Login In
2020 Volume 78 Issue 5
2020, 78(5): 373-381
doi: 10.6023/A20020045
Abstract:
Near infrared Ⅱ (NIR Ⅱ, 1000~1700 nm) biological imaging, as a new developing optical imaging technology in recent years, has longer fluorescence wavelength compared with the traditional near infrared Ⅰ (NIR Ⅰ, 750~900 nm) and visible light (Vis, 400~750 nm) imaging. Due to the longer emission wavelength, weaker interference by light scattering and tissue autofluorescence, result in higher temporal and spatial resolution with deeper tissue penetration. This technology is more suitable for in vivo imaging in situ. In this review, we mainly introduced research progress on NIR Ⅱ instrument technology for in vivo imaging, and summarized its major features. Finally, we provided a prospect that the development of chemical materials, optoelectronic instruments, and multi-modal technologies can promote NIR Ⅱ technology innovation, which is expected to be widely and deeply applied in clinical transformation.
Near infrared Ⅱ (NIR Ⅱ, 1000~1700 nm) biological imaging, as a new developing optical imaging technology in recent years, has longer fluorescence wavelength compared with the traditional near infrared Ⅰ (NIR Ⅰ, 750~900 nm) and visible light (Vis, 400~750 nm) imaging. Due to the longer emission wavelength, weaker interference by light scattering and tissue autofluorescence, result in higher temporal and spatial resolution with deeper tissue penetration. This technology is more suitable for in vivo imaging in situ. In this review, we mainly introduced research progress on NIR Ⅱ instrument technology for in vivo imaging, and summarized its major features. Finally, we provided a prospect that the development of chemical materials, optoelectronic instruments, and multi-modal technologies can promote NIR Ⅱ technology innovation, which is expected to be widely and deeply applied in clinical transformation.
2020, 78(5): 382-396
doi: 10.6023/A20020032
Abstract:
Organic solar cells have been developing quite rapidly in the past two decades. Tang fabricated the first organic solar cell with planar heterojunction in 1986, while the power conversion efficiency (PCE) was only 1%. The PCE of single-junction organic solar cell has increased to over 17% in 2019. However, the single-junction solar cells are limited in performance by the severe energy loss. Tandem organic solar cells that use an interconnecting layer connecting two sub-cells provide the possibility of optimizing the devices performance. The two different active layers of sub-cells have non-overlapping light absorption scales, which make the light utilized more adequately. Therefore, the tandem architecture of devices can extend the light absorption within the solar spectrum and effectively reduce energy loss resulting from thermalization loss and transmission loss. According to Shockley and Queisser's calculation, the limitation of the PCE of a tandem solar cell is 42%, which is higher than 33.8% of a single-junction solar cell. In organic photovoltaics field, the developments of the tandem solar cells benefit from the optimization of active layers, interconnecting layers and construction methods. These achievements have resulted in higher PCEs and the devices approaching practical application. At present, the highest PCE of tandem organic solar cell is 17.3% obtained by Chen's group in 2018, but it is still far from the PCE limitation. According to Kirchhoff's law, the open-circuit voltage (VOC) in series tandem cells is theoretically equal to the sum of the VOCs of sub-cells, and the short-circuit current (JSC) in parallel cells is equal to the sum of the JSCs of sub-cells. Hence, the series tandem solar cells still face with the challenge of the unmatched JSCs and the complexed processing methods. Here, this review mainly focuses on the materials used in tandem solar cells, the structure of the interconnecting layers, the processing methods, the measurement methods and the applications. The critical achievements on tandem organic solar cells in recent years and the progress of larger scale, flexible tandem devices are summarized in this review. It also presents the outlooks of the high performance tandem solar cells based on the material and structure requirements.
