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2020 Volume 78 Issue 10
2020, 78(10): 1017-1029
doi: 10.6023/A20070335
Abstract:
Transition metal-catalyzed coupling reactions are powerful synthetic methods for the C-C bond formation. Many coupling reactions such as Heck reaction, Negishi coupling, and Suzuki coupling have been widely applied in the syntheses of pharmaceuticals, functional materials and fine chemicals. In those coupling reactions, a C(sp2)-C(sp2) bond is formed in high efficiency and selectivity. However, in contrast to the C(sp2)-C(sp2) couplings, the C(sp3)-C(sp3) couplings are more difficult and develop late. Because the C(sp3)-C(sp3) bonds are ubiquitous in organic compound, the C(sp3)-C(sp3) bond formation is the central task of research in organic chemistry. In the past two decades, a great effort has been devoted to the development of cross-coupling reactions between alkyls to construct C(sp3)-C(sp3) bonds and impressive progress has been achieved. Among the transition metal catalysts that have been used in the construction of C(sp3)-C(sp3) bonds, nickel was found to be a preferable one, exhibiting unique activity and selectivity. Nickel catalysts promote the activation of alkyl electrophiles via radical catalytic cycles and inhibit and/or manipulate β-H elimination reactions. Nickel has several variable valence states and can flexibly participate in tandem reactions and reductive cross-coupling reactions. All these characteristic natures contribute to the success of nickel catalysts in the construction of C(sp3)-C(sp3) bonds. In this review, we will describe the advances on the nickel-catalyzed C(sp3)-C(sp3) bond-forming reactions. The main contents of this review include:the cross-coupling of alkyl electrophiles with organometallic reagents; the coupling involving a C(sp3)-H bond activation in the presence of directing group; the coupling co-catalyzed by nickel and photocatalyst; the reductive coupling of two alkyl electrophiles; and the additions of nucleophiles or electrophiles to alkenes such as hydroalkylation and difunctionalization of alkenes. The review will focus on the latest developments of nickel-catalyzed alkyl coupling reactions in the past two decades. The mechanisms of each reaction are discussed in detail for understanding the reactions.
Transition metal-catalyzed coupling reactions are powerful synthetic methods for the C-C bond formation. Many coupling reactions such as Heck reaction, Negishi coupling, and Suzuki coupling have been widely applied in the syntheses of pharmaceuticals, functional materials and fine chemicals. In those coupling reactions, a C(sp2)-C(sp2) bond is formed in high efficiency and selectivity. However, in contrast to the C(sp2)-C(sp2) couplings, the C(sp3)-C(sp3) couplings are more difficult and develop late. Because the C(sp3)-C(sp3) bonds are ubiquitous in organic compound, the C(sp3)-C(sp3) bond formation is the central task of research in organic chemistry. In the past two decades, a great effort has been devoted to the development of cross-coupling reactions between alkyls to construct C(sp3)-C(sp3) bonds and impressive progress has been achieved. Among the transition metal catalysts that have been used in the construction of C(sp3)-C(sp3) bonds, nickel was found to be a preferable one, exhibiting unique activity and selectivity. Nickel catalysts promote the activation of alkyl electrophiles via radical catalytic cycles and inhibit and/or manipulate β-H elimination reactions. Nickel has several variable valence states and can flexibly participate in tandem reactions and reductive cross-coupling reactions. All these characteristic natures contribute to the success of nickel catalysts in the construction of C(sp3)-C(sp3) bonds. In this review, we will describe the advances on the nickel-catalyzed C(sp3)-C(sp3) bond-forming reactions. The main contents of this review include:the cross-coupling of alkyl electrophiles with organometallic reagents; the coupling involving a C(sp3)-H bond activation in the presence of directing group; the coupling co-catalyzed by nickel and photocatalyst; the reductive coupling of two alkyl electrophiles; and the additions of nucleophiles or electrophiles to alkenes such as hydroalkylation and difunctionalization of alkenes. The review will focus on the latest developments of nickel-catalyzed alkyl coupling reactions in the past two decades. The mechanisms of each reaction are discussed in detail for understanding the reactions.
2020, 78(10): 1030-1040
doi: 10.6023/A20060243
Abstract:
Room-temperature phosphorescence (RTP) can not only intuitively reflect the excited state transition process of the phosphorescent luminescence, but also has wide potential applications in optoelectronics, sensing, bioimaging and security devices. Consequently, more and more attention and interests on RTP materials have been attracted, which turned it to be one of hot topics in luminescence materials, especially, organic luminescence materials in recent years. The halogen bonds and hydrogen bonds between the molecules can fix the phosphor to suppress non-radiative transitions. A twisted donor-acceptor skeleton can promot efficient thermally activated delayed fluorescence (TADF) and also benefit to the RTP. Moreover, circularly polarized room-temperature phosphorescence (CP-RTP) also remains a daunting challenge to implant circularly polarized luminescence (CPL) in metal-free RTP materials. This review summarizes recent research progress on RTP of small organic molecules, mainly focusing on RTP materials based on hydrogen bonds, RTP materials containing halogens, RTP materials based on D-A structures and RTP materials with CPL properties.
Room-temperature phosphorescence (RTP) can not only intuitively reflect the excited state transition process of the phosphorescent luminescence, but also has wide potential applications in optoelectronics, sensing, bioimaging and security devices. Consequently, more and more attention and interests on RTP materials have been attracted, which turned it to be one of hot topics in luminescence materials, especially, organic luminescence materials in recent years. The halogen bonds and hydrogen bonds between the molecules can fix the phosphor to suppress non-radiative transitions. A twisted donor-acceptor skeleton can promot efficient thermally activated delayed fluorescence (TADF) and also benefit to the RTP. Moreover, circularly polarized room-temperature phosphorescence (CP-RTP) also remains a daunting challenge to implant circularly polarized luminescence (CPL) in metal-free RTP materials. This review summarizes recent research progress on RTP of small organic molecules, mainly focusing on RTP materials based on hydrogen bonds, RTP materials containing halogens, RTP materials based on D-A structures and RTP materials with CPL properties.
