To explore the potential utilization of Elaeagnus mollis,we conducted a comprehensive assessment of its phytochemical composition,antioxidant properties,cholinesterase inhibition,and anti-HepG2 cell proliferation acti...To explore the potential utilization of Elaeagnus mollis,we conducted a comprehensive assessment of its phytochemical composition,antioxidant properties,cholinesterase inhibition,and anti-HepG2 cell proliferation activity across different plant parts(branch wood,branch bark,and pericarp)using various solvents(water,methanol,ethanol,and n-hexane).Our findings revealed that water extracts displayed superior antioxidant activities in ABTS and RP assays,while methanol extracts exhibited better performance in DPPH and FRAP assays.Moreover,methanol extracts demonstrated the highest effectiveness against anti-HepG2 cell proliferation,whereas n-hexane extracts showed greater efficiency in cholinesterase inhibition.Notably,branch bark extracts exhibited the highest levels of phytochemical compounds,with both branch bark and pericarp extracts demonstrating significant effects in cholinesterase inhibition and anti-HepG2 cell proliferation.Correlation analysis indicated that phytochemical compounds were primarily responsible for the observed biological activities.Overall,extracts from the branch bark and pericarp of E.mollis showed promising potential for antioxidant and anticancer activities,suggesting their suitability for applications in the pharmaceutical industry as health-promoting products.展开更多
Decoupling electrical and thermal properties to enhance the figure of merit of thermoelectric materials underscores an in-depth understanding of the mechanisms that govern the transfer of charge carriers.Typically,a f...Decoupling electrical and thermal properties to enhance the figure of merit of thermoelectric materials underscores an in-depth understanding of the mechanisms that govern the transfer of charge carriers.Typically,a factor that contributes to the optimization of thermal conductivity is often found to be detrimental to the electrical transport properties.Here,we systematically investigated 26 dimeric MX_(2)-type compounds(where M represents a metal and X represents a nonmetal element)to explore the influence of the electronic configurations of metal cations on lattice thermal transport and thermoelectric performance using first-principles calculations.A principled scheme has been identified that the filled outer orbitals of the cation lead to a significantly lower lattice thermal conductivity compared to that of the partly occupied case for MX_(2),due to the much weakened bonds manifested by the shallow potential well,smaller interatomic force constants,and higher atomic displacement parameters.Based on these findings,we propose two ionic compounds,BaAs and BaSe_(2),to realize reasonable high electrical conductivities through the structural anisotropy caused by the inserted covalent X_(2) dimers while still maintaining the large lattice anharmonicity.The combined superior electrical and thermal properties of BaSe_(2) lead to a high n-type thermoelectric ZT value of 2.3 at 500 K.This work clarifies the structural origin of the heat transport properties of dimeric MX_(2)-type compounds and provides an insightful strategy for developing promising thermoelectric materials.展开更多
As an extreme physical condition,high pressure serves as a potent means to substantially modify the interatomic distances and bonding patterns within condensed matter,thereby enabling the macroscopic manipulation of m...As an extreme physical condition,high pressure serves as a potent means to substantially modify the interatomic distances and bonding patterns within condensed matter,thereby enabling the macroscopic manipulation of material properties.We employed the CALYPSO method to predict the stable structures of RbB_(2)C_(4)across the pressure range from 0 GPa to 100 GPa and investigated its physical properties through first-principles calculations.Specially,we found four novel structures,namely,P6_(3)/mcm-,Amm2-,P1-,and I4/mmm-RbB_(2)C_(4).Under pressure conditions,electronic structure calculations reveal that all of them exhibit metallic characteristics.The calculation results of formation enthalpy show that the P6_(3)/mcm structure can be synthesized within the pressure range of 0–40 GPa.Specially,the Amm2,P1,and I4/mmm structures can be synthesized above 4 GPa,6 GPa,10 GPa,respectively.Moreover,the estimated Vickers hardness value of I4/mmm-RbB_(2)C_(4)compound is 47 GPa,suggesting that it is a superhard material.Interestingly,this study uncovers the continuous transformation of the crystal structure of RbB_(2)C_(4)from a layered configuration to folded and tubular forms,ultimately attaining a stabilized cage-like structure under the pressure span of 0–100 GPa.The application of pressure offers a formidable impetus for the advancement and innovation in condensed matter physics,facilitating the exploration of novel states and functions of matter.展开更多
The rare earth(RE)-transition metal(TM)based compounds have emerged as one of the best candi-dates for the application in eco-friendly and effective cooling technology due to their outstanding cryogenic magnetocaloric...The rare earth(RE)-transition metal(TM)based compounds have emerged as one of the best candi-dates for the application in eco-friendly and effective cooling technology due to their outstanding cryogenic magnetocaloric performances.In this work,three RE-TM germanides RE_(3)Co_(2)Ge_(4)(RE=Gd,Tb and Dy)were synthesized and characterized,aiming to investigating their structural,magnetic and magnetocaloric properties.These compounds crystallize in the Tb_(3)Co_(2)Ge_(4)-type monoclinic structure(space group C2/m,Z=2).Two successive ferromagnetic transitions are observed with T_(c) of 31 and 135 K for Gd_(3)Co_(2)Ge_(4),ferromagnetic and spin reorientation transitions are observed with Tc of 24 K and T_(s) of 19 K for Dy_(3)Co_(2)Ge_(4),all of which are second ordered.In contrast,Tb_(3)Co_(2)Ge_(4)exhibits a second order antiferromagnetic transition with T_(n) of 36 K,accompanied with a spin reorientation transition with T_(s) of 17 K.Furthermore,the ferromagnetic ground state for Gd_(3)Co_(2)Ge_(4)is also confirmed by the first-principles calculations.Significant cryogenic magnetocaloric performances are observed in these compounds,.The determined maximum magnetic entropy change(-ΔS_(M)^(max))under a magnetic field change(△H)of 0-7 T are 10.7,5.3 and 11.6 J/(kg·K)for Gd_(3)Co_(2)Ge_(4),Tb_(3)Co_(2)Ge_(4)and Dy_(3)Co_(2)Ge_(4),respectively.Our results suggest that Gd_(3)Co_(2)Ge_(4)and Dy_(3)Co_(2)Ge_(4)compounds are attractive candidates for cryogenic magnetic refrigeration applications.展开更多
