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2017 Volume 33 Issue 7
2017, 33(7):
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2017, 33(7): 1267-1268
doi: 10.3866/PKU.WHXB201704241
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2017, 33(7): 1269-1270
doi: 10.3866/PKU.WHXB201704261
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2017, 33(7): 1271-1272
doi: 10.3866/PKU.WHXB201705031
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2017, 33(7): 1273-1274
doi: 10.3866/PKU.WHXB201704262
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2017, 33(7): 1275-1276
doi: 10.3866/PKU.WHXB201705021
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2017, 33(7): 1277-1287
doi: 10.3866/PKU.WHXB2017040702
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Well-developed conventional single-reference electron-correlation methods usually fail to describe the dissociation of covalent bonds, di(or poly)radical systems or electronic structures of the excited states. Based on a multi-determinantal wave function, recently emerged multireference perturbation theories and coupled cluster theories can give drastically improved results; however, there is still no satisfactory scheme so far. In this monograph, alternative multireference perturbation theories and coupled cluster theories based on the "block-correlation" framework has been introduced and illustrated in detail, together with proper comparisons with other common electron-correlation methods. Future perspectives upon multireference theories have also been briefly discussed.
Well-developed conventional single-reference electron-correlation methods usually fail to describe the dissociation of covalent bonds, di(or poly)radical systems or electronic structures of the excited states. Based on a multi-determinantal wave function, recently emerged multireference perturbation theories and coupled cluster theories can give drastically improved results; however, there is still no satisfactory scheme so far. In this monograph, alternative multireference perturbation theories and coupled cluster theories based on the "block-correlation" framework has been introduced and illustrated in detail, together with proper comparisons with other common electron-correlation methods. Future perspectives upon multireference theories have also been briefly discussed.
2017, 33(7): 1288-1296
doi: 10.3866/PKU.WHXB201704074
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The future of nanotechnology lies in the "bottom up" approach, which aims at building nanostructures at an atomic or molecular level so as to minimize the sizes of chips and other nano-devices. However, one of the long-term unresolved issues for "bottom up" nanotechnology is the precise control of the topologies of fabricated nanostructures. In this contibution, we review recent studies with regard to the control of the topologies of nanostructures formed via the on-surface Ullmann reaction of haloarenes. This includes three aspects:control of the shape of the organometallic chain via lattice matching between the adsorbate nanostructure and the substrate; tailoring the chains by employing super-gratings or supramolecular templates; and steering the covalent ring-chain competition in the reaction of precursors towards ring formation through adsorbate-substrate symmetry matching. Further, we present future directions for the development of more general templates for the regulation of the topologies of a broader range of nanostructures.
The future of nanotechnology lies in the "bottom up" approach, which aims at building nanostructures at an atomic or molecular level so as to minimize the sizes of chips and other nano-devices. However, one of the long-term unresolved issues for "bottom up" nanotechnology is the precise control of the topologies of fabricated nanostructures. In this contibution, we review recent studies with regard to the control of the topologies of nanostructures formed via the on-surface Ullmann reaction of haloarenes. This includes three aspects:control of the shape of the organometallic chain via lattice matching between the adsorbate nanostructure and the substrate; tailoring the chains by employing super-gratings or supramolecular templates; and steering the covalent ring-chain competition in the reaction of precursors towards ring formation through adsorbate-substrate symmetry matching. Further, we present future directions for the development of more general templates for the regulation of the topologies of a broader range of nanostructures.
2017, 33(7): 1310-1323
doi: 10.3866/PKU.WHXB201704172
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Nanoparticles of precious metals play an important role in many heterogeneous catalytic reactions due to their excellent catalytic performance. As an idealized model, gas phase metal clusters have been extensively utilized to understand catalytic mechanisms at a molecular level. Here we provide an overview of our recent studies on H2 dissociative chemisorption on nickel family clusters. The structure evolution and the stability of the metal clusters were first compared. H2 dissociation on the clusters was then carefully addressed to understand the capability of metal clusters to break the H-H bond. Two key parameters, the dissociative chemisorption energy (ΔECE) and the H sequential desorption energy (ΔEDE),were employed to characterize the catalytic activity of metal clusters. Our results show that both ΔECE and ΔEDE decline significantly as the H coverage increases. Since the catalyst is in general covered entirely by H atoms and H2 molecules in a typical hydrogenation process, and maintained at a pre-determined pressure of H2 gas, we can rationally use the calculated ΔECE and ΔEDE values at full H saturation to address the activity of metal clusters. Our results suggest that at full H coverage, each Pt atom is essentially capable of adsorbing 4 H atoms, while each Ni or Pd atom can only accommodate 2 H atoms. Considering the similar values of H desorption energies on Pt and Pd clusters, the higher average H capacity per Pt atom could probably lead to a faster reaction rate because more active H atoms are produced on the Pt catalyst particles in the hydrogenation process. Finally, the charge sensitivity of the key catalytic properties of Pt clusters for hydrogenation was systematically evaluated. The results show that the dissociation of H2 and H desorption are strongly correlated to the charge state of the Pt clusters at low H coverage. However, at high H-capacities, both ΔECE and ΔEDE fall into a narrow range, suggesting that the charge can be readily dispersed and that the Pt-H bonds average the interaction between clusters and H atoms. As a result, the H-capacities on charged clusters were found to be similar as the cluster size increased; in case of sufficiently large clusters, the reactivity of a fully saturated cluster was no longer sensitive to its charge state.
