened, the V-V ferromagnetic (FM) coupling is weakened, while the antiferromagnetic (AFM) coupling isstrengthened. Polymetallocenes a and b favor the FM ground state, while c prefers the AFM ground state. EachV atom in the FM state of a and b has a magnetic moment of ~3.0μB, three times larger than that in the Vbenzeneor V-cyclopentadiene multidecker complex. The transport properties of a-c are in good agreementwith their electronic structures. Their conductivities follow the sequence c > b > a. For a and b, the spin-downstate has slightly higher conductivity than the spin-up state. Polymetallocenes a and c can both display evidentnegative differential resistance (NDR) behavior, while b cannot. This difference may originate from theorientation of the two V(Cp)2 units, which is V-shaped for a and c (odd number of SiH2 units), leading to ioniclikeinter-quantum dot coupling, and parallel for b (even number of SiH2 units), leading to covalent-like interquantumdot coupling. In addition, the conductivity of a-c is sensitive to the current direction because of theasymmetric coupling between the scattering region and two electrodes.
2016, 32(10): 2503-2510
doi: 10.3866/PKU.WHXB201607051
Abstract:
Exploring and fabricating organic solar cell devices with the high power conversion efficiency (PCE) has kept a major challenge and hot topic in organic electronics research. In this study, we have used quantum chemical and molecular dynamics calculations in conjunction with the Marcus-Hush charge transfer model to investigate the photovoltaic properties of BBPQ-PC61BM. The results revealed that the BBPQ-PC61BM (BBPQ:7,12-bis((triisopropylsilyl)-ethynyl)benzo(g)pyrido(2',3':5,6)pyrazino(2,3-b)quinoxalin-2(1H)-one; PC61BM:(6, 6)-phenyl-C61-butyric acid methyl ester) system theoretically possesses a large open-circuit voltage (1.22 V), high fill factor (0.90), and high PCE of 9%-10%. The calculations also reveal that the BBPQ-PC61BM system has a medium-sized exciton binding energy (0.607 eV), with relatively small reorganization energies (0.345 and 0.355 eV) for its exciton-dissociation and charge-recombination processes. Based on a simplified molecular complex, the exciton dissociation rate constant, kdis, was estimated to be as large as 1.775×1013 s-1 at the BBPQPC61BM interface. In contrast, the charge-recombination rate constant, krec, was very small under the same conditions (<1.0 s-1), which indicated a rapid and efficient exciton-dissociation process at the donor-acceptor interface. Overall, our calculations show that the BBPQ-PC61BM system is a very promising organic solar cell system that is worthy of further research.
Exploring and fabricating organic solar cell devices with the high power conversion efficiency (PCE) has kept a major challenge and hot topic in organic electronics research. In this study, we have used quantum chemical and molecular dynamics calculations in conjunction with the Marcus-Hush charge transfer model to investigate the photovoltaic properties of BBPQ-PC61BM. The results revealed that the BBPQ-PC61BM (BBPQ:7,12-bis((triisopropylsilyl)-ethynyl)benzo(g)pyrido(2',3':5,6)pyrazino(2,3-b)quinoxalin-2(1H)-one; PC61BM:(6, 6)-phenyl-C61-butyric acid methyl ester) system theoretically possesses a large open-circuit voltage (1.22 V), high fill factor (0.90), and high PCE of 9%-10%. The calculations also reveal that the BBPQ-PC61BM system has a medium-sized exciton binding energy (0.607 eV), with relatively small reorganization energies (0.345 and 0.355 eV) for its exciton-dissociation and charge-recombination processes. Based on a simplified molecular complex, the exciton dissociation rate constant, kdis, was estimated to be as large as 1.775×1013 s-1 at the BBPQPC61BM interface. In contrast, the charge-recombination rate constant, krec, was very small under the same conditions (<1.0 s-1), which indicated a rapid and efficient exciton-dissociation process at the donor-acceptor interface. Overall, our calculations show that the BBPQ-PC61BM system is a very promising organic solar cell system that is worthy of further research.
2016, 32(10): 2511-2517
doi: 10.3866/PKU.WHXB201607131
Abstract:
An effective method for improving the performance of a photocatalyst is to construct a suitable hetero-/homo-structure. This strategy can also lead to improvements in the stability of the photocatalysts that suffer with photo-corrosion (such as CdS). The preparation of CdS-based composite photocatalysts has therefore been widely studied. Unfortunately, however, some of the fundamental and more significant aspects of this strategy still need to be evaluated in greater detail. In this study, we have evaluated the interfacial microstructure and properties of a CdS/FeP composite photocatalyst with a hetero-structure using a series of the firstprinciples calculations. The results revealed that the electronic structure of the interface model exhibited different features compared with the bulk and surface models, because of the partially saturated dangling bonds. However, several obvious interfacial states were observed. At the interface of the CdS/FeP hetero-structure, the energy bands of CdS and FeP were relatively down-shifted, whereas the energy band of FeP was inserted below the conduction band of CdS. Furthermore, the direction of the built-in electric field of the hetero-structure projected out from the FeP layer towards the CdS layer under the equilibrium conditions. The photo-generated electron-hole pairs were therefore spatially separated by the CdS/FeP interface, which was favorable for improving the photocatalytic performance. The construction of a CdS/FeP hetero-structure can also lead to further improvements in the absorption properties of CdS in the visible-light region. The results of this study have provided mechanical explanations and theoretical support for the construction of highly efficient composite photocatalyst with hetero-structures.