2020, 78(10): 1041-1053
doi: 10.6023/A20060256
Abstract:
Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) are representative crystalline porous polymers. Due to their high surface area, high porosity, open channels, abundant functional groups and easy functionalization, they show great applications in gas storage and separation, catalysis, energy storage, photovoltaic devices, etc. Amino acids are the basic structural units that constitute peptides and proteins, which not only have important biological functions, but also play an important role in industrial applications such as pharmaceutical production, biodegradable plastics, and chiral catalysts. The introduction of amino acids into MOFs and COFs could endow them with diverse and flexible frameworks, special pore environment, and chiral sites, improving their biocompatibility and degradability to some extent and enriching their functions and applications. This review focuses on the progress of the amino acid functionalized MOFs and COFs, including their synthetic strategies, such as employing amino acids and their derivatives as building unit, covalent modification of amino acids onto the framework, and utilizing amino acids as modulators. The advantages and disadvantages of these strategies are compared and their challenges are discussed. In addition, we also introduce their applications in chiral separation, catalysis, adsorption and proton conduction. Finally, we summarize the current challenges in the preparation of amino acid functionalized crystalline porous polymers and outlook the future research direction in this field.
Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) are representative crystalline porous polymers. Due to their high surface area, high porosity, open channels, abundant functional groups and easy functionalization, they show great applications in gas storage and separation, catalysis, energy storage, photovoltaic devices, etc. Amino acids are the basic structural units that constitute peptides and proteins, which not only have important biological functions, but also play an important role in industrial applications such as pharmaceutical production, biodegradable plastics, and chiral catalysts. The introduction of amino acids into MOFs and COFs could endow them with diverse and flexible frameworks, special pore environment, and chiral sites, improving their biocompatibility and degradability to some extent and enriching their functions and applications. This review focuses on the progress of the amino acid functionalized MOFs and COFs, including their synthetic strategies, such as employing amino acids and their derivatives as building unit, covalent modification of amino acids onto the framework, and utilizing amino acids as modulators. The advantages and disadvantages of these strategies are compared and their challenges are discussed. In addition, we also introduce their applications in chiral separation, catalysis, adsorption and proton conduction. Finally, we summarize the current challenges in the preparation of amino acid functionalized crystalline porous polymers and outlook the future research direction in this field.
2020, 78(10): 1054-1063
doi: 10.6023/A20070295
Abstract:
Nowadays malignant tumors are still one of the disastrous diseases. It is necessary to explore new strategies for the treatment of malignant tumor. Nanomaterials refer to materials with at least one dimension of the three dimensions in the nanometer range (1~100 nm). They show a wide range of applications in tumor treatment while disadvantages of low targeting efficiency, poor tumor penetration and obvious side effects still limit their applications. As a method for tumor treatment, bacterial therapy has a long history. Some facultative anaerobic and obligate anaerobic bacteria and their secretions have the characteristics of targeting hypoxic tumor tissue, strong tumor penetration and stimulating immune responses. After genetically modification or attenuation treatment, it can be used for tumor treatment. However, the safety issues and low therapeutic efficiency still needs to be solved. The combination of nanomaterials and bacteria can complement the limitation of each other, and shows great potential in tumor therapy. On one hand, bacteria could enhance the targeting efficiency of nanomaterials, and decrease the side effects. On the other hand, nanomaterials could help improve the safety and solve the problem of low therapeutic efficiency of bacterial therapy. In this review, the combination of nanomaterials and bacteria is divided into three categories based on the role of bacteria in the treatment. Firstly, the preparation of composites of nanomaterials and bacteria by chemical bonds, electrostatic interaction, and other ways to enhance tumor targeting. Secondly, bacterial enzyme could react with nanomaterials to control the release of drug. Thirdly, secretions of bacteria after plasmids were introduced and outer membrane vesicles secreted by bacteria could be combined with nanomaterials for anti-tumor therapy. The mechanisms of the combination therapy are also discussed. Finally, we summarized and discussed the current challenges, especially the safety of the combination therapy. The prospect of the combination of nanomaterials and bacterial for tumor treatment is also proposed.
Nowadays malignant tumors are still one of the disastrous diseases. It is necessary to explore new strategies for the treatment of malignant tumor. Nanomaterials refer to materials with at least one dimension of the three dimensions in the nanometer range (1~100 nm). They show a wide range of applications in tumor treatment while disadvantages of low targeting efficiency, poor tumor penetration and obvious side effects still limit their applications. As a method for tumor treatment, bacterial therapy has a long history. Some facultative anaerobic and obligate anaerobic bacteria and their secretions have the characteristics of targeting hypoxic tumor tissue, strong tumor penetration and stimulating immune responses. After genetically modification or attenuation treatment, it can be used for tumor treatment. However, the safety issues and low therapeutic efficiency still needs to be solved. The combination of nanomaterials and bacteria can complement the limitation of each other, and shows great potential in tumor therapy. On one hand, bacteria could enhance the targeting efficiency of nanomaterials, and decrease the side effects. On the other hand, nanomaterials could help improve the safety and solve the problem of low therapeutic efficiency of bacterial therapy. In this review, the combination of nanomaterials and bacteria is divided into three categories based on the role of bacteria in the treatment. Firstly, the preparation of composites of nanomaterials and bacteria by chemical bonds, electrostatic interaction, and other ways to enhance tumor targeting. Secondly, bacterial enzyme could react with nanomaterials to control the release of drug. Thirdly, secretions of bacteria after plasmids were introduced and outer membrane vesicles secreted by bacteria could be combined with nanomaterials for anti-tumor therapy. The mechanisms of the combination therapy are also discussed. Finally, we summarized and discussed the current challenges, especially the safety of the combination therapy. The prospect of the combination of nanomaterials and bacterial for tumor treatment is also proposed.
2020, 78(10): 1064-1068
doi: 10.6023/A20070296
Abstract:
The development of new synthetic methodology and reagent is always a hot topic in organic synthesis community. Among the strategies used, chemical property investigation of synthetic intermediates with multifunctional groups represents a direct and efficient way. In this paper, as a systematic continuation of α-aminomalononitrile based synthetic application studies, α-aminomalononitrile has been developed for the first time as a surrogate for carbamoyl anions and applied to the synthesis of tertiary amides via a copper-catalyzed decyanation reaction. This strategy features simple reaction conditions, scalability, and wide substrate scope. This work not only further enriches the reaction model of aminonitrile compounds, but also provides an alternative synthetic strategy for the synthesis of substituted amides from simple formamides. In this process, the substrates could be readily synthesized through the nucleophilic addition or substitution reaction of α-aminomalononitriles, and they would be converted to corresponding tertiary amide in the presence of CuF2 in DMSO. As an example, the formal hydrocarbamoylation reaction of unsaturated bonds could be achieved. A general procedure for the strategy is as follows:α-aminomalononitrile derived from formamide is used to undergo nucleophilic addition or substitution reaction with electrophilic reagents. Next, the two cyano groups of the synthesized substrates could be removed under the catalysis of CuF2 to form a C=O double bond in situ, thereby achieving the synthesis of corresponding tertiary amide. During the reaction, the α-aminomalononitrile substrate (0.4 mmol), CuF2 (5 mol%), DMSO (3 mL) were placed in a sealed reaction tube at 100℃ at an argon atmosphere for about 32 hours. Then, the reaction system was washed out with ethyl acetate, and the organic phase was washed with water to remove DMSO. Next, the aqueous phase was extracted with ethyl acetate. Finally all organic phases were combined, washed once with saturated brine. After drying the organic phase over anhydrous sodium sulfate, it was concentrated by a vacuum pump. Finally, the residue was purified by flash column chromatography to give amide product.
