Crystalline 2D Covalent Organic Framework Membranes for High-Flux Organic Solvent Nanofiltration

Abstract

Two-dimensional (2D) covalent organic framework (COF) materials have the most suitable microstructure for membrane applications in order to achieve both high flux and high selectivity. Here, we report the synthesis of a crystalline TFP-DHF 2D COF membrane constructed from two precursors of 1,3,5-triformylphloroglucinol (TFP) and 9,9-dihexylfluorene-2,7-diamine (DHF) through the Langmuir-Blodgett (LB) method, for the first time. A single COF layer is precisely four-unit-cell thick and can be transferred to different support surfaces layer-by-layer. The TFP-DHF 2D COF membrane supported on anodic aluminum oxide (AAO) porous supports displayed remarkable permeabilities for both polar and nonpolar organic solvents, which were approximately 100 times higher than that of the amorphous membranes prepared by the same procedure and similar to the best of the reported polymer membranes. The transport mechanism through the TFP-DHF 2D COF membrane was found to be a viscous flow coupled with a strong slip boundary enhancement, which was also different from those of the amorphous polymer membranes. The membrane exhibited a steep molecular sieving with a molecular weight retention onset of approximately 600 Da and a molecular weight cut-off of approximately 900 Da. The substantial performance enhancement was attributed to the structural change from an amorphous structure to a well-defined ordered porous structure, which clearly demonstrated the high potential for the application of 2D COFs as the next generation of membrane materials.

Acid Exfoliation of Imine‐linked Covalent Organic Frameworks Enables Solution Processing into Crystalline Thin Films

“…Furthermore, they retained up to 80 % of the powder surface area as confirmed by nitrogen adsorption measurements (Figure S41), as well as the characteristic FT‐IR imine stretch at approximately 1620 cm −1 (Figure S44). These materials ( S BET =1750 m 2 g −1 ) represent some of the highest quality freestanding COF films reported to date …”

Enzyme‐Decorated Covalent Organic Frameworks as Nanoporous Platforms for Heterogeneous Biocatalysis

“…Carbon atoms in the C=O group were observed at 288.1, 288.7 and 289.2 eV and the peaks at 291.5, 290.7 and 290.9 eV were attributed to the C(H)=O of the aldehyde group. Signals referent to C=O, C−O, and O−H were also observed in the spectra of O 1s (Figure d–f) …”

“…Signals referentt oC =O, CÀ O, and OÀHw ere also observedi nt he spectra of O1s ( Figure 3d-f). [42][43][44] An itrogen/oxygen ratio (N/O) of 0.72 was observed for the PPF-2.C onsidering that both PPF-2-CHO and PPF-2-NH 2 were synthesized with excesso fo ne type of the building blocks, it was expected that this approach would generateachange in the surface composition, thus increasing the N/O ratio forP PF-2-NH 2 and decreasing for PPF-2-CHO. As expected, PPF-2-NH 2 presentedagreater nitrogen/oxygen ratio than PPF-2 (0.94), consequence of free NH 2 groups on the surface due to the excesso fT TA during the synthesis, whereas PPF-2-CHO presentedas maller N/O ratio (0.35),d ue to the free CHO groups on the surface, showing that the surfacec ompositionc an be modulated by changing the molar ratio between the building blocksi nt he synthesis.…”

Interfacial Synthesis of a Monolayered Fluorescent Two‐Dimensional Polymer through Dynamic Imine Chemistry

“…The structure change from 1D to 2D at the molecular level is particularly interesting and promising for applications in optoelectronic devices, energy conversion, sensors, and biomimetic devices . In addition, the 2D, ultrathin and porous natures of the 2DPs are efficiently utilized in osmotic energy conversion, also demonstrating high‐performance power capture by mixing artificial river water and sea water . Therefore, the 2DPs provide new prospects of potential applications in promising fields such as the salinity gradient energy conversion and ion screening .…”

“…[27][28][29] In addition, the 2D, ultrathin and porous natures of the 2DPs are efficiently utilized in osmotic energy conversion, also demonstrating high-performance power capture by mixing artificial river water and sea water. [30][31][32] Therefore, the 2DPs provide new prospects of potential applications in promising fields such as the salinity gradient energy conversion and ion screening. [33][34][35] Nevertheless, the synthesis of the 2DPs is usually challenging, especially the monolayer synthesis.…”