Alkali-metal atomic magnetometers employing longitudinal carrier magnetic field have ultrahigh sensitivity to measure transverse magnetic fields and have been applied in a variety of precise-measurement science and te...Alkali-metal atomic magnetometers employing longitudinal carrier magnetic field have ultrahigh sensitivity to measure transverse magnetic fields and have been applied in a variety of precise-measurement science and technologies.In practice,the magnetometer response is not rigorously proportional to the measured transverse magnetic fields and the existing fundamental analytical model of this magnetometer is effective only when the amplitudes of the measured fields are very small.In this paper,we present a modified analytical model to characterize the practical performance of the magnetometer more definitely.We find out how the longitudinal magnetization of the alkali metal atoms vary with larger transverse fields.The linear-response capacity of the magnetometer is determined by these factors:the amplitude and frequency of the longitudinal carrier field,longitudinal and transverse spin relaxation time of the alkali spins and rotation frequency of the transverse fields.We give a detailed and rigorous theoretical derivation by using the perturbation-iteration method and simulation experiments are conducted to verify the validity and correctness of the proposed modified model.This model can be helpful for measuring larger fields more accurately and configuring a desirable magnetometer with proper linear range.展开更多
As the lightest two-dimensional material,monolayer borophene exhibits great potential as electrode materials,but it suffers from stability issues in the free-standing form.Here,the striped-borophene and graphene bilay...As the lightest two-dimensional material,monolayer borophene exhibits great potential as electrode materials,but it suffers from stability issues in the free-standing form.Here,the striped-borophene and graphene bilayer(sB/Gr)is found to be a high-performance anode material for rechargeable alkali-metal ion batteries.The first-principles results show that all the three alkali-metal atoms,Li,Na,and K,can be strongly adsorbed on sB/Gr with ultra-low diffusion barriers than that on pristine borophene/graphene,indicating good charge-discharge rates.Remarkably,high storage capacities are proposed for LIBs(1880 mA·h/g),NIBs(1648 mA·h/g),and KIBs(470 m A·h/g)with relatively small lattice change rate(<2.9%)in the process of alkali-metal atoms intercalations.These intriguing features of sB/Gr make it an excellent choice for batteries.展开更多
Introduction CsEuF;, CsYbF;and RbYbF;are the first members of divalent rare earth ternary halides obtained via reduction of trivalent rare earth halides by alkali metals. Recently we adopted a new synthesis route in p...Introduction CsEuF;, CsYbF;and RbYbF;are the first members of divalent rare earth ternary halides obtained via reduction of trivalent rare earth halides by alkali metals. Recently we adopted a new synthesis route in preparing divalent rare earth chlorides and bromides and the five titled compounds were suc-展开更多
Using the particle swarm optimization algorithm on structural search methods, we focus our crystal structures search on boron-rich alkali metal compounds of MB_(12)(M = Be, Mg, Ca, Sr) with simulation cell sizes of 1...Using the particle swarm optimization algorithm on structural search methods, we focus our crystal structures search on boron-rich alkali metal compounds of MB_(12)(M = Be, Mg, Ca, Sr) with simulation cell sizes of 1–2 formula units(f.u.)at 0 GPa. The structure, electronic, and mechanical properties of MB_(12) are obtained from the density functional theory using the plane-wave pseudopotential method within the generalized gradient approximations. The formation enthalpies of MB_(12) regarding to solid metal M and solid alpha-boron suggested the predicted structures can be synthesized except for BeB12. The calculated band structures show MB_(12)(M = Be, Mg, Ca, Sr) are all indirect semiconductors. All the calculated elastic constants of MB_(12) satisfy the the mechanical stable conditions. The mechanical parameters(i.e., bulk modulus,shear modulus, and Young’s modulus) are derived using the Voigt–Reuss–Hill method. The G/B ratios indicated that the MB_(12) should exhibit brittle behavior. In addition, the hardness, Debye temperature, universal anisotropic index, and the percentage of anisotropy in compression and shear are also discussed in detail. We hope our results can inspire further experimental study on these boron-rich alkali-metal compounds.展开更多
