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2019 Volume 77 Issue 7
2019, 77(7): 581-597
doi: 10.6023/A19040128
Abstract:
Polysaccharides are a class of bio-macromolecules with highly complex structures that are widely found in living organisms such as microorganisms, plants and animals. Polysaccharides serve not only as structural components and energy sources of cells, but also as important signaling molecules which are involved in many key biological processes. Studies on polysaccharide-mediated biological processes require access to structurally defined molecules, which approach the size and complexity of those found in nature, but naturally-occurring polysaccharides usually exist in microheterogeneous forms, making it difficult or even impossible to isolate pure polysaccharides from natural sources in most cases. Chemical synthesis represents a reliable solution to this problem, which can provide polysaccharide samples with defined chemical structures for functional studies and even a library of analogs of natural glycans for structure-activity relationship investigations. But unlike oligonucleotides and peptides, which can already be obtained by automated synthesizers in a very short of time, the chemical synthesis of glycans remains a great challenge for synthetic chemists. The major challenge for glycan synthesis lies in the need to handle both stereo-and regio-chemistry in the construction of each glycosyl linkage, and the extensive protecting-group manipulations as well as much intermediate separation make it a tedious and time-consuming process. Over the past decades, carbohydrate chemists have developed many glycosylation reactions. A series of strategies for glycan assembly have been also established. The advances in both synthetic methods and strategies have significantly increased the synthetic efficiency of carbohydrate molecules, and many great accomplishments in the field of polysaccharide synthesis have been witnessed in recent decades. Some representative methods and strategies, and their successful applications in the chemical synthesis of complex polysaccharides are summarized in this review.
Polysaccharides are a class of bio-macromolecules with highly complex structures that are widely found in living organisms such as microorganisms, plants and animals. Polysaccharides serve not only as structural components and energy sources of cells, but also as important signaling molecules which are involved in many key biological processes. Studies on polysaccharide-mediated biological processes require access to structurally defined molecules, which approach the size and complexity of those found in nature, but naturally-occurring polysaccharides usually exist in microheterogeneous forms, making it difficult or even impossible to isolate pure polysaccharides from natural sources in most cases. Chemical synthesis represents a reliable solution to this problem, which can provide polysaccharide samples with defined chemical structures for functional studies and even a library of analogs of natural glycans for structure-activity relationship investigations. But unlike oligonucleotides and peptides, which can already be obtained by automated synthesizers in a very short of time, the chemical synthesis of glycans remains a great challenge for synthetic chemists. The major challenge for glycan synthesis lies in the need to handle both stereo-and regio-chemistry in the construction of each glycosyl linkage, and the extensive protecting-group manipulations as well as much intermediate separation make it a tedious and time-consuming process. Over the past decades, carbohydrate chemists have developed many glycosylation reactions. A series of strategies for glycan assembly have been also established. The advances in both synthetic methods and strategies have significantly increased the synthetic efficiency of carbohydrate molecules, and many great accomplishments in the field of polysaccharide synthesis have been witnessed in recent decades. Some representative methods and strategies, and their successful applications in the chemical synthesis of complex polysaccharides are summarized in this review.
2019, 77(7): 598-612
doi: 10.6023/A19050166
Abstract:
The reduction of esters to alcohols is one of the most important chemical transformations in the production of fine chemicals, such as pharmaceuticals, agricultural chemicals, fragrances, and biofuels. Homogeneous catalytic hydrogenation of esters represents a green, atom-economic, and sustainable alternative to conventional stoichiometric approaches, avoiding the generation of large amount of wastes and the difficulties arose in work-up procedure by using metal hydride reductants. Although challenges still exist, significant progress has been made in catalytic hydrogenation of esters over the last ten years. Numerous transition metal catalysts including noble metal (such as ruthenium, osmium, and iridium) complexes and base metal catalysts (such as iron, cobalt, and manganese) have been developed for the hydrogenation of esters. The ligands of the catalysts have been well studied. A wide range of bidentate ligands including diamines, amino-phosphines, pyridine-amines, N-heterocyclic carbene-amines, and bipyridines, tridentate pincer ligands containing diethylamine and pyridine skeletons, tetradentate ligands containing pyridine and bipyridine skeletons have been applied in the hydrogenation of esters. The efficiency of hydrogenation of esters has been significantly improved, and the highest turnover number (TON) reached 90000 for the hydrogenation of benchmark substrates such as ethyl acetate, ethyl benzoate, and γ-valerolactone. A significant breakthrough has also been made in the catalytic asymmetric hydrogenation of esters to chiral primary alcohols. The asymmetric hydrogenations of ketoesters, racemic δ-hydroxyesters, and racemic α-aryl/alkyl substituted lactones provided efficient methods for the asymmetric synthesis of optically active chiral diols including chiral 1, 5-diols and 1, 4-diols. The significant progress achieved in recent years in the area of homogeneous catalytic hydrogenation of esters to alcohols is presented in this review. The focus of this review are the development of ligands and catalysts, and the advances in the catalytic asymmetric hydrogenation of esters and lactones.
