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2018 Volume 76 Issue 4
2018, 76(4): 237-245
doi: 10.6023/A17120555
Abstract:
The traditional "lock and key" sensor models pursue the "one to one" sensing response for the specific testing and the low limitation of detection, which neglect the practical sample detecting application with multi-analytes and complex contains. Utilizing multi-sensor compounds, the sensor array chip offers multiplex differential sensing response signal to process the multi-analytes discrimination. The critical requirement for successful multi-analyte recognition is to acquire abundant sensing information. However, the "multi to multi" sensor chip needs large numbers of serial probe compounds, which involve com-plicated chemical synthesis and valid compound screening. Inspired by the human sense organ, scientists developed various "cross-reactive" sensor arrays. Here, The recent research progress of multi-analysis and "one to multi" high-efficient detection were introduced. From chemical information excavation, physical signal enhancement, devices integration design, we summarize and forecast the multi-analysis advancement and intelligent sensors.
The traditional "lock and key" sensor models pursue the "one to one" sensing response for the specific testing and the low limitation of detection, which neglect the practical sample detecting application with multi-analytes and complex contains. Utilizing multi-sensor compounds, the sensor array chip offers multiplex differential sensing response signal to process the multi-analytes discrimination. The critical requirement for successful multi-analyte recognition is to acquire abundant sensing information. However, the "multi to multi" sensor chip needs large numbers of serial probe compounds, which involve com-plicated chemical synthesis and valid compound screening. Inspired by the human sense organ, scientists developed various "cross-reactive" sensor arrays. Here, The recent research progress of multi-analysis and "one to multi" high-efficient detection were introduced. From chemical information excavation, physical signal enhancement, devices integration design, we summarize and forecast the multi-analysis advancement and intelligent sensors.
2018, 76(4): 246-258
doi: 10.6023/A17110504
Abstract:
Functional materials with unique properties or specific functions, have been developed greatly in the areas of information, aerospace, energy, biology and so forth. Recently, organic/organometallic mechanoluminescence (ML) has attracted considerable attention owing to its unique optical properties induced by external stimulus, which demonstrates great potential as a candidate for sensing of impact, stress, tension or pressure, display and lighting, as well as imaging. In this review, the recent progress on organic/organometallic ML materials, the relationship between molecular structures and properties, their luminescent mechanisms, as well as the applications are summarized. Currently, the organic/organometallic ML systems mainly contain small molecules, including organometallic complexes and pure organic compounds, and polymers. In comparison to the design and preparation of materials, the progress of underlying mechanisms still remains ambiguous without a universal acknowledgement. Up to now, it is generally accepted that organic/organometallic ML materials should have non-centrosymmetric molecular structures, dipolar structures and piezoelectric properties. Because when the crystals are stimulated under grinding, rubbing, cutting, cleaving, shaking, scratching, compressing, or crushing, the center asymmetric molecular structures of organic/organometallic materials are broken, resulting in disruption of the crystal and electronic discharge at the crack surface, then emitting obvious light from the surface of solids state. This organic ML mechanism is mainly derived from the mechanism of inorganic ML. Mechanisms of organic/organometallic ML materials need to be verified by further experiments and theoretical study. As to the mechanism of mechanically activated luminescence of pure organic polymers, it was reported that when the material was stimulated by mechanical forces, the excited state went back to the ground state and emitted light. This review will focus on the recent progress of organic/organometallic mechanoluminescent materials including rare-earth organometallic complex, transition organometallic complex, pure organic small molecule materials and pure organic polymer materials, and their mechanisms during the past decades. Finally, the challenges and the outlook of the organic/organometallic ML have been discussed.
Functional materials with unique properties or specific functions, have been developed greatly in the areas of information, aerospace, energy, biology and so forth. Recently, organic/organometallic mechanoluminescence (ML) has attracted considerable attention owing to its unique optical properties induced by external stimulus, which demonstrates great potential as a candidate for sensing of impact, stress, tension or pressure, display and lighting, as well as imaging. In this review, the recent progress on organic/organometallic ML materials, the relationship between molecular structures and properties, their luminescent mechanisms, as well as the applications are summarized. Currently, the organic/organometallic ML systems mainly contain small molecules, including organometallic complexes and pure organic compounds, and polymers. In comparison to the design and preparation of materials, the progress of underlying mechanisms still remains ambiguous without a universal acknowledgement. Up to now, it is generally accepted that organic/organometallic ML materials should have non-centrosymmetric molecular structures, dipolar structures and piezoelectric properties. Because when the crystals are stimulated under grinding, rubbing, cutting, cleaving, shaking, scratching, compressing, or crushing, the center asymmetric molecular structures of organic/organometallic materials are broken, resulting in disruption of the crystal and electronic discharge at the crack surface, then emitting obvious light from the surface of solids state. This organic ML mechanism is mainly derived from the mechanism of inorganic ML. Mechanisms of organic/organometallic ML materials need to be verified by further experiments and theoretical study. As to the mechanism of mechanically activated luminescence of pure organic polymers, it was reported that when the material was stimulated by mechanical forces, the excited state went back to the ground state and emitted light. This review will focus on the recent progress of organic/organometallic mechanoluminescent materials including rare-earth organometallic complex, transition organometallic complex, pure organic small molecule materials and pure organic polymer materials, and their mechanisms during the past decades. Finally, the challenges and the outlook of the organic/organometallic ML have been discussed.
