In‐Plane Epitaxial Growth of Highly c‐Oriented NH₂‐MIL‐125(Ti) Membranes with Superior H₂/CO₂ Selectivity

Abstract

Preferred‐orientation control has significant impact on the separation performance of MOF membranes. Under most conditions the preferred orientation of MOF membranes is dominated by the Van der Drift mechanism of evolutionary growth selection so that the obtained orientation may not be optimized for practical application. In this study, highly c‐oriented NH2‐MIL‐125 membranes were prepared on porous α‐alumina substrates by combining oriented seeding and controlled in‐plane epitaxial growth. Dynamic air–liquid interface‐assisted self‐assembly of c‐oriented NH2‐MIL‐125(Ti) seed monolayers, the use of layered TiS2 as the metal precursor, and single‐mode microwave heating were crucial in ensuring the preferred c‐orientation while simultaneously suppressing undesired twin growth. Owing to reduced grain boundary defects, the prepared c‐oriented membranes showed an ideal H2/CO2 selectivity of 24.8, which was 6.1 times higher than that of their randomly oriented counterparts under similar operating conditions.

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

“…For the solvothermal secondary growth, besides the preferential growth along the out-of-plane direction, the unavoidable deposition of nucleation and growth of ZIF-95 crystals produced in the bulk solution will also lead to the formation of a random and thick ZIF-95 membrane (Figure S11b). [38] Further, it should be noted that the presence of synthesis building blocks (Zn 2+ and cbIM) in the colloidal suspension of ZIF-95 seeds is necessary for the formation of a dense ZIF-95 membrane through epitaxial growth. As shown in Figure S12, the ZIF-95 seed crystals can still grow together and then form a rather continuous and oriented ZIF-95 membrane layer through vapor-assisted in-plane epitaxial growth, but observable gaps still exist if the synthesis building blocks Zn 2+ and cbIM were not added to the colloidal suspension of the ZIF-95 seeds during vacuum filtration, which can be attributed to an insufficient concentration of precursor nutrients for secondary growth for a dense ZIF-95 membrane.…”

“…[25][26][27][28][29][30][31][32][33][34] So far, there are only a few reports of the preparation of oriented MOF membrane. [35][36][37][38][39] In the present work, we report the preparation of highly c-oriented and hydrogen permselective ZIF-95 membranes via vapor-assisted in-plane epitaxial growth method. ZIF-95 shows a high thermal stability (over 500 8C) [40] and 2D layer structure (Figures 1 a,b).…”

“…Similar to the synthesis of oriented zeolite membranes, oriented MOF membranes can be prepared through solvothermal secondary growth of oriented seeds layer. [37][38][39] However, it should be noted that the secondary growth time has to be strictly controlled to obtain a perfect oriented membrane. It is usually found that the degree of random orientation increases with the secondary growth time.…”

Fabrication of a Hydrogen‐Bonded Organic Framework Membrane through Solution Processing for Pressure‐Regulated Gas Separation

“…[3] During the last several decades, ordered porous materials such as zeolite, metal-organic frameworks (MOFs), and covalent organic frameworks (COFs) have been successfully prepared into membranes for efficient gas separation, which can exhibit superior gas permeability and selectivity simultaneously. [4][5][6][7][8][9] However, this type of polycrystalline membranes are usually prepared via hydrothermal or solvothermal methods, which are challenging for scale-up, compared to the solution processing of polymer. Mixed-matrix membranes composed of polymers and inorganic microporous fillers are therefore under intensive study today, [10] while the issues of interfacial gaps and inhomogeneous dispersion still needs to be solved.…”

Fabrication of a Kagomé‐type MOF Membrane by Seeded Growth on Amino‐functionalized Porous Al2O3 Substrate

“…Nevertheless, the preparation of a homogeneous seed layer is not easy due to the poor adhesion bond between MOF particle and surface of common substrate materials such as Al 2 O 3 . Some methods have been developed so far to prepare a uniform seed layer [16–19] . 3‐aminopropyltriethoxysilane(APTEs) is used to chemically modify substrates to enhance the interaction between the substrate surface and MOF [20,21] .…”