In order to solve the water solubility and difficult re-use of plant polyphenol (PP) in Cd(II) adsorption, PP was immobilized on the surface of magnetic material in this study. A core-shell nanocomposite Fe3O4/SiO2/PP (∼18 nm) was synthesized with 3-8 nm SiO2 and 2-5 nm PP. TGA analysis revealed the PP coating amount was 2.39%. VSM detection suggested that saturation magnetization of Fe3O4/SiO2/PP was 45.94 emu/g. The adsorption equilibrium was reached in 2 h and the adsorption kinetics followed a pseudo-second-order model. The adsorption data fitted well to a Langmuir isotherm, achieving a 98.6% of Cd(II) removal at 0.6 g, pH 7.0, 298 K and 160 rpm. The adsorption capacity of Cd(II) on Fe3O4/SiO2/PP highly depended on the pH. The adsorption capacity increased as the initial solution pH was increased in the range of 3.0-8.0. The adsorbed Cd(II) on Fe3O4/SiO2/PP could be effectively desorbed by 0.1 mol/L of HNO3 and the Fe3O4/SiO2/PP still maintained a stable adsorption capacity after five cycles. The adsorption mechanism of Cd(II) on Fe3O4/SiO2/PP is mainly dependent on complexation and electrostatic adsorption from the FTIR and XPS analyses. This study provided a new way for PP to remove Cd(II) from aqueous solution.
Keywords: Adsorption; Cd(II); Fe3O4; magnetic adsorbent; plant polyphenol.