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2017 Volume 33 Issue 2
2017, 33(2):
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2017, 33(2): 263-263
doi: 10.3866/PKU.WHXB201612211
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2017, 33(2): 264-264
doi: 10.3866/PKU.WHXB201612271
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2017, 33(2): 265-265
doi: 10.3866/PKU.WHXB201612221
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2017, 33(2): 266-267
doi: 10.3866/PKU.WHXB201612231
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2017, 33(2): 268-269
doi: 10.3866/PKU.WHXB201701031
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2017, 33(2): 270-282
doi: 10.3866/PKU.WHXB201611022
Abstract:
Solid acid catalysts have been widely used in advanced petrochemical processes because of their environmental friendliness, high product selectivity, and easy product separation. Solid-state nuclear magnetic resonance (NMR) spectroscopy is a well-established tool for structure determination and dynamic study of various functional materials. In this review, we focus mainly on our research using solid-state NMR to characterize the acid properties and elucidate the catalytic reaction mechanism of solid acid catalysts. The acid strength of solid acids can be quantitatively measured from the chemical shifts of adsorbed probe molecules such as pyridine, acetone, trialkylphosphine oxides, and trimethylphosphine. The spatial proximity and synergetic effect of various acid sites on solid acid catalysts can be ascertained by two-dimensional (2D) double-quantum magic angle spinning (DQ MAS) NMR spectroscopy. Additionally, in situ solid-state NMR spectroscopy can be used to explore heterogeneous catalytic reaction mechanisms by monitoring the evolution of the reactants, intermediates, and products.
Solid acid catalysts have been widely used in advanced petrochemical processes because of their environmental friendliness, high product selectivity, and easy product separation. Solid-state nuclear magnetic resonance (NMR) spectroscopy is a well-established tool for structure determination and dynamic study of various functional materials. In this review, we focus mainly on our research using solid-state NMR to characterize the acid properties and elucidate the catalytic reaction mechanism of solid acid catalysts. The acid strength of solid acids can be quantitatively measured from the chemical shifts of adsorbed probe molecules such as pyridine, acetone, trialkylphosphine oxides, and trimethylphosphine. The spatial proximity and synergetic effect of various acid sites on solid acid catalysts can be ascertained by two-dimensional (2D) double-quantum magic angle spinning (DQ MAS) NMR spectroscopy. Additionally, in situ solid-state NMR spectroscopy can be used to explore heterogeneous catalytic reaction mechanisms by monitoring the evolution of the reactants, intermediates, and products.
2017, 33(2): 283-294
doi: 10.3866/PKU.WHXB201611071
Abstract:
Fuel cell vehicles (FCVs) have been a burgeoning industry in China, and are currently on the verge of widespread commercialization. The platinum-based electrocatalyst is one of the key materials in proton exchange membrane fuel cells (PEMFCs). The relatively low activity and durability, and high cost of the electrocatalyst impede the further development of PEMFCs as a clean energy technology. It has been widely anticipated that core-shell structured low-platinum electrocatalysts with high performance toward oxygen reduction reaction (ORR) will eventually resolve this bottleneck issue. Regardless of significant progress, there are still many remaining issues, such as complicated synthesis route, the large sizes of core materials like Pd, and lack of macroscopic characterization of the core-shell structures. Herein, we introduce two new synthetic methods (one pot synthesis and regioselective atomic layer deposition (ALD) combined with a wet chemical method) for the fabrication of core-shell structured Pd3Au@Pt/C electrocatalysts with high ORR performance. These two synthetic approaches allow us to well control the diameter of the core nanoparticle to around 5 nm. Cyclic voltammetry (CV) and formic acid oxidation reaction (FAOR) were found to be suitable for investigating the integrity of the Pt shell on the core particles. This work represents a new avenue for the macroscopic characterization of the core-shell structured electrocatalysts with Pd or Pd alloy as the core material.
Fuel cell vehicles (FCVs) have been a burgeoning industry in China, and are currently on the verge of widespread commercialization. The platinum-based electrocatalyst is one of the key materials in proton exchange membrane fuel cells (PEMFCs). The relatively low activity and durability, and high cost of the electrocatalyst impede the further development of PEMFCs as a clean energy technology. It has been widely anticipated that core-shell structured low-platinum electrocatalysts with high performance toward oxygen reduction reaction (ORR) will eventually resolve this bottleneck issue. Regardless of significant progress, there are still many remaining issues, such as complicated synthesis route, the large sizes of core materials like Pd, and lack of macroscopic characterization of the core-shell structures. Herein, we introduce two new synthetic methods (one pot synthesis and regioselective atomic layer deposition (ALD) combined with a wet chemical method) for the fabrication of core-shell structured Pd3Au@Pt/C electrocatalysts with high ORR performance. These two synthetic approaches allow us to well control the diameter of the core nanoparticle to around 5 nm. Cyclic voltammetry (CV) and formic acid oxidation reaction (FAOR) were found to be suitable for investigating the integrity of the Pt shell on the core particles. This work represents a new avenue for the macroscopic characterization of the core-shell structured electrocatalysts with Pd or Pd alloy as the core material.
