The propylene/propane(C_(3)H_(6)/C_(3)H_(8))separation is particularly challenging due to their highly similar physical properties,but of industrial importance.Herein,we report a bifunctional ultramicroporous metal-or...The propylene/propane(C_(3)H_(6)/C_(3)H_(8))separation is particularly challenging due to their highly similar physical properties,but of industrial importance.Herein,we report a bifunctional ultramicroporous metal-organic framework(Co-aip-pyz)with customized pore environment and selective binding sites for the challenging C_(3)H_(6)/C_(3)H_(8) separation.Co-aip-pyz exhibits a good C_(3)H_(6) uptake with an ultrahigh C_(3)H_(6) packing density(931 g/L),as well as possesses a remarkable C_(3)H_(6)/C_(3)H_(8) uptake ratio with 911% and distinguished C_(3)H_(6)/C_(3)H_(8) selectivity(>10^(4))at 298 K and 1.0 bar.Furthermore,Co-aip-pyz possesses a record high C_(3)H_(6) packing density with 859 g/L at 313 K and 1.0 bar,which is unprecedented in the C_(3)H_(6)/C_(3)H_(8) separation.Its high performance for the C_(3)H_(6)/C_(3)H_(8) separation has been further confirmed by breakthrough experiments and molecular simulations.Combined with good stability,facilely synthesized procedure by low-cost precursors,record-high C_(3)H_(6) packing density,as well as good C_(3)H_(6)/C_(3)H_(8) separation performance,it highlights Co-aip-pyz as a benchmark adsorbent to address daunting challenge for industrial C_(3)H_(6)/C_(3)H_(8) separation.This work provides valuable insights into constructing top-performing MOF materials for addressing the industrial separation challenges.展开更多
The ultrafast carrier relaxation processes in CdTe quantum dots are investigated by femtosecond fluorescence upconversion spectroscopy.Photo-excited hole relaxing to the edge of the forbidden gap takes a maximal time ...The ultrafast carrier relaxation processes in CdTe quantum dots are investigated by femtosecond fluorescence upconversion spectroscopy.Photo-excited hole relaxing to the edge of the forbidden gap takes a maximal time of ～ 1.6 ps with exciting at 400 nm,depending on the state of the photo-excited hole.The shallow trapped states and deep trap states in the forbidden gap are confirmed for CdTe quantum dots.In addition,Auger relaxation of trapped carriers is observed to occur with a time constant of ～ 5 ps.A schematic model of photodynamics is established based on the results of the spectroscopy studies.Our work demonstrates that femtosecond fluorescence up-conversion spectroscopy is a suitable and effective tool in studying the transportation and conversion dynamics of photon energy in a nanosystem.展开更多
Upconversion nanosensitizers have been widely considered to have important applications in the treatment of major diseases such as tumors and the utilization of solar energy.Majority of the efforts so far have been fo...Upconversion nanosensitizers have been widely considered to have important applications in the treatment of major diseases such as tumors and the utilization of solar energy.Majority of the efforts so far have been focused on improving the efficiency of energy transfer(ET)between upconversion nanoparticles(UCNPs)and the anchored sensitizers with premise that high ET efficiency will lead to high acceptor efficacy.This premise is,however,proved by our current work to be invalid for commonly used load.Interaction between adjacent sensitizing molecules was found to be critical which undermines the amount of excited monomer sensitizers and thus fades the efficacy.Here NaYF_(4):Yb^(3+),Er^(3+)UCNPs and rose bengal(RB)photosensitizer molecules were used as the model energy donors and acceptors,respectively.Contrary to monotonous increase of the ET efficiency from UCNPs to RB species with increasing RB loading,acceptor efficacy characterized by the reactive oxygen species,as well as the RB fluorescence,exhibits bizarre dependence on the RB loading.The underlying mechanism was well studied by the steady-state and time-resolved spectroscopy of a series of samples.RB aggregates are believed to be responsible for the severe deviation between the ET efficiency and acceptor efficacy.The conclusion was validated by in vitro test where the photodynamic therapy with the most monomer RB in UCNPs-RB nanosensitizers kills 35.8%more cells than that with the highest RB loading.This understanding sheds light on construction of new ET based nanosystems for broad applications,such as medicine,solar energy utilization and optical storage.展开更多
A bound state formalism derived from a fermion-boson symmetric Lagrangian has been used to calculate the nucleon masses, the charge neutrality of the neutron, the magnetic moments and the electromagnetic form factor r...A bound state formalism derived from a fermion-boson symmetric Lagrangian has been used to calculate the nucleon masses, the charge neutrality of the neutron, the magnetic moments and the electromagnetic form factor ratios μpGEp/GMpand μnGEn/GMn. A quantitative description is obtained, assuming a mixing of a scalar bound state of 3(f f¯)fstructure with its corresponding vector (f f¯)fstate (f indicating massless elementary fermions). Only a few parameters are needed, mainly fixed by energy and momentum conservation. The nucleon stability is explained by an extra binding in the confinement potential, negative for electric and positive for magnetic binding of the proton, and opposite for the neutron. The stronger electric extra binding of the proton allows a decay of the neutron to proton and electron.展开更多
