Rh is an important catalyst that is widely used in a variety of organic reactions. In recent years, many efforts have focused on improving its catalytic efficiency by fabricating catalyst nanoparticles with controlled...Rh is an important catalyst that is widely used in a variety of organic reactions. In recent years, many efforts have focused on improving its catalytic efficiency by fabricating catalyst nanoparticles with controlled size and morphology. However, the frequently employed synthesis route using organic compounds either as the reaction medium or capping agent often results in residual molecules on the catalyst surface, which in turn drastically diminishes the catalytic performance. Herein, we report a facile, aqueous, surfactant-free synthesis of a novel Rh flower- like structure obtained via hydrothermal reduction of Rh（acac）3 by formaldehyde. The unique Rh nanoflowers were constructed from ultrathin nanosheets, whose basal surfaces comprised {111} facets with an average thickness of -1.1 nm. The specific surface area measured by CO stripping was 79.3 m2-g-1, which was much larger than that of commercial Rh black. More importantly, the Rh nanoflower catalyst exhibited excellent catalytic performance in the catalytic hydrogenation of phenol and cyclohexene, in contrast to the commercial Rh black and polyvinyl pyrrolidone （PVP）-capped Rh nanosheets exposed by similar {111} basal surfaces.展开更多
Researchers appear to have neglected a special form of crystallites, pentagonal cyclic twinning, in which an obvious two-dimensional lattice expansion exists leading to novel physical-chemical properties associated wi...Researchers appear to have neglected a special form of crystallites, pentagonal cyclic twinning, in which an obvious two-dimensional lattice expansion exists leading to novel physical-chemical properties associated with the changes in geometric and electronic structures. Using the storage and release of hydrogen in Pd nanocrystals as a probe, we have found that icosahedral pentagonal cyclic twinned Pd nanocrystals had distinct hydrogen storage properties, due to the two-dimensional lattice expansions, quite different from those of the octahedral single crystalline counterpart. In addition, the two-dimensional lattice expansion in pentagonal cyclic twinned Pd nanocrystals causes a change in electronic structure, which results in novel catalytic properties involving in situ formation of PdHx pentagonal cyclic twinned nanocrystals.展开更多
The determination of catalytically active sites is crucial for the design of efficient and stable catalysts toward desired reactions.However,the complexity of supported noble metal catalysts has led to controversy ove...The determination of catalytically active sites is crucial for the design of efficient and stable catalysts toward desired reactions.However,the complexity of supported noble metal catalysts has led to controversy over the locations of catalytically active sites(e.g.,metal,support,and metal/support interface).Here we develop a structurally controllable catalyst system(Pd/SBA-15)to reveal the catalytic active sites for the selective hydrogenation of ketones to alcohol using acetophenone hydrogenation as model reaction.Systematic investigations demonstrated that unsupported Pd nanocrystals have no catalytic activity for acetophenone hydrogenation.However,oxidized Pd species were catalytically highly active for acetophenone hydrogenation.The catalytic activity decreased with the decreased oxidation state of Pd.This work provides insights into the hydrogenation mechanism of ketones but also other unsaturated compounds containing polar bonds,e.g.,nitrobenzene,N-benzylidene-benzylamine,and carbon dioxide.展开更多
Microwave absorbing materials(MAMs)are playing an increasingly essential role in the development of wireless communications,high-power electronic devices,and advanced target detection technology.MAMs with a broad-band...Microwave absorbing materials(MAMs)are playing an increasingly essential role in the development of wireless communications,high-power electronic devices,and advanced target detection technology.MAMs with a broad-bandwidth response are particularly important in the area of communication security,radiation prevention,electronic reliability,and military stealth.Although considerable progress has been made in the design and preparation of MAMs with a broad-bandwidth response,a number of challenges still remain,and the structure–function relationship of MAMs is still far from being completely understood.Herein,the advances in the design and research of MAMs with a broad-bandwidth response are outlined.The main strategies for expanding the effective absorption bandwidth of MAMs are comprehensively summarized considering three perspectives:the chemical combination strategy,morphological control strategy,and macrostructure control strategy.Several important results as well as design principles and absorption mechanisms are highlighted.A coherent explanation detailing the influence of the chemical composition and structure of various materials on the microwave absorption properties of MAMs is provided.The main challenges,new opportunities,and future perspectives in this promising field are also presented.展开更多