The catalytic effects for the oxidative methylation of toluene with methane over the basic zeolite catalysts prepared by promoting KY, KX, KM, KZSM-5 or KP with alkali-metal bromides and alkali-metal oxides have been ...The catalytic effects for the oxidative methylation of toluene with methane over the basic zeolite catalysts prepared by promoting KY, KX, KM, KZSM-5 or KP with alkali-metal bromides and alkali-metal oxides have been investigated comparatively. The alkali-metal bromides promoted substrates are more effective than the alkali-metal oxides promoted systems. Moreover, the NaBr promoted systems are more active than KBr promoted systems. The most effective catalytic system (8wt%NaBr)/KZSM-5 gave a toluene conversion as high as 76.3% and a total C-8 selectivity of 76.4% (styrene/ethylbenzene=9.76) resulting in a total C-8 yield of 58.3%.展开更多
For Li^+ and Na^+ ions scattered from high work function metal surfaces, efficient neutralization is observed, and it cannot be explained by the conventional free electron model. In order to explain these experiment...For Li^+ and Na^+ ions scattered from high work function metal surfaces, efficient neutralization is observed, and it cannot be explained by the conventional free electron model. In order to explain these experimental data, we investigate the velocity-dependent neutral fraction with the modified Brako–Newns(BN) model. The calculated results are in agreement with the experimental data. We find that the parallel velocity effect plays an important role in neutralizing the Li^+ and Na^+ ions for large angle scattering. The nonmonotonic velocity behavior of neutral fraction is strongly related to the distance-dependent coupling strength between the atomic level and metal states.展开更多
Covalent organic frameworks(COFs)are a class of porous crystalline polymers that have been widely investigated in various fields,including energy storage,photo/electrocatalysis,drug delivery.The covalent-bond intercon...Covalent organic frameworks(COFs)are a class of porous crystalline polymers that have been widely investigated in various fields,including energy storage,photo/electrocatalysis,drug delivery.The covalent-bond interconnection allows COFs extraordinary chemical and thermal stability,and the porous structure ensures a high ion-diffusion coefficient.These merits compensate for the drawbacks of organic electrodes that are easy to dissolve and have low charge conductivity,and promote the development of novel electrode materials with excellent performance,environmental friendliness,and low price.However,the application of COFs also encountered many problems,such as poor electronic conductivity due to the large band gap.Moreover,in some three-dimensional(3D)COFs and stacked two-dimensional(2D)COFs,the huge crystal structure,aligned ultralong channels,and numerous crystal defects usually impede ion transport,and the large molecular weights of COFs generally decrease the specific capacities.These issues are urgently needed to be solved.Here in this review,we summarize the latest progress,core challenges and coping strategies concerning with the use of COFs in alkali-metal ion batteries,discuss the impact of material structure on energy storage,and propose strategies for the construction of high-performance COF-based electrodes.展开更多
It is reported that alkali-metal borohydrides (MBH4, M = Li, Na and K) are efficient catalysts for ring opening polymerization (ROP) of α-amino acid N-carboxyanhydrides (NCAs). Polypeptides are prepared in quan...It is reported that alkali-metal borohydrides (MBH4, M = Li, Na and K) are efficient catalysts for ring opening polymerization (ROP) of α-amino acid N-carboxyanhydrides (NCAs). Polypeptides are prepared in quantitative yields with relatively narrow molecular weight distributions (MWDs = 1.1-1.5) which depend on the reaction temperature. End groups of the produced polypeptide are studied in detail by MALDI-ToF MS, IH-NMR, 13C-NMR, IH-1H COSY and IH-13C HMQC analyses. The results indicate that α-hydroxy-ω-aminotelechelic polypeptides are formed which are suitable for post- polymerization functionalization.展开更多
Various internal and external defects present in the perovskite film are one of the main factors that causelow efficiency and stability, and in order to realize high-performance perovskite solar cells, it is necessary...Various internal and external defects present in the perovskite film are one of the main factors that causelow efficiency and stability, and in order to realize high-performance perovskite solar cells, it is necessaryto develop a method to effectively suppress them. In this study, a heterofunctional dopants strategy wasattempted to integrate the effect of alkali metal cations (Rbþ and Kþ) and formate anion (HCOO) throughdoping engineering with alkali-metal formates, i.e., rubidium formate (RbHCOO) and potassium formate(KHCOO). Inclusive physical and photoelectric analysis revealed that doping with a small amount ofalkali-metal formate leads to crystal growth and reduction of grain boundaries, and further passivates orinhibits bulk and surface defects. As a result, the photogenerated charge recombination was reduced andthe charge carrier transport was improved, leading to improved PSC performance. RbHCOO-dopedinverted planar PSCs achieved a PCE of up to 20.41% with long-term stability. Our findings provide away for producing high-quality perovskite films with low defect densities that are essential for realizinghigh-performance PSCs.展开更多