2018, 76(4): 259-277
doi: 10.6023/A17110517
Abstract:
Ternary layered oxides {Li[NixCoyMz]O2 (0 < x, y, z < 1, M=Mn, NMC; M=Al, NCA)} are one of the most promising cathode materials of lithium-ion batteries (LIBs). However, in the traditional electrolyte system, they will undergo dramatic structural changes and interface side reactions at high potential and high temperature, which will bring great challenges to their practical application, especially for their cycle life and safety. Developing appropriate electrolyte additive is one of the most economical and effective methods to improve the electrochemical performance of LIBs. Based on the intrinsic structure of material, electrolyte additives used for NMC and NCA ternary cathode and their reaction mechanism in the past 5 years are reviewed in this paper, which include vinylene carbonate (VC), fluoro-compounds, new lithium salts, P-based, B-based, S-based, nitrile, others and combinative additives. Among them, VC becomes a kind of universal additive, which can improve the efficiency and cycle life at low voltage and normal temperature. Fluoro-compounds have been developed from mono substituted such as Fluorinated ethylene carbonate (FEC) to multi-fluorine substituted, which can improve the stability of electrode/electrolyte interface under high voltage. New lithium salt additives are mainly used to improve the film forming performance under high voltage and high temperature, such as Lithium bis(fluorosulfonyl)imide (LiFSI), Lithium difluorophosphate (LiDFP). P-contained additives[such as Tris(trimethylsilyl) phosphite (TMSPi)] are mainly to improve the stability of anode-electrolyte interface, and it has obvious synergistic effect when they combined with additives such as VC. B-contained additives are mainly used to improve the dissociation degree and stability of lithium salt, such as Tris(trimethylsilyl)borate (TMSB). S-contained additives are mainly used to improve the ionic conductivity and stability of anode SEI film, such as Prop-1-ene-1, 3-sultone (PES). Nitriles are benefited from the strong electron withdrawing effect of -CN, which can improve the stability of the electrode/electrolyte interface at high voltage. Other types of additives are some heterocyclic compounds having film forming ability and various silanes which can eliminate HF and H2O. Combinative addi-tives are developed from VC based composite to PES and PBF (pyridine boron trifluoride) system, which can endure even harsher conditions.
Ternary layered oxides {Li[NixCoyMz]O2 (0 < x, y, z < 1, M=Mn, NMC; M=Al, NCA)} are one of the most promising cathode materials of lithium-ion batteries (LIBs). However, in the traditional electrolyte system, they will undergo dramatic structural changes and interface side reactions at high potential and high temperature, which will bring great challenges to their practical application, especially for their cycle life and safety. Developing appropriate electrolyte additive is one of the most economical and effective methods to improve the electrochemical performance of LIBs. Based on the intrinsic structure of material, electrolyte additives used for NMC and NCA ternary cathode and their reaction mechanism in the past 5 years are reviewed in this paper, which include vinylene carbonate (VC), fluoro-compounds, new lithium salts, P-based, B-based, S-based, nitrile, others and combinative additives. Among them, VC becomes a kind of universal additive, which can improve the efficiency and cycle life at low voltage and normal temperature. Fluoro-compounds have been developed from mono substituted such as Fluorinated ethylene carbonate (FEC) to multi-fluorine substituted, which can improve the stability of electrode/electrolyte interface under high voltage. New lithium salt additives are mainly used to improve the film forming performance under high voltage and high temperature, such as Lithium bis(fluorosulfonyl)imide (LiFSI), Lithium difluorophosphate (LiDFP). P-contained additives[such as Tris(trimethylsilyl) phosphite (TMSPi)] are mainly to improve the stability of anode-electrolyte interface, and it has obvious synergistic effect when they combined with additives such as VC. B-contained additives are mainly used to improve the dissociation degree and stability of lithium salt, such as Tris(trimethylsilyl)borate (TMSB). S-contained additives are mainly used to improve the ionic conductivity and stability of anode SEI film, such as Prop-1-ene-1, 3-sultone (PES). Nitriles are benefited from the strong electron withdrawing effect of -CN, which can improve the stability of the electrode/electrolyte interface at high voltage. Other types of additives are some heterocyclic compounds having film forming ability and various silanes which can eliminate HF and H2O. Combinative addi-tives are developed from VC based composite to PES and PBF (pyridine boron trifluoride) system, which can endure even harsher conditions.
