Study On Mechanical High Pressure Stability Of MOFs Materials

In recent years,people have great interest in the research on the synthesis,properties and applications of MOFs materials.In order to fully realize its application functions in different fields,in addition to high chemical stability and thermal stability,MOFs materials must be stable enough to withstand different mechanical constraints.We assembled a diamond-to-anvil(DAC)high-pressure device,which used this device to conduct high-pressure studies on some MOFs with different structural characteristics,and explored the causes of mechanical stability of materials and the structural changes of materials during high-pressure processes.The high-pressure X-ray diffraction experiments and molecular dynamics simulations of Zn(II)and pyrazolecarboxylic acid were used to study the high-pressure-inlaid-inlaid MOFs system based on Zn(II)and pyrazolecarboxylic acid.Gaussian fitting and Rietveld crystal structure refinement were carried out on the high-pressure experimental results of these three materials.The crystallinity of three structures and the change of unit cell parameters with pressure were calculated.The third-order Birch–Murnaghan solid state equation was used for the refinement results.By fitting,the bulk moduli of the three materials were calculated to be 19.02GPa,10.89GPa,and 14.48Gpa,respectively.The bulk moduli of the three materials were calculated by molecular dynamics simulation methods to be 20.88GPa,11.08GPa,and16.18GPa,respectively,which were consistent with the experimental results.The mechanical energy absorbed by the calculated system at the pressure to critical pressure was 764.376 k J/mol,3272.255 k J/mol,and 1893.330 k J/mol,respectively.The results show that after the complete MOFs structure becomes a defective MOFs structure with ordered vacancies,the structural compressibility becomes stronger,and the mechanical stability and mechanical energy storage potential of the material are significantly improved.This will have some guiding significance for us to design new structure MOFs materials or modify materials to improve mechanical stability.We prepared 3d-4f heterometallic Cu Eu-organic framework NBU-8 with a density of 1921kg/m~3,belonging to dense packing materials(dense MOFs).This material is a very promising DMF molecular chemical sensor.Characterization by powder X-ray diffraction and high-pressure X-ray diffraction and molecular dynamics simulation were used to study the high pressure of NBU-8.High pressure results indicate that NBU-8 is a material with negative linear compressibility(NCL).Because the(0 0 6)diffraction peak of the crystal structure moves to a low angle as the pressure increases under the driving of mechanical pressure,the phenomenon of the interplanar spacing increases,and the(1 0-2)diffraction peak follows the pressure.Increasing the movement to a high angle,and finally combining the(0 0 6)diffraction peaks into one peak,the amplitude of the interplanar spacing is greatly reduced,indicating that NBU-8 is subjected to hydrostatic pressure due to most of the organic ligands.It is connected in the z direction,so part of the pressure can be shared during the pressurization process,resulting in a large compression deformation along the x-axis direction,which also causes the ligands connected along the z-axis to rotate to cause(0 0 6)crystal faces.The phenomenon of increased spacing.Materials with negative linear compressibility have potential applications for pressure sensors and artificial muscles.For the high-pressure experiment results,we also carried out the Rietveld crystal structure refinement and the Birch–Murnaghan solid state equation fitting.The bulk modulus of the material was calculated to be 45.68 GPa,which is consistent with the simulation results.The rigidity is the current reported MOFs.The strongest material in the material exceeds Cu-BTC.Molecular dynamics simulations calculated that the mechanical energy absorbed by the system when pressurized to 5.128 GPa was 1043.407 k J/mol.