Nanoparticles of precious metals play an important role in many heterogeneous catalytic reactions due to their excellent catalytic performance. As an idealized model, gas phase metal clusters have been extensively utilized to understand catalytic mechanisms at a molecular level. Here we provide an overview of our recent studies on H2 dissociative chemisorption on nickel family clusters. The structure evolution and the stability of the metal clusters were first compared. H2 dissociation on the clusters was then carefully addressed to understand the capability of metal clusters to break the H-H bond. Two key parameters, the dissociative chemisorption energy (ΔECE) and the H sequential desorption energy (ΔEDE),were employed to characterize the catalytic activity of metal clusters. Our results show that both ΔECE and ΔEDE decline significantly as the H coverage increases. Since the catalyst is in general covered entirely by H atoms and H2 molecules in a typical hydrogenation process, and maintained at a pre-determined pressure of H2 gas, we can rationally use the calculated ΔECE and ΔEDE values at full H saturation to address the activity of metal clusters. Our results suggest that at full H coverage, each Pt atom is essentially capable of adsorbing 4 H atoms, while each Ni or Pd atom can only accommodate 2 H atoms. Considering the similar values of H desorption energies on Pt and Pd clusters, the higher average H capacity per Pt atom could probably lead to a faster reaction rate because more active H atoms are produced on the Pt catalyst particles in the hydrogenation process. Finally, the charge sensitivity of the key catalytic properties of Pt clusters for hydrogenation was systematically evaluated. The results show that the dissociation of H2 and H desorption are strongly correlated to the charge state of the Pt clusters at low H coverage. However, at high H-capacities, both ΔECE and ΔEDE fall into a narrow range, suggesting that the charge can be readily dispersed and that the Pt-H bonds average the interaction between clusters and H atoms. As a result, the H-capacities on charged clusters were found to be similar as the cluster size increased; in case of sufficiently large clusters, the reactivity of a fully saturated cluster was no longer sensitive to its charge state.
2017, 33(7): 1297-1309
doi: 10.3866/PKU.WHXB201704101
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Well-defined gold nanoclusters have been documented as new and promising materials in the field of nanoscience. They have been well explored for the nanocatalysis of reactions like selective oxidation and hydrogenation, carbon-carbon coupling, etc. These Au nanoclusters possess unique electronic properties and crystal structure, which provide an excellent opportunity to correlate atomic structure with intrinsic catalytic property and to investigate the mechanisms of reactions over Au nanoclusters. In this review, we generalize the catalytic application of gold nanoclusters in carbon-carbon coupling reactions, including Ullmann, Sonogashira, Suzuki, and A3-coupling reactions. Herein, we have discussed ligand engineering (e.g., aromatic and aliphatic thiolate) as well as the effect of metal dopants (e.g., Cu, Ag, Pt, and Pd). Finally, the tentative catalytic mechanisms and the structure-performance relationships were discussed at the atomic level, which will give some clue for the design of efficient gold cluster catalysts.
Well-defined gold nanoclusters have been documented as new and promising materials in the field of nanoscience. They have been well explored for the nanocatalysis of reactions like selective oxidation and hydrogenation, carbon-carbon coupling, etc. These Au nanoclusters possess unique electronic properties and crystal structure, which provide an excellent opportunity to correlate atomic structure with intrinsic catalytic property and to investigate the mechanisms of reactions over Au nanoclusters. In this review, we generalize the catalytic application of gold nanoclusters in carbon-carbon coupling reactions, including Ullmann, Sonogashira, Suzuki, and A3-coupling reactions. Herein, we have discussed ligand engineering (e.g., aromatic and aliphatic thiolate) as well as the effect of metal dopants (e.g., Cu, Ag, Pt, and Pd). Finally, the tentative catalytic mechanisms and the structure-performance relationships were discussed at the atomic level, which will give some clue for the design of efficient gold cluster catalysts.
2017, 33(7): 1324-1337
doi: 10.3866/PKU.WHXB201704112
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Gold nanorods (AuNRs) have been the focus of considerable attention in the nano-biotechnology and biomedicine fields because of their unique optical activities, adjustable aspect ratios, ease of surface modification, and good biocompatibility. AuNRs offer specific tunable surface plasmon resonance (SPR) effects (including TSPR and LSPR), which can tune their fluorescence-emission between the visible and near-infrared (NIR) zones. Controlled synthesis and surface modification determine the physical and chemical properties of AuNRs, which ultimately determine their biocompatibility and biomedical applicability. In this review, the four main types of controlled synthesis (template, electrochemical synthesis, photochemical synthesis, and seeded growth methods), controlled surface modification methods, as well as the nano-biological and biomedical applications of AuNRs, are summarized. The controlled surface modification methods of AuNRs and their application to molecular probes, bio-sensing, bio-imaging, gene carriers, pharmaceutical carriers, and cancer photothermal therapy are discussed in detail. Finally, we outline our personal perspectives on the main issue affecting AuNRs in biological applications. That is, chiral molecular and smart polymers can be introduced onto the surfaces of AuNRs to improve the specific recognition of tumor cells and to increase fluorescence quantum yields, thus providing a new direction for the development of AuNRs.
Gold nanorods (AuNRs) have been the focus of considerable attention in the nano-biotechnology and biomedicine fields because of their unique optical activities, adjustable aspect ratios, ease of surface modification, and good biocompatibility. AuNRs offer specific tunable surface plasmon resonance (SPR) effects (including TSPR and LSPR), which can tune their fluorescence-emission between the visible and near-infrared (NIR) zones. Controlled synthesis and surface modification determine the physical and chemical properties of AuNRs, which ultimately determine their biocompatibility and biomedical applicability. In this review, the four main types of controlled synthesis (template, electrochemical synthesis, photochemical synthesis, and seeded growth methods), controlled surface modification methods, as well as the nano-biological and biomedical applications of AuNRs, are summarized. The controlled surface modification methods of AuNRs and their application to molecular probes, bio-sensing, bio-imaging, gene carriers, pharmaceutical carriers, and cancer photothermal therapy are discussed in detail. Finally, we outline our personal perspectives on the main issue affecting AuNRs in biological applications. That is, chiral molecular and smart polymers can be introduced onto the surfaces of AuNRs to improve the specific recognition of tumor cells and to increase fluorescence quantum yields, thus providing a new direction for the development of AuNRs.
