Abstract
Despite the rapid development of two-dimensional covalent organic frameworks (2D COFs) in recent years, it remains a great challenge to synthesize highly crystalline COF materials. Here, a CNC-assisted approach was adopted to synthesize high crystallinity COF materials. A series of 2D COF films were synthesized at the air–water interface by using cellulose nanocrystals (CNCs) as the template. The occurrence of Schiff reactions based on the imine bond was demonstrated by Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). Scanning electron microscopy (SEM) exhibited the appearances of 2D COF films were flower-like. When CNCs were added to a certain extent, the size of a single petal in the flowers gradually increased with the amount of CNCs. The film with large petals was characterized by Ultraviolet–Visible diffuse reflectance spectroscopy (UV–Vis DRS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). In UV–Vis DRS curves, the S-band of COF-366 film was red-shifted by 24 nm compared with that of 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H-porphyrin (TAPP), confirming the existence of extended conjugation in COF-366 film. XPS was used to identify the surface composition of the sample. The N1s signal of the film indicated that each TAPP formed four imine bonds with 2,5-dihydroxyterephthalaldehyde (DHTA) in COF-366 film. TEM images showed that CNCs had an influence on the crystal size. It was observed from SAED that the crystallinity of the film with CNCs was higher than the film without CNCs. This work provided a new template for improving the crystallinity of 2D COF films.
Highlights
Two-dimensional covalent organic frameworks (2D COFs), as a new class of crystalline porous materials [1,2,3], have attracted great attention and exhibited broad application prospects in many fields such as gas adsorption and separation [4,5], catalysis [6,7,8], electrochemistry [9,10], molecular electronics [11], and so on
This work provided a new template for improving the crystallinity of 2D COF films, which broadens the potential application of cellulose nanocrystals (CNCs)
TAPP and DHTA constituted the basic framework structure, the co-reagent p-toluenesulfonic acid monohydrate (PTSA) was used as the acid catalyst to help the reaction proceed [33], and CNCs were used as a template to improve the crystallinity of the film
Summary
Two-dimensional covalent organic frameworks (2D COFs), as a new class of crystalline porous materials [1,2,3], have attracted great attention and exhibited broad application prospects in many fields such as gas adsorption and separation [4,5], catalysis [6,7,8], electrochemistry [9,10], molecular electronics [11], and so on. Due to the poorly controlled nucleation and growth processes, the resulting 2D COFs usually form insoluble amorphous or polycrystalline thin films with small crystalline domains (usually less than 50 nm) [17,18]. To meet these challenges, many approaches have been attempted. As the amorphous regions in the cellulose are removed by acid hydrolysis, the resulting CNCs often showed a high crystallinity and a high aspect ratio These characteristics of CNCs make it a feasible template for the preparation of crystalline material. This work provided a new template for improving the crystallinity of 2D COF films, which broadens the potential application of CNCs
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