The development of new synthetic methodology and reagent is always a hot topic in organic synthesis community. Among the strategies used, chemical property investigation of synthetic intermediates with multifunctional groups represents a direct and efficient way. In this paper, as a systematic continuation of α-aminomalononitrile based synthetic application studies, α-aminomalononitrile has been developed for the first time as a surrogate for carbamoyl anions and applied to the synthesis of tertiary amides via a copper-catalyzed decyanation reaction. This strategy features simple reaction conditions, scalability, and wide substrate scope. This work not only further enriches the reaction model of aminonitrile compounds, but also provides an alternative synthetic strategy for the synthesis of substituted amides from simple formamides. In this process, the substrates could be readily synthesized through the nucleophilic addition or substitution reaction of α-aminomalononitriles, and they would be converted to corresponding tertiary amide in the presence of CuF2 in DMSO. As an example, the formal hydrocarbamoylation reaction of unsaturated bonds could be achieved. A general procedure for the strategy is as follows:α-aminomalononitrile derived from formamide is used to undergo nucleophilic addition or substitution reaction with electrophilic reagents. Next, the two cyano groups of the synthesized substrates could be removed under the catalysis of CuF2 to form a C=O double bond in situ, thereby achieving the synthesis of corresponding tertiary amide. During the reaction, the α-aminomalononitrile substrate (0.4 mmol), CuF2 (5 mol%), DMSO (3 mL) were placed in a sealed reaction tube at 100℃ at an argon atmosphere for about 32 hours. Then, the reaction system was washed out with ethyl acetate, and the organic phase was washed with water to remove DMSO. Next, the aqueous phase was extracted with ethyl acetate. Finally all organic phases were combined, washed once with saturated brine. After drying the organic phase over anhydrous sodium sulfate, it was concentrated by a vacuum pump. Finally, the residue was purified by flash column chromatography to give amide product.
2020, 78(10): 1069-1075
doi: 10.6023/A20070315
Abstract:
The cobalt manganese oxide (CMO), with the advantages of high safety, non-toxicity, easy to obtain, multiple active sites, holds great potential in constructions of Zn-ion batteries (ZIBs). Yet, the dissolution of electrode materials into the electrolyte usually causes the structural collapse during repeated charge/discharge courses, which greatly limits the lifespan of ZIBs and thus restricts their further development. Herein, an in-situ coating method is developed to address this issue. Via a simple one-step hydrothermal method, a nanoscale carbon layer (denoted as nC) is introduced onto the surface of CMO (CMO@C) to prolong its cycling stability. Specifically, 30 mmol NH4F and 75 mmol CO(CH2)2 are first dissolved in 100 mL deionized water. Then, 11.25 mmol Mn(CH3COO)2 and 3.75 mmol Co(CH3COO)2 are added and stirred until the solid completely dissolves. Finally, 0.5 g glucose is dissolved in the solution and stirred for 5 min. The precursor solution is transferred into the 25 mL Teflon-lined stainless-steel autoclave and heated at 125℃ for 6 h in the oven. The as-obtained powder is washed three times by water and then dried at 60℃ overnight. The CMO@C sample is obtained after annealing the powder in air at 450℃ for 1 h. The X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectra (Raman) characterizations demonstrate that the introduction of the nC coating layer does not alter the composition and structure of CMO. Moreover, taking advantages of the superior conductivity of the carbon coverage, the CMO@C possesses a smaller charge transfer resistance and higher Zn ion diffusion capability compared with the CMO counterpart. The quicker charge transfer and faster ion exchange characteristics are both beneficial to the electrochemical performance optimization, both for the capacity enlargement and for the lifespan extension. As a proof of concept, at the current density of 0.5 A·g-1, the CMO@C shows a high specific capacity of 271.9 mAh·g-1 and no capacity loss is detected after 1000 cycle tests, which substantially outstrip those of the CMO (103.7 mAh·g-1 and 130 cycle lifespan). The work sheds light on the rational design of bimetal oxides as high-performance cathodes for ZIBs assembly.
The cobalt manganese oxide (CMO), with the advantages of high safety, non-toxicity, easy to obtain, multiple active sites, holds great potential in constructions of Zn-ion batteries (ZIBs). Yet, the dissolution of electrode materials into the electrolyte usually causes the structural collapse during repeated charge/discharge courses, which greatly limits the lifespan of ZIBs and thus restricts their further development. Herein, an in-situ coating method is developed to address this issue. Via a simple one-step hydrothermal method, a nanoscale carbon layer (denoted as nC) is introduced onto the surface of CMO (CMO@C) to prolong its cycling stability. Specifically, 30 mmol NH4F and 75 mmol CO(CH2)2 are first dissolved in 100 mL deionized water. Then, 11.25 mmol Mn(CH3COO)2 and 3.75 mmol Co(CH3COO)2 are added and stirred until the solid completely dissolves. Finally, 0.5 g glucose is dissolved in the solution and stirred for 5 min. The precursor solution is transferred into the 25 mL Teflon-lined stainless-steel autoclave and heated at 125℃ for 6 h in the oven. The as-obtained powder is washed three times by water and then dried at 60℃ overnight. The CMO@C sample is obtained after annealing the powder in air at 450℃ for 1 h. The X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectra (Raman) characterizations demonstrate that the introduction of the nC coating layer does not alter the composition and structure of CMO. Moreover, taking advantages of the superior conductivity of the carbon coverage, the CMO@C possesses a smaller charge transfer resistance and higher Zn ion diffusion capability compared with the CMO counterpart. The quicker charge transfer and faster ion exchange characteristics are both beneficial to the electrochemical performance optimization, both for the capacity enlargement and for the lifespan extension. As a proof of concept, at the current density of 0.5 A·g-1, the CMO@C shows a high specific capacity of 271.9 mAh·g-1 and no capacity loss is detected after 1000 cycle tests, which substantially outstrip those of the CMO (103.7 mAh·g-1 and 130 cycle lifespan). The work sheds light on the rational design of bimetal oxides as high-performance cathodes for ZIBs assembly.