2017, 33(7): 1338-1353
doi: 10.3866/PKU.WHXB201704113
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Capacitive deionization (CDI) is a novel technology to remove ions from water using electrostatic force. Owing to its excellent electrical conductivity and large specific surface area, graphene has become a material of interest for CDI electrodes, crucial components of the system involved. So far, research on graphene-based electrodes has focused on the synthesis of the material, while there has not been a review of the relationship between the performance of CDI and the characteristics of the graphene-based material or the electrode preparation methods to acquire these characteristics. Hence, this paper systematically reviews the principles and performance index of CDI, research undertaken on graphene-based electrode materials, and the approach for electrode preparation for CDI. The influence of characteristics (pore structure, electrical conductivity and hydrophilicity/hydrophobicity) of the graphene-based material on the performance of CDI is summarized and analyzed. Finally, the development of graphene-based electrode material is overlooked.
Capacitive deionization (CDI) is a novel technology to remove ions from water using electrostatic force. Owing to its excellent electrical conductivity and large specific surface area, graphene has become a material of interest for CDI electrodes, crucial components of the system involved. So far, research on graphene-based electrodes has focused on the synthesis of the material, while there has not been a review of the relationship between the performance of CDI and the characteristics of the graphene-based material or the electrode preparation methods to acquire these characteristics. Hence, this paper systematically reviews the principles and performance index of CDI, research undertaken on graphene-based electrode materials, and the approach for electrode preparation for CDI. The influence of characteristics (pore structure, electrical conductivity and hydrophilicity/hydrophobicity) of the graphene-based material on the performance of CDI is summarized and analyzed. Finally, the development of graphene-based electrode material is overlooked.
2017, 33(7): 1354-1365
doi: 10.3866/PKU.WHXB201704144
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Molecular dynamics simulation (MDS) has gained increasing importance in current-day scientific research, as the supplement, guidance, or even replacement of experiments. In this review, we briefly introduce the history of the development of molecular dynamics simulation, focusing on recent progress including new-generation force fields, modern enhanced sampling schemes, and application for the investigation of complex biomolecules.
Molecular dynamics simulation (MDS) has gained increasing importance in current-day scientific research, as the supplement, guidance, or even replacement of experiments. In this review, we briefly introduce the history of the development of molecular dynamics simulation, focusing on recent progress including new-generation force fields, modern enhanced sampling schemes, and application for the investigation of complex biomolecules.
2017, 33(7): 1366-1378
doi: 10.3866/PKU.WHXB201704173
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Fuel cells allow the direct conversion of the chemical energy in chemical fuels to electricity, with particular advantages of being highly effective, environment-friendly, and portable. For those fuel cells using oxygen or air as the oxidant, the oxygen reduction reaction (ORR) occurring on the cathode remains the major obstacle for the commercialization of fuel cell technologies because of its slow kinetics, which in turn results in relatively low catalytic efficiency and high price due to excessive use of precious metals like Pt. In recent years, dealloyed nanoporous metals have garnered widespread attention in the field of electrocatalysis due to their unique structural properties, such as three-dimensionally interconnected pore/ligament structure, excellent conductivity, and structural flexibility. This review summarizes the recent advances in nanoporous metal catalysts for ORR, with an emphasis on their unique structural properties for the development of new-generation high-performance fuel cell catalysts.
Fuel cells allow the direct conversion of the chemical energy in chemical fuels to electricity, with particular advantages of being highly effective, environment-friendly, and portable. For those fuel cells using oxygen or air as the oxidant, the oxygen reduction reaction (ORR) occurring on the cathode remains the major obstacle for the commercialization of fuel cell technologies because of its slow kinetics, which in turn results in relatively low catalytic efficiency and high price due to excessive use of precious metals like Pt. In recent years, dealloyed nanoporous metals have garnered widespread attention in the field of electrocatalysis due to their unique structural properties, such as three-dimensionally interconnected pore/ligament structure, excellent conductivity, and structural flexibility. This review summarizes the recent advances in nanoporous metal catalysts for ORR, with an emphasis on their unique structural properties for the development of new-generation high-performance fuel cell catalysts.
2017, 33(7): 1379-1389
doi: 10.3866/PKU.WHXB201704182
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Perovskite solar cells have undergone rapid development because of their high solar absorption efficiencies, long carrier lifetime and diffusion length, high tolerance to lattice defects, and tunable bandgaps. In the past few years, the solar energy conversion efficiency of the perovskite solar cells has increased to 22.1%. However, despite their promising prospects, as demonstrated by the laboratory-fabricated prototypes, lead toxicity and instability of perovskite solar cells severely impeded their industrialization and applications. Recently, inorganic lead-free perovskite solar cells (such as ABX3 and A2BB'X6), which use Sn, Ge, Bi, Ag, and other metals as replacements for Pb, and Cs and Rb as replacements for methylamine, have been pursued as potential solutions for the toxicity and stability issues. This review highlights the recent research efforts in the development of inorganic lead-free perovskite solar cells and provides a perspective on future developments.
Perovskite solar cells have undergone rapid development because of their high solar absorption efficiencies, long carrier lifetime and diffusion length, high tolerance to lattice defects, and tunable bandgaps. In the past few years, the solar energy conversion efficiency of the perovskite solar cells has increased to 22.1%. However, despite their promising prospects, as demonstrated by the laboratory-fabricated prototypes, lead toxicity and instability of perovskite solar cells severely impeded their industrialization and applications. Recently, inorganic lead-free perovskite solar cells (such as ABX3 and A2BB'X6), which use Sn, Ge, Bi, Ag, and other metals as replacements for Pb, and Cs and Rb as replacements for methylamine, have been pursued as potential solutions for the toxicity and stability issues. This review highlights the recent research efforts in the development of inorganic lead-free perovskite solar cells and provides a perspective on future developments.