The reduction of esters to alcohols is one of the most important chemical transformations in the production of fine chemicals, such as pharmaceuticals, agricultural chemicals, fragrances, and biofuels. Homogeneous catalytic hydrogenation of esters represents a green, atom-economic, and sustainable alternative to conventional stoichiometric approaches, avoiding the generation of large amount of wastes and the difficulties arose in work-up procedure by using metal hydride reductants. Although challenges still exist, significant progress has been made in catalytic hydrogenation of esters over the last ten years. Numerous transition metal catalysts including noble metal (such as ruthenium, osmium, and iridium) complexes and base metal catalysts (such as iron, cobalt, and manganese) have been developed for the hydrogenation of esters. The ligands of the catalysts have been well studied. A wide range of bidentate ligands including diamines, amino-phosphines, pyridine-amines, N-heterocyclic carbene-amines, and bipyridines, tridentate pincer ligands containing diethylamine and pyridine skeletons, tetradentate ligands containing pyridine and bipyridine skeletons have been applied in the hydrogenation of esters. The efficiency of hydrogenation of esters has been significantly improved, and the highest turnover number (TON) reached 90000 for the hydrogenation of benchmark substrates such as ethyl acetate, ethyl benzoate, and γ-valerolactone. A significant breakthrough has also been made in the catalytic asymmetric hydrogenation of esters to chiral primary alcohols. The asymmetric hydrogenations of ketoesters, racemic δ-hydroxyesters, and racemic α-aryl/alkyl substituted lactones provided efficient methods for the asymmetric synthesis of optically active chiral diols including chiral 1, 5-diols and 1, 4-diols. The significant progress achieved in recent years in the area of homogeneous catalytic hydrogenation of esters to alcohols is presented in this review. The focus of this review are the development of ligands and catalysts, and the advances in the catalytic asymmetric hydrogenation of esters and lactones.
2019, 77(7): 613-624
doi: 10.6023/A19030094
Abstract:
Observations of OH Radical Reactivity in Field Studies Yang, Xinpinga, b Wang, Haichaoa, b Tan, Zhaofenga, b, c Lu, Keding*, a, b Zhang, Yuanhang*, a, b, d, e (a State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871) (b International Joint Research Center for Atmospheric Research, Peking University, Beijing 100871) (c Institute of Energy and Climate Research, IEK-8:Troposphere, Forschungszentrum Jülich GmbH, Jülich, Germany 52425) (d CAS Center for Excellence in Regional Atmospheric Environment, Chinese Academy of Sciences, Xiamen 361021) (e Beijing Innovation Center for Engineering Sciences and Advanced Technology, Peking University, Beijing 100871) Abstract The hydroxyl radical (OH) is the main source of atmospheric oxidation capacity, which oxidizes the primary pollutants into the secondary pollutants. Therefore, the measurements and characterization of source and sink of OH radical are critical to understand the formation mechanism of regional secondary pollution. However, the removal routes of OH radical still cannot be quantified accurately. OH radical reactivity can describe the OH total loss rate and the atmospheric oxidation, thus playing an important role in the OH budget analysis. The OH radical reactivity is defined as the total pseudo first-order rate coefficient for all atmospheric reactions of OH in an air parcel. It is challenging to accurately measure the OH radical reactivity due to the high activity and short life of OH radical. In this paper, we summarized all kinds of measurement techniques used in the field observations of OH radical reactivity, including Total OH Loss-rate Measurement (TOHLM), Laser flash Photolysis-Laser Induced Fluorescence (LP-LIF), Chemical Ionisation Mass Spectrometry (CIMS) and Comparative Reactivity Method (CRM). The techniques were reviewed on the aspects of measurement principles, instrument modules, and so on. Overall, LP-LIF is proposed to be the best technical approach. In addition, the measured OH radical reactivity and the major scientific findings of corresponding measurement campaigns conducted in typical tropospheric conditions as urban, forest and rural environments, etc. were outlined. The OH radical reactivity varies significantly in different conditions, ranging from less than 10 per second to hundreds. Comparison of measured OH radical reactivity and the calculated or modeling results reveals a significant missing reactivity, ranging from 20% to over 80% in some environments. Depending on the emission and pollution characteristics of the field observation sites, the sources of missing reactivity are generally attributed to the undetected or unknown organic species, i.e. primary organic species, secondary organic species or a combination of both. The accurate observation and the numerical modeling of the OH radical reactivity can provide a possibility for achieving numerical closure study of ROx radicals. Finally, we discussed the current research difficulties and possible new directions for future studies of the OH radical reactivity.
