The Fe3O4@SiO2@APTMS core–shell magnetic nanohybrid was produced using rice husk amorphous silica as a novel, eco–friendly and sustainable adsorbent. The characterization of the produced adsorbent was done using FT–IR, SEM, VSM, XRD and TEM techniques, and applied for Cd(II) adsorption from aqueous solutions. The Cd(II) adsorption optimization was performed based on the central composite design (CCD) and studied by the response surface methodology (RSM). The adsorption process was investigated as a function of three independent variables including the solution pH (in the range of 3–7), adsorbent dosage (in the range of 0.1–2 g L–1) and Cd(II) concentration (in the range of 10–100 mg L–1). Hereupon, the optimum conditions for Cd(II) adsorption were identified as 5.17, 0.1 g L–1 and 100 mg L–1 for corresponding variables. Under these conditions, the removal efficiency (R) and adsorption capacity (qe) of the Fe3O4@SiO2@APTMS adsorbent for Cd(II) ions were obtained to be 58.71% and 305.64 mg g–1. Likewise, the obtained result for desirability function was 0.722. The isotherm models were used to describe the adsorption process. The Sips model presented the most acceptable appropriate with the equilibrium data. The kinetic investigation revealed that the experimental data show better fit with the pseudo–second–order model than the pseudo–first–order and intraparticle diffusion models. The thermodynamic parameters revealed that the adsorption process considerably depends on temperature and indicating the exothermic behavior and spontaneous nature of the adsorption. Adsorbent regeneration study showed an acceptable redaction in removal efficiency after five cycles.