2017, 33(2): 295-304
doi: 10.3866/PKU.WHXB201610172
Abstract:
Traditional semiconductor photocatalysts with a wide band gap can achieve visible light responses through element doping. However, the localized levels introduced by impurities may act as recombination centers of charge carriers, which may lower the photocatalytic activity of the doped materials. The solid solution method can realize precise regulation of the band gap and band edge positions of materials to obtain an optimal balance between their optical absorption and redox potentials. The solid solution method is therefore an effective approach to improve the photocatalytic performance of semiconductor materials. In the present review, considering our recent research, we briefly discuss the latest progress of the solid solution method to tune the band gap and band edge positions of photocatalytic materials as well as examining its influence on carrier separation and migration properties. Finally, challenges and prospects for further development of this method are presented.
Traditional semiconductor photocatalysts with a wide band gap can achieve visible light responses through element doping. However, the localized levels introduced by impurities may act as recombination centers of charge carriers, which may lower the photocatalytic activity of the doped materials. The solid solution method can realize precise regulation of the band gap and band edge positions of materials to obtain an optimal balance between their optical absorption and redox potentials. The solid solution method is therefore an effective approach to improve the photocatalytic performance of semiconductor materials. In the present review, considering our recent research, we briefly discuss the latest progress of the solid solution method to tune the band gap and band edge positions of photocatalytic materials as well as examining its influence on carrier separation and migration properties. Finally, challenges and prospects for further development of this method are presented.
2017, 33(2): 305-313
doi: 10.3866/PKU.WHXB201611012
Abstract:
Supercapacitors (SCs) have been explored as one of the electrical sources because of their fast charge and discharge rates, good safety, and long cycle life. However, the limited energy densities of SCs hinder their further application. Thus, current research on SCs focuses on increasing their energy density. Enhancing specific capacitance is an effective way to increase energy density. In this review, we describe several approaches to achieve superior electrochemical properties by optimizing electrode materials and electrolytes. Considering electrode materials, their electrochemical performance is related to their specific surface area, pore structure, and electroconductivity. On one hand, the optimization of specific surface area and pore structure can increase their content of exposed active sites as well as electrolyte ion conductivity, which is beneficial for improved specific capacitance. On the other hand, enhanced electroconductivity leads to higher specific capacitance. The specific capacitances of electric double-layer capacitors and pseudocapacitors have been increased by optimizing carbon-based materials and metal hydroxides/oxides, respectively. Moreover, specific capacitance can be further enhanced by adding a redox mediator to the electrolyte as a pseudocapacitive source. This review offers perspectives to aid the development of next-generation supercapacitors with high specific capacitance.
Supercapacitors (SCs) have been explored as one of the electrical sources because of their fast charge and discharge rates, good safety, and long cycle life. However, the limited energy densities of SCs hinder their further application. Thus, current research on SCs focuses on increasing their energy density. Enhancing specific capacitance is an effective way to increase energy density. In this review, we describe several approaches to achieve superior electrochemical properties by optimizing electrode materials and electrolytes. Considering electrode materials, their electrochemical performance is related to their specific surface area, pore structure, and electroconductivity. On one hand, the optimization of specific surface area and pore structure can increase their content of exposed active sites as well as electrolyte ion conductivity, which is beneficial for improved specific capacitance. On the other hand, enhanced electroconductivity leads to higher specific capacitance. The specific capacitances of electric double-layer capacitors and pseudocapacitors have been increased by optimizing carbon-based materials and metal hydroxides/oxides, respectively. Moreover, specific capacitance can be further enhanced by adding a redox mediator to the electrolyte as a pseudocapacitive source. This review offers perspectives to aid the development of next-generation supercapacitors with high specific capacitance.
2017, 33(2): 314-328
doi: 10.3866/PKU.WHXB201611091
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With the development of thin film technology, new methods to grow thin films is emerging. This review introduces one type of polymer-assisted deposition to grow thin films. Polymer-assisted deposition is one of the chemical solution ways to grow high-quality thin films. In this process, metal ions coordinate with a polymer by covalent bonding, hydrogen bonding, or static electricity to form a stable precursor. The controllable viscosity and homogeneous solution system ensure high-quality growth of thin films or nanoparticles. The diverse components of thin film range from a metal-oxides, metal-carbides, metal-nitrides, metal-sulfides/selenides to elementary substance (e.g. metals) even dopant composites. This method provides an alternative strategy to grow thin films. In addition, the prospects and challenges of the polymer-assisted deposition are discussed in the review as well.
With the development of thin film technology, new methods to grow thin films is emerging. This review introduces one type of polymer-assisted deposition to grow thin films. Polymer-assisted deposition is one of the chemical solution ways to grow high-quality thin films. In this process, metal ions coordinate with a polymer by covalent bonding, hydrogen bonding, or static electricity to form a stable precursor. The controllable viscosity and homogeneous solution system ensure high-quality growth of thin films or nanoparticles. The diverse components of thin film range from a metal-oxides, metal-carbides, metal-nitrides, metal-sulfides/selenides to elementary substance (e.g. metals) even dopant composites. This method provides an alternative strategy to grow thin films. In addition, the prospects and challenges of the polymer-assisted deposition are discussed in the review as well.
2017, 33(2): 329-343
doi: 10.3866/PKU.WHXB201611072
Abstract:
Conductive polymers implemented in fibrous energy devices have drawn considerable attention because of their economic importance, good environmental stability, and electrical conductivity. Conductive polymers demonstrate interesting mechanical, electronic, and optical properties, controllable chemical and electrochemical behavior, and facile processability. This review elaborates on the latest research in conductive polymers in fibrous energy devices, such as fibrous supercapacitors, fibrous solar cells, and fibrous integrated energy devices. The performance requirements of these fibrous energy devices, with specific reference to related materials, fabrication techniques, fiber structure, and electronic transport as well as mechanical functionality, are also reviewed in this paper.