An effective method for improving the performance of a photocatalyst is to construct a suitable hetero-/homo-structure. This strategy can also lead to improvements in the stability of the photocatalysts that suffer with photo-corrosion (such as CdS). The preparation of CdS-based composite photocatalysts has therefore been widely studied. Unfortunately, however, some of the fundamental and more significant aspects of this strategy still need to be evaluated in greater detail. In this study, we have evaluated the interfacial microstructure and properties of a CdS/FeP composite photocatalyst with a hetero-structure using a series of the firstprinciples calculations. The results revealed that the electronic structure of the interface model exhibited different features compared with the bulk and surface models, because of the partially saturated dangling bonds. However, several obvious interfacial states were observed. At the interface of the CdS/FeP hetero-structure, the energy bands of CdS and FeP were relatively down-shifted, whereas the energy band of FeP was inserted below the conduction band of CdS. Furthermore, the direction of the built-in electric field of the hetero-structure projected out from the FeP layer towards the CdS layer under the equilibrium conditions. The photo-generated electron-hole pairs were therefore spatially separated by the CdS/FeP interface, which was favorable for improving the photocatalytic performance. The construction of a CdS/FeP hetero-structure can also lead to further improvements in the absorption properties of CdS in the visible-light region. The results of this study have provided mechanical explanations and theoretical support for the construction of highly efficient composite photocatalyst with hetero-structures.
Monte-Carlo Simulations of the Effect of Surfactant on the Growth of Silver Dendritic Nanostructures
2016, 32(10): 2518-2522
doi: 10.3866/PKU.WHXB201605272
Abstract:
The bias diffusion-limited aggregation model is used to study the growth of silver dendritic nanostructures in solution. In the simulation, right-angled isosceles triangle particles are introduced in twodimensional square grids and the sticking possibilities of different particle sides are introduced to describe the effect of the surfactant. Our simulation results show that the dendritic nanostructures become denser with increasing bias voltage. It is also found that the dendritic nanostructures become much more symmetrical and regular when the surfactant is applied. Furthermore, if the effect of the surfactant is strong enough and the bias voltage is small, the branches of the nanostructures are assembled into silver plates. Our simulation results are helpful to explain the experimental results qualitatively.
The bias diffusion-limited aggregation model is used to study the growth of silver dendritic nanostructures in solution. In the simulation, right-angled isosceles triangle particles are introduced in twodimensional square grids and the sticking possibilities of different particle sides are introduced to describe the effect of the surfactant. Our simulation results show that the dendritic nanostructures become denser with increasing bias voltage. It is also found that the dendritic nanostructures become much more symmetrical and regular when the surfactant is applied. Furthermore, if the effect of the surfactant is strong enough and the bias voltage is small, the branches of the nanostructures are assembled into silver plates. Our simulation results are helpful to explain the experimental results qualitatively.
2016, 32(10): 2523-2530
doi: 10.3866/PKU.WHXB201606292
Abstract:
Molecular dynamics (MD) simulations were performed to study the transport properties of gases (oxygen, nitrogen, and methane) in amorphous cis-1,4-polyisoprene over a wide range of temperatures. The COMPASS force field was used as the molecular mechanics force field in the simulations. Experimental values of density and glass transition temperature were successfully reproduced using the atomistic potentials determined by COMPASS. Diffusion coefficients were determined from long NVT simulation times (up to 3 or 1.5 ns) in the temperature range of 278-378 K. The diffusion coefficients calculated fromthe Einstein relationship agree well with available experimental data. Further studies on the temperature dependence of diffusion coefficients indicate that curvature is observed in the Arrhenius plot of diffusivity versus inverse temperature for methane, but the plots are linear over the investigated temperature range for oxygen and nitrogen. These simulation results are useful to understand the temperature dependence of diffusion coefficients, and provide a basis for the determination of diffusion coefficients at high temperatures and the modeling of thermo-oxidative degradation of polyisoprene.
Molecular dynamics (MD) simulations were performed to study the transport properties of gases (oxygen, nitrogen, and methane) in amorphous cis-1,4-polyisoprene over a wide range of temperatures. The COMPASS force field was used as the molecular mechanics force field in the simulations. Experimental values of density and glass transition temperature were successfully reproduced using the atomistic potentials determined by COMPASS. Diffusion coefficients were determined from long NVT simulation times (up to 3 or 1.5 ns) in the temperature range of 278-378 K. The diffusion coefficients calculated fromthe Einstein relationship agree well with available experimental data. Further studies on the temperature dependence of diffusion coefficients indicate that curvature is observed in the Arrhenius plot of diffusivity versus inverse temperature for methane, but the plots are linear over the investigated temperature range for oxygen and nitrogen. These simulation results are useful to understand the temperature dependence of diffusion coefficients, and provide a basis for the determination of diffusion coefficients at high temperatures and the modeling of thermo-oxidative degradation of polyisoprene.
