Side-Chain Engineering of Hollow Spheres of Covalent Organic Frameworks for High-Efficiency Boron Capture from Brine

Covalent organic frameworks (COFs) hold grand promise in chemical separations owing to their tunable pore architectures and rich functionalities. However, their practical efficacy is often plagued by disordered stacking and restricted accessibility of functional groups. In this study, we present a side-chain engineering strategy, which synergistically manipulates pore-wall functionalization, dynamic structural reconstruction, and bond stabilization, to fabricate hollow, stable, and polyol-functionalized COFs (HSPCOF) adsorbents for high-efficiency capture of boron from brine. For the first time, we demonstrate that side-chain-engineering can be employed to introduce polyol groups, enabling boron chelation while concurrently enhancing the crystallinity of COFs. The resultant HSPCOF exhibits a high specific surface area, interconnected channels, and exceptional boron adsorption capacity of 150.05 mg g^-1 at 298 K, within 180 min, 10.29-fold higher than commercial resin MK51. Density functional theory (DFT) simulations reveal that the HSPCOF preferentially binds borate anions via bidentate cyclic ester formation with polyol groups, affording strong affinity and high selectivity. Remarkably, HSPCOF maintains robust borate anion adsorption performance in harsh Salt Lake brine, achieving 848.79 mg g^-1 capacity and 91.51% removal efficiency, validating its practical utility. This work affords generic guidelines for designing crystal and functionally precise COF materials by side-chain engineering.