2017, 33(7): 1390-1398
doi: 10.3866/PKU.WHXB201704111
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A novel Pt(II)-based metallointercalator terpyridine complex linked with a 2,2,6,6-tetramethyl-1-piperidinyl N-oxide (TEMPO) derivative was prepared by a reaction between 4'-TEMPO-terpyridine (L) and a Pt(II) salt. This complex presented unusual luminescence quenching owing to the effect of the stable nitroxide radical. The crystal structure of[Pt(terpy-TEMPO)Cl]Cl·H2O·CH3OH (terpy=2,2':6',2"-terpyridine) was elucidated by X-ray crystallography. Additionally, the effect of TEMPO on the photophysical properties of[Pt(terpy-TEMPO)Cl] Cl·H2O·CH3OH was investigated by UV-Vis, fluorescence emission, and electron paramagnetic resonance (EPR) spectroscopy. Data from the absorption and luminescence properties (298 K) of the[Pt(terpy-TEMPO)Cl]+ complex indicated the presence of two groups of typical bands:an intense band B with distinct vibronic structures (270-350 nm, ε>104 dm3·mol-1·cm-1) and a less intense band A (370-450 nm, ε~103 dm3·mol-1·cm-1). These two bands are generally assigned to ligand-to-ligand charge transfer (LLCT) and metal-to-ligand charge transfer (MLCT) excited states, respectively. Furthermore, efficient photoluminescent quenching behavior was observed in the emission spectra of this complex system. Quantum calculations of the molecular energy gaps and bands were performed by Gaussian 09 software. The calculated results verified that TEMPO greatly affects the energy gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital. Thus, the relationship between efficient photoquenching and molecular structure was theoretically interpreted. EPR results indicated that when TEMPO is attached to a macrocyclic terpyridine platinum complex, e.g.,[Pt(terpy)Cl]+, the terpyridine platinum complex does not affect the hyperfine coupling constant (A value) and g factor (g values) but the rotation and relaxation times of the TEMPO radical.
A novel Pt(II)-based metallointercalator terpyridine complex linked with a 2,2,6,6-tetramethyl-1-piperidinyl N-oxide (TEMPO) derivative was prepared by a reaction between 4'-TEMPO-terpyridine (L) and a Pt(II) salt. This complex presented unusual luminescence quenching owing to the effect of the stable nitroxide radical. The crystal structure of[Pt(terpy-TEMPO)Cl]Cl·H2O·CH3OH (terpy=2,2':6',2"-terpyridine) was elucidated by X-ray crystallography. Additionally, the effect of TEMPO on the photophysical properties of[Pt(terpy-TEMPO)Cl] Cl·H2O·CH3OH was investigated by UV-Vis, fluorescence emission, and electron paramagnetic resonance (EPR) spectroscopy. Data from the absorption and luminescence properties (298 K) of the[Pt(terpy-TEMPO)Cl]+ complex indicated the presence of two groups of typical bands:an intense band B with distinct vibronic structures (270-350 nm, ε>104 dm3·mol-1·cm-1) and a less intense band A (370-450 nm, ε~103 dm3·mol-1·cm-1). These two bands are generally assigned to ligand-to-ligand charge transfer (LLCT) and metal-to-ligand charge transfer (MLCT) excited states, respectively. Furthermore, efficient photoluminescent quenching behavior was observed in the emission spectra of this complex system. Quantum calculations of the molecular energy gaps and bands were performed by Gaussian 09 software. The calculated results verified that TEMPO greatly affects the energy gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital. Thus, the relationship between efficient photoquenching and molecular structure was theoretically interpreted. EPR results indicated that when TEMPO is attached to a macrocyclic terpyridine platinum complex, e.g.,[Pt(terpy)Cl]+, the terpyridine platinum complex does not affect the hyperfine coupling constant (A value) and g factor (g values) but the rotation and relaxation times of the TEMPO radical.
2017, 33(7): 1399-1410
doi: 10.3866/PKU.WHXB201704132
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Understanding the reaction mechanism of phenol ozonation in coking wastewater is very important for industrial applications of the ozonation process. Ozonation of p-nitrophenol in water at 300 K was simulated by ReaxFF force field molecular dynamics (ReaxFF MD) employing the GPU-enabled high-performance code of GMD-Reax and a unique code of VARxMD developed in authors' group. Evolution trends of aromatic ring opening, CO2 generation, dominant radicals (·OH, ·O2, ·O), and H2O clusters were obtained. The simulated CO2 generation and reduction of aromatic ring could be described with pseudo-first-order kinetics. Moreover, the reaction pathways for the ozonation of p-nitrophenol can be divided into three stages:hydrogen abstraction, opening of the six-membered-ring structure, and the breaking of C-C bonds. The simulations revealed the important role of radicals and water clusters in the ozonation of p-nitrophenol. This work is an attempt to investigate the ozonation mechanism of phenols in aqueous solutions at room temperature using ReaxFF MD, which should be helpful for further experimental or theoretical investigation of the mechanism.