2016, 32(10): 2531-2537
doi: 10.3866/PKU.WHXB201606223
Abstract:
Electrochemical and thermodynamic studies on the formation of La-Ni intermetallic compounds in molten LiCl-KCl-(3.5%(w))LaCl3 at 773 K were performed. The electrochemical reduction of La(III) ions was investigated on inert W and reactive Ni electrodes by cyclic voltammetry. The reduction potential of La(III)/La on a Ni electrode was observed at more positive potential than that on a W electrode because of the formation of La-Ni intermetallic compounds when La ions reacted with the Ni substrate. Square-wave voltammetry, chronopotentiometry, and open-circuit chronopotentiometry provided further evidence for the formation of La-Ni intermetallic compounds. Potentiostatic electrolysis on a Ni electrode led to the formation of three La-Ni intermetallic compounds, LaNi5, La7Ni16 and La2Ni3, according to X-ray diffraction (XRD) and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS) analyses. The standard Gibbs free energies of formation for LaNi5 were estimated from open-circuit chronopotentiometric measurements using the Gibbs-Helmholtz equation and Hess law. The formation of the La-Ni alloy layer could be controlled by the applied potential and time. Potentiostatic electrolysis was an effective method for electrochemical extraction of La.
Electrochemical and thermodynamic studies on the formation of La-Ni intermetallic compounds in molten LiCl-KCl-(3.5%(w))LaCl3 at 773 K were performed. The electrochemical reduction of La(III) ions was investigated on inert W and reactive Ni electrodes by cyclic voltammetry. The reduction potential of La(III)/La on a Ni electrode was observed at more positive potential than that on a W electrode because of the formation of La-Ni intermetallic compounds when La ions reacted with the Ni substrate. Square-wave voltammetry, chronopotentiometry, and open-circuit chronopotentiometry provided further evidence for the formation of La-Ni intermetallic compounds. Potentiostatic electrolysis on a Ni electrode led to the formation of three La-Ni intermetallic compounds, LaNi5, La7Ni16 and La2Ni3, according to X-ray diffraction (XRD) and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS) analyses. The standard Gibbs free energies of formation for LaNi5 were estimated from open-circuit chronopotentiometric measurements using the Gibbs-Helmholtz equation and Hess law. The formation of the La-Ni alloy layer could be controlled by the applied potential and time. Potentiostatic electrolysis was an effective method for electrochemical extraction of La.
2016, 32(10): 2538-2544
doi: 10.3866/PKU.WHXB201607202
Abstract:
To prepare Al-Tb alloys from Tb4O7 assisted by AlF3 in NaCl-KCl melts, we initially studied the effect of AlF3 on the dissolution of Tb4O7 by analyzing the supernatant and bottom salts. X-ray diffraction (XRD) results revealed that Tb4O7 was fluorinated by AlF3 to form TbF3. The electrochemical behavior of the NaCl-KCl-AlF3-Tb4O7 system was investigated using a Mo electrode at 1073 K. Cyclic voltammetry (CV), square wave voltammetry (SWV), chronopotentiometry (CP) and open circuit chronopotentiometry (OCP) analyses indicated that the under-potential deposition of Tb(III) occurred on pre-deposited Al. The co-deposition of Al-Tb alloys was investigated by galvanostatic electrolysis under different conditions. These samples were characterized by XRD and scanning electron microscopy and energy dispersive spectrometry (SEM-EDS). The Al-Tb alloy obtained by galvanostatic electrolysis at -2.5 A consisted of Al and Al3Tb phases. The effects of the electrolysis conditions on the composition of the alloy and current efficiency were studied by analyzing the compositions of the Al-Tb alloys by inductively coupled plasma-atomic emission spectrometer (ICP-AES). The current efficiency could reach 76.5% under the conditions of galvanostatic electrolysis at -1.5 A for 2 h.
To prepare Al-Tb alloys from Tb4O7 assisted by AlF3 in NaCl-KCl melts, we initially studied the effect of AlF3 on the dissolution of Tb4O7 by analyzing the supernatant and bottom salts. X-ray diffraction (XRD) results revealed that Tb4O7 was fluorinated by AlF3 to form TbF3. The electrochemical behavior of the NaCl-KCl-AlF3-Tb4O7 system was investigated using a Mo electrode at 1073 K. Cyclic voltammetry (CV), square wave voltammetry (SWV), chronopotentiometry (CP) and open circuit chronopotentiometry (OCP) analyses indicated that the under-potential deposition of Tb(III) occurred on pre-deposited Al. The co-deposition of Al-Tb alloys was investigated by galvanostatic electrolysis under different conditions. These samples were characterized by XRD and scanning electron microscopy and energy dispersive spectrometry (SEM-EDS). The Al-Tb alloy obtained by galvanostatic electrolysis at -2.5 A consisted of Al and Al3Tb phases. The effects of the electrolysis conditions on the composition of the alloy and current efficiency were studied by analyzing the compositions of the Al-Tb alloys by inductively coupled plasma-atomic emission spectrometer (ICP-AES). The current efficiency could reach 76.5% under the conditions of galvanostatic electrolysis at -1.5 A for 2 h.
