Role of polydopamine in the enhancement of binding stability of TiO2 nanoparticles on polyethersulfone ultrafiltration membrane

Strong adhesion of nanoparticles (NPs) onto the membrane surface to provide the prolonged effects during membrane filtration has been always challenging. In this work, polydopamine (PDA) was utilized to increase adhesion of titanium dioxide (TiO2) NPs onto the polyethersulfone (PES) ultrafiltration membrane. For this aim, polymerization of PDA on the membrane surface was followed by the NPs deposition (0.1 and 0.5 wt%). Washing and wiping analyses were utilized to evaluate the strength of NPs adhesion onto the membrane surface, before and after the pre-modification of PES membrane with PDA. Scanning electron microscopy (SEM) images revealed that increment of NPs concentration as well as deposition time of PDA resulted in the increase of attachment of NPs onto the membrane surface. Furthermore, the impressive role of PDA in retaining greater deal of NPs clusters on the PES membrane surface that were rinsed under 1 h filtration or undergone wiping test was also substantiated through SEM analysis. Indeed, hydrophilic natures of PDA and TiO2 NPs as well as the ability of PDA' catechol groups to bind with both Lewis acid and Bronsted acid sites of TiO2 through varied binding mechanisms (a mixture of bidentate and monodentate bonding) can be considered as plausible explanations for the enhanced stabilization of TiO2 NPs on the PDA-modified PES membrane. Evaluation of the membrane performance in term of pure water flux demonstrated that both NPs and PDA coatings on the membrane surface led to flux decrease, owing to the increased hydraulic resistance. Ultimately, assessing antifouling properties through BSA filtration exhibited that the membrane modification caused BSA rejection and flux recovery ratio to rise, primarily due to the hydrophilicity increment in the modified membranes.