2018, 76(4): 278-285
doi: 10.6023/A17120544
Abstract:
Ginsenoside Re (1) and Notoginsenoside R1 (2) are two representative dammarane type protopanaxatriol-6, 20-O-bisglycosides occurring widely founded in Panaxginseng. Ginsenoside Re (1) showed potent antioxidative, anti-inflammatory and antihyperlipemia activities, and Notoginsenoside R1 (2) showed potent antioxidative and antiinflammatory activities, so it would be helpful to synthesize these homogeneous natural products in appreciable amounts by accelerating their structure-activity relationship study. As a persistent effort on the chemical syntheses of the diverse ginsenosides in our group, we report herein the efficient syntheses of these two complex natural products. Thus, based on the reactivity sequence of the four hydroxyl groups (i.e., 12-OH > 3-OH > 6-OH >> 20-OH) of the protopanaxatriol aglycon, an orthogonal and efficient protecting group strategy was applied to distinguish these hydroxyl groups. The subsequent installation of the 6, 20-O-bisglycosides are challenging, given the poor reactivity of the secondary 6-OH and tertiary 20-OH, moreover, with the latter being labile toward acidic conditions. Taking advantage of the neutral conditions of the Au(Ⅰ)-catalyzed glycosylation reaction (0.3 equiv. Ph3PAuNTf2, 4 Å MS, CH2Cl2, r.t.), the glycosylation of the acid-labile 20-hydroxyl group was achieved effectively in a high 84% yield firstly. To be convergent for the syntheses of these two ginsenosides, the 6-O-disaccharide residues were installed in a stepwise manner. For the glycosylation of the 6-OH of protopanaxatriol, a higher loading of the catalyst Ph3PAuNTf2 (0.5 equiv.) was employed in order to increase the glycosylation yield while reduce the orthoester formation, thus, the desired 6β-O-glucosides were prepared in satisfactory yields (77%~83%). Both terminal α-L-Rha/β-D-Xyl moieties at the 2' position of 6-O-glc were installed efficiently under 0.2 equiv. Ph3PAuNTf2 catalyzing condition (ClCH2CH2Cl, 5 Å MS, 40℃) with 86% and 81% yields, respectively. After global deprotection, Ginsenoside Re (1) and Notoginsenoside R1 (2) were synthesized with the longest 13 linear steps in 5.1% and 4.5% overall yields, respectively.
Ginsenoside Re (1) and Notoginsenoside R1 (2) are two representative dammarane type protopanaxatriol-6, 20-O-bisglycosides occurring widely founded in Panaxginseng. Ginsenoside Re (1) showed potent antioxidative, anti-inflammatory and antihyperlipemia activities, and Notoginsenoside R1 (2) showed potent antioxidative and antiinflammatory activities, so it would be helpful to synthesize these homogeneous natural products in appreciable amounts by accelerating their structure-activity relationship study. As a persistent effort on the chemical syntheses of the diverse ginsenosides in our group, we report herein the efficient syntheses of these two complex natural products. Thus, based on the reactivity sequence of the four hydroxyl groups (i.e., 12-OH > 3-OH > 6-OH >> 20-OH) of the protopanaxatriol aglycon, an orthogonal and efficient protecting group strategy was applied to distinguish these hydroxyl groups. The subsequent installation of the 6, 20-O-bisglycosides are challenging, given the poor reactivity of the secondary 6-OH and tertiary 20-OH, moreover, with the latter being labile toward acidic conditions. Taking advantage of the neutral conditions of the Au(Ⅰ)-catalyzed glycosylation reaction (0.3 equiv. Ph3PAuNTf2, 4 Å MS, CH2Cl2, r.t.), the glycosylation of the acid-labile 20-hydroxyl group was achieved effectively in a high 84% yield firstly. To be convergent for the syntheses of these two ginsenosides, the 6-O-disaccharide residues were installed in a stepwise manner. For the glycosylation of the 6-OH of protopanaxatriol, a higher loading of the catalyst Ph3PAuNTf2 (0.5 equiv.) was employed in order to increase the glycosylation yield while reduce the orthoester formation, thus, the desired 6β-O-glucosides were prepared in satisfactory yields (77%~83%). Both terminal α-L-Rha/β-D-Xyl moieties at the 2' position of 6-O-glc were installed efficiently under 0.2 equiv. Ph3PAuNTf2 catalyzing condition (ClCH2CH2Cl, 5 Å MS, 40℃) with 86% and 81% yields, respectively. After global deprotection, Ginsenoside Re (1) and Notoginsenoside R1 (2) were synthesized with the longest 13 linear steps in 5.1% and 4.5% overall yields, respectively.