Organic solar cells have been developing quite rapidly in the past two decades. Tang fabricated the first organic solar cell with planar heterojunction in 1986, while the power conversion efficiency (PCE) was only 1%. The PCE of single-junction organic solar cell has increased to over 17% in 2019. However, the single-junction solar cells are limited in performance by the severe energy loss. Tandem organic solar cells that use an interconnecting layer connecting two sub-cells provide the possibility of optimizing the devices performance. The two different active layers of sub-cells have non-overlapping light absorption scales, which make the light utilized more adequately. Therefore, the tandem architecture of devices can extend the light absorption within the solar spectrum and effectively reduce energy loss resulting from thermalization loss and transmission loss. According to Shockley and Queisser's calculation, the limitation of the PCE of a tandem solar cell is 42%, which is higher than 33.8% of a single-junction solar cell. In organic photovoltaics field, the developments of the tandem solar cells benefit from the optimization of active layers, interconnecting layers and construction methods. These achievements have resulted in higher PCEs and the devices approaching practical application. At present, the highest PCE of tandem organic solar cell is 17.3% obtained by Chen's group in 2018, but it is still far from the PCE limitation. According to Kirchhoff's law, the open-circuit voltage (VOC) in series tandem cells is theoretically equal to the sum of the VOCs of sub-cells, and the short-circuit current (JSC) in parallel cells is equal to the sum of the JSCs of sub-cells. Hence, the series tandem solar cells still face with the challenge of the unmatched JSCs and the complexed processing methods. Here, this review mainly focuses on the materials used in tandem solar cells, the structure of the interconnecting layers, the processing methods, the measurement methods and the applications. The critical achievements on tandem organic solar cells in recent years and the progress of larger scale, flexible tandem devices are summarized in this review. It also presents the outlooks of the high performance tandem solar cells based on the material and structure requirements.
2020, 78(5): 397-406
doi: 10.6023/A20030081
Abstract:
As important chemical raw materials and energy source, C4~C6 hydrocarbons are mainly used to produce polymer rubber, plastics and high-quality gasoline, which requires high purity of the raw materials. For example, the purity requirement in 1, 3-butadiene polymerization reactor is higher than 99.5%. When producing butyl rubber, tert-butylamine, pivalic acid, etc., the purity of isobutylene should surpass 99%. In the traditional petrochemical industry, C4~C6 hydrocarbons are mostly separated and purified through distillation, yet suffering from large energy consumption, high equipment cost and poor economic benefits. Adsorption separation with solid adsorbents can not only reduce energy cost and environmental footprints, but also improve separation efficiency. Metal-organic frameworks (MOFs) are a class of crystalline porous materials assembled from metal ions or clusters and organic linkers. Compared with zeolite, activated carbon and silica gel, MOFs feature high porosity, well-defined open channels, rich functional groups and diverse structures, showing great potentials in gas storage and separation, sensing, catalysis, photoelectric devices, drug release and delivery. Up to now, there have been many reports on separation and purification of C4~C6 hydrocarbons using MOFs by different mechanisms. Specifically, highly selective separation can be achieved by precisely adjusting the size and shape of the MOF channels to match the size of the target molecule. Besides, selecting MOFs with specific functional groups, open metal sites or flexible skeletons to regulate the interactions between the gas molecules and backbone, can also achieve efficient separation. This review introduced the importance of C4~C6 hydrocarbons separation and summarized the current research progress of using MOFs to separate and purify C4~C6 hydrocarbons. In addition, we also summed up the challenges of using MOFs as industrial adsorbents and pointed out the possible research directions in the future, which may provide ideas for designing new MOFs with high performance for crucial separation processes.
As important chemical raw materials and energy source, C4~C6 hydrocarbons are mainly used to produce polymer rubber, plastics and high-quality gasoline, which requires high purity of the raw materials. For example, the purity requirement in 1, 3-butadiene polymerization reactor is higher than 99.5%. When producing butyl rubber, tert-butylamine, pivalic acid, etc., the purity of isobutylene should surpass 99%. In the traditional petrochemical industry, C4~C6 hydrocarbons are mostly separated and purified through distillation, yet suffering from large energy consumption, high equipment cost and poor economic benefits. Adsorption separation with solid adsorbents can not only reduce energy cost and environmental footprints, but also improve separation efficiency. Metal-organic frameworks (MOFs) are a class of crystalline porous materials assembled from metal ions or clusters and organic linkers. Compared with zeolite, activated carbon and silica gel, MOFs feature high porosity, well-defined open channels, rich functional groups and diverse structures, showing great potentials in gas storage and separation, sensing, catalysis, photoelectric devices, drug release and delivery. Up to now, there have been many reports on separation and purification of C4~C6 hydrocarbons using MOFs by different mechanisms. Specifically, highly selective separation can be achieved by precisely adjusting the size and shape of the MOF channels to match the size of the target molecule. Besides, selecting MOFs with specific functional groups, open metal sites or flexible skeletons to regulate the interactions between the gas molecules and backbone, can also achieve efficient separation. This review introduced the importance of C4~C6 hydrocarbons separation and summarized the current research progress of using MOFs to separate and purify C4~C6 hydrocarbons. In addition, we also summed up the challenges of using MOFs as industrial adsorbents and pointed out the possible research directions in the future, which may provide ideas for designing new MOFs with high performance for crucial separation processes.