Understanding the reaction mechanism of phenol ozonation in coking wastewater is very important for industrial applications of the ozonation process. Ozonation of p-nitrophenol in water at 300 K was simulated by ReaxFF force field molecular dynamics (ReaxFF MD) employing the GPU-enabled high-performance code of GMD-Reax and a unique code of VARxMD developed in authors' group. Evolution trends of aromatic ring opening, CO2 generation, dominant radicals (·OH, ·O2, ·O), and H2O clusters were obtained. The simulated CO2 generation and reduction of aromatic ring could be described with pseudo-first-order kinetics. Moreover, the reaction pathways for the ozonation of p-nitrophenol can be divided into three stages:hydrogen abstraction, opening of the six-membered-ring structure, and the breaking of C-C bonds. The simulations revealed the important role of radicals and water clusters in the ozonation of p-nitrophenol. This work is an attempt to investigate the ozonation mechanism of phenols in aqueous solutions at room temperature using ReaxFF MD, which should be helpful for further experimental or theoretical investigation of the mechanism.
2017, 33(7): 1411-1420
doi: 10.3866/PKU.WHXB201704078
Abstract:
A series of highly ordered TiO2 nanotube (TiO2NTs) electrodes are prepared via potentiostatic anodization of Ti foil followed by calcining in air. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), and potential steps determination are used to characterize the electrodes. The electrochemical reduction of CO2 on these three TiO2NTs electrodes is investigated by cyclic voltammetry and potentiostatic electrolysis in 0.1 mol·L-1 KHCO3 aqueous solution. Methanol is found to be the major product in electrochemical CO2 reduction, while formic acid, formaldehyde, methane, and CO are formed as minor products. Compared with the electrodes sintered at 550 and 650℃, the optimal TiO2NTs electrode is found to be the one calcined at 450℃ (TiO2NTs-450). After 120 min of reaction, the Faradaic efficiency and partial current density of methanol is 85.8% and 0.2 mA·cm-2 at -0.56 V vs. reversible hydrogen electrode (RHE), respectively. The trivalent titanium in TiO2 serves as an efficient site for adsorption of CO2 and stabilization of the adsorbed ·CO2- radical. Consequently, the reduction of CO2 on TiO2NTs electrodes involves a fast first electron and proton transfer followed by a slow second proton transfer as the rate-limiting step.
A series of highly ordered TiO2 nanotube (TiO2NTs) electrodes are prepared via potentiostatic anodization of Ti foil followed by calcining in air. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), and potential steps determination are used to characterize the electrodes. The electrochemical reduction of CO2 on these three TiO2NTs electrodes is investigated by cyclic voltammetry and potentiostatic electrolysis in 0.1 mol·L-1 KHCO3 aqueous solution. Methanol is found to be the major product in electrochemical CO2 reduction, while formic acid, formaldehyde, methane, and CO are formed as minor products. Compared with the electrodes sintered at 550 and 650℃, the optimal TiO2NTs electrode is found to be the one calcined at 450℃ (TiO2NTs-450). After 120 min of reaction, the Faradaic efficiency and partial current density of methanol is 85.8% and 0.2 mA·cm-2 at -0.56 V vs. reversible hydrogen electrode (RHE), respectively. The trivalent titanium in TiO2 serves as an efficient site for adsorption of CO2 and stabilization of the adsorbed ·CO2- radical. Consequently, the reduction of CO2 on TiO2NTs electrodes involves a fast first electron and proton transfer followed by a slow second proton transfer as the rate-limiting step.
2017, 33(7): 1421-1428
doi: 10.3866/PKU.WHXB201704077
Abstract:
Self-assembled microspheres of α-MnO2 nanotubes were successfully synthesized by hydrothermal method using KMnO4 and HCl as reactants, and H2SO4 and NH4Cl as auxiliaries. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) were used to characterize the structure and morphology of the products. The H+ and Cl- ion concentrations substantially influence the crystal form of the product. Increasing either H+ or Cl- ion concentration decreases the diameter of nanotubes but increases their length. In contrast, increasing both H+ and Cl- ion concentrations, changes the product from α phase to β phase. Moreover, NH4+ ion plays the key role of maintaining the product crystal and its tubular morphology. The electrochemical performance results showed that the microspheres of α-MnO2 nanotubes with a unique morphology have a high first cycle discharge capacity of 1783.5 mAh·g-1 at the current density of 20 mA·g-1, along with a good rate performance. This suggests that the self-assembled microspheres were a promising material for lithium-ion batteries.
Self-assembled microspheres of α-MnO2 nanotubes were successfully synthesized by hydrothermal method using KMnO4 and HCl as reactants, and H2SO4 and NH4Cl as auxiliaries. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) were used to characterize the structure and morphology of the products. The H+ and Cl- ion concentrations substantially influence the crystal form of the product. Increasing either H+ or Cl- ion concentration decreases the diameter of nanotubes but increases their length. In contrast, increasing both H+ and Cl- ion concentrations, changes the product from α phase to β phase. Moreover, NH4+ ion plays the key role of maintaining the product crystal and its tubular morphology. The electrochemical performance results showed that the microspheres of α-MnO2 nanotubes with a unique morphology have a high first cycle discharge capacity of 1783.5 mAh·g-1 at the current density of 20 mA·g-1, along with a good rate performance. This suggests that the self-assembled microspheres were a promising material for lithium-ion batteries.
2017, 33(7): 1429-1435
doi: 10.3866/PKU.WHXB201704131
Abstract:
Transition metal-nitrogen doped carbon-based catalysts have become promising alternatives to precious metal catalysts for the oxygen reduction reaction (ORR). Here, we report a nitrogen-doped carbon nanofiber electrocatalyst coordinated with highly dispersed cobalt atoms (Co-N/C) with a high specific surface area prepared by an electrospinning method. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) results confirmed that Co was highly dispersed within the prepared Co-N/C catalyst. X-ray photoelectron spectroscopy for N 1s spectra showed that the N species mainly existed in the forms of pyridinic N and graphitic N. This Co-N/C catalyst exhibited considerable ORR performance with onset and half-wave potentials at 0.92 and 0.80 V (relative to the reversible hydrogen electrode (RHE)), which are comparable to those of commercial Pt/C. With the prepared Co-N/C catalyst as the cathode, a Zn-air battery displayed an open-circuit potential of 1.54 V and a peak power density of 190 mW·cm-2 at 25℃, which suggest a promising application.
