Selective Molecular Sieving in Self‐Standing Porous Covalent‐Organic‐Framework Membranes

Abstract

Self-standing, flexible, continuous, and crack-free covalent-organic-framework membranes (COMs) are fabricated via a simple, scalable, and highly cost-effective methodology. The COMs show long-term durability, recyclability, and retain their structural integrity in water, organic solvents, and mineral acids. COMs are successfully used in challenging separation applications and recovery of valuable active pharmaceutical ingredients from organic solvents.

Ultrastable Imine‐Based Covalent Organic Frameworks for Sulfuric Acid Recovery: An Effect of Interlayer Hydrogen Bonding

“…[4] We have already attempted to overcome the stability issues in COFs,b yi ntroducing the enol to keto tautomerization phenomenon during the framework crystallization. [6] However, for the widespread implementation of such chemically stable imine based COFs,t he synthetic process should:1 )bed evoid of toxic solvents or synthetic difficulty, [5] 2) be rapid and easily scalable (unlike the traditional solvothermal process), [5,7] and 3) provide the opportunity to process the as-synthesized COFs into pellets,beads as well as membranes keeping their properties intact. [4a, 5] However,t his idea is entirely restricted to b-ketoenamine COFs,w hich provides minimal substrate scope and thus are limited in their widespread exploration.…”

“…By using this approach, we could achieve as et of COFs with significantly enhanced chemical stability (aqueous,a cid, and base). [5] Keeping all these in perspective,h erein, we report 2,4,6trimethoxy-1,3,5-benzenetricarbaldehyde (TpOMe) as ap rime aldehyde building unit for scalable and rapid construction of six new stable imine-linked COFs via the PTSA (p-toluenesulfonic acid)-mediated solid-state mixing approach (Figure 1a;S upporting Information, Figure S4, Section S2). Hence,i ti s necessary to diversify this approach and extend this idea for the production of more versatile ÀC=NÀ (imine) linked COFs.T he exploration of imine-based COFs has increased dramatically in recent years owing to their superior hydrolytic stability compared to boronic acid COFs along with their extensive substrate-library availability.…”

“…[4a, 5] However,t his idea is entirely restricted to b-ketoenamine COFs,w hich provides minimal substrate scope and thus are limited in their widespread exploration. [5] Thei ntroduction of three bulky methoxy ( À OCH 3 )g roups adjacent to the aldehyde (ÀCHO) functionalities provide significant steric hindrance,a nd the hydrophobic environment around the imine bonds promotes impregnable COF crystallization. [6] However, for the widespread implementation of such chemically stable imine based COFs,t he synthetic process should:1 )bed evoid of toxic solvents or synthetic difficulty, [5] 2) be rapid and easily scalable (unlike the traditional solvothermal process), [5,7] and 3) provide the opportunity to process the as-synthesized COFs into pellets,beads as well as membranes keeping their properties intact.…”

“…[5] However,the exploration of the PTSA mediated solid-state mixing approach is not straightforward for the construction of imine-linked COFs.T he primary concern is the chemical stability of the as-synthesized frameworks under the given reaction conditions.O wing to the intense acidic nature of PTSA (pK a = À2.8;water), the imine-linked COF crystallites, during the framework formation, readily decompose under the experimental conditions,leading ahigh extent of amorphization (Supporting Information, Figures S5-S7). [5] However,the exploration of the PTSA mediated solid-state mixing approach is not straightforward for the construction of imine-linked COFs.T he primary concern is the chemical stability of the as-synthesized frameworks under the given reaction conditions.O wing to the intense acidic nature of PTSA (pK a = À2.8;water), the imine-linked COF crystallites, during the framework formation, readily decompose under the experimental conditions,leading ahigh extent of amorphization (Supporting Information, Figures S5-S7).…”

Tailoring Covalent Organic Frameworks To Capture Water Contaminants

“…Using COFs as the main component of a hybrid membrane, highly size‐selective materials can be obtained taking advantage of the highly ordered crystalline COF structures, with customizable channels typically ranging from ≈0.7–4.7 nm . In addition, due to the reduced thickness of the obtained hybrid membranes, higher permeance can be achieved when compared to conventional polymeric membranes …”