Multi-walled carbon nanotubes (MWCNTs) were modified by in situ polymerization of acrylic acid (AA) in aqueous solution in the presence of potassium persulfate (KPS) as initiator and ethylene glycol (EG) as cross-linker to obtain stable grafted polyacrylic acid (PAA) on MWCNTs surface. Effects of raw MWCNT, PAA modified MWCNT and grafting efficiency of PAA on characteristics of nanocomposite polyethersulfone (PES) nanofiltration (NF) membranes were investigated. The results revealed that the existence of PAA modified MWCNTs (PAA-g-MWCNT) in the membrane matrix improves water flux and antifouling properties of NF membrane. The membranes containing 0.1 wt.% of modified MWCNTs showed highest Na2SO4 rejection due to functional groups of modified MWCNTs, which provides negatively charged surface. The graft polymerization of PM on the mixed matrix membranes led to further hydrophilicity enhancement of prepared membranes. PM grafting yield of PAA-g-MWCNT/PES membrane (37%) was significantly higher than that of raw MWCNT blended (29%) and bare PES (25%) membranes. The PM grafted nanocomposite membrane exhibited high water flux (40 kg/m(2) h at 0.4 MPa), superior antifouling properties and more efficient salt rejection revealing the success of simultaneous use of various modification methods. FTIR, AFM and FESEM techniques and contact angle measurements were successfully employed to verify the observations. (c) 2012 Elsevier B.V. All rights reserved.