Conductive polymers implemented in fibrous energy devices have drawn considerable attention because of their economic importance, good environmental stability, and electrical conductivity. Conductive polymers demonstrate interesting mechanical, electronic, and optical properties, controllable chemical and electrochemical behavior, and facile processability. This review elaborates on the latest research in conductive polymers in fibrous energy devices, such as fibrous supercapacitors, fibrous solar cells, and fibrous integrated energy devices. The performance requirements of these fibrous energy devices, with specific reference to related materials, fabrication techniques, fiber structure, and electronic transport as well as mechanical functionality, are also reviewed in this paper.
2017, 33(2): 344-355
doi: 10.3866/PKU.WHXB201611023
Abstract:
A new CaCl2-formic acid dissolution method was used to prepare silk fibroin (SF) films. Films SF-1.5 and SF-3.0 were prepared using 1.50% (w, mass fraction) and 3.00% (w) CaCl2-formic acid solutions, respectively. The molecular conformations and crystal structures of the films were characterized by Fourier transform infrared spectroscopy and X-ray diffraction. The thermal stability, thermal decomposition properties, and effect of CaCl2 concentration on the thermodynamic parameters, kinetic parameters, and formation mechanism of the SF films were investigated using thermogravimetry techniques and the models of Kissinger, Ozawa, and Vyazovkin. The results showed that the SF-1.5 film mainly contained β-sheet structure, while the main molecular conformation in the SF-3.0 film was random coils. The decomposition temperature, activation energy, and activation enthalpy of SF-3.0 were lower than those of SF-1.5, while the thermal stability of SF-1.5 was higher than that of SF-3.0. In addition, the thermal decomposition of the SF films was studied by the Achar and Coats-Redfern methods. The mechanism of decomposition of these SF films followed the two-dimensional diffusion (cylindrical symmetry) law in the temperature range of 190.00-330.00℃.
A new CaCl2-formic acid dissolution method was used to prepare silk fibroin (SF) films. Films SF-1.5 and SF-3.0 were prepared using 1.50% (w, mass fraction) and 3.00% (w) CaCl2-formic acid solutions, respectively. The molecular conformations and crystal structures of the films were characterized by Fourier transform infrared spectroscopy and X-ray diffraction. The thermal stability, thermal decomposition properties, and effect of CaCl2 concentration on the thermodynamic parameters, kinetic parameters, and formation mechanism of the SF films were investigated using thermogravimetry techniques and the models of Kissinger, Ozawa, and Vyazovkin. The results showed that the SF-1.5 film mainly contained β-sheet structure, while the main molecular conformation in the SF-3.0 film was random coils. The decomposition temperature, activation energy, and activation enthalpy of SF-3.0 were lower than those of SF-1.5, while the thermal stability of SF-1.5 was higher than that of SF-3.0. In addition, the thermal decomposition of the SF films was studied by the Achar and Coats-Redfern methods. The mechanism of decomposition of these SF films followed the two-dimensional diffusion (cylindrical symmetry) law in the temperature range of 190.00-330.00℃.
2017, 33(2): 356-363
doi: 10.3866/PKU.WHXB201610191
Abstract:
Three acyl hydrazones N'-((2-hydroxynaphthalen-1-yl)methylene)-2-phenylacetohydrazide (1), N'-((2-hydroxynaphthalen-1-yl) methylene)-2-(4-hydroxyphenyl)acetohydrazide hydrate (2), and N'-((2-hydroxynaphthalen-1-yl) methylene)-2-(2-methoxyphenyl) acetohydrazide hydrate (3) were synthesized and then characterized by elemental analysis and single-crystal X-ray diffraction. The crystallographic data indicated that both compounds 2 and 3 crystallized in the monoclinic crystal lattice, space group C2/c, while compound 1 crystallized in the orthorhombic space group Pbca. The thermal decomposition processes of the three hydrazones were studied by thermogravimetry. The thermal decomposition temperatures of compounds 1, 2, and 3 were 318.23, 319.04, and 323.01℃, respectively. Meanwhile, the apparent activation energies for thermal decomposition for compounds 1, 2, and 3 were 115.90, 145.18, and 129.38 kJ·mol-1, respectively, calculated according to the Kissinger and Ozawa equations. The interactions of compounds 1-3 with calf thymus (CT)-DNA were evaluated by microcalorimetry. The results indicated these interactions were homogenous endothermic processes with non-identical interaction time (1.00-50.0 min) and interaction enthalpies (0.47-15.50 kJ·mol-1). The interaction enthalpies of compounds 1 and 2 were higher than those of their precursors, while the interaction enthalpy of compound 3 was lower than that of its precursor.
Three acyl hydrazones N'-((2-hydroxynaphthalen-1-yl)methylene)-2-phenylacetohydrazide (1), N'-((2-hydroxynaphthalen-1-yl) methylene)-2-(4-hydroxyphenyl)acetohydrazide hydrate (2), and N'-((2-hydroxynaphthalen-1-yl) methylene)-2-(2-methoxyphenyl) acetohydrazide hydrate (3) were synthesized and then characterized by elemental analysis and single-crystal X-ray diffraction. The crystallographic data indicated that both compounds 2 and 3 crystallized in the monoclinic crystal lattice, space group C2/c, while compound 1 crystallized in the orthorhombic space group Pbca. The thermal decomposition processes of the three hydrazones were studied by thermogravimetry. The thermal decomposition temperatures of compounds 1, 2, and 3 were 318.23, 319.04, and 323.01℃, respectively. Meanwhile, the apparent activation energies for thermal decomposition for compounds 1, 2, and 3 were 115.90, 145.18, and 129.38 kJ·mol-1, respectively, calculated according to the Kissinger and Ozawa equations. The interactions of compounds 1-3 with calf thymus (CT)-DNA were evaluated by microcalorimetry. The results indicated these interactions were homogenous endothermic processes with non-identical interaction time (1.00-50.0 min) and interaction enthalpies (0.47-15.50 kJ·mol-1). The interaction enthalpies of compounds 1 and 2 were higher than those of their precursors, while the interaction enthalpy of compound 3 was lower than that of its precursor.
