Redox‐Induced Sequestration of Oxoanions: Detoxification of Cr(VI) and Immobilization of TcO ₄ ⁻ at ppb Level in Aqueous Systems

Metal oxoanions present significant challenges because of their high solubility in water and their charge characteristics. Among these, carcinogenic chromate and radioactive pertechnetate are particularly concerning. Conventional adsorbents often suffer from low recyclability and reduced selectivity to remove oxoanionic pollutants. Herein, we report a guanidinium-based porous organic polymer (POF-3) that selectively adsorbs CrO₄ ^2-and TcO₄ ^- from real-life water samples. POF-3 displays maximum adsorption capacities of 123 mg g^-1 for chromate and 177 mg g^-1 for perrhenate at pH = 6. The removal efficiency of POF-3 at low concentrations of chromate and pertechnetate is very far below the corresponding EPA limit. The adsorption mechanism mainly follows electrostatic interaction and the ion exchange mechanism. Reducing carcinogenic Cr(VI) to Cr(III) is a crucial step; introducing thiophene in the structural backbone of POF-3 facilitates the redox properties. Morphological transformation into a sheet-like structure confirms the effective sorption of chromate and perrhenate. In this context, NMR titration of monomeric compound also suggests interaction of POF-3(M) with guanidium sites of material towards chromate and perrhenate effectively, as proven by solid phase study. These effective adsorption capacities, faster kinetics, and ion exchange ability make it a promising solution for environmental remediation.