Effect Of Temperature And Substituent On Adsorption And Separation Properties Of Metal-Organic Frameworks

Low-temperature distillation technology is an important industrial process for gas separation,but there are problems such as high energy consumption and heavy pollution in the application process.Metal-Organic Frameworks?also known as MOFs?are expected to replace the traditional cryogenic distillation separation technology application practice in gas separation and purification due to their high specific surface area and permanent porosity.In the practical application process of MOFs as the adsorbent,the external temperature has an important influence on the separation effect of the adsorbent.First,for the MOFs material itself,most materials?including MOFs?have thermal expansion and contraction effects.At low temperatures,the structure of the MOF material will shrink to some extent,which will affect the dynamic gas adsorption capacity.Second,For gas molecules,the higher the temperature,the more active,the faster the gas molecules diffuse inside the pores of the MOFs;at low temperatures,the gas molecules are less active and the diffusion rate is slower.However,few studies have investigated the effect of temperature on the separation of MOF materials.In this paper,five materials,UTSA-16,Co-MOF-74,ZIF-8,UiO-66 and UiO-66NH₂,which have good separation performance for CO₂/CH₄ separation,were selected.Through penetration experiments,273K and 298K were studied.The effect of these five materials on CO₂/CH₄ separation at 313K and 323K showed that the separation effect of Co-MOF-74,ZIF-8,UiO-66 and UiO-66-NH₂ increased linearly with the decrease of temperature.Different from the above four,the separation effect of UTSA-16 at 273K is worse than 298K.The reason may be that UTSA-16 has some shrinkage at low temperature.Therefore,in dynamic penetration experiments,the dynamic equilibr ium adsorption capacities of CH₄ and CO₂ are both There was a decrease in the separation effect in the 273K penetration test compared to 298K.Through this research,it helps to promote the practical pace of MOFs.The functional groups have a certain influence on the adsorption properties of metal organic frameworks?MOFs?,especially the amino group?-NH₂?,because the amino group sometimes acts as a Lewis basic group and interacts with acid gas molecules?such as CO₂?.,resulting in enhanced selective gas adsorption capacity.However,not all MOF materials increase their gas adsorption properties after amino functionalization,and may also block the pores and reduce the selective gas adsorption capacity of MOFs.In this paper,FJU-31and amino-functionalized FJU-31-NH₂ were synthesized by hydrothermal method,which has good thermal stability.The properties of adsorption and CO₂/N₂ separation were studied.It was found that the solid-state fluorescence of FJU-31 was shifted to the white light region by CIE under the excitation of ultraviolet light due to the difference of the guest molecules?solvent molecules?in the pores.