Synthesis and Characterization of Two New Pillar-Layered Metal-Organic Frameworks for CO2 Capture and Sensing

The continuous development of the current economy has resulted in the burning of fossil fuels, which has caused a gradual increase in carbon dioxide concentration in the atmosphere. This has subsequently led to greenhouse effects and various climate problems. Selectively capturing and efficiently separating carbon dioxide is of paramount significance in ameliorating the current climate problems. Metal-organic framework (MOF) materials have gained widespread attention due to their high specific surface area, controllable pore size, high thermal stability, and mechanical stability, and have been extensively used in the field of gas adsorption, particularly in the capture and separation of carbon dioxide, with important practical application value.

This study reports the synthesis of two new pillar-layered metal-organic frameworks using Zn(II) as the central metal and three nitrogen atoms and two carboxylic acid ligands via the solvothermal method. The gas adsorption separation, structural transformation, and fluorescence sensing properties of the MOFs were investigated. A new pillar-layered metal-organic framework material, the complex [Zn2(ATZ)2(SQA)]'DMF', was synthesized by mixing the ligands SQA and ATZ with Zn(NO3)2'6H2O' under solvothermal conditions. The complex exhibited good thermal and chemical stability. The adsorption and separation performance of this material for CO2/N2 was studied, and a selectivity separation ratio of CO2/N2 at normal temperature and pressure was calculated by the ideal adsorption solution theory, which was found to be 74, satisfying the requirements of CO2 separation.

Furthermore, the dicarboxylic acid pillar in the two-dimensional interlayer support was replaced with 9,10-anthracene dicarboxylic acid (H2ADC), and reacted with Zn(NO3)2'6H2O' and TRZ under solvothermal conditions to obtain a second isomorphic pillar-layered metal-organic framework material, the complex [Zn2(TRZ)2(ADC)]'DMF'. The transformation behavior of this structure was mainly studied, and the MOF underwent a structural transformation after passing CO2 gas, which can be observed through the change of PXRD diffraction peaks. The fluorescence transformation of the complex [Zn2(TRZ)2(ADC)]'DMF' was also investigated, which changed from the original synthesized blue-violet light to the white light of the activated phase. Further introduction of CO2 into the activated phase caused the white light to change back to blue-violet light, indicating potential application in CO2 gas sensing.

In conclusion, the study presents the synthesis and characterization of two new pillar-layered metal-organic frameworks with potential application in CO2 separation and sensing. The findings of this research provide insights into the development of MOF materials for environmental protection and sustainability.