Amino-modified hollow alumina spheres: effective adsorbent for Cd²⁺, Pb²⁺, As(V), and diclofenac removal

A simple sol-gel method and external gelatinization method of hollow alumina spheres synthesis were developed in this study. The spheres were modified with polyethyleneimine (PEI) producing PEI-Al₂O₃ via (3-glycidyloxypropyl)trimethoxy-silane, GLYMO, linker. Characterization results, obtained using XRD and SEM microscopy revealed spherical geometry with a hollow core of PEI-Al₂O₃ adsorbent. Introduction of a large number of the amino group, 6.9 mmol g^-1, contributes to achieving high adsorption capacities, q_m, of 95.6, 124.9, 61.3, and 125.9 mg g^-1 for Cd²⁺, Pb²⁺, As(V), and DCF, respectively, which is obtained by using the Langmuir model. Thermodynamic studies indicated feasible adsorption and higher spontaneity with temperature increase. The kinetic study conveniently modeled using pseudo-second-order (PSO) and Weber-Morris kinetic model, as well as single resistance mass transfer model, indicated a change of the contribution of diffusional processes during adsorption with a dominance of intra-particle diffusion. The fixed-bed column adsorption data, fitted using Bohart-Adams, Clark, Yoon-Nelson, and Thomas models, showed lower capacity in comparison to batch study, and thus clear potential applicability of PEI-Al₂O₃ was deduced even at a high loading of feed water.