Porphyrinic MOFs for reversible fluorescent and colorimetric sensing of mercury(II) ions in aqueous phase

Developing an effective method that could provide simple, rapid and visual determination of Hg2+ in water has attracted great attention. In this work, a novel chemical sensor with a porphyrin-based luminescent metal-organic framework (LMOFs) which exhibited a dual-mode response to trace amounts of mercury ions (Hg2+) has been successfully constructed. The porous LMOF probe was fabricated using a simple solvothermal reaction, and assembled with Zr-O clusters as inorganic nodes and meso-tetra(4-carboxyphenyl) porphyrin (TCPP) ligands as organic bridging struts. The sensing activity was realized by using the inherent TCPP struts as recognition sites and signal reporter, which presented a specific interaction with Hg2+ over other potentially interfering metallic cations. The LMOFs which were developed exhibited a visible fluorescent quenching (bright red-dark red) and a colorimetric response (purple-light green) in the presence of Hg2+ with a response rate as rapid as 2 min. Additionally, the fluorescence quenching showed a linear correlation in the Hg2+ concentration range from 0.1 to 10 mM and the limit of detection was calculated to be 6 nM, which was in agreement with the acceptable level of Hg2+ in drinking water mandated by the United States Environmental Protection Agency. Furthermore, the sensor for Hg2+ detection was reversible after the treatment with potassium iodide solution, which suggested that it has great potential as an economical alternative for practical Hg2+ quantification in water. The easily constructed sensory probe was also applied to determine the concentration of Hg2+ in tap water to demonstrate its practical applications.