The removal of trace propyne(C_(3)H_(4))from propyne/propylene(C_(3)H_(4)/C_(3)H_(6))mixtures is a technical and challenging task during the production of polymer-grade propylene in view of their very similar size and...The removal of trace propyne(C_(3)H_(4))from propyne/propylene(C_(3)H_(4)/C_(3)H_(6))mixtures is a technical and challenging task during the production of polymer-grade propylene in view of their very similar size and physical properties.While some progress has been made,it is still very challenging to use some highly stable and commercially available porous materials via an energy-efficient adsorptive separation process.Herein,we report the ultrafine tuning of the pore apertures in type-A zeolites for the highly efficient removal of trace amounts of C_(3)H_(4)from C_(3)H_(4)/C_(3)H_(6)mixtures.The resulting ion-exchanged zeolite 5 A exhibits a large C_(3)H_(4)adsorption capacity(2.3 mmol g^(-1)under 10^(-4)MPa)and high C_(3)H_(4)/C_(3)H_(6)selectivity at room temperature,which were mainly attributed to the ultrafine-tuned pore size that selectively blocks C_(3)H_(6)molecules,while maintaining the stro ng adsorption of C_(3)H_(4)at low pressure region.High purity of C_(3)H_(6)(>99.9999%)can be directly obtained on this material under ambient conditions,as demonstrated by the experimental breakthrough curves obtained for both 1/99 and 0.1/99.9(V V)C_(3)H_(4)/C_(3)H_(6) mixtures.展开更多
Typically, a Lewis acid and a Lewis base can react with each other and form a classical Lewis adduct. The neutralization reaction can however be prevented by ligating the acid and base with bulky substituents and the ...Typically, a Lewis acid and a Lewis base can react with each other and form a classical Lewis adduct. The neutralization reaction can however be prevented by ligating the acid and base with bulky substituents and the resulting complex is known as a "frustrated Lewis pair"(FLP). Since the Lewis acid and base reactivity remains in the formed complex, FLPs can display interesting chemical activities, with promising applications in catalysis. For example, FLPs were shown to function as the first metal-free catalyst for molecular hydrogen activation. This, and other recent applications of FLPs, have opened a new thriving research field. In this short-review, we recapitulate the computational and experimental studies of the H_2 activation by FLPs. We discuss the thus-far uncovered mechanistic aspects, including pre-organization of FLPs,the reaction paths for the activation, the polarization of He H bond and other factors affecting the reactivity. We aim to provide a rather complete mechanistic picture of the H_2 activation by FLPs, which has been under debate for decades since the first discovery of FLPs. This review is meant as a starting point for future studies and a guideline for industrial applications.展开更多
The massive vector bosons Z o, W ± and the scalar Higgs-boson H o assumed in weak interaction theory, but also the six quarks required in strong interactions are well understood in an alternative quantum field th...The massive vector bosons Z o, W ± and the scalar Higgs-boson H o assumed in weak interaction theory, but also the six quarks required in strong interactions are well understood in an alternative quantum field theory of fermions and bosons: Z o and W ± as well as all quark-antiquark states (here only the tt¯state is discussed) are described by bound states with scalar coupling between their massless constituents and have a structure similar to leptons. However, the scalar Higgs-boson H o corresponds to a state with vector coupling between the elementary constituents. Similar scalar states are expected also in the mass region of the mesons ω (0.782 GeV) - Υ ( 9.46 GeV). The underlying calculations can be run on line using the Web-address https://h2909473.stratoserver.net.展开更多
Both, the dilemma to find a quantum field theory consistent with Einstein’s law of relativity and the problem to describe existing particles as bound states of matter has been solved by calculating bound state matrix...Both, the dilemma to find a quantum field theory consistent with Einstein’s law of relativity and the problem to describe existing particles as bound states of matter has been solved by calculating bound state matrix elements from a dual fermion-boson Lagrangian. In this formalism, the fermion binding energies are compensated by boson energies, indicating that particles can be generated out of the vacuum. This yields quantitative solutions for various mesons ω (0.78 GeV) - Υ (9.46 GeV) and all leptons e, μ and τ, with uncertainties in the extracted properties of less than 1‰. For transparency, a Web-page with the address htpps://h2909473.stratoserver.net has been constructed, where all calculations can be run on line and also the underlying fortran source code can be inspected.展开更多
The solid oxide electrolytic cell(SOEC)is one of the most promising energy conversion and storage devices,which could convert CO_(2) to CO with high Faradaic efficiency and production rate.However,the lack of active a...The solid oxide electrolytic cell(SOEC)is one of the most promising energy conversion and storage devices,which could convert CO_(2) to CO with high Faradaic efficiency and production rate.However,the lack of active and stable cathode materials impedes their practical applications.Here we focus on the promising perovskite oxide cathode material Sr_(2)Fe_(1.5)Mo_(0.5)O_(6)-σ,with the aim of understanding how A-atom stoichiometry and catalytic performance are linked.We find that increasing the strontium content in the perovskite improves the chemisorption of CO_(2) on its surface,forming a SrCO_(3) phase.This hinders the charge transfer and oxygen exchange processes.Simulta-neously,strontoium segregation to the cathode surface facilitates coking of the surface during CO_(2) electrolysis,which poisons the electrode.Consequently,a small number of Sr deficiencies are optimal for both electrochemical performance and long-term stability.Our results provide new insights for designing high-performance CO_(2) electrolysis cathode materials.展开更多
