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Efficient Separation of Xylene Isomers by a Pillar-Layer Metal–Organic Framework
Summary:
The authors from Dalian Institute of Chemical Physics, CAS & University of CAS developed the pillar-layer MOF Co(aip)(bpy)0.5 (aip = 5-aminoisophthalate, bpy = 4,4′-bipyridine) with ultrahigh para-selectivity, achieving record liquid-phase selectivities of 30 (pX/mX) and 16 (pX/oX) for xylene-isomer separation.
Background:
1. PX/MX/OX separation is one of the “seven challenging separations” because of nearly identical boiling points (138–144 °C) and kinetic diameters (≈6 Å); conventional BaX/KBaY zeolites give selectivities ≤10 and limited capacity.
2. The authors proposed a π-rich pillar-layer Co-MOF whose channels combine size-matching and host–guest π···π/C–H···π interactions; they obtained unprecedented selectivity and full single-crystal reversibility.
Research Content:
1. Synthesis: Solvothermal reaction of Co(CH₃COO)₂·4H₂O, 5-aminoisophthalic acid and 4,4′-bipyridine in MeOH/H₂O at 60 °C for 72 h, followed by methanol exchange and 150 °C activation.
2. Characterizations:
1) CO₂ adsorption at 0 °C reveals micropores matching xylene dimensions; N₂ at 77 K negligible, proving aperture-sieving.
2) SEM shows 2–5 µm pillared plates; PXRD confirms phase purity and thermal stability up to 400 °C.
3) TPD, breakthrough curves and IGA sorption kinetics quantify uptake (156 mg g⁻¹ pX) and diffusion time constants.
3. Application: Liquid-phase batch & breakthrough tests give 15.6 wt % pX capacity with 30-fold selectivity over mX; vapor TPD enriches pX from 1:1 to 38:1 in desorbed product.
4. Mechanism: DFT (GGA-PBE) shows interaction energy ΔE(pX) = ‑0.568 eV vs ‑0.544/-0.547 eV for oX/mX; electrostatic potential maps reveal stronger π-electron transfer and better packing of pX inside the pillar-layer channels, leading to displacement of competing isomers.
Outlook:
The study delivers a scalable, reusable MOF adsorbent that surpasses industrial BaX zeolite benchmarks and opens a practical route for energy-saving adsorptive separation of p-xylene in a single-crystalline pillar-layer platform.
Efficient Separation of Xylene Isomers by a Pillar-Layer Metal–Organic Framework
Authors: Liping Yang, Hanbang Liu, Danhua Yuan, Jiacheng Xing, Yunpeng Xu*, Zhongmin Liu
DOI: 10.1021/acsami.1c10462
Link: https://doi.org/10.1021/acsami.1c10462
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