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2020 Volume 78 Issue 6
2020, 78(6): 463-465
doi: 10.6023/A20040110
Abstract:
Interfacial adhesion occurs by covalent bonding or noncovalent interactions that are ubiquitous in nature. Adhesive materials are widely desired in many fields including wearable devices, electronic devices, medical surgeries, etc. In recent years, bio-inspired structural adhesive materials and adhesives have been rapidly developed, and some artificial adhesive materials have been put into practical use. However, the restrictions of structural microfabrication and the complexity of synthetic routes limit their large-scale production. In contrast, the nanoparticle solutions provide a simpler and easier alternative to achieve strong adhesion. Here this article makes a highlight on the recent research of "strong anisotropic adhesion of cellulose nanocrystals suspension".
Interfacial adhesion occurs by covalent bonding or noncovalent interactions that are ubiquitous in nature. Adhesive materials are widely desired in many fields including wearable devices, electronic devices, medical surgeries, etc. In recent years, bio-inspired structural adhesive materials and adhesives have been rapidly developed, and some artificial adhesive materials have been put into practical use. However, the restrictions of structural microfabrication and the complexity of synthetic routes limit their large-scale production. In contrast, the nanoparticle solutions provide a simpler and easier alternative to achieve strong adhesion. Here this article makes a highlight on the recent research of "strong anisotropic adhesion of cellulose nanocrystals suspension".
2020, 78(6): 466-477
doi: 10.6023/A20030088
Abstract:
The increasing shortage of freshwater resources and water pollution are important challenges facing the world, and vigorous development of seawater desalination and water treatment technologies is an effective way to alleviate this problem. In recent years, low energy consumption and green membrane-separation technology has been widely used in the fields of seawater desalination and water treatment. Covalent organic framework (COF) membranes are potential high-performance membrane separation materials due to their adjustable pore size and chemical environment. In this paper, the research progress of COF-membranes synthesis methodology is introduced in detail, the research of COF membranes in seawater desalination and water treatment is summarized, and the challenges and perspectives of COF membranes for seawater desalination and treatment are elaborated.
The increasing shortage of freshwater resources and water pollution are important challenges facing the world, and vigorous development of seawater desalination and water treatment technologies is an effective way to alleviate this problem. In recent years, low energy consumption and green membrane-separation technology has been widely used in the fields of seawater desalination and water treatment. Covalent organic framework (COF) membranes are potential high-performance membrane separation materials due to their adjustable pore size and chemical environment. In this paper, the research progress of COF-membranes synthesis methodology is introduced in detail, the research of COF membranes in seawater desalination and water treatment is summarized, and the challenges and perspectives of COF membranes for seawater desalination and treatment are elaborated.
2020, 78(6): 478-489
doi: 10.6023/A20040103
Abstract:
Cholesteric liquid crystals (CLCs) are a kind of intriguing soft photonic crystal materials, in which the orientation of LC molecules varies in a helical fashion, and selectively reflect light, known as structural color, according to Bragg's law. Moreover, the structural color determined by the pitch length of the helices in CLCs can be tuned owing to the dynamic control of inherent self-organized helical superstructures in response to external stimuli. Currently, light-driven CLCs have attracted extensive interest because light, compared to other stimuli, has unique advantages of remote, temporal, local and spatial manipulation. Such elegant systems are generally formulated by doping light-driven chiral switches, mainly consisting of chiral centers and photoswitches, into a nematic LC host. The chiral centers are able to twist the nematic LC host into helical superstructures, which is represented by helical twisting power (HTP). The photoswitches undergo configurational changes upon photoisomerization, leading to the variation in HTP and the pitch length of the helices, and consequently tune the structural color of the CLCs. These light-driven CLCs provide opportunities for various photonic applications such as tunable filters, sensors, tunable optical lasers, and optically addressed displays. In this review, we summarize diverse light-driven CLC systems according to the type of the photoswitch in doped chiral switches. Azobenzene-and motor-based chiral switches usually have high HTP and large variation in HTP, which enables the tuning range of the resultant CLC to cover visible spectrum. Besides, chiral switches based on dithienylethenes have also been synthesized and utilized to tune the reflection of the CLC across red, green and blue colors that remain unchanged in darkness even after one week because of the excellent thermal stability of dithienylethenes. Chiral switches based on dicyanoethene are used to construct an optically tunable reflective-photoluminescent CLC system. Importantly, the design of the light-driven chiral switches is analyzed in detail to reveal the structure-property correlation. Potential and demonstrated practical applications of light-driven CLCs are discussed, and forecast of existing challenges and opportunities in CLC systems are concluded.
Cholesteric liquid crystals (CLCs) are a kind of intriguing soft photonic crystal materials, in which the orientation of LC molecules varies in a helical fashion, and selectively reflect light, known as structural color, according to Bragg's law. Moreover, the structural color determined by the pitch length of the helices in CLCs can be tuned owing to the dynamic control of inherent self-organized helical superstructures in response to external stimuli. Currently, light-driven CLCs have attracted extensive interest because light, compared to other stimuli, has unique advantages of remote, temporal, local and spatial manipulation. Such elegant systems are generally formulated by doping light-driven chiral switches, mainly consisting of chiral centers and photoswitches, into a nematic LC host. The chiral centers are able to twist the nematic LC host into helical superstructures, which is represented by helical twisting power (HTP). The photoswitches undergo configurational changes upon photoisomerization, leading to the variation in HTP and the pitch length of the helices, and consequently tune the structural color of the CLCs. These light-driven CLCs provide opportunities for various photonic applications such as tunable filters, sensors, tunable optical lasers, and optically addressed displays. In this review, we summarize diverse light-driven CLC systems according to the type of the photoswitch in doped chiral switches. Azobenzene-and motor-based chiral switches usually have high HTP and large variation in HTP, which enables the tuning range of the resultant CLC to cover visible spectrum. Besides, chiral switches based on dithienylethenes have also been synthesized and utilized to tune the reflection of the CLC across red, green and blue colors that remain unchanged in darkness even after one week because of the excellent thermal stability of dithienylethenes. Chiral switches based on dicyanoethene are used to construct an optically tunable reflective-photoluminescent CLC system. Importantly, the design of the light-driven chiral switches is analyzed in detail to reveal the structure-property correlation. Potential and demonstrated practical applications of light-driven CLCs are discussed, and forecast of existing challenges and opportunities in CLC systems are concluded.
