Covalent Organic Frameworks‐Based Membranes as Promising Modalities from Preparation to Separation Applications: An Overview

Abstract

Covalent organic frameworks (COFs) are a promising class of porous crystalline materials made up of covalently connected and periodically protracted network topologies through organic linkers. The tailorability of organic linker and intrinsic structures endow COFs with a tunable porosity and structure, low density, facilely‐tailored functionality, and large surface area, attracting increasing amount of interests in variety of research areas of membrane separations. COF‐based membranes have spawned a slew of new research projects, ranging from fabrication methodologies to separation applications. Herein, we tried to emphasis the major developments in the synthetic approaches of COFs based membranes for a variety of separation applications such as, separation of gaseous mixtures, water treatment as well as separation of isomeric and chiral organic compounds. The proposed methods for fabricating COF‐based continuous membranes and columns for real world applications are also thoroughly explored. Finally, a viewpoint on the future directions and remaining challenges for COF research in the area of separation is provided.

Scalable, Interfacially Synthesized, Covalent–Organic Framework (COF)-Based Thin-Film Composite (TFC) Hollow Fiber Membranes for Organic Solvent Nanofiltration (OSN)

“…This is attributed to the less crystallinity of Tp-Tta, which also results in the smaller relative intensity of 100 and 001 peaks. 20 The formation of the COF membrane over the PAN HFM substrate was further characterized by 13 C nuclear magnetic resonance (NMR) and FTIR spectroscopy (Figure 2b,c). As explained above, the solid-state 13 C NMR spectra of the COF were carried out using the PAN layer-removed thin COF film.…”

“…20 The formation of the COF membrane over the PAN HFM substrate was further characterized by 13 C nuclear magnetic resonance (NMR) and FTIR spectroscopy (Figure 2b,c). As explained above, the solid-state 13 C NMR spectra of the COF were carried out using the PAN layer-removed thin COF film. The characteristic peak at ∼183 and 107 ppm reveals the presence of carbonyl (−C�O) and exocyclic (−C�C) carbon atoms, respectively.…”

Recent advances in the fabrication of organic solvent nanofiltration membranes using covalent/metal organic frameworks

“…2,6,25 As a burgeoning class of porous materials with ordered networks and good crystallinity, COFs have been considered an important material and excellent candid to form innovative separating layers and membrane applications. [26][27][28][29][30][31][32][33][34][35][36] The appeal of COFs lies in their array of desirable features including boasting well-organized structures, permanent porosity, high permeability, layered macromolecules, ease of modifying pores, customizability, high surface area, heat and chemical stability in aqueous and harsh media, hydrophilicity, structural diversity, crystallinity, and fully organic nature 37 These materials, consisting of lightweight elements such as H, B, C, N, and O linked through robust covalent connections, 37 were first synthesized by Yaghi's team in 2005 marking the commencement of their rapid development and widespread exploration across various scientific domains. [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54] Owing to the ordered channels, pre-design capabilities, structurally stabilized construction, and diverse bonding organizations, COFs have emerged as an excellent choice for the development of composite-based membranes.…”

COF‐Molecular Sieving Membrane Fabrication and Applications for Dye Separation

“…Based on size exclusion, molecular sieving membranes with ordered and controllable pores can display quick water permeance (pressure‐normalized flux) and great selectivity in the separation of bigger pollutants [35] . COFs are attractive options for producing high‐performance molecular sieving membranes because of their diverse topologies and easily adjusted functionality [36] . Despite many attempts, the development of COF polymer mixed matrix membranes (MMMs) has been sluggish, and there are only a few examples of continuous COF membranes fabricated on porous substrates being employed as separating membranes.…”

“…[35] COFs are attractive options for producing highperformance molecular sieving membranes because of their diverse topologies and easily adjusted functionality. [36] Despite many attempts, the development of COF polymer mixed matrix membranes (MMMs) has been sluggish, and there are only a few examples of continuous COF membranes fabricated on porous substrates being employed as separating membranes. Banerjee et al have reported the first self-standing COF membrane employed for organic-solvent nanofiltration (NF); [37] however, the membrane must be hundreds of micrometres thick without support to achieve mechanical stability.…”