A PAN/Al₂O₃/MWCNTs-L-Cys composite hollow fiber for Pb²⁺ and Cu²⁺ removal: Comparative performance and adsorption behavior assessment

In this research, a modified polyacrylonitrile hollow fiber (PAN HF) adsorbent was fabricated for the selective removal of Pb²⁺ and Cu²⁺ ions from aqueous samples. To improve the adsorption process, γ-alumina (γ-Al₂O₃) nanoparticles were bio-synthesized and immobilized on PAN HF surface. Also, multi-walled carbon nanotubes (MWCNTs) were added to the composite to increase the active surface area. To significantly improve the selectivity of the nanocomposite, the PAN HF surface was also modified with l-Cys. The fabrication, successful surface modification, and increasing hydrophilicity were confirmed by morphological studies. The adsorption experiments showed maximum adsorption capacities of 136.9 and 22.5 mg/g for Pb²⁺ and Cu²⁺ ions, respectively. The adsorption data were in good agreement with Freundlich isotherm and second-order kinetic models, and the adsorption mechanism controlled by intraparticle diffusion was also confirmed. Temkin and Dubinin–Radushkevich isotherms fitting showed the physical adsorption process. Thermodynamic analysis showed complete spontaneous adsorption of Pb²⁺ ions and to a lesser extent of Cu²⁺ ions. Therefore, the adsorption performance of Cu2+ ions improved with increasing temperature up to 60 °C. The re-cyclability of the adsorbent was investigated during the sequential adsorption-desorption process using hydrochloric acid 0.1 M. The results showed that the HF can be used for at least four cycles without significant reduction in its capacity.