2020, 78(6): 490-503
doi: 10.6023/A20030086
Abstract:
The selective oxyfunctionalization of unactivated C-H bonds is one of long-standing issues and current topics in synthetic chemistry. One of the major synthetic targets for these reactions is the direct and selective hydroxylation of alkanes to alcohols, however, which faces many severe challenges in controlling chemoselectivity, regioselectivity and stereoselectivity. In nature, the oxidative metalloenzymes is capable of selectively catalyzing the insertion of oxygen into inert C-H bonds of alkanes, such as methane monooxygenases (MMO), soluble butane monooxygenases (sBMO), fungal peroxygenases and Cytochrome P450 monooxygenases (P450s). Among them, P450s that catalyze a variety of oxygenation reactions have attracted special attentions because of some intrinsic advantages. P450s are widely distributed in plants, animals and microorganisms and over 41000 sequences of P450 genes have been named from various databases, which enhances the potentials of P450s in developing the oxidative biocatalysts. In addition, compared with MMOs, P450s that have smaller molecule weight (≈45 kDa) are simple and amenable to recombinant expression and engineering. Herein, we reviewed the recent progress of alkanes hydroxylation by P450 enzymes either in its natural forms or engineered variants, as well as chemical activated systems. The related background and the catalytic mechanism of P450s for alkanes hydroxylation were firstly discussed. The representative examples by natural P450s mainly from CYP153, CYP52 and other P450 families were then outlined. The strategies of rational design and directed evolution on P450s engineering were then summarized focusing on the native/non-native alkane substrates. Three unusual strategies, including substrate engineering, decoy molecule, and dual-functional small molecule co-catalysis, were also discussed on their applications for activating P450s to hydroxylate non-native small alkanes. Finally, we perspective the challenges and solutions that faced by P450 enzymes in the development of new biocatalytic systems toward selective hydroxylation of alkanes. In conclusion, cytochrome P450 enzymes in both of their native and modified form are promising biocatalysts for alkanes hydroxylation and need further be investigated to gain the practical industrial applications.
The selective oxyfunctionalization of unactivated C-H bonds is one of long-standing issues and current topics in synthetic chemistry. One of the major synthetic targets for these reactions is the direct and selective hydroxylation of alkanes to alcohols, however, which faces many severe challenges in controlling chemoselectivity, regioselectivity and stereoselectivity. In nature, the oxidative metalloenzymes is capable of selectively catalyzing the insertion of oxygen into inert C-H bonds of alkanes, such as methane monooxygenases (MMO), soluble butane monooxygenases (sBMO), fungal peroxygenases and Cytochrome P450 monooxygenases (P450s). Among them, P450s that catalyze a variety of oxygenation reactions have attracted special attentions because of some intrinsic advantages. P450s are widely distributed in plants, animals and microorganisms and over 41000 sequences of P450 genes have been named from various databases, which enhances the potentials of P450s in developing the oxidative biocatalysts. In addition, compared with MMOs, P450s that have smaller molecule weight (≈45 kDa) are simple and amenable to recombinant expression and engineering. Herein, we reviewed the recent progress of alkanes hydroxylation by P450 enzymes either in its natural forms or engineered variants, as well as chemical activated systems. The related background and the catalytic mechanism of P450s for alkanes hydroxylation were firstly discussed. The representative examples by natural P450s mainly from CYP153, CYP52 and other P450 families were then outlined. The strategies of rational design and directed evolution on P450s engineering were then summarized focusing on the native/non-native alkane substrates. Three unusual strategies, including substrate engineering, decoy molecule, and dual-functional small molecule co-catalysis, were also discussed on their applications for activating P450s to hydroxylate non-native small alkanes. Finally, we perspective the challenges and solutions that faced by P450 enzymes in the development of new biocatalytic systems toward selective hydroxylation of alkanes. In conclusion, cytochrome P450 enzymes in both of their native and modified form are promising biocatalysts for alkanes hydroxylation and need further be investigated to gain the practical industrial applications.
2020, 78(6): 504-515
doi: 10.6023/A20030070
Abstract:
Electrochemical reaction is a continuous dynamic process, accompanied by generation of short-lived intermediates and complex structural substances. Therefore, precisely and effectively capturing the products of the reaction process is helpful to accurately deduce its reaction mechanism, optimize the reaction parameters and improve the reaction efficiency. At present, the mainstream electrochemical on-line monitoring techniques include spectroscopy, cyclic voltammetry and linear polarization curves. These methods are capable to detect the structure and composition changes of most substances in the reaction process. However, in order to more systematically and accurately grasp the information of all products, the real-time and in situ reaction monitoring technologies needs to be further expanded. Mass spectrometry (MS) has the advantages of high sensitivity, good selectivity, rapid response time and structural analysis, making itself an ideal research method for electrochemical reactions. In recent years, more and more reports on the study of electrochemical reaction by MS have been published. In particular, ambient ionization sources such as electrospray ionization (ESI) and its derived ionization techniques developed for electrochemistry have become a research hotspot. This review introduced the recently published electrochemistry-mass spectrometry (EC-MS) techniques, and described the electrochemical ion sources that designed and developed for different types of electrochemical reactions.
Electrochemical reaction is a continuous dynamic process, accompanied by generation of short-lived intermediates and complex structural substances. Therefore, precisely and effectively capturing the products of the reaction process is helpful to accurately deduce its reaction mechanism, optimize the reaction parameters and improve the reaction efficiency. At present, the mainstream electrochemical on-line monitoring techniques include spectroscopy, cyclic voltammetry and linear polarization curves. These methods are capable to detect the structure and composition changes of most substances in the reaction process. However, in order to more systematically and accurately grasp the information of all products, the real-time and in situ reaction monitoring technologies needs to be further expanded. Mass spectrometry (MS) has the advantages of high sensitivity, good selectivity, rapid response time and structural analysis, making itself an ideal research method for electrochemical reactions. In recent years, more and more reports on the study of electrochemical reaction by MS have been published. In particular, ambient ionization sources such as electrospray ionization (ESI) and its derived ionization techniques developed for electrochemistry have become a research hotspot. This review introduced the recently published electrochemistry-mass spectrometry (EC-MS) techniques, and described the electrochemical ion sources that designed and developed for different types of electrochemical reactions.
