A smart self-indicating metal–organic framework with real-time fluorochromic response for ultraselective thorium remediation

The efficient separation and simultaneous detection of thorium from complex aqueous environments remain a critical challenge in radioactive waste management, where minimizing secondary waste and reducing adsorbent consumption are paramount. Here we report a fluorochromic metal–organic framework (MOF), Eu-NDC, that functions as a self-indicating adsorbent for ultraselective Th(IV) sensing and separation. Eu-NDC exhibits a distinctive red-to-blue emission transition upon Th(IV) binding, achieving an ultralow detection limit of 9.2 nM while selectively distinguishing Th(IV) from other tetravalent cations. Furthermore, the material combines high Th(IV) adsorption capacity (504.3 mg g⁻¹) with superior selectivity, indicated by a distribution coefficient of 2.8 × 10⁶ml g⁻¹ and a Th(IV)/U(VI) separation factor of 1,806. Mechanistic studies reveal that Th(IV) uptake occurs via a dissolution–recrystallization process. Importantly, the fluorochromic response of Eu-NDC provides a self-indicating capability, whereby changes in emission colour directly reflect adsorption progress. This dual-functionality, integrating ultraselective adsorption with direct optical feedback, establishes MOFs as a multifunctional platform for smart, self-indicating radionuclide separation and environmental remediation.