Pore chemistry and size control in hybrid porous materials for acetylene capture from ethylene

Home > News > Pore chemistry and size control in hybrid porous materials for acetylene capture from ethylene

Summary:
The authors from Zhejiang University, University of Limerick, University of Amsterdam, National Institute of Standards and Technology, King Abdullah University of Science and Technology, and University of Texas–San Antonio developed SIFSIX series materials (SIFSIX-1-Cu, SIFSIX-2-Cu, SIFSIX-2-Cu-i, SIFSIX-3-Zn, SIFSIX-3-Ni, SIFSIX-3-Cu) with controllable pore chemistry and size, achieving excellent acetylene (C₂H₂) capture and separation performance from ethylene (C₂H₄) in the field of gas separation.

Background:
1. To address the trade-off between physical adsorption capacity and selectivity of porous materials in gas separation, previous researchers studied materials like MOF-74 (high C₂H₂ uptake but low selectivity) and M’MOF (high selectivity but low C₂H₂ uptake), yet these materials failed to balance both key properties for efficient C₂H₂/C₂H₄ separation.
2. The authors proposed an innovative method of constructing metal coordination networks with hexafluorosilicate (SiF₆²⁻) and organic linkers, obtaining SIFSIX series materials that balance high C₂H₂ adsorption capacity and selectivity.

Research Content:
1. Synthesis
-SIFSIX-1-Cu: Dissolved 4,4’-bipyridine in ethylene glycol at 338 K, added aqueous solution of Cu(BF₄)₂·xH₂O and (NH₄)₂SiF₆, heated at 65 °C for 3 h, filtered, washed with methanol, and exchanged with methanol for 3 days.
-SIFSIX-2-Cu: Layered ethanol solution of 4,4’-bipyridylacetylene onto ethylene glycol solution of CuSiF₆·xH₂O, obtained crystals after 2 weeks, and exchanged with ethanol for 4 days.
-SIFSIX-2-Cu-i: Mixed methanol solution of 4,4’-bipyridylacetylene with aqueous solution of Cu(BF₄)₂·xH₂O and (NH₄)₂SiF₆, heated at 85 °C for 12 h, and exchanged with methanol for 3 days.
-SIFSIX-3-Zn: Layered methanol solution of pyrazine onto methanol solution of ZnSiF₆·xH₂O, obtained colorless crystals after 2 days, and exchanged with ethanol for 1 day.
-SIFSIX-3-Ni: Mixed methanol solution of NiSiF₆ and pyrazine, heated at 85 °C, obtained blue powder after 3 days, and exchanged with ethanol for 3 days.
-SIFSIX-3-Cu: Slowly added hot methanol solution of pyrazine into hot methanol solution of CuSiF₆·H₂O, filtered after 1 minute of stirring, dried in air, and degassed under high vacuum at 50 °C for 12 h.
2. Characterizations
1.BET and pore size:
   - SIFSIX-1-Cu: BET surface area 1178 m²/g, pore size 8.0×8.0 Å;
   - SIFSIX-2-Cu: 1881 m²/g, 10.5×10.5 Å;
   - SIFSIX-2-Cu-i: 503 m²/g, 5.2×5.2 Å;
   - SIFSIX-3-Zn: 250 m²/g, 4.2×4.2 Å;
   - SIFSIX-3-Ni: 368 m²/g, 4.2×4.2 Å.
2.XRD and neutron diffraction: XRD (SHIMADZU XRD-6000) confirmed crystal structure; neutron diffraction (BT-1 diffractometer) revealed ordered C₂D₂ adsorption (e.g., SIFSIX-1-Cu·4C₂D₂ with C-D···F H-bonding at 2.063 Å).
3.Gas adsorption tests: Used ASAP 2050 and 3Flex analyzers to measure C₂H₂/C₂H₄ sorption isotherms at 273–313 K; calculated isosteric heat of adsorption (Qst) via Clausius-Clapeyron equation (e.g., SIFSIX-2-Cu-i Qst for C₂H₂ is 41.9 kJ/mol).
3. Application
-Breakthrough tests: Conducted with 1/99 and 50/50 (v/v) C₂H₂/C₂H₄ mixtures. For 1/99 mixture, SIFSIX-2-Cu-i captured 0.73 mmol/g C₂H₂, with outlet C₂H₂ <2 ppm and C₂H₄ purity >99.998%; SIFSIX-1-Cu captured 5533 mmol/L C₂H₂ from 50/50 mixture. Trace CO₂, H₂O, and O₂ had little effect on separation; materials maintained performance over 16 cycles (SIFSIX-2-Cu-i).
4. Mechanism
-Binding interactions: DFT calculations showed C₂H₂ binds via C-H···F H-bonding (e.g., 2.017 Å in SIFSIX-1-Cu) and van der Waals interactions with organic linkers; guest-guest dipole-dipole interactions (Hδ⁺···Cδ⁻) enhanced adsorption.
-Pore control: SiF₆²⁻ anions and organic linkers tuned pore size/chemistry; SIFSIX-2-Cu-i’s interpenetrated structure enabled dual C-H···F H-bonding (ΔE=52.9 kJ/mol) for high low-pressure uptake; SIFSIX-1-Cu’s larger pores allowed high C₂H₂ packing (8.5 mmol/g at 1 bar).

Outlook:
This research realizes precise control of pore chemistry and size in SIFSIX materials, balancing C₂H₂ adsorption capacity and selectivity for efficient C₂H₂/C₂H₄ separation. It provides a design strategy for porous materials in gas separation, promoting industrial applications in high-purity C₂H₂/C₂H₄ production.

Pore chemistry and size control in hybrid porous materials for acetylene capture from ethylene
Authors: Xili Cui, Kaijie Chen, Huabin Xing, Qiwei Yang, Rajamani Krishna, Zongbi Bao, Hui Wu, Wei Zhou, Xinglong Dong, Yu Han, Bin Li, Qilong Ren, Michael J. Zaworotko, Banglin Chen
DOI: 10.1126/science.aaf2458
Link: https://www.science.org/doi/10.1126/science.aaf2458

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