Removal of hexavalent chromium ions using polyaniline/silica gel composite

In this study, a composite composed of polyaniline and silica gel was successfully prepared via in situ polymerization. The prepared polyaniline/silica gel (PANI/SiO2) composite was used as an adsorbent for the removal of Cr(VI) ions from the aqueous solutions. Structure and morphology of the composite were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscope equipped with an energy dispersive X-ray analyzer (SEM-EDX). A batch adsorption system was applied to study the ability of the adsorbent to remove Cr(VI) ions from aqueous solution. Results revealed that the PANI/SiO2 composite requires minimum contact time as 60 min, pH 4.2, a dosage of 0.1 g and 50 mg/L as an initial concentration of Cr(VI) ions for the maximum removal capacity at 303 K. Langmuir and Freundlich adsorption isotherm models were studied to describe isotherm constants. The Cr(VI) ion uptake by the composite follows Freundlich isotherm. The maximum Cr(VI) ion adsorption capacity of PANI/SiO2 composite was found to be 63.41 mg/g at 303 K. Thermodynamic parameter studies concluded that the nature of Cr(VI) ion adsorption was spontaneous and endothermic. The kinetic study revealed that the adsorption of Cr(VI) ions by the composite follows the pseudo-second-order and pore diffusion models. The mechanism was mainly driven by both ion exchange and adsorption coupled reduction.