Three sandwich-like[Ln_(2)Fe_(2)(B-α-FeW_9O_(34))_(2)]^(10-) clusters(Ln_(2)Fe_(4),Ln=Dy(1),Ho(2),and Y(3)) were obtained by reacting Na_9[B-α-SbW_9O_(33)],Ln_(2)O_(3),FeCl_(3)·6H_(2)O and KH_(2)PO_(4).The[B-α...Three sandwich-like[Ln_(2)Fe_(2)(B-α-FeW_9O_(34))_(2)]^(10-) clusters(Ln_(2)Fe_(4),Ln=Dy(1),Ho(2),and Y(3)) were obtained by reacting Na_9[B-α-SbW_9O_(33)],Ln_(2)O_(3),FeCl_(3)·6H_(2)O and KH_(2)PO_(4).The[B-α-FeW_9O_(34)]^(11-) units were formed via the in situ conversion of lacunary polyoxometalates(POM)[B-α-SbW_9O_(33)]^(9-)and the Ln^(3+)ions were generated from the slow dissolution of Ln_(2)O_(3),both of which play important roles in the synthesis of Ln_(2)Fe_(4).Ln_(2)Fe_(4) is the first 3d-4f cluster assembled from d-metal heteroatom-containing POM.The Dy_(2)Fe_(4) cluster exhibits single-molecule magnet properties with an 80 K energy barrier in an optimal DC field.Cyclic voltammetry tests and controlled-potential coulometry experiments show that the polyoxometalate Fe heteroatom in clusters 1-3 is also electrochemically active.展开更多
Metallic iron particles are of great potential for microwave absorption materials due to their strong magnetic loss ability.However,the oxidation susceptibility of metallic iron particles in the atmospheric environmen...Metallic iron particles are of great potential for microwave absorption materials due to their strong magnetic loss ability.However,the oxidation susceptibility of metallic iron particles in the atmospheric environment is regarded as a major factor causing performance degradation.Although many efforts have been developed to avoid their oxidation,whether partial surface oxidized iron particles can improve the microwave absorbing performance is rarely concerned.In order to explore the effect of partial surface oxidation of iron on its properties,the designed yolk–shelled(Fe/FeO_(x))@C composites with multiple heterointerfaces were synthesized via an in-situ polymerization and a finite reduction–oxidation process of Fe_(2)O_(3)ellipsoids.The performance enhancement mechanisms of Fe/FeO_(x)heterointerfaces were also elaborated.It is demonstrated that the introduction of Fe-based heterogeneous interfaces can not only enhance the dielectric loss,but also increase the imaginary part of the permeability in the higher frequency range to strengthen the magnetic loss ability.Meanwhile,the yolk–shell structure can effectively improve impedance matching and enhance microwave absorption performances via increasing multiple reflection and scattering behaviors of incident microwaves.Compared to Fe@C composite,the effective absorption(reflection loss(RL)<−10 dB)bandwidth of the optimized(Fe/FeO_(x))@C-2 increases from 5.7 to 7.3 GHz(10.7–18.0 GHz)at a same matching thickness of 2 mm,which can completely cover Ku-band.This work offers a good perspective for the enhancement of magnetic loss ability and microwave absorption performance of Fe-based microwave absorption materials with promising practical applications.展开更多
This paper describes a robust method for the synthesis of high-quality ZIF-8 nanocrystals using reverse micelles as discrete nanoscale reactors.The precise size control of ZIF-8 nanocrystals is conveniently achieved b...This paper describes a robust method for the synthesis of high-quality ZIF-8 nanocrystals using reverse micelles as discrete nanoscale reactors.The precise size control of ZIF-8 nanocrystals is conveniently achieved by tuning the concentration of precursors,reaction temperatures,the amount of water,and the structure of surfactants.The as-synthesized ZIF-8 nanocrystals are of narrow distribution and tunable size.A size-dependent catalytic activity for Knoevenagel condensation reaction is further demonstrated by using ZIF-8 nanocrystals with different sizes as the catalysts.This facile method opens up a new opportunity in the synthesis of various ZIFs nanocrystals.展开更多
Recently,metal-organic framework(MOF)-based multienzyme systems integrating different functional natural enzymes and/or nanomaterial-basedartificial enzymes are attracting increasing attention due to their high cataly...Recently,metal-organic framework(MOF)-based multienzyme systems integrating different functional natural enzymes and/or nanomaterial-basedartificial enzymes are attracting increasing attention due to their high catalytic efficiency and promising application in sensing.Simpleand controllable integration of enzymes or nanozymes within MOFs is crucial for achieving efficient cascade catalysis and high stability.Here,we report a facile electrochemical assisted biomimetic mineralization strategy to prepare an artificial multienzyme system for efficient electrochemicaldetection of biomolecules.By using the G0x@Cu-MOF/copper foam(G0x@Cu-MOF/CF)architecture as a proof of concept,efficientenzyme immobilization and cascade catalysis were achieved by in situ encapsulation of glucose oxidase(GOx)within MOFs layer grown onthree-dimensional(3D)porous conducting CF via a facile one-step electrochemical assisted biomimetic mineralization strategy.Due to thebio-electrocatalytic cascade reaction mechanism,this well-designed GOx@Cu-MOF modified electrode exhibited superior catalytic activityand thermal stability for glucose sensing.Notably,the activity of GOx@Cu-MOF/CF still remained at ca.80%after being incubated at 80℃.In sharp contrast,the activity of the unprotected electrode was reduced to the original 10%after the same treatment.The design strategypresented here may be useful in fabricating highly stable enzyme@MOF composites applied for efficient photothermal therapy and otherplatform under high temperature.展开更多
