Synthesis,Crosslinking Modification And Hydrogen Storage Properties Of UIO-66 Type Metal Organic Framework

In the past 20 years,the metal organic framework(MOF)has been subjected to extensive academic research and still appearing on an industrial scale.Incredible surface area,adjustable functional groups,and atomic-level regulation of the pore structure are among the characteristics that make these materials promising for various applications.When the hydrogen storage material adsorbs hydrogen,it will release the heat of adsorption,which will cause the temperature to increase,and the cross-linking modification of the MOF material will help to enhance the stability of the MOF frame structure and improve the hydrogen storage performance.This paper mainly designs and synthesizes the crosslinkable UIO-66 MOFs material UIO-66-DETA composed of Zr(IV)metal ion and 2,5-diallyl ether terephthalic acid,and then crosslinks by initiating double bonds,a new cross-linked MOFs material named UIO-66-DETA-CL was obtained.UIO-66-DETA and UIO-66-DETA-CL were characterized by FTIR spectrometer,powder X-ray diffraction,solid-state nuclear magnetic resonance hydrogen spectroscopy,scanning electron microscopy,nitrogen adsorption,thermal analysis,and hydrogen storage test to analyze their structure and properties.The results show that the crosslinked structure has been formed,UIO-66-DETA-CL can maintain its structure before340 ℃,compared with UIO-66-DETA,the remaining quality is improved by 6%,indicating that cross-linking modification improved the thermal stability.At the same time,the hydrogen adsorption capacity of UIO-66-DETA-CL at 77 K and 4 MPa reached 5.36 wt%.In addition,the hydrogen adsorption enthalpy of UIO-66-DETA-CL calculated by the Anius equation reached 0.889 kJ/mol,which was significantly improved by crosslinking modification.The crosslinked structure changes the pore size and increases the active adsorption sites in the organic ligand.Because the smaller HOMO-LUMO energy gap will cause some hydrogen molecules to be negatively charged,the lower LUMO energy level of UIO-66-DETA-CL has a stronger negative charge acceptance.Therefore,the cross-linking modificationimproves the hydrogen storage capacity of the material.This result provides a new idea for the cross-linking modification of MOF.The main content of the paper:(1)The organic ligand 2,5-dihydroxyterephthalic acid with two diallyl groups was synthesized in three steps,and characterized by nuclear magnetic and infrared.The ligand and zirconium metal ion were used to synthesize the crosslinkable metal organic framework material UIO-66-DETA.The synthesis used solvothermal method to study the effect of the ratio and reaction temperature on the crystal,and activated with chloroform.At the same time,a series of characterizations were carried out to prove that UIO-66-DETA has the double bonds required for cross-linking modification,which creates conditions for the next step of cross-linking modification.(2)The crosslinkable UIO-66 MOFs material UIO-66-DETA obtained in the previous step was used to initiate the double bond on the ligand with AIBN,and a new crosslinked MOFs material was obtained with the name UIO-66-DETA-CL.Infrared,powder X-ray diffraction,solid-state nuclear magnetic resonance hydrogen spectroscopy,scanning electron microscopy,nitrogen adsorption and thermal analysis were used to characterize UIO-66-DETA-CL and analyze its structure.The results show that a cross-linked structure has been formed,and the cross-linking modification improves the thermal stability.(3)The hydrogen storage performance of the metal-organic framework materials before and after cross-linking modification was tested,and finally the hydrogen adsorption capacity of UIO-66-DETA-CL at 77 K and 4 MPa reached 5.36 wt%.In addition,the hydrogen storage adsorption enthalpy of UIO-66-DETA-CL calculated by Arrhenius equation reached 0.889kJ/mol,and it is proved that the cross-linking modification made UIO-66-DETA-CL have a stronger hydrogen storage capacity.(4)The calculation simulation software Gaussian09 was used to calculate the HOMO-LUMO energy level and energy gap of the ligands 2,5-diallyl ether terephthalic acid,UIO-66-DETA and UIO-66-DETA-Cl structures,Because the smaller HOMO-LUMO energy gap of UIO-66-DETA-Cl will cause certain hydrogen molecules to be negatively charged,the lower LUMO energy level ofUIO-66-DETA-CL has a stronger negative charge acceptance.Therefore,the cross-linking modification improves the hydrogen storage capacity of the material.Figure [28] Table [4] Reference [82]...