2020, 78(10): 1076-1081
doi: 10.6023/A20060235
Abstract:
Exosomes are nanoscale bilayer membrane vesicles actively secreted by cells, which carry abundant cell-specific substances. They can directly reflect the physiological and functional status of the secreting cells and play important roles in intercellular communication, physiological and pathological processes. In this work, we combined membrane modification technique with fluorescence imaging technique and blended CD63 aptamers into a highly stable and universal DNA tetrahedral structure to construct a cell membrane-anchored DNA sensor for real-time monitoring the secretion of exosomes. We designed four functional toes on each vertex of the tetrahedral sensor, respectively. A signal report toe on the top vertex consisted of fluorophore-modified CD63 aptamer, quencher-modified quencher probe(QP) binding part of the CD63 aptamer, and block probe (BP) binding the rest of the CD63 aptamer. The other three extended toes on the vertices were immobilized to the cell membrane by hybridizing with cholesterol-modified anchor probes(AP), which spontaneously incorporated to a lipid bilayer via hydrophobic interaction between the cholesterol moieties and the cellular membrane. In the initial state, the proposed DNA tetrahedral sensor was tethered to membrane with fluorophores quenched by QP and CD63 aptamer blocked by QP and BP. Trigger probes (TP) were add to bind to BP, resulting in the activation of the sensor. Subsequently, CD63 aptamers were specifically bound to the secreted exosomes, leading to the release of QP and concurrent fluorescence restoration of fluorophore. The intensity of the fluorescent signal in cell membrane was proportional to the amount of exosomes captured, thus realizing the real-time monitoring of the exosomes by analysis the changes of the fluorescence intensity. The experimental results showed that the sensor exhibited a good stability and a high capture efficiency for secreted exosomes. This strategy would provide a potentially useful tool for a variety of applications in biomedical research, drug discovery and tissue engineering.
Exosomes are nanoscale bilayer membrane vesicles actively secreted by cells, which carry abundant cell-specific substances. They can directly reflect the physiological and functional status of the secreting cells and play important roles in intercellular communication, physiological and pathological processes. In this work, we combined membrane modification technique with fluorescence imaging technique and blended CD63 aptamers into a highly stable and universal DNA tetrahedral structure to construct a cell membrane-anchored DNA sensor for real-time monitoring the secretion of exosomes. We designed four functional toes on each vertex of the tetrahedral sensor, respectively. A signal report toe on the top vertex consisted of fluorophore-modified CD63 aptamer, quencher-modified quencher probe(QP) binding part of the CD63 aptamer, and block probe (BP) binding the rest of the CD63 aptamer. The other three extended toes on the vertices were immobilized to the cell membrane by hybridizing with cholesterol-modified anchor probes(AP), which spontaneously incorporated to a lipid bilayer via hydrophobic interaction between the cholesterol moieties and the cellular membrane. In the initial state, the proposed DNA tetrahedral sensor was tethered to membrane with fluorophores quenched by QP and CD63 aptamer blocked by QP and BP. Trigger probes (TP) were add to bind to BP, resulting in the activation of the sensor. Subsequently, CD63 aptamers were specifically bound to the secreted exosomes, leading to the release of QP and concurrent fluorescence restoration of fluorophore. The intensity of the fluorescent signal in cell membrane was proportional to the amount of exosomes captured, thus realizing the real-time monitoring of the exosomes by analysis the changes of the fluorescence intensity. The experimental results showed that the sensor exhibited a good stability and a high capture efficiency for secreted exosomes. This strategy would provide a potentially useful tool for a variety of applications in biomedical research, drug discovery and tissue engineering.
2020, 78(10): 1082-1088
doi: 10.6023/A20070316
Abstract:
Light-responsive CO2 adsorbents can effectively adjust their ability to capture CO2 through external light irradiation, and have the advantages of good controllability and high energy efficiency during the adsorption process. However, the currently reported light-responsive CO2 adsorbents can only realize the regulation of weak adsorption sites, and the regulation of strong adsorption sites is still a challenging task. In this work, a light-responsive smart adsorbent was constructed by in situ synthesis, and the light-responsive control of strong adsorption sites for CO2 was realized. The construction of adsorbent was achieved by introducing the azobenzene derivative with cis and trans isomers and silane coupling agent containing primary amines into mesoporous silica. The characterization results show that the adsorbents have uniform pore channels, and primary amine and light-responsive groups are dispersed on the pore walls. The strong interaction between primary amine and CO2 can lead to the selective adsorption of CO2, while azobenzene as a molecular switch can regulate the adsorption performance of primary amine. Before light irradiation, azobenzene is in trans configuration, which decreases the electrostatic potential of the primary amine, and exposes the active site, thus CO2 can be freely adsorbed; after light irradiation, azobenzene is converted to the cis configuration, which increases the electrostatic potential of the primary amine and shields the active sites. The change amount of adsorption capacity can reach 43%, and this process is reversible. Both the light-responsive properties of azobenzene groups and the adsorptive performances of adsorbents can be well maintained after 5 cycles. Azobenzene in different configuration has distinctive influences on the electrostatic potential of primary amine, thereby achieving the regulation of adsorption ability. This work utilizes the specific interaction between stimuli-responsive groups and target-specific adsorption sites, realizing the regulation of strong active cites for CO2, which gives clues to the development of new smart adsorbents.
Light-responsive CO2 adsorbents can effectively adjust their ability to capture CO2 through external light irradiation, and have the advantages of good controllability and high energy efficiency during the adsorption process. However, the currently reported light-responsive CO2 adsorbents can only realize the regulation of weak adsorption sites, and the regulation of strong adsorption sites is still a challenging task. In this work, a light-responsive smart adsorbent was constructed by in situ synthesis, and the light-responsive control of strong adsorption sites for CO2 was realized. The construction of adsorbent was achieved by introducing the azobenzene derivative with cis and trans isomers and silane coupling agent containing primary amines into mesoporous silica. The characterization results show that the adsorbents have uniform pore channels, and primary amine and light-responsive groups are dispersed on the pore walls. The strong interaction between primary amine and CO2 can lead to the selective adsorption of CO2, while azobenzene as a molecular switch can regulate the adsorption performance of primary amine. Before light irradiation, azobenzene is in trans configuration, which decreases the electrostatic potential of the primary amine, and exposes the active site, thus CO2 can be freely adsorbed; after light irradiation, azobenzene is converted to the cis configuration, which increases the electrostatic potential of the primary amine and shields the active sites. The change amount of adsorption capacity can reach 43%, and this process is reversible. Both the light-responsive properties of azobenzene groups and the adsorptive performances of adsorbents can be well maintained after 5 cycles. Azobenzene in different configuration has distinctive influences on the electrostatic potential of primary amine, thereby achieving the regulation of adsorption ability. This work utilizes the specific interaction between stimuli-responsive groups and target-specific adsorption sites, realizing the regulation of strong active cites for CO2, which gives clues to the development of new smart adsorbents.
