Removal of Cr(vi) from water using polypyrrole/attapulgite core–shell nanocomposites: equilibrium, thermodynamics and kinetics

Abstract

In this study polypyrrole (PPy) was synthesised chemically on the surface of attapulgite (ATP) to form nanocomposites using ATP as nucleus and PPy as shell. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) showed that ATP was coated with a PPy layer. PPy/ATP nanocomposites as adsorbents were used to remove Cr(VI) from aqueous solutions. External factors were investigated, including contact time, adsorbent dose, initial concentration of adsorbate and pH. The experimental data are well fitted with the Langmuir isotherm model. The thermodynamic parameters were evaluated and the results revealed that the adsorption process was exothermic and spontaneous. The kinetic data indicated that the adsorption process followed a pseudo-second-order equation, implying that the adsorption process was predominantly controlled by chemical processes. The associated adsorption mechanism for Cr(VI) removal by the PPy/ATP nanocomposites was investigated using X-ray photoelectron spectroscopy (XPS), which suggests that ion change and reduction processes on the surface of the nanocomposites may be the possible mechanism.