Synergistic adsorption of mixed anionic and cationic dyes by polyaniline/CuFe2O4 composites

Mixed anionic and cationic dyes in industrial wastewater demand adsorbent materials with tunable surface charge behaviour, a challenge unmet by conventional single-function materials. This work develops a magnetically separable polyaniline/copper ferrite (PANI/CuFe 2 O 4 ) nanocomposite through in-situ oxidative polymerisation for dual-mode dye capture via engineered interfacial architecture. Structural characterisation by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and Fourier-transform infrared (FTIR) spectroscopy confirmed integration of inverse-spinel CuFe 2 O 4 nanoparticles (crystallite size 39.8 nm by Scherrer analysis on the (311) reflection, cubic spinel structure, ICDD PDF 89-598) within the emeraldine-salt PANI matrix. Brunauer–Emmett–Teller analysis revealed specific surface area enhancement (44.2 m 2 g -1 for the composite vs. 37.2 m 2 g -1 for pristine PANI), with embedded ferrite nanoparticles disrupting polymer chain aggregation. Batch adsorption experiments demonstrated maximum capacities of 305.5 mg g -1 for anionic Acid Blue 40 (AB40, optimal pH 2–3) and 291.2 mg g -1 for cationic Basic Blue 3 (BB3, optimal pH 9–11) on pristine PANI, and 202.8 mg g -1 (AB40) and 67.08 mg g -1 (BB3) on the magnetically separable PANI/CuFe 2 O 4 composite, exceeding those of conventional activated-carbon adsorbents. Kinetic analysis fitted pseudo-second-order models (R 2 = 0.983–0.994) with activation energies of 21.7–35.7 kJ mol -1 , confirming a physisorption-dominated regime. Thermodynamic parameters (ΔG° = −7.6 to −15.5 kJ mol -1 , ΔH° = −30.2 to −49.6 kJ mol -1 , ΔS° = −223.7 to −496.3 J mol -1 K -1 ) indicated spontaneous, exothermic adsorption. Combined spectroscopic evidence quantified four synergistic mechanisms: electrostatic attraction (40–50%), π–π stacking (25–30%), hydrogen bonding (15–20%), and metal coordination (5–10%). The composite exhibited superparamagnetic behaviour enabling rapid magnetic recovery (>99.5% within 5 min) and maintained 87% adsorption capacity after five regeneration cycles, demonstrating industrial viability for treating complex textile effluents containing mixed-dye systems.