Adsorption of Cu(II) on Rhamnolipid-Layered Double Hydroxide Nanocomposite

Abstract

AbstractA rhamnolipid-layered double hydroxide (RL-LDH) nanocomposite, derived from the rhamnolipid (RL) biosurfactant, was synthesized through a delamination/reassembling process. The adsorption characteristics of Cu(II) on RL-LDH were investigated in detail and the results indicated the potential of using RL-LDH as an environmentally friendly adsorbent to remove Cu(II). The fabricated RL-LDH nanocomposite was characterized using powder X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, elemental chemical composition, and specific surface area analyses. Batch adsorption experiments were conducted to study the influence of various factors, such as contact time, initial Cu(II) concentration, temperature, initial solution pH, and electrolyte concentration on Cu(II) adsorption by the RL-LDH nanocomposite. The RL-LDH nanocomposite had a low surface area of 11.71 m2 g−1, which suggests that surface adsorption would not be important in Cu(II) adsorption. The Cu(II) adsorption data fitted the Freundlich model well at pH 5.5, whereas the adsorption kinetics were accurately described by a pseudo-second-order kinetics model. Chemical binding, that is, the formation of a RL-Cu(II) complex in the LDH interlayer, was assumed to be the rate-limiting step in the adsorption process. Thermodynamic parameters that included Gibbs free energy, enthalpy, and entropy changes were also calculated. The adsorption was found to be a spontaneous and exothermic chemisorption process. Furthermore, the adsorption properties of RL-LDH for Cu(II) were compared to Cu(II) adsorption using other adsorbents.