The H2Ge=Ge：, as well as and its derivatives （X2Ge=Ge：, X=H, Me, F, C1, Br, Ph, At, ...） is a kind of new species. Its cycloaddition reactions is a new area for the study of germylene chemistry. The mechanism of t...The H2Ge=Ge：, as well as and its derivatives （X2Ge=Ge：, X=H, Me, F, C1, Br, Ph, At, ...） is a kind of new species. Its cycloaddition reactions is a new area for the study of germylene chemistry. The mechanism of the cycloaddition reaction between singlet Me2Ge=Ge： and acetaldehyde was investigated with the B3LYP/6-31G＊ method in this work. From the potential energy profile, it could be predicted that the reaction has one dominant reaction pathway. The reaction rule is that the two reactants firstly form a four-membered Ge-heterocyclic ring germylene through the [2＋2] cycloaddition reaction. Because of the 4p unoccupied orbital of Ge： atom in the four-membered Ge-heterocyclic ring germylene and the ~ orbital of acetaldehyde forming a r^--~p donor-acceptor bond, the four-membered Ge-heterocyclic ring germylene further combines with acetaldehyde to form an intermedi- ate. Because the Ge atom in intermediate happens sp3 hybridization after transition state, then, intermediate isomerizes to a spiro-Ge-heterocyclic ring compound via a transition state. The research result indicates the laws of cycloaddition reaction between Me2Ge=Ge： and ac- etaldehyde, and lays the theory foundation of the cycloaddition reaction between H2Ge=Ge： and its derivatives （X2Ge=Ge：, X=H, Me, F, C1, Br, Ph, At, ...） and asymmetric ^-bonded compounds, which are significant for the synthesis of small-ring and spiro-Ge-heterocyclic ring compounds.展开更多
H2Ge=Si： and its derivatives （X2Ge=Si：, X=H, Me, F, C1, Br, Ph, Ar, ...） are new species. Its cycloaddition reactions are new area for the study of silylene chemistry. The cycloaddition reaction mechanism of singl...H2Ge=Si： and its derivatives （X2Ge=Si：, X=H, Me, F, C1, Br, Ph, Ar, ...） are new species. Its cycloaddition reactions are new area for the study of silylene chemistry. The cycloaddition reaction mechanism of singlet H2Ge=Si： and formaldehyde has been investigated with the MP2/aug-cc-pVDZ method. From the potential energy profile, it could be predicted that the reaction has one dominant reaction pathway. The reaction rule is that two reactants firstly form a four-membered Ge-heterocyclic ring silylene through the [2＋2] cycloaddition reaction. Because of the 3p unoccupied orbital of Si： atom in the four-membered Ge-heterocyclic ring silylene and the π orbital of formaldehyde forming a π--p donor-acceptor bond, the four-membered Ge-heterocyclic ring silylene further combines with formaldehyde to form an intermediate. Because the Si： atom in the intermediate undergoes sp3 hybridization after transition state, then the intermediate isomerizes to a spiro-Si-heterocyclic ring compound involving Ge via a transition state. The result indicates the laws of cycloaddition reaction between H2Ge=Si： or its derivatives （X2Ge=Si：, X=H, Me, F, Cl, Br, Ph, Ar, ...） and asymmetric π-bonded compounds are significant for the synthesis of small-ring involving Si and Ge and spiro-Si-heterocyclic ring compounds involving Ge.展开更多
A new supramolecular compound, { [2-（2-pyridyl）benzimidazoleH2]2＋.[SBC15]2-}2, was synthesized by the hydrothermal reaction of o-diaminobenzene, 2-pyridinecarboxylie acid and SbCl3 in 1：1 HC1 solution, and charact...A new supramolecular compound, { [2-（2-pyridyl）benzimidazoleH2]2＋.[SBC15]2-}2, was synthesized by the hydrothermal reaction of o-diaminobenzene, 2-pyridinecarboxylie acid and SbCl3 in 1：1 HC1 solution, and characterized by chemical analysis, elemental analysis, IR spectra, thermogravimetfic analysis and fluorescence spectra. The crystal structure was deter- mined by X-ray single-crystal diffraction. The crystal belongs to the monoclinic system, space group P211c, with a = 16.0397（13）, b = 14.3189（12）, c = 15.6370（13） A, β = 105.8980（10）°, V = 3454.0（5） A3, Z = 4, C24H22Cl10N6Sb2, Mr = 992.48, Dc = 1.909 g/cm3,/z = 2.366 mm-1, S = 1.010, F（000） = 1920, R = 0.0254 and wR = 0.0555. The coordination anion, [SbCl5]2- which is a distorted tetragonal pyramid, is composed by coordinating action with Sb3＋ ion and five adjacent chloride ions. Every four coordination anions of [SbCl5]2- form a biquaternion ring structure through the secondary bonding of Sb...Cl. Moreover, the compound adopts a three-dimensional network supramolecular structure because of the hydrogen bonds and π-π stacking between the rings and the 2-（2-pyridyl）benzimidazole divalent cations. The title compound also shows good fluorescent behaviors.展开更多
Acid-catalyzed dehydration of alcohols has been widely employed for the synthesis of alkenes. However, activated alcohols when employed as substrates in dehydration reactions are often pla-gued by the lack of alkene s...Acid-catalyzed dehydration of alcohols has been widely employed for the synthesis of alkenes. However, activated alcohols when employed as substrates in dehydration reactions are often pla-gued by the lack of alkene selectivity. In this work, the reaction system can be significantly improved through enhancing the performance of Lewis acid catalysts in the dehydration of activated alcohols by combining with a Lewis base. Observations of the reaction mechanism revealed that the Lewis base component might have changed the reaction rate order. Although both the principal and side reaction rates decreased, the effect was markedly more observed on the latter reaction. Therefore, the selectivity of the dehydration reaction was improved. On the basis of this observation, a new route to synthesize 2-cinnamyl-1,3-dicarbonyl compounds was developed by using 2-aryl-3,4- di-hydropyran as a starting substrate in the presence of a Lewis acid/Lewis base combined catalyst system.展开更多
A simple and efficient method for the iodination of aromatic compounds has been achieved in the presence of iodine and 1,4- bis（triphenylphosphonium）-2-butene peroxodisulfate.