The direct one-step separation of polymer-grade C_(2)H_(4) from complex light hydrocarbon mixtures has high industrial significance but is very challenging.Herein,an ethylene-adsorption-weakening strategy is applied f...The direct one-step separation of polymer-grade C_(2)H_(4) from complex light hydrocarbon mixtures has high industrial significance but is very challenging.Herein,an ethylene-adsorption-weakening strategy is applied for precise regulation of the pore geometry of four tailor-made metal–organic frameworks(MOFs)with pillar-layered structures,dubbed TYUT-10/11/12/13.Based on its pore geometry design and functional group regulation,TYUT-12 exhibits exceptional selective adsorption selectivity toward C_(3)H_(8),C_(3)H_(6),C_(2)H_(6),C_(2)H_(2),and CO_(2) over C_(2)H_(4);its C_(2)H_(6)/C_(2)H_(4) adsorption selectivity reaches 4.56,surpassing the record value of 4.4 by Fe_(2)(O_(2))(dobdc)(dobdc^(4-)=2,5-dioxido-1,4-benzenedicarboxylate).The weak p–p stacking binding affinity toward C_(2)H_(4) in TYUT-12 is clearly demonstrated through a combination of neutron powder diffraction measurements and theoretical calculations.Breakthrough experiments demonstrate that C_(2)H_(4) can be directly obtained from binary,ternary,quaternary,and six-component light hydrocarbon mixtures with over 99.95%purity.展开更多
Homochiral metal–organic frameworks(HMOFs)are attractive materials for asymmetric catalysis because they possess high surface area and uniform active sites.A variety of catalytic applications reported so far indicate...Homochiral metal–organic frameworks(HMOFs)are attractive materials for asymmetric catalysis because they possess high surface area and uniform active sites.A variety of catalytic applications reported so far indicate that HMOFs catalyse a range of transformations,including cyanosilylation,aldol condensation and hydrogenation reactions.Besides contribution to fundamental knowledge,it is also important to evaluate the relevance of organic transformations catalysed by HMOFs and how existing achievements compare with already established enantioselective catalysts.This mini-review gives an overview of the structural design and the catalytic performance of HMOFs and it focuses on the relevance of the chemical reactions tested.It aims at combining the existing demand for heterogeneous asymmetric catalysts with the current knowledge on HMOFs.This is important for the MOF community since it highlights relevant broad scope asymmetric catalytic transformations performed in industry and the insight gained from the catalytic reactions carried out using HMOFs as catalysts.We hope that this work will motivate researchers to rationally design HMOFs with a goal to unveil reaction mechanisms and the interactions between the HMOFs and the reaction molecules for industrially relevant catalytic reactions.展开更多
Nitrogen-doped carbons are promising candidates for replacing platinum catalysts in fuel cell electrodes.They typically contain graphitic and amorphous domains,both of which contribute to the oxygen reduction reaction...Nitrogen-doped carbons are promising candidates for replacing platinum catalysts in fuel cell electrodes.They typically contain graphitic and amorphous domains,both of which contribute to the oxygen reduction reaction(ORR)activity.Here,we aim at revealing the catalytic functions of each domain as well of the surface functional groups,and ultimately at maximizing the catalytic performance of the materials in the ORR.We develop a sequential oxidative-pyrolytic treatment to remove the amorphous domains and to alter the surface functionalities.The effectiveness of this approach is evidenced by various techniques.Our electrochemical results show a positive correlation between the ORR activity and the degree of graphitization/oxygen functional group removal.While the oxidation-induced oxygen-containing group impairs the ORR,the amorphous domains seem facilitate the 2-electron transfer ORR,lack electrical conductivity and are rich in oxygen-containing groups.The ORR activity of the optimized sample increases considerably in the alkaline electrolyte,giving a half-wave potential>0.85 V(vs.a reversible hydrogen electrode)that is comparable to that of commercial platinum on carbon.展开更多
The application of metal-organic molecular hosts as“molecular flasks”has precipitated a surge of interest in the reactivity and properties of molecules within well-defined spaces.Here we report an approach to constr...The application of metal-organic molecular hosts as“molecular flasks”has precipitated a surge of interest in the reactivity and properties of molecules within well-defined spaces.Here we report an approach to construct supramolecular systems for photo-catalytic hydrogen production and carbon dioxide reduction by encapsulating an organic dye molecule into the pocket of the redox-active metal-organic macrocycle.The assembled Ni_(3)L_(3)tricycle consists of three ligands and three nickel ions that alternately connect together.The special geometry enforces the distortion of the square planar coordinated configuration,and the coordination of the sulphur atoms enables the modification of redox potentials suitable for proton reduction and carbon dioxide reduction.The supramolecular systems that have fluorescein molecules being encapsulated as the photosensitive vips feature efficient activity for the photocatalytic carbon dioxide conversion and production reduction.The new reaction pathways within the confined space demonstrate the power of the supramolecular system over related systems.展开更多