2018, 76(4): 286-291
doi: 10.6023/A17120533
Abstract:
Sodium ion batteries (SIBs) have become one of candidates for post-lithium batteries due to the rich sodium resources and the similar physico-chemical properties between sodium and lithium, while the larger sodium ion radius affects the kinetic properties and ion mobility of the sodium ion batteries system, so finding the right electrode material has become the key to develop SIBs. Vanadium Disulfide (VS2) as a typical family member of transition metal chalcogenides (TMCs) has the graphene-like layered structure and excellent electrical conductivity, which provides sufficient space for the storage of sodium ions and ensures its high performance as anode for SIBs. In this work, we used the combination of hydrothermal method and ultrasonic stripping method to prepared three different Coin-like VS2 (VS2-Long, VS2-Middle, and VS2-Short) for sodium storage research. The results show that Coin-like VS2-Short (VS2-S) with the lowest stacking degree can expose more active sites and has a more stable structure so that it has a high capacity of 410 mAh·g-1 after 300 cycles at 100 mA·g-1 and a high rate capability of 333 mAh·g-1 even at 2000 mA·g-1. In addition, we also studied the mechanism of vanadium disulfide as electrode material of sodium ion batteries by using the ex-situ X-ray diffraction (XRD) and transmission electron microscopy (TEM). During discharge process, sodium ion was inserted into the layer of VS2 resulting in NaxVS2 at the voltage of 2.5~1.0 V, and then, NaxVS2 convert to sodium sulfide and vanadium between the voltage of 1.0~0.2 V, on the opposite charging process, sodium sulfide with vanadium will convert to NaxVS2 firstly and then vanadium disulfide will appeared again with the sodium ion deserted from the NaxVS2. This means that vanadium disulfide appears to be an insertion-conversion mechanism between 0.2~2.5 V.
Sodium ion batteries (SIBs) have become one of candidates for post-lithium batteries due to the rich sodium resources and the similar physico-chemical properties between sodium and lithium, while the larger sodium ion radius affects the kinetic properties and ion mobility of the sodium ion batteries system, so finding the right electrode material has become the key to develop SIBs. Vanadium Disulfide (VS2) as a typical family member of transition metal chalcogenides (TMCs) has the graphene-like layered structure and excellent electrical conductivity, which provides sufficient space for the storage of sodium ions and ensures its high performance as anode for SIBs. In this work, we used the combination of hydrothermal method and ultrasonic stripping method to prepared three different Coin-like VS2 (VS2-Long, VS2-Middle, and VS2-Short) for sodium storage research. The results show that Coin-like VS2-Short (VS2-S) with the lowest stacking degree can expose more active sites and has a more stable structure so that it has a high capacity of 410 mAh·g-1 after 300 cycles at 100 mA·g-1 and a high rate capability of 333 mAh·g-1 even at 2000 mA·g-1. In addition, we also studied the mechanism of vanadium disulfide as electrode material of sodium ion batteries by using the ex-situ X-ray diffraction (XRD) and transmission electron microscopy (TEM). During discharge process, sodium ion was inserted into the layer of VS2 resulting in NaxVS2 at the voltage of 2.5~1.0 V, and then, NaxVS2 convert to sodium sulfide and vanadium between the voltage of 1.0~0.2 V, on the opposite charging process, sodium sulfide with vanadium will convert to NaxVS2 firstly and then vanadium disulfide will appeared again with the sodium ion deserted from the NaxVS2. This means that vanadium disulfide appears to be an insertion-conversion mechanism between 0.2~2.5 V.
