Hierarchically textured superhydrophilic polyvinylidene fluoride membrane via nanocasting and post-fabrication grafting of surface-tailored silica nanoparticles†
Fouling is widely recognized as a main barrier to the sustainable development of membrane separation technologies. This study demonstrated a hierarchically textured superhydrophilic membrane, which was fabricated via nanocasting and post-fabrication grafting of surface-tailored silica nanoparticles. Nanocasting, using a prepared polydimethylsiloxane plate as an intermediate transfer template, gave rise to a micro-scaled surface texture resembling the surface pattern of a stainless-steel mesh. The resultant textured membrane surface was then sequentially grafted with poly(methacrylic acid) and surface-tailored silica nanoparticles through plasma induced graft copolymerization and self-assembly dip-coating, respectively, thereby resulting in an extra nano-scaled nanoparticle layer. The appropriate hierarchical structure and high surface energy of the membrane surface enormously improved its affinity with water, thus rendering the resultant functionalized membrane (designated as textured_F) superhydrophilic (water contact angle instantly reduced to 0° upon contact). Compared with a commercial 0.22 μm membrane, the textured_F membrane exhibited a slightly higher permeability and a significantly improved rejection ability, probably owing to the dense silica nanoparticle layer which functioned as a selective barrier. Moreover, in the systematic multi-cycle filtration experiments with a practical membrane bioreactor supernatant, the textured_F membrane exhibited a ∼2.4 times higher cleaning efficiency than the commercial membrane, demonstrating a dramatically improved antifouling capability. This improvement was probably due to the superhydrophilic and hierarchical membrane surface, which potentially facilitated the formation of an in situ hydration layer and peripheral turbulent flow thus resisting the adhesion of foulants.