The separation of C_(2)H_(2)/C_(2)H_(4) mixtures is of industrial importance in the production of high-purity C_(2)H_(4) and C_(2)H_(2).The primary objective of this work is to enhance the selectivity of C_(2)H_(2)/C_...The separation of C_(2)H_(2)/C_(2)H_(4) mixtures is of industrial importance in the production of high-purity C_(2)H_(4) and C_(2)H_(2).The primary objective of this work is to enhance the selectivity of C_(2)H_(2)/C_(2)H_(4) separation by developing a method for appropriate modification of porous adsorbents.Toward this end,directly doping low-content Na+ions into covalent organic frameworks(COFs)via cation exchange is proposed in this work.Relative to the pristine COF,COF-ECUT-1,with C_(2)H_(2) and C_(2)H_(4) adsorption capacities of 55.39 cm^(3) g^(-1) and 28.63 cm^(3) g^(-1),the Na+-anchored phase with just 4.0 wt%sodium content,Na@COF-ECUT-1,enables largely enhanced adsorption ability with the corresponding values of 89.70 cm^(3) g^(-1) and 49.26 cm^(3) g^(-1),respectively.As a result,the adsorption selectivity of C_(2)H_(2) over that of C_(2)H_(4) is enhanced from 6.33 to 9.41,and the separation potential estimated by the simulated transient breakthrough is largely improved about three-fold.The density functional theory(DFT)calculation reveals that the trap of Na+within the COF channel affords strong affinity towards C_(2)H_(2) or C_(2)H_(4) through Na-πinteractions and relatively stronger contact for C_(2)H_(2) than for C_(2)H_(4) is observed.This result is in line with the experimental results of both enhanced C_(2)H_(2) and C_(2)H_(4) adsorption capacity and C_(2)H_(2)/C_(2)H_(4) separation performance.This work outlines a general and simple method to enhance the gas separation performance upon COF materials.展开更多
Four novel metal–organic frameworks(MOFs)built from alkaline-earth metal ions and the flexible tetrahedral carboxylate ligand tetrakis[4-(carboxyphenyl)oxamethyl]methane acid(H_(4)L)were synthesized using solvotherma...Four novel metal–organic frameworks(MOFs)built from alkaline-earth metal ions and the flexible tetrahedral carboxylate ligand tetrakis[4-(carboxyphenyl)oxamethyl]methane acid(H_(4)L)were synthesized using solvothermal methods.A variety of three-dimensional frameworks were obtained when employing different alkaline earth ions with the formula[Mg_(2)(L)(H_(2)O)(DMA)]·DMA(1),[Ca_(4)(L)_(2)(DMA)_(3)](2),[Ca_(4)(L)_(2)(H_(2)O)_(2)(DMA)_(2)]·(3DMA)(3)and[Sr_(4)(L)_(2)(DMF)_(4)]·(2DMF)(4)reflecting the variation in the ionic radius of alkaline-earth ions as well as the key role of the synthetic conditions used.By removing the vip molecules,a framework shrinking was observed driven by the structural flexibility of the H_(4)L ligand.This resulted in large diffusional resistances towards N_(2)over CO_(2)molecules,therefore leading to a good CO_(2)/N_(2)separation selectivity.Both Ca-based MOFs were very stable up to 98%relative humidity,while Mgand Sr-based MOFs were much less stable.展开更多
Here,Friedel-Crafts(FC)reaction is used to synthesize a purely organic cage in a one-pot manner.The trigonal prismatic cage is composed of two trisfuran platforms,bridged by three phenanthrene pillars each bearing two...Here,Friedel-Crafts(FC)reaction is used to synthesize a purely organic cage in a one-pot manner.The trigonal prismatic cage is composed of two trisfuran platforms,bridged by three phenanthrene pillars each bearing two methoxy(OMe)units.The organic cage exhibited good kinetic inertness,allowing for a synthetic post-functionalization.During this transforming process,the electron-donating methoxy(OMe)groups were converted into electron-withdrawing carbonyl groups without any degradation on the cage framework.The cage exhibits multiple vip recognition modes.The oxygen atoms as the Lewis base present in either methoxy or carbonyl before and after post-functionalization,endow the cage with the ability to recognize Lewis acidic vips such as alkali cations.The OMe and carbonyl units grated on the phenanthrene pillars endow the cage with anπ-electron-rich andπ-electron-deficient cavity,respectively,whereπ-electron-deficient andπ-electron-rich vips can be accommodated.展开更多
A new series of cyanide-bridged assemblies,{KH[Ln_(2)(2,3-pzdc)_(2)(CH_(3)OH)(H_(2)O)_(7)][M(CN)_(8)]}·5H_(2)O(Ln^(3+)=Nd,Gd,Tb,and Dy;M^(4+)=Mo and W),were synthesised by self-assembling lanthanide ions and octa...A new series of cyanide-bridged assemblies,{KH[Ln_(2)(2,3-pzdc)_(2)(CH_(3)OH)(H_(2)O)_(7)][M(CN)_(8)]}·5H_(2)O(Ln^(3+)=Nd,Gd,Tb,and Dy;M^(4+)=Mo and W),were synthesised by self-assembling lanthanide ions and octacyanometallate ions in the presence of pyrazine-2,3-dicarboxylic acid(2,3-H_(2)pzdc).These compounds have a 3D structure in which octagon-like Ln_(4)M_(4)(CN)_(8)rings are connected through a second Ln^(3+)center via the carboxylate groups of one 2,3-pzdc.The resulting 1D channels are filled with K^(+)ions and lattice water molecules.The temperature and field dependent magnetization studies as well as ab initio calculations indicate weak ferromagnetic interactions between the Gd^(3+)ions within the GdMo compound whilst no magnetic interactions exist in GdW analogues.The magnetic properties of Nd^(3+),Tb^(3+)and Dy^(3+)compounds are strongly dominated by the magnetic anisotropy of the lanthanide ions,irrespective of the octacyanometallate building-block used.展开更多
Industrial purification processes for ethylene from steam pyrolysis or cracking gases generally employ multiple energy-intensive steps to remove C_(2)H_(2),C_(2)H_(6),CO_(2),and C_(3) hydrocarbons.Designing multifunct...Industrial purification processes for ethylene from steam pyrolysis or cracking gases generally employ multiple energy-intensive steps to remove C_(2)H_(2),C_(2)H_(6),CO_(2),and C_(3) hydrocarbons.Designing multifunctional molecular separators that integrate multiple structural characteristics capable of removing several impurities simultaneously is highly desired but not yet realized.Here,we address this challenge using a custom-designed multifunctional,and industry-compatible ultramicroporous crystalline physisorbent(CALF-20)to purify C_(2)H_(4) from a seven-component cracking gas mixture(C_(2)H_(4),C_(2)H_(2),C_(2)H_(6),CO_(2),C_(3)H_(4),C_(3)H_(6),and C_(3)H8)by one-step separation with remarkable performance.Verified by breakthrough experiments,C_(2)H_(4)(>99.99%)can be recovered not only from binary C_(2)H_(6)/C_(2)H_(4)(50/50),ternary C_(2)H_(2)/C_(2)H_(4)/C_(2)H_(6)(33/33/33),and quaternary C_(2)H_(2)/C_(2)H_(4)/C_(2)H_(6)/CO_(2)(25/25/25/25)mixtures,but also from a typical seven-component gas cracking mixture of C_(2)H_(2)/C_(2)H_(4)/C_(2)H_(6)/CO_(2)/C_(3)H_(4)/C_(3)H_(6)/C_(3)H8(0.6/62/10/0.3/0.6/26/0.5),even at the high humidity of 74%.Notably,CALF-20 can be easily produced on the kilogram scale,showing great commercial application potential.Together with its framework flexibility and appropriate pore geometry,CALF-20 exhibits a sorbent-sorbate induced-fit behavior strengthening multiple specific recognition sites for the corresponding vips,validated by single-crystal X-ray diffraction study and molecular modeling.This work is the first example of using a single physisorbent to purify C_(2)H_(4) from a seven-component cracking gas mixture and opens an avenue to address complicated hydrocarbon mixture separation challenges.展开更多
