Cobalt-Based Metal-Organic Frameworks and Its Mixed-Matrix Membranes for Discriminative Sensing of Amines and On-Site Detection of Ammonia

Developing suitable materials that can differentiate between chemically similar substances such as aliphatic and aromatic amines is challenging. Aliphatic and aromatic amines vary considerably in size and electronic properties despite possessing the same functional group. This makes the entire separation process more tedious. Metal-organic frameworks known for their inherent permanent porosity can be designed using appropriate building blocks that can lead to multifunctional materials. Here we utilize two Co-based multifunctional MOFs for discriminative sensing of amines and on-site detection of ammonia. Both the MOF materials display unique fluorescence behavior where aliphatic amines lead to "turn-off", and aromatic amines show "turn-on" fluorescence intensities of the two MOFs. Real-time sensing experiments with MOF-based mixed matrix membranes show an instant color change when ammonia is liberated from a chemical reaction. Density functional theory calculations unravel that the aliphatic and aromatic amines interact with the MOF structures in different ways that lead to "turn-off" and "turn-on" fluorescence behavior, respectively.