Polypyrrole-Coated Cobalt Ferrite Nano-Sorbent for Efficient Removal of Fast Green Dye: A Kinetic and Thermodynamic Approach

Water contamination constitutes a substantial global issue that affects the environment. The discharge of manufacturing waste substantially contributes to this issue. Adsorption materials have demonstrated huge potential in wastewater treatment. For the efficient removal of an anionic dye, fast green (FG), a polypyrrole-coated cobalt ferrite (PPy@CoFe₂O₄) magnetic nanosorbent is prepared via in-situ polymerization of pyrrole on CoFe₂O₄ nanoparticles. Scanning electron microscopy (SEM) analysis demonstrated spherical nanoparticles with sizes around 50 nm, which was further supported by XRD data. FTIR spectra identified characteristic peaks in the 400–600 cm^–1 range, confirming the presence of M–O bonds and indicating the formation of spinel ferrite. Zeta-potential study showed that the surface charge of PPy@CoFe₂O₄ is negative in alkaline media and positive in acidic media. The adsorption system adhered to a pseudo-second-order kinetic model, with the equilibrium time being determined at 50 min. The Langmuir model accurately simulated the adsorption isotherms. Under optimal conditions (pH = 5.0, volume –25 mL, adsorbent dose –100 mg, and at 303 K temperature), the maximum monolayer adsorption capacity of PPy/CoFe₂O₄ is 85.25 mg g^–1. Even after five desorption-adsorption cycles, the removal efficiency remained above 90%. Negative ΔG° and ΔH° indicate spontaneous FG adsorption onto PPy/CoFe₂O₄, decreasing with temperature. These findings demonstrate that the PPy/CoFe₂O₄ composite is a highly effective adsorbent with broad potential applications for treating wastewater containing anionic dye.