2020, 78(5): 407-411
doi: 10.6023/A20040134
Abstract:
Precisely modulating the structure of nanoparticles in a controlled manner is still a challenging and inspiring topic. Although the single or few-metal atom tailoring of gold nanoparticles has been reported, local structural replacement involving over three net metal atoms (module replacement, MR) has not been hitherto achieved. Herein, we report the synthesis of cyclohexanethiolated metal nanoclusters (NCs) Au48(CHT)26 and their MR by a so-called pseudo-anti-galvanic reaction (AGR) process. The MR product Au37(CHT)23 shares a similar Au31(CHT)12 unit with its predecessor Au48(CHT)26; however, it differs from its predecessor in the remaining section (Au6(CHT)11 vs. Au16(CHT)14), as revealed by single-crystal X-ray crystallography (SCXC). Interestingly, the MR inhibits the photothermy but enhances the emission of Au48(CHT)26 NCs, which might endow the as-obtained NC better potential for bi(multiple)-functional application. The counter effects of the MR on the emission and photothermy indicate that photoluminescence and photothermy can be at least partly converted into each other, which has some important implications for the understanding of their interaction.
Precisely modulating the structure of nanoparticles in a controlled manner is still a challenging and inspiring topic. Although the single or few-metal atom tailoring of gold nanoparticles has been reported, local structural replacement involving over three net metal atoms (module replacement, MR) has not been hitherto achieved. Herein, we report the synthesis of cyclohexanethiolated metal nanoclusters (NCs) Au48(CHT)26 and their MR by a so-called pseudo-anti-galvanic reaction (AGR) process. The MR product Au37(CHT)23 shares a similar Au31(CHT)12 unit with its predecessor Au48(CHT)26; however, it differs from its predecessor in the remaining section (Au6(CHT)11 vs. Au16(CHT)14), as revealed by single-crystal X-ray crystallography (SCXC). Interestingly, the MR inhibits the photothermy but enhances the emission of Au48(CHT)26 NCs, which might endow the as-obtained NC better potential for bi(multiple)-functional application. The counter effects of the MR on the emission and photothermy indicate that photoluminescence and photothermy can be at least partly converted into each other, which has some important implications for the understanding of their interaction.
2020, 78(5): 412-418
doi: 10.6023/A20030077
Abstract:
Single-molecule magnets (SMMs), exhibiting magnetic bistability and slow magnetization relaxation, have fascinated scientific community for their promising applications in data storage and information processing. Great development has been achieved in lanthanide-based SMMs due to the unquenched orbital momentum and strong anisotropy of lanthanide ions. According to the crystal-field theory, the magnetic anisotropy of lanthanide ions arises from crystal-field splitting. Appropriate arrangement of coordination environment of lanthanide ion (including the local symmetry as well as the charge distribution) is key to design high-performance SMMs. However, it still remains a huge challenge to generate lanthanide-containing compounds with certain coordination environment. Taking advantage of metallacrown (MC) approach, herein a series of 3d-4f complexes {TbNi5X2} (X=F, Cl, Br) were successfully isolated via solvothermal reactions. To obtain these complexes, a mixture of stoichiometric metal salt and quinaldichdroxamic acid with excess of pyridine derivative was dissolved in methanol and then heated at 75℃ for 2 d. X-ray single-crystal diffraction analysis indicated that the Tb(Ⅲ) site equatorially coordinates with[15-MCNi(Ⅱ)-5], whilst is axially capped by halide ions. As a result, the lanthanide ion possesses high axiality with a pentagonal bipyramid geometry (D5h). Alternative current magnetic susceptibility data revealed that the electrostatic interactions between f-electrons and ligand electrons play an important role in modulating the magnetic relaxation dynamics. Maximizing the axial charge density in {TbNi5F2} where the[F-Ln-F]+ moiety is firstly reported in lanthanide chemistry, the oblate Tb(Ⅲ) is placed in a judicious crystal field. The out-of-phase signal of {TbNi5F2} shows obvious temperature and frequency dependence under 1 kOe applied dc field. Additionally, the slow magnetization relaxation of {TbNi5F2} can be fitted by the power law or Arrhenius plot with reversal barrier of 19.0 K. By lowering the electrostatic interactions of axial ligation, the out-of-phase signal significantly weakens in {TbNi5Cl2} and even vanishes in {TbNi5Br2}. The decline of magnetic anisotropy in {TbNi5Cl2} and {TbNi5Br2} accelerates the fast quantum tunneling of magnetization. The results demonstrate for the first time that the Off/Part/On slow magnetization relaxation can be modulated via the improvement of electronegativity of axial ligands.
