Synthesis And Catalytic Properties Of Two-Dimensional Lanthanide MOFs Nanosheets

Metal-organic framework compounds（MOFs）are porous crystalline materials constructed from organic ligands and metal ions or metal clusters.Compared with conventional 3D bulk-phase MOFs,2D MOFs nanosheets not only have the characteristics of 3D MOFs（such as high specific surface area and high porosity）,but also have high density active sites of surface,short diffusion paths and high diffusion efficiency,which facilitate the contact between substrates and active sites and have unique advantages in the fields of heterogeneous catalysis,chemical sensing,electrochemical energy storage,and electrocatalysis.In this thesis,two-dimensional Ln-MOFs nanosheets were rapidly synthesized by microwave synthesis using trivalent lanthanide metal ions(Ln³⁺)as ionic nodes and the conjugated photoactive carboxylic acid ligand 1,3,6,8-tetra（4-carboxyphenyl）pyrene（H₄TBAPy）with D_4h symmetry as organic ligand;using benzoic acid as modifier,the thickness,size and The two-dimensional Ln-MOFs nanosheets with adjustable thickness,size and morphology were synthesized using benzoic acid as the modifier;the two-dimensional Ln-MOFs nanosheets were used as visible light catalysts and stationary phases of chromatographic columns to study their photocatalytic performance and separation of organic small molecules,and to explore the conformational relationships between their photocatalytic and separation capabilities and the thickness,size and morphology of the nanosheets.The research of this thesis is divided into four main parts as follows.（1）Synthesis of two-dimensional Sm-MOFs nanosheets and their performance in photocatalytic degradation of mustard simulantsSm-TBAPy two-dimensional nanosheets were synthesized by microwave synthesis using benzoic acid（BA）as a modifier.The catalytic mechanism of visible light-catalyzed oxidation of CEES by Sm-TBAPy two-dimensional nanosheets was proposed in combination with electron paramagnetic resonance spectroscopy,which can efficiently and selectively oxidize the mustard simulant,2-chloroethyl ethyl sulfide（CEES）,to the sulfoxide product,CEESO,and maintain high catalytic performance after four cycles.（2）Synthesis of two-dimensional Tb-MOFs nanosheets and their photocatalytic oxidation of thioether organicsBased on the above synthesis of Sm-TBAPy nanosheets,Tb-TBAPy two-dimensional nanosheets with tunable thickness,size and morphology were synthesized by controlling the amount of BA（0 eq～200 eq）using Tb³⁺as the metal ion.It was also found that controlling BA to 10 eq and varying the concentration of the reaction,such as increasing from3 m M（1c）to 15 m M（5c）,increased the size of Tb-TBAPy from 200 nm to 2μm and the thickness from 10 nm to 300 nm.The selective oxidation of anisole to methyl phenyl sulfoxide was used as a model reaction to study the above the visible photocatalytic performance of Tb-TBAPy was investigated using the selective oxidation of anisole to methyl phenyl sulfoxide as a model reaction,and the results showed that Tb-TBAPy with monodisperse and thickness around 10～50 nm has excellent photocatalytic performance.（3）Synthesis and chromatographic separation application of two-dimensional Ln-MOFs nanosheetsAfter obtaining the optimal reaction conditions,the above synthesis method was further extended to the synthesis of a full series of Ln-MOFs,and a total of 14 Ln-MOFs two-dimensional nanosheets were synthesized.The synthesized series of Ln-MOFs 2D nanosheets have similar morphology and monodispersity,all with diameters around 200～350 nm.Under UV light irradiation,the Ln-MOFs nanosheets dispersed in ethanol solution emitted cyan fluorescence,and their fluorescence intensity was related to the electronic conformation of Ln³⁺,the 4f orbitals were fully empty(La³⁺),fully full(Lu³⁺),and half full(Gd³⁺)2D MOFs nanosheets with the strongest fluorescence intensity.In addition,the separation performance of La,Eu,Er,Lu-MOFs nanosheets as gas chromatographic stationary phases was investigated for straight chain alkanes(C₆-C₁₀),alkane isomers（C₈）,xylene,ethyl toluene isomers and chlorotoluene isomers,and the separation ability of the above MOFs has an opposite trend to the radius of their metal ions.（4）Synthesis of polymetallic-doped 2D Ln-MOFs nanosheets and their chromatographic separation performanceThe bimetallic MOFs nanosheets and trimetallic MOFs nanosheets were synthesized using a mixed-metal strategy with similar chemical properties of Ln³⁺.The elemental compositions of the above multi-Ln-MOFs were analyzed by ICP-OES and elemental mapping,and it was found that the elemental compositions of the multi-Ln-MOFs were correlated with the radii of metal ions at the same feeding ratio,the smaller the radius of metal ions,the higher their fractions in the Ln-MOFs,indicating that the mixed-metal strategy synthesized multi-Ln-MOFs,and the reaction system of Ln³⁺ions exist in a competitive relationship.The bimetallic MOFs nanosheets were applied to the separation of straight-chain alkanes(C₆-C₁₀),alkane isomers（C₈）,xylene,ethyltoluene isomers and chlorotoluene isomers,and it was found that the performance of the doped Ln-MOFs was intermediate between the single-component Ln-MOFs,and no synergistic enhancement effect was found.