A fluid deionizer includes at least one graphene sheet perforated with apertures dimensioned to allow a flow of fluid and to disallow at least one particular type of ion contained in the flow of fluid. A purge valve is placed in an open position so as to collect the at least one particular type of ion disallowed by the graphene sheet so as to clean off the at least one graphene sheet. Another embodiment provides a deionizer with graphene sheets in cylindrical form. A separation apparatus is also provided in a cross-flow arrangement where a pressurized source directs a medium along a path substantially parallel to at least one sheet of graphene from an inlet to an outlet. The medium flows through the plural perforated apertures while a remaining portion of the medium and the disallowed components in the medium flow out the outlet.