One-pot synthesis of wormhole-like mesostructured silica with a high amine loading for enhanced adsorption of clofibric acid

A series of ordered amine-functionalized hexagonal mesoporous silicas (HMS-NH2) were synthesized successfully via direct co-condensation using dodecylamine as a structure-directing agent in the presence of 3-aminopropyltrimethoxysilane (APS), [aminoethylamino]propyltrimethoxysilane or [(2-aminoethylamino)ethylamino]propyltrimethoxysilane (AEEA) as amine group precursors. Tetrahydrofuran was used as the organic solvent to control the interaction and sol–gel reaction of the silica source and aminosilanes. The effect of the type and concentration of the added aminosilanes on the physicochemical properties of the resulting HMS-NH2 materials were investigated. Thermogravimetric analysis, Fourier-transform infrared spectroscopy and solid-state 29Si nuclear magnetic resonance spectroscopy confirmed a successful functionalization of the HMS surface with different amine groups. X-ray diffraction and transmission electron microscopy indicated that their wormhole-like mesostructured framework was retained after functionalization at a high APS loading level (15 mol%) or using AEEA as the aminosilane precursor. A high degree (88–98%) of aminosilanes was incorporated into the HMS framework, corresponding to an amine concentration of 0.72–2.16 mmol g−1. The HMS-NH2 materials had a high surface area (272–627 m2 g−1), a large total pore volume (0.48–1.92 cm3 g−1) and exhibited an enhanced adsorption capacity for clofibric acid in aqueous solution.