Ion beam irradiation was used to modify the surface of a sulfonated polysulfone water treatment membrane. A beam of 25 keV H+ ions with three irradiation fluences (1 x 10(13) ions/cm(2), 5 x 10(13) ions/cm(2), and 1 X 10(14) ions/cm(2)) was used for membrane irradiation. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) analyses were performed on the virgin and irradiated membranes in order to determine the changes to chemical structure incurred by ion beam irradiation. The results show that some of the sulphonic and C-H bonds were broken and new C-S bonds were formed after irradiation. Atomic force microscope (AFM) analyses show that membrane roughness decreased after irradiation. A significant increase in flux after ion beam irradiation was also observed, while the amount of cake accumulation on the membrane was decreased after ion beam irradiation. Hydrophobicity, pore size distribution and selectivity of the membrane were not affected by ion beam irradiation. (c) 2006 Elsevier B.V. All rights reserved.