A Stable Dual-Functional Fluorescent Sensor Derived from a Zn(II) Metal–Organic Framework for the Visual Detection of VB9 and Fe ³⁺

Vitamin B9 (VB9, also known as folic acid) and Fe 3+ play critical roles in biological, environmental, and industrial processes. However, an imbalance in their concentrations can lead to serious health and ecological issues. Fluorescent sensors serve as highly effective detection tools, enabling simple, rapid, and highly sensitive monitoring of VB9 and Fe 3+ . By means of a mixed-ligand strategy, a novel Zn(II) metal–organic framework (MOF), namely {[Zn 2 (BIBT) 2 (TPDC)(HCOO) 2 ]·2CH 3 OH} n ( JXUST-66, BIBT = 4,7-bi(1 H -imidazol-1-yl)benzo-[2,1,3]thiadiazole, H 2 TPDC = [1,1′:4′,1″-terphenyl]-4,4″-dicarboxylic acid) was synthesized and explored as a fluorescence sensor for VB9 and Fe 3+ detection. JXUST-66 exhibits a two-dimensional layered structure along with good fluorescence properties and stability. Further studies have revealed that JXUST-66 functions as a dual-functional fluorescent sensor for the selective detection of VB9 and Fe 3+, with detection limits determined to be 0.12 and 0.13 μM, respectively. Both experimental and theoretical results indicate that the fluorescence quenching of JXUST-66 by VB9 and Fe 3+ is attributed to the combined effects of förster resonance energy transfer and photoinduced electron transfer. Additionally, JXUST-66 was used to fabricate fluorescent portable composite films, lamp beads, and test papers, enabling the visual detection of VB9 and Fe 3+ . This work underscores a stable Zn(II) MOF-derived fluorescence platform for the selective and efficient sensing of VB9 and Fe 3+ .