Self-generated microporous hydrogel coating on mesoporous silica: A hierarchical porous structure for...

Conventional coated stationary phases often suffer from surface area loss due to dense coatings, limiting separation efficiency and interaction site availability. A hierarchical porous structure may overcome this drawback while enabling efficient mass transport for polar compound analysis. In this work, we address this challenge by fabricating a hydrophilic interaction chromatography (HILIC) stationary phase (Sil@CMC-Na/β-CD) via a "rigid-flexible synergistic" coating strategy, using carboxymethylcellulose sodium (CMC-Na, flexible) and β-cyclodextrin (β-CD, rigid) as hydrogel monomers.

The CMC-Na/β-CD hydrogel formed abundant self-generated micropores (0.6-1.8 nm) during film formation, which interconnected with the silica's native mesopores to create a continuous hierarchical porous structure. This unique structure unexpectedly increased the specific surface area from 372.88 m² g^-1 (bare silica) to 411.66 m² g^-1 (Sil@CMC-Na/β-CD). Consequently, the stationary phase achieved efficient and symmetric baseline separation of three categories of polar compounds (acidic, basic, and zwitterionic/neutral) with markedly improved resolution and peak symmetry compared to commercial NH₂ and Diol columns. The performance stems from the "rigid-flexible synergistic" coating strategy: the flexible CMC-Na network provides hydrophilicity and weak anion-exchange ability, while the rigid β-CD cavities contribute hydrophobic inclusion sites and help maintain the hierarchical porous structure, enabling enhanced mass transport.

This work presents a versatile HILIC stationary phase that overcomes the typical surface-area loss of coated materials. The hierarchical porous structure establishes a new paradigm for integrated "structure-performance" platforms, enabling effective discrimination of polar compounds with widely differing acid-base properties. This approach offers a rational route for broad-spectrum analysis of complex polar samples and advances the development of functional separation materials with customized porosity.