Methane Uptakes in Covalent Organic Frameworks with Double Halogen Substitution

The methane uptakes of six double halogen substituted covalent organic frameworks (COFs) based on COF-102 were simulated with grand canonical Monte Carlo simulation at 298 K and pressure ranges from 1 to 80 bar. The simulation shows that COF-102-1,4-2I reaches the DOE target of 180 V­(STP)/V for methane delivery. The current study highlights the correlation between the structure and the adsorption property of the double halogen substituted COF-102. In COF-102-1,4-2I, the triangle arrangement of the six I atoms around the central B₃O₃ ring brings close contact between I atom and B₃O₃ ring, and thus enhances the attraction of CH₄ with high CH₄ density in the vicinity above and below this region, especially in particular adsorption sites. Such favorable structural arrangement, altogether with the strongest I–CH₄ attraction among the halogen substituent in this study, gives the highest isosteric heat as well as the CH₄ uptakes at 298 K and 35 bar in the hypobaric region. The result in this study demonstrates that double halogen substituted COF-102 is capable of increasing CH₄ uptakes for practical applications