Biomass-Derived Activated Carbon as a Fluorescent Probe for Sensitive Detection of Mercury (II) in Wastewater

Mercury (Hg²⁺) contamination in water poses severe environmental and health risks due to its extreme toxicity and bioaccumulation potential. Herein, we report a sulfur doped activated carbon derived from banana stem (BS-AC (400)), synthesized via H₂SO₄ activation and low-temperature annealing under N₂, as a low-cost yet highly efficient fluorescent probe for Hg²⁺ detection. Comprehensive characterization (XPS, FTIR, XRD, HR-TEM/SAED) confirmed successful heteroatom incorporation, high porosity, and graphitic domains. BS-AC (400) exhibited intense photoluminescence with a maximum emission at 335 nm upon 230 nm excitation, which was selectively and efficiently quenched by Hg²⁺ even in the presence of 14 competing metal ions. The sensor achieved a detection limit of 9.73 µM and demonstrated excellent reproducibility, photostability, and applicability in real water samples, achieving 94-103% recovery. Comparative analysis with recent biomass-derived sensors revealed that BS-AC (400) offers competitive sensitivity and superior selectivity, attributed to strong Hg²⁺-S interactions (soft-soft binding) and enhanced surface chemistry from heteroatom doping. These results highlight BS-AC (400) as a sustainable, scalable, and versatile platform for real-time mercury monitoring in environmental water systems.