Selective adsorption of luteolin and aloe-emodin on ionic liquids-bonded silica

Ionic liquids (ILs)-bonded silica adsorbents were prepared by chemical modification of the silica surface using N-alkylimidazolium-based ILs with Cl^?, BF₄ ^?, PF₆ ^? or NO₃ ^? anion, and applied to selective separation of the model mixture of luteolin and aloe-emodin. Among the investigated ILs-bonded silica materials, the silica grafted with N-octyllimidazolium hexafluorophosphate ([C₈mim]PF₆@SiO₂) exhibited higher adsorption capacity and selectivity of luteolin from the model mixed solution of luteolin and aloe-emodin. The isotherm data of luteolin on [C₈mim]PF₆@SiO₂ correlated better to the Freundlich model than the Langmuir model, and the calculated thermodynamic parameters indicated that the adsorption of luteolin was spontaneous and exothermic. The dynamic adsorption and elution experiments demonstrated that the high adsorption capacity and good desorption efficiency of luteolin on fixed bed packed with the [C₈mim]PF₆@SiO₂. Moreover, the results from batch adsorption and dynamic adsorption showed well selective separation towards the model mixture of luteolin and aloe-emodin.