基金financially supported by the National Natural Science Foundation of China(No.22275102)NCC Fund(No.NCC2022FH01)。
文摘The propylene/propane(C_(3)H_(6)/C_(3)H_(8))separation is particularly challenging due to their highly similar physical properties,but of industrial importance.Herein,we report a bifunctional ultramicroporous metal-organic framework(Co-aip-pyz)with customized pore environment and selective binding sites for the challenging C_(3)H_(6)/C_(3)H_(8) separation.Co-aip-pyz exhibits a good C_(3)H_(6) uptake with an ultrahigh C_(3)H_(6) packing density(931 g/L),as well as possesses a remarkable C_(3)H_(6)/C_(3)H_(8) uptake ratio with 911% and distinguished C_(3)H_(6)/C_(3)H_(8) selectivity(>10^(4))at 298 K and 1.0 bar.Furthermore,Co-aip-pyz possesses a record high C_(3)H_(6) packing density with 859 g/L at 313 K and 1.0 bar,which is unprecedented in the C_(3)H_(6)/C_(3)H_(8) separation.Its high performance for the C_(3)H_(6)/C_(3)H_(8) separation has been further confirmed by breakthrough experiments and molecular simulations.Combined with good stability,facilely synthesized procedure by low-cost precursors,record-high C_(3)H_(6) packing density,as well as good C_(3)H_(6)/C_(3)H_(8) separation performance,it highlights Co-aip-pyz as a benchmark adsorbent to address daunting challenge for industrial C_(3)H_(6)/C_(3)H_(8) separation.This work provides valuable insights into constructing top-performing MOF materials for addressing the industrial separation challenges.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11074003 and 20973001)the Key Program of Educational Commission of Anhui Province of China (Grant No. KJ2010A132)
文摘The ultrafast carrier relaxation processes in CdTe quantum dots are investigated by femtosecond fluorescence upconversion spectroscopy.Photo-excited hole relaxing to the edge of the forbidden gap takes a maximal time of ～ 1.6 ps with exciting at 400 nm,depending on the state of the photo-excited hole.The shallow trapped states and deep trap states in the forbidden gap are confirmed for CdTe quantum dots.In addition,Auger relaxation of trapped carriers is observed to occur with a time constant of ～ 5 ps.A schematic model of photodynamics is established based on the results of the spectroscopy studies.Our work demonstrates that femtosecond fluorescence up-conversion spectroscopy is a suitable and effective tool in studying the transportation and conversion dynamics of photon energy in a nanosystem.
基金Project supported by the National Natural Science Foundation of China(51972052,11604043,11604044,51772122,11674316)Scientific and Technological Developing Scheme of Jilin Province(20190201243JC)+5 种基金Science and Technology Research Project of Education Department of Jilin Province(JJKH20211275KJ)the Fundamental Research Funds for the Central Universities(2412019FZ033)the 111 Project(B13013)Netherlands Organization for Scientific Research in the framework of the Fund New Chemical Innovation(731.015.206)EU H2020-MSCA-ITN-ETN Action program,ISPIC(675743)EU H2020-MSCA-RISE Action program,CANCER(777682)。
文摘Upconversion nanosensitizers have been widely considered to have important applications in the treatment of major diseases such as tumors and the utilization of solar energy.Majority of the efforts so far have been focused on improving the efficiency of energy transfer(ET)between upconversion nanoparticles(UCNPs)and the anchored sensitizers with premise that high ET efficiency will lead to high acceptor efficacy.This premise is,however,proved by our current work to be invalid for commonly used load.Interaction between adjacent sensitizing molecules was found to be critical which undermines the amount of excited monomer sensitizers and thus fades the efficacy.Here NaYF_(4):Yb^(3+),Er^(3+)UCNPs and rose bengal(RB)photosensitizer molecules were used as the model energy donors and acceptors,respectively.Contrary to monotonous increase of the ET efficiency from UCNPs to RB species with increasing RB loading,acceptor efficacy characterized by the reactive oxygen species,as well as the RB fluorescence,exhibits bizarre dependence on the RB loading.The underlying mechanism was well studied by the steady-state and time-resolved spectroscopy of a series of samples.RB aggregates are believed to be responsible for the severe deviation between the ET efficiency and acceptor efficacy.The conclusion was validated by in vitro test where the photodynamic therapy with the most monomer RB in UCNPs-RB nanosensitizers kills 35.8%more cells than that with the highest RB loading.This understanding sheds light on construction of new ET based nanosystems for broad applications,such as medicine,solar energy utilization and optical storage.
文摘A bound state formalism derived from a fermion-boson symmetric Lagrangian has been used to calculate the nucleon masses, the charge neutrality of the neutron, the magnetic moments and the electromagnetic form factor ratios μpGEp/GMpand μnGEn/GMn. A quantitative description is obtained, assuming a mixing of a scalar bound state of 3(f f¯)fstructure with its corresponding vector (f f¯)fstate (f indicating massless elementary fermions). Only a few parameters are needed, mainly fixed by energy and momentum conservation. The nucleon stability is explained by an extra binding in the confinement potential, negative for electric and positive for magnetic binding of the proton, and opposite for the neutron. The stronger electric extra binding of the proton allows a decay of the neutron to proton and electron.