2018, 76(4): 292-297
doi: 10.6023/A17110478
Abstract:
Ethanol oxidation reaction (EOR) is a common anode process for direct ethanol fuel cell (DEFC) and ethanol reforming electrolyzer. Au@Pt and AuPt alloy are widely used bimetallic catalysts, yet no comparative study has been reported of electrocatalysis of EOR on these two differently structured catalysts. The present work aims to synthesize and characterize carbon supported Au@Pt and AuPt with controlled composition and size, and compare their electrocatalytic activities and stabilities toward EOR in alkaline media. For the synthesis of Au@Pt/C, a 5-nm Au colloid was first obtained by adding excessive amount of sodium borohydride to a chloroauric acid precursor containing sodium citrate with a mixed ice-water bath. CO gas was bubbled into the Au colloidal solution at 60℃ under strong stirring to reduce a desired amount of potassium tetrachloroplatinate(Ⅱ) to terminate Pt quasi-monolayer shell on Au nanoparticle core. A sonicated carbon black (Vulcan XC-72) aqueous slurry was then dropwise added to the above Au@Pt colloid, and the mixture was kept stirring for 48 h to ensure the exhaustive loading of Au@Pt nanoparticles onto the carbon support. For the synthesis of AuPt/C with the same Au:Pt molar ratio and metal loading as that for Au@Pt/C, coreduction of the Au(Ⅲ) and Pt(Ⅱ) species was attained by using sodium borohydride as the reducing agent with the rest procedures being same as the above mentioned. X-ray diffractometry (XRD) revealed that the diffraction peaks for Au@Pt/C were virtually same as those for Au/C, consistent with a Pt quasi-monolayer, while the diffraction peaks for AuPt/C located in between those for Au/C and Pt/C. X-ray photoelectron spectroscopy (XPS) results were consitent with the different structures of the two catalysts, and the Pt core level shift suggested an upshift of Pt d-band center for both bimetallic catalysts. Cyclic voltammetry and chronoamperometry revealed markedly increased EOR current on Au@Pt/C and AuPt/C, as compared to that of Pt/C and Au/C. CO-stripping voltammetry on Au@Pt/C and AuPt/C indicated that surface reconstruction occurred by potential cycling, resulting in a decrease of exposed Pt sites but not the electrocatalytic activities. 1H NMR analysis confirmed the C2 pathway is predominant. Nevertheless, Au@Pt/C outperformed AuPt/C and Pt/C with a lower onset oxidation potential and a higher peak current for EOR, as well as a slightly higher selectivity toward C1 pathway. Although the synergetic effect of Au-Pt bimetallic interface for EOR is not well understood, the enhanced adsorption of ethanol, OH, acetyl and CO on Pt sites may be accountable for the observed results.
Ethanol oxidation reaction (EOR) is a common anode process for direct ethanol fuel cell (DEFC) and ethanol reforming electrolyzer. Au@Pt and AuPt alloy are widely used bimetallic catalysts, yet no comparative study has been reported of electrocatalysis of EOR on these two differently structured catalysts. The present work aims to synthesize and characterize carbon supported Au@Pt and AuPt with controlled composition and size, and compare their electrocatalytic activities and stabilities toward EOR in alkaline media. For the synthesis of Au@Pt/C, a 5-nm Au colloid was first obtained by adding excessive amount of sodium borohydride to a chloroauric acid precursor containing sodium citrate with a mixed ice-water bath. CO gas was bubbled into the Au colloidal solution at 60℃ under strong stirring to reduce a desired amount of potassium tetrachloroplatinate(Ⅱ) to terminate Pt quasi-monolayer shell on Au nanoparticle core. A sonicated carbon black (Vulcan XC-72) aqueous slurry was then dropwise added to the above Au@Pt colloid, and the mixture was kept stirring for 48 h to ensure the exhaustive loading of Au@Pt nanoparticles onto the carbon support. For the synthesis of AuPt/C with the same Au:Pt molar ratio and metal loading as that for Au@Pt/C, coreduction of the Au(Ⅲ) and Pt(Ⅱ) species was attained by using sodium borohydride as the reducing agent with the rest procedures being same as the above mentioned. X-ray diffractometry (XRD) revealed that the diffraction peaks for Au@Pt/C were virtually same as those for Au/C, consistent with a Pt quasi-monolayer, while the diffraction peaks for AuPt/C located in between those for Au/C and Pt/C. X-ray photoelectron spectroscopy (XPS) results were consitent with the different structures of the two catalysts, and the Pt core level shift suggested an upshift of Pt d-band center for both bimetallic catalysts. Cyclic voltammetry and chronoamperometry revealed markedly increased EOR current on Au@Pt/C and AuPt/C, as compared to that of Pt/C and Au/C. CO-stripping voltammetry on Au@Pt/C and AuPt/C indicated that surface reconstruction occurred by potential cycling, resulting in a decrease of exposed Pt sites but not the electrocatalytic activities. 1H NMR analysis confirmed the C2 pathway is predominant. Nevertheless, Au@Pt/C outperformed AuPt/C and Pt/C with a lower onset oxidation potential and a higher peak current for EOR, as well as a slightly higher selectivity toward C1 pathway. Although the synergetic effect of Au-Pt bimetallic interface for EOR is not well understood, the enhanced adsorption of ethanol, OH, acetyl and CO on Pt sites may be accountable for the observed results.