2020, 78(6): 516-527
doi: 10.6023/A20020036
Abstract:
Secondary organic aerosol (SOA) is a major component of aerosols in the atmosphere, which plays a crucial role in climate change, regional pollution and human health. Laboratory simulations are usually used to mimic SOA formation. The most commonly used simulation facilities are environmental chambers and potential aerosol mass (PAM) reactors. Here in this work, we review the studies about influencing factors and mechanisms of SOA formation, as well as the evolution of SOA aging. We summarize the influencing factors on SOA yields, i.e. OH exposure, NOx level, and the loading and chemical composition of seed particles. The effects of NOx level (i.e. VOCs/NOx) and OH exposure are nonmonotonic. The NOx level influences the fate of RO2 radicals, so SOA yields will increase and then decrease with the addition of NOx. Similarly, the increase of OH exposure affects the major oxidation mechanism from functionalization to fragmentation, leading to the up and down trend of SOA yields. The higher seed particle loading provides more surface area for condensable products and then increases the SOA yields. The particle acidity favors the uptake process for gas-phase products and promote the SOA formation via further reactions in the condense phase. Trace components e.g. transition metals and minerals can be involved in the SOA formation and aging by catalysis or affecting the uptake of oxidants and their products. Chambers and PAM reactors are usually used to explore SOA formation potential of different sources. SOA formation potential from vehicles will be influenced by engine types, engine loading and composition of fuel. The highest SOA enhancement ratio (SOA/POA) from gasoline engines is about 4~14, when the equivalent photochemical days are 2~3 d. The SOA production mass from gasoline vehicles is from about 10~40 to 400~500 mg/kg fuel. The SOA formation potential is about 400~500 mg/kg fuel. The largest SOA enhancement ratio for biomass burning is 1.4~7.6, which occurs at 3~4 photochemical days. The SOA enhancement ratio from ambient air differs from region to region. However, the highest ratios all occur at the photochemical age of about 2~4 d. We summarize the SOA characteristics evolution with aging. Oxidation state of particles will increase with OH exposure. Changes of H/C and O/C with increasing OH exposure can be plotted in the Van Krevelen diagrams. The slopes of fitted curve range from -1 to 0, indicating OA evolution chemistry involving addition of carboxylic acids or addition of alcohols/peroxides. In addition, the volatility and hygroscopicity of oxidized OA will be higher than primary organic aerosols. In the future, more studies should be focused on developing new technologies to measuring the oxidized intermediate products at a molecular level. Also the researches on the mechanism of SOA formation from complex precursors are also crucial to understand the SOA formation at real atmosphere.
Secondary organic aerosol (SOA) is a major component of aerosols in the atmosphere, which plays a crucial role in climate change, regional pollution and human health. Laboratory simulations are usually used to mimic SOA formation. The most commonly used simulation facilities are environmental chambers and potential aerosol mass (PAM) reactors. Here in this work, we review the studies about influencing factors and mechanisms of SOA formation, as well as the evolution of SOA aging. We summarize the influencing factors on SOA yields, i.e. OH exposure, NOx level, and the loading and chemical composition of seed particles. The effects of NOx level (i.e. VOCs/NOx) and OH exposure are nonmonotonic. The NOx level influences the fate of RO2 radicals, so SOA yields will increase and then decrease with the addition of NOx. Similarly, the increase of OH exposure affects the major oxidation mechanism from functionalization to fragmentation, leading to the up and down trend of SOA yields. The higher seed particle loading provides more surface area for condensable products and then increases the SOA yields. The particle acidity favors the uptake process for gas-phase products and promote the SOA formation via further reactions in the condense phase. Trace components e.g. transition metals and minerals can be involved in the SOA formation and aging by catalysis or affecting the uptake of oxidants and their products. Chambers and PAM reactors are usually used to explore SOA formation potential of different sources. SOA formation potential from vehicles will be influenced by engine types, engine loading and composition of fuel. The highest SOA enhancement ratio (SOA/POA) from gasoline engines is about 4~14, when the equivalent photochemical days are 2~3 d. The SOA production mass from gasoline vehicles is from about 10~40 to 400~500 mg/kg fuel. The SOA formation potential is about 400~500 mg/kg fuel. The largest SOA enhancement ratio for biomass burning is 1.4~7.6, which occurs at 3~4 photochemical days. The SOA enhancement ratio from ambient air differs from region to region. However, the highest ratios all occur at the photochemical age of about 2~4 d. We summarize the SOA characteristics evolution with aging. Oxidation state of particles will increase with OH exposure. Changes of H/C and O/C with increasing OH exposure can be plotted in the Van Krevelen diagrams. The slopes of fitted curve range from -1 to 0, indicating OA evolution chemistry involving addition of carboxylic acids or addition of alcohols/peroxides. In addition, the volatility and hygroscopicity of oxidized OA will be higher than primary organic aerosols. In the future, more studies should be focused on developing new technologies to measuring the oxidized intermediate products at a molecular level. Also the researches on the mechanism of SOA formation from complex precursors are also crucial to understand the SOA formation at real atmosphere.