In order to reduce the curing temperature, shorten the curing time of phenol-formaldehyde(PF) resin adhesive, and ensure the good water-solubility, NaOH and Ba(OH)_2 were used as compound catalysts. The influences of ...In order to reduce the curing temperature, shorten the curing time of phenol-formaldehyde(PF) resin adhesive, and ensure the good water-solubility, NaOH and Ba(OH)_2 were used as compound catalysts. The influences of the adding time of Ba(OH)_2, the adding amount of NaOH, Ba(OH)_2 and resorcinol on the properties of adhesives were studied. The properties of NaOH catalyzed phenol-formaldehyde(PF) adhesive, NaOH and Ba(OH)_2 compound catalyzed PF adhesive, NaOH and Ba(OH)_2 compound catalyzed phenol-resorcinol-formaldehyde(PRF) adhesive, and the prepared recombinant bamboo with three kinds of adhesives were compared. The experimental results show that NaOH and Ba(OH)_2 compound catalyst not only shortens the curing time of PF adhesive, but also guarantees the suitable water solubility of adhesive. After copolycondensation with resorcinol, the curing time of adhesive is further shortened, the water solubility is improved obviously, and the highest bonding strength is obtained. Infrared spectrum analysis shows that the reaction activity point of NaOH and Ba(OH)_2 compound catalyzed PRF adhesive will increase, so that both the curing temperature and curing enthalpy decrease.展开更多
The CeTi 2O 6, which is formed above 1300 ℃ by ceramic method, was obtained at 700 ℃ using sol gel synthesis method. XRD analysis shows that there is 8% deficient of Ce in the structure. The chemical formula is C...The CeTi 2O 6, which is formed above 1300 ℃ by ceramic method, was obtained at 700 ℃ using sol gel synthesis method. XRD analysis shows that there is 8% deficient of Ce in the structure. The chemical formula is Ce 0.92 Ti 2O 5.84 , which has a monoclinic structure with space group of C 2/ m . Its cell parameters are a =0.9811(8) nm, b =0.3726(3) nm, c =0.6831(6) nm, and β =118.84°. After being treated at 1300 ℃ for 3 h, the system keeps stable but the deficient disappears, while the chemical formula change to the normal CeTi 2O 6, and the cell parameters are a =0.9813(3) nm, b =0.3752(4) nm, c =0.6883(5) nm, β =119.05°. The key to synthesis the precursors of CeTi 2O 6 is that Ti 4+ and Ce 3+ ions must reach the atomistic distributing state and prevent the oxidation of Ce 3+ during sol gel process.展开更多
Photodegradation ofpentachlorophenol （PCP） and p-nitrophenol （PNP） in soil was carried out in a designed rotary reactor, which can provide the soil particles with continually uniform irradiation, and on a series o...Photodegradation ofpentachlorophenol （PCP） and p-nitrophenol （PNP） in soil was carried out in a designed rotary reactor, which can provide the soil particles with continually uniform irradiation, and on a series of thin soil layers. TiO2, as a kind of environmental friendly photocatalyst, was introduced to the soil to enhance the processes. Compared with that on the soil layers, photodegradation of PCP at initial concentration of 60 mg/kg was improved dramatically in the rotary reactor no matter whether TiO2 was added, with an increase of 3.0 times in the apparent first-order rate constants. The addition of 1 wt% TiO2 furthered the improvement by 1.4 times. Without addition of TiO2, PNP （initial concentration of 60 mg/kg） photodegradation rate in the rotary reactor was similar to that on the soil layers. When 1 wt% additional TiO2 was added, PNP photodegradation was enhanced obviously, and the enhancement in the rotary reactor was 2 times of that on the soil layers, which may be attributed to the higher frequency of the contact between PNP on soil particles and the photocatalyst. The effect of soil pH and initial concentrations of the target compounds on the photodegradation in the rotary reactor was investigated. The order of the degradation rate at different soil pH was relative to the aggregation of soil particles during mixing in the rotary reactor. Photodegradation of PCP and PNP at different initial concentrations showed that addition of TiO2 to enhance the photodegradation was more suitable for contaminated soil with higher concentration of PCP, while was effective for contaminated soil at each PNP concentration tested in our study.展开更多
Layered compounds play pivotal roles as precursors for producing 2D materials through mechanical exfoliation(micro-mechanical cleavage) or chemical approaches. Therefore, searching for layered compounds with sharp ani...Layered compounds play pivotal roles as precursors for producing 2D materials through mechanical exfoliation(micro-mechanical cleavage) or chemical approaches. Therefore, searching for layered compounds with sharp anisotropic chemical bonding and properties becomes emergent. In this work, the stability, electronic structure, elastic properties, and lattice dynamics of YBCwere investigated. Strong anisotropy in elastic properties is revealed, i.e., high Young’s modulus in a-b plane but low Young’s modulus in c direction. The maximum to minimum Young’s modulus ratio is 2.41 and 2.45 for YBCwith P42/mmc and P4/mbm symmetry, respectively. The most likely systems for shear sliding or microdelaminating are(001)[100] and(001)[010]. The anisotropic elastic properties are underpinned by the anisotropic chemical bonding, i.e., strong bonding within the BCnets and weak bonding between Y atom layers and BCnets. YBCis electrically conductive and the contributions to the electrical conductivity are from delocalized Y 4deas well as Bpandpzelectrons. The layered crystal structure, sharp anisotropic mechanical properties, and metallic conductivity endorse YBCpromising as a precursor for new 2D BCnets.展开更多
