The geometrical structures of wurtzite CrX （X=As, Sb, O, Se, and Te） were optimized, then their electric and magnetic properties were investigated by the first-principle calculations within the generalized gradient ...The geometrical structures of wurtzite CrX （X=As, Sb, O, Se, and Te） were optimized, then their electric and magnetic properties were investigated by the first-principle calculations within the generalized gradient approximation for the exchange-correlation functional based on the density functional theory. These Cr-phosphides and Cr-sulphides were predicted to be half-metallic ferromagnets whose spin-polarization at the Fermi level is absolutely 100%. The molecular magnetic moments of Cr-phosphides and Cr-sulphides are 3.00 and 4.00 μB, which arise mainly from Cr-ions, respectively. There is ferromagnetic coupling in both Cr- phosphides and Cr-sulphides. The Curie temperatures of Cr-sulphides and Cr-phosphides are high. The electronic structures of Cr-ions are a1g^2↑↓t1u^4↑↓t1u^1↑↓eg^2↑↓in Cr-phosphides and a1g^2↑↓t1u^4↑↓t1u^1↑t2g^3↑in Cr-sulphides, respectively.展开更多
Iron porphyrins have high activity and selectivity for electrocatalytic CO_(2)reduction reaction(CO_(2)RR)in nonaqueous solutions,but they usually display poor or moderate selectivity for CO_(2)RR in aqueous solutions...Iron porphyrins have high activity and selectivity for electrocatalytic CO_(2)reduction reaction(CO_(2)RR)in nonaqueous solutions,but they usually display poor or moderate selectivity for CO_(2)RR in aqueous solutions because of the competitive hydrogen evolution reaction.Using water as the electrocatalytic reaction solvent is more favored because not only it is cheap,green and abundant but also it can sufficiently provide protons required for CO_(2)RR.Therefore,developing Fe porphyrins as electrocatalysts for efficient and selective CO_(2)RR in aqueous solutions is of both fundamental and practical significance.Herein,we report the design and synthesis of Fe porphyrin 1 with an appended guanidyl group and its electrocatalytic features for CO_(2)RR in both nonaqueous and aqueous solutions.In acetonitrile,Fe porphyrin 1 and its guanidyl-free analogue,tetrakis(3,4,5-trimethoxyphenyl)porphyrin 2,are both efficient for electrocatalytic CO_(2)-to-CO conversion,but the turnover frequency with 1(3.9´10^(5)s^(-1))is one order of magnitude larger than that with 2(1.7´10^(4)s^(-1)),showing the critical role of the appended guanidyl group in improving electrocatalytic CO_(2)RR activity.More importantly,in 0.1 mol L^(-1)KHCO_(3)aqueous solutions,1 showed very high selectivity for electrocatalytic CO_(2)-to-CO conversion with a Faradaic efficiency of 96%,while 2 displayed a Faradaic efficiency of 65%for the CO_(2)-to-CO conversion.This work is of significance to show the effect of appended guanidyl group on improving both activity and selectivity of Fe porphyrins for CO_(2)RR electrocatalysis.展开更多
Within the t-J model, the charge transport and spin response of the doped bilayer triangular antiferromagnetare studied by considering the bilayer interaction. Although the bilayer interaction leads to the band splitt...Within the t-J model, the charge transport and spin response of the doped bilayer triangular antiferromagnetare studied by considering the bilayer interaction. Although the bilayer interaction leads to the band splitting in theelectronic structure, the qualitative behaviors of the physical properties are the same as in the single layer case. Theconductivity spectrum shows the low-energy peak and unusual midinfrared band, the temperature-dependent resistivityis characterized by the nonlinearity metallic-like behavior in the higher temperature range and the deviation from themetallic-like behavior in the lower temperature range and the commensurate neutron scattering peak near the half-fillingis split into six incommensurate peaks in the underdoped regime, with the incommensurability increasing with the holeconcentration at lower dopings, and saturating at higher dopings.展开更多
