Synthesis of a hydrophilic covalent–organic framework@silica composite via an oxidation reaction for mixed-mode liquid chromatographic separation

Abstract

In this work, the oxidation of imine-linked TAPT–TA-COF@SiO₂ was prepared using 2,4,6-tris(4-aminophenyl-1,3,5-thiazine) (TAPT) and 1,4-benzenedicarboxaldehyde (TA) as monomers via a one-pot cascade polymerization reaction on the surface of silica spheres, achieving high yield and specificity. Notably, the pore size distribution (PSD) and specific surface area (SSA) of the amide-TAPT-TA-COF@SiO₂ remained similarl to the original porous silica microspheres prepared in this work. Chromatographic performance and multiple retention mechanisms were investigated, demonstrating efficient separation of neutral polar solutes and nonpolar compounds in the reverse-phase chromatography mode compared to that achieved with the unmodified COF. Moreover, an improved separation method was established for representative saccharides, and complex oligosaccharide samples confirmed that the post-modification amide TAPT–TA-COF@SiO₂-based core–shell stationary phases were hydrophilic compared to the imine-linked TAPT–TA-COF@SiO₂ materials. These findings provide new opportunities for advancing the understanding and application of COFs as HILIC stationary phases in separation science.