Controlled Synthesis and Supercapacitive Performance of Heterostructured MnO2/H-TiO2 Nanotube Arrays
2016, 32(10): 2545-2554
doi: 10.3866/PKU.WHXB201606161
Abstract:
This study used the target-controlled anodizing process for the controllable fabrication of TiO2 nanotube arrays (TiO2 NTAs) film substrate with large specific surface area and well-separated nanotubes. After annealing crystallization, TiO2 NTAs were successively functional modified by electrochemical hydrogenation and sequential chemical bath deposition of high specific capacitance MnO2 nanoparticles onto both the outer and inner surfaces of the nanotubes, thus constructing the heterostructured MnO2/H-TiO2 NTAs electrode. The as-prepared samples were fully characterized by field emission scanning electron microscopy (FESEM), highresolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy. The supercapacitive performance and stability of the resulting samples were systematically evaluated using electrochemical workstation. The results from the current study revealed that conductivity and electrochemical properties of H-TiO2 NTAs were dramatically enhanced through electrochemical hydrogenation and the specific capacitance of H-TiO2 NTAs could achieve 7.5 mF·cm-2 at current density of 0.2 mA·cm-2, which is almost 75 times the performance of TiO2 NTAs (0.1 mF·cm-2). Furthermore, the specific capacitance of MnO2/H-TiO2 NTAs-2 could achieve 481.26 F·g-1 at a current density of 3 mA·mg-1 as well as outstanding long-term cycling stability with only 11% reduction of initial specific capacitance at a current density of 5 mA·mg-1 after 1000 cycles.
This study used the target-controlled anodizing process for the controllable fabrication of TiO2 nanotube arrays (TiO2 NTAs) film substrate with large specific surface area and well-separated nanotubes. After annealing crystallization, TiO2 NTAs were successively functional modified by electrochemical hydrogenation and sequential chemical bath deposition of high specific capacitance MnO2 nanoparticles onto both the outer and inner surfaces of the nanotubes, thus constructing the heterostructured MnO2/H-TiO2 NTAs electrode. The as-prepared samples were fully characterized by field emission scanning electron microscopy (FESEM), highresolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy. The supercapacitive performance and stability of the resulting samples were systematically evaluated using electrochemical workstation. The results from the current study revealed that conductivity and electrochemical properties of H-TiO2 NTAs were dramatically enhanced through electrochemical hydrogenation and the specific capacitance of H-TiO2 NTAs could achieve 7.5 mF·cm-2 at current density of 0.2 mA·cm-2, which is almost 75 times the performance of TiO2 NTAs (0.1 mF·cm-2). Furthermore, the specific capacitance of MnO2/H-TiO2 NTAs-2 could achieve 481.26 F·g-1 at a current density of 3 mA·mg-1 as well as outstanding long-term cycling stability with only 11% reduction of initial specific capacitance at a current density of 5 mA·mg-1 after 1000 cycles.
2016, 32(10): 2555-2562
doi: 10.3866/PKU.WHXB201606281
Abstract:
The thermoelectric performance of traditional thermogalvanic cells is relatively low and a more efficient conversion mechanism is required. In this paper, the distribution of glycerol/glycerin in an aqueous sodium chloride solution in a carbon nanotube (CNT) is investigated by molecular dynamics (MD) simulation. The distributions of ions, molecule net charge, and electrical potential of the system are markedly affected by temperature. We propose a novel nanofluid thermoelectric conversion method based on the CNT and glycerol/glycerin aqueous sodium chloride solution. The thermoelectric performance of the proposed system is much higher than that of most of current liquid thermogalvanic cells, and the application temperature range is also widened considerably. A preliminary thermal-to-electrical energy conversion experiment based on nanoporous carbon withmixtures of sodiumchloride and glycerol is also conducted to qualitatively verify the numerical results.
The thermoelectric performance of traditional thermogalvanic cells is relatively low and a more efficient conversion mechanism is required. In this paper, the distribution of glycerol/glycerin in an aqueous sodium chloride solution in a carbon nanotube (CNT) is investigated by molecular dynamics (MD) simulation. The distributions of ions, molecule net charge, and electrical potential of the system are markedly affected by temperature. We propose a novel nanofluid thermoelectric conversion method based on the CNT and glycerol/glycerin aqueous sodium chloride solution. The thermoelectric performance of the proposed system is much higher than that of most of current liquid thermogalvanic cells, and the application temperature range is also widened considerably. A preliminary thermal-to-electrical energy conversion experiment based on nanoporous carbon withmixtures of sodiumchloride and glycerol is also conducted to qualitatively verify the numerical results.