We adopt the nonequilibrium Green＇s function method to theoretically study the Kondo effect in a deformed molecule, which is treated as an electron-phonon interaction （EPI） system. The self-energy for phonon part i...We adopt the nonequilibrium Green＇s function method to theoretically study the Kondo effect in a deformed molecule, which is treated as an electron-phonon interaction （EPI） system. The self-energy for phonon part is calculated in the standard many-body diagrammatic expansion up to the second order in EPI strength. We find that the multiple phonon-assisted Kondo satellites arise besides the usual Kondo resonance. In the antiparallel magnetic configuration the splitting of main Kondo peak and phonon-assisted satellites only happen for asymmetrical dot-lead couplings, but it is free from the symmetry for the parallel magnetic configuration. The EPI strength and vibrational frequency can enhance the spin splitting of both main Kondo and satellites. It is shown that the suppressed zero-bias Kondo resonance can be restored by applying an external magnetic field, whose magnitude is dependent on the phononic effect remarkably. Although the asymmetry in tunnel coupling has no contribution to the restoration of spin splitting of Kondo peak, it can shrink the external field needed to switch tunneling magnetoresistance ratio between large negative dip and large positive peak.展开更多
[4Fe-4S]-dependent radical S-adenosylmethionine(SAM)proteins are a superfamily of oxidoreductases that can catalyze a series of challenging transformations using the common 5-d Ado radical intermediate.Although the st...[4Fe-4S]-dependent radical S-adenosylmethionine(SAM)proteins are a superfamily of oxidoreductases that can catalyze a series of challenging transformations using the common 5-d Ado radical intermediate.Although the structures and functions of radical SAM enzymes have been extensively studied,the electronic state-dependent reactions of the[4Fe-4S]clusters in these enzymes are still elusive.Herein we performed QM/MM calculations to elucidate the electronic state-dependent reactivity of the[4Fe-4S]cluster in pyruvate-formate lyase activating enzyme.Our calculations show that the electronic statedependent SAM activation by the[4Fe-4S]clusters in radical SAM enzyme is determined by both the super-exchange and exchange-enhanced reactivities.The super-exchange coupling in the[4Fe-4S]cluster favors the antiferromagnetic coupling between two neighbouring pairs,which results in theα-electron rather than theβ-electron donation from the[4Fe-4S]^(1+)cluster toward the SAM activation.Meanwhile,in the most favorable electronic state for the reductive cleavage of S-C5′,Fe4 would donate itsα-electron to gain the maximum exchange interactions in the Fe4-block.Such super-exchange and exchange-enhanced reactivity could be the general principles for reactivities of[4Fe-4S]cluster in RS enzymes.展开更多
Nickel hexacyanoferrate (NiHCF) film was synthesized on porous three-dimensional carbon felt (PTCF) substrate by repetitious batch chemical depositions, and the NiHCF/PTCF electrode was used as electrochemically switc...Nickel hexacyanoferrate (NiHCF) film was synthesized on porous three-dimensional carbon felt (PTCF) substrate by repetitious batch chemical depositions, and the NiHCF/PTCF electrode was used as electrochemically switched ion exchange (ESIX) electrode in a packed bed for continuous separation for cesium ions. The morphologies of the prepared electrodes were characterized by scanning electron microscopy and the effects of solution concentration on the ion-exchange capacity of the electrodes were investigated by cyclic voltammetry technique. Cycling stability and long-term storage stability of NiHCF/PTCF electrodes were also studied. The NiHCF/PTCF electrodes with excellent ion-exchange ability were used to assemble a diaphragm-isolated ESIX reactor for cesium separation. Continuous separation of cesium and regeneration of NiHCF/PTCF electrode based on the diaphragm-isolated reactor were performed in a laboratory-scale two-electrode system.展开更多
