A Simple Approach for Surface Functionalization of Polyvinylidene Fluoride (PVDF) Membranes for Desalination of Oil-Contaminated Saline Water Using Membrane Distillation

Desalination of oil-contaminated water resources using membrane distillation requires membranes with specific characteristics. In this process, the body of membrane needs to be hydrophobic, but the surface in contact with oil-water emulsion requires to be highly oil-repellant (oleophobic). For this reason, the surface of membrane needs to become hydrophilic. In addition, the surface morphology of membrane requires to be djusted such that water can be trapped between the surface structures, preventing oil from wetting the surface during a dynamic process (e.g., membrane distillation). We propose a simple approach to control the structure of Polyvinylidene Fluoride (PVDF) membranes and functionalize their surface. It is shown that the morphology of the PVDF membrane can be simply adjusted by changing the composition of polymer solution and properties the coagulation bath. Moreover, through a simple one-step process we chemically functionalize the surface of the membrane using an alkaline solution. The successfulness of the chemical modification was confirmed by x-ray photoelectron spectroscopy (XPS), flourier transformed infrared spectroscopy (FTIR), zeta potential, and under-water oil contact angle. The scanning electron microscopy graphs showed that alkaline treatment did not damage the membrane structure. Also, a stable underwater contact angle of about 150o was observed for the Hexane droplets in contact with the modified surface. The membranes were tested in a direct contact membrane distillation process to desalinate a saline solution including 500 ppm oil. The results showed that oil did not wet the membrane during the test done for 12 hours, where the average flux and salt rejection were about 13 Lm-2h-1 and 99.98%, respectively.