High-order dispersion coefficients C9, C11, C12, and C13 for the ground-state alkali-metals were calculated by combining the 1-dependent model potential of alkali-metal atoms and linear variation method based on B-spl...High-order dispersion coefficients C9, C11, C12, and C13 for the ground-state alkali-metals were calculated by combining the 1-dependent model potential of alkali-metal atoms and linear variation method based on B-spline basis functions. The results were compared.展开更多
Protonation and alkali-metal cation adduction are the most important ionization processes in soft-ionization mass spectrometry.Studies on the fragmentation mechanism of protonated and alkali-metal-cationized compounds...Protonation and alkali-metal cation adduction are the most important ionization processes in soft-ionization mass spectrometry.Studies on the fragmentation mechanism of protonated and alkali-metal-cationized compounds in tandem mass spectrometry are essential and helpful for structural analysis.In some cases,it was often observed that a compound attached by different alkali-metal cations(or proton)exhibits similar fragmentation patterns but the relative abundances of product ions are different.This difference was considered to derive from the different electrostatic interactions of alkali-metal cations(or the bonded effect of proton)with the analyte.The alkali-metal cation with a smaller ionic radius shows stronger electrostatic interaction with the molecule because of its higher charge density.In addition,the bonded effect of the proton is stronger than the electrostatic interaction of the alkali-metal cation.In the present study,which used McLafferty-type rearrangements of even-electron ions([M+Cat]+,Cat=H,Li,Na,K)as model reactions,the effect of cation size in mass spectrometric fragmentation reactions is highlighted.These considerations were also successfully applied to interpret the similar but distinct fragmentation behavior of proton and alkali-metal cation adducts of a synthetic compound(2-(acetamido(phenyl)methyl)-3-oxobutanoate)and a drug(entecavir).展开更多
基金the Hunan Graduate Research and Innovation Project(Grant No.CX2018B009)the Natural Science Foundation of Hunan(Grant No.2018JJ3608)+1 种基金the Research Project of National University of Defense Technology(Grant Nos.ZK170204 and ZZKY-YX-07-02)the National Natural Science Foundation of China(Grant Nos.61671458 and 61701515).
文摘Alkali-metal atomic magnetometers employing longitudinal carrier magnetic field have ultrahigh sensitivity to measure transverse magnetic fields and have been applied in a variety of precise-measurement science and technologies.In practice,the magnetometer response is not rigorously proportional to the measured transverse magnetic fields and the existing fundamental analytical model of this magnetometer is effective only when the amplitudes of the measured fields are very small.In this paper,we present a modified analytical model to characterize the practical performance of the magnetometer more definitely.We find out how the longitudinal magnetization of the alkali metal atoms vary with larger transverse fields.The linear-response capacity of the magnetometer is determined by these factors:the amplitude and frequency of the longitudinal carrier field,longitudinal and transverse spin relaxation time of the alkali spins and rotation frequency of the transverse fields.We give a detailed and rigorous theoretical derivation by using the perturbation-iteration method and simulation experiments are conducted to verify the validity and correctness of the proposed modified model.This model can be helpful for measuring larger fields more accurately and configuring a desirable magnetometer with proper linear range.
基金Project supported by the National Natural Science Foundation of China(Grant No.12174084)the Scientific and Technological Research Foundation of Hebei Province,China(Grant No.ZD2021065)the Key Program of Natural Science Foundation of Hebei Province,China(Grant No.A2021205024)。
文摘As the lightest two-dimensional material,monolayer borophene exhibits great potential as electrode materials,but it suffers from stability issues in the free-standing form.Here,the striped-borophene and graphene bilayer(sB/Gr)is found to be a high-performance anode material for rechargeable alkali-metal ion batteries.The first-principles results show that all the three alkali-metal atoms,Li,Na,and K,can be strongly adsorbed on sB/Gr with ultra-low diffusion barriers than that on pristine borophene/graphene,indicating good charge-discharge rates.Remarkably,high storage capacities are proposed for LIBs(1880 mA·h/g),NIBs(1648 mA·h/g),and KIBs(470 m A·h/g)with relatively small lattice change rate(<2.9%)in the process of alkali-metal atoms intercalations.These intriguing features of sB/Gr make it an excellent choice for batteries.
