MB-UiO-66-NH₂ Metal-Organic Framework as Chromogenic and Fluorogenic Sensor for Hydrazine Hydrate in Aqueous Solution

Zirconium(IV)-based MOFs UiO-66-NH₂ and UiO-66-NH₂ encapsulated with methylene blue (MB) MB-UiO-66-NH₂ were successfully prepared using a facile solvothermal method and were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), nitrogen physisorption analysis (BET), and X-ray and photoelectron spectroscopy(XPS). Both the materials were 60–80 nm size and had large surface areas. MB-UiO-66-NH₂ appears to be a potential candidate for the sensing of hydrazine hydrate. Selective changes in both the chromogenic and fluorogenic characteristics of MB-UiO-66-NH₂ were observed upon treatment with hydrazine hydrate in an aqueous solution. The change in the photophysical properties of the MB-UiO-66-NH₂ was attributed to the selective conversion of methylene-blue-encapsulated UiO-66-NH₂ to leucomethylene blue (LB) after the addition of hydrazine hydrate to the aqueous solution. The hydrazine hydrate detection limit for MB-UiO-66-NH₂ was found to be 0.012 ppm in the aqueous solution.