Porphyrin-based metal-organic framework and polyvinylchloride composites for fluorescence sensing of divalent cadmium ions in water

Toxic metal contamination of Earth’s scarce fresh water sources creates a persistent necessity for the development of new materials and techniques to detect metal ions in water. Cadmium in particular is released into the environment by ubiquitous phosphate fertilizers, and chronic cadmium exposure can lead to internal organ damage and bone weakening. The present study shows that NU-902, a water stable zirconium porphyrin-based metal-organic framework (MOF), is fluorescent and undergoes a detectable change in photoluminescent emission properties in the presence of divalent cadmium ions. The MOF displays detectable fluorescence quenching in the presence of cadmium at levels of 0.3 ppb, far below concentrations deemed acceptable by most regulatory agencies, indicating its potential as a fast, reliable chemosensor for cadmium in drinking water. After establishing the fluorescent properties of the powder MOF, it was immobilized within plasticized polyvinylchloride (PVC) to create a membrane with potential for easy in field use as a sensor. The MOF-PVC composite displayed fluorescence quenching within five minutes of exposure to an aqueous cadmium solution. This study shows the potential use of a water stable porphyrin-based MOF for fast, sensitive detection of metal ion contamination in water in powder form, as well as in a polymer composite.