Adsorption of arsenic on iron modified attapulgite (Fe/ATP): surface complexation model and DFT studies

The adsorption behaviors of arsenic As(V) on the iron modified attapulgite (Fe/ATP) were studied. Two types of Fe/ATP nanoparticles, including Fe(III)/ATP and Fe(II,III)/ATP were prepared by ultrasonic co-precipitation method and characterized using SEM, XRD, XPS, FT-IR and zeta potential analyses. The adsorption isotherms of As(V) on Fe/ATP were well fitted by Freundlich model. The adsorption kinetics data were followed by the pseudo-second-order model with the pseud-second-order rate constant (k, min(-1)) of - 0.033 for Fe(III)/ATP and - 0.037 for Fe(II,III)/ATP, respectively. Adsorption capacities of Fe/ATP were 5-6 times higher than ATP (5.2 mg g(aEuro'1)). The Fe-O(H) groups on Fe/ATP contributed to the strong interaction for As(V), confirmed with FT-IR and XPS analyses. The higher adsorption capacity of Fe(III)/ATP than that of Fe(II,III)/ATP was attributed to more surface hydroxyl groups on Fe(III)/ATP. Surface complexation models and density functional theory calculations demonstrated that As(V) sorption on Fe/ATP was by virtue of the formation of monodentate complexes.