2020, 78(6): 528-533
doi: 10.6023/A20040121
Abstract:
Herein, we report a Janus supramolecular polymer consisting of two chemically distinct hyperbranched polymers, which is coined as Janus hyperbranched polymer (JHBP). Firstly, hydrophilic hyperbranched polyglycerol with an apex of β-cyclodextrin (CD-g-HPG) and hydrophobic hyperbranched poly(3-ethyl-3-oxetanemethanol) with an apex of a ferrocene (Fc-g-HBPO) were synthesized according to the anionic ring-opening multi-branching polymerization and cationic ring-opening polymerization, respectively. Then, amphiphilic supramolecular JHBP HBPO-b-HPG was constructed by adding H2O to cosolvent DMF through the special Fc/CD host-guest interactions and such an amphiphilic supramolecular polymer can further aggregated into assemblies. The formation and self-assembly process of supramolecular JHBP HBPO-b-HPG was tracked by dynamic light scattering (DLS). The results showed that when the volume percentage ratio of H2O/DMF was increased to 16%, the HBPO-b-HPG was formed with Dh of 5.6 nm, which is close to the size of the 1:1 complex of CD-g-HPG and Fc-g-HBPO, then, with H2O/DMF ratio continuing to increase, HBPO-b-HPG rapidly aggregated into assemblies. The 2D NOESY and cyclic voltammetry (CV) curves were also used to verify the Fc/CD host-guest complexation ability. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to characterize the morphology of the assemblies. The results showed that the HBPO-b-HPG self-assembled into unilamellar bilayer vesicles of around 260 nm. When NaCl was added after electrochemical oxidation, such vesicles could disassemble due to the cooperation of the transformation of Fc to oxidation state Fc+ and equal potential destruction. Finally, DLS tracking proved that such vesicles showed excellent stability under the conditions of heating and adding host and guest competition molecules.
Herein, we report a Janus supramolecular polymer consisting of two chemically distinct hyperbranched polymers, which is coined as Janus hyperbranched polymer (JHBP). Firstly, hydrophilic hyperbranched polyglycerol with an apex of β-cyclodextrin (CD-g-HPG) and hydrophobic hyperbranched poly(3-ethyl-3-oxetanemethanol) with an apex of a ferrocene (Fc-g-HBPO) were synthesized according to the anionic ring-opening multi-branching polymerization and cationic ring-opening polymerization, respectively. Then, amphiphilic supramolecular JHBP HBPO-b-HPG was constructed by adding H2O to cosolvent DMF through the special Fc/CD host-guest interactions and such an amphiphilic supramolecular polymer can further aggregated into assemblies. The formation and self-assembly process of supramolecular JHBP HBPO-b-HPG was tracked by dynamic light scattering (DLS). The results showed that when the volume percentage ratio of H2O/DMF was increased to 16%, the HBPO-b-HPG was formed with Dh of 5.6 nm, which is close to the size of the 1:1 complex of CD-g-HPG and Fc-g-HBPO, then, with H2O/DMF ratio continuing to increase, HBPO-b-HPG rapidly aggregated into assemblies. The 2D NOESY and cyclic voltammetry (CV) curves were also used to verify the Fc/CD host-guest complexation ability. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to characterize the morphology of the assemblies. The results showed that the HBPO-b-HPG self-assembled into unilamellar bilayer vesicles of around 260 nm. When NaCl was added after electrochemical oxidation, such vesicles could disassemble due to the cooperation of the transformation of Fc to oxidation state Fc+ and equal potential destruction. Finally, DLS tracking proved that such vesicles showed excellent stability under the conditions of heating and adding host and guest competition molecules.
2020, 78(6): 534-539
doi: 10.6023/A20040130
Abstract:
Recovering C2H4 from refinery gas is an effective way to broaden the source of ethylene. However, it's a challenging task to separate C2H4 and C2H6 due to their very close physical properties and molecular size. Metal-organic frameworks (MOFs) are shown broad prospects in the field of light hydrocarbon separation in recent years. In this work, NH3 is used to modify the structure of UTSA-280, the efficient separation of C2H4/C2H6 can be achieved through the adjustment of one-dimensional channels. UTSA-280 has undergone stepwise adsorption of ammonia gas at 298 K and 100 kPa. After partial ammonia removal, we obtained the modified UTSA-280 that ammonia adsorption modification with a mass loading of 5.6% for UTSA-280-M1 and 2.8% for UTSA-280-M2. The NH3 modified UTSA-280 shows a unique ultramicroporous structure that can enhance the adsorption of C2H4 and does not adsorb the slightly larger C2H6, achieving the ideal C2H4/C2H6 adsorption selectivity (more than 1000). Ammonia molecules play the role of perfectly adjusting the size of one-dimensional channels and realize the ideal screening effect of C2H4/C2H6. The C2H4 adsorption capacity of NH3 modified UTSA-280-M2 can be improved to 2.83 mmol/g at 298 K and 100 kPa (an increase of 29% compared with initial material). And its ultramicroporous structure can fully block the adsorption of C2H6, which finally achieves a C2H4/C2H6 selectivity over 1200. Grand Canonical Monte Carlo (GCMC) simulation of C2H4/C2H6 mixed gases (equal volume) adsorption results showed that the modified UTSA-280 had more C2H4 adsorption distribution in the mixed components than C2H6. Through the C2H4/C2H6 mixed gases breakthrough test at 298 K, NH3 modified UTSA-280-M2 shows a separation time of more than 48 min, which is more than the initial 25 min. Compared with the unmodified material, the separation performance is nearly doubled. Scalable synthesis, stable structure, and the advantages of controllable performance after ammonia modification have prompted this material to have great prospects in the industrialization of C2H4/C2H6 separation.
Recovering C2H4 from refinery gas is an effective way to broaden the source of ethylene. However, it's a challenging task to separate C2H4 and C2H6 due to their very close physical properties and molecular size. Metal-organic frameworks (MOFs) are shown broad prospects in the field of light hydrocarbon separation in recent years. In this work, NH3 is used to modify the structure of UTSA-280, the efficient separation of C2H4/C2H6 can be achieved through the adjustment of one-dimensional channels. UTSA-280 has undergone stepwise adsorption of ammonia gas at 298 K and 100 kPa. After partial ammonia removal, we obtained the modified UTSA-280 that ammonia adsorption modification with a mass loading of 5.6% for UTSA-280-M1 and 2.8% for UTSA-280-M2. The NH3 modified UTSA-280 shows a unique ultramicroporous structure that can enhance the adsorption of C2H4 and does not adsorb the slightly larger C2H6, achieving the ideal C2H4/C2H6 adsorption selectivity (more than 1000). Ammonia molecules play the role of perfectly adjusting the size of one-dimensional channels and realize the ideal screening effect of C2H4/C2H6. The C2H4 adsorption capacity of NH3 modified UTSA-280-M2 can be improved to 2.83 mmol/g at 298 K and 100 kPa (an increase of 29% compared with initial material). And its ultramicroporous structure can fully block the adsorption of C2H6, which finally achieves a C2H4/C2H6 selectivity over 1200. Grand Canonical Monte Carlo (GCMC) simulation of C2H4/C2H6 mixed gases (equal volume) adsorption results showed that the modified UTSA-280 had more C2H4 adsorption distribution in the mixed components than C2H6. Through the C2H4/C2H6 mixed gases breakthrough test at 298 K, NH3 modified UTSA-280-M2 shows a separation time of more than 48 min, which is more than the initial 25 min. Compared with the unmodified material, the separation performance is nearly doubled. Scalable synthesis, stable structure, and the advantages of controllable performance after ammonia modification have prompted this material to have great prospects in the industrialization of C2H4/C2H6 separation.
