Polypyrrole-metal oxide nanocomposites for enhanced adsorption of Pb(II) and Cd(II) ions

Polypyrrole (PPy) and its nanocomposites with CuO and ZnO were synthesized via a surfactant-free in situ oxidative polymerization route without post-synthesis doping. Structural analysis revealed predominantly amorphous PPy with short-range ordering, while distinct crystalline phases of CuO and ZnO were retained in the composites. BET analysis demonstrated a significant increase in surface area from 77.31 m² g⁻¹ (PPy) to 161.87 m² g⁻¹ (CuO/PPy) and 179.02 m² g⁻¹ (ZnO/PPy). Adsorption studies for Pb(II) and Cd(II) showed enhanced capacities for nanocomposites, with maximum adsorption capacities reaching 211.03 mg g⁻¹ for Pb(II) and 187.03 mg g⁻¹ for Cd(II) in ZnO/PPy. Kinetic studies followed a pseudo-second-order model, indicating chemisorption, while equilibrium data were best described by the Sips isotherm, suggesting combined Langmuir-Freundlich behaviour. Regeneration studies confirmed stability over six cycles with minimal efficiency loss. The improved adsorption performance is attributed to the combined effects of increased surface area, enhanced accessibility of adsorption sites, interfacial interactions between PPy and metal oxides, and multiple metal-ion binding pathways.