Observations of OH Radical Reactivity in Field Studies Yang, Xinpinga, b Wang, Haichaoa, b Tan, Zhaofenga, b, c Lu, Keding*, a, b Zhang, Yuanhang*, a, b, d, e (a State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871) (b International Joint Research Center for Atmospheric Research, Peking University, Beijing 100871) (c Institute of Energy and Climate Research, IEK-8:Troposphere, Forschungszentrum Jülich GmbH, Jülich, Germany 52425) (d CAS Center for Excellence in Regional Atmospheric Environment, Chinese Academy of Sciences, Xiamen 361021) (e Beijing Innovation Center for Engineering Sciences and Advanced Technology, Peking University, Beijing 100871) Abstract The hydroxyl radical (OH) is the main source of atmospheric oxidation capacity, which oxidizes the primary pollutants into the secondary pollutants. Therefore, the measurements and characterization of source and sink of OH radical are critical to understand the formation mechanism of regional secondary pollution. However, the removal routes of OH radical still cannot be quantified accurately. OH radical reactivity can describe the OH total loss rate and the atmospheric oxidation, thus playing an important role in the OH budget analysis. The OH radical reactivity is defined as the total pseudo first-order rate coefficient for all atmospheric reactions of OH in an air parcel. It is challenging to accurately measure the OH radical reactivity due to the high activity and short life of OH radical. In this paper, we summarized all kinds of measurement techniques used in the field observations of OH radical reactivity, including Total OH Loss-rate Measurement (TOHLM), Laser flash Photolysis-Laser Induced Fluorescence (LP-LIF), Chemical Ionisation Mass Spectrometry (CIMS) and Comparative Reactivity Method (CRM). The techniques were reviewed on the aspects of measurement principles, instrument modules, and so on. Overall, LP-LIF is proposed to be the best technical approach. In addition, the measured OH radical reactivity and the major scientific findings of corresponding measurement campaigns conducted in typical tropospheric conditions as urban, forest and rural environments, etc. were outlined. The OH radical reactivity varies significantly in different conditions, ranging from less than 10 per second to hundreds. Comparison of measured OH radical reactivity and the calculated or modeling results reveals a significant missing reactivity, ranging from 20% to over 80% in some environments. Depending on the emission and pollution characteristics of the field observation sites, the sources of missing reactivity are generally attributed to the undetected or unknown organic species, i.e. primary organic species, secondary organic species or a combination of both. The accurate observation and the numerical modeling of the OH radical reactivity can provide a possibility for achieving numerical closure study of ROx radicals. Finally, we discussed the current research difficulties and possible new directions for future studies of the OH radical reactivity.
2019, 77(7): 625-633
doi: 10.6023/A19010040
Abstract:
Na-ion batteries with lower cost than Li-ion batteries would be developed to large-scale energy-storage device to store solar and wind energies. However, large radius renders Na+ ions to insert into/extract out the layered transition metal oxides (LTMOs) sluggishly. To improve the intercalation dynamics of Na+ ions, the interlayer spacing of crystals has to be expanded for those LTMOs that are capable of fast lithiation and delithiation. Herein, a LTMO based on vanadium is firstly doped with larger K+ ions to expand the interlayer spacing to yield K+-doped sodium vanadate (Na5KxV12O32) cathode material by a hydrothermal method at 200℃ for 24 h followed by calcination at 500℃ for 3 h. The samples were characterized by scanning electron microscope (SEM)/transmission electron microscope (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) technologies. Effect of the doping amount of K+ on the structure and sodium-storage performance of the sample was studied in detail. The synthesized materials display nanoplate morphology viewing from the TEM images. K+ ions are doped into the interlayer of the sodium vanadate crystallites, which is proved by analysis of the XRD patterns and XPS spectra. Expanded interlayer spacing favors Na+ ions' intercalation and deintercalation between the[V3O8]- layers, which is testified by the chemical diffusion coefficient of cathodes, thus enhancing the rate capability. On the other hand, the chemically pre-intercalated K+ ions are pinned in the crystallites during insertion and extraction of Na+ ions and act as pillars to stabilize the layered structure, improving the cycliability of the cathode. However, excessive doping of K+ leads to a discounted rate capability of the cathode, suggesting an optimized amount of K+ doping into the crystal. The results from galvanostatic charge-discharge tests indicate that the obtained NVO(3K) sample, in which 0.118 mol of K+ ions are doped into per mol of Na5V12O32, presents the best electrochemical performance among the various samples. It can deliver the maximum capacities of 169, 160, 148, 132, 98 and 69 mAh·g-1 at the rates of 0.1C, 0.2C, 0.5C, 1C, 3C and 10C after activated for several times over the voltage window of 4.0~1.5 V (vs. Na+/Na), respectively. Even run at 3C rate, it can retain 93.0% of the maximum capacity after 1000 cycles, exhibiting excellent rate capability and stable cycliability. The results suggest that doping of K+ ions into the interlayer of crystallites can significantly improving the rate capability as well as cycling performance of the obtained Na5V12O32. Our investigation demonstrates that design of K+-doped sodium vanadate cathode materials is beneficial for harvesting superior performance, of which the Na5K0.118V12O32 nanoplates can be developed into a novel cathode material for sodium-ion batteries in the future.
