Graphene Oxide/Polydopamine (GO/PDA) Coated Membranes for Selective Filtration of Cationic and Anionic Dyes

Abstract

The discharge of synthetic dyes into industrial effluents represents a major environmental challenge due to their high stability and persistence in aquatic systems. Among available treatment strategies, membrane-based separation processes have emerged as promising alternatives for removing organic contaminants from water. However, improving membrane selectivity and efficiency toward different classes of dyes remains an important challenge. In this study, commercial PVDF membranes were modified with polydopamine (PDA) and a graphene oxide/polydopamine (GO/PDA) composite to evaluate their performance in removing methylene blue (MB, a cationic dye) and Congo red (CR, an anionic dye). The modified membranes were prepared through surface deposition of active layers and characterized using UV–Vis spectroscopy, FTIR spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and water contact angle (WCA) measurements. Filtration experiments were carried out to assess dye removal efficiency and selectivity. The results showed that PDA-modified membranes achieved the highest retention efficiency for MB and the mixture, indicating a significant improvement over the unmodified PVDF membrane. However, the pristine membrane exhibited a higher retention of the anionic dye. The incorporation of GO contributed to a more homogeneous surface and enhanced selective filtration behavior. In mixed dye solutions (1:1 MB: CR), the GO/PDA membrane demonstrated a greater ability to preferentially remove CR, with a selectivity factor of 3.50. Overall, the deposition of PDA-based layers proved a promising strategy for enhancing nanofiltration membrane performance in the treatment of dye-containing effluents, while GO/PDA modification improved membrane selectivity.

Keywords:
Membrane filtration; membrane modification; dye retention; graphene oxide composite; selective filtration