Methylene blue (MB), a persistent dye with potential carcinogenicity, poses serious threats to both human health and environmental safety. Therefore, accurate monitoring of MB in aquatic systems is essential for the assessment of water quality. In this study, we report a dual mode optical detection strategy based on a cerium–benzene-1,3,5-tricarboxylate metal–organic framework supported on microcrystalline cellulose (Ce-BTC@MCC). The composite was synthesized and characterized using FTIR, SEM, EDX, XRD, and BET analyzes. Two sensing strategies were developed: (i) a powder-based Ce-BTC@MCC sensing system and (ii) an optical sensing film fabricated by incorporating Ce-BTC@MCC into carboxylated poly (vinyl chloride). Both platforms are based on fluorescence detection of MB, with emission at 677 nm upon excitation at 611 nm. The powder-based system provided a linear response in the range of 10 to 200 ppb with a detection limit of 2.7 ppb, while the film-based sensor exhibited a range of 25 to 200 ppb with a detection limit of 4.0 ppb. Both sensing modes demonstrated excellent selectivity against structurally similar industrial dyes, including Congo Red, Indigo Carmine, Malachite Green, Bromophenol Blue, Methyl Orange, and Rhodamine B. The validation of the method by spiking tap and wastewater samples yielded recovery rates between 91.1% and 106.8%, confirming robustness and practical applicability. Furthermore, the sensing film showed high reversibility and reproducibility. These findings highlight the potential of Ce-BTC@MCC-based dual fluorescence sensing systems for monitoring ultratrace concentrations of MB in environmental water sources.
Mobarez et al. (Mon,) studied this question.