Na-ion batteries with lower cost than Li-ion batteries would be developed to large-scale energy-storage device to store solar and wind energies. However, large radius renders Na+ ions to insert into/extract out the layered transition metal oxides (LTMOs) sluggishly. To improve the intercalation dynamics of Na+ ions, the interlayer spacing of crystals has to be expanded for those LTMOs that are capable of fast lithiation and delithiation. Herein, a LTMO based on vanadium is firstly doped with larger K+ ions to expand the interlayer spacing to yield K+-doped sodium vanadate (Na5KxV12O32) cathode material by a hydrothermal method at 200℃ for 24 h followed by calcination at 500℃ for 3 h. The samples were characterized by scanning electron microscope (SEM)/transmission electron microscope (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) technologies. Effect of the doping amount of K+ on the structure and sodium-storage performance of the sample was studied in detail. The synthesized materials display nanoplate morphology viewing from the TEM images. K+ ions are doped into the interlayer of the sodium vanadate crystallites, which is proved by analysis of the XRD patterns and XPS spectra. Expanded interlayer spacing favors Na+ ions' intercalation and deintercalation between the[V3O8]- layers, which is testified by the chemical diffusion coefficient of cathodes, thus enhancing the rate capability. On the other hand, the chemically pre-intercalated K+ ions are pinned in the crystallites during insertion and extraction of Na+ ions and act as pillars to stabilize the layered structure, improving the cycliability of the cathode. However, excessive doping of K+ leads to a discounted rate capability of the cathode, suggesting an optimized amount of K+ doping into the crystal. The results from galvanostatic charge-discharge tests indicate that the obtained NVO(3K) sample, in which 0.118 mol of K+ ions are doped into per mol of Na5V12O32, presents the best electrochemical performance among the various samples. It can deliver the maximum capacities of 169, 160, 148, 132, 98 and 69 mAh·g-1 at the rates of 0.1C, 0.2C, 0.5C, 1C, 3C and 10C after activated for several times over the voltage window of 4.0~1.5 V (vs. Na+/Na), respectively. Even run at 3C rate, it can retain 93.0% of the maximum capacity after 1000 cycles, exhibiting excellent rate capability and stable cycliability. The results suggest that doping of K+ ions into the interlayer of crystallites can significantly improving the rate capability as well as cycling performance of the obtained Na5V12O32. Our investigation demonstrates that design of K+-doped sodium vanadate cathode materials is beneficial for harvesting superior performance, of which the Na5K0.118V12O32 nanoplates can be developed into a novel cathode material for sodium-ion batteries in the future.
2019, 77(7): 634-640
doi: 10.6023/A19030103
Abstract:
In this study, electrochemical impedance spectroscopy (EIS) combined with cyclic volt-ampere (CV), charge-discharge measurement and scanning electron microscope were used. The electrode interface characteristics of hard carbon electrodes for sodium ion batteries in 1 mol/L NaClO4-EC:DEC and 1 mol/L-NaClO4-EC:DEC:PC electrolyte systems were discussed. The hard carbon material electrode is composed of 80 wt% active material, 10 wt% PVDF-HFP adhesive and 10 wt% conductive carbon black. The charge and discharge performance was tested with 2032 button battery and metal sodium sheet as counter electrode, the charge and discharge rate was 0.1 C, and the cut-off voltage was 0~3 V. The three-electrode glass cell system was used for CV and EIS test, and the metal sodium sheet was used as the reference and auxiliary electrode. In the CV test, the scanning speed is 1 mV/s, EIS and the frequency scanning range is 105 to 10-2 Hz. The amplitude of AC signal applied by 2 mV is 5 mV. The electrochemical impedance spectra obtained in the experiment were simulated by Zview software. The results of CV show that the intercalation process of sodium ion in hard carbon materials is mainly divided into two steps, that is, the filling process of sodium ion in nano-pores, the intercalation of sodium ion in graphene layer and the adsorption and desorption of sodium ion on the surface or defect. The filling process of sodium ion in the nanoporous is accompanied by the formation of solid electrolyte interface (SEI) film on the surface of the electrode. The results of electrochemical impedance spectroscopy show that the spectrum consists of two semicircles and a oblique line, which can be attributed to the contact impedance, the diffusion of sodium ions through SEI film and the process of charge transfer. The oblique domain reflects the oblique line related to the solid diffusion of sodium ion in the particles of hard carbon materials. By selecting the appropriate equivalent circuit and fitting the experimental results, we can get the variation of SEI film resistance and electron resistance with the electrode polarization potential in the process of sodium insertion in the first week of the hard carbon electrode.