Construction of Nitric Oxide (NO)-Responsive Fluorescent Polymer and Its Application in Cell Imaging
2020, 78(10): 1089-1095
doi: 10.6023/A20060280
Abstract:
Nitric oxide (NO) is a ubiquitous physiological signal messenger, but the use of NO as a trigger event to delicately tune the self-assembly behaviors of biomimetic polymers has been far less exploited. In this work, a single primary amine-containing 2-(3-(2-aminophenyl)ureido)ethyl methacrylate (APUEMA) monomer was first synthesized by the reaction between o-phenylenediamine and 2-isocyanatoethyl methacrylate. Then, the well-defined double hydrophilic block copolymer (DHBC), poly[oligo(ethylene glycol)methyl ether methacrylate]-b-poly[2-(3-(2-aminophenyl)ureido)ethyl methacrylate-co-4-(2-methylacryloyloxyethylamino)-7-nitro-2, 1, 3-benzoxadiazole)] (POEGMA-b-P(APUEMA-co-NBD)), was synthesized via sequential reversible addition-fragmentation chain transfer (RAFT) polymerization. Since there is a free amine group in the APUEMA monomer, it can be competent to quench the fluorescence of dyes and react with NO showing NO-responsiveness property. The reaction product of APUEMA and NO was purified by column chromatography, and 1H and 13C NMR results displayed the formation of urea-functionalized benzotriazole residual. The pKa values of APUEMA monomer and POEGMA-b-P(APUEMA-co-NBD) block polymer were measured to be 3.36 and 2.15, respectively, indicating that APUEMA monomer and PAPUEMA moieties of POEGMA-b-P(APUEMA-co-NBD) showed hydrophilic ability at acidic medium and hydrophobic ability at neutral medium. The aqueous solution of POEGMA-b-P(APUEMA-co-NBD) block copolymer exhibited a small diameter with about 5.0 nm at pH 2.0, which illustrates that block copolymer can dissolve into water with a unimer state. After changing the solution pH value to 7, the solution diameter increased to about 10 nm recorded by dynamic light scattering (DLS). Transmission electron microscope (TEM) results displayed micelles of POEGMA-b-P(APUEMA-co-NBD) block copolymer aqueous solution with spherical structures at pH 7.4. Furthermore, the fluorescence intensity of the block copolymer solution was decreased quickly after the pH value increased from 2 to 7. The NO-responsive property of block copolymer POEGMA-b-P(APUEMA-co-NBD) was also detected by DLS and fluorescent spectrometry methods. At pH 2.0, the diameter of the block copolymer aqueous solution increased from 5 nm to about 150 nm upon sparging with NO for 24 h. At pH 7.0, the diameter of block copolymer micelles increased from 10 nm to about 100 nm after exposure to NO for 24 h. The transmittance of POEGMA-b-P(APUEMA-co-NBD) block copolymer aqueous solution at pH 2.0 or pH 7.0 decreased upon NO addition, which were in accorded with DLS results. Moreover, the fluorescence intensity of the block copolymer solution at pH 2.0 improved rapidly upon sparging with NO for 0.5 h, implying that the NO-triggered self-assembly of micelles decreased environmental polarity. The fluorescence intensity decreased with further addition. The fluorescence intensity of block copolymer micelles at pH 7.0 exhibited 15-fold increased after addition with NO for 24 h. The in vitro study of block copolymer POEGMA-b-P(APUEMA-co-NBD) was conducted in normal MRC-5 cells. The block copolymer showed negligible cytotoxicity even at the block copolymer concentration of 100 g/mL. We herein report on a novel pH-responsive DHBC with unique NO-reactive feature, where NO can spontaneously trigger the self-assembly and morphological transformation in acidic and neutral milieus, respectively. After the introduction of fluorophores, these transitions are also associated with significant fluorescence turn-on due to eliminations of photoinduced electron transfer (PET) process in the presence of NO, imparting the opportunities to visualize intracellular NO.
Nitric oxide (NO) is a ubiquitous physiological signal messenger, but the use of NO as a trigger event to delicately tune the self-assembly behaviors of biomimetic polymers has been far less exploited. In this work, a single primary amine-containing 2-(3-(2-aminophenyl)ureido)ethyl methacrylate (APUEMA) monomer was first synthesized by the reaction between o-phenylenediamine and 2-isocyanatoethyl methacrylate. Then, the well-defined double hydrophilic block copolymer (DHBC), poly[oligo(ethylene glycol)methyl ether methacrylate]-b-poly[2-(3-(2-aminophenyl)ureido)ethyl methacrylate-co-4-(2-methylacryloyloxyethylamino)-7-nitro-2, 1, 3-benzoxadiazole)] (POEGMA-b-P(APUEMA-co-NBD)), was synthesized via sequential reversible addition-fragmentation chain transfer (RAFT) polymerization. Since there is a free amine group in the APUEMA monomer, it can be competent to quench the fluorescence of dyes and react with NO showing NO-responsiveness property. The reaction product of APUEMA and NO was purified by column chromatography, and 1H and 13C NMR results displayed the formation of urea-functionalized benzotriazole residual. The pKa values of APUEMA monomer and POEGMA-b-P(APUEMA-co-NBD) block polymer were measured to be 3.36 and 2.15, respectively, indicating that APUEMA monomer and PAPUEMA moieties of POEGMA-b-P(APUEMA-co-NBD) showed hydrophilic ability at acidic medium and hydrophobic ability at neutral medium. The aqueous solution of POEGMA-b-P(APUEMA-co-NBD) block copolymer exhibited a small diameter with about 5.0 nm at pH 2.0, which illustrates that block copolymer can dissolve into water with a unimer state. After changing the solution pH value to 7, the solution diameter increased to about 10 nm recorded by dynamic light scattering (DLS). Transmission electron microscope (TEM) results displayed micelles of POEGMA-b-P(APUEMA-co-NBD) block copolymer aqueous solution with spherical structures at pH 7.4. Furthermore, the fluorescence intensity of the block copolymer solution was decreased quickly after the pH value increased from 2 to 7. The NO-responsive property of block copolymer POEGMA-b-P(APUEMA-co-NBD) was also detected by DLS and fluorescent spectrometry methods. At pH 2.0, the diameter of the block copolymer aqueous solution increased from 5 nm to about 150 nm upon sparging with NO for 24 h. At pH 7.0, the diameter of block copolymer micelles increased from 10 nm to about 100 nm after exposure to NO for 24 h. The transmittance of POEGMA-b-P(APUEMA-co-NBD) block copolymer aqueous solution at pH 2.0 or pH 7.0 decreased upon NO addition, which were in accorded with DLS results. Moreover, the fluorescence intensity of the block copolymer solution at pH 2.0 improved rapidly upon sparging with NO for 0.5 h, implying that the NO-triggered self-assembly of micelles decreased environmental polarity. The fluorescence intensity decreased with further addition. The fluorescence intensity of block copolymer micelles at pH 7.0 exhibited 15-fold increased after addition with NO for 24 h. The in vitro study of block copolymer POEGMA-b-P(APUEMA-co-NBD) was conducted in normal MRC-5 cells. The block copolymer showed negligible cytotoxicity even at the block copolymer concentration of 100 g/mL. We herein report on a novel pH-responsive DHBC with unique NO-reactive feature, where NO can spontaneously trigger the self-assembly and morphological transformation in acidic and neutral milieus, respectively. After the introduction of fluorophores, these transitions are also associated with significant fluorescence turn-on due to eliminations of photoinduced electron transfer (PET) process in the presence of NO, imparting the opportunities to visualize intracellular NO.
