Fabrication of hierarchically porous University of Oslo-66@silica shell-core stationary phase by phosphoric acid etching strategy for enhanced separation performance in liquid chromatography

Metal-organic frameworks (MOFs) are promising packing materials in liquid chromatography, but their micropore character extremely prevents the separation performance. Herein, we proposed an acidic etching strategy to fabricate a hierarchically porous University of Oslo-66 (HP-UiO-66) coated silica shell-core composite by using phosphoric acid as an etchant. The prepared composite, namely HP-UiO-66@silica-PA, was characterized by SEM, TEM, FT-IR, and N 2 -adsorption–desorption isotherms, demonstrating the generation of mesopores in HP-UiO-66 shell with pore width ranging in 4–5 nm. The chromatographic performance of HP-UiO-66@silica-PA-1 (etched by 1 mL phosphoric acid for 2 h) as HPLC stationary phase was evaluated in reversed-phase mode, and the separations of three groups of small solutes were studied and compared with the microporous UiO-66@silica (MP-UiO-66@silica) column. The results proved the obviously improved performances with narrower peak width, better resolution, and higher symmetry were achieved by the HP-UiO-66@silica-PA-1 column. The faster diffusion and mass transfer kinetics in the HP-UiO-66 shell signally reduce the plate height and improve the column efficiency. Specifically, the plate number of o -xylene was 18,442 plates m −1 , which was about 18.5 times higher than that on the MP-UiO-66@silica column (993 plates m −1 ). Furthermore, good repeatability and reproducibility with RSDs of both retention time and peak area less than 0.5 % confirmed the high stability and outstanding reliability of the HP-UiO-66@silica-PA-1 column. This study demonstrates that the phosphoric acid etching strategy is simple, mild, and controllable to fabricate hierarchically porous MOFs-based stationary phase for enhancing the HPLC separation performance.