Fluorescent ink has become an effective anti-counterfeiting material to prevent counterfeiters from making and selling fake products[1–4].From its practical application,an ideal fluorescent ink should be environmenta...Fluorescent ink has become an effective anti-counterfeiting material to prevent counterfeiters from making and selling fake products[1–4].From its practical application,an ideal fluorescent ink should be environmentally friendly,have high stability and good viscosity,and exhibit excellent luminescent performance.To obtain such fluorescent inks,different fluorescent materials,such as carbon dots[5–7],lanthanide-doped compounds[8–10],inorganic semiconductor complexes[11–13],organic dyes[14–16],metal-organic frameworks[17–19],lanthanide coordination compounds[20,21]and cluster compounds[22,23],have been used to prepare fluorescent inks.Although these fluorescent materials have their own advantages as fluorescent inks,they also have their own disadvantages.For example,organic dyes used as fluorescent inks often encounter the problems of aggregation-induced quenching and small Stokes shifts[14–16],while carbon dots suffer from unclear structures,and concerns about the reproducibility of carbon dots have affected their widespread use[5,6].展开更多
Electrospray ionization time-of-flight mass spectrometry(ESI-TOF-MS)has been recognized as a powerful technique for studying metal clusters’chemical composition and reaction mechanisms.It is a great challenge in mass...Electrospray ionization time-of-flight mass spectrometry(ESI-TOF-MS)has been recognized as a powerful technique for studying metal clusters’chemical composition and reaction mechanisms.It is a great challenge in mass spectrometry analysis to maintain the metal cluster molecules intact without fragmentation,which is achieved in this work by using mixed solvents to change the interaction between cluster molecules and solvent molecules,further affecting the fragmentation behaviors of the metal cluster in MS.Theoretical analysis reveals that the stability of the[(C)Au_(6)Ag_(2)(C_(18)H_(14)ONP)_(6)]^(4+)cluster in ESI-TOF-MS is related to the strength of the chemical bonds between its own atoms and the bonding between the solvent and the cluster molecules.展开更多
In wet chemical syntheses of noble metal nanocrystals,surfactants play crucial roles in regulating their morphology.To date,more attention has been paid to the effect of the surfactant on the surface energy of crystal...In wet chemical syntheses of noble metal nanocrystals,surfactants play crucial roles in regulating their morphology.To date,more attention has been paid to the effect of the surfactant on the surface energy of crystal facets,while less attention has been paid to its effect on the growth kinetics.In this paper,using the growth of Au-Pd alloy nanocrystals as an example,we demonstrate that different concentration of surfactant hexadecyltrimethyl ammonium chloride(CTAC)may cause the different packing density of CTA+bilayers on different sites(face,edge or vertex)of crystallite surface,which would change the crystal growth kinetics and result in preferential crystal growth along the edge or vertex of crystallites.The unique shape evolution from trisoctahedron to excavated rhombic dodecahedron and multipod structure for Au-Pd alloy nanocrystals was successfully achieved by simply adjusting the concentration of CTAC.These results help to understand the effect of surfactants on the shape evolution of nanocrystals and open up avenues to the rational synthesis of nanocrystals with the thermodynamically unfavorable morphologies.展开更多
Seed-mediated growth is the most general way to controllably synthesize bimetal nano-heterostructures. Despite successful instances through trial and error were reported, the way for second metal depositing on the see...Seed-mediated growth is the most general way to controllably synthesize bimetal nano-heterostructures. Despite successful instances through trial and error were reported, the way for second metal depositing on the seed. namely whether the symmetry of resulted nano-heterostructure follows the original crystal symmetry of seed metal, remains an unpredictable issue to date. In this work, we propose that the ther- modynamic factor, i.e., the difference of equilibrium electrochemical potentials （corresponding to their Fermi levels） of two metals in the growth solution, plays a key role for the symmetry breaking of bimetal nano-heterostructures during the seed-mediated growth. As a proof-of-principle experiment, by revers- ing the relative position of Fermi levels of the Pd nanocube seeds and the second metal Au with changing the concentration of reductant （L-ascorbic acid） in the growth solution, the structure of as-prepared prod- ucts successfully evolved from centrosymmetric Pd@Au core-shell trisoctabedra to asymmetric Pd-Au hetero-dimers. The idea was further demonstrated by the growth of Ag on the Pd seeds. The present work intends to reveal the origin of symmetry breaking in the seed-mediated growth of nano-heterostructures from the viewpoint of thermodynamics, and these new insights will in turn help to achieve rational con- struction of bimetal nano-heterostructures with soecific functions.展开更多
