The effects of organic acids with different structures and acidic strengths on the preparation of polysulfone (PS) nanofiltration membranes were investigated in terms of membrane morphology, characteristics, permeation, and retention performance in separation of xenobiotics (2,4-dinitrophenol (DNP) and p-nitrophenol (PNP)) from aqueous media at different solution pHs. The prepared membranes were characterized by water contact angle and zeta potential measurements, SEM, AFM, FTIR-ATR, and dead-end nanofiltration. The water contact angle measurements prove that the hydrophilicity of PS membrane strongly increases by increasing of the concentration of additives in the casting solution. The SEM and AFM images declare that the membrane porosity increases and the pore size of the membranes decreases after addition of additives. The results show that addition of organic acids results in membranes with superior pure water flux and higher permeation and rejection compared to PS membrane. Also, it was found that rejection of DNP and PNP molecules strongly depends on the solution pH, structural properties of the solutes and characteristics of the membranes. (C) 2012 Elsevier B.V. All rights reserved.