Study on Assemblies and Properties of Metal-Organic Frameworks Incoporating Functional Group-Modified Phenylcarboxylic Acid

Author:Li Xiu Zuo

Supervisor:hou lei


Degree Year:2019





Metal-organic frameworks(MOFs)are crystalline materials possessing highly ordered structures consisting of networks formed by single metal ions or metal clusters connected by multidentate organic groups acting as linkers.Because of its high structural tunability,MOFs with a variety of properties can be synthesized by changing metal ions and/or organic ligands,which play a very important role in the fields of energy,environment,biomedicine,etc.To achieve a wider range of practical applications,the functionalization of MOFs materials is a primarily important and effective tool to alter the interaction/affinity between the guest and framework of MOFs.The widely used method is to assemble MOFs materials by using prefunctionalized organic ligands.In this dissertation,six MOFs,were constructed by oxalamide and triazole modified phenylcarboxylic acid ligands with lanthanide,alkaline and Zn2+ions,and their structures and properties,such as fluorescence,gas adsorption separation and CO2 catalytic conversion,were studied in detail.The full text is divided into five chapters:The chapter 1 is an introduction,the author briefly introduces the MOFs,the modification and application of MOFs,and puts forward the ideas of research and introduces the research progress of this dissertation.In chapter 2,three isostructural lanthanide MOFs,{[Ln2(BDPO)1.5(DMA)3(H2O)]·5H2O}n(1-3,Ln=Eu,Gd and Tb)were constructed by a less-investigated large delocalizedπ-electron conjugated ligand N,N′-bis(3,5-dicarboxyphenyl)-oxalamide(H4BDPO).Ln-MOFs reveal unprecedented trinodal(4,4,6)-connected networks based on binuclear cluster units and planar BDPO linkers.DFT and time dependent-DFT calculations were performed on the ground and excited states to provide insight to geometries,the frontier molecular orbitals and singlet and triplet state energies of H4BDPO ligand.1 and 3 exhibit strong typical red and green emission of Eu3+and Tb3+ions,respectively,originating from the highly efficient energy transfer from BDPO to metal centers,as demonstrated by the comparison of triplet excited energies of ligands and metal ions.Importantly,by doping different concentrations of Eu3+and Tb3+ions,a series of dichromatic doped EuxTb1-x MOFs were fabricated,showing an unusual fluent change of luminescent color among green,yellow,orange and red.Meanwhile,the trimetallic doped Eu0.0855Gd0.6285Tb0.2860emits white light,with the correlated color temperature of 5129 K as well as an absolute quantum yield of 22.4%.In chapter 3,carrying out the strategy of incorporating Lewis acid metal sites and polar functional groups in MOFs to accomplish the capture and chemically catalytic conversion of CO2,an oxalamide-decorated ligand N,N′-bis(isophthalic acid)-oxalamide(H4BDPO)has been designed.The solvothermal reaction of H4BDPO with the less utilized alkaline earth Sr2+ion afforded an unprecedented Sr-MOF,{[Sr(BDPO)0.5(H2O)]·2H2O}n(4),which shows a good chemical and thermal stability.The activated framework presents polar tubular channels embedded with high density of open Lewis acidic metal sites and basic oxalamide group,which lead to not only high CO2 and C2H6 adsorption capability and significant selectivity for CO2 over both CH4 and CO,and C2H6 over CH4,but also serving as a heterogeneous catalyst showing size-selective chemical conversion of CO2with epoxides producing cyclic carbonates under ambient conditions.The interaction mechanisms between the framework and CO2 or propylene oxide were explored by Grand Canonical Monte Carlo(GCMC)simulations.In chapter 4,carrying out the strategy of incorporating rod secondary building units and polar functional groups in MOFs to accomplish the separation of CO2 and C2 hydrocarbons over CH4 as well as CO2 fixation,an oxalamide-functionalized ligand N,N′-bis(isophthalic acid)-oxalamide(H4BDPO)has been designed.The solvothermal reaction of H4BDPO with the oxophilic alkaline earth Ba2+ion afforded a honeycomb Ba-MOF,{[Ba2(BDPO)(H2O)]·DMA}n(5).Due to the existence of Lewis basic oxalamide groups and unsaturated Lewis acid metal sites in the tubular channels,the activated framework presents not only high C2H6,C2H4 and CO2 uptakes and selective capture from CH4,but also efficient CO2 chemical fixation as a recyclable heterogeneous catalyst.Grand Canonical Monte Carlo(GCMC)simulations were combined to explore the adsorption selectivities for C2H6-CH4 and C2H4-CH4 mixtures as well as the interaction mechanisms between the framework and epoxides.In chapter 5,to comparably analyze the influence of porous environment on the gas adsorption in MOFs,based on an imidazole-decorated MOF,{[Zn(imtp)]·DMA·1.5H2O}n(6-im,H2imtp=2-(imidazol-1-yl)terephthalic acid),an analogue MOF,{[Zn(tztp)]·DMA}n(6-tz,H2tztp=2-(1H-1,2,4-triazol-1-yl)terephthalic acid)has been synthesized by replacing imidazole to triazole motifs.Two MOFs are isostructural frameworks containing 1D channels,however,possess different porous wall environments.The open nitrogen-decorated channels in 6-tz lead to significant enhanced C2H6(76.5 cm3g-1)and C2H4(73.1 cm3 g-1)uptakes at 298 K and 1 atm,which are five times of the adsorption amounts of C2H6 and C2H4 in 6-im that is absence of exposed N atoms in the channels.Furthermore,the activated 6-tz also reveals higher adsorption selectivities for C2H6 and C2H4 over CH4.The different sorption properties were further uncovered by theoretical simulations.