In this study, electrochemical impedance spectroscopy (EIS) combined with cyclic volt-ampere (CV), charge-discharge measurement and scanning electron microscope were used. The electrode interface characteristics of hard carbon electrodes for sodium ion batteries in 1 mol/L NaClO4-EC:DEC and 1 mol/L-NaClO4-EC:DEC:PC electrolyte systems were discussed. The hard carbon material electrode is composed of 80 wt% active material, 10 wt% PVDF-HFP adhesive and 10 wt% conductive carbon black. The charge and discharge performance was tested with 2032 button battery and metal sodium sheet as counter electrode, the charge and discharge rate was 0.1 C, and the cut-off voltage was 0~3 V. The three-electrode glass cell system was used for CV and EIS test, and the metal sodium sheet was used as the reference and auxiliary electrode. In the CV test, the scanning speed is 1 mV/s, EIS and the frequency scanning range is 105 to 10-2 Hz. The amplitude of AC signal applied by 2 mV is 5 mV. The electrochemical impedance spectra obtained in the experiment were simulated by Zview software. The results of CV show that the intercalation process of sodium ion in hard carbon materials is mainly divided into two steps, that is, the filling process of sodium ion in nano-pores, the intercalation of sodium ion in graphene layer and the adsorption and desorption of sodium ion on the surface or defect. The filling process of sodium ion in the nanoporous is accompanied by the formation of solid electrolyte interface (SEI) film on the surface of the electrode. The results of electrochemical impedance spectroscopy show that the spectrum consists of two semicircles and a oblique line, which can be attributed to the contact impedance, the diffusion of sodium ions through SEI film and the process of charge transfer. The oblique domain reflects the oblique line related to the solid diffusion of sodium ion in the particles of hard carbon materials. By selecting the appropriate equivalent circuit and fitting the experimental results, we can get the variation of SEI film resistance and electron resistance with the electrode polarization potential in the process of sodium insertion in the first week of the hard carbon electrode.
2019, 77(7): 641-646
doi: 10.6023/A19040156
Abstract:
The promising application of surface-enhanced Raman spectroscopy (SERS) was definitely based on the high quality substrates which were restricted to the rough noble metals and colloidal nanoparticle materials. However, semiconductor has become a potential substrate for the SERS investigation due to its high stability and reproducibility. It remains significant challenges in interpreting the enhancement mechanisms. Herein, broom-like ZnO nanoparticles with novel morphology and uniform size was prepared by pyrolysis of (CH3COO)2Zn. By using p-nitrophenylthiophenol (PNTP), phenylthiophenol (TP) and p-aminophenylthiophenol (PATP) as probe molecules, the SERS effect on ZnO surfaces was systematically studied under the irradiation of excitation lines with the wavelength of 532 nm and 638 nm. The different substituents in p-position of TP allowed to change the energy levels by the electron withdrawing or donating group, it was beneficial to match the energy level gap between the probe molecules and semiconductor for triggering the photon driven charge transfer. The surface enhancement factor (EF) of broom-like ZnO nanoparticles were estimated accordingly, and the contribution of non-resonance and charge transfer to SERS effect was distinguished. The results demonstrated that the surface enhancement factor was about 10 to 35 times depending on the probe molecules and excitation wavelengths. Therefore, the different enhancement origination contributed to the different molecules on the ZnO substrate. For the TP and PATP, the charge transfer from the HOMO level of molecule to CB of ZnO was achieved by the assistance of the laser photon with the appropriate energy. Moreover, the higher energy of the photon is, the stronger the SERS enhancement effect. As for the PNTP, the photon driven charge transfer was absent due to the significant change of the HOMO and LUMO level caused by the electron withdrawing group of NO2. It revealed that the enhancement effect of PNTP molecule about 10 times was contributed by the non-resonance enhancement mechanism which was mainly due to the changes in the polarizability caused by the chemical adsorption. Comparing to the noble metal surface, the enhancement of charge transfer on ZnO was decreased with 1~2 orders of magnitude. The relatively lower rate of charge transfer in semiconductor resulted in the decrease of the charge transfer enhancement. The preliminary studies provided a novel approach for the preparation and regulation of new semiconductor SERS substrates.
