Theory Study Of Ti-based MOF-MIL-125 Or Its Analogues On The Electronic Structure And Stable Property

In this paper,the geometric structures,electronic structures,orbital and mechanical properties of photocatalyst MIL-125 were systematically investigated by means of density functional theory calculation.MIL-125 is a kind of MOF,which the organic ligand is benzene dicarboxylate and the metal cluster is cyclic octamers of edge-and coner-sharing TiO5(OH)octahedral.The geometric structures,electronic structure and thermodynamic properties of MIL-125 organic linker functionated were detailly investigated.We have thoroughly studied the geometric structures,electronic structure and mechanical properties of metal substituted or anion substituted MIL-125.The conclusions of this paper are listed as follow:1.The investigation of tetragonal MIL-125 indicates that C 2p orbital in the benzene ring of organic ligand form conjugate orbital and the contributed to the vakence band,carboxyl C and connected C 2p orbital in organic chain form p-p conjugate orbital as well as Ti 3d and adjoining O 2p orbital in the metal oxygen core form hybrid orbital and contributed to the bottom of the conduction band.MIL-125 uses much more than MOF-5 in gas adsorption application.2.The investigation of the MIL-125 organic ligand functionated indicates that the election donating ability of functional group is F<Cl<Br<I<NH2,then the band gap is MIL-125-nF>MIL-125-nCl>MIL-125-nBr>MIL-125-nI>MIL-125-nNH2,showing that the electron donating ability of function group in the organic ligand is related to the band gap,but increasing organic ligand functional group degree almost unchanged band gap.Thermodynamic stability analysis reminds MIL-125-F,MIL-125-NH2 and MIL-125-Cl are more stable than MIL-125 in the thermodynamic stability,however,only with lower concentration functional groups of MIL-125-Br and MIL-125-1 are more stable than MIL-125 in the thermodynamic stability.3.The investigation of the MIL-125 metal cation substitution indicated that for theⅣ B metal substitution,metal change with Ti→Zr→Hf,and at first the band gap increase and then reduce.As to IVA metal substitution,along with Ge→Sn→Pb,the more bigger the periodicity,the litter the band gap.The nsnp ortbial of Ge,Sn and Pb in the IVA metal contributed to the conduction band,with O 2p form hybridization orbital,resulting in the bottom of conduction band move to Fermi energy and the reduced band gap.MIL-125-Sn uses much more than MIL-125 in gas adsorption application.4.The investigation of the MIL-125 anion substitution indicates that S or Se substituted O,the band gap is decreasing,resulting in more the visible light absorption.S or Se atoms are electron-rich atom relative to the O atom in the MIL-125,this is consider to be the main reason for the reduced band gap of MIL-125-S and MIL-125-Se.The anion substituted analogue uses much more than MIL-125 in gas adsorption application.