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Dynamic channels of a porous coordination polymer responding to external stimuli
Summary:
The authors from Osaka Gas Co., Ltd. developed a dynamic copper-terephthalate-4,4′-bipyridine interpenetrating coordination polymer whose pores reversibly widen under CH₄ or methanol pressure, achieving 0.26 cm³ g⁻¹ micropore capacity and 700 m² g⁻¹ BET area for stimulus-responsive gas storage.
Background:
1. While first- and second-generation MOFs offer rigid pores, truly “third-generation” frameworks that reversibly restructure during adsorption remain scarce, limiting on-demand selectivity and actuator applications.
2. This work proposes an innovative one-pot heterogeneous synthesis to obtain an interpenetrated 3D network; high-pressure adsorption reveals a guest-induced phase transition that enlarges channels only when threshold pressure is exceeded.
Research Content:
1. Synthesis:
Methanol solutions of CuSO₄·5H₂O, terephthalic acid, formic acid and 4,4′-bipy reacted at 313 K for several days; yellow-green powder was vacuum-dried at 373 K.
2. Characterizations:
1) BET (N₂, 77 K): 700 m² g⁻¹; DR/Horvath-Kawazoe pore size 5.4 Å; micropore volume 0.26 cm³ g⁻¹.
2) SEM/TEM: sub-micron polycrystalline aggregates (exact size not quoted).
3) In-situ XRD: methanol uptake enlarges d-spacing 6.53 → 7.05 Å; full reversibility after 373 K desorption.
3. Application:
CH₄ isotherm (298 K, 3.5 MPa) shows gate-opening at ~0.8 MPa with 6 wt % uptake and reproducible hysteresis over three cycles; methanol vapor gives similar stepped isotherm (148 cm³ g⁻¹).
4. Mechanism:
Cooperative rotation of 4,4′-bipy pyridine rings in the interpenetrated framework locally dilates 3.4 × 3.4 Å channels, lowering the chemical potential barrier for guest ingress; desorption restores original conformation.
Outlook:
The study delivers a prototype stimulus-responsive sorbent whose pore aperture can be pressure-gated on-command, offering a practical platform for methane storage, sensing and gas-separation devices.
Dynamic channels of a porous coordination polymer responding to external stimuli
Author: Kenji Seki
DOI: 10.1039/B110899A
Link: https://doi.org/10.1039/B110899A
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