2017, 33(2): 364-369
doi: 10.3866/PKU.WHXB201611082
Abstract:
The present work demonstrates that extended energy loss fine structure (EXELFS) analysis can be used to investigate the microstructure of Uranium dioxide. First, EXELFS was extracted by IFEFFIT package from oxygen-K edge in electron energy-loss spectrometry (EELS) spectrum of UO2. Next, the EXELFS was Fourier transformed to obtain the experimental real-space spectrum, which was then back-Fourier transformed to obtain the experimental reciprocal-space spectrum. In the next step, the two experimental spectra were fitted with the IFEFFIT package to obtain information about the local structure of the oxygen atoms. Finally, the lattice constant of UO2 determined by EXELFS analysis was found to be merely 1.4% lower than that experimentally obtained by X-ray diffraction (XRD). This result confirms that EXELFS analysis is a feasible method of investigating UO2 microstructural information.
The present work demonstrates that extended energy loss fine structure (EXELFS) analysis can be used to investigate the microstructure of Uranium dioxide. First, EXELFS was extracted by IFEFFIT package from oxygen-K edge in electron energy-loss spectrometry (EELS) spectrum of UO2. Next, the EXELFS was Fourier transformed to obtain the experimental real-space spectrum, which was then back-Fourier transformed to obtain the experimental reciprocal-space spectrum. In the next step, the two experimental spectra were fitted with the IFEFFIT package to obtain information about the local structure of the oxygen atoms. Finally, the lattice constant of UO2 determined by EXELFS analysis was found to be merely 1.4% lower than that experimentally obtained by X-ray diffraction (XRD). This result confirms that EXELFS analysis is a feasible method of investigating UO2 microstructural information.
2017, 33(2): 370-376
doi: 10.3866/PKU.WHXB201610311
Abstract:
Phosphomolybdic acid was investigated as a mediator for indirect carbon electrooxidation at low temperatures. Linear sweeping voltammetry and chronoamperometry experiments showed that the carbon electrooxidation process was influenced by the type of carbonaceous material, reaction conditions, reaction time, and phosphomolybdic acid concentration. The mechanism underlying indirect carbon electrooxidation was explored using cyclic voltammetry. The results showed that the reactivity of coconut-derived activated carbon was higher than that of coal-derived activated carbon or coal in the chemical reaction between phosphomolybdic acid and carbon materials. Sunlight and heating to 80℃ similarly improved the efficiency of the indirect carbon electrooxidation. The electrooxidation mechanism is as follows:MoVI in phosphomolybdic oxidizes carbon to form MoV, and is then electrooxidized back to MoVI in an anodic reaction, releasing the electron obtained from the carbon material. This process facilitated the indirect electrooxidation of carbon at low temperatures. Sunlight was found to enhance the rate of the chemical reaction between phosphomolybdic acid and carbon materials in two ways:1) thermally by increasing the reaction temperature and thus improving the reaction rate; 2) photocatalytically, as sunlight absorbed by phosphomolybdic acid is converted into chemical energy, which is the main effect. A full cell test with phosphomolybdic acid demonstrated a power density of 0.087 mW·cm-2 at room temperature, indicating that the concept of low-temperature carbon fuel cells is feasible.
Phosphomolybdic acid was investigated as a mediator for indirect carbon electrooxidation at low temperatures. Linear sweeping voltammetry and chronoamperometry experiments showed that the carbon electrooxidation process was influenced by the type of carbonaceous material, reaction conditions, reaction time, and phosphomolybdic acid concentration. The mechanism underlying indirect carbon electrooxidation was explored using cyclic voltammetry. The results showed that the reactivity of coconut-derived activated carbon was higher than that of coal-derived activated carbon or coal in the chemical reaction between phosphomolybdic acid and carbon materials. Sunlight and heating to 80℃ similarly improved the efficiency of the indirect carbon electrooxidation. The electrooxidation mechanism is as follows:MoVI in phosphomolybdic oxidizes carbon to form MoV, and is then electrooxidized back to MoVI in an anodic reaction, releasing the electron obtained from the carbon material. This process facilitated the indirect electrooxidation of carbon at low temperatures. Sunlight was found to enhance the rate of the chemical reaction between phosphomolybdic acid and carbon materials in two ways:1) thermally by increasing the reaction temperature and thus improving the reaction rate; 2) photocatalytically, as sunlight absorbed by phosphomolybdic acid is converted into chemical energy, which is the main effect. A full cell test with phosphomolybdic acid demonstrated a power density of 0.087 mW·cm-2 at room temperature, indicating that the concept of low-temperature carbon fuel cells is feasible.
