A phenothiazine metal-organic frameworks for highly efficient detection of trace S2O42−/CrO42−

The selective recognition of trace amounts of CrO₄ 2− and S₂O₄ 2− individually in aqueous solutions using a single metal-organic framework (MOF) platform has been scarcely explored. In this study, a ligand, 3,7-di(4-pyridyl) phenothiazine, was synthesized and employed to develop a zinc-based MOF (Zn-PTZpy) through a solvothermal process. The resulting Zn-PTZpy material exhibited strong luminescent characteristics. Acting as a dual fluorescent sensor for CrO₄ 2− and S₂O₄ 2− , Zn-PTZpy showed remarkable chemical stability and enabled highly selective detection of chromate ions (CrO₄ 2− ) through a fluorescence quenching process, exhibiting a high Stern-Volmer quenching constant ( K sv ) of 3.56 × 10 4  M −1 . In addition, when Zn-PTZpy interacted with dithionite (S₂O₄ 2− ) in aqueous solution, a pronounced fluorescence enhancement was observed, with an amplification constant ( K sv ) of 6.69 × 10 3  M −1 . The framework exhibited strong resistance to interference from other ions and achieved low detection limits of 0.09 μM for CrO₄ 2− and 0.12 μM for S₂O₄ 2− . Moreover, Zn-PTZpy demonstrated a rapid response, with detection times of 10 s for CrO₄ 2− and 3 min for S₂O₄ 2− . The Zn-PTZpy material exhibited remarkable effectiveness in real environmental and sample analyses, confirming its strong potential for practical applications. In addition, the Zn-PTZpy sensor achieved satisfactory recovery rates ranging from 93% to 111% when tested with spiked lake water samples. For the first time, this study presents the dual functional potential of Zn-PTZpy for applications in environmental monitoring.