Over the last two decades, more than 90,000 metal–organic frameworks (MOFs) structures have been identified and characterized. Due to the plethora of structural variances and chemical turnability, MOFs continue to find applications in catalysis, chemical separations, and green technologies. Typically, MOFs are synthesized via solvothermal methods which often pose several disadvantages: i) utilization of toxic reagents, ii) difficulty of pure-phase isolation, iii) irregularities in structural and physical properties of the desired product phase. To overcome these challenges, it is imperative for innovative synthetic methods to be explored. Herein, we report a phase-selective, high-yield, solvent-free, green synthetic method for the aluminum trimesates (Al–BTCs) MOF systems (MIL-100(Al), MIL-96(Al), and MIL-110(Al)). Al–BTCs phases synthesized by this method demonstrated similar physical and structural parameters to Al-BTC MOFs prepared under standard solvothermal conditions. To help ascertain the energetic landscape of the Al-BTCs MOF system, combustion calorimetric measurements were performed on phase pure activated MIL-100(Al), MIL-96(Al), and MIL-110(Al), as well as the mixed-phase MIL-100/96(Al). Our results demonstrate the enthalpic metastability of the Al-BTCs MOF system in comparison to its binary oxides. Additionally, the MIL-100/96(Al) mixture was more enthalpically favorably than the pure Al-BTCs phases in agreement with previous experimental observations. Lastly, the thermodynamic parameters provided in this work were combined with structural analyses to help elucidate the driving forces responsible for the phase selectivity obtained by this new synthetic method, thus giving insight into the mechanism of Al–BTC MOF formation and speciation.

Solvent-free and phase-selective synthesis of aluminum-trimesate metal–organic frameworks

ACS Spring Meeting 2021

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