Smart light responsive polypropylene membrane switching reversibly between hydrophobicity and hydrophilicity for oily water separation

Abstract Smart membranes with switchable wettability are perfect choices for oily water separation, which limited in numerous practical applications as before. Hereof, one method of chemical grafting azobenzene groups on SiO2 roughened polypropylene (PP) membranes has been realized. This smart membrane surface reveals rapid light-triggered wettability transition between hydrophobicity and hydrophilicity through alternate irradiation with UV and Vis light, respectively. After modification, maximal water contact angle (WCA) of 160° is obtained in the trans state of 7-[(trifluoromethoxyphenylazo)phenoxy]pentanoic acid (CF3AZO), which convert into cis state by UV (365 nm) irradiation. In cis state, since the high free energy of CF3AZO, hydrophilic surface (WCA ≤ 5°) is acquired and can swap back to trans state under Vis (440 nm) irradiation. Simultaneously, the photosensitive membranes possess exceptional physical and chemical stabilities, which can endure cruel ambient conditions and repeated mechanical deformation along with multiple rinsing. What's more, on account of the outstanding photosensitivity, multifarious eliminable and reproducible patterns with apparent wetting characteristics upon optional illumination can be acquired. The positive outcomes indicate that photosensitive CF3AZO grafted PP membranes with outstanding switchable wettability is a prospective material for oil/water separation membranes.