Multistage Condensation Pathway Minimizes Hysteresis in Water Harvesting with Large-Pore Metal–Organic Frameworks
Journal Article
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· Chemistry of Materials
- Department of Chemistry, The University of Utah, Salt Lake City, Utah 84112-0850, United States; Departamento de Matemáticas y Ciencias de Datos, Universidad San Pablo-CEU, CEU Universities, Madrid 28003, Spain
- Department of Chemistry, The University of Utah, Salt Lake City, Utah 84112-0850, United States; Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires 1428, Argentina
- Department of Chemistry, The University of Utah, Salt Lake City, Utah 84112-0850, United States
Metal-organic frameworks (MOFs) have emerged as promising materials for atmospheric water harvesting (AWH). Large-pore MOFs provide high water capacity, but their significant hysteresis between sorption and desorption makes them unsuitable for AWH. Co2Cl2(BTDD) is a noteworthy exception. This MOF has large, 2.2 nm diameter one-dimensional pores, and combines both record-high water capacity and minimal hysteresis, making it an excellent material for water capture in arid areas. Sorption reversibility in Co2Cl2(BTDD) has been attributed to continuous water uptake. However, the sharp adsorption/desorption in the isotherms supports a discontinuous first-order transition. Here we use molecular simulations to compute the water adsorption and desorption pathways and isotherms in a Co2Cl2(BTDD) model, to elucidate how does this MOF achieve reversibility despite its large pore size. The simulations reveal a multi-stage mechanism of discontinuous water uptake facilitated by spatial segregation of rows of hydrophilic metal sites bridged by ~1 nm hydrophobic ligands. The multi-stage mechanism breaks the barrier of capillary condensation into smaller, easier to surmount ones, resulting in a facile process despite the sharp density discontinuity between confined liquid and vapor. Our results explain why exchanging Co2+ for Ni2+ or Clfor F- in the MOF have minimal impact on the condensation and desorption pressures. On the other hand, we predict that a decrease in hydrophilicity of the MOF vertices would strongly increase the hysteresis. We expect that the relationships between spatial distribution of hydrophilic sites and hysteresis unraveled in this study assist the design of water harvesting materials with maximal capacity and reversibility.
- Research Organization:
- University of Utah
- Sponsoring Organization:
- Army Research Laboratory; Basic Energy Sciences
- Grant/Contract Number:
- SC0023213
- Other Award/Contract Number:
- W911NF-12-2-0023
- OSTI ID:
- 2860177
- Alternate ID(s):
- OSTI ID: 2577255
- Journal Information:
- Chemistry of Materials, Journal Name: Chemistry of Materials Journal Issue: 2 Vol. 36; ISSN 1520-5002; ISSN 0897-4756
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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