Preparation of Nano-TiO2-Modified PVDF Membranes with Enhanced Antifouling Behaviors via Phase Inversion: Implications of Nanoparticle Dispersion Status in Casting Solutions

Titanium dioxide (TiO2) nanoparticles have been applied in membrane antifouling performance modification for years. However, the influence of TiO2 nanoparticle dispersion status during the blending process on membrane properties and the inner mechanism has seldom been focused on. Herein, we investigated the influence of the various dispersing statuses of TiO2 nanoparticles on membrane properties and antifouling performance by exploring various blending processes without changing the original recipe. Polyethylene glycol (PEG) was employed as a pore-forming agent during the membrane preparation process, and also as a pre-dispersing agent for the TiO2 nanoparticles via the steric hindrance effect. Compared to the original preparation process of the PVDF/TiO2 composite membrane, the pre-dispersing of TiO2 via PEG ensured a modified membrane with uniform surface pores and structures on cross-sectional morphologies, larger porosity and water permeability, and more negative zeta potential. The contact angle was decreased by 6.0%, implying better hydrophilicity. The improved antifouling performance was corroborated by the increasing free energy of cohesion and adhesion, the interaction energy barrier (0.43 KT) between the membrane surfaces and approaching foulants assessed by classic XDLVO theory and the low flux decline in the filtration experiment. A kinetics mechanism analysis of the casting solutions, which found a low TSI value (<1.0), substantiated that the pre-dispersion of TiO2 with PEG contributed to the high stability and ultimately favorable antifouling behaviors. This study provides an optimized approach to the preparation of excellent nano-TiO2/polymeric composite membranes applied in the municipal sewage treatment field.