Selective Molecular Separation by Interfacially Crystallized Covalent Organic Framework Thin Films

Abstract

Exponential interest in the field of covalent organic frameworks (COFs) stems from the direct correlation between their modular design principle and various interesting properties. However, existing synthetic approaches to realize this goal mainly result in insoluble and unprocessable powders, which severely restrict their widespread applicability. Therefore, developing a methodology for easy fabrication of these materials remains an alluring goal and a much desired objective. Herein, we have demonstrated a bottom-up interfacial crystallization strategy to fabricate these microcrystalline powders as large-scale thin films under ambient conditions. This unique design principle exploits liquid-liquid interface as a platform, allowing simultaneous control over crystallization and morphology of the framework structure. The thin films are grown without any support in free-standing form and can be transferred onto any desirable substrate. The porous (with Tp-Bpy showing highest S of 1 151 m g) and crystalline thin films, having high chemical as well as thermal stability, also hold the merit to tune the thickness as low as sub-100 nm. These nanostructured thin COF films demonstrate remarkable solvent-permeance and solute-rejection performance. A prominent instance is the Tp-Bpy thin film, which displays an unprecedented acetonitrile permeance of 339 L m h bar.

Large Area Self‐Assembled Ultrathin Polyimine Nanofilms Formed at the Liquid–Liquid Interface Used for Molecular Separation

“…This result is typical for nanofiltration membranes in pore size ranges above ≈1 nm. The polyimine nanofilm membranes have almost equivalent water permeance to that of the reported ≈60 nm thick TFP‐DHF 2D COF thin‐film membrane with MWCO of 900 g mol −1 prepared by Langmuir–Blodgett method and four‐times lower than the 2.1 µm thick interfacially crystallized COF thin films . Presumably, the amorphous nature of our 14 nm thick polyimine nanofilms leads to relatively lower water permeance compared to the crystalline COFs.…”

“…On the other hand, integrally skinned asymmetric membranes are known for separating small molecules from the organic feed, with marginal selectivity . Recently, interest in imine based porous organic polymers (POPs), and covalent organic frameworks (COFs), has grown due to their unique porous structures, which could be used for molecular separation with high MWCO . Caro and co‐workers demonstrated the excellent performance of COF‐LZU1 membranes for selective separation of dyes with water permeance of ≈76 L m −2 h −1 bar −1 and favorable rejection (rates exceeding 90%) for water‐soluble dyes larger than 1.2 nm.…”

Imidazolium‐Salt‐Functionalized Covalent Organic Frameworks for Highly Efficient Catalysis of CO2 Conversion

“…[7][8][9] Various catalysts have been investigated for the cycloaddition reaction. [12][13][14] Covalent organic frameworks (COFs) [15][16][17] are anothern ovel class of crystalline porous materials with wide applicationsi n molecule storage and separation, [18][19][20] catalysis, [21][22][23][24][25][26] energy storage, and others. [10,11] For example, metal-organic frameworks (MOFs) have served as excellent heterogeneousc atalysts for this reaction.…”

Tailoring Covalent Organic Frameworks To Capture Water Contaminants

“…Additionally, interfacial polymerization, polymerization at the interface of two immiscible phases that contain the monomers, was used to obtain self‐standing COF thin films with different thicknesses (Figures c–e) . Banerjee and co‐workers synthesized a crystalline porous 2D network at the liquid–liquid interface between dichloromethane and water.…”