Pollutant removal with organic macrocycle-based covalent organic polymers and frameworks

doi:10.1016/j.chempr.2021.01.002

Chem

Volume 7, Issue 4, 8 April 2021, Pages 882-918

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The bigger picture

The problems of environmental pollution and its consequences are so severe that clean water and good health and well-being have been designated as two of the UN sustainable development goals. Researchers in various fields are looking for ways to remove pollutants from the environment. Materials scientists have largely contributed to this goal by developing materials that can serve as capturers of toxic molecules present in contaminated waters, air, or soil. A potent adsorbent material needs to form non-covalent interactions with pollutants that are strong enough to prevent dissociation during the adsorption yet weak enough for the interaction to be reversible. Organic macrocycles are some of the best candidates in this regard. Incorporating them into covalent polymeric structures brings additional advantages of robustness, stability, and insolubility. Some of these systems have already been commercialized, while others are still rather unexplored.

Summary

Air, water, and soil pollution devastate countless ecosystems and deteriorate human health. Adsorption has commonly been used as a pollutant removal technique, but ongoing materials science research is still searching for more efficient, cheaper, and scalable sorbent materials. Herein, we discuss the synthesis and pollutant-capturing abilities of covalent polymeric structures, including covalent organic polymers and covalent organic frameworks that contain organic macrocycles in the backbone of their structures. These organic macrocycles (cyclodextrin, calixarene, cucurbituril, pillararene, and porphyrin) possess cavities and functional groups that can sequester pollutants by forming supramolecular interactions. The insolubility of these materials prominently aids in their regeneration and recyclability potentials. Following a discussion on the synthetic strategies used in the polymerization of each type of macrocycle, environmental applications of these materials are presented. Here, we focus on the removal of micropollutants, charged species, metal ions, oils and organic solvents, perfluorinated substances, iodine, and volatile organic compounds.

Graphical abstract

UN Sustainable Development Goals

SDG6: Clean water and sanitation

Keywords

supramolecular interactions

host-guest chemistry

organic macrocycles

covalent polymers

covalent organic frameworks

adsorption

environmental remediation