Validation of 'lock-and-key' mechanism of a metal-organic framework in selective sensing of triethylamine.

To develop the metal-organic framework (MOF)-based sensing of triethylamine (TEA) in an aqueous phase, Al-MIL-101-NH (MIL: Material Institute Lavoisier) with a tripod-like cavity was utilized based on a lock-and-key model. Al-MIL-101-NH (Al-MOF) was found to be an excellent fluorescent sensor for the TEA molecules in the range of 0.05-0.99 mM. The limit of detection (LOD) and linear calibration range of this probe towards TEA were found to be 3 μM and 0.05-0.40 mM, respectively. The mechanism of the sensing process indicates the dominant role of physical processes (, non-covalent bond interactions). In addition, the exact fit of the TEA molecule (6.5 Å) in the tripod-like cavity (6.78 Å) supported the strong interaction between three ethyl groups (TEA) and aromatic rings (MOF). This kind of specific suitability between size/shape of the TEA and tripod-like cavity of MOF (Δ: -46.7 kJ mol) was not found in other molecules such as ethylamine (Δ: -2.20 kJ mol and size: 3.7 Å), formaldehyde (Δ: +1.50 kJ mol and size: 2.8 Å), and ammonia (Δ: +0.71 kJ mol and size: 1.6 Å). As such, Al-MOF was found to be a selective and stable sensor for TEA.