A Highly Selective Ammonia Ratiometric Fluorescence Sensor Based on Multifunctional Metal–Organic Framework Platform with Rich Brønsted Acidic Metal Clusters

Ammonia is a critical chemical in industry and our daily life, but its corrosiveness and toxicity also require enough attention. With the increasing pursuit of beauty, the safety of cosmetics has aroused widespread concern. Aqueous ammonia has been widely used as a universal additive in cosmetics, especially in different types of hair dye products. However, a high concentration of ammonia is toxic to human beings. In addition, improper treatment and discharge of substances with high ammonia content can also cause pollution of human domestic water. Therefore, it is of great significance to accurately monitor the level of aqueous ammonia in relative cosmetics for safe beauty and in our domestic water for daily health. In this work, a highly selective and sensitive ratiometric fluorescent sensor UiO-66-NH₂@O170 was carefully designed to quickly and accurately detect the concentration of aqueous ammonia in different brands of hair dyes and human domestic water. The detection limit was as low as 83.5 nM, and the recovery rate ranged from 98.2 to 102.9%. In addition, while evaluating the actual application performance of the sensor, a novel detection mechanism based on the rich Brønsted acidic response sites on the metal clusters of the fluorescent MOF materials was demonstrated here.