2017, 33(2): 377-385
doi: 10.3866/PKU.WHXB201610272
Abstract:
With the widespread use of mobile electronic devices and increasing demand for electric energy storage in the transportation and energy sectors, lithium-ion batteries (LIBs) have become a major research and development focus in recent years. The current generation of LIBs use graphite as the anode material, which has a theoretical capacity of 372 mAh·g-1. Tin-based materials are considered promising anode materials for next-generation LIBs because of their favorable working voltage and unsurpassed theoretical specific capacity. However, overcoming the rapid storage capacity degradation of tin caused by its large volumetric changes (>200%) during cycling remains a major challenge to the successful implementation of such materials. In this paper, SnO2 nanoparticles with a diameter of 2-3 nm were used as active materials in LIB anodes and a threedimensional (3D) graphene hydrogel (GH) was used as a buffer to decrease the volumetric change. Typically, SnCl4 aqueous solution (18 mL, 6.4 mmol·L-1) and graphene oxide (GO) suspension (0.5% (w, mass fraction), 2 mL) were mixed together via sonication. NaOH aqueous solution (11.4 mmol·L-1, 40 mL) was slowly added and then the mixture was stirred for 2 h to obtain a stable suspension. Vitamin C (VC, 80 mg) was then added as a reductant. The mixture was kept at 80℃ for 24 h to reduce and self-assemble. The resulting black block was washed repeatedly with distilled deionized water and freeze-dried to obtain SnO2-GH. In this composite, GH provides large specific surface area for efficient loading (54% (w)) and uniform distribution of nanoparticles. SnO2-GH delivered a capacity of 500 mAh·g-1 at 5000 mA·g-1 and 865 mAh·g-1 at 50 mA·g-1 after rate cycling.This outstanding electrochemical performance is attributed to the 3D structure of GH, which provides large internal space to accommodate volumetric changes, an electrically conducting structural porous network, a large amount of lithium-ion diffusion channels, fast electron transport kinetics, and excellent penetration of electrolyte solution. This study demonstrates that 3D GH is a potential carbon matrix for LIBs.
With the widespread use of mobile electronic devices and increasing demand for electric energy storage in the transportation and energy sectors, lithium-ion batteries (LIBs) have become a major research and development focus in recent years. The current generation of LIBs use graphite as the anode material, which has a theoretical capacity of 372 mAh·g-1. Tin-based materials are considered promising anode materials for next-generation LIBs because of their favorable working voltage and unsurpassed theoretical specific capacity. However, overcoming the rapid storage capacity degradation of tin caused by its large volumetric changes (>200%) during cycling remains a major challenge to the successful implementation of such materials. In this paper, SnO2 nanoparticles with a diameter of 2-3 nm were used as active materials in LIB anodes and a threedimensional (3D) graphene hydrogel (GH) was used as a buffer to decrease the volumetric change. Typically, SnCl4 aqueous solution (18 mL, 6.4 mmol·L-1) and graphene oxide (GO) suspension (0.5% (w, mass fraction), 2 mL) were mixed together via sonication. NaOH aqueous solution (11.4 mmol·L-1, 40 mL) was slowly added and then the mixture was stirred for 2 h to obtain a stable suspension. Vitamin C (VC, 80 mg) was then added as a reductant. The mixture was kept at 80℃ for 24 h to reduce and self-assemble. The resulting black block was washed repeatedly with distilled deionized water and freeze-dried to obtain SnO2-GH. In this composite, GH provides large specific surface area for efficient loading (54% (w)) and uniform distribution of nanoparticles. SnO2-GH delivered a capacity of 500 mAh·g-1 at 5000 mA·g-1 and 865 mAh·g-1 at 50 mA·g-1 after rate cycling.This outstanding electrochemical performance is attributed to the 3D structure of GH, which provides large internal space to accommodate volumetric changes, an electrically conducting structural porous network, a large amount of lithium-ion diffusion channels, fast electron transport kinetics, and excellent penetration of electrolyte solution. This study demonstrates that 3D GH is a potential carbon matrix for LIBs.
2017, 33(2): 386-392
doi: 10.3866/PKU.WHXB201610104
Abstract:
Tubular electrolyte-supporting solid oxide fuel cells (SOFCs) are particularly suitable for fundamental research of direct carbon SOFCs (DC-SOFCs) because they exhibit high stability, have simple seal requirements and are compatible with a variety of electrode materials. We have developed a dip-coating technique for the simple preparation of tubular electrolyte-supporting SOFCs using tubular yttria-stabilized zirconia (YSZ) electrolyte membrane substrates. Single SOFCs were assembled with a cermet consisting of gadolinium doped ceria (GDC) mixed with silver as both the cathode and anode. The single cells were tested with humidified hydrogen and 5% Fe-loaded activated carbon (w, mass fraction) as the fuel. Ambient air was used as the oxidant. The open-circuit voltages were comparable to the theoretical values and the scanning electron microscopy (SEM) results showed that the electrolyte membrane was quite dense. The cell that used activated carbon as fuel exhibited a maximum power density of 280 mW·cm-2 at 800℃, which was close to that of a cell that used hydrogen as fuel (330 mW·cm-2). The results of impedance spectroscopy showed that the performance of the cells was mainly influenced by the electrolyte ohmic resistance. The discharge time of the DC-SOFC at a constant current of 1 A was 2.1 h, which represented a fuel utilization of 36%. The performance of the DC-SOFC with reloaded fuel was nearly identical to its initial performance, which indicated that the YSZ electrolyte membrane substrate was stable when used in the DC-SOFCs. The degradation performance of the DC-SOFC during the discharge test was also analyzed.
