Aqueous Flow Reactor and Vapour‐Assisted Synthesis of Aluminium Dicarboxylate Metal–Organic Frameworks with Tuneable Water Sorption Properties

Abstract

Energy‐efficient indoors temperature and humidity control can be realised by using the reversible adsorption and desorption of water in porous materials. Stable microporous aluminium‐based metal–organic frameworks (MOFs) present promising water sorption properties for this goal. The development of synthesis routes that make use of available and affordable building blocks and avoid the use of organic solvents is crucial to advance this field. In this work, two scalable synthesis routes under mild reaction conditions were developed for aluminium‐based MOFs: (1) in aqueous solutions using a continuous‐flow reactor and (2) through the vapour‐assisted conversion of solid precursors. Fumaric acid, its methylated analogue mesaconic acid, as well as mixtures of the two were used as linkers to obtain polymorph materials with tuneable water sorption properties. The synthesis conditions determine the crystal structure and either the MIL‐53 or MIL‐68 type structure with square‐grid or kagome‐grid topology, respectively, is formed. Fine‐tuning resulted in new MOF materials thus far inaccessible through conventional synthesis routes. Furthermore, by varying the linker ratio, the water sorption properties can be continuously adjusted while retaining the sigmoidal isotherm shape advantageous for heat transformation and room climatisation applications.

Porosimetry for Thin Films of Metal–Organic Frameworks: A Comparison of Positron Annihilation Lifetime Spectroscopy and Adsorption‐Based Methods

“…MOFs are highly suitable for PALS analysis thanks to their uniform pores. Since the first PALS measurement on MOF-5, [22] PALS has been used to characterize MOF powders with pore sizes ranging from ultramicropores (<0.7 nm) to narrow mesopores (<2.5 nm): Al-MIL-53-Mes, [45] Al-MIL-53-Fum, [45] ZIF-8, [46] MOF-5, [47] IRMOF-3, [48] IRMOF-8, [47] MAF-6 [49] (Figure 3). Nonetheless, understanding the behavior of positrons in MOFs and other porous materials is an active research field.…”

“…Their values should be established from PALS measurements of well-characterized reference samples, and the corresponding pore sizes compared with values obtained with other methods (e.g., Ar physisorption on powder at 87 K), or calculations based on the crystal structure (e.g., Monte Carlo, molecular dynamics, or density functional theory). [10,51,54] Besides the pore size characterization of MOFs, [55,56] other usages of PALS have been demonstrated in literature. Pore size changes upon chemical treatment [57,58] (e.g., lithiation) or thermal treatment [59,60] (e.g., pore activation, framework amorphization) have been investigated.…”

Metal-Organic Frameworks for Metal-Ion Batteries: Towards Scalability

“…Next highly promising approach is chemical vapour deposition (CVD) [65][66][67][68][69][70][71][72][73][74]. Indeed, CVD as a non-solvent method is a well-known industrial approach for obtaining surfaces suitable for micro-and optoelectronics since the corrosion and contamination issues are solved.…”

“…The report by Stassin et al [72] creates a basis for the direct comparison of the solvothermal and vapour deposition methods for the synthesis of functional and polymorphic MOFs. MOFs Al-MIL-53-Fum and Al-MIL-53-Mes (Al-MIL-68-Mes) were synthesized with and without modulators.…”

Vapor-Phase Processing of Metal–Organic Frameworks

“…Through the mechanistic study of the vapor–solid reaction, the optimized deposition conditions (e.g., process temperature, oxide thickness, humidity, and linker exposure time) were identified and successfully translated to 200 mm Si wafer substrates (Figure c). Acidic vapors such as formic acid and acetic acid can also facilitate the precursor-to-MOF transformation, as illustrated for the conversion of aluminum nitride by the fumaric acid linker to form Al-MIL-53-Fum …”