Adsorption of Phthalate Esters from Aqueous Solution by Mg–Al Layered Double Hydroxide

Abstract

Mg–Al layered double hydroxide (Mg–Al LDH) was investigated for adsorption of dimethyl phthalate (DMP), di-(2-ethylhexyl) phthalate (DEHP) and dioctyl phthalate (DOP) from water samples. The adsorption capability of the Mg–Al LDH was compared with that of activated carbon. Adsorption of the three phthalate esters (PAEs) fitted pseudo-second-order kinetics, and the Langmuir or Freundlich equations described the adsorption isotherms. Adsorption of the PAEs was exothermic, and was mainly dominated by physical interactions including dispersion, induction, orientation and hydrogen bond forces. Compared with activated carbon, the Mg–Al LDH removal efficiency of the relatively small PAE, DMP, was about 20 % lower. The removal efficiencies of the larger PAEs, DEHP and DOP, were about the same on both sorbents. After three regeneration cycles of the Mg–Al LDH at 300 °C for 2 h, its adsorption capacity remained above 90 %. The infrared (IR) spectra and the X-ray diffraction (XRD) patterns for the Mg-Al-LDH before and after regeneration showed no large differences, which indicates that the structure of the Mg–Al LDH does not change after regeneration.