Density Functional Theory Study On The Configuration And Electronic Structure Of Noble Metal Atoms Supported On Metal-Organic Frameworks

Metal-organic frameworks(MOFs),established as a new class of photocatalytic material,has important application prospects in the photocatalytic hydrogen production and CO2 photocatalytic reduction.In recent years,the modification of the photocatalytic properties of MOFs by means of the modification of organic/inorganic ligands or loading of transition metal clusters in their pores has become a research hotspot in materials science.Taking MIL-125 and UiO-66 two typical MOF materials as the research object,the density functional theory method was used to investigate the influence of the geometric configuration,electronic structure and photocatalytic performance of the system after their terephthalate(BDC)organic ligands have been modified with different groups.Based on this,the dissertation also studied the loading configuration and electronic structure of amino-modified MIL-125 with different sizes of Au and Pt clusters.The conformation,electronic structure and absorption spectra of MIL-125 and UiO-66 modified by NH2,OH and NO2 groups were systematically studied.The results of the study shown that after the introduction of the above new groups,new energy band(ie,bandgap state)would appear in the band gap of the original MOFs,resulting in a change in the bandgap of the system.Among them,the amino group modification can significantly reduce the bandgap of these two MOFs,and with the increase of the number of amino groups,the bandgap can be further reduced.From the calculation of the edge position,it can be seen that although the introduction of NH2 groups will weaken the ability of MIL-125 to photocatalytic oxidation of water to produce oxygen However,the reduction of the bandgap can significantly improve the utilization of visible light by the material,so that can be helpful to increase the hydrogen production efficiency of MIL-125.In addition,the introduction of amino groups increases the adsorption sites of water and the binding energy between H2O and MIL-125,which facilitates the water decomposition reaction.The loading configurations and electronic structures of Au clusters in different sizes were investigated in NH2-MIL-125 pores.The most stable adsorption site of a single Au atom is a bridge site between two adjacent amino N atoms;multiple Au atoms always tend to aggregate in the form of clusters in the pores of MOFs.For Au3 and Au4 clusters,they tend to adsorb in tetrahedral pores with smaller space in NH2-MIL-125.After adsorption of Au,some electrons in the ?-conjugated system of the organic ligands around the cluster transfer to the Au atom,and further affect the interaction between the titanium oxygen cluster and the organic ligands in NH2-MIL-125.The most stable loading configurations of Pt clusters in NH2-MIL-125 are different from those of Au clusters.A single Pt atom tends to adsorb on the bridging position between the bridge oxygen and the N atom in the amino group;the stable adsorption sites of the Pt clusters(Pt2,Pt3,and Pt4)are on the interface between larger octahedral pores and the smaller tetrahedral pores in the MOFs.The adsorption site has little effect on the pore size of the system and the physical adsorption of small molecules,which is more conducive to contact with the reactant molecules dispersed in pores of different sizes.At the same time,the loaded Pt atoms get electrons and are activated to provide more active sites for photocatalytic redox reactions.