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. 2022 Jul 27;8(7):926-932.
doi: 10.1021/acscentsci.2c00398. Epub 2022 Jun 16.

Hydrazine-Hydrazide-Linked Covalent Organic Frameworks for Water Harvesting

Ha L Nguyen  1   2 , Cornelius Gropp  1 , Nikita Hanikel  1 , Anna Möckel  1 , Alicia Lund  3 , Omar M Yaghi  1   2
Affiliations

Hydrazine-Hydrazide-Linked Covalent Organic Frameworks for Water Harvesting

Ha L Nguyen et al. ACS Cent Sci. .

Abstract

We report a postsynthetic strategy and its implementation to make covalent organic frameworks (COFs) with irreversible hydrazide linkages. This involved the synthesis of three 2D and 3D hydrazine-linked frameworks and their partial oxidation. The linkage synthesis and functional group transformation-hydrazine and hydrazide-were evidenced by 15N multi-CP-MAS NMR. In addition, the isothermal water uptake profiles of these frameworks were studied, leading to the discovery of one hydrazine-hydrazide-linked COF suitable for water harvesting from air in arid conditions. This COF displayed characteristic S-shaped water sorption profiles, a steep pore-filling step below 18% relative humidity at 25 °C, and a total uptake capacity of 0.45 g g-1. We found that even small changes made on the molecular level can lead to major differences in the water isotherm profiles, therefore pointing to the utility of water sorption analysis as a complementary analytical tool to study linkage transformations.

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Conflict of interest statement

The authors declare the following competing financial interest(s): Omar M. Yaghi is co-founder of Water HarvestingInc., aiming at commercializing related technologies.

Figures

Scheme 1
Scheme 1. Synthetic Strategy for Hydrazide-Linked COFs
This strategy was applied to a molecular model system and two 2D (hcb, sql) and one 3D (dia) COFs.
Scheme 2
Scheme 2. Overview of the Synthesis of (a) 2D hcb, (b) 2D sql, and (c) 3D dia Hydrazide-Linked COFs
The synthesis of hydrazine-linked COFs is detailed in the Supporting Information.
Figure 1
Figure 1
Water vapor sorption analysis of AB-COF (a) and COF-480-hydrazide (b) at different temperatures (15, 25, and 35 °C). P: water vapor pressure. Psat: saturation water vapor pressure at the given temperature. Water cycling stability test of 230 adsorption–desorption cycles of COF-480-hydrazide (c) subjected to an isobaric (1.7 kPa water vapor) temperature-swing adsorption between 30 and 85 °C, corresponding to 40% and 3% RH, respectively. The full data set is reported in the Supporting Information, section S8.
Figure 2
Figure 2
Overlay of water isotherms of Py-COF-2D and COF-482-hydrazide at 25 °C. P: water vapor pressure. Psat: saturation water vapor pressure.
Figure 3
Figure 3
Structural models of the six-fold framework of COF-670-hydrazine (a) and the oxidation of COF-670-hydrazine to COF-670-hydrazide (b). Overlay of PXRD patterns of COF-670-hydrazine modeled structures (from one-fold to seven-fold) and its experimental PXRD pattern (c). PXRD patterns of simulated COF-670-hydrazine compared to the experimental ones of COF-670-hydrazine and COF-670-hydrazide (d).
See this image and copyright information in PMC

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