2018, 76(4): 298-302
doi: 10.6023/A18010003
Abstract:
Temperature dependent near-infrared (NIR) spectroscopy has been developed for structural analyses, especially for the study of hydrogen bonding, due to the distinct influence of temperature on both intra-and inter-molecular interactions. In this work, the hydrogen bonding of primary aliphatic amines (amylamine, hexylamine and heptylamine) were studied using the NIR spectra measured from 25 to 80℃ with a step of 5℃. Continuous wavelet transform (CWT) was applied to enhance the resolution of the NIR spectra, and independent component analysis (ICA) was adopted for analyzing the temperature effect. High resolution spectra were obtained by CWT, from which the peaks of free and hydrogen-bonded NH groups can be identified. The results obtained by ICA show that three independent components (ICs) can be obtained, corresponding to the spectral information of the free, linearly and cyclically hydrogen-bonded NH groups, respectively. Therefore, with the reconstructed spectra from the three ICs, the variation of the three forms of NH groups with temperature can be analyzed. When temperature increases, the hydrogen-bonded NH groups transform into the free form, and the cyclic form dissociates through the linear form. Furthermore, NIR spectra of the amines in carbon tetrachloride (CCl4) solution were measured at 25℃ in the concentration range of 0.1~1.0 mol/L. The three ICs can also be obtained by ICA from the spectra after CWT. From the variation of the ICs with concentration, it was shown that NH groups in the amines prefer to be linearly aggregated at low concentration, but the cyclic aggregation increases with the increase of concentration. In addition, a comparison was performed on the results obtained by ICA from the spectra of the three amines measured at different temperatures. The result shows that there is no obvious difference for the temperature effect of the three amines, the variation of the three forms of NH groups with temperature, however, is different. With the increase of the carbon chain length, the variation of free and cyclically hydrogen-bonded NH group slows down, but there is a slight increase for the change rate of linearly hydrogen-bonded NH group. Therefore, temperature dependent near-infrared (NIR) spectroscopy may provide a new tool for studying the hydrogen bonding in liquid and solution samples with the help of chemometric calculations. The method may be promising for analyzing the complicated interactions in bio-systems, particularly the hydrogen bonding or inter-and intra-molecular interactions.
Temperature dependent near-infrared (NIR) spectroscopy has been developed for structural analyses, especially for the study of hydrogen bonding, due to the distinct influence of temperature on both intra-and inter-molecular interactions. In this work, the hydrogen bonding of primary aliphatic amines (amylamine, hexylamine and heptylamine) were studied using the NIR spectra measured from 25 to 80℃ with a step of 5℃. Continuous wavelet transform (CWT) was applied to enhance the resolution of the NIR spectra, and independent component analysis (ICA) was adopted for analyzing the temperature effect. High resolution spectra were obtained by CWT, from which the peaks of free and hydrogen-bonded NH groups can be identified. The results obtained by ICA show that three independent components (ICs) can be obtained, corresponding to the spectral information of the free, linearly and cyclically hydrogen-bonded NH groups, respectively. Therefore, with the reconstructed spectra from the three ICs, the variation of the three forms of NH groups with temperature can be analyzed. When temperature increases, the hydrogen-bonded NH groups transform into the free form, and the cyclic form dissociates through the linear form. Furthermore, NIR spectra of the amines in carbon tetrachloride (CCl4) solution were measured at 25℃ in the concentration range of 0.1~1.0 mol/L. The three ICs can also be obtained by ICA from the spectra after CWT. From the variation of the ICs with concentration, it was shown that NH groups in the amines prefer to be linearly aggregated at low concentration, but the cyclic aggregation increases with the increase of concentration. In addition, a comparison was performed on the results obtained by ICA from the spectra of the three amines measured at different temperatures. The result shows that there is no obvious difference for the temperature effect of the three amines, the variation of the three forms of NH groups with temperature, however, is different. With the increase of the carbon chain length, the variation of free and cyclically hydrogen-bonded NH group slows down, but there is a slight increase for the change rate of linearly hydrogen-bonded NH group. Therefore, temperature dependent near-infrared (NIR) spectroscopy may provide a new tool for studying the hydrogen bonding in liquid and solution samples with the help of chemometric calculations. The method may be promising for analyzing the complicated interactions in bio-systems, particularly the hydrogen bonding or inter-and intra-molecular interactions.