Transition metal-nitrogen doped carbon-based catalysts have become promising alternatives to precious metal catalysts for the oxygen reduction reaction (ORR). Here, we report a nitrogen-doped carbon nanofiber electrocatalyst coordinated with highly dispersed cobalt atoms (Co-N/C) with a high specific surface area prepared by an electrospinning method. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) results confirmed that Co was highly dispersed within the prepared Co-N/C catalyst. X-ray photoelectron spectroscopy for N 1s spectra showed that the N species mainly existed in the forms of pyridinic N and graphitic N. This Co-N/C catalyst exhibited considerable ORR performance with onset and half-wave potentials at 0.92 and 0.80 V (relative to the reversible hydrogen electrode (RHE)), which are comparable to those of commercial Pt/C. With the prepared Co-N/C catalyst as the cathode, a Zn-air battery displayed an open-circuit potential of 1.54 V and a peak power density of 190 mW·cm-2 at 25℃, which suggest a promising application.
2017, 33(7): 1436-1445
doi: 10.3866/PKU.WHXB201704076
Abstract:
Here, we fabricated a pyridine-copolymerized g-C3N4 by a novel and cost-effective approach based on Schiff-base chemistry. Thus produced g-C3N4 showed significantly enhanced and stable visible-light photocatalytic H2 evolution performance compared to pristine g-C3N4 obtained from urea. Subsequently, we constructed a composite of pyridine-modified g-C3N4 and N-doped reduced graphene oxide (N-rGO) by facile one-pot calcination to elevate the photocatalytic efficiency further. The peak H2 production rate achieved using this composite was 304 μmol·h-1, about 11.7 and 3.1 times as those obtained using pure g-C3N4 and pyridine-modified g-C3N4, respectively. In addition to enhanced visible light absorbance and enlarged surface area, the promoted separation, transfer, and surface reactivity of photogenerated charge carriers by the pyridine ring as intramolecular electron acceptor and N-rGO as "electron-transfer activation region" are considered responsible for the remarkably enhanced photocatalytic activity.
Here, we fabricated a pyridine-copolymerized g-C3N4 by a novel and cost-effective approach based on Schiff-base chemistry. Thus produced g-C3N4 showed significantly enhanced and stable visible-light photocatalytic H2 evolution performance compared to pristine g-C3N4 obtained from urea. Subsequently, we constructed a composite of pyridine-modified g-C3N4 and N-doped reduced graphene oxide (N-rGO) by facile one-pot calcination to elevate the photocatalytic efficiency further. The peak H2 production rate achieved using this composite was 304 μmol·h-1, about 11.7 and 3.1 times as those obtained using pure g-C3N4 and pyridine-modified g-C3N4, respectively. In addition to enhanced visible light absorbance and enlarged surface area, the promoted separation, transfer, and surface reactivity of photogenerated charge carriers by the pyridine ring as intramolecular electron acceptor and N-rGO as "electron-transfer activation region" are considered responsible for the remarkably enhanced photocatalytic activity.
2017, 33(7): 1446-1452
doi: 10.3866/PKU.WHXB201704102
Abstract:
Monodisperse La1-xEuxF3 nanoparticles (NPs) were functionalized by poly(acrylic acid) (PAA) via a one-pot modified hydrothermal method. The morphology, crystal structure, surface groups, and luminescence properties of the as-produced La1-xEuxF3@PAA NPs were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and photoluminescence (PL) spectroscopy. The produced nanoparticles were (7±3) nm in size, water soluble, and buffer stable, with good photostability and biocompatibility. In vitro imaging revealed the low cytotoxicity of the as-synthesized NPs incubated with HeLa cancer cells. Thus, the colloidal La1-xEuxF3@PAA NPs exhibit great potential for use as optical imaging probes in biological applications.
Monodisperse La1-xEuxF3 nanoparticles (NPs) were functionalized by poly(acrylic acid) (PAA) via a one-pot modified hydrothermal method. The morphology, crystal structure, surface groups, and luminescence properties of the as-produced La1-xEuxF3@PAA NPs were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and photoluminescence (PL) spectroscopy. The produced nanoparticles were (7±3) nm in size, water soluble, and buffer stable, with good photostability and biocompatibility. In vitro imaging revealed the low cytotoxicity of the as-synthesized NPs incubated with HeLa cancer cells. Thus, the colloidal La1-xEuxF3@PAA NPs exhibit great potential for use as optical imaging probes in biological applications.
2017, 33(7): 1453-1461
doi: 10.3866/PKU.WHXB201704104
Abstract:
We report an efficient catalyst composed of ternary components prepared by inlaying Pd/Co3O4 nanoparticles in alkaline Al2O3 nanosheets for catalytic oxidation of methane. Pd/Co3O4 inlaid in alkaline Al2O3 exhibited a higher ability to break the C-H bond of methane than Pd/Co3O4 supported on SiO2, ZrO2, CeO2, and acidic or neutral Al2O3. Our results show more oxygen vacancies and higher amounts of surface adsorbed oxygen on the surface of Pd/Co3O4/alkaline Al2O3 than on other catalysts, which is responsible for methane activation and conversion. Further, the Pd/Co3O4/alkaline Al2O3 catalyst can almost restore to its initial value in the absence of water when 5% (volume fraction) vapor water was cut off, although a decrease in activity occurred when water vapor was introduced to the reaction system. Even under a condition similar to the exhaust of a lean-burn natural gas engine, the catalytic performance of the Pd/Co3O4/alkaline Al2O3 catalyst is excellent, that is, methane could be completely converted when the sample temperature in the reaction atmosphere was ramped to 400℃.
