One-step preparation of PVDF‒polydopamine blend ultrafiltration membranes via nonsolvent-induced phase separation and their characterization and antifouling mechanism analysis

To address the existing shortcomings in the polydopamine (PDA) modification of ultrafiltration membranes, in this study, dopamine monomers were directly added to a casting solution, and a low-concentration NaClO solution was used as the coagulation bath to prepare a polyvinylidene fluoride (PVDF)/PDA blend membrane by nonsolvent-induced phase separation. The results revealed that an extremely thin PDA coating formed on the surface and cross-section of the membrane during the phase separation process, which featured a short reaction time, high dopamine utilization efficiency and simple operation. Compared to the PVDF membrane, the hydrophilicity and permeate flux of the PVDF/PDA membrane simultaneously improved, overcoming the trade-off faced by traditional PDA modification methods. The PVDF/PDA blend membrane also exhibited superior mechanical strength and a more negative charge. Moreover, PDA modification weakened the hydrophobic force and strengthened the electrostatic repulsion force between the foulants and the membrane, thereby causing the comprehensive force between the foulants and the membrane to decrease significantly. In turn, the weaker interaction between the foulants and the membrane not only decreased the deposition rate of the foulants onto the PVDF/PDA membrane but also enabled easier peeling off of the accumulated foulants on the membrane during the cleaning process. As a result, the PVDF/PDA blend membrane exhibited excellent anti-fouling ability for organic matter.