2018, 76(4): 303-310
doi: 10.6023/A18010026
Abstract:
With the rapidly increasing number of reported metal-organic frameworks (MOFs), conventional trial-and-error method is obviously not applicable to the development of high-performance MOFs for formaldehyde adsorption, due to its low efficiency, high cost and long developing period. Thus, high-throughput computational screening (HTCS) strategy based on grand canonical Monte Carlo (GCMC) simulation is proposed to quickly explore the top-performing MOFs with high adsorption capability towards formaldehyde. In this work, the computation-ready experimental (CoRE)-MOF database consisting of 2932 MOF structures carrying density derived electrostatic and chemical (DDEC) charges obtained from density function (DFT) theory calculations, were employed in high-throughput GCMC simulations for formaldehyde adsorption from the air. The structure-property relationship from HTCS revealed that the MOF candidates with high formaldehyde uptakes exhibited small pore sizes, relatively high selectivity and moderate heat of adsorption (Qst). Afterwards, the top MOFs with both high uptake and selectivity towards formaldehyde were chosen for further experimental evaluation. Three selected MOFs Y-BTC, ZnCar and Ni-BIC were successfully synthesized and characterized by powder X-ray diffraction (PXRD) and BET surface area analysis. In order to validate our HTCS strategy, the representative Cu-BTC and activated carbon (AC) were also adopted as controls. The formaldehyde adsorption test was performed in a sealed container with the formaldehyde concentration of 100 mg/m3 at 298 K. After 24 h adsorption, the formaldehyde uptakes of the adsorbents were obtained according to the concentration changes prior to and after formaldehyde exposure by UV-vis spectrometer. It was found that the adsorption capacities of Y-BTC, ZnCar and Ni-BIC were 0.38, 0.25 and 0.11 mol/kg, respectively, which were remarkably higher than Cu-BTC (0.08 mol/kg) and AC (0.06 mol/kg). The recyclability of the best performer Y-BTC was also verified. These findings open up the possibility of employing HTCS strategy for highly efficient exploration of MOF adsorbents for formaldehyde removal.
With the rapidly increasing number of reported metal-organic frameworks (MOFs), conventional trial-and-error method is obviously not applicable to the development of high-performance MOFs for formaldehyde adsorption, due to its low efficiency, high cost and long developing period. Thus, high-throughput computational screening (HTCS) strategy based on grand canonical Monte Carlo (GCMC) simulation is proposed to quickly explore the top-performing MOFs with high adsorption capability towards formaldehyde. In this work, the computation-ready experimental (CoRE)-MOF database consisting of 2932 MOF structures carrying density derived electrostatic and chemical (DDEC) charges obtained from density function (DFT) theory calculations, were employed in high-throughput GCMC simulations for formaldehyde adsorption from the air. The structure-property relationship from HTCS revealed that the MOF candidates with high formaldehyde uptakes exhibited small pore sizes, relatively high selectivity and moderate heat of adsorption (Qst). Afterwards, the top MOFs with both high uptake and selectivity towards formaldehyde were chosen for further experimental evaluation. Three selected MOFs Y-BTC, ZnCar and Ni-BIC were successfully synthesized and characterized by powder X-ray diffraction (PXRD) and BET surface area analysis. In order to validate our HTCS strategy, the representative Cu-BTC and activated carbon (AC) were also adopted as controls. The formaldehyde adsorption test was performed in a sealed container with the formaldehyde concentration of 100 mg/m3 at 298 K. After 24 h adsorption, the formaldehyde uptakes of the adsorbents were obtained according to the concentration changes prior to and after formaldehyde exposure by UV-vis spectrometer. It was found that the adsorption capacities of Y-BTC, ZnCar and Ni-BIC were 0.38, 0.25 and 0.11 mol/kg, respectively, which were remarkably higher than Cu-BTC (0.08 mol/kg) and AC (0.06 mol/kg). The recyclability of the best performer Y-BTC was also verified. These findings open up the possibility of employing HTCS strategy for highly efficient exploration of MOF adsorbents for formaldehyde removal.