2016, 32(10): 2563-2573
doi: 10.3866/PKU.WHXB201607122
Abstract:
A new kind of cellulose-lignin composite hydrogel (UCHy) was prepared under ultrasonic irradiation using cellulose and lignin as raw materials. The resulting material was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD) analysis. The swelling properties of UCHy were also investigated at a variety of different Pb(II) concentrations, whilst its adsorption capacity was studied as a function of pH, reaction time, temperature, and concentration of the Pb (II) solution under ambient conditions. The results showed that cellulose and lignin were beneficial to the formation of a denser structure, and that the ultrasonic treatment promoted the formation of the continuous pore microstructure of the hydrogel, resulting in a high swelling ratio and pollutant adsorption capacity. The swelling kinetics indicated that the initial solution intake of the composite hydrogel followed a non-Fickian type diffusion, and that the whole swelling process was fit for the Schott's model well. The adsorption capacity of Pb(II) increased as the pH of the solution increased, and decreases with increasing temperature. The adsorption isotherm data followed the Langmuir and Freundlich models, with an optimum adsorption value of 786.16 mg·g-1. The adsorption rate closely followed a pseudo-second order model. As a result, UCHy showed good responsive and adsorption properties towards heavy metal ions, and therefore represents a promising material for the detection and removal of heavy metal ions from aqueous solutions.
A new kind of cellulose-lignin composite hydrogel (UCHy) was prepared under ultrasonic irradiation using cellulose and lignin as raw materials. The resulting material was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD) analysis. The swelling properties of UCHy were also investigated at a variety of different Pb(II) concentrations, whilst its adsorption capacity was studied as a function of pH, reaction time, temperature, and concentration of the Pb (II) solution under ambient conditions. The results showed that cellulose and lignin were beneficial to the formation of a denser structure, and that the ultrasonic treatment promoted the formation of the continuous pore microstructure of the hydrogel, resulting in a high swelling ratio and pollutant adsorption capacity. The swelling kinetics indicated that the initial solution intake of the composite hydrogel followed a non-Fickian type diffusion, and that the whole swelling process was fit for the Schott's model well. The adsorption capacity of Pb(II) increased as the pH of the solution increased, and decreases with increasing temperature. The adsorption isotherm data followed the Langmuir and Freundlich models, with an optimum adsorption value of 786.16 mg·g-1. The adsorption rate closely followed a pseudo-second order model. As a result, UCHy showed good responsive and adsorption properties towards heavy metal ions, and therefore represents a promising material for the detection and removal of heavy metal ions from aqueous solutions.
2016, 32(10): 2574-2580
doi: 10.3866/PKU.WHXB201606294
Abstract:
In this paper, boron-modified titanium silicalite-1 (B-TS-1) was synthesized, and its catalytic performance was studied. B-TS-1 improved the stability of cyclohexanone ammoximation. Combined with the root of deactivation of the catalyst and H2O2 reaction behavior in the liquid-phase ammoximation process, analysis showed that H2O2 is the key to control the side reactions of the cyclohexanone ammoximation system to form organic byproducts, and these byproducts result in the deactivation of catalyst because they block pores. It is concluded that B-TS-1 could effectively decrease the residual H2O2 to suppress the side reactions and prolong the catalyst lifetime in cyclohexanone ammoximation. Simultaneous introduction of appropriate amounts of B and Al to form B/Al-TS-1 resulted in a material that further improved the stability of cyclohexanone ammoximation.
In this paper, boron-modified titanium silicalite-1 (B-TS-1) was synthesized, and its catalytic performance was studied. B-TS-1 improved the stability of cyclohexanone ammoximation. Combined with the root of deactivation of the catalyst and H2O2 reaction behavior in the liquid-phase ammoximation process, analysis showed that H2O2 is the key to control the side reactions of the cyclohexanone ammoximation system to form organic byproducts, and these byproducts result in the deactivation of catalyst because they block pores. It is concluded that B-TS-1 could effectively decrease the residual H2O2 to suppress the side reactions and prolong the catalyst lifetime in cyclohexanone ammoximation. Simultaneous introduction of appropriate amounts of B and Al to form B/Al-TS-1 resulted in a material that further improved the stability of cyclohexanone ammoximation.
2016, 32(10): 2581-2592
doi: 10.3866/PKU.WHXB201606226
Abstract:
Nanosheet materials obtained from laminar compounds are new two-dimensional anisotropic nanomaterials that can even reach the sub-nanometer scale. These materials possess unique physical and chemical properties. An example of such a nanosheet materials is graphitic carbon nitride (g-C3N4) nanosheets transformed from bulk g-C3N4. Here, g-C3N4 nanosheets were prepared from bulk g-C3N4 by high-temperature thermal oxidation. The photocatalytic activity of eosin (EY)-sensitized g-C3N4 nanosheets for hydrogen evolution was about 2.6 times higher than that of bulk g-C3N4. The structure of the g-C3N4 nanosheets and process of electron transfer between EY and the g-C3N4 nanosheets were investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis, fluorescence spectroscopy, and photoelectrochemical measurements. The g-C3N4 nanosheets possessed high specific surface area. The g-C3N4 nanosheets not only effectively absorbed dye molecules, but also enhanced the separation and electron transport efficiencies of photogenerated charges because of their quantum confinement effect. The quantum confinement effect of g-C3N4 nanosheets widened their bandgap, improved electron transfer ability along the in-plane direction, and lengthened the lifetime of photoexcited charge carriers. As a result, the photocatalytic activity of the g-C3N4 nanosheets was improved compared with that of bulk g-C3N4.