The promising application of surface-enhanced Raman spectroscopy (SERS) was definitely based on the high quality substrates which were restricted to the rough noble metals and colloidal nanoparticle materials. However, semiconductor has become a potential substrate for the SERS investigation due to its high stability and reproducibility. It remains significant challenges in interpreting the enhancement mechanisms. Herein, broom-like ZnO nanoparticles with novel morphology and uniform size was prepared by pyrolysis of (CH3COO)2Zn. By using p-nitrophenylthiophenol (PNTP), phenylthiophenol (TP) and p-aminophenylthiophenol (PATP) as probe molecules, the SERS effect on ZnO surfaces was systematically studied under the irradiation of excitation lines with the wavelength of 532 nm and 638 nm. The different substituents in p-position of TP allowed to change the energy levels by the electron withdrawing or donating group, it was beneficial to match the energy level gap between the probe molecules and semiconductor for triggering the photon driven charge transfer. The surface enhancement factor (EF) of broom-like ZnO nanoparticles were estimated accordingly, and the contribution of non-resonance and charge transfer to SERS effect was distinguished. The results demonstrated that the surface enhancement factor was about 10 to 35 times depending on the probe molecules and excitation wavelengths. Therefore, the different enhancement origination contributed to the different molecules on the ZnO substrate. For the TP and PATP, the charge transfer from the HOMO level of molecule to CB of ZnO was achieved by the assistance of the laser photon with the appropriate energy. Moreover, the higher energy of the photon is, the stronger the SERS enhancement effect. As for the PNTP, the photon driven charge transfer was absent due to the significant change of the HOMO and LUMO level caused by the electron withdrawing group of NO2. It revealed that the enhancement effect of PNTP molecule about 10 times was contributed by the non-resonance enhancement mechanism which was mainly due to the changes in the polarizability caused by the chemical adsorption. Comparing to the noble metal surface, the enhancement of charge transfer on ZnO was decreased with 1~2 orders of magnitude. The relatively lower rate of charge transfer in semiconductor resulted in the decrease of the charge transfer enhancement. The preliminary studies provided a novel approach for the preparation and regulation of new semiconductor SERS substrates.
2019, 77(7): 647-652
doi: 10.6023/A19040119
Abstract:
Lithium ion batteries have dominated the field of energy storage for portal electronics during the past twenty years, and now it is ambitious to power electric vehicles. However, drawbacks of limited power density and cycle life time as well as cost and safety concerns lead to limitations for the emerging large-scale stationary energy storage application. Therefore, researchers all over the world have been dedicated to find alternative next-generation energy storage technologies. Rechargeable Al-ion battery is emerging as one of the most promising sustainable candidates for the usage of large-scale energy storage because of its low-cost, high charge/discharge rate capability and extremely long cycling life. However, currently most of the Al-ion battery has been developed by using of liquid electrolyte, such as ionic liquid, urea and molten salt electrolyte, which has the risk of electrolyte leakaging. Electrolyte evaporation also occurs when batteries undergo extremely long cycling charge/discharge process. While making all-solid-state Al-ion battery is able to effectively solve the leakaging problem, but there are few reports on this topic. What is more, the all-solid-state Al-ion battery also has higher energy density due to device structure design of using no separators and bulky packaging. In this paper, we have developed a new kind of solid Al-ion electrolyte by using crown ether as both functional additive and coordination group and polyethyleneglycols (PEO) as basement through a solution casting method. Experiment tests indicates that the crown ether could not only yield a good stability and compatibility of Al ions with PEO but also reduce the crystallinity of composite electrolyte, which is helpful for achieving high ion conductivity. The obtained AF solid-state electrolyte has a high ion-conductivity (5.5×10-6 S/cm at room temperature, 1.86×10-3 S/cm at 100℃), broad electrochemical potential window (0~3 V) and strong mechanical property. This work provides applicable high-performance polymer electrolyte and paves the way to develop the full all-solid-state Al-ion batteries.