Synthesis of N-Carboxy Alanine Anhydride from Alanine and Dimethyl Carbonate over NaZnPO4 in One-pot
2020, 78(6): 540-546
doi: 10.6023/A20020024
Abstract:
In this paper, the environmentally friendly synthesis of N-carboxy alanine anhydride (Ala-NCA) from alanine and dimethyl carbonate (DMC) over NaZnPO4 was carried out in one-pot, and the NaZnPO4 catalyst with the acid-base double active sites was prepared by the solid phase synthesis method. The X-ray diffraction spectrometer (XRD) was used to characterize the structure of NaZnPO4, and the reaction products were analyzed by the high performance liquid chromatography (HPLC) with evaporative light scattering detector (ELSD). The GC-MS characterized result of obtained Ala-NCA was extremely consistent with that of the standard sample, which indicated that Ala-NCA was synthesized successfully. When the reaction was carried out at 150℃ for 8 h, the maximum 46.84% yield of Ala-NCA can be obtained in DMF solvent. As the reaction temperature increased to 160℃, Ala-NCA yield significantly declined because of the instability of Ala-NCA at higher temperature. However, there was no Ala-NCA formation without catalyst existence because DMC is not easy to undergo carboxymethylation with amino acids. NaZnPO4 could be recycled, but Ala-NCA yield declined to 38.62% after the fifth cycle. The reasons for that were attributed to the catalyst surface area reduction and the active site loss of Na-O and Zn2+. The reaction between DMC and amino acids over NaZnPO4 were characterized by TG-MS-IR, and the possible catalytic mechanism was provided. Namely, Zn2+ and Na-O in NaZnPO4 perform an effective acid-base synergistic catalysis, on the one hand the basic Na-O active sites play an key role on amino group deprotonation, which promotes the carboxymethylation of amino acids with DMC, on the other hand the acid active sites of Zn2+ can well catalyze the cyclization of intermediate into Ala-NCA. In this cyclization process, NaZnPO4 also can transfer the trapped protons to carboxymethylation intermediate to facile the formation of target compounds.
In this paper, the environmentally friendly synthesis of N-carboxy alanine anhydride (Ala-NCA) from alanine and dimethyl carbonate (DMC) over NaZnPO4 was carried out in one-pot, and the NaZnPO4 catalyst with the acid-base double active sites was prepared by the solid phase synthesis method. The X-ray diffraction spectrometer (XRD) was used to characterize the structure of NaZnPO4, and the reaction products were analyzed by the high performance liquid chromatography (HPLC) with evaporative light scattering detector (ELSD). The GC-MS characterized result of obtained Ala-NCA was extremely consistent with that of the standard sample, which indicated that Ala-NCA was synthesized successfully. When the reaction was carried out at 150℃ for 8 h, the maximum 46.84% yield of Ala-NCA can be obtained in DMF solvent. As the reaction temperature increased to 160℃, Ala-NCA yield significantly declined because of the instability of Ala-NCA at higher temperature. However, there was no Ala-NCA formation without catalyst existence because DMC is not easy to undergo carboxymethylation with amino acids. NaZnPO4 could be recycled, but Ala-NCA yield declined to 38.62% after the fifth cycle. The reasons for that were attributed to the catalyst surface area reduction and the active site loss of Na-O and Zn2+. The reaction between DMC and amino acids over NaZnPO4 were characterized by TG-MS-IR, and the possible catalytic mechanism was provided. Namely, Zn2+ and Na-O in NaZnPO4 perform an effective acid-base synergistic catalysis, on the one hand the basic Na-O active sites play an key role on amino group deprotonation, which promotes the carboxymethylation of amino acids with DMC, on the other hand the acid active sites of Zn2+ can well catalyze the cyclization of intermediate into Ala-NCA. In this cyclization process, NaZnPO4 also can transfer the trapped protons to carboxymethylation intermediate to facile the formation of target compounds.
2020, 78(6): 547-556
doi: 10.6023/A20030054
Abstract:
The direct measurement of the dielectric properties of the confined water is exceedingly challenging, result in the lack of a quantitative understanding of its critical roles in electrochemistry, interfacial reactivity and transport thermodynamics. In this paper, we employ the equilibrium molecular dynamics simulation and the linear response theory-based analytical expressions for the local permittivity tensor, to calculate the static and dynamic dielectric response properties of the monolayer ice and water confined in the 0.65 nm size hydrophobic slab pore under 5×108 Pa lateral pressure and different temperatures. We carry out a detailed comparative study on the performance of predicting the confined structure and dielectric response properties between two well known water molecule models, i.e., constant dipole moment SPC/E model and polarizable SWM4-NDP water model. We have analyzed the probability distributions of the instantaneous SWM4-NDP water molecular dipole moments and calculated the static structure factor, radial dipole-dipole correlation function, static dielectric tensor, total dipole autocorrelation function and Debye relaxation time of each simulation system. For the first time, we found the novel variation of the water molecular polarities, in the monolayer confined liquid and solid phase of water, due to the extreme confinement condition. The performance in describing the structural properties are found comparable between the two water models, and the enhancement of the confinement weakens the advantage of the SWM4-NDP model in predicting the static dielectric property. However, in the prediction of the dynamic properties such as dielectric relaxation time, SWM4-NDP water model is superior to the SPC/E model. Therefore, we suggest that using SWM4-NDP model in the future investigation of the structural phase transition kinetics, ionic transportation and solvation kinetics would be the better choice. The current achievement of the fundamental insight and computational data could potentially facilitate the theoretical advancements in designing new devices of energy storage, sensor, and medicine delivery based on confined water systems.