Technetium-99(~99Tc),largely produced by nuclear fission of ~235U or ~239Pu,is a component of radioactive waste.This study focused on a remediation strategy for the reduction of pertechnetate(Tc O_4^-)by studying its ...Technetium-99(~99Tc),largely produced by nuclear fission of ~235U or ~239Pu,is a component of radioactive waste.This study focused on a remediation strategy for the reduction of pertechnetate(Tc O_4^-)by studying its chemical analogue rhenium(Re(VⅡ))to avoid the complication of directly working with radioactive elements.Nanoscale zero-valent iron particles supported on graphene(NZVI/r GOs)from GOs-bound Fe ions were prepared by using a H_2/Ar plasma technique and were applied in the reductive immobilization of perrhenate(Re O_4^-).The experimental results demonstrated that NZVI/r GOs could efficiently remove Re from the aqueous solution,with enhanced reactivity,improved kinetics(50 min to reach equilibrium)and excellent removal capacity(85.77 mg/g).The results of X-ray photoelectron spectroscopy analysis showed that the mechanisms of Re immobilization by NZVI/r GOs included adsorption and reduction,which are significant to the prediction and estimation of the effectiveness of reductive Tc O_4^- by NZVI/r GOs in the natural environment.展开更多
The characteristics of inclusions in two types of low-carbon steels by different deoxidization methods have been investigated by using the welding thermal simulation, the optical microscopy and scanning electron micro...The characteristics of inclusions in two types of low-carbon steels by different deoxidization methods have been investigated by using the welding thermal simulation, the optical microscopy and scanning electron microscopy. In addition, the effects of inclusions on microstructure and properties of heat-affected-zone were studied. The nucleation and growth of intragranular acicular ferrite was observed in situ by the laser scanning confocal microscopy. The distribution of Mn element near the inclu- sion was also analyzed by the auger electron spectroscopy. The results showed that the inclusions in A1 killed steel are mainly aluminum oxides, manganese sulfide and titanium nitrides, and that the inclusions in Ti killed steel are mainly titanium oxide, manganese sulfide complex inclusion and single manganese sulfide. The auger electron spectroscopy showed that there is an Mn-depleted zone near the interface of TiOffMnS complex inclusion in the size of 1-3 gm. It could be the effective nucleus of intragranular acicular ferrite which could divide the prior austenite grains, inhibit the growth of low-temperature microstruc- ture, and refine the final microstructure, so as to improve the toughness of heat-affected-zone significantly.展开更多
Oxygen vacancy, a kind of native point defects in ferroelectric ceramics, usually causes an increase of the dielectric loss. Based on experimental observations, it is believed that all of the oxygen vacancies are an u...Oxygen vacancy, a kind of native point defects in ferroelectric ceramics, usually causes an increase of the dielectric loss. Based on experimental observations, it is believed that all of the oxygen vacancies are an unfavorable factor for energy saving. By using molecular dynamics simulations, we show that the increase of coercive and saturated electric fields is due to the difficulty to switch local polarization near an oxygen vacancy, and so that a ferroelectric device has to sustain the rising consumption of energy. The simulation results also uncover how oxygen vacancies influence ferroelectric properties.展开更多
基金ACKNOWLEDGMENTS This work was supported by the Chongqing Natural Science Foundation （No.CSTC2007BB4391 and No.CSTC2008BB4083） and the Chongqing Science and Technology Foundation （No.kj060515 and No.kj080518）
文摘The geometrical structures of wurtzite CrX （X=As, Sb, O, Se, and Te） were optimized, then their electric and magnetic properties were investigated by the first-principle calculations within the generalized gradient approximation for the exchange-correlation functional based on the density functional theory. These Cr-phosphides and Cr-sulphides were predicted to be half-metallic ferromagnets whose spin-polarization at the Fermi level is absolutely 100%. The molecular magnetic moments of Cr-phosphides and Cr-sulphides are 3.00 and 4.00 μB, which arise mainly from Cr-ions, respectively. There is ferromagnetic coupling in both Cr- phosphides and Cr-sulphides. The Curie temperatures of Cr-sulphides and Cr-phosphides are high. The electronic structures of Cr-ions are a1g^2↑↓t1u^4↑↓t1u^1↑↓eg^2↑↓in Cr-phosphides and a1g^2↑↓t1u^4↑↓t1u^1↑t2g^3↑in Cr-sulphides, respectively.