Single-molecule magnets (SMMs), exhibiting magnetic bistability and slow magnetization relaxation, have fascinated scientific community for their promising applications in data storage and information processing. Great development has been achieved in lanthanide-based SMMs due to the unquenched orbital momentum and strong anisotropy of lanthanide ions. According to the crystal-field theory, the magnetic anisotropy of lanthanide ions arises from crystal-field splitting. Appropriate arrangement of coordination environment of lanthanide ion (including the local symmetry as well as the charge distribution) is key to design high-performance SMMs. However, it still remains a huge challenge to generate lanthanide-containing compounds with certain coordination environment. Taking advantage of metallacrown (MC) approach, herein a series of 3d-4f complexes {TbNi5X2} (X=F, Cl, Br) were successfully isolated via solvothermal reactions. To obtain these complexes, a mixture of stoichiometric metal salt and quinaldichdroxamic acid with excess of pyridine derivative was dissolved in methanol and then heated at 75℃ for 2 d. X-ray single-crystal diffraction analysis indicated that the Tb(Ⅲ) site equatorially coordinates with[15-MCNi(Ⅱ)-5], whilst is axially capped by halide ions. As a result, the lanthanide ion possesses high axiality with a pentagonal bipyramid geometry (D5h). Alternative current magnetic susceptibility data revealed that the electrostatic interactions between f-electrons and ligand electrons play an important role in modulating the magnetic relaxation dynamics. Maximizing the axial charge density in {TbNi5F2} where the[F-Ln-F]+ moiety is firstly reported in lanthanide chemistry, the oblate Tb(Ⅲ) is placed in a judicious crystal field. The out-of-phase signal of {TbNi5F2} shows obvious temperature and frequency dependence under 1 kOe applied dc field. Additionally, the slow magnetization relaxation of {TbNi5F2} can be fitted by the power law or Arrhenius plot with reversal barrier of 19.0 K. By lowering the electrostatic interactions of axial ligation, the out-of-phase signal significantly weakens in {TbNi5Cl2} and even vanishes in {TbNi5Br2}. The decline of magnetic anisotropy in {TbNi5Cl2} and {TbNi5Br2} accelerates the fast quantum tunneling of magnetization. The results demonstrate for the first time that the Off/Part/On slow magnetization relaxation can be modulated via the improvement of electronegativity of axial ligands.