The direct measurement of the dielectric properties of the confined water is exceedingly challenging, result in the lack of a quantitative understanding of its critical roles in electrochemistry, interfacial reactivity and transport thermodynamics. In this paper, we employ the equilibrium molecular dynamics simulation and the linear response theory-based analytical expressions for the local permittivity tensor, to calculate the static and dynamic dielectric response properties of the monolayer ice and water confined in the 0.65 nm size hydrophobic slab pore under 5×108 Pa lateral pressure and different temperatures. We carry out a detailed comparative study on the performance of predicting the confined structure and dielectric response properties between two well known water molecule models, i.e., constant dipole moment SPC/E model and polarizable SWM4-NDP water model. We have analyzed the probability distributions of the instantaneous SWM4-NDP water molecular dipole moments and calculated the static structure factor, radial dipole-dipole correlation function, static dielectric tensor, total dipole autocorrelation function and Debye relaxation time of each simulation system. For the first time, we found the novel variation of the water molecular polarities, in the monolayer confined liquid and solid phase of water, due to the extreme confinement condition. The performance in describing the structural properties are found comparable between the two water models, and the enhancement of the confinement weakens the advantage of the SWM4-NDP model in predicting the static dielectric property. However, in the prediction of the dynamic properties such as dielectric relaxation time, SWM4-NDP water model is superior to the SPC/E model. Therefore, we suggest that using SWM4-NDP model in the future investigation of the structural phase transition kinetics, ionic transportation and solvation kinetics would be the better choice. The current achievement of the fundamental insight and computational data could potentially facilitate the theoretical advancements in designing new devices of energy storage, sensor, and medicine delivery based on confined water systems.
2020, 78(6): 557-564
doi: 10.6023/A20030068
Abstract:
Perovskite-type catalytic materials have received wide attention as high-performance and low-cost alternatives to precious metal catalysts on the market at present, which have much considerable activity and stability as catalysts for oxygen reduction reactions. Current efforts are mainly focused on the use of perovskite make-up and preparation techniques to influence elemental composition, morphology, surface area, and structural control. For a typical perovskite oxide (ABO3), due to the high calcination temperature in the preparation process, the perovskite material usually has a small specific surface area, which limits the increase of activity in heterogeneous catalytic reactions. In this paper, the perovskite La0.7Sr0.3MnO3 (LSMO) material with large specific surface and high catalytic activity is prepared by means of the SiO2 template. The physicochemical properties of the synthesized materials are characterized by scanning electron microscope (SEM), energy dispersed X-ray spectroscopy (EDS), X-ray diffraction (XRD) and BET. The catalytic activity of LSMO as an oxygen reduction reaction (ORR) catalyst is measured by a rotating disk test system. After that, the catalyst material is applied to a flexible aluminum-air battery and its discharge behavior and flexibility is studied and tested. The test results show that the LSMO prepared by template method has a large specific surface area (31.1825 m2·g-1), and pore volume (0.161113 cm3·g-1), and it also shows higher electrocatalytic activity in the electrochemical test system. When it is used in aluminum-air batteries, the activity of 3D porous LSMO is significantly better than that of sheet and bulk LSMO. The aluminum-air battery assembled by LSMO prepared by the template method has a higher discharge voltage (up to 1.46 V) at a constant current. Compared to the template-free method and the sol-gel method, the discharge voltage in flexible aluminum-air battery can be increased by 8.2% and 24.5%, respectively, and the performance degradation is significantly slowed during high-current discharge. The specific capacity and energy density of the battery are up to 1048.6 mA·h·g-1 and 1020.6 mW·h·g-1, respectively. When the battery is in a deformed state, its output voltage can be stabilized above 1.38 V. Once released, the voltage can be immediately restored to over 99% of the initial value. This paper not only provides a solution for the commercialization of fuel cell, but also provides a new direction for the future development of variable power supply.
Perovskite-type catalytic materials have received wide attention as high-performance and low-cost alternatives to precious metal catalysts on the market at present, which have much considerable activity and stability as catalysts for oxygen reduction reactions. Current efforts are mainly focused on the use of perovskite make-up and preparation techniques to influence elemental composition, morphology, surface area, and structural control. For a typical perovskite oxide (ABO3), due to the high calcination temperature in the preparation process, the perovskite material usually has a small specific surface area, which limits the increase of activity in heterogeneous catalytic reactions. In this paper, the perovskite La0.7Sr0.3MnO3 (LSMO) material with large specific surface and high catalytic activity is prepared by means of the SiO2 template. The physicochemical properties of the synthesized materials are characterized by scanning electron microscope (SEM), energy dispersed X-ray spectroscopy (EDS), X-ray diffraction (XRD) and BET. The catalytic activity of LSMO as an oxygen reduction reaction (ORR) catalyst is measured by a rotating disk test system. After that, the catalyst material is applied to a flexible aluminum-air battery and its discharge behavior and flexibility is studied and tested. The test results show that the LSMO prepared by template method has a large specific surface area (31.1825 m2·g-1), and pore volume (0.161113 cm3·g-1), and it also shows higher electrocatalytic activity in the electrochemical test system. When it is used in aluminum-air batteries, the activity of 3D porous LSMO is significantly better than that of sheet and bulk LSMO. The aluminum-air battery assembled by LSMO prepared by the template method has a higher discharge voltage (up to 1.46 V) at a constant current. Compared to the template-free method and the sol-gel method, the discharge voltage in flexible aluminum-air battery can be increased by 8.2% and 24.5%, respectively, and the performance degradation is significantly slowed during high-current discharge. The specific capacity and energy density of the battery are up to 1048.6 mA·h·g-1 and 1020.6 mW·h·g-1, respectively. When the battery is in a deformed state, its output voltage can be stabilized above 1.38 V. Once released, the voltage can be immediately restored to over 99% of the initial value. This paper not only provides a solution for the commercialization of fuel cell, but also provides a new direction for the future development of variable power supply.
