Kinetic and isotherm modeling of manganese adsorption onto functionalized NiAl/polyaniline composites

Abstract The presence of manganese (Mn) in contaminated water sources poses significant environmental and public health concerns, particularly in industrially impacted regions. In this study, functionalized nickel alumina (NiAl)–polyaniline (PA) were synthesized and evaluated for their effectiveness as adsorbents for manganese removal from aqueous solutions. The NiAl/PA composites were synthesized by surface modification of NiAl using PA to improve surface area, thermal stability, and active binding sites. Batch adsorption studies were conducted under varying contact times (30–210 minutes) and Mn concentrations (5–50 mg/L) at pH 7, 25 °C, and a 0.05 g adsorbent dosage. The prepared composites were characterized using Fourier Transform Infrared Spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) and point of zero charge (pH p zc), followed by isotherm and kinetics analysis to elucidate the adsorption behavior. FTIR confirmed successful surface modification, with NiAl/PA exhibiting characteristic peaks at 3260–3600 cm −1 due to the overlapping of O–H and N–H stretching vibrations, amide (–CONH 2 ) stretching at 1649 cm −1 and C–N stretching at 1283 cm −1 . An intensified peak at 513 cm −1 indicated enhanced Ni–O and Al–O bonding due to PA coating. BET analysis revealed a decrease in specific surface area from 128.6 m 2 g −1 for pristine NiAl to 92.4 m 2 g −1 for NiAl/PA following PA incorporation. The pH p zc NiAl/PA was determined to be 6.1, suggesting a negatively charged surface at pH values above this point. The NiAl/PA composite achieved 70 % Mn(II) removal at equilibrium contact time of 150 minutes, corresponding to an adsorption capacity of 56 mg/g. Adsorption followed the Freundlich isotherm model (R 2 = 0.9944), indicating a heterogeneous surface and multilayer adsorption. Kinetic modeling showed that the intraparticle diffusion model best described the rate-limiting step (R 2 = 0.915), followed by the pseudo-first-order model (R 2 = 0.9045), while the pseudo-second-order model showed weaker correlation (R 2 = 0.5823). These findings demonstrate that NiAl/PA composites, especially those functionalized with conductive polymers, offer a promising, sustainable, and cost-effective solution for the remediation of Mn-contaminated water.