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Zeolitic Imidazolate Framework Membrane with Molecular Sieving Properties by Microwave-Assisted Solvothermal Synthesis
Summary:
The authors from Leibniz University Hannover (Germany) and Dalian Institute of Chemical Physics, Chinese Academy of Sciences (China) developed a ZIF-8 membrane with high thermal stability, hydrophobicity, and molecular sieving properties, achieving excellent H₂ separation performance in gas separation applications.
Background:
1. To address the difficulty of synthesizing dense MOF layers on porous supports and poor thermal/chemical stability of some MOFs, previous researchers attempted MOF layer synthesis but rarely obtained dense coatings; existing MOF membranes (e.g., Cu₃(btc)₂) had low H₂/CH₄ separation factors (~6).
2. The authors proposed an innovative microwave-assisted solvothermal method, using methanol as solvent and adding sodium formate, successfully synthesizing dense ZIF-8 membranes with high H₂ selectivity.
Research Content:
1.Synthesis
The authors synthesized ZIF-8 membranes via microwave-assisted solvothermal method: dissolved 1.078g ZnCl₂, 0.972g 2-methylimidazole, and 0.540g sodium formate in 80mL methanol, immersed a 18×1mm porous TiO₂ support, heated at 100°C for 4h, then washed and dried.
2.Characterizations
1) BET: Specific surface area of ZIF-8 was 1496 m²/g, micropore volume 0.77 cm³/g.
2) SEM tests showed a crack-free, continuous ZIF-8 polycrystalline layer; large ZIF-8 crystals (up to 300 μm) were obtained via conventional heating.
3) XRD: ZIF-8 membrane had randomly oriented crystallites, lattice constant a=1.70174(4) nm; TG: No mass loss below ~360°C, total mass loss 63.3%.
3.Application
The membrane was tested in single/mixed gas permeation: Single-gas H₂ permeance was 6.04×10⁻⁸ mol·m⁻²·s⁻¹·Pa⁻¹; H₂/CH₄ (1:1) mixed-gas separation factor was 11.2 at 298K and 1 bar.
4.Mechanism
ZIF-8’s 3.4 Å six-membered ring pores enable molecular sieving; its flexible framework allows slightly larger CH₄ to pass slowly. Large cages (~11.4 Å) reduce CH₄’s inhibition on H₂ diffusion, differing from zeolites. Methanol’s weak interaction with ZIF-8 facilitates removal, reducing crystal stress.
Outlook:
This research successfully synthesized high-performance ZIF-8 membranes via microwave-assisted solvothermal method, balancing flux and selectivity. It provides a new approach for MOF membrane preparation and promotes the development of advanced gas separation membranes.
Zeolitic Imidazolate Framework Membrane with Molecular Sieving Properties by Microwave-Assisted Solvothermal Synthesis
Authors: Helge Bux, Fangyi Liang, Yanshuo Li, Janosch Cravillon, Michael Wiebcke, Ju¨rgen Caro
DOI: 10.1021/ja907359t
Link: https://pubs.acs.org/doi/10.1021/ja907359t
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