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
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.
1. D'Alessandro, D. M.; Smit, B.; Long, J. R., Carbon Dioxide Capture: Prospects for New Materials. Angew. Chem. Int. Ed. 2010, 49, 6058-82.
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.
3. Millward, A. R.; Yaghi, O. M., Metal-Organic Frameworks with Exceptionally High Capacity for Storage of Carbon Dioxide at Room Temperature. J. Am. Chem. Soc. 2005, 127, 17998-17999.
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.