2020, 78(10): 1096-1101
doi: 10.6023/A20070284
Abstract:
It is of great significance to identify new oxidation state of actinide, which will enrich actinide coordination chemistry and advance its exploration of chemical bond and reactivity. So far, uranium with +3~+6 oxidation states has been widely recognized in complexes. Comparatively, isolated, crystallographically identified U(Ⅱ) complexes remain rare. Inspired by the pioneering work of Evans and co-workers that Y·[UⅡ(Cp')3] (Y=[K(2.2.2-cryptand)]+, Cp'=[C5H4SiMe3]-) was structurally characterized, several uranium(Ⅱ) complexes such as Y·[ULE] (LE=[(Ad, MeArO)3 mesitylene]3-, Ad=adamantyl), [U(NHAriPr6)2] (AriPr6=2, 6-(2, 4, 6-iPr3C6H2)2C6H3), Y·[U{N(SiMe3)2}3] and[U(η5-C5iPr5)2] were synthetically accessible. Inspection finds that all these U(Ⅱ) complexes were prepared in the same route, i.e., utilizing potassium graphite or potassium sphere to reduce respective U(Ⅲ) parent at low temperature. Cyclopentadiene (Cp) and arene (Ar)-based ligands are involved. They are key to determine U(Ⅱ) electron configuration, leading to 5f36d1 and 5f4, respectively. Moreover, δ(U-Ar) bonds play a significant role in stabilizing arene-ligated complexes. With the supporting of Cp-derived ligands, actinide(Ⅱ) complexes were extended to Th, Np and Pu. Unfortunately, it is not the case for the arene ligands, even with massive efforts. Given the prevailing route that actinide(Ⅱ) complex was synthesized by reducing its trivalent parent, the exploration of redox property will help to guide the synthesis of more novel U(Ⅱ) and even other actinide(Ⅱ) complexes. In this respect, theoretical computation based on accurate methodology is greatly appealing. Herein, relativistic density functional theory was exploited to investigate structural and redox properties of[AnL]z (An=Ac~Pu; L=[(Me, MeArOH)3Ar]3-; z=0 and -1), where analogues of uranium complexes were experimentally known. It is found that the central arene moiety is redox-active for Ac and Th complexes in the reduction reaction, while the metal center is reduced for other complexes. So Ac and Th in reduced products still remain +3 oxidation states, whereas metals in others turn +2. The 5fn electronic configuration is unraveled for actinide of[AnL]- (An=Pa~Pu), having 3~6 electrons, respectively. Calculated redox potential (E0) increases from Ac to Pu in general, where U and Np show lower values than adjacent elements. A good correlation has been built between E0 and Δ(An-CAr/An-Arcent)/electron affinity. In brief, the study is expected to provide theoretical support for the synthesis of novel arene-based actinide(Ⅱ) complexes.
It is of great significance to identify new oxidation state of actinide, which will enrich actinide coordination chemistry and advance its exploration of chemical bond and reactivity. So far, uranium with +3~+6 oxidation states has been widely recognized in complexes. Comparatively, isolated, crystallographically identified U(Ⅱ) complexes remain rare. Inspired by the pioneering work of Evans and co-workers that Y·[UⅡ(Cp')3] (Y=[K(2.2.2-cryptand)]+, Cp'=[C5H4SiMe3]-) was structurally characterized, several uranium(Ⅱ) complexes such as Y·[ULE] (LE=[(Ad, MeArO)3 mesitylene]3-, Ad=adamantyl), [U(NHAriPr6)2] (AriPr6=2, 6-(2, 4, 6-iPr3C6H2)2C6H3), Y·[U{N(SiMe3)2}3] and[U(η5-C5iPr5)2] were synthetically accessible. Inspection finds that all these U(Ⅱ) complexes were prepared in the same route, i.e., utilizing potassium graphite or potassium sphere to reduce respective U(Ⅲ) parent at low temperature. Cyclopentadiene (Cp) and arene (Ar)-based ligands are involved. They are key to determine U(Ⅱ) electron configuration, leading to 5f36d1 and 5f4, respectively. Moreover, δ(U-Ar) bonds play a significant role in stabilizing arene-ligated complexes. With the supporting of Cp-derived ligands, actinide(Ⅱ) complexes were extended to Th, Np and Pu. Unfortunately, it is not the case for the arene ligands, even with massive efforts. Given the prevailing route that actinide(Ⅱ) complex was synthesized by reducing its trivalent parent, the exploration of redox property will help to guide the synthesis of more novel U(Ⅱ) and even other actinide(Ⅱ) complexes. In this respect, theoretical computation based on accurate methodology is greatly appealing. Herein, relativistic density functional theory was exploited to investigate structural and redox properties of[AnL]z (An=Ac~Pu; L=[(Me, MeArOH)3Ar]3-; z=0 and -1), where analogues of uranium complexes were experimentally known. It is found that the central arene moiety is redox-active for Ac and Th complexes in the reduction reaction, while the metal center is reduced for other complexes. So Ac and Th in reduced products still remain +3 oxidation states, whereas metals in others turn +2. The 5fn electronic configuration is unraveled for actinide of[AnL]- (An=Pa~Pu), having 3~6 electrons, respectively. Calculated redox potential (E0) increases from Ac to Pu in general, where U and Np show lower values than adjacent elements. A good correlation has been built between E0 and Δ(An-CAr/An-Arcent)/electron affinity. In brief, the study is expected to provide theoretical support for the synthesis of novel arene-based actinide(Ⅱ) complexes.