Magnetic refrigeration,which is based on the magnetocaloric effect(MCE)of magnetic materials,is a powerful cooling technique[1-4].In addition to its high efficiency and environmental friendliness,magnetic refrigeratio...Magnetic refrigeration,which is based on the magnetocaloric effect(MCE)of magnetic materials,is a powerful cooling technique[1-4].In addition to its high efficiency and environmental friendliness,magnetic refrigeration can replace the expensive and increasingly rare helium-3 in ultralow-temperature(<<1 K)refrigeration[5-8].展开更多
The high cost and poor durability of Pt nanoparticles(NPs)have always been great challenges to the commercialization of proton exchange membrane fuel cells(PEMFCs).Pt-based intermetallic NPs with a highly ordered stru...The high cost and poor durability of Pt nanoparticles(NPs)have always been great challenges to the commercialization of proton exchange membrane fuel cells(PEMFCs).Pt-based intermetallic NPs with a highly ordered structure are considered as promising catalysts for PEMFCs due to their high catalytic activity and stability.Here,we reported a facile method to synthesize N-doped carbon encapsulated PtZn intermetallic(PtZn@NC)NPs via the pyrolysis of Pt@Zn-based zeolitic imidazolate framework-8(Pt@ZIF-8)composites.The catalyst obtained at 800℃(10%-PtZn@NC-800)was found to exhibit a half-wave potential(Ev2)up to 0.912 V versus reversible hydrogen electrode(RHE)for the cathodic oxygen reduction reaction in an acidic medium,which shifted by 26 mV positively compared to the benchmark Pt/C catalyst.Besides,the mass activity and specific activity of 10%-PtZn@NC-800 at 0.9 V versus RHE were nearly 3 and 5 times as great as that of commercial Pt/C,respectively.It is worth noting that the PtZn@NC showed excel Ient stability in oxygen reducti on reacti on(ORR)with just 1 mV of the Ev2 loss after 5,000 cycles,which is superior to that of most reported PtM catalysts(especially those disordered solid solutions).Furthermore,such N-doped carb on shell encapsulated PtZn intermetallic NPs showed significa ntly enha need performances towards the anodic oxidation reaction of organic small molecules(such as methanol and formic acid).The synergistic effects of the N doped carbon encapsulation structure and intermetallic NPs are responsible for outstanding performances of the catalysts.This work provides us a new engineering strategy to acquire highly active and stable multifunctional catalysts for PEMFCs.展开更多
The asymmetric assembly and spontaneous resolution of chiral heterometal-organic frameworks from achiral precursors remain a great challenge. Herein, we report the formation and spontaneous resolution of three-dimensi...The asymmetric assembly and spontaneous resolution of chiral heterometal-organic frameworks from achiral precursors remain a great challenge. Herein, we report the formation and spontaneous resolution of three-dimensional(3 D) chiral 3 d-4 f heterometal-organic frameworks from achiral ligands in the presence of lactic acid enantiomers as chiral inducers. In the absence of a chiral inducer, the reactants randomly generated both enantiopure crystals in equal measure. However, enantiopure lactic acid induced asymmetric resolution to achieve single chiral crystallization. DFT theoretical calculations showed that the absolute chiral resolution of the enantiomers is due to the difference in the interactions between the two enantiomeric Λ/Δ-[Fe L_(3)]^(3-)units and the chiral inducer.展开更多
The structural phase transition compound {[（CH3）2CHCH2]2NH2}·[CF3COO] （1） has been synthesized based on the diisobutylamine and trifluoroacetic acid. The DSC data reveal that 1 undergoes a phase transition at...The structural phase transition compound {[（CH3）2CHCH2]2NH2}·[CF3COO] （1） has been synthesized based on the diisobutylamine and trifluoroacetic acid. The DSC data reveal that 1 undergoes a phase transition at 277 K （Tc）. When one chlorine atom replaces one fluorine atom on trifluoroacetate anion, three order-disorder phase transitions at 251 K （Ti）, 282 K （T2） and 290 K could be achieved owing to a stepwise release of rotation motions of the anion and cation in {[（CH3）2CHCH2]2NH2}·[CF2C[COO] （2）. Based on the variable temperature crystal structures, the phase transition in compound 1 is triggered by the rotation of three fluorine atoms on the trifluoroacetate anion synchronized with the motions of the methyl groups on the diisobutylammonium cation. However, in compound 2, the phase transitions can be realized by a sequence of motions of both the anion and cation. Besides, the dielectric- temperature dependences were investigated in order to prove this regulation process. All of this investigation will be beneficial to design and synthesis of the novel phase transition materials and molecular dielectric materials on pur- pose.展开更多
基金This work was supported by the National Basic Research Program of China （Nos. 2011CBA00508 and 2015CB932301）, the National Natural Science Foundation of China （Nos. 21131005, 21333008, and J1310024）, and the Natural Science Foundation of Fujian Province of China （No. 2014J01058）.