基金financial support from the National Natural Science Foundation of China(21922810,21908153,21908155)program of Innovative Talents of Higher Education Institutions of Shanxithe supported by Cultivate Scientific Research Excellence Programs of Higher Education Institutions in Shanxi(CSREP)。
文摘The removal of trace propyne(C_(3)H_(4))from propyne/propylene(C_(3)H_(4)/C_(3)H_(6))mixtures is a technical and challenging task during the production of polymer-grade propylene in view of their very similar size and physical properties.While some progress has been made,it is still very challenging to use some highly stable and commercially available porous materials via an energy-efficient adsorptive separation process.Herein,we report the ultrafine tuning of the pore apertures in type-A zeolites for the highly efficient removal of trace amounts of C_(3)H_(4)from C_(3)H_(4)/C_(3)H_(6)mixtures.The resulting ion-exchanged zeolite 5 A exhibits a large C_(3)H_(4)adsorption capacity(2.3 mmol g^(-1)under 10^(-4)MPa)and high C_(3)H_(4)/C_(3)H_(6)selectivity at room temperature,which were mainly attributed to the ultrafine-tuned pore size that selectively blocks C_(3)H_(6)molecules,while maintaining the stro ng adsorption of C_(3)H_(4)at low pressure region.High purity of C_(3)H_(6)(>99.9999%)can be directly obtained on this material under ambient conditions,as demonstrated by the experimental breakthrough curves obtained for both 1/99 and 0.1/99.9(V V)C_(3)H_(4)/C_(3)H_(6) mixtures.
文摘Typically, a Lewis acid and a Lewis base can react with each other and form a classical Lewis adduct. The neutralization reaction can however be prevented by ligating the acid and base with bulky substituents and the resulting complex is known as a "frustrated Lewis pair"(FLP). Since the Lewis acid and base reactivity remains in the formed complex, FLPs can display interesting chemical activities, with promising applications in catalysis. For example, FLPs were shown to function as the first metal-free catalyst for molecular hydrogen activation. This, and other recent applications of FLPs, have opened a new thriving research field. In this short-review, we recapitulate the computational and experimental studies of the H_2 activation by FLPs. We discuss the thus-far uncovered mechanistic aspects, including pre-organization of FLPs,the reaction paths for the activation, the polarization of He H bond and other factors affecting the reactivity. We aim to provide a rather complete mechanistic picture of the H_2 activation by FLPs, which has been under debate for decades since the first discovery of FLPs. This review is meant as a starting point for future studies and a guideline for industrial applications.
文摘The massive vector bosons Z o, W ± and the scalar Higgs-boson H o assumed in weak interaction theory, but also the six quarks required in strong interactions are well understood in an alternative quantum field theory of fermions and bosons: Z o and W ± as well as all quark-antiquark states (here only the tt¯state is discussed) are described by bound states with scalar coupling between their massless constituents and have a structure similar to leptons. However, the scalar Higgs-boson H o corresponds to a state with vector coupling between the elementary constituents. Similar scalar states are expected also in the mass region of the mesons ω (0.782 GeV) - Υ ( 9.46 GeV). The underlying calculations can be run on line using the Web-address https://h2909473.stratoserver.net.
文摘Both, the dilemma to find a quantum field theory consistent with Einstein’s law of relativity and the problem to describe existing particles as bound states of matter has been solved by calculating bound state matrix elements from a dual fermion-boson Lagrangian. In this formalism, the fermion binding energies are compensated by boson energies, indicating that particles can be generated out of the vacuum. This yields quantitative solutions for various mesons ω (0.78 GeV) - Υ (9.46 GeV) and all leptons e, μ and τ, with uncertainties in the extracted properties of less than 1‰. For transparency, a Web-page with the address htpps://h2909473.stratoserver.net has been constructed, where all calculations can be run on line and also the underlying fortran source code can be inspected.
基金financially supported by the National Natural Science Foundation of China(No.21975163)Natural Science Foundation of Guangdong Province of China(2020A1515011165)Shenzhen Sci-ence and Technology Program(No.KQTD20190929173914967)and(No.JCYJ20220818100004009)。
文摘The solid oxide electrolytic cell(SOEC)is one of the most promising energy conversion and storage devices,which could convert CO_(2) to CO with high Faradaic efficiency and production rate.However,the lack of active and stable cathode materials impedes their practical applications.Here we focus on the promising perovskite oxide cathode material Sr_(2)Fe_(1.5)Mo_(0.5)O_(6)-σ,with the aim of understanding how A-atom stoichiometry and catalytic performance are linked.We find that increasing the strontium content in the perovskite improves the chemisorption of CO_(2) on its surface,forming a SrCO_(3) phase.This hinders the charge transfer and oxygen exchange processes.Simulta-neously,strontoium segregation to the cathode surface facilitates coking of the surface during CO_(2) electrolysis,which poisons the electrode.Consequently,a small number of Sr deficiencies are optimal for both electrochemical performance and long-term stability.Our results provide new insights for designing high-performance CO_(2) electrolysis cathode materials.
基金supported by National Key Research and Development Program of China(2022YFB3806800)National Natural Science Foundation of China(22278288 and 22090062).
文摘The direct one-step separation of polymer-grade C_(2)H_(4) from complex light hydrocarbon mixtures has high industrial significance but is very challenging.Herein,an ethylene-adsorption-weakening strategy is applied for precise regulation of the pore geometry of four tailor-made metal–organic frameworks(MOFs)with pillar-layered structures,dubbed TYUT-10/11/12/13.Based on its pore geometry design and functional group regulation,TYUT-12 exhibits exceptional selective adsorption selectivity toward C_(3)H_(8),C_(3)H_(6),C_(2)H_(6),C_(2)H_(2),and CO_(2) over C_(2)H_(4);its C_(2)H_(6)/C_(2)H_(4) adsorption selectivity reaches 4.56,surpassing the record value of 4.4 by Fe_(2)(O_(2))(dobdc)(dobdc^(4-)=2,5-dioxido-1,4-benzenedicarboxylate).The weak p–p stacking binding affinity toward C_(2)H_(4) in TYUT-12 is clearly demonstrated through a combination of neutron powder diffraction measurements and theoretical calculations.Breakthrough experiments demonstrate that C_(2)H_(4) can be directly obtained from binary,ternary,quaternary,and six-component light hydrocarbon mixtures with over 99.95%purity.
