Separation of organic ions from aqueous solutions by membrane capacitive deionization

•Membrane capacitive deionization (MCDI) can be used to separate permanently charged organic cations or anions such as ionic liquids that can differ greatly in polarity and size.•The separation efficiency depends on the symmetry of mobility of the respective anion and cation.•Supports the suitability of MCDI for pollutant removal from (waste)water.