Surface PEGylation of polyacrylonitrile membrane via thiol-ene click chemistry for efficient separation of oil-in-water emulsions

Abstract

Because of their low hydrophilic properties, the polymeric membranes are always subjected to fouling problems, which have become a major obstruction in the path of the practical application of membrane technology in oil–water separation. The present work describes a highly hydrophilic polyacrylonitrile (PAN) membrane successfully developed via thiol-ene click chemistry. To fabricate the membrane, the pristine PAN membrane was first hydrolyzed and then reacted with cysteamine hydrochloride to create a thiolated surface. Afterward, poly(ethylene glycol) methyl ether methacrylate (PEGMA) was covalently grafted onto the thiolated surface to obtain the PEGylated membrane. The effects of the number-average molecular weight (Mn) of PEGMA monomers on the structure, surface wettability, anti-fouling abilities and separation performances of the PEGylated membrane were investigated systematically. The grafting density of PEGMA chains increases with the increase in PEGMA concentration in the reaction solution, whereas it diminishes with the increasing Mn of PEGMA monomers as a result of the steric hindrance. The PEGylated PAN membrane has the superhydrophilic and underwater superoleophobic characteristics when it is grafted with the low-Mn PEGMA monomers. It is observed that the surface grafting of PEGMA chains results in the reduction of membrane pore size, which endows the PEGylated PAN membrane with a low flux. The separation efficiency of PEGylated membrane for several kinds of oil-in-water emulsions is as high as 99.9%, indicative of an excellent separation performance. The cycle filtrations of oil-in-water emulsions demonstrate that the flux decline of PEGylated membrane caused by both the irreversible and reversible fouling is suppressed effectively, as compared with the pure PAN membrane. Even after the three-cycle filtration of the oil-in-water emulsion, the recovery ratio of pure water flux of PEGylated membrane remains greater than 95%, suggesting a high fouling-resistant ability in the permeation process of emulsions.