文摘Rh is an important catalyst that is widely used in a variety of organic reactions. In recent years, many efforts have focused on improving its catalytic efficiency by fabricating catalyst nanoparticles with controlled size and morphology. However, the frequently employed synthesis route using organic compounds either as the reaction medium or capping agent often results in residual molecules on the catalyst surface, which in turn drastically diminishes the catalytic performance. Herein, we report a facile, aqueous, surfactant-free synthesis of a novel Rh flower- like structure obtained via hydrothermal reduction of Rh（acac）3 by formaldehyde. The unique Rh nanoflowers were constructed from ultrathin nanosheets, whose basal surfaces comprised {111} facets with an average thickness of -1.1 nm. The specific surface area measured by CO stripping was 79.3 m2-g-1, which was much larger than that of commercial Rh black. More importantly, the Rh nanoflower catalyst exhibited excellent catalytic performance in the catalytic hydrogenation of phenol and cyclohexene, in contrast to the commercial Rh black and polyvinyl pyrrolidone （PVP）-capped Rh nanosheets exposed by similar {111} basal surfaces.
基金This work was supported by the National Basic Research Program of China （Nos. 2011CBA00508 and 2015CB932301）, the National Natural Science Foundation of China （Nos. 21171142, 21171141, 21131005, and 21333008）, and the program for New Century Excellent Talents in University （No. NCET-11-0294）. X. Y. W. is grateful for the support of NFFTBS （No. J1310024）.
文摘Researchers appear to have neglected a special form of crystallites, pentagonal cyclic twinning, in which an obvious two-dimensional lattice expansion exists leading to novel physical-chemical properties associated with the changes in geometric and electronic structures. Using the storage and release of hydrogen in Pd nanocrystals as a probe, we have found that icosahedral pentagonal cyclic twinned Pd nanocrystals had distinct hydrogen storage properties, due to the two-dimensional lattice expansions, quite different from those of the octahedral single crystalline counterpart. In addition, the two-dimensional lattice expansion in pentagonal cyclic twinned Pd nanocrystals causes a change in electronic structure, which results in novel catalytic properties involving in situ formation of PdHx pentagonal cyclic twinned nanocrystals.
基金supported by the National Natural Science Foundation of China(Nos.92261207,21890752,and 22002126)。
文摘The determination of catalytically active sites is crucial for the design of efficient and stable catalysts toward desired reactions.However,the complexity of supported noble metal catalysts has led to controversy over the locations of catalytically active sites(e.g.,metal,support,and metal/support interface).Here we develop a structurally controllable catalyst system(Pd/SBA-15)to reveal the catalytic active sites for the selective hydrogenation of ketones to alcohol using acetophenone hydrogenation as model reaction.Systematic investigations demonstrated that unsupported Pd nanocrystals have no catalytic activity for acetophenone hydrogenation.However,oxidized Pd species were catalytically highly active for acetophenone hydrogenation.The catalytic activity decreased with the decreased oxidation state of Pd.This work provides insights into the hydrogenation mechanism of ketones but also other unsaturated compounds containing polar bonds,e.g.,nitrobenzene,N-benzylidene-benzylamine,and carbon dioxide.
基金supported by the National Natural Science Foundation of China(Nos.21771151 and 21931009).
文摘Microwave absorbing materials(MAMs)are playing an increasingly essential role in the development of wireless communications,high-power electronic devices,and advanced target detection technology.MAMs with a broad-bandwidth response are particularly important in the area of communication security,radiation prevention,electronic reliability,and military stealth.Although considerable progress has been made in the design and preparation of MAMs with a broad-bandwidth response,a number of challenges still remain,and the structure–function relationship of MAMs is still far from being completely understood.Herein,the advances in the design and research of MAMs with a broad-bandwidth response are outlined.The main strategies for expanding the effective absorption bandwidth of MAMs are comprehensively summarized considering three perspectives:the chemical combination strategy,morphological control strategy,and macrostructure control strategy.Several important results as well as design principles and absorption mechanisms are highlighted.A coherent explanation detailing the influence of the chemical composition and structure of various materials on the microwave absorption properties of MAMs is provided.The main challenges,new opportunities,and future perspectives in this promising field are also presented.
