Enhancing adsorption capacity of magnetic magnesium-aluminum layered double hydroxide by surface modification with sodium dodecyl sulfate for efficient removal of organic contaminants

Abstract

A magnetic magnesium-aluminum layered double hydroxide (Mag-MgAl) was prepared, and its surface was modified using surfactant sodium dodecyl sulfate (SDS) and utilized as adsorbents for antibiotic ciprofloxacin (CIP) and dyes ponceau red (PR) and methylene blue (MB). Mag-MgAl/SDS demonstrated twice the adsorption capacity for CIP compared to Mag-MgAl, confirming that the surface modification by SDS aided the adsorption capacity. At pH 3.5, Mag-MgAl removed CIP and PR, attributed to electrostatic effect and hydrogen bonding, whereas it did not interact with MB. Conversely, Mag-MgAl/SDS successfully removed both MB and CIP, suggesting that SDS micelles acted as nanoreactors attracting cationic contaminants. The PR removal efficiency was low, possibly due to electrostatic repulsion. A binary dye system adsorption assessment was performed by mixing MB and PR aqueous solutions with Mag-MgAl and Mag-MgAl/SDS as selective adsorbents. Mag-MgAl removed around 80% of PR and 45% of MB, whereas Mag-MgAl/SDS removed less than 40% of PR and 80% of MB. SDS remains adsorbed on the surface of Mag-MgAl/SDS after the adsorption process of CIP, MB, or PR. The inversion in the affinity for the target molecules suggests that the surface of the composite can be adjusted to modulate the behavior of the adsorbent toward organic contaminants.