Selective Adsorption of o-Xylene From all C8 Aromatics via Secondary Connectivity Manipulation in B←N Frameworks

Separating o-xylene from all C8 aromatic isomers (m-xylene, p-xylene, and ethylbenzene) is critical for industry but remains a formidable challenge due to their quite similar physicochemical properties. While metal-free frameworks offer an ideal solution via selective adsorption, their development lags behind metal-based systems. For instance, due to the limited connection modes and lack of suitable linkers, B←N frameworks (BNFs) struggle to handle complex separations. To address this limitation, we report a programmed assembly strategy by rationally integrating secondary connectivity into bridging linkers. Implementing this strategy yielded stable BNFs, BN-DPTA1 and BN-DPTA2, featuring tunable and confined cavities. BN-DPTA1 exhibits specific abstraction of toluene, while BN-DPTA2 selectively adsorbs o-xylene from benzene derivatives. Notably, BN-DPTA2 represents the first metal-free framework to achieve highly selective adsorption of o-xylene over all C8 aromatic isomers. The multiple non-covalent interactions between the BNF cavities and guest molecules facilitate tight encapsulation, enabling the effective removal of toluene and o-xylene from the atmosphere (97.4% and 96.0% removal efficiency at 50 ppm, respectively). The dynamic, reversible adsorption/desorption behavior of BNFs allows for single-step purification of toluene and o-xylene via solid-phase extraction columns, achieving purities exceeding 99.9%.