Isophthalate and N-Chelating Linker-Based Luminescent Cd-MOF for "Turn-On" EtOH Sensing via RGB-Assisted Smartphone Platform and "Turn-Off" Fe Monitoring in Biodiesel Specimens.

Monitoring trace solvent and metal adulteration in biodiesel is crucial for quality control and commercialization. This study explores a mesoporous Cd(II)-MOF for dual-mode fluorescence sensing: "turn-on" detection of EtOH and "turn-off" monitoring of Fe in aqueous and biodiesel samples. Synthesized using N-chelating, π-conjugated 2,2'-bipyridine and μ-η,η,η bridging 5-hydroxyisophthalic acid, the MOF exhibits high phase purity, lamellar rod morphology, and high thermal stability, attributed to its robust framework, reinforced by supramolecular H-bonding and interlayer π-π stacking interactions. The MOF's blue luminescence enables rapid detection of EtOH (6.27-fold enhancement, LOD: 6.33 ppm, 40s response time) and Fe (>90% quenching, LOD: ≈1.17 μM, K: 1.318 × 10 M , 30 s response time). The EtOH sensing ensues via restriction of photo-induced electron transfer in the MOF, aided by hydrogen bonding with MOF hydroxyls and polarity effects, while Fe quenching arises from absorption competition quenching and electrostatic interactions. The sensor detects EtOH and Fe in pretreated biodiesels derived from Jatropha and waste cooking oil (recovery: 78-90% and 73-75%, respectively). Further, a 4.89-fold "turn-on" for EtOH and 81% quenching for Fe is evidenced when analytes are directly added into untreated Jatropha biodiesel. A smartphone-based RGB calibration further enhances real-time ethanol analysis, ensuring practical applicability.