Issue 46, 2021

Enhanced surface area and reduced pore collapse of methylated, imine-linked covalent organic frameworks

Abstract

Covalent Organic Frameworks (COFs) are thermally and chemically stable, nanoporous materials with high surface areas, making them interesting for a large variety of applications including energy storage, gas separation, catalysis and chemical sensing. However, pore blocking and pore collapse may limit their performance. Reducing the capillary forces by using solvents with low surface tension, like supercritical CO2, for activation, and the introduction of bulky isopropyl/methoxy groups were found to reduce pore collapse. Herein, we present an easy-to-use alternative that involves the combination of a new, methylated building block (2,4,6-trimethylbenzene-1,3,5-tricarbaldehyde, Me3TFB) with vacuum drying. Condensation of Me3TFB with 1,4-phenylenediamine (PA) or benzidine (BD) resulted in imine-linked 2D COFs (Me3TFB-PA and Me3TFB-BD) with higher degrees of crystallinity and higher BET surface areas compared to their non-methylated counterparts (TFB-PA and TFB-BD). This was rationalized by density functional theory computations. Additionally, the methylated COFs are less prone to pore collapse when subjected to vacuum drying and their BET surface area was found to remain stable for at least four weeks. Within the context of their applicability as sensors, we also studied the influence of hydrochloric acid vapour on the optical and structural properties of all COFs. Upon acid exposure their colour and absorbance spectra changed, making them indeed suitable for acid detection. Infrared spectroscopy revealed that the colour change is likely attributed to the cleavage of imine bonds, which are only partially restored after ammonia exposure. While this limits their application as reusable sensors, our work presents a facile method to increase the robustness of commonly known COFs.

Graphical abstract: Enhanced surface area and reduced pore collapse of methylated, imine-linked covalent organic frameworks

Supplementary files

Article information

Article type
Paper
Submitted
08 Sept. 2021
Accepted
09 Nov. 2021
First published
09 Nov. 2021
This article is Open Access
Creative Commons BY license

Nanoscale, 2021,13, 19446-19452

Enhanced surface area and reduced pore collapse of methylated, imine-linked covalent organic frameworks

E. Dautzenberg, M. Lam, G. Li and L. C. P. M. de Smet, Nanoscale, 2021, 13, 19446 DOI: 10.1039/D1NR05911D

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