2020, 78(5): 419-426
doi: 10.6023/A20030079
Abstract:
Highly sensitive and accurate analysis of significant biomarkers such as alkaline phosphatase (ALP) is essential for early detection and treatment of diseases. In this work, a fluorescence/UV-vis dual-mode sensing platform was constructed for amplified detection of ALP and pyrophosphate ion (PPi) based on mimic enzyme-natural enzyme cascade reactions. Cu-Based metal-organic frameworks HKUST-1 which possesses of oxidase-like activity and can effectively catalyze the oxidation of indicator o-phenylenediamine (OPD) by the surface-active sites were prepared. The oxidation products of OPD exhibit strong UV-vis absorption and fluorescent signals at 416 and 568 nm, respectively. After adding PPi, the catalytic activity of HKUST-1 was selectively inhibited due to the combination of PPi with Cu2+ on the surface of HKUST-1, that resulted in fluorescence and UV-vis signal reducing. Once ALP was introduced into the system, PPi can be specifically hydrolyzed into phosphate ions (Pi), and the oxidase-like activity of HKUST-1 recovered. Thus, the fluorescent and UV-vis signals were regenerated by an ALP-triggered mimic enzyme-natural enzyme cascade reaction. On account of the inhibition of oxidase-like activity of HKUST-1 by PPi and the recovery by ALP, an ultrasensitive dual-mode sensing platform of biomarkers based on mimic enzyme-natural enzyme cascade reactions has been developed. Under optimal conditions, the linear range of ALP by fluorescence/UV-vis detection is 0.02~3.5 and 0.04~3.5 nmol·L-1, and the detection limit of fluorescence and UV-vis assay is as low as 0.0078 and 0.039 nmol·L-1, respectively. As far as we know, it is the first time that the mimic enzyme-natural enzyme cascade reaction is applied to dual-mode bioanalysis. Due to the enzyme cascade amplification and dual-mode signal output, this developed strategy has the advantages of high sensitivity, low detection limit, high accuracy and reliability, and can realize ultrasensitive analysis of ALP in human serum samples, which shows great potential for clinical diagnosis.
Highly sensitive and accurate analysis of significant biomarkers such as alkaline phosphatase (ALP) is essential for early detection and treatment of diseases. In this work, a fluorescence/UV-vis dual-mode sensing platform was constructed for amplified detection of ALP and pyrophosphate ion (PPi) based on mimic enzyme-natural enzyme cascade reactions. Cu-Based metal-organic frameworks HKUST-1 which possesses of oxidase-like activity and can effectively catalyze the oxidation of indicator o-phenylenediamine (OPD) by the surface-active sites were prepared. The oxidation products of OPD exhibit strong UV-vis absorption and fluorescent signals at 416 and 568 nm, respectively. After adding PPi, the catalytic activity of HKUST-1 was selectively inhibited due to the combination of PPi with Cu2+ on the surface of HKUST-1, that resulted in fluorescence and UV-vis signal reducing. Once ALP was introduced into the system, PPi can be specifically hydrolyzed into phosphate ions (Pi), and the oxidase-like activity of HKUST-1 recovered. Thus, the fluorescent and UV-vis signals were regenerated by an ALP-triggered mimic enzyme-natural enzyme cascade reaction. On account of the inhibition of oxidase-like activity of HKUST-1 by PPi and the recovery by ALP, an ultrasensitive dual-mode sensing platform of biomarkers based on mimic enzyme-natural enzyme cascade reactions has been developed. Under optimal conditions, the linear range of ALP by fluorescence/UV-vis detection is 0.02~3.5 and 0.04~3.5 nmol·L-1, and the detection limit of fluorescence and UV-vis assay is as low as 0.0078 and 0.039 nmol·L-1, respectively. As far as we know, it is the first time that the mimic enzyme-natural enzyme cascade reaction is applied to dual-mode bioanalysis. Due to the enzyme cascade amplification and dual-mode signal output, this developed strategy has the advantages of high sensitivity, low detection limit, high accuracy and reliability, and can realize ultrasensitive analysis of ALP in human serum samples, which shows great potential for clinical diagnosis.