基金supported by the National Natural Science Foundation of China(Nos.21871224,92161104,92161203 and 21721001)Innovation Laboratory for Sciences and Technologies of Energy Materials of Fujian Province(IKKEM No.RD2021040301)。
文摘Three sandwich-like[Ln_(2)Fe_(2)(B-α-FeW_9O_(34))_(2)]^(10-) clusters(Ln_(2)Fe_(4),Ln=Dy(1),Ho(2),and Y(3)) were obtained by reacting Na_9[B-α-SbW_9O_(33)],Ln_(2)O_(3),FeCl_(3)·6H_(2)O and KH_(2)PO_(4).The[B-α-FeW_9O_(34)]^(11-) units were formed via the in situ conversion of lacunary polyoxometalates(POM)[B-α-SbW_9O_(33)]^(9-)and the Ln^(3+)ions were generated from the slow dissolution of Ln_(2)O_(3),both of which play important roles in the synthesis of Ln_(2)Fe_(4).Ln_(2)Fe_(4) is the first 3d-4f cluster assembled from d-metal heteroatom-containing POM.The Dy_(2)Fe_(4) cluster exhibits single-molecule magnet properties with an 80 K energy barrier in an optimal DC field.Cyclic voltammetry tests and controlled-potential coulometry experiments show that the polyoxometalate Fe heteroatom in clusters 1-3 is also electrochemically active.
基金supported by the National Natural Science Foundation of China(Nos.21771151 and 21931009)the Natural Science Foundation of Fujian Province of China(No.2022J01042).
文摘Metallic iron particles are of great potential for microwave absorption materials due to their strong magnetic loss ability.However,the oxidation susceptibility of metallic iron particles in the atmospheric environment is regarded as a major factor causing performance degradation.Although many efforts have been developed to avoid their oxidation,whether partial surface oxidized iron particles can improve the microwave absorbing performance is rarely concerned.In order to explore the effect of partial surface oxidation of iron on its properties,the designed yolk–shelled(Fe/FeO_(x))@C composites with multiple heterointerfaces were synthesized via an in-situ polymerization and a finite reduction–oxidation process of Fe_(2)O_(3)ellipsoids.The performance enhancement mechanisms of Fe/FeO_(x)heterointerfaces were also elaborated.It is demonstrated that the introduction of Fe-based heterogeneous interfaces can not only enhance the dielectric loss,but also increase the imaginary part of the permeability in the higher frequency range to strengthen the magnetic loss ability.Meanwhile,the yolk–shell structure can effectively improve impedance matching and enhance microwave absorption performances via increasing multiple reflection and scattering behaviors of incident microwaves.Compared to Fe@C composite,the effective absorption(reflection loss(RL)<−10 dB)bandwidth of the optimized(Fe/FeO_(x))@C-2 increases from 5.7 to 7.3 GHz(10.7–18.0 GHz)at a same matching thickness of 2 mm,which can completely cover Ku-band.This work offers a good perspective for the enhancement of magnetic loss ability and microwave absorption performance of Fe-based microwave absorption materials with promising practical applications.
基金support from the Ministry of Science and Technology of China(2011CB932403)the National Natural Science Foundation of China(21131005,21333008,20925103,21021061)
文摘This paper describes a robust method for the synthesis of high-quality ZIF-8 nanocrystals using reverse micelles as discrete nanoscale reactors.The precise size control of ZIF-8 nanocrystals is conveniently achieved by tuning the concentration of precursors,reaction temperatures,the amount of water,and the structure of surfactants.The as-synthesized ZIF-8 nanocrystals are of narrow distribution and tunable size.A size-dependent catalytic activity for Knoevenagel condensation reaction is further demonstrated by using ZIF-8 nanocrystals with different sizes as the catalysts.This facile method opens up a new opportunity in the synthesis of various ZIFs nanocrystals.
基金This work was supported by the National Key Research and Development Program of China(Nos.2017YFA0206500 and 2017YFA0206801)the National Basic Research Program of China(No.2015CB932301)the National Natural Science Foundation of China(Nos.21671163,21721001,and J1310024).
文摘Recently,metal-organic framework(MOF)-based multienzyme systems integrating different functional natural enzymes and/or nanomaterial-basedartificial enzymes are attracting increasing attention due to their high catalytic efficiency and promising application in sensing.Simpleand controllable integration of enzymes or nanozymes within MOFs is crucial for achieving efficient cascade catalysis and high stability.Here,we report a facile electrochemical assisted biomimetic mineralization strategy to prepare an artificial multienzyme system for efficient electrochemicaldetection of biomolecules.By using the G0x@Cu-MOF/copper foam(G0x@Cu-MOF/CF)architecture as a proof of concept,efficientenzyme immobilization and cascade catalysis were achieved by in situ encapsulation of glucose oxidase(GOx)within MOFs layer grown onthree-dimensional(3D)porous conducting CF via a facile one-step electrochemical assisted biomimetic mineralization strategy.Due to thebio-electrocatalytic cascade reaction mechanism,this well-designed GOx@Cu-MOF modified electrode exhibited superior catalytic activityand thermal stability for glucose sensing.Notably,the activity of GOx@Cu-MOF/CF still remained at ca.80%after being incubated at 80℃.In sharp contrast,the activity of the unprotected electrode was reduced to the original 10%after the same treatment.The design strategypresented here may be useful in fabricating highly stable enzyme@MOF composites applied for efficient photothermal therapy and otherplatform under high temperature.
