Facile aqueous synthesis of ionic liquid/phosphotungstic acid co-functionalized MOF-808@silica composite for...

Metal organic frameworks (MOFs) are eminently suited for liquid chromatographic separation. MOF-808 is a type of MOF assembled through the coordination of zirconium clusters with 1,3,5-benzenetricarboxylic acid, which possesses an ultrahigh specific surface area and excellent stability. These features make MOF-808 an ideal modifier for HPLC stationary phase. Moreover, further functionalization represents a key strategy for advancing MOF@SiO₂ stationary phase, as it offers a direct route to superior separation performance and broader utility. Therefore, a facile functionalization strategy for MOF-808@SiO₂ is essential to enable green synthesis and practical application of high-performance MOF-based stationary phase.

In this study, a room-temperature aqueous synthesis method was employed to co-immobilize phosphotungstic acid (PTA) and ionic liquid (IL) onto the MOF-808@SiO₂. The coordination bonds between the Zr clusters and the IL/PTA modifiers, together with the electrostatic attraction between IL and PTA, jointly enable the stable anchoring of the IL/PTA modifiers within MOF-808. Additionally, PTA, characterized by strong electronegativity and high acidity, enhances electrostatic interactions and serves as a rich source of hydrogen bond acceptors, and IL introduces cationic sites, while MOF-808 offers a stable framework with an abundant pore structure. The MOF-808@SiO₂ is combined with PTA and IL to achieve a unique synergistic effect, improving the separation performance and application range. Experimental results show that the IL/PTA/MOF-808@SiO₂ exhibits good separation performance for various analytes, including positional isomers, nucleosides, sulfonamides, vitamins, and benzoic acid compounds, with its applicability further demonstrated through the analysis of food samples.

In this work, PTA and IL have been sequentially introduced onto MOF-808@SiO₂via a facile and green stepwise strategy to fabricate a mixed-mode stationary phase. Benefiting from the complementary retention mechanisms provided by anionic PTA and cationic IL, the as-prepared IL/PTA/MOF-808@SiO₂ exhibits favorable separation performance. This IL/PTA co-functionalization strategy shows good application prospects for constructing high-performance mixed-mode stationary phase and provides a feasible reference for the performance regulation of MOF-based separation material.