Postsynthetic tuning of hydrophilicity in pyrazolate MOFs to modulate water adsorption properties

Abstract

Metal-organic frameworks (MOFs) have attracted interest as adsorbents in water-based adsorption heat pumps owing to their potential for increased water loading capacities and structural and functional tunability versus traditionally used materials such as zeolites and silica. Although pyrazolate-based MOFs exhibit exceptional hydrolytic stability, the water adsorption characteristics of this class of frameworks have remained unexplored in this context. In this report, we describe the modular synthesis of novel dipyrazole ligands containing naphthalenediimide cores functionalized with -H (H 2 NDI-H), -NHEt (H 2 NDI-NHEt), or -SEt (H 2 NDI-SEt) groups. Reaction of these ligands with Zn(NO 3 ) 2 afforded an isostructural series of MOFs, Zn(NDI-X), featuring infinite chains of tetrahedral Zn 2+ ions bridged by pyrazolate groups and $16 Å-wide channels with functionalized naphthalenediimide linkers lining the channel surface. The Type V water adsorption isotherms measured for these materials show water uptake in the 40-50% relative humidity range, suggesting hydrophobic channel interiors. Postsynthetic oxidation of Zn(NDI-SEt) with dimethyldioxirane was used to generate ethyl sulfoxide and ethyl sulfone groups, thereby rendering the channels more hydrophilic, as evidenced by shifts in water uptake to the 30-40% relative humidity range. Such tunability in water adsorption characteristics may find utility in the design of new adsorbents for adsorption-based heat transfer processes. An original MATLAB script, MOF-FIT, which allows for visual modeling of breathing and other structural deformations in MOFs is also presented. Broader contextThe transfer of heat via adsorption/desorption of various gases or vapors by porous materials has long been recognized for potential applications in heat storage and transformation. The possible benets of adsorption-based heat pump systems include the ability to utilize low temperature waste heat and/or solar thermal energy and use of environmentally benign working uids such as water. Porous materials such as silica and zeolites have traditionally been studied as adsorbents in water-based adsorption heat pump applications. However, these materials suffer from a lack of structural and functional tunability, hindering modulation of hydrophilicity and water exchange capacity which directly correlate to their efficiency in water adsorption-based applications. Recently, a new class of porous hybrid materials, metal-organic frameworks (MOFs), has emerged which allow for unprecedented control over structure and chemical functionality. In this study, we describe the use of a simple postsynthetic modication strategy to control the hydrophilicity and water vapor adsorption properties of a new set of water stable Zn 2+ -pyrazolate MOFs. This postsynthetic modication strategy, along with a scalable, modular ligand synthesis, represent promising new approaches for the design of water sorption materials with tunable hydrophilicity and applications in energy efficient and environmentally friendly a...

Thermally-promoted post-synthetic Pummerer chemistry in a sulfoxide-functionalized metal–organic framework

“…Bridging ligands with similarly substituted sulfoxide groups have been shown to endow MOFs with highly hydrophilic properties, and can be created post-synthetically by oxidizing sulfide groups. 40 To the best of our knowledge, thermally-promoted reactions of sulfoxide groups in MOFs have not been reported. Simultaneous thermogravimetric and differential thermal analysis (TG-DTA) data were obtained using a Shimadzu DTG-60 fitted with a FC-60A flow rate controller and TA-60WS thermal analyser.…”

Facile Deposition of Multicolored Electrochromic Metal–Organic Framework Thin Films

“…[45] These MOFs (Zn(NDI-X), Figure 1) were obtained as microcrystalline powders by heating 1.1:1 molar mixtures of Zn(NO 3 ) 2 ·6 H 2 O and H 2 NDI-X (X = H, S-C 2 H 5 , NH-C 2 H 5 ) in N,N-dimethylformamide (DMF) at 130 8C. [45] These MOFs (Zn(NDI-X), Figure 1) were obtained as microcrystalline powders by heating 1.1:1 molar mixtures of Zn(NO 3 ) 2 ·6 H 2 O and H 2 NDI-X (X = H, S-C 2 H 5 , NH-C 2 H 5 ) in N,N-dimethylformamide (DMF) at 130 8C.…”

Labeling of HeLa cells using ZrO 2 : Yb 3 + - Er 3 + nanoparticles with upconversion emission

“…[11][12][13] Some efforts have been made to convert hydrophobic UPC nanoparticles into hydrophilic ones using techniques such as polymer capping, surface silanization, and surface ligand oxidation. [13][14][15][16][17][18] Recent methods also include ligand exchange in NaGdF 4 ∶Ho 3þ -Yb 3þ and NaYF 4 ∶Yb 3þ -Er 3þ phosphors. 19 Cancer detection in early stages is a priority for many medical groups around the world.…”