Dual engineering of thermodynamics and kinetics in covalent organic frameworks for separation

Dual engineering thermodynamics and kinetics is crucial for achieving high-performance separation, but remains challenging. Here, we pioneer in the engineering of covalent organic framework (COF) from both thermodynamic and kinetic perspectives by rational design of a hollow trifluoromethyl functionalized COF (HTpBPa-F) for enhanced chromatographic separation of halogenated isomers. The trifluoromethyl introduction not only promotes the thermodynamic selectivity for halogenated isomers but also enhances separation kinetics by facilitating formation of a hollow structure. As a result, HTpBPa-F yields higher resolution and column efficiency for pairs of halogenated isomers than either solid fluorinated COF or trifluoromethyl-free COF. Density functional theory calculations reveal thermodynamic selectivity of HTpBPa-F for halogenated isomers results from C-H···π, π-π and dipole-dipole interactions. Molecular dynamics simulations demonstrate high diffusion coefficient of hollow structure leads to low transport resistance, enhancing the kinetics of separation. This work offers insights into simultaneously tailoring COFs from thermodynamics and kinetics for the high-performance separation.