文摘Iron porphyrins have high activity and selectivity for electrocatalytic CO_(2)reduction reaction(CO_(2)RR)in nonaqueous solutions,but they usually display poor or moderate selectivity for CO_(2)RR in aqueous solutions because of the competitive hydrogen evolution reaction.Using water as the electrocatalytic reaction solvent is more favored because not only it is cheap,green and abundant but also it can sufficiently provide protons required for CO_(2)RR.Therefore,developing Fe porphyrins as electrocatalysts for efficient and selective CO_(2)RR in aqueous solutions is of both fundamental and practical significance.Herein,we report the design and synthesis of Fe porphyrin 1 with an appended guanidyl group and its electrocatalytic features for CO_(2)RR in both nonaqueous and aqueous solutions.In acetonitrile,Fe porphyrin 1 and its guanidyl-free analogue,tetrakis(3,4,5-trimethoxyphenyl)porphyrin 2,are both efficient for electrocatalytic CO_(2)-to-CO conversion,but the turnover frequency with 1(3.9´10^(5)s^(-1))is one order of magnitude larger than that with 2(1.7´10^(4)s^(-1)),showing the critical role of the appended guanidyl group in improving electrocatalytic CO_(2)RR activity.More importantly,in 0.1 mol L^(-1)KHCO_(3)aqueous solutions,1 showed very high selectivity for electrocatalytic CO_(2)-to-CO conversion with a Faradaic efficiency of 96%,while 2 displayed a Faradaic efficiency of 65%for the CO_(2)-to-CO conversion.This work is of significance to show the effect of appended guanidyl group on improving both activity and selectivity of Fe porphyrins for CO_(2)RR electrocatalysis.
文摘Within the t-J model, the charge transport and spin response of the doped bilayer triangular antiferromagnetare studied by considering the bilayer interaction. Although the bilayer interaction leads to the band splitting in theelectronic structure, the qualitative behaviors of the physical properties are the same as in the single layer case. Theconductivity spectrum shows the low-energy peak and unusual midinfrared band, the temperature-dependent resistivityis characterized by the nonlinearity metallic-like behavior in the higher temperature range and the deviation from themetallic-like behavior in the lower temperature range and the commensurate neutron scattering peak near the half-fillingis split into six incommensurate peaks in the underdoped regime, with the incommensurability increasing with the holeconcentration at lower dopings, and saturating at higher dopings.
基金Supported by the National Natural Science Foundation of China under Grant No. 10974058the Guangdong Natural Science Foundation under Grant No. 9451063101002088+1 种基金the Shanghai Natural Science Foundation of China under Grant No. 09ZR1421400Science and Technology Program of Shanghai Maritime University under Contract No. 2008475
文摘We adopt the nonequilibrium Green＇s function method to theoretically study the Kondo effect in a deformed molecule, which is treated as an electron-phonon interaction （EPI） system. The self-energy for phonon part is calculated in the standard many-body diagrammatic expansion up to the second order in EPI strength. We find that the multiple phonon-assisted Kondo satellites arise besides the usual Kondo resonance. In the antiparallel magnetic configuration the splitting of main Kondo peak and phonon-assisted satellites only happen for asymmetrical dot-lead couplings, but it is free from the symmetry for the parallel magnetic configuration. The EPI strength and vibrational frequency can enhance the spin splitting of both main Kondo and satellites. It is shown that the suppressed zero-bias Kondo resonance can be restored by applying an external magnetic field, whose magnitude is dependent on the phononic effect remarkably. Although the asymmetry in tunnel coupling has no contribution to the restoration of spin splitting of Kondo peak, it can shrink the external field needed to switch tunneling magnetoresistance ratio between large negative dip and large positive peak.
基金supported by the National Natural Science Foundation of China (No.22073077, No.21933009,and No.21907082)
文摘[4Fe-4S]-dependent radical S-adenosylmethionine(SAM)proteins are a superfamily of oxidoreductases that can catalyze a series of challenging transformations using the common 5-d Ado radical intermediate.Although the structures and functions of radical SAM enzymes have been extensively studied,the electronic state-dependent reactions of the[4Fe-4S]clusters in these enzymes are still elusive.Herein we performed QM/MM calculations to elucidate the electronic state-dependent reactivity of the[4Fe-4S]cluster in pyruvate-formate lyase activating enzyme.Our calculations show that the electronic statedependent SAM activation by the[4Fe-4S]clusters in radical SAM enzyme is determined by both the super-exchange and exchange-enhanced reactivities.The super-exchange coupling in the[4Fe-4S]cluster favors the antiferromagnetic coupling between two neighbouring pairs,which results in theα-electron rather than theβ-electron donation from the[4Fe-4S]^(1+)cluster toward the SAM activation.Meanwhile,in the most favorable electronic state for the reductive cleavage of S-C5′,Fe4 would donate itsα-electron to gain the maximum exchange interactions in the Fe4-block.Such super-exchange and exchange-enhanced reactivity could be the general principles for reactivities of[4Fe-4S]cluster in RS enzymes.
