Carboxymethyl micro-nanocellulose enhanced cellulose-based fluorescent membranes for the selective detection of Cu²⁺ and Hg²⁺

A CA-CMCNF-CDs fluorescent sensing membrane was developed by incorporating carboxymethylated micro/nanocellulose (CMCNF) and carbon dots into a cellulose acetate (CA) matrix for the selective detection of Cu²⁺ and Hg²⁺ in water. The incorporation of an appropriate amount of CMCNF significantly improved the fluorescence intensity, mechanical properties, and sensing performance of the membrane by generating an interconnected porous structure that facilitated metal-ion transport. The proposed sensing membrane exhibited a wide linear detection range (0–10 mg/L), low detection limits of 0.040 mg/L for Cu²⁺ and 0.034 mg/L for Hg²⁺, together with excellent selectivity and anti-interference capability. Mechanistic studies revealed that oxygen- and nitrogen-containing functional groups served as the primary coordination sites for Cu²⁺ and Hg²⁺. Fluorescence quenching was dominated by static quenching through the formation of ground-state coordination complexes, whereas Hg²⁺ additionally involved dynamic quenching, as confirmed by fluorescence lifetime analysis. The sensing membrane exhibited satisfactory accuracy and precision for the determination of Cu²⁺ and Hg²⁺ in real water samples, demonstrating its potential as a rapid and reliable fluorescent sensing platform for environmental heavy metal monitoring.