Tubular electrolyte-supporting solid oxide fuel cells (SOFCs) are particularly suitable for fundamental research of direct carbon SOFCs (DC-SOFCs) because they exhibit high stability, have simple seal requirements and are compatible with a variety of electrode materials. We have developed a dip-coating technique for the simple preparation of tubular electrolyte-supporting SOFCs using tubular yttria-stabilized zirconia (YSZ) electrolyte membrane substrates. Single SOFCs were assembled with a cermet consisting of gadolinium doped ceria (GDC) mixed with silver as both the cathode and anode. The single cells were tested with humidified hydrogen and 5% Fe-loaded activated carbon (w, mass fraction) as the fuel. Ambient air was used as the oxidant. The open-circuit voltages were comparable to the theoretical values and the scanning electron microscopy (SEM) results showed that the electrolyte membrane was quite dense. The cell that used activated carbon as fuel exhibited a maximum power density of 280 mW·cm-2 at 800℃, which was close to that of a cell that used hydrogen as fuel (330 mW·cm-2). The results of impedance spectroscopy showed that the performance of the cells was mainly influenced by the electrolyte ohmic resistance. The discharge time of the DC-SOFC at a constant current of 1 A was 2.1 h, which represented a fuel utilization of 36%. The performance of the DC-SOFC with reloaded fuel was nearly identical to its initial performance, which indicated that the YSZ electrolyte membrane substrate was stable when used in the DC-SOFCs. The degradation performance of the DC-SOFC during the discharge test was also analyzed.
2017, 33(2): 393-398
doi: 10.3866/PKU.WHXB201611033
Abstract:
Melamine and melem molecules are widely used precursors for synthesizing graphitic carbon nitride (g-C3N4), the latter also a hot two-dimensional material with photocatalytic applications. The molecular structures of both are respectively identical to the repeating units of two distinct g-C3N4 phases. In this work, the adsorption and self-assembly of melamine and melem on an Au(111) surface were investigated with low-temperature scanning tunneling microscopy (STM). Particularly, the patterns of hydrogen bonds (HBs) in their assemblies were identified and compared. It was found that melamine can only form one type of HB and two kinds of assembly structures, whereas melem can form three types of HBs and six kinds of assembly structures in total. Moreover, the involved HBs can be transformed by tip manipulation. These findings may provide a new strategy for tuning the functionality of surface self-assemblies by manipulating intermolecular hydrogen bonds. This also paves a route for the in situ synthesis of g-C3N4 on metallic surfaces and subsequent investigations of their physicochemical properties.
Melamine and melem molecules are widely used precursors for synthesizing graphitic carbon nitride (g-C3N4), the latter also a hot two-dimensional material with photocatalytic applications. The molecular structures of both are respectively identical to the repeating units of two distinct g-C3N4 phases. In this work, the adsorption and self-assembly of melamine and melem on an Au(111) surface were investigated with low-temperature scanning tunneling microscopy (STM). Particularly, the patterns of hydrogen bonds (HBs) in their assemblies were identified and compared. It was found that melamine can only form one type of HB and two kinds of assembly structures, whereas melem can form three types of HBs and six kinds of assembly structures in total. Moreover, the involved HBs can be transformed by tip manipulation. These findings may provide a new strategy for tuning the functionality of surface self-assemblies by manipulating intermolecular hydrogen bonds. This also paves a route for the in situ synthesis of g-C3N4 on metallic surfaces and subsequent investigations of their physicochemical properties.
Facet Effect on Surface Thermodynamic Properties and In-situ Photocatalytic Thermokinetics of Ag3PO4
2017, 33(2): 399-406
doi: 10.3866/PKU.WHXB201611092
Abstract:
Cubic{100}, tetrahedral{111}, and rhombic dodecahedral{110} Ag3PO4 microcrystals were synthesized via a facile wet chemical method. Their components, structure, morphology, and photoelectrical properties were characterized by field emission scanning electron microscopy (FE-SEM), X-ray powder diffraction (XRD), ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), photocurrent and photoluminescence (PL) analyses. The photocatalytic activity of the Ag3PO4 crystallites with different morphologies were investigated under visible illumination using rhodamine B (RhB) as a target contaminant. Meanwhile, the surface molar Gibbs free energy of the Ag3PO4 crystallites was determined by microcalorimetry via transition state theory and the thermochemical cycle principle. The corresponding values for cubic, tetrahedral, and rhombic dodecahedral microcrystals were 1.2972, 0.9621, and 0.5414 kJ·mol-1, respectively. The heat effect of the in-situ photocatalytic degradation of RhB and heat flow of the stable exothermic stage over the Ag3PO4 crystallites was detected by a LED-photocalorimeter. The results showed that the catalytic activity of Ag3PO4 crystallites and the heat effect and heat flow of the stable exothermic stage were positively correlated with their molar Gibbs free energy.Additionally, the main active species for the photocatalytic degradation of RhB over Ag3PO4 crystallites were determined by trapping experiments and electron paramagnetic resonance (ESR) spectroscopy.
