Eco‐Friendly Nanocellulose‐Based Fluorometric Sensor for Ultra‐Sensitive Detection and Removal of Mercury Ions From Water

A novel solid‐state fluorometric sensor based on wastepaper‐derived nanocellulose (NC) functionalized with 4‐hydroxy‐3‐(((2‐mercaptophenyl)imino)methyl)benzyl)triphenylphosphonium hexafluorophosphate (TPPAT) was developed for the ultra‐sensitive detection and simultaneous removal of Hg 2+ ions from water. The NC‐TPPAT composite exhibits a linear detection range of 0–50 μM and a limit of detection (LOD) of 4.11 × 10 −8 M with the fluorescence technique and 3.31 × 10 −8 M with UV–Vis technique. Rapid fluorescence response kinetics achieve signal equilibration within 100 s under optimized conditions (pH 4.5, 25 °C, 30 mg sensor dose). In parallel, batch adsorption studies revealed a Langmuir monolayer capacity of q max = 225.6 mg g −1 and pseudo‐second‐order kinetics (R 2 = 0.996), with equilibrium reached at 60 min (pH 5.3, 25 °C). Selectivity assays demonstrated negligible interference (< 5% signal deviation) from competing metal ions, including Cu 2+ ions. The sensor maintains > 90% performance over five reuse cycles. This integrated NC‐TPPAT platform combines eco‐friendly material design, high sensitivity, and efficient Hg 2+ ions removal, achieving a remarkable removal efficiency of up to 97.42%, offering a practical approach for real‐time environmental monitoring and water purification.