2020, 78(6): 565-571
doi: 10.6023/A20030084
Abstract:
The study on the reaction mechanism of organonitrile and sodium azide catalyzed by transition metals has always been a challenging and controversial task. Due to the difficulty in capturing the reaction intermediates, there is still no direct evidence to uncover the nature of the reaction. In this paper, the reaction mechanism has been explored by using a combining theoretical and experimental method. Based on the theoretical analysis of the stability of two types of intermediates (H2O)3M…N3- and (H2O)3M…NCCH3 and the successful capture of two activated intermediates containing metal cadmium ions Cd2(μ3-N3)(μ3-OH)(μ5-CHDA) (1) and Cd(μ2-N3)(μ3-IBA) (2) (H2CHDA=1, 3-cycloadipic acid and HIBA=4-(imi-dazol-1-yl) benzoic acid), which were achieved under the hydrothermal conditions and characterized by single-crystal XRD analysis. For the first time, the experimental and theoretical results reveal that the transition metal ions activate the azide rather than the cyano group of nitriles. In addition, the results of both the electrostatic potential basins analysis of activated intermediates (H2O)3M…N3- and acetonitrile molecules obtained by the theoretical calculation and our recently reported experimental results reveal that the intermediates (H2O)3M…N3- can be used as electrophilic reagent. Its uncoordinated terminal N atom can attack the N atom of the cyano group of acetonitrile to undergo a nucleophilic addition reaction during the chemical reaction progress, and then it may undergo a[2+3] cycloaddition reaction to in-situ form tetrazole. Moreover, with the aid of water molecules, its adducts may also occur similar to the Ritter-like reaction to in-situ form polynitrogen anion. Our findings may open a novel field of the in-situ synthesis of polynitrogen compounds based on the transition metal-catalyzed reactions of organonitrile and azide.
The study on the reaction mechanism of organonitrile and sodium azide catalyzed by transition metals has always been a challenging and controversial task. Due to the difficulty in capturing the reaction intermediates, there is still no direct evidence to uncover the nature of the reaction. In this paper, the reaction mechanism has been explored by using a combining theoretical and experimental method. Based on the theoretical analysis of the stability of two types of intermediates (H2O)3M…N3- and (H2O)3M…NCCH3 and the successful capture of two activated intermediates containing metal cadmium ions Cd2(μ3-N3)(μ3-OH)(μ5-CHDA) (1) and Cd(μ2-N3)(μ3-IBA) (2) (H2CHDA=1, 3-cycloadipic acid and HIBA=4-(imi-dazol-1-yl) benzoic acid), which were achieved under the hydrothermal conditions and characterized by single-crystal XRD analysis. For the first time, the experimental and theoretical results reveal that the transition metal ions activate the azide rather than the cyano group of nitriles. In addition, the results of both the electrostatic potential basins analysis of activated intermediates (H2O)3M…N3- and acetonitrile molecules obtained by the theoretical calculation and our recently reported experimental results reveal that the intermediates (H2O)3M…N3- can be used as electrophilic reagent. Its uncoordinated terminal N atom can attack the N atom of the cyano group of acetonitrile to undergo a nucleophilic addition reaction during the chemical reaction progress, and then it may undergo a[2+3] cycloaddition reaction to in-situ form tetrazole. Moreover, with the aid of water molecules, its adducts may also occur similar to the Ritter-like reaction to in-situ form polynitrogen anion. Our findings may open a novel field of the in-situ synthesis of polynitrogen compounds based on the transition metal-catalyzed reactions of organonitrile and azide.
2020, 78(6): 572-576
doi: 10.6023/A20030085
Abstract:
Li-O2 batteries have received much attention due to the high theoretical energy density. However, they still suffer from many challenges such as unsatisfactory practical specific capacity, cycle stability, and relatively high overpotential. The electrochemical performance of Li-O2 batteries is closely related to the reversibility of the discharge (oxygen reduction reaction, ORR) and charge (oxygen evolution reaction, OER) processes. During the discharge process, non-conductive Li2O2 product is formed and gradually covers on the surface of the positive electrode material, leading to the deactivation of battery. The charging process is accompanied by the electrochemical decomposition of Li2O2 products. Therefore, how to achieve the highly reversible formation and decomposition of the Li2O2 product is the key to improve the electrochemical performance of Li-O2 batteries. To date, two strategies have been developed:(ⅰ) sp2 carbon materials with large specific surface area, suitable pore structure and high conductivity are used as cathode materials to disperse/accommodate the Li2O2 product and promote the electron transfer; (ⅱ) the soluble redox mediators with ORR/OER bifunctionally catalytic activities are adopted as the electrolyte additive to promote the formation and decomposition of the Li2O2 product and lower the overpotentials. Recently, we reported a novel 3D hierarchical carbon nanocages (hCNC) featuring on the ultrahigh specific surface area, multiscale pore structure (micro-meso-macropore coexistence), high conductivity, and abundant defects, which demonstrated the excellent electrochemical performances in energy conversion and storage. Herein, taking advantages of hCNC, the high performances of Li-O2 batteries were fabricated, showing high full discharge specific capacity (14080 mAh·g-1) and good cyclability. After adding acetylacetone ferrous (Fe(acac)2) as the redox mediator to electrolyte, the electrochemical performances are further promoted. Namely, the discharge capacity reaches to 23560 mAh·g-1 at the current density of 0.1 A·g-1 (7.82 times of XC-72), and the cycle numbers are up to 138 cycles at the current density of 0.5 A·g-1 and the discharge/charge depth of 800 mAh·g-1 (far higher than 68 cycles of hCNC without Fe(acac)2 and 13 cycles of XC-72). Especially, at the high current density of 5.0 A·g-1, the cycle numbers still reach to 63 cycles, far higher than 21 cycles of hCNC without Fe(acac)2. Such excellent electrochemical performances can be ascribed to:the unique structure of hCNC facilitating electron transfer, reversible conversion of 2Li++O2+2e-⇆Li2O2(s), and dispersion/accommodation of the insulating Li2O2 product; the soluble redox mediator of Fe(acac)2 effectively catalyzing the discharge products of Li2O2 to form uniformly dispersed small-sized particles and decompose completely during the charge process. This provides a promising strategy for improving the performance of Li-O2 batteries via designing novel carbon-based positive electrode materials and adding efficient soluble redox mediators.
