Fluorescent Eu-MOF@nanocellulose-based nanopaper for rapid and sensitive detection of uranium (Ⅵ)

Radioactive uranium leaks into natural water bodies mainly in the form of uranyl ions (UO₂²⁺), posing ecological and human health risks. Fluorescent europium-based metal-organic frameworks (Eu-MOFs) have been demonstrated to be effective fluorescent sensors for UO₂²⁺, but the large size, powder state and poor dispersity limit their further application. In this work, fluorescent Eu-MOFs were in-situ grown on TEMPO-oxidized cellulose nanofibers (TOCNFs), which is the first time that spherical Eu-MOF crystals with sizes below 10 nm were prepared. Fluorescence spectral analysis revealed a nine-fold increase in the fluorescence intensity of TOCNF@Eu-MOF compared to Eu-MOF. The nanocomposites achieved rapid and sensitive fluorescence quenching to UO₂²⁺ through the "antenna effect" and unsaturated Lewis basic sites on the ligands binding with UO₂²⁺. Moreover, TOCNF@Eu-MOF demonstrated excellent selectivity and anti-interference for UO₂²⁺ detection. For the nanopaper-based sensor made from TOCNF@Eu-MOF, the Stern-Volmer quenching constant (K_SV) was calculated as 8.21 × 10⁴ M^-1, and the lowest limit of detection (LOD) was 6.6 × 10^-7 M, significantly lower than the 1.32 × 10^-6 M of Eu-MOFs. In addition, the nanopaper exhibited good fluorescence stability and cyclic detection performance, enabling the rapid and convenient detection of UO₂²⁺ in the aqueous phase within 30 s by simple dipping.