Metal-organic frameworks, MOFs are of significant interest to separations, environmental remediation, catalysis, and biomedicine. While many MOFs are unstable in water and aqueous solutions, aluminum MOFs (Al-MOFs) show an unprecedented stability to water. For emerging applications of MOFs in biomedicine and related fields, high-purity materials are needed. We report an improved chemical synthesis of Al-MOF MIL-160(Al), its thorough purification, the spectroscopic FTIR assignments of its major impurity 2,5-furandicarboxylic acid, and detailed assignments of peaks due to specific functional groups in MIL-160(Al). Further, we describe an in-situ kinetic study of sorption of water vapor in air on MIL-160(Al) by the two complementary methods: ATR-FTIR spectroscopy under ambient conditions, and gravimetric analysis in the time-dependent regime. Chemical kinetics of water sorption follows the pseudo-first order rate law, and proceeds toward formation of the stoichiometric solid-state adsorption complex [MIL-160(Al)]1[H2O]4. Then, the in-situ FTIR spectroscopy provides the reliable assignments of the multiple FTIR peaks to specific vibrations of functional groups in MIL-160(Al). An in-situ time-resolved FTIR spectra provide solid evidence of formation and evolution of transient structures, in which water molecules are bonded to the -OH group and heterocyclic ring of linker in the MOF. Understanding hydrophilic behavior of MIL-160(Al) and related MOFs contributes to applications other than water sorption, such as heat storage and reallocation, purification of foods, and using MOFs as chemical matrix for encapsulation and release of medical drugs, vitamins and cosmetics.

Unusual highly hygroscopic Al-MOF MIL-160(Al): Synthesis, purification, advanced spectroscopic characterization, and kinetics of water sorption by in-situ FTIR and gravimetric measurements

ACS Spring Meeting 2021

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