Li-O2 batteries have received much attention due to the high theoretical energy density. However, they still suffer from many challenges such as unsatisfactory practical specific capacity, cycle stability, and relatively high overpotential. The electrochemical performance of Li-O2 batteries is closely related to the reversibility of the discharge (oxygen reduction reaction, ORR) and charge (oxygen evolution reaction, OER) processes. During the discharge process, non-conductive Li2O2 product is formed and gradually covers on the surface of the positive electrode material, leading to the deactivation of battery. The charging process is accompanied by the electrochemical decomposition of Li2O2 products. Therefore, how to achieve the highly reversible formation and decomposition of the Li2O2 product is the key to improve the electrochemical performance of Li-O2 batteries. To date, two strategies have been developed:(ⅰ) sp2 carbon materials with large specific surface area, suitable pore structure and high conductivity are used as cathode materials to disperse/accommodate the Li2O2 product and promote the electron transfer; (ⅱ) the soluble redox mediators with ORR/OER bifunctionally catalytic activities are adopted as the electrolyte additive to promote the formation and decomposition of the Li2O2 product and lower the overpotentials. Recently, we reported a novel 3D hierarchical carbon nanocages (hCNC) featuring on the ultrahigh specific surface area, multiscale pore structure (micro-meso-macropore coexistence), high conductivity, and abundant defects, which demonstrated the excellent electrochemical performances in energy conversion and storage. Herein, taking advantages of hCNC, the high performances of Li-O2 batteries were fabricated, showing high full discharge specific capacity (14080 mAh·g-1) and good cyclability. After adding acetylacetone ferrous (Fe(acac)2) as the redox mediator to electrolyte, the electrochemical performances are further promoted. Namely, the discharge capacity reaches to 23560 mAh·g-1 at the current density of 0.1 A·g-1 (7.82 times of XC-72), and the cycle numbers are up to 138 cycles at the current density of 0.5 A·g-1 and the discharge/charge depth of 800 mAh·g-1 (far higher than 68 cycles of hCNC without Fe(acac)2 and 13 cycles of XC-72). Especially, at the high current density of 5.0 A·g-1, the cycle numbers still reach to 63 cycles, far higher than 21 cycles of hCNC without Fe(acac)2. Such excellent electrochemical performances can be ascribed to:the unique structure of hCNC facilitating electron transfer, reversible conversion of 2Li++O2+2e-⇆Li2O2(s), and dispersion/accommodation of the insulating Li2O2 product; the soluble redox mediator of Fe(acac)2 effectively catalyzing the discharge products of Li2O2 to form uniformly dispersed small-sized particles and decompose completely during the charge process. This provides a promising strategy for improving the performance of Li-O2 batteries via designing novel carbon-based positive electrode materials and adding efficient soluble redox mediators.
2020, 78(6): 577-586
doi: 10.6023/A20040109
Abstract:
As one of the most important characteristics of nature, chirality is closely related to life activities. Therefore, chiral nanomaterials have caused great attention in material, biology and some related fields. In this paper, a new preparation method for chiral graphene quantum dots (L-GQDs and D-GQDs) was proposed via one-step hydrothermal method. This method used citric acid and L(or D)-tryptophan as raw materials to synthesize chiral graphene quantum dots. Circular dichroism spectroscopy proved that the two chiral graphene quantum dots had two chiral signals with high symmetry, and the absorption peaks were located at 230 nm and 305 nm, respectively. A lot of thermodynamic parameters have been obtained by using fluorescence. The results of viscosity measurement, DNA melting experiments and multi-spectroscopic methods indicated that there was a large chiral difference between the combination of chiral graphene quantum dots and ctDNA. UV-Vis absorption spectrometry proved that the two different chiral graphene quantum dots caused the slightly red shift of absorption peak and hypochromic effect of ctDNA. These quantum dots increased the melting temperature of DNA, but reduced the relative viscosity of ctDNA. Through hydrogen bonding and van der Waals interaction, both graphene quantum dots were inserted into the G-C base pair of ctDNA, which affected the right-handed B-form helicity of ctDNA significantly. The steric hindrance effects of L-GQDs and D-GQDs were different, resulting in the differences of them in their intercalation and binding with ctDNA. Comparably, D-GQDs with right-handedness exhibited the strongest intercalative binding ability with ctDNA, and were easier to intercalate into ctDNA with the right-handed B-helical structure, causing the significant influence on right-handed B-helical structure of ctDNA. These results revealed the molecular mechanisms of the intercalative binding interactions between chiral graphene quantum dots and DNA, which provided valuable information for the development of chiral nanomaterials in chemistry, biology, and medicine areas.
As one of the most important characteristics of nature, chirality is closely related to life activities. Therefore, chiral nanomaterials have caused great attention in material, biology and some related fields. In this paper, a new preparation method for chiral graphene quantum dots (L-GQDs and D-GQDs) was proposed via one-step hydrothermal method. This method used citric acid and L(or D)-tryptophan as raw materials to synthesize chiral graphene quantum dots. Circular dichroism spectroscopy proved that the two chiral graphene quantum dots had two chiral signals with high symmetry, and the absorption peaks were located at 230 nm and 305 nm, respectively. A lot of thermodynamic parameters have been obtained by using fluorescence. The results of viscosity measurement, DNA melting experiments and multi-spectroscopic methods indicated that there was a large chiral difference between the combination of chiral graphene quantum dots and ctDNA. UV-Vis absorption spectrometry proved that the two different chiral graphene quantum dots caused the slightly red shift of absorption peak and hypochromic effect of ctDNA. These quantum dots increased the melting temperature of DNA, but reduced the relative viscosity of ctDNA. Through hydrogen bonding and van der Waals interaction, both graphene quantum dots were inserted into the G-C base pair of ctDNA, which affected the right-handed B-form helicity of ctDNA significantly. The steric hindrance effects of L-GQDs and D-GQDs were different, resulting in the differences of them in their intercalation and binding with ctDNA. Comparably, D-GQDs with right-handedness exhibited the strongest intercalative binding ability with ctDNA, and were easier to intercalate into ctDNA with the right-handed B-helical structure, causing the significant influence on right-handed B-helical structure of ctDNA. These results revealed the molecular mechanisms of the intercalative binding interactions between chiral graphene quantum dots and DNA, which provided valuable information for the development of chiral nanomaterials in chemistry, biology, and medicine areas.