Magnetic susceptibility of Al2RE （RE=Y, Ce, Sm, Gd, Dy, Ho, Yb） compounds was studied experimentally in wide temperature （T=290–2000 K） and field （B=0.3–1.3 T） intervals. The abnormal increase in susceptibilit...Magnetic susceptibility of Al2RE （RE=Y, Ce, Sm, Gd, Dy, Ho, Yb） compounds was studied experimentally in wide temperature （T=290–2000 K） and field （B=0.3–1.3 T） intervals. The abnormal increase in susceptibility beginning above the melting point was fixed for all the compositions. The values for the effective magnetic moments per RE atoms in these compounds were found to be smaller than the values typical for free ions RE3＋. The results were discussed in supposition of the directed bonds between aluminum and rare-earth atoms.展开更多
To solve the problem of the poor plasticity and to meet the requirements of high temperature for forming titanium alloy,mechanical properties of TC2 titanium alloy under the compound energy-field(CEF)with temperature ...To solve the problem of the poor plasticity and to meet the requirements of high temperature for forming titanium alloy,mechanical properties of TC2 titanium alloy under the compound energy-field(CEF)with temperature and ultrasonic vibration were studied.The effects of CEF on tensile force,elongation,microstructure and fractography of the TC2 titanium alloy were compared and analyzed.The results show that,under the same thermal conditions,the deformation resistance of TC2 titanium alloy decreases with the increase of ultrasonic vibration energy.The formability is also improved correspondingly due to the input of ultrasonic vibration energy and its influence on the microstructure of the material.However,when the ultrasonic vibration energy is larger,the fatigue fracture will also appear,which reduces its formability.展开更多
A novel supramolecular compound,{[2-（2-pyridyl）benzimidazoleH2]2·[BiCl6]·Cl},was synthesized by the hydrothermal reaction of o-phenylenediamine and α-pyridinecarboxylic acid with BiCl3 in 6.0 mol·L-1...A novel supramolecular compound,{[2-（2-pyridyl）benzimidazoleH2]2·[BiCl6]·Cl},was synthesized by the hydrothermal reaction of o-phenylenediamine and α-pyridinecarboxylic acid with BiCl3 in 6.0 mol·L-1 HCl solution,and characterized by elemental analysis,IR,X-ray single-crystal diffraction and photoluminescence spectroscopy.The crystal （C24H22N6Cl7Bi,Mr= 851.61） belongs to the triclinic system,space group P1 with a =7.2887（18）,b =9.548（2）,c= 12.469（3）,α=85.306（4）,β=82.814（4）,γ=71.349（4）°,Z=1,V=814.9（3）3,Dc=1.735 g/cm3,μ（MoKα）=6.007 mm-1,F（000）=410,R=0.0307 and wR=0.0787.The bismuth ion and six chlorine ions construct a distorted octahedral configuration.The three-dimensional supramolecular network is built from electrostatic attractions,hydrogen bonds and π-π interaction between the BiCl6 anion,Cl anion and [2-（2-pyridyl）benzimidazoleH2] cation.The photoluminescence spectroscopy study shows that the title compound has a blue fluorescent emission at 450 nm in the solid state.展开更多
Magnetocaloric material is the key working substance for magnetic refrigerant technology,for which the low-field and low-temperature magnetocaloric effect(MCE)performance is of great importance for practical applicati...Magnetocaloric material is the key working substance for magnetic refrigerant technology,for which the low-field and low-temperature magnetocaloric effect(MCE)performance is of great importance for practical applications at low temperatures.Here,a giant low-field magnetocaloric effect in ferromagnetically ordered Er_(1-x)Tm_(x)Al_(2)(0≤x≤1)compounds was reported,and the magnetic structure was characterized based on low-temperature neutron powder diffraction.With increasing Tm content from 0 to 1,the Curie temperature of Er_(1-x)Tm_(x)Al_(2)(0≤x≤1)compounds decreases from 16.0 K to 3.6 K.For Er_(0.7)Tm_(0.3)Al_(2) compound,it showed the largest low-field magnetic entropy change(–SM)with the peak value of 17.2 and 25.7 J/(kg K)for 0–1 T and 0–2 T,respectively.The(–SM)max up to 17.2 J/(kg K)of Er0.7Tm0.3Al2 compound for 0–1 T is the largest among the intermetallic magnetocaloric materials ever reported at temperatures below 20 K.The peak value of adiabatic temperature change(Tad)max was determined as 4.13 K and 6.87 K for 0–1 T and 0–2 T,respectively.The characteristic of second-order magnetic transitions was confirmed on basis of Arrott plots,the quantitative criterion of exponent n,rescaled universal curves,and the mean-field theory criterion.The outstanding low-field MCE performance with low working temperatures indicates that Er_(1-x)Tm_(x)Al_(2)(0≤x≤1)compounds are promising candidates for magnetic cooling materials at liquid hydrogen and liquid helium temperatures.展开更多
基金National Natural Science Foundation of China(Grant No.31600549).
