Air pollution caused by the combustion of fossil fuels and other sources continues to be a pressing environmental issue. As the demand for energy increases with modernization and population growth, burning fossil fuels and other materials releases significant amounts of NOx into the atmosphere. Detecting, capturing, and removing NO2 gas is of great interest due to its detrimental effects. In this context, optical sensing of NO2 using metal-organic frameworks (MOFs) has emerged as an interesting and cost-effective approach. MOFs are a class of materials known for their permanent porosity, high thermal stability, and large surface area.
Researchers at IFIMAC have enhanced the optical sensing capabilities of MOF-808 by incorporating synergistic binding sites through post-synthetic modification with copper. To characterize these materials and elucidate the atomic structure of the copper sites, we employed a combination of conventional characterization techniques, computational modelling, and advanced synchrotron characterization tools that led us to a tetrahedral configuration of the copper single sites around the smallest pore of the MOF. We also demonstrated that Cu-MOF-808 exhibited an unprecedented optical sensing response towards NO2 when compared with MOF-808. The limit of detection (LOD) for the Cu-MOF-808-based optical sensor was calculated to be 16 parts per billion (ppb), to the best of our knowledge, this is the lowest LOD reported for luminescent MOFs. The excellent performance of Cu-MOF-808 can be attributed, thanks to DFT calculations, to the synergistic effect between the hydroxo/aqua-terminated Zr6O8 clusters and the copper-hydroxo single sites, where NO2 is adsorbed through combined dispersive and metal-bonding interactions. Thus, by harnessing weak-binding interactions through post-synthetic chemical modifications, we have opened exciting possibilities for detecting and monitoring NO2 and other toxic gases using luminescent MOFs. [Full article]
