A facile approach to fabrication of superhydrophilic ultrafiltration membranes with surface-tailored nanoparticles

A hydrophilic membrane commonly performs better in resisting fouling. But most prevailing polymeric membrane materials are hydrophobic thus prone to be fouled in practical operations. The current study presents a facile strategy for the fabrication of superhydrophilic polyvinylidene fluoride (PVDF) ultrafiltration membranes on the basis of a blending method and a dip-coating technique. A carboxyl-rich substance was firstly blended as an additive in the PVDF membrane matrix during fabrication. The incorporated carboxyl groups acted as anchor sites for the subsequent binding of amine-grafted silica nanoparticles (NPs). After a simple dip-coating operation, the PVDF membrane would be covalently functionalized to be superhydrophilic. Three types of carboxyl-rich additives including poly(methacrylic acid sodium salt), sodium alginate, and ethylenediaminetetraacetic acid (EDTA) were separately used to prepare different primary membranes for respective functionalization operations. The resultant membranes were systematically characterized in terms of hydrophilicity, morphology, permeability, and antifouling performance. Consequently, the simple dip-coating functionalization dramatically enhanced the surface hydrophilicity of all the additive-blended PVDF membranes. All the functionalized membranes obtained a significantly lower initial contact angle, which instantly reduced to < 5 degrees within several seconds. This could be attributed to the hydrophilic chains grafted on the NPs and the proper micro-/nano topography offered by the stack of NPs. Particularly, the EDTA-blended membranes achieved a higher and more stable hydrophilicity. Also, all the functionalized membranes obtained higher water permeabilities as compared with the pristine membrane. Moreover, all the superhydrophilic membranes restored over 80% flux (much higher than the similar to 53% for the pristine membrane) after cleaning in the fouling tests, demonstrating dramatically enhanced antifouling capacity.