We report an efficient catalyst composed of ternary components prepared by inlaying Pd/Co3O4 nanoparticles in alkaline Al2O3 nanosheets for catalytic oxidation of methane. Pd/Co3O4 inlaid in alkaline Al2O3 exhibited a higher ability to break the C-H bond of methane than Pd/Co3O4 supported on SiO2, ZrO2, CeO2, and acidic or neutral Al2O3. Our results show more oxygen vacancies and higher amounts of surface adsorbed oxygen on the surface of Pd/Co3O4/alkaline Al2O3 than on other catalysts, which is responsible for methane activation and conversion. Further, the Pd/Co3O4/alkaline Al2O3 catalyst can almost restore to its initial value in the absence of water when 5% (volume fraction) vapor water was cut off, although a decrease in activity occurred when water vapor was introduced to the reaction system. Even under a condition similar to the exhaust of a lean-burn natural gas engine, the catalytic performance of the Pd/Co3O4/alkaline Al2O3 catalyst is excellent, that is, methane could be completely converted when the sample temperature in the reaction atmosphere was ramped to 400℃.
2017, 33(7): 1462-1473
doi: 10.3866/PKU.WHXB201704103
Abstract:
Mesoporous SBA-15 with mesopore diameter up to 10.1 nm was prepared by a hydrothermal method, and was further functionalized to obtain different surface properties. Thus-prepared SBA-15 was employed as a template to synthesize rhombohedrally crystallized mesoporous La0.8Sr0.2CoO3 perovskite via a nanocasting method. The surface properties of the SBA-15 were adjusted by treatment with concentrated hydrochloric acid, trimethylchlorosilane (TMCS), and 3-aminopropyltriethoxysilane (APTES). A series of characterization techniques verified that all the synthesized templates possessed ordered two-dimensional hexagonal mesoporous structure, and the surface was successfully modified with methyl and amino groups. The mesoporous perovskite structure was formed in the samples and the surface properties of SBA-15 significantly influenced the structure and properties of La0.8Sr0.2CoO3 perovskite oxides. Wide-angle X-ray diffraction patterns suggested that the modified silica templates were conducive to the formation of pure perovskite frameworks with good crystallinity. The catalysts also possessed mesoporous structure, as confirmed by small-angle XRD patterns, high-resolution transmission electron microscopy images, and nitrogen adsorption analysis. Moreover, the La0.8Sr0.2CoO3 materials synthesized using surface-functionalized templates exhibited relatively higher catalytic activity and stability in CO oxidation. Complete CO conversion could be achieved at 140℃ using the thus-prepared La0.8Sr0.2CoO3 materials, and no significant loss in catalytic activity was observed after 100 h of on-stream reaction experiments. X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, and O2 temperature-programmed desorption experiments revealed that the existence of Co4+, Sr enrichment in the perovskite structure, and high content of adsorbed oxygen species play a critical role in the enhanced catalytic activity of the catalysts. We also proposed the possible reasons for the effect of surface properties of the silica templates on the structure and properties of the La0.8Sr0.2CoO3 nanomaterials.
Mesoporous SBA-15 with mesopore diameter up to 10.1 nm was prepared by a hydrothermal method, and was further functionalized to obtain different surface properties. Thus-prepared SBA-15 was employed as a template to synthesize rhombohedrally crystallized mesoporous La0.8Sr0.2CoO3 perovskite via a nanocasting method. The surface properties of the SBA-15 were adjusted by treatment with concentrated hydrochloric acid, trimethylchlorosilane (TMCS), and 3-aminopropyltriethoxysilane (APTES). A series of characterization techniques verified that all the synthesized templates possessed ordered two-dimensional hexagonal mesoporous structure, and the surface was successfully modified with methyl and amino groups. The mesoporous perovskite structure was formed in the samples and the surface properties of SBA-15 significantly influenced the structure and properties of La0.8Sr0.2CoO3 perovskite oxides. Wide-angle X-ray diffraction patterns suggested that the modified silica templates were conducive to the formation of pure perovskite frameworks with good crystallinity. The catalysts also possessed mesoporous structure, as confirmed by small-angle XRD patterns, high-resolution transmission electron microscopy images, and nitrogen adsorption analysis. Moreover, the La0.8Sr0.2CoO3 materials synthesized using surface-functionalized templates exhibited relatively higher catalytic activity and stability in CO oxidation. Complete CO conversion could be achieved at 140℃ using the thus-prepared La0.8Sr0.2CoO3 materials, and no significant loss in catalytic activity was observed after 100 h of on-stream reaction experiments. X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, and O2 temperature-programmed desorption experiments revealed that the existence of Co4+, Sr enrichment in the perovskite structure, and high content of adsorbed oxygen species play a critical role in the enhanced catalytic activity of the catalysts. We also proposed the possible reasons for the effect of surface properties of the silica templates on the structure and properties of the La0.8Sr0.2CoO3 nanomaterials.
2017, 33(7): 1474-1482
doi: 10.3866/PKU.WHXB201703312
Abstract:
Here we reported the effect of the Cu-Mn-Ce-SiO2 (CMC-SiO2) interaction on the physical and chemical aspects of the catalytic combustion of toluene by adjusting the loading amount of the CMC mixed oxide on SiO2. Notably, the CMC/KIT-6 catalyst with low CMC loading performed poorly with an obvious deactivation, owing to the inhibition of the metal oxides active sites, while the activity recovered after washing away some SiO2. The catalysts were characterized by X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), N2 adsorption, and high-resolution transmission electron microscopy (HRTEM). Although there is no change in crystal structure after loading on SiO2, active oxygen species immigrate from lattice to surface for SiO2 surface rich in hydroxyl groups and having high dispersion of CMC, leading to deactivation of the CMC catalyst. However, it is worth mentioning that the lattice oxygen played a key role in catalytic combustion. The activity of the CMC catalyst recovered when the quantity of lattice oxygen increased upon removing surface -OH groups by calcination or removing some SiO2 by alkali washing.
