Covalent organic frameworks comprise a unique class of functional materials that has recently emerged as a versatile tool for energy-related, photocatalytic, environmental, and electrochromic device applications. A plethora of structures can be designed and implemented through a careful selection of ligands and functional units. On the other hand, porous materials for heavy metal absorption are constantly on the forefront of materials science due to the significant health issues that arise from the release of the latter to aquatic environments. In this critical review, we provide insights on the correlation between the structure of functional covalent organic frameworks and their heavy metal absorption. The elements we selected were Pb, Hg, Cr, Cd, and As metal ions, as well as radioactive elements, and we focused on their removal with functional networks. Finally, we outline their advantages and disadvantages compared to other competitive systems such as zeolites and metal organic frameworks (MOFs), we analyze the potential drawbacks for industrial scale applications, and we provide our outlook on the future of this emerging field.
Covalent triazine frameworks (CTFs) synthesized through nucleophilic substitution of 4,4’ bipyridine on the carbon atoms of cyanuric chloride were studied as fluorescent sensors. The band gap of the materials was...
In
this work, we reveal the coordination of copper ions absorbed
by a series of covalent organic frameworks. The frameworks were synthesized
through the nucleophilic substitution of either cyanuric chloride
or phosphonitrilic chloride trimer by 4,4′-bipyridine, and
they were utilized as absorbers for the removal of copper ions from
aqueous solutions. The exfoliated counterpart of the layered network
was compared to the bulk materials in terms of the copper retention
capacity and efficiency. The ion absorption capacity of copper ranged
from 100 to 290 mg/g depending on the morphology and chemical structure
of the framework. As evidenced by the SEM and XRD analysis, the copper
absorption induced certain morphological changes in the networks.
EPR spectroscopy revealed the key finding of this study: the trigonal
bipyramidal configuration of the copper ions in their divalent state,
coordinated with the nitrogen of the core units, 4,4′-bipyridine,
and chlorine ions. The analysis of the thoroughgoing experiments
bridges the gap between coordination molecular chemistry and the field
of covalent organic frameworks. EPR explores how the unique trigonal
bipyramidal coordination could be suppressed in the end by the environment
and, more specifically, by the addition of glycerol to the aqueous
dispersions of the covalent organic frameworks.
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