2020, 78(5): 427-436
doi: 10.6023/A20030065
Abstract:
In this work, the separation performance of methane/ethane/propane (C1, C2 and C3) mixture in the 137953 hypothetical metal-organic frameworks (MOFs) is calculated by high throughput computational screening and multiple machine learning (ML) algorithms. First, to avoid the competitive adsorption of water vapor, 31399 hydrophobic MOFs (hMOFs) were screened out. Then, grand canonical Monte Carlo (GCMC) simulations were employed to calculate the adsorption behavior of a mixture with a mole ratio of C1:C2:C3=7:2:1 in these hMOFs, respectively. Second, the relationships among six MOF structures/energy descriptors (the largest cavity diameter (LCD), void fraction (f), volumetric surface area (VSA), Henry coefficient (K), heat of adsorption (Qst), density of MOF (ρ)) and three performance indicators of MOFs (selectivities (S), adsorption capacities (N) of C1, C2, C3 and their trade-offs (TSN)) were established. The LCDs were calculated by Zeo++software, and VSAs were calculated using RASPA software using He and N2 as probes, respectively, and Qst and K were calculated in an infinite dilution of each gas molecule in an infinite dilution state using NVT-MC method in RASPA software. Then, we found that there existed the "second peaks" of N and S in part of structure-property relationships, and all the optimal MOFs located in the range of second peaks, especially for the separation of C1 or C2. Third, the above-mentioned six MOF descriptors and three MOF performance indicators were trained, tested and predicted by four ML algorithms, including decision tree, random forest (RF), support vector machine and Back Propagation neural network. Although the predictive effect for the selectivity was very low, the introduction of TSN can significantly improve the accuracy of ML prediction, especially for RF algorithm (R=0.99). Therefore, the RF was used to quantitatively analyze the relative importance of each MOF descriptor, and found that three descriptors (K, LCD and ρ) possessed the highest importance for the separation of C1 and C2, and three other descriptors (K, Qst and ρ) for the separation of C3. Moreover, three simple and clear paths of optimal MOFs for C1, C2 and C3 adsorption were designed by the decision tree model with the descriptors. Based on those paths, there were 96%, 85%, 95% probability that we can search for high-performance MOFs, respectively. Finally, the best 18 MOFs were identified for different separation applications of C1, C2 and C3. This study reveals the second peaks and key MOF descriptors governing the adsorption of light alkane, develops quantitative structure-property relationships by ML, and identifies the best adsorbents from a large collection of MOFs for the separation of C1, C2 and C3 from natural gas.
In this work, the separation performance of methane/ethane/propane (C1, C2 and C3) mixture in the 137953 hypothetical metal-organic frameworks (MOFs) is calculated by high throughput computational screening and multiple machine learning (ML) algorithms. First, to avoid the competitive adsorption of water vapor, 31399 hydrophobic MOFs (hMOFs) were screened out. Then, grand canonical Monte Carlo (GCMC) simulations were employed to calculate the adsorption behavior of a mixture with a mole ratio of C1:C2:C3=7:2:1 in these hMOFs, respectively. Second, the relationships among six MOF structures/energy descriptors (the largest cavity diameter (LCD), void fraction (f), volumetric surface area (VSA), Henry coefficient (K), heat of adsorption (Qst), density of MOF (ρ)) and three performance indicators of MOFs (selectivities (S), adsorption capacities (N) of C1, C2, C3 and their trade-offs (TSN)) were established. The LCDs were calculated by Zeo++software, and VSAs were calculated using RASPA software using He and N2 as probes, respectively, and Qst and K were calculated in an infinite dilution of each gas molecule in an infinite dilution state using NVT-MC method in RASPA software. Then, we found that there existed the "second peaks" of N and S in part of structure-property relationships, and all the optimal MOFs located in the range of second peaks, especially for the separation of C1 or C2. Third, the above-mentioned six MOF descriptors and three MOF performance indicators were trained, tested and predicted by four ML algorithms, including decision tree, random forest (RF), support vector machine and Back Propagation neural network. Although the predictive effect for the selectivity was very low, the introduction of TSN can significantly improve the accuracy of ML prediction, especially for RF algorithm (R=0.99). Therefore, the RF was used to quantitatively analyze the relative importance of each MOF descriptor, and found that three descriptors (K, LCD and ρ) possessed the highest importance for the separation of C1 and C2, and three other descriptors (K, Qst and ρ) for the separation of C3. Moreover, three simple and clear paths of optimal MOFs for C1, C2 and C3 adsorption were designed by the decision tree model with the descriptors. Based on those paths, there were 96%, 85%, 95% probability that we can search for high-performance MOFs, respectively. Finally, the best 18 MOFs were identified for different separation applications of C1, C2 and C3. This study reveals the second peaks and key MOF descriptors governing the adsorption of light alkane, develops quantitative structure-property relationships by ML, and identifies the best adsorbents from a large collection of MOFs for the separation of C1, C2 and C3 from natural gas.
