Whilst studying the changes in the optical properties of lanthanide metal-organic frameworks (Ln-MOFs) in the presence of various NO2 concentrations, researchers found that the lanthanide ion in the MOFs influences its luminescence intensity.
Nitrogen dioxide (NO2) is released by burning fossil fuels. When the air contains high levels of this pollutant, it be harmful to the health of humans. Detecting the levels of NO2 concentrations in the air often involves erecting air quality measurement stations, which is often a costly and time consuming process.
MOFs are materials that are often porous in nature. They have already shown promise in helping scientists overcome the limitations of the current sensing technologies. Prior to this study researchers used MOFs to detect low concentrations of analytes.
Using MOFs to detect NO2 concentrations
A team of scientists from IMDEA Nanociencia (Spain), National Center De La Recherche Scientifique (France), and University of Valencia (Spain), have found that levels of lanthanide ion in the MOF structure can increase or decrease its luminescence intensity. This discovery was made whilst researchers were investigating the optical properties of Ln-MOFs in the presence of NO2 gas.
Using spectroscopic measurements, scientists found the modulation of the emitted light intensity is ascribed to the energy transfer rate from the MOF organic ligands to the lanthanide, which is strongly dependent on the presence of the NO2 molecule.
Published in The Journal of Physical Chemistry Letters, researchers state that the changes in the optical property of MOFs are reversible, and detectable upon NO2 concentrations as low as 500ppb.
Despite the weak MOF-NO2 interaction the luminescence modulation, it can detect low NO2 concentrations with high sensitivity at room temperature.
Exploiting NO2 interactions
The discovery of these supramolecular interactions between NO2 and amino groups could pave the way for new materials with improved properties. “Sensitivity to NO2 may be even more amplified by increasing the number of amino groups available in the MOF internal structure” said Juan Cabanillas, a lead researcher from this study.
Unfortunately, these detection techniques are still costly and difficult to implement in the field. “What we propose in this work is an alternative to the conventional methods to go beyond the state-of-the-art and be a solution in the implementation of portable sensors” says José Sanchez-Costa, another lead researcher of this study.
This collaborative work has been led by IMDEA Nanociencia researchers Reinhold Wannemacher, Cabanillas and Sanchez-Costa, and is partially funded by the Severo Ochoa Programme for Centres of Excellence in R&D.
