Ultranarrow bandgap-engineered redox-active organic material for high-efficiency Sr²⁺ removal via capacitive...

Nuclear wastewater discharge has exacerbated the global freshwater crisis, as radioactive strontium (Sr), a persistent and mobile fission product, progressively accumulates in ecosystems and human skeletal tissues, thereby posing serious ecological and health risks. Although capacitive deionization (CDI) is considered as an energy-efficient and environmentally benign technology, its practical application for Sr²⁺ removal remains limited by the inadequate performance and potential secondary environmental risks associated with conventional carbon- and metal-based electrodes. Herein, we report for the first time a novel metal-free organic material, TDPH, designed specifically for efficient Sr²⁺ capture via CDI approach. Owing to its π-electron-delocalized architecture, ultra-narrow HOMO-LUMO gap (1.23 eV), and redox-active CO and CN moieties, TDPH exhibits markedly enhanced electrochemical behaviors toward Sr²⁺ uptake. As a proof of concept, the TDPH-based CDI device delivers a record-high Sr²⁺ removal capacity of 205 mg g^-1 and a rapid rate of 5.10 mg g^-1 min^-1 at 1.2 V, surpassing conventional electrodes. Moreover, the CDI device demonstrates high selectivity and regeneration stability, maintaining 91.5 % removal efficiency over 200 cycles in a multicomponent solution. This work not only illustrates a molecular-level design strategy for organic CDI electrodes but also opens a sustainable pathway for selective radionuclide remediation.