Polypyrrole-polyaniline copolymer coated green rice husk ash as an effective adsorbent for the removal of hexavalent chromium from contaminated water

The acute toxicity and mobility of hexavalent chromium [Cr(vi)] in water and wastewater pose a severe risk to the environment and human health. In view of this, the present work is focused on the fabrication and characterization of polypyrrole-polyaniline coated rice husk ash (termed as PPY-PANI@RHA) by in situ polymerization and its application as an adsorbent in the removal of Cr(vi) from the aqueous solution. Our findings have shown a Cr(vi) removal rate of similar to 98% at room temperature (303 K) under optimum conditions with an adsorbent dose of 0.8 g L-1, an adsorbate concentration of 50 mg L-1, a solution pH of similar to 2, and a contact time of 300 min. The adsorption of Cr(vi) followed the Elovich kinetics and is better described using the Freundlich isotherm with a maximum adsorption capacity of 769.15 mg g(-1). The co-existing ion study result shows that the Cr(vi) removal efficiency is slightly decreased in the presence of high concentrations of Na+, Mg2+, Ca2+, Cl-, HCO3-, NO3-, SO42- and PO43- ions. Thermodynamic investigations have shown that the adsorption phenomenon of Cr(vi) on PPY-PANI@RHA is endothermic, feasible, and spontaneous in nature. Additionally, the reusability study of the spent PPY-PANI@RHA adsorbent indicated its high removal efficiency for several times. Finally, PPY-PANI@RHA was also successfully used to remove Cr(vi) ions from the highly polluted raw tannery wastewater sample. Our findings clearly demonstrated that PPY-PANI-coated rice hush ash could be an alternative as an effective bio adsorbent in the removal of Cr(vi) for wastewater treatment and benefit the industries in the future.