Dye Removal from Contaminated Water Through PES Membranes Enhanced with the Incorporation of Switchable Polyacrylic Acid Grafted on Graphene Oxide.

Membrane fouling remains a critical challenge in wastewater treatment that ultimately reduces flux, compromised water quality, and higher operational costs. This study addresses such fouling issues by grafting polyacrylic acid (PAA) polymer brushes onto graphene oxide (GO) via surface-initiated atom transfer radical polymerization (SI-ATRP) and incorporating the functionalized GO-PAA into polyether sulfone (PES) membranes. The functionalized graphene oxide with poly-(acrylic acid) (GO-PAA) was blended into a poly-(ether sulfone) (PES) membrane at different concentrations, and its effects on nanocomposite membrane performance were systematically analyzed. The nanocomposite membranes containing 0.5% GO-PAA demonstrated significant improvements in hydrophilicity and water flux, with a contact angle of 36° and a flux rate of 74 L/m·h at pH 7, compared to the pristine PES membrane with contact angle = 79° and flux rate of 30 L/m·h. Furthermore, the functionalized membranes have exhibited enhanced antifouling properties, with the flux recovery ratio improving from 38% (pristine PES) to 83%. The modified membranes also demonstrated superior dye removal efficiency at neutral pH, with rejection rates of 54% for methylene blue (MB) and 64% for methyl orange (MO) as compared to only 26% and 28% for the pristine membrane, respectively. The availability of hydrophilic groups in the GO and GO-PAA may explain the superiority of the nanocomposite membranes. As the pH shifted from 3 to 11, both water flux and dye rejection exhibited noticeable changes that resulted from the pH-driven structural transformations of the grafted PAA brushes. When the pH reaches 11, the carboxyl groups of PAA undergo deprotonation which induces chain elongation and partial pore blockage due to increase repulsive forces among the negatively charged carboxylate ions, resulting in enhanced dye rejection. Using response surface methodology (RSM), pH and transmembrane pressure were optimized to pH 11 and 6 bar to achieve dye removal efficiencies of 82.5% for MO and 91% for MB. These key experimental observations have provided valuable insights to design high-performance membranes for consideration in wastewater treatment systems.