文摘Introduction CsEuF;, CsYbF;and RbYbF;are the first members of divalent rare earth ternary halides obtained via reduction of trivalent rare earth halides by alkali metals. Recently we adopted a new synthesis route in preparing divalent rare earth chlorides and bromides and the five titled compounds were suc-
基金Projected supported by the National Natural Science Foundation of China(Grant Nos.U1904179,U1904178,and 51501093)the Key Science Fund of Educational Department of Henan Province,China(Grant Nos.19A140013 and 20B140010)the Science Technology Innovation Talents Fund in Universities of Henan Province,China(Grant No.19HASTIT019)。
文摘Using the particle swarm optimization algorithm on structural search methods, we focus our crystal structures search on boron-rich alkali metal compounds of MB_(12)(M = Be, Mg, Ca, Sr) with simulation cell sizes of 1–2 formula units(f.u.)at 0 GPa. The structure, electronic, and mechanical properties of MB_(12) are obtained from the density functional theory using the plane-wave pseudopotential method within the generalized gradient approximations. The formation enthalpies of MB_(12) regarding to solid metal M and solid alpha-boron suggested the predicted structures can be synthesized except for BeB12. The calculated band structures show MB_(12)(M = Be, Mg, Ca, Sr) are all indirect semiconductors. All the calculated elastic constants of MB_(12) satisfy the the mechanical stable conditions. The mechanical parameters(i.e., bulk modulus,shear modulus, and Young’s modulus) are derived using the Voigt–Reuss–Hill method. The G/B ratios indicated that the MB_(12) should exhibit brittle behavior. In addition, the hardness, Debye temperature, universal anisotropic index, and the percentage of anisotropy in compression and shear are also discussed in detail. We hope our results can inspire further experimental study on these boron-rich alkali-metal compounds.
基金The project was supported by the National Natural Science Foundation of China !(GrantNo.29803005) China Postdoctoral Science
文摘The catalytic effects for the oxidative methylation of toluene with methane over the basic zeolite catalysts prepared by promoting KY, KX, KM, KZSM-5 or KP with alkali-metal bromides and alkali-metal oxides have been investigated comparatively. The alkali-metal bromides promoted substrates are more effective than the alkali-metal oxides promoted systems. Moreover, the NaBr promoted systems are more active than KBr promoted systems. The most effective catalytic system (8wt%NaBr)/KZSM-5 gave a toluene conversion as high as 76.3% and a total C-8 selectivity of 76.4% (styrene/ethylbenzene=9.76) resulting in a total C-8 yield of 58.3%.
基金supported by the National Natural Science Foundation of China(Grant Nos.11405078 and 11474140)the Fundamental Research Funds for the Central Universities,China(Grant Nos.lzujbky-2014-169 and lzujbky-2015-244)+1 种基金sponsored by the Scientific Research Foundation for the Returned Overseas Chinese Scholarsthe State Education Ministry,and the National Students’ Innovation and Entrepreneurship Training Program(Grant Nos.201410730069 and 201510730078)
文摘For Li^+ and Na^+ ions scattered from high work function metal surfaces, efficient neutralization is observed, and it cannot be explained by the conventional free electron model. In order to explain these experimental data, we investigate the velocity-dependent neutral fraction with the modified Brako–Newns(BN) model. The calculated results are in agreement with the experimental data. We find that the parallel velocity effect plays an important role in neutralizing the Li^+ and Na^+ ions for large angle scattering. The nonmonotonic velocity behavior of neutral fraction is strongly related to the distance-dependent coupling strength between the atomic level and metal states.
基金This work was financially supported by the Natural Science Foundation of Jiangsu Province of China(BK20180086).
文摘Covalent organic frameworks(COFs)are a class of porous crystalline polymers that have been widely investigated in various fields,including energy storage,photo/electrocatalysis,drug delivery.The covalent-bond interconnection allows COFs extraordinary chemical and thermal stability,and the porous structure ensures a high ion-diffusion coefficient.These merits compensate for the drawbacks of organic electrodes that are easy to dissolve and have low charge conductivity,and promote the development of novel electrode materials with excellent performance,environmental friendliness,and low price.However,the application of COFs also encountered many problems,such as poor electronic conductivity due to the large band gap.Moreover,in some three-dimensional(3D)COFs and stacked two-dimensional(2D)COFs,the huge crystal structure,aligned ultralong channels,and numerous crystal defects usually impede ion transport,and the large molecular weights of COFs generally decrease the specific capacities.These issues are urgently needed to be solved.Here in this review,we summarize the latest progress,core challenges and coping strategies concerning with the use of COFs in alkali-metal ion batteries,discuss the impact of material structure on energy storage,and propose strategies for the construction of high-performance COF-based electrodes.
