Water Adsorption in Porous Metal–Organic Frameworks and Related Materials

Abstract

Water adsorption in porous materials is important for many applications such as dehumidification, thermal batteries, and delivery of drinking water in remote areas. In this study, we have identified three criteria for achieving high performing porous materials for water adsorption. These criteria deal with condensation pressure of water in the pores, uptake capacity, and recyclability and water stability of the material. In search of an excellently performing porous material, we have studied and compared the water adsorption properties of 23 materials, 20 of which are metal-organic frameworks (MOFs). Among the MOFs are 10 zirconium(IV) MOFs with a subset of these, MOF-801-SC (single crystal form), -802, -805, -806, -808, -812, and -841 reported for the first time. MOF-801-P (microcrystalline powder form) was reported earlier and studied here for its water adsorption properties. MOF-812 was only made and structurally characterized but not examined for water adsorption because it is a byproduct of MOF-841 synthesis. All the new zirconium MOFs are made from the Zr6O4(OH)4(-CO2)n secondary building units (n = 6, 8, 10, or 12) and variously shaped carboxyl organic linkers to make extended porous frameworks. The permanent porosity of all 23 materials was confirmed and their water adsorption measured to reveal that MOF-801-P and MOF-841 are the highest performers based on the three criteria stated above; they are water stable, do not lose capacity after five adsorption/desorption cycles, and are easily regenerated at room temperature. An X-ray single-crystal study and a powder neutron diffraction study reveal the position of the water adsorption sites in MOF-801 and highlight the importance of the intermolecular interaction between adsorbed water molecules within the pores.

Chemical Crystallography at the Advanced Light Source

“…Evacuation of single crystals in the gas cell commonly results in the removal of solvent molecules, leaving a desolvated crystal that may, e.g., in the case of Co 2 (dobdc)(H 2 O) 2 ·solvate (aka Co 2 (dhtp)(H 2 O) 2 , CPO-27-Co or MOF-74-Co, dobdc = dhtp = 2,5-dioxido-1,4-benzenedicarboxylate) [63], or may not, e.g., Zr 6 O 4 (OH) 4 (fumarate) 6 ·solvate (aka MOF-801) [64], contain vacant coordination sites as a result. Upon re-exposure to the atmosphere, the location and order of occupation of any water adsorption sites may be monitored.…”

Mass transport through metal organic framework membranes

“…Thus, MOFs demonstrate great potential applications in various fields. Owing to the decades' efforts of researchers, thousands of structures of MOFs have been discovered and applied in various fields, such as separation [31][32][33][34][35][36][37][38], adsorption [20,[39][40][41][42], optics [43][44][45][46][47][48][49][50], catalysis [19,[51][52][53][54][55][56], sensors [57][58][59][60][61][62][63], etc. However, most of these studies are based on MOFs powders.…”

Explicit treatment of hydrogen bonds in the universal force field: Validation and application for metal-organic frameworks, hydrates, and host-guest complexes

“…[5,6] Water is an important solvent for MOFs, it serves as a synthetic medium, [7][8][9] a structural component, [10] and an adsorbate. [11] Water plays a major role in mediating defects and dissolution of many MOFs. [12][13][14] Some MOFs, such as the UiO series, are highly water stable [15], while others break down or transform [16][17][18][19] when exposed to water.…”

“…[12][13][14] Some MOFs, such as the UiO series, are highly water stable [15], while others break down or transform [16][17][18][19] when exposed to water. Proposed applications of MOFs include separation of organic contaminants [20] and arsenic [21] from aqueous mixtures and capture of water from air [11].…”