Cubic{100}, tetrahedral{111}, and rhombic dodecahedral{110} Ag3PO4 microcrystals were synthesized via a facile wet chemical method. Their components, structure, morphology, and photoelectrical properties were characterized by field emission scanning electron microscopy (FE-SEM), X-ray powder diffraction (XRD), ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), photocurrent and photoluminescence (PL) analyses. The photocatalytic activity of the Ag3PO4 crystallites with different morphologies were investigated under visible illumination using rhodamine B (RhB) as a target contaminant. Meanwhile, the surface molar Gibbs free energy of the Ag3PO4 crystallites was determined by microcalorimetry via transition state theory and the thermochemical cycle principle. The corresponding values for cubic, tetrahedral, and rhombic dodecahedral microcrystals were 1.2972, 0.9621, and 0.5414 kJ·mol-1, respectively. The heat effect of the in-situ photocatalytic degradation of RhB and heat flow of the stable exothermic stage over the Ag3PO4 crystallites was detected by a LED-photocalorimeter. The results showed that the catalytic activity of Ag3PO4 crystallites and the heat effect and heat flow of the stable exothermic stage were positively correlated with their molar Gibbs free energy.Additionally, the main active species for the photocatalytic degradation of RhB over Ag3PO4 crystallites were determined by trapping experiments and electron paramagnetic resonance (ESR) spectroscopy.
2017, 33(2): 407-412
doi: 10.3866/PKU.WHXB201611032
Abstract:
The incorporation of europium-substituted polyoxometalate (PM) into chiral amphiphiles is attractive for the fabrication of multifunctional chiral luminescent liquid crystalline materials. Chiral amphiphiles acted as good promoters to trigger the achiral PM to show induced supramolecular chirality through electrostatic interactions, as illustrated by circular dichroism (CD) spectra. Differential scanning calorimetry (DSC), polarized optical microscopy (POM), and temperature-dependent X-ray diffraction (XRD) analysis confirmed that the organic/inorganic hybrid polyoxometalate complex exhibited thermotropic mesomorphic behaviors. In a cast film, the complex displayed intrinsic luminescence that could be adjusted by accurately controlling the temperature. The electrostatic encapsulation of PM with chiral mesomorphic promoters provides an effective method for constructing PM-based chiral luminescent liquid crystalline materials.
The incorporation of europium-substituted polyoxometalate (PM) into chiral amphiphiles is attractive for the fabrication of multifunctional chiral luminescent liquid crystalline materials. Chiral amphiphiles acted as good promoters to trigger the achiral PM to show induced supramolecular chirality through electrostatic interactions, as illustrated by circular dichroism (CD) spectra. Differential scanning calorimetry (DSC), polarized optical microscopy (POM), and temperature-dependent X-ray diffraction (XRD) analysis confirmed that the organic/inorganic hybrid polyoxometalate complex exhibited thermotropic mesomorphic behaviors. In a cast film, the complex displayed intrinsic luminescence that could be adjusted by accurately controlling the temperature. The electrostatic encapsulation of PM with chiral mesomorphic promoters provides an effective method for constructing PM-based chiral luminescent liquid crystalline materials.
2017, 33(2): 413-418
doi: 10.3866/PKU.WHXB201610241
Abstract:
Oxygen-containing hydroxyl (-C-OH) and carboxyl (-COOH) functional groups on both the basal planes and edges of the graphite oxide (GO) structure can dissociate to form H+ in water, thus providing cation exchange ability. The cation exchange capacity (CEC) of GO was measured accurately using the Stiasny method and the intermediate products of cation exchange processes of oxygen-containing functional groups and structure development were analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results indicated that the CEC of GO was up to 541.48 mmol/100 g. After NH4+ and Ca2+ exchange processes, GO still maintained a stable lamellar structure, and the c axis spacing increased by 0.1499 and 0.2905 nm, respectively. NH4+ and Ca2+ were mainly in the form of exchangeable cations in the interlayer space of GO, and formed a hydrated cation layer with water molecules, part of the containing[NH4(H2O)6]+ or[Ca(H2O)6]2+ formed near the edge of the structural layer, balancing the negative charges originating from hydrolysis of the carboxyl groups of the GO structural layer.
Oxygen-containing hydroxyl (-C-OH) and carboxyl (-COOH) functional groups on both the basal planes and edges of the graphite oxide (GO) structure can dissociate to form H+ in water, thus providing cation exchange ability. The cation exchange capacity (CEC) of GO was measured accurately using the Stiasny method and the intermediate products of cation exchange processes of oxygen-containing functional groups and structure development were analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results indicated that the CEC of GO was up to 541.48 mmol/100 g. After NH4+ and Ca2+ exchange processes, GO still maintained a stable lamellar structure, and the c axis spacing increased by 0.1499 and 0.2905 nm, respectively. NH4+ and Ca2+ were mainly in the form of exchangeable cations in the interlayer space of GO, and formed a hydrated cation layer with water molecules, part of the containing[NH4(H2O)6]+ or[Ca(H2O)6]2+ formed near the edge of the structural layer, balancing the negative charges originating from hydrolysis of the carboxyl groups of the GO structural layer.
2017, 33(2): 419-425
doi: 10.3866/PKU.WHXB201610192
Abstract:
PbTe thin films were epitaxially grown on BaF2(111) substrate using molecular beam epitaxy (MBE). In situ characterization by reflection high energy electron diffraction (RHEED) revealed a transition of the growth mode from 3D to 2D. Rotational symmetry studies combined with first principles density functional theory (DFT) calculations revealed that under Pb-rich and 350℃ substrate temperature (Tsub) growth conditions, stable (2×1) reconstructions appear on the PbTe(111) surface. When the surface of PbTe(111)-(2×1) was covered with Te, the stable (2×1) reconstructions could be retrieved under 300℃ annealing. This provides an effective method for the protection of PbTe film surfaces from the atmospheric environment.