Nanosheet materials obtained from laminar compounds are new two-dimensional anisotropic nanomaterials that can even reach the sub-nanometer scale. These materials possess unique physical and chemical properties. An example of such a nanosheet materials is graphitic carbon nitride (g-C3N4) nanosheets transformed from bulk g-C3N4. Here, g-C3N4 nanosheets were prepared from bulk g-C3N4 by high-temperature thermal oxidation. The photocatalytic activity of eosin (EY)-sensitized g-C3N4 nanosheets for hydrogen evolution was about 2.6 times higher than that of bulk g-C3N4. The structure of the g-C3N4 nanosheets and process of electron transfer between EY and the g-C3N4 nanosheets were investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis, fluorescence spectroscopy, and photoelectrochemical measurements. The g-C3N4 nanosheets possessed high specific surface area. The g-C3N4 nanosheets not only effectively absorbed dye molecules, but also enhanced the separation and electron transport efficiencies of photogenerated charges because of their quantum confinement effect. The quantum confinement effect of g-C3N4 nanosheets widened their bandgap, improved electron transfer ability along the in-plane direction, and lengthened the lifetime of photoexcited charge carriers. As a result, the photocatalytic activity of the g-C3N4 nanosheets was improved compared with that of bulk g-C3N4.
2016, 32(10): 2593-2598
doi: 10.3866/PKU.WHXB201607071
Abstract:
The adsorption and chiral features of a self-assembled CuPc monolayer on a semi-metallic Bi(111) surface have been evaluated using the low temperature scanning tunneling microscopy (LT-STM). Under low coverage conditions, the individual CuPc molecules rotated around the molecular center at 78 K until they interacted with other molecule to form clusters, because of the relatively weak interfacial interactions between the CuPc molecules and the Bi(111) surface. As the level of molecular coverage increased, the CuPc molecules self-assembled into two-dimensional domains with each molecule exhibiting chiral features. Beyond one monolayer, the CuPc molecules underwent an orientational transition from a flat-lying to a standing-up configuration. The chiral features of the CuPc molecules were attributed to the combined effect of asymmetric charge transfer between the CuPc molecules and the Bi(111) substrate and the formation of asymmetric intermolecular van der Waals interactions.
The adsorption and chiral features of a self-assembled CuPc monolayer on a semi-metallic Bi(111) surface have been evaluated using the low temperature scanning tunneling microscopy (LT-STM). Under low coverage conditions, the individual CuPc molecules rotated around the molecular center at 78 K until they interacted with other molecule to form clusters, because of the relatively weak interfacial interactions between the CuPc molecules and the Bi(111) surface. As the level of molecular coverage increased, the CuPc molecules self-assembled into two-dimensional domains with each molecule exhibiting chiral features. Beyond one monolayer, the CuPc molecules underwent an orientational transition from a flat-lying to a standing-up configuration. The chiral features of the CuPc molecules were attributed to the combined effect of asymmetric charge transfer between the CuPc molecules and the Bi(111) substrate and the formation of asymmetric intermolecular van der Waals interactions.
2016, 32(10): 2599-2605
doi: 10.3866/PKU.WHXB201607181
Abstract:
Low concentration ammonia is a widespread indoor air contaminant, which represents a considerable hazard to human health. The removal of ammonia can be difficult, especially when it is present at very low concentrations. In this study, we developed a new kind of mesoporous carbon with a high capacity for removing ammonia by adsorption. The ammonia-removing performance of this mesoporous carbon material was much better than that of activated carbon treated with nitric acid. The mesoporous carbon was prepared using aluminum phosphate as a hard template and contained a large number of oxygen-containing functional groups on its surface. The characterization results showed that the surface carboxyl and lactone groups play an important role in the adsorption of ammonia. For example, these groups could act as acidic sites capable of reacting with ammonia, and could therefore be responsible for the high capacity of mesoporous carbon to remove low ammonia contaminants under low concentration conditions.
Low concentration ammonia is a widespread indoor air contaminant, which represents a considerable hazard to human health. The removal of ammonia can be difficult, especially when it is present at very low concentrations. In this study, we developed a new kind of mesoporous carbon with a high capacity for removing ammonia by adsorption. The ammonia-removing performance of this mesoporous carbon material was much better than that of activated carbon treated with nitric acid. The mesoporous carbon was prepared using aluminum phosphate as a hard template and contained a large number of oxygen-containing functional groups on its surface. The characterization results showed that the surface carboxyl and lactone groups play an important role in the adsorption of ammonia. For example, these groups could act as acidic sites capable of reacting with ammonia, and could therefore be responsible for the high capacity of mesoporous carbon to remove low ammonia contaminants under low concentration conditions.
