Molecular Hosts for the Sensing and Separation of ⁹⁹TcO₄

In recent years, European Union member states have hastened energy policy deliberations to address supply and sustainability concerns, placing a significant emphasis on nuclear energy as a means to achieve decarbonization goals. However, despite its significant role in power generation, nuclear energy faces significant challenges linked to fuel reprocessing and waste disposal, that hinder its broader expansion. In this context, the separation of technetium represents a concerning issue. Indeed, technetium's catalytic activity can impede the extraction of uranium, neptunium, and plutonium, affecting waste reprocessing efficiency. Additionally, the stable form of technetium in aerobic conditions, pertechnetate (TcO₄ ^-), poses risks of groundwater contamination due to its mobility and solubility. Hence, sensing and separation of TcO₄ ^- is imperative for both nuclear fuel processing and minimising radioactive contamination in the environment. However, the binding of TcO₄ ^- and its separation from contaminated solutions present challenges due to the acidic (or basic) waste components and the high ionic strength in real matrices. Supramolecular chemists have addressed these issues by designing receptors inspired by molecular recognition principles. This article explores recent advancements and future directions in TcO₄ ^- sensing and separation (using extraction and sorption) with a focus on molecular hosts. Metal-organic receptors will also be discussed.