Enhanced removal of Cr(VI) from aqueous solution using polypyrrole/Fe3O4 magnetic nanocomposite

Fe3O4 coated polypyrrole (PPy) magnetic nanocomposite was prepared via in situ polymerization of pyrrole monomer for the removal of highly toxic Cr(VI). Structure and morphology of the prepared nanocomposite were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction pattern, Field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HR-TEM). Electron spin resonance (ESR) studies confirmed that the nanocomposite is magnetic in nature. Up to 100% adsorption was found with 200 mg/L Cr(VI) aqueous solution at pH 2. Adsorption of Cr(VI) on the surface of the adsorbent was confirmed by the ATR-FTIR and X-ray photoelectron spectroscopy (XPS). XPS studies also suggested that ion exchange and reduction on the surface of the nanocomposite may be the possible mechanism for Cr(VI) removal by the PPy/Fe3O4 nanocomposite. Adsorption results showed that Cr(VI) removal efficiency by the nanocomposite decreased with an increase in pH. Adsorption kinetics was best described by the pseudo-second-order rate model. Isotherm data fitted well to the Langmuir isotherm model. Thermodynamic study revealed that the adsorption process is endothermic and spontaneous in nature. Desorption experiment showed that in spite of the very poor recovery of the adsorbed Cr(VI); the regenerated adsorbent can be reused successfully for two successive adsorption-desorption cycles without appreciable loss of its original capacity.