Polypyrrole Modified Granular Activated Carbon Nanocomposite for Treatment of Wastewater Containing Highly Toxic Hexavalent Chromium

This study explored the fabrication of Polypyrrole (PPy) and Granular Activated Carbon (GAC) composites (PPy-GAC) for effective removal of toxic hexavalent chromium (Cr(VI)) from aqueous solutions. Two synthesis methods are employed: (1) electrostatic deposition of PPy onto pre-charged GAC paper and (2) in-situ chemical polymerization of pyrrole monomer with GAC particles. Batch adsorption experiments investigated the impact of various operational parameters on Cr(VI) removal. Compared to pristine GAC (54.64 mg g⁻¹), the PPy-GAC composite exhibited a remarkable 3-fold increase in equilibrium adsorption capacity, reaching 175.44 mg g⁻¹. Pseudo-second-order kinetic model (R² > 0.999) accurately described the adsorption kinetics, while the Langmuir isotherm model (R² > 0.99) provided a good fit for the equilibrium data. Maximum adsorption capacity (q_max) increased with temperature, reaching 204.08, 243.90, and 270.27 mg g⁻¹ at 298, 308, and 318 K, respectively. Furthermore, a fixed-bed column experiment examined the composite's effectiveness in continuous Cr(VI) removal, demonstrating its suitability for practical applications. Notably, the PPy-GAC composite successfully removed Cr(VI) from a real wastewater sample containing 68 µg L⁻¹ Cr(VI) obtained from a ferrochrome industry, highlighting its potential for real-world remediation.