Here we reported the effect of the Cu-Mn-Ce-SiO2 (CMC-SiO2) interaction on the physical and chemical aspects of the catalytic combustion of toluene by adjusting the loading amount of the CMC mixed oxide on SiO2. Notably, the CMC/KIT-6 catalyst with low CMC loading performed poorly with an obvious deactivation, owing to the inhibition of the metal oxides active sites, while the activity recovered after washing away some SiO2. The catalysts were characterized by X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), N2 adsorption, and high-resolution transmission electron microscopy (HRTEM). Although there is no change in crystal structure after loading on SiO2, active oxygen species immigrate from lattice to surface for SiO2 surface rich in hydroxyl groups and having high dispersion of CMC, leading to deactivation of the CMC catalyst. However, it is worth mentioning that the lattice oxygen played a key role in catalytic combustion. The activity of the CMC catalyst recovered when the quantity of lattice oxygen increased upon removing surface -OH groups by calcination or removing some SiO2 by alkali washing.
2017, 33(7): 1483-1491
doi: 10.3866/PKU.WHXB201704133
Abstract:
After hydrogen pre-treatment at different temperatures, the textural and physicochemical properties of Zn/HZSM-5 were studied by X-ray diffraction (XRD), N2 adsorption-desorption, Fourier transform infrared (FT-IR) spectroscopy, temperature programmed desorption of NH3 (NH3-TPD), and X-ray photoelectron spectroscopy (XPS) techniques. The results showed that the temperatures for hydrogen pretreatment of Zn/HZSM-5 exerted a significant influence on both the contents and state of zinc species. The pre-treatment with hydrogen at temperature higher than 600℃ resulted in a significant leaching of zinc species from the catalysts, which occurred due to the reduction and sublimation of zinc species. The XPS characterization revealed that the hydrogen pre-treatment at different temperatures causes the redistribution of ZnOH+ and ZnO species in the zeolite. A linear correlation between the amount of ZnOH+ species and the selectivity to aromatics over the Zn/HZSM-5 catalysts pretreated with hydrogen at different temperatures was observed, suggesting that ZnOH+ species may promote the formation of aromatics in ethylene aromatization reaction.
After hydrogen pre-treatment at different temperatures, the textural and physicochemical properties of Zn/HZSM-5 were studied by X-ray diffraction (XRD), N2 adsorption-desorption, Fourier transform infrared (FT-IR) spectroscopy, temperature programmed desorption of NH3 (NH3-TPD), and X-ray photoelectron spectroscopy (XPS) techniques. The results showed that the temperatures for hydrogen pretreatment of Zn/HZSM-5 exerted a significant influence on both the contents and state of zinc species. The pre-treatment with hydrogen at temperature higher than 600℃ resulted in a significant leaching of zinc species from the catalysts, which occurred due to the reduction and sublimation of zinc species. The XPS characterization revealed that the hydrogen pre-treatment at different temperatures causes the redistribution of ZnOH+ and ZnO species in the zeolite. A linear correlation between the amount of ZnOH+ species and the selectivity to aromatics over the Zn/HZSM-5 catalysts pretreated with hydrogen at different temperatures was observed, suggesting that ZnOH+ species may promote the formation of aromatics in ethylene aromatization reaction.
2017, 33(7): 1492-1498
doi: 10.3866/PKU.WHXB201704141
Abstract:
To study the activity of a composite photocatalyst for photocatalytic hydrogen production, we prepared and loaded MoS2 nanosheets with TiO2 nanoparticles using a hydrothermal method, thus forming a MoS2/TiO2 heterojunction composite catalyst. The structural and optical properties of the catalyst were characterized and analyzed by field-emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray powder diffraction, UV-Vis absorption spectra, Raman spectroscopy, and X-ray photoelectron spectroscopy. The activity of the photocatalyst was evaluated by its photocatalytic hydrogen production rate. The corresponding MoS2 content of the catalyst was found to be 30%, and upon the exposure to 365nm UV light, a high photocatalytic hydrogen production rate of 1004 μmol-1·h-1·g-1 was obtained. The catalytic rate is much greater than that obtained with MoS2 or TiO2 catalysts. The high hydrogen production rate indicated that the use of a MoS2/TiO2 composite catalyst can significantly improve the UV-induced photocatalytic hydrogen production performance. Because of the excellent photocatalytic hydrogen production performance of the MoS2/TiO2 composite, we studied and analyzed the hydrogen production mechanism.
To study the activity of a composite photocatalyst for photocatalytic hydrogen production, we prepared and loaded MoS2 nanosheets with TiO2 nanoparticles using a hydrothermal method, thus forming a MoS2/TiO2 heterojunction composite catalyst. The structural and optical properties of the catalyst were characterized and analyzed by field-emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray powder diffraction, UV-Vis absorption spectra, Raman spectroscopy, and X-ray photoelectron spectroscopy. The activity of the photocatalyst was evaluated by its photocatalytic hydrogen production rate. The corresponding MoS2 content of the catalyst was found to be 30%, and upon the exposure to 365nm UV light, a high photocatalytic hydrogen production rate of 1004 μmol-1·h-1·g-1 was obtained. The catalytic rate is much greater than that obtained with MoS2 or TiO2 catalysts. The high hydrogen production rate indicated that the use of a MoS2/TiO2 composite catalyst can significantly improve the UV-induced photocatalytic hydrogen production performance. Because of the excellent photocatalytic hydrogen production performance of the MoS2/TiO2 composite, we studied and analyzed the hydrogen production mechanism.
