A Systematic Approach for Incorporating Structural Flexibility in High-Throughput Computational Screening of Metal–Organic Frameworks for Xylene Separation

Separation of xylene isomers poses
a significant challenge
due
to their similar physicochemical properties. Currently, zeolites are
utilized as adsorbents for this purpose in the chemical industry despite
suboptimal separation performance. With tunable pore size and chemical
functionality, metal–organic frameworks (MOFs) are promising
adsorbents for separation. By virtue of high-throughput computational
screening (HTCS), the adsorption performance of a large collection
of MOFs can be evaluated in silico by using Monte
Carlo (MC) simulations. Unlike prior studies assuming rigid structures
of MOFs during screening, we develop a systematic approach for incorporating
flexibility in HTCS for xylene separation. First, MOFs are judiciously
classified with external flexibility (volume/shape changes) and internal
flexibility (intraframework fluctuations), respectively, based on
the nature and extent of structural deformation from molecular dynamics
(MD) simulations. Afterward, adsorption in MOFs with external flexibility
is simulated by hybrid MC/MD method, the flexible snapshot method
is used for MOFs with a sort of internal flexibility, and grand-canonical
MC (GCMC) method is employed for MOFs with negligible flexibility.
Finally, top-performing MOFs are identified for xylene separation.
While substantially reducing computational cost, this study also delivers
more reliable results compared to the assumption of rigid structures.
The HTCS approach is versatile and can be extended beyond MOFs, offering
a robust tool for the virtual screening of other soft-porous materials
for a wide range of important applications.