PbTe thin films were epitaxially grown on BaF2(111) substrate using molecular beam epitaxy (MBE). In situ characterization by reflection high energy electron diffraction (RHEED) revealed a transition of the growth mode from 3D to 2D. Rotational symmetry studies combined with first principles density functional theory (DFT) calculations revealed that under Pb-rich and 350℃ substrate temperature (Tsub) growth conditions, stable (2×1) reconstructions appear on the PbTe(111) surface. When the surface of PbTe(111)-(2×1) was covered with Te, the stable (2×1) reconstructions could be retrieved under 300℃ annealing. This provides an effective method for the protection of PbTe film surfaces from the atmospheric environment.
2017, 33(2): 426-434
doi: 10.3866/PKU.WHXB201609291
Abstract:
Carbohydrates chips are powerful tools for quantitatively studying protein-carbohydrate interactions. Typically, carbohydrate chips are prepared using the self-assembly of carbohydrate thiol/disulfide, which always requires multiple hydroxyl group protection/deprotection steps resulting low conversion in the preparation. In this paper, a kind of carbohydrate derivatives containing dithiocarbamate (DTC) group was synthesized through a two-step reaction to prepare self-assembled monolayers presenting carbohydrate (glycol-DTC SAMs). The glycol-DTC SAMs was characterized using X-ray photoelectron spectroscopy (XPS) and the protein binding activity was quantitatively analysized using surface plasma resonance (SPR) and enzyme linked lectin assay (ELLA). By mixed self-assembly of carbohydrate dithiocarbamate and sarcosine dithiocarbamate, Glycol-DTC SAMs with different glucose density were prepared. The protein binding kinetics was monitored in real time and the thermodynamics was calculated. Interestingly, a 1:1 binding of concanavalin A (Con A) was obtained on the SAMs prepared in solution containing 1% glucose-DTC, as the dissociation constant (Kd) was calculated to be (39.10±0.12) μmol·L-1. A 1:2 binding of Con A was obtained on the SAMs prepared in solutions containing >2% glucose-DTC, as the Kd was calculated to be (1.17±0.18) μmol·L-1. By simply mixed selfassembly, multivalent binding of Con A can be realized and separate kinetic parameters can be obtained. Our work would promote the study of protein-carbohydrate interactions and be helpful for revealing the relevant biological progress.
Carbohydrates chips are powerful tools for quantitatively studying protein-carbohydrate interactions. Typically, carbohydrate chips are prepared using the self-assembly of carbohydrate thiol/disulfide, which always requires multiple hydroxyl group protection/deprotection steps resulting low conversion in the preparation. In this paper, a kind of carbohydrate derivatives containing dithiocarbamate (DTC) group was synthesized through a two-step reaction to prepare self-assembled monolayers presenting carbohydrate (glycol-DTC SAMs). The glycol-DTC SAMs was characterized using X-ray photoelectron spectroscopy (XPS) and the protein binding activity was quantitatively analysized using surface plasma resonance (SPR) and enzyme linked lectin assay (ELLA). By mixed self-assembly of carbohydrate dithiocarbamate and sarcosine dithiocarbamate, Glycol-DTC SAMs with different glucose density were prepared. The protein binding kinetics was monitored in real time and the thermodynamics was calculated. Interestingly, a 1:1 binding of concanavalin A (Con A) was obtained on the SAMs prepared in solution containing 1% glucose-DTC, as the dissociation constant (Kd) was calculated to be (39.10±0.12) μmol·L-1. A 1:2 binding of Con A was obtained on the SAMs prepared in solutions containing >2% glucose-DTC, as the Kd was calculated to be (1.17±0.18) μmol·L-1. By simply mixed selfassembly, multivalent binding of Con A can be realized and separate kinetic parameters can be obtained. Our work would promote the study of protein-carbohydrate interactions and be helpful for revealing the relevant biological progress.
2017, 33(2): 435-440
doi: 10.3866/PKU.WHXB201611101
Abstract:
An Au nanoparticle/agarose composite film was fabricated using room temperature electron reduction with argon glow discharge as a cheap electron source. The synthetic procedure was facile, easy, and green. Characterization by UV-Vis spectrophotometry (UV-Vis), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) revealed that the distribution of Au nanoparticles in the composite film could be tuned by varying the concentration of HAuCl4, while the shape of Au nanoparticles could be controlled by adding polyvinyl pyrrolidone (PVP). The Au nanoparticles were closely packed in the composite film, making an excellent surface enhanced Raman scattering (SERS)-active substrate. A SERS enhanced factor (EF) of over 106 and detection limit as low as 10-12 mol·L-1 were obtained for SERS detection using 4-aminothiophenol (4-ATP) as the probe. Moreover, the composite film possessed good uniformity and stability as a SERS substrate.
An Au nanoparticle/agarose composite film was fabricated using room temperature electron reduction with argon glow discharge as a cheap electron source. The synthetic procedure was facile, easy, and green. Characterization by UV-Vis spectrophotometry (UV-Vis), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) revealed that the distribution of Au nanoparticles in the composite film could be tuned by varying the concentration of HAuCl4, while the shape of Au nanoparticles could be controlled by adding polyvinyl pyrrolidone (PVP). The Au nanoparticles were closely packed in the composite film, making an excellent surface enhanced Raman scattering (SERS)-active substrate. A SERS enhanced factor (EF) of over 106 and detection limit as low as 10-12 mol·L-1 were obtained for SERS detection using 4-aminothiophenol (4-ATP) as the probe. Moreover, the composite film possessed good uniformity and stability as a SERS substrate.
