Water Adsorption in Porous MOFs

Home > News > Water Adsorption in Porous MOFs

Summary:
The authors from UC Berkeley, Lawrence Berkeley National Laboratory, and NIST developed a series of Zr-MOFs (MOF-801, MOF-841, etc.) with tuned pore sizes and hydrophilic sites, achieving record water uptake (22–44 wt %) at low relative pressure (P/P₀ ≤ 0.3) and excellent cycling stability for atmospheric-water harvesting and thermal-battery applications.

Background:
1. To address the lack of porous solids that combine low-pressure steep water uptake, high capacity, easy regeneration and hydrothermal stability, previous researchers tested zeolites, carbons and MOFs; success was limited by either too-strong binding (high regeneration cost) or too-weak interaction (high onset pressure).
2. The authors here proposed an isoreticular Zr-MOF platform (Zr₆O₄(OH)₄(-CO₂)ₙ SBUs with systematically varied linkers) and obtained materials whose pore diameter (4.8–18 Å) and μ₃-OH density precisely position water condensation steps below P/P₀ = 0.3 while keeping adsorption enthalpy moderate (~50–60 kJ mol⁻¹).

Research Content:
1. Synthesis: Solvothermal reaction of ZrOCl₂·8H₂O with linear/ditopic/tritopic carboxylate linkers (fumarate, PZDC, MTB, BTC, etc.) in DMF/formic acid at 100–130 °C, followed by solvent exchange and super-critical CO₂ activation.
2. Characterizations:
   1) BET surface area 690–2220 m² g⁻¹; pore volumes 0.27–0.88 cm³ g⁻¹; narrow micropore distribution centred at 4.8–12.6 Å.
   2) SEM/TEM show 100–300 nm octahedral single-crystals (MOF-801-SC) or ~50 nm aggregated particles (MOF-801-P).
   3) Water sorption isotherms (25 °C) exhibit sharp steps at P/P₀ = 0.05–0.3; maximum uptake 450 cm³ g⁻¹ (36 wt %) for MOF-801-P and 640 cm³ g⁻¹ (44 wt %) for MOF-841; five-cycle regeneration at 25 °C/5 Pa with <5 % loss.
3. Application: Demonstrated 6.3 L water per day per 15 kg MOF-841 under desert day–night cycle (40 °C/5 %RH → 25 °C/35 %RH); MOF-801-P delivers 1.8 kW h⁻¹ thermal power when 20 wt % water is adsorbed (60 kJ mol⁻¹ heat).
4. Mechanism: Single-crystal X-ray and neutron diffraction locate five D₂O sites: primary μ₃-OH···D₂O (I, II), interior cubic water cluster (III), and secondary cavity-centred sites (IV, V). Cooperative H-bonding network lowers condensation pressure without over-stabilization, enabling low-temperature regeneration.

Outlook:
The work establishes design rules (pore size ≈ 6–9 Å, moderate hydrophilic anchors, fcu/flu topology) for MOF water harvesters and thermal batteries, and provides two benchmark materials ready for device-scale testing.

Water Adsorption in Porous Metal–Organic Frameworks and Related Materials
Authors: Hiroyasu Furukawa, Felipe Gándara, Yue-Biao Zhang, Juncong Jiang, Wendy L. Queen, Matthew R. Hudson, Omar M. Yaghi
DOI: 10.1021/ja500330a
Link: https://pubs.acs.org/doi/10.1021/ja500330a

The above review is for academic progress sharing. For any errors or copyright issues, please contact us for correction or removal.