Lithium ion batteries have dominated the field of energy storage for portal electronics during the past twenty years, and now it is ambitious to power electric vehicles. However, drawbacks of limited power density and cycle life time as well as cost and safety concerns lead to limitations for the emerging large-scale stationary energy storage application. Therefore, researchers all over the world have been dedicated to find alternative next-generation energy storage technologies. Rechargeable Al-ion battery is emerging as one of the most promising sustainable candidates for the usage of large-scale energy storage because of its low-cost, high charge/discharge rate capability and extremely long cycling life. However, currently most of the Al-ion battery has been developed by using of liquid electrolyte, such as ionic liquid, urea and molten salt electrolyte, which has the risk of electrolyte leakaging. Electrolyte evaporation also occurs when batteries undergo extremely long cycling charge/discharge process. While making all-solid-state Al-ion battery is able to effectively solve the leakaging problem, but there are few reports on this topic. What is more, the all-solid-state Al-ion battery also has higher energy density due to device structure design of using no separators and bulky packaging. In this paper, we have developed a new kind of solid Al-ion electrolyte by using crown ether as both functional additive and coordination group and polyethyleneglycols (PEO) as basement through a solution casting method. Experiment tests indicates that the crown ether could not only yield a good stability and compatibility of Al ions with PEO but also reduce the crystallinity of composite electrolyte, which is helpful for achieving high ion conductivity. The obtained AF solid-state electrolyte has a high ion-conductivity (5.5×10-6 S/cm at room temperature, 1.86×10-3 S/cm at 100℃), broad electrochemical potential window (0~3 V) and strong mechanical property. This work provides applicable high-performance polymer electrolyte and paves the way to develop the full all-solid-state Al-ion batteries.
2019, 77(7): 653-660
doi: 10.6023/A19040113
Abstract:
It is a more attractive strategy that the selective oxidation of amines to the corresponding imines driven by visible light and photocatalyst. However, it is still necessary to look further into the mechanism of the transformation. In order to advance a new green photocatalysts system under milder conditions, hierarchical In2S3 nanotubes, which maintained the mother skeleton of NH2-MIL-68(In), was prepared from NH2-MIL-68(In) and thiourea, and a cation exchange method was used to synthesize hierarchical In2S3/CdIn2S4 heterostructured composites. The structure, morphology and photoelectric properties of the catalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS), fluorescence spectroscopy (PL) and electrochemical impedance spectra (EIS) analysis. The results showed that the existence of heterojunction between In2S3 and CdIn2S4 could minimize the recombination rate of photogenerated electron-hole pairs, which made the In2S3/CdIn2S4 show superior catalytic activity. The results of the evaluated experiments under visible light illumination showed that lots of synergy existed between the hierarchical structure, and the heterostructure could help to enhance the efficiency of carriers transfer and separation, which resulting in a high photocatalytic efficiency of In2S3/CdIn2S4 nanohybrids for the oxidation coupling of benzyl amines to imines under visible light irradiation. Interestingly, the further investigation concerned to the reaction condition revealed that the product could be detected not only in air but also in N2 conditions, which burst out of the restriction of the reported reaction conditions and made the condition of the conversion become milder. The possible photocatalytic mechanism for the transformation was investigated by a series of experiments which concerned to the catching of the active species. The results showed that the reason for the occurring of the reaction was initiated by the presence of the nitrogen-centered radical cations and the carbon-centered radicals which were induced by the photogenerated hole (h+) in the photocatalyst. As for these situations, the conditions for the conversion of benzyl amines to imines were milder than the reported ones ever. What's more, from our experiments, the catalysts can be recycled five times at least, which indicated good reusability of hierarchical In2S3/CdIn2S4 nanohybrids.
It is a more attractive strategy that the selective oxidation of amines to the corresponding imines driven by visible light and photocatalyst. However, it is still necessary to look further into the mechanism of the transformation. In order to advance a new green photocatalysts system under milder conditions, hierarchical In2S3 nanotubes, which maintained the mother skeleton of NH2-MIL-68(In), was prepared from NH2-MIL-68(In) and thiourea, and a cation exchange method was used to synthesize hierarchical In2S3/CdIn2S4 heterostructured composites. The structure, morphology and photoelectric properties of the catalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS), fluorescence spectroscopy (PL) and electrochemical impedance spectra (EIS) analysis. The results showed that the existence of heterojunction between In2S3 and CdIn2S4 could minimize the recombination rate of photogenerated electron-hole pairs, which made the In2S3/CdIn2S4 show superior catalytic activity. The results of the evaluated experiments under visible light illumination showed that lots of synergy existed between the hierarchical structure, and the heterostructure could help to enhance the efficiency of carriers transfer and separation, which resulting in a high photocatalytic efficiency of In2S3/CdIn2S4 nanohybrids for the oxidation coupling of benzyl amines to imines under visible light irradiation. Interestingly, the further investigation concerned to the reaction condition revealed that the product could be detected not only in air but also in N2 conditions, which burst out of the restriction of the reported reaction conditions and made the condition of the conversion become milder. The possible photocatalytic mechanism for the transformation was investigated by a series of experiments which concerned to the catching of the active species. The results showed that the reason for the occurring of the reaction was initiated by the presence of the nitrogen-centered radical cations and the carbon-centered radicals which were induced by the photogenerated hole (h+) in the photocatalyst. As for these situations, the conditions for the conversion of benzyl amines to imines were milder than the reported ones ever. What's more, from our experiments, the catalysts can be recycled five times at least, which indicated good reusability of hierarchical In2S3/CdIn2S4 nanohybrids.
