Improved oily wastewater rejection and flux of hydrophobic PVDF membrane after polydopamine-polyethyleneimine co-deposition and modification

Abstract

The surface structure and properties of a membrane largely determine its in-service performance during a filtration process. Polyvinylidene fluoride (PVDF) hydrophobic membrane is widely used in the separation of oily wastewater because of its mechanical strength, but is susceptible to oil fouling, whereas hydrophilic membranes are easily damaged in water due to their wettability but are resistant to oil. The advantages of the two membranes are then combined by modifying the hydrophobic membrane to be hydrophilic to maintain stability, mechanical strength, and antifouling performance. PVDF ultrafiltration membranes were modified with a mixture of different concentrations of polydopamine (PDA) and polyethyleneimine (PEI) using different deposition times (6, 12, and 24 h) and characterized using SEM, FTIR, and contact angle. Membrane performance was tested using a dead-end module for 60 min. The PDA-modified membrane showed a decrease in hydrophilicity from 88.1° to 77.7° after being coated with 0.5 g/L PDA for 6 h, while with the addition of 2 g/L PEI, the hydrophilicity reached 64.6° SEM characterization showed the presence of aggregates formed during the PDA polymerization process and decreased with the addition of PEI. This is in line with the results obtained from the performance test with the dead-end module where the smaller the aggregate, the greater the flux produced. FTIR characterization showed a strong bond between PDA and PDA-PEI with the membrane as the concentration and coating time increased.