To understand better the molecular-level details of ≡Si＋ （SC） or ≡SiO- （SOA） ion group to -NH2 teminated poly（amido-amine） dendrimers in the gas phase, density functional theory is used to optimize the minimu...To understand better the molecular-level details of ≡Si＋ （SC） or ≡SiO- （SOA） ion group to -NH2 teminated poly（amido-amine） dendrimers in the gas phase, density functional theory is used to optimize the minimum energy and transition state structures with UB3LYP/6- 311G（d） and HF/6-31G levels. The tertiary amine nitrogen and the amide oxygen are found to be the most favorable binding sites. The activation energies of the different active sites and the reaction steps of SC and/or SOA ion group and the amide sites are also analyzed. The stable compounds are formed via the electrostatic interaction and the coordination effect. The orientation of the amide O and the rotation of the branches minimizes the energy of the whole system.展开更多
The molecular structures of indazole and 3-halogeno-indazole tautomers were calculated by the B3LYP method at the 6-311G^＊＊ level, both in the gaseous and aqueous phases, with full geometry optimization. The geometr...The molecular structures of indazole and 3-halogeno-indazole tautomers were calculated by the B3LYP method at the 6-311G^＊＊ level, both in the gaseous and aqueous phases, with full geometry optimization. The geometry and electronic structure of the tautomers of indazole, 3-halogeno-indazole and their transition states were obtained. The Onsager solvate theory model was employed for the aqueous solution calculations. The results of the calculation indicated that the N1-H form of the studied molecule is more stable than that of the N2-H form. The influences of the different 3-halogeno and solvent effects on the geometry, energy, charge and activation energy were discussed. The reaction mechanism of the tautomerization of indazole and 3-halogeno-indazole was also studied and a three-membered cyclic transition state of the tautomer reaction has been obtained.展开更多
Electrocatalytic ammonia synthesis under mild conditions is an attractive and challenging process in the earth’s nitrogen cycle,which requires efficient and stable catalysts to reduce the overpotential.The N2 activat...Electrocatalytic ammonia synthesis under mild conditions is an attractive and challenging process in the earth’s nitrogen cycle,which requires efficient and stable catalysts to reduce the overpotential.The N2 activation and reduction overpotential of different Ti3C2O2-supported transition metal(TM)(Sc,Ti,V,Cr,Mn,Fe,Co,Ni,Cu,Zn,Mo,Ru,Rh,Pd,Ag,Cd,and Au)single-atom catalysts have been analyzed in terms of the Gibbs free energies calculated using the density functional theory(DFT).The end-on N2 adsorption was more energetically favorable,and the negative free energies represented good N2 activation performance,especially in the presence Fe/Ti3C2O2(﹣0.75 eV).The overpotentials of Fe/Ti3C2O2,Co/Ti3C2O2,Ru/Ti3C2O2,and Rh/Ti3C2O2 were 0.92,0.89,1.16,and 0.84 eV,respectively.The potential required for ammonia synthesis was different for different TMs and ranged from 0.68 to 2.33 eV.Two possible potential-limiting steps may be involved in the process:(i)hydrogenation of N2 to*NNH and(ii)hydrogenation of*NH2 to ammonia.These catalysts can change the reaction pathway and avoid the traditional N–N bond-breaking barrier.It also simplifies the understanding of the relationship between the Gibbs free energy and overpotential,which is a significant factor in the rational designing and large-scale screening of catalysts for the electrocatalytic ammonia synthesis.展开更多
The interaction between radionuclides and solid/water interfaces is important to understand the physicochemical processes of radionuclides in the natural environment.Herein,the interaction of 60Co(Ⅱ) with TiO 2 in aq...The interaction between radionuclides and solid/water interfaces is important to understand the physicochemical processes of radionuclides in the natural environment.Herein,the interaction of 60Co(Ⅱ) with TiO 2 in aqueous solution as a function of pH and ionic strength was studied by using batch technique combined with surface complexation model and density functional theory(DFT) calculations.The batch experimental results showed that the adsorption of 60Co(Ⅱ) was dependent on pH and independent of ionic strength,indicating the formation of inner-sphere surface complexes on TiO 2 surfaces.The results of surface complexation models and DFT calculations indicated that the surface species of 60Co(Ⅱ) adsorbed on TiO 2 followed the trend:B structure(i.e.,60Co(Ⅱ) was linked to one bridge oxygen site) was the dominant surface species at low pH,and TT structure(i.e.,60Co(Ⅱ) was linked to two terminal oxygen sites) became the important surface complex at neutral and alkaline pH values.These results demonstrated that a multi-technique approach could lead to definitive information on the structures of adsorbed 60Co(Ⅱ) at the molecular level at the TiO 2 /water interfaces,as well as realistic models to rationalize and accurately evaluate the macroscopic manifestations of radionuclide adsorption phenomena.展开更多
Black phosphorus （BP） is a good candidate for studying strain effects on two- dimensional （2D） materials beyond graphene and transition-metal dichalcogenides. This is because of its particular ability to sustain h...Black phosphorus （BP） is a good candidate for studying strain effects on two- dimensional （2D） materials beyond graphene and transition-metal dichalcogenides. This is because of its particular ability to sustain high strain and remarkably anisotropic mechanical properties resulting from its unique puckered structure. We here investigate the dependence of lattice vibrational frequencies on cry- stallographic orientations in uniaxially strained few-layer BP by in-situ strained Raman spectroscopy. The out-of-plane A1 mode is sensitive to uniaxial strain along the near-armchair direction whereas the in-plane B2g and A2 modes are sensitive to strain in the near-zigzag direction. For uniaxial strains applied away from these directions, all three phonon modes are linearly redshifted. Our experimental observation is explained by the anisotropic influence of uniaxial tensile strain on structural properties of BP using density functional theory. This study demonstrates the possibility of selective tuning of in-plane and out-of-plane phonon modes in BP by uniaxial strain and makes strain engineering a promising avenue for extensively modulating the optical and mechanical properties of 2D materials.展开更多
文摘To understand better the molecular-level details of ≡Si＋ （SC） or ≡SiO- （SOA） ion group to -NH2 teminated poly（amido-amine） dendrimers in the gas phase, density functional theory is used to optimize the minimum energy and transition state structures with UB3LYP/6- 311G（d） and HF/6-31G levels. The tertiary amine nitrogen and the amide oxygen are found to be the most favorable binding sites. The activation energies of the different active sites and the reaction steps of SC and/or SOA ion group and the amide sites are also analyzed. The stable compounds are formed via the electrostatic interaction and the coordination effect. The orientation of the amide O and the rotation of the branches minimizes the energy of the whole system.
