Highly porous MOFs can trap toxic gas molecules and prevent them from entering the atmosphere and can also be used to build sensors. This illustration shows the material’s normal luminescence (left) switched off in the presence of harmful gases (right).
The Science
Metal organic frameworks (MOFs) are essentially a microscopic matrix of metal atoms connected by organic molecules. MOFs show promise for a large range of applications. In this research, scientists studied MOFs that could be used to trap toxic molecules and mitigate their harmful effects. The scientists used beams of neutrons and X-rays to better understand how the structure of the MOF can be tuned to enhance and optimize how the MOFs trap dangerous gas molecules. Specifically, the MOFs in the study are tuned to trap nitrogen dioxide and sulfur dioxide (NO2 and SO2), both of which are harmful to the environment and human health.
The Impact
Upon entering the atmosphere, NO2 and SO2 can travel hundreds of miles, polluting the air and causing acid rain that damages buildings, trees, and crops. Exposure to these toxic gases can also lead to respiratory infections, asthma, and chronic lung disease. MOFs act as cage-like sponges that can soak up toxic particles. This research used neutron and X-ray studies to determine how the atoms in the MOFs are arranged and how to improve the MOFs’ performance. The optimized MOFs could provide the basis for building novel devices that can sense the presence of toxic molecules and alleviate their harmful effects.
Summary
The acid gases NO2 and SO2 are high on the list of pollutants targeted by the Clean Air Act, which requires the Environmental Protection Agency to regulate and set limits on their emissions. In response, scientists are developing materials for technologies that can detect and trap acid gases. In some cases, the captured molecules can also be stored and reused. For example, carbon dioxide can be reused in certain applications to promote photosynthesis and plant growth. MOFs could take acid-gas sequestration to the next level, making it a more viable, practical approach to improving air quality on a global scale.
Searching for candidate materials, researchers from Oak Ridge National Laboratory (ORNL), Sandia National Laboratories, and the University of Tennessee-Knoxville studied a large family of MOFs that can be made from any of the lanthanide rare-earth metals. The research combined computer simulations and X-ray studies with neutron scattering experiments at the Spallation Neutron Source, a Department of Energy (DOE) Office of Science user facility at ORNL, to map the atomic arrangement of each design. The scientists also learned how defects in the cage matrices increase their effectiveness of trapping toxic molecules, which could be developed for novel devices for sensing and capturing harmful gases.
Funding
This work was supported as part of the Center for Understanding and Control of Acid Gas-Induced Evolution of Materials, an Energy Frontier Research Center funded by the DOE Office of Science, Office of Basic Energy Sciences. A portion of this research used resources at the Spallation Neutron Source, a DOE Office of Science user facility at Oak Ridge National Laboratory.
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