2020, 78(5): 437-443
doi: 10.6023/A19110413
Abstract:
Imines and the intermediate methylamine by the aldimine condensation of primary amines with aldehydes have a potential application in the field of pharmacy, life science, catalysis, material science, etc. In this reaction, the hydrogen transfer in the dehydration step normally prefers the pathway via a water bridge in aqueous solution or a directly dehydration in organic solvent. It is a different mechanism for the aldimine condensation of amine owning neighbouring nitrogenous heterocycle. Herein we investigated the mechanism of aldimine condensation of primary amine containing nitrogenous heterocycle with aldehyde in dichloromethane under acidic conditions using density functional theory (DFT) at ωB97X-D/6-31++G(d, p) level, the calculated results show that compared with specific acid catalysis, the heterocyclic nitrogen with stronger basicity is easier to be protonated than the oxygen of carbonyl group. The whole reaction proceeds two hydrogen transfer steps via nitrogen bridge owning an energy span of 13.08 kcal/mol. The rate-determing step is the second hydrogen transfer step. In each step the heterocyclic nitrogen is a bridge to assist the hydrogen transfer, which could reduce the free energy barrier of the aldimine condensation. It is unfavorable for the reaction pathway via directly hydrogen transfer with a four-membered ring transition state owning a free energy barrier of 32.73 kcal/mol, and the reaction pathway via a water bridge is not located. Meanwhile, the energy barriers increased for systems in which the N atom in heterocycle of primary amine is replaced by P/As atoms. The rate-determining step changes from the second hydrogen transfer step for N system to the first hydrogen transfer step for As system. The position effect of adjacent nitrogen atom is also investigated. The γ position owns the highest reactivity of the aldimine condensation, which implies that the ring strain plays an important role in the aldimine condensation of primary amine containing nitrogenous heterocycle with aldehyde. This theoretical study may provide insights to unveil the nature of aldimine condensation of aldehyde and primary amine owning nitrogeneous heterocycle.
Imines and the intermediate methylamine by the aldimine condensation of primary amines with aldehydes have a potential application in the field of pharmacy, life science, catalysis, material science, etc. In this reaction, the hydrogen transfer in the dehydration step normally prefers the pathway via a water bridge in aqueous solution or a directly dehydration in organic solvent. It is a different mechanism for the aldimine condensation of amine owning neighbouring nitrogenous heterocycle. Herein we investigated the mechanism of aldimine condensation of primary amine containing nitrogenous heterocycle with aldehyde in dichloromethane under acidic conditions using density functional theory (DFT) at ωB97X-D/6-31++G(d, p) level, the calculated results show that compared with specific acid catalysis, the heterocyclic nitrogen with stronger basicity is easier to be protonated than the oxygen of carbonyl group. The whole reaction proceeds two hydrogen transfer steps via nitrogen bridge owning an energy span of 13.08 kcal/mol. The rate-determing step is the second hydrogen transfer step. In each step the heterocyclic nitrogen is a bridge to assist the hydrogen transfer, which could reduce the free energy barrier of the aldimine condensation. It is unfavorable for the reaction pathway via directly hydrogen transfer with a four-membered ring transition state owning a free energy barrier of 32.73 kcal/mol, and the reaction pathway via a water bridge is not located. Meanwhile, the energy barriers increased for systems in which the N atom in heterocycle of primary amine is replaced by P/As atoms. The rate-determining step changes from the second hydrogen transfer step for N system to the first hydrogen transfer step for As system. The position effect of adjacent nitrogen atom is also investigated. The γ position owns the highest reactivity of the aldimine condensation, which implies that the ring strain plays an important role in the aldimine condensation of primary amine containing nitrogenous heterocycle with aldehyde. This theoretical study may provide insights to unveil the nature of aldimine condensation of aldehyde and primary amine owning nitrogeneous heterocycle.