2020, 78(10): 1102-1110
doi: 10.6023/A20060275
Abstract:
In this paper, the synthesis of poly(3, 4-ethylenedioxythiophene) (PEDOT) by cyclic voltammetry (CV) electrochemical deposition and its application in the counter electrode of solid-state dye-sensitized solar cells were studied. The influence of cycle times (10~50 times) on the morphology, thickness and optical properties of PEDOT films were explored by Fourier transform infrared spectroscopy (FTIR), atomic force microscope (AFM), scanning electron microscope (SEM) and ultraviolet-visible spectroscopy (UV-Vis). The photoelectrochemical properties of solid-state dye-sensitized solar cells based on PEDOT transparent counter electrode were characterized by J-V, electrochemical impedance spectroscopy (EIS), intensity modulated photocurrent spectrum/photovoltage spectrum (IMPS/VS) and Tafel analysis. The results showed that an un-uniform film with the thickness of 0.5 μm and light transmittance of 80% was formed when CV cycle times was 10, where the PEDOT film was not completely covered on the substrate. When the CV cycles reached 30~40, a uniform and dense transparent film was obtained and the highest photoelectric conversion efficiency of the corresponding solid-state dye-sensitized solar cells reached 5.34%. This is because uniform and dense surface, good optical properties and high photo-electric catalysis properties (J0=2.51×10-3 A·cm-2) for I3- in the electrolyte, made the device obtain larger diffusion coefficient (Dn=28.80 μm2·ms-1) and carrier diffusion length (L=21.41 μm), which were favorable for charge transfer. When the number of CV cycles was further increased to 50 times, showing greater roughness, the PEDOT film was no longer growing uniformly. The PEDOT film deposited on the FTO surface underwent some dissolution and desorption, the PEDOT film became uneven, and the catalytic activity of PEDOT electrode to I3- in electrolyte was reduced. The device with PEDOT transparent counter electrode film deposited by cyclic voltammetry could also achieve double-side illumination with good catalytic activity to the electrolyte. Under the condition of double-side illumination, the photoelectric performance of the device using electrodeposited PEDOT as transparent counter electrode was improved by about 20%. The improvement of the photoelectric performance of the device is mainly due to the increase in the absorption of photons by the double-sided illumination.
In this paper, the synthesis of poly(3, 4-ethylenedioxythiophene) (PEDOT) by cyclic voltammetry (CV) electrochemical deposition and its application in the counter electrode of solid-state dye-sensitized solar cells were studied. The influence of cycle times (10~50 times) on the morphology, thickness and optical properties of PEDOT films were explored by Fourier transform infrared spectroscopy (FTIR), atomic force microscope (AFM), scanning electron microscope (SEM) and ultraviolet-visible spectroscopy (UV-Vis). The photoelectrochemical properties of solid-state dye-sensitized solar cells based on PEDOT transparent counter electrode were characterized by J-V, electrochemical impedance spectroscopy (EIS), intensity modulated photocurrent spectrum/photovoltage spectrum (IMPS/VS) and Tafel analysis. The results showed that an un-uniform film with the thickness of 0.5 μm and light transmittance of 80% was formed when CV cycle times was 10, where the PEDOT film was not completely covered on the substrate. When the CV cycles reached 30~40, a uniform and dense transparent film was obtained and the highest photoelectric conversion efficiency of the corresponding solid-state dye-sensitized solar cells reached 5.34%. This is because uniform and dense surface, good optical properties and high photo-electric catalysis properties (J0=2.51×10-3 A·cm-2) for I3- in the electrolyte, made the device obtain larger diffusion coefficient (Dn=28.80 μm2·ms-1) and carrier diffusion length (L=21.41 μm), which were favorable for charge transfer. When the number of CV cycles was further increased to 50 times, showing greater roughness, the PEDOT film was no longer growing uniformly. The PEDOT film deposited on the FTO surface underwent some dissolution and desorption, the PEDOT film became uneven, and the catalytic activity of PEDOT electrode to I3- in electrolyte was reduced. The device with PEDOT transparent counter electrode film deposited by cyclic voltammetry could also achieve double-side illumination with good catalytic activity to the electrolyte. Under the condition of double-side illumination, the photoelectric performance of the device using electrodeposited PEDOT as transparent counter electrode was improved by about 20%. The improvement of the photoelectric performance of the device is mainly due to the increase in the absorption of photons by the double-sided illumination.
2020, 78(10): 1111-1119
doi: 10.6023/A20060246
Abstract:
Cyclohexanol is an important chemical intermediate material. At present, ZSM-5 is mainly used as a catalyst in the industry to produce cyclohexanol by one-step hydration of cyclohexene. Its core is the development of high-performance catalysts. TS-1 is a high efficient catalyst for industrial liquid-phase ammoniation of cyclohexanone, which shows a typical Brønsted acidity after deactivation. Based on this, we applied the deactivated TS-1 as catalyst for cyclohexene hydration reaction, and investigated systematically the effects of reaction time, reaction temperature, catalyst dosage and mass ratio of water to oil on the hydration reaction of cyclohexene. The results showed that the deactivated TS-1 could offer a high catalytic performance with 11.0% yield and 99.8% selectivity towards cyclohexanol under the optimized reaction conditions, which indicated that the deactivated TS-1 is a high-performance catalyst and possesses the characteristics of high activity, high selectivity and high stability. Combined with nitric acid treating modification, potassium ion exchange experiment and the characterization techniques such as UV-Vis (UV-visible spectroscopy), FT-IR (Fourier transform infrared spectrometer), 29Si MAS NMR (29Si magic angle solid nuclear magnetic resonance), and NH3-TPD (temperature-programmed desorption of ammonia), it was found that the deactivated TS-1 possesses two kinds of Brønsted acid sites, whereas its real active center for the hydration reaction of cyclohexene is silanol group adjacent to titanium hydroxyl group (Si-OH(Ti)). The structure of this Brønsted acid site is completely different from the skeleton bridge Brønsted acid site (Si-(OH)-Al) of ZSM-5 zeolite, meanwhile shows relatively weak acid strength. The unique acid property of Si-OH(Ti) could promote the main reaction path of cyclohexanol formation and inhibit the side reaction path of cyclohexene isomerization in cyclohexene hydration reaction, which determined its characteristic of high cyclohexanol selectivity. The discovery and application of the special Brønsted acid site of the deactivated TS-1 waste catalyst can provide a new idea for resource utilization of solid waste resources of spent catalyst.