2016, 32(10): 2606-2619
doi: 10.3866/PKU.WHXB201606202
Abstract:
Endothelial lipase (EL) has been implicated in high-density lipoprotein (HDL) metabolism and the pathogenetic progress of atherosclerosis, so its specific inhibitors are expected to be useful for the treatment of cardiovascular disease. In addition to the high homology of EL with other lipases such as lipoprotein lipase (LPL), the scoring bias of current docking programs toward large molecules and large protein-binding pockets also makes it difficult to find specific EL inhibitors by docking-based virtual screening. Herein, we conducted docking-based virtual screening of the Specs database for EL and LPL firstly, and we found the scoring bias phenomenon. From the docking results of the Specs database, we established standard curves for the binding energies of EL and LPL based on heavy atom number and contact area to correct the dock energy score statistically. We then validated the correctional effects of these curves in the screening of a validation set. Furthermore, the traditional Chinese medicine database (TCMD) was screened by docking using the score correction strategy. The dock ranks before and after correction were compared to confirm the screening effectiveness. Moreover, some compounds exhibiting better affinity for EL than LPL after correction as well as some compounds with antihyperlipidemic activity that may be specific EL inhibitors were analyzed to study their interaction mechanisms. The developed score correction strategy should be helpful to improve the hit rate in docking-based virtual screening. The molecules we identified should be useful for experimental scientists to prioritize drug candidates and provide groundwork for potential therapies of hyperlipidemia and atherosclerosis.
Endothelial lipase (EL) has been implicated in high-density lipoprotein (HDL) metabolism and the pathogenetic progress of atherosclerosis, so its specific inhibitors are expected to be useful for the treatment of cardiovascular disease. In addition to the high homology of EL with other lipases such as lipoprotein lipase (LPL), the scoring bias of current docking programs toward large molecules and large protein-binding pockets also makes it difficult to find specific EL inhibitors by docking-based virtual screening. Herein, we conducted docking-based virtual screening of the Specs database for EL and LPL firstly, and we found the scoring bias phenomenon. From the docking results of the Specs database, we established standard curves for the binding energies of EL and LPL based on heavy atom number and contact area to correct the dock energy score statistically. We then validated the correctional effects of these curves in the screening of a validation set. Furthermore, the traditional Chinese medicine database (TCMD) was screened by docking using the score correction strategy. The dock ranks before and after correction were compared to confirm the screening effectiveness. Moreover, some compounds exhibiting better affinity for EL than LPL after correction as well as some compounds with antihyperlipidemic activity that may be specific EL inhibitors were analyzed to study their interaction mechanisms. The developed score correction strategy should be helpful to improve the hit rate in docking-based virtual screening. The molecules we identified should be useful for experimental scientists to prioritize drug candidates and provide groundwork for potential therapies of hyperlipidemia and atherosclerosis.
2016, 32(10): 2620-2627
doi: 10.3866/PKU.WHXB201606224
Abstract:
At present, p53 is the tumor suppressor protein with the highest known frequency of mutation. Mutations in p53 will lead to the loss of its anti-cancer function and initiate cancers. The majority of the mutations in p53 are located in its core DNA binding domain (p53C). One of the most frequent mutation in p53C is Y220C. However, the molecular mechanism of the conformational transition of the Y220C mutant of p53C remains unclear, although it is known that the Y220C mutant greatly decreases the stability of p53C. In this study, molecular dynamics (MD) simulations are used to probe the conformational transition of the Y220C mutant of p53C. The Y220C cluster including residues 138-164 and 215-238, which are strongly affected by the mutant, is identified. The Y220C mutant decreases the content of β-sheets in the Y220C cluster. The Y220C mutation not only disrupts the hydrogen bonds between the mutated residue and surrounding residues such as Leu145 and Thr155, but also weakens the hydrogen bonds between S3 and S8 of the Y220C cluster. This causes the volume of the hydrophilic cavity to increase, accelerating water molecule entry into the cavity, which eventually unfolds the protein. The above MD results explain the molecular mechanism of the Y220C mutant in the conformational transition of p53C. These findings will benefit virtual screening and design of novel stabilizers of the mutant Y220C of p53C.
At present, p53 is the tumor suppressor protein with the highest known frequency of mutation. Mutations in p53 will lead to the loss of its anti-cancer function and initiate cancers. The majority of the mutations in p53 are located in its core DNA binding domain (p53C). One of the most frequent mutation in p53C is Y220C. However, the molecular mechanism of the conformational transition of the Y220C mutant of p53C remains unclear, although it is known that the Y220C mutant greatly decreases the stability of p53C. In this study, molecular dynamics (MD) simulations are used to probe the conformational transition of the Y220C mutant of p53C. The Y220C cluster including residues 138-164 and 215-238, which are strongly affected by the mutant, is identified. The Y220C mutant decreases the content of β-sheets in the Y220C cluster. The Y220C mutation not only disrupts the hydrogen bonds between the mutated residue and surrounding residues such as Leu145 and Thr155, but also weakens the hydrogen bonds between S3 and S8 of the Y220C cluster. This causes the volume of the hydrophilic cavity to increase, accelerating water molecule entry into the cavity, which eventually unfolds the protein. The above MD results explain the molecular mechanism of the Y220C mutant in the conformational transition of p53C. These findings will benefit virtual screening and design of novel stabilizers of the mutant Y220C of p53C.
