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Flexible molecular sieving of C₂H₂ from CO₂ by a new cost-effective metal organic framework with intrinsic hydrogen bonds
Summary:
The authors from Zhejiang Normal University and Zhejiang University developed a hydrogen-bonded flexible metal-organic framework ZNU-3, achieving excellent performance in the application of C₂H₂/CO₂ separation.
Background:
1. To address the challenge of separating C₂H₂ and CO₂ (similar physical properties and molecular size), previous researchers developed MOFs like UTSA-300a and ZNU-1, yet they suffered from low C₂H₂ capacity or poor selectivity, and high synthesis costs.
2. The authors proposed an innovative strategy using low-cost commercial ligands and hydrogen-bond regulation, obtaining ZNU-3 with both high C₂H₂ capacity and selectivity.
Research Content:
1. Synthesis
The authors synthesized ZNU-3 via a room-temperature solution method using Cu²⁺ salts (e.g., Cu(NO₃)₂·3H₂O) and 3,5-pyridinedicarboxylic acid (H₂Pdc) as precursors, with a yield of 48.9%.
2. Characterizations
1) BET surface area reaches 463 m²/g, with a pore size range of 3.27-4.19 Å and a total pore volume of 0.694 cm³/g;
2) SEM/TEM tests show ZNU-3 forms blue crystalline particles, with a 3D framework and 1D ultramicroporous channels;
3) TGA confirms thermal stability up to 280 °C; PXRD verifies a new topological structure (zyb) and single crystal parameters (a=12.3506 Å, b=10.5595 Å, c=15.0121 Å).
3. Application
In C₂H₂/CO₂ separation: At 298 K and 1.0 bar, C₂H₂ uptake is 81.0 cm³(STP)g⁻¹, CO₂ uptake is 5.4 cm³(STP)g⁻¹, with a C₂H₂/CO₂ ratio of 14.9; dynamic breakthrough experiments show C₂H₂ retention time is twice that of CO₂, maintaining stability for 3 cycles.
4. Mechanism
Hydrogen bonds between -COOH and -COO⁻ regulate framework flexibility, enabling selective gate-opening for C₂H₂; C₂H₂ is trapped by carboxylate hydrogen bonds and π⋅⋅⋅π stacking (binding energy -36.7 kJ/mol), while CO₂ has weak adsorption (binding energy -4.8 kJ/mol) and higher diffusion barrier (184.9 kJ/mol vs. 91.1 kJ/mol for C₂H₂).
Outlook:
This research develops a low-cost, high-performance C₂H₂/CO₂ separation material, provides a "hydrogen-bond regulated flexible sieving" strategy, and promotes MOF industrialization in gas separation.
Flexible molecular sieving of C₂H₂ from CO₂ by a new cost-effective metal organic framework with intrinsic hydrogen bonds
Authors: Wan-Qi Sun, Jian-Bo Hu, Yun-Jia Jiang, Nuo Xu, Ling-Yao Wang, Jia-Hao Li, Yong-Qi Hu, Simon Duttwyler, Yuan-Bin Zhang
DOI: 10.1016/j.cej.2022.135745
Link: https://www.sciencedirect.com/science/article/pii/S1385894722012451
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