Multifunctionality in an Ion-Exchanged Porous Metal-Organic Framework

Porous robust materials are typically the primary selection of several industrial processes. Many of these compounds are, however, not robust enough to be used as multifunctional materials. This is typically the case of Metal-Organic Frameworks MOFs) which rarely combine several different excellent functionalities into the same material. In this report we describe the simple acid-base postsynthetic modification of isotypical porous rare-earth-phosphonate MOFs into a truly multifunctional system, maintaining the original porosity features: [Ln(H(3)pptd)]center dot xSolvent [where Ln(3+) = Y3+ (1) and (Y0.95Eu0.05)(3+) (1_Eu)] are converted into [K(3)Ln(pptd)]center dot zSolvent [where Ln(3+) = Y3+ (1K) and (Y0.95Eu0.05)(3+) (1K_Eu)] by immersing the powder of 1 and 1_Eu into an ethanolic solution of KOH for 48 h. The K+-exchanged Eu3+-based material exhibits a considerable boost in CO2 adsorption, capable of being reused for several consecutive cycles. It can further separate C2H2 from CO2 from a complex ternary gas mixture composed of CH4, CO2, and C2H2. This high adsorption selectivity is, additionally, observed for other gaseous mixtures, such as C3H6 and C3H8, with all these results being supported by detailed theoretical calculations. The incorporation of K+ ions notably increases the electrical conductivity by 4 orders of magnitude in high relative humidity conditions. The conductivity is assumed to be predominantly protonic in nature, rendering this material as one of the best conducting MOFs reported to date.

Automated summary

This report describes the acid-base postsynthetic modification of isotypical porous rare-earth-phosphonate MOFs to create a truly multifunctional system with enhanced CO2 adsorption and the ability to separate various gases. The introduction of K+ ions notably increases the electrical conductivity of the material, making it one of the best conducting MOFs reported to date.