Adsorption of aqueous Cd(II) over a Fe₃O₄/plant polyphenol magnetic material

A magnetic plant polyphenol (PP)-coated Fe₃O₄ material (Fe₃O₄/PP) was synthesized and removed Cd(II) from aqueous solution. The structure, morphology, magnetic properties, and thermal stability of the magnetic composite were studied by field emission scanning electron microscopy (FE-SEM), vibrating sample magnetometry (VSM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and zeta-potential measurements. The effect of different parameters (e.g. pH, initial metal ion concentration, contact time, adsorbent dosage, agitation speed, and coexisting ions) on the adsorption process was studied. The adsorption fitted well to the Langmuir isotherm and the adsorption capacity of Cd(II) reached maximum at 0.951 mg/g. The adsorption equilibrium was reached in 2 h and the adsorption kinetic was fitted better to the pseudo-second order equation. The adsorption capacity increased with the pH in the 3.0–8.0 range. Unlike NO₃⁻ and SO₄²⁻, common coexisting cations such as Na⁺, K⁺, Mg²⁺, and Cl⁻ negatively affected Cd(II) adsorption. Thermodynamic parameters such as free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) showed that the adsorption process was spontaneous and endothermic. As revealed by FT-IR and XPS, PP and Cd(II) interacted mainly via generation of CdO, CdO₂, or Cd(OH)₂ species after Cd(II) adsorption. This study successfully changes the way that PP is used in the removal of Cd(II) and indicates an effective desorption and regeneration performance.