文摘To explore the potential utilization of Elaeagnus mollis,we conducted a comprehensive assessment of its phytochemical composition,antioxidant properties,cholinesterase inhibition,and anti-HepG2 cell proliferation activity across different plant parts(branch wood,branch bark,and pericarp)using various solvents(water,methanol,ethanol,and n-hexane).Our findings revealed that water extracts displayed superior antioxidant activities in ABTS and RP assays,while methanol extracts exhibited better performance in DPPH and FRAP assays.Moreover,methanol extracts demonstrated the highest effectiveness against anti-HepG2 cell proliferation,whereas n-hexane extracts showed greater efficiency in cholinesterase inhibition.Notably,branch bark extracts exhibited the highest levels of phytochemical compounds,with both branch bark and pericarp extracts demonstrating significant effects in cholinesterase inhibition and anti-HepG2 cell proliferation.Correlation analysis indicated that phytochemical compounds were primarily responsible for the observed biological activities.Overall,extracts from the branch bark and pericarp of E.mollis showed promising potential for antioxidant and anticancer activities,suggesting their suitability for applications in the pharmaceutical industry as health-promoting products.
基金financial support from the Natural Science Foundation of China(No.11904089,12174092,11674087)the Overseas Expertise Introduction Center for Discipline Innovation(D18025)+1 种基金the Program for Key Research and Development of Science and Technology in Hubei Province(grant No.2023BEB002)supported by the Young Science Foundation of Hubei University(Grant No.430/184303000047).
文摘Decoupling electrical and thermal properties to enhance the figure of merit of thermoelectric materials underscores an in-depth understanding of the mechanisms that govern the transfer of charge carriers.Typically,a factor that contributes to the optimization of thermal conductivity is often found to be detrimental to the electrical transport properties.Here,we systematically investigated 26 dimeric MX_(2)-type compounds(where M represents a metal and X represents a nonmetal element)to explore the influence of the electronic configurations of metal cations on lattice thermal transport and thermoelectric performance using first-principles calculations.A principled scheme has been identified that the filled outer orbitals of the cation lead to a significantly lower lattice thermal conductivity compared to that of the partly occupied case for MX_(2),due to the much weakened bonds manifested by the shallow potential well,smaller interatomic force constants,and higher atomic displacement parameters.Based on these findings,we propose two ionic compounds,BaAs and BaSe_(2),to realize reasonable high electrical conductivities through the structural anisotropy caused by the inserted covalent X_(2) dimers while still maintaining the large lattice anharmonicity.The combined superior electrical and thermal properties of BaSe_(2) lead to a high n-type thermoelectric ZT value of 2.3 at 500 K.This work clarifies the structural origin of the heat transport properties of dimeric MX_(2)-type compounds and provides an insightful strategy for developing promising thermoelectric materials.
基金Project supported by the Jilin Provincial Science and Technology Development Joint Fund Project(Grant No.YDZJ202201ZYTS581)supported by the Scientific and Technological Research Project of Jilin Provincial Education Department(Grant No.JJKH20240077KJ).
文摘As an extreme physical condition,high pressure serves as a potent means to substantially modify the interatomic distances and bonding patterns within condensed matter,thereby enabling the macroscopic manipulation of material properties.We employed the CALYPSO method to predict the stable structures of RbB_(2)C_(4)across the pressure range from 0 GPa to 100 GPa and investigated its physical properties through first-principles calculations.Specially,we found four novel structures,namely,P6_(3)/mcm-,Amm2-,P1-,and I4/mmm-RbB_(2)C_(4).Under pressure conditions,electronic structure calculations reveal that all of them exhibit metallic characteristics.The calculation results of formation enthalpy show that the P6_(3)/mcm structure can be synthesized within the pressure range of 0–40 GPa.Specially,the Amm2,P1,and I4/mmm structures can be synthesized above 4 GPa,6 GPa,10 GPa,respectively.Moreover,the estimated Vickers hardness value of I4/mmm-RbB_(2)C_(4)compound is 47 GPa,suggesting that it is a superhard material.Interestingly,this study uncovers the continuous transformation of the crystal structure of RbB_(2)C_(4)from a layered configuration to folded and tubular forms,ultimately attaining a stabilized cage-like structure under the pressure span of 0–100 GPa.The application of pressure offers a formidable impetus for the advancement and innovation in condensed matter physics,facilitating the exploration of novel states and functions of matter.
基金the Science and Technology Development Fund,Macao SAR,China(006/2022/ALC).