文摘Homochiral metal–organic frameworks(HMOFs)are attractive materials for asymmetric catalysis because they possess high surface area and uniform active sites.A variety of catalytic applications reported so far indicate that HMOFs catalyse a range of transformations,including cyanosilylation,aldol condensation and hydrogenation reactions.Besides contribution to fundamental knowledge,it is also important to evaluate the relevance of organic transformations catalysed by HMOFs and how existing achievements compare with already established enantioselective catalysts.This mini-review gives an overview of the structural design and the catalytic performance of HMOFs and it focuses on the relevance of the chemical reactions tested.It aims at combining the existing demand for heterogeneous asymmetric catalysts with the current knowledge on HMOFs.This is important for the MOF community since it highlights relevant broad scope asymmetric catalytic transformations performed in industry and the insight gained from the catalytic reactions carried out using HMOFs as catalysts.We hope that this work will motivate researchers to rationally design HMOFs with a goal to unveil reaction mechanisms and the interactions between the HMOFs and the reaction molecules for industrially relevant catalytic reactions.
基金support from the Netherlands Organization for Scientific Research(NWO)NWO-GDST Advanced Materials program(project no.729.001.022).
文摘Nitrogen-doped carbons are promising candidates for replacing platinum catalysts in fuel cell electrodes.They typically contain graphitic and amorphous domains,both of which contribute to the oxygen reduction reaction(ORR)activity.Here,we aim at revealing the catalytic functions of each domain as well of the surface functional groups,and ultimately at maximizing the catalytic performance of the materials in the ORR.We develop a sequential oxidative-pyrolytic treatment to remove the amorphous domains and to alter the surface functionalities.The effectiveness of this approach is evidenced by various techniques.Our electrochemical results show a positive correlation between the ORR activity and the degree of graphitization/oxygen functional group removal.While the oxidation-induced oxygen-containing group impairs the ORR,the amorphous domains seem facilitate the 2-electron transfer ORR,lack electrical conductivity and are rich in oxygen-containing groups.The ORR activity of the optimized sample increases considerably in the alkaline electrolyte,giving a half-wave potential>0.85 V(vs.a reversible hydrogen electrode)that is comparable to that of commercial platinum on carbon.
基金financial support from the National Natural Science Foundation of China(21531001 and 21421005).
文摘The application of metal-organic molecular hosts as“molecular flasks”has precipitated a surge of interest in the reactivity and properties of molecules within well-defined spaces.Here we report an approach to construct supramolecular systems for photo-catalytic hydrogen production and carbon dioxide reduction by encapsulating an organic dye molecule into the pocket of the redox-active metal-organic macrocycle.The assembled Ni_(3)L_(3)tricycle consists of three ligands and three nickel ions that alternately connect together.The special geometry enforces the distortion of the square planar coordinated configuration,and the coordination of the sulphur atoms enables the modification of redox potentials suitable for proton reduction and carbon dioxide reduction.The supramolecular systems that have fluorescein molecules being encapsulated as the photosensitive vips feature efficient activity for the photocatalytic carbon dioxide conversion and production reduction.The new reaction pathways within the confined space demonstrate the power of the supramolecular system over related systems.
基金National Science Foundations of China(21871047 and 21661001)the Natural Science Foundation of Jiangxi Province of China(20181ACB20003).
文摘The separation of C_(2)H_(2)/C_(2)H_(4) mixtures is of industrial importance in the production of high-purity C_(2)H_(4) and C_(2)H_(2).The primary objective of this work is to enhance the selectivity of C_(2)H_(2)/C_(2)H_(4) separation by developing a method for appropriate modification of porous adsorbents.Toward this end,directly doping low-content Na+ions into covalent organic frameworks(COFs)via cation exchange is proposed in this work.Relative to the pristine COF,COF-ECUT-1,with C_(2)H_(2) and C_(2)H_(4) adsorption capacities of 55.39 cm^(3) g^(-1) and 28.63 cm^(3) g^(-1),the Na+-anchored phase with just 4.0 wt%sodium content,Na@COF-ECUT-1,enables largely enhanced adsorption ability with the corresponding values of 89.70 cm^(3) g^(-1) and 49.26 cm^(3) g^(-1),respectively.As a result,the adsorption selectivity of C_(2)H_(2) over that of C_(2)H_(4) is enhanced from 6.33 to 9.41,and the separation potential estimated by the simulated transient breakthrough is largely improved about three-fold.The density functional theory(DFT)calculation reveals that the trap of Na+within the COF channel affords strong affinity towards C_(2)H_(2) or C_(2)H_(4) through Na-πinteractions and relatively stronger contact for C_(2)H_(2) than for C_(2)H_(4) is observed.This result is in line with the experimental results of both enhanced C_(2)H_(2) and C_(2)H_(4) adsorption capacity and C_(2)H_(2)/C_(2)H_(4) separation performance.This work outlines a general and simple method to enhance the gas separation performance upon COF materials.
基金the Advanced Light Source,which is a DOE Office of Science User Facility under contract no.DE-AC02-05CH11231.
