Ultrafast selective ionic transport through heat-treated polyethylene terephthalate track membranes with sub-nanometer pores

12-μm-thick polyethylene terephthalate (PET) track membranes with sub-nanometer pores fabricated with the newly developed track-UV technique without chemical etching showed ultrahigh selective ionic transport yet low permeability. We discovered that the permeability of these track membranes were irreversibly improved by two to three orders of magnitude via heat treatment. Meanwhile, these heat-treated track membranes maintained the high selectivity of ions. Our experimental results suggest heat treatment on the track membranes with sub-nanometer pores could provide a reliable and controllable way to enlarge nanopore size, and bring the track membrane to promising applications on ion separations, water purification, diaphragm material and so on.