(682d) Atomistic Understandings of the CO2 Uptake Difference in Photo Responsive Metal-Organic Frameworks

Global climate change owing to anthropogenic CO₂ emissions has prompted nationwide actions from academia to industries to look for strategies to reduce atmospheric CO₂ concentrations. To this end, carbon capture and sequestration has been regarded as a promising technology to substantially reduce the CO₂ emission from power plants, one of the largest point emission sources. Conventionally, amine absorbers are used to separate CO₂, but the energy requirement of a plant can be increased by 25-40%.^1-2 Recently, metal-organic frameworks (MOFs) have drawn significant attention as a promising alternative because of their desirable properties (e.g., large surface area, adjustable chemical functionality, high selectivity of CO₂ over N₂, etc.).³ Moreover, experimentists have further developed photo-switchable (azobenzene functionalized) MOFs whose affinity for CO₂ adsorption can be modified by light irradiation (transformation from trans to cis configurations), resulting in a CO₂ uptake difference of more than 50%.⁴ This has potentially led to a more energy-efficient CO₂ capture process as compared to traditional materials. Despite the success, the atomistic understandings of the root cause behind the observed uptake difference remain limited. In this study, by using state-of-the-art molecular simulations and density functional theory calculations, we investigate the adsorption mechanisms in azobenzene functionalized MOF-5 (azo-MOF5) that leads to the experimentally observed CO₂ uptake difference between cis and trans configurations. The free energy landscape of CO₂ molecules as well as minimum energy configurations will be computed and analyzed in detail to identify preferential adsorption sites in azo-MOF5 for CO₂. The effect of the azobenzene density on the uptake difference will also be studied. The outcomes of this study are anticipated to provide insights into the design of this stimulus-responsive MOFs to push the development of CO₂ capture and sequestration.

Reference

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2. Huck, J. M.; Lin, L. C.; Berger, A. H.; Shahrak, M. N.; Martin, R. L.; Bhown, A. S.; Haranczyk, M.; Reuter, K.; Smit, B., Evaluating Different Classes of Porous Materials for Carbon Capture. Energ. Environ. Sci. 2014, 7, 4132-4146.

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4. Park, J.; Yuan, D. Q.; Pham, K. T.; Li, J. R.; Yakovenko, A.; Zhou, H. C., Reversible Alteration of Co2 Adsorption Upon Photochemical or Thermal Treatment in a Metal-Organic Framework. J. Am. Chem. Soc. 2012, 134, 99-102.