Synthesis and application of polypyrrole/CoFe2O4 nanocomposite for chromium(VI) removal: mechanistic and kinetic insights

The contamination of water, especially through the presence of toxic and carcinogenic hexavalent chromium (Cr(VI)), represents a significant global challenge, threatening both human health and ecosystems. Hexavalent chromium presents considerable threats, including organ damage, genetic mutations, and carcinogenic effects, underscoring importance for its effective removal (down to 10 µg/L) from wastewater. Adsorption materials show significant promise in wastewater remediation. By in situ polymerizing pyrrole on CoFe₂O₄ nanoparticles, a polypyrrole-coated cobalt ferrite (PPy@CoFe₂O₄) magnetic nanosorbent is synthesized to achieve effective removal of Cr(VI). XRD data corroborated the findings of the SEM examination, which showed spherical nanoparticles with diameters of about 50 nm. Spinel ferrite production was suggested by the FTIR spectra, which showed clear peaks in the 400–600 cm⁻¹ region, confirming the evidence of M–O bonds. The investigation of zeta potential revealed that the polypyrrole-coated cobalt ferrite nanoparticles have a positive surface charge in an acidic medium and a negative surface charge in alkaline media. The adsorption behavior aligned with a pseudo-second-order kinetic model. The adsorption isotherms were accurately represented by the Langmuir model. PPy/CoFe₂O₄ demonstrates a maximal monolayer adsorption capacity of 369.6 mg g⁻¹ under optimum conditions (330 K temperature, 60.0 mg adsorbent dose, and pH 2.0). The removal efficiency was still higher than 91% following the five adsorption–desorption cycles. The adsorption of Cr(VI) onto PPy/CoFe₂O₄ takes place spontaneously, as indicated by a negative ΔG°. The results indicate that the PPy/CoFe₂O₄ composite functions as a highly efficient adsorbent, showcasing extensive applicability in the treatment of wastewater contaminated with heavy metal ions.

Graphical Abstract