| Layered polytitanates(niobates)are a new type of photocatalytic material.In order to construct a new type of high efficiency desulfurization photocatalyst and realize its controllable assembly and modification,In this study,the geometry and electronic structure of layered polytitanates(niobates)were calculated by density functional theory,and the influence of interlayer cations on the band structure of layered materials was analyzed.The main factors affecting the photocatalytic oxidation performance of layered polytitanates(niobates)and the mechanism of adsorption and photocatalytic oxidation of organic sulfur pollutants were discussed.It provides a useful reference for the construction and development of green and efficient photocatalytic materials for the removal of organic sulfur pollutants.Based on the density functional theory,the geometric structure,energy band composition and density of state of layered polytitanates(niobates)are systematically calculated by the CASTEP and DMol3 programs in Materials Studio,and the structural characteristics and band gap genesis of different types of layered polytitanates(niobates)are theoretically explained.The band gap energy of titanate changes with the composition.The valence band is mainly composed of O2p and Ti3d,and the conduction band is mainly composed of Ti3d and O2p.Meanwhile,O2s and Ti4s participate in the formation of valence band and conduction band in varying degrees,which has a certain influence on the change of band gap energy of the system.The valence band of layered niobates is mainly composed of O2p and Nb4d,and the conduction band is mainly composed of Nb4d and O2p.At the same time,O2s and Nb5s also participate in the formation of valence band and conduction band in varying degrees,so that the band gap energy changes.The energy band structure of layered titanium niobate is relatively complex,the composition of energy band changes with the change of the system.In K3Ti5NbOi4 and KTi6Nb5O25,O2p,Nb4d,Nb5s,Ti3d and Ti4s all participate in the formation of valence band,and Nb4d,Ti3d and O2p orbit all participate in the formation of conduction band,However,in K3Ti5NbO14,Ti3p,Nb5s and Ti4s all contribute to the formation of valence band and conduction band,resulting in the band gap width of K3Ti5NbO14 being 0.863eV wider than that of KTi6Nb5O25.In terms of geometry,in K2Ti2O5,K2Ti3O7,KNbO3 and K3Ti5NbO14 systems,the cations are in the open interlayer,which can be modified and modified by ion-exchange in experiments;in K2Ti4O9,K2Ti6O13,K2Ti7O15,K2Ti8O17,KNb3O8,K2Nb4O11,K3Nb7O19 and KTi6Nb5O25 systems,the cations are in the closed interlayer tunnel and are not easy to be replaced.The effect of interlayer cations on the band gap structure of layered titanium(niobium)polyacids are discussed.The influence of Coulomb force field.With the decrease of the interlayer ion radius,the Coulomb force field increases,and the polarization of O2p in the octahedral MO6(M=Ti,Nb)increases,which leads to the distortion of the M-O-M' bond,and then affects the valence band and the conduction band position of the material.With the increase of the interlayer cation charge,the interaction between the interlayer cation and the laminate increases.The high charge cation interacts with multiple MO6 octahedrons and the distance between the high charge cation and the oxygen atom increases,which weakens the interaction between the interlayer cation and the oxygen,weakens the hybridization between the valence orbit and O2p,and narrows the band gap.The influence of cation hybridization.There is hybridization between the interlayer cations and the O2p orbital,and it has a certain contribution in the valence band and the conduction band.The degree of hybridization is different,the contribution is different,and the influence on the band gap energy depends on the energy levels of the hybrid orbital provided by the cation and the O2p orbital.The influence of the electronic structure of cations.When the electronic configuration of interlayer ion changes,the contribution to valence band and conduction band changes,which leads to different band gap energy.The band gap energy of SnNb2O6 is obviously smaller than that of SrNb2O6,which is mainly because Sn5s participates in the formation of SnNb2O6 valence band and promotes the position of the valence band.Sn5p orbit participates in the formation of SnNb2O6 conduction band and makes it move down.Characteristics of hydrogen ions(H+).H+ often combines with O2-,which enhances the polarization of O2p compared with metal cation,resulting in the change of band gap energy and the shift of spectral response range.In KNbO3 and HNbO3,KNb3O8 and HNb3O8,K2Nb4O11 and H2Nb4O11,K2Ti4O9 and H2Ti4O,K4Nb6O17 and H4Nb6O17,KTiNbO5 and HTiNbO5,K3Ti5NbO14 and H3Ti5NbO14,the band gap energy is smaller than that of corresponding salt due to the polarization of H+;The effect of K2Ti2O5 and H2Ti2O5,K2Ti6O13 and H2Ti6O13 is opposite,which is mainly related to the overall energy change of the system when H1s participates in the formation of energy band.The adsorption and photocatalytic oxidation of organic sulfur pollutants by layered polytitanates(niobates)were studied by experiments and theoretical calculations.The effect of the composition and structure of the laminate on the adsorption properties of sulfide.The spectral response of the material varies with the metal oxides that make up the main structure of the laminate.The adsorption of sulfide on the material changes with the degree of polymerization(Ti/O,Nb/O or Ti/Nb).The change of the phase structure of the materials has great influence on the catalytic oxidation of sulfide.The influence of cation structure on the adsorption of sulfide.The changes of spectral response range caused by different electronic structures of interlayer cations were discussed,which affected their adsorption properties for sulfide.In the energy band analysis of SrNb2O6 and SnNb2O6,When the valence configuration of the interlayer ion changed from 4d0 to 4d105s2,the 5s orbital of Sn2+participated in the formation of the valence band of SnNb2O6,which raised the position of the valence band,and the electrons on the 5 s orbital preferentially filled the valence band,thus changing the band gap energy of SnNb2O6 and the adsorption properties of sulfide were affected.The possible oxidation mechanism of layered niobate to ethanethiol was proposed.According to the basic principle of semiconductor photocatalysis oxidation,through the summary of a large number of experimental data,and then through the theoretical calculation and analysis of the active sites of the organic sulfur pollutant ethanethiol,the possible mechanism of adsorption and photocatalysis oxidation of organic sulfur pollutants(represented by Methyl mercaptan)by layered titanium niobate is proposed.Through the study of the structural characteristics,band gap formation,adsorption of organic sulfur pollutants and photocatalytic oxidation of layered titanium niobate,it provides a theoretical reference for the further construction,development and modification of new photocatalytic materials.Figure 129 Table 18 Reference 265... |
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