文摘The rare earth(RE)-transition metal(TM)based compounds have emerged as one of the best candi-dates for the application in eco-friendly and effective cooling technology due to their outstanding cryogenic magnetocaloric performances.In this work,three RE-TM germanides RE_(3)Co_(2)Ge_(4)(RE=Gd,Tb and Dy)were synthesized and characterized,aiming to investigating their structural,magnetic and magnetocaloric properties.These compounds crystallize in the Tb_(3)Co_(2)Ge_(4)-type monoclinic structure(space group C2/m,Z=2).Two successive ferromagnetic transitions are observed with T_(c) of 31 and 135 K for Gd_(3)Co_(2)Ge_(4),ferromagnetic and spin reorientation transitions are observed with Tc of 24 K and T_(s) of 19 K for Dy_(3)Co_(2)Ge_(4),all of which are second ordered.In contrast,Tb_(3)Co_(2)Ge_(4)exhibits a second order antiferromagnetic transition with T_(n) of 36 K,accompanied with a spin reorientation transition with T_(s) of 17 K.Furthermore,the ferromagnetic ground state for Gd_(3)Co_(2)Ge_(4)is also confirmed by the first-principles calculations.Significant cryogenic magnetocaloric performances are observed in these compounds,.The determined maximum magnetic entropy change(-ΔS_(M)^(max))under a magnetic field change(△H)of 0-7 T are 10.7,5.3 and 11.6 J/(kg·K)for Gd_(3)Co_(2)Ge_(4),Tb_(3)Co_(2)Ge_(4)and Dy_(3)Co_(2)Ge_(4),respectively.Our results suggest that Gd_(3)Co_(2)Ge_(4)and Dy_(3)Co_(2)Ge_(4)compounds are attractive candidates for cryogenic magnetic refrigeration applications.
文摘The H2Ge=Ge：, as well as and its derivatives （X2Ge=Ge：, X=H, Me, F, C1, Br, Ph, At, ...） is a kind of new species. Its cycloaddition reactions is a new area for the study of germylene chemistry. The mechanism of the cycloaddition reaction between singlet Me2Ge=Ge： and acetaldehyde was investigated with the B3LYP/6-31G＊ method in this work. From the potential energy profile, it could be predicted that the reaction has one dominant reaction pathway. The reaction rule is that the two reactants firstly form a four-membered Ge-heterocyclic ring germylene through the [2＋2] cycloaddition reaction. Because of the 4p unoccupied orbital of Ge： atom in the four-membered Ge-heterocyclic ring germylene and the ~ orbital of acetaldehyde forming a r^--~p donor-acceptor bond, the four-membered Ge-heterocyclic ring germylene further combines with acetaldehyde to form an intermedi- ate. Because the Ge atom in intermediate happens sp3 hybridization after transition state, then, intermediate isomerizes to a spiro-Ge-heterocyclic ring compound via a transition state. The research result indicates the laws of cycloaddition reaction between Me2Ge=Ge： and ac- etaldehyde, and lays the theory foundation of the cycloaddition reaction between H2Ge=Ge： and its derivatives （X2Ge=Ge：, X=H, Me, F, C1, Br, Ph, At, ...） and asymmetric ^-bonded compounds, which are significant for the synthesis of small-ring and spiro-Ge-heterocyclic ring compounds.
文摘H2Ge=Si： and its derivatives （X2Ge=Si：, X=H, Me, F, C1, Br, Ph, Ar, ...） are new species. Its cycloaddition reactions are new area for the study of silylene chemistry. The cycloaddition reaction mechanism of singlet H2Ge=Si： and formaldehyde has been investigated with the MP2/aug-cc-pVDZ method. From the potential energy profile, it could be predicted that the reaction has one dominant reaction pathway. The reaction rule is that two reactants firstly form a four-membered Ge-heterocyclic ring silylene through the [2＋2] cycloaddition reaction. Because of the 3p unoccupied orbital of Si： atom in the four-membered Ge-heterocyclic ring silylene and the π orbital of formaldehyde forming a π--p donor-acceptor bond, the four-membered Ge-heterocyclic ring silylene further combines with formaldehyde to form an intermediate. Because the Si： atom in the intermediate undergoes sp3 hybridization after transition state, then the intermediate isomerizes to a spiro-Si-heterocyclic ring compound involving Ge via a transition state. The result indicates the laws of cycloaddition reaction between H2Ge=Si： or its derivatives （X2Ge=Si：, X=H, Me, F, Cl, Br, Ph, Ar, ...） and asymmetric π-bonded compounds are significant for the synthesis of small-ring involving Si and Ge and spiro-Si-heterocyclic ring compounds involving Ge.
基金Supported by the Natural Science Foundation of Henan Province (No. 0611023700)Natural Science Foundation of Education Department of Henan Province (No. 2006150019)
文摘A new supramolecular compound, { [2-（2-pyridyl）benzimidazoleH2]2＋.[SBC15]2-}2, was synthesized by the hydrothermal reaction of o-diaminobenzene, 2-pyridinecarboxylie acid and SbCl3 in 1：1 HC1 solution, and characterized by chemical analysis, elemental analysis, IR spectra, thermogravimetfic analysis and fluorescence spectra. The crystal structure was deter- mined by X-ray single-crystal diffraction. The crystal belongs to the monoclinic system, space group P211c, with a = 16.0397（13）, b = 14.3189（12）, c = 15.6370（13） A, β = 105.8980（10）°, V = 3454.0（5） A3, Z = 4, C24H22Cl10N6Sb2, Mr = 992.48, Dc = 1.909 g/cm3,/z = 2.366 mm-1, S = 1.010, F（000） = 1920, R = 0.0254 and wR = 0.0555. The coordination anion, [SbCl5]2- which is a distorted tetragonal pyramid, is composed by coordinating action with Sb3＋ ion and five adjacent chloride ions. Every four coordination anions of [SbCl5]2- form a biquaternion ring structure through the secondary bonding of Sb...Cl. Moreover, the compound adopts a three-dimensional network supramolecular structure because of the hydrogen bonds and π-π stacking between the rings and the 2-（2-pyridyl）benzimidazole divalent cations. The title compound also shows good fluorescent behaviors.
