A commercial polyamide reverse osmosis (RO) membrane was surface modified in a sequential two-step dip coating process for improvement of the hydrophilicity and fouling resistance.In the first step,an ultrathin metal-polyphenol precursor layer was deposited onto the membrane surface via the self-assembly of tannic acid (TA) and Fe(Ⅲ) ions,and polyethylenimine (PEI) was added as a covalent cross-linker.In the second step,poly (N-vinylpyrrolidone) (PVP),was immobilized onto the metal-polyphenol precursor layer through the strong hydrogen bonding interactions between the lactam groups in PVP and the phenolic hydroxyl groups in the precursor layer.The resultant membrane was fully characterized.The water flux of the modified membrane was only slightly decreased and the salt rejection was almost unchanged.More importantly,static contact angle measurement showed that the membrane surface hydrophilicity was significantly improved (contact angle from 59.0±1.2° to 14.5 ± 2.4°).The results of the fouling experiments,shown in Fig.1 revealed that the fouling resistance of the RO membrane was obviously improved.