2020, 78(5): 444-450
doi: 10.6023/A20010011
Abstract:
Rechargeable magnesium batteries (rMBs) are promising next-generation secondary batteries owing to the low-cost, high safety and dendrite-free property of Mg metal. The key of rMBs technology is to develop high-performance cathode materials. Usually, the intercalation-type cathodes such as Mo6S8, MoS2 and Ti3C2Tx suffer from the inferior rate performance owing to the sluggish Mg2+ ions solid-diffusion kinetics, and the conversion-type cathodes such as S and CuS are beset with the poor cycling stability owing to the pulverization and loss of active species. Recently, sp2 carbon materials exhibited considerable magnesium storage performance through an interfacial charge storage/release. Ideal carbon-based cathodes for rMBs should possess the features of high specific surface area and abundant active sites for magnesium storage, high conductivity and porous structure for facilitating charge transfer, as well as high mechanical stability. Herein, we employed the hierarchical nitrogen-doped carbon nanocages (hNCNC) featuring large surface area, abundant surface defects, coexisting micro-meso-macropores and high conductivity as the rMBs cathode for the first time, which exhibited high discharge capacity of 71 mAh·g-1 at 100 mA·g-1, excellent rate performance (60 mAh·g-1 at 2000 mA·g-1) and ultra-high cycling stability (83% capacity retention after 1000 cycles at 1000 mA·g-1). The capacitive magnesium storage mechanism is predominant in the charging-discharging process. Theoretical studies reveal that magnesium ions are adsorbed on the carbon, pyridinic-nitrogen or pyrrolic-nitrogen atoms at the edge of micropores. The excellent magnesium storage performance of hNCNC is attributed to the following reasons:(i) the hNCNC with large surface area (1590 m2·g-1), abundant micropore defects and high content of pyridinic and pyrrolic nitrogen (4.49 at.%) provides sufficient active sites for magnesium storage, resulting in the high discharge capacity; (ii) the coexisting micro-meso-macropores structure, good conductivity and improved wettability via N-doping facilitate the charge transfer kinetics, and decrease the equivalent series resistance of rMBs, thereby leading to the improved rate capability; (iii) the robust scaffold of hNCNC and the capacitive-dominated magnesium storage mechanism ensure the high cycling stability. This study demonstrates the high-rate and durable performance of hNCNC in rMBs, and suggests a promising strategy to improve the rMBs performance by increasing edges and suitable dopants of nanocarbons.
Rechargeable magnesium batteries (rMBs) are promising next-generation secondary batteries owing to the low-cost, high safety and dendrite-free property of Mg metal. The key of rMBs technology is to develop high-performance cathode materials. Usually, the intercalation-type cathodes such as Mo6S8, MoS2 and Ti3C2Tx suffer from the inferior rate performance owing to the sluggish Mg2+ ions solid-diffusion kinetics, and the conversion-type cathodes such as S and CuS are beset with the poor cycling stability owing to the pulverization and loss of active species. Recently, sp2 carbon materials exhibited considerable magnesium storage performance through an interfacial charge storage/release. Ideal carbon-based cathodes for rMBs should possess the features of high specific surface area and abundant active sites for magnesium storage, high conductivity and porous structure for facilitating charge transfer, as well as high mechanical stability. Herein, we employed the hierarchical nitrogen-doped carbon nanocages (hNCNC) featuring large surface area, abundant surface defects, coexisting micro-meso-macropores and high conductivity as the rMBs cathode for the first time, which exhibited high discharge capacity of 71 mAh·g-1 at 100 mA·g-1, excellent rate performance (60 mAh·g-1 at 2000 mA·g-1) and ultra-high cycling stability (83% capacity retention after 1000 cycles at 1000 mA·g-1). The capacitive magnesium storage mechanism is predominant in the charging-discharging process. Theoretical studies reveal that magnesium ions are adsorbed on the carbon, pyridinic-nitrogen or pyrrolic-nitrogen atoms at the edge of micropores. The excellent magnesium storage performance of hNCNC is attributed to the following reasons:(i) the hNCNC with large surface area (1590 m2·g-1), abundant micropore defects and high content of pyridinic and pyrrolic nitrogen (4.49 at.%) provides sufficient active sites for magnesium storage, resulting in the high discharge capacity; (ii) the coexisting micro-meso-macropores structure, good conductivity and improved wettability via N-doping facilitate the charge transfer kinetics, and decrease the equivalent series resistance of rMBs, thereby leading to the improved rate capability; (iii) the robust scaffold of hNCNC and the capacitive-dominated magnesium storage mechanism ensure the high cycling stability. This study demonstrates the high-rate and durable performance of hNCNC in rMBs, and suggests a promising strategy to improve the rMBs performance by increasing edges and suitable dopants of nanocarbons.
