A magnetic core-shell dodecyl sulfate intercalated layered double hydroxide nanocomposite for the adsorption of cationic and anionic organic dyes

Abstract A magnetic dodecyl sulfate (DS−) anions intercalated layered double hydroxide (LDH) nanocomposite, Fe3O4@(DS-LDH), was synthesized by coprecipitation-ion exchange method. The Fe3O4@(DS-LDH) nanocomposite was characterized and the results showed that the Fe3O4@(DS-LDH) particles possessed core (Fe3O4)-shell (DS-LDH) structures and magnetic properties, and DS− anions were successfully introduced into LDH interlayers. Adsorption of cationic methylene blue (MB) or anionic methyl orange (MO) by Fe3O4@(DS-LDH) were comprehensively clarified with magnetic separation in (MB or MO) sole and (MB + Cu(II) or MO + Cu(II)) binary solutions by adsorption kinetics, thermodynamic and isotherm models. The adsorption of both MB and MO on Fe3O4@(DS-LDH) were governed by the pseudo-second-order kinetic model. The adsorption isotherm data for MB (in sole and binary solutions) and MO in binary solution agreed well with the Freundlich model, and that for MO in sole solution was accorded with the linear model. MB uptake decreased with the addition of Cu(II) ions, whereas the existence of Cu(II) ions enhanced MO removal. According to the adsorption mechanism investigation by XRD and XPS analysis, the main driving force for MB/MO adsorption, the hydrophobic interaction between MB/MO molecules and the three-dimensional hydrophobic region formed by DS−anions in LDH interlayers of Fe3O4@(DS-LDH), was proposed; Cu(II) ions could act as a bridge between Fe3O4@(DS-LDH) and MO, which slightly enhanced MO adsorption; whereas, the adsorption capacity for MB decreased in the presence of Cu(II) ions due to competitive adsorption.