基金financially supported by the National Natural Science Foundation of China(No.21174122)Special Funds for Major Basic Research Projects(No.G2011CB606001)Zhejiang Provincial Natural Science Foundation of China(No.Y4110115)
文摘It is reported that alkali-metal borohydrides (MBH4, M = Li, Na and K) are efficient catalysts for ring opening polymerization (ROP) of α-amino acid N-carboxyanhydrides (NCAs). Polypeptides are prepared in quantitative yields with relatively narrow molecular weight distributions (MWDs = 1.1-1.5) which depend on the reaction temperature. End groups of the produced polypeptide are studied in detail by MALDI-ToF MS, IH-NMR, 13C-NMR, IH-1H COSY and IH-13C HMQC analyses. The results indicate that α-hydroxy-ω-aminotelechelic polypeptides are formed which are suitable for post- polymerization functionalization.
基金supported by the Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(2020R1I1A1A01051961 and 2021R1A2C2010353).
文摘Various internal and external defects present in the perovskite film are one of the main factors that causelow efficiency and stability, and in order to realize high-performance perovskite solar cells, it is necessaryto develop a method to effectively suppress them. In this study, a heterofunctional dopants strategy wasattempted to integrate the effect of alkali metal cations (Rbþ and Kþ) and formate anion (HCOO) throughdoping engineering with alkali-metal formates, i.e., rubidium formate (RbHCOO) and potassium formate(KHCOO). Inclusive physical and photoelectric analysis revealed that doping with a small amount ofalkali-metal formate leads to crystal growth and reduction of grain boundaries, and further passivates orinhibits bulk and surface defects. As a result, the photogenerated charge recombination was reduced andthe charge carrier transport was improved, leading to improved PSC performance. RbHCOO-dopedinverted planar PSCs achieved a PCE of up to 20.41% with long-term stability. Our findings provide away for producing high-quality perovskite films with low defect densities that are essential for realizinghigh-performance PSCs.
基金Supported by the National Natural Science Foundation of China under Grant Nos. 10947101 and 11074070, the Science and Technology Foundation of Guizhou Province under Grant Nos. J[201212345 and LKZS[2012]02, the Hunan Provincial Natural Science Foundation under Grant No. 10J J4001, the Special Foundation of Governor of Guizhou Province for Science and Technology and Education Talents under Grant No. [2012]87, the Doctor Foundation of Zunyi Normal College under Grant Nos. 2012BSJJ17 and the Key Support Discipline of Guizhou province under Grant No. [20111275. Ding's work is supported by Hunan Provincial Natural Science Foundation under Grant No. 11JJ3014 and the Scientific Research Fund of Hunan Provincial Education Department under Grant No. 11B067
文摘High-order dispersion coefficients C9, C11, C12, and C13 for the ground-state alkali-metals were calculated by combining the 1-dependent model potential of alkali-metal atoms and linear variation method based on B-spline basis functions. The results were compared.
基金financially supported by the National Natural Science Foundation of China(21025207,21372199)
文摘Protonation and alkali-metal cation adduction are the most important ionization processes in soft-ionization mass spectrometry.Studies on the fragmentation mechanism of protonated and alkali-metal-cationized compounds in tandem mass spectrometry are essential and helpful for structural analysis.In some cases,it was often observed that a compound attached by different alkali-metal cations(or proton)exhibits similar fragmentation patterns but the relative abundances of product ions are different.This difference was considered to derive from the different electrostatic interactions of alkali-metal cations(or the bonded effect of proton)with the analyte.The alkali-metal cation with a smaller ionic radius shows stronger electrostatic interaction with the molecule because of its higher charge density.In addition,the bonded effect of the proton is stronger than the electrostatic interaction of the alkali-metal cation.In the present study,which used McLafferty-type rearrangements of even-electron ions([M+Cat]+,Cat=H,Li,Na,K)as model reactions,the effect of cation size in mass spectrometric fragmentation reactions is highlighted.These considerations were also successfully applied to interpret the similar but distinct fragmentation behavior of proton and alkali-metal cation adducts of a synthetic compound(2-(acetamido(phenyl)methyl)-3-oxobutanoate)and a drug(entecavir).