In-column click chemistry for preparation of octadecyl spherical covalent organic framework modified silica...

The common method for grafting various groups on the covalent organic framework (COF) modified silica is post-modification reaction, which often occurs in round-bottom flask. However, the reaction in round-bottom flask has the disadvantages of complex operation and poor flexibility. To address these challenges and advance the concept of portable, flexible synthesis, this work innovatively developed a flow-through modification program. By utilizing a chromatographic column as a microreactor, a more efficient "in-column" modification strategy was designed to streamline the preparation of COF-based stationary phases.

Two monomers, 1,3,5-Tri (4-aminophenyl)benzene (TPB) and 1,4-Phenyldiformaldehyde (DVA) were successively modified on the 3-Glycidoxypropyltrimethoxysilane functionalized silica (Sil-GPTS) through bottom-up method to construct the COF modified silica material (Sil-COF). Fourier transform infrared spectrometry (FT-IR), scanning electron microscope (SEM), elemental analysis (EA), thermogravimetric analysis (TGA), N₂ adsorption-desorption and X-ray diffraction (XRD) were employed to characterize the Sil-GPTS and Sil-COF materials, indicating that the base COF-modified silica material (Sil-COF) was successfully constructed. The chromatographic behavior of various compounds including alkylbenzenes, polynuclear aromatic hydrocarbons (PAHs) and positional isomers on Sil-COF and Sil-COF-C18 was compared to investigate the differences of prepared columns before and after in-column "click chemistry" reaction. The results proved that the C18 chain was successfully post-modified on the COF modified silica through in-column "click chemistry" reaction. The Sil-COF-C18 column also showed practical value in the separation of complex samples.

This study introduced a transformative methodology for the functionalization of silica-based materials, shifting from traditional flask-based reactions to a more integrated, flow-through microreactor system. The in-column modification strategy not only simplifies the synthesis of COF-modified silica but also enhances the flexibility of stationary phase design. More important, the "click chemistry" reaction and stationary phase materials can be characterized on-line by chromatographic method.