Real-Time Uranyl Ion Adsorption Monitoring Based on Cellulose Hydrogels

Hydroxypropyl cellulose has attracted significant attention due to its unique structure and optical properties. However, its inherent rigidity and large pitch limit its application in the visual sensing of heavy metal ions and as flexible films. In this article, we designed and fabricated flexible structural color hydrogels via photocuring cellulose with acrylamide and acrylic acid. The resulting composite hydrogel showed excellent flexibility, with the toughness of the hydrogel containing 50 wt % cellulose reaching 107.42 kJ m^–3. This enhancement is attributed to the intercalation of acrylamide and acrylic acid into the periodic structure of cellulose through hydrogen bonding. The hydrogel (G50) with 50 wt % cellulose also demonstrated high water retention, maintaining 97.21% retention even after 12 h in saturated brine. Using the uranyl ion as a model, G50 exhibited a maximum adsorption capacity of 572.3 mg/g and showed good selectivity among mixed nuclide ions and alkali metal ions. The adsorption process was identified as chemisorption, fitting well with the Freundlich isotherm and pseudo-second-order model. The minimum detection limit was 100 mg/L, accompanied by a color shift from red to purple. X-ray photoelectron spectrometry and molecular simulation revealed that the adsorption mechanism of UO₂²⁺ involved coordination with amido and carboxyl groups, as well as electrostatic interaction. These findings expand the potential for resource utilization of natural products and enhance the application of cellulose in visual analysis and detection.