Adsorptive nanofibrous membranes for bidirectional removal of cationic and anionic dyes

The effective treatment of dye wastewater is critical due to its widespread occurrence and substantial impacts on human health and the environment. While established methods, such as membrane filtration and adsorption, are available, the simultaneous presence of anionic and cationic dyes, along with various competing substances, requires robust, bidirectional dye removal approaches. In response, adsorptive nanofibrous membranes were designed with a hydrophobic backbone grafted with sulfonate and quaternary ammonium moieties, exhibiting high adsorption capacities ranging from 541-691 mg/g for the anionic methylene orange (MO(-)) and from 762-875 mg/g for the cationic crystal violet (CV(+)) across a broad pH range of 4.1-10.2. Through gravitational force, these membranes achieved removal efficiencies of 99.5 % of MO(-) and 99.3 % of CV(+), with removal efficiencies consistently retained after six cycles of reuse. This durability was attributed to the stable chemical composition and synergistic adsorption mechanisms, including electrostatic, hydrophobic, π-π stacking, and H-bonding interactions. Additionally, high salinity and inorganic ions exerted minimal impact on the removal efficiency, and the effects of co-existing surfactants were also assessed. With demonstrated bidirectional dye removal, chemical stability, and reliable performance under diverse water conditions, these membranes present a promising solution for dye wastewater remediation.