Covalent Organic Polymer Nanoparticle-Supported Monolithic Foams for Separation of Nitrotoluene Isomers

Abstract

The combination of micron-scale macropores with meso-/micropores into three-dimensional (3D) macroscopic architectures could give increasing attention to both fast diffusion and mass transfer and exposure of the intrinsic micropores, thereby improving the performance and realizing the real-world applicability of nanoscale functionalized materials. In this report, the emulsion-droplet-templated method was used for the preparation of a hierarchically porous macroscopic covalent organic polymer (COP) monolithic foam, showing compressibility, high mass transfer, and excellent chromatographic separation capacity. The as-synthesized COP nanoparticles with the size of about 40 nm possessed good crystallization and high chemical and thermal stability. More importantly, the resulting COP nanoparticles showed interfacial activity, absorbing and accumulating the water/mesitylene interface, thus producing the COP nanoparticle film. As a result, a series of Pickering emulsions stabilized by COP nanoparticles were formed. Emulsion droplets of approximately 4.90 μm could serve as templates, producing hierarchically porous COP monolithic foams via freeze-drying of the starting Pickering emulsions. In view of the effective merging of macropores with meso-/micropores, the very thin disklike COP monolith (1 mm height × 10 mm i.d.) can serve as a separation column, which is highly efficient in differentiating the isomers of p- < o- < m-nitrotoluenes and chloronitrobenzenes. Clearly, the macropores guarantee high mass transfer, while the micropores provide many active sites. Therefore, the resulting COP foam shows excellent chromatographic separation capacity. Finally, the as-prepared COP monolithic foam has great potential as a prospective chromatographic column for highly efficient separation of isomers.