Ferrofluid composed of amino-functionalized magnetic nanoparticles and hydrophobic deep eutectic solvent for selective dispersive micro-solid-phase extraction of cationic dyes

In this study, a novel magnetically responsive ferrofluid, composed of (3-aminopropyl)triethoxysilane (APTES)-modified Fe 3 O 4 nanoparticles (Fe 3 O 4 -NH 2 ) and a thymol/n-decanol hydrophobic deep eutectic solvent (DES), was developed and coupled with vortex-assisted dispersive micro-solid phase extraction (VA-D-μSPE) for the separation of dyes. Four dyes, including cationic malachite green oxalate (MG) and brilliant green (BG), and anionic amaranth (AM) and lemon yellow (LY), were selected as target analytes to investigate the extraction selectivity of the DES-Fe 3 O 4 -NH 2 ferrofluid. The results demonstrated that the DES-Fe 3 O 4 -NH 2 ferrofluid exhibited selective extraction towards cationic dyes. The extraction parameters, including salt concentration, pH, extraction time, and extractant volume, were systematically optimized. Under the optimal conditions, the extraction efficiencies for MG and BG reached 98.40 % and 97.95 %, respectively. Mechanism studies suggested that the DES-Fe 3 O 4 -NH 2 ferrofluid could interact with the dyes through hydrogen bonding, π-π interactions, electrostatic attraction, and hydrophobic interactions. The enrichment factors for MG and BG were 54.17 and 39.55, respectively. Additionally, the ferrofluid showed satisfactory recoveries for MG and BG in real water samples, ranging from 90.38 % to 112.63 % and 72.96 % to 121.12 %, respectively, with RSD of 0.53 % to 5.85 % and 0.37 % to 4.77 %. Comparison with other extractants confirmed the superior performance of the DES-Fe 3 O 4 -NH 2 ferrofluid, attributed to the synergistic effect of the magnetic nanoparticles and the DES carrier liquid. Overall, the DES-Fe 3 O 4 -NH 2 ferrofluid, characterized by its simple operation, rapid separation, environmental friendliness, and high efficiency, emerges as a promising candidate for the removal of dyes from aqueous environments.