Nanofiltration membranes were prepared from polyacrylonitrile (PAN). The microstructure and desalination property of the as-prepared PAN nanofiltration membranes were tuned by a preoxidation method. The thermal stability of PAN membranes is significantly enhanced after preoxidation due to the crosslinking structure formation in the membrane matrix. The crosslinking degree for PAN membranes is improved by preoxidation at high temperatures or low air flowrates. For modified membranes a change in rejection was observed as a function of feed pH. Nanofiltration results have shown that the optimum rejection of 99.98% was achieved for CaCl2 when the PAN membranes were preoxidized at 220 degrees C with an air flowrate of 416 mL/min, under the feed concentration of 50 mg/L and pH value of 3. (C) 2014 Elsevier B.V. All rights reserved.