ZIF‐8 Membrane Separation Performance Tuning by Vapor Phase Ligand Treatment

Abstract

Vapor phase ligand treatment (VPLT) of 2‐aminobenzimidazole (2abIm) for 2‐methylimidazole (2mIm) in ZIF‐8 membranes prepared by two different methods (LIPS: ligand induced permselectivation and RTD: rapid thermal deposition) results in a notable shift of the molecular level cut‐off to smaller molecules establishing selectivity improvements from ca. 1.8 to 5 for O2/N2; 2.2 to 32 for CO2/CH4; 2.4 to 24 for CO2/N2; 4.8 to 140 for H2/CH4 and 5.2 to 126 for H2/N2. Stable (based on a one‐week test) oxygen‐selective air separation performance at ambient temperature, 7 bar(a) feed, and 1 bar(a) sweep‐free permeate with a mixture separation factor of 4.5 and oxygen flux of 2.6×10−3 mol m−2 s−1 is established. LIPS and RTD membranes exhibit fast and gradual evolution upon a 2abIm‐VPLT, respectively, reflecting differences in their thickness and microstructure. Functional reversibility is demonstrated by showing that the original permeation properties of the VPLT‐LIPS membranes can be recovered upon 2mIm‐VPLT.

Current Progress and Future Directions in Gas‐Phase Metal‐Organic Framework Thin‐Film Growth

“…Recently, it has been reported that the ZIF-8 membrane grown on porous alumina substrates can be modified via a post-synthesis process by using vaporized 2aminobenzimidazloe (2-abIm). [43] The ligand exchanged ZIF-8 membrane, which consists of mixed 2-mIm and 2-abIm, showed enhanced gas separation capability between small molecules, such as O 2 over N 2 and CO 2 over CH 4 . [43] Although CVD-based methods have various advantages in the growth of homogeneous MOF thin films, it also has some disadvantages which originate from its fundamental growth concept.…”

“…[43] The ligand exchanged ZIF-8 membrane, which consists of mixed 2-mIm and 2-abIm, showed enhanced gas separation capability between small molecules, such as O 2 over N 2 and CO 2 over CH 4 . [43] Although CVD-based methods have various advantages in the growth of homogeneous MOF thin films, it also has some disadvantages which originate from its fundamental growth concept. As we briefly mentioned above, the conversion of ZnO to ZIF-8 is initiated from the top surface of the ZnO layers.…”

Anisotropic Gas Separation in Oriented ZIF‐95 Membranes Prepared by Vapor‐Assisted In‐Plane Epitaxial Growth

“…Steam/vapor‐assisted conversion has been applied for the synthesis of zeolite and MOF films due to its simplicity [42–46] . In this case, a precursor/seeds layer is firstly coated on the support, followed by steam/vapor‐assisted conversion to form a continuous membrane layer [42–44] .…”

Effective aperture tuning of a zeolitic-imidazole framework CdIF-1 by controlled thermal amorphization

“…7 For instance, the systematic mixing of 2-methylimidazolate (mIm) and bulkier benzimidazolate (bIm) led to an orderly reduction in the effective aperture size of the resulting mixed-linker ZIF-7-8. [8][9][10] Likewise, mixing Zn 2+ and Co 2+ enabled the tuning of the effective apertures of the mixed-metal ZIF-8-67. 11,12 Another effective strategy is to restrict the exibility of the ZIF-8 framework by an electric eld 13,14 or a rapid heat treatment, 15 thereby enhancing its molecular sieving effect.…”