Modification of polyacrylonitrile (PAN) membrane with anchored long and short anionic chains for highly effective anti-fouling performance in oil/water separation

Conventional polymeric membranes are usually prone to fouling by oily substances and therefore are greatly hindered in their applications for oil/water separation. In this study, we carried out a new strategy of modifying PAN membrane for highly effective anti-oil fouling performance. The modified membrane surface was anchored with negatively charged long and short chains, where the long chains could reject oil droplets at far away from the membrane surface while the short chains near the membrane surface could increase its hydrophilicity and thus enhance the permeate flux during the filtration of oil emulsion. The negatively charged long chains were constructed with sulfonate-terminated units and the short chains with carboxylate units. The prepared PAN membranes were tested to show both superhydrophilic and underwater superoleophobic surface properties, and displayed very high resistance to the adhesion of various types of oils. In the membrane separation experiments with 1000 mg‧L-1 surfactant-stabilized oil-in-water emulsion, the developed PAN membrane exhibited an initial water flux of 115.4 L·m−2·h−1, and less than 16% of flux decay but higher than 97% in flux recovery after 3 filtration cycles (45 min each). Furthermore, in a challenging test, the membrane also showed excellent recovery in its performance after being fouled by a heavy fuel oil but cleaned simply by the action of soaking it into water. Therefore, the current study appeared to provide a new and effective alternative in the modification of conventional PAN membrane to enhance or expand its anti-oil fouling performance, especially for oil recovery or oil removal in oily wastewater treatment.