基金supported by the National Natural Science Foundation of China (21173089 and 21373093)the Fundamental Research Funds for the Central Universities of China (2014ZZGH019)the Cooperative Innovation Center of Hubei Province
文摘Acid-catalyzed dehydration of alcohols has been widely employed for the synthesis of alkenes. However, activated alcohols when employed as substrates in dehydration reactions are often pla-gued by the lack of alkene selectivity. In this work, the reaction system can be significantly improved through enhancing the performance of Lewis acid catalysts in the dehydration of activated alcohols by combining with a Lewis base. Observations of the reaction mechanism revealed that the Lewis base component might have changed the reaction rate order. Although both the principal and side reaction rates decreased, the effect was markedly more observed on the latter reaction. Therefore, the selectivity of the dehydration reaction was improved. On the basis of this observation, a new route to synthesize 2-cinnamyl-1,3-dicarbonyl compounds was developed by using 2-aryl-3,4- di-hydropyran as a starting substrate in the presence of a Lewis acid/Lewis base combined catalyst system.
文摘A simple and efficient method for the iodination of aromatic compounds has been achieved in the presence of iodine and 1,4- bis（triphenylphosphonium）-2-butene peroxodisulfate.
基金Funded by the China Postdoctoral Science Foundation Funded Project(2015M572276)the Natural Science Foundation of Hunan Province,China(2016JJ3184)the Hunan Major Science and Technology Projects(2011FJ1006)
文摘In order to reduce the curing temperature, shorten the curing time of phenol-formaldehyde(PF) resin adhesive, and ensure the good water-solubility, NaOH and Ba(OH)_2 were used as compound catalysts. The influences of the adding time of Ba(OH)_2, the adding amount of NaOH, Ba(OH)_2 and resorcinol on the properties of adhesives were studied. The properties of NaOH catalyzed phenol-formaldehyde(PF) adhesive, NaOH and Ba(OH)_2 compound catalyzed PF adhesive, NaOH and Ba(OH)_2 compound catalyzed phenol-resorcinol-formaldehyde(PRF) adhesive, and the prepared recombinant bamboo with three kinds of adhesives were compared. The experimental results show that NaOH and Ba(OH)_2 compound catalyst not only shortens the curing time of PF adhesive, but also guarantees the suitable water solubility of adhesive. After copolycondensation with resorcinol, the curing time of adhesive is further shortened, the water solubility is improved obviously, and the highest bonding strength is obtained. Infrared spectrum analysis shows that the reaction activity point of NaOH and Ba(OH)_2 compound catalyzed PRF adhesive will increase, so that both the curing temperature and curing enthalpy decrease.
文摘The CeTi 2O 6, which is formed above 1300 ℃ by ceramic method, was obtained at 700 ℃ using sol gel synthesis method. XRD analysis shows that there is 8% deficient of Ce in the structure. The chemical formula is Ce 0.92 Ti 2O 5.84 , which has a monoclinic structure with space group of C 2/ m . Its cell parameters are a =0.9811(8) nm, b =0.3726(3) nm, c =0.6831(6) nm, and β =118.84°. After being treated at 1300 ℃ for 3 h, the system keeps stable but the deficient disappears, while the chemical formula change to the normal CeTi 2O 6, and the cell parameters are a =0.9813(3) nm, b =0.3752(4) nm, c =0.6883(5) nm, β =119.05°. The key to synthesis the precursors of CeTi 2O 6 is that Ti 4+ and Ce 3+ ions must reach the atomistic distributing state and prevent the oxidation of Ce 3+ during sol gel process.
基金The National Basic Research Program of China (No. 2004CB418504 2003CB415006)
文摘Photodegradation ofpentachlorophenol （PCP） and p-nitrophenol （PNP） in soil was carried out in a designed rotary reactor, which can provide the soil particles with continually uniform irradiation, and on a series of thin soil layers. TiO2, as a kind of environmental friendly photocatalyst, was introduced to the soil to enhance the processes. Compared with that on the soil layers, photodegradation of PCP at initial concentration of 60 mg/kg was improved dramatically in the rotary reactor no matter whether TiO2 was added, with an increase of 3.0 times in the apparent first-order rate constants. The addition of 1 wt% TiO2 furthered the improvement by 1.4 times. Without addition of TiO2, PNP （initial concentration of 60 mg/kg） photodegradation rate in the rotary reactor was similar to that on the soil layers. When 1 wt% additional TiO2 was added, PNP photodegradation was enhanced obviously, and the enhancement in the rotary reactor was 2 times of that on the soil layers, which may be attributed to the higher frequency of the contact between PNP on soil particles and the photocatalyst. The effect of soil pH and initial concentrations of the target compounds on the photodegradation in the rotary reactor was investigated. The order of the degradation rate at different soil pH was relative to the aggregation of soil particles during mixing in the rotary reactor. Photodegradation of PCP and PNP at different initial concentrations showed that addition of TiO2 to enhance the photodegradation was more suitable for contaminated soil with higher concentration of PCP, while was effective for contaminated soil at each PNP concentration tested in our study.