2018, 76(4): 311-318
doi: 10.6023/A18010015
Abstract:
The reaction class of a free radical with a molecule are non-elementary reactions with negative activation energies and they are usually proceeded through two reaction steps with the first step being a reactant complex formation. This class of reactions are widespread in the atmospheric chemistry and the mechanism of hydrocarbon fuel combustion, so they are extensively studied in the theoretical calculation and experimental studies. The reaction class of α-H abstraction from alkyl hydroperoxides (ROOH) by hydroxyl radicals, which are important in the mechanism of hydrocarbon fuel combustion, are chosen as the object of this study. The regularity of this reaction class are revealed by quantum chemical calculations and their kinetic parameters are accurately calculated. When the standard molar Gibbs free energy change of the formation of the reactant complex in the first step is equal to zero, the corresponding temperature is defined as the conversion temperature Tc in this study, and it is shown that a steady state approximation method are applicable for this kind of reaction system to calculate the overall reaction rate constants when the temperature is much higher than the Tc. Geometric optimization and frequency analysis for all species were conducted at the BHandHLYP/6-311G(d, p) level. Five reactions are chosen as the representative for the reaction class and their single point energies are calculated using the method of CCSD(T)/CBS and it is shown that the highest conversion temperature for the five reactions is 195.17 K, far below usual modeling lowest temperature of the hydrocarbon fuel combustion, and therefore, the steady state approximation method is reasonable. It is also shown that the reaction-center geometries of the transition states are conserved, and thus the isodesmic reaction method is applicable to this reaction class to correct the energy barriers and rate constants at low-level BHandHLYP method. The obtained energy barriers are compared with the results using high-level ab initio CCSD(T)/CBS method and it is shown that the maximum absolute deviation of reaction energy barriers can be reduced from 19.99 kJ·mol-1 before correction to 1.47 kJ·mol-1 after correction, indicating that the isodesmic reaction method are applicable for the accurate calculation of the kinetic parameters for large-size molecular systems with the negative activation energy reaction. Finally, energy barriers for 20 reactions in the class are calculated with the isodesmic reaction method, and then based on steady state approximation, the rate constants for the overall reactions are calculated using the transition state theory in combination with the isodesmic correction scheme. It is shown that the negative activation energy relationship for the reaction class only exists in the low temperature region.
The reaction class of a free radical with a molecule are non-elementary reactions with negative activation energies and they are usually proceeded through two reaction steps with the first step being a reactant complex formation. This class of reactions are widespread in the atmospheric chemistry and the mechanism of hydrocarbon fuel combustion, so they are extensively studied in the theoretical calculation and experimental studies. The reaction class of α-H abstraction from alkyl hydroperoxides (ROOH) by hydroxyl radicals, which are important in the mechanism of hydrocarbon fuel combustion, are chosen as the object of this study. The regularity of this reaction class are revealed by quantum chemical calculations and their kinetic parameters are accurately calculated. When the standard molar Gibbs free energy change of the formation of the reactant complex in the first step is equal to zero, the corresponding temperature is defined as the conversion temperature Tc in this study, and it is shown that a steady state approximation method are applicable for this kind of reaction system to calculate the overall reaction rate constants when the temperature is much higher than the Tc. Geometric optimization and frequency analysis for all species were conducted at the BHandHLYP/6-311G(d, p) level. Five reactions are chosen as the representative for the reaction class and their single point energies are calculated using the method of CCSD(T)/CBS and it is shown that the highest conversion temperature for the five reactions is 195.17 K, far below usual modeling lowest temperature of the hydrocarbon fuel combustion, and therefore, the steady state approximation method is reasonable. It is also shown that the reaction-center geometries of the transition states are conserved, and thus the isodesmic reaction method is applicable to this reaction class to correct the energy barriers and rate constants at low-level BHandHLYP method. The obtained energy barriers are compared with the results using high-level ab initio CCSD(T)/CBS method and it is shown that the maximum absolute deviation of reaction energy barriers can be reduced from 19.99 kJ·mol-1 before correction to 1.47 kJ·mol-1 after correction, indicating that the isodesmic reaction method are applicable for the accurate calculation of the kinetic parameters for large-size molecular systems with the negative activation energy reaction. Finally, energy barriers for 20 reactions in the class are calculated with the isodesmic reaction method, and then based on steady state approximation, the rate constants for the overall reactions are calculated using the transition state theory in combination with the isodesmic correction scheme. It is shown that the negative activation energy relationship for the reaction class only exists in the low temperature region.
