Fabrication and surface modification of PVDF membrane for zinc and cadmium ions removal.

Abstract

Rapid industrialization and urbanization in this era have leads to water pollution and worsen the water scarcity. In this study, a modified poly(vinylidene fluoride) (PVDF) membrane was used to remove zinc and cadmium ions from solutions with concentrations of 10 ppm and 50 ppm, respectively. The hydrophobic PVDF support membrane was modified by a Layer-by-Layer (LbL) deposition technique with polycation, chitosan, and polyanion, poly(styrene sulfonate) to increase its hydrophilicity and metal ions rejection percentage as well as decreasing membrane fouling. Chitosan's hydroxyl and amine groups created an electrostatic interaction with the sulfonate group of poly(styrene sulfonate).The polyelectrolyte-modified membranes were characterized by using infrared spectroscopy and water contact angle measurements. The membrane filtering experiments revealed that the 5, 6, 9, and 10 layers of polyelectrolytes deposited membranes retained zinc/ and cadmium ions well, demonstrating the practicality of polyelectrolytes deposition on organic membranes because all rejection percentages were greater than 25%. The robustness of modified membranes was also tested by repeating 10 consecutive filtrations with the same membrane, and it was demonstrated that the modified membrane still had a higher rejection percentage that was two times higher and was less likely to foul due to less decreasing trends in permeate flux when compared to the unmodified membrane. It is expected that electrostatic repulsion and attraction as well as the steric effect were the primary mechanisms by which the modified membrane removed metal ions from contaminated solution.