Gum Acacia-grafted multifunctional fluorescent hydrogel for ultra-trace sensing and sustainable recovery of samarium(III)

Samarium (Sm) is an important rare earth element (REE) critical for permanent magnets, nuclear technologies, and advanced electronics. Limited accessibility and recent supply-chain disruptions associated with Sm have motivated efforts towards its recovery and reuse from waste streams. Existing approaches typically focus on either detection or recovery, thereby triggering the necessity for single reusable material serving as a platform for selective Sm(III) sensing, recovery, and post-adsorption applications. Herein, we report the design of a recyclable multifunctional gum acacia-grafted fluorescent copolymer hydrogel (GAFluoroCoP), which exhibits simultaneous selective sensing, efficient adsorption, and recovery of Sm(III) within a single framework. The GAFluoroCoP is synthesized via a one-pot strategy coupling 2-methylidenebutanedioic acid and methyleneacetic acid (synthetic) with naturally occurring gum acacia (GA), resulting in a material that exhibits self-healing, pH-responsive swelling, and moist adhesion properties. Importantly, GAFluoroCoP hydrogel displays intrinsic blue fluorescence with selective turn-off sensing of Sm(III) at ultra-trace concentrations (limit of detection = 37.5 pM), while simultaneously showing high adsorption capacity (127 mg g⁻¹), rapid uptake kinetics, and efficient desorption over five cycles, thereby demonstrating its reusability. Furthermore, the Sm-loaded GAFluoroCoP (SmGAFluoroCoP) exhibits semiconducting behavior (E<inf>gap</inf> = 1.44 eV), electrochemical stability up to 500 bending cycles, and oxidative stress-mediated cytotoxicity, indicating potential electronic and biomedical applications. Collectively, this work establishes a closed-loop strategy for Sm management by integrating biopolymer-enabled fluorescence sensing, adsorption-enrichment, and sustainable recovery, thereby advancing environmentally compatible rare earth element recycling technologies.