基金supported by the National Science Foundation of China under Grant No. U1435206 and No. 51672064the Beijing Municipal Science & Technology Commission under grant number Z151100003315012 and D161100002416001
文摘Layered compounds play pivotal roles as precursors for producing 2D materials through mechanical exfoliation(micro-mechanical cleavage) or chemical approaches. Therefore, searching for layered compounds with sharp anisotropic chemical bonding and properties becomes emergent. In this work, the stability, electronic structure, elastic properties, and lattice dynamics of YBCwere investigated. Strong anisotropy in elastic properties is revealed, i.e., high Young’s modulus in a-b plane but low Young’s modulus in c direction. The maximum to minimum Young’s modulus ratio is 2.41 and 2.45 for YBCwith P42/mmc and P4/mbm symmetry, respectively. The most likely systems for shear sliding or microdelaminating are(001)[100] and(001)[010]. The anisotropic elastic properties are underpinned by the anisotropic chemical bonding, i.e., strong bonding within the BCnets and weak bonding between Y atom layers and BCnets. YBCis electrically conductive and the contributions to the electrical conductivity are from delocalized Y 4deas well as Bpandpzelectrons. The layered crystal structure, sharp anisotropic mechanical properties, and metallic conductivity endorse YBCpromising as a precursor for new 2D BCnets.
基金Project supported by RFBR (Grant N N 09-03-90450-Ukr)FTP (NK-255P/1, NK-16P/1)
文摘Magnetic susceptibility of Al2RE （RE=Y, Ce, Sm, Gd, Dy, Ho, Yb） compounds was studied experimentally in wide temperature （T=290–2000 K） and field （B=0.3–1.3 T） intervals. The abnormal increase in susceptibility beginning above the melting point was fixed for all the compositions. The values for the effective magnetic moments per RE atoms in these compounds were found to be smaller than the values typical for free ions RE3＋. The results were discussed in supposition of the directed bonds between aluminum and rare-earth atoms.
基金Funded by the National Natural Science Foundation of China(Nos.52075347,51575364)
文摘To solve the problem of the poor plasticity and to meet the requirements of high temperature for forming titanium alloy,mechanical properties of TC2 titanium alloy under the compound energy-field(CEF)with temperature and ultrasonic vibration were studied.The effects of CEF on tensile force,elongation,microstructure and fractography of the TC2 titanium alloy were compared and analyzed.The results show that,under the same thermal conditions,the deformation resistance of TC2 titanium alloy decreases with the increase of ultrasonic vibration energy.The formability is also improved correspondingly due to the input of ultrasonic vibration energy and its influence on the microstructure of the material.However,when the ultrasonic vibration energy is larger,the fatigue fracture will also appear,which reduces its formability.
基金Supported by the Natural Science Foundation of Henan Province (No. 0611023700)
文摘A novel supramolecular compound,{[2-（2-pyridyl）benzimidazoleH2]2·[BiCl6]·Cl},was synthesized by the hydrothermal reaction of o-phenylenediamine and α-pyridinecarboxylic acid with BiCl3 in 6.0 mol·L-1 HCl solution,and characterized by elemental analysis,IR,X-ray single-crystal diffraction and photoluminescence spectroscopy.The crystal （C24H22N6Cl7Bi,Mr= 851.61） belongs to the triclinic system,space group P1 with a =7.2887（18）,b =9.548（2）,c= 12.469（3）,α=85.306（4）,β=82.814（4）,γ=71.349（4）°,Z=1,V=814.9（3）3,Dc=1.735 g/cm3,μ（MoKα）=6.007 mm-1,F（000）=410,R=0.0307 and wR=0.0787.The bismuth ion and six chlorine ions construct a distorted octahedral configuration.The three-dimensional supramolecular network is built from electrostatic attractions,hydrogen bonds and π-π interaction between the BiCl6 anion,Cl anion and [2-（2-pyridyl）benzimidazoleH2] cation.The photoluminescence spectroscopy study shows that the title compound has a blue fluorescent emission at 450 nm in the solid state.
基金supported by the National Key Research and Development Program of China(Nos.2021YFB3501202 and 2019YFB2005800)the Science Center of the National Science Foundation of China(No.52088101)+1 种基金the National Natural Science Foundation of China(Nos.51871019,52171170,52130103,51961145305,51971026,and 52171169)the Beijing Natural Science Foundation Key Program(Grant Nos.Z190007 and Z200007),and“111 Project”(No.B170003).
文摘Magnetocaloric material is the key working substance for magnetic refrigerant technology,for which the low-field and low-temperature magnetocaloric effect(MCE)performance is of great importance for practical applications at low temperatures.Here,a giant low-field magnetocaloric effect in ferromagnetically ordered Er_(1-x)Tm_(x)Al_(2)(0≤x≤1)compounds was reported,and the magnetic structure was characterized based on low-temperature neutron powder diffraction.With increasing Tm content from 0 to 1,the Curie temperature of Er_(1-x)Tm_(x)Al_(2)(0≤x≤1)compounds decreases from 16.0 K to 3.6 K.For Er_(0.7)Tm_(0.3)Al_(2) compound,it showed the largest low-field magnetic entropy change(–SM)with the peak value of 17.2 and 25.7 J/(kg K)for 0–1 T and 0–2 T,respectively.The(–SM)max up to 17.2 J/(kg K)of Er0.7Tm0.3Al2 compound for 0–1 T is the largest among the intermetallic magnetocaloric materials ever reported at temperatures below 20 K.The peak value of adiabatic temperature change(Tad)max was determined as 4.13 K and 6.87 K for 0–1 T and 0–2 T,respectively.The characteristic of second-order magnetic transitions was confirmed on basis of Arrott plots,the quantitative criterion of exponent n,rescaled universal curves,and the mean-field theory criterion.The outstanding low-field MCE performance with low working temperatures indicates that Er_(1-x)Tm_(x)Al_(2)(0≤x≤1)compounds are promising candidates for magnetic cooling materials at liquid hydrogen and liquid helium temperatures.
