Exploration Of High-pressure And Elastic Properties Of Zeolitic Metal-azolitic Zinc Framework

According to their internaleigen channel of structure of metal-organic framework?MOF?,they can be divied into porous and dense MOFs.In compared with traditional inorganic porous materials?For example,zeolite?,porous MOFs are of the larger porosity,higher specific surface area,regulable pore size and modifiable functional groups,thus they have potential applications in gas storage/separation?especially,the separation of methane and carbon dioxide?,drug delivery,catalysis,and so on.Due to the dense structure of dense MOF and its physical proerties are close to inorganic non-metallic materials,so they can show excellent piezoelectric,ferroelectric,multiferroic and so on physical properties,dense MOF have important applications in energy capture and conversion,sensing and information storage,and other fields.In the large-scale industrial production,the metal-organic frameworks often need to crushing,ball mill,granulation,such as processing and generally need to sustain 1 GPa?about 10000 atmospheres?stress.So MOF materials all need to have a certain mechanical strength,which can withstand the corresponding environment under the influence of all kinds of stress?such as axial and shear stress,hydrostatic pressure,etc?when they have applied in gas storage,separation,energy conversion,ferroelectric sensing applications.Therefore,it has important guiding significance for the realization of large-scale industrial application by systematically researching the selection,optimization and control of MOF materials of the mechanical properties.Due to the variety and structure complexity of MOF materials,it is unrealistic for of all materials from the experiment to conduct a comprehensive characterization and exploration.This paper aimed at some typical MOF material to carry on deeply and systematically exploring the mechanical properties,specific content is as follows:1.Metal zinc-3-methyl-1,2,4-triazolate framework was prepared.Through the use of X-ray powder diffraction and single crystal X-ray diffraction,high-pressure X-ray diffraction,density functional theory calculations,such as representation,we have systematically analysis its high pressure properties and obtained the bulk modulus?B?of the framework material is 10.8?15?GPa,the corresponding axial compression ratio of ? is 18.0?3.7?X 10-3 GPa.The experimental results are coincided with density functional theory calculation values.This results show that metal zinc-3-methyl-1,2,4-triazolate framework is not easy to compressibility compared with the isostructural Zn?2-methylimidazolate?2?ZIF-8?.2.The elastic constants of Metal zinc-3-methyl-1,2,4-triazolate framework are obtained by density functional theory calculations,and then through application of ELAM and tensor analysis getting the young's modulus,shear modulus,poisson ratio and modulus were 2.828-4.659 GPa,0.97-1.64 GPa,0.23 to 0.64 and 10.29 GPa,respectively.To illustrate the theory of reliability,the nanoindentation experiment was performed to obtain the young's modulus E100 and E110 were 3.07?15?GPa and 3.71?19?GPa,the relative hardness were 0.23?1?GPa and 0.46?5?GPa.The experiment results are consistent with theoretical calculation results.Compared with the isostructural ZIF-8,the young's modulus and shear modulus of Metal zinc-3-methyl-1,2,4-triazolate framework are larger,which showed stronger mechanical stability.Poisson's ratio range is wider than ZIF-8?0.33-0.57?,it shows that this material was of stronger anisotropy under the axial tensile or compression.3.Metal-formate zinc framework material?Zn?HCOO?₂·2H₂O?was Prepared.Through the use of X-ray powder diffraction and single crystal X-ray diffraction,nano indentation experiment characterization and analysis of its mechanical properties,the experimental young's modulus of Zn?HCOO?₂·2H₂O E00-2/E100/E110 were 35.5?6?/35.0?9?/27.1?5?GPa,repsectively.And the relative hardness H were 2.04?8?/1.83?8?/0.47?3?GPa.In compared with formic acid base metal organic framework materials,the mechanical properties of anisotropic of metal-formate zinc matrix material are discussed in detail,expounds the reasons for this difference: strong Zn-O and the presence of hydrogen bonds make the structure more stable under stress.4.Variable temperature single crystal X-ray diffraction experiment was conduncted to analysis crystal structure of Zn?HCOO?₂·2H₂O and its relationship with the temperature change.We summarized the hydrogen bonding and the lattice constant?principal axis?with the temperature,its thermal expansion coefficient obtained by PASCal program are ?a = 5.3?1.5?,?b = 33?1?and ?c =-26?2?MK-1,repsectively.We applied the "hinge-strut" model to in detail explore the mechanism of negative thermal expansion.The results show that the formate framework materials MO6 octahedral and the number of hydrogen bonds and its trend play a significant role in thermal expansion properties of materials.