基金the National Natural Science Foundation of China(21673184 and 21721001)。
文摘Fluorescent ink has become an effective anti-counterfeiting material to prevent counterfeiters from making and selling fake products[1–4].From its practical application,an ideal fluorescent ink should be environmentally friendly,have high stability and good viscosity,and exhibit excellent luminescent performance.To obtain such fluorescent inks,different fluorescent materials,such as carbon dots[5–7],lanthanide-doped compounds[8–10],inorganic semiconductor complexes[11–13],organic dyes[14–16],metal-organic frameworks[17–19],lanthanide coordination compounds[20,21]and cluster compounds[22,23],have been used to prepare fluorescent inks.Although these fluorescent materials have their own advantages as fluorescent inks,they also have their own disadvantages.For example,organic dyes used as fluorescent inks often encounter the problems of aggregation-induced quenching and small Stokes shifts[14–16],while carbon dots suffer from unclear structures,and concerns about the reproducibility of carbon dots have affected their widespread use[5,6].
基金supported by the National Natural Science Foundation of China(Nos.91961107,21827801,21805231)。
文摘Electrospray ionization time-of-flight mass spectrometry(ESI-TOF-MS)has been recognized as a powerful technique for studying metal clusters’chemical composition and reaction mechanisms.It is a great challenge in mass spectrometry analysis to maintain the metal cluster molecules intact without fragmentation,which is achieved in this work by using mixed solvents to change the interaction between cluster molecules and solvent molecules,further affecting the fragmentation behaviors of the metal cluster in MS.Theoretical analysis reveals that the stability of the[(C)Au_(6)Ag_(2)(C_(18)H_(14)ONP)_(6)]^(4+)cluster in ESI-TOF-MS is related to the strength of the chemical bonds between its own atoms and the bonding between the solvent and the cluster molecules.
基金supported by the National Basic Research Program of China (2015CB932301)the National Key Research and Development Program of China (2017YFA0206801)the National Natural Science Foundation of China (21333008, 21773190 and J1310024)
文摘In wet chemical syntheses of noble metal nanocrystals,surfactants play crucial roles in regulating their morphology.To date,more attention has been paid to the effect of the surfactant on the surface energy of crystal facets,while less attention has been paid to its effect on the growth kinetics.In this paper,using the growth of Au-Pd alloy nanocrystals as an example,we demonstrate that different concentration of surfactant hexadecyltrimethyl ammonium chloride(CTAC)may cause the different packing density of CTA+bilayers on different sites(face,edge or vertex)of crystallite surface,which would change the crystal growth kinetics and result in preferential crystal growth along the edge or vertex of crystallites.The unique shape evolution from trisoctahedron to excavated rhombic dodecahedron and multipod structure for Au-Pd alloy nanocrystals was successfully achieved by simply adjusting the concentration of CTAC.These results help to understand the effect of surfactants on the shape evolution of nanocrystals and open up avenues to the rational synthesis of nanocrystals with the thermodynamically unfavorable morphologies.
基金supported by the National Basic Research Program of China(2015CB93230)the National Key Research and Development Program of China(2017YFA0206801)+1 种基金the National Natural Science Foundation of China(21333008,21671163,21721001,and 21773190)the Fundamental Research Funds for the Central Universities(20720160026)
文摘Seed-mediated growth is the most general way to controllably synthesize bimetal nano-heterostructures. Despite successful instances through trial and error were reported, the way for second metal depositing on the seed. namely whether the symmetry of resulted nano-heterostructure follows the original crystal symmetry of seed metal, remains an unpredictable issue to date. In this work, we propose that the ther- modynamic factor, i.e., the difference of equilibrium electrochemical potentials （corresponding to their Fermi levels） of two metals in the growth solution, plays a key role for the symmetry breaking of bimetal nano-heterostructures during the seed-mediated growth. As a proof-of-principle experiment, by revers- ing the relative position of Fermi levels of the Pd nanocube seeds and the second metal Au with changing the concentration of reductant （L-ascorbic acid） in the growth solution, the structure of as-prepared prod- ucts successfully evolved from centrosymmetric Pd@Au core-shell trisoctabedra to asymmetric Pd-Au hetero-dimers. The idea was further demonstrated by the growth of Ag on the Pd seeds. The present work intends to reveal the origin of symmetry breaking in the seed-mediated growth of nano-heterostructures from the viewpoint of thermodynamics, and these new insights will in turn help to achieve rational con- struction of bimetal nano-heterostructures with soecific functions.
