Bifunctional magnetic chitosan microspheres for simultaneous adsorption of Cu(II) and sodium dodecylbenzene sulfonate (SDBS)

This study presents the synthesis and application of a bifunctional modified magnetic chitosan microsphere (MCS-II) for the simultaneous removal of Cu 2+ and sodium dodecylbenzene sulfonate (SDBS) from electroplating wastewater. The adsorbent was functionalized with polyethyleneimine (PEI) and ethylenediaminetetraacetic acid (EDTA) and embedded with Fe 3 O 4 nanoparticles to enhance adsorption capacity and magnetic separability. Batch adsorption experiments demonstrated that MCS-II exhibited a maximum adsorption capacity of 141.0 mg/g for Cu 2+ (pH = 6, T = 55 °C) with a removal efficiency of 96 %, and a maximum adsorption capacity of 1632 mg/g for SDBS (pH = 2, T = 25 °C) with a removal efficiency of 95 %. Kinetic studies revealed that the adsorption processes for both pollutants followed pseudo-second-order kinetics, indicating chemisorption as the dominant mechanism. Isotherm analysis showed that Cu 2+ adsorption fitted the Langmuir model, suggesting monolayer coverage, while SDBS adsorption exhibited characteristics of both monolayer and multilayer adsorption. Thermodynamic parameters indicated that Cu 2+ adsorption was endothermic (ΔH > 0) and spontaneous (ΔG < 0), whereas SDBS adsorption was exothermic (ΔH < 0) and spontaneous (ΔG < 0). In binary systems, synergistic effects were observed, with SDBS enhancing Cu 2+ adsorption via additional binding sites, while Cu 2+ exerted minimal inhibition on SDBS removal. Characterization techniques (SEM, FT-IR, XPS, etc.) confirmed the successful incorporation of amino and carboxyl groups, which facilitated chelation with Cu 2+ and electrostatic/hydrophobic interactions with SDBS. Moreover, MCS-II demonstrated excellent recyclability and magnetic recovery: after 4 adsorption-desorption cycles, its Cu 2+ adsorption capacity remained at ∼85–92 % of the original, and SDBS removal rate stayed at ∼95 % through 5 cycles, maintaining high adsorption efficiency for practical application. This work provides a promising strategy for designing multifunctional adsorbents to treat complex wastewater containing both heavy metals and anionic surfactants, offering potential for practical environmental remediation applications.