Insights into simultaneous efficient removal of cationic and anionic dyes by nitrogen-rich seaweed carbon adsorbent

Textile dyes, including methylene blue (MB) and methyl orange (MO), pose a significant threat to water quality. This study delves into the competitive adsorption mechanisms pivotal for the concurrent removel of cationic MB and anionic MO dyes using nitrogen-rich seaweed-based carbon adsorbents. Synthesized through the pyrolysis and NaOH activation of Enteromorpha seaweed biomass, the preparation method is both uncomplicated and cost-effective, holding promising applications in industry. Characterization unveiled a commendable specific surface area of 911 m2/g, accompanied by abundant nitrogen- and oxygen-containing functional groups. Batch adsorption experiments showcased exceptional removal efficiencies surpassing 99.8% for both dyes. Molecular dynamics simulations offered valuable insights into the dynamic multi-stage adsorption behavior, while density functional theory calculations clarified the chemisorption-based interaction mechanism. Notably, MB displayed superior adsorption affinity compared to MO. An integrated adsorption mechanism was proposed, encompassing electrostatic attraction, migration, and enhanced chemisorptive binding of dye aggregates at active sites on the adsorbent surface. The innovative adsorption mechanism adopted by this carbon-based adsorbent prepared from nitrogen-rich seaweed can effectively remove cationic and anionic dyes, laying a solid foundation for future research on real water bodies with complex compositions.