Efficient removal of Sunset Yellow by silicon-phosphorus modified alumina: Adsorption mechanisms and regeneration...

The removal of harmful dyes such as Sunset Yellow from industrial wastewater requires the design of materials with high adsorption capacity and excellent regenerability, as well as a comprehensive understanding of the adsorption mechanisms and regeneration phenomenon. In this study, we developed silicon-phosphorus modified alumina with high adsorption capacity and regenerability for Sunset Yellow, in which the deposition of silicon and phosphorus inhibited primary particle growth and interlayer sintering. The adsorption capacity of silicon-phosphorus modified alumina was 89.9 mg/g at pH 6.89, 13.65 % higher than unmodified alumina, and increased to 175.5 mg/g after the fourth regeneration cycle. The adsorption mechanism involved ion exchange between OH^- on the surface of modified alumina and D-SO₃^- from Sunset Yellow. For the first time, the study demonstrated that both the sulfonic acid groups of Sunset Yellow molecules undergo ion exchange with hydroxyl ions on the surface of alumina, rather than a single sulfonic acid group. Notably, a novel approach based on hydroxyl group quantification was proposed to explain changes in adsorption capacity, providing insights into the observed increase in adsorption during regeneration process. This innovative study will considerably promote the application of adsorbents for organic dye removal and promising prospects for industrialization.