Using magnetic micelles as adsorbents to remove dyes from aqueous solutions

Dyes have been widely used in various industries for coloring different materials. The discharge of dyes into wastewater remains an issue due to its polluting effect on the environment. Therefore, it is important to develop methods to effectively remove dyes from wastewater. In this study, we explore a new and facile method that can be used to rapidly remove dyes, i.e., methylene blue (MB) and methyl orange (MO), from aqueous solutions simply by using magnetic metal ions, (i.e., Gd³⁺ and Fe³⁺) as probes. We impose magnetism on anionic surfactants such as sodium dodecyl sulfate (SDS) when their concentrations reach a certain level (e.g., their critical micelle concentrations (CMC)), by attaching magnetic metal ions via electrostatic interactions. The generated magnetic Gd³⁺-SDS conjugates possess manipulable magnetism and can be simply isolated by applying an external magnet. The trapping capacities of our Gd³⁺-SDS probes against MB and MO are ∼425 and ∼25 μmol g^-1, respectively. The dissociation constants of our probes toward MB and MO are 9.63 × 10^-6 and 2.42 × 10^-5, respectively. Dishwashing detergent solutions spiked with MB and MO are also used as the real samples to demonstrate the feasibility of using Gd³⁺ and Fe³⁺ as probes for real-world applications.