2016, 32(10): 2628-2635
doi: 10.3866/PKU.WHXB201606296
Abstract:
In this paper, novel pH-sensitive amphiphilic diblock copolymers[mPEG-b-PDPAn (n=100-200, polymerization degree; PEG is polyethylene glycol and PDPA is polydiphenylamine)] with and without a fluorescent group (fluorescein isothiocyanate, FITC) were synthesized by atom transfer radical polymerization (ATRP). The copolymers were used to prepare micelles by solvent evaporation to act as drug carriers. The micelles were spherical with a uniform diameter of 180-240 nm (0.3 mg·mL-1). The model drug doxorubicin (DOX) could be encapsulated into the micelles with a high loading efficiencyof about 11% (w, mass fraction). The micelles were stable at pH 7.4 and became looser upon the protonation of the PDPA block in a weakly acidic environment. The release of DOX accelerated when the micelles were exposed to weakly acidic conditions, and the amount released reached 80%after 2-3 h. Cell toxicity assays of the micelles were carried out using human cancer cells (Huh7), and the micelles showed good cytocompatibility. The micelles labeled with FITC displayed high cell transfection efficiency. As a result, micelles labeled with fluorescent groups may open up new perspectives for real-time tracking of drug delivery and/or distribution during chemotherapy.
In this paper, novel pH-sensitive amphiphilic diblock copolymers[mPEG-b-PDPAn (n=100-200, polymerization degree; PEG is polyethylene glycol and PDPA is polydiphenylamine)] with and without a fluorescent group (fluorescein isothiocyanate, FITC) were synthesized by atom transfer radical polymerization (ATRP). The copolymers were used to prepare micelles by solvent evaporation to act as drug carriers. The micelles were spherical with a uniform diameter of 180-240 nm (0.3 mg·mL-1). The model drug doxorubicin (DOX) could be encapsulated into the micelles with a high loading efficiencyof about 11% (w, mass fraction). The micelles were stable at pH 7.4 and became looser upon the protonation of the PDPA block in a weakly acidic environment. The release of DOX accelerated when the micelles were exposed to weakly acidic conditions, and the amount released reached 80%after 2-3 h. Cell toxicity assays of the micelles were carried out using human cancer cells (Huh7), and the micelles showed good cytocompatibility. The micelles labeled with FITC displayed high cell transfection efficiency. As a result, micelles labeled with fluorescent groups may open up new perspectives for real-time tracking of drug delivery and/or distribution during chemotherapy.
2016, 32(10): 2636-2644
doi: 10.3866/PKU.WHXB201606282
Abstract:
In this work, graphene oxide sheets are cut into graphene quantum dots (GQDs) by acidic oxidation, then GQDs are hydrothermally treated with ammonia (NH3) at 100℃ to form amino-functionalized graphene quantum dots (N-GQDs). Atomic force microscopy (AFM) shows smaller dots in ammonia treated GQDs, and holey graphene structure is directly observed. Fourier transform infrared (FTIR) spectra confirm that NH3 can effectively react with epoxy and carboxyl groups to form hydroxylamine and amide groups, respectively. The absorption and photoluminescence (PL) properties of the samples are determined by ultraviolet-visible-near infrared (UV-Vis-NIR) spectra and steady-state fluorescence spectra. Three PL excitation peaks occurring at around 250, 290, and 350 nm are attributed to C=C related π-π* transition, C-O-C and C=O related n-π* transitions, respectively. After amino functionalization, the C-O-C related n-π* transition is suppressed, and the PL emission spectrum of N-GQDs is less excitation wavelength. The fluorescence quantum yield of the N-GQDs is 9.6%, which is enhanced by 32 times compared with that of the unmodified GQDs (~0.3%). Timeresolved PL spectra are also used to investigate the N-GQDs. The PL lifetimes depend on the emission wavelength and coincide with the PL spectrum, and are different from most fluorescent species. This result reveals the synergy and competition between defect derived photoluminescence and amino passivation of the N-GQDs. Compared with oxygen-related defects, nitrogen-related localized electronic states are expected to have a longer lifetime and enhanced radiative decay rates.
In this work, graphene oxide sheets are cut into graphene quantum dots (GQDs) by acidic oxidation, then GQDs are hydrothermally treated with ammonia (NH3) at 100℃ to form amino-functionalized graphene quantum dots (N-GQDs). Atomic force microscopy (AFM) shows smaller dots in ammonia treated GQDs, and holey graphene structure is directly observed. Fourier transform infrared (FTIR) spectra confirm that NH3 can effectively react with epoxy and carboxyl groups to form hydroxylamine and amide groups, respectively. The absorption and photoluminescence (PL) properties of the samples are determined by ultraviolet-visible-near infrared (UV-Vis-NIR) spectra and steady-state fluorescence spectra. Three PL excitation peaks occurring at around 250, 290, and 350 nm are attributed to C=C related π-π* transition, C-O-C and C=O related n-π* transitions, respectively. After amino functionalization, the C-O-C related n-π* transition is suppressed, and the PL emission spectrum of N-GQDs is less excitation wavelength. The fluorescence quantum yield of the N-GQDs is 9.6%, which is enhanced by 32 times compared with that of the unmodified GQDs (~0.3%). Timeresolved PL spectra are also used to investigate the N-GQDs. The PL lifetimes depend on the emission wavelength and coincide with the PL spectrum, and are different from most fluorescent species. This result reveals the synergy and competition between defect derived photoluminescence and amino passivation of the N-GQDs. Compared with oxygen-related defects, nitrogen-related localized electronic states are expected to have a longer lifetime and enhanced radiative decay rates.
