Hydrolytically Stable Phosphonate-Based Metal-Organic Frameworks for Harvesting Water from Low Humidity Air

Area of Science:

• Materials Science
• Environmental Science
• Chemical Engineering

Background:

• Global water crisis necessitates innovative water harvesting solutions.
• Existing sorbents face challenges in arid climates like low capacity and instability.
• Phosphonate-based metal-organic frameworks (MOFs) offer potential due to water stability but are underexplored for water harvesting.

Purpose of the Study:

• To systematically investigate phosphonate-based MOFs (STA-12 and STA-16) as water sorbents.
• To evaluate their performance under various humidity conditions, particularly in arid environments.
• To develop scalable synthesis methods and demonstrate a functional water harvesting device.

Main Methods:

• Synthesis and characterization of STA-12 (M=Co, Ni, Mg) and STA-16 (M=Co, Ni) MOFs.
• Water sorption measurements across a range of relative humidity (RH).
• Molecular simulations and solid-state Nuclear Magnetic Resonance (NMR) spectroscopy.
• Development of scalable aqueous synthesis and prototype device fabrication.

Main Results:

• STA-12 MOFs exhibited significant adsorption at ultra-low humidity (<10% RH).
• STA-16(Co) demonstrated high water uptake (0.54 g/g at 10-50% RH; 0.72 g/g at 34% RH).
• Molecular simulations and NMR identified liquid-like water as key to STA-16(Co)'s performance.
• Scalable synthesis yielded tens of grams of MOFs per batch.
• A prototype device using STA-12(Ni) confirmed material feasibility for water harvesting.

Conclusions:

• Phosphonate-based MOFs, specifically STA-12 and STA-16(Co), are highly effective water sorbents.
• These materials overcome limitations of existing sorbents, showing promise for arid regions.
• Scalable synthesis and prototype demonstration highlight their potential for addressing global water scarcity.