Cyclohexanol is an important chemical intermediate material. At present, ZSM-5 is mainly used as a catalyst in the industry to produce cyclohexanol by one-step hydration of cyclohexene. Its core is the development of high-performance catalysts. TS-1 is a high efficient catalyst for industrial liquid-phase ammoniation of cyclohexanone, which shows a typical Brønsted acidity after deactivation. Based on this, we applied the deactivated TS-1 as catalyst for cyclohexene hydration reaction, and investigated systematically the effects of reaction time, reaction temperature, catalyst dosage and mass ratio of water to oil on the hydration reaction of cyclohexene. The results showed that the deactivated TS-1 could offer a high catalytic performance with 11.0% yield and 99.8% selectivity towards cyclohexanol under the optimized reaction conditions, which indicated that the deactivated TS-1 is a high-performance catalyst and possesses the characteristics of high activity, high selectivity and high stability. Combined with nitric acid treating modification, potassium ion exchange experiment and the characterization techniques such as UV-Vis (UV-visible spectroscopy), FT-IR (Fourier transform infrared spectrometer), 29Si MAS NMR (29Si magic angle solid nuclear magnetic resonance), and NH3-TPD (temperature-programmed desorption of ammonia), it was found that the deactivated TS-1 possesses two kinds of Brønsted acid sites, whereas its real active center for the hydration reaction of cyclohexene is silanol group adjacent to titanium hydroxyl group (Si-OH(Ti)). The structure of this Brønsted acid site is completely different from the skeleton bridge Brønsted acid site (Si-(OH)-Al) of ZSM-5 zeolite, meanwhile shows relatively weak acid strength. The unique acid property of Si-OH(Ti) could promote the main reaction path of cyclohexanol formation and inhibit the side reaction path of cyclohexene isomerization in cyclohexene hydration reaction, which determined its characteristic of high cyclohexanol selectivity. The discovery and application of the special Brønsted acid site of the deactivated TS-1 waste catalyst can provide a new idea for resource utilization of solid waste resources of spent catalyst.
2020, 78(10): 1120-1126
doi: 10.6023/A20060230
Abstract:
Using solar energy to split CO2 can realize the conversion and storage of solar energy at the same time, and alleviate the carbon emissions caused by the transitional use of fossil energy. Solar energy based photo-thermochemical reaction is a promising method for the CO2 splitting. To further study the photo-thermochemical reaction mechanism and explore the non-titanium-based catalytic materials, the ZnO/Zn2GeO4 composite material (Z/ZGO) was prepared by solution precipitation method and used for photo-thermochemical CO2 splitting. Composite semiconductor combined the advantages of the two components which made CO production reach 5.55 times that of pure ZnO. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to illustrate the crystal structure and chemical composition of the samples. The XRD pattern found that the samples crystallized well, and no obvious crystal form changes occurred after the reaction. Using SEM to observe the samples before and after the reaction, the particle size did not increase significantly and no obvious sintering phenomenon was found, which indicated that the material has good reaction stability. Photoluminescence (PL), UV-visible diffuse reflectance spectra (UV-visible DRS) and Mott-Schottky plots were used to evaluate the material's light absorption characteristics and energy band position. The band gap of ZnO and Zn2GeO4 samples were 3.27 eV and 4.56 eV, respectively, and the heterojunction was formed in the Z/ZGO sample. The presence of ZnO extended the spectral response range of Zn2GeO4, and due to the migration of photogenerated electron-hole pairs (EHPs) to ZnO, the recombination of EHPs was reduced. XPS analyses were also used to investigate change of oxygen vacancies during the reaction. The O 1s XPS spectra of the samples in the three cases (Case A:before light irradiation, Case B:after light irradiation and Case C:after reaction) were analyzed and found that the signal of the oxygen near the vacancies increased after light irradiation and decreased after reaction, which may indicate that oxygen vacancies were formed after light irradiation then consumed by CO2 in the reaction. The Zn2GeO4 sample showed the largest increase in oxygen vacancies signal after light irradiation, indicating that Zn2GeO4 had a strong ability to form oxygen vacancies. Zn2GeO4 improves the capacity of oxygen vacancies formation in the sample, and further improved the yield of photo-thermochemical CO2 splitting reaction. As a result, Z/ZGO combined the advantages of ZnO in light response and Zn2GeO4 in oxygen vacancies formation and improved the CO2 splitting yield. This research has a positive effect on expanding the photo-thermochemical material system and further deepening the photo-thermochemical reaction mechanism.
Using solar energy to split CO2 can realize the conversion and storage of solar energy at the same time, and alleviate the carbon emissions caused by the transitional use of fossil energy. Solar energy based photo-thermochemical reaction is a promising method for the CO2 splitting. To further study the photo-thermochemical reaction mechanism and explore the non-titanium-based catalytic materials, the ZnO/Zn2GeO4 composite material (Z/ZGO) was prepared by solution precipitation method and used for photo-thermochemical CO2 splitting. Composite semiconductor combined the advantages of the two components which made CO production reach 5.55 times that of pure ZnO. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to illustrate the crystal structure and chemical composition of the samples. The XRD pattern found that the samples crystallized well, and no obvious crystal form changes occurred after the reaction. Using SEM to observe the samples before and after the reaction, the particle size did not increase significantly and no obvious sintering phenomenon was found, which indicated that the material has good reaction stability. Photoluminescence (PL), UV-visible diffuse reflectance spectra (UV-visible DRS) and Mott-Schottky plots were used to evaluate the material's light absorption characteristics and energy band position. The band gap of ZnO and Zn2GeO4 samples were 3.27 eV and 4.56 eV, respectively, and the heterojunction was formed in the Z/ZGO sample. The presence of ZnO extended the spectral response range of Zn2GeO4, and due to the migration of photogenerated electron-hole pairs (EHPs) to ZnO, the recombination of EHPs was reduced. XPS analyses were also used to investigate change of oxygen vacancies during the reaction. The O 1s XPS spectra of the samples in the three cases (Case A:before light irradiation, Case B:after light irradiation and Case C:after reaction) were analyzed and found that the signal of the oxygen near the vacancies increased after light irradiation and decreased after reaction, which may indicate that oxygen vacancies were formed after light irradiation then consumed by CO2 in the reaction. The Zn2GeO4 sample showed the largest increase in oxygen vacancies signal after light irradiation, indicating that Zn2GeO4 had a strong ability to form oxygen vacancies. Zn2GeO4 improves the capacity of oxygen vacancies formation in the sample, and further improved the yield of photo-thermochemical CO2 splitting reaction. As a result, Z/ZGO combined the advantages of ZnO in light response and Zn2GeO4 in oxygen vacancies formation and improved the CO2 splitting yield. This research has a positive effect on expanding the photo-thermochemical material system and further deepening the photo-thermochemical reaction mechanism.