文摘The molecular structures of indazole and 3-halogeno-indazole tautomers were calculated by the B3LYP method at the 6-311G^＊＊ level, both in the gaseous and aqueous phases, with full geometry optimization. The geometry and electronic structure of the tautomers of indazole, 3-halogeno-indazole and their transition states were obtained. The Onsager solvate theory model was employed for the aqueous solution calculations. The results of the calculation indicated that the N1-H form of the studied molecule is more stable than that of the N2-H form. The influences of the different 3-halogeno and solvent effects on the geometry, energy, charge and activation energy were discussed. The reaction mechanism of the tautomerization of indazole and 3-halogeno-indazole was also studied and a three-membered cyclic transition state of the tautomer reaction has been obtained.
基金financially supported by the National Natural Science Foundation of China(21625604,21776251,21671172,21706229,21878272)~~
文摘Electrocatalytic ammonia synthesis under mild conditions is an attractive and challenging process in the earth’s nitrogen cycle,which requires efficient and stable catalysts to reduce the overpotential.The N2 activation and reduction overpotential of different Ti3C2O2-supported transition metal(TM)(Sc,Ti,V,Cr,Mn,Fe,Co,Ni,Cu,Zn,Mo,Ru,Rh,Pd,Ag,Cd,and Au)single-atom catalysts have been analyzed in terms of the Gibbs free energies calculated using the density functional theory(DFT).The end-on N2 adsorption was more energetically favorable,and the negative free energies represented good N2 activation performance,especially in the presence Fe/Ti3C2O2(﹣0.75 eV).The overpotentials of Fe/Ti3C2O2,Co/Ti3C2O2,Ru/Ti3C2O2,and Rh/Ti3C2O2 were 0.92,0.89,1.16,and 0.84 eV,respectively.The potential required for ammonia synthesis was different for different TMs and ranged from 0.68 to 2.33 eV.Two possible potential-limiting steps may be involved in the process:(i)hydrogenation of N2 to*NNH and(ii)hydrogenation of*NH2 to ammonia.These catalysts can change the reaction pathway and avoid the traditional N–N bond-breaking barrier.It also simplifies the understanding of the relationship between the Gibbs free energy and overpotential,which is a significant factor in the rational designing and large-scale screening of catalysts for the electrocatalytic ammonia synthesis.
基金Progress of Projects Supported by NSFCsupported by the National Basic Research Program of China (2011CB933700)the National Natural Science Foundation of China (20907055,20971126,21071147,91126020,21077107)
文摘The interaction between radionuclides and solid/water interfaces is important to understand the physicochemical processes of radionuclides in the natural environment.Herein,the interaction of 60Co(Ⅱ) with TiO 2 in aqueous solution as a function of pH and ionic strength was studied by using batch technique combined with surface complexation model and density functional theory(DFT) calculations.The batch experimental results showed that the adsorption of 60Co(Ⅱ) was dependent on pH and independent of ionic strength,indicating the formation of inner-sphere surface complexes on TiO 2 surfaces.The results of surface complexation models and DFT calculations indicated that the surface species of 60Co(Ⅱ) adsorbed on TiO 2 followed the trend:B structure(i.e.,60Co(Ⅱ) was linked to one bridge oxygen site) was the dominant surface species at low pH,and TT structure(i.e.,60Co(Ⅱ) was linked to two terminal oxygen sites) became the important surface complex at neutral and alkaline pH values.These results demonstrated that a multi-technique approach could lead to definitive information on the structures of adsorbed 60Co(Ⅱ) at the molecular level at the TiO 2 /water interfaces,as well as realistic models to rationalize and accurately evaluate the macroscopic manifestations of radionuclide adsorption phenomena.
文摘Black phosphorus （BP） is a good candidate for studying strain effects on two- dimensional （2D） materials beyond graphene and transition-metal dichalcogenides. This is because of its particular ability to sustain high strain and remarkably anisotropic mechanical properties resulting from its unique puckered structure. We here investigate the dependence of lattice vibrational frequencies on cry- stallographic orientations in uniaxially strained few-layer BP by in-situ strained Raman spectroscopy. The out-of-plane A1 mode is sensitive to uniaxial strain along the near-armchair direction whereas the in-plane B2g and A2 modes are sensitive to strain in the near-zigzag direction. For uniaxial strains applied away from these directions, all three phonon modes are linearly redshifted. Our experimental observation is explained by the anisotropic influence of uniaxial tensile strain on structural properties of BP using density functional theory. This study demonstrates the possibility of selective tuning of in-plane and out-of-plane phonon modes in BP by uniaxial strain and makes strain engineering a promising avenue for extensively modulating the optical and mechanical properties of 2D materials.