2019, 77(7): 661-668
doi: 10.6023/A19040124
Abstract:
Glyphosate is one of the most widely used herbicides in the world. Current production of glyphosate starts with iminodiacetic acid (IDA). One method of producing IDA starts with the catalytic dehydrogenation of diethanolamine (DEA) using Cu-ZrO2 (CZ), which is a fairly simple, pollution-free, and cost-effective process. The Cu-ZrO2 catalysts used in this dehydrogenation are fairly efficient and inexpensive, but they tend to agglomerate and inactivate. The development of highly efficient and stable Cu-ZrO2 catalyst is of great significance. Carbon coated nano-metal particles are a new type of nano-carbon/metal composite materials. Metal materials can be imparted in a small space due to the surface acidity and alkalinity of carbon coated materials and their unique structural characteristics, which is of great significance for the dispersion and oxidation resistance of the loaded nano-metal materials. In this study, melamine was used as a carbon source and a nitrogen source to prepare a Cu-ZrO2 nanocatalyst (CZ@CN catalyst) coated with nitrogen-doped carbon (CN) with core-shell structure. The effect of different molar ratios of copper and melamine on the catalyst was studied. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N2 physical adsorption and desorption test (BET), H2 temperature-programmed reduction (H2-TPR) were used to investigate the morphology and structure of the catalyst. The catalytic performance of the catalyst for the dehydrogenation of diethanolamine was investigated. When the molar ratio of copper to melamine is 4:1, the prepared CZ@CN-1 catalyst has the highest catalytic activity. The yield of sodium iminodiacetic acid is 92.80%, and the reaction time is shorter than that of ordinary CZ catalyst by 40%. The yield of sodium iminodiacetic acid still reaches 88.45% after reusing 8 times. The results showed that the introduction of the CN layer makes the catalyst exhibit more Lewis basicity. Meanwhile, it is beneficial to the activation of hydroxyl groups and the transfer of hydrogen in the dehydrogenation reaction. The CN layer can also stabilize copper nanoparticles and improve the stability of the catalyst.
Glyphosate is one of the most widely used herbicides in the world. Current production of glyphosate starts with iminodiacetic acid (IDA). One method of producing IDA starts with the catalytic dehydrogenation of diethanolamine (DEA) using Cu-ZrO2 (CZ), which is a fairly simple, pollution-free, and cost-effective process. The Cu-ZrO2 catalysts used in this dehydrogenation are fairly efficient and inexpensive, but they tend to agglomerate and inactivate. The development of highly efficient and stable Cu-ZrO2 catalyst is of great significance. Carbon coated nano-metal particles are a new type of nano-carbon/metal composite materials. Metal materials can be imparted in a small space due to the surface acidity and alkalinity of carbon coated materials and their unique structural characteristics, which is of great significance for the dispersion and oxidation resistance of the loaded nano-metal materials. In this study, melamine was used as a carbon source and a nitrogen source to prepare a Cu-ZrO2 nanocatalyst (CZ@CN catalyst) coated with nitrogen-doped carbon (CN) with core-shell structure. The effect of different molar ratios of copper and melamine on the catalyst was studied. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N2 physical adsorption and desorption test (BET), H2 temperature-programmed reduction (H2-TPR) were used to investigate the morphology and structure of the catalyst. The catalytic performance of the catalyst for the dehydrogenation of diethanolamine was investigated. When the molar ratio of copper to melamine is 4:1, the prepared CZ@CN-1 catalyst has the highest catalytic activity. The yield of sodium iminodiacetic acid is 92.80%, and the reaction time is shorter than that of ordinary CZ catalyst by 40%. The yield of sodium iminodiacetic acid still reaches 88.45% after reusing 8 times. The results showed that the introduction of the CN layer makes the catalyst exhibit more Lewis basicity. Meanwhile, it is beneficial to the activation of hydroxyl groups and the transfer of hydrogen in the dehydrogenation reaction. The CN layer can also stabilize copper nanoparticles and improve the stability of the catalyst.
