Organic ligands for the development of adsorbents for Cs+ sequestration: A review

Sorbents utilizing organic molecules as Cs+-selective ionophores have increasingly gained attention over the years as the need for stable and reusable materials became ever more apparent with the poor performance of inorganic sorbents in acidic and alkaline aqueous environments. Aside from this, organic molecules offer a great degree of flexibility in terms of structure, function, and performance which can be harnessed for sorbent development. As such, various kinds of organic ligands have been employed for sorbent preparation, which include macrocycles like calixarenes and crown ethers, and acyclic molecules like tetraphenylborate and resorcinol formaldehyde. In this review, organic-based sorbents and ligands for Cs+ are described and compared, and the mechanisms underlying their efficacy for Cs+ sequestration are discussed. Improvements to ligand and sorbent development are proposed to address issues on adsorption selectivity, capacity, and material reusability. Moreover, a platform for the preparation of stimuli-responsive ligands and sorbents is presented.