Adsorption behavior and mechanism of core–shell magnetic rhamnolipid–layered double hydroxide nanohybrid for phenolic compounds from heavy metal–phenolic pollutants

Abstract A core–shell magnetic rhamnolipid (RL)–layered double hydroxide (LDH) nanohybrid (Fe3O4@(RL–LDH)) was synthesized by the delamination of magnetic LDH (Fe3O4@LDH) initially and then assembling with RL/NaOH water solution to remove p-cresol/hydroquinone from heavy metal–phenolic pollutants in aqueous solution. The characteristics of the obtained Fe3O4@(RL–LDH) nanohybrid was analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, inductively coupled plasma atomic emission spectrometry, CHN elemental analysis, transmission electron microscopy, vibrating sample magnetometer, thermogravimetry and differential scanning calorimetry, specific surface area, and zeta potential. Results confirmed that the Fe3O4@(RL–LDH) particles possessed core (Fe3O4)–shell (RL–LDH) structures and magnetic properties, and RL− anions were successfully introduced into interlayers of Fe3O4@LDH. The adsorption of p-cresol/hydroquinone by Fe3O4@(RL–LDH) from Cu2+–phenolic pollutants in aqueous solution was studied with magnetic separation in detail. The effect of factors, including the initial solution pH, contact time, initial p-cresol/hydroquinone concentration, and temperature, on the adsorption were investigated. Findings revealed that (1) the adsorption capacities of Fe3O4@(RL–LDH) for p-cresol and hydroquinone were much greater than those of Fe3O4@LDH in the presence/absence of Cu2+ and (2) the adsorption amount of p-cresol by Fe3O4@(RL–LDH) was higher than that of hydroquinones with (or without) Cu2+ ions. The efficient p-cresol/hydroquinone adsorption was mainly due to the dissolution of p-cresol/hydroquinone in the hydrophobic interlayer region formed by RL− anions, and the adsorption mechanism was confirmed by the difference between the adsorption capacities of Fe3O4@(RL–LDH) for p-cresol and hydroquinone.