基金supported by the Innovation Laboratory for Sciences and Technologies of Energy Materials of Fujian Province(RD2021040301)the National Natural Science Foundation of China(21431005,21721001,and 21971214)。
文摘Magnetic refrigeration,which is based on the magnetocaloric effect(MCE)of magnetic materials,is a powerful cooling technique[1-4].In addition to its high efficiency and environmental friendliness,magnetic refrigeration can replace the expensive and increasingly rare helium-3 in ultralow-temperature(<<1 K)refrigeration[5-8].
基金This work was supported by the National Key Research and Development Program of China(Nos.2017YFA0206500 and 2017YFA0206801)the National Basic Research Program of China(No.2015CB932301)the National Natural Science Foundation of China(Nos.21671163 and 21721001).
文摘The high cost and poor durability of Pt nanoparticles(NPs)have always been great challenges to the commercialization of proton exchange membrane fuel cells(PEMFCs).Pt-based intermetallic NPs with a highly ordered structure are considered as promising catalysts for PEMFCs due to their high catalytic activity and stability.Here,we reported a facile method to synthesize N-doped carbon encapsulated PtZn intermetallic(PtZn@NC)NPs via the pyrolysis of Pt@Zn-based zeolitic imidazolate framework-8(Pt@ZIF-8)composites.The catalyst obtained at 800℃(10%-PtZn@NC-800)was found to exhibit a half-wave potential(Ev2)up to 0.912 V versus reversible hydrogen electrode(RHE)for the cathodic oxygen reduction reaction in an acidic medium,which shifted by 26 mV positively compared to the benchmark Pt/C catalyst.Besides,the mass activity and specific activity of 10%-PtZn@NC-800 at 0.9 V versus RHE were nearly 3 and 5 times as great as that of commercial Pt/C,respectively.It is worth noting that the PtZn@NC showed excel Ient stability in oxygen reducti on reacti on(ORR)with just 1 mV of the Ev2 loss after 5,000 cycles,which is superior to that of most reported PtM catalysts(especially those disordered solid solutions).Furthermore,such N-doped carb on shell encapsulated PtZn intermetallic NPs showed significa ntly enha need performances towards the anodic oxidation reaction of organic small molecules(such as methanol and formic acid).The synergistic effects of the N doped carbon encapsulation structure and intermetallic NPs are responsible for outstanding performances of the catalysts.This work provides us a new engineering strategy to acquire highly active and stable multifunctional catalysts for PEMFCs.
基金the National Natural Science Foundation of China (21871224, 21673184, 21721001)。
文摘The asymmetric assembly and spontaneous resolution of chiral heterometal-organic frameworks from achiral precursors remain a great challenge. Herein, we report the formation and spontaneous resolution of three-dimensional(3 D) chiral 3 d-4 f heterometal-organic frameworks from achiral ligands in the presence of lactic acid enantiomers as chiral inducers. In the absence of a chiral inducer, the reactants randomly generated both enantiopure crystals in equal measure. However, enantiopure lactic acid induced asymmetric resolution to achieve single chiral crystallization. DFT theoretical calculations showed that the absolute chiral resolution of the enantiomers is due to the difference in the interactions between the two enantiomeric Λ/Δ-[Fe L_(3)]^(3-)units and the chiral inducer.
基金This work was financially supported by the 973 Pro- ject from the Ministry of Science and Technology of China （No. 2014CB84561）, and the National Natural Science Foundation of China （Nos. 21571150, 21431005 and 21390391）.
文摘The structural phase transition compound {[（CH3）2CHCH2]2NH2}·[CF3COO] （1） has been synthesized based on the diisobutylamine and trifluoroacetic acid. The DSC data reveal that 1 undergoes a phase transition at 277 K （Tc）. When one chlorine atom replaces one fluorine atom on trifluoroacetate anion, three order-disorder phase transitions at 251 K （Ti）, 282 K （T2） and 290 K could be achieved owing to a stepwise release of rotation motions of the anion and cation in {[（CH3）2CHCH2]2NH2}·[CF2C[COO] （2）. Based on the variable temperature crystal structures, the phase transition in compound 1 is triggered by the rotation of three fluorine atoms on the trifluoroacetate anion synchronized with the motions of the methyl groups on the diisobutylammonium cation. However, in compound 2, the phase transitions can be realized by a sequence of motions of both the anion and cation. Besides, the dielectric- temperature dependences were investigated in order to prove this regulation process. All of this investigation will be beneficial to design and synthesis of the novel phase transition materials and molecular dielectric materials on pur- pose.