基金Supported by the National Natural Science Foundation of China (21276173)the National Science Foundation of Shanxi Province (2012011020-5, 2012011006-1)the International Joint Research Project of Shanxi Province (2011081028)
文摘Nickel hexacyanoferrate (NiHCF) film was synthesized on porous three-dimensional carbon felt (PTCF) substrate by repetitious batch chemical depositions, and the NiHCF/PTCF electrode was used as electrochemically switched ion exchange (ESIX) electrode in a packed bed for continuous separation for cesium ions. The morphologies of the prepared electrodes were characterized by scanning electron microscopy and the effects of solution concentration on the ion-exchange capacity of the electrodes were investigated by cyclic voltammetry technique. Cycling stability and long-term storage stability of NiHCF/PTCF electrodes were also studied. The NiHCF/PTCF electrodes with excellent ion-exchange ability were used to assemble a diaphragm-isolated ESIX reactor for cesium separation. Continuous separation of cesium and regeneration of NiHCF/PTCF electrode based on the diaphragm-isolated reactor were performed in a laboratory-scale two-electrode system.
基金the National Natural Science Foundation of China(21477133,41273134,91326202,21225730)
文摘Technetium-99(~99Tc),largely produced by nuclear fission of ~235U or ~239Pu,is a component of radioactive waste.This study focused on a remediation strategy for the reduction of pertechnetate(Tc O_4^-)by studying its chemical analogue rhenium(Re(VⅡ))to avoid the complication of directly working with radioactive elements.Nanoscale zero-valent iron particles supported on graphene(NZVI/r GOs)from GOs-bound Fe ions were prepared by using a H_2/Ar plasma technique and were applied in the reductive immobilization of perrhenate(Re O_4^-).The experimental results demonstrated that NZVI/r GOs could efficiently remove Re from the aqueous solution,with enhanced reactivity,improved kinetics(50 min to reach equilibrium)and excellent removal capacity(85.77 mg/g).The results of X-ray photoelectron spectroscopy analysis showed that the mechanisms of Re immobilization by NZVI/r GOs included adsorption and reduction,which are significant to the prediction and estimation of the effectiveness of reductive Tc O_4^- by NZVI/r GOs in the natural environment.
基金supported by the National Basic Research Program of China ("973" Program) (Grant No. 2010CB630801)
文摘The characteristics of inclusions in two types of low-carbon steels by different deoxidization methods have been investigated by using the welding thermal simulation, the optical microscopy and scanning electron microscopy. In addition, the effects of inclusions on microstructure and properties of heat-affected-zone were studied. The nucleation and growth of intragranular acicular ferrite was observed in situ by the laser scanning confocal microscopy. The distribution of Mn element near the inclu- sion was also analyzed by the auger electron spectroscopy. The results showed that the inclusions in A1 killed steel are mainly aluminum oxides, manganese sulfide and titanium nitrides, and that the inclusions in Ti killed steel are mainly titanium oxide, manganese sulfide complex inclusion and single manganese sulfide. The auger electron spectroscopy showed that there is an Mn-depleted zone near the interface of TiOffMnS complex inclusion in the size of 1-3 gm. It could be the effective nucleus of intragranular acicular ferrite which could divide the prior austenite grains, inhibit the growth of low-temperature microstruc- ture, and refine the final microstructure, so as to improve the toughness of heat-affected-zone significantly.
基金the National Natural Science Foundation of China(Grant Nos.11172024 and 11232013)the National Key Basic Research Program of China(Grant No.2012CB937500)+3 种基金the Research Grant Council of the Hong Kong Special Administrative Region,China(Grant No.9042201(City U 11211015))resources provided by the Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australiathe LNMGrid of the State Key Laboratory of Nonlinear Mechanics and the Sc Grid of Supercomputing CenterComputer Network Information Center of the Chinese Academy of Sciences
文摘Oxygen vacancy, a kind of native point defects in ferroelectric ceramics, usually causes an increase of the dielectric loss. Based on experimental observations, it is believed that all of the oxygen vacancies are an unfavorable factor for energy saving. By using molecular dynamics simulations, we show that the increase of coercive and saturated electric fields is due to the difficulty to switch local polarization near an oxygen vacancy, and so that a ferroelectric device has to sustain the rising consumption of energy. The simulation results also uncover how oxygen vacancies influence ferroelectric properties.
