However, ionic liquids tend to separate from the activated carbon when exposed to water even for a relatively short period. RESULTS: Characterization of spherical activated carbon (SAC) modified with poly(1-vinyl-3-butylimidazolium hexafluorophosphate) (PIL) showed that 1-vinyl-3-butylimidazolium hexafluorophosphate (IL) was adsorbed and polymerized on SAC. Stability studies of PIL-SAC in water demonstrated that it was more stable against IL desorption in water than the non-polymerized IL-SAC. The adsorption data showed that the modification improved the adsorption capacity of SAC at least 2-fold. The results also indicated that although the pH and ionic strength of the solution played a significant role in the adsorption process, there was no significant influence on the adsorption capacity. Moreover, PIL-SAC could be reused at least five times with only minor losses in its adsorption capacity. CONCLUSION: The activated carbon modified with PIL produces a remarkable increase in the ibuprofen adsorption capacity and strongly decreases undesirable desorption of ionic liquids. (C) 2015 Society of Chemical Industry