| Metal-organic frameworks(MOFs)have attracted great attention from chemists in various applications,including gas absorption and separation,organic catalysis,chemical sensing and electrochemistry,due to their high surface area,tunable porosity and versatile functionalities.However,most MOFs suffer poor water stability because of the weak coordination bonds between the metals and ligands.The poor water resistance greatly hinders the applications of MOFs.To address the issue,water-stable MOFs can be constructed by using metal ions of hard Lewis acid such as Ti,Zr,Fe,A1 in combination with carboxylates of hard Lewis bases.Because the bond formation between the hard acid and hard base is very fast,it is usually difficult to obtain such MOFs.In this thesis,we explore the construction of new water-stable MOFs by using multifunctional ligands and hard Lewis acid Zr and Fe.The properties and application of the resulting MOFs in photocatalysis,oranocatalysis,gas adsorption and electrochemical are studied in detail.Since Garcia et al showed that UiO-66 exhibits photocatalytic activity for hydrogen generation in methanol or water/methanol upon UV light irradiation,the MOFs-based photocatalysts have been attracted great interest.However,as the effective photocatalysts,MOFs materials have two major drawbacks:instability in moisture and limited absorption of ultraviolet light.To address these issues,we design and synthesize an UiO-66-analogous MOF material UiO-66(AN)(AN=anthracene-9,10-dicarboxylic acid)using chromophoric anthracene-9,10-dicarboxylic acid instead of terephthalate as linker.Experimental data show that UiO-66(AN)not only possesses great hydrothermal stability,also shows an extra absorption band in the visible light region with the absorption edge extending to around 510 nm.In addition,the UiO-66(AN)shows better photocatalytic activity for methyl orange decomposition compared with the UiO-66 and UiO-66(NA).This work provides a new perspective of tuning the optical properties of MOF materials as photocatalysts.Due to the fast formation of strong Zr-O bonds and variable structures of Zr-based clusters,it is usually difficult to obtain pure phases of Zr-MOF crystals.In chapter 3,we present a successful fabrication of a novel flexible porous Zr-MOF(compound 1),based on flexible tetrahedral carboxylate linker.Compound 1 unprecedentedly contains two different Zr6O8 SBUs in the framework,thus resulting in a novel 3D(4,4,6,8)-connected Zr-MOF,which enriches topological chemistry of Zr-MOFs.Additionally,due to the good hydrothermal stability and unsaturated Lewis acidic sites in the 6-connected Zr6O8,Compound 1 has excellent catalytic performances in CO2 epoxidation,which makes compound 1 a very promising MOF-based catalyst for chemical fixation of CO2.Fe(?)is an ideal metal ion to construct stable MOFs because of its low toxicity,abundance,and strong coordinating bonds with carboxylates.We successfully obtain a 3D Fe-based MOF by using the SBUs Fe3(?3-O)(COO)6(H2O)3 and ligand TPBTM,which is denoted as Fe-TPBTM.Fe-TPBTM inherits the excellent water and thermal stability from Fe-MOFs.Since the amide bonds of TPBTM have high affinity for carbon dioxide,the carbon dioxide absorption of Fe-TPBTM in 273 K reaches 160 cm3/g,overtaking most reported MOFs.Additionally,Fe-TPBTM can be used as an anode material for lithium ion battery.When the Fe-TPBTM-based Li-battery was discharged at a current density of 500 mA g-1,the specific capacity of the Fe-TPBTM anode reached 643 mAhg-1 after the 200th cycle.The results show that Fe-TPBTM is a potential candidate material for carbon dioxide absorption and anode material of lithium ion battery. |
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