文摘Four novel metal–organic frameworks(MOFs)built from alkaline-earth metal ions and the flexible tetrahedral carboxylate ligand tetrakis[4-(carboxyphenyl)oxamethyl]methane acid(H_(4)L)were synthesized using solvothermal methods.A variety of three-dimensional frameworks were obtained when employing different alkaline earth ions with the formula[Mg_(2)(L)(H_(2)O)(DMA)]·DMA(1),[Ca_(4)(L)_(2)(DMA)_(3)](2),[Ca_(4)(L)_(2)(H_(2)O)_(2)(DMA)_(2)]·(3DMA)(3)and[Sr_(4)(L)_(2)(DMF)_(4)]·(2DMF)(4)reflecting the variation in the ionic radius of alkaline-earth ions as well as the key role of the synthetic conditions used.By removing the vip molecules,a framework shrinking was observed driven by the structural flexibility of the H_(4)L ligand.This resulted in large diffusional resistances towards N_(2)over CO_(2)molecules,therefore leading to a good CO_(2)/N_(2)separation selectivity.Both Ca-based MOFs were very stable up to 98%relative humidity,while Mgand Sr-based MOFs were much less stable.
基金supported by the Starry Night Science Fund of Zhejiang University Shanghai Institute for Advanced Study(No.SN-ZJU-SIAS-006)the support from the Leading Innovation Team grant from Department of Science and Technology of Zhejiang Province(No.2022R01005)+1 种基金the Natural Science Foundation of Zhejiang Province(No.LZ24B020002)the National Natural Science Foundation of China(No.22471240)。
文摘Here,Friedel-Crafts(FC)reaction is used to synthesize a purely organic cage in a one-pot manner.The trigonal prismatic cage is composed of two trisfuran platforms,bridged by three phenanthrene pillars each bearing two methoxy(OMe)units.The organic cage exhibited good kinetic inertness,allowing for a synthetic post-functionalization.During this transforming process,the electron-donating methoxy(OMe)groups were converted into electron-withdrawing carbonyl groups without any degradation on the cage framework.The cage exhibits multiple vip recognition modes.The oxygen atoms as the Lewis base present in either methoxy or carbonyl before and after post-functionalization,endow the cage with the ability to recognize Lewis acidic vips such as alkali cations.The OMe and carbonyl units grated on the phenanthrene pillars endow the cage with anπ-electron-rich andπ-electron-deficient cavity,respectively,whereπ-electron-deficient andπ-electron-rich vips can be accommodated.
基金China Scholarship Council for a PhD fellowshipthe MINECO for a Juan de la Cierva research fellowship+1 种基金the support of Romanian UEFISCDI,grant PCE108/2017partially funded by the MCCC(CTQ2016-75671-P)。
文摘A new series of cyanide-bridged assemblies,{KH[Ln_(2)(2,3-pzdc)_(2)(CH_(3)OH)(H_(2)O)_(7)][M(CN)_(8)]}·5H_(2)O(Ln^(3+)=Nd,Gd,Tb,and Dy;M^(4+)=Mo and W),were synthesised by self-assembling lanthanide ions and octacyanometallate ions in the presence of pyrazine-2,3-dicarboxylic acid(2,3-H_(2)pzdc).These compounds have a 3D structure in which octagon-like Ln_(4)M_(4)(CN)_(8)rings are connected through a second Ln^(3+)center via the carboxylate groups of one 2,3-pzdc.The resulting 1D channels are filled with K^(+)ions and lattice water molecules.The temperature and field dependent magnetization studies as well as ab initio calculations indicate weak ferromagnetic interactions between the Gd^(3+)ions within the GdMo compound whilst no magnetic interactions exist in GdW analogues.The magnetic properties of Nd^(3+),Tb^(3+)and Dy^(3+)compounds are strongly dominated by the magnetic anisotropy of the lanthanide ions,irrespective of the octacyanometallate building-block used.
基金supported by the National Natural Science Foundation of China(grant nos.22201304,22178378,and 22127812)the Science Foundation of China University of Petroleum-Beijing(grant nos.2462021QNXZ011 and 2462022YXZZ007).
文摘Industrial purification processes for ethylene from steam pyrolysis or cracking gases generally employ multiple energy-intensive steps to remove C_(2)H_(2),C_(2)H_(6),CO_(2),and C_(3) hydrocarbons.Designing multifunctional molecular separators that integrate multiple structural characteristics capable of removing several impurities simultaneously is highly desired but not yet realized.Here,we address this challenge using a custom-designed multifunctional,and industry-compatible ultramicroporous crystalline physisorbent(CALF-20)to purify C_(2)H_(4) from a seven-component cracking gas mixture(C_(2)H_(4),C_(2)H_(2),C_(2)H_(6),CO_(2),C_(3)H_(4),C_(3)H_(6),and C_(3)H8)by one-step separation with remarkable performance.Verified by breakthrough experiments,C_(2)H_(4)(>99.99%)can be recovered not only from binary C_(2)H_(6)/C_(2)H_(4)(50/50),ternary C_(2)H_(2)/C_(2)H_(4)/C_(2)H_(6)(33/33/33),and quaternary C_(2)H_(2)/C_(2)H_(4)/C_(2)H_(6)/CO_(2)(25/25/25/25)mixtures,but also from a typical seven-component gas cracking mixture of C_(2)H_(2)/C_(2)H_(4)/C_(2)H_(6)/CO_(2)/C_(3)H_(4)/C_(3)H_(6)/C_(3)H8(0.6/62/10/0.3/0.6/26/0.5),even at the high humidity of 74%.Notably,CALF-20 can be easily produced on the kilogram scale,showing great commercial application potential.Together with its framework flexibility and appropriate pore geometry,CALF-20 exhibits a sorbent-sorbate induced-fit behavior strengthening multiple specific recognition sites for the corresponding vips,validated by single-crystal X-ray diffraction study and molecular modeling.This work is the first example of using a single physisorbent to purify C_(2